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 http://www.archive.org/details/prostheticdentisOOprot 
 
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Prosthetic Dentistry 
 
 JAMES HARRISON PROTHERO, D. D. S. 
 
 I'ROFESSOR OF PROSTHETIC TKCHNIC. PROSTHETIC 
 DENTISTRY, AXl) METALLIRCY 
 
 NORTHWESTERN UNIVERSITY DENTAL SCHOOL 
 CHICAGO 
 
 Second Edition Revised and Enlarged 
 1200 Pages 1400 Illustrations 
 
 MeDICO-DkNTAL PUBLISHINC, Co. 
 
 
 c. 
 
 Ash & Sons 
 
 CHICAGO 
 
 Distributors 
 1916 
 
 
 London 
 
\ i\ 
 
 bs 
 
 
 Entered according to Act of Congress, in the year 1916, 
 
 By J. H. PROTHERO 
 
 In the office of the Librarian of Congress. Washington. D. C. 
 
 Entered at Stationers' Hall. 
 
 London, England. 
 
 THR I1I,.\KEI,T PBINTINO CO.. TRIXTERS. CIIICMI 
 

 e 
 
 AS A SLIGHT TOKEN OF ADMIRATION 
 AND APPRECIATION FOR KINDLY HELP 
 AND AD\'ICE RENDERED THE WRITER 
 THROUGH YEARS OF ASSOCIATION, THIS 
 BOOK IS DEDICATED TO THE MEMORY OF 
 
 GREENE VARDIMAN BLACK, M.D., D.D.S.,Sc.D., LLD. 
 WHOSE PERSISTENT AND UNTIRING EF- 
 FORTS IN THE FIELDS OF SCIENCE HAVE 
 IMMEASURABLY BENEFITED NOT ONLY 
 THE PROFESSION OF WHICH HE WAS A 
 MOST DISTINGUISHED MEMBER, BUT HU- 
 MANITY AS WELL. 
 
PREFACE 
 
 'I'lic rcvisiiiii (if a foriiicv cditidii (if tlii> Imok lia> rc>iilli'<l 
 in \cry nearly a t'lmi-rdld ciilar.iAfincnt. 
 
 I*r('\aiiin,y- dental educational ine1li(Hl>. altlmuuli eoxcrin- 
 (inly those sulijects I'dlisidered essential, leave little time to I lie 
 he.niiiiH'i- I'oi' eollatei-al readin.ii'. In tlie lionr to lioiir transition 
 ot" his mind from one recitation to another llie student some 
 times fails to realize the hreadtJJ and scope of some iiarticular 
 subject, or its relation as a ])art to the whole. This is esjieciallv 
 true in the prosthetic field. Innumeralile de\ ices and nu'tlio(ls 
 of teolinie have been evolved Tor the replacement ot lost natn 
 ral teeth. To bnrdeu the student'-- mind with all of these 
 would he im])racticable. 
 
 The writer has endeavored to introduce the essentials in 
 four main subjects of jjrosthesis. \i/.., denture, crown. Iu-id,i;c 
 and inlay construction, with sul'licient elahoratimi to enahle 
 the be^'inner to acquire a ]M-actical as well as theoretical 
 knowledii'e of them. Sti'ess is laid upon the fad that, althou,i;h 
 involvin.i;' many ]u-olilenis in ])hysics and mechanics, the call 
 ing of a prosthetist is nuich more than that of a mechanic. 
 The appliances which he constructs are jilaced in ajiposition 
 to or rest upon living, sensitive tissue susceiitilile to i>atho 
 logic changes when substitutes are not well ]ilainied. Fre 
 (juently, as a result of improjjer itlanning, many restorations, 
 although well executed from a mechanical standjioint, result 
 in infinitely more harm than benefit. 
 
 A synopsis of color ])rinciples has been included because. 
 without a knowledge of crude jirimary colors and their com 
 l)lenients, it is impossible to discern fine distinctions between 
 attenuated tints and their comi)leineiits, as should he done in 
 the harmonious selection of teeth. 
 
 A section on metallurgy has been incoriiorated, since the 
 prosthetist is constantly dealing with metals and alloys in one 
 form or otlier; conse(iuently a knowledge of their pliysical 
 properties is essential. The niifliiw of recent discoveries has 
 been added, with the idea of exciting further interest in the 
 wonderful phenomena of the elements and their relation to 
 eacli other. 
 
 A section on the history of prosthesis has been added, so 
 that the student may form some conception of the sequent 
 
growth ami proj-rcss in tlii> licM. Uriel' thouiiii it is, the 
 subject-matter lu-eseiiteil iiixoKctI a iMinsidcraMc cxiiemlituve 
 of time. It is IioikmI that i1 ma> aiil in i-nundiiig nut the 
 beginner's (•()ncc|)ti()ii of the brca(hli and scoiic dl' the hchl he 
 is entering. 
 
 Tlie writer desires to e\])ress iiis ap]>reeiation to various 
 individuals, organizations and supply houses, as follows: 
 
 To the National Dental Assoeiatioii, tlirougli its officers, 
 for the use of cuts which appeared in Dr. (Jnerini's History 
 of Dentistry. 
 
 To tile S. S. W'iiite Denial Aiannfacturing Conipany for 
 inauy cuts throughout the text, and i)articularly those relating 
 to crown and bridge work, included in the chapter on history. 
 
 To the Dentists' Supply Company of New York for Dr. 
 .). Leon Williams' typal forms of teeth and Dr. Gysi's aiipli- 
 ances. 
 
 To II. D. .lusti & Son, tiirough -Mr. IJowe; Ash »& Sons, 
 through Mr. Sykes; Lee S. Smith & Co., Samuel A. Crocker, 
 Ransom & liandolj)h, Cleveland Dental Supply Company, 
 J. W. Ivor3% Lea & Fel)iger, Johnson & Lund, Goldsmith Bros., 
 Detroit Dental Manufacturing Com]iany and others for vari- 
 ous cuts used through the text. 
 
 To Dr. A. J. Bush of Columbus, Ohio, for his essay and 
 <'harts on the classification of fixed bridgework. 
 
 To Dr. L. J. Weinstein of New York for his recent work 
 on alloys of gold, investments and fluxes. 
 
 Finally, thanks are due to the untiring efforts of my 
 assistant, Dr. Joseph Ridgway, for help in arranging text and 
 illustrations and in ]n'oofreading. 
 
 James Hakkison Protheko. 
 Chicago, January 25, 1916. 
 
TABLE OF CONTENTS 
 
 CHAi'Tl-:R 1 
 
 PROSTHETIC DENTISTRY 
 
 General remarks — The three principal objects desirable to attain in den- 
 ture construction — Restoration of the function of mastication — Restora- 
 tion of disturbed facial contour and fulfillment of general esthetic re- 
 quirements — The construction of dentures that may be worn with com- 
 fort Pages I to (I 
 
 CllAl'Tl'lR II 
 
 BODILY FUNCTION'S CONCERNED IN DIGESTION 
 
 Metabolism — Impairment of bodily functions — The mouth — The lips — 
 The vestibule — The oral cavity proper — Mucous membrane — Epithe- 
 lium — The palatine vault — The liony structure of the hard palate — 
 Palatine foramina — Thickness of the palatine process of the maxilla — 
 Mucous membrane of the palate — The rugae — The tongue — The sense of 
 taste — The salivary slands Pages 7 to Ki 
 
 CHAPTKR III 
 
 EXAMINATION OF THE MOUTH 
 
 Position of patient — Examination of mouth when natural teeth are present — 
 Examination of edentulous mouths — Preparation of the mouth tor den- 
 tures — Spongy borders — Reduction of sjiongy borders — Temporary den- 
 tures — Permanent dentures Pages lii to 22 
 
 chapt]':r IV 
 
 ARTIFICIAL DENTURES 
 
 Physical and mechanical problems involved in their con'struction — I<'ull den- 
 tures — Adhesion — Atmospheric pressure — Retention by means of atmos- 
 pheric pressure — Conditions necessary for retention — Relieving pressure 
 over hard areas in upper dentures — Vacuum rhaTiibers — Compensating 
 for expansion of the cast — Position and outline form of the distal mar- 
 gin of an upper denture — Preparation of lower impressions — Soft alveo- 
 lar l)orders Pages 2" to 32 
 
 CHAPTI'.R \ 
 
 IMPRESSION TKAYS 
 
 Definitions of some commonly used terms — Use of the terms "Cast'' and 
 "Model" — Impression trays — Tray nomenclature — Tray adaptation — Con- 
 forming the tray by bending — Conforming by cutting — Additions to the 
 tray — Special trays — Cast — Swaged — Trays of ideal baseplate — Metallic 
 extensions to stock trays Pages ^^'■', In 4n 
 
 (11 M'TI'.R \l 
 
 IMPRESSIONS AND IMPRESSION MATERIALS 
 
 Ri'(|uircmenls — Classification — Plaster of Paris — Manufacture — Physical 
 properties — Setting — Strength of hardened gypsum — Time required to 
 crystallize — Size of crystals — Influence of mixing on quality — Expansion, 
 measurement of — Contraction — Warpage — Means of obviating — Compres- 
 sibility of — Advantageous properties of — Impression compounds similar to 
 plaster — Cement used as an impression material — Modeling compound — 
 
 Beeswax — Beeswax and paraffin — Hard bite wax — Gutta percha 
 
 Pages t1 to 112 
 
viii •lAI'.l.l'", ()!■• CONTENTS 
 
 CIlAl'Tl'.k \ll 
 TECHNIC OF IMPRESSION TAKINH 
 I'lilHT iiiipressions indications for use of plaster — Preliminary steps — 
 I'osition of patient — Position of operator — Selecting and fitting trays — 
 .\Iixins tlie plaster— Introduetion of filled tray — Securing peripheral 
 adaptation — Muscle marking the periphery — Dislodgins and removal 
 of impression — Lower impressions — Selection of tray — Position of 
 patient — Position of operator — Muscle marking — Partial cases, classi- 
 fications of — Taking impressions of partial cases — Combination ini- 
 liressions of wax or modeling compound and plaster — Removal of 
 impression — Assembling the fracturd pieces — Hreakiug an impression 
 along definite lines — Impressions of modeling compound — Full cases — 
 Manner of softening the compound — Introducing the filled tray — Secur- 
 ing adaptation — Reheating for corrective measure — Summary of steps. 
 Pages G:i to Sy 
 
 (•ii.\1''I'i-:r \'iii 
 
 PRODI'CTIOX OF CASTS 
 
 I'lcainifnt and tillint; of impression in the production of casis aiul models — 
 Staining fluids — Separating mediums — Classification of separating me- 
 diums — Requirements — Alcoholic solution — Varnishes — Ethereal solu- 
 tions — Collodion — Soap — Aciueous solutions — Oils — Forms for casts and 
 models — For celluloid cases — For cast metal bases — Models for the 
 production of dies — Models with cores — Materials used for casts — Mag- 
 nesium oxychloride — Spence's plaster compound — Coarse building plas- 
 ter — French's regular plaster — French's impression plaster — Commercial 
 plaster — Deleterious effect of accelerators on casts — Maniinilation of 
 various kinds of materials in cast production — Filling impressions — Re- 
 moval of impressions from hardened casts — Full and partial cases — 
 Artificial stone — Description of — Advantages and Disadvantages — Dis- 
 covery of Pages 90 to 117 
 
 ciiArrh:!'; ix 
 
 BASES FOR ARTIFICIAL DENTURES 
 
 Re(|uisite properties — liases of gold — Platinum — Aluminum — Tin Alloy — 
 Vulcanite — Celluloid — Thermal conductivity — Cause of oral inflam- 
 matory conditions under vulcanite bases — Deleterious effect of color- 
 ing matter in vegetable bases — Mechanical irritation — Unhygienic 
 conditions Pages IIS to 12.', 
 
 CHATTER X 
 
 SWAGED JIETAL BASE DENTURES 
 
 Comparative results in adaptation of swaged and vulcanite bases — 
 Sequent steps in swaged base denture construction — Sequent steps in 
 vulcanite denture construction — Appliances and accessories used in 
 die and counterdie construction — Molding flasks — Molding sand — Sieve 
 — Talcum powder — Straight edge — Heating appliances — Melting ladle — 
 Die metal — Zinc — Shrinkage of metals in passing from liquid to solid 
 state — Treatmetit of plaster models to arrest expansion — Babbitt metal 
 — Melotte's metal and other fusible alloys — Composition of fusible 
 
 alloys — Counterdie metal — Whiting and alcohol solution — Brushes 
 
 Pages 126 to 1 oS 
 
 CHAPTER XI 
 
 TE'CHNIC OF DIE AND COUNTERDIE CONSTRUCTION 
 
 Forming the sand matrix — Various methods of removitig the model from the 
 sand — Necessity for the use of cores — Construction of sand matrix in 
 the Hawe's flask — Forming the die — Melting the die metal — Casting the 
 die — Inspection and correction of the die — Construction of the counter- 
 
TABl.E OF CONTENTS ix 
 
 (iic — .Melting the counterdie metal — Casting the counterdie — Construction 
 lit the counterdie by dipping — Separation of the die and counterdie — 
 I'artial counterdies, construction of — Matrix counterdies — Parker shot 
 swaser — Counterdies for partial cases F^ages 139 to lO'i 
 
 CllAl'll'k XII 
 
 CONSTIilCTION OF SWACFD DENTURE BASES OF COLD— ( Upiier 
 Cases) -^,^^ 
 
 Seciiiiiin pattern for the gold plate — Carat and gauges of .yold used for den- 
 lure liases — Annealing the plate — Oiling the die and counterdie — Cleans- 
 ing the plate — Pickling — Conforming the plate to die — I'pper cases — 
 Various steps of — Use of partial counterdies — Swaging in the counter- 
 die — Final trimming and finish — Securing anchorage for the teeth to 
 ' baseplate — Various means employed — Forming peripheral shoulder for 
 finish of the vulcanite — Locating position of wire line on baseplate — 
 Attaching wire anchorage loops — Swaging full lower denture bases — 
 Various steps described — ^Construction of jiartial baseplates of gold — 
 Various ways of reinforcing the baseplate — How to estimate the proper 
 ihickness of a double baseplate — Soldering doubled bases — Application 
 of frictional appliances in partial cases — .Method of securing exact rela- 
 tionshi]! — Attaching teeth to baseplate by soldering. ... Pages ICC to IS'.t 
 
 ch.\pt]':r XI] 1 
 
 ALUMINUM BASE DENTURES 
 
 Cast bases of aluminum — Cause of warpage in cast bases — Imperfect den- 
 sity of cast bases — Action of oral fluids on aluminum — Granular struc- 
 ture of aluminum — Casting by the indirect method — Technic of form- 
 ing the wax model — Investment of the wax mode! — Preparing the case 
 lor casting — Casting the fused metal — Finisliing and swaging — Attach- 
 ing teeth to base with vulcanite — Direct method of producing a cast 
 base aluminum denture — X^se of centrifugal casting machine — Technic — 
 -Vli.xing and applying the investment to the wax model base and cast — 
 Investing the case in flask — Drying out the case— iCasting — Important 
 projierties of aluminum in reference to casting — Swaged bases of alum- 
 inum — Comparative durability of cast and sw'aged bases of aluminum — 
 Summary of causes of deterioration of swaged bases — Technic of swag- 
 ing — Developing the vulcanite shoulders and anchorages — Forming the 
 shoulder — Spurring the base — Anchorage by perforation — Use of a 
 
 doubler — Some facts on the history of aluminum castings 
 
 '. Pages 189 to 22li 
 
 CILVPTF-R Xl\ 
 
 WEIGHTED LOWER DENTURES 
 
 Dentures of weighted vulcanite — Vulcanite dentures weighted by means of 
 a metallic core — ^Cast metal bases — Technic of a weighted cast base — 
 Flasking the w-ax model base plate — Casting the base — Modification of 
 the foregoing method — History of the cheoplastic process. 
 
 VULCANITE BASEPLATES (Double Vulcanization! 
 
 Technic of construction — Construction of temiiorary baseplates — Meal base- 
 plate — "Special" — Temporary Ijasejilates of metal Pages -21 to 2^.2 
 
 ■ ClLM'Tl-.K X\- 
 
 RETENTION OF PARTIAL DENTURES 
 
 Atmospheric pressure and adhesion — Frictional retention of partial den 
 tures — Specialized frictional appliances — ^Clasps — Objection to the use 
 of clasps — Advantages derived from the use of clasps — Reciuisites of a 
 clasp — Adaptation — Resiliency — Inherent strength — Gauges of metal 
 lommonly employed — Types of clasps most commonly used — Partial 
 
X TAIil.K OF CONTENTS 
 
 Hal band clasp — Half round wire t-lasp — Wire or loop clasp — The stop 
 clasp — The double stay — The stay clasp — Indications and contraindica- 
 tions governing the application of clasps — Denture balance — Fulcrum 
 line — Object in using specialized frictional appliances. . Pages 233 to 24!t 
 
 CHAPTER XVI 
 
 TECHKIC OF CLASP CONSTRUCTION 
 
 Axial contour forms of bicuspids and molars — Outline of steps of clasp con- 
 struction — Securing impression of tooth to be clasped — Rebuilding im- 
 pression for reception of molten die metal — Casting the die — Cutting 
 the clasp metal to suitable dimensions — Securing peripheral adaptation 
 of strip to die with pliers — Securing surface adaptation with hammer — 
 Final adaptation of clasp to die — Soldering stops and anchorage lugs 
 to clasp — Finishing the clasp — Various methods of clasp construction — 
 Combination of pure gold with clasp metal — Cast clasps — The wire loop 
 clasp — Continuous and open loop clasp — Securing relation between 
 clasps, the teeth they embrace and the baseplate — Taking impression 
 
 of clasps, teeth and baseplate — Soldering clasps to baseplate 
 
 Pages 25(1 to 2fiS 
 
 CHAPTER X\'H 
 
 THE MASTICATORY .MECHANISM 
 
 The .Masticatory apparatus — The maxilla — The mandible — Functions — Gen- 
 eral description — Movements — Tempero-mandibular articulation — The 
 condyles — The condyle path — Variations in pitch of paths — Muscles of 
 mastication — The masseter — Temporal — External pterygoid — Internal 
 pterygoid — Jluscles which depress the mandible — Muscles which con- 
 trol the position of food — Summary of muscular action on the mandible 
 — Mandibular ligaments — Capular — External lateral — Internal lateral — 
 Spheno-mandibular — Stylo-Mandibular — The teeth — Occlusal surface 
 markings — The central sulci of bicuspid and molar teeth — The bucco- 
 lingual grooves — The masticatory or rectangular groove — Arrangement 
 of the teeth in the dental arches — Occlusal view — Anterior curvature — 
 Incisal view — Alignment of the posterior teeth — Buccal view of upper 
 arch — The plane of occlusion — Curvature of occlusal plane — Relation- 
 ship of planes of occlusion to condyle paths — Governing factors in man- 
 dibular movement — The incisor path — Condyle movement in protrusion 
 — Function of incisor teeth in protrusive effort — Lateral movements of 
 
 the mandible — ^Centers of mandibular rotation Relation of lower to 
 
 upper teeth on pivotal side — Side movements not controlled by rotat- 
 ing centers — Relation of lower to upper teeth on protruded or balancing 
 side — The compensating curve — The curve of Spee — Modification of the 
 compensating curve Pages 2011 to 30?, 
 
 CHAPTER XVHT 
 
 CONSTRUCTIO.X OF FULL DENTURES 
 
 Anatomic method — Masticatory movements of the carnivora. herbivora and 
 omnivora — Main features of anatomic methods — Present methods of 
 technic in anatomic denture construction — Snow appliances and meth- 
 ods — Face bow — Bite gauges — General constructive steps — Occlusion and 
 contour models — Requirements of a baseplate — Requirements of the 
 occlusion rim — Construction of occlusion models — Approximate depth 
 of occlusion rims — Bucco-lingual position of upper and lower wax rims in 
 relation to border crests — Trial of occlusion models in the mouth — 
 Testing adaptation of each baseplate to its ridge — Establishing height 
 of lower occlusion rim — Restoring disturbed facial contour — Marking 
 high and low lip lines — Jlarking median line — Locating outer ends of 
 condyles — ^Application of bite fork to upper occlusion model — Meaning 
 of the term, "Taking the bite" — Difficulty encountered in taking the 
 bite — Various methods of securin.g the bite — A practical method tor 
 securing a correct bite — Inserting bite fork in upper occlusion model — 
 
TABI-E OF CONTENTS xi 
 
 Adjusting face bow to occlusion models — Adjusting face bow with 
 occlusion models attached to the occluding frame — Attaching casts to 
 the occluding frame — Registering condyle paths of patient — Christen- 
 sen's method — Technic of condyle registration — Limit of protrusive 
 mandibular movement — Adjusting condyle paths of occluding frame — 
 Developing compensating curves — Fundamental principles — Practical 
 steps — The Ulsaver method — Omitting development of compensating 
 curve Pages 304 to 354 
 
 CHAPTER XIX 
 
 ESTHETICS OF TOOTH SELECTION 
 
 General considerations — Classification of temperaments — Harmony defined — 
 Esthetics defined — Intuitive and acquired esthetics — Facial outlines — 
 Natural tooth forms — Reproduction of natural tooth forms in porcelain 
 — Observed outlines of natural teeth in the mouth — The color problem 
 in tooth selection — A synopsis of color principles — Color — Primary col- 
 ors (pigments) — Secondary colors — Tertiary colors — Intermediate col- 
 ors — Complementary colors — Color functions of the visual organs — Colors 
 found in natural teeth — Suggestions Pages 350 to 381 
 
 CHAPTER XX 
 
 ARRANGING AND OCCLUDING THE TEETH 
 
 Tipper arch — Arranging the six anterior teeth — Arranging the posterior teeth 
 — Arranging the lower in occlusion with the upper teeth — Testing the 
 occlusal surfaces for working efficiency — Securing contact of the lingual 
 marginal ridges — Arranging the six lower anterior teeth — Developing 
 balancing contact — Final test with carbon i)aper — Developing the con- 
 tour of dentures in wax — Artistic principles involved — Developing the 
 gum festoons — Trimming peripheral outline of the dentures — Finishing 
 touches in carving gums — Finishing lingual surfaces of wax model den- 
 tures — Development of the rugae — Trial of the dentures in the mouth 
 — Final finish of the model dentures — Removing the casts from occlud- 
 ing frame Pages 382 to 40(; 
 
 CHAPTER XXI 
 
 REPRODUCTION OF THE WAX MODEL DENTURES IN PERMANENT 
 MATERIALS 
 
 Sectional molds — Flasks — Fitting cast and wax model denture in Hask — Flasl\- 
 ing the wax model denture — Separating the flask — Preparatory steps — 
 Opening the flask — Clearing the matrix of wax and baseplate material 
 — Treatment of first section of mold containing cast — Providing for 
 escape of surplus rubber — Steps preparatory to packing the matrix — 
 Heating the rubber before introducing it in the matrix — Heating the 
 matrix previous to packing the rubber — Preparing the rubber for pack- 
 ing — Basic rubber — Packing the matrix — Packing the gum facing — Pack- 
 ing the basic rubber — Gauging the amount of rubber required — Flask 
 closing — Estimating the force exerted by the screw — Test closing of the 
 flask — Treatment of cast surfaces for vulcanization — Screw presses.... 
 Pages 406 to 435 
 
 CHAPTER XXII 
 
 VULCANITE 
 
 Rubber — Caoutchouc — Formulas for dental rubbers — Vulcanizable rubbers 
 employed for denture bases — Pink rubber employed for gum facing — 
 Pink granular gum facing — Chemical constituents of rubber — ^Chemis- 
 try of vulcanization — Porosity of vulcanite and how to obviate it — Clos- 
 ing flasks with spring pressure — Dimensional changes occurring in rub- 
 ber during vulcanization — Expansion — Contraction — Vulcanizers — Safety 
 devices — The thermometer — Steam gauge — Table of steam pressure — 
 Gas regulators — Time regulators — The safety valve — Vulcanization of 
 cases in whicli automatic flask closing devices are used — Vulcanization 
 
xii TAItl.l': OK CONTEXTS 
 
 of cases in which flasks are closer! and bolted before viilciirii/.alion — 
 Summary of facts of importance in regard to time of vulcanization — 
 Removal of the flask from vulcanizer — Removal of denture from flask — 
 Finishing the denture — Reiiroduction of the rugae — Use of calipers — 
 Final polishing of the denture — p-inishing touches — Final fitting in the 
 mouth — Finishing the palatine surfaces of a denture — Construction of 
 ;i full ui)]ier or lower denture — Upper cases — I>ower cases. 
 
 THE GYSl SYSTEM OF ANATOMIC APPI^IANCES 
 
 Applicaiiou in denture construction — Registering the forward condyle move- 
 ment — -Mounting casts on the articulator — Registering the incisor jiath 
 — Registering the lateral condyle paths — Angular inclination of the 
 lateral condyle paths — Subsenuenl steps in denture construction.... 
 Ha.ges 4:jri to il^> 
 
 CILM'TI'.R XXIll 
 
 CONSTRICTION OF PARTIAL OENTl'RKS 
 
 Various types — Planning a partial denture — Baseplates for dcuture.s — Par 
 tial dentures of vulcanite — Technic of construction of partial upper den- 
 tures of vulcanite without clasps — Taking the protrusive bite — Select 
 ing and grinding the teeth — Waxing the case — Flasking — Partial upper 
 dentures of vulcanite with clasps — Partial lower denture of vuleanite — 
 Mounting casts on occluding frame — Registering condyle paths — Arrang- 
 ing teeth — Flasking case — Partial lower gold base dentures — Forming 
 the finishing shoulder for vulcanite — Adjusting the shoulder wire — Ex- 
 tent to which the wire is applied peripherally — Lingual bar dentures — 
 Relation of lingual bar to oral tissues — Forms of lingual bars — Technical 
 steps in lingual bar cases — Variation in form of connection between 
 lingual bar and clasps — Soldering clasps and bar in correct relation to 
 each other — Taking the wax bite — Taking the impression — Artificial 
 stone for casts in partial case.s — The lingual bar combined with gold 
 saddles — Settling of dentures from use — Compensating for settling of 
 gold base saddles — The Roach continuous loop clasp — Technic of con- 
 struction — The open loop clasp — The Balkwill clasp — The Roach ball and 
 tube attachment — Application of the Roach attachment — The .Morgan 
 attachment — Technic of application — The Condit attachment — The Gil 
 more attachment — T.echnic of application — Adjustment of clasps to bars 
 — The palatal arch bar — The Kelly attachment — Technic of applica- 
 tion — The Griswold attachment. 
 
 for:ms of porcelain teeth 
 
 '^lain teeth — Means of anchorage — Plain teeth for vulcanite work — Advan 
 tages — Objections — Diatoric teeth — Countersunk pin teeth — Ash's tube 
 teeth — Plain plate teeth — Various forms of plain teeth — Ash's flat back 
 repair facing — Ash's helix tooth — Saddle back teeth — Continuous gum 
 teeth — Gum teeth for vulcanite work — Gum teeth for metal work — 
 Proportionate parts of teeth^Ridge lap — Shut — Bite — The tooth shade 
 guide — Application of the tooth shade guide in practice. 
 
 A NEW GUM FACING 
 
 Protesyn — Natural dentures reproduced in porcelain teeth and wax 
 
 Pages 170 to .")50 
 
 CHAPTER XXI\' 
 
 CELIATLOID DENTURES 
 
 Discovery of celluloid — Composition — Manufacture — Advantages — Compara- 
 tive strength of celluloid and vulcanite — Disadvantages — General meth- 
 ods of manipulation — Construction of the wax model denture — Flasking 
 — Cutting the waste gates — Clearing the matrix — Selection of blank — 
 Pressing the case — Removal from flask — Finishing — General remarks — 
 Casts for celluloid cases > Pages 551 to 560 
 
TAHLI-: OF CONTKNTS xiii 
 
 CHAl'TER XX \' 
 
 REPAIRING VULCANITE DENTURES 
 
 Kractuie of vulcanite base — Reassembling a fractured baseplate — Securing 
 cast — Melbod of joining the fractured pieces — Forming a bevel joint — 
 Technical steps in repairing a median line fracture — ^Method of flask- 
 ing case — Replacing a displaced tooth by vulcanization — Replacing by 
 casting — Rei)lacement by fusible metal in dovetail — Repairing with 
 amalgam — Repair involving substitution of new tooth — Preliminary dove- 
 tailing of the denture base — Substituting artificial for lost natural teeth 
 in partial cases — Repairing gum section cases — Substitution of a base- 
 plate — Construction of the matrix — Removal of teeth from old baseplate 
 — Forming the wax baseplate — Modified methods of reconstruction — 
 .Mounting casts and old denture on occluding frame — Forming the matrix 
 — Forming the wax baseplate — Correcting imperfect adaptation by sub- 
 stitution of new base — Correcting adaptation by addition of new rub- 
 ber to old base — Correcting adaptation with rubber paste — ^Correcting 
 adaptation with Furlong's plastic rubber — To correct occlusion when 
 adaptation Is satisfactory Pages 5C1 to 587 
 
 CHAPTER XX\1 
 
 CONTINUOUS GUM DENTURES 
 
 Advantages — Disadvantages — Technic — Forming the baseplate — Fitting base 
 plate to mouth — Reinforcing the baseplate — Forming the finishing 
 shoulder for porcelain — Reswaging and cleansing the baseplate — De- 
 veloping the occlusion and contour model — Continuous gum teeth — 
 Selection and arrangement of the teeth — Trial of the wax model den- 
 ture in the mouth — Developing the contour matrix — Investment of the 
 wax model denture — Fitting metal support between teeth and baseplate 
 — Supporting the teeth with wire — Continuous gum body and enamel — 
 Preparation of the body — Application of body to teeth and baseplate — 
 Support for continuous gum cases while fusing — Poreclain furnaces — 
 First baking of the case — Second baking — Preparation of case for third 
 baking — Application of the gun enamel — Fusing the enamel — Special 
 uses of porcelain — Interstitial blocks of iiorcelain — Gum sections — Con- 
 struction of gum section blocks for special cases Pages 58S to (j24 
 
 CHAPTER XXVH 
 
 CROWN WORK 
 
 Preliminary considerations — Structures of the teeth and investing tissues 
 — Physiological relations — Oral pathological conditions — Therapeutic 
 methods of treatment of diseased conditions — Local ansesthetics — Treat- 
 ment after setting a crown — Anatomic and esthetic forms of teeth — 
 Flare of the axial surfaces of bicuspids and molars — Cutting molar and 
 bicuspid bands by the conic system — Stress — Hygienic requirements of 
 crowns. 
 
 PORCELAIN-FACED CROWNS FOR THE ANTERIOR TEEFH 
 
 Technic of construction of a porcelain-faced crown — Upper central incisor 
 — Devitalization, treatment and filling of root canal — Removal of re- 
 maining portion of natural crown — Preparation of root — Removal of en- 
 amel — Smoothing root periphery with files — General form of |)repared 
 root — Testing — Flare of root surfaces — Securing measurement of root 
 periphery — Measurijig and cutting band for root cap — Forming and solder- 
 ing band — Sweating band — Scribing band to gingival outline — Fitting 
 scribed band to root — Trimming band to proper width — Construction of 
 root cap — Soldering band to disc — Removing peripheral excess of disc — 
 Construction of cap by indirect method — Taking impression of root — 
 Constructing the root die — Imbedding die in swaging ring — Swaging root 
 cap — Fitting cap to root — Enlarging root canal for reception of dowel 
 — Countersinking canal opening — Indenting cap in countersunk area — 
 Perforating root cap for reception of dowel — Forcing dowel through cap 
 
xiv ■lAltlJO OF CCX'IION'IS 
 
 into root canal — Maintaining correct relation helwceii diiwcl ;inil ca|i 
 while removing from root — Investing the cap and dowel lor soldering 
 — Taking bite and impression — Use o£ face bow in crown work — Details 
 of taking bite — Securing an impression in plaster — Production of cast 
 from impression — Attaching casts to occluding frame — Selection of fac- 
 ing — Grinding facing to root cap — Beveling incisal edge of facing — 
 Change of color in porcelain due to metal backing — Backing facing with 
 gold — Perforating backing for pins — The Mason spacing calipers — The 
 Young plate perforator — Adapting the backing to facing by burnishing 
 — Swaging the backing — Fixing backing to facing — Fitting backed facing 
 to root cap — Investment of the assembled crown for soldering — 
 Trimming investment preparatory to soldering — Removal of wax — Ap- 
 plying the flux — Developing the lingual contour of crown with solder — 
 Finishing the crown — Setting the crown — Removal of excess cement — 
 Setting a crown temporarily — Removal of a ciown or bridge set with 
 gutta-percha. 
 
 DIFFERENT METHODS OF APPLYING PORCELAIN FACINGS AND RE 
 
 PLACEABLE TEETH IN SINGLE CROWNS AND DUMMIES 
 
 FOR BRIDGES 
 
 Interchangeable tooth facings — Steele's facings — Application to anterior 
 teeth — Application to posterior crowns — Technic for cast dummies — 
 Construction of dummies with swaged cusps — Reflecting the backing 
 over cervical margin of porcelain — Utilizing long pin plate teeth for re- 
 movable facings — The Evslin interchangeable tooth — Technic for anterior 
 crowns — Technic for posterior crowns — Technic for anterior dummies in 
 bridgework — Interchangeable teeth — The Goslee tooth — Technic of ap- 
 plication in crown and bridge work — The Gardner replaceable tooth — 
 Application in crown and bridge work — The Merker replaceable tooth — 
 Diatoric teeth used as replaceable teeth. 
 
 FULL-CONTOURED PORCELAIN CROWNS 
 
 Fixed dowel crowns — Technic of plain Logan crownwork — Adapting crown 
 to root — Securing peripheral adaptation of crown base to root — Setting 
 the crown — The banded Logan crown — Technic of application — As- 
 sembling the several parts — Investing — Soldering — Finishing — The Davis 
 crown — Application of plain Davis crown — Reducing peripheral shoulder 
 — General modification of crown by grinding — Setting I he crown — The 
 Davis crown in bridgework — The cast base Davis crown — Technic of 
 
 a cast base crown — The banded Davis crown — Technic 
 
 Pages fi24 to T-'it 
 
 CHAPTER XXVIII 
 
 THE GOLD SHELL CROWN 
 
 Advantages — Disadvantages — Where indicated — .Modifications — Technic of 
 construction — Preliminary preparation of tooth or root — Restoring badl.\' 
 decayed natural teeth for ancliorage purposes — Amalgam restoration — 
 Cast restoration — Cases of excessive restoration — Wedging — Prepara- 
 tion of tooth for band — Reduction of occlusal surface — Reduction of 
 axial wall — ^General form of prepared tooth or root — Testing correctnes.'-; 
 of root preparation — Securing peripheral measurement — Determining 
 width of band — Cutting band — Cutting a cone band — Soldering — Fitting 
 band to root — Contouring — Forcing band to position on root — Taking 
 the bite — Mounting the bite on occluding frame — Developing cusps of 
 crown in plaster — Typical forms of natural teeth — Upper right first 
 molar — Lower right first molar — Lower right second molar — Upper left 
 first bicuspid — Upper right second bicuspid — Lower left first 
 bicuspid — Lower left second bicuspid — Reproducing the cusp sur- 
 faces in gold — Constructing the counterdie — Direct method — Indirect 
 method — Developing a counterdie with Metalline compound — Swag- 
 ing the cusps in an open counterdie — Removal of peripheral sur- 
 plus of gold — Adapting occlusal cap to liand — Developing the marginal 
 ridges of crown on axial band — Developing the cusp surfaces in a 
 
TABLJi; OF CONTENTS xv 
 
 swager — Assembling and soldering the band and occlusal cap — Finisliing 
 the crown — Setting — Casting the cusps — Cast crowns — The shoulder 
 crown — Preparation of the natural tooth — Construction of the crown — 
 Seamless crowns — The matrix method — Swagins the crown — The die 
 method — Swaging the crown — Finishing — Reproducing natural tooth 
 tdi'nis in inlay wax Pages 735 to 782 
 
 CHAPTER XXIX 
 
 BRIDGBWORK 
 
 Engineering principles — Application of stress to substructure of a bridge — 
 The arch bridge — Girder or truss liridges — Ponton bridges — Cantilever 
 bridges. 
 
 DENTAL BRIDGEWORK 
 
 (General classification of bridges — Distinction between fixed and removable 
 bridges — Fixed bridges — Fixed bridges so constructed as to be remov- 
 able — Fixed saddle bridges — Individual saddles — Sanitary bridges — Ex- 
 tension bridges — Important factors to be considered in planning fixed 
 bridges — Abutments and piers — Preparation of abutment and pier roots 
 — Inlay abutments — Displacement of inlay abutments. 
 
 CLASSIFICATION OF FIXED BRIDGEWORK 
 By Dr. A. .1. Bush 
 Multiplicity of methods — Prime object of crown and bridge application — 
 The basis of success — Advantages of classifying fixed bridges — Simple 
 — Compound — Complex bridges — Proposed law — Simple bridge defined 
 — Compound bridge defined — Complex bridge defined — Argument in sup- 
 port of the classification and law proposed — Possible masticatory stress 
 — Various charts of compound and complex bridges formed by joining 
 simple anterior bridges, uni- and bilaterally with simple posterior 
 bridges. 
 
 APPLICATION OF FIXED BRIDGEWORK 
 
 Technic — Requirements of dummies — Construction — Variation in the forms 
 of dummies — Assembling the bridge — Investment — Soldering — Finishing 
 —Setting. 
 
 THE CARMICHAEL ATTACHMENT 
 
 Construction — Finishing — :Modified technic — Application to cuspid and bi- 
 cuspid teeth. 
 
 REMOVABLE ATTACH.MENTS FOR FIXED BRIDGES 
 
 The Corcoran attachment — Application — Construction — The Heddy attach- 
 ment. 
 
 REMOVABLE BRIDGES 
 
 Attachments — Telescoping crown — The split dowel crown — Assembling the 
 parts — Constructing the crown base — Constructing the saddle — Attach- 
 ing the teeth — Finishing the bridge — Setting the root caps — General re- 
 marks — The Goslee inlay clasp attachment — The split dowel — Lingual 
 half crown — Construction — Finishing the attachment — Modification of the 
 telescoping molar crown. 
 
 REPAIRING CROWNS AND BRIDGES 
 
 Replacing porcelain facings — The Ash fiat back repair facing — The Dime- 
 low facing — The Steele repair outfit — The Br\ ant repair outfit — Long 
 pin facings used in Repairs — Starr's method — Riveting facing to back- 
 ing — Removing c banded dowel crown — Replacing facing on crown 
 removed as described — Removing dowels from root canals — Little Giant 
 post puller — The S. S. White crown repair outfit — Removal of a dowel 
 from the deeper portion of a root canal — Removing a shell crown by 
 slitting — Removing a shell crown by leverage force — Repairing crowns, 
 
 slit in the manner described — Repairing a fractured bridge 
 
 Pages 7S3 to 872 
 
xvi 'I'Alil.l': t)l'' COXTICXTS 
 
 CIIAI'TI'.W X\.\ 
 
 PORCELAIN CROWN AND RRIDGE WORK 
 
 I'Dicrliiiii frown work — Indications for use — The banded, liaked iiortrlaiii 
 crown — Constructing root cap — Application of porcelain Ijody — Modified 
 forms of porcelain crowns — I'orcelain jacket crown — Technic of con- 
 strucljon — Taking imjiression of tooth — Constructing the die — Forming 
 the platinum cap — Constructing the casts — Application of porcelain — 
 Baking the crown — The "Land Jacket Crown" — Prei)aration of tooth 
 — Construction of cap — Taking bite and impression — Selection and grind- 
 ing of facing — Application and fusing of porcelain — Porcelain bridge- 
 work — Cleneral considerations — Porcelain bridge construction — Prepara 
 tion of roots or teeth — Construction of cap and shell crowns for abut- 
 ments — Construction of saddle — Locating and fitting truss bars — Solder- 
 ing — Application of body — Fusing the porcelain — Finishing and setting 
 the bridge — X'arious types of metal structures Pages STH to ttoii 
 
 fllAl'Tl'.K XXXl 
 
 PORCELAIN AND .METALLIC INLAYS 
 
 Porcelain — Eaily application of porcelain in denture construction — Correc- 
 tion of warpage in the all-porcelain denture — Basic ingredients of por 
 celain — Kaolin — Preparation — Feldspar — Preparation — Silex — Prepara- 
 tion — Properties — Proportions — Oxides of metal used in coloring porce 
 lain — Gun enamel — Crown bridge and inlay porcelains — High and low 
 fusing porcelain bodies — Comparative value. 
 
 PORCELAIN INLAY WORK 
 
 Advantages — Objections — Friability — Constructive difficulties — Inlay reten- 
 tion — ^Warpage of the matrix — Annealing the foil — Warpage due 
 to improper support — Careless handling — Locations favorable for 
 Iiorcelain inlays — General rules for cavity i)reparation — Details — Gingival 
 third cavities in the anterior teeth — Proximal cavities in the anterior 
 teeth not involving angle.s — Buccal cavities — Proximal cavities in an- 
 terior teeth involving angles — Bicuspid and molar cavities involving 
 an axial and an occlusal surface — Restoration of incisal edges and 
 angles — Production of the matrix — Burnishin.g — Removal — Final anneal 
 ing — Selection — Application and fusing of the porcelain — Selection of 
 shade — Mixing the porcelain — .Application to the matrix — Furnaces and 
 appliances used in fusing — First baking — Second baking — Deleterious 
 effect of overfusing — The shadow |)robIem — Removing the matrix — 
 Etching the cavity surfaces of the inlay — Setting. 
 
 GOLD INLAYS 
 
 ("!avity preparation for gold inlays — Outline form — Resistance form — Reten 
 tion form — Pin anchorages — Convenience form — Removal of any remain- 
 ing carious dentine — Finish of enamel walls — Toilet of cavity — Some 
 special methods of cavity preparation. 
 
 THE MATRIX METHOD OF INLAY PRODUCTION 
 
 Direct method of producing a matrix — Variation in method — Indirect method 
 of forming the matrix. 
 
 CAST GOLD I.XLAYS 
 
 General remarks — Physical properties of the materials employed in castinc 
 — Expansive and contractile forces — Principal sources of error in inlay 
 construction — Waxes — Paraffin — Effect of combining wax and paraffin 
 — Essential properties of a wax — Elastic properties of wax — Investment 
 materials — Expansion of investment ring and investment material — 
 Essential properties of an investment material — Dimensional changes 
 in gold due to temperature changes — Comiiensating for errors due to 
 contraction of gold — Result of contraction of gold on inlay adaptation 
 — Technic of cast gold inlays — Forming the wax model — Investment 
 
TABLE OF rOXTEXTS xvii 
 
 ot llip wax model — Drying out the investment and eliminating llie wax 
 — Variation in the method of preparing the invested ease lor casting — 
 The casting of gold — Rough finishing the casting — Settling the inlay 
 Finishing Pages 9(il to flo!! 
 
 CHAPTER XXXIl 
 
 AX OUTLINE OF .METALI-fRGY 
 
 Facts, hypotheses, theories and speculations — Discovery of elements liy 
 means of the spectroscope — The mutability of matter — Brief outline 
 of recent discoveries — Elemental gases — Discovery of the X-ray — Dis 
 covery of radio-active substances — Decomposition of radium compounds 
 Character of the emanations from radio-active substances — The de- 
 gradation of copper — Debasement of various substances into hydrogen 
 — Summary of statements presented — The elements arranged in the 
 order of their discovery — Arranged in the order of their atomic weighti. 
 — The Kinetic constitution of matter — The viliration of matter — The un 
 equal distribution of elements — Elements and their atomic relation tn 
 each other — Prout's hypothesis — The triads of Dobereiner — The octave. 
 of Xewianrt.s — The periodic system of Mendeleeff — New elements— 
 The elements considered in groups — The elements considered in series. 
 Metals — Metalloids — Forms of matter — Occurrence of metals — Min- 
 erals — Xative metals — Ores — Xoble metals — Base metals — Physical prop 
 erties of metals — Atomic weight — Specific gravity — Melting points 
 Malleability — Ductility — Tenacity — Annealing — Tensile strength — Elas- 
 ticity — Flow — Conductivity — Heat and electricity — Exceptions — Specific 
 heat — Expansion — Co-efficient of expansion of substances — Color — Weld- 
 ing — Welding copper to iron — Aluminothermy — Temperatures common 
 and extraordinary — Soldering — Conditions essential to successful solder- 
 ing — The structure of flame — The Bunsen flame — The blowpipe flame — 
 Micro-structure of metals — Alloys — Matthiessen's theories as to the 
 nature of alloys — Affinity of metals for each other — Liquation — Object 
 in alloying metals — Eutectic alloys^Amalgams — Specific gravity of 
 alloys — Table of some of the physical pro])prties of fifteen metals. 
 
 GOLD 
 
 Occurrence and distribution — Placer deposits — Placer mining — Vein gold — 
 Extraction of gold from ores — Chlorination process — Cyanide process — 
 Physical properties — Preparation of pure gold — Treatment of scrap plate 
 — Alloying gold — Reduction of gold — Boser's rule — Gold solders — Table 
 of mixed caratation — Clasp gold — Platinum solder. 
 
 SOME RECENT WORK CONCERXIXG GOLD ALLOYS 
 By Dr. L. J. Weinstein 
 Author's preface — Introduction — Binary alloy.s — Necessity of a knowledge 
 of binary alloys. 
 
 Section I — Gold and Silver 
 Effect of silver upon gold — Gold and copper — Gold and platinum — Gold ami 
 palladium — Gold and the metals in .group 11 — Iridium — Osmium — Rho- 
 dium — Gold and metals in group III — Gold and metals in group IV. 
 
 Section II — A New Series of Alloys 
 Gold for crown, bridge and plate work — Gold plate No. 2 — Alloys for pros- 
 thetic casting — Gold for inlay casting. 
 
 Section III— Clasp Metals 
 Composition ot clasp metals — Results of rolling and annealing on elasticity 
 of clasp gold of I'arious formulte. 
 
 Section IV — Gold Solders 
 Alloys of gold with metals in group III — Formulae for gold solders. 
 
 Section V — Compounding of Gold Alloys 
 Difficulty of alloying gold with platinum in small quantity — Necessity for pre- 
 venting oxidation in gold and copper alloys. 
 
xviii TABLE OP" CONTENTS 
 
 Section VI — Refractory Materials 
 Investment compounds for soldering — Plaster of Paris — Powdered silex — 
 Formula for investment fompound (soldering) — Investment compounds 
 for casting — Hot or cold mold, using illuminating gas and compressed 
 air blowpipe — Hot or cold mold, using illuminating gas and nitrous 
 oxide or oxygen blowpipe — Compounding of investment materials — Heat- 
 ing of investments. 
 
 Section VII — Fluxes for Soldering and Casting 
 Formula for soldering flux — Reducing flux — Formula for reducing flux — 
 Oxidizing flux — Formula — Formula for soldering flux (substitute) — 
 Table No. 4 — Melting point of tbe new series of alloys and standard den- 
 tal golds — Some of tbe applications of the new series of alloys in the 
 Peeso system of removable bridgework — ^Construction of floors, bands 
 and inner caps — Outer halt bands and telescope caps — Inlay abutments 
 — Construction of saddles — Construction of dummies. 
 
 IRON 
 Occurrence in nature — Reduction of iron ores — Production of wrought iron 
 — Production of steel — The Bessemer process — The cementation process 
 — Hardening and tempering of steel. 
 
 PLATINUM 
 Discovery — Distribution — Occurrence — Physical i)ropertie.s — Fusing point — 
 Uses — Alloys — Dental alloy — Platinum solder and clasp metal. 
 
 IRIDIUM 
 Physical properties and uses — Silver — Ores — Reduction — Amalgamation — 
 Wet method — Lead method — Uses in dentistry — Alloys of silver — Uses 
 in photography — ^Chemistry of photography. 
 
 COPPER 
 Ores — Reduction-uses — Alloys — Brass — Bronze. 
 
 ALUMINUM 
 Occurrence — Reduction — Physical properties — ^Soldering-uses — Alloys. 
 
 ZINC 
 Ores — ^Reduction-properties — LIses. 
 
 CADMIUM 
 Occurrence — Reduction-uses — Alloys. 
 
 LEAD 
 Occurrence — ^Reduction-properties — Uses — ^Alloys. 
 
 TIN 
 Occurrence — Reduction-iiroperties — Uses — Haskell's babbitt metal. 
 
 MERCURY 
 Occurrence — Distribution — Compounds — Alloys — Properties — Reduction. 
 
 Properties — Alloys — Uses. 
 Properties — Alloys — Uses. 
 Properties — Alloys — Uses. 
 Properties — Uses. 
 
 NICKEL 
 
 BISMUTH 
 
 ANTIMONY 
 
 TUNGSTEN 
 
TABLE OF CONTENTS xix 
 
 MEASUREMENT OF PLATE AND WIRE 
 
 The unit of measurement of gauges — Lack of uniformity of the various gauge 
 systems — The Birmingham gauge — Discrepancies of the Birmingham 
 gauge — The Brown and Sharp gauge — Forms of gauges — The jeweler's 
 gauge — The plate and wire gauge — The micrometer caliper — Various sys- 
 tems of wire and plate gauges and their equivalents in thousandths 
 of an inch Pages 960 to 1100 
 
 CHAPTER XXXIII 
 
 A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 The Ebers papyrus — Antiquity of the papyrus — Guerini's History of Dentistry 
 — The Phoenicians — Effect of Egyptian civilization on Phcenicia — One 
 of the most ancient specimens of prosethetic art — The Etruscans — 
 Etruscan dental art — First references in history to prosthesis — Dentistry 
 among the ancient Hebrews — Slow progress of dental prosthesis in the 
 middle ages — First reference to the use of models — First reference to 
 full lower dentures — First record of application of mineral substances 
 for dentures — Retention of partial dentures without the use of ligatures 
 or wires — Fauchard's writings — Transplantation of natural teeth — Crown 
 work in Fauchard's time — Mediaeval bridgework — Full dentures — Con- 
 struction of full dentures by Fauchard — Summary of Fauchard's work 
 — Beneficial influence of Fauchard's writings upon the profession — First 
 work confined exclusively to dental prosthesis — First mention of plaster 
 — First mention of gold bases — Implantation of teeth — Berdmore's ref- 
 erence to artificial dentures — Principal materials used as denture bases 
 — First suggestion of porcelain work — Du Chateau's efforts in porcelain 
 work — The work of Dubois de Chemant — Introduction of single teeth 
 and blocks of porcelain — Introduction of porcelain in the United States 
 — First manufacturer of porcelain teeth in America — Introduction of 
 gold for denture bases — Dies for swaging metal bases — First use of 
 cast denture bases — Special forms of teeth for use with cast bases — 
 Dental vulcanite litigation — Collodion and celluloid as denture bases — 
 Vulcanizing rubber between metal surfaces — Denture bases pioduced 
 by electro-deposition of gold and silver. 
 
 ARTICULATORS 
 
 Casts extended distally to form articulating surfaces — 'Evans articulator — 
 Bonwill articulator — Plain line articulator — Starr articulator — Hayes 
 articulator — ^First suggestion of the face bow — Study of condylar move- 
 ments — Walker's research work — Walker's anatomical articulator — 
 Facial clinometer — Gritman articulator — Snow face bow — Kerr articu- 
 lator — Christensen's work — Snow anatomical articulator — Schwarze 
 articulator — Gysi's work and anatomical appliances. 
 
 CROWN WORK 
 
 Pivot teeth of De Chemant — The grooved flat back facing — Ash's tube 
 teeth — The Wood pivot tooth — The Smith crown — The Clark crown — 
 The Lawrence-Foster crown — The Dwindle crown — The Wood crowns 
 — The Morrison crown — The Black crown — The Bean crown — The 
 Mack crown — The Beers crown — The Gates crown — The Richmond 
 crown — The Gates-Bonwill crown — The Biittner crown — The How 
 crown — The Weston crown — The Logan crown — The Brown crown. 
 
 BRIDGEWORK 
 
 The Bing bridge — Webb's work — Litch's work — Williams' work — Starr's work 
 — Basis of our present system of bridgework — Porcelain bridges — Re- 
 movable bridges. 
 
 INLAYS 
 
 First recorded attempts in filling teeth — First mention of inlays in dental 
 literature — Prehistoric inlay work — The beginning of modern inlay 
 work — Brief summary of inlay work beginning with 1820 — Land's method 
 
XX TABLE OF CONTENTS 
 
 of porcelain inlay work — Bing's metallic lacing — Rollins' method — 
 Dunn's method — Stoke's method — Ames' uielhod — Various methods of 
 inlay production in recent years — Alexander's method — Slow progress 
 of inlay work — Progress of gold inlay methods. 
 
 INCEPTION OF THE WAX MODEL METHOD 
 
 Analysis of the casting process — Forming models in wax of the cast- 
 ing to be produced — Method of forming a sprue or pouring gate — 
 Enclosing the wax model in a single investment — Eliminating the 
 wax pattern by heat — Fusing the metal in close proximity to the 
 mold — Applying pressure to the fused metal to induce sharpness of de- 
 tail in casting — Pioneers in the production of cast work — The Blandy 
 process — Bean's method of casting aluminum — Sauer's method — Reese's 
 method — Hayford's method — The Watt's flask — Martin's method of cast- 
 ing — The Carroll method — The Zeller casting appliances — The Fenner 
 casting appliances — Harper's cast crowns and bridges — The Alexander 
 method — The HoUingworth method — Flask designed by writer — Phil- 
 brook's method — Schottler's clinic — The Lentz casting process — The 
 OUendort casting process — Summary of progress in casting operations 
 — Causes of failure in casting operations — Taggart's method of casting 
 — Recent appliances — The Solbrig casting pliers — The Biber casting ap- 
 pliance — Summary of foregoing facts Pages 1101 to 1201 
 
CHAPTER T 
 PROSTHETIC DENTISTRY 
 
 GENERAL REMARKS 
 
 The science of dentistry pertains to tlie recognition 
 and treatment of diseases of the teeth and oral tissues, of the 
 general neuritic conditions of the head and neck that may 
 have their direct origin in, or be indirectly connected with, 
 the fifth cranial nerve, and of the repair and replacement by 
 operative or prosthetic procedures, of the partial or com- 
 plete loss of the teeth through accident or by disease. 
 
 Prosthetic dentistry is that braucli of dental science 
 which treats of the various methods of replacing the lost 
 organs of the mouth in whole or in part, -the artistic and me- 
 chanical processes involved in such restoration, together with 
 a description of the physical properties and peculiarities of 
 the various materials employed. 
 
 Sjieciiically considered, prosthetic operations may be 
 classed as follows: Construction of crowns, bridges and 
 dentures, obturators and appliances for correcting defects of 
 the palate, appliances for correcting irregularities of the 
 teeth and jaws, appliances for retaining in position fractured 
 bones of the face when reduced, and the construction of me- 
 tallic and porcelain inlays. 
 
 In all prosthetic procediires the attainment of three 
 objects is desirable : First, the restoration of the function of 
 mastication; Second, the esthetic requirements should he 
 given due consideration and ivrought out correctly; Third, the 
 snhstitvte, of whatever character, should cause the wearer no 
 discomfort. The late Dr. Pritchett concisely stated this by 
 saying that in prosthetic procedures "we strive to give our 
 patients dentures that are useful, will lool- well, and he 
 comfortahle." 
 
 RESTORATION OF THE FUNCTIONS OF MASTICATION- 
 UTILITY 
 
 The first consideration is the most im]iortant. When 
 from any cause the function of mastication is interfered with 
 or impaired, the digestive organs are necessarily required to 
 do an extra amount of work for which they are unfitted, and 
 
 1 
 
2 PROSTHETIC DENTISTRY 
 
 which will (iventually result in impaired digestion, systemic 
 disturbances and general ill health of a more or less serious 
 character. Without doubt, many lives are shortened by years 
 because of the partial or total loss of this most important 
 function, and in constructing substitutes for the natural teeth, 
 they should be made to restore, as fully as possible, the 
 function of the natural organs. This point is of such im- 
 portance as to bear repetition by restatement. Ability to 
 masticate and digest food means good health and generally 
 normal bodily functions, while inability to do so entails dis- 
 comfort, ill health, disease and a curtailing of the span of 
 life. 
 
 ESTHETICS 
 
 The second consideration — esthetics — relates to the 
 artistic pliase of i;)rosthesis, the ability to produce or create 
 appropriate and natural appearing devices and substitutes 
 to take the place of the lost natural teeth, to reproduce by 
 skillful teehnic not only a successful masticatory apparatus, 
 but to restore lost facial contour as well. 
 
 The principal part of the face to suffer change by 
 the loss of the teeth, and the consequent absorption of the 
 alveolar process, is the mouth, although at times a consider- 
 able portion of the lower half of the face is modified in out- 
 line. The lips lose their normal pose and assume an un- 
 natural expression, more or less marked in proportion to 
 the loss of the bony substructure. Premature wrinkles form 
 upon and encompass the mouth and cheeks, and an appear- 
 ance of age, not warranted by years, sets its seal upon the 
 subject. 
 
 It is the province of the prosthetist to correct, as far 
 as possible, the ravages occasioned by disease, and time, as 
 well, and restore to the patient his normal appearance. 
 
 To do this the prosthetist should be a master of liis 
 ai't — one who can, at will, imitate nature in her ideal, as we-U 
 as less typical forms and moods. From the nature of his 
 vocation, he should be an anatomist, a sculptor, an artist and 
 an artisan, thorough and proficient in each field mentioned, 
 in order to fulfill, in the highest degree, the requirements im- 
 posed upon him by his profession. 
 
 Many eulogistic effusions on the beauty, attractive- 
 ness and importance of the mouth and teeth are to be found. 
 They have emanated from the artists and poets of every 
 race and clime. They emphasize the high regard and even 
 
PKOS'IHKTIC DKXTlSTltV 3 
 
 veiifi'aiioii in wliidi these features oi' the face have been 
 held by tlie human race in general from time immemorial. 
 The following are some of the selections referred to. 
 
 Lavater, one of the early writers on physiognomy, 
 says, in reference to the mouth: "The mouth is the inter- 
 preter of the mind and of the heart. It combines, both in 
 a state of rest and in the infinite variety of its motions, a 
 world of characters. It is eloquent even in its. silence." * * * 
 "I conjure our painters and every artist whose mission it is 
 to represent man, I conjure them with all my might to study 
 the most precious of all our organs in all its varieties; in all 
 its proportions; in all its harmonies." 
 
 "What shall I say, jjaiuters and designers, that may 
 induce you to study this sacred organ in all its beauteous 
 expressions, in all its harmony and proportions." "Take 
 plaster impressions of characteristic mouths (lips) of the 
 living and the dead: draw after, attentively examine them, 
 learn, observe, continue day after day to study one only; 
 and having perfectly studied that, you will have studied 
 many. * * * Among ten or twenty draughtsmen to whom 
 for three years I have preached, whom I have instructed, 
 have drawn examples for, not one have I found who felt as 
 he ought to feel, saw what was to be seen, or could represent 
 that which was evident." * * * "I expect everything 
 from a collection of characteristic plaster impressions which 
 might so easily be made, were such a collection once formed — 
 but who can say whether such observations might not de- 
 clare too much. The human machine may be incapable of 
 suffering to be analyzed; man, perhaps, might not endure 
 such a close inspection, and therefore, having eyes, he sees 
 not." Lavater further lays down rules for the guidance of 
 the artist, as follows: 
 
 "Distinguish in each mouth a the ujiper lip, singly; 
 h the under lip, the same ; c the line formed by the union of 
 both when tranquilly closed, if they can be closed without 
 constraint; d the middle of the upper lip in particular, and e 
 of the under lip ; / the bottom of the middle line at each end, 
 and lastly g the extending of the middle line on both sides, 
 for unless you disiinguish you will not be able to delineate 
 the mouth accurately." 
 
 Herder, the eminent German poet and critic, says 
 of this prominent feature of the face : "It is from the mouth 
 that the voice issues, interpreter of the heart and soul, ex- 
 
1 PROS'I'UKTIC IJKNTISTRY 
 
 IMTssioii ((f JVcliii.ii', (>r I'liciulsliip, and ol' tlif purest enthu- 
 siasiii. The upi)er li]) translates the inclinations, the appe- 
 tite, the disquietude of love; pride and passion contract it; 
 cunning attenuates it; goodness of heart reflects it; de- 
 bauchery enervates and debases it; love and the passions 
 incarnate themselves there in an inexjiressible charm." 
 
 (Concerning the teeth, Paolo Mantegazza, the noted 
 Italian anthropologist, says: "It is a flaw in beauty to have 
 bad teeth; it is like a spot on the sun. Since the hygiene of 
 the teeth is at the same time the hygiene of beaut^', good 
 dentists merit a golden statue, or at least a place of honor 
 among the principal benefactors of humanit>'. " * * * 
 "The most beautiful teeth are not enough to make a man 
 beautiful ; but ugly teeth would spoil the beauty of the Venus 
 of Milo herself."" 
 
 Again reverting to Lavater's remarks on the teeth, 
 he says: "Nothing is more certain, striking or continually 
 visible than the characteristics of the teeth, and the manner 
 in which they display themselves. " * * * "Whoever leaves 
 his teeth foul and does not attempt to clean them, certainly 
 betrays much of the negligence of his character, which does 
 him no honor. As are the teeth of man, that is to say, their 
 form, position and cleanliness (so far as the latter depends 
 upon himself), so is his taste." 
 
 The loss of the teeth and consequent absorption, 
 to a greater or less extent of the bony substructure support- 
 ing the lips and cheeks, results in marked disfigurement. 
 The exterior of the dental arch, as well as the face, is con- 
 vex. The lips form a movable curtain or pallium, to close 
 the oral opening. They are supported by the dental arches 
 and alveolar borders. The loss of the teeth allows the lips 
 to sink in, and the profile, as well as contour of the face, 
 suffers. 
 
 It requires a keen artistic sense to determine the 
 correct lines of contour to develop in order to restore har- 
 mony in each individual type or cast of countenance. Too 
 much or too slight convexity of the substitute will mar the 
 symmetry and poise of the patient's face, through improper 
 support of the lips. The color of the teeth in artificial cases 
 must harmonize with the color of the eyes, hair and general 
 tone of the patient's complexion. The form, size and ar- 
 rangement of the teeth and their general treatment by grind- 
 ing to simulate wear appropriate to the age of the patient. 
 
PROSTHF-TIC DENTISTRY 5 
 
 must also be determined. No two cases will be exactly the 
 same. Each factor must be studied by itself, and all of the 
 factors considered as a whole in every case that presents. 
 
 The prosthetist's highest attainment in the esthetic 
 field consists in imitating nature so closely that his work 
 cannot be detected by casual or even close observation, and 
 so well done that his patient does not seriously feel the loss 
 of the natural teetli, or will not lie disturbed by the presence 
 of the substitute. 
 
 COMFORT 
 
 The third desirable object sought in denture con- 
 struction is a most important one. It is possible to construct 
 substitutes that fulfill requirements from the standpoint of 
 utility and esthetics as well, and yet cannot be worn by the 
 patient with ease or comfort. Imperfect adaptation of den- 
 ture to tissues, causing undue or uneven pressure at certain 
 jioints; extension of baseplate on palatal muscles so far as 
 to cause irritation, retching, or by the contraction of the 
 muscles, dislodgement of the substitute; impingement of the 
 ])eri])hery of the denture on the labial or buccal muscles or 
 the frenae; rough, unpolished surfaces, particularly in the 
 palatine portion of the denture, are some of the sources of 
 discomfort that impair, and at times seriously inhibit the use- 
 fulness of otherwise well-constructed dentures. 
 
 The ability to recognize such annoying conditions 
 as mentioned, and be able to anticipate and overcome them 
 during constructive processes, is a most important attain- 
 ment, and should be developed by every prosthetist. 
 
 In entering upon the study of dentistry, the student 
 should understand and thoroughly appreciate the fact that 
 the vocation of a dentist embraces a much broader field than 
 is usually accorded it by the public or the uninformed in gen- 
 eral. Dentistry is a specialty of the healing art — medicine — 
 and has been so recognized from ancient times. 
 
 Herodotus (500 to 425 B. C), in writing of the prac- 
 tice of medicine in Egypt, says : ' ' The exercise of medicine 
 is regulated and divided amongst the Egyptians in such a 
 manner that special doctors are deputed to the curing of 
 every kind of infirmity; and no doctor would ever lend him- 
 self to the treatment of ditferent maladies. Thus Egypt is 
 quite full of doctors; those for the eyes; those for the head; 
 some for the teeth; others for the belly; or for occult 
 maladies." (Guerini.) 
 
6 i'UOSTHEtiC DKNTiStRY 
 
 lu tliis (];iy tlic dt-ntisl is a scieutilic sjx'ciulist wlio is 
 constantly called upon to treat living, sensitive, vital tissue; 
 to recognize and treat obscnre, as well as plainly apparent 
 disorders and diseases having their origin in, and adjacent 
 to, the oral cavity. In addition to such treatment, it is the 
 province of the prosthetist, through highly developed me- 
 chanical skill, to replace teeth and parts of teeth that have 
 been lost through accident or by disease. 
 
 The knowledge, skill and handcraft necessary to 
 carry out the requirements mentioned come only with close, 
 long-continued and patient application. The artistic and 
 esthetic, as well as the mechanical faculties, should be en- 
 couraged and developed in the course of study laid down in 
 the dental curriculum, for the student's success depends upon 
 the thorough, harmonious and balanced development of all 
 of these faculties. lie gets out of his course only what he 
 puts into it. The half-hearted acquirement of a few smatter- 
 ing facts is not sufficient in these days of strenuous competi- 
 tion to fit one for the practice of dentistry in general, or any 
 one of its special branches. 
 
 Patience, persistence, energy and enthuiasm are 
 essential to success in the acquirement of a dental education, 
 as well as in other departments of science. Ecjuipjjed witli 
 these qualities, no one can place a limit to the heights attain- 
 able by a student or practitioner in his chosen work. The 
 field is broad. Many scientific problems are still unsolved. 
 Investigators are few and in demand. Preventive measures 
 are being devised and introduced for the benefit of the patient. 
 The public is being gradually educated in the principles of 
 personal care of, and attention to, the teeth. Dental inspec- 
 tion in public schools is being realized, and the children are 
 being taught that good teeth, good health and good minds 
 go hand in hand, in the order named, for without good teeth 
 the health suffers and the mind and mental processes are 
 disturbed. 
 
C n A P T E R 1 1 
 
 BODILY FUNCTIONS 
 
 The human body is an organism, whicli exhibits the 
 I)henomena of life and in and throngii wliich tiie vital forces 
 act. The history of a living entity, its daily routine of life 
 from inception to final dissolution, is one of perpetual change. 
 
 The general epochs in the life of an individual are con ' 
 caption, liirth, a varying period of growth, a vaguely de- 
 terminate period of existence unmarked by radical change, 
 and finally, gradual or sudden diminution and cessation of 
 the vital functions, terminating in death, with ultimate reso- 
 lution of the organism into primal chemical elements or 
 compounds. 
 
 METABOLISM 
 
 In the human body during life, constant changes are 
 continually going on. Every mental effort, every movement 
 of the body or any portion of it, the normal or abnormal, 
 voluntary or involuntary, action of the functional organs 
 themselves, call for the expenditure of energy and result in 
 loss of substance. These changes are known as metabolism. 
 
 Every normal living organism contains within itself a 
 varying amount of reserve force or stored up energy ready 
 for use on demand. To maintain equilibrimn and consequentlj' 
 a normal condition of health, the stock of energy when de- 
 pleted, and the loss of substance as it occurs, must be re- 
 plenished. 
 
 In the human organism this repair of loss is accom 
 plished by taking into the body substances known as food, 
 capable of being masticated, digested, absorbed, circulated 
 and assimilated. Food is composed, more or less, of ex- 
 traneous matter. That is, the intrinsic or nutritive elements 
 contained therein, capable of being assimilated, or replacing 
 waste tissue and developing heat, energy, etc., represent in 
 bulk only a poi-tion of the juaterial taken into the body as 
 food. 
 
 liulky and in fart all varieties of food, when lu-okeu up 
 and finely divided, are more readily acted upon l»y the saliva, 
 the gastric juice and intestinal digestive fluids, and the 
 
 7 
 
8 BODILY FUNCTIONS 
 
 Diitritivi' elements more (jnickly approijriated than when 
 taken into the system unprei)ared by mastication. 
 
 IMPAIRMENT OF BODILY FUNCTIONS 
 
 The bodily functions are carried on by various organs, 
 each of which performs its part in the maintenance of life. 
 Some of the organs are of minor importance. Their functions 
 may cease or the organs themselves may atrophy or be oblit- 
 erated by disease or traumatism, and yet the general healtli 
 of the individual may not be seriously impaired. 
 
 The organs of the special senses are examples of this 
 tyjje, as the loss of hearing, the sense of smell, taste or eye- 
 siglit are of common occurrence, and although the loss of 
 any one of these senses may be keenly felt, yet existence may 
 be prolonged for many years, with a greater or less degree 
 of comfort. 
 
 Other organs are of vital importance. Should they from 
 any cause be destroyed or cease to carry out their functions, 
 the result usually involves serious and permanent impairment 
 of health, or even the cessation of life itself. The respiratory, 
 circulatory, masticatory and digestive organs are examples of 
 the type under consideration. 
 
 THE MOUTH 
 ITS IMPORTANCE IN THE HUMAN ECONOMY 
 
 The cavity of the mouth contains those tissues and or- 
 gans which are of special interest to the oral surgeon and 
 dentist. Through it all food substances and liquids are taken 
 into the body. By the organs contained therein the food is 
 triturated, insalivated, and prepared for deglutition. From it 
 articulate sounds proceed. 
 
 In the oral cavity many forms of bacteria find lodgment, 
 and, on account of tlie heat and moisture present, it furnishes 
 a favorable soil for their propagation and growth. The aver- 
 age mouth usually contains from twenty to fifty varieties of 
 micro-organisms, some harmless, while others are pathogenic 
 in character. The latter, while not always, are frequently 
 present, ready to exhibit destructive energy when favorable 
 conditions develop. For this reason the mouth, under normal 
 conditions, although a neutral focus of infection, is a con- 
 stant menace to the health of tlie individual, unless given 
 proper care and attention. 
 
BODILY FUNCTIONS 9 
 
 The mouth consists of two parts, viz., the vestibule aud 
 tlie oral cavity proper. 
 
 THE LIPS 
 
 One of the most prominent features of the face is the 
 external orifice of the mouth. This is a transverse fissure 
 bounded above and below by the upper and lower lips, respect- 
 ively. At their extremities they unite to form the commissures. 
 Internally they are covered with mucous tissue, and externally 
 with integument. The orbicularis muscle, which largely de- 
 velops mobility aud closes the lips, is situated between the in- 
 tei'nal and external surfaces. Composed as they are of two 
 thick, fleshy folds, and containing within themselves no bony 
 support, they settle inward and liaekward when loss of the 
 teeth, and the resultant absorption of the alveolar process, 
 occurs. It is the province of the prosthetist to restore such 
 deformity of the face by means of suitably constructed and 
 contoured substitutes as conditions require. 
 
 THE VESTIBULE 
 
 The vestibule is that portion of the oral cavity which lies 
 external to tlie teeth and alveolar arches, and internal to the 
 cheeks and lips. It extends from the space just back of the 
 third molar on one side, through which it connnunieates with 
 the oral cavity proper, around the labial aud buccal surfaces 
 of the teeth and arches, to the corresponding space on the op- 
 posite side. Its upper and lower boundaries are tei-minated 
 by the attachment or blending of the mucous membrane of 
 the cheeks and lips witli that covering tlie upper and lower 
 alveolar arches. 
 
 When the jaw and lips are closed, and the teeth are in 
 normal occlusion the mucous membrane of the cheeks and lips 
 rests against the outer surfaces of the teeth aud arches, and 
 no appreciable space between these surfaces is noticeable. 
 By inflation from within, or liy parting the lips and distending 
 the cheek walls, the cavity of the vestibule becomes apparent. 
 
 The upper and lower peripheral circumferences of the 
 vestibule are known as the superior and inferior cul de sacs. 
 
 The salivary secretions from the parotid glands are dis- 
 charged into the vestibule opposite the second upper molar 
 through the ducts of Stenson. 
 
 THE ORAL CAVITY PROPER 
 
 The oral cavity is bounded anteriorly and on each side 
 by the lingual surfaces of all the teeth and the alveolar 
 
]0 BODILY FUNCTIONS 
 
 arches; above by tlic palatal vault, iucludiug both the hard 
 and soft palate; below by the tongue and its mueous mem- 
 brane reflected against the lingual surfaces of the lower 
 alveolar arch; posteriorly it merges into the pharyngeal space 
 through the isthmus of the fauces. The tongue and palatal 
 muscles acting conjointly form a temporary distal boundary, 
 or wall, to the oral cavity as occasion requires, in the act of 
 mastication, deglutition or phonation. 
 
 MUCOUS MEMBRANE 
 
 The entire interior of the oral space is lined with mucous 
 membraue, being "composed of a layer of stratified squamous 
 epithelium, supported upon a tunica propria, which is usually 
 described as composed of two parts — the papillary layer and 
 the reticular layer. The epithelium and the tunica i^ropria 
 make up the mucous membrane proper, which is supported 
 upon a submucous layer composed of a coarse network of 
 white and elastic tibres, containing the larger blood vessels" 
 
 EPITHELIUM 
 
 "The stratified squamous epithelium is provided with a 
 horny, or cornous layer only in the portions covering the 
 alveolar process and the hard palate, or in other words, 
 where the submucosa is firmlj^ attached to the periosteum. 
 In these positions the horny layer consists of dead cells which 
 have lost their nuclei, and whose cytoplasm has been con- 
 verted into keratin or hornv material." (Noves' Histology, 
 p. 323.) 
 
 The mucous membrane is continuous over cheeks and gum 
 tissue and extends from the lips to, and merges with, that in 
 the naso-pharyngeal space. 
 
 THE. PALATINE VAULT 
 
 The vault of the mouth is formed anteriorly by the hard, 
 and posteriorly by the soft palate. The lingual surfaces of 
 the alveolar arch form the lateral and anterior boundaries 
 of the vault, while the free margin of the soft jjalate forms 
 the posterior boundary. 
 
 THE BONY STRUCTURE OF THE HARD PALATE 
 
 The hard palate is formed by the junction of the palatine 
 lirocesses of the superior maxillae and the horizontal ]ilates 
 of the palate bones. These processes unite in the median 
 
BODILY FUNCTIONS 11 
 
 line to form a suture or linear ridge called the raphe. tSonie- 
 times this ridge is quite prominent and irrcguhir, and renders 
 the fitting of dentures a difficult task. 
 
 PALATINE FORAMINA 
 
 Just back of the central incisors in the median line is 
 situated the anterior palatine fossa, in which are seen the 
 orifices of four small canals. Two of these, the foramina of 
 Stenson, are located one on either side of the median suture, 
 and transmit the anterior i^alatine vessels and nerves. Sit- 
 uated just inside the alveolar arch and about opposite the 
 location of the third molars on either side, two, and some- 
 
 THE MAXJLLA, WITH FULL LOMPLEMEXT OF TEETH SHOWING 
 ANTERIOR ANT) POSTERIOR PALATINE FORAMIN.E 
 
 times three, openings are seen. Thc^ larger, or anterior of 
 these canals transmits the posterior palatine vessels and 
 nerves, which pass forward in grooves parallel with the inner 
 alveolar plates. These bony grooves are nearly always 
 plainly marked at their beginning, but usually become indis- 
 tinct and finally obliterated about opposite the bicuspid teeth. 
 The vessels and nerves coming foi'ward from these canals 
 supply the mucous tissues of the hard palate. Some fila- 
 ments of the nerves and liranches from the arteries pass for- 
 ward and anastomose with the vessels and nerves transmitted 
 through the anterior jialatine canal. 
 
 When denuded of the soft tissues covering it, the bony 
 surface of the palate presents a more or less irregular ap- 
 pearance. Freqvrently sharp, well-defined points of bone, and 
 occasionally nodules of varying sizes, are present, sometimes 
 
12 liODILY FUNCTIONS 
 
 along tlie margins of tlie grooves which transmit the pala- 
 tine vessels, but more eommonly at various places on the 
 alveolar border. The sore spots and areas which so often 
 develop on introducing a denture are often traceable to the 
 presence of such irregular ])oints and nodules, which, under 
 pressure of the base plate, naturally become sources of irrita- 
 tion to the overlying soft tissues. It is advisable in such 
 cases to relieve the pressure of the denture over these areas, 
 as well as opposite the openings of the posterior and anterior 
 ])alatine canals, especially when the mucous and su])mucous 
 tissues are thin, hard and unyielding. Excessive continued 
 l^ressure on the vessels and nerves, transmitted through 
 those canals, will undoubtedly lower the nutrition of the parts 
 sup])lied, tem]iorarily at least, and cause unnecessary dis- 
 conifort and pain to the wearer of the denture. 
 
 THICKNESS OF THE PALATINE PROCESS OF THE MAXILLiE 
 
 The palatine processes of the superior maxilla^ by their 
 upper surfaces form the floor of the nasal fossa. The thick- 
 ness of the bony partition lietween the oral and nasal cavities 
 varies in different individuals. In some specimens of young 
 adults the thickness of these plates scarcely exceeds 1-100 of 
 an inch at a point about midway between the raphe and the 
 outer wall of the nasal fossa. 
 
 The extreme thinness of the palatine processes in this 
 location converts them hito sounding boards, so to speak, and 
 gives a finer, clearer quality to both nasal and oral sounds 
 than would be possible if the bony floor were thick. Base 
 l)lates, whether of metal or vulcanite, frequently tend to im- 
 pair tone quality, and therefore care should be taken in 
 denture construction to avoid unnecessary bulk in the vault 
 jioj'tion. 
 
 Strength is given to the thin, bony vault on the nasal 
 side in its central portion, by the junction of the nasal septum 
 with the palatine processes at the median suture opposite 
 and above the raphe. 
 
 THE MUCOUS MEMBRANE OF THE PALATE 
 
 The mucous membrane covering the hard palate and 
 alveolar arches is provided with a horny or cornuous layer, 
 as before stated. This layer is less sensitive than the or- 
 dinary mucous membrane, as well as firmer, denser and more 
 fibrous. These charactei'istics render it less liable to injury 
 
BODILY B'UNCTIONS 
 
 during the mastication of liard varieties of food, and less 
 irritable to friction or stress tlian are membranes devoid of 
 the cornnous laver. 
 
 THE RUG^ 
 Situated just back of the central incisors and slightly in 
 front of the position of the anterior palatine canal, is a 
 small pear-shaped eminence called the papUla of ihe pnhiic. 
 
 THK TONUIE SIK 
 
 Iltrt'.MVAI.I.ATE I'AI'ILL.E (St-e |). 14) 
 
 Extending jiosteriorly from tliis, and folldwiiig tlic raphe, is 
 also a ridge of mucous tissue. 
 
 A number. of smaller irregular ridges pass out lateral! \, 
 usually running obliquely, but not necessarily paralleling 
 each other, sometimes extending l)ack as far as the second 
 l)icus])id. Tliese are called pliav palutliitr, or folds of the 
 jialate. The papilla, with its distal extension, together with 
 
14 r.ODILY KIINCTIONS 
 
 llic hilcials wliicli arc arranged on either side, are kuown as 
 the I'lKjir, I'ruiJi inga — a fold or wrinkle. Oftentimes when 
 well detiued, the central ridge and laterals present tlie ay)- 
 pearance of a synnnetrical tree trnnk with spreading 
 branches. 
 
 THE TONGUE 
 
 The tongue is the organ of the special sense of taste; it 
 is one of the principal organs of speech, and is an indispensi- 
 ble factor in mastication and deglutition. When at rest it 
 occupies the space between the internal walls of the body of 
 the mandible, the lingual surface of the lower alveolar arch 
 and ]iractirally all of the teeth (see cut, page 13). 
 
 THE SENSE OF TASTE 
 
 The special sense of taste is located pi-iiicipally in tln' 
 circumvallate paiiilla? which are situated on the dorsum (if 
 the tongue. They are in two rows, arranged in V form, the 
 
 V FIURKS (IH' VARKII S T()N(iUE MlISCr.ES 
 
 apex being on the median line and pointing distally, the rows 
 running forward and outward. They are of large size and 
 vary in number from eight to ten, or even more. In addi- 
 tion to these, there are numerous other papilte, called fili- 
 form papill.T, distributed over the sides and dorsum of the 
 
BODILY FUNCTIONS 15 
 
 tongue, which give it a roughened, or furred, appearance. 
 Still another variety, called fungiform, are foiaud interspersed 
 with tlie filiform papilhe, but are less numerous than the latter. 
 
 THE SALIVARY GLANDS 
 
 The parotid submaxillary and sublingual glands to a lim- 
 ited extent, empty the salivary secretions in the mouth at all 
 
 SYMPHYSIS 
 
 THE SALIVAKT GLANDS 
 
 times, l)ut more or less profusely during the mastication of 
 food. The saliva is the first digestive fluid to act on the food, 
 partially converting the starches into sugars, and in conjunc- 
 tion with the mucous secretions, luln-icates the bolus of food 
 and prepares it for deglutition. 
 
CHAPTER III 
 EXAMINATION OF THE MOUTH 
 
 GENERAL REMARKS 
 
 To render the most skillful service to a patient it is nec- 
 essary for the dentist to know the exact conditions of the 
 tissues and organs of the mouth in detail. Such knowledge 
 can only be acquired by a close examination of the parts. In- 
 telligent questioning of the patient will assist, to a certain 
 extent, but the burden of the diagnosis rests upon the 
 operator. 
 
 He must be a histologist and pathologist as well, to recog- 
 nize conditions of health and disease. No detail, that has a 
 direct or even a remote bearing on the dental aspect of the 
 case in hand, should escape his notice. The general method 
 of procedure for an examination, as here outlined, may be 
 followed with good results. 
 
 POSITION OF PATIENT 
 
 Seat the patient and adjust the chair, first, so that he 
 may feel comfortable ; second, so as to bring the mouth within 
 convenient range for examination. Adjust a towel over the 
 patient's clothing, attaching it around the neck. A mouth 
 mirror, probe, explorer, tongue depressor, pliers, cotton, 
 water syringe, and a small electric mouth lamp, are the in- 
 struments most useful for examination, and should be placed 
 conveniently at hand, although not necessarily in sight. 
 
 Everything being in readiness, the operator should 
 cleanse his hands in the presence of the patient, or so 
 the latter may know it is being done. This is necessary for 
 two reasons — first, to prevent possible danger of carrying in- 
 fection to the patient's mouth, and second, to engender within 
 the mind of the latter a feeling of confidence in the operator's 
 knowledge and ability to cope with disease. The free appli- 
 cation of tepid water, or normal salt solution, with the syringe 
 to the teeth and oral tissues is nearly always advisable be- 
 fore beginning an examination. 
 
 The lips guard the entrance to the alimentary tract, and 
 as they are first encountered, the examination should begin 
 with them. Note whether they are of good color and normal 
 
 16 
 
EXAMINATION OF THE MOUTH 17 
 
 in appearance, or if lesions are present such as fissures, cold 
 sores, etc. If so, avoid giving any unnecessary pain 
 by distension, or pressure on the parts. If in a healthy 
 condition, the index finger should be passed around between 
 the alveolar process and cheeks, a general idea being thus 
 gained of the distensibility of the lips and cheek walls. The 
 first glance in the mouth, in most cases, discloses to the ex- 
 aminer something of the character of the patient and the 
 class of operations required. 
 
 EXAMINATION OF MOUTH WHEN NATURAL TEETH ARE 
 PRESENT 
 
 Note specifically the general appearance of the mouth 
 as to health and cleanliness. If any natural teeth are present, 
 look for calculus, pyori'hea pockets, alveolar and gingival ab- 
 scesses, dead pulps, peridental inflammation and gingivitis. 
 
 Note any and all peculiarities of the mucous membrane, 
 redness, discoloration and swelling usually being signs of 
 some irritated or diseased condition. Stomatitis, leukoplakia, 
 mucous patches, cancrum oris, etc., are liable to be present, 
 and if so should be recognized immediately. If any condition 
 found is infectious in character, the operator should take due 
 precautions for his own safety during the examination, and 
 thoroughly sterilize all instruments as soon as the patient is 
 out of the chair. If teeth are carious, observe the extent to 
 which the disease has progressed, the teeth affected, and the 
 probable method of treatment. Note also the relation of the 
 teeth in the same arch to each other, and to those in the op- 
 posite arch, as well. Observe the forms of the teeth them- 
 selves, whether constricted at the neck; elongated or normal; 
 whether tissues have receded, leaving them standing more or 
 less unsupported; whether they diverge or converge to an 
 unusual degree; whether loss of proximate contact has oc- 
 curred; the form of the spaces where the teeth and spaces 
 alternate. By noticing the extent of abrasion on the occlusal 
 surfaces of the teeth, some idea can be formed of the stress 
 exerted in masticatory effort. 
 
 If the patient is past middle age and no signs of occlusal 
 abrasion appear, as it normally should at such an age, try 
 to discover the cause, whether due to mal-occlusion or to a 
 diseased condition of the peridental membrane of one or more 
 of the natural teeth. Tenderness of the peridental mem- 
 brane, and slight elongation of a single tooth, will often— 
 
IS EXAMINATION OK THK MOUTH 
 
 sometimes I'or yeurs — inhibit or sciiously iiii])air proper 
 masticatory eti'ort. 
 
 EXAMINING EDENTULOUS MOUTHS 
 
 111 edeiitulous cases, note particular!}- the i'oriu oC tlir 
 alveolar processes, or as Dr. G. V. Black has appropriately 
 termed tliem the residual ridges, the amount of absorption 
 that has occurred, the extent and position of muscular at- 
 tachments to the labial, buccal and lingual surfaces. In the 
 upper jaw, determine the location and extent of the hard 
 and soft areas, and the thickness of the mucous and sub- 
 mucous tissues in the vault portion. Notice particularly the 
 form of the raphe (the bony ridge formed by the union of 
 the palatine processes of the upper maxillae) and compare 
 the thickness of the mucous membrane which covers it with 
 that covering the crest of the borders. Determine whether 
 there are any sensitive or tender areas on which tlie pros- 
 pective denture will rest. These areas usually will be found 
 on either side of the vault just internal to, and a little in 
 front of the tuberosities, and in the median line, just back 
 of the central incisors, where the four canals are situated 
 which transmit the posterior and anterior palatine vessels 
 and nerves. 
 
 When the mucous and submucous tissues are sparse and 
 thin on these areas, the pressure of the denture is at times 
 very disagreeable, sometimes producing pain. It can be ob- 
 viated by properly relieving the impression. Examine par- 
 ticularly the buccal aspect of the tuberosities as well as other 
 locations, to determine whether undercuts are present. If 
 so, what efifect, if any, tliey will have on the removal of the 
 impression. When the vault is deep, rising abruptly back 
 of the incisor region, there will frequently be an undercut 
 area in the anterior portion of the mouth, the distance from 
 the labial to the palatine alveolar plates through the region 
 of the incisive fossa being less than through the border por- 
 tion near the crest. 
 
 In examining the arch and tissues of the lower jaw, ob- 
 serve the amount of absorption and the position and extent 
 of muscular attachment to the outer and inner sides of the 
 alveolar arch, whether the tongue and cheek muscles, and 
 the tissues above the submaxillary glands are liable to inter- 
 fere in impression taking; how far distally and downward the 
 lingual wings of a full denture case can extend without impp<l- 
 ing tongue movements. Notice the relative size of the arches, 
 
EXAMINATION OF THK MOUTH 19 
 
 and the probable ease or difficulty of introducing tlie impres- 
 sion tray through the oral opening. 
 
 A pad of charts having diagrams of the upper and lower 
 arches should be on the bracket, and any points of interest 
 should be marked thereon as soon as found. While the chart 
 can, or may not, be used after the examination is completed, 
 the marking of the important points will fix them fii-mly in 
 the mind. Every peculiarity of the teeth or tissues that may 
 have a direct or even a remote bearing on prosthetic pro- 
 cedures, should be recognized and kept in mind in order that 
 the most efficient service may be rendered. 
 
 PREPARATION OF THE MOUTH FOR DENTURES 
 
 All operative procedures, as a rule, such as the placing 
 of fillings and inlays, removal of calcareous deposits, and 
 treatment of the soft tissues, should be completed before tak- 
 ing impressions. Useless teeth and roots should be extracted, 
 and in some cases the tissues should be allowed to heal before 
 introducing a denture. Further surgical procedures are at 
 times very necessary, such as freeing muscle fibers and tissues 
 of the cheek wall that may at some previous time have been 
 lacerated, and in healing, have been drawn over and become 
 attached to the tissues on the process, in such manner as to 
 interfere with the correct seating of the denture. The late 
 Dr. Burchard's suggestion is a good one, of taking an im])res- 
 sion of the mouth, including the cicatrized tissue, and from 
 this securing a cast. This is then trimmed to represent the 
 normal form of the ridge, that portion representing the 
 cicatrized soft tissues being dissected away on the cast, and 
 leaving the trimmed portion rather more prominent than the 
 natural hard tissues. A denture of vulcanite is constructed, 
 the margins rounded and polished smoothly, which when in 
 position holds the severed tissues apart until healed, and thus 
 the normal alveolar surfaces are regained. 
 
 SPONGY BORDERS 
 
 Often, when- the teeth have been lost from phagedenic 
 troubles, the bony process is practically all absorbed, or de 
 stroyed. The border in such cases, although presenting a 
 fairly good form, is soft and tlabby, consisting of thickened, 
 sometimes fibrous, mucous membrane, devoid of bony sup- 
 port. Such a ridge affords an unsatisfactory foundation for 
 
20 EXAMINATION OF THE MOUTH 
 
 a (It'iitiirc, without sonu' ]ii'('liiiiiiiarv treatment of tlic iiioutli 
 itself, or ol' the cast to lie used in coiistiuetiou. 
 
 REDUCING SPONGY BORDERS 
 
 Three metliods are in \(),!;u<' for iniuiiiiiziii.i;' this vvvy 
 annoying condition : 
 
 First. A metiiod wliereliy the treatment of tlie east used 
 in denture construction will, in certain cases, correct the dif- 
 ficulty mentioned. This will be described later in proper 
 order. 
 
 Second. A very satisfactory method suggested by Dr. C. 
 P. Pruyn of absorbing excess tissue — construct a temporary 
 ])asei)late for the case, or if the patient is wearing an old, 
 even though ill-fitting, denture, it will serve the purpose. Line 
 the interior with oxychloride or oxyphosphate of zinc, mixed 
 to medium consistency. Place it labially and lingually of the 
 border position, thus leaving sort of a groove for the crest 
 of the ridge to enter. Under pressure the cement is com- 
 pressed between the basej^late and the unyielding tissues, and 
 is forced from l)oth sides against the flabby ridge, reducing 
 its bulk without materially distorting or changing its position 
 or depth. Two or three weeks' constant wear, of this cement 
 corrected denture, will imjirove the density of the border 
 very noticeably. If furtlier absori)tion is deemed advisable, 
 the denture is thoroughly cleansed, an additional layer of 
 cement is spread over that already adapted, and the ridge 
 subjected to pressure as before. When the density of the 
 border is satisfactory, a permanent denture is constructed. 
 
 Third. The most severe method of treatment consists in 
 surgically removing such portion of the spongy border as 
 may be deemed necessary, and stitching the margins of the 
 membrane together to accelerate the healing process. 
 
 When, in ])reparing a mouth, extractions are performed, 
 care should be taken to see that the sharp or prominent pieces 
 of alveolar ]n-ocess that frequently project from the border, 
 are removed. This can easily be done with a cutting forcep 
 or bur while the trauma is fresh. The border, if left smooth 
 and rounded, and free from sharp projections, will afford 
 a bettej- foundation for a denture, and the soft tissues will 
 heal more ra])idly than when this smoothing up process is 
 neglected. 
 
 When sharp, bony jioints are ])resent as the result of 
 previous operations, it is advisable, in most cases, to dissect 
 away the gum and periosteum, remove the prominences, and 
 
EXAMINATION OF THE MOUTH 21 
 
 if the wound gaps open, stitch the gum tissue together. If, 
 for any reason, it is not advisable to remove the points by 
 cutting, then tliose areas in the impression impressed by 
 the points should be scraped to obviate pressure and conse- 
 quent irritation, when tlie denture is introduced. 
 
 TEMPORARY DENTURES 
 
 When, by i-ecent extraction, the mouth has been cleared 
 of all remaining teeth, the problem confronting the patient 
 and prosthetist is — Hoio soon shall dentures he fitted to the 
 edentulous borders? Without qiiestion, iu most cases, the 
 patient will be best served by constructing dentures imme- 
 diately, that is to say, within a few days after the loss of the 
 teeth. It is a noticeable fact that patients who have never 
 worn dentures become accustomed to the presence of sub- 
 stitutes with less effort, when introduced soon after the loss 
 of the natural teeth than do patients for whom the introduc- 
 tion of dentures has been deferred for a varying period of 
 from six months to a year. Just why this is so, is not clear. 
 Perhaps the inconvenience felt from the introduction of the 
 temporary dentures is so slight as to be nearly lost sight of, 
 while the cataclysmic effect, both physical and mental, result- 
 ing from the loss of the natural teeth and the consequent in- 
 ability to masticate food, is engrossing the attention of the 
 patient. 
 
 Another factor of importance is the marked aversion 
 most persons have of presenting themselves, toothless, in 
 public, or to their friends. Almost without exception they 
 will submit to much inconvenience, and pain as well, rather 
 than suffer the humiliation occasioned by the absence of the 
 teeth. This is the psychological moment and should not be 
 neglected by the operator. The ability to tolerate the pres- 
 ence of temporary dentures in the mouth is positive assurance 
 that the permanent substitutes will prove both useful and 
 comfortable. Another point in favor of temporary substitutes 
 is that the alveolar processes absorb more uniformly, as to 
 density of tissue, and the ridges will maintain their form 
 for a longer period with less change, tlian where the intro- 
 duction of the dentwes is deferi'ed. 
 
 PERMANENT DENTURES 
 
 Usually the jcnipdravy should be rcphu-ccl with perma- 
 nent dentures in from six to twelve months. The inequalities 
 of the borders will usually in this period have become smooth 
 
L'2 KXAMINATION OK 'J'HE MOUTH 
 
 and rounded, the alveoli filled in, and the soreness will have 
 disappeared from the soft tissues. Since as a result of the 
 absorption that has occurred tiie adaptation of the denture 
 to the tissues is imperfect, deferring the construction of the 
 permanent sets beyond the time mentioned usually results 
 in unnecessary and deleterious absorption of the alveolar 
 process. Stress therefore should be laid upon this fact, and 
 the patient advised accordingly. 
 
 In the examination of any mouth with a view of carrying 
 oi;t prosthetic procedures, certain tilings should be kept in 
 mind by the operator. 
 
 First, he sJiould carefully consider what class of substi- 
 tute will give the patient the best service, as indicated by the 
 conditions in the mouth. 
 
 Second, when the class of work indicated is not to be 
 considered on account of expense, what other method can be 
 followed to the best advantage. 
 
 Third, the operator and not the patient should determine 
 what class of work is indicated, and how it should be done. 
 This he can do if by his ability and sincerity he can ins]iire 
 within the mind of his patient, confidence in his knowledge, 
 judgment, and honesty of purpose, all of which are essential 
 in order to bring together and hold a desirable clientele. 
 
CHAP T K R I V 
 
 ARTIFICIAL DENTURES 
 
 PHYSICAL AND MECHANICAL PROBLEMS INVOLVED 
 IN THEIR CONSTRUCTION 
 
 THE THREE ESSENTIAL REQUIREMENTS 
 
 The production of artificial dentures, either full or par- 
 tial, is accomplished by the carrying out of a series of tech- 
 nical details that follow each other in sequence. 
 
 The degree of success attained in denture construction 
 is directly dependent on the skill with which the details are 
 wrought out. The test of success lies first, in the patient's 
 ability to use the dentures successfully in masticatory effort ; 
 Second, in the greater or less complete fulfillment of es- 
 thetic requirements; and third in the ability of the wearer 
 to use them without inconvenience or to briefly summarize — 
 usefulness — good looks — comfort. 
 
 FULL DENTURES 
 
 Perhaps the most difficult problem confronting the pros- 
 thetist is that of retention or securing stability of the finished 
 dentures when introduced and subjected to use. In full cases, 
 the natural teeth having been lost, no mechanical aids to re- 
 tention can be resorted to, such as are used in partial sub- 
 stitutes. In extreme instances spiral springs can be applied 
 but they are objectionable, on account of the constant pres- 
 sure exerted to force the mandible and maxilla apart, also 
 on account of unhygienic conditions caused by their presence. 
 Retention of full dentures is largely a question of physics 
 and not of mechanics, although good mechanical judgment 
 and skill must be exercised in developing the physical aids to 
 retention. 
 
 Full upper and lower dentures are retained in position 
 on tlio alveolar borders by adliesion and atmospheric pres- 
 sure. In lower cases gravity also assists. Partial den- 
 tures are usually' retained with some form of clasps, or me- 
 chanical devices, which attach to some of the remaining nat- 
 ural teeth or roots. In favorable cases both means first men- 
 tioned, viz. adhesion and atmospheric pressure, are utilized. 
 The same general conditions which are requisite for develop- 
 
 23 
 
:i4 AKTIKUUAL DENTURES 
 
 ing good atmospheric pressure, are also essential iDr develop- 
 ing good adliesive qualities. 
 
 ADHESION 
 
 (a) Adliesiou is deliued as "tlie molecular attraction ex- 
 erted between the surfaces of bodies in contact. ' ' 
 
 (b) This peculiar property is attributed to some recip- 
 rocal action between the contact surfaces. The par- 
 ticles must be brought, within the limit or distance of 
 molecular attraction. 
 
 (c) "The attraction increases as the contact is-prolonged 
 and is greater in proportion as tlie contact is closer." 
 
 Adhesion takes place between dissimilar substances. It 
 is more powerful between a solid and a liquid than between 
 solids, or between the molecules of a liquid itself. 
 
 If a thin layer of oil is interposed between two perfect 
 planes of metal, they will adhere firmly, but when pulled 
 asunder each i^late is moistened by the oil, showing that in 
 separating the plates, the cohesion of the liquid is overcome, 
 but not the adhesion of the oil to the metal. (Ganot's 
 Physics.) 
 
 That adhesion plays a part in the retention of dentures 
 is beyond question, but the conditions surrounding a denture 
 when in position and in use in the mouth, tend to reduce the 
 effectiveness of adhesion, viz., the slight yet unavoidable 
 movement which occurs when the denture is subjected to 
 stress, due to the natural resiliency of the tissues. This 
 movement is opposed to prolonged as well as close contact. 
 (8ee paragraph c.) 
 
 ATMOSPHERIC PRESSURE 
 
 The atmosphere is the aeriform fluid which envelopes the 
 earth and extends outward from its surface a distance of 
 almost 50 miles. It is composed mostly of free oxygen (21) 
 and nitrogen (79), with about 4 parts of carbonic acid to 
 10,000. Ammonia, sulphuretted hydrogen and other gases are 
 also present in varying quantities in diiferent places, due to 
 local causes. 
 
 The air has weight. One hundred cubic inches of dry air, 
 rmder ordinary atmospheric pressure of 30 inches, and at a 
 temperature of 62 F., weigh 31 grains. Twelve cubic feet of 
 air under the same conditions, weigh 1 pound. The air in 
 a room 16x16x10 feet weighs 210 pounds. 
 
 Since the air has weight, and the earth's surface is at 
 
ARTIFICIAL DENTURES 25 
 
 the bottom of the aei'ial sea, the outer layers of the atmos- 
 phere are constantly pressing down upon the deeper layers 
 with a very considerable force, the earth's surface being the 
 site of greatest pressure. 
 
 This pressure is not noticeable under ordinary conditions, 
 as the air presses equally in all directions, and upon all ob- 
 jects. If, however, it is excluded from between two surfaces, 
 the pressure is immediately apparent. In case of perfect 
 exclusion of the air, the pressure at sea level amounts to 14.7 
 pounds per square inch. When two perfectly ground plane 
 plates of glass or metal are placed together, and the air be- 
 tween the contact surfaces is excluded, it will require a force 
 equal to the area of the plates in square inches multiplied 
 by 14.7, to separate them. If the plates are 4 inches square, 
 tiie formula would be stated thus: 4X4X14.7=235.2. 
 
 To summarize, it would require a pull of 235.2 ]>ounds 
 to overcome atmospheric pressure and separate the plates, 
 without considering the adhesive force which is also present, 
 and which would have to be overcome before separation 
 could take place. 
 
 RETENTION BY MEANS OF ATMOSPHERIC PRESSURE 
 
 In ai^plying the principle of atmospheric pressure to the 
 retention of an artificial denture, it is necessar^^ to develop 
 certain ^conditions between the denture and the tissues on 
 which it rests, similar to those present in the plane plates 
 mentioned, viz., close or uniform adaptation of the contact sur- 
 faces iiarticularly peripheral contact. 
 
 The denture is seated upon the mucous membrane of the 
 mouth, which in turn is supported by and rests on a bony 
 structure or foundation. The thickness of the mucous tissue 
 varies in different mouths, and often varies greatly in dif- 
 ferent areas of the same mouth. 
 
 For example, as often happens, the central vault portion 
 of the mouth is covered with a thin, un^delding, and the max- 
 illary area with a thick and yielding, layer of mucous tissue. 
 Unless precaiitionary measures are taken to prevent, a denture 
 fitted to such a mouth will be readily dislodged under stress, 
 the hard central -area acting as a fulcrum on which tlie base 
 plate will tip, the side on which stress is exerted being forced 
 upward, tlie opposite side being carried downward corre- 
 spondingly, just as the arms of a lever rotate about the ful- 
 crum. This movement disturbs the equilibrium of the denture, 
 
26 AKTIFICIAT. DENTURES 
 
 breaks the contact surfaces, and the air, if at first exchided. 
 rushes in between the denture and tissues. 
 
 The same condition would prevail were the mai'gins of 
 the plane plates previously alluded to soft and yieldinc^ and 
 the central area hard and unyielding. Pressure produced 
 on the margins of the plates on one side, to force them to- 
 gether, brings the hard central area into action as a fulcrum, 
 separates the opposite sides and destroys atmosyiheric pres- 
 sure. By proper precautionary measures the difficulty men- 
 tioned in denture construction may, to a great extent, lie 
 obviated. 
 
 NECESSARY CONDITIONS FOR RETENTION 
 
 First, there must be uniform contact, or lieai'ing, of th( 
 denture against the tissues on which it rests. 
 
 Second, the peripheral margins of the denture at al/ 
 points should be so formed that the tissues when at rest, or 
 under muscular tension, will remain in close contact with these 
 margins, thus preventing the ingress of air between the 
 denture and tissues. 
 
 With the first requirement realized, it is comparatively 
 easy to develop the second one. In both cases the necessary 
 conditions are developed, principally during the taking of 
 the impression, the details of which will be given in the chap- 
 ter on this subject. 
 
 Briefly stated, the principle involved in carrying out the 
 first requirement, viz., uniform bearing on hard and soft areas, 
 consists in exerting pressure on the soft areas by means of 
 suitable impression material, of proper plasticity, to com- 
 press them so that the finished denture will bear firmly on 
 the soft, and lightly and in some cases not at all on the hard 
 areas. This condition can be still further carried out and 
 accentuated by scraping the impression in certain areas, the 
 details of which will shortly be given. 
 
 The second requirement, viz., close peripheral adaptation, 
 is accomplished first by careful manipulation of the impres- 
 sion materials against the peripheral areas, and second, by 
 having the patient exercise the muscles actively while the im- 
 pression material is still soft and plastic, and thus mark their 
 form, direction and limit of attachment to the alveolar process. 
 
 The ol)ject sought in carrying out this step is to seeui'e 
 a iieripheral outline to the denture that will not impinge on, 
 or cause irritation of, the muscular or soft tissues, and yet 
 
AUTIFK'IAL DRNTUUKS 27 
 
 will have such close aila])tiitiuu as to seal against the ingress 
 of air — to atTord "relief without leak," as Dr. J. W. Greene 
 expresses it. 
 
 RELIEF FROM PRESSURE BY SCRAPING THE IMPRESSION 
 
 When the impression is secured, those parts imjiressed 
 by the exceedingly hard and nnjdelding areas of the month 
 shonld be scrajied slightly to insure relief from bearing of 
 the finished denture on these areas. It is especially necessary 
 to atford such relief in the central palatine portion of the 
 mouth when the raphe is distinctly mai'ked and prominent 
 and is covered with oulv a thin laver of tissues. 
 
 AN IMl'RKSSIDX SHOWING MBDIIM AMOINT OF liELlEK 
 
 In relie\'ing this area the scraping should extend sligldly 
 btyo)i(l the margins of the hard outline in every direction. 
 Usually the relief should not exceed 1/25 of an inch in depth 
 in the deepest part, and should gradually taper out to a 
 thin invisible jDeriphery, losing itself in the general contour 
 of the vault impression. 
 
 The idea in thus treating the impression is not to pro- 
 duce a vacuum chamber in the denture, but to alford relief 
 from pressure on the raphe and adjacent tissue, and thus pre- 
 vent the hard areas from serving as a fulcrum to tip the 
 denture when stress is applied. 
 
 A little experience will enable one to readily detei-mine 
 the outline and extent of the hard areas by merely scanning 
 the impression. It is a good plan, however, to make a digital 
 examination of the mouth, either immediately before or after 
 
28 AUTIKU^IAL DENTURES 
 
 flic iiii|ii'cssi(iii is taken, to he alisdliitclv' ccrtHin (if tln' extent 
 of relief iieeessary to pi'ov'idc! i'or. 
 
 VACUUM CHAMBERS 
 
 Vacuum eliambeivs, oi'teu incorrectly called iilr chamhern, 
 are shallow, depressed areas with a definite outline, usually 
 formed in the central palatine surfaces of dentures during 
 the constructive steps, and which are supposed to assist in 
 retention. As ordinarily constructed, they are not intended 
 to, nor do they seldom afford, relief from pressure. The ef- 
 ficiency of a vacimni chamber is dependent ujion its area, 
 
 AN IMPItESSION SIKPWlNi; SI.IIiHT AMOIXT OF PALATINE REUEF 
 
 depth, adaptation of its peripheral margins to the opppsing 
 tissues, and the ability of the patient to exhaust the air from 
 the interior. 
 
 Under the most favorable conditions, the usefulness of 
 the vacuum chamber is questionable. The tissues are soon 
 drawn into, and usually after a time permanently fill, the 
 cavity, thereby defeating the object for which it was designed. 
 When the chamber is very deep, the tissues, while they may 
 not fill it entirely, are kept in an irritated condition, more or 
 less annoying and frequently painful to the patient. On the 
 other hand, when the chamber is shallow and the tissues are 
 not drawn into it, it is not, as its name would indicate — a 
 vacuum chamber — but merely a useless and unsightly de- 
 pression which increases the thickness of the dentiire in a 
 
ARTIFICIAL DENTURES 29 
 
 region where Inilk is objectionable on accoiuit of its tendency 
 to modify the resonance of the voice. 
 
 For more tlian fifteen years past the nse of this very 
 questional)le method of retention has been discontinued by 
 the writer, both in clinical work and in private practice. The 
 results during- this time furnish convincing proof of the 
 greater advantages over vacuum chamber for retention pur- 
 poses of well defined uniform bearing developed in taking the 
 impression and by scrainng the cast to secure peripheral 
 adaptation of the denture. 
 
 COMPENSATING FOR EXPANSION OF THE CAST— FULL UPPER 
 DENTURES 
 
 Since all plasters expand in setting, to a greater or less 
 extent, some means of compensating for the enlargement of 
 the cast should be adopted. 
 
 I'RAriNC THE PERIPHERY OP A 
 
 The plan followed, and which has proven very satisfac- 
 tory, is to scrape a slight groove, extending from one tube- 
 rosity to the other, on the buccal and labial surfaces of the 
 cast. This groove should be made with a discoid 20 or small 
 Kingsley scraper, to avoid the formation of any angles, and 
 be very shallow, — so slight as to scarcely be noticeable ex- 
 cept on close inspection. -It should occupy a position about 
 midway between the crest of the border and the peri];)heral 
 line of termination of the denture, and as before stated ex- 
 tend from one tuberosity to the other on the labial and buccal 
 surfaces. This groove on the cast produces a slight, rounded 
 liead on the iimer asi)ect of the labial and buccal surfaces of 
 the denture, reducing the diameter of the latter by an amount 
 equal to the elevation of the bead, thus insuring close peri- 
 pheral adaptation, and overcoming any slight enlargement of 
 the cast due to expansion. 
 
So AUTIKlCtAL I)IONTlIHES 
 
 POSITION AND OUTLINE FORM OF THE DISTAL MARGIN OF 
 UPPER DENTURES 
 
 The distal terminal inaigiii of an ii]»iier denture should 
 follow the Hue of junction of the soft with tiie hard ])alate, 
 or be laid on tlie soft immovable area, being careful to avoid 
 encroaching on the soft movable tissues or palate muscles. 
 The latter liecome an active cause of displacement when the 
 denture overrides them to any appreciable extent. 
 
 Usually the distal margin of the denture should assume 
 a double compound curve, extending either way from the 
 median line, to correspond in general with the distal margin 
 of the hard palate. 
 
 In those cases where the tissue between the luird central 
 area and the tuberosities is soft, the terminal line on eitiier 
 side of the center may be carried forward somewhat, witliout 
 
 DISTAL FOItM (IF ri'I'EI! liASEPLATE 
 
 impairing the adaptation. Such trimming will also relieve 
 pressure to a certain extent on the posterior palatine vessels 
 and nerves which find their exit from the canals situated just 
 inside of the tuberosities. Pressure of the denture directly 
 on the overlying tissues and indirectly on the nerves in this 
 region is a frequent cause of nausea. 
 
 The distal terminal line when proiDeiij^ laid will form 
 a pleasing symmetrical curve which will harmonize well with 
 the buccal and labial outlines of the denture. 
 
 PREPARATION OF LOWER IMPRESSIONS 
 
 In full lower cases it frequently happens that the al- 
 veolar border is thin and the crest of the process is very 
 
AKTIFICIAL DENTURES 
 
 liard. In such cases the impression should be trinuued or 
 scraped in the deepest part with a discoid instrument similar 
 to the one used in the peripheral scraping of the upper cast. 
 The scraping of the impression of the crest should not be 
 
 SCRAI'IXG THE DEEPER PORTION OF LOWER IMPRESSION 
 TO RELIEVE STRESS ON HORUER CREST 
 
 carried too close to the distal terminals, for when extended 
 entirely back, a vent is formed, through which the air finds 
 its way, affecting adversely the stability of the denture. 
 
 The effect of scraping an impression as described, is to 
 
 -^ 
 
 i.INEAK DISTANTE USUALLY RELIEVED ON LOWER IMPRESSION 
 \ 
 
 increase the "'^eight of the crest of the ])order on tlie cast so 
 that a denture when numlded on tlie cast will not rest on the 
 extreme crest, wJiile the labial, Iniccal and lingual flanges will 
 lie brought in closer contact with their respective surfaces, 
 the air forced out and atmospheric pressure utilized for re- 
 
32 ARTIFICIAL DENTURES 
 
 tention purposes. In many cases, a considerable amount of 
 adhesion that could not otherwise })e realized, will be devel- 
 oped in this manner. 
 
 SOFT ALVEOLAR BORDERS 
 
 When the alveolar border in either upi^er or lower cases 
 is of average form, but devoid of bony support due to ex- 
 cessive absorption of the process, it is frequently advanta- 
 geous to pare the labial or buccal and lingual surfaces of 
 the cast, slightly, being careful not to reduce the height of the 
 crest, so that these surfaces of the border will be compressed 
 when the denture is introduced. In many cases in practice 
 the carrying out of this plan has added greatly to the sta- 
 bility of dentures, the effect in most instances being to con- 
 dense and render the tissues permanently harder without any 
 ill effects. A method of correcting extreme cases of soft and 
 yielding borders — spongy or flabby gums, as they are some- 
 times called — is detailed in another chapter. 
 
 Partial dentures are usually retained in position by 
 means of clasps, or some of the forms of frictional appli- 
 ances in common use. In the case of a clasp, the ]3ressure of 
 the appliance, which is slightly smaller than the tooth it em- 
 braces, is due to the resiliency or springiness in the metal of 
 which it is composed. When in position in the mouth, the 
 clasp which is attached to the denture, grasps the tooth more 
 or less firmly and prevents displacement. So also with the 
 various specialized appliances, except that usually they are 
 made in two parts, one of which is permanently attached to 
 a natural tooth, or crown set on a root, the other to the den- 
 ture. They are so adjusted that when in jiosition the friction 
 between the two jiarts holds the substitute in place. The 
 various iappliances used for this purpose will be described 
 later. 
 
CHAP TEE V 
 
 DEFINITIONS OF SOME COMMONLY USED TERMS 
 
 IMPRESSION TRAYS 
 
 DEFINITIONS 
 
 An impression is a iicfjatire copy or conntorpart oi some 
 object impressed. In prosthetic procediires, to which the fol- 
 lowing definitions will refer, an imiDression is obtained by 
 pressing- a plastic material, such as plaster or modeling com- 
 pound, against some portion of the oral tissues or teeth. 
 
 A cast is a positive copy or likeness of the object im- 
 pressed and is obtained by casting plaster, or some similar 
 plastic material, Into the impression or mold. Casts are used 
 for giving tlie negative form of the month to plastic base 
 dentures. 
 
 A model is a positive or duplicate copy of the mouth or 
 some portion of it, and is used for producing a similar posi- 
 tive of itself, and consequently of the movith, in metal. A 
 model is produced in the same general manner as a cast, but 
 differs from it in its use, and slightly in its form, being so 
 shaped as to be readily withdrawn from the sand in which it 
 is imbedded, in the sequent steps of die construction. 
 
 A die is a metal duplicate of the mouth or some portion 
 of it, also of the model from which it is derived. In construct- 
 ing dentures with swaged metal bases, a die fulfils a sim- 
 ilar purjiose to that of a cast in the production of plastic 
 base dentures, viz., giving the reverse form of the mouth to 
 the metal base denture. A die is formed by pouring molten 
 metal or alloy into a sand matrix derived from the model, 
 or, in some cases, by pouring directly into the impression. 
 
 A counterdie is a negative or reverse of the die, and is 
 ol)tained by pouring a similar or a lower fusing m(>tal or alloy 
 directly against the face of the die. 
 
 USE OF THE TERMS "CAST" AND "MODEL" 
 
 Tlie ioYwvDiodd has been and is still veiy generally used 
 instead of cast 1o designate the ])roduct obtained by filling 
 the impression with plaster or ])laster compound. All such 
 products so obtained are in reality casts. The term cast, is 
 gradually coming into use to designate the prod^ict of the im- 
 
 33 
 
 c 
 
34 DI'JKINITIOXS OK SOMK COMMONI^Y USRI) TERMS 
 
 prcssioii wlioii it is used In give tlic reverse form of tlie mouth 
 to a plastie base, and the term iiniilfl, when it is used as a 
 means to reproduce a die which is a duplicate of itself. 
 
 The folhjwing definitions of liie two terms are given in 
 the Standard Dictionary : 
 
 "Cast. — An ohject fouiidcil (ir run in, or as iji a mold, as 
 of metal, plaster, wax, etc." 
 
 "A reverse copy of pUister of Paris, or simiU\r material, 
 of a mold, usually distinguished from a casting whicli is of 
 iron or other metal or alloy." 
 
 "Model. — An object usually in miniature, representing 
 something to be made or already existing; a material pattern 
 of natural size; more rarely a plan or drawing as a mode! 
 of an invention ; a model of a building; to draw a model." 
 
 "Specifically: In sculpture the plaster or clay original 
 of a work to be executed in stone or metal. A person who 
 does duty as a copy or pattern for sculptors and painters." 
 
 "A pattern is always, in modern use, that which is to l)e 
 copied; a model may be either the thing to he copied or the 
 copy that has been made from it, as the models in tlie Patent 
 Office. A pattern is commonly superficial; a model is usually 
 in relief. A pattern must be closely followed in its minutest 
 ])articulars ])y a faithful copyist. A model may allow a great 
 degree of freedom; a scul]itor may idealize his living model; 
 his workmen must exactly copy, in marble or metal, the model 
 he has made in clay." 
 
 Before the introduction of vulcanite, the plaster cast de- 
 rived from an impression was used almost exclusively for the 
 making of metal dies on which to swage gold, silver and 
 platinum bases. For this ]inr])ose it is a true model, since it 
 serves as a co])y from which sometiiing like it (the die) is 
 Ijrodnced. 
 
 On the introduction of \ulcani1(', which came into use 
 rather gradually, the same geneial form of cast as was used 
 in die construction, served as a shape over which to mold the 
 vulcanite. The similarity in method of production and form 
 of a cast accounts for the retention of the term model, even 
 though it does not fulfill the pur])ose of a model. 
 
 IMPRESSION TRAYS 
 
 An imjjression tray is an a])iiliance used for conveying 
 iTn])ression material to, and liolding it in position against, the 
 tissues of the mouth or teeth while hardening. It is also of 
 
DEFIN'ITIOXS OF SOMK COMMOXl.V I'SEO TERMS 35 
 
 material assistance in reiiuixiiiii' the impression t'lom the 
 montli, and in holding the parts of the impression, when 
 fractured and removed, in correct relation to each other while 
 securing the cast. 
 
 A large assortment of trays, in vai'ving sizes and forms, 
 and constructed of metal, rubber, celluloid, i)orcelain and 
 papier-mache, are proeurab](> at the sui)ply houses. The 
 trays most commonly used are nuide of Britannia metal, brass, 
 German silver or aluminum, all of which uuiy be bent with- 
 out much etfort. This latter feature is an imjiortant one. 
 since the stock tray will require more or less moditication in 
 each case, to meet some peculiar unbalanced or abnormal con- 
 dition of the alveolar ridge or oral tissue. 
 
 The other classes of trays, l)eing rigid, are incapable of 
 much change, and are therefore limited in their application. 
 In difHcult cases, special trays are frequently constructed of 
 block tin by casting, or from sheet metal by swaging, the de- 
 tails of which will be given later. 
 
 TRAY NOMENCLATURE 
 
 The various siirfaces of the oral cavity are definitely 
 named and those areas of the inipi-essicm tray that come in 
 close proximity to these oral surfaces are named accordingly. 
 For instance, the outer surfaces (right and left) of the ujijier 
 and lowei' alveolar arches, fi-oni the distal of the cusiuds back 
 ward, are termed the JutccdJ siirldccs because of the close 
 proximil\- of the buccal muscles to these surfaces. From cus- 
 pid to cuspid, anteriorly, the outei' surfaces of the arches are 
 called the labial surfaces because the labial muscles are in 
 close proximity. Those areas on the imier side of the l)order 
 that are touched by, and are in close ]u-oximity to, the tongue 
 are termed lingual surfaces. 
 
 In order to describe clearly the adjustment of the tray 
 and the taking of im]iressions, the tray nomenclature as 
 given by Dr. G. IT. Wilson in "Dental Prosthetics" will be 
 made use of. 
 
 "A tray has a hitihi and a IuiikUi'. The Ixxly consists of 
 a ^00/- and faiigcs. ITjiper trays have a raiilf portion. There 
 are two types cf floors, oval for edentulous jaws and fat for 
 accommodating the remaining teeth. The flanges are called 
 outer and inner. The outer flange has two portions, the an- 
 terior, or labial, and the ]iosterior, or buccal. The dividing 
 line is the proximity of the distal surface of the cuspid tooth. 
 
36 DEFINITIONS OF SOME COMMONIA' ISEl) TERMS 
 
 TIk' inner liange is called tlie lingual tiange. The surfaces of 
 the tray are named for the surfaces they aijproxiniate, as 
 maxillary, labial, buccal and lingual." 
 
 "The vault portion spans the space described by the 
 curve of the lingual flange of the ui)per tray. The handle 
 is an extension from the union of the floor and the anterior 
 flange. ' ' 
 
 A tray when fitted should conform closely in general 
 outline and contour to the mouth. Since it receives or par- 
 tially encloses the oral tissues, it should be slightly larger to 
 accommodate the impression material, a uniform space of 
 about one-eighth of an inch or less between the tray and 
 tissues being sufficient for this purpose. 
 
 Conforming the tray to meet the conditions mentioned, 
 viz., close adaptation and uniform space for impression 
 material, is accomi)lished )iy liending, cutting, or making 
 addition to the tray at points where deficient. Occasionally 
 all three methods are resorted to in adjusting a tray to a 
 given case. 
 
 CONFORMING THE TRAY BY BENDING 
 
 Trays are narrowed or widened by lieuding tlie flanges 
 inward or outward, or by compressing or expanding the body 
 of the tray across its buccal diameter. Compression of the 
 ])ody of upper trays increases and expanding reduces the 
 height of the vault portion. 
 
 In lower trays, decreasing the buccal diameter l)y bend- 
 ing the body of the tray usually narrows the sjiace between 
 the labial and lingual flanges anteriorly. To correct this 
 fault the lingual flange can be slit in the median line and the 
 adjacent portions bent and allowed to overlap so as to gain 
 the necessary space. The flanges are l)ent inward or outward, 
 as the position and form of the border indicates, always keep- 
 ing in mind two points — the maintenance of the proper space 
 for the reception of impression material, and freedom from 
 nniscle impingement by the flanges. 
 
 CONFORMING BY CUTTING 
 
 Frequently it l)ecomes necessary to reduce the height 
 of the flanges of a tray, particulai'ly in edentulous cases. 
 While trays with deep or wide flanges may be used in such 
 cases and fairly good impressions of the mouth secured, it 
 will, in most eases, be found that the labial or buccal muscles, 
 or both, have been distorted and forced out of normal posi- 
 
DEFI.N'ITIOXS OF SOME COMMOXLY USED TERMS 'i1 
 
 tion. In fact, the i'(iin])r('ssi(>ii may Ix' so scN'erc as to i)blit- 
 erate the surface iudicatioiis n\' their presence or jiosition 
 on the cast when secured. 
 
 These nnisch's and the freinun frequently have their ori- 
 gin near the crest or maxilhiry portion of the alveolar process, 
 while the border itself may he deep or high, and if not con- 
 sidered in outlining the peripheral margin of the base plate, 
 may become active causes of displacement by lifting the den- 
 ture off the crest of the border, thus breaking the adhesion. 
 
 It is foimd that by selecting trays with narrow flanges 
 which do not impede the muscular action, and having the i)a- 
 tieut exercise these muscles at the proper time, while the 
 impression material is still soft, that their ]tosition, under 
 tension, can be (h'ternrmcd and indicated on the iin]n'essi(in 
 
 and the iieripheral outline of the denture ytroperly laid on the 
 cast. 
 
 Therefore, in selecting trays for edentulous cases, the 
 Avidtli of the flanges should be noted; when too wide, the 
 excess should be cut away with the shears, and the margins 
 smoothed with a file to prevent tissue injury, should the 
 trimmed margin be forced through the impression material. 
 In very flat upper arches it is at times necessary to cut away 
 almost the entire labio-buccal flange, while in lower cases 
 both outer and inner flanges are frequently to a great extent 
 removed. The goveruing factor, in all cases of flange cutting, 
 is the form of the bony tissue or border enclosed by the tray 
 and the muscidar attachments to the border with which the 
 flanges may interfere. 
 
 A commop location calling for the iise of the shears is in 
 the median line of both upper and lower trays, in notching 
 the labial flanges to relieve impingement at this point and on 
 the lingual of the lower to obviate contact with the lingual 
 frenum. 
 
3S DEPINITIOXS OF SOMP: COMMONLY USED TERMS 
 
 MAKING ADDITIONS TO THE TRAY 
 
 When tlie tray selected is of correct outline form and 
 generally siiitalile to the case, but slightl.v deficient in some 
 locations, additions may be nmde where required by build- 
 ing up the deficient ])ortiou with wax or modeling com])ound, 
 or by splicing a ])iece of metal to the tray. The most common 
 location for building u)) a tray is on the vault portion, increas- 
 ing its height and frequently extending it posteriorly. This 
 applies almost exclusively to trays designed for plaster im- 
 pressions, both full and i^artial. 
 
 In most cases of ])laster impressions, better results can 
 l)e secured by taking a i)reliminary impression in beeswax or 
 modeling com|)ound, cutting off the excessive surplus and 
 using this preliminary impression as a tray for holding the 
 plaster. In partial cases the wax or compound is removed 
 from around the impressions of the teeth, thus enlarging the 
 ojjenings to make room for a fair thickness of plaster to sur- 
 round the teeth, so thai when fractured the parts may be 
 readily replaced. 
 
 Where marked irregularity of the border is noticeable, 
 or in some cases where a few of the natural teeth are present, 
 it is sometimes advisable to construct a tray for the case. 
 This may be done by casting it of block tin or some fusible 
 metal, or by running a die and counterdie and swaging a tray 
 of brass, German silver or aluminum. Or by swaging a tra>' 
 of Ash's metal over plaster casts in screw press with rubber 
 pads. 
 
 SPECIAL TRAYS 
 CAST 
 
 Secure as good an impression as possible with the trays 
 at hand. From this a cast is formed, and over the cast a sheet 
 of wax is molded to represent the form of the desired tray, 
 including a handle. The wax pattern is removed from the 
 cast and invested in some suitable investment comjiound, 
 placing the handle portion u]iward. Heat is then applied and 
 the wax burned out, after which the fusible metal is poured 
 in through the gate left by melting out the wax handle. 
 
 Dr. Walter M. Bartlett of St. Louis has followed a sim- 
 ilar method for many years, but has very materially im- 
 proved the efficiency of the tray by beading it. He applies a 
 narrow wax rim entirely around the inner periphery of the 
 wax model, which is, of course, reproduced in the casting. 
 This rim or bead serves to confine the impression ma- 
 
DEKINITIOXS OF SOME COMMONLY USED TERMS 39 
 
 terial witliin the compass of the tray, and minimizes the 
 anionnt required. A tray eonstrneted in this manner, when 
 introduced in tlie mouth without any impression material 
 present, Avill fre(|uently exliihit a ninrkcd amount of adhesive- 
 
 ness due to close ])eripheral adaptation. In constructing the 
 tray, plaster may he used as the matrix and the latter may 
 he of the tliree or four piece separable ty]ie, hut the pieces 
 
 MATRIX OF ri.ASTKR IX nHICH TRAY IS TO HE CAST 
 
 should he reasoualily tliin, and before casting- should be 
 warm and dry. The several pieces are held together with 
 binding wire. 
 
 SWAGED TRAYS 
 
 A swaged tray may lie made by securing a die and 
 counterdie from tlic cast ol' tlic mouth. I'rass, German silver 
 or aluminum, usually L'4 or Jl' gauge, is cut to appropriate 
 
40 dp:finitio.\s of some commoxly i'Sed terms 
 
 si/,(', Hiid coiiror-incd ))y swaging. I'lic sur])lus is ji-iiiiiiicd 
 away to give the tray its correct ])eriplieral outline, and a 
 liandle aitaehed in the nsnal location 1)y soldering or riveting. 
 
 SPECIAL TRAYS OF IDEAL BASE PLATE 
 
 A (|uickly formed and convenient tray for ])laster im- 
 pression work can be made by adapting a sheet of special 
 Ideal base plate to the cast, secured, as in the cases just 
 mentioned. The surplus is trimmed off and correct periph- 
 eral outline given the base plate; a piece of 12-gauge Ger- 
 inan silver or steel wire is bent to the form of the border and 
 extended forward to serve as a handle and laid on the base 
 plate. With a hot spatula the scraps can be melted over the 
 wire and at various points to strengthen the tray and give it 
 necessary rigidity. Sometimes a second sheet of base plate 
 is added to the first, the wire being between the two layers. 
 
 METALLIC EXTENSIONS OR ADDITIONS TO STOCK TRAYS 
 
 The distal vault portion of a tray is frequently too short 
 to suiiport the plaster against this area of the mouth. An 
 extension may quickly be made by cutting a piece of sheet 
 metal of suitable form so as to overlap the vault portion. 
 Punch two or three holes to correspond, through the addition 
 and the tray, with the plate punch, and attach together with 
 l)inding wire. Usually, however, additions to the vault por- 
 tion are made quite as well and more quickly with wax or 
 compound. 
 
 In taking im]3ressions where modeling compound is the 
 sole medium used, tray extension or contouring is not so 
 essential, since the compound which escapes distally can be 
 conformed and adapted to the tissues with the fingers, as well 
 in this location as peripherally. 
 
 The modeling compound tracing sticks are very con- 
 venient for making slight additions to trays, particularly 
 along the rim portion. All additions, whether of wax, com- 
 l)ouiid or metal, should be tested by trial in the mouth before 
 introducing the impression material. 
 
 As a rule, trays that are too large and with labio-buccal 
 flanges much too broad, are selected for edentulous cases. 
 When it is undei-stood that with close-fitting trays and a mini- 
 muni (piantity of im])ression material, more accurate impres- 
 sions can be secui-ed than when an excessive amount is used, 
 much of the difficulty arising from lack of adaptation of den- 
 tures will be eliminated. 
 
C TT A P T K R V T 
 IMPRESSIONS AND IMPRESSION MATERIALS 
 
 GENERAL REMARKS 
 
 An impression, in its dental sense, is an imprint, a re- 
 verse cojiy or connterpart of some portion of the oral cavity. 
 It is seenred by aiiplying to the parts involved, some plastic 
 medium that conforms readily to the surfaces impressed, and 
 which, when adapted, will harden and retain its form. 
 
 The surfaces embraced by an impression may vary from 
 an area involving only a small portion of the mouth, or even 
 of a tootli, to one containing- the full complement of teeth, 
 together with the alveolar border in which they are imbedcied, 
 and in edentulous cases (mouths devoid of teeth) to the bor- 
 der and adjacent areas. 
 
 The character and size of the substitute or rejjlacement 
 under construction determines the area to be included in an 
 impression. It is a safe plan generally, and in partial cases 
 especially, to extend the impression beyond the areas actually 
 involved in an operation, since when the cast is secured, a 
 better conce])tion may lie formed of the I'elationship and pro- 
 liortions of the contem]ilated sul)stitute to the remaining nat- 
 ui'al teeth than when the impression is restricted in size. 
 
 Absolute accuracy of the impression in representing tlie 
 parts impressed is positively essential, except in cases to be 
 noted later, and no effort should be spared to secure such an 
 end, since the cast, derived from an impression, becomes the 
 basis and forms the ground work on which most technical 
 procedures are carried out. If the foundation is faulty and 
 imperfect, the structure built thereon will lie pro]iortionately 
 inaccurate, and a probable failure. 
 
 It does not follow, however, that all impressions for any 
 purpose should be taken in tlie same manner and under the 
 same conditions, nor do impressions always represent a true 
 reverse copy of the parts im^iressed. For instance, it is found 
 that in certain caSes pressure sufficient to distort or com- 
 press the soft and yielding tissues of the mouth is desirable, 
 while in other cases, siich compression is not only uncalled 
 for, but detrimental to tinal results. In any procedure, the 
 l)rosthetist must first plan his substitute, and then thought- 
 fully and skillfully work out the details of the impression to 
 
 41 
 
42 IMPRESSIONS AND IMPRESSION MATERIALS 
 
 uuH't tlic i('(|uir('iiiciits of tilt' case in hand. Witliout doubt, 
 most of the misliai)s and mi.sfits in prostiietic procedures are 
 due, in part, to faulty manipulation in impression taking. 
 The slighting of this o})eration in the carrying out of details 
 in a perfunctory and careless manner, is a widespread evil, 
 and cannot be too strongly condemned. 
 
 It sliould be the amliition of the student, and of every 
 practitioner as well, to perfect himself in the technical details, 
 the art of impression taking, so that he may overcome any 
 obstacle and meet every emergency that may arise. A thor- 
 ough understanding of the conditions governing each case, 
 together with painstaking effort in the handling of the mate- 
 erial employed, both in and out of the oral cavity, will ac- 
 comiilisli the desired results. 
 
 IMPRESSION MATERIALS 
 
 Since accuracy in impression taking is an absolute ne- 
 cessity, the choice of the medium used for this i)urpose re- 
 quires careful consideration. Tlie following statement of the 
 requirements of an impression material represents tlie ideal, 
 rather than the aftaiiinhle, because no sxilistance has yet been 
 found which is absolutely free from imperfections. Several, 
 however, approach closely to the ideal requirements, and with 
 a knowledge of the desirable and detrimental qualities of each, 
 fairly satisfactory and accurate results may be secured in 
 most instances. 
 
 REQUIREMENTS 
 
 An impression material should possess, as nearly as pos- 
 sible, the following qualities : 
 
 First — It should be composed of some material that will 
 not be unduly disagreeable to the patient. 
 
 Second — It shoidd become plastic at a temperature the 
 oral tissues can tolerate. 
 
 Third — It should copy accurately the fine lines and ir- 
 regular surfaces to which it is* applied, and retain the form 
 so coined, without becoming distorted in removal from the 
 mouth. 
 
 Fourth — It should harden in a reasonably short time — 
 from one to three minutes. 
 
 Fifth — It should neither expand, contract nor war]) at 
 ordinary teini)eratures to any a]i]>recial)le degree. 
 
 CLASSIFICATION 
 
 Several varieties of impression materials are in common 
 use. These may be divided into two groups. First, those which 
 
IMPRESSIONS AND IMPRESSION MATERIALS 43 
 
 are rendered plastic with a liquid and harden by crystalliza- 
 tion. This class includes plaster, impression compounds, and 
 the various dental cements, as oxy-chloride and oxy-i)hos- 
 pliate of zinc, magnesia, and the silicates. 
 
 The second class embraces those materials that are ren- 
 dered plastic by heat and harden on cooling. The principal 
 materials in this group are modeling compound, beeswax (both 
 pure, and combined with other substances), paraffin and 
 gntta percha. The most commonly used, as well as practical, 
 of these materials are modeling compound and gutta percha. 
 
 GROUP I 
 
 Impression Materials That Harden by Crystallization 
 PLASTER OF PARIS 
 riastcr of Paris is so called because in former times 
 large (piantities were produced at the gyi)sum (juarries at 
 Montmarte, near Paris. 
 
 Plaster is made from gyjjsum. a hydrated calcium sulphate 
 the chemical formula of which is CaS04 -f- iH.O. It occurs in 
 a number of different forms, the transparent and crystalline 
 variety being called selciiitc, from the (ireek word selene, 
 meaning the moon, due to its peculiar soft lustre. This variety 
 sometimes occurs in large plates, and formerly was used 
 instead of glass for window lights. In this form it some- 
 what resembles mica, but is much softer, and the plates, al- 
 though slightly flexible, are brittle and inelastic. When it 
 occurs in needle-shaped crystals or in fibrous form, it is known 
 as fibrous gypsum or satin spar. The ordinary massive, 
 oi)aque crystals are called gypsum. This form presents many 
 varying colors — red, brown, black and yellow — from the en- 
 closed coloring matter, usually the oxides of iron. It also 
 occurs amorphous, in comi>act, ti'anslucent and snowy white 
 masses, and is then termed alahasfcr. This variety is very 
 beautiful, and as it is easily carved, it is much used for small 
 ornaments and statuary. 
 
 Gypsum frequently contains more t)r less foreign matter, 
 such as sanck clay, oxide of iron, or calcium or magnesium 
 carbonate. These impurities are not usually present in ex- 
 cessive quantities, and. when not exceeding three per cent, 
 do not seriously impair the conmiercial grades of ])laster. 
 Dental jilaster, iiowexcr. should be )>rodu<'e(l from the purest 
 
■M IMl'liKSSIONS AND I.MI'HKSSIOX MA'I'KKI AI.S 
 
 liualily of oypsuni o))tainable, and special care uslmI in it.s 
 inaimracturc to iiisurp niiifoi-m results. 
 
 MANUFACTURE OF PLASTER 
 
 Dental plaster is a half hydrated calcium sul- 
 pliate, formula CaSO* + ]/2H,0. It is formed by heating 
 gypsum, CaSoj + 2H.(), at a temperature ranging from 130 
 deg. to 190 deg. C. If heated above 190 deg. C, the product 
 is uiisuitalile for dental jnirposes, but a plaster is produced 
 which has a wide range of usefulness in the manufacturing and 
 building fields. 
 
 Two general methods are employed in the conversion of 
 gyi)sum into plaster. First, by pulverizing and then de- 
 hydrating. Second, by dehydrating and then pulverizing the 
 rock. The first method and the oldest is known as the kettle 
 process, in which the gypsum is crushed, ground, tlien placed 
 in large kettles and subjected to heat. This process drives 
 off some of the water of crystallization, and if conducted at 
 the right temperature and for the proper length of time, will 
 produce a fairly uniform half liydrate. Glasenap, however, 
 says that on account of tlie difliculty of maintaining a perfectly 
 uniform temperature, a small per cent of the mass may be 
 reduced below a half hydrate or become a partially dehydrated 
 half hydrate, which renders the ])roduct slower setting than 
 the half hydi'ate. 
 
 The second method is a more recent one, made possible 
 by improved machinery. The gypsum is broken up into mod- 
 erate sized pieces, and htirned to drive off a portion of the 
 water of crystallization, reducing it to a half hydrate. It is 
 then led into a rotary drum and pulverized. In some cases, 
 by means of a partial vacuum, the finest particles of the pul- 
 verized ])roduct are drawn out into a suitable receptacle, and 
 this constitutes the better grade of dental plaster. The qual- 
 ity of the plaster, however, as before stated, is also dependent 
 upon the purity of the gypsum used in its manufacture, the 
 purer varieties producing the best grades. 
 
 PHYSICAL PROPERTIES 
 
 Regardless of the fact that jilastcr of Paris has been em- 
 ployed for many years in dentistry, but little knowledge of 
 its physical properties is current among those who use it, 
 further than that it becomes ])lastic by mixture with water, 
 that it sets or hardens quickly, and that it is more or less re- 
 
IMPRESSIONS AND IMPRESSION MATERIALS 45 
 
 sistant to stress. Why or how it sets, or liow imich pressure 
 it will withstand without hecomiug distorted, are points of 
 vital importance, practically unknown \v, or at least disre- 
 garded by, prosthetists. 
 
 The entire bulk of jtlaster used by the dental profes- 
 sion represents but a very small per cent of the vast output 
 of this material. Tlie greater ])ortion is used in the arts, 
 building trades, and in glass-making industries. A numl)er 
 of investigators, thoroughly competent, by training and with 
 suitable apparatus, have made extended researches in the 
 chemical and physical aspect of this material, and some of the 
 results of tlieir findings, together with some experimental 
 work carried out liy the writer, will here be presented. 
 
 Professor M. Grlasenapp, chief of the technical department 
 of the University of Eiga, Russia, an authority on Iniilding 
 materials, has gone into this subject exhaustively. Although 
 not relevant in all respects to the use of plaster in the pros- 
 thetic field, the following extracts from his writings will shed 
 much light on the chemical as well as the physical aspects of 
 this material. The translation of Glasenapp's work is by Dr. 
 W. Michaels of Chicago. 
 
 SETTING 
 
 "If ordinary plaster of paris, representing mainly the 
 half hydrate C'aSOj -f l/^HoO is mixed with water and exam- 
 ined under the microscope, a lively process of crystallization 
 can be observed to set in after five or six minutes. In the 
 beginning, very thin needle-crystals form on the cover glass 
 and shortly afterwards also in the liquid and on the particles 
 of gyi)sum. After 15 or 20 minutes, single needle-crystals 
 and groups of them can be seen in great numbers, and espe- 
 cially the larger fragments of the half hydrate are covered 
 with needle-crystals radiating from them, also the character- 
 istic twin crystals appear abundantly. As fast as the crystals 
 form, the original ]iarticles of the half hydrate disappear. 
 After an hour they are completely used up and transformed 
 into crystajs, whereby the larger fragments of them be- 
 come centers of accumulation of crystals, while the smaller 
 have been converted into isolated star-shaped groujis. After 
 the same gyjisnm was heated for several hours to a teni])era- 
 tnre of 170 deg. C. (whereliy the amount of water still re- 
 mained ():2 per cent, corres])onding with the half hydrate) 
 crystallization began after •"! t" 4 iiiiiiutcs, and was prac- 
 tically completed afti-r half an hour; imly the largest particles 
 required almost an hour to dissolve and re-erystallize." 
 
4P IJIPRESSIONS AND IMPrtRSSION MATERIALS 
 
 "Tlie ])r('Sont stiili' ot' our knowledge ol' llic liardciiiiif;- ol' 
 liypsmn is that, after having l)een mixed witli water, tlie hall' 
 hydrate, plaster of paris, and the first anhydrous modification 
 ol' gyi)siun, wliicli is snp]iosed to l)e formed hetween !'.]() and 
 ■JDO deg. C, form over-satnrated solutions, from whieh the di- 
 liydrate precipitates in the sliapc of small crystals, a process 
 which is finished only aftci- nil hall' hydrate or anhydrite is 
 dissolved and transformed into crystals of di-hydrate. Ap- 
 parently tlie lialf hydrate goes into solution more rai)idly and 
 crystallizes in a shorter time than the first modification of 
 anhydrite; at least I conclude this from the fact that this first 
 anhydrite, which is considered tn he 'easily s()lul)le,' dis- 
 solves the more slowly at a higher tcmiteraturc than it was 
 pi'odnced." * * * 
 
 "To judge from excii llie most j-eeent statemenis to he 
 found in hooks on chemical technology, only a few chemists 
 seem to he aware of the fact t'.iat a complete transformation 
 of every particle of i)laster is an essential point in its hard- 
 ening. Owing to the greater soluhility in water of burnt 
 gyi)smn over crystallized gypsum, the hardening of plaster 
 of paris has l>een attriljuted to a process of crystallization for 
 some time; yet, this crystallizing has mostly been regarded as 
 of secondary importance. The ]>r('vailing explanation was 
 that the partly or completely dehydrated gypsiun hydrated, 
 combined with water, and hardened without changing its 
 form or place; that is to say, without previous going into 
 solution. The process, therefoi'e, was considered to be sim- 
 ilar to the hydration of calcined magnesia, and in many per- 
 sons' opinion seemed to resemble the hardening of Portland 
 cement and of hydraulic limes. This erroneous conception 
 likewise led to the Itelief that the strength of the casting de- 
 ])ended ui)on the hardness of the native gypsum from which 
 the plaster was burned. In fact, the ditference in hardness 
 between two kinds of raw gyi)sum is a matter of no conse- 
 (|ncnce. 
 
 THE STRENGTH OF HARDENED GYPSUM 
 
 The strength of the liardeiied gyjisum depends solely 
 upon the shape of the ci'ystals, upon their size, and ujjon their 
 more or less close contact. The more slowly the plaster hard- 
 ens, the larger and stronger the crystals of di-hydrate grow, 
 and the less water is mixed with the plaster, the denser and 
 less ]iorous the casting becomes. Molds which absorb water 
 readily, therefore rc(|uire a jilaster coiitaining as little an- 
 hydrite as ])ossible; furthermore, such molds call foi' a lib 
 
IMPRESSIONS AND IMPRESSION MATERIALS 47 
 
 eral aiiioiiiit of water. Adinixturtvs to the ])laster, wliieli re- 
 tard the setting, so-ealled negative eatalyzers, create large 
 crystals and consequently are tlie cause of more resisting and 
 stronger castings." " '" * 
 
 "The microscopical examination of samples of powdered 
 gyjisum, burnt at temperatures higher than :200 deg. C, teaclies 
 nothing essentially different from the behavior of the half 
 hydrate or plaster of paris toward water. Only the ability 
 of this anhydrite to form over-saturated solutions is impaired; 
 it is limited the more the higher the burning temperature has 
 been, and the longer the material was heated. Transformation 
 into crystals of di-hydrate takes place in the same manner, 
 but more slowly. The following table gives the various tem- 
 peratures to which the gypsum was exi)osed, as well as the 
 time of heating in many instances, and the beginning and ter 
 mination of the process of crystallization corresponding with 
 them : 
 
 Burnino; Time 
 
 Tt 
 
 Miiperature 
 
 107 
 
 Centigrade 
 
 .130 
 
 " 
 
 170 
 
 
 200 
 
 ( ( 
 
 200- : 
 
 250 " 
 
 250-; 
 
 ;!00 " 
 
 400 
 
 " 
 
 450 
 
 " 
 
 hours 
 
 ALLIZATION" 
 
 OF PLASTER 
 
 Beginning of 
 
 Crystallization 
 
 Crystallization 
 
 Completed After 
 
 0- 7 minutes i U hour 
 
 G- 7 
 
 1., to 1 houi 
 
 3- 4 
 
 i/o hour 
 
 30-45 
 
 iZ day 
 
 00 
 
 7 days 
 
 40 
 
 O i I 
 
 l->4 hours 
 
 17 " 
 
 10 davs 
 
 30 ' ' 
 
 14 
 
 1 o hour 
 
 "As the hardening of the castings of plaster is caused 
 mainly by the transformation into the di-hydrate, and as this 
 process of crystallization is the same also for 'overburnt' 
 gypsum, the lack of hardening in the case of the latter must 
 doubtlessly be ascribed, wherever it has I)een observed, to the 
 drying out of the uncovered castings; tlie process of crystal- 
 lization, therefore, was interruj^ted and the casting could not 
 ol)tain its full strength, which it otherwise would have done. 
 This must happen, esjjecially in cases in which the pi'ocess 
 of crystallization.takes a number of days. With gypsum liurnt 
 at 200 deg. o^ntigrade the transformation into crystallized 
 di-hydrate is almost completed within 24 hours; only the 
 larger particles take more time, and as, especially in the case 
 of large castings, still a sufficient amount of water remains 
 for crystallization after 24 or even 4S hours, this explains 
 
48 IMPRESSIONS AND IMPRESSION MATERIALS 
 
 the fact tliat gypsum, hurlit at 200 dog. centigrade and even 
 above this temperature, unless heated for too long a time, or 
 mixtures of this with standard plaster of Paris, show normal 
 hardening and high strength. Rohland, who assumes that 
 only a small portion of the gypsum, its active part, takes a 
 share in the hardening, is therefore mistaken; the entire mass 
 is active, if given time and opportunity to exhibit its activity, 
 which is greatly diminished, indeed. 'Complete hydration 
 and transformation into di-hydrate without hardening,' as 
 Rohland describes it, is consequently out of tlie question. The 
 term "overburnt or dead burnt" gypsum is therefore mis- 
 leading; the proper name for gypsum burnt at temjieratures 
 between 200 deg. and 300 deg. centigrade would be 'slow 
 setting. ' 
 
 "The process of hardening of such slow setting jjlaster 
 shows two distinct phases. In the first place, the plastic 
 dough assumes a dull surface and becomes stiff owing to the 
 transformation of the anhydrite into the half hydrate. This 
 point is reached after 1 or 2 minutes in the case of gypsum 
 heated to 200 deg. centigrade and after 30 minutes or more 
 with gypsum burnt at temperatures between 250 deg. and 300 
 deg. centigrade. If further absorption of water is interrupted 
 at this point by a rapid drying process, the stiff jjlaster is 
 found to contain from 6 to (>.5 per cent of water of combina- 
 tion, corresi^onding about with the half hydrate. During the 
 second phase, which requires more time, the half hydrate 
 previously formed goes into solution and crystallizes as di- 
 hydrate. Setting and hardening are, therefore, two well pro- 
 nounced processes in this case. Castings that have only time 
 to set yield insufticient strength; they must be given time to 
 harden. « * * # 
 
 SIZE OF CRYSTALS OF ORDINARY PLASTER 
 
 "The reason why castings made from ordinary quick set- 
 ting plaster are low in strength and possess little resistance 
 toward atmospheric influences, is evidently to be found in 
 the minute size of the interlacing needle-crystals of di- 
 hydrate, which, owing to the rapid process of crystallization, 
 have not time to develop and grow larger. The following 
 table illustrates this point by giving the dimensions of the 
 crystals in millimeters and the corresponding temperatures 
 at which the various kinds of quick-setting and slow-setting 
 plasters have been burned : 
 
IMPRESSIONS AND IMPRESSION MATERIALS 49 
 
 Largest Dimensions of Crys- 
 tals. 
 
 Rurnino- 
 
 Temperature. 
 
 Diameter. 
 
 Length. 
 
 107-130 
 
 centigrade 
 
 0.0025 
 
 mm. 
 
 0.04 mm 
 
 140 
 
 " 
 
 0.012 
 
 " 
 
 0.14 " 
 
 250-300 
 
 (I 
 
 0.075 
 
 " 
 
 0.50 " 
 
 400 
 
 a 
 
 0.050 
 
 ( ( 
 
 0.35 " 
 
 450 . 
 
 _ " 
 
 0.035 
 
 " 
 
 0.60 '* 
 
 "Tlie plaster burnt at 400 centigrade was heated only for 
 half an hour; that burnt at. 250-300 centigrade, however, for 
 several hours. This explains the ditTerenee in the dimensions 
 of the crystals. The first two of the plasters given in the jire- 
 ceding table are quick-setting, the last three slow-setting. 
 
 "The diameters of the needle-crystals of the plaster burnt 
 at 107-130 centigrade are 30 times smaller than those origin- 
 ating from the plaster burnt at 250-300 centigrade; their sec- 
 tional areas are, consequently, 900 times smaller. It is, there- 
 fore, evident that, other things being equal, a casting made 
 from slow-setting plaster must show greater strength. Hence, 
 whenever time has not to be considered, and increased strength 
 of the casting is desired, as, for instance, in the case of stat- 
 ues for art galleries and so forth, experiments with slow- 
 setting plaster seem to bo very adxisablc. 
 
 ''In conclusion, the various calcined produced obtainable 
 from raw gy^jsum may be classified in accordance with the 
 results derived from the foregoing research. The limits of 
 temperatures stated must only be considered as approximate 
 figures, of course, as the change from one kind to the other 
 takes place very gradually, and because, as repeatedly stated, 
 not only the height of temperature, but also its duration, deter- 
 mine the properties of the calcined gypsum product. 
 
 A. Native gypsum Di-hydrate containing two mole- 
 
 cules of water. 
 
 B. 107 centigrade Half hydrate containing lo mole- 
 
 cule of water. 
 
 ('. 107-170 centigrade. . .Consists mainly of half hydrate. 
 
 D. 170-200 centigrade. . .More or less dehydrated half hy- 
 drate. Combines with water 
 readily until half hydrate is ob- 
 tained. 
 C. and D. represent the commer- 
 cial plaster of Paris. 
 
50 IMPRESSIONS AND IMPRESSION MATERIALS 
 
 K. L'OO-'JaO centigrade. . .(Vmtaiiis a very small aiiiomit of 
 
 water. Sets more slowly tliaii 
 tlie I'oi'mei'. 
 
 F. L'r)()-400 eeiitii'rade. . .(\)iitains only a trace of water. 
 
 Slow-setting. B., ('., D., K. 
 and F. foi'm crystals of di-liy- 
 drate, if mixed with water. 
 Hardening dne to crystalliza- 
 tion. 
 
 G. 400-750 centigrade. . .Completely dehydrated, anhy- 
 
 drite, overhnrnt from a prac- 
 tical point of view. 
 
 H. 750-800 centigrade. . .Gradual transformation into the 
 
 granular modification of anhy- 
 drite; heginning of the forma- 
 tion of hydraulic gyijsum. 
 G. and H. show in contact with 
 water. No hardening, or only 
 very imperfect hardening. 
 
 T. 800 centigrade. . .Hydraulic gypsum containing 
 
 minute grains of anhydrite. 
 
 K. 900-1000 centigrade. . .Genuine hydraulic gypsum, 
 
 grains fully developed. 
 
 L. 1000-1400 centigrade. . .Hydraulic gypsum showing 
 
 grains increasing in size and 
 hardness with rising tempera- 
 tui"e. The i^ercentage of "basic 
 calcium sulphate" likewise in- 
 creases in the same ratio. 
 I., K. and L. harden slowly with 
 
 water without crystallizing. 
 G., H., I., K. and L. crystallize 
 with alum solution. 
 
 "A temperature of from 1300 deg. to 1400 deg. centi- 
 grade, in my opinion, can be employed in the manufacture of 
 hydraulic gypsum only in cases in which gypsum does not 
 come in immediate contact with the fuel, as, for instance, in 
 laboratory experiments, in which the burning is done witli 
 gas. 
 
 "Where coal is used, the ashes of it, as well as the reduc- 
 ing carbon, are bound to contaminate and R]3oil the calcined 
 product. Moreover, tem]ieratures as high as these are almost 
 out of the (juestion in ]n"actical operations." 
 
IMPRESSIONS AND IMPKKSSION MATERIALS 51 
 
 TIk' I'on'goiug extracts refer esijeeially to the eliemistry 
 of setting, and the effects of varying temperatures and time 
 in burning on the time of setting and hardness of plaster. 
 The metliod of nianii)ii!ation is not considered. This to tlie 
 prostlietist is a matter of imi)ortance that cannot be over- 
 looked. 
 
 INFLUENCE OF MIXING ON QUALITY 
 
 I'laster mixi^d at a medium to tliick consisteucy will set 
 more rapidly and be of better density when set than if an ex- 
 cess of water is present. Too thick a mix, however, should 
 I)e avoided, ])articularly where accelerators are used, as 
 under such circumstances the setting freciueutly begins before 
 tlie mass is of uniform ccmsistency, and further stirring breaks 
 uji the already forming crystals, 'i'liis interference results 
 in a mass of nnccrtaiii density, oflcntimcs willi nianv si)ac('s 
 present. 
 
 Tlie other extreme, too much water, should ))e avoided, as 
 it retards the setting, and the plaster, when set, is less resist- 
 ant to stress. Various substances are added to accelerate 
 thb setting, particularly in impression woi'k. Common table 
 salt (NaCl) is frequently used, but should never be incor- 
 l)orated in ])laster used for casts for vulcanite work, since its 
 atlinity for moisture causes rapid softening and deterioration 
 in the presence of steam or water. Sulphate of i)otassium 
 (K0SO4) is by far the best accelerator, because it not only 
 hastens the setting, but lias a controlling intluence on expan- 
 sion. This medium, however, should not be used in east con- 
 struction for the same reasons that apply to NaCl. Potas- 
 sium alum has lieen highly recommended as an accelerator 
 and hardening medium for plaster in dental lalioratory ])ro- 
 cedures, but tests made with this substance fail to verify the 
 claims made for it. 
 
 EXPANSION OF PLASTER 
 
 The tendency of plaster to ex]iand during and after 
 setting and the deleterious effects of this movement in denture 
 adaptation has long lieen recognized Ity some, but its im- 
 l)ortance is not fully understood. 
 
 When freshly mixed plaster begins to set, it contracts 
 slightly, then remains stationary foi' a short lime, then ex- 
 pauds, and after assuming a thoroughly dry condition it again 
 contracts to a very slight degree. From fi deg. to 10 deg. 
 rise ill tcnipcratni'c is n()ticeal)l(' during the setting proct'ss, 
 due to llie clieniical action that oc<'Uis. 
 
52 I.Vll'KESSIONS AND IMPRESSION' MATKKIAI.S 
 
 111 an ordimiry mix of iiiipressiuii plaster that harck'us in, 
 say, 3 minutes, the first contractile period occurs between the 
 time of mixing and that of the beginning of setting. Since 
 the consistency of plaster, when freshly mixed, is soft and 
 the mass yielding, no accurate record can be made of any 
 change that may occur within the first minute after mixing. 
 From tlie beginning of tlie second minute, usually, the mass 
 being hard enough to resist the tention spring of the microme- 
 ter, the contraction is perceptible and usually continues for 
 about 2 minutes, or until the evolution of heat is noticeable. 
 This would establish the contractile period in the last two of 
 the three minutes that elapse between the time of mixing and 
 that of setting. Any variation in the time required for set- 
 ting would undoubtedly produce a corresponding change in tlie 
 contractile period. 
 
 The contractile stage is followed by a short period of 
 inertia of usually about one-half minute, after which expan- 
 sion sets in, slowly at first, then increases rapidly for two or 
 three minutes, then decreases gradually, and finally ceases 
 altogether. Usually the greatest expansion is over in ten 
 minutes, although the movement continues in a gradually 
 decreasing ratio for twenty-four hours or more. 
 
 The rate and amount of expansion is very greatly influ- 
 enced by the manner in which the plaster is mixed with the 
 water, and the method and length of time the mass is stirred 
 Long and rajiid stirring increases the rapidity of setting, and 
 the rate and amount of expansion as well, while on the other 
 hand slight stirring for a sliort time induces only moderate 
 movement. 
 
 MEASUREMENT OF EXPANSION AND CONTRACTION OF 
 PLASTER 
 
 For the purjtose of studying the behavior of plaster under 
 different conditions, the writer constructed a micrometer 
 which registers both the expansive and contractile movements 
 of this and other materials as well. 
 
 This instrument is graduated to read to the 1/10,000 of an 
 incli and the 1/500 of a mm. In reality readings can be made 
 to the 1/40,000 of an inch. The spring actuating the conta<-t 
 rod is very delicate and offers but slight resistance to expan- 
 sion, so that practically all of this movement can be noted. 
 
 The following records, taken from many hundreds, show 
 the results of stirring the several mixes varying lengths of 
 time. French's impression plaster was the material used. 
 
IMPRESSIONS AND IMPRKSSION MATKRIALS 51] 
 
 tilt' mixes being practically identical as to weight, aniouiit of 
 water, temperature of room and material. Nothing was added 
 to accelerate setting or control exj^ansion. The plaster was 
 sifted into the water in the rubber bowl. The only api)reci- 
 able difference was in the length of time each mix was stirred. 
 
 Expansion 
 After 
 Time Stirred. 10 
 X( 
 
 
 Time Stirred. 
 
 10 
 
 Minutes. 
 
 1^4 Hours. 
 
 .r .Mix. 
 
 Minutes. 
 
 
 I^)ints. 
 
 Points. 
 
 1 
 
 % 
 
 
 •) 
 
 (il 
 
 •) 
 
 1 
 
 
 ?>•! 
 
 101.5 
 
 3 
 
 11/4 
 
 
 fil 
 
 !i:'..5 
 
 4 
 
 114 
 
 
 !)3 
 
 118.5 
 
 5 
 
 1% 
 
 
 118 
 
 i;!4 
 
 (5 
 
 2 
 
 
 137 
 
 157.5 
 
 7 
 
 -"y4 
 
 
 140 
 
 1()0 
 
 8 
 
 '^^ 
 
 
 U2 
 
 159 
 
 9 
 
 2% 
 
 
 147 
 
 165 
 
 10 
 
 3 
 
 
 145 
 
 162 
 
 The point is 1/10,000 of an inch. 
 
 Tlic mixes were of a consistency suitable for impression 
 work. 
 
 Further experiments indicate that thinly mixed plaster 
 exhibits less expansion than when more thickly mixed, but 
 the density is proportionately less, as the mixes are made 
 thinner. 
 
 CONTROL OF EXPANSION 
 
 Many experiments have been made with different sub- 
 stances, singly, in combination, and in varying proportions, 
 in an effort to control this expansive movement, but with the 
 exception now to be mentioned, only negative results were 
 ol)served. 
 
 Potassium sulphate in definite pro^jortions acts as an 
 accelerator, and also decreases expansive movement. The 
 slightest amount of stirring consistent with the production of 
 a imiformly plastic mass is also important in keeping down tlie 
 expansive movement. 
 
 WARPAGE 
 
 In prosthetic procedures the princi]ial difficulty resulting 
 from expansion is in the warpage of impressions and models 
 when allowed to remain in the tray for any length of time 
 after the plaster has set. 
 
54 IMPRKSSIONS AND IMPRESSION MATP.'RIAI.S 
 
 Dr. I)iickiii.niiain, in 1860, first noticed the (;'xi)aiisiv(' 
 movement in ])liister, lint he failed to realize tlie deleterions ef- 
 fect of it. Dr. \y. Txiwrnan McLeod of Kdinl»nr.nii, Scotland, 
 in 1880, tii'st calliMl attention to tlie warpauc of plaster when 
 
 HXI'AXSKIN MAI 1 1 INK 
 
 coiiliiicd ill an iin|ii'ession tra\". Ilis cxpcrinieiit consisted in 
 clanipini;' nietai liars td llii' edi-cs of a ri.ii'id iiielal ]ila1e and 
 tillin,^' the enclosed s]iace with jiroperly mixed plaster. 
 
 After twenty-fonr hours the hars were removed, and the 
 slal) of plaster sawed dia,i;(mally tlironi;h the center, when it 
 was found that in the central ])or1ion it had arched up to a 
 consideralile extent, while the edges remained in contact with 
 the plate. This was due to the fact that lateral exjiansion was 
 
IMPRESSIONS AND IMPRESSION MATERIALS 55 
 
 prevented by llic fixed in;u',i;iiial bars, whicli, however, did not 
 confine the material on its npper surface, and movement 
 occurred in that direction. 
 
 An impression tray with its fixed sides cori'esponds to the 
 shil) witli clamped bars. Tlie sides of the tray prevent lateral 
 
 C 
 
 WARPED IMPRESSION DUB TO FIXED TRAY FLANGES 
 
 ex])ansion, so that the movement is noticeal)le by the arching- 
 up or war])ing of the palatine portion of the impression, while 
 the sides inclosed by the buccal and labial fianges of the tray 
 remain in close contact with them. The result is that the pala- 
 tine portion of the ini]iression raises, while no corresponding 
 
 a> d' 
 
 WARPED f'AST DUE TO RESTRICTED LATERAL MOVEMENT 
 
 movement occurs in the alveolar portion. Now if the plaster 
 for the cast is introduced in the impression and allowed to re- 
 main for some time, a similar error due to a corresponding 
 cause will result, and thus establish an additional increase in 
 the height of the jialatine arch of the cast. 
 
 ERRORS DUE TO WARPAGE 
 
 Two errors, due to warpage, have therefore occurred, 
 either one of which might, and certainly both together will, 
 result in the cast being an imperfect reproduction of the 
 mouth it is intended to re]>resent. A denture molded over 
 such a cast will touch the palatine portion of the mouth before 
 it is firmly seated on the alveolar borders, and under stress 
 
56 IMPRESSIONS AND IMPRKSSION MATERIALS 
 
 ol' masticatioii will readily li|t. In some iustaiiccs tliere will 
 be no adhesion whatever. The method for reducing or par- 
 tially controlling and overcoming expansion of i)laster impres- 
 sions and casts will he taken np when considering the teclinic 
 of this work. 
 
 COMPRESSIBILITY OF PLASTER OF PARIS 
 
 An object composed of plaster of Paris appears like a 
 solid substance and is resistant to ordinary stress without 
 change of form. When we examine this material under a 
 microscope, however, it is found, as before stated, to be com- 
 posed of numerous crystals grouped irregularly in masses 
 with many spaces between the masses and between the crys- 
 tals themselves. Within and below the modulus of resist- 
 ance of these crystals, they retain their form and resist a 
 verv considerable annnuit of stress witliont ciushing. 
 
 ronrpRTSSTOx MAnrpTC 
 
 In certain technical procedures, particularly in vulcanite 
 work, plaster is usually subjected to heavy pressure. By ex- 
 l)eriment it has been found that, in many cases, an amount of 
 force far in excess of the modulus of resistance of this ma- 
 terial is ordinarily used in laboratory procedures. While 
 perhaps in some instances the physical change is not apparent 
 to the eye, it can be readily discerned in others. In many in- 
 stances where no visual change is noticeable, the adaptation 
 of dentures is seriously interfered with, which can be laid to 
 no other cause than that of compvessihility. Further discus- 
 sion of this important problem will be continued under the 
 subject of the flasking of vulcanite cases. 
 
 ADVANTAGEOUS PROPERTIES OF PLASTER OF PARIS 
 
 Plaster has, however, a number of good (puilities which 
 commend it for impression work, and notwithstanding the 
 
IMPRESSIONS AND IMPRESSION MATERIALS 57 
 
 serious disadvantages which have already been cited, it is an 
 indispensable material in prosthetic procedures. Its plasticity 
 when freshly mixed, its tastelessness and freedom from odor, 
 the facility with which the most irregular surfaces can be 
 copied, its rapid setting property, and the fact that it can be 
 introduced in the mouth at ordinary temperatures, commend 
 it for general use. Being inelastic and brittle, it breaks with 
 a clean fracture, and the broken pieces can easily be placed 
 togetlier again in exact relation to each other, so that liy its 
 use the impression of any surface, however irregvilar, may be 
 secured with accuracy. 
 
 Only the finest grades of dental plaster should be used 
 for impression-taking, and it should be kept dry and in air- 
 tight receptacles to retain its setting quality. When used 
 with skill and in properly selected cases, it is an excellent 
 medium for imi^ression work, and indispensable for many 
 other purposes. 
 
 In mixing plaster, the best results are secured by plac- 
 ing the required amount of water in the bowl and sifting the 
 plaster into it until a sufficient amount has been added to 
 take up the water. No excess of water should be present, 
 while an excess of plaster results in an insufficient amount of 
 water to bring the half hydrate into solution. It should be 
 sul)jected to the slightest amount of stirring — just enough to 
 make the plastic mass homogeneous and of uniform consist- 
 ency throughout. 
 
 IMPRESSION COMPOUNDS 
 
 These are manufacturers' products intended for impres- 
 sion work, and into which, on drying, metal dies can be run 
 without resorting to the usual steps in such cases. The basis 
 of all such compounds, however, is plaster of Paris, which 
 acts as a cementing medium between the particles of refrac- 
 tory material, usually pulverized or granular calcium car- 
 bonate, silex, pumice-stone or coarsely ground asl)estos. But 
 little, if any, advantage is dci'ivcd from tlieir use. 
 
 CEMENTS 
 
 Tlie various dental cements are at times employed in 
 taking inqu'essions of limited areas, as, for instance, of pre- 
 pared teetli for inlay work, or in certain procedures in crown 
 and bridge work. They are used to such a limited extent as 
 not to be considered as general im])ression materials, 
 
58 lAII'lUOSSIONS AND IMI'KIOSSION MATIOIUAI.S 
 
 GROUP II 
 
 IMPRESSION MATERIALS RENDERED PLASTIC BY HEAT 
 MODELING COMPOUND 
 
 Modeling coiiipouiKl, as its iiiunc implies, is iiiiulc ii]) of 
 several ingrodients ('()ral)ined in sueli proportions as to pro- 
 duce a material that is plastic and workable at low tempera- 
 tures, which will copy accurately the surfaces against which 
 it is pressed, and cool or harden quickly. Since the formulae 
 of the manufacturers are not jmblished, it is not possible to 
 give exact data on this subject. The base of this material, 
 in practically all cases, consists of one or more of the natural 
 resinous gums used in varnish making, such as dammar, copal 
 or kauri. These gums are more or less hard when dry and 
 cold, but become sticky and plastic on heating. Stearin is 
 added to reduce the stickiness, while pulverized soapstone 
 is incorporated to give body to the mass. Carmine is usually 
 used to tint the material, and sometimes a little aromatic 
 flavoring substance is added to render it pleasant in taste 
 and odor. 
 
 FORMULA FOR MODELING COMPOUND 
 
 A formula which will serve to illustrate the compounding 
 of this material was given to the writer a number of years ago 
 by Dr. E. Lloyd Williams of Ijondon : 
 
 Kauri 1 part 
 
 French chalk 1% parts 
 
 Stearin 1 Vi; parts 
 
 The stearin is first melted, the kauri added, and the two 
 thoroughly incorporated, then the chalk is gradually sifted in 
 and the mass kneaded until well mixed. The coloring and 
 flavoring ingredients should be incorporated in the stearin 
 and gum before adding the soapstone. 
 
 Some varieties of conii)ound show a decided tendency to 
 contract, or warp, on cooling, which projierties make them 
 unreliable in impression work, while some, to render them 
 efficiently })lastic, require a degree of temperature unbearable 
 to the oral tissues. While the tissues of the mouth can tol- 
 erate temperatures ranging from 140 to 170 deg. F. without 
 much discomfort, a compound should be selected that will 
 copy fine lines and irregular surfaces at even lower tempera- 
 tures than those mentioned, in order to be efficiently workable. 
 
 As a rule, modeling compound is heated in water to soften 
 i'oi- inqiression work, but should never be sul)jected to l)oiIing 
 temperature, as its quality is soon impaired and the material 
 
IMPRESSIONS AND IMPRESSION MATERIALS 59 
 
 is too sticky to liaiidk' (•(uncniciilly wIr'U oNcrlicated. The 
 bottom of the vessel used for lieatiii,i;' shoukl be covered with 
 a piece of rubber dam, or clean pajjer, to prevent the compound 
 adiiering to it. Softening in water is preferable to dry heat, 
 although some use the latter method. Modeling compound is 
 inelastic and therefore when iinjjressed against a surface it 
 should be thoroughly hardened l)efore removal from the 
 mouth, since in the act of loosening the impression or in its 
 withdrawal, pressure upon the iirominent portions is liable to 
 distort it. This precaution also ai>])lies to most of the sub- 
 stances made jilastic with heat. 
 
 BEESWAX 
 
 This material is elaborated by bees out of substances col- 
 lected from flowers and from it the honeycomb is formed. 
 The wax is pre})ared for use l)y melting the comb in water 
 after removal of the honey. Impurities lighter than the wax 
 are skimmed oiT, or if heavier are removed by trimming the 
 under surface of the hardened cake. The natural color of 
 beeswax is yellow. It may be bleached by forming it into thin 
 sheets and exposing it to l)right sunlight, or by the use of 
 dilute acids in the melting pan. It may be given almost any 
 tint desired by the addition of suitable pigments. 
 
 It was formerly much used as an impression material, 
 but has been to a great extent supplanted by modeling com- 
 ])ound. There are two serious objections to the use of bees- 
 wax as a material for general im|)ression work: First, when 
 (lis]>osed around the laliial and buccal portions of the alveolar 
 border unsu]i]iorted by the tray, in a thin layer, it is very apt 
 to be distorted in removal because of lack of inherent rigidity, 
 even when chilled; second, there is a tendency for it to warji 
 and contract in changing from a heated, plastic condition to 
 a cold state. When manipulated with care it may be used to 
 advantage in some cases, although it is difficult to say in what 
 instances it would be ]ireferable to modeling compound, since 
 in recent years the quality of the latter has been so materialh' 
 improved. 
 
 Wax is furnished by the manufacturers in the form of 
 sheets and cakes, both in a pure state and combined with 
 other substances, .such as paraffin or some of the resins, to 
 render it harder or more adhesive, as desired. 
 
 BEESWAX AND PARAFFIN 
 
 The addition of paraffin to beeswax lowers its melting 
 point and renders it harder when cold, but reduces the ad- 
 
liO IMFRKSSIONS AND IMF'Rp:SS10.\ MATKKlALS 
 
 liesivcuess of the wax if used in cxcctss. Tallow is fr('(|ii('ntiy 
 used as an adiiltoiaiit of wax. The coinhinatioii, however, is 
 worthless for dental i)nri)oses. The sticky wax, so useful for 
 many purposes in tiie lal)oi'atory, oonies in the form of small 
 sticks or cylinders, and is made l)y combining some of llu- 
 I'esins with beeswax. It is adhesive and hard wlien cold, 
 and is nuicli used in the assembling of parts in crown and 
 bi'idge work. 
 
 HARD BITE WAX 
 
 A material known as hard hifc ifax is procurable, which 
 is very convenient in the making of wax contour models for 
 use in warm weather. When formed of this wax, the rims 
 withstand the stress of trial in the mouth, as well as the effect 
 of oral temijcrature, without becoming distorted. AVax of 
 this class usually contains rosin. 
 
 Beeswax is mani]mlated much the same as modeling com- 
 ])ound, being softened in warm water. It should be broken 
 uj) in small pieces, if in bulk, or in sheets of moderate thick- 
 ness, so that tlie heat may ])enetrate readily at rather low 
 temperatures, say 130 deg. to 140 deg. F. When thoroughly 
 warmed, it is kneaded with the fingers into a uniform ])lastic 
 mass and pressed with a towel to take up any moisture that 
 may be present. 
 
 None of the plastic, non-elastic impression materials, with 
 one exception, are suitable for taking impressions in under- 
 cut spaces, or in partial cases where the teeth have constricted 
 services or the embrasures and inter]iroximate spaces are de- 
 void of gum tissue. Under certain conditions and by follow- 
 ing methods to be outlined later, modeling compound may be 
 ri^ed. 
 
 The difficulty encountered in such cases is due to the 
 drawing or distorting of the impression material in with- 
 drawal from the teeth and spaces designated. 
 
 Beeswax is frequently employed as a preliminary im- 
 pression material in partial as well as full cases, the impres- 
 sion thus obtained being relieved of excessive surplus and 
 used as a matrix or improvised tray for holding the ])laster 
 for the final impression. By this means, the wax having been 
 conformed to the tissues, a minimum quantity of plaster is 
 carried to every surface involved, with less discomfort to the 
 patient, while the ratio of expansion in the plaster is corre- 
 spondingly less. In partial cases, however, the wax should be 
 trinuned well away from around the remaining teeth, so that 
 the plaster enclosing them may be of sufficient thickness when 
 
IMPRESSIONS AND IMPRESSION MATERIALS 61 
 
 fractured iii renioval, lo be readily plai-t'd together again in 
 the wax matrix. 
 
 GUTTA PERCHA 
 
 This material is ()l)taiued from the juice of a tree, the 
 Isonandra or Dichopsis Gutta, found in the Malay Archipel 
 ago, on either side of the equator, for a distance of two or 
 three degrees. 
 
 The word "gutta" iu the Malay language means "gum" 
 and "percha" is the name of the tree, so the term means the 
 "gum of the percha tree." The juice is collected by a method 
 similar to that followed in tapping the rubber tree (Siphouica 
 Klastica) by making a long diagonal cut entirely through the 
 bark and adjusting a trough under the incision, througli 
 which the escaping juice is carried into vessels to receive it. 
 As more or less dirt and impurity is mixed with the juice, the 
 crude material is nufit for use. It is refined by first tearing 
 it into shreds iu a special machine, washing and agitating in 
 water, and afterward boiling, to bring it into a coherent mass, 
 in which form it is known as commercial gutta percha. It 
 is nearly similar in composition to rubber, being a hydro- 
 carbon, but, unlike that substance, it deteriorates slowly if 
 exposed to the air, the oxygen of the air uniting with it and 
 causing the gum to become brittle and lose its elasticity and 
 strength. It can be mixed with sulphur and vulcanized, but 
 the product, while more durable than the crude material, is 
 not so permanent or lasting as vulcanite, and consequently 
 is not used iu this form to any great extent. 
 
 The fresh commercial product is sometimes used for 
 taking impressions of the mouth. It becomes plastic enough 
 for this purpose at a temperature of 130 deg. to 150 deg. F. 
 and is prepared by softening in water. It will contract, how- 
 ever, unless dried and heated sufificiently to adhere to the sides 
 of the tray. In general, it is manipulated the same as model- 
 ing compound, except that s]iecial care must be observed to 
 cement it to the tray before introduction into the mouth and 
 to chill it thoroughly befoi'e removal. Being elastic, it will 
 readily draw away from undercuts and teeth with constricted 
 cervices, and immediately resume its proper form when pres- 
 sure is relieved. 
 
 CONSTITUENTS OF GUTTA PERCHA 
 
 As it is difficult, or almost imi)ossible, to secure the fresh, 
 unadulterated product, its use as an impression material is 
 very limited. The base plate gutta percha furnished by the 
 
62 IMPRESSIONS AND IMPRKSSION MATERIALS 
 
 sii])ply liduscs is not coiiiiKiscd of the pure .i4'iiin, liul (•(iiitniiis 
 chalk, niannesia or oxide of zinc, and t'rcciuently coloring umt- 
 ter. The addition of these suhstanoes prevents, to a certain 
 extent, rapid deterioration, and also renders the product nioi'c 
 rig'id. Wliile sometimes used for the base of trial plates, 
 gutta percha is not sufficiently rigid to insure accuracy in 
 such procedures. The sheet base plate is frequently used foi 
 taking impressions of faced roots in cro\Yn and bri age work 
 where it is desirable to force the giiigivie apically to obtain 
 an outline of the root periphery.- 
 
 (intta jx'reha consists of a ('(inihinatioii of iixdrocai-bons 
 similar to caoutchouc. 
 
 Payen's analysis shows the following: 
 
 Gutta 78 to 82 per cent 
 
 Albane 16 to 14 per cent 
 
 Fluavile (i to 4 i^er cent 
 
 Chemical coin])osition : 
 
 ( "arlion 86.36 
 
 Hydrogen 12.15 
 
 Oxygen 1.4!) 
 
 Since the juice is coli(M'tcd from several varieties of trees 
 and comes from dilTerent localities, it is a natural cansequence 
 that the physical as well as chemical proportions of constitu- 
 ents must vary more or less, so the above may be considei'ed 
 as representing the general comiiosition of this material and 
 not an absolute unchangeable chcinical foi-mula. 
 
C If A P T K R V 1 1 
 TECHNIC OF TAKING IMPRESSIONS 
 
 GENERAL REMARKS 
 
 In i>t'iieral, tlie taking' of improssioiis in plaster for full 
 and partial, njjper and lower cases, is similar in many tech- 
 nical details. A comparatively fnll description of the mani])- 
 ulative details carried out in taking an impression of an 
 upper edentulous cast, will serve as a basis for all classes 
 of plaster impressions. The difference in details will be pre- 
 sented as each class is descrilied. 
 
 INDICATIONS FOR THE USE OF PLASTER 
 
 The value of plaster as an impression material lies in 
 the fact that it can be readily adapted to the most irregular 
 surfaces and carried into deeji undercuts and embrasures, 
 from which it can be removed by fracturing, and the broken 
 j^arts readjusted with ease. 
 
 An outline of those cases where plaster is most strongly 
 indicated, is here in order: 
 
 First — In all eases where any of the natural teeth are 
 present. 
 
 Second — In case undercuts exist, either on the opposite 
 surfaces of the borders, or in spaces formed as the result 
 of the loss of the natural teeth. 
 
 Third — Where flabby ridges are itresent, such as have 
 jireviously been described. 
 
 Fourth — In edentulous cases where the nuicous and sub- 
 nnicous tissues are thick and elastic, i)articularly in the pal- 
 atine portion of the mouth. When such a condition prevails, 
 the tissues, if compressed uniformly, as when modeling com- 
 pound is used, assert their resiliency, on pressure being re- 
 lieved, which breaks the jieripheral adai^tation of the im- 
 pression, and later on, of the denture that may be constructed 
 when such an iniju'ession is used as a basis. 
 
 In ]iractically all of the cases just cited, the use of bees- 
 wax or modeling compound, as an im])ression material, is 
 contra-indicated, but the use of either of these substances as 
 a preliminary impression material, in wliich to hold tlic plaster 
 for the final impression, is strongly indicated. 
 
 63 
 
G4 TECHNIC OF TAKING IMPRKSSIONS 
 
 UPPER EDENTULOUS CASES 
 PRELIMINARY STEPS IN IMPRESSION TAKING 
 
 Taking it for granted that the mouth has been previously 
 examined and is in condition to receive prosthetic substitutes 
 the patient is seated in tlie o]ici'ating chair. 
 
 POSITION AND COMFORT OF THE PATIENT 
 
 As a general rule in all plaster impression work the patient 
 should sit in an upright position. The chair may be slightly 
 inclined backward, ])ut not to any marked degree. The chair 
 should be raised high enough to ))ring the patient's mouth 
 within convenient range for manipulation. Further adjustment 
 of the chair should be made for the comfort of the patient, 
 so far as may be consistent with the work in hand. 
 
 A covering should be adjusted to protect the patient's 
 clothing from becoming soiled with particles of plaster, or 
 the dripping or overflow of saliva from the mouth. When 
 possible to do so, the saliva ejector should be used to over- 
 come this difficulty. Before taking the impression, the mouth 
 should be rinsed with tepid water, or, preferably, normal salt 
 solution, to remove the viscid, stringy mucous. A glass of 
 water should be placed on the bracket so that the patient 
 may rinse the mouth after the removal of the impression. 
 
 POSITION OF THE OPERATOR 
 
 For upper impressions the operator should stand on the 
 right side of the chair, and slightly back of the patient. He 
 should stand erect and work with the upper arms perpen- 
 dicular, and tlie forearm horizontal. In introdiicing an npi)er 
 impression, his left arm should pass to the left of the patient's 
 face, so that the left hand may manijmlate that angle of the 
 mouth, and later, snjiport the tray. 
 
 In taking lower impressions, the operator will find it 
 more convenient to stand slightly in front, to the riglit of, and 
 facing the patient. In this position, both hands have more 
 freedom of action, and the line of vision is less obsti-uctcd 
 than when the operator stands back of the chair. 
 
 SELECTING AND FITTING TRAY TO MOUTH 
 
 By a glance in tlie nioutli, the opcraidr can determine tlie 
 approximate form and size of Irny to use, and select one 
 accordingly. This is introduced in the mouth, and its gen- 
 
TBCHNIC OF TAKING IMPRESSIONS 65 
 
 eral adaptability to the case aseertaiued. If apiiroximately 
 of the right form, but not exactly adapted to the case, the 
 points needing modification are noted. By placing the tray 
 in position and subjecting it to a side-to-side movement, th(; 
 excess of buccal space can be estimated. By holding the 
 distal margin of the tray against the palatine vault in ap- 
 proximately the correct mesio-distal position that it should 
 occupy, and letting the anterior portion of the tray drop down 
 below the Ixirder level, so that a view above the tray of the 
 vault and tray curvature may be obtained, the adaptation of 
 the vault portion of tray to tissue can be determined. 
 
 
 FULL ITTKR Un'RESSlON TRAV SlITAiiLE FOK EDEXTULOIS CASES 
 
 The relative width of the labio-buccal flange to the al- 
 veolar border, and the several points of muscular attachment 
 can be determined by holding the tray in position, rather 
 loosely, of course, since the impression material is not pres- 
 ent, and subjecting the lips and cheeks to outward and down- 
 ward traction. If too broad, the amount of excess width 
 can be determined br alternately pressing upward on the 
 central portion of 'the tray and pulling downward on the 
 lips and cheeks, the amount of movement in the tray indicat- 
 ing the excess present. 
 
 Hold the tray in normal position witli one hand and pass 
 the index finger of the other hand backward along the central 
 
66 TKCHNIC OF TAKING IMPRKSSIONS 
 
 vault portion, past tlie tray margin, onto the oral tissue, and 
 determine whether this portion of the tray extends to the 
 line of junction of hard with soft palate. If not, make an ex- 
 tension, as descrihed elsewhere. The usnal syjace outline of 
 an eighth of an inch, or less, hetween tray and tissue, should 
 he closely adhered to, since a sjnall amount of impression ma- 
 terial, properly applied, will yield more accurate results and 
 be less objectionable to the patient than an excessive bulk. 
 
 MIXING THE PLASTER 
 
 A clean rubber liowl is tilled about one-fourth full of 
 slightly warm water, into which should be sifted some im- 
 pression plaster (plaster which contains an accelerator). Or, 
 if French's regular dental plaster is used, dissolve about one- 
 half gram of sulphate of potassium in the water before sifting 
 in the plaster. This will hasten the setting and also have a 
 slight control on expansion. 
 
 Add enough plaster to take up the excessive moisture, 
 and produce a plastic mass, which, when stirred slightly, will 
 stand when piled upon itself, or in other words, will not drop 
 from the inverted tray. Distribute the mixture in the tray 
 selected, spreading it uniformly over the various surfaces and 
 building it slightly higher on the vault portion than else- 
 where, to insure a sufificient amount of material being present. 
 The general contour of the plaster in the tray should be sim- 
 ilar to the general contour of the mouth, but reversed, of 
 course. 
 
 INTRODUCING THE FILLED TRAY IN THE MOUTH 
 
 The tray handle is held in the right hand, thumb on top 
 of handle, index and middle fingers underneath, to support 
 the body on the right side. The right angle of the tray is 
 inserted well back in the right angle of the mouth, while the 
 o])posite side is rotated through the left angle of the mouth, 
 the latter l)eing distended with the index or middle finger 
 of the left hand. 
 
 After the greatest diameter of the tray has passed the 
 oral opening, its adjustment, although requiring care, is 
 easily accomplished. 
 
 See that the tray is centered. The direction of the handle 
 indicates this to a certain extent, although it cannot be de- 
 pended on in those cases where the buccal alveolar process 
 has been absorbed more on one side than on the other, or 
 
Tkchnic of taking impressions 6? 
 
 where the aheuhir processes are not synunetrieally related to 
 the medium line of the cranium. 
 
 Pass the tray back until the labial surface of the border 
 is within about one-fourth of an inch of the flange, and press 
 the tray upward until the border is fairly well imbedded in 
 the plaster, not, liowever, to the full extent, as at this time 
 nmscular impingement is not yet relieved. The index and 
 middle fingers of l)oth hands are placed under the floor of 
 the tray to carry the impression to place. This is the first, 
 or pressure position of the hands. Apply the index and middle 
 fingers of the left hand to the vault portion to support the 
 tray, and quickly pass the index finger of the right hand 
 along the Imccal border of the right side of the tray, at the 
 same time producing tension on the buccal muscles, drawing 
 them outward to prevent them from becoming caught by and 
 folded interiorly over the tray margin. Then reverse the 
 position of the liands and carry out a similar procedure on 
 the opposite side, being careful not to disturb the relation 
 of the impression to the border during this step. Now return 
 to first, or pressure position, and apply sufficient force to 
 carry tlie impression firmly to place. 
 
 SECURING PERIPHERAL ADAPTATION 
 
 Eeturn to the second, or tray supporting position, and 
 with the free hand press against the lips and cheeks, 
 directing the pressure from low down near the floor of 
 the tray, inward and upward against the outer flange, so as to 
 carry the plaster that has been forced outside the flange, up- 
 ward against the labial and buccal surfaces of the border. 
 
 MUSCLE MARKING OF THE PERIPHERY 
 
 While still supporting the impression, instruct the pa- 
 tient to produce buccal and labial muscular tension on the 
 peripheral plaster margins, in order to indicate distinctly 
 the position and form of muscle tendons and labial frenum. 
 
 All of these steps should l)e carried out quickly, before 
 the plaster has set to any appreciable extent, for if allowed 
 to set too hard, the mu'scle markings will not show distinctly. 
 Usually all of tlie details as outlined can be carried out in from 
 thirty to forty seconds. 
 
 Steady, moderate and uniform pressure maintained on 
 the floor of the tray with the index and middle fingers of 
 both hands, until the plaster has become well hardened, is 
 
68 TECHNIC OF TAKING IMPRKSSIONS 
 
 essential. Tlie liavdness of the plaster is determiued by break- 
 ing some of that i-emaining in the bowl. When it breaks with 
 a clean fracture, and without crumbling, the impression is 
 ready for removal. 
 
 DISLODGING THE IMPRESSION 
 
 If the impression is correct and well adapted, it should 
 adhere to the tissues firmly, and require considerable effort 
 to effect its removal. An impression that requires but slight 
 effort to dislodge it can rarely be relied upon to serve as a 
 basis for an accurately fitting denture. 
 
 To break the adhesion, the index finger is passed back- 
 ward inside the cheek opposite the buccinator muscles, and 
 pressure made outward and upward on them. These regions on 
 either side are the natural air valves to the vault portion, and 
 with some slight traction on the handle, at the same time the 
 buccal muscles are lifted as described, the adhesion of the 
 impression will be broken without much difficulty. Should 
 this method fail, instruct the patient to cough, and at the 
 same time press upward on the tray handle. The sudden 
 muscular contraction occurring in the soft palate lifts these 
 muscles up from the distal margin of the impression, and at 
 the same time forces the air in between the tissues and the 
 plaster. 
 
 REMOVAL OF THE IMPRESSION 
 
 When loosened, the impression is dropped down, clear of 
 the border, and rotated out of the mouth in much the same 
 manner as it was introduced, but with reversal of movement, 
 and without the necessity for distending the oral angle with 
 the finger. 
 
 In edentulous cases where decided undercuts are present, 
 it is advisable to oil the tray before introducing the plaster, 
 and when the impression is ready for removal, dislodge and 
 remove the tray first. The impression can then be weakened 
 by cutting, so as to be removed in pieces, thus preventing 
 injuries to the tissues that, in some cases, would most certainly 
 follow its removal as a whole. 
 
 INSPECTION OF THE IMPRESSION 
 
 On removal, the impression should be carefully inspected 
 to see that all essential surfaces have been copied, and that 
 it is intact. If fractured at any point, the broken parts are 
 
TECHNIC OF TAKING IMPRESSIONS G'J 
 
 recovered, placed iu their respective positions, and held there 
 by melting a little wax along the external fracture line. 
 
 The treatment of the impression and the production of 
 the cast will be described in a subsequent chapter. 
 
 EDENTULOUS LOWER CASES IN PLASTER 
 SELECTING THE TRAY 
 
 The tray in these cases should be of such size that the 
 ci'est of the alveolar process will occu]3y a central position 
 between the outer and the inner flanges. The usual eighth of 
 an inch space allowance for impression material should be 
 present. The flanges should not impinge on the buccal, labial 
 or lingual muscles or franse. This requirement is essential 
 
 I.UUKR TRAY 
 
 in order that their subsequent movements may be unre- 
 stricted. 
 
 When considerable absorption of the border has occurred, 
 either uniform or unequal, a preliminary impression in wax 
 or modeling compound should be taken, the excessive surplus 
 trimmed away, and this modified impression used as a tray. 
 
 Frequently, by extending the lingual wings of lower den- 
 tures distally, when the shape of the mandible permits, and 
 muscular attachments do not interfere, much greater stability 
 of the substitute is assured. If such a plan is feasible, a tray 
 with deep lingual wings should be selected, or if the tray at 
 hand most suitable in other respects is deficient in this, addi- 
 tions of suitable length to carry the impression material 
 against the desired areas should be made with wax or com- 
 pound, and tested in the mouth before attempting to take an 
 im])ression. 
 
 The tendency in selecting trays for lower cases is to 
 choose one with too wide buccal and too narrow lingual flanges. 
 
70 TECIINK" OF TAKING iMPliKSSIONS 
 
 Tilt' ])lastc'r is mixed as dcscrilx'd lur upitcr cases. It should 
 he distributed in the tray in a uniform layer about one-fourth 
 of an ineli thick, confinins' it within the tray flanges. 
 
 POSITION OF PATIENT 
 
 'I'he position and elevation of the patient in the chair 
 slioidd Itc about tlic same as in taking imjiressicm of the upper 
 arch. 
 
 POSITION OF OPERATOR 
 
 The operator should stand on the rigiit side, somewhat 
 iu front of, and facing the patient. Some prefer to lower the 
 chair a trifle below the point designated, and stand back of 
 
 LOWER THAV UlTIl UKIOl' LINGUAL FLAN(iKS 
 
 the patient during the manipulative procedures. The first de- 
 scribed position is to be j^referred iu most cases, for, as before 
 stated, the line of vision is less obstructed and the hands have 
 more freedom of movement than when the operator stands 
 behind the patient. 
 
 INTRODUCING THE TRAY 
 
 The operator holds the inverted tray between the thumb 
 and index and middle fingers of the right liaud, the thumb 
 beneath and the index finger on the handle, the middle finger 
 resting on the right side, just back of the first finger. The 
 index finger of the left hand distends the right angle of the 
 patient's mouth. The left angle of the tray is inserted in 
 the left angle of the mouth, while with a deft rotary movement 
 the tray is brought into position over the border. 
 
TECHNIC OF TAKING IMPRESSIONS 71 
 
 When the operator assumes the position back of the 
 chair, the right angle of tlie tray is inserted in the right 
 angle of tlie month, while its left angle is rotated into position 
 throngh the left angle of the montli, which is being distended 
 with the ojierator's left index finger. 
 
 SEATING THE IMPRESSION 
 
 Tlie technic of carrying the impression to place is as 
 follows — the operator standing in front of the patient: The 
 tray being centralized, the index fingers are placed on either 
 side of the body, the thumbs under the mandible, and pressure 
 applied to carry it partiallj' to position. Now place the thumb 
 of one hand under the mandible, the index finger across the 
 tray body to steady it, and grasp the cheek well back with 
 the thumb and index finger of the other hand and pull out- 
 ward, to draw any folds of the cheek or buccal muscles out- 
 ward that may have been caught under the tray margins. 
 
 Eeverse the hands and carry out the same procedure on 
 the opposite side. Grasp the lip in a similar manner, draw- 
 ing it out from under tlie tray margin. Instruct the patient 
 to lift the tip of the tongue up and touch the high jjart of the 
 vault. These movements clear the tray margins of all ab- 
 normal muscle folds. With thumbs under the mandible and 
 index fingers on the sides of the tray, the latter is forced 
 down to place. Now steady the tray by placing the index and 
 middle fingers of one hand across it from side to side, thumb 
 under the mandible, and with the other apply pressure on the 
 outer side of the cheek and lip to force the surplus plaster 
 along the flange margins into close contact with the border. 
 
 Eeverse the hands and carry out similar steps on the op- 
 posite side. With each free hand, in turn, pass the index 
 finger around the periphery of the lingual flange margin to 
 adapt the plaster in this location also, particularly under the 
 tongue and along the disto-lingual surfaces. 
 
 "MUSCLE MARKING" THE IMPRESSION 
 
 Steady the tray with both hands and instruct the patient 
 to exert active muscular etTort with cheeks, lower lip anof 
 tongue, to indicate clearly in the ]ilaster the muscular attach- 
 ments. As before stated, the time required to carry out all 
 of these several steps ought not to exceed thirty or forty sec- 
 onds, for the final muscle viarkiiig must l)e accomplished while 
 
72 TECHNIC OF TAKING IMPRESSIONS 
 
 tlie plaster is still soft aud capable of yielding to moderate 
 pressure. 
 
 REMOVAL OF THE IMPRESSION 
 
 Lower impressions require a little longer time for hard- 
 ening than do uppers, because of the excess of moisture pres- 
 ent, the saliva usually accumulating in excessive quantity and 
 retarding the crystallization somewhat. 
 
 When well hardened, the impression is loosened by gently 
 l)ulling the lips and cheeks away from the outer flange. Trac- 
 tion up and down on the tray handle is made at the same time, 
 and the air finds its way readily between impression and 
 tissues. 
 
 Should the lingual wings extend downward and outward, 
 the anterior part of the impression should be raised above 
 the border and the tray carried back a short distance. As the 
 space between the lingual borders widens constantly from be- 
 fore backward, this brings the flanges into more open terri- 
 tory. By tipping or lifting one side of the tray higher than 
 the other and rotating the elevated side forward, the im- 
 pression can be disengaged and rotated out of the mouth, 
 usually without fracture. Inspect it carefully before allowing 
 the patient to rinse the mouth, and if fractured, recover the 
 broken pieces, place in position, and lute with wax. 
 
 PARTIAL IMPRESSIONS OF THE MOUTH IN PLASTER 
 
 Partial cases are those in which some but not all of the 
 natural teeth are missing. Substitutes designed for such 
 cases contain a less number of teeth than are usually placed 
 in full dentures. For obvious reasons, therefore, an im- 
 pression of such a case, although usually involving as much 
 area as an edentulous one, is termed a partial impression. 
 
 While partial impressions may be secured in plaster 
 alone, as a rule a preliminary imjiression in wax or modeling 
 compound, corrected before introducing the plaster by freely 
 enlarging the impressions made by the teeth, and cutting away 
 the excessive surplus, will yield more accurate results than 
 plaster alone. 
 
 In practically all cases of partial impression work where 
 plaster alone is used, the tray, having been previously oiled 
 on the inside, is removed as soon as the plaster has set. 
 
 The operator, being familiar with the undercuts present 
 and spaces between the teeth, cuts the impression in suitable 
 places to weaken it, so that with a little effort it may be frac- 
 
TECHNIC OF TAKING IMPRESSIONS Ti 
 
 tured and removed in pieces. Sometimes the breaking of one 
 or two pieces is sufficient to release the impression so that it 
 will come away in very nearly a whole condition. Again, when 
 teeth and spaces alternate, tlie teeth being long and having 
 constricted crevices, the impression must be broken in a num- 
 ber of pieces to effect its removal. In all cases an effort 
 should be made to break away all areas that, if not discon- 
 nected, would either injure the tissue or be marred or de- 
 stroyed in the removal of the impression. If the fractured 
 pieces are not too small, and are of reasonal)le thickness, pre- 
 senting clean-cut fractures, the impression may be practically 
 restored, even though broken in many i^ieces. The accuracy 
 of the impression depends on how perfectly the broken parts 
 are reassembled. 
 
 The wide flange trays designed by Dr. Angle are intended 
 for carrying the impression material, not only against the 
 labial, buccal and lingual surfaces of the teeth, but for holding 
 it in contact with these surfaces of the alveolar border as 
 well. When a tray with narrow flanges is used in partial 
 cases, the necessity for using wax or modeling compound as 
 a preliminary impression material for increasing the width 
 of the flange is apparent. 
 
 CLASSIFICATION OF COMMONLY OCCURRING PARTIAL CASES 
 
 Partial cases may be grouped into six general classes, 
 according to the teeth lost: 
 
 First — Posterior teeth on both sides missing; anterior 
 teeth in place. 
 
 Second — Posterior teeth on one side missing; opposite 
 and anterior teeth present. 
 
 Third — Anterior teeth missing; posterior teeth on both 
 sides in place. 
 
 Fourth — Anterior, and posterior teeth on one side miss- 
 ing; posterior teeth on opposite side in place. 
 
 Fifth — Teeth and spaces alternating with more or less 
 regularity. 
 
 Sixth — An occasional tooth missing. 
 
 IMPRESSIONS OF PARTIAL CASES 
 Combination Modeling Compound and Plaster — Class 1 
 
 SELECTING THE TRAY 
 A tray of the flat-bottom type, with flanges of moderate 
 width that will not impinge on the muscles, is best adapted to 
 this case. Place sufficient softened compound for a regular 
 
74 TKCHNIC OP TAKING IMPRESSIONS 
 
 impression in the tray, luiilding it up thicker wliere the teeth 
 are missing than anteriorly. The compound should be dis- 
 posed in the tray to conform as nearly as possible to the sur- 
 faces being copied, and be reasonably soft. 
 
 TAKING THE PRELIMINARY IMPRESSION 
 
 Introduce tilled tray in the mouth, centralize and press 
 up slightly. Steady with one hand and draw lip and cheek 
 muscles outward to prevent them from folding inwardly, 
 and press to place. 
 
 Steady the tray and apply linger along buccal and labial 
 surfaces, to secure sufficient height and peripheral adaptation. 
 
 TRAY FOR PjVRTIAL CASES. FLAT HOTTDM TYI'E 
 
 Instruct patient to exercise buccal and lip muscles freely 
 to indicate their position. Chill with cold water applied with 
 napkin, sponge or syringe, or with cold air, and remove. 
 
 PREPARING THE PRELIMINARY IMPRESSION FOR THE 
 PLASTER 
 
 Trim off excessive surj^lus buccaily, distally, and periph- 
 erally. Enlarge freely, both labially and lingually, the im- 
 pressions made by the teeth. Frequently the larger part of 
 the anterior portion of the impression is removed to give 
 greater bulk to the plaster which surrounds the teeth. 
 
 TAKING THE FINAL IMPRESSION 
 
 Mix the plaster to medium consistency, ]ilace in the tray 
 to the depth of an eighth of an inch or so, quickly introduce 
 
TECHNIC OF TAKING IMPRESSIONS 75 
 
 in file inoiitli, partially carry to place, centralize and ))ress 
 it lip against the teeth so they will occupy a1)out the same re- 
 lation to the tray flange as in the tirst impression. 
 
 Steady the tray firmly, draw the lip over the lahial flange, 
 and the buccal muscles away from the imjiression margin. 
 
 ritKI.IMINARY IMPBESSIOX IX MODELING 
 
 With slight vil)ratory movement and moderate i)ressure. carry 
 the tray to place. 
 
 With outside pressure against the lips and cheeks, adapt 
 the plaster which extends above the compound margin to the 
 boi'der, holding the tray firmly while doing so. Instruct the 
 patient to exercise the buccal and labial muscles freely and 
 vigorously. 
 
76 
 
 TECHNIC OF TAKING IMPRKSSIONS 
 
 REMOVING THE IMPRESSION 
 
 Wlit'ii set, traction on the tray handle will loosen tlie iiii- 
 pressiou, although if the teeth are long, considerahle force 
 may be required to dislodge it, since in most cases the plaster 
 impression must necessarily be fractured. On removal, place 
 the impression within convenient reach on the l)racket, and 
 recover the fractured pieces before permitting the patient to 
 rinse the mouth. As each piece is removed it is placed out- 
 
 side of the impression periphery, but as near to its proper 
 position as i^ossible, to simplify the adjustment of the several 
 parts later. 
 
 ASSEMBLING THE FRACTURED PIECES 
 
 The fractured surfaces of both the impression and the 
 pieces are cleared of small adhering particles with a mod- 
 erately stiff camel's hair brush. Care should be taken to 
 clear the general surfaces of the modeling compound matrix 
 of debris at the same time. The character of the fracture 
 determines the order of assembling, those pieces in the deep- 
 est ]iortion of the tray oi- comjiound matrix being usually 
 first placed in position. 
 
 The pieces are luted together by applying a little wax to 
 the fracture lines at various points, usually outside, in such 
 
TECHNIC OK TAKING IMPRESSIONS 77 
 
 mauuer as not to form an accretiou to tlie impression proper 
 and thus change its form. Wax does not adliere firmly to 
 damp plaster unless the latter is well heated. To effect a 
 good union of the pieces, a spatula is heated almost to redness 
 and applied to the small piece of wax already placed on the 
 fracture line. The spatula should be laid against the plaster 
 so as to heat it quite hot. The wax in the meantime is melted 
 and penetrates the substance, thus cementing the pieces to- 
 gether much more fimly than when the imion is superficial. 
 
 CLASS 2 
 BICUSPIDS AND MOLARS OF ONE SIDE MISSING 
 
 A flat-bottomed tray, similar to No. 16, is selected, and 
 wax or comiJound heated and adjiisted for a preliminary im- 
 
 hrSt 
 
 'r-^> 
 
 ^ 
 
 
 ^^ ^^^^.^K, 
 
 
 Wu ^ri ^^^^H 
 
 ^•^\ 
 
 l^^K hHB 
 
 
 JLS" 
 
 3 
 
 
 
 ANGLE TRAY ADAPTED TO BORDER AND XATIRAI. TEETH 
 
 pression, placing it thicker on the one side where the teeth 
 are missing than elsewhere, to make uji for loss of teeth and 
 tissues. 
 
 The general steps for securing the impression are similar 
 to those in Class 1. When removed, the impression material 
 is freely cut away around the impressions of the teeth, botli 
 labially and bucally, as well as lingually, to give ample space 
 for the ])laster which is to enclose them. 
 
 CLASS 3 
 
 ANTERIOR TEETH MISSING; BICUSPIDS AND MOLARS ON 
 BOTH SIDES PRESENT 
 
 The same general style of tray is selected as in the pre- 
 ceding case. Wax or compound for preliminary impression 
 
78 'nOCIINIC OK TAKINC! IM l'lil';SSK)NS 
 
 is introduced in llie form of ratlior a wide roll extending from 
 labial flange, over vault portion, to distal margin of tray. 
 
 The impression, when taken, will not extend out to the 
 buccal surfaces of the teeth, nor will it usually be necessary 
 to include them in the preliminary imjiression, since the tray 
 flange, is UKSually wide enough to support the plaster against 
 the buccal surfaces of the teeth and the adjacent gingival 
 margin of the border as well. However, if it is necessary to 
 secure an impression of the entire buccal surfaces of the 
 border, tlie tray flange can be increased in width by spread- 
 ing the preliminary impression material over the entire tray. 
 
 CLASS 4 
 
 ANTERIOR AND POSTERIOR TEETH ON ONE SIDE MISSING; 
 THE OPPOSITE POSTERIOR TEETH IN PLACE 
 
 The same general style of tray can be used as in the pre- 
 ceding class. The compound should be thicker on the side 
 where the teeth are missing. The preliminary impression is 
 obtained, trimmed and enlarged at the proper points, and 
 the final impression seciired in plaster. 
 
 CLASS 5 
 
 TEETH AND SPACES ALTERNATING WITH MORE OR LESS 
 REGULARITY 
 
 Teeth and spaces alternating, in impression work, usually 
 requires that the impression will be broken into several pieces 
 in order to effect its removal. Such a case always requires 
 special care to secure accurate results. 
 
 The usual routine described for the preceding cases is 
 applicable here, although with a deep-sided tray of the Angle 
 type, vase lined inside to prevent the plaster adhering, will 
 often times prove more satisfactory than the combined im- 
 pression. In fact, the Angle tray can be used for most any 
 of the partial cases described, either with plaster alone, or 
 combined with wax or modeling comiiound. The one serious 
 objection to its use is due to the very wide flange, preventing 
 ease of finger adaptation of the impression material. 
 
 CLASS 6 
 AN OCCASIONAL MISSING TOOTH 
 
 These cases are handled in a similar manner to the pre- 
 ceding class. A preliminary, ('om])ound or wax, impression is 
 taken, enlarged and used as a receptacle for the plaster. 
 
TECHNIC OF TAKING IMPRESSIONS 79 
 
 Frequently, however, wliere teeth and spaces alternate 
 throughout a considerable extent of the arch, a properly se- 
 lected Angle tray, oiled to more readily part from the im- 
 pression, and with plaster alone used as the impression mate- 
 rial, will iJrove as satisfactory as the combined use of com- 
 pound and plaster. The vault adai^tation can, in most in- 
 stances, be nuich improved with wax or compound additions. 
 On removal of the tray, the plaster which fills the spaces is 
 notched and pried apart, to release the impression. 
 
 TO BREAK AN IMPRESSION ALONG DEFINITE LINES 
 
 Strips of sheet wax are attached edgewise to the floor 
 of the tray, and so adjusted as to pass into the spaces where 
 the teeth are missing. These strips, if properly adjusted, will 
 serve to divide the plaster in a similar manner, Init more ef- 
 fectively than can usually be done by notching with a knife. 
 By inserting the knife blade into the wax and prying slightly, 
 the impression can easily be broken. 
 
 TAKING IMPRESSIONS OF ELONGATED AND LOOSE TEETH 
 
 It is frequently necessary to secure an impression of one 
 or more elongated or loose teeth, which if taken in the ordi- 
 nary manner would very likely result in injiary to the already 
 weakened peridental membrane of tlie tooth, or at least cause 
 the patient some discomfort. 
 
 The following method, if carried out as detailed, is con- 
 venient, accurate, and practically painless : 
 
 Mix a small amoimt of plaster of medium consistency, and 
 apply to the lingual surfaces of the loose teeth and as mxich 
 of the ]»rocess as the final imjjression should cover in this area. 
 
80 TECHNIC OP TAKING IMPRESSIONS 
 
 If other teeth are present, it may sometimes be best to extend 
 the impression so as to include them for subsequent support. 
 Now mix some plaster of medium consistency, and with the 
 point of a spatula apply to the lingual surfaces of the teeth, 
 making such additions as to give reasonable thickness to the 
 body of the impression. The plaster should be forced into 
 the embrasures and extend from where ]:)eripheral plate line 
 will rest to the incisal edge. Should the embrasures be open, 
 the plaster contained in them, which is forced labially to the 
 point of shortest diameter of the space, should be removed 
 with excavators, so that this half of the impression may be 
 removed lingually without difficulty. 
 
 When set, this portion is removed and trimmed smoothly, 
 so as to flare from gingival to incisal or occlusal surfaces. 
 It is then entirely coated with separating fluid and re- 
 turned to its former position in the mouth. Another mix of 
 plaster is applied to the labial or buccal surfaces, securing 
 good adaptation to those surfaces, and against the lingual 
 body of plaster presenting in the embrasures and at the in- 
 cisal or occlusal surfaces. When the plaster is hard, insert 
 the point of an instrument between the two halves, carefully 
 pry them apart, and remove. Trim them so that when again 
 returned to the teeth and set in position, they form a trun- 
 cated cone, the base of which rests against the alveolar pro- 
 cess, the smaller end coming evQn with or covering the incisal 
 or occlusal surfaces, as the case demands. Usually the two 
 pieces will be retained firmly in position without tying, but 
 they can be ligated together if necessary. In trimming, re- 
 duce the jjieces labio or bucco-lingually as much as possible, 
 yet without weakening them, so that there will be no excessive 
 bulk to interfere with the next step. 
 
 Now fit a tray over this matrix, or in reality, the core-to- 
 he, and see that it also conforms elsewhere to the tissue to be 
 included in the impression. Either plaster or modeling com- 
 pound can be used for the impression material, as the case 
 requires. The impression is obtained in the ordinary manner, 
 and removed. When the matrix or core has been properly 
 flared, the impression will part from it without difficulty. The 
 two halves of the matrix are now removed from the teeth 
 they enclose, placed in their respective positions in the im- 
 pression, and luted firmly with wax. 
 
 This method is especially valuable in taking impressions 
 
TECHNIC OF TAKING IMPRESSIONS 81 
 
 of teeth in pyorrhea cases. It is also capable of application 
 to a variety of difficult conditions that are frequently met with 
 in practice. 
 
 IMPRESSIONS IN MODELING COMPOUND 
 
 When manipulated properly, in well selected cases, mod- 
 eling compound is a most reliable impression material. By 
 reference to the "Indications for the Use of Plaster," it will 
 readily be seen when to avoid the use of modeling compound. 
 
 taIjAtim; \ii:\v of keiui thw uic.movakj.e handle 
 
 In probably 70 per cent of edentulous cases presenting, com- 
 pound can be used to better advantage than plaster. 
 
 FULL UPPER EDENTULOUS CASES IN MODELING COMPOUND 
 
 The fitting of the impression tray differs in no respect 
 from the fitting of a tray where plaster is used, except that 
 the distal extension of the vault portion, so commonly re- 
 quired for plaster, is unnecessary when compound is used. 
 Narrow flange, close-fitting trays of the Kerr-Greene type 
 are especially indicated, although other forms of trays can 
 often be used to advantage. The compoiuid selected should 
 become plastic "at a low temperature, and liarden quickly. 
 
 The Perfection C'Ompound made by the Kerrs of Detroit 
 fulfills the requirements better, perhaps, than any other mate- 
 rial on the market. It is furnished in the form of cakes for 
 impressions, and also of tracing sticks for making additions 
 
82 TECIINIC OF TAKING IMPRKSSIOXS 
 
 when necessary lo the iieripliery, or any ;irea nf the iiiiiires- 
 sion. 
 
 'I'lie aniouiit tif compouiHl i-e(|uire(l I'or an impression, 
 when tlie tray is chise tittiiiM', is very slii^'ht, nsually h'ss than 
 (irie hair a eak'e. 
 
 SOFTENING THE COMPOUND 
 
 The modeling compound is tlioronghly warmed, prefer 
 ably in hot water, removed, and the moisture taken up with 
 a towel or napkin. With the lingers it is formed into a ball, 
 working the wrinkles from above, underneatli. Tliis ball is then 
 
 I.INdlAL MEW OF 
 
 set in the center of the vault portion of the tray, and with 
 the fingers the compound is disposed against the fiange so as 
 to assume the general form of the impression. Or the com- 
 pound may be worked out in a sheet of more or less uniform 
 thickness, and disposed evenly in the interior of the tray. 
 The former method is to be preferred, as a perfectly smooth 
 imjiression surface is readily secured, while with the latter 
 method, creases are apt to form while adjusting the material. 
 The tray is heated around the flange and maxillary por- 
 tion, over a small frame, to cause the compound to adhere 
 to it slightly. The tray is inverted and the sus-face to be im- 
 in-essed is reheated over the flame, to render it soft and plas- 
 tic. It should then be quickly dii^ped in warm water to prevent 
 
TUCIINIC OF TAKING IMPRESSIONS SI! 
 
 the eouipoiniil stickiiiii' to the tissues while ])assiii,n' tiiruiii;li 
 the lips. 
 
 INTRODUCING THE FILLED TRAY 
 The tray is then introchiced in the montli hy the same 
 method of procedure as outlined under the head of "Full 
 Cases in Plaster." In fact, almost the same technie is fol 
 lowed with comjwund as with plaster, viz. : centering the tray ; 
 partial seating of the impression on the ridge; drawing out 
 the lip and cheeks from the flange margin; carrying the im- 
 pression to place under pressure; forcing the periyjheral sur- 
 plus in close adaptation to the tissues, particularly along 
 the distal vault portion. The index and middle fingers ot 
 both hands can be applied to the compound which extends 
 distally beyond the tray margin, to lift up and hold it in con- 
 tact with the palatine tissues. These fingers can alternately 
 support the tray, and develop adaptation of the compound to 
 the tissues from one tuberosity to the other. 
 
 When the adaptation is completed, moderate pressure is 
 maintained on the central portion of the tray, and the im- 
 pression chilled with cold water, applied with syringe or small 
 sponge or najikin. 
 
 On removal, the imi^ression is inspected closely to see 
 that all essential areas have been copied. The excessive 
 peripheral surplus is then trimmed away and the sharp 
 angles caused by the cutting smoothed off. Should there be 
 any slight deficiency at any point, a little heated compound 
 applied with the tracing stick and the impression returned 
 to place and firmly seated will correct the error. 
 
 PERIPHERAL READAPTATION 
 
 The impression, as it now stands, even if the steps have 
 been accurately carried out, is no better, and (juite likely not 
 as good, as an ordinary plaster impression. 
 
 The ef ficiency of modp ''"^; /.oi>^ppn.i.^ l ies in the fact th at 
 with proper technie the soft areas of the mouth mav be com - 
 l)resse(J, and a corresponding relief from ]>ressure on the 
 hard area be secured. As a result, the denture, when con- 
 structed, will. bear uniformly on the hard and soft areas alike, 
 and in those cases of prominent, hard raphae, practically en- 
 tire relief from pressure may be afforded. 
 
 To secure the compressive effect of the comjiound, the 
 impression, on removal, is thoroughly chilled, the surplus 
 trimmed away, and the entire impressed areas heated quite 
 
84 TKCHNIC OF TAKING IMl'KKSaiONS 
 
 hot over a small Buiiscn or alcoliol flame, to the depth of 
 about one-sixteenth of an inch. In this condition it is again 
 returned to the mouth, properly seated, the muscles drawn 
 outward, and steady pressure applied for two or three min- 
 utes. The amount of force necessary to apply varies from 
 three to ten, or even fifteen pounds, according to conditions. 
 Extremely soft, spongy, but not resilient, tissiies are copied 
 better with moderate, while harder areas require a greater 
 amount of pressure. 
 
 DISTRIBUTION OF THE PLASTIC COMPOUND UNDER 
 MAINTAINED PRESSURE 
 
 When the layer of softened compound is of uniform thick- 
 ness and is sufficiently plastic, under continued pressure the 
 material gradually flows from the hard to the soft areas, com- 
 pressing the latter and relieving the pressure on the former, 
 until a sort of equilibrium is established. If care is taken 
 in carrying out the technical details, the finished denture will 
 have a similarly uniform bearing on the tissues, which will 
 add greatly to its stability. 
 
 At the time of forcing the impression up against the tis- 
 sues, the excess compound is naturally moved from the in- 
 terior of the tray, externally and over the flange margin. The 
 tendency is for the compound to curl outward, away from the 
 process. It therefore becomes necessary to readapt the 
 periphery of the impression to the border, to seal against the 
 ingress of air. This step is accomplished as follows : 
 
 PERIPHERAL READAPTATION 
 
 On removal of the impression the second time, it is 
 chilled and the peripheral margins, buccally, labially, and 
 lingually, are reheated. It is again returned to the mouth and 
 seated. With the index finger the softened margins are firmly 
 pressed into close contact with the border, buccally and labiallj^ 
 first, correcting the vault portion last. Sometimes, however, 
 the adaptation of this margin is carried out as a separate, 
 final step. Only the periphery is softened in this rim adjust- 
 ment, since if the whole impression is reheated, the effect of 
 the previous compressive steps would be lost and adaptation 
 would be impaired. 
 
 The inqiression can be tested as to adaptation by having 
 the patient make muscular effort to displace it or by biting 
 on something to see if it can be tipped. The removable handle 
 
TECHNIC OP TAKING IMPRESSIONS 85 
 
 trays of the Greeue type are very conveuient for testing' 
 tlie stal)ility of the impression. They are also, on account of 
 their small size and g-enerally correct form, especially adapted 
 to work in edentulous mouths with compound, eitlier alone, 
 or eonibined witli phister. 
 
 AN T TI'EIl IMI-IIKSSIOX SIIOWIN'G ■■MrSCLE TRIMMEl 
 
 If the impression is readily displaced by the patient's 
 efforts — can be thrown down in laughing, speaking, biting, or 
 even coughing — the adaptation is not perfect, and an effort 
 should be made to determine the weak ]ioint and correct it. 
 
 A SUMMARY OF STEPS IN MODELING COMPOUND 
 IMPRESSION WORK 
 
 To summarize, the steps for compound impression work 
 are as follows : 
 
 Examination of the mouth. 
 
 Selection and adaptation of tray. 
 
 Heating and adapting modeling compound to tray. 
 
 Introduction into mouth, and centering tray. 
 
 Partial seating of the impression. 
 
 Steadying tray while lip and cheek muscles are pulled 
 outward from tray margin. 
 
 Carrying tray to place under medium pressure. 
 
 General adaptation of peripheral surplus. 
 
 Muscular exertion by patient to indicate location and 
 extent of muscular attachment. 
 
 All of these manipulative details should 1)e quickly cai'- 
 ried out, so that the last step mentioned may 1)e accomplished 
 while the compound, is still capable of yielding under the 
 stress of, and being indented by, the lip and cheek muscles. 
 
 On removal the impression is chilled, the surplus mois- 
 ture al)sorl)ed, the impressed areas heated to a depth of one 
 to one and one-half millimeters, and the tray returned to the 
 mouth. It is correctly seated, and steady pressure applied 
 for two or three minutes, or mitil fairly well hardened. 
 
S() TIOCIINIC OF TAKING IMPRESSIONS 
 
 Kl'Iuovc, chill, sol'tcii the iici'i|)lieral iiiai'giii lo (he dcplli 
 of ubout two millimeters, and return to the mouth. 
 
 Adapt labial and buccal periphery to the process, and the 
 distal margin of the vault portion to tissues, using finger 
 pressure, applied directly to the compound rim. 
 
 Test stability; if satisfactory, remove, heat the periphery 
 to a slight depth, and quickly return to the mouth for final 
 muscular adaptation by the patient. 
 
 Now remove the impression, again examine tlie vault por- 
 lion of the mouth to detei'mine the extent of the hard area, 
 and with a scraper relieve that portion impressed by tlie 
 r.-ililic to the depth of one-fourth to one millimeter, depending 
 OH the condition of soft tissues. 
 
 Return to tlie mouth for final trial. As before inti- 
 mated, the best way to test an impression is for the patient 
 to subject it to every muscular action the denture will be 
 subjected to, as well as its resistance to tipping stress. In no 
 case will the cast derived from an impression be more ac- 
 curate than the impression itself. It therefore follows that 
 if an impression is easily dislodged, the resultant denture 
 will be even more readily dislodged than the impression. 
 
 IMPRESSIONS OF LOWER EDENTULOUS CASES IN MODELING 
 COMPOUND 
 
 The general details of handling modeling compound, as 
 just described for upper, applies in man\' respects to the lower 
 cases as well. 
 
 The fitting of the tray; heating and placing the com- 
 pound; introduction into the mouth; centering; partial seat- 
 ing; drawing the tissue folds out from under the tray margin ; 
 forcing the impression to place ; steadying tray while gen- 
 eral adaptation to the border is secured liy pressure on lips 
 and cheeks, are similar in detail to upper cases. 
 
 The adaptation of the compound against the lingual sur- 
 faces should be carefully wrought out. When the steps have 
 been carried out as just mentioned, the tray should be held 
 firmly in ])lace and the compound adapted to the lingual border 
 with the fingers, l)eing especially careful to secure as perfect 
 ada])lation against the lower disto-lingual tissues as possible. 
 The final test for the depth of impression is obtained by 
 contraction of the mylo-hyrid muscles. 
 
 On first introducing the impression, the ]iaiient should 
 elevate the tongue while the operator directs the compound 
 into correct position with finger pressure. Wlien adapted, the 
 
TECHNIC OF TAKING IMPRESSIONS 87 
 
 compound is cliilled, tlie impression is removed, and the ex- 
 cessive surplus is trimmed awaj'. The impressed areas are 
 then reheated and the impression again returned to the 
 moutli. After drawing- the muscles from under the tray mar 
 gins, pressure is applied to force the compound from liard to 
 soft areas, as outlined ])reviously, peripheral adaptation with 
 linger pressure is secured, and the impression is chilled and 
 removed. 
 
 A method for securing close peripheral adaptation of 
 lower dentures to the process, with relief from pressure on 
 the crest of the border, is suggested by Dr. J. W. Greene. A 
 
 stream of hot water from a small-s})outed vessel is allowed 
 to run through the deepest part of the impression until the 
 compound in this location is thoroughly softened, care being- 
 taken not to heat the edges. The entire impression is then 
 quickly dipped in hot water so as to soften all of the im- 
 pressed areas to a slight extent. The impression is then 
 quickly returned to the mouth, and with a springy or "wave 
 like" motion, it is lightly pressed down upon the border, 
 chilled and removed. 
 
 PARTIAL IMPRESSIONS IN MODELING COMPOUND 
 
 There are few partial cases, indeed, where modeling com- 
 pound will meet the requirements as well as plaster. Almost 
 without exception in the class of cases under consideration. 
 
88 TECHNIC OF TAKING IMPRESSIONS 
 
 undercut surfaces are present, which cau only be copied by 
 an unyielding material that will break on removal, or by tak- 
 ing a sectional impression which can be separated along pre- 
 determined lines. 
 
 Modeling compound can l)e used to advantage in sec- 
 tional work, the character and extent of the undercut 
 surfaces determining the form and number of the sections. 
 The manner of procedure is as follows : 
 
 The form of the first section is decided upon. Compound 
 is applied slightly in excess of what is needed to form this 
 part. When cool, it is properly shaped and those surfaces of 
 the first section which form contact areas with the second 
 section, are varnished with sliellac, and before it has become 
 dry thin tin-foil is spread evenly over them and laid down 
 smoothly. When this first section is chilled and the tin-foil 
 slightly oiled, the next section can be adapted to it, and by 
 quickly chilling the latter no change of form will occur in the 
 first section. 
 
TECHNIC OF TAKING IMPRESSIONS 89 
 
 The two or more sections necessary to inclose teeth with 
 constricted necks, fill nndercnt spaces, or open embrasures, 
 should be so trimmed as to permit the impression proper, in 
 which they are finally inclosed, to separate from them witli- 
 out distortion. On removal of the im^jression, the sections are 
 separated and placed in their respective locations in the ma- 
 trix formed by them in the impression. They may be held 
 firmly in position by Inting a little wax along the joints. 
 Either compound or plaster may be used for the general 
 impression material in these cases of "coring." If the for- 
 mer is used, the entire core should be covered with foil and 
 ■oiled, and the manipulative procedures carried out rapidly, so 
 that the inherent heat in the sectional material may not 
 isoften, and the pressure in placing it distort the impression. 
 With plaster, as an impression material, the oiling of the 
 cores is sufficient. 
 
(MI AFTER VTTI 
 TREATMENT AND FILLING OF IMPRESSIONS 
 
 PRODUCTION OF CASTS 
 
 As previously stated, tlie degree of success attained in 
 denture construction depends on the development of three 
 essential requisites, viz: xtse.fulness, good looks and comfort. 
 
 The realization of two of these, usefulness and comfort; 
 dejieuds primarily upon the impression and the cast derived 
 therefrom, since the latter gives the reverse form to the 
 denture. The necessity, therefore, for accuracy in impression 
 taking and cast construction is imperative, for, if the founda- 
 tion is faulty, the superstimcture will fail. A defective im- 
 pression invariahly yields an imperfect cast. It does not 
 follow, however, that a satisfactory impression will always 
 yield a perfect cast. The accuracy of the cast depends upon 
 the care and precision exercised in its production. 
 
 The technique of cast construction is similar, whether 
 the impression is of plaster or of modeling compound. The 
 details differ slightly. Each class will be taken up separately, 
 and the important details noted. 
 
 TREATMENT OF PLASTER IMPRESSIONS IN EDENTULOUS 
 CASES 
 
 Certain preparatory steps must be carefully carried out 
 in the impression before the cast is produced : 
 
 First — The impression should be examined closely to see 
 that it is intact. If broken, the pieces should be placed in 
 correct position, firmly luted with wax, and the impression 
 itself secured in the tray. 
 
 Second — The scraping of those parts impressed by the 
 hard areas of the mouth, as detailed in a previous chapter, 
 should be carefully execvited, and the impression freed from 
 debris with a clean sable brush. 
 
 Third — A staining medium which will ])euetrate to the 
 depth of 1 to 2 mm should be applied to the exposed surfaces, 
 so that in cutting the impression to weaken it, in removal from 
 the cast, the stained portion will indicate the near approach 
 to the line of demarkation between the two, and thus prevent 
 injury from the knife. 
 
 Fourth — A separating medium must be applied to the 
 
 9Q 
 
TREATMENT AND FILLINC OF IMPKESSIOXS 91 
 
 iini)r('ssi()ii to i)rev('iit the plaster coiistitntiiii;' I lie cast from 
 heeomiiig so firmly adherent to it that the two cannot be 
 separated without defacing the cast. 
 
 The reason wliy a second addition of plaster adheres to 
 one previously hardened, unless steps are taken to prevent, 
 is due to the fact that plaster crystallizes in setting and the 
 crystals are grouped so as to leave many spaces between, 
 as has been i^reviously shown. The face of an impression 
 presents just such a formation. It has also been shown that 
 in a fresh mix of plaster, the granules of the half hydrate 
 are actually dissolved in the water, and that in and from this 
 solution the crystals of di-hydrate form. 
 
 Where such a mixture is applied to a surface of plaster 
 previously set, the solution, to a certain, extent, is taken up 
 by, and tills some of the interspaces in the hardened plaster, 
 and there crystallizes. These crystals are in reality so many 
 irregular points projecting from the freshly set plaster, ex- 
 tending in various directions into the face of the previously 
 set mass, thus anchoring the two bodies of plaster together. 
 
 In separating the two, many of these projecting crystals 
 are necessarily broken, and in breaking, the faces of both 
 masses are more or less injured. Sometimes the two masses 
 adhere so closely as to render separation impossible with- 
 out destroying the cast and impression as well. The remedy 
 lies in literally waterproofing the surface of plaster against 
 which the fresh mix is to be cast, which prevents the plaster 
 in solution from entering the spaces referred to. 
 
 The selection and proper application of suitable staining 
 and separating mediums is therefore of the greatest impor- 
 tance where the production of accurate casts is desired. 
 
 STAINING FLUIDS 
 
 A staining fluid should be capable of penetrating either 
 moist or dry plaster to a depth of 1 or 2 mm for reasons 
 before stated. Since its purpose is to stain only, it should 
 l)e absorbed by the plaster to which applied, without form- 
 ing a film on the surface. 
 
 A thin alcoholic solution of orange shellac is a most ex- 
 cellent medium for staining. If used thin, quite a dark tinge 
 may be imparted to the impression by applying two or three 
 coats without glazing the applied surfaces. Each application 
 should be allowed to dry before the next is laid on. 
 
 An aqueous solution of some of the analine colors is 
 frequently used, hut, unless carefully handled, will stain the 
 
92 TKKATMKNT AM) I'lhlJNC OK IMPKKSSJOiNS 
 
 fingers, and is difficult to roniove. Coloring matter is some- 
 times added to the separating medium, the idea heing to con- 
 vert it into a staining medium as weU. 
 
 Most separating mediums, however, do not penetrate tlie 
 plaster to any appreciable dei)th, and therefore tlie stain is 
 (!onfined very closely to the line of demarkation between the 
 impression and the cast. The stain applied to an impression 
 in this manner will not give sufficient warning when cutting 
 the impression away, and in partial cases especially, the cast 
 is very liable to be injured. The aqueous solutions to be 
 described later may, by adding a suitable pigment, be ef- 
 fective both as a separating and staining medium. 
 
 SEPARATING MEDIUMS 
 
 The preparations used for separating purposes are known 
 under various names, as separating or parting mediums, 
 fluids, varnishes, etc. They may be procured of the supply 
 houses, or compounded in the laboratory with very little 
 effort. 
 
 REQUIREMENTS 
 
 To accomplish the desired result, a separating medium 
 to be used in cast production particuarly, should possess cer- 
 tain requisite qualities : 
 
 First — It should be impervious to moisture, after being 
 applied to j^laster and allowed to dry. 
 
 Second — It should not modify the areas covered to any 
 aj^preciable extent, and hence, should be effective when ap- 
 plied in an extremely thin film. 
 
 Third — It should present a smooth, glazed surface when 
 dry, so as to produce a correspondingly smooth surface to 
 the cast. 
 
 Fourth — It should have sufficient cohesiveness to stick 
 to the applied surface, and not become adherent to the cast. 
 
 Fifth — It should dry or harden quickly, and not combine 
 chemically with the plaster, or be subject to deleterious change 
 itself. 
 
 CLASSIFICATION OF SEPARATING MEDIUMS 
 
 A simple classification of the separating mediums in com 
 mon use are here presented : 
 
 Alcoholic solutions 
 Ethereal solutions 
 Aqueous solutions 
 Oils 
 
TREATMENT AND KILLING OF LMPKESSIONS 93 
 
 ALCOHOLIC SOLUTIONS 
 SANDARAC VARNISH 
 
 Sandarac is a resinous exudate from the Thyia Articulata 
 of the pine family, wliich grows in northern Africa. The 
 gum exudes from the tree in the form of small globules, 
 called tears, ranging in color from pale yellow to brown. The 
 light variety is considered the best, and selected tears of this 
 color should be used in making the varnish for separating 
 purposes. It comliines in various proportions with alcohol, 
 but if too small a percentage of the latter is used in its com- 
 position, or if the alcohol is allowed to evaporate, the varnish 
 becomes too thick for use in accurate cast production. If 
 from any cause it is too thick, the addition of a little alcohol 
 will, after standing a time, reduce it to proper consistency. 
 
 Sandarac and alcohol in the following proportions make 
 a satisfactory varnish for separating purposes : 
 
 Selected light sandarac 6 oz. 
 
 Grain alcohol 24 oz. 
 
 Digesting in a water bath of moderate temperature will 
 aid in dissolving the gum. 
 
 It is not advisable to add a pigment to this varnish in 
 order that it may serve as a staining medium also. Sandarac 
 varnish does not penetrate the surface of plaster to any ap- 
 preciable depth, and the stain will not extend beyond the 
 depth penetrated. 
 
 The best plan is to stain the impression, as before sug- 
 gested, with thin shellac, which readily i^enetrates, and after 
 it is dry, apply the sandarac. If of proper fluid consistency, 
 one coat of sandarac is sufficient. If rather thin, two coats 
 should be applied, allowing the first to dry before making 
 the second application, and the second should be dry before 
 making the cast. 
 
 ETHEREAL SOLUTIONS 
 
 Under this division two substances will be described 
 which are dissolved in ether, viz: collodion and soap. 
 
 COLLODION 
 
 Collodion may be procured at any drug store, or it can 
 be compounded in the dental laboratory. It is made by dis- 
 solving gun cotton in ether, using enough of the latter to ' 
 make a thin, syrupy liquid. Since gun cotton is highly in- 
 
(»4 TREATMKNT AND FII.UNG OF IMPHKSSIONS 
 
 ll;niiiii;ilil(' and ctlicT also, to a lesser extent, care must be 
 exercised in making the solution to keep it away from a 
 tlamc. The impression should be stained, as previously 
 described, before using collodion as a seijaraling medium. 
 
 ETHEREAL SOAP 
 
 I'Jthereal soap is frequently used in tlie class of work 
 under consideration. A fine quality can be procured from 
 drug houses, and if used properly on a previously stained 
 impression, will serve as a good separating material. 
 
 AQUEOUS SOLUTIONS 
 BORAX AND SHELLAC 
 
 A saturated solution of borax in water will dissolve 
 shellac, producing a fluid capaljle of staining the impression. 
 This is really the only separating medium that combines both 
 staining and separating qualities so as to get the desired re- 
 sults. It can be compounded in the dental lalioratory as 
 follows : 
 
 Water in large-mouth bottle 1 gal. 
 
 Borax lA lb. 
 
 By applying heat (water bath) and stirring occasionally, 
 the water becomes saturated. A little excess of borax re- 
 maining in the bottom of the vessel will do no harm, and in- 
 sures full saturation of the water. 
 
 To this solution add X^ lb. of ordinary brown shellac 
 in flakes, and let stand a few days. It will be gradually dis- 
 solved, and the liquid will assume a purplish tinge, due to 
 the action of the borax on the shellac. The solution of the 
 shellac may be hastened by the application of moderate heat, 
 and also by stirring occasionally. A white scimi arises to 
 the surface of the fluid, which should be removed before 
 bottling. By siphoning the liquid out of the bottle, neither 
 the scum on top nor the excess of borax and shellac in the 
 bottom will be disturbed. The best quality of medium is 
 produced by allowing the solution to stand a week or more, 
 stirring occasionally, before siphoning into bottles. It should 
 be kept tightly corked when not in use, to prevent evaporation 
 of the water. 
 
 In using this as a separating medium, it should be ap- 
 plied freely and quickly with a fair-sized brush, bathing the 
 entire impression surfaces with the liquid. The brush should 
 be used to distribute it evenly at first, and before it begins 
 
TREATMENT AND FILUNG OF IMPRESSIONS 95 
 
 to thiokeu, to take up the suri^his. Tlie tirst application is 
 absorbed by the plaster without leaving a decided tilni, and 
 in this manner the impression is stained. When dry, a second 
 coat is a])plied and also allowed to dry before producing a 
 cast. The tinal coat should, and if properly applied will, pre- 
 sent a smooth, glazed, thin, uniform layer on all surfaces cov- 
 ered, and enable the impression to be readily removed from 
 the cast. The tirst mention of this solution that the writer 
 is aware of appeared in Gorgas, Ed. 1895. 
 
 SOAP SOLUTION— AQUEOUS 
 
 Soap lather serves as a good separating medium when 
 applied to a shellac stained impression. The soap should be 
 worked well into the surfaces so as to till the interspaces be- 
 tween the crystals, after which practically all excess should 
 be removed with clear water and a clean brush. In partial 
 cases, special care must be taken to free the impressions of 
 the teeth from the lather, or the air contained therein will 
 prevent the settling of the cast plaster into the matrices, or 
 impressions of the teeth. 
 
 WATER AS A SEPARATING MEDIUM 
 
 By thoroughly saturating a plaster impression with 
 water, no other separating medium need be applied. The 
 impression must be filled while saturated, and separated from 
 the cast as soon as the latter has set. Very good results can 
 be secured in this manner, if the precautions mentioned are 
 observed. If, however, the impression and cast are not sep- 
 arated very soon after the latter has set, a union of the two 
 occui's which will inhibit separation without injuring one or 
 both. 
 
 OILS 
 
 Oils are not good separating mediums luider any circum- 
 stances, although commonly used for flask sei)aration, and 
 sometimes in impression work. The surface of the cast 
 plaster contains many minute air bubbles not present when 
 some of the other mediums mentioned are used. Lard, sperm 
 and the paraffin oils are usually used for this purpose. When 
 employed as f. separating medium, the impression should be 
 previously stained with shellac. 
 
 GENERAL REMARKS 
 
 A thorough understanding of the ])hysical nature of 
 ]ilaster and of the separating mediums in use is essential 
 
96 TREATMENT AND PILIjING OP IMPRESSIONS 
 
 in securing accurate results. Carelessness in applying a mo 
 dium to an impression usually results in an imperfect cast. 
 
 Care and attention to details is just as necessary in th;; 
 class of work being considered, as in any of the other essential 
 details of denture construction. 
 
 A chain is only as strong as its weakest link, and therefore 
 an imi3erfect cast, regardless of how accurately all other de- 
 tails are carried out, will result in the finished denture prov- 
 ing more or less disappointing to both patient and pros- 
 thetist. 
 
 FORMS FOR CASTS AND MODELS 
 
 All casts, whether full or partial, u]iper or lower, should 
 have flat bases with sides either i)arallel or slightly converging 
 from the base to the peripheral face outline. The flaring 
 form is essential when the cast is to be used as a model. 
 
 The central palatine portion of upper and floor of lower 
 casts should be about one-half an inch thick to give stability 
 throughout the various steps to which they are subjected in 
 denture and die construction. In general the peripheral out- 
 line of casts should conform to those of the alveolar arches. 
 In trimming, the peripheral surplus of plaster should be re- 
 duced, so as to bring the sides close to the reflection of the 
 labial and buccal tissues, so that later on, in waxing and 
 flasking, there will be no excessive surplus to interfere with 
 these steps. The crescent shape so frequently given lower 
 cases is not recommended because of the liability of the cast 
 to break in removal of the impression, and later on, when 
 detaching the cast from the occluding frame. This form may 
 l)e adopted when the Kerr metal forms are used in conjunc- 
 tion with plaster. 
 
TREATMENT AND PILLING OF IMPRESSIONS 97 
 
 CASTS FOR CELLULOID CASES 
 
 In constructing casts for celluloid cases, they should be 
 made sufficiently thick and of a coarse variety of plaster, or 
 of Spence's Compound, so as to withstand heavy stress. 
 Spence's Plaster Compound makes a very resistant and satis- 
 factory cast for celluloid cases much better than any grade 
 of plaster procurable. Casts for this class of work are made 
 of the same general form as previously described. 
 
 Magnesium oxy-chloride is also an excellent material for 
 casts for celluloid work, but is extremely difficult to remove 
 from the dentiire. 
 
 CASTS FOR PLASTIC METAL BASES 
 
 Cast metal base plates are formed by casting aluminum, 
 tin, tin alloys, or gold into matrices composed of some re- 
 fractory investment compound. The usual materials used 
 are finely ground silex, asbestos, pumice stone, marble dust, 
 soapstone. etc., combined in varying proportions with suffi- 
 cient plaster to till the voids between the granules, and thus 
 act as a cementing medium. The refractory material is in- 
 corporated to prevent cracking of the investment when heated, 
 and because less change in form will occur when and while 
 heated, than with plaster alone. Casts for this class of work 
 are of the same general form as those pre\'iously described. 
 
 CASTS DESIGNED FOR MODELS IN THE PRODUCTION OF 
 METAL DIES 
 
 In shajting a cast for a model it should possess certain 
 characteristics: 
 
 First — Its sides should flare outward from face to base. 
 at an angle ranging from 75 to 80 degrees from the hori- 
 zontal, to facilitate its easy removal from the sand matrix. 
 
 Second — It should be as thin as ]iossible to be consistent 
 with strength, since, according to brass and iron molders. 
 thin patterns or models are less apt to distort the matrix in 
 removal than when thick and bulky ones are employed. 
 
 Third — The base should be flat, to accord a firm founda- 
 tion for the model in packing the sand matrix. 
 
 Foiirtli — Tha base should bear such relation to the vault 
 portion that the inclination of the latter upward from the 
 deeper or alveolar iiortions of the matrix shall be uniform 
 and highest at the distal margin. If the central vault portion 
 is higher than the distal margin of the matrix, a dome-shaped 
 space in the die results, in which gases accumulate and find 
 
98 
 
 TREATMBNT AMI FILIJNC Op" IMPIt?:SS10NS 
 
 vent tlirons'li the partially solidiiicd metal. This fretiuently 
 causes so serious a defect as to render the die worthless. This 
 danger is obviated by so forming the base of the model as to 
 raise the anterior higher than the posterior portion. It may 
 also be obviated by packing sand mider the anterior portion of 
 
 PLASTER MODEL SHOWING PKOJECTIONS OF TBIilllED TEETH 
 
 tlie model and elevating it in this manner, before placing the 
 molding ring. The better plan is to develop the correct form 
 of the model in plaster. 
 
 CASTS DESIGNED FOR MODELS FOR PARTIAL DENTURES 
 
 Models for partial cases are given the same general 
 flaring form as those for full cases. In addition, the teeth 
 must be cut off squarely about one-sixteenth of an incli from 
 
 DIAGRAMSLVTIC VIEW OF TIllMilED MODEL 
 
 the gingival line. This is necessary, first, because the gen- 
 eral contour of the teeth will not permit of their withdrawal 
 from the sand matrix without distorting the latter. Second, 
 it permits the plate to be reflected against their surface, there- 
 by strengthening it. If reduced to the length suggested, the 
 
TREATMENT AXD FILLING OP IMPRESSIONS 99 
 
 removal of the model from the sand can in most oases be 
 accomplished readily. 
 
 In lower partial cases when the anterior teeth are pres- 
 ent, these teeth on the model should have only their incisal 
 thirds removed. When the die is secured and the base is 
 swaged, the latter should be allowed to extend up over the 
 cingulaj, to afford stability to the denture and protect the 
 gums from stress, as well as to guard against the ingress of 
 food between the teeth and substitute in this location. 
 
 UNDERCUTS AREAS 
 
 Any depressions or decided undercuts on the laliial or 
 buccal surfaces of the model, not involving areas covered by 
 the denture, can be eliminated by filling in with plaster or 
 hard wax and giving such surfaces the proper flare for with- 
 drawal from the matrix. 
 
 The outer surfaces, as well as the bases of models, should 
 be finished with fine sandpaper to render them smooth, and 
 the entire model varnished with two or three coats of shellac 
 evenly applied. 
 
 CORES 
 
 A core is an addition of investment compound, or some 
 refractory material, which, when built against an undercut 
 surface on a model and properly trimmed, is used for develop- 
 
 ing the negative of that surface in the sand matrix, and fur- 
 nishing a form against which the die may be cast. The con- 
 structive steps are as- follows : 
 
 The varnished model is oiled over the area to be covered 
 by the core. The investment compound is mixed to a thick 
 consistency and applied to the undercut surface of the model, 
 extending it from the base to near the crest of the l)order, and 
 slightly beyond the undercut area at either end. It should be 
 from 6 to 8 mm thick. If too tiiin, it is lialile to warp in dry- 
 
mo TREATMENT AND KILLING OP LMPRESSlOXS 
 
 iug, or break wlieu iu use. If too thick, it will interfere with 
 the centering of the model in the molding ring. When set, it 
 is trimmed so that its outer surface is parallel with the side 
 of the model it covers. The ends, as well as the sides, should 
 converge slightly, from base to crest. The upper portion of 
 the core, where it finishes against the border, should present 
 a right angle to this surface, and tlius give the core a flat 
 
 MODEL WITH CORE IN POSITION 
 
 seat in the sand matrix. When trimmed and sandpapered it 
 is removed from the model and the moisture driven off at 
 moderate temperature to prevent warping. The surface is 
 rendered smooth by rubbing soapstone into it. When fin- 
 ished as described, it is returned to the model and is ready 
 for use. 
 
 CONSTRUCTION OF CASTS— GENERAL REMARKS 
 
 The construction of the cast is ordinarily spoken of as 
 "pouring the impression." The term is incorrect and mis- 
 leading as well, for the reason that plaster intended for 
 casts and in the fiasking of cases should never be so thin 
 as to be readily "i>oured" from the bowl. 
 
 Plaster of such consistency, when set, is inherently weak, 
 low in density, and less resistant to stress than is the case 
 when the mix is thicker. This is due to the fact that when 
 thin, an excess of water is present and occupying space that 
 should contain calcium half hydrate. When crystallization 
 sets in, the plaster in solution in the water is gradually taken 
 up to complete the crystals partly formed, and to form the 
 nuclei for other crystals. 
 
 The half hydrate solution is thus constantly being de- 
 pleted of its calcium sulphate in the building up of new 
 crystals, with no corresponding diminution in the bulk of 
 water. In other words, when set and the excess water has 
 evaporated, the mass will contain fewer crystals and more 
 
TREATMENT AND FILLlNfJ OP IMPRESSIONS 101 
 
 spaces thau will a mass of similar hulk mixed to proper 
 consistency. 
 
 A cast produced from a thin mix of plaster, as before 
 stated, will be less resistant to stress thau a denser one, and 
 when subjected to heavy pressure, as in the closure of an over- 
 packed flask, will yield, the crystals l)reaking under the load. 
 
 DELETERIOUS PROPERTIES OF PLASTER 
 
 Special care should be exercised in the mixing of plaster 
 for any purpose to have it of proper consistency ; also in 
 avoiding excessive stirring, which induces needless expansion. 
 It should be sufficiently plastic to conform to all irregular sur- 
 faces by slight jarring, but not so thin as to pour readily. 
 Disregard of the peculiar properties of this most sensitive 
 material, viz : its tendency to expand, its susceptibility to 
 compression imder load, and the deleterious action of heat 
 and moisture upon it, results in manifold errors and mishaps 
 that lead to impaired adaptation and frequent failures in 
 denture construction. 
 
 The recognition of these deleterious properties has re- 
 sulted in greater care being exercised by many in manipulative 
 procedures with plaster than was formerlj' displayed, as well 
 as in the introduction of more stable and resistant materials 
 for casts. Among these may be mentioned Spence's Plaster 
 Compound — a mixture of plaster, Portland cement, and other 
 substances for controlling expansion. This compound is much 
 less compressible, while its expansive index is lower, than the 
 best grades of plaster. 
 
 MATERIALS USED FOR CASTS 
 
 The materials commonly used for casts for both vul- 
 canite and other cases are here presented in order, ranging 
 from those having the greatest to those showing the least 
 resistance to stress: 
 
 a. Magnesiiim Oxy-chloride. 
 
 1. Spence's Plaster Compound. " 
 
 2. Coarse Building Plaster, 
 o. French's Regular Plaster. 
 
 4. French'*; Impression Plaster. 
 
 5. Ordinary Commercial Plaster. 
 
 DELETERIOUS EFFECT OF ACCELERATORS ON CASTS 
 
 Plaster easts containing accelerators such as common 
 salt or potassium sulphate have a greater affinity for mois- 
 
102 TREATMENT AND FILLING OF IMPRESSIONS 
 
 ture and soften nioro quickly in the vulcanizer in tlie presence 
 of heat and steam, than do those from wliich these substances 
 have been omitted. Therefore, to avoid danger of distortion 
 of easts in vulcanizing, Impression Plasters should not be 
 used for casts, as they contain accelerators — usually potas- 
 sium sulphate. The fourth class, therefore, for causes de- 
 tailed, is unsuited for cast production. 
 
 The fifth class mentioned is usually a plaster of uncer- 
 tain quality, sometimes over or imder burned, containing im- 
 l)urities which render it more or less granular, and of uncer- 
 tain density when set. 
 
 FINAL TREATMENT OF THE IMPRESSION 
 
 The impression having l)een ])roperly prepared by reliev- 
 ing, staining and varnishing, as jireviously described, should 
 be immersed and allowed to remain in water for a minute 
 or two, while a camel's hair brush is passed over its surface 
 to dislodge the air bubbles present. It is then removed and 
 freed from the excess water by throwing it out or passing 
 a good sized pellet of absorbent cotton lightly over the sur- 
 faces. The idea is to moisten the surfaces of the impression 
 immediately before filling, so that the cast material will 
 flow freely over all areas, and that the face of tlie cast, when 
 set, will be smooth and free from air spaces. 
 
 MANIPULATION OF SPENCE'S PLASTER COMPOUND 
 
 Tliis material is slow setting and therefore can be mixed 
 very thick. The instructions are to use four oimces of tlie 
 compound to one of water. The first step is to place three 
 ounces of the compound in the bowl and add the full amount 
 of water (one ounce) to it. Thoroughly mix until it be- 
 comes soft and uniformly plastic throughout, then add the 
 other ounce, a little at a time, working each portion in well 
 before making the next addition. The essential point in 
 mixing this material, as in plaster, is to distribute the water 
 evenly through the mass, so that each particle and granule 
 may have an equal proportion to any other. 
 
 FILLING THE IMPRESSION 
 
 Since the mass is thick and plastic — much like putty — 
 only a small quantity should be placed in the impression at 
 a time, and by jarring and finger pressure, forced to place. 
 The entire impression is filled in this manner,, a little at a 
 
TREATMENT AND FILLING OF IMPRESSIONS UK! 
 
 time, and tlie form of the cast developed with the spatula, 
 squaring u\) the sides and making the base flat. The cast 
 should be about one-half inch thick in the central portion 
 for necessary strength. 
 
 In lower cases the space between the lingual portions of 
 the impression should be bridged across with the compound. 
 ■This may be accomplished with the spatula, or ])y placing the 
 impression on the bench after the deeper portions have been 
 filled, and packing the lingual space with a compact mass of 
 moist paper; a temporary support will thus be afforded the 
 material while being bridged over and in setting. 
 
 Another method often resorted to is to bridge over the 
 lingual space with a sheet of wax before filling the impression. 
 This should be fitted neatly and luted firmly to the lingual 
 margins of the impression, so as not to interfere with the 
 develoiunent of the areas on which tlie denture is to rest. 
 
 MANIPULATION OF PLASTER IN CAST CONSTRUCTION 
 
 Fill the bowl about one-third full of water, and into this 
 sift French's regular dental jilaster until the free water is 
 all taken up. By adding the plaster slowly, as it settles into 
 the water, solution takes place quickly, and but little stirring 
 will be required to render the mix homogeneous. It should 
 be stirred slightly, but not to excess. The plastic mass should 
 be stiff enough to require jarring to settle it to place. 
 
 FILLING THE IMPRESSION WITH PLASTER 
 
 A portion is placed near the central part of the im- 
 pression and the tray grasped in the fingers and tapped on 
 the edge of the bench to settle the plaster in the deepest por- 
 tions. If the impression has been broken in a number of 
 pieces and luted, it is sometimes best to use the fingers which 
 grasp the tray as a cushion in jarring the plaster to place, 
 to prevent the impression or the pieces from becoming de- 
 tached — a mishap which sometimes occurs if the vibration is 
 sharp and rapid. Additions of plaster are made and the 
 \ibration continued until the entire impression is filled and 
 the cast given its' proper outline with the spatula. Care 
 should be taken in forming the cast to avoid excessive bulk, 
 either in thickness or peripheral outline, as the surplus periph 
 erally inqtedes the removal of the inqiression and must even- 
 tually lie cut away, while a thick base interferes with proper 
 mounting of the cast on the frame, and later on in flasking, it 
 
104 TREATMENT AND FILLING OF IMPRESSIONS 
 
 must be reduced to centralize the case in tlie flask. Lower 
 casts are produced in the same manner described in tlie use of 
 the Spence compound. 
 
 CASTS OF PARTIAL CASES— SPENCE'S COMPOUND 
 
 In filling partial impressions with Speuce's compound, 
 the material should be forced into each tooth matrix with a 
 suitable square end instrument, but care must be taken to 
 avoid marring the impression in doing so. Each matrix is 
 filled, and the compound as it is placed in the impression is 
 jarred and pressed to place, to make a compact union with 
 that already packed. The general form of the cast should be 
 the same as for full cases. 
 
 CASTS OF PARTIAL CASES— PLASTER 
 
 The plaster mix for partial should be of al)out the same 
 consistency as for full impressions. If too thick, it will be 
 
 difficult, if not impossible, to fill the matrices of the teeth, 
 while if too thin, the teeth on the cast will be frail and easily 
 broken, because of the imperfect density of the plaster. 
 
 In introducing the plaster into the impression, the first 
 portion should be placed near, but not over, one of the tootli 
 matrices, and liy inclining the impression somewhat and jar- 
 ring, the plaster will flow down one side of the matrix, spread 
 out and settle over the bottom, and then rise up the opposite 
 side until the opening is filled. Each matrix should receive 
 individual attention in order that a perfect cast of each tooth 
 may be obtained. If an attempt is made to fill several mat- 
 rices at once, the plaster is liable to flow too freely into some 
 of the openings, confining the air in the deeper portions, and 
 thus result in an imperfectly filled impression. 
 
TREATMENT AND FILLING OF IMPRESSIONS 105 
 
 STRENGTHENING ISOLATED PLASTER TEETH ON CASTS 
 
 Ofteutimes wbeii the uatural teeth are long and isolated, 
 the plaster teeth can be materially strengthened by inserting 
 a small piece of orange wood in each matrix, while the plaster 
 is yet plastic, and before the impression is entirely filled. The 
 small round Japanese toothpicks of orangewood are well 
 adapted for this purpose, being of suitable size and especially 
 tough. The sharp point should be cut off, the stick cut to 
 suitable length, usually an inch, and placed conveniently at 
 hand before filling the impression. The advantage of wood 
 over metal pins is that in ci;tting off the ends of the plaster 
 teeth in flasking, the wood will cut as readily as the plaster, 
 while metal pins must be cut very carefully, or the plaster 
 teeth enclosing them will be fractured. 
 
 CASTS FROM MODELING COMPOUND IMPRESSIONS 
 
 Preliminary Treatment for Cast Production 
 
 EQUALIZING DENTURE BEARING BY SCRAPING HARD AREAS 
 OF THE IMPRESSION 
 
 Since the character of the material used, and the manner 
 of manipulation followed in taking impressions in modeling 
 compound, tend to relieve pressure of the denture on the 
 hard, and increase its bearing on the soft, areas of the mouth, 
 it is not necessary to scrape the areas impressed by the hard 
 tissues to the same extent in modeling compoimd as in plaster 
 impressions. Some slight relief, however, in most cases will 
 prove beneficial, and with the variation just stated, the in- 
 structions given in reference to the treatment by scraping 
 of plaster impressions, apply to the class under consideration. 
 
 TREATMENT OF THE SURFACE OF THE IMPRESSION 
 
 Modeling compound impressions are waterproof, and 
 therefore no separating or staining mediums are needed, as 
 in plaster work. The impression, however, should be dipped 
 in water, the air bubbles dislodged with a brush, and the 
 excess moisture removed with absorbent cotton. No free 
 water should be allowed to remain in the deeper portions, 
 for if present it will reduce the density of the plaster in the 
 cast in that area, and weaken it, as previously explained. 
 While the impression can be filled without moistening, a 
 smoother surface to the cast can be produced if this precaution 
 is taken. 
 
106 TREATMENT AND KlLLlNi; OF IMPRESSIONS 
 
 Exception to tlii.s inctliud of treatuiciit miiist l)o made 
 when magnesium oxy-cliloride is used. The impression should 
 bo given a tliin film of sandarae varnish, the latter allowed 
 to dry, and the surfaces not moistened previous to filling. 
 
 FILLING THE IMPRESSION— FULL CASES 
 
 The mix of plaster should be made in the same manner, 
 and of similar consistency to that used in plaster work. 
 If any variation is made, the mass should be thicker, since 
 the impression can be tapped sharply in settling the contents 
 to place, without danger of dislodging it from the tray, and 
 a comparatively thick mix can be readily adapted to full 
 u])ppr or lowei' impressions with ease. 
 
 FILLING THE IMPRESSION IN PARTIAL CASES 
 
 As previously stated, modeling compound is not a suit- 
 able material for partial cases unless the sectional method is 
 employed, but if used for impression purjooses, the casts are 
 produced in the same manner as from partial impressions in 
 plaster. Isolated plaster teeth should also be strengthened 
 in the same manner as outlined. 
 
 TIME REQUIRED FOR PLASTER CASTS TO SET BEFORE RE- 
 MOVING THE IMPRESSION 
 
 From fifteen to twenty minutes' time should be given the 
 plaster cast to harden before removing the impression. If 
 this step is carried out too soon, the face of the cast is liable 
 to be marred by handling, since it takes some time for the 
 plaster to develop a reasonable degree of hardness. On the 
 other hand, the separation should not be delayed too long, 
 since at the beginning of crystallization expansion sets in 
 rapidly, and continues in a gradually decreasing ratio for 
 twenty-four liours or more. 
 
 WARPING OF THE IMPRESSION AND CAST 
 
 As previously stated in the consideration of plaster, when 
 an impression is allowed to remain in the tray and the cast 
 in the imjiression for some time, both will be more or less 
 warped. To obviate this difficulty as much as possible, the 
 tray and impression should be removed as soon as the ]»laster 
 constituting the cast has hardened sufficiently to permit. 
 
 REMOVAL OF THE TRAY 
 
 The first step in separating the impression and cast is 
 the removal of all excess of the impression material extend- 
 
TREATMENT AND FILLING OF LMPRESSIONS 107 
 
 hig over tlic outer surfaces of the labio-lmeeal flange of tlie 
 tray. This is easily accomplished 1)y i)aring it off with a 
 suitable plaster knife. 
 
 The cast and margins of the impression are then grasped 
 with one hand, avoiding contact with the tray flange, when, 
 by tapping the handle, and if necessary the flange, the tray 
 and impression will readily separate. 
 
 REMOVAL OF IMPRESSIONS— FULL CASES 
 
 With a sharii knife carefully ]iare away the impression 
 opi)osite the alveolar crest until the staining medium indi- 
 cates the near approach to the cast. The paring should ex- 
 tend from one tuberosity around the crest of the border to 
 the opposite side. 
 
 A few light taps on the Ijuccal and labial portions of the 
 impression, followed by inserting the point of tlie knife be- 
 tween the latter and the cast at the peripheral line of junc- 
 tion, will break away the outer portions of the impression. 
 
 By tapping the vault portion and inserting the point of 
 the knife at the line of demarkation distally, the remainder 
 can be removed without difificulty. If, however, the rugae are 
 prominent, and the vault is deep and narrow, it will be best 
 to cut a ^^-shaped groove mesio-distally through the central 
 vault portion and practically divide it. The groove should 
 be carried deep enough to disclose the stained area. A slight 
 prying movement on either half will cause fracture, when they 
 will come away readily. 
 
 REMOVAL OF THE IMPRESSION— PARTIAL CASES 
 
 The same steps as to removal of the surplus of the im- 
 pression from the tray, and the tray itself, as previously de- 
 scribed in full, apply to partial cases as well. The removal 
 of the impression from the cast, however, re(|uires more care 
 and necessitates the fracturing of the impression into smaller 
 pieces, to oliviate the breaking of the teeth from the cast. 
 
 First — The impression opposite the occlusal and incisal 
 l)ortions of the teeth should be carefully pared away until 
 the stained area .opposite each tooth and <'usp as well, is 
 l)lainly visible.- If the cusps of the teeth are particularly sharp 
 and well defined, to avoid breaking them, the paring may 
 be carried along the mesial and distal slopes of the cusj)s 
 until the stain(>d areas present two nearly unbroken lines, 
 indicating the position of the buccal and lingual marginal 
 
108 TREATMENT AND FILI.INC OE IMPRESSIONS 
 
 ridges. This ]iractically separates tlie labio-ljuecal portion 
 from the body of tlie impression. 
 
 CUTTING V-SHAPED GROOVES TO WEAKEN THE IMPRESSION 
 
 Second — A V-shaped j^roove is usually cut opposite each 
 cuspid tooth and eminence perpendicularly, if not already cut 
 in removing the im]iression from the month, extending from 
 incisal to peripheral margin. The plaster which fills the 
 voids occasioned by missing teeth should be carefully di- 
 vided with the knife mesio-distally at the points of shortest 
 diameter of the spaces. This permits the labial or l)uccal sec- 
 tions of plaster to be removed in an outward direction, and 
 the lingual portions to be removed inwardly later on, without 
 engaging with, or marring the adjacent teeth. 
 
 If sheets of wax have been attached to the floor of the 
 tray in fitting, so as to enter the spaces, these of themselves 
 
 I'ARTIAl, IMI'IIKSSKIX l'Ain'1,1 c;Hii(i\i;|i Fill! RF;M0VAI. 
 
 partially divide the impression where placed, and facilitate 
 the cutting with the knife. The sections should be tapped 
 lightly to start them, or the point of the knife may be applied 
 and slightly pressed into the peripheral line of junction of 
 the cast and impression. By prying outward, the sections 
 will come away readily, thus exposing the labial and buccal 
 surfaces of the teeth. 
 
 Third — A V-shaped groove is cut around the lingual 
 surface of the impression, near the occlusal third of the teeth, 
 and divided perpendicularly opposite each tooth. These sec- 
 tions are then removed one at a time, which, when completed, 
 exposes the occlusal and a portion of the lingual surfaces of 
 the teeth. 
 
 Still another groove is cut entirely around the lingual 
 surface of the impression, the apex of which is directed toward 
 the gingival area, and the plaster divided in sections as just 
 
TREATMENT AND FILLING OP IMPRESSIONS 109 
 
 described, wliicli when removed will leave the teeth entirely 
 exposed. 
 
 Fouiih — The central or vault portion still requires re- 
 moval. If the vault is flat and no undercuts are pi'esent, a 
 few light taps with a slight prying movement at the line of 
 junction of the impression with the cast posteriorly, will dis- 
 lodge it. When the vault is deep, the better plan will be to 
 divide the remaining portion into two or three sections and 
 remove them separately. If the point of the knife has been 
 well under control, the removal of the impression, when car- 
 ried out in detail as described, will result in a cast with un- 
 broken teeth or cusps, and r;nmarred surfaces. 
 
 REMOVAL OF MODELING COMPOUND IMPRESSIONS FROM 
 CASTS 
 
 Modeling comi^ound impressions, both full and partial. 
 can be removed from casts l)y the application of either dry or 
 moist heat, preferably by softening in hot water. The tray, 
 impression and cast are placed in a pan of water, and the 
 latter heated sufficiently to render the compound plastic, but 
 not excessively soft. The tray is iirst removed and the com- 
 pound at the peripheral margins peeled away from the buccal 
 and labial surfaces of the border, drawing it occlusally and 
 incisally and away from the cast. But little difficulty will 
 occur in removal in full cases, unless the compound has been 
 overheated, in which case it will adhere to the cast. In re- 
 moving the impression in partial cases, time should be given 
 for the heat to penetrate through the compound and render 
 it plastic throughout. If this precaution is not observed and 
 an attempt is made to remove the compound from the voids 
 or spaces, fracture of some of the teeth, in most instances, 
 will occur. 
 
 Should any of the comjiound adhere to the cast in various 
 places, as it frequently does, it may be readily removed by 
 heating some dry compound in the Bunsen flame until quite 
 sticky, then dip the cast in warm water, first to slightly soften 
 the undetached compound, and second, to prevent the heated 
 mass from adhering to the cast. The dry, heated compound 
 is firmly pressed against the adliereut pieces and quickly 
 withdrawn, reheating it in the flame each time, if necessary, 
 to keep it adhesive, until all of the remaining portions are 
 removed. 
 
110 TKKATMKNT AND FILLING OK LMI'KKSSIONS 
 
 SPECIAL MATERIALS USED FOR CASTS IN VULCANITE WORK 
 
 It is a well-establislied fact that when plaster is sub- 
 jected to stress, or compressive force, the surface crystals, or 
 those first takin<i; the load crush and break down, when the 
 stress passes the modulus of resistance of the material. 
 
 It has also been demonstrated, tliat the force ordinarily 
 Hxcrled in closin.a; an overpaeked flask is far in excess of that 
 which ]ilaster can stand without the crystals crushing and 
 the face of the cast becoming distorted. 
 
 The effect of such distortion, he it small or great, on 
 casts against whicli vulcanite or celluloid dentures are 
 molded, is to impair, if not altogether destroy, the ada])tati()n 
 of tlie dentures to the oral tissues. 
 
 Two ways are possible for lessening if not entirely over- 
 coming the danger of distortion of dentures, due to yielding 
 of the plaster casts under the influence of excessive pres- 
 sure, heat, and moisture, during vulcanization. 
 
 The first of these does not require the use of any special 
 materials other than those commonly employed in the dental 
 laboratory. The method of technic differs in some respects 
 from that usually followed in such procedures, the variations 
 being noted undei' the rlosivg of flasks, preparatory to vul- 
 canizing. 
 
 The second plan recpiires that the cast be constructed of 
 a material harder and more resistant to stress, and to dele- 
 terious influences in general, than is plaster. 
 
 Several matei'ials. capable of withstanding much greater 
 crushing strain than i)laster, may be made use of, the proper- 
 ties of one of the most important of which will now be con- 
 sidered, since its value when properly manii)ulated is unques- 
 tioned. 
 
 ARTIFICIAL STONE 
 
 OXYCHLORIDE OF MAGNESIUM 
 
 Several years ago the idea occurred to the writer that 
 because of its density, smoothness of surface, and impervious- 
 iiess to water, the materials used in the manufacure of arti- 
 ficial stone might l)e employed in cast construction, and the 
 ])roblem of denture warpage be solved, or the difficulties re- 
 sulting therefrom greatly reduced. 
 
 From data furnished by the late Prof. Vernon J. Hall 
 many exi)eriments were made with various materials, ])articu- 
 larly with the oxide and chloride of magnesium. The first 
 experiments, conducted with chemically pure products, were 
 
TREATMENT AND FILLING OF IMPRESSION'S 111 
 
 unsuccessful. Attention was then given the commercial prod- 
 ucts, since these were extensively used in various industrial 
 lines. From the first, difficulties were encountered, due prin- 
 cipally to fracture lines forming in the mass in hardening. In 
 some cases very perceptible contraction was noticeable. 
 
 Fracture was later found to be due to the presence of 
 carbon dioxide in the oxide of magnesia. Its presence may be 
 accounted for in two ways. Magnesium oxide is produced 
 usually by burning magnesium carbonate, just as calcium 
 oxide or lime is produced by burning calcium carbonate. In 
 both cases the carbondioxide is driven off when the process 
 is properly conducted. Unless the calcination is thorough 
 all of the CO2 will not be eliminated. Again, the oxide of 
 magnesia may be properly prepared, but if left exposed to the 
 air, it will take up moisture and carbon-dioxide, and gradually 
 return to the carbonate. From whatever source it may come, 
 its presence in the oxide of magnesia renders the latter worth- 
 less for cast construction. The remedy consists in recalcining 
 the mixed oxide and carbonate above a red heat, to expel the 
 CO2, or if this is not practicable, discard it for a better grade 
 of material. 
 
 Contraction in the hardened mass, noticable in the space 
 seen between the impres.sion and cast when the latter has 
 hardened, is the result of using an under-saturated solution of 
 the chloride, the liquid with which the powdered oxide is com- 
 bined. By increasing the strength of the liquid to full satura- 
 tion, adding crystal chloride until there is a slight excess in 
 the bottom of the stock vessel, contraction can be overcome. 
 
 The length of time required for setting — about twelve 
 hours — is considered an objection by some, but the advan- 
 tages gained in more perfect adaptation of the denture to the 
 oral tissues and in increased density of the vulcanite far 
 outweigh the disadvantages mentioned. 
 
 ADVANTAGES OF OXYCHLORIDE OF MAGNESIUM 
 
 The jDrincipal advantages of oxychloride of magnesium 
 for casts in vulcanite work are these : hardness, density, 
 smoothness of surface and an extremely low expansive index, 
 less than one-fourth that of the ])est grades of plaster. It 
 is sufficiently impervious to moisture and heat to maintain its 
 form without crushing, even under heavy pressure. The 
 writer has vulcanized two baseplates on the same cast, both of 
 
112 TREATMENT AND EILLINC, OF IMPRESSIONS 
 
 which showed satisfaftory achqitatioii to the oral tissues. At 
 the end of tlie second vidcaiiization, the cast, although per- 
 meated with moisture, was quite hard and resistant to stress 
 and on evaporation of the moisture appeared much harder 
 than casts constructed from the best grades of plaster before 
 vulcanization. 
 
 Rubber of any shade vulcanized in contact with oxy- 
 chloride of magnesium is hard, dense, elastic, capable of tak- 
 ing a high polish, and on account of the density of the cast is 
 practically free from nodules. 
 
 Partial dentures vulcanized on casts of this material show 
 all the characteristic lines and fine surface markings of the 
 teeth and tissues against which it is molded as clearly as 
 an accurate plaster impression can reproduce them, because 
 the cast is not changed or defaced in the slightest degree by 
 manipulative procedures. 
 
 EXPANSION 
 
 In tests made for expansion, the greatest movement 
 registered, from the buccal face of one tuberosity to the 
 corresponding opposite surface, was 15/10,000 of an inch, 
 against from 60/10,000 to 100/10,000 of an inch in casts made 
 from the best grades of plaster. 
 
 COMPRESSION 
 
 Comparative compression tests on blocks of plaster and 
 of magnesium comiJound, set over night, showed the following 
 result : size of blocks ly^xli/oxi^ inches ; area of plunger, 14 
 inch. In the plaster blocks, the plunger began sinking into 
 the block at twenty pounds, and under continued pressure 
 penetrated about '^/g inch, the block breaking at 100 pounds. 
 
 The magnesium blocks showed no ijerceptible compres- 
 sion up to 1,000 pounds, at which point they suddenly crushed. 
 In one-inch cubes, the oxychloride of magnesium will stand a 
 crushing strain of nearly 5,000 pounds, according to Major 
 Gilmore, U. S. A. 
 
 MATERIALS USED FOR CAST CONSTRUCTION 
 
 The following instruction in reference to procuring and 
 handling the magnesium materials for casts covers the essen- 
 tial points to be kept in mind. 
 
 MAGNESIUM OXIDE 
 
 There are two varieties of magnesium oxide, known as the 
 light and heavy oxide. The difference, which is one of specific 
 
TREATMENT AND FILL-ING OF IMPRESSIONS 113 
 
 gravity and not of chemical constitution, is bvonglit about by 
 tlie manner in wliicli tlie magnesite (MgCOj) is burned. In 
 "Cements, Limes, and Plasters," E. C. Eckel says: "If 
 MgCOs be strongly heated, the effect, as with lime carbonate, 
 is to drive off the CO2, leaving the MgO as a white solid. A 
 curious and technologically important phenomenon connected 
 with the temperature employed is to be noted. If the calcina- 
 tion is carried on quickly at a red heat the magnesia resulting 
 will have a specific gravity of o.OO to 3.07, while if the cal- 
 cination is long continued or carried on at a higher tempera- 
 ture the resulting MgO will be much denser, possessing a 
 specific gravity of 3.61 to 3.80." 
 
 For the construction of casts, the heavy oxide commer- 
 cially known as porcdered magnesite, or calcined magnesia, 
 should be employed. To prevent its return to MgCOa, by 
 absorbing COo and moisture from the air, as indicated by its 
 becoming granular and lumpy, it should be kept in airtight 
 containers, just as ]ilaster must be protected in damp climates. 
 
 MAGNESIUM CHLORIDE 
 
 Magnesium chloride is a crystalline, deliquescent suli- 
 stance, having much the appearance of sea salt. It is obtained 
 in several ways, a common source being by heating mag- 
 nesium ammonium chloride (MgC'L NHj CI) to about 460 C. 
 The ammonium chloride volatilizes, leaving anhydrous MgCL. 
 
 The ordinary commercial product, instead of the chem- 
 ically pure chloride, is suitable for use in cast construction ; 
 some of the commercial products occasionally contain HSO4 
 as an impurity. When present, in the chloride solution, it will 
 in time render the hardened mass of oxychloride somewhat 
 soluble in water. The sulphuric acid can be eliminated by 
 adding barium hydrate to the chloride solution. When the re- 
 sulting precipitate, bariimi sulphate ceases to form, it indi- 
 cates that the acid has been neutralized. From 6 per cent to 
 10 per cent liy weight of the reagent compared with the 
 chloride is required. This method of neutralizing the acidity 
 of the magnesium chloride solution is more strongly indicated 
 when the oxychloride material is to be wrought into work of a 
 ])ermanent character and is not as essential for vulcanite casts, 
 since the latter are destroyed after vulcanization, in removal 
 from the dentures. After two years almost constant use of 
 magnesium oxychloride, the writer has not found it neces- 
 sary to purify any commercial chloride solution, but has fre- 
 
114 TREATMENT AND FIT.LIN(; OP IMPRESSIONS 
 
 queiitly been obliged to re-ealcine the oxide to drive off tlie 
 COo, as previously mentioned. 
 
 PREPARING THE MAGNESIUM CHLORIDE SOLUTION 
 
 In the average dental practice but a comparatively small 
 amount of magnesium oxychloride will be used in the course 
 of a month, so the preparation of a large quantity is not ad- 
 visable. It is a better plan to make up one or two quarts of 
 the licjuid chloride, renewing the solution from time to time 
 as needed. In this way the quality of the liquid can easily be 
 kept ui^ to standard. 
 
 To make the solution, put 2 pints of water in a clean 
 2 quart glass bottle, and add the crystal chloride until com- 
 plete saturation of the water is effected. The visible test of 
 full saturation of the water appears in the presence of undis- 
 solved crystals of chloride in the bottom of the vessel. 
 
 A half-inch layer of crystals in the bottom of the vessel at 
 all times will do no harm and will keep the solution fully satu- 
 rated. If the crystals disappear, add more until the usual 
 amount of excess is restored, and if they increase, due to 
 evaporation of the water, add more of the latter. After full 
 saturation of the water has occurred, the liquid should not be 
 shaken up nor the crystals disturbed in decanting off a por- 
 tion for use. 
 
 MANNER OF MIXING THE OXIDE WITH THE CHLORIDE 
 SOLUTION 
 
 Place a sufficient amount of the chloride solution to form 
 a cast in the plaster bowl and sift in the oxide just as plaster 
 is manipulated, stirring much more vigorously and for a 
 longer time than when plaster is used. Additions of the oxide 
 are made from time to time and the stirring continued until 
 the mass is sufficiently thick to stand alone. This is an ex- 
 tremely important requirement, for when too thin the oxy- 
 chloride overflows the bounds of the impression and the cast 
 cannot be built up to proper form. 
 
 The object in vigorous stirring is to eliminate all air 
 that may be in the powdered magnesite and to coat every 
 granule with a film of the liquid. The tendency of all begin- 
 ners in using this material is to slight the stirring, and econo- 
 mize on the powder, with the result that although the mass 
 hardens well and is smooth, there is an excess of the chloride 
 present and the cast will more readily fracture under stress 
 
TREATMENT AND PRILLING OF IMPRESSIONS 115 
 
 than when tlie material is thickly mixed. It is also inclined 
 to soften more readily during vulcanization. 
 
 TREATMENT OF IMPRESSIONS 
 
 To get an al)solutely smooth surface (o a cast of this 
 material it is necessary to have a smooth surface to the im- 
 pression. This can best lie secured by treating either plaster 
 or modeling compound impressions with a varnish hav- 
 ing a sandarac base. Gilbert's Imperial Varnish fulfills the 
 requirements well. 
 
 In filling modeling compound imjiressions with plaster 
 the surfaces are merely moistened with water to accellerate 
 the flow of plaster over the impressed areas. With oxy- 
 chloride, although moisture on the surface of the impression 
 would insure ease of introduction, its in'esence would eventu- 
 ally deteriorate the surface of the cast, rendering it softer and 
 less resistant to stress. 
 
 Modeling compound impressions are varnished because 
 unless so treat''d tlie compound is at times extremely dif- 
 ficult to remove from the oxychloride cast. 
 
 FILLING THE IMPRESSIONS 
 
 The impression is tilled with oxychloride mixture in much 
 the same manner as with plaster, with this exception: Since 
 the face of the impression is dry, for reasons previously 
 stated, to prevent the formation of creases in the east where 
 two or more additions of the mixture may meet, it is best to 
 a])]ily each subsequent addition to an area already covered, 
 and l)y vibration let the mass last added settle down and push 
 the margins of tliat already adapted over the uncovered areas 
 of the impression. 
 
 In partial cases, impressions of teeth sliould be tilled 
 with a small tamper to avoid the confinement of air in the 
 matrix. 
 
 The mass of oxychloride should be built to the proper 
 form of the cast, being careful to avoid any excess, since when 
 set, it is very difficult to cut with a knife. By adjusting a 
 bead of wax on the periphery of the impression to outline 
 th(> extreme margi-ns of the cast, and by Imilding the iruitei'ial 
 to this head much amioyance will be averted later on. 
 
 GENERAL REMARKS 
 
 By mixing from 50 to SO ])er cent of clean sand with 50 
 to 20 per cent of the oxide of magnesum a harder and much 
 
116 TREATMENT AND FILLINCJ OF IMPRESSIONS 
 
 more resistant mass M'ill result than if the oxide and i-IMoride 
 alone are used. 
 
 By tilling the impression partially with oxy('hh)ride jnix- 
 ture and inserting a previously selected metal model form 
 (Kerr's), an extremely small amount of the material will be 
 required and the jteripheral outline, as well as the depth of the 
 cast, will be kept within minimum limits, since the oxy- 
 chloride need not cover the metal form on these surfaces. 
 
 Tlie material should not be disturbed by attempting to 
 remove the im]iression until thoroughly Jiardened. It usually 
 reciuires about 12 hours to set. Should the mass have spread 
 out over the sides of the impression much more than is desir- 
 able it may be trimmed peripherally in four or five hours 
 after mixing without endangering the cast. 
 
 Thorp's applied Chemistry has this to say in reference 
 to the chemical reaction which occurs in combining the oxide 
 and chloride of magnesium. 
 
 "When highly claimed magnesia is treated with a strong 
 solution of magnesium chloride it dries in a few hours to a 
 hard mass of oxychloride, capable of receiving a high polish. 
 A sample prepared in this manner and hardened by six 
 months' exposure to the air was found to consist of a mixture 
 of Mg C O, with a compound of Mg CL 5 Mg 17 H, O. On 
 heating to 180° C. it was converted into Mg CL 5 Mg O 6 H, 0. 
 By prolonged treatment with water the whole of the mag- 
 nesium chloride was extracted and the compound 2 Mg 3 H. 
 O left. 
 
 "This residual hydrate is a compact solid as hard as 
 sandstone and possessing a brilliant sui'face. 
 
 "Magnesia cement is used very extensively as a binder 
 in connection with briquetting in the manufacture of artificial 
 building stones, tiles, grindstones, and emery and polishing 
 wheels. Its binding quality is very considerable and it is very 
 plastic and cheap. 
 
 "A good mixture for this use consists of: 
 
 "25 parts magnesia (!):■! Mg O). 
 
 "25 parts magnesium chloride (45 per cent solution). 
 
 "50 parts water. 
 
 "About 5 pounds of this mixture will serve to cement 
 95 parts of stone, emery, etc. The resulting blocks are very 
 solid and harden thoroughlj^ in a few hours." 
 
 (Eckel. Cements, Limes, and Plasters.) 
 
TREATMENT AND FILUNG OF IMPRESSIONS 117 
 
 HISTORY 
 
 In 1853 M. Sorel, an eminent French chemist, discovered 
 that zinc chloride when mixed with zinc oxide formed a 
 cement. This is essentially the hasis of our oxychloride of 
 zinc cements today, bnt it was not introduced to nor used by 
 the dental profession until many years after its discovery. 
 
 Shortly after this discovery Sorel found that the 
 chlorides and oxides of several other metals possessed similar 
 properties. 
 
 TJie most imjiortant and valuable combination he discov- 
 ered was that the oxide and chloride of magnesium united to 
 form a substance as hard as stone. Further, that by com- 
 bining coarsely crushed rock, as marble, granite, limestone, 
 etc., with a small percentage of the oxychloride of mag- 
 nesium the resulting mass would stand an enormous strain be- 
 fore crushing. 
 
 The value of this discovery was immediately recoguized 
 and made use of in the industrial field in the production of 
 artificial stone known as Sorel 's stone. 
 
 (Bibliography.) 
 
 A practical treatise on Coignet-Beton and other artificial 
 stone. Q. A. Gillmore, 1871. 
 
 Cements, Limes, aucl Plasters. E. C. Eckel, 1909. 
 
(' II A I'T K \l 1 X 
 
 BASES FOR ARTIFICIAL DENTURES 
 
 ill pi-(islli('tic iiroctMlurcs, that pdi-lioii ol' a (Iciiturc wliicli 
 rests upon the oral tissues, and to which tlie teeth are attached 
 by various means, is called a base. 
 
 REQUISITE PROPERTIES OF A DENTURE BASE 
 
 'i'he material selected for a base for an artilicial dentui'e 
 should i)ossess certain requisite i)roperties : 
 
 First — It should be rigid, in order to retain its form under 
 stress. 
 
 Second — It should be dense and ndn-jx irons. 
 
 Third — It should be free from action by oral secretions 
 or food piroducts. 
 
 Fourth — It should l)e odorless and tasteless. 
 
 Fifth — It should be a reasonably good conductor of ther- 
 mal changes. 
 
 Sixth — It should be readily adapted to the die or cast 
 of the mouth. 
 
 Seventh — It should be ca})able of takirg and retaining a 
 high polish. 
 
 Two general classes of materials are utilized as bases 
 for artificial dentures. The first consists of metals, as gold 
 and its alloys, platinum, aluminum, and various alloys of tin. 
 The second class consists of plastic vegetable substances, as 
 vulcanite, gutta ])ercha. and celluloid. 
 
 GOLD BASES 
 
 Pure gold, because of its softness and lack of rigidity, 
 is not used as a base for artificial dentures, except in special 
 cases, and then only when combined with gold of a lower 
 carat. Twenty Karat gold is most commonly employed in 
 denture construction, although 18K gold is frequently used. 
 The objections to the latter are on accov;nt of its greater 
 rigidity, which renders it more difficult to conform to the die, 
 and its tendency to discolor in some mouths. 
 
 Twenty Karat gold plate more nearly fulfills the re- 
 quirements mentioned as a base than any of the other mate- 
 
 118 
 
BASES FOR ARTIFICIAI. DENTURES 119 
 
 rials employed for this piir]iose, except jilatiuiim. Its beau- 
 tiful, rich yellow color, freedom from taste, odor or oxidation, 
 or tendency to discolor, its rigidity in comparatively thin 
 sheets, its high conductivity and the ease with which it can 
 be polished, place it in the front rank for materials used for 
 dentures. The principal objections to its universal use are 
 due principally to the difficulty in securing close adaptation 
 to the oral tissues, as a result of the sequent steps of con- 
 struction, and to the expense involved in the production of 
 such substitutes. It could and should be used in many cases 
 where dentures of the less expensive class are now consiructed, 
 particuarly in partial cases. 
 
 In addition to the advantages mentioned, gold combines 
 the greatest strength with the least bulk, of any other base. 
 
 PLATINUM BASES 
 
 The oral tissues under a well adapted platinum base re- 
 tain their normal tone, while but little change occurs in the 
 bony processes. It has been noticed in porcelain crown and 
 bridge work, the frame work of which is composed of i3lat- 
 inum, that the tendency for food to accumulate or plaques to 
 form on exposed or partially protected platinum surfaces, is 
 decidedly negative as compared with alloyed or pure gold in 
 similar situations. This is supposed to be due to some un- 
 known, inherent quality in the platinum itself, not possessed 
 by other metals, which tends to preserve hygienic conditions, 
 even under adverse circumstances. Whether this view is 
 correct or not, the fact remains that when platinum base den- 
 tures are well adapted and free from mechanical causes of 
 irritation, the tissues remain remarkalily healtliy and normal 
 under such substitutes. 
 
 In addition to the peculiarly benign effect of platinum on 
 the oral tissues, this metal possess practically all of the good 
 (jualities ascribed to gold. In color it is bluish-white. It is 
 practically infusible under the ordinary blowpipe flame. It 
 may be used as a base plate in the same manner as gold is 
 employed, the teeth being attached either by soldering, or 
 with vulcanite,- An alloy of platinum and iridium, which is 
 harder and more resistant than platinum itself, would be 
 jireferable, however, since pure platinum is slightly softer and 
 more easily bent than 20K, gold of equal thickness. 
 
 The usual method followed in making use of platinum in 
 denture construction is in conjunction with porcelain. The 
 
120 BASES FOR ARTIFICIAL DEMTtJRES 
 
 teeth are first attached b.y soldering, the porcelain, which 
 gives the denture its contour, being subsequently fused around 
 them and over the base, blending with teeth and base to form 
 a homogeneous mass. The advantages and disadvantages of 
 continuous gum dentures will be discussed when dentures of 
 tliis class are described. 
 
 ALUMINUM BASES 
 
 Aluminum is frequently used as a base for artificial den- 
 tures in both cast and swaged form. It is the lightest of all 
 of the metals, is a good conductor of thermal changes, and is 
 non-irritating to the tissues when properly constructed. 
 
 Since this metal cannot be soldered successfully, it re- 
 quires considerable care to develop the means for attaching 
 the teeth to the base with vulcanite in swaged base dentures. 
 When the base is produced by casting, this difficulty is easily 
 overcome, the necessary anchorage for the vulcanite being 
 formed in the wax model and reproduced in the casting- 
 process. 
 
 Cast base aluminum dentures are inclined to disintegrate 
 in some mouths, due largely to castings of this metal being 
 of more or less imperfect density. When examined under a 
 magnifying glass, many minute spaces are disclosed. When 
 broken, and the fractured surfaces are examined, these spaces 
 are present and can be seen in the body of the casting, as 
 well as on the outer surfaces. The use of a pure aluminum, 
 with proper technic in casting, will largely overcome this 
 difficulty. 
 
 For various reasons, however, a swaged base is usually 
 more satisfactory and less inclined to irritate the tissues than 
 a east base. 
 
 TIN ALLOY BASES 
 
 Alloys of tin and cadmium, tin and bismuth, and other 
 similar combinations, are frequentlj^ used in the production 
 of bases for lower substitutes, to give weight to the finished 
 denture, and by gravity assist in its retention. When prop- 
 erly constructed, they are non-irritating to the tissues and 
 serve well the purpose for which they are intended. Care 
 should be taken, however, in the construction of dentures of 
 this class to avoid excessive weight, on account of the tendency 
 of the substitute to tire the mandibular muscles and produce 
 irritation of the soft tissues. 
 
BASES FOR AilTIFICIAL DENTURES 121 
 
 VULCANITE BASES 
 
 Because of the slight expense involved and the com- 
 paratively simple technical details attending its manipulation, 
 vulcanite is very extensively used as a base for artificial den 
 tures. When pro])er care is exercised, most efficient and serv- 
 iceable substitutes for the natural teeth can be produced 
 when this material is used as a base. 
 
 ADVANTAGES 
 
 First — Better adaptation can be secured with vulcanite 
 than with any other basic material. 
 
 Second — Ease of manipulation in the constructive steps. 
 
 Third — Inexpensive, first, as to cost of material, and sec- 
 ond, as to production ; consequently dentures of this type are 
 possible for persons of moderate means. 
 
 DISADVANTAGES 
 
 First — Vulcanite is a poor conductor of thermal changes. 
 
 Second — In order to have the inherent strength to resist 
 stress, vulcanite bases are necessarily more bulky than metal 
 bases. 
 
 Third — Vulcanite decreases the acoustic properties of 
 the palatine vault to a greater extent than do metal bases. 
 
 Fourth — Unless special care is exercised in finishing the 
 palatine, as well as all surfaces of vulcanite dentures, inflam- 
 matory conditions of the mucous tissues frequently ensue. 
 Such conditions have been erroneously ascribed to other 
 causes, some of which will be discussed later. 
 
 THERMAL CONDUCTIVITY OF VARIOUS DENTURE 
 BASE MATERIALS 
 
 Vegetable substances, as compared with the metals, are 
 poor conductors of thermal changes. The following table 
 by Prof. R. von Wardroff (slightly modified) on the conduc- 
 tivity of various substances, gives the conductivity of vulcan- 
 ite, as well as of the metals used in denture construction. "The 
 coefficient of thermal conductivity of a substance indicates the 
 amount of heat energy, measured in calories, conducted from 
 one face to the op]iosite face of a centimeter cube of the sub- 
 stance, when one of the faces is maintained one degree hotter 
 than the other. The amount of heat energy conducted is pro- 
 
122 BASICS FOR ARTIFICIAL DENTURES 
 
 portional to the difference in temperature l)etween the op- 
 posite faces." 
 
 "A calorie is the amount of heat energy required to raise 
 the temperature of a gram of water one degree Centigrade." 
 
 Silver at zero C 1.00000=1 
 
 Copper at zero C 1.00000=1 
 
 (lold at zero C TS200=% (Approx.) 
 
 Aluminum at zero C 34300=1/3 " 
 
 Platinum at zero C 11500=1/9 " 
 
 Paraffin at zero C 00061=1/166 
 
 Vulcanite at zero C 00040=1/250 
 
 Beeswax at zero C 00009=1/1111 
 
 Silver being rated as 1, gold transmits only %, aluminum 
 1/3, platinum 1/9 and vulcanite 1/250 calories in the same 
 length of time. 
 
 CAUSE OF ORAL INFLAMMATORY CONDITIONS UNDER 
 VULCANITE BASES 
 
 Several tlieories have been advanced as to the cause of 
 inflanmiatory conditions frequently arising from the wearing 
 of vulcanite dentures, the principal ones of which are as 
 follows : 
 
 (1) Lack of proper conduction of thermal changes to, 
 and radiation of heat from, the oral tissues. 
 
 (2) Deleterious effects of coloring matter in vegetable 
 bases. 
 
 (3) Mechanical irritation. 
 
 (4) Unhygienic conditions. 
 
 CONDUCTIVITY OF THERMAL CHANGES 
 
 While there is a marked difference in the rate of con- 
 ductivity of the metals and the vegetable bases, there is no 
 evidence to prove that the noticeable deficiency of vulcanite 
 in tills respect is directly responsible for the troubles some- 
 times ascribed to it. 
 
 Possibly in rare cases, particularly wlien other active 
 causes are present, the oral mucoids membrane may be in- 
 fluenced by, and its general tonicity impaired through, the non- 
 responsive medium of a vulcanite base. However, the fact 
 that many hundreds of thousands of vulcanite dentures 
 are l)eing worn with comfort, under which no inflammatory 
 conditions of the mucous membranes have developed, is evi- 
 
BASES FOR ARTIFICIAL DENTURES 123 
 
 dence in itself that the pereentaiic of eases due solely to poor 
 coudnctivity is extremely small. 
 
 Many cases of so-called rubber sore mouths have come 
 under the observation of the writer. Some of these were 
 corrected by the substitution of metal base dentures of con- 
 tinuous gums, gold or aluminum, and others with gold-lined 
 vulcanite dentures. The largest percentage of cases presented 
 were satisfactorily relieved on the introduction of properly 
 fitted and finished vulcanite cases. In no instance that can 
 now be recalled was there a recurrence of the inflammatory 
 conditions, which would undoulitedly have occurred had the 
 primal cause been due to non-conductivity. 
 
 DELETERIOUS EFFECT OF COLORING MATTER IN 
 VEGETABLE BASES 
 
 The red, ])iuk, brown and maroon rubliers, as well as 
 celluloid and zylouite, are usually given their tints by the 
 addition of ^■arying• i^roportions of vermilion or the sulphuret 
 of mercury Hg.S. The idea has been advanced that during 
 tlic process of vulcanization some of the sulphuret may fail 
 to unite closel}^ with, or it may be expelled from, the rubber, 
 thus leaving the pigment comparatively free or only weakly 
 combined with the base. After introduction and use of the 
 denture, the vermilion becomes an irritant to the tissues and 
 the inflammatory conditions mentioned follow. Again, it 
 has been thought possible that the comparatively free sul- 
 phuret b}" the action of the fluids of the mouth, which are 
 sometimes slightly acid, may be converted into mercuric chlor- 
 ide or corrosive su.blimate, a decided irritant, and the con- 
 ditions mentioned be thus produced. These ideas, however, 
 are unproven theories and cannot account for the fact that 
 inflammatory conditions sometimes develop under dentures 
 of black vulcanite which contain no mercury or other irritat- 
 ing pigment of any character, and sometimes under metal base 
 dentures as well. 
 
 The more logical explanation of the conditions under con- 
 sideration is that they are due to rough or defective surfaces 
 of the denture, as well as to lack of hygienic attention to the 
 mouth and denture on the part of the patient. 
 
 MECHANICAL IRRITATION 
 
 The negative form of the mouth is given to a vulcanite 
 denture by molding the rubber while in a plastic state over a 
 cast of plaster, or some similar material, and holding it in 
 contact with the cast, under pressure, while hardening. 
 
124 BASES FOR ARTIFU'IAl. DENTURES 
 
 As lias been mentioned beloie, tlie manner ol' erystal- 
 lization of plaster results in the formation of minute spaces 
 between the crystals. When examined under a magnifying 
 glass, the sui'face of a plaster cast presents many minute ir- 
 regularities. In addition to the spaces between the crystals, 
 there are other and larger spherical spaces, due to the pres- 
 ence of air in the plastic mass itself, and also to air heing 
 caught between the latter and the impression surface in tilling. 
 These spherical spaces are sometimes quite numerous, some 
 visible, and others lying just under the surface of the cast, 
 obscured by a thin film of plaster. 
 
 Under the pressure exerted in closing the packed flask, 
 tlie rubber is forced into the visible as well as some of the 
 obscured irregularities and spherical spaces, and in vulcan- 
 izing, hardens in the irregular form thus assumed. 
 
 When the case is vulcanized, removed from the flask, 
 thoroughly cleaned with a scrub l)rush, and examined, that 
 portion moiilded against the surfaces of the cast will be found 
 irregular and nodular, as a result of the conditions mentioned. 
 Unless thoroughly removed and the surfaces highly polished, 
 these nodules and irregularities become mechanical sources 
 of irritation, frequently sufficient to set up inflammatory con- 
 ditions. 
 
 Hyiiersemic conditions and oftentimes traumatic injury 
 frequently develop at local points, imder a vulcanite denture. 
 The cause may nearly always be traced to soiue defect in the 
 denture at that point, either from roughness, ruidue pres- 
 sure, or imperfect adaptation. Sometimes obscure spiculse 
 are present in the palatine vault, and the pressure of the den- 
 ture on the mucous tissues overlying these points causes dis- 
 comfort, and frequently marked inflammation develops. 
 Sharp, uneven points in the process, resulting from recent 
 extraction, are also sources of irritation. Such conditions de- 
 velop under metal base, as well as vulcanite dentures. 
 
 UNHYGIENIC CONDITIONS 
 
 Lack of care of the denture on the part of the patient is a 
 most common source of inflammatory conditions of the oral 
 mucous membrane. Mucous plaques seem to form on, and 
 particles of food to become attached more readily to, vulcanite 
 than to metal base dentures. Tlie reason for this is ob- 
 vious. A metal base as a rule is usually smoothly finished, 
 while vulcanite is seldom given the high polish it is capable 
 of taking on. 
 
Bases for artificiai. dentures 125 
 
 The rough surfaces on the palatine portion of a denture, 
 previously referred to, furnish a favorable location for the 
 formation of plaques in whieh micro-organisms flourish. Dr. 
 G-. V. Black called attention to this fact many years ago, and 
 stated his belief that the by-products of the bacteria were 
 largely responsible for many cases of rubber sore mouths. 
 These plaques often form in protected locations on reasonably 
 well-polished vulcanite, and occasionaly on metal, base den- 
 tures, if the patient does not cleanse them thoroughly and 
 regularly. 
 
 Most of the disadvantages ascribed to vulcanite can be 
 greatly reduced, or practically eliminated, if proper care is 
 observed in the construction of dentures of this material, and 
 they are given proper care by the patient. 
 
 CELLULOID BASES 
 
 Celluloid is a mixture of gun cotton, camphor gum, oxide 
 of zinc, and vermilion. As prepared for dental purposes it 
 comes moulded in blanks of various sizes. A blank is placed 
 in the flask matrix, subjected to heat, and the flask closed 
 under heavy pressure. If imperfections are present in the 
 cast, the negative of these will be reproduced in the denture. 
 The avoidance of such imijerfeclions is the first consideration; 
 the second, equally as important, is their removal from the 
 denture, if any are present. Otherwise, similar irritation of 
 the oral mucous membrane is liable to occur, as in vulcanite 
 cases. 
 
 Celluloid is not as resistant to wear nor to the action of 
 the oral fluids as vulcanite. Alcohol acts on it somewhat, and 
 in some mouths it discolors badly. It is of a beautiful pink 
 shade and occupies a place between porcelain and the best 
 quality of pink vulcanite, in its resemblance to the natural 
 gum tissues. When carefully manipulated and properly fin- 
 ished, it is an excellent base for temporary dentures, and in 
 some mouths will prove satisfactory for permanent substi- 
 tutes. It is capable of taking an extremely high polish, which, 
 however, is soon lost if abrasive powders are used in cleans- 
 ing it. 
 
 When properly finished, the tissues retain their tonicity 
 under celluloid fully as well as under metal base dentures. As 
 a matter of fact, if reasonable skill is exercised in the technical 
 details, good substitutes can be produced with any of the mate- 
 rials here described ; while on the other hand, poor teclmic 
 with the best materials is productive of indifferent results, if 
 not positive failure. 
 
li A P T E R X 
 
 SWAGED METAL BASE DENTURES 
 
 Swaging is the process of adapting or conforming metal, 
 usually in sheet form, to a carved, cast, or prepared harder 
 object called a die, by means of blows or pressure. 
 
 Swaged metal bases of gold, ]ilatinum or aluminum, such 
 as are used in denture construction, are given the reverse or 
 negative form of the mouth by swaging a plate of suitable 
 thickness between a metallic die, and a counterdie of metal 
 or some other luaterial which fulfills the purpose of a metal 
 counterdie, as rubber, soap, clay, etc. In case any of the latter 
 named substances are employed, they must be confined within 
 a suitable receptacle. 
 
 In the production of a swaged, metallic l)ase denture, 
 therefore, a die fulfills a similar ])urpose to that of a plaster 
 cast in the production of a plastic base denture. 
 
 COMPARATIVE RESULTS IN ADAPTATION OF 
 SWAGED, AND VULCANITE BASES 
 
 As a general proposition it is more difficult to secure as 
 close an adaptation of a swaged metal base to the oral tissues, 
 as can be secured when vulcanite is employed. This statement 
 is based on the fact that in the production of dentures with 
 metal bases, a greater numlier of constructive steps must be 
 carried out than are required in the production of vulcanite 
 dentures. 
 
 SEQUENT STEPS IN SWAGED BASE DENTURE 
 CONSTRUCTION 
 
 a. An impression of the moutli is secured. 
 
 b. From the impression a cast of the mouth is obtained, 
 which, by proper trimming, with additions if necessary, and 
 final varnishing, is converted into a model. 
 
 c. By imbedding the model in molding sand and with 
 drawing it, a sand matrix is formed. 
 
 d. A die is produced by casting molten metal in the sand 
 matrix. 
 
 e. By imbedding all but the face of the die in sand, and 
 casting a lower fiising metal over the exposed portion, a 
 counterdie is obtained. 
 
SWAGED METAL BASE DENTURES 127 
 
 f. A baseplate is produced by swaging a sheet of metal 
 of the required character and thickness l)etween the counter- 
 die and die, until the plate metal closely conforms to all sur- 
 faces of the latter. 
 
 g. Wiring the periphery and lingual surface of the base 
 and attaching anchoi'ages for the vulcanite. 
 
 h. Includes the general steps of occluding the teeth, wax- 
 ing, flasking, packing, closing the flask, vulcanizing and finish- 
 ing the case. 
 
 In carrying out each one of the sequent steps mentioned, 
 except (e), some loss of detail or departure from the true con- 
 tour of the oral tissues to be covered by the denture, is liable 
 to occur, which may impair the adaptation of the finished 
 product. If more than one error occurs, the tendency is to 
 increase, rather than diminish, any previous defect, while 
 in the end any one, or the several errors combined, may seri- 
 ously impair or entirely destroy the adaptation of the denture. 
 
 SEQUENT STEPS IN VULCANITE DENTURE CONSTRUCTION 
 
 In the sequent steps of vulcanite denture construction, it 
 is necessary to carry out (a), the first part of (b), and (h), 
 as detailed; (c), (d), (e), (f) and (g) are neither necessary 
 nor applicable. Thus it is seen that of the eight general steps 
 carried out in the production of swaged metal base dentures, 
 but three are required to produce vulcanite substitutes. 
 
 The intermediate steps, unnecessary in vulcanite work, 
 but essential in the swaging process, require the greatest care 
 in execution, to avoid errors. The principal mishaps liable 
 to occur in these intermediate steps are as follows : 
 
 (c) Distortion of the sand matrix in removal of the 
 model. 
 
 (d) (1) Distortion of the sand matrix in pouring the 
 
 molten die metal. 
 
 (2) Accumulation of steam or gas in the matrix, 
 
 causing roughness and imperfections in the 
 die. 
 
 (3) Warpage of the die, due to contraction in 
 
 cooling. 
 (f) (1) .Marring the high ])oints on the face of the 
 die in adapting the plate with the horn mal 
 let, and subsequently in swaging. 
 
 (2) Spreading or sjilitting of tlie die under hammer 
 
 lilows or i^ressure. 
 
 (3) Failure to secure perfect adaptation of the 
 
 baseplate to the face of the die. 
 
128 SWAGED METAL BASE DENTURES 
 
 (g) Distortion of the plate in soldering, in attaching 
 the rim wires and anchorages for the vulcanite. 
 
 All of these steps, if carefully carried out, may be com- 
 ]ileted without ]iercei)tible errors occurring, and the adapta- 
 tion of the baseplate to the oral tissues may, on trial, be found 
 satisfactory, yet under (h), in the final closing of the flask, 
 when overpacked and subjected to undue pressure, the adapta- 
 tion of the denture is frequently impaired or destroyed. 
 
 The excess rubber in the overpacked matrix, in closure 
 of the flask, forces the baseplate against the supporting plas- 
 ter, and if excessive stress is applied, causes distortion not 
 only of the foundation on which it rests, but bends the base- 
 plate as well. The warped condition the denture thus assumes 
 becomes permanent after vulcanization. 
 
 This brief summary of the commonly occurring errors 
 which tend to impair the adaptation of swaged base dentures 
 is not intended to disparage the utility of substitutes of this 
 type, nor to discourage their more general production, but 
 rather to emphasize the need of accuracy in technical proced 
 ures. "When properly constructed, the usefulness, beauty and 
 comfort of swaged metal base dentures — their general ex- 
 cellence, in fact, is thoroughly established and unquestioned. 
 
 APPLIANCES AND ACCESSORIES USED IN DIE AND 
 COUNTERDIE CONSTRUCTION 
 
 The necessary appliances used in the production of dies 
 and counterdies are as follows: 
 
 1. 
 
 Molding flasks. 
 
 o 
 
 Molding sand. 
 
 3. 
 
 Sieve. 
 
 4. 
 
 Talcum powder. 
 
 5. 
 
 Straight edge. 
 
 6. 
 
 Laboratory knife. 
 
 7. 
 
 TTeating ajijiliances. 
 
 s. 
 
 Melting ladles. 
 
 9. 
 
 Die metal. 
 
 10. 
 
 Counterdie metal. 
 
 n. 
 
 Wliiting and alcohol, 
 
 12. 
 
 Sable brush. 
 
 MOLDING FLASKS 
 
 The ordinary molding flasks are l>and-likc, slightly taper 
 ing rings of cast iron, open at both ends. Peripherally, they 
 
SWAGED METAL BASE DENTURES 129 
 
 conform to the outline of the alveolar arches. They vary in 
 size, the usual set consisting of a nest of four rings, ranging 
 from -i to 21 2 inches in diameter, and 214 inches in depth. The 
 smallest flask, which corresponds in size and general outline 
 form to the base of the average model, is used for confining 
 the metal within the base outline of the die, and thus increas- 
 ing its depth, to avoid spreading or splitting during swaging 
 Various forms of special flasks, such as the Bailey, Lewis, 
 and Hawes flasks, are also in common use. The two former 
 are designed to increase the depth of the die over that of the 
 model, while the latter is intended to obviate the use of cores, 
 when imdercuts are present on the labial or buccal surfaces 
 of the model. 
 
 MOLDING SAND 
 
 Sand of the finer vai'iety, such as is used by brass or iron 
 molders mav be iised to advantage in the laljoratorv. It is 
 
 NEST OF lIOLDrNG RINGS 
 
 rendered moist and workable by spraying occasionally with 
 water, just enough being incorporated to render it cohesive. 
 An excessive amount of moisture present would develop an 
 excessive quantity of steam in casting, and result in imper- 
 fections in the die. The sand should be sifted, thoroughly 
 worked with the hands, and allowed to stand a short time 
 before use, to develop uniform density and cohesiveness, or 
 temper, as it is called. 
 
 The supply houses furnish prepared molding sand, such 
 as "Chase's," a combination of fine sand with oil, and "Cal- 
 ear," a combiuatioii of marble dust with glycerin or oil. With 
 moderate use, these prepared sands give good service, last a 
 considerable length of time, and are more convenient to use 
 than the common sand. Used frequently, they soon deteri- 
 orate and lose the cohesive property, because of the burning 
 out of the oil or glycerin. The addition of a small quantity 
 
1311 SWAGED MKTAL BASE DENTURES 
 
 of the latter, and the thorough sifting and working of the 
 mass will restore cohesiveness. 
 
 THE SIEVE 
 
 It is essential that sand of any variety should be kept 
 free from lumps, foreign substances and particles of metal 
 that may become detached from the die and counterdie in 
 casting. For this purpose a No. 20 mesh sieve should be kept 
 at hand, and before forming the matrix, the sand should be 
 run through it once or twice. This treatment not only re- 
 moves debris, but renders the sand more workable by dis- 
 seminating the drier particles among the damper portions, 
 and develops cohesive property as well. 
 
 TALCUM POWDER 
 
 The model, which should be flaring, smooth, varnished and 
 perfectly dry, is dusted and thoroughly rubbed with soapstone 
 to i^revent the sand from adhering to it. The excess should 
 be removed with a soft brush before imbedding the model in 
 sand. 
 
 THE STRAIGHT EDGE 
 
 A straight edge of metal or wood is used for striking off 
 the excess sand that extends above the molding flask after 
 packing. Since this surface of the sand becomes the base 
 of the matrix and must support the weight of the molten 
 metal in casting, it should set flat at all points upon the bench 
 on which it rests, so that it will not yield or break under the 
 weight of the molten die metal. 
 
 THE LABORATORY KNIFE 
 
 A straight blade knife is used for removing a tapering 
 section of sand, beginning at the ring margin and slightly 
 increasing in depth to the periphery of the model. This 
 trimming is necessary to free the model at its periphery and 
 allow it to drop from the sand without fracturing the matrix 
 margins. 
 
 HEATING APPLIANCES 
 
 A burner capable of developing a considerable amount 
 of heat is an essential factor in laboratory procedures. It 
 is a time and money saver as well. The very common method 
 of placing the ladle over an ordinary Bnnsen burner and 
 applying the blow-pipe flame directly on the die metal to more 
 rapidly fuse it, is to be discouraged, since this procedure in- 
 
SWAGED MKTAL BASK IIKXTHRKS 131 
 
 duces oxidation and deterioration of the nietai in a very 
 short time. The application of the hU)w-pipe tlame underneatli 
 the ladle is not objectionable, further than that it is usually 
 unnecessary, if sufficient heat is developed by the burner. 
 
 MELTING LADLES 
 
 Toadies used for melting the die metal should be of cast 
 iron or stamped from heavy iron of not less than one-eighth 
 inch in thickness. Ladles of this tyi)e are preferable to those 
 made of thin sheet metal, first, because, being thicker, they 
 absorb and retain more heat, thereby accelerating the fusing 
 of the metal, and second, because of their greater rigidity. 
 There should be a lip or spout on the side, through which the 
 molten metal may be directed in a small stream while pouring 
 
 jrELTISG LADLES 
 
 it into the matrix. Ladles used for melting zinc should be 
 coated inside with whiting until the iron is thoroughly oxi- 
 dized, to prevent the zinc from alloying with it. The alloy 
 of zinc and iron, if it is allowed to form, is taken up by the 
 molten zinc, which is thus rendered harder, while the ladle 
 sides are gradually reduced in thickness by the constant alloy- 
 ing process, and are eventually perforated. 
 
 DIE METAL 
 
 A metal used for die purposes should possess certain 
 requisite properties. 
 
 First — It should neither expand nor contract in assuming 
 a solid state. 
 
 Second — It should fuse at a moderately low temperature. 
 
132 SWACJED MKTAL BASK DKNTURKS 
 
 Third — It should be sufficiently hard and resistant to 
 stress so that the high points and general surface markings 
 of the die will not be defaced or battered down in swaging the 
 plate. 
 
 Fourth — It should be cohesive, so as to maintain its 
 form without splitting or spreading under pressure or hammer 
 blows. 
 
 Zinc, Babbitt's metal, Melotte's metal and a variety of 
 alloys similar in composition to the latter, are used for die 
 pm-poses. 
 
 ZINC 
 
 Zinc has long been used and is still very extensively em- 
 ployed in the making of dies for dental purposes. It fuses 
 at the highest temperature and is the hardest of any of the 
 metals or alloys commonly used for dies for prosthetic pur- 
 poses. Its fusing point is about 433 deg. C. In cooling, it 
 contracts perceptibly and oftentimes warps to a marked de- 
 gree, depending on the form of the matrix in which it is 
 cast. 
 
 For years it has been known that plaster expands in 
 setting and zinc contracts in cooling. From these facts, the 
 axiom was deduced that the expansion of the plaster model 
 compensates for the contraction of the zinc die. This cer- 
 tainly would be a simple solution of the problem if the amount 
 of contraction in the die equaled the expansion of the plaster 
 model, and if the factor of warpage could be eliminated. Since 
 there is no correlation of the movements, however, the ab- 
 surdit.y of the axiom is apparent. 
 
 SHRINKAGE OF METALS IN PASSING FROM LIQUID TO 
 SOLID STATE 
 
 The following table from Kent's "Engineers' Pocket 
 Book" on the shrinkage of castings is as follows: 
 
 Cast Iron % inch per linear foot — 1 inch sectional area 
 
 Brass 3/16 " " " " " " " " 
 
 Steel % " " " " " " 
 
 Malleable Iron. % " " " " " " " " 
 
 Zinc .5/16 " " " " " " 
 
 Tin 1/12 " " " " " " 
 
 Aluminum .... 3/16 " " " " " " " " 
 
 Britannia 1/32 " " " " " " 
 
 Larger or bulkier castings shrink slightly less propor- 
 tionately, while smaller ones shrink more than the amounts 
 indicated in the table. 
 
SWAGED METAL BASE DENTURES 133 
 
 A die of zinc derived from a sand matrix 21/2 inches 
 across from one bnccal surface to the other shrinks about 
 1/16 of an inch, while a plaster model, in which the expansive 
 movement is high, expands less than 1/64 of an inch. In 
 cooling, the tendency of the metal is to rest on the dome, or 
 that portion of the matrix which gives form to the palatal 
 vault of the die, and for the borders to draw inward from the 
 sides and upward from the base of the mold. The warpage 
 thus resulting decreases the height of the palatine vault and 
 reduces the buccal diameter, in many cases, to such an extent 
 as to require the construction of a more accurate die on which 
 to finish the base. 
 
 When zinc dies are used, it is the common practice to 
 cast two, and frequently three, as a preliminary step in swag- 
 ing a denture. It also frequently occurs that a baseplate, 
 when adapted to one, will fit neither the other dies nor the 
 plaster model from which they were derived. It is then a 
 problem as to which die most nearly represents the true oral 
 contour. This can only be determined by trial of the base in 
 the mouth, after swaging on each die sei^arately. 
 
 To partially overcome the errors occurring in the use of 
 zinc, as well as other dies, the following steps are recom- 
 mended : 
 
 TREATMENT OF PLASTER MODELS TO ARREST 
 EXPANSION 
 
 First — As soon as the plaster cast from which the model 
 is to be formed has set sufficiently hard to permit, the im- 
 pression should be removed and the cast converted into model 
 form by trimming and additions, as required. The moisture 
 present sliould then be expelled by applying moderate heat. 
 Overheating tends to both warp the model and disintegrate 
 the plaster. The varnish should lie applied last, since, if ap- 
 plied before heating, it prevents the ready evaporation of the 
 moisture. Drying the model in tliis manner stops the chemical 
 action, and hence expansion in the plaster, which otherwise 
 woiild continue for twenty-four hours or more. 
 
 Second — When the sand mold is secured, the molten die 
 metal is cast into it at as low a temperature and in as thickly 
 liquid a condition as may be, and yet be plastic enough to 
 insure its becoming adapted to all portions of the matrix. In 
 other words, thorough evaporation of moisture from the 
 model, if driven off soon after the cast is constructed, lessens 
 its expansion, and filling the matrix with the die metal, poured 
 
1H4 SWAUKD METAL BASK 1>KNTUKKS 
 
 at HS low a tempei'ature as possible, reduct^s contraction and 
 lessens warpage. If cast while overheated, the metal assumes 
 a decidedlj^ crystalline strncture, is very brittle on hardening, 
 and contracts perceptibly. 
 
 Zinc dies, after cooling, may be annealed and rendered 
 much tougher and more cohesive if heated to a temperature 
 of between 100 to 150 deg. ('. If heated nnicli above 150 deg. 
 C. they again become very brittle. This process of annealing 
 is resorted to in the production of sheet zinc, the cast ingot 
 being heated as above indicated and passed through rolls 
 until reduced to the required thickness. The malleability im- 
 parted to it by annealing is retained on cooling. 
 
 BABBITT METAL 
 
 Babbitt metal is an alloy of copper, tin and antimony in 
 varying proportions. It was designed by the man whose name 
 it bears — Isaac Babbitt — as an anti-friction metal for bear- 
 ings. As commonly compounded it is too soft for die purposes, 
 but when combined in the proportions suggested by Dr. L. P. 
 Haskell, the alloy is non-shrinking, resistant to stress, nearly 
 equal to zinc as to hardness, fuses at a lower temperature, and 
 is superior in other respects. Dr. Haskell's formula is as 
 follows: 
 
 Copper 1 part 
 
 Antimony 2 parts 
 
 Tin 8 parts 
 
 This Babbitt metal fuses at 260 deg. C, casts well, and 
 copies accurately the surfaces against which it is poured, if 
 of proper fluid consistency. The antimony present, which 
 imder ordinary conditions expands in cooling, eliminates to 
 a great extent, if not altogether, any tendency of the alloy to 
 contract in passing from the fused to the solid state. A die 
 made of Babbitt metal therefore more nearly represents 
 the form and proportion of the plaster model than does one 
 made of zinc. Its comparatively low fusibility is also a de- 
 cided advantage. For these reasons, principally, the use of 
 Babbitt metal for dies is gradually increasing. 
 
 Haskell's Babbitt metal, properly compoimded, can be 
 procured of the supply houses. If it is deemed advisable to 
 make it in the laboratory, the following directions by Hall will 
 aid in producing a well-alloyed product : "Melt the copper and 
 half of the tin, then add the antimony and the remainder of 
 the tin. Stir vigorously and keep the surface of the alloy 
 covered with powdered charcoal." 
 
SWAGED METAL BASE DENTURES 135 
 
 When melted repeatedly, and especially at high temper- 
 atures, Babbitt metal deteriorates, owing to the formation 
 and retention within the alloy of some of the oxides of the 
 component metals. These oxides may be partially removed 
 and the metal restored to working condition by heating to a 
 a high temperature, adding scrap beeswax, stirring thor- 
 oughly, and skimming off the dross as it accumulates on the 
 surface. Covering the surface of the molten metal with fine 
 charcoal and stirring well also removes soiue of the oxides 
 present. 
 
 Dr. Haskell recommends the addition from time to time 
 of a little tin for restoring the fluidity of the alloy, since by 
 repeated fusing some of the latter metal is lost by oxidation 
 and volatilization. 
 
 As previously intimated, all die metals and alloys, if over- 
 heated, deteriorate rapidly. Care should therefore be observed 
 to remove the metal from the fire before the entire mass is in 
 a molten condition. The heat absorl^ed by the already melted 
 metal is usually sufficient to melt one-fourth, and frequently 
 one-half, its Imlk of the still unfused portion after removal 
 from the fire. This plan obviates overheating, and consequent 
 excessive oxidation. It also insures smoother castings, since 
 the metal being poured at low temperature generates less gas 
 or steam on coming in contact with the sand matrix, than when 
 overheated. 
 
 MELOTTE'S METAL AND OTHER FUSIBLE ALLOYS 
 
 A class of metallic compounds known as fusible alloys or 
 triple alloys are much used for die purposes in crown and 
 bridge construction, and occasionally as dies for dentures. 
 These alloys are not as hard as zinc or Babbitt metal, but on 
 account of their low fusiliility and the sharpness of castings 
 produced, the.v are very serviceable and much used. 
 
 The triple alloys contain three metals, usually tin, lead 
 and bismuth, in varying proportions. Bismuth has the prop- 
 erty of expanding, imparting hardness, and reducing the fus- 
 ing point of the alloy considerably below the mean fusing 
 point of the three metals, which is 272 deg. C. When alloyed, 
 the metals melt at about 100 deg. C. 
 
 Another class of alloys similar in character to the triple 
 alloys, but composed usually of four metals, are also in com- 
 mon use. These, in addition to the metals mentioned, contain 
 antimony or cadmii>m, both of which, like bismuth, have the 
 property of reducing the fusing point of the alloy of which 
 
13« SWAGED METAL BASE DENTURES 
 
 they are a part. They also expand in cooling, and when in- 
 corporated, impart this property to alloys, resulting in the 
 production of sliarj) castings. The low fusibility of this type 
 of compounds jiermits of their being poured into fresh plaster 
 impressions direct, without the necessity for drying out the 
 latter. Such castings as a rule are very shai'p, well defined, 
 and of reasonable hardness. 
 
 COMPOSITION OF FUSIBLE ALLOYS 
 
 Melting 
 
 Name. Tin. Lead. Bismuth. Antimony. Cadmium. Point. 
 
 Melotte's 5 3 8 lOO'C. 
 
 Newton's 3 5 8 95°C. 
 
 D'Arcet's 1 1 2 93°C. 
 
 Dalton's 3 .5 lOVa 92°C. 
 
 Onion's 2 3 5 92°C. 
 
 Rose's 3 8 8 79°C. 
 
 Wood's 1 2 4 1 71°C. 
 
 CUnch6 48 32,.5 9 IOV2 
 
 Richmond's 20 19 < 48 13 65.5°C. 
 
 Hodgen's 3 5 8 2 106.6°C. 
 
 The fusible alloys, being hard and more or less crystalline, 
 lack the coliesiveness of zinc or Babbitt's metal. Dies for 
 full dentures, composed of such alloys, should, tlierefore, be 
 made sufficiently thick to ])revent fracturing under hammer 
 blows. When used under hydraulic or screw ])res.sure, a die 
 of moderate thickness will resist stress without change, if its 
 base and that surface of the iiress on which it rests are fiat. 
 
 COUNTERDIE METAL 
 
 A counterdie should be composed of a softer metal than 
 the die of which it is the complement. This is essential for 
 three reasons : 
 
 First — If the die and counterdie were of e(iual hardness, 
 both must yield in swaging, the die becoming slightly smaller 
 and the counterdie slightly larger, in order to make room for 
 the interposed plate. Such change in the die and its conse- 
 quent effect on the baseplate would impair, if not altogether 
 destroy, the adaptation of the latter to the oral tissues. 
 
 Second — The tendencies of a die and counterdie of equal 
 hardness to shear, or at least reduce in thickness, the plate 
 being swaged over o])posite parallel surfaces, as on the buccal 
 surfaces of prominent tuberosities, is very marked. This 
 tendency is not apparent when the counterdie is composed of 
 a softer metal than the die. 
 
 Third — A somewhat yielding counterdie opposed to an 
 unyielding die carries the plate into the inequalities of the 
 
SWAGED METAL BASE DENTURES 137 
 
 die, with its irregularly disposed surfaces, better than if the 
 two were of equal hardness. 
 
 A eouuterdie is usually made by pouring molten metal 
 over the face of a die. To prevent fusion of the face of the 
 die, and consequent union of the two masses of metal while 
 casting, the counterdie metal should, as a rule, melt at a lower 
 temperature than that of the die; the die should be cold, and 
 the counterdie metal should be poured at as low a temperature 
 as possible. 
 
 When melted, the casting of the counterdie metal should 
 be deferred until it begins to thicken around the sides of the 
 ladle, when it may be cast against the face of the die in a 
 semi-liquid condition. 
 
 Lead is used for counterdies with zinc dies, the difference 
 in the fusing points of the two metals being 124 deg. C. An 
 alloy of 7 parts lead and 1 part tin is used for counterdies 
 with Babbitt metal dies, the difference in the fusing points of 
 the alloys being about 50 deg. C. 
 
 Both die and counterdie can be made from the same alloy 
 in the bismntii compounds, the only precautions necessary to 
 observe to prevent union being to have the die cold, and to 
 allow the metal for the counterdie to assume a pasty condition 
 before casting. A square-end tamper pressed against the 
 plastic mass immediately after casting will force it against 
 the face of the die. and insure close adaptation of the former 
 to the latter. 
 
 Usually, however, tiie fusible alloys are used in con- 
 junction with some swaging device or press. In such cases, 
 only the die or the counterdie is formed of the fiisible alloy, 
 the plate to be swaged being adapted between the metallic 
 form on one side, and some yielding material on the opposite 
 side, such as soft rubber, moldine, damp tissue paper, or 
 modeling compound. Si;ch methods, however, are only 
 adapted to the swaging of the purer and thinner forms of 
 gold plate, or of pure platinum. 
 
 WHITING AND ALCOHOL SOLUTION 
 
 A solution of whiting (preciintatcd chalk) and alcohol is 
 essential for coatifig the surface of a die previous to casting 
 the counterdie." A solution of whiting in water will fulfiill 
 the same purpose, but alcohol is much better, as this solution, 
 when applied, dries immediately, while the aqueous solution 
 does not. A little gum arabic added to the solution will im- 
 part adhesiveness to the film when applied, and dry and pre- 
 
l.'iS SWAGED MKTAL BASE DENTURES 
 
 veut exposure of the juetal surfaces by tlie Tul)biug off of the 
 film, should anything come in contact with the die face. Car- 
 bonizing the die is also recommended, Imt the process, although 
 effective, is a filthy one and soils the hands imnecessarily. 
 
 BRUSHES 
 
 A medium-sized sable or soft bristle brush is very useful 
 for removing soa]istone or sand from the model, and for 
 cleaning up the outer surfaces of the matrix generally before 
 removing the model. 
 
CHAPTER XI 
 
 TECHNIC OF DIE AND COUNTER DIE 
 CONSTRUCTION 
 
 FORMING THE SAND MATRIX 
 
 The table or laboratory beiieli should be covered with a 
 large sheet of clean paper, to assist in recovering the sand 
 after the die is cast. 
 
 The model, having been prepared as previously de- 
 scribed, is placed on the paper face up, the largest molding 
 flask of the iiest of four placed over it, the large ead 
 down, and so adjusted that the model will occupy a central 
 position within. 
 
140 TECHNIC OF DIB AND COUNTER DIE CONSTRUCTION 
 
 Sifted sand is now filled in the molding- flask until even 
 with the face of the model, and packed into the space between 
 the latter and the flask periphery. The pressure on the sand 
 should be light at first, so as not to move the model from its 
 central position. As soon as the model is firmly fixed in 
 place, the sand should be still further compressed, until firm 
 and compact, special stress l)eing exerted to force it outward 
 against the flask walls. More sand is added, and with the 
 fingers pressed compactly against the flask walls imtil the 
 packed portion stands slightly above the crest of the model. 
 The sand in the vault or central portion of the model, which 
 is not yet compressed, should cover this area at this stage to 
 a depth of about one-half an inch. 
 
 Careful, uniform pressure with the fingers should be 
 made on the sand over the central area of the model, sufficient 
 
 SKCTIONAI- VIEW ()]'' CAST AND MdT.DIXG RING 
 
 to bring the granules in fairly close contact, without render- 
 ing the surface too dense or compact, or wedging the sand 
 too tightly between the lingually inclined walls of the model. 
 If too loosel}^ packed, the sand will lack cohesion and be dis- 
 turbed in pouring the molten metal into the matrix. If too 
 densely compressed, the gases or steam generated by the hot 
 metal coming in contact with the moisture or oil in the sand 
 cannot escape through the densely packed matrix as rapidly 
 as formed. It then finds its way out lietween the matrix walls 
 and the die, or forms vent holes through the die itself, in 
 either case causing roughness and imperfections of the latter. 
 
 When the sand is wedged too tightly in the vault portion 
 of the model, it frequently fractures and parts from the matrix 
 when the model is withdrawn. 
 
 The remaining space in the flask is filled and compressed 
 until the sand stands above the margin. The straight edge 
 is now passed over the top of the flask and the surplus sand 
 struck off. The flask is inverted and that surface from which 
 
TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 141 
 
 the excess sand was struck now becomes the base of the 
 matrix. 
 
 The surface of the packed tiask pointing upwards shows 
 the base of the model surrounded by the sand. A thin 
 V-shaped section l)eginning at the flask periphery and ex- 
 tending to that of the model is sliced oft" with the knife, so 
 as to expose the angle of the model base, and thus clear it 
 from the matrix margins. By lifting and tipping the flask, 
 the detached sand will fall off. The finer particles can lie 
 
 nEMO\IXG EXCKSS OF SAND FKOM PACKED RINf! 
 
 removed with the lirush, and by gently blowing them from the 
 surface. 
 
 REMOVAL OF THE MODEL FROM THE MATRIX 
 
 When iiroperly flared, dried, varnished and rubbed witli 
 talcum powder, the model can usually be removed from the 
 matrix without difiSculty. Unfavorable conditions, principally 
 due to some peculiar form of the model itself, are sometimes 
 present. In such cases, the exercise of extreme care is neces- 
 sary to avoid distortion of the essential surfaces of the matrix 
 in removing the model. The adhesion of the sand to the 
 surfaces of the model, as the result of compression in pack- 
 
Ha TECHNIC OK DUO AND COUNTER DIE CONSTRUCTION 
 
 ing, must be overcome or broken, when, it' no undercuts are 
 present, the model will come away readily. 
 
 The following is the usual order of removal of the model 
 from the matrix, ranging from the simi^lest metliods to those 
 requiring careful attention : 
 
 1. Gravity — Weight of model si;fficient to dislodge it. 
 
 2. Vibration — Tapping the side of tlie flask. 
 
 HEMOVINC Till> 
 
 3. Removal of model by rotation. 
 
 4. Tapping base of model to break sand adhesion and 
 rotating. 
 
 5. Prying to break adhesion and rotating. 
 
 6. Tapping and lifting outward. 
 
 7. Removal of models with undercuts — cores. 
 
 8. Removal of models with undercuts overcome with 
 Hawes flask. 
 
TECHNIC OF DIE AND COUNTER DIE CONSTRUCTIOX 143 
 REMOVAL OF THE MODEL IN LIFTING THE FLASK 
 
 When the form of tlie model is correct, the condition of 
 the sand suitable, and the packing of the flask is of the proper 
 density, the model will occasionally drop from the matrix in 
 lifting tlie flask to invert it. This, however, occurs more often 
 when tlie sand has been but loosely packed in the flask, or when 
 tlie sides of the model are excessivelv flared. It niav occur. 
 
 r.i!i;.\KiN(; ai'hesiox hktwf.kx sand axd MonEi> v.\ TAri'iNo base of latteh 
 
 as before stated, under proper conditions. When the model 
 drops out by its own weight, a close inspection of the matrix 
 should be made to see that its several surfaces are smooth 
 and the sand sufficiently compact to insure smooth surfaces to 
 the die when cast. 
 
 TAPPING THE MODEL BASE TO BREAK ADHESION 
 
 A few light taps on the base of the model, near the center, 
 with a small hammer or light instrument, will usually l)reak 
 
144 TECHNIC OF DIB AND COUNTER DIE CONSTIUICTION 
 
 the adhesion of the «aud to tlie several surfaces. The tapping 
 should not be sufficiently heavy to produce perceptible move- 
 ment of the model in the matrix. Heavy or unequal tapping 
 is liable to distort the sand and result in an imperfect matrix. 
 By rotating the flask as before described, the model can usually 
 be dislodged. 
 
 REMOVAL OF THE MODEL BY ROTATION 
 
 The flask is lifted from the bench, the base resting in the 
 palm of tlie hand, tlie tlmmb against tlie flat side, when, with a 
 
 ROTATING MODEI-. OUT OF POSITION 
 
 quick pronatiiJg nlo^■emont, the model may be rotated outward. 
 If it is not dislodged in this manner, the flask should be set 
 on a clear surface of the bench, so that the sand base may be 
 lirmh' supported over its entire area. 
 
 REMOVAL OF THE MODEL BY VIBRATION 
 
 A simple method of removal, frequently successful, con- 
 sists in inverting the flask and tapping the sides lightly with 
 a small instrument. The vibration thus produced will often 
 be sufficient to dislodge the model. Vibration produced in 
 
TECHNIC OF DIB AND COUNTER DIE CONSTRUCTION 145 
 
 this manner may also be applied in difficult cases after other 
 means have been resorted to, for breaking the adhesion be- 
 tween sand and model. 
 
 BREAKING ADHESION BY PRYING THE MODEL 
 
 If the preceding steps fail to break the adhesion of the 
 sand and free the model, it can be overcome by inserting the 
 point of a knife against the back of the model, the blade rest- 
 ing on the flask margin, which will serve as a fiilcrnm, and 
 with a slight prying movement lift the back of the model the 
 least perceptible amount. Rotation of the flask should again 
 be made, when the model will readily come away. 
 
 REMOVAL OF THE MODEL BY GRAVITY 
 
 Occasionally, wlien the vault portion of the model is deep 
 and the labial, buccal and lingual surfaces of the border at 
 various jjoints, particularly in the anterior portion, are nearly 
 parallel with each other, it may not be possible to rotate the 
 model out, as described, without distorting the matrix. In 
 other words, the relationship of the several surfaces men- 
 tioned, to each other, requires that the model be removed in a 
 line of direction approximately parallel to these surfaces, in- 
 stead of attempting to rotate it out. Removal in such cases 
 may be accomplished in two ways : 
 
 First — Tap the model base to break adhesion. Invert the 
 flask, maintaining the model in position with finger pressure 
 while doing so; place the inverted flask over the edge of the 
 bench, holding it flat and moving forward until the model is 
 well supi>orted before releasing finger pressure, until finally 
 the entire flask base rests on the bench ; lift the flask, and if the 
 model is still retained in the matrix, with a small instrument 
 tap the outer side of the flask lightly. The vibration thus 
 produced is usually sufficient to dislodge the model. 
 
 Second — Should the preceding steps fail to free the model 
 from the matrix, it may be removed by direct traction. The 
 projection of the model margins above the sand is so slight 
 that it cannot be accurately and carefull.y lifted from the mat- 
 rix by grasping- its periphery. So other means for grasping- 
 it must be provided. A small hole may be drilled in the center 
 of the base, into which a taper instrument can be driven to 
 serve as a handle, or two grooves may be cut on either side of 
 the center, about one-fourth of an inch apart. The sides of 
 the intervening section of plaster should be parallel to each 
 
14« TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 
 
 other, thus affording means for grasping the base of llic model 
 centrally with a pair of tweezers. 
 
 While this method of removal is positive and can be 
 applied to any model without undercuts, unless care is ob- 
 served the matrix mav be marred. To avoid error, the instru- 
 
 RELEASINC iMODEI. I'.Y TArTIXG SIDE OF PM.ASK 
 
 ment or tweezers must not be gras^jed too rigidly, while the 
 line of traction must coincide with and be approximately par- 
 allel to the several surfaces to be released. Holders follow a 
 similar method in removing patterns from the sand. To break 
 adliesion and free the pattern, they usually tap the instriunent 
 which serves as a handle, sideways in various directions, 
 while traction is at the same time applied for the removal of 
 the pattern. 
 
 In prosthetic j^rocedures, the instrument which serves 
 as a handle in removing the model should not be tapped lat- 
 erally, as the tendency would be to enlarge the matrix 
 
 With a properly flared model having no undercuts, and 
 the sand packed to proper density, the prj-ing or lifting 
 
TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 147 
 
 process for breaking the adhesion of the sand and dislodging 
 the model, need seldom be resorted to. It shonld be borne in 
 mind that the least possible manipulation of the model in 
 effecting its removal will yield the most accurate matrix. 
 
 NECESSITY FOR THE USE OF CORES 
 
 Models having undercuts cannot be removed from the 
 sand without distorting the matrix, unless means are taken to 
 overcome the difficultv. The usual method resorted to is bv 
 
 MFTINU MDIiEl. H(OM 
 
 means of cores, the construction of which has been previously 
 described. 
 
 A model having a core addition to its outer surface 
 usuallj' presents an unsymmeti'ical peripheral outline. In 
 placing the molding flask over such a model, the former should 
 
148 TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 
 
 be SO adjusted that the model will occupy a central position, 
 regardless of the form or position of the core. 
 
 Sand is packed around and over tlie model and core, 
 care being taken to wedge the latter firmly against the model 
 in the condensing process. Removal of the model and core 
 from the matrix is effected by some of the methods described, 
 usually by tapping and rotation. 
 
 After removal, the core is separated from the model, 
 dried, and returned to its position in the matrix, where its 
 inner surface completes the matrix wall and reproduces the 
 reverse form of the undercut surface of the model. 
 
 Sufficient pressure should be made on the core in seating- 
 it in the matrix to wedge it slightly in the sand, so as to 
 
 THE HAW I' 
 
 prevent displacement, since, if not firmly attached, the molten 
 metal, when introduced, on account of its greater specific 
 gravity, will raise the core out of its position. 
 
 CONSTRUCTION OF THE MATRIX IN THE HAWE'S 
 FLASK 
 
 An accurate sand matrix may be secured from a model 
 having external undercut areas, without the use of cores, by 
 means of the Hawe's Molding Flask. 
 
 This appliance is cylindrical in form, five inches in di- 
 ameter and three inches deep. It is divided into an upper and 
 a lower section, held in proper relation by means of guide 
 pins. The lower half consists of three sections hinged to open 
 outward. Each section has a flange at either end, directed 
 radially inward. When pinned together, the end flange of 
 each section approximates the flange of the adjoining section, 
 thus dividing the interior space of the flask into three partial 
 sectors. 
 
 The model is placed between the three flanges of the lower 
 section, its median line opposite one and its tuberosities op- 
 posite the two other points, respectively. The crest of the 
 border should rise slightly above the level of the ring. 
 
TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 149 
 
 Sand is packed around the outer sides, into and above all 
 undercut surfaces of the border, but not over the face of the 
 model. Particular care should be taken to condense the sand 
 firmly in each sector of the flask and against the model, so 
 
 LOWER SECTION' OP HAWE'S EI.ASK SHOWINYi MOPET. IX I'OSITION 
 
 FIKST SECTION WITH SAND PACKED AROUND 5I0DEL 
 
 that it will not- be displaced in the subsequent steps of free- 
 ing the model. 
 
 Powdered charcoal is sifted over the packed sand and 
 model face to prevent adhesion of the sand now to be added, 
 the surplus blown off, the second section of the ring adjusted. 
 In this the sand is packed and the surplus struck off in the 
 
160 TKCHNIC OF DIK AND COUNTER UlE CONSTRUCTION 
 
 usual manner. The upper half of the flask is now lifted off, 
 inverted, and set aside so as not to disturb the sand surface 
 which has copied the model face. 
 
 SKCOXIl SHCTIUX OK KI.ASK SET I.N I'OSITI 
 
 SECOND SECTION r. 
 
 The model is removed by drawing the pin from one 
 of the disto-buccal flange joints and carefully opening the 
 ring. As the sectors separate, the sand between the flange 
 ends and the model breaks with a clean fracture, and, on ac- 
 
TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 151 
 
 count of the flask form, the matrix is thus divided into three 
 sections. The model is drawn out through the open side of 
 
 Li'l'EIt Sm'TIlIN 1U;M(I\EIi. l.dWKU SECTION SEI'ARATKl), KOI! RELEASE OK MODEL 
 
 the ring. When tlie model is removed and the flask sections 
 are brought together again, the fractured surfaces of sand 
 are again readapted to each other as before, and form the con- 
 tinuous outer wall of the matrix. 
 
 MODEL REMOVED. SECTIONAL PART OF FLASN CLliSED 
 
 Special care should be taken to remove any sand that 
 mav have become lodged between the flask joints and flanges. 
 
152 TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 
 
 for if allowed to remain, the sections cannot be closed pi'op- 
 erly. 
 
 The pin removed in opening the flask is now slipped into 
 its joint, and the inverted top half of the flask is lifted and 
 oarefnlly set in place on the sectional portion, the projecting 
 pins guiding it to position. The entire flask is turned over, 
 and if the ste])s have been properly carried out, the matrix 
 will be found to be satisfactory. 
 
 Should a margin of sand along any of the sectional lines 
 be broken lightly, it will seldom be found necessary to at- 
 tempt restoration of the matrix, as the metal which will fill 
 the opening can easily be removed from the die when cast. 
 
 UI'I'EK HALF IIF FLASK SET AND CASK INAESTED FOR RECEI'TIOX OF THE METAL 
 
 The utility of this special flask, both for accuracy of re- 
 sults and the saving of time, is keenly appreciated by those 
 who have used it. Unfortunately, its good points are unknown 
 to many, and the core method, although less accurate and re- 
 quiring longer time, is most frequently resorted to in cases 
 of external undercut models. 
 
 EXAMINATION OF THE MATRIX 
 
 When, by whatever method, the sand matrix is formed, 
 it should be closely examined to see that none of the essential 
 surfaces have been disturbed; to see that the sand is suffi- 
 ciently compact to insure smooth surfaces to the die when 
 cast, and before pouring the molten metal, to see that no 
 loose sand is present. 
 
TKCHNIC OF DIE AND COUNTER DIE CONSTRUCTION 153 
 
 FORMING THE DIE 
 MELTING THE DIE METAL 
 
 A satisfactory saud mold or matrix liaving been secured 
 from the model, it is ready to receive the molten die metal. 
 To conserve time, the ladle containing the latter is usually 
 placed on the fire before making the matrix, since the pro- 
 duction of the latter usually requires less time than is con- 
 sumed in fusing the metal. The progress of fusion should be 
 noted, however, and when about three-fourths melted, the 
 ladle should be removed from the fire. The excess of heat 
 absorbed by the metal up to this point is usually sufficient to 
 
 COMPLETED MATIilX IX SAND 
 
 effect the fusion of the unmelted portion after removal from 
 the fire. This plan also lowers the temperature of the mass 
 to somewhere near the proper degree for casting. 
 
 A thin spatula of soft wood should be used for stirring 
 the metal and removing the oxides and impurities. If the wood 
 burns or chars, it indicates that the metal is too hot to cast. 
 The lower the temperature at which the metal can be intro- 
 duced into the matrix and yet be sufficiently fluid to conform 
 accurately to all irregularities, the less shrinkage of the die 
 will occur. Also a less quantity of gas or steam will be gen- 
 erated in the matrix, and as a result a smoother die will be 
 produced. 
 
 CASTING THE DIE 
 
 When the metal is melted, the oxides removed, and the 
 proper degree of fluidity attained, the ladle is carried to one 
 
154 TECHNIC OK UIB AND COUNTER DIE CONSTRUCTION 
 
 of the disto-bnecal angles of the flask, and as close to the 
 sand as possible without disturbing the latter by contact of 
 the ladle lip. 
 
 The object in bringing the ladle close to the matrix is 
 to prevent displacement of the sand which occurs when, in 
 pouring, the metal falls from a considerable distance upon it. 
 
 Through the ladle spout a small stream of metal is di- 
 rected into the back of the mold and the entire matrix is 
 filled in this manner, even with the sand margins. The ladle 
 
 should be returned to the tire immediately in order to keep 
 the remainder of the metal in a molten condition while ad- 
 justing the ring for increasing the depth of the die with addi- 
 tional metal. A flask ring, usually the smallest of the set. 
 the periphery of which should be slightly greater than that of 
 the matrix margin, is i^laced, large end down, and pressed 
 slightly into the sand. Some sand should be quickly packed 
 around its outer base to prevent the escape of the metal now 
 to be added to the die. 
 
TECHNIC OF DIK ANU COUNTER DIE CONSTKUCTJON 155 
 
 Tlif ladle (iontainin^ tlie reuiaimler of tlie molten metal 
 is brought close to the edge of the small ring jiist placed 
 and a sufficient amount of metal added to tliat first cast to 
 give the die a depth of about 2 inches in its central part. 
 This step can and should be carried out so rapidly tlmt miion 
 between the first and second casts of metal will be effected 
 and a solid one-piece die result. 
 
 When hardened, the die is removed b>' tipping the flask 
 rings over and tai)]nug to free the i)acked sand from the 
 interior, while that on the outer surface of the die is scraped 
 and brushed awav. Tlie die and flasks are usuallv cooled im- 
 
 SECTIOXAL VIEW OF SMALL RING ADJUSTED TO SAND MATRIX 
 
 mediately in water and wiped dry, preparatory to casting the 
 counterdie. The die, however, will be more tenacious and less 
 inclined to crack under the hammer blows if allowed to cool 
 slowly. 
 
 INSPECTION AND CORRECTION OF THE DIE 
 
 Any projecting imperfection on the die due to holes in the 
 sand matrix should be removed with scrapers, chisels or burs, 
 if necessarj', and tlie surfaces, where such defects exist, made 
 to correspond with those of the model. Any serious defects 
 in the die, when cast, either as accretions, holes or pits are 
 liable to result in imperfect adaptation of the plate when 
 swaged. 8uch a die should be discarded and a perfect one 
 secured. 
 
156 TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 
 
 r.AII.EV FLASK 
 
 DIE AND COUNTERDIE PHODUCED LX BAILEY FLASK 
 
TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 157 
 
 DIE AXD ( iHNTEIililB SEPARATED 
 
 LEWIS FLASIC 
 
ir>S TKCHNK' OK DUO AND COHNTKK DUO CONSTRUCTION 
 
 DIE AN"I> I'dr.NTKltDIK I'lKllHrKU IN I.KU IS l-I.ASK 
 
 DIE AND f'OTINTERDIE SEPABATEH 
 
TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 159 
 
 CONSTRUCTION OF THE COUNTERDIE 
 PREPARATORY STEPS 
 
 The large flask iu which the matrix for the die was formed 
 is now inverted or placed small end down on the hench and 
 partially filled with sand. In this the die is set and evenly 
 centered to the ring. The depth of sand under the die base 
 should be sufficient to raise the entire labial and buccal sur- 
 faces of the die border slightly above the upper margin of 
 the flask. 
 
 Tlie space between the flask walls and the die is now 
 filled in with sand which should be firmly condensed and 
 finished off evenly with the top margin of the flask, the 
 inner margin of the sand terminating against the peripheral 
 plate line on the die. This leaves only the essential surfaces 
 of the die ^asible and standing above the general level of 
 the sand and flask margin. 
 
 The exposed surfaces of the die are now carefully brushed 
 to remove any adhering sand. In case of decided undercuts, 
 sand is tightly packed into them at this time so as to preclude 
 the counterdie metal, when cast, from entering such areas 
 and later preventing the ready separation of the die and 
 counterdie. Subsequently, when swaging, this defect of the 
 counterdie is overcome by placing strips of lead or tin against 
 the plate opposite the deficient area, the strips being of suf- 
 ficient thickness to make up for the lack of contour in the 
 counterdie. 
 
 The die is now coated with a solution of whiting and al- 
 cohol, to which a little gum Arabic is added to render it ad- 
 hesive after the alcoliol evaporates. The film of whiting 
 practically obviates the tendency of the counterdie metal to 
 imite with the die in casting. 
 
 A flask ring, corresponding in size with the one in which 
 the die is imbedded, is adjusted peripherally to the latter, 
 large end down, to form the matrix in which to cast the 
 counterdie. A smaller ring, however, may be used for form- 
 ing the matrix walls for the counterdie, when the die is of 
 medium or small" size. Such a ring reduces the counterdie 
 peripherally and adds to convenience in handling. Wlien 
 the small ring is used, it is set on the sand surrounding the 
 die and its lower margin l)anked up with sand to prevent 
 the escape of the molten metal while casting. 
 
160 TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 
 MELTING THE COUNTERDIE METAL 
 
 The fusing of the counterdie metal is accomplished in 
 essentially the same manner as is employed for the die 
 metal. It should be removed from the fire before the entire 
 mass is melted and stirred to lower the temperature and col- 
 lect the oxides and impurities present. These should be 
 skimmed off and the stirring continued until the metal be- 
 gins to assume a pasty condition. 
 
 The object in allowing the metal to cool somewhat and 
 thicken slightly before casting, is to avoid danger of fusion 
 of the die and its consequent union with the counterdie, a mis- 
 
 hap which frequently occurs when the latter metal is cast 
 while overheated. 
 
 CASTING THE COUNTERDIE 
 
 When the metal begins to congeal around the ladle, it is 
 quickl}^ emptied into the ring and over the face of the die. 
 Should the metal be in such a thickly plastic state that it fails 
 to assume a level position in the ring when cast, it should be 
 pressed down, while yet soft, with a square-end tamper, to 
 give a flat base to the counterdie. 
 
 As a matter of fact, the counterdie metal can be cast 
 while in a liquid condition if proper precautions are taken, 
 
TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 161 
 
 viz: the die must be cold, its exposed surfaces coated with 
 whiting, the metal allowed to cool to about the point of con- 
 gealing, or so that it will not char soft wood, and in easting, 
 directing the stream of metal on the sand surrounding the die, 
 and not on the die face. 
 
 When poured in a liquid condition, the metal should be 
 cast slowly. In this manner it rises gradually up over the 
 surfaces of the die, and at the same time, from exposure to 
 the air and through contact with the cold die, sand, and 
 ring, the metal, if at or slightly above the point of fusion, is 
 reduced in temperature so that union of the two will not 
 occur. 
 
 CONSTRUCTION OF THE COUNTERDIE BY DIPPING 
 
 A method sometimes followed for securing a counterdie 
 consists in pouring the metal into a ring of suitable size and 
 immersing the face of the chilled die in it the necessary depth 
 to cover the surfaces involved by the base plate. The die is 
 held with the fingers or a pair of tongs until the counterdie 
 metal has hardened sufficiently to sustain its weight. 
 
 THICKNESS OF THE COUNTERDIE 
 
 In the swaging process the die and plate are driven more 
 or less deeply into the counterdie, the latter yielding under 
 the hammer blows. To prevent the defacement of the prom- 
 inent points on the die, the counterdie should have a depth of 
 at least one-half inch in its shallowest part, or that portion 
 between the high points of the die face and the base of the 
 counterdie, which rests on the anvil. A good die may be 
 readily distorted when the counterdie is too shallow and 
 much stress is applied in swaging. 
 
 SEPARATION OF THE DIE AND COUNTERDIE 
 
 When the counterdie metal has solidified, the rings are 
 tipped over and disengaged, the sand brushed off, and the 
 die and counterdie chilled in cold water. 
 
 The two are loosened by placing on the swaging block 
 and striking the die base sharplv with the hammer, when they 
 may readily be separated. If this procedure fails to break 
 adhesion between the two, the die should be struck sideways 
 in various directions. Should this effort prove futile, the 
 source of adhesion will be the result of mechanical anchor- 
 age, due to undercut surfaces on the die into which the coun- 
 
162 TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 
 
 terdie metal has flowed in easting, or to fusion of the two 
 masses of metal at some point. If due to undercuts on the 
 die, properly directed hammer blows against its sides will 
 enlarge 'the eounterdie sufficiently to release the die. Ad- 
 hesion from this source is the result of carelessness, and will 
 not occur if the undercut surfaces of the die are corrected 
 with sand before casting the coimterdie. 
 
 When adhesion is di;e to fusion and luiion of the two 
 masses of metal, the die and eounterdie are separated by 
 hammering, prying, wedging or chiseling, as is found most 
 convenient. Such means result in the defacement of both 
 die and eounterdie and usually necessitates the reconstruction 
 of each. 
 
 Special care should be exercised in such cases where 
 fusion of the two occurs, to entirely remove and cast aside 
 that portion of the die and eounterdie that have become 
 united, before melting either one. 
 
 If the alloy thus formed is allowed to remain adherent 
 to the die metal, the harness and fusibility of the latter, if 
 used again, will be reduced, and if with the eounterdie, it will 
 render that alloy harder and higher fusing. 
 
 PARTIAL COUNTERDIES 
 
 A method of using several eounterdies of gradually in- 
 creasing area has been in vogue for many years. The object 
 in using these progressive eounterdies is to insure the close 
 and uniform adaptation of the base plate to the central vault 
 portion first, before the labial and buccal surfaces have been 
 lapped over and conformed to the border. 
 
 Such eounterdies are very efTeetive in those cases where 
 the arch is narrow and the palatine vault is deep, as by their 
 use the tearing of the plate is obviated. 
 
 Usually in this method, three eounterdies are required; 
 the first covering the palatine vault and terminating some- 
 what inside of the border crest ; the second should cover the 
 vault and extend somewhat outside of the border crest; the 
 third consists of a eounterdie of the regular form, made in 
 the manner previously described. 
 
 CONSTRUCTION OF PARTIAL COUNTERDIES 
 
 To construct a partial eounterdie, the die is set, base 
 down, on the table, a large molding flask set evenly over it 
 and sand packed around it and even with the top of the flask, 
 
TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION l«:j 
 
 leaving the central portion of the die exposed. With a suit- 
 able instrument the sand is cleared away so as to make a 
 slightly flaring matrix in the sand, the floor of which con- 
 sists of that portion of the die to be covered by the partial 
 counterdie. The exposed face of the die is coated with whit- 
 ing and the partial counterdie cast in the matrix in the ordi- 
 nary manner. 
 
 Partial counterdies should be of sufficient depth or ex- 
 tend far enough above the die, when in position, to enable 
 them to be grasped firmly with the fingers and thumb while 
 swaging. The metal used for partial counterdies may be of 
 lead, the regular counterdie metal of lead and tin, or com- 
 posed of one of the triple alloys, such as Melottes metal. 
 
 MATRIX COUNTERDIES 
 
 A^arious substances, such as soap, clay, modeling com- 
 pound, shot, etc., as previously mentioned, may be used in- 
 stead of the ordinary cast coimterdie, when the material is 
 confined a suitable receptacle, or matrix. 
 
 The Parker shot s wager is one type of appliance used 
 for such purpose. This device, however, is intended more 
 particularly for seciiring the final adaptation of a base plate 
 to the die or plaster model itself, if such step is deemed ad- 
 visable. 
 
 The device in which the other materials mentioned are 
 used consists of a heavy cast iron base, in the center of which 
 is a deep recess corresponding peripherally with the inner 
 walls of the small casting ring used for increasing the depth 
 of the die. The soap or other material is placed in the re- 
 cess and covered with a sheet of soft, pliable leather, to pre- 
 vent adhesion of the swaging material to tlie plate. 
 
 When the adaptation of the plate has been fairly de- 
 veloped with the horn mallet, it is placed on the die and the 
 latter introduced into the recess. 
 
 Since the periphery of the die coincides with and closely 
 fits the opening in the ring, escape of the plastic material is 
 prevented. Under hammer blows or screw power, the force 
 tlius delivered distributes the material and equalizes the pres- 
 sure so as to drive the plate into all inequalities and against 
 all surface of the die. 
 
 This device obviates tlie making of counterdies in many 
 instances, since it is applical)le to the swaging of base plates 
 of almost any form when the dies are properlj' constructed. 
 
Ui-! TKCHNIC OF DUO AND COUNTKIt Dll!: CONSTRUCTION 
 
 The leatlu'i- should ))e vciuovcd, (he plastic material built 
 liigli in the center, and the leather again returned to place, for 
 each new case swaged. This step is necessary to insure pal- 
 atine adaptation of the ])late liefore the pressure is brought 
 on the buccal surfaces. 
 
 TOP OP PAHKEU SHOT SWAGBR 
 
 The method here outlined is especially useful in the 
 swaging of aluminum base plates. On account of its stiffness 
 and elasticity, 18K gold cannot be readily adapted by this 
 means. The device, however, as a time saver, is a valuable 
 adjunct to tlie laboratory e(|uipment. 
 
 S34 I'eiiii ^\^ 
 
 BASE OF PARKER SHOT SWAGER 
 
 COUNTERDIES FOR PARTIAL CASES 
 
 In constructing counterdies for partial dentures, the 
 die is imbedded in the sand, so as to leave exposed the area 
 to be covered by the baseplate, the surfaces of the teeth re- 
 moved by cutting and possibly a slight amount of the labial 
 
TECHNIC OF DIE AND COUNTER DIE CONSTRUCTION 165 
 
 and buccal surfaces of the die to ouide and liold it iu position 
 in the couuterdie while swaging. 
 
 Nothing is gained by having tlio die deeply depressed in 
 
 the counterdie. In fact, such a condition is a disadvantage, 
 rendering the removal of the plate more difficult, as from time 
 to time it is taken out for inspection and trimming. 
 
C TT A P T K R X I T 
 
 CONSTRUCTION OF SWAGED DENTURE BASES 
 OF GOLD 
 
 SECURING PATTERN FOR THE GOLD PLATE 
 
 Suitable dies and counter dies having been constructed, 
 the next step is to secure a pattern for cutting the gold plate. 
 By the use of a pattern two important objects are attained, 
 viz.: 
 
 First. Unnecessary loss of gold will be obviated. The 
 trimmings and tilings that accumulate in adapting a gold plate 
 to a die are classed as "scrap," which must either be refined 
 before using again, or be returned to the refiners at a loss of 
 about 1-5 the original cost. When care is taken in keeping the 
 scraps assorted and free from solder, filings and impurities, 
 they can be remelted, rolled into plate, and used again without 
 loss. 
 
 Second. A piece of gold, cut to the required outline of 
 the denture, is more easily adapted to the die than an exces- 
 sively large piece. The tendency of the plate to shift slightly 
 in the preliminary ste^Ds of swaging necessitates a surplus of 
 about 1-16 of an inch peripherally in tlie gold for full as 
 well as partial cases. 
 
 Tin foil, sheet lead or paper may l)e used as a pattern. 
 A sheet of No. 60 tin or lead foil is conformed to the die with 
 finger pressure or a large pellet of compact cotton, and the 
 excessive surplus trimmed off. It is again returned to the die, 
 readapted and finally swaged in tlie counterdie. One or two 
 light lilows with the hammer, or the weight of the die itself, 
 will secure close adaptation. Wlien removed, the excess is 
 trimmed away, allowing for the l-Ki-inch surplus previously 
 mentioned. 
 
 With the fingers the ])attern is carefully bent aiad reduced 
 to nearly a flat condition, care being taken not to strain or 
 draw it more in one area than another. It is now laid on the 
 flat joalm of one hand and struck a sharp blow with the open 
 palm of the other. This reduces the foil to flat sheet form, 
 slightly wrinkled in some places and possibly torn in others 
 from the swaging, yet representing reasonably well the re- 
 quired perijiheral outline of the denture. 
 
 166 
 
CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 167 
 
 The foil itself may be used as a pattern or its outline 
 may be traced on a sheet of thin cardboard, which, when cut, 
 facilitates the marking of the gold plate because of its greater 
 thickness and stiffness. The tracing of the pattern on the gold 
 is most easily aecomijlished with a round shauk, sharp pointed 
 instrument, held perpendicularly. If neither tin or lead foil 
 is at hand, ordinary tough writing paper, although not as sat- 
 isfactory, will serve for the pattern. 
 
 "When trimmed to pro])er outline, the pattern is laid on 
 the sheet of gold plate, so that when the latter is cut the grain 
 or lamina developed in rolling rims crosswise or from buccal 
 to buccal, this being the line of direction of greatest stress on 
 the baseplate, in swaging as well as in masticatory effort. 
 
 CARAT OF GOLD USED FOR DENTURE BASES 
 
 Twenty carat gold is the standard tineness of plate 
 used for denture bases. The advantages of this grade of gold 
 are: excellent color, but little tendency to discolor in the 
 mouth, no metallic taste, comparatively easy to adapt to dies, 
 good resiliency when medium to thick gauges are used. 
 
 The only disadvantage noticeable is the tendency of the 
 lighter gauges to become distorted under heavy stress. Obvi- 
 ated by using gauges of i)late appropriate to the stress the 
 denture will be subjected to in masticatory effort. 
 
 Eighteen carat gold is frequently employed for both full 
 and partial denture bases. The only decided advantage it has 
 over twenty carat gold is in having greater resiliency than the 
 latter in plates of equal thickness, and, therefore, lighter 
 gauges can be employed to advantage in some cases than when 
 higher carats of plate are used. 
 
 The disadvantages of eighteen carat jilate are : color not 
 so good as the twenty carat, decided tendency to discolor in 
 the mouth, and in some cases to exhibit a metallic taste. 
 
 Pure, twenty-two and coin gold are deficient in 
 resiliency and are not adapted for denture bases unless com- 
 bined with gold of lower carat. In difficult cases, where the 
 maxillary surfaces are very rough and irregular, and the 
 rugae are well defined, a thin sheet of, 22 carat or 24 carat 
 gold is sometimes adapted to the die and a second piece of 18 
 or 20 carat swaged over and attached to the maxillary plate 
 with solder. The use of the finer and softer grade of gold 
 next the die permits all of the irregularities to be accurately 
 copied, while the second plate, being harder and more resili- 
 
168 CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 
 
 ent, furnishes the necessary rigidity. This method of forming 
 a double base is frequently followed in partial cases, but is 
 seldom required in full dentures. 
 
 GAUGES OF GOLD USED FOR DENTURE BASES 
 
 For full upper dentures, 28, 27, and 26 gauges of gold 
 are used as conditions require. Twenty-eight-gauge, 20-carat 
 plate is sufficiently rigid for narrow arclies where the stress 
 of mastication is light to medium heavy. Twenty-seven-gauge, 
 20-carat is indicated for arches of medium width, medium 
 stress, and in narrow arches when stress is heavy. Twenty- 
 six-gauge is indicated for wide arches when the denture will 
 be subjected to heavy stress. 
 
 Full lower dentures seldom require heavier than 28-gauge 
 plate, since the vulcanite which furnishes attachment for the 
 teeth usually covers the entire base, and this, together with 
 the peripheral wiring, sujoplies the needed rigidity. Frequent- 
 ly 29-gauge will prove satisfactory. 
 
 That one may form a just estimate of the relative thick- 
 ness of the gauges mentioned, their value according to the 
 Brown & Sharp micrometer scale is here given. This mi- 
 crometer scale is given entire in the section on metallurgy. 
 
 26 gauge equals .01594 of an inch 
 
 27 " " .01419 " " Difference between 26 and 27 gauge equals .00175 
 
 28 " " .01264 '■ " " " 27 " 28 " " .00155 
 
 29 " " .0112(1 •' " " " 28 " 29 " " .00138 
 
 30 " " .01002 " •• ■' '■ 29 " 30 " " .00123 
 
 To gain rigidity within restricted areas, partial denture 
 bases are frequently formed of two pieces of plate, swaged 
 separately, then together, and finally soldered. Usually two 
 pieces of 30-gauge or one of .30 and one of 29 gauge are com- 
 bined in this manner. The two pieces of 30-gauge equal 
 .0200, or approximately 24-gauge, which is .0201. The other 
 combination equals .0212, or about 23y2 gauge. Various other 
 combinations of gauges can be utilized, as the conditions of 
 individual cases demand, broad bases requiring thin, while 
 narrow bases call for thicker gauges of plate. 
 
 ANNEALING THE PLATE 
 
 Gold plate, as usually furnished by the supply houses, is 
 not in its softest possible condition, and therefore should be 
 annealed before attempting to adapt it to the die, as well as 
 at various times during the swaging process. 
 
 Hammering, rolling, bending, liurnishing and polishing 
 tend to stiffen and render the gold, as well as other metals, 
 
CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 169 
 
 hard, more oi* less spring}' and elastic, and reduces their pli- 
 ability. 
 
 Molecular tension is also developed by working the plate, 
 a property which tends to bring the molecules back to the 
 original relation they sustained to each other before the plate 
 was subjected to working stress. 
 
 The hardness, tension and loss of pliability increase in 
 proportion to the stress to which the molecules are subjected. 
 Hardness and reduction of pliability render the securing of 
 perfect adaptation of the base plate to the die difficult. Mol- 
 ecular tension tends to destroy adaptation by warping the 
 plate when swaged to correct form, particularly when sub- 
 jected to high temperatures, as in soldering on the peripheral 
 wires and the attachments for the vulcanite. 
 
 Gold plate is annealed by laying it on a clean charcoal 
 or asbestos soldering block and applying the soft brush flame 
 of the blowpipe until the plate assumes a cherry red color, 
 when it should be thrown quickly into clean, cold water or 
 alcohol. Care should be taken not to overheat or fuse the 
 gold at any point, or its toughness and cohesiveness will be 
 impaired. 
 
 OILING THE DIE AND COUNTERDIE 
 
 Before beginning to adapt the plate, the surfaces of both 
 die and couuterdie should be coated with a thin film of thick, 
 viscid oil, such as vaseline or heavy lubricating oil. This is 
 done for two reasons : First, to prevent, as much as possible, 
 the adhesion of the base metals to the gold under the heavy 
 sliding friction induced by swaging the plate l^etween the die 
 and the counterdie. Second, the oil acts as a lubricant and 
 permits the gold to slide over surfaces which, if not oiled, 
 would result in tearing or shearing the plate. The oiling of 
 the die and the counterdie is extremely important, and under 
 no circumstances should it bo neglected. Dies and counterdies 
 composed of the triple alloys, such as are used in crown and 
 bridge work, should receive the same treatment for similar 
 reasons as stated. 
 
 The old method of interposing a thin sheet of rubber dam 
 between the plate and couuterdie to prevent contamination by 
 the base metal is. not to be commended, as the rubber acts as 
 a cushion and reduces the positive action of the metal matrix 
 against the gold. 
 
 CLEANSING THE PLATE— PICKLING 
 
 When gold plate becomes contaminated by any of the base 
 metals such as are employed for die and counterdie purposes, 
 
17(1 CONSTRUCriON OK SVV.V(iKI) DKNTrHK HASKS OK VAHJ) 
 
 and i.s subjected to the blow pi pc or l')iiiis("ii flame in the an 
 iiealing process, an alloy is formed at the points affected, which 
 is brittle and low fusing in character. When this occurs, the 
 strength and fusibility of the plate is reduced. Subsequently, 
 in soldering operations, the areas so contaminated are very 
 liable to fuse and result in the formation of pits or holes, 
 sometimes called "burning the plate." This is an incorrect 
 term, as the alloy is merely fused and its tendency to spheroid 
 causes it to draw back to the more infusible portions of the 
 plate not so affected. 
 
 To remove the base metal that adheres to the plate as 
 a result of hanmiering and friction between the die and 
 counterdie, it should be boiled in dilute sulphuric acid from 
 ten to tifty per cent strength. Even the action of the acid fails 
 at times to remove all of the base metal, particularly the lead 
 and tin, in reasonable time. Sulphuric acid, either full 
 strength or diluted, does not act readily on these metals, as 
 is apparent by the fact that it is often kept in lead containers 
 for a long period without injury to the vessel. This, how- 
 ever, is partly due to the fact that after a time a film of lead 
 sulphate is gradually formed, which limits further action of 
 the acid on the unaffected lead. 
 
 A positive and final method of removing particles of 
 base metal from the gold is by the application of pumice stone 
 to the i)late with a stiff brush wheel on the lathe. This should 
 be resorted to after boiling in acid and rinsing in water. 
 
 CONFORMING THE PLATE TO THE DIE 
 STEPS OF ADAPTING THE GOLD, IN FULL UPPER CASES 
 
 The gold plate having been cut according to i)attern, is 
 now evenly centered over the die, and with finger or thumb 
 pressure forced down into the vault ])ortions as closely as 
 possible in this manner. Tlie adaptation is carried further 
 with a horn mallet, being careful not to mar the plate un- 
 necessarily with the pointed end. Two or three forms of 
 mallet, with ends of different shapes and sizes, should be at 
 hand to meet the varying conditions which present. The small 
 end of the average new horn mallet is usually too sharp and 
 too pointed to be serviceable and should be cut ot¥ and some- 
 what rounded with a rasp. 
 
 From the very beginning, and until thoroughly close 
 adaptation is secured, wrinkles or folds in the plate are very 
 liable to develop. Such mishaps usually occur when an at- 
 
CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 171 
 
 tempt is made to closely conform a considerable area of plate 
 to an irregular or constantly varying surface of the die, as 
 for instance a deep palatine vault, the labial surfaces of a 
 prominent or V-shaped arch, or prominent tuberosities. 
 
 The physical conditions bearing upon the changing of a 
 flat plate to the irregular form, assumed by a well-adapted 
 base plate should be borne in mind. Certain areas must be 
 raised, others depressed, and still others will require but 
 little general modification. Molecular changes must be 
 brought about uniformly. In some locations the molecules 
 will be stretched and pulled — occasionally to the point of de- 
 stroying their cohesion, which will result in thinning and tear- 
 ing the plate. 
 
 THE HORN M.VLLET 
 
 In other areas, the molecules must be comi^ressed upon 
 themselves, the first noticeable effect of which is in the forma- 
 tion of wrinkles, with a slight tendency to thicken the plate. 
 The folds and wrinkles must be obliterated as soon as they 
 are formed and before they are januned too closely together 
 for correction. Flat and round-nosed pliers and the plate 
 benders are used to advantage for this purpose. The judicious 
 use of the horn mallet or a small riveting hammer will also 
 correct the difficulty by striking the fold with a sliding blow 
 peripherally, at the point on the adfii)t('d surface where it first 
 appears. 
 
 The vault portion having been fairly well adajited, cither 
 by the aid of the partial counterdie or with the horn mallet 
 alone, the next step is to conform the plate to and over the 
 
172 CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 
 
 crest of the maxillary borders. The die can conveniently be 
 held in the hand, the thumb pressing the plate and keeping it 
 closely in contact with the vault portion, while adapting the 
 metal to the border crest. 
 
 USE OF PARTIAL COUNTERDIES 
 
 The large end of the horn mallet is applied here, using 
 moderate blows to prevent thinning the plate unnecessarily 
 — usually a few well-directed blows will accomplish the de- 
 sired end. When partial counterdies have been constructed, 
 the second or largest of the two partials is applied to advan- 
 tage following the use of the horn mallet, for setting the plate 
 against the maxillary border. 
 
 In difficult cases, where much irregularity of the border 
 surface is present, a clamp may be used to advantage for 
 holding the adapted vault portion of the plate firmly in con- 
 tact with the die. A wad of compact, damp paper is placed 
 against the vault portion of tlie plate to give bearing to the 
 clamp screw, prevent the latter. from marring the plate, and 
 by its tendency to spread slightly under screw pressure, force 
 and hold a considerable area of the adapted portion against 
 the die. When partial counterdies have been constructed, the 
 smallest of these can be used in lieu of the paper. 
 
 The die, with the plate in position, can be clamped to the 
 bench, when necessary, to give the prosthetist the free use of 
 lioth hands, but usually it will he found best to clamp the die 
 and plate together so that they may be held in the hand and 
 turned in any convenient position for the application of the 
 mallet blows. 
 
 Tlie plate is adapted to tlie Jal)ial and liueeal surfaces of 
 the die by striking a sliding blow from the border crest to 
 the periphery. The adaptation should begin at the median 
 line on the lalnal surface and be gradually developed distally, 
 about equally on both sides. In other words, secure reason- 
 ably close adaptation from the median line to the cuspid 
 eminence on one side, then direct the effort to the opposite 
 side in like manner, continuing the adaptation similarly on the 
 buccal surfaces and finishing at the tuberosities. 
 
 Another method in common practice is to slit the plate 
 in the median line, on the labial surface, from the periphery 
 to the crest of the border. The buccal surfaces are then 
 adapted and the surplus plate worked forward, allowing it 
 to lap at the median line. The excessive surplus of plate at 
 the lap joint is removed with the shears and the joint soldered 
 
CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 173 
 
 before the final swaging. The method first described is usually 
 to be preferred, although at times, when the general form of 
 the arch is narrow and the labial and buccal surfaces are deep 
 from the border crest periplierally, slitting and soldering the 
 plate as outlined will be convenient and satisfactory, and will 
 enable the prosthetist to economize on time. 
 
 It is not expected that the adaptation of the base plate 
 to the die with the horn mallet will be very close, but it should 
 be reasonably well developed to i)revent folds from foi-ming 
 in the final swaging in the counterdie. 
 
 The peripheral excess of the base plate is trimmed away 
 to the required outline of the finished denture, the plate 
 pickled in dilute acid, polished on the lathe with a stiff brush 
 wheel and pumice stone, to remove any adherent particles of 
 base metal which the acid does not remove, washed clean, and 
 thoroughly annealed, before the final swaging. 
 
 SWAGING IN THE COUNTERDIE 
 
 The base plate being clean and soft from annealing, and 
 the counterdie freshly oiled, the final adaptation is quickly 
 secured. The base plate is placed on the die and settled evenly 
 into the counterdie, as far as the latter will receive it. Place 
 the counterdie on the swaging block, and with a four to six 
 pound hammer, strike the base of the die squarely, one rea- 
 sonably sharp blow, separate, remove the plate, and note 
 whether any folds or wrinkles have develo]ied, and if so, re- 
 move them. Beturn the plate and strike the die two or three 
 heavy blows and again inspect, first for folds, and finally for 
 adaptation. Bepeat as often as may be necessary to secure 
 perfect approximation of the plate to the die surfaces and 
 especially around the periphery. 
 
 Finally, when the adaptation is satisfactory, pickle, polish, 
 anneal and I'eturn to the countei'die and strike a final blow to 
 correct the warpage occasioned by the last annealing, and 
 which almost invariably occurs. A single well-delivered, 
 heavy blow following this final annealing corrects warpage and 
 does not develop any further appreciable molecular tension. 
 
 This latter step is very important, for if not cari'ied out 
 as described and' the wiring of the base plate is undertaken 
 while any molecular strain is present, warpage is most certain 
 to occur. 
 
 The periphery of the baseplate sliould be trimmed with 
 shears and files, as accurately as possible, to the required out- 
 line of the finished denture before the final swaging, for if 
 
174 CONSTRUCTION OF SWAGED DENTURE BASES OP GOLD 
 
 after trial in the moutli the shears arc used, distortion of the 
 base plate is liable to follow from the strain. Should this 
 occur, correction must be made by reswaging. 
 
 PRELIMINARY STEPS IN SECURING ANCHORAGE FOR 
 TEETH TO BASEPLATE 
 
 lu full gold base denture eases, the teeth are usually at- 
 tached to the gold base by means o¥ vulcanite. This method 
 of attachment obviates the many angles and spaces which 
 result from backing plate teeth and joining them to the base 
 with solder. Again, when more or less absorption of the 
 border has occurred, and for esthetic reasons restoration of 
 such loss is necessary, it can be most easily accomplished in 
 vulcanite. Therefore, for hygienic and esthetic reasons, this 
 method is resorted to in practically all full denture cases. 
 
 When rubber is molded and vulcanized against a smooth 
 surface of gold plate, the two materials adhere quite firmly, 
 but unless some positive mechanical anchorage is provided, 
 the vulcanite will part from the baseplate sooner or later, 
 under the constant vibratory stress of mastication. 
 
 VARIOUS MEANS EMPLOYED FOR VULCANITE ANCHORAGE 
 
 Several methods of anchorage can be utilized for in- 
 creasing the bond of union between the gold and vulcanite, 
 none of which alone will prove sufficient, but by combining 
 usually three, a permanent and lasting attachment can be 
 effected. 
 
 USE OF WIRE LOOPS 
 
 First, in full cases, from three to five loops of wire or 
 narrow corrugated strips of plate should be soldered to the 
 maxillary surface of the gold base, at various points along 
 the border, in such manner as subsequently not to interfere 
 with the arrangement of the teeth. In closing the packed 
 flask, the rubber is molded around and imder these anchor 
 loops, where it hardens during vulcanization. This is the best 
 and most positive form of mechanical anchorage possible to 
 develop. 
 
 SPURRING THE BORDER SURFACES 
 
 Second, with a diamond point engraver, many opposing 
 spurs should be raised over the entire area covered by the 
 vulcanite. The spurs should extend to the extreme margins 
 to prevent the thin edges of vulcanite from eventually warp- 
 ing and curling away from the baseplate. 
 
CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 175 
 APPLICATION OF RUBBER CEMENT 
 
 Third, by applyiug a thin fihn of ehloro-rubber to the 
 surface of gold involved, just before closing the packed flask, 
 it will act as a cementing medium and aid the mechanical re- 
 tention otherwise provided. 
 
 FORMING THE PERIPHERAL SHOULDER 
 
 In order that the line of junction of the vulcanite with 
 the gold base may be symmetrical, and to further guard 
 against tlie extreme margins of the vulcanite from curling 
 
 SOLDERING THE SIKIll.nEr. WIRES TO AX VPI'ER EASE 
 
 away from the baseplate, a fine wire, usually 19 gauge, and 
 L'O carat, is soldered to the labial and buccal surfaces and 
 continued around the tuberosities along the lingual aspect of 
 the border. The surface included within this wire loop repre- 
 sents the area to be covered by the vulcanite. When soldered, 
 the inner periphery of the wire is scjuared out with small 
 stones and burs so as to present a square shoulder against 
 which the vulcanite finishes. In attaching the wire, care 
 sliould be taken to avoid filling with solder the angle formed 
 by the junction of the baseplate with the inner periphery of 
 the wire. The application of an anti-flux will prevent the 
 
176 CONSTRUCTION OK SWAGED DENTURE BASES OF GOLD 
 
 solder from tilling angles and ooveriug surfaces fi-om which 
 it should be excluded. 
 
 The outer side of the wire, or that surface presenting 
 toward the periphery of the base and to the central vault 
 portion, is filled in with solder and afterward ground to meet 
 the baseplate, merging it into a symmetrical curve, thus 
 obviating the formation of an angle into which food might 
 find its way. 
 
 LOCATING THE POSITION OF THE WIRE ON THE BASEPLATE 
 
 The location! of this wire which marks the boundaries of 
 the vulcanite is determined by occluding and waxing the teeth 
 to the base in the position they will occupy in the finished 
 denture. On the lingual side the wax is contoured to repre- 
 sent the normal curvature of the palatine vault, terminating 
 it as soon as possible without forming an angle at its junction 
 
 SECTIONAL VIEW OK BASE SHOWING FINISHED 
 SHOULDERS WITH VULCANITE IN POSITION 
 
 with the base or alveolar border. On the other hand, it should 
 not be extended too far toward the center of the vault, or the 
 contour of the finished case will be imnecessarily bulky. 
 
 The wire is attached to the labial and buccal surfaces of 
 the baseplate about one-eighth of an inch from the peripheral 
 margin. It is placed in from the margins to this extent so that 
 after the denture is instroduced, should perijjheral trimming 
 of the base become necessary, it may be accomplished with- 
 out cutting into the vulcanite. 
 
 The exact position of the wire is determined by scratching 
 a line on the gold base with a sharp instrument, just within 
 the peripheral margin of the contoured wax rim. The posi- 
 tion of the anchor loops can also be determined at this time 
 by thrusting a sharp pointed instrument through the wax 
 rim to the basepalte and scratching it in the lingual embra- 
 sures between the first and second molars, the first and second 
 biscuspids, and as close in to the mesio-lingual angles of the 
 central incisors as possible, so that this loop will not inter- 
 
CONSTRUCTION OK SWAGED DENTL^KE BASKS OK GOLD 177 
 
 fere with the proper lingual contour of tlie vulcanite, hack of 
 the incisor teeth. 
 
 The denture is now removed from the occluding frame 
 on which it has previously been mounted, the teeth and wax 
 rims are detached, and the baseplate thoroughly cleansed. A 
 piece of wire about 9 inches long is required for forming the 
 peripheral shoulder. One end of this is conformed and 
 clamped to the wire line, beginning usually at one of the 
 tuberosities, where it is fluxed and tacked with a small piece 
 of solder. The baseplate is chilled, the wire is further con- 
 formed along the line for a distance of one-half to one inch 
 and again clamped and soldered. This is repeated until the 
 wire is attached to the entire peripheral outline on the base- 
 
 plate marked. The application of an anti-tlux to the inner 
 margin of the wire, before each section is soldered, will pre- 
 vent the filling in of the angle with solder. 
 
 ATTACHING THE WIRE LOOPS 
 
 A convenient method of applying the wire anchorage 
 loops is as follows : Make a right angle bend near the end 
 of a piece of 19 or 20 gauge wire and touch the angle with 
 flux ; i^lace a small piece of solder on the baseplate at a point 
 indicated for a loop ; apply the blowpipe and when the solder 
 is fused touch the bent wire to the solder, remove the flame 
 holding wire until solder congeals; clip oiT the long end of 
 the wire near the baseplate, leaving two short spurs projecting 
 for anchorage. By using a iwire 6 or 8 inches long it will 
 serve as a handle for holding the loop while soldering. In 
 arranging the teeih, if the ends of the wire interfere they may 
 be bent out of the way. The teeth are now returned to the 
 baseplate and their position and occlusion verified by trial in 
 the mouth. The steps of flaskiug, packing, ^mlcanizing and 
 finishing differ in no essential particulars from those em- 
 ployed in vulcanite work to which the reader is referred. 
 
ITS CONSTRIK'TION OK SWAOKD nKNTURIO liASl<:S OK COLD 
 
 SWAGING FULL LOWER BASEPLATES OF GOLD 
 CUTTING THE PATTERN AND PLATE 
 
 The pattern for a full lower base is obtained in the same 
 manner as for a full upper denture. Special care should 
 be observed in flattening out the foil or tea lead not to dis- 
 tort it by undue stretching of either the labial or lingual 
 surfaces. When the labial surface is stretched more than 
 the lingual, the pattern will l)e too narrow around the curve 
 of the arch, or from buccal to buccal, while if the lingual 
 surface is distorted the reverse conditions prevail. 
 
 The lamina of the gold plate should run from buccal to 
 buccal, as in full cases, to give strength in the median line to 
 the finished denture. 
 
 CONFORMING THE PLATE TO THE DIE ^ 
 
 It is somewhat more difficult, at the outset, to adapt the 
 metal plate to a lower than to an upper die, because its nar- 
 row, curved foi'm, as well as the peculiar shape of the die, 
 renders it a difficult task to prevent the plate from sliding. 
 
 The base should be evenly centered over the oiled die, 
 and with the fingers and thumb held as firmly as possible by 
 its outer periphery. The lingual surfaces are bent down- 
 ward and outward against the lingual surfaces of the die 
 with liglit blows of the horn mallet. 
 
 No attempt need be made to secure close adaptation at 
 the start ; the lingual surfaces, however, should be conformed 
 sufficiently to prevent the plate from sliding while bending 
 the labio-buccal flange downward in contact with the outer 
 surfaces of the ridge. The plate benders are very convenient 
 for starting the plate over the border. (See page 189.) 
 
 Usually far too much time is devoted to tlie use of the 
 liorn mallet in conforming the plate to the die. 
 
 The beating of the metal with the mallet develops undue 
 molecular strain, thins the plate itself and reduces the high 
 points on the die, all of which unfavorable features can be 
 obviated, or at least greatly lessened, by the early use of 
 the die and counterdie. 
 
 Except in cases of marked irregularity of the alveolar 
 ridge, the swaging may begin as soon as the plate is con- 
 formed sufficiently to retain its position on the die. 
 
 SWAGING IN THE COUNTERDIE 
 
 A method applicable to all classes of cases for prelim- 
 inary conformation of the plate to the die, with the minimum 
 malleting, is as follows: 
 
CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 179 
 
 Place the partially-conformed plate in the counterdie 
 and set the die in position upon it. Place the palm of the 
 hand over the die, the fingers and thumb grasping the peri- 
 phery of the counterdie. Lift the die and counterdie, the 
 plate being interposed, and strike the anvil once only with 
 the base of the counterdie. The resulting impact will drive 
 the die partially into the counterdie, the plate being carried 
 with it. Remove the die and plate and examine the latter 
 for folds or wrinkles. Should any have developed, correct 
 with pliers or mallet and repeat the step until all tendency 
 of the plate to buckle is overcome. 
 
 General adaptation of the plate to the die can be secured 
 in this manner in a very short time. Final swaging is accom- 
 plished and close adaptation is developed with a heavy ham- 
 mer on the swaging block, the same as in upper cases, pre- 
 viously described. 
 
 When extreme irregularity of the maxillary ridge and 
 border surfaces in general exists, it is sometimes advisable. 
 in order to insure close adaptation of the baseplate to the 
 tissues, to swage two thin plates of 30 or 31 gauge separately, 
 then together, pickle, polish and unite with solder. After 
 soldering, reswage to correct warpage. This method of 
 doubling the plate in difficult cases of any class is productive 
 of excellent results. 
 
 SWAGING THE PL.'^TE AGAINST UNDERCUT SURFACES 
 
 In case undercut surfaces are present on the die, and 
 these areas have been filled with sand in the production of 
 the counterdie, as previously described, the latter will be 
 deficient opposite such filled-in areas of the die. To conform 
 the plate to the die and against these surfaces, strips of 
 lead of approximately the thickness of the depth of under- 
 cut are laid between the plate and deficient counterdie area, 
 and the die and plate driven deeply into the counterdie. 
 
 It is usually useless, however, to force the baseplate into 
 deep undercuts, because it must necessarily be distorted in 
 removal from the die. The better plan is to allow the plate 
 to enter the undercut to a slight extent only, so that in re- 
 moval, although requiring to be sprung in passing over the 
 bulge of the die, its inherent elasticity will return it to origi- 
 nal form. The deficiency of the base, in such cases, can 
 usually be corrected with the vulcanite by means of which 
 the teeth are attached. 
 
 The same general steps of trimming: to as nearly cor- 
 
180 CONSTRUCTION OK SWAGED DENTURE BASES OF GOLD 
 
 rect peripheral outline as possible, before trial in the mouth, 
 pickling, polishing and annealing to relieve molecular strain, 
 followed by the final blow to correct warpage, applies to 
 lower as well as all classes of swaged base dentures which 
 must subsequently be subjected to soldering operations. 
 
 PARTIAL BASEPLATES OF GOLD 
 
 The construction of gold base i)artial dentures requires 
 the exercise of as mucli, and in many instances more care, than 
 is involved in the production of full gold bases. 
 
 The forms of dentures for partial eases vary widely, 
 depending on the number of teeth to be replaced, the rela- 
 tion to each other of the spaces to be filled, the stress liable 
 to be exerted in masticatory effort and the means of retention 
 to be employed. 
 
 In a full-gold base denture the baseplate continues with- 
 out a break, from the palatine vault, over the maxillary sur- 
 faces, to the labial and buccal areas, against which its peri- 
 pheral margins terminate. The constantly varying, continu- 
 ous surfaces of such a baseplate, when adaptation has been 
 secured and molecular strain relieved, together with the at- 
 tachment of the teeth to the base by means of vulcanite, tend 
 to impart rigidity to the entire denture base. 
 
 In partial cases, however, the presence of some of the 
 natural teeth, against the lingual surfaces of which the peri- 
 phery of the baseplate must terminate, necessitates cutting 
 or notching the outer margin of the denture to receive them. 
 This step materially weakens the base wherever such notch- 
 ing occurs. 
 
 REINFORCING PARTIAL BASEPLATES OF GOLD 
 
 To develop the required rigidity, so that under stress 
 of mastication, or in handling, the denture may not become 
 permanently distorted, one of the several methods in vogue 
 for reinforcing baseplates may be adopted. 
 
 REINFORCING THE BASEPLATE BY DOUBLING 
 
 First: Develop the base from two pieces of comparatively 
 thin gold plate, swage each piece separately, then together, 
 and finally unite them with solder. 
 
 Advantages: Ease of adaptation, high degree of rigid 
 ity, uniform thickness of baseplate. 
 
 Objections : None, aside from the extra work of solder- 
 ing. 
 
CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 181 
 
 REINFORCING THE BASEPLATE BY REFLECTION OF 
 MARGINS AND WITH SOLDER 
 
 Second: Construct the base of a single sheet of gold plate, 
 27 or 28 gauge, reflect the margins against the lingiial sur- 
 faces of the teeth involved and fill the resulting lingual 
 angle with high-grade solder. 
 Advantages : Rigidity combined with comparatively thin 
 base. 
 
 Objections: Possible tendency of the solder to discolor 
 with use in the mouth. 
 
 REINFORCING WITH WIRE AND SOLDER 
 
 Third: Adapt plate or wire to the baseplate over the weak 
 areas onlj', and attach with solder. 
 
 Advantages : Rigiditj' over weak areas, where specially 
 needed, witli use of minimum amount of material. 
 
 Objections: Unequal thickness of the baseplate because 
 the reinforcement is not uniform. 
 
 SECURING NEEDED RIGIDITY BY USE OF THICK PLATE 
 
 Fourth : Use a single piece of thicker gauge than that men- 
 tioned in the second method, No. 25 or 26 gauge being 
 usually employed. 
 
 Advantages : Rigidity. 
 
 Objections : Difficult to adapt. 
 
 DEVELOPING RIGIDITY BY USE OF SOLDER 
 
 Fifth: Flow solder alone over the weak areas of the base- 
 plate. 
 
 Advantages : Rigidity. 
 
 Objections: Tendency of the solder to discolor; unequal 
 thickening of the baseplate, due to solder filling the inequali- 
 ties and seeking its level. 
 
 The first and second methods are most frequently fol- 
 lowed and have proven most successful. In certain cases, 
 however, some of the other methods mentioned may be used 
 to advantage. 
 
 The first-mentioned method of doubling the baseplate is 
 specially applicable to those cases where the teeth and spaces 
 alternate with considerable regularity, where the rugae are 
 pronounced and well defined, and where the surface markings 
 of the oral tissues in general are prominent. In such cases 
 a baseplate consisting of a single piece, sufficiently rigid to 
 
lS:i CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 
 
 withstand stress, cannot, because of its inlierent rigidity, be 
 driven into all of the irregularities of the die. 
 
 By substituting two thin pieces for the single, thicker 
 plate, and conforming and uniting them as mentioned, the 
 necessary rigidity and required adaptation are readily se- 
 cured. 
 
 HOW TO ESTIMATE THE APPROXIMATE THICKNESS OF A 
 DOUBLED BASEPLATE 
 
 Experience has shown that in partial dentures, where 
 the baseplate is narrow, it should range in thickness from 27 
 to 22 gauge, depending on its width, in order that it may have 
 the necessary rigidity to withstand stress. 
 
 The best method for determining the thickness of the 
 comi^onent plates, where two are used, so that they may have 
 approximately the same rigidity as the single, thicker plate, 
 is by means of the table of gauges. 
 
 By reference to this table it will be seen that 24 gauge, 
 for example, the probable required thickness of the base, is 
 .0201 of an inch thick. Now by combining two thicknesses of 
 plate of lighter gauge as follows, the doubled plate will be 
 approximately equivalent to No. 24 gauge : 
 
 27 g. = .0149 
 34 g. = . 0063 
 
 .0212 
 
 28 g. = .0126 
 31 g. = . 0089 
 
 .0215 
 
 29 g. = .0112 
 
 30 g. = . 0100 
 
 .0212 
 These three possible combinations range about midway 
 between No. 24 and No. 23 gauge, any one of which can be 
 used when deemed advisable. Other combinations, varying 
 in thickness, are made in a similar manner, depending on the 
 requirements of the case. 
 
 SWAGING PARTIAL GOLD BASES 
 
 When the base is to be of a single thickness of plate, re- 
 inforced by reflection of the margins and with solder as out- 
 lined in the second method, the construction steps are as fol- 
 lows: 
 
CONSTRUCTION OF SWAGED DKNTl'RE BASES UF GOLD is:^ 
 
 Oil the die and oouuterdie; seom-e tin or lead foil pat- 
 terns and trim to the desired form ; cnt the base from plate 
 gold, 27 or 28 gauge, and 20 carat, according to pattern; an- 
 neal and adapt to the die, first with the fingers, then with horn 
 mallet sufficiently to retain its ]iosition between the die and 
 
 TIXFCIII, I'ATTKItN Flllt I'AHTIAJ, 
 
 counter die in the initial stages of swaging; swage between 
 die and counter die, using weight of die as previously sug- 
 gested; with pliers correct any folds or wrinkles that form; 
 return to counter die and strike one or two heavy, square 
 blows with hammer; correct wrinkles, trim off excess and 
 again swage. 
 
 APPLICATION IW THE CHASER OK BURNISHER 
 
 To drive the gold into the linguo-gingival angles and em- 
 brasures, and reflect it against the lingual surfaces of the 
 teeth, a small instrument, shaped somewhat like a cold chisel, 
 is used. Although in general form its end is chisel-shaped, 
 its edge is rounded to prevent cutting the gold. 
 
 This instrument is held firmly with the pen grasp, against 
 the gold, opposite the depressions on the die into which it is 
 
184 CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 
 
 to be carried. Under light, rapid mallet or light hammer 
 blows, the chaser is gradually moved over the plate, along 
 the lingno-gingival angles until finally the gold is foroed into 
 all of the depressions and inequalities of the die without the 
 chaser perceptibly marring the plate or die. 
 
 From time to time the plate is pickled, polished and an- 
 nealed, and the surplus trimmed away with the shears, plate 
 nippers and files. The plate nippers are very useful for cut- 
 ting out or notching the plate where the teeth pass through, 
 or for cutting any short-curved margin, where the use of the 
 shears would distort the plate. (See page 186.) 
 
 The reflected plate margin, which extends from the 
 linguo-gingival angle, of tissues with teeth, occlusally or in- 
 cisally, against the lingual surfaces of such teeth as are in- 
 volved, should be about 1/16 of an inch wide. This margin 
 serves two purposes, first, being bent at a decided angle to 
 the baseplate proper, it imparts marked rigidity to the 
 periphery of the denture in decidedly weak areas ; second, the 
 increased frictional bearing afforded by reflecting the plate 
 against the teeth, adds stability to the denture. By flowing 
 solder into the lingual angle of the plate and reflected portion 
 the rigidity can be still further increased. 
 
 SWAGING DOUBLED UPPER BASES 
 
 To develop the required degree of rigidity, together with 
 the closest possible adaptation of the denture to the oral tis- 
 sues, and, by the simplest means, the baseplate should be 
 swaged from two pieces of plate and united by soldering as 
 previously suggested. The steps are as follows: 
 
 Cut two pieces 9^ 20 carat gold plate, according to pat- 
 tern, selecting from the gauge table two gauges of plate of 
 suitable thickness, which when comlnned will afford the neces- 
 sary^ strength. No. 29 and 31 gauge are commonly used. 
 
 Adapt and swage the thinnest piece to the die. Trim it 
 peripherally to the required outline of the baseplate, reflect- 
 ing it against the lingual surfaces of the teeth as previously 
 described. By using care in trimming to the exact outline 
 at this time, the loss, both of material and time, will be 
 avoided. When swaged, trimmed, annealed and finally re- 
 swaged to the die to correct warpage it is laid aside. 
 
 Now swage the second or thicker piece of plate. The 
 adaptation of this piece of gold will not be qiaite so sharp as 
 that of the first piece, first, because the plate is thicker, and 
 
CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 185 
 
 second, because some loss of detail of the die must naturally 
 occur during the swaging of the first plate. 
 
 When much loss of detail occurs to the die, a new one 
 should be run up, but not necessarily a new counter die, as 
 one or two hammer blows will force the old counter die sur- 
 faces into all the inequalities of the new die. 
 
 The two plates are now swaged together, the first, or 
 thinnest, being jilaced next the die, since being sharpest, and 
 showing the finest details, it should lie next the tissues. 
 
 The peripheral surplus of the second base swaged is 
 usuallj^ allowed to extend beyond the margins of the first 
 base, to afford a shoulder on which to lay the solder while 
 uniting them. 
 
 SHOWING TWO METHODS OF APPLYING THE DOUBLER 
 
 In some cases, however, it is advisable to reduce the sec- 
 ond base periphery until it lies entirely within that of the 
 first base. This method obviates the use of an excessive 
 amomit of gold, but is not always so convenient in soldering. 
 
 SOLDERING THE DOUBLED BASE 
 
 After swaging, the bases are pickled^- polislied and washed 
 in clean water. A film of clean borax paste is spread on their 
 contact surfaces and three or four small steel soldering 
 clamps are applied to hold them in contact. The clamped 
 bases are now laid on the solder block, and small pieces of 
 solder placed peripherally on the marginal shelf, and in close 
 contact with the edge of the first plate. 
 
 The brush flame of the blowpipe, properly applied, will 
 fuse and draw the solder between the two plates until the 
 space is perfeetl,v filled and the two are united. Merely unit- 
 ing the two bases at the peripheral margins will not be suffi- 
 cient nor will the needed strength be developed; the solder 
 must be drawn through from one margin to the other, and the 
 base plates imited into one solid mass. A good plan to insure 
 complete union between the two plates is to set the clamped 
 
186 CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 
 
 piece on tlie block so tliat the shelf on which the solder is 
 placed is higher than the opposite margin on which no solder 
 is laid. Heating the piece uniformly, until the solder fuses, 
 will result in its being drawn down until it shows continuously 
 
 VARlUlS FdFiMS 
 
 along the lower margin of the now united base. A break in 
 the line of solder on either margin indicates that some of the 
 area between the plates is not filled. 
 
 The peripheral surplus is now removed with shears, 
 plate nippers, files and stones, and the plate reswaged to cor- 
 
 PLATE NIPI'ERb FOR t I TTING PI VTE AROUND TEETH 
 
 rect warpage due to soldering and from cutting. It is again 
 pickled, polished, washed and is ready for trial in the mouth. 
 
 DOUBLING PARTIAL LOWER BASES 
 
 Frequently a lower partial denture of single thickness 
 may be rendered sufficiently rigid by burnishing or swaging 
 
CONSTRUCTION OF SWAGED DENTITRE BASES OF GOLD 187 
 
 and soldering to it a piece of plate hut little larj^er than the 
 weak areas. 
 
 Lower partial dentures, involving the replacement of tlie 
 posterior teeth only, are frequently reinforced anteriorly by 
 a second piece of plate overlaying the iirst, the ends of which 
 pass backward and terminate about % inch back of the last 
 natural teeth, or so as to extend well onto the saddle portion 
 of the base and outward to or beyond the crest of the border. 
 
 In dentures of this type the baseplate should extend well 
 up over the cingulse of all of the anterior teeth present, to af- 
 ford support to the denture in tliis region; prevent it set- 
 tling down when subjected to stress, and thus avoid injury 
 to the soft tissues underlying it. 
 
 DEVELOPING RIGIDITY BY USE OF WIRE AND SOLDER 
 
 When teeth are to be attached to the gold base plate by 
 means of a plastic base, the wire which is soldered on to form 
 a shoulder against which to finish the vulcanite can fre 
 quently be placed in such position or extended onto weak 
 areas so that when soldered the required rigidity is devel- 
 oped without the necessity of doubling tlie entire baseplate, 
 the wire and the solder used for the shoulder thus fulfilling 
 two purposes. 
 
 One of the most important considerations in the plan- 
 ning and construction of partial dentures is to determine the 
 means of retention that will render the appliance most effi- 
 cient. At the time of planning the denture retention means 
 must be decided upon, as these, to a certain extent, determine 
 the form of the baseplate. 
 
 APPLICATION OF FRICTIONAL APPLIANCES 
 
 When specialized frietional appliances, as the Roach or 
 Grilmore attachments, are to be used, the crowns or inlays to 
 which the stationary parts of the appliances are fixed are 
 usually constructed before the impression is secured, from 
 whicli in sequence the die will eventually be formed. In case 
 crowns are used for the attachment of retention appliances, 
 these are set in position on their respective roots, afterward 
 reproduced in the die, wholly or in part, and the baseplate 
 swaged to conform to them just as to the natural teeth. The 
 application of the attachments under consideration will be 
 given in another section. 
 
188 CONSTRUCTION OF SWAGED DENTURE BASES OF GOLD 
 
 When any of tlie ordinary foi'ins of clasps aro to he em- 
 ployed the order of procedure is as follows : 
 
 The clasps and baseplate having heen constructed, the 
 clasps are placed in position on the teeth thej^ are to embrace. 
 The baseplate is introduced, the points of interference with 
 the clasps noted and filed away until it can be firmly and 
 evenly seated on the tissues, without displacing the clasps or 
 itself becoming dislodged by them. 
 
 An impression in plaster is now taken of the clasps, 
 teeth and baseplate; when removed the clasps are returned 
 to position in the im})re,ssion, wedged apart, luted to place and 
 a east secured, by means of which the clasps and baseplate are 
 held in correct relation; they are then attached to the 
 baseplate by soldering in such manner as to interfere the 
 least possible extent with the resiliency of the clasp. 
 
 TAKING THE BITE 
 
 In partial cases, when a number of natural teeth are 
 present and in normal occlusion, a mash bite, sufficiently bulky 
 to receive and hold firmly the bite stem of the face bow in 
 front of the anterior teeth and without interference with oc- 
 clusion, will usually fulfil all requirements for occluding the 
 teeth, after the casts have been secured and mounted on the 
 occluding frame by means of the face bow. 
 
 When any complications are present, or when a consid- 
 erable number of teeth are being replaced, the best plan is to 
 occlude the teeth, attach them to the baseplate with sticky 
 wax and try the model denture in the mouth. This method 
 proves the occlusion, the degree of esthetic success attained 
 as to form, color and arrangement of the teeth, the position 
 for the lingual shoulder wire against which the vulcanite will 
 finish, when such means of attachment of teeth to base is 
 employed, and enables the prosthetist to judge the value of 
 his work at a time when corrections can readily be made, 
 should occasion require. 
 
 ATTACHING TEETH TO BASEPLATE BY SOLDERING 
 
 When but little absorption of the process has occurred, 
 in spaces occasioned by loss of the natural teeth, the best 
 means of attaching the porcelain substitutes to the gold base 
 is usually by backing a plate tooth with gold, in the usual 
 manner, grinding it to position on the cast, attaching it to the 
 base with sticky wax, investing the case in some good invest- 
 
CONSTRUCTION OF SWAGED DKNTURE BASES OF GOLD 189 
 
 iiieiit iiiaterial, and liually tlowiiig .solder ovpr the entire back- 
 ing and against the baseplate at its jnnction with the latter. 
 
 Frequently, in order to render the repairing of the case 
 simple, in case of accident, some of the replaceable types of 
 crowns or facings in common use, as the Steele, Groslee, Davis, 
 etc., can be used to advantage. 
 
 AVlien the bite is extremely close, so close, in fact, that 
 porcelain cannot stand the stress of mastication without frac- 
 turing, a wax tooth of the dimensions refjuired may lie formed 
 and cast, or a cusp may be swaged. IiIKmI in solidly and 
 attached to the base with solder. 
 
 PLATE BENDEKS. VKRY ISEFUI^ FOR CON- 
 FORMING A BASEPLATE ALONG THE BOR- 
 DER IX PRELIMINARY SWAGING (SEE 
 PAGE 1-.S) 
 
CHAPTER XIII 
 
 ALUMINUM BASE DENTURES 
 
 Aluminum is used to a considerable extent, in both 
 cast and swaged form, as a base for dentures. The ^ood 
 qualities of this metal may be summed up as follows : It is 
 malleable, tough, comparatively rigid, good color, shows but 
 little tendency to discolor, odorless, tasteless, and a good con- 
 ductor of thermal changes. 
 
 Some of the objections and disadvantages of the metal, 
 in general, in its application to denture construction are as 
 follows: It is extremely difficult. to solder, and when sol- 
 dered the joints, under the influence of oral secretions, dis- 
 color badly ; in some cases the solder itself is rapidly dissolved 
 away, particularly when mercury is one of its constituents. 
 
 Since soldering operations are difficult, the ordinary 
 means for forming finishing shoulders, attaching loop anchor- 
 ages, and, in partial cases, imiting one or more isolated teeth 
 to the base, as carried out in gold base denture construction, 
 are not practicable. Other means, therefore, must be resorted 
 to for developing the attachment of the vulcanite to the den- 
 ture base, and while these means are more or less efficient, 
 they require more care and involve greater effort than when 
 accomplished by soldering. 
 
 Aluminum is susceptible to the action of dilute hydro- 
 chloric acid, the alkalis, and salt solutions in general. Since 
 food, and consequently the oral secretions at times, contain 
 these substances more or less diluted, of course, aluminum 
 bases frequently show a decided tendency to disintegration in 
 the mouth. These facts are in accordance with observations 
 made by Figuier in his Year Book for 1858. One of the early 
 editions of Richardson quotes him as follows: "Caustic 
 alkalis, potash and soda, and even ammonia, dissolve alumi- 
 num sensibly." He also states that common salt and acetic 
 acid (vinegar), especially when mixed, attack and dissolve 
 aluminum. He adds that the mixture of salt and vinegar for 
 seasoning a salad, made in a spoon of aluminum, feebly but 
 inevitably attacks it. 
 
 The same edition further says : ' ' Calvert states that when 
 aluminum is immersed in water for anv considerable length 
 
ALUMINUM BASE DENTURES 191 
 
 of time, oxidation takes place slowly. ' ' It is therefore plainly 
 apparent why the snrfaces of dentures of this type, both cast 
 and swaged, become etclied and roughened with use, and in 
 time so reduced in thickness as to be useless. 
 
 Pure aluminum is more resistent to the action of the sol- 
 vents mentioned than the more or less impure commercial 
 varieties, and, therefore, in both cast and swaged work, only 
 the purest jiroducts obtainable should be employed. 
 
 Aside from the general disadvantages just cited of the use 
 of aluminum for denture bases, there are certain deleterious 
 properties which arise in casting the material and whicli will 
 need special mention. 
 
 CAST BASES OF ALUMINUM 
 
 The principal advantage of a cast aluminum hase lies in 
 the fact that the vulcanite anchorage can be more readily 
 developed on a cast than on a swaged base. Loops and 
 spurs of wax, in addition to the usual periplieral rims, can be 
 arranged on the model, and all reproduced at the time of cast- 
 ing. Peripheral rims are of decided advantage, as when iiro])- 
 erly formed tliey will effectually prevent the thin margins of 
 vulcanite from curling away from the base, a defect which 
 is specially noticeable in both cast and swaged aluminum 
 bases. 
 
 Another decided advantage of a cast over a swaged base, 
 from an esthetic point of view, is that in case absorption of 
 the border has ]irogressed irregularly, the greater j^ortion of 
 the required restoration can be accomplished in metal instead 
 of vulcanite, as is necessary with swaged bases. Tlie distribu- 
 tion of the vulcanite can therefore be made symmetrical in 
 cast bases, while in swaged bases it can seldom be accom- 
 plished, the finished case often presenting a very unsightly 
 and unbalanced appearance after the necessary contour has 
 been developed. 
 
 Cast aluminum base dentures, although promising much 
 from an esthetic standpoint, usually fall very mueli short 
 of perfection from the practical point of view. Two very 
 serious drawbacks are manifest in dentures of this type ; first, 
 the tendency of castings to warp in the making, thus impair- 
 ing, if not entirely inhibiting, successful adaptation and reten- 
 tion of the denture; second, imperfect density of the casting 
 when produced. 
 
192 ALUMINUM BASE DKNTURES 
 
 WARPAGE OF CAST BASES 
 
 "Warpage of a cast base is due to two causes; tirst, the 
 inherent tendency of most metals to contract in passing 
 from a fused to a solid state is very marked in aluminum; 
 second, the heat necessary to volatilize the wax and prepare 
 the matrix to receive the molten metal causes contraction and 
 warpage in the investment itself, so that when east the fused 
 metal is forced against a distorted form. In addition to this, 
 warpage in the metal, due to contraction, also occurs to fur- 
 ther complicate the difficulty. Warpage is a most serious 
 fault, and because of the resulting misfits it occasions has 
 retarded the use of the cast base more than all other causes 
 combined. The method for correcting warpage will be de- 
 tailed later. 
 
 IMPERFECT DENSITY OF CAST ALUMINUM BASES 
 
 Imperfect density in a casting is due to contraction of 
 the metal toward many centers as it assumes a crystalline, or 
 rather granular, form in cooling, each granule or crystal be- 
 coming a center toward which the cooling metal contracts. 
 As a result of this contractile tendency, many spaces neces- 
 sarily result throughout the substance of the casting. Very 
 often they are invisible to the eye, and in a newly finished 
 case, the metal appears dense and homogeneous, but with use 
 in the mouth the porosity becomes apparent. A low power 
 magnifying glass discloses many open spaces on the surface 
 of any aluminum casting. If broken, the spaces will be found 
 more or less generally disseminated throughout the fractured 
 sections. 
 
 ACTION OF ORAL FLUIDS ON ALUMINUM 
 
 Fluids of the mouth find their way into these pits 
 and open spaces, and in those mouths where solution of the 
 metal does occur the action is much more rapid than when 
 the metal is free from such imperfections. 
 
 The oral fluids contain during and for some time after 
 each meal attenuated particles of food; these find their way 
 into the pits, are retained, and after a time deconi])ose, often 
 giving rise to very disagreeable odors. Bicarbonate of soda 
 solution and sometimes, in extreme cases, dilute caustic soda 
 are used for cleansing and removing odors from vulcanite and 
 gold base dentures. These solutions should not be used for 
 cleansing aluminum base dentures because of their solvent 
 action on the metal. Dilute nitric or sulphuric acids, neither 
 
ALUMINUM BASK DENTUKKS 193 
 
 of which liave any perce])tibh^ action on alnniinum, may lie 
 used instead of the alkalis for removing odors. The acid 
 should be neutralized with weak aqua ammonia and the den- 
 ture washed thoroughly in water to remove all traces of the 
 latter. 
 
 GRANULAR STRUCTURE OF CAST ALUMINUM 
 
 As before stated, in passing from a fused to solid con- 
 dition aluminum assumes a granular form. The metal con- 
 tracts toward the granular centers and thus produces the 
 open spaces referred to. In addition to this change there is 
 a molecular rearrangement distinctly noticeable by the slight 
 crackling sound on removal of the case from the flask, appar- 
 ently regardless of the length of time it remains in the flask. 
 This is no doubt due to the release of tension on the already 
 contracted and warped base, by the removal of the cast and 
 matrix, the presence of which, at the time of solidifying of 
 the metal, partially restricted full contractile movement. 
 
 For these and various other reasons not here detailed the 
 casting of dense, well fitting baseplates of aluminum is prac- 
 tically an impossible task. Summarized, the advantages and 
 objectionable features of cast aluminum bases may be stated 
 as follows : 
 
 Advantages : Convenience in developing required vul- 
 canite anchorage ; great esthetic possibilities. 
 
 Disadvantages : Warpage of the base during and after 
 casting; imperfect density of the casting when produced; 
 susceptibility of cast bases to solution by the oral fluids. 
 
 There are many methods of technic in vogue, also many 
 kinds of casting devices in use at the ]iresent time for the 
 production of cast bases of aluminum. Lack of time and 
 space as well will preclude more than an outline of the essen- 
 tial steps common to most systems of casting. Two general 
 methods will be described, known as the indirect and direct 
 methods. Dr. Hart J. Goslee has recently described in detail 
 an indirect system of casting he has formulated, and which 
 promises to correct some of the disadvantages of the cast 
 base (Dental Eeview, August, 1914). The following is a 
 brief outline of the indirect methods referred to. 
 
 CASTING BASES BY THE INDIRECT METHOD 
 
 The advantages of the indirect over the direct method of 
 casting depends upon the preservation of the original cast 
 (model) of the mouth until after the base has been produced. 
 
194 AX,UMINUM BASE DKNTURES 
 
 and of the correction by swaging of this usually warped 
 base on the original cast of the mouth. The technic of 
 the system is as follows : 
 
 TECHNIC OF FORMING THE WAX MODEL 
 
 An accurate impression of the arch is secured in the im- 
 pression material most strongly indicated. 
 
 This impression is filled with either a hard cast jolaster, 
 or, better still, a mixture of oxy-chloride of magnesia, be- 
 cause of its much greater hardness. 
 
 The cast, of whatever material composed, should have a 
 fiat base, and be of good depth, to prevent fracture under the 
 stress of subsequent swaging. 
 
 To this cast of the mouth a sheet of pink wax slightly 
 thicker than the base is to be, is conformed, and trimmed to 
 correct outline of the baseplate. 
 
 Small rolls of wax, about one-eighth of an inch in diame- 
 ter, are adjusted peripherally, and burnished smoothly to the 
 required form to afford finishing shoulders for the vulcanite. 
 
 Anchorage loops for the vulcanite are attached at several 
 points, in such manner as not to interfere with the correct 
 arrangement of the teeth. 
 
 Three rolls of wax, also an eighth of an inch in diameter 
 or slightly larger, are attached, one to the most distal point 
 of each tuberosity and the other to the extreme median, 
 labial, surface of the baseplate. These are brought into a 
 common jjoint opposite the center of the palate and there 
 united with a slightly larger roll standing at right angles, 
 which serves as a sprue former. This arrangement of the 
 wax rolls which form the smaller sprues is applicable to cases 
 when invested in the open end ring flask. This type of 
 flask is usually shallow. In such ease the three sprue formers 
 should be placed nearly horizontal and as close to the base- 
 plates as possible, to conserve perpendicular space and make 
 room for ample depth to the crucible in the toj) of the flask. 
 
 When the deep box flask is used, the rolls of wax are at- 
 tached to the baseplate in the same location as above de- 
 scribed, but are all brought back of the distal margin of the 
 cast and there united to a slightly larger sprue former, or 
 they may be attached separately but close to each other to the 
 crucible former. The flasked case in this instance will then 
 present three separate openings leading from the base of 
 the crucible to the matrix, while in the former instance there 
 
ALUMINUM HASK UKNTUKKS 19r. 
 
 is ouly one exit, the divergeuce of tlie small sprues occurring 
 in the investment. 
 
 In both cases, regardless of whether the molten metal 
 leaves the crucible by one or three exits, it enters the matrix 
 at three widely divergent points. The three streams of metal 
 which issue from the several entrances must spread out, till 
 the entire matrix, meet, and coalesce without forming seams. 
 The pressiire exerted on the molten metal must be sufficient to 
 force the contained air within the matrix into the invest- 
 
 WAX FORMETl FOR MAIilNG SPRDE RODS 
 
 ment, or out through sprue vents, otherwise it will be caught 
 and confined somewhere between the margins of the inflowing 
 portions and result in holes. 
 
 Still another method of attaching the wax sprue formers, 
 applicable when. the case is to be cast by centrifugal force, is 
 as follows: A roll of wax three-sixteenths of an inch in 
 diameter is attached to the extreme labial surface of the base- 
 plate and extends up to the crucible to form the feed sprue. 
 
 Two smaller vent sprue formers extend from the highest 
 point of each tuberosity to the outer margin of the crucible, 
 
i:i(i ALUMINUM BASK ] )IO.\TI'KKS 
 
 al)()\'(^ tlic l('\('l of tile iMiiilaiiicil nict.'il w licii I'liscd. In rasting, 
 the metal eiitcsrs llic iiiatiix IVdin tlif crucible at the lowest 
 point, and on the priiici]ilc that a liiinid will seek its level it 
 rises njjward in the matrix, the air escaping through the vent 
 sprues. Since the exits of these sprues are higher than the 
 level of the metal in the crucible the latter will rise nearly 
 to the top of the ojienings of the vent sprues, but cannot 
 escape. 
 
 INVESTMENT OF THE WAX MODEL 
 
 Tlie baseplate having been given its required form, and 
 the anchorage lugs attached, it is ready for flasking. 
 
 A fine grained, slight porous investment material, 
 which is hard when set, should be selected for flasking the 
 wax model. A small amount of this is mixed moderately 
 thin, and with a brush is spread carefully and evenly over 
 the entire surface of the baseplate to eliminate all air bubbles. 
 With a spatula more is now added, care being taken to work it 
 under and aroimd the sprue formers so as to entirely enclose 
 them ; the labial and buccal surfaces should also be fully cov- 
 ered with a layer sufficiently thick to withstand handling when 
 the cast is removed. Altogether the investment should cover 
 the baseplate from one-fourth to three-eighths of an inch 
 thick. 
 
 When hardened, the half invested wax l)aseplate is care- 
 fully removed from the cast of the mouth on which it has been 
 formed, another mix of investment made, and with a brush 
 the entire interior of the baseplate is covered with it, care 
 being taken here as before to eliminate all air bubbles. More 
 investment is added to this, to take the place of the original 
 cast, extending it labially, distally, and buccally, to overlap 
 and unite firmly with that on the reverse side. 
 
 The wax model and most of the sprue formers are now 
 encased in a comparatively rigid shell of hardened invest- 
 ment, which should be trimmed so as to enter the flask with- 
 out encroaching on the sides at any point. Completion of the 
 investment in a ring flask is carried out as follows : 
 
 Sufficient investment material to surround the ease and 
 till the ring is mixed somewhat thicker than that used in first 
 covering the wax model. This is filled in the ring, the hard- 
 ened core containing the wax model is soaked in water for 
 a moment to exclude the air and insure perfect union between 
 it and the freshly mixed mass, and is then pressed well down 
 to the bottom of the ring to give ample space for the crucible 
 
ALUMINUM BASK DENTURES 197 
 
 ill the Upper end. A slight vihiatorv iiioveiiient of tiie spatiihi 
 in tlie plastic mass will cause it to settle around and over 
 the core and permit the air to escape. 
 
 The investment is smoothed up level with the top of the 
 flask and around the wax sprue former which should occupy 
 a central ]iosition in the upper surface and extend above the 
 upper margin of the flask. 
 
 When hardened, the investment is trimmed out to form 
 a crucible for containing the metal while fusing and prepara- 
 tory to casting. This should be deep and wide enough to hold 
 considerably more metal than the matrix will contain. In 
 some forms of flasks the wax sjDrue formers before the case is 
 invested are united with a crucible former, which, by means 
 of guides, is carried to correct position in the flask and the 
 investment is molded arormd it, thus obviating the necessity 
 of cutting the crucible. 
 
 PREPARING THE CASE FOR CASTING THE METAL 
 
 The flask should lie placed above a low flame and gradu- 
 all.y heated to dissipate the wax. The heat may be increased 
 from time to time to aecellerate the volatilizing of the wax, 
 but at no time should it exceed 370 degrees F., as that is the 
 temi^erature at which iilaster is readily and quickly disinte- 
 grated. By heating the case for a long time at low tempera- 
 ture the wax can be removed, the matrix cleared of residue, 
 and the integrity of the investment maintained far better 
 than with the I'apid application of intense heat. 
 
 As in inlay work, smoother castings will result if, after 
 clearing the matrix, the invested case is allowed to cool some- 
 what before introducing the molten metal. The temperature 
 should not be allowed to drop too low or the metal, wliich even 
 when well fused is slightly sluggish, will lose some of its 
 heat by radiation and contact with cooler media, become 
 chilled, and clog in the matrix, or in some cases in the sprues 
 and result in an imperfect casting. 
 
 CASTING THE FUSED METAL 
 
 Aluminum may be cast by vai'ious means, compressed 
 gas or air, by ]%artial vacuum, by a combination of the two 
 means just mentioned, by steam, centrifugal force, and liy 
 actual mechanical pressure. 
 
 In any case and by whatever means the casting is accom- 
 plished, the object in utilizing one or more of the forces men- 
 
I'.'S ALUMINUM IIASK I IION'l'l I ItKS. 
 
 tioned is ti) lid the niiilri\ nl' I he coiitaiiiud air, eilluu- at the 
 instant of easting, as in tlic case ol' the vacnnm appliance, 
 or force the molten metal into the matrix with sufficient pres- 
 sure to drive the air into tlic jiorous investment or through 
 vent sprues, and fill the entire space with fused metal under 
 compression. 
 
 Although more difficult to cast shar^jly than some of its 
 alloys, pure aluminum should he used hecause of its greater 
 resistance to chemical action. 
 
 A thin, slightly tough film of oxide quickly forms on the 
 surface of molten aluminum, which limits further oxidation. 
 Because of the lightness of the metal and the slight tenacious- 
 ness of the surrounding film of oxide the molten metal does 
 not fall into or fill even a large sprue, as would be the case 
 with any of the metals of greater specific gravity, but requires 
 vibration or some applied force to drive it into the matrix. 
 
 When first fused, aluminum, although plastic, is sluggish, 
 and if cast in this condition will not copy fine lines sharply. 
 The blowpipe flame should, therefore, be continued on the mol- 
 ten mass a sufficient time to bring it to a thinly liquid condi- 
 tion, yet without overfusing, before forcing it into the matrix. 
 
 A new, clean ingot (not scraps nor previously used pieces) 
 containing nearly twice as much metal as the case requires is 
 placed in the crucible and the blowpipe flame applied. The 
 flame should be large and the heat forced as rapidly as pos- 
 sible, to melt the metal before any great degree of heat is 
 transmitted to the matrix, and thereby cause unnecessary 
 dimensional changes in its walls. 
 
 When brought to a thoroughly liquid condition, the film of 
 oxide is cleared away, the casting force, of whatever character 
 employed, is applied and the metal is driven into the matrix. 
 
 Since metals having much greater specific gravity than 
 aluminum require pressure of 7 poimds or more to cast 
 densely, it naturally follows that to produce sharp, well defined 
 and dense castings of this much lighter metal more force 
 should be applied in injecting it into the matrix. From 8 to 12 
 pounds direct pressure, or 14.7 pounds, full vacuum pressure, 
 which, however, even though the gauge records it is never 
 realized, is none too much. Pressure should be maintained 
 until the metal congeals, the idea being to condense upon 
 themselves the granules or crystals as long as the harden- 
 ing nu^ss will yielcl under the applied pressure. 
 
 When cast, the case should be allowed to cool down gradu- 
 
ALUMINUM BASE DENTURES 199 
 
 ally; suddeu cliilling will induce more warpage and greater 
 molecular change in the casting than will occur when the tem- 
 perature is gradually lowered. 
 
 FINISHING AND SWAGING 
 
 On removal of the casting from the flask the waste gates 
 are removed witli a saw, the surfaces and margins smoothed 
 
 up with files, stones, and fine emery cloth on the lathe mandrel. 
 All nodules and irregular areas are removed from the palatine 
 and border surfaces. The baseplate should, in fact, be prac- 
 tically finished, except the freshening of the margins of the 
 viilcanite shoulder, which on account of danger of marring 
 should be deferred until after the final swaging. 
 
 PARTIALLY FINISHED CASTING, NOT Sl'URKED 
 
 The baseplate is now set on the original cast of the mouth, 
 placed in the swaging device, and subjected to screw or 
 hydraulic pressure sufficiently heavy to adapt it to all parts of 
 the cast face. The final finishing is now given the shoulder 
 against wliich the vulcanite is to nliut, witli square edge stones. 
 
200 ALUMINUM HASK UKNTUKKS 
 
 Any other areas that may need attention are smoothed, and 
 the baseplate is ready for the application of the wax rims. 
 The constrnctive steps from this i^oint on are the same as in 
 vulcanite work. 
 
 ATTACHING THE TEETH TO BASE WITH VULCANITE 
 
 In addition to the anchorage loops nsually provided in the 
 waxing of the case before flasking, a graver is used to raise 
 heavy spurs in various directions around and under which the 
 vulcanite will be molded. A film of chloro-rubber ]iainted on 
 the surfaces to be covered by the vulcanite acts as a cement- 
 ing medium and increases the efficiency and permanency of 
 the joint between the latter and the metal base. 
 
 DIRECT METHOD OF PRODUCING A CAST BASE OF 
 ALUMINUM 
 
 The direct method of producing a cast base of aluminum 
 is identical to that followed in indirect casting, up to the point 
 of removal of the wax model from the cast, previous to invest- 
 ing the case. In this method, the wax model baseplate remains 
 with the cast, the two are invested together, the cast becomes 
 a ]»art of the matrix, and is destroyed in the production of the 
 easting. To correct a misfit due to warpage by this method a 
 new impression and another cast must be produced, on which 
 the wai'ped casting can be readapted by swaging or the entire 
 case must be reconstructed, beginning with the impression. 
 
 Since the average cast baseplate, made by the direct 
 method, lacks that positive adhesion to the tissues so desir- 
 able, and, in fact, essential to usefulness and comfort, and 
 since a casting of this type can be readily corrected by swaging 
 on an accurate cast of the mouth, it is obvious that the so- 
 called indirect method is literally the most direct, because one 
 impression and one oast of the mouth fulfills all requirements 
 while the direct method usually requires two, since to secure 
 the desired adaptation it must be reswaged. 
 
 Until the dimensional changes in both investment mate- 
 rials and aluminum due to thermal variations can be over- 
 come to a greater extent than is possible by present methods, 
 the adaptation and general usefulness of cast aluminum bases 
 can be greatly inqircncd liy swaging. 
 
 CENTRIFUGAL CASTING OF ALUMINUM 
 
 Another mctliod of casting aluminum bases with centri- 
 fugal force l).\ tlic Dr. "W. W. Wood's ai)|)liances will now be 
 
ALUMINUM r.ASh: lHON'I'rUKS 201 
 
 brieliy describt'd. These appliances consist ol' a sjiecial llask, 
 au adjustable cover, a crncibie roinier, a base Wn attacliiiig tlie 
 wax model to the sin'ue I'oi-nier, a hi,i;li ,i;'ear<Ml cenli'ifnual 
 machine for forcing the molten metal into the matrix, dou 
 ble-burner stove for heatin.u' the invested case and for mell- 
 uvj; the alnminmn, a small ifon crncibie I'or holdinn llie metal 
 while heating, and from whicli it is ponred into the crncibie 
 of the flask, and, tinally, two sheet-iron hoods for <'onfining 
 the heat aronnd both tiask and crncibie in the preliminary 
 steins. 
 
 TECHNIC 
 
 The crucible former has thi-ee openings in its apex, and 
 in these, three rods of wax al)ont one inch long are luted. 
 
 CHIICIBLE FORMER ANn WAX MODEL READY FOR ATTACHMENT 
 
 The crucible former is adjusted to the cast-iron base. The 
 wax rods bent to unite with the baseplate at each tuberosity 
 and in the central vault portion. 
 
 The cast should not extend beyond the round end of the 
 base, otherwise, in forcing the crucible to place the wax 
 sprues are liable to be disconnected. 
 
 MIXING AND APPLYING THE INVESTMENT TO THE WAX 
 MODEL BASE AND CAST 
 
 A mix of some good quality of investment is applied to 
 the wax base with a brush, jiainting it against all surfaces 
 so as to eliminate the air. A mix of coarser investment can 
 
ALUMINUM BAS1<; DKNTURKS 
 
 ATTACHING WAX MODEL TO CRDCIBLE FORMER 
 
 WAX MODEI, ATTACHED BEADY FOB imTISTMENT 
 
ALUMINUM BASE DENTUHKS 203 
 
 be made and extended not only over the wax, but carried 
 up around the exposed sides of the crucible former in a layer 
 sufficiently thick, when hardened, to rigidly unite the cast, 
 wax base and crucible former. 
 
 When hardened, the attached cast and crucible former 
 are removed from the cast-iron base and investment applied 
 to the opposite side in a similar manner as described. 
 
 INVESTING THE CASE IN THE FLASK 
 
 The tiask is now tilled about two-thirds full of coarse 
 iii\('stiiu'nt mixed modoratclv tliin. 
 
 '••t*-^ 
 
 INTEODUCING THE PARTIALLY INVESTED WAX MODEL IN FLASK 
 
 The invested wax model and crucible former are dipped 
 in water and introduced in the partially-filled flask, with a 
 churning motion to eliminate air and cause the investment 
 to settle closely around that already hardened. The cnicible 
 former should rest upon the margins of the flask. 
 
 When set. the flask is inverted over the flame to slightly 
 warm the wax sprues and crucible former when the latter, 
 by tapping slightly, will readily come away. By oiling the 
 
ALUMINUM BASK DKNTUUES 
 
 crucible former befor( 
 easily from the flask. 
 
 apjilyiui;- tlic 
 
 'stiiieiit it will part 
 
 DRYING OUT THE CASE 
 
 The flask is ])laced on its side over a low flame until wax 
 has melted and partially flowed out through the sprues. 
 
 It is now inverted over the flame, the size of which is in- 
 creased, the sheet-iron hood adjusted, heat maintained until 
 investment is thoroughly dry. 
 
 While the invested case is drying out, which rcMjuires 
 usiuilly about an hour, the aluiniiiuiii should 1)e ]>lac('(l in the 
 
 IIKATINC; THE 
 
 ,\SE AM) ALUMINUM 
 
 iron crucible, set over the smaller burner and the hood 
 adjusted. 
 
 Since aluminum rec(uires a higher temperature to fuse 
 than that developed by the burner, the blow pipe flame should 
 be applied, and the metal brough to a well-fused liquid con- 
 dition. 
 
 CASTING 
 
 When the nu)isture has been driven from the investment, 
 and the latter has attained ]iractically a low, red heat 
 (900° F.), the flask is adjusted to the arm of the casting ma- 
 chine, the cover set in position and firmly clamped. 
 
ALUMINUM BASE DENTURES 
 
 Ari'l.VlNU THE COVER 
 
2&6 
 
 ALUMINUM BASK UENTURKS 
 
 POURING THE MOLTEN ALCMINXTW 
 
ALUMINUM BASE DENTURES 207 
 
 The melted metal is now quickly poured into the cru- 
 cible, through the small opening in the cover, and the ma- 
 chine set in motion as rapidly as possible. 
 
 To thoroughly condense the metal the centrifugal force 
 should be continued for at least three minutes or until the 
 aluminum has solidified. 
 
 APPE.AJIA-NIE OF AN UPPER A>T1 LOWER BASE AS THEY COM^ FROII FLASK 
 
 The methods here outlined vary somewhat from those 
 previously described, principally in the manner and amount 
 of heat applied. The results, however, in both density of cast- 
 ings and low shrinkage produced, justify the writer in 
 
 DR. WOOD'S METHOD OF PP.EPARING THE ^TJLCANITE ATTACHSfENT 
 
 strongly recommending the centrifugal method and processes 
 similar to those just described. 
 
 IMPORTANT PROPERTIES OF ALUMINUM IN 
 REFERENCE CASTING 
 
 Schnabel gives the following data in reference to alumi- 
 num. These facts are more appropriately placed here than 
 in the section on metallurgy. 
 
208 ALUMINUM BASK DENTUUKS 
 
 "The I'ractuic of cast nluiniiiuiii shows a coarse fiber 
 and irregular grain, while it is sinewy or tine grained, and 
 shows a high silky iiistic alter being liannnered and rolled." 
 
 According to l)e\ille, alnininuni crystallizes in regular 
 octaliedra, if cooled slowly. According to Rose, the crystals 
 /do not belong to the regular system. 
 
 The specific gravity of aluminum at 22° C. is 2.64 for 
 cast, and 2.70 for drawn metal. Its specific beat is 0.202. 
 
 It melts at red heat, between 600 and 700 C. At a higher 
 temperature it volatilizes, but the exact boiling point has not 
 yet been determined. 
 
 As its specific heat is high, it needs much heat and some 
 time to fuse; and as its latent heat is also great, it takes a 
 long time to cool and solidify. 
 
 According to Deville, when it is cast into small bars it is 
 several hours before these can be held in the hand. 
 
 There is a diminution of volume during solidifying, the 
 shrinkage being 1.8 per cent of the original volume." 
 
 SWAGED BASES OF ALUMINUM 
 
 Because of the difficulty in the past, and even at the 
 present time, attending the jiroduction of successful cast 
 base aluminum dentures, yet recognizing the need of a metal- 
 lic base less expensive than gold, many prosthetists have 
 turned to the swaged aluminum liase, hoping to find in that 
 the much desired substitute. 
 
 Swaged aluminum bases have been employed for years, 
 with varying degrees of success, or what is more literally 
 true, of disapointment, for in the larger percentage of cases 
 they have not fulfilled the hopes of the prosthetist nor the 
 practical needs of the patient. 
 
 The principal and valid objections to swaged bases of 
 aluminum, as ordinarily' constructed, are as follows : 
 
 First, general deterioration of the metal in the mouth. 
 The solvent action of the oral fluids and foodstuffs on alumi- 
 num is manifested in several ways, first, by destroying the 
 polish of the base, followed by deeper etching of the exposed 
 surfaces; this in turn results in gradual thinning and eventual 
 weakening of the base jjlate, distortion under stress, forma- 
 tion of holes, and finally loss of adhesion. 
 
 Second, difficulty in securing effective and permanent 
 anchorage between the metal and vulcanite, and of prevent- 
 ing the lingual margins of vulcanite from curling away from 
 
ALUMINUM BASK DENTURES 20<l 
 
 the baseplate, a fault wliicli often occurs c\cn tliouuli the gen- 
 eral anchorage may he satisfactory. 
 
 COMPARATIVE DURABILITY OF CAST AND SWAGED BASES 
 OF ALUMINUM 
 
 T]ie statement is frequently n:ade that the east is more 
 generally satisfactory and permanent than the swaged alumi- 
 num base. This is undoubtedly true of the average swaged 
 base as made today, but is not iu accordance with fact with 
 reference to bases of heavy gauge, constructed by the more 
 improved methods of teclmic. 
 
 Let us, for a moment, consider the difference in tiiick- 
 ness, and bulk of metal in general, between the aierage cast, 
 and the average swaged base. 
 
 The wax whicli forms the model l)aseplate determines 
 the thickness of the cast base, since the investment matrix 
 is formed against and around it. Those familiar with the 
 casting of aluminum know that it cannot with certainty and 
 at all times be east into constricted spaces. Therefore, to 
 be certain of producing a reasonably perfect casting, and, 
 further, to insure its having the required inherent strength, 
 the wax of which the model baseplate is formed must be of 
 sufficient thickness to meet the above requirements in the 
 formation of the matrix. 
 
 Usually the base of the wax model is formed by applying 
 a sheet of pink baseplate wax over the face of the cast. This 
 is further strengthened by the addition of the wax rolls which 
 form tlie vulcanite finishing shoulders. In nearly every case 
 a slight additional film of wax will be added to the palatine 
 area, the prostlietist feeling that such an addition will make 
 certain a perfect casting, while if too thick, the baseplate can 
 be reduced without injury. 
 
 Now the thickness of the av^erage pink baseplate wax i 
 16 gauge, or 0.050 of an inch thick. The completed wax model, 
 and consequently the casting, on account of the addition of 
 wax noted, usually measures 14 or 13 gauge, or 0.064 or 
 0.072 thousandths. It is true, some of this thickness may be 
 lost in the final finishing of the denture, but in the many prac- 
 tical cases observed and gauged by the writer of work done 
 by the best prosthetists, all exceeded 17 gauge or 0.045 of an 
 inch in thickness, while a number ranged between 15 and 14 
 gauge. 
 
 Most of the swaged base dentures at the present time 
 are constructed of 26 gauge, 0.016. It will be observed that 
 
210 ALUMINUM BASE DENTURES 
 
 '26 gauge is aiiproxiuiatcly only oiic-tliird the thickness oi' 17 
 gauge, therefore the cast base, being three times thicker than 
 the plate ordinarily used in swaged work, besides being thick- 
 ened and thereby gi'eatly strengthened by the peripheral rims, 
 should outlast the swaged base a proportionate length of 
 time under conditions most favorable to the swaged base, 
 while under adverse conditions to be mentioned later the time 
 efficiency of the latter becomes greatly reduced. 
 
 The first well-written description within the writer's 
 knowledge of the swaged aluminum base appeared in the 
 American System of Dentistry, 1888. In that article, 20 
 gauge plate was recommended as being most suitable and 
 practical and, unfortimately, many still adhere to the use of 
 that and even lighter gauges. 
 
 The anchorage for the vulcanite was obtained by 
 raising opposite spurs on the labial, buccal and lin- 
 gual border surfaces. Practically, this method of anchor- 
 age proved insufficient. Later someone suggested drill- 
 ing a number of holes, one sixteenth of an inch or 
 larger,, through the baseplate, at vaiious points along 
 the border surfaces, countersinking the border or palatine 
 ends of the holes, filling the holes with wax in flasking to ex- 
 clude the plaster so that the vulcanite would fill both holes 
 and countersunk portions and l)ecome riveted, as it were, at 
 several points, to the baseplate. Another method of anchor- 
 age consists in developing loops in the Ijorder surface of the 
 base itself by means of a special plier-like device. In a gen- 
 eral way these methods solved the question of anchorage and 
 obviated the frequent mishap of the body of vulcanite in which 
 the teeth were mounted from being dislodged from the base- 
 plate. 
 
 In this system of technic as first outlined, no provision 
 was made for a finishing shoulder for the vulcanite, conse- 
 quently it was found that after being in use a short time 
 the thin, sharp margins of vulcanite where they joined the 
 base, particularly on the lingual side, would curl up, break 
 off or draw away from the metal, leaving an unsightly joint, 
 annoying to the tongue, into which food would find its way. 
 To overcome this very objectionable feature, a groove in the 
 baseplate was cut at the line of termination of the vulcanite 
 with the base, in order to thicken and strengthen the margin 
 of the vulcanite. 
 
 This method of forming tlie finishing shoulder on 26 
 gauge and even somewhat thicker bases is not successful, be- 
 
ALUMINUM BASE DENTURES 211 
 
 cause if the groove is cut deeply enough to give the needed 
 strength to the vulcanite, the baseplate is so weakened that 
 fracture often occurs under stress in a short time. 
 
 When 26 or even heavier gauges of aluminum are swaged 
 in the ordinary manner, the plate being first adapted to the 
 die with the horn mallet, the injudicious application of mallet 
 force, particularly on high points and in deep depressions, 
 as the central portion of a high vault, will result in thinning 
 the base over such areas. These same high points and de- 
 pressed areas are subject to special stress in waging between 
 the die and counter die. They are very liable to, and usually 
 do, become contaminated with die and counter die metal. Un- 
 less the base metal is removed by thoroughly polishing before 
 annealing, an alloy is formed which apparently is more readily 
 acted upon by the oral fluids than is the iincontaminated 
 plate. The result of such action is seen in the formation of 
 holes in the affected areas. The thinning of the plate from 
 careless malleting undoubtedly aids in the early formation 
 of these openings, probably through the disturbance of nor- 
 mal molecular cohesion, thus reducing the resistance of the 
 aluminum to chemical action. 
 
 SUMMARY OF THE CAUSES OF DETERIORATION OF SWAGED 
 BASES OF ALUMINUM 
 
 Briefly summed up, the real causes of the rapid deteriora- 
 tion and general failure of the 26-gauge swaged aluminum 
 base appears to be due to the following: 
 
 First, contamination of the aluminum by the die and 
 counter die metal, with possible formation of an alloy, easily 
 disintegrated chemically. 
 
 Second, excessive thinning by mechanical working, of a 
 plate, which is conceded to be the lightest of the series of 
 gauges used, suitable for denture bases of this type. 
 
 Third, molecular disturbance of the metal in certain 
 areas, which reduces its integrity as sheet metal and lowers its 
 resistance to chemical action. 
 
 Fourth, reduction of the inherent strength of the base- 
 plate by the cutting of a lingual groove. 
 
 Fifth, failure. to develop thoroughly, the several means 
 of anchorage possible, as previously outlined. 
 
 It is the opinion of the writer, based on a number of 
 years practical and clinical experience, that, comjiared bulk 
 for bulk, the base swaged from sheet aluminum will outlast 
 the cast base. 
 
2:2 ALUMINUM BASK DKNTURKS 
 
 CONSTRUCTION OF SWAGED ALUMINUM BASES 
 
 As has been previously iutimated, only the heavier gauges 
 of aluminum should be employed in the construction of swaged 
 bases for dentures, in order that the basej^late, when weak- 
 ened as it nnist be liy grooving, to form the vulcanite 
 shoulder, may still have sufficient inherent strength to resist 
 masticatory stress. 
 
 For a number of years past no lighter than 18, and fre- 
 quently 16, gauge has been recommended and used in prac- 
 tice by the writer, in most instances with very gratifying- 
 results. Aluminum plate of these gauges and even heavier 
 can, with proper technic, be conformed to a die with com- 
 parative ease. The plate should not be annealed before be- 
 ginning nor at any time during or after the swaging opera- 
 tion. Any base metal from die or counterdie can l)e removed 
 with polishing wheels and tlius the formation of the low 
 fusing alloy, due to annealing, either of which apparently 
 renders the base more susceptible to oral fluids and food 
 chemicals, can be avoided. 
 
 TECHNIC OF SWAGING 
 
 The actual constructive steps are as follows: 
 A die and counter die are secured in the usual manner. 
 Both are oiled with a film of heavy, viscid, oil. Vaseline will 
 answer if a thicker oil is not obtainable. The oil will, to a 
 great extent, prevent contamination of the aluminum by the 
 die and counter die and lubricate the surfaces, thus obviating 
 the tearing of the base. 
 
 Several large sheets of an ordinary newspaper are sat- 
 urated with water and the excess expressed under heavy 
 pressure, as one would squeeze the water out of a wadded up 
 towel. The ball of condensed paper should be about three 
 inches in diameter. This is placed directly over the opening 
 of and on the counter die, and flattened slightly by pressure. 
 On the paper a sheet of suitable size of 18 or 16 gauge alumi- 
 num, as the case requires, is placed, the die set in position on 
 the plate and held firmly with the fingers, and its base struck 
 two or three heavy blows with the swaging hammer. The 
 first effect of the swaging will be to drive the plate into the 
 palatine vault of the die, to a greater or less extent, withoul 
 bending it over the outer sides of the border, the sheet sliding 
 over the inclined surfaces of the oiled die without tearing or 
 becoming thinned to any appreciable degree. The plate is 
 
ALUMINUM BASE UENTUKES 
 
 ROLL OF DAMP PAPER ARTt'STED TO fOVXTERDlE 
 
 RESULT OF FIRST SWAGING ON I'AFER MASS 
 
214 ALUMINUM BASE DENTURES 
 
 now examiued, and wrinkles corrected if any have formed. 
 Tliis preliminary swaging does not drive the plate or die 
 into the counter die, but into the ball of paper which should 
 now be reformed and the plate swaged again as before. Two 
 or three swagings are usually sufficient to secure fair palatine 
 and partial border adaptation. In case the palatine arch is 
 deep and it is difficult to drive the plate into the dee])est por- 
 tion of it, the die may he set, base down, on the swaging block, 
 a ball of paper large enough fill the vault space is adjusted, 
 and a piece of hardwood about an inch in diameter and long 
 enough to serve as a handle, the end of which is rounded, is 
 set against the paper, and with the hammer adaptation is 
 quickly secured. The paper is now removed from the counter 
 die and re-formed into a layer about one-fourth inch thick. 
 
 ItKSri.T OF FIRST SWAGING ON I'lATi: 
 
 This is spread over the counterdie and into its depression, 
 the plate set in i^osition, and with the die it is driven partially 
 to place, with two or three light blows of the hammer. Re- 
 move, correct wrinkles, trim oft" excessive surplus, and repeat 
 the swaging until adaptation is secured, always keeping a 
 considerable layer of paper between the counterdie and plate. 
 The time required for swaging a base of heavy plate by 
 this method is usuallj* less than ten minutes, after the die and 
 counterdie have been secured and the paper ball prepared. 
 The lingual surface of the base does not show an indentation 
 or scratch, if reasonable care is observed. The baseplate 
 is not perceptibly thinned at any ])oint, and an adaptation to 
 the die, equal to that secured in the usual way with thinner 
 plate, can readily be developed. 'I'he paper acts as a cushion, 
 and obviates tearing, stretching, and excessive thinning of 
 the plate. With a thick die, heavy smashing blows can be 
 delivered with a heavy hammer, and the plate quickly brought 
 
ALUMINUM BASH IJENTUKKS 215 
 
 into shape, tlie ousliioii-like aetiun of the paper obviating to 
 a great extent the marring of the die face. 
 
 Care should be taken to keep the anterior margin of die 
 back of the corresponding opening in: the counter die while 
 swaging in the paper ball, otherwise there is danger of shear- 
 ing the plate anteriorly as the die is driven into the flattening 
 mass of paper. 
 
 Practically the same results can be secured with the Ash 
 liubber Cushion Swager, or with any good hydravilic press in 
 which a yielding or plastic material can be interposed be- 
 tween the plate and counterdie or which, by confining prop- 
 erly, will answer for the counter die. 
 
 DEVELOPING THE VULCANITE SHOULDERS AND 
 ANCHORAGES 
 
 In all cases, whenever possible, the location of the finish- 
 ing shoulder for the vulcanite should be determined after 
 having occluded the teeth, waxed up the case and tried the 
 denture in the mouth. This plan enables the prosthetist to 
 develop the correct lingual contour of the denture in wax, so 
 that enunciation may be normal, and lay the shoulder line at 
 the margin of the wax as determined by this final test. The 
 groove is cut and the shoulder developed in the aluminum 
 base after the case is flasked and separated. Or this may be 
 the order of jorocedure : 
 
 The line may be located and the groove cut, after having 
 occluded the teeth, before trial in the mouth. This plan will 
 give approximately accurate results, but occasionally it will 
 be found necessary to restrict or extend the area as first out- 
 lined. In case extension is necessary this can be easily ac- 
 complished, but when the area must be restricted, the shoulder 
 having already been formed too far to the lingual, an un- 
 sightly marring of the baseplate results which is difificult. 
 if at all possible, to eliminate. Finally this method may be 
 adopted. 
 
 It is conmion practice, but decidedly a wrong method, to 
 locate the position of and form the shoulder by guesswork 
 iiefore trial in the mouth or even arranging the teeth, because 
 in nearly every ipstance some modification will be found 
 necessary when the teeth have been occluded. 
 
 TECHNIC OF FORMING THE SHOULDER 
 
 The shoulder is formed by first cutting a groove with a 
 small wheel bur in the engine, following the line scratched on 
 
21(i ALUMINUM BASK DIONTCIiKS 
 
 the ]ilate wliich marks tlio line of jimetioii of tlie wax with 
 tiie l)aseplate. This groove usually extends from slightly in- 
 side the center of the tuberosity on one side, lingually, around 
 to the corresponding point on the opposite side. The outer 
 or buccal margin of the groove is chiseled or ground away, 
 cutting the plate freely and broadly, to give the necessary 
 depth to the vulcanite margin which will later occupy the 
 angle and adjacent area. The shoulder is not extended around 
 the labial niid Imccal surfaces in these cases as it is in cast 
 
 bases, or in gold base dentures, since, if pi'operly anchored, 
 the vulcanite will not curl or warp away from the baseplate. 
 
 SPURRING THE BASE 
 
 The general anchorage for the vulcanite is developed by 
 raising 7nany heavy opposed spurs on the area to be covered 
 by it. These spurs can be made heavier and longer, and are 
 therefore much more effective than it is possible to develop 
 on lighter gauges of plate. 
 
 ANCHORAGE BY PERFORATING THE BASE 
 
 In addition to the spurs, five or more holes, oiie-sixteenth 
 ■jf an inch in diameter or slightly larger, are drilled through 
 the base, one on each tuberosity, one opposite each cuspid 
 eminence, on the labial surface, and one on the border crest 
 opposite or between the central incisors. It is essential that 
 holes be placed in these locations for obvious reasons ; there 
 is no objection to increasing the number, when by so doing 
 the efficiency of the anchorage can be improved. The palatine 
 
ALUMINUM BASE DENTUKKS 217 
 
 ends of the holes are conutersunk, and hiter the entire hole 
 should be filled witli wax, to exclude the plaster in flasking, 
 thus insuring the rubber becoming firmly anchored to tlie 
 base at several divergent points. The loop forming plier 
 may be used to raise anchorage loo])s instead of forming the 
 holes as described. 
 
 In fliese cases, as in all other classes of dentures where 
 vulcanite and metal join, cliloro-rubber or ordinary rubber 
 
 cement should be painted on the metal ])arts just ])efore clos- 
 ing the packed matrix, to insui'e a permanent and water 
 tight joint. 
 
 FORMATION OF THE VULCANITE SHOULDER BY 
 MEANS OF A DOUBLER 
 
 A method recently introduced fni' fdrming tlie lingual 
 shoulder without grooving the baseplate is accomplished by 
 swaging a partial base, covering the palatine portion of the 
 base proper, its margins laid in correct i)osition to form the 
 lingual tinisliing shoulder. The doubler is attached to the 
 base by three or more aluminum rivets, which are invisible if 
 the holes on both sides of the plate are slightly coiintersunk 
 
218 ALUMINUM BASK DENTURES 
 
 and tlie wire which serves as rivets fills the holes accurately. 
 Since there is no actual union between tJie two pieces of plate 
 other than being lield in contact with the rivets, fluids of the 
 mouth must sooner or later find their way between, and a 
 disagreeable odor develop. With a successful solder for 
 uniting the two plates the doubler would prove of great ad- 
 vantage in many cases, particularly in badly absorbed cases. 
 In such instances the margin of the doubler in, the absorbed 
 area could be lifted away from the base and raised to a level 
 with the plate at the corresponding point on the opposite 
 side. This will permit the proper palatine contour to be 
 
 APPLICATION OV A DOUBLER HELD BY RIVETING 
 
 developed without showing an unsymmetrical area of vul- 
 canite at any point. 
 
 SOME FACTS ON THE HISTORY OF ALUMINUM 
 CASTING 
 
 The first efforts within tlie writer's knowledge of at- 
 tempts at casting aluminum were made by Dr. J. B. Bean, of 
 Baltimore, who, in 1867, had granted to liim Patent No. 68548, 
 for a device for casting aluminum, a description of which may 
 be found in the patent records of that year. 
 
 The essential points of the apparatus consisted of a box- 
 like flask, in which the matrix was formed in an investment of 
 plaster and pumice stone. There were three openings com- 
 municating with the interior of the flask, one for the intro- 
 duction and another for the exit of liydrogen gas, which was 
 forced into and filled the matrix at the instant of casting. 
 
VLLIMINLIM IJASK UENTLUtKS 21!l 
 
 tbereb}' excluding tliL- atmosphere and preventing oxidation 
 of the metal. 
 
 The third opening had litted to it a long, tapering, de- 
 tachable conduit of soapstoue, which served also as a reser- 
 voir for sustaining a standing column, of considerable height, 
 of excess molten aluminum. The specific claim made for the 
 conduit was that it atTorded means for "supplying fluid metal 
 to compensate for contraction of the metal in the mold, as 
 well as to secure a denser casting by means of the detach- 
 able reservoir, D, heated previous to the pouring of the metal 
 as described." 
 
 Dr. Bean's demise occurred in 1870, and as no one at that 
 time seemed to have succeeded in mastering the technic of 
 his process, but little progress was made in aluminum cast- 
 ing until the latter part of the eighties. 
 
 In June, 1888. the Dental Register, Dr. C. C. Carroll, pre- 
 sented a method of casting aluminum under pressure, together 
 with a description of his apparatus for carrying out the steps 
 as detailed. While interesting, time and space are too limited 
 to present his method in full, and since it has no direct bear- 
 ing on present day technic, for fuller details than those which 
 follow the reader is referred to the article in the journal 
 mentioned or to Harris', edition of 1892. 
 
 The essential features of the Carroll apparatus consisted 
 of a flax in which the matrix was formed of a mixture of 
 three parts plaster and one of fine sand or marble dust. 
 
 The crucible was detachable, and served as a receptacle 
 for the metal while fusing. After adjusting the metal to the 
 flask, the fused metal was cast directly into the matrix through 
 a central sprue, which subdivided within the investment into 
 three, one leading to each tuberosity, the other to the distal 
 vault portion. At the time Of easting, the top of the crucible 
 was closed with a tightly fitting plug. To this a rubber hand 
 bulb was connected, which on compressing forced the molten 
 metal into the matrix. 
 
 In the hands of careful prosthetists, the Carroll appa- 
 ratus was capable of producing a fairly dense casting, with 
 probably no more warpage than occurs in the eastings of 
 today. The apparatus was easily thrown out of adjustment, 
 while the melting of the metal was difficult to accomplish. 
 These objections coupled with the frequent failures, due to 
 various causes, lead to its final abandonment. 
 
 Between 1892 and 1895, the Fenner and the Zeller ap- 
 pliances were introduced. These were similar in this respect, 
 
220 ALUMINUM HASK DKNTUKKS 
 
 tliat each consisted of a l\vo-])iece tlask in wliicli the wax model 
 was invested, and to one of the lialvos of the tlask was lixcd a 
 (!i'ncible in wliicli tlie ahnninuin was fnscd. 
 
 In tlie Fenner appliance, the top of the crncihle was turned 
 true and a close fitting cap adjusted to it. A tube was set in 
 the cap. through whicli was transmitted tlie compressed air, 
 by means of which the metal was forced into the matrix. 
 
 In the Zeller appliance a partial vacuimi was created in 
 the matrix and the metal was drawn in by suction. 
 
 Later on Dr. R. C. Brophy demonstrated that by having 
 reasonalily large sprues, the aluminum when sufficiently fluid, 
 could be made to fill the matrix by tapping the flask. An alloy 
 of 90 per cent of aluminum and to w^hich some other metals, 
 were added to increase the specific gravity, cast lietter 
 by this method than the pure aluminum. 
 
( ' n A P T K H X [ V 
 
 WEIGHTED LOWER DENTURES 
 
 Weighted lower dentures are indicated in those cases in 
 which the alveolar border is badly absorbed, and where a 
 denture of ordinary weight is liable to be more or less dis- 
 turbed by the action of the tongue and cheek muscles. Be- 
 cause of their greater specific gravity, dentures of this type 
 retain their position better under masticatory stress and in 
 speaking than do those corai)osed of vulcanite alone. The 
 weight for dentures of this class is provided for in three 
 ways : 
 
 First, by using weighted, instead of ordinary, rubber for 
 the base. 
 
 Second, by inclosing a bar of metal within an ordinary 
 vulcanite case. 
 
 Third, by casting a base of metal, to whicli the teeth are 
 attached, usually with vulcanite. 
 
 DENTURES OF WEIGHTED VULCANITE 
 
 Weighted rubber consists of ordinary dental rubber, hav- 
 ing uniformly incor])orated within it coarse filings of tin or 
 some metal that does not readily oxidize. In the construction 
 of weighted dentures, this rubber is substituted for the ordi- 
 nary basic material, the incorporated metal furnishing the 
 additional weight required. The technic of construction dif- 
 fers in no respect from that of an ordinary vulcanite case. 
 
 VULCANITE DENTURES WEIGHTED BY MEANS OF A 
 METALLIC CORE 
 
 Additional weight may be given a vulcanite denture dur- 
 ing the constructive steps as follows : Shape a bar of tin or one 
 of its alloys, so that it will fit within the matrix walls of the 
 flasked case without interfering with those walls, the border 
 crest of the cast, or the ridge lap of the enclosed porcelain 
 tooth. The outer wall or gum portion of the matrix is packed 
 with pink rubber first; the lingual portion is lined with basic 
 material, packing it carefully imder the pins of the teeth : 
 the bar of metal, previously conformed, and tested, is laid 
 in the partially filled matrix, the remainder of the rubber is 
 
 221 
 
■Z22 VVKKiHTKU LUWIOH UKNTII KICK 
 
 added, and tbo flask is closed and viilcaui/.i'd in tlie usual 
 manner. 
 
 This simple method of imparting varying degrees of 
 weight to a denture, as the conditions of the case requires, is 
 oftentimes very effective. 
 
 CAST METAL BASES 
 
 When a denture of considerable weight is indicated, a 
 base is cast in metal for supplying the required weiglit, and to 
 this the teeth are attached by various means, the most con- 
 venient being vulcanite. Since the metal which forms the 
 base is cast, the entire matrix into which it is cast must be 
 composed of some refractory material that will not change 
 form perceptibly under the heat to which it will be subjected 
 in preparing it to receive the molten metal. Plaster is un- 
 suited for this purpose because of its tendency to crack under 
 
 heat. A number of good investment compounds are procur- 
 able, those ordinarily used for crown and bridge purposes 
 being applicable to the casting of this type of denture bases. 
 
 TECHNIC OF A WEIGHTED CAST BASE 
 
 The details of construction of a cast lower base is as 
 follows : 
 
 From a suitable impression of the lower arch, develop a 
 cast in investment material. 
 
 Soften a sheet of pink baseplate wax, and apply to the 
 face of the cast. 
 
 Trim it to the approximate outline of the denture base. 
 
 Adapt rolls of wax to the labio-buccal and lingual peri- 
 pheries of the case, burnishing them so as to form a con- 
 tinuous shoulder against which the vulcanite will rest. The 
 outer surfaces of these strips, which in reality form the outer 
 and inner walls of the denture base, should be squared up 
 practically parallel with each other, so that the metal base 
 
WEIGHTED LOWER DENTURES 223 
 
 and the vulcanite may form a continuous surface from the 
 margins of the denture base to the gingivae of the teeth. 
 These surfaces may be, and usually are, more or less curved, 
 but the line of junction of the vulcanite with the base should 
 be free from angles. Or stated differently, both buccal and 
 lingual surfaces of the metal base should meet the corre- 
 sponding surfaces of the vulcanite so as to form continuous 
 surfaces without forming angles. 
 
 Usually one thickness of baseplate wax over the general 
 surface of the cast, increased by the rims around its margin, 
 will prove sufficiently bulky, when reproduced in metal, to 
 give the necessary weight to the denture for retention 
 purposes. 
 
 Excessive weight in lower base dentures should be avoid- 
 ed, as they tire the masticatory muscles, frequently to such an 
 extent that the patient cannot wear a dentiu'e of this type 
 with comfort, or continuously, but must lay it aside from time 
 
 SHOULDER SURFACES 
 
 to time, to give the muscles and oral tissues a rest. Irritable 
 areas frequently develop under the denture base at various 
 points, apparently without cause, but which are in reality 
 directly traceable to the heavy, shifting load to which the 
 mucous tissues overlying the hard, bony points are constantly 
 subjected. Such cases are relieved by reducing the weight 
 of the denture, and by scraping the base over the irritated 
 areas. 
 
 FLASHING THE WAX MODEL BASEPLATE 
 
 When the wax model is formed and anchorage loops for 
 the vulcanite are properly placed, the case is invested in a 
 Watt's flask. Or an ordinary vulcanite flask will answer the 
 same purpose, by making two half round openings in each 
 side of the flask, Cpposite the tuberosities, through which the 
 metal may be poured. 
 
 The cast of the mouth on which the wax model has been 
 formed is now trimmed peripherally, and reduced in depth, 
 so that when set in the lower half of the flask, the peripheral 
 
224 WEIOHTEU LOWER U'ENTURES 
 
 or border margin of wax is level with the line of sejjaration 
 between the two halves of the flask. The east, when ])roperly 
 trimmed, is removed, a mix of investment is made and spread 
 over the bottom and against the sides of the lower half flask. 
 The cast is dijjped in water, so that it will not absorb the 
 moisture in the freshly mixed investment, and thus interfere 
 with its proper setting, pressed into the investment, and the 
 latter smoothed evenly from the inner margin of the flask 
 to the periphery of the wax base. That portion of the flask 
 in which the casting gates are formed should also be filled 
 level at this time. When set, the exposed surfaces of the 
 investment are treated with soapstone, rubbing it in thor- 
 oughly, to prevent adhesion of the investment in the upper 
 half of the flask, when added. Slight grooves, leading from 
 
 I'-I.ASK FOK !■ 
 
 the distal ends of the baseplate to the outer ends of the gate 
 projections, should l)e drawn on the upper surface of the 
 investment of the half flasked case, to indicate the width and 
 direction of the sprues to be cut, through which to pour the 
 molten metal. These groves on the lower produce ridges on 
 the upper investment, which coincide in location and direction 
 with the grooves. When half round grooves are scraped be- 
 tween these lines, the latter of which should diverge from 
 within outward to give a funnel form to the feed sprue, and 
 the two halves of the flask are placed together, a full, free, 
 open gate is formed, leading from without inward to each 
 distal end of the matrix. 
 
 The second mix of investment is now made, and the top 
 half of the flask entirely filled with it. Before adjusting the 
 two halves of the flask together, some of the freshly mixed 
 
WEIGHTED LOWER DENTURES 225 
 
 investment, of whk'li tliere should l)e a surplus, is applied to 
 the exposed surface of the wax base, care being taken to work 
 it into all of tlie irregular surfaces and angles. By piling 
 the investment somewhat higher in tlie middle of the case 
 than at the edges, adjusting the upper half of the flask, and 
 closing under pressure, the excess is forced out around the 
 margins and through the openings on the top and bottom of 
 the flask, thus eliminating air spaces. 
 
 When the investment has set, the flask is separated, the 
 wax removed, the half gates cut on each side of the flask, all 
 delicate margins are removed, the matrix freed from all 
 debris, and its entire interior, togetlier with the cast face, 
 are brushed thoroughly with No. 1 graphite to aid in the 
 production of smooth surfaces to the casting. The flask is 
 closed and clamped, and the joint between the two halves 
 luted with a paste of equal parts soapstone and plaster, which 
 should be carefully forced into every crevice, to prevent the 
 escape of the molten metal when poured. 
 
 The flask is now set over a low flame to expel the moisture 
 from the investment. The heat should not be so intense as 
 to disintegrate the plaster binder of the investment. Tests 
 for moisture should be made, from time to time, by holding 
 a piece of polished cold steel or glass over the gate openings ; 
 when no steam condenses, the case is ready for casting. 
 
 CASTING THE BASE 
 
 For weighted dentures any of the several alloys pre- 
 pared and sold for this purpose may be used, or an alloy 
 which will serve equally as well can be compounded in the 
 dental laboratory. Kingsley's alloy is composed of tin, 16 
 parts, and bismuth, 1 part. Another which serves equally as 
 well is tin, 16 parts, cadmium, 1 ])art. Tin alone will not cast 
 sharply, nor is it as hard as an alloy of this type should be 
 for the ]Hirpose intended, therefore one or the other of the 
 metals mentioned is added to correct the fault. 
 
 The flask is now set upright, an ingot of alloy is fused in 
 a small ladle and ])oured in one of the o]ienings. If the ease 
 is sufficiently hot, perfectly free from moisture, and no cracks 
 have develoi3ed in drying out, the metal will fill the matrix 
 and rise in the opposite gate, thus indicating that the space 
 is filled. Should crevices develop in the investment while pre- 
 paring the case for casting, the flask should be entirely sur- 
 rounded with molding sand, well packed around the sides, 
 leaving only the sprues exposed, otherwise the metal will 
 
2i!G WEIGHTED LOWER DENTURES 
 
 escape through some of the opeuings, and the niatiix be im- 
 perfectly filled. 
 
 When the metal has crystallized, the tlask is chilled in 
 cold water, and the casting removed and cleansed. The ex- 
 cess metal is removed with saw and fies, and those surfaces 
 of the base not to be covered by the vulcanite are smoothly 
 finished. 
 
 With a graver retention is secured by raising heavy, 
 opposing spurs on the area to be covered hy the vulcanite. 
 These spurs are developed in addition to tlic l(i(i]>s which are 
 formed in casting. 
 
 When ])roj)er]y triuHiicd and iiolished, a roll of wax can 
 
 ST BASE WITJl TEETH WAXED 1-N I'OSITIOX 
 
 be mounted on the cast base and a wax contour model devel- 
 oped in the usual manner. 
 
 MODIFICATION OF THE FOREGOING METHOD 
 
 Since the recent improvements in the technic of casting 
 and in investments, and waxes, it is found that these weighted 
 base dentures can lie handled much the same as aluminum, 
 that is, making a singh' investment and dissipating the wax 
 by heat. 
 
 The specific gi'a\'ity nl' the allov is sufricient to insure a 
 dense and usually perfect casting without the ajipli cation of 
 pressure, as required in aluminum casting. 
 
 In flasking a weighted base denture, preparatory to pack- 
 ing and vulcanization, the line of sejiaration of the flask should 
 occur at the line of junction of the vulcanite with the metal, 
 thus leaving the base in the lower half, while the matrix con- 
 taining the teeth is in the upper half of the flask. 
 
 The surface of the metal to be covered by the vulcanite 
 should be painted with a film of chloro-rubber, or rubber 
 cement, just before the final closure of the flask. 
 
WEIGHTRn LOWER DENTTIRES 227 
 
 HISTORY 
 
 lu 1856, Di'. A. A. Blniidy introduced a system oi' cast- 
 ing denture bases, similar to the method just outlined, and 
 which he designated the Cheoplastic Process, signifying "the 
 making of i)lates hy i)nii ring a metal nmde plastic hy heat" 
 (Harris). 
 
 The production of a denture in those days, by forming it 
 in a matrix, of a plastic material which hardened, was an in- 
 novation. Vulcanite and celluloid were not yet introduced, 
 and, therefore, this was the first plastic process of denture 
 construction. 
 
 The exact composition of Blandy's alloy is not known, 
 but the metals consisted of silver, bismuth and antimony. 
 
 The introduction of vulcanite as well as celluloid follow- 
 ing shortly after lessened the interest in cast metallic bases in 
 general, but because of the advantages of the weighted base 
 for lowers, more or less use has been made of it where 
 indicated. 
 
 Weston, Wood, Watt, Rose, Kingsley and others have 
 formulated alloys for denture bases, which are mentioned 
 elsewhere. 
 
 VULCANITE BASEPLATES 
 
 In cases where it is ajjparent that good adaptation of a 
 denture to the oral tissues may be difficult to secure, because 
 of peculiarities in form of the Itorder or some unusual con- 
 dition of the oral tissues, a preliminary baseplate of vulcanite 
 can oftentimes be constructed to good advantage. This vul- 
 canite form, molded over an accurate cast of the mouth, 
 affords a reliable test as to adaptation and stability of the 
 baseplate, before the bulk of technical details have been car- 
 ried out and if successful becomes the permanent base. If 
 imsuccessful, another one can be constructed, or a different 
 plan of procedure adopted, early in the constructive stages, 
 and without further loss of time. 
 
 TECHNIC OF CONSTRUCTION 
 
 Over an accurate cast of the mouth sheet wax is adapted 
 in the usual manner, and trimmed to correct peripheral out- 
 line. The wax baseplate should be slightly thicker than the 
 permanent base is to be, so as to allow for loss of material 
 in finishing. A roll of wax about one-eighth inch in diameter 
 is laid, in a svmmetrical curve, around the lingual surface of 
 
WEKIHTKIJ LOWKK UENTUKES 
 
 the border, beginning- a little t(i the buccal of one tuberosity, 
 passing lingually and terminating at a corresponding point 
 on the opposite side. The margin of wax presenting toward 
 the border crest sliduld lie finislied squarely and without 
 
 vri.rAxrTK iiASi: ueahv to hkckive wax oi'ciasion rims 
 
 undercuts, for it is against this shoulder of the vulcanite that 
 the rubber which encloses the teeth is molded. The shoulder 
 should be carried well u]) toward the crest of the boi'der, but 
 must be broadened linguallx' ti> furnish an amjile liase for the 
 
 I.INCIAL \Ii:\\ III' \ I IMSIII II III \ll HL COM- 
 POSED OF THHEI; COLORS OF M LCAXITE 
 
 bicuspids and molars. If l)roader than necessary, it is easily 
 reduced in the final finishing of the denture. 
 
 It is not necessary to extend the strip around the labial 
 and buccal periphery of the baseplate, as the pink vulcanite 
 
WEIGHTED LOWER DENTURES 229 
 
 will present a better appearance than a rim of basic material 
 in this location. That margin of the strip presenting toward 
 the central vault portion of the liaseplate should be burnished 
 down smoothly so as to form a synunetrical curve witli the 
 general palatal arcli. 
 
 Having been given its pro})er form and being smoothly 
 finished, the wax liaseplate, on its cast, is flasked in the usual 
 
 IK Ari'Llr.\Tlll\ OF IIASEPLATES 
 
 manner, the flask i)acked, ami \iilcanized. The baseplate is 
 now only roughly finished on the lingual, but thoroughly pol- 
 ished on the palatine surface. In this condition it is ready to 
 receive the wax rim, tlie formation and a]i)>lication of which 
 will be described later. 
 
 It is common iiractice to form the baseplate of dark or jet 
 black rubber, and attach the teeth to it in the second A'ulcan- 
 ization with marodu oi- sonic of the lighter shades of red 
 
 \ri'i.iKi) T( 
 
 rubber. When this plan is carefully executed most beautiful 
 and artistic substitutes can be produced. Such a denture, 
 finished, will present palatine and border surfaces entirely 
 black, a similar lingual surface extending well out to the 
 lingual surfaces of the teeth, a narrow, symmetrical band of 
 maroon or red vulcanite l)etween the black vault ] portion and 
 the teeth, with full gum restoration of granular ]iink on the 
 labio-buccal surface. 
 
2;i0 WEIC.HTICII LOWKK DKNTURBS 
 
 CONSTRUCTION OF TEMPORARY BASEPLATES 
 USING "IDEAL BASEPLATE, SPECIAL" 
 
 The following directions should he ohserved in the con- 
 struction of temporary haseplates : 
 
 Place cast on bench, face up. Center a sheet of rigid 
 baseplate material (preferably Ideal, Special) over it. Ap- 
 ply tJie soft brush flame of the blowjiipc, moving it quickly 
 
 IDB.VI, BASEPLATE KEMOVED FROM CAST 
 
 so as not to overheat any particular area and cause adhesion 
 to the cast, bnt rather to soften the whole sheet uniformly. 
 As soon as it begins to settle, remove the flame, and with 
 the fingers apply light pressure to adapt it to all surfaces 
 of the cast. Avoid undue pressure which thins and weakens 
 the material unnecessarily. Apply the blowpipe to the labio- 
 
 SECTIONAL VIEW OF CAST AND BASEPLATE UNIFORMLY AD/VPTED 
 
 buccal portions to soften somewhat, remove the partially 
 adapted baseplate, and with shears cut the base to approx- 
 imately its correct peripheral outline. Eeturn to the cast, 
 correct the distortion that has occurred from the use of the 
 shears, complete the adaptation, chill and use the vulcanite file 
 for the final finish of the peri]iheral margins. The file should 
 
WElGHTEn LOWER DENTURElg 231 
 
 be applied diagoiitilly nr suuiewliat along the line of direc- 
 tion of the margin rather than crosswise, to obviate fractur- 
 ing the baseplate. A thin blade spatula, heated quite hot, may 
 be used instead of the shears for cutting the baseplate to 
 correct peripheral outline, passing it along the peripheral 
 line while the baseplate is on the cast. 
 
 The baseplate may be reinforced in several ways, one 
 of the most common methods being to melt some of the sur 
 plus material against the areas it is desired to strengthen, 
 and smooth the addition down with a very hot spatula. 
 Another method is to bend a piece of 11 or 12 gauge brass, 
 German silver, or iron wire to the form of the arch, but slight- 
 ly smaller, attach it by warming and with melted wax to the 
 baseplate just inside the border crest, so as neither to inter- 
 fere with the proper arrangement of the teeth nor with the 
 development of correct lingual contour in the final waxing of 
 the dentui-e. 
 
 When trimmed to correct peri^iheral outline, strengthened 
 in the weak areas, and tinal close adaptation has been se- 
 cured, the baseplate is ready for the application and pre- 
 liminary contouring of the wax rims. 
 
 TEMPORARY BASEPLATES OF METAL 
 
 Sheet tin or lead, 14 to 16 gauge, when properly adapted 
 to the cast makes a most excellent base for wax contour 
 models. The simplest method of developing a base of this 
 class is as follows : A cast of the mouth having been secured 
 and its l)ase made flat, it is placed on the rubber cushion of 
 the Ash Swaging Machine, a sheet of metal of suitable size 
 is laid over its face, the other rubber cushion laid on the 
 sheet and pressure api)lied to force the metal partially to 
 ])lace. The surplus is trimmed off with shears, the wrinkles 
 cori'ected, and final swaging comjileted on returning to the 
 press. If care is observed in these steps, no injury will occur 
 to the cast, and it can be used subsequently for the comple- 
 tion of the case. In work of this class, the use of oxy-chloride 
 of magnesia for casts is most strongly indicated, as, in fact, 
 it is in all vulcanite ^lenture construction. 
 
 Another method, whereby a metal baseplate similar to the 
 one just described can be formed without subjecting the 
 permanent or final casts to the ]iressiu'e of swaging, is car- 
 ried out as follows: 
 
 A reasonably good impression of the arch, involving all 
 of the areas to be covered bv the finished denture, is secured 
 
2;!2 WKIGHTEIl LOWER DION'TrKBS 
 
 ill iiiodcliiiy coiupouiul, oiuitting- the rt'lieutiiig .stops pre- 
 viously mentioned. From this impression a east is secured 
 and a. tin base swaged as described. Tliis base is trimmed 
 to correct periplieral outline and tested by trial in the mouth. 
 A thin layer of softened modeling compound not more than 
 oue-sixteentli of an inch thick is laid evenly over the interior 
 of the baseplate, which now is to serve also as an improvised 
 impression tray. An impression, worked out by reheating 
 and the various corrective steps previously mentioned, is 
 secured, and all excess carefully removed. This now con- 
 stitutes an impression-baseplate, on wliicli rims of wax can 
 be built to form the wax contour model. When transferred 
 from the mouth to the occluding frame b,\- means of the face 
 bow, instead of droi:)ping tlie original casts on which the 
 metal bases were formed into the wax contour model, freshly 
 mixed plaster or the magnesia compound is filled in and built 
 against the bows of the occluding frame. If oiled before 
 forming the cast and no undercuts are i)resent, the wax model 
 denture will readily separate, when removed for final trial in 
 the mouth. The advantage of this method consists almost 
 solely in the increased stability of the wax model dentures 
 during trial in the mouth, over temporary baseplates, of any 
 type, adapted to casts in the ordinary manner. 
 
C HAP T K R X A' 
 
 RETENTION OF PARTIAL DENTURES 
 
 A partial denture, to l)e successful, uuist fulfill certain 
 requirements : 
 
 First: It should restore as fully as possible the function 
 of mastication so far as the latter may have been impaired 
 by the loss of the natural teeth. 
 
 Second: It should restore the esthetic features of the 
 dental arch by supplying substitutes wliich harmonize in form 
 and color with the remaining,' natural organs. 
 
 Third : It should be so adapted to the remaining teeth 
 and tissues as to maintain its position with oertaint}^ and 
 comfort when the masticatory apparatus is in an active, as 
 well as a passive, state without causing immediate or gradual 
 decay or injury to the natural teeth present. 
 
 Of the several requirements mentioned, that of retention 
 — is usuallj' the most difficult of accomi)lishment. Various 
 means, both physical and mechanical, are employed to attain 
 this end, the most important of which are atmospheric pres- 
 sure, adhesion, fricfio)i and specialised fricfional appliances. 
 
 ATMOSPHERIC PRESSURE AND ADHESION 
 
 The principles of retention l)y means of atmospheric 
 pressure, and adhesion also, have previously been explained. 
 For various reasons these forces, although of value, are not 
 as effective in the retention of partial as of full dentures. 
 
 The degree of force exerted by the atmosphere and ad 
 hesion upon objects from between the contact surface of which 
 the air has been exhausted and close ada])tation secured, is 
 directly jiroportional to the square of the area involved. 
 Therefore the more limited the area of oral tissues covered 
 by the baseplate, the less can these forces be relied upon for 
 retention purposes. 
 
 In partial cases the presence of natural teeth necessarily 
 restricts the size t.f the baseplate, since the periphery of the 
 latter must fall within, or terminate against, the lingual sur- 
 faces of the teeth involved. This reduction in size of the 
 baseplate therefore reduces the et¥ectiveness of adhesive 
 force. Again, the line of junction of the dentui'e with the 
 
 233 
 
231 KK'rKNTlOX OF PAH'I'IAL DlONTtTIiKS 
 
 iiaturui tec'tli is m pcciiliaily \ ulrHMahlc ijoiiil Tor the ingress 
 of air, since tlie mueons tissues of the eheeks, lips and palate 
 cannot be utilized for sealing up and i)rotecting the margins 
 against the return of air when once withdrawn from between 
 baseplate and tissues, as is the case in full dentures, and this 
 also is a further cause for reducing the force of adhesion. 
 
 FRICTIONAL RETENTION OF PARTIAL DENTURES 
 
 The simplest form of frictional retention available for 
 partial dentures consists in abutting tlie sides of the latter 
 against the lingual surfaces of, and in the embrasures be- 
 tween, teeth situated on opposite sides of the arch, or suf- 
 ficiently far apart to present opposing surfaces, which, when 
 the denture is in position, tend to resist displacement. The 
 alignment of the teeth must be favoralile for such retention. 
 
 CUT SHOWING INCM.NATIIIN TOWARD EACH OTHER OF TEETH OX OI'I'OSITE SIDES 
 OF THE AKCH 
 
 viz., the distance between the cervices of the teeth opposite 
 each other in the same arch must be greater than at the points 
 of greatest lingual convexities, or points of their nearest 
 ai^proach. 
 
 A denture moulded over the cast of a mouth with teeth 
 bearing the relation to each otlier as stated, will spring as 
 it passes over the points of nearest approach of the teeth 
 involved, and resume its normal width without undue lateral 
 pressure when firmly seated on the oral tissues. Such an 
 appliance is called a spring plate or denture, and yet it does 
 not exert lateral pressure against the teeth except on intro 
 duction and removal. 
 
 When the lingual surfaces of the teeth diverge from gin- 
 gival to occlusal this means of retention cannot usually be 
 utilized, as the constantly diverging surfaces are mechanically 
 opposed to such retention. Frequently, however, by allowing 
 
RETENTION OF PARTIAL DENTURES 235 
 
 the denture margius to extend into the embrasures, when the 
 latter are well defined, frietional retention may be developed 
 even in those eases where the general alignment of the teeth 
 presents more or less parallel relation of surfaces. 
 
 In such cases, and especially when the crowns of the teeth 
 are too short for clasping, the writer has inserted inlays with 
 projecting lugs in two suitably situated opjiosiug teeth in 
 such manner that the lugs will engage with, and offer frie- 
 tional resistance to, the displacement of the denture. Some- 
 times, too, How anchor screws inserted in the lingual sur- 
 faces of the teeth will fulfill the requirements of the case. 
 The use of the inlays and wire lugs, as suggested, have proven 
 very useful in many difficult cases, while no serious results 
 have followed this method of practice. 
 
 In case either the anchor wires or the lug inlays are used, 
 the projections should lie rounded so as to permit the denture 
 
 KETENTION OP BASEPLATE BY MEANS OP WIRE LUGS 
 
 to spring in and out of position without catching on the lug 
 margins or straining the teetli to an undue extent. 
 
 SPECIALIZED FRICTIONAL APPLIANCES 
 
 Various forms of specialized frietional appliances are 
 in common use for retaining partial dentures in position in 
 the mouth. These usually are attached to and become a part 
 of the denture itself. In other cases the attachment consists 
 of two parts, one of which is attached to the denture, the 
 other to a natural tooth, to an inlay, to a crown set upon a 
 natural tooth or root, or to a wire or bar permanently fixed 
 to crown or inlay. 
 
 Among the appliances in general use may l)e mentioned 
 clasps of various forms, double bars or stays, and special 
 attachment, such as the Roach, Grilmore, Morgan, etc. 
 
236 RETENTION OF PAKTIAL UBNTURP^S 
 
 CLASPS 
 
 Clasps arc partial Uiiiid-likc apj)liaiiccs ailajitcd to tlu; 
 natural teeth for retaining in the month tiie partial denture 
 of which they form a i)art. They are usually constructed 
 of flat plate or half round wii-c of gold clasp inetal, composed 
 of pure gold, platinum, silver and copper. This alloy pos- 
 sesses well defined elastic i)roi)erties. The proportions of 
 silver and copper may he A-aried, however, or the silver 
 omitted altogether, as its i)resence imparts hut little 
 resiliency. 
 
 Considerahle difference of opinion exists as to the ulti- 
 mate value and utility of clasps, the argument of those op- 
 posed to their use being that the injury to the natural teeth 
 far outweighs the good derived from their use. Those who 
 favor the application of these appliances are e(|ually as posi- 
 tive in their conviction of the benefits of such attachments. 
 A statement of the objections and advantages of clas^JS will 
 be in order. 
 
 OBJECTIONS TO THE USE OF CLASPS 
 
 The princi])al ol)jections ui'ged against the use of clasps 
 are as follows : 
 
 First — The accumulation, retention and fermentation of 
 food in the space between clasp and tooth will invite, and 
 in many cases does, induce caries. 
 
 Second — Frictional action of the clasp against the enamel 
 will abrade the latter, induce hypersensitiveness in the tooth 
 structure, set up gingival, and in some cases, peridental ir- 
 ritation. As consequence the patient suffers more or less 
 discomfort, and in time the crown or the entire tooth may be 
 lost. 
 
 The deleterious conditions here cited are fretpiently ob- 
 served and therefore these objections have an apparently 
 good foundation. They can, however, in almost every in- 
 stance be traced to one or more of several causes, most of 
 which may be averted, as for instance, injudicious applica- 
 tion of clasps to teeth unsuited for the extra stress they must 
 sustain; imperfect technic in the construction of the appli- 
 ances; or to lack of habitual care of the natural teeth and 
 denture on the part of the patient. 
 
 ADVANTAGES DERIVED FROM THE USE OF CLASPS 
 
 First — Stability of the denture at all times, in speak- 
 ing, laughing, and in masticatory effort is practically insured. 
 
RETENTION OF PARTIAL DENTURES 237 
 
 Second — By their u«e the basephite wliich carries the 
 replaced teeth need cover but a very small area of the oral 
 tissues, since adhesion and atmospheric pressure as a means 
 of retention are unimportant factors when clasps are used. 
 
 When judiciously applied, properly constructed, and the 
 moutli is given reasonal)le care and attention by the patient, 
 clasps are of the itreatest convenience and comfort, and will 
 cause but little injury to the teeth or tissues. In the expe- 
 rience of the writer, the advantages gained from the use of 
 clasps, where indicated, are infinitely greater and far out- 
 weigh any harm that may result from their presence. 
 
 Should sensitiveness be induced, or caries eventually 
 develop, the tooth can be devitalized and crowned when oc- 
 casion requires, and be made to render still further service, 
 by carrying a newly adapted clasp. It is seldom advisable to 
 crown a tooth to be clasped in anticipation of subsequent 
 caries, as such procedure may never be required. 
 
 REQUISITES OF A CLASP 
 
 A clasp, as its name implies, is an appliance which 
 grasps or clings to the tooth to which it is adapted. To be 
 effective it should embrace more than one-half, usually about 
 two-thirds, of the periphery of the tooth. A clasp should be 
 so constructed that when in position tirm, frictional contact 
 is established between both its gingival and occlusal peri- 
 pheries and the axial walls of the tooth to which it is adapted. 
 In fact, the efficiency of a clasp depends on closeness of 
 adaptation to the tooth, resUiency, and inlwient strength. 
 
 ADAPTATION 
 
 Closeness of adaptation insures stability by lessening the 
 tendency of the clasp to rotate, cant or slide when in posi- 
 tion on the tooth, all of which movements tend to unbalance 
 the denture when subjected to masticatory stress. The nearly 
 parallel relationship of the axial walls of most teeth suitable 
 for clasping renders the attainment of this requisite dif- 
 ficult, in clasps of the ordinary partial band type. Stability 
 may be secured, when good ada]itation has been developed, 
 by the addition of- a small but rigid lug extending from the 
 occlusal margin of the clasp, up to and over the mesial or 
 distal marginal ridge of the tooth clasped. The lug should be 
 located as centrally as })ossible between the two extremities 
 of the clasp. Such an addition converts an ordinary partial 
 band clasp into a stop clasp. 
 
238 RETENTION OF PARTIAL DENTURES 
 
 Without doubt this form of clasi), or some modification 
 of it, in whicli tlie stop principle is embodied, is the most 
 satisfactory and serviceable of any of the common types of 
 partial band clasps. By the addition of tlie stop, frictional 
 wear of the enamel is practically overcome, undue pressure 
 on tlie alveolar ]irocess covered by the denture and on the 
 gingiva surrounding the tooth clasped is obviated, and a 
 feeling of security and comfort to the wearer of the denture 
 results, not possible to be realized from the use of the ordi- 
 nary type of clasp. The credit of having evolved, demon- 
 strated and described the practical ai^plicability of the stop 
 clasp should be ascribed to Dr. Bonwill. 
 
 THKEE CASES IIY BO.NWH.L SUOWINCI HIS ArPl.lr.VTlO.N UF THE STOP CLASP. AND WIBE 
 ATTACHMENT OF CLASP TO BASEPLATE 
 
 The degree of perfection of adaptation of the clasp to 
 the tooth depends on the skill displayed by the prosthetist, 
 the technical steps employed, and to a certain extent on the 
 character and thickness of the metal used in its construction. 
 
 RESILIENCY OF THE CLASP 
 
 Resiliency in a clasp is that property which permits it 
 to spring over the enlarged portion of the tooth it embraces 
 in introducing and removing the denture, without becoming 
 permanently distorted when subjected to such stress. This 
 
RETENTION OP PARTIAL DENTURES 239 
 
 quality depeiids ou the character of the metal of which the 
 clasp is composed, as well as on the width and gauge of the 
 clasp itself. The gold alloy known as clasp metal, previ- 
 ously mentioned, is used almost exclusively for clasp con- 
 struction because of its hardness and well defined elastic 
 property. The elasticity noticeable in a clasp when sub- 
 jected to stress would be classified in pliysics under the term 
 of elasticity of flexure, in which the molecules of the clasp 
 metal on the inner periphery are elongated when subjected 
 to stress, while those on the outer side are compressed. Per- 
 manent distortion occurs when the stress applied carries the 
 metal beyond the modulus limit, in which condition it is said 
 to be strained, as when stress is removed, the piece, of what- 
 ever shape, does not return to its original form. 
 
 THE INHERENT STRENGTH OF CLASPS 
 
 A clas}) may be well adaiited to a tooth, possess sutificient 
 resiliency to be carried to, and removed from, position in the 
 mouth without becoming distorted under ordinary stress, and 
 yet prove imsatisfactory with use. 
 
 Undue stress exerted on clasps in iDolishing on the lathe, 
 in introducing and removing the denture, careless handling 
 in cleansing, letting the denture fall, as well as other acci- 
 dental causes, frequently distort and oftentimes destroy the 
 eft'ectiveuess of these a^jpliances. Many clasps otherwise 
 suitable fail because of lack of inherent strength, and con- 
 sequently the very oliject for which they are designed is 
 defeated. 
 
 The remedy lies in correctly estimating the proper width 
 and thickness of the clasp in proportion to its length, and 
 developing the appliance accordingly. These two factors 
 are determined by the length of tooth to be clas^jed. Short 
 teeth require narrow, but rather thick, clasps, the thicker 
 gauge compensating for the weakuess resulting from re- 
 stricted width. 
 
 A thick, narrow clasp, hoAvever, is not as resilient as a 
 thinner, wider appliance of equal length containing an equal 
 amount of metal as the former. The truth of this proposition 
 is plainly apparent -by noting the difference in resiliency of 
 steel springs of Varying widths and gauges. A spring should 
 be so proportioned as to carry the extreme load to which it 
 may be subjected without tlie occuri'ence of permanent dis- 
 tortion. In fact, it should possess a considerable range of 
 elasticitv between the extreme load limit to which it will be 
 
240 RKTKNTION OK I'AR'I'IAI, DIONTURKS 
 
 subjected and tlu' iiiodulus limit, or point wlicnc |)ernianeut 
 distortion occurs. 
 
 Inlierent strength with bulk to carry extreme loads, while 
 a high degree of resiliency is retained, is imioarled to springs 
 in tlie mechanical field by dividing the necessary bulk of 
 metal into comparatively thin layers called leaves. In other 
 words, the spring is made u]) of several members consisting 
 of the principal spring reinforced by a series of leaves of 
 gradually decreasing length, but of approximately the same 
 thickness, rigidly fixed to the main spring, usually at the point 
 where stress is api)lied. The leaves throughout the greater 
 ])ortion of their length are free to slide or move freely against 
 each other as the load or stress varies, and thus the resilient 
 power of each member of the s])ring is utilized in reducing 
 shock and avoiding strain. 
 
 This i^rinciple of reinforcement of clasps for dental pur- 
 poses cannot well be applied for obvious reasons, although 
 
 at times it is necessary to vary the flexibility of a clasp at 
 different points throughout its length. For instance, when 
 a clasp must of necessity be narrow, thick and almost devoid 
 of resiliency where it passes through the interijroximate 
 space, the buccal and lingual flanges may be increased in 
 width and decreased in thickness to develop greater elas- 
 ticity. In sucb cases extra thick plate is used for the clasp 
 to give strength in its narrowest part, and the necessary re- 
 duction in thickness on the l)road areas is made by filing, 
 grinding and polishing. In a numl)er of cases the writer 
 has secured excellent results by cutting a section from the 
 central portion of the broad areas of a clasp after adapta- 
 tion has been developed, without reducing the thickness of 
 the appliance. 
 
 Various modifications of the ordinary flat band clasp, 
 specially of the broad type, are employed to decrease rigidity 
 
RETENTION OF PARTIAL DENTURES 241 
 
 and increase resiliency. In addition to removing a central 
 section from the flange as detailed, it may be divided 
 throughout a portion of its length, as suggested by Dr. G. H. 
 Gushing, or the central area may be removed, and the gin- 
 gival portion severed. 
 
 While a clasp must possess inherent strengtli sufficient 
 to withstand unusual stress, it should not be too unyielding. 
 When deficient in elasticity because of its bulk, and at the 
 same time possessing excessive inherent strength, the tooth 
 
 A CASE CONSTRUCTED BY DB. G. H. CrSHIXG IN ISCO 
 
 which it embraces will be subjected to unnecessary strain in 
 removal of the denture if the adaptation of the clasp to the 
 tooth is reasonably close. 
 
 GAUGES OF CLASP METAL COMMONLY EMPLOYED 
 
 Many clasps fail under stress of usage, as before stated, 
 because of lack of inherent strength. This is usually the re- 
 sult of using too thin a gauge of clasp metal, or so reducing 
 their width as to render them weak. 
 
 As a rule, 26-gauge clasp metal is as thin as should be 
 
 VARIOUS .METH(III.S OF IXrltKA.'^INC ItF.SI MKM'I IX CLASl'S. KI CI'AI, VIEW 
 
 used. When 28 gauge is employed, unless very wide, it should 
 be stiffened by flowing 18K solder on the outer periphery. 
 While this method imparts rigidity, it reduces resiliency, and 
 therefore should seldom be adopted. 
 
 Usually three gauges of clasp metal will answer for all 
 ordinary cases that may present : 26 gauge for long, 24 gauge 
 for medium and 22, or in extreme cases 20 gauge may be re- 
 quired, for short teeth. Clasps of equal length may vary in 
 width, thickness and resiliency, and yet contain essentially 
 
242 RKTENTION OF PARTIAL DRNTURKS 
 
 the same auioiint in bulk of material. For example, a elasi3 
 one-eighth inch wide, composed of :20-gange plate, which 
 equals .03196 of an inch thick, will contain essentially the 
 same amount of metal as one of equal length and twice as 
 wide of 26 gauge, which equals .01594 inch thick. Its re- 
 silient index, however, will be noticeably less tlian that of the 
 26 gauge clasp. 
 
 TYPES OF CLASPS MOST COMMONLY USED 
 
 Clasps vary in form according to the requirements of 
 the case for which they are constructed. These requirements 
 include the class and forms of teeth to which they are adapted, 
 the part they are to fulfill in the retention of the denture, and 
 the load they are required to carry. 
 
 The ordinary forms of clasps may l)e talnilated as fol 
 lows: 
 
 1. Partial fiat band clasp. 
 
 2. Half-round wire clasp. 
 
 3. Double wire or bow clasp. 
 
 4. Stop, wire or band clasp. 
 
 5. Double-stay clasp. 
 
 6. Stay clasp. 
 
 THE PARTIAL FLAT BAND CLASP 
 
 This form of clasp, as its name indicates, consists of a 
 partial flat band, usually of clasp metal, of suitable gauge and 
 width, which embraces about two-thirds of the tooth peri- 
 phery. The gingival and occlusal margins of the clasp should 
 be iDractically parallel to insure as nearly equal resiliency 
 throughout its entire length. This, however, does not imply 
 that these margins should be straight, but curved somewhat 
 similar to, but usually less pnmounced than, the gingival gum 
 curvature. 
 
 Band clasps, should be reasonably broad, the average 
 width varying from two to five millimeters. The broader the 
 clasp, the more stability will be afforded the denture. 
 
 On the other hand, a clasp of this type should not be so 
 broad as to encroach upon the gum tissue and thereby induce 
 irritation; neither should it interfere with occlusion of the 
 opposite teeth. The buccal and lingual flanges can usually 
 be so formed as to avoid impingement on the soft tissues. 
 When the tooth clasped proximates with two others, and the 
 gum septum in the embrasures through which the appliance 
 
RETENTION OP PARTIAL DENTURES 243 
 
 passes is normal, or nearly so, it is sometimes difficult to en- 
 tirely avoid impingement on the tissues in such locations. 
 
 While it is advisable in most instances to avoid the use 
 of clasps where tissues fill the embrasures, it becomes neces- 
 sary to apply them in other cases, especially where there are 
 no other teeth of suitable form, or in proper location, to be 
 utilized. 
 
 When a clasp is applied in such cases, extreme care 
 should be taken to conform it closely to the mesial or distal 
 axial wall of the tooth clasped, to reduce it to the minimum 
 width consistent with strength, and to smoothly round otf all 
 angles iDresenting toward the gingiva. The tissues, although 
 subject to compression for a time, will usually adjust them- 
 selves to the clasp without permanent injury resulting. 
 
 THE HALF-ROUND WIRE CLASP 
 ADVANTAGES 
 
 Various gauges of half round clasp metal wire are fre- 
 fjuently used in clasp construction. The advantages of half- 
 round wire for this purpose are as follows: 
 
 First — The clasp is of uniform thickness and resiliency 
 throughout its entire length, except where attached to the 
 plate, at which point it is rendered more ligid because of the 
 solder. 
 
 Second — It can be adapted to teeth witli comparative 
 ease. 
 
 Third — Less tooth surface need be covered by the clasp, 
 and consequently there is loss liahiJifji for food to acmimnlate. 
 
 OBJECTIONS 
 
 First — Wider space is required between proximating 
 teeth for the accommodation of the clasp. 
 
 Second — Limited stability afforded the denture because 
 it does not grasj) the axial walls of the tooth as firmly as a 
 broader clasp. 
 
 THE DOUBLE WIRE CLASP 
 
 This type of cjasp consists of a wire of 18 or 19 gauge 
 clasp metal looped on itself and the ends soldered so as to 
 I'orm an elongated, more or less parallel sided, endless band. 
 The distance between the gingival and occlusal wires varies 
 from one to four m.m., depending on the length and form of 
 the tooth clasped. To retain a firm grasp on the tooth, the 
 
244 RETENTION OF PARTIAL DENTURES 
 
 gingival wire should lie to the gingival and the other wire to 
 the occlusal of the greatest diameter of the tooth, thus tend- 
 ing to resist displacement either gingivally or occlusally. 
 
 The doul)le-wire clasp may he converted into a stop clasp 
 by the addition of a strip of heavy clasp metal of 19 or 20 
 gauge, or square wire 18 gauge, bent so as to form an occlusal 
 lug, and extending so as to connect the two wires and further 
 furnish attachment of the clasp to the gold liase or vulcanite, 
 as the case requires. 
 
 Another modification of this chisiJ, suggested by Dr. P. E. 
 Roach, and by him designated the "double-bow clasp," con- 
 sists in adapting the gingival wire closely to the proximate 
 surface of tlie tooth, and leaving it unattached to the lug bar. 
 More Hexilile adjustment is claimed for the clasp constructed 
 in this manner, particularly in those cases where the substi- 
 tute is designed to correct a space between two natural teeth, 
 and where they lean slightly toward each other. (Dental Re- 
 view, October, 1913.) 
 
 While lacking the strengtli of some of the other forms of 
 clasps described, when well planned and properly constructed 
 the double-wire clasp clings to a tooth with wonderful 
 tenacity, and will sustain a denture with firmness and com- 
 fort to the wearer. 
 
 The principal advantages of the double-wire clasp may 
 l)e summed up as follows : 
 
 First — The large extent of linear contact existing be- 
 tween the clasp peripherally and the tooth surfaces, with the 
 minimum amount of surfaces actually covered. 
 
 Second — Great resiliency and ready adaptability of the 
 clasp to the tooth surfaces. 
 
 Third — Comparatively simple to construct. 
 
 The principal disadvantage lies in possible lack of in- 
 herent strength, particularly in those cases where the tooth 
 is large, requiring a long clasp peripherally, and where the 
 denture will be subjected to heavy sti'ess or careless handling. 
 
 THE STOP CLASP 
 
 The stop clasp Juts been in'eviously mentioned under 
 "Requisites of a Clasp." Clinical experience with this type 
 of clasp has been so satisfactory as to lead to its adoption in 
 practically every case. 
 
 Any of the forms of clasi)s described may be converted 
 into a stop clasp by the addition of an occlusal lug. In case 
 of the flat-band clasp the lug may be formed of the same piece 
 
RETENTION OF PARTIAL DENTURES 245 
 
 of plate as the clasp by allowing for the extra width in cntting 
 the clasp metal, or it may be soldered on after the appliance 
 is constructed. 
 
 The lug- should be so placed that, when the clasp is in 
 position, it rests on, or hooks over, the mesial or distal mar- 
 ginal ridge of the tooth clasped. If the ridge is excessively 
 prominent, it may be reduced by grinding and polishing so 
 that the lug may not interfere with the occlusion of the tooth 
 
 ORDINARY HAM) II.ASI' WITH STOP. LINGUAL VIEW 
 
 in the opposite arch, or the tip of the occluding cusp may be 
 ground and polished until clearance space is gained. In case 
 the tooth clasped is carious and suitalile for the reception of 
 an inlay, it may be restored in this manner and a depression 
 made in the occlusal surface of the inlay, so as to permit the 
 occlusal surface of the lug to rest flush with that of the re- 
 stored part. It is essential that the lug should be slightly 
 hook-shaped and the surface on which it rests correspondingly 
 curved, to ])revent the tendency of the clasp to slide away 
 from the tooth when the denture is subjected to stress. 
 
 THE DOUBLE, STAY 
 
 A method much in vogue in Europe, but infrequently ap- 
 plied in this country, consists in attaching two rather thin 
 pieces of clasp metal of 28 or 29 gauge to the baseplate. The 
 strips should be in close apposition to each other, so as to pass 
 through the interproximate space between two suitably lo- ' 
 cated proximating teeth. The ends of the stays which ter- 
 minate in the buccal embrasure are bent away from each 
 other so as to lie in close apposition to the teeth they proxi- 
 mate. 
 
 Retention by means of this "Doppel Klammern" (double 
 clasp), as the Germans term it, is very effective in favorable 
 cases. The retention does not depend on mesial and distal 
 frictional contact, but on the action of the reflected ends of 
 the two flanges tending to draw the two teeth inward toward 
 the baseplate. The stops themselves should not exert spring 
 
246 RETENTION OF PARTIAL DENTURES 
 
 pressure on the proximating surfaces of the teeth, or in time 
 gradual and permanent separation of the latter will occur. 
 
 THE STAY 
 
 This appliance is commonly called a stay clasp, but the 
 term is incorrect since it embraces less than one-half of the 
 
 THE DODBI-E STAY, SllOWJXf; EI.EMKXTAL CONSTRUCTION DETAILS 
 
 periphery of the tooth to which applied, and therefore does 
 not perform the function nor fulfill the purpose of a clasp. 
 
 AjJijliances of this tyi)e are seldom indicated, l)eing usu- 
 ally applied in those cases where ordinary frictional reten- 
 tion of the denture is uncertain because of the parallel, or 
 slightly diverging, relation of the lingual surfaces of the 
 teeth on opposite sides of the arch, and when for any reason 
 clasps are contra-indicated. Two well adapted, opposed stays. 
 
 THE STAT CLASP 
 
 the ends of which pass well into the lingual embrasures, will 
 frequently give the required stability. 
 
 INDICATIONS AND CONTRA-INDICATIONS GOVERNING 
 THE APPLICATION OF CLASPS 
 
 For the rdontion of partial dentures, clasps may gen- 
 erally Ije used to advantage in all cases when the mouth is in 
 a comparatively healthy condition and the teeth are so situ- 
 ated that when the clasp denture is introduced it will balance 
 and not become displaced. 
 
RETENTION OF PARTIAL DENTURES 247 
 
 Unless the teeth clasped are suitably located, displace- 
 ment of the denture by gravity, muscular strain, or the two 
 forces combined, will sooner or later occur, regardless of the 
 presence of the clasps. For example, in an upper case where 
 all of the teeth, except the third molars, are missing and re- 
 tention of the denture depends solely on clasping these two 
 teeth, gravity and the action of the lip and cheek muscles will 
 overcome the i'esiliency of the clasps and result in partial, if 
 not complete, displacement. Or if the clasps are heavy 
 enough to resist these displacing foi'ces, the teeth themselves 
 will be gradually and permanently tipped liackward, thus per- 
 mitting the denture to become unseated and the clasps will 
 then be a detriment instead of an advantage. 
 
 DIAGR^VJIMATIC VIEW Or CASE SHOWIXC •DEXTIRE liAT.ANCE" 
 
 The location for clasps best suited to insure stability is at 
 a point midway between the anterior and posterior terminals 
 of the denture on either side. The tendency to tip anteriorly 
 is thus instantly coimteracted by pressure of the. distal end of 
 the denture against the tissues, and vice versa. Such bal- 
 ancing requirement really limits the number of teeth that may 
 be clasped to advantage to the second bicuspid and first molar 
 on either side, aKhough at times the first bicuspid and second 
 molar, if present and on opposite sides of the arch, may be 
 utilized for such purpose. Although neither clasp would be 
 situated midway between the mesial and distal terminal, yet 
 a straight line drawn from one clasp to the other would dis- 
 
248 HETRNTION OF PARTIAI. DENTURES 
 
 close a diagonal balance quite as effective as when the more 
 centrally located teeth are clasped. 
 
 There is oftentimes a temptation to utilize the diagonal 
 l)alance by clasping the cuspid on one side — all of the poste- 
 rior teeth on that side having been lost — and the second or 
 third molars on the opposite side. Usually such attempts re- 
 sult in failure because the conical form of the cuspid tooth 
 precludes the application of a stable, partial-baud clasp, ex- 
 cept in those cases where tissue absorption has progressed 
 to such an extent as to expose the constricted jjortion of the 
 tooth, tlius allowing the clas]i to extend well up over the 
 cingulum. 
 
 When but little absori)tion of tissue has occurred, a modi- 
 fied form of band clasp is sometimes constructed for cuspids, 
 involving considerable elTort in construction, but resulting in 
 marked stability. A cavity is formed on the lingual surface 
 
 LINGUAL, DISTAL AND LABIAL \IE\V OP CUSPID WITH LIXOUAI. LUG CLASP 
 
 of the cuspid extending about two-thirds of the distance from 
 distal to mesial, and from near tlie gingiva to the incisal third. 
 In this cavity an inlay is placed, in which is formed a round- 
 bottomed groove extending from its disto-lingual angle to 
 near its mesial margin. This groove should be near the gin- 
 gival margin of the inlay. The distance between the bottom 
 of the groove and the labio-gingival surface of the tooth 
 should be less than l)etween that point and the diameter of 
 the tooth immediately to the incisal of it. A clasp is now 
 adajited to the gingival portion of the tooth as closely as pos- 
 sible, and embracing more than one-half of the periphery. A 
 piece of iridio-platinum or clasp metal wire is fitted in the 
 groove and connected to the clasp by interposing a piece of 
 plate or wire, and soldering. 
 
 Usually some other form of specialized frictional appli- 
 ance which involved no display of metal labially can be used 
 to better advantage than the form of clasp just described. 
 
RETENTION OF PARTIAL DENTURES 249 
 
 Sometimes the iugemiity of tlie prosthetist will be taxed to 
 the utmost to devise adequate means of reteution in i)artial 
 cases. Frequently, although several teeth are present, they 
 may not be suitable in form to carry clasps, or be in correct 
 position to insure denture balance should clasps be adapted 
 to them. In such cases specialized frictional apj^liances can 
 usually be applied in some manner so as to (leveh)p the re- 
 quired sta))ility. 
 
 SPECIALIZED FRICTIONAL APPLIANCES 
 
 Many forms of specialized frictional retention appliances 
 liave been devised in an effort to overcome the disadvantages 
 and weak points of the various types of clasps commonly used. 
 Specitically the main objects sought in devising and using 
 these special appliances are, to avoid danger of caries, as well 
 as other injuries to the natural teeth; to secure greater stabil- 
 ity to the dentuite than can be derived from the use of clasps ; 
 to produce esthetic restorations of the highest tyi)e; and 
 finally, to develop a means of reteution applicable in cases 
 where clasps for any reason are contra-indicated. 
 
 Most of these appliances consist of two parts, and re((uire 
 for their api)lication the crowning of, or placing inlays in, one 
 or more of the natural teeth. One of the parts is attached 
 either directly or indirectly to the crown or inlay, the other 
 to the denture. 
 
c H A p ^r 1^". n X \' 1 
 
 TECHNIC OF CLASP CONSTRUCTION 
 
 AXIAL CONTOUR FORMS OF BICUSPIDS AND MOLARS 
 
 The form of the crown of a bicuspid or molar tooth usu- 
 ally represents sections of two more or less regular cones 
 reversed, the bases of which meet in a common plane passing 
 through the greatest bucco-liugual diameter of the tooth, Cut 
 I. The gingival cone is quite regular, since the buccal, lin- 
 
 CUT I 
 rUOXlMATE \IE\\ OF A lilCUSI'lD SHOWING THE OCCLUSAL AND GINGIVAL CONES 
 
 gual, mesial and distal axial surfaces converge from the in- 
 tersecting mid-plane gingivally. The occlusal cone is less 
 typical in form, the buccal and lingual axial surfaces converg- 
 ing more or less regularly from the mid-plane (A, B) 
 occlusally, while the mesial and distal surfaces are to a greater 
 or less extent parallel or divergent. 
 
 An elemental factor of great importance, relative to the 
 stability of clasps, should here be mentioned. 
 
 In Cut II let a represent the buccal and h the lingual 
 flange of a clasp in sectional area. It will readily be seen 
 that a clasp, so adjusted to the occlusal cone, when possess- 
 ing any appreciable grasping properties, will tend to lift or 
 unseat the denture from the border. 
 
 Again, a clasp without a stop, adjusted to the gingival 
 cone as represented by c, d, Cut III, would offer no re- 
 sistance to masticatory stress, and if capable of grasping the 
 
TKC'HNIC OK CLASP CONSTRUCTION 
 
 tooth, would constantly cause imduo pressure of the denture 
 against tlie border. As a result, elongation of the tooth or 
 absorption of the border must eventually occur. 
 
 Third, let e, f, or g, h, Cuts IV and V, represent 
 a clasp, one flange of which embraces the occlusal and the 
 other the gingival cone of a tooth. In this case, while passive 
 
 CUT II 
 ADAPTED TO OCCLUSAL 
 CONE OF TOOTH 
 
 CUT III 
 ■LASP ADAPTED TO GIN- 
 filVAL CONE OP TOOTH 
 
 stability may be developed, little or no resistance to move- 
 ment, either giugivally or occlusally, will result. 
 
 It is therefore apparent, that in order to develop maxi- 
 mum stability under all conditions, a clasp should embrace a 
 portion of each cone base, i. /, Cut VI, on both buccal and lin- 
 gual surfaces of the tootli. While it is not always possible to 
 secure this ideal I'elationship between clasp and tooth, the 
 
 CLASP jUJAPTED to 
 BUCCOOCCLUSAL AND 
 L I N G U O - G INGIVAL 
 CONE OF TOOTH 
 
 CLASP ADAPTED TO BUCCO 
 GINGIVAL AND LINGCO-OC 
 CLUSAL CONT; of TOOTH 
 
 CLASP ADAPTED TO 
 EMBRACE BOTH OC- 
 CLUSAL AND GIN- 
 GIVAL CON-ES 
 
 principle should be kept in mind, and an eti'ort made to utilize 
 it as fully as conditions permit. 
 
 OUTLINE OF THE VARIOUS STEPS 
 
 To encourage precise technic in the construction of 
 clasj3s, and in the application of these appliances to denture 
 retention, the various steps which have proven satisfactory 
 will now be given in se<|uen('e, witli more or less detail. 
 
252 TECHNIC OF ChASI' CONSTRIK'TION 
 
 Assuming that tlio ]jlan of the deiituro has been deter- 
 mined, and that suitable teeth for clasping are present and 
 in proper i^osition to insure denture balance, the outline of 
 procedures is as follows. 
 
 First — Securing an imi)ression of each tootli to be 
 clasped. 
 
 Second — Rebuilding tiie iin])r('ssion for receiving and 
 retaining the die metal. 
 
 Third — Melting the die metal and casting the die. 
 
 Fourth — Cutting the clasp metal to suitable dimensions. 
 
 Fifth — Consideration of the axial contour forms of bi- 
 cuspids and molars. 
 
 Sixth — Preliminary concaving of the strip to aid in sur- 
 face adaptation. 
 
 Seventh — Securing peripheral ada]3tation of the strip 
 to the die with pliers. 
 
 Eighth — Securing surface adaptation with hammer. 
 
 Ninth — Developing final surface and peri])heral aday)ta- 
 tiou with pliers. 
 
 Tenth — Soldering stops and anchorage lugs. 
 
 Eleventh — Finishing with files and polishing. 
 
 Twelfth — Securing the correct relation between the 
 clasps, the teeth they embrace, and the baseplate. 
 
 Thirteenth — Uniting the several factors of the denture. 
 
 SECURING AN IMPRESSION OF THE TOOTH TO 
 BE CLASPED 
 
 An impression of the tooth to be clasped, as well as those 
 teeth which jiroximate it, if any are present, should be taken 
 in plaster. The impression should include not only the tooth 
 crowns but extend well onto the buccal and lingual alveolar 
 borders as well. 
 
 By using a small sectional or hinged tray, jointed mesio- 
 distally along its occlusal floor, the plaster may be fractured 
 and removed in two principal sections. This manner of re- 
 moval obviates the breaking of the plaster which surrounds 
 the crevices of, and fills the embrasures between, the teeth. 
 An improvised cardboard tray, when properly shaped, will 
 fulfill the same purpose as a divided metal tray. An ordinary 
 metal tray may be used, but should first be oiled before in- 
 troducing the plaster, to permit its ready removal from the 
 impression before the removal of the latter from the teeth. 
 The impression may then be divided and removed, and re- 
 turned to the tray, or the parts may be adjusted and the 
 
TECHNIC OF CI.ASP CONSTRUCTION 253 
 
 impression rebuilt, as subsequently described. In such case, 
 the impression should be grooved along its occlusal surface, 
 when by pressure outward on the buccal, and inward on the 
 lingual parts, it can be easily fractured and removed. 
 
 HINGED TRAV. WITH FRAITIREI) IMI'RESSIOX I'l.OSED 
 
 To facilitate the ready fracture of the impression for 
 removal, on introduction, it should be carried occlusally until 
 the floor of the tray touches the cusps, thus reducing the 
 
 IMPRESSION, TAKEN' WITH CARDHOARD TRAY 
 
 depth of plaster in this area so that on pressure it will read- 
 ily break 
 
 ]\lodehng conijjound is not a suitable material for im- 
 
 slclKNll IHW SlirKBII lOR IMI'UE.SSKIX OK AN ISOLATED TOOTH 
 
 pressions in clasp work for two reasons ; first, because it 
 usually distorts in removal, and second, because fusible metal 
 will not cast sharply in such an impression. It may. how- 
 
254 TIOCHNU; OK CLASP ( 'ONSTUrCTION 
 
 ever, be employed by the seetioual nietliod, wlieii the models 
 are to be rnn in ('cmciil or modelite. 
 
 REBUILDING THE IMPRESSION FOR RECEIVING AND 
 RETAINING THE DIE METAL, WHEN CAST 
 
 An impression of one or more teeth intended for die con- 
 struction in clasp work must be rebuilt, or prepared for the 
 reception of the die metal. The steps are as follows : 
 
 The impression, having been removed from the mouth, 
 the fractured surfaces are freed from debris, the broken 
 parts replaced in proper relation to each other and luted with 
 sticky wax sufficiently to hold them together. No wax should 
 occupy any portion of the matrix, as its presence, on pouring 
 the molten metal, would generate gas and result in an im- 
 
 IMPRESSION OF TOOTIt TO BE CLASrED, TAKEN WITH HINGED TRAT 
 
 perfect casting. By exercising care in handling the assembled 
 impression the use of wax can frequently be dispensed with. 
 
 To strengthen the assembled impression and hold it 
 firmly together a mix of plaster is made and spread on a 
 piece of paper on the bench. Into this plastic mass, the im- 
 pression, and tray, if the latter has been used for holding the 
 fractured pieces together, should be sunk deeply, and the sur- 
 plus built around the sides and into the ends of the impres- 
 sion to form walls for confining the metal in casting. It is 
 frequently' necessary to make additions to the buccal and 
 lingual margins of the impression so as to bring them up to 
 uniform height, and give good depth to the die. 
 
 For convenience in clas]) consti'uction, the die should be 
 from % to 1 inch in diameter across its base and about 1 
 inch in depth. These dimensions insure ease of handling, 
 
TECHNIC OP CLASP CONSTRUCTION 255 
 
 and afford sufficient weight to the die to render hammei' 
 blows effective when directed against the clasp. A die of 
 these dimensions will require about l^^ to 2 ingots of 
 Melotte's metal. The use of too light and small a die is re- 
 
 REBriLT IMPRESSION". TRAY AXD 
 IMTRESSION ENCLOSED IN SFK- 
 ItOUNDINO PLASTER 
 
 sponsible for nuich of the difficulty encountered iu clasp 
 construction. 
 
 Since the matrix gives form to the die, with these di- 
 mensions in mind, its formation, by imbedding the impression 
 
 TOP MEW OF ftEBUILT IMPRESSION SHOWING BINDING 
 WIRES STILL IN POSITION 
 
 in plaster as described and by proper trimming, is readily ac- 
 complished. The usual method of forming the matrix liy the 
 addition of mouldiiie is more tedious and less accurate than 
 when plaster is employed. Unless firmly luted, the broken 
 
256 TECHNIC OP Cl.ASP CONSTRUCTION 
 
 parts are very liable to hecoiiic distorted iind weds^cd apart 
 in applying the clay. 
 
 When teeth proximate luesially and distally with the 
 tooth to be clasped, the impression of the tooth adjacent to 
 the interproximate space throngh which the clasp is to pass 
 shonld be tilled in with plaster or mouldine, to exclude the 
 molten metal in casting. The presence of a tooth in such lo- 
 cation on the die seriously interferes with clasp construction. 
 The other proximating tooth should be developed in the cast- 
 ing, as it serves as a guide in finishing the terminal ends of 
 the clasp. Any unnecessary irregularities such as higli points 
 or depressions, present within the matrix, should be corrected 
 by trimming or additions as required. The general form of 
 tJse die should be cone shaped, from its base occlusally. 
 
 The impression having been converted into a matrix as 
 described it should be closely inspected to see that all essential 
 parts are in place, that no loose particles of debris are pres- 
 
 JIELTINO LADLE FOR Ki:SnU.E JIETAL 
 
 ent, and that no openings exist at any jMjint through which 
 the molten metal can escape when cast. 
 
 Drying the plaster matrix before casting the die is not 
 essential, since the fused metal, when poured at a low tem- 
 perature, generates but little steam, while that which does 
 form finds ready exit outwardly through the matrix walls. On 
 the other hand, overheated metal cast into a damp or even 
 partially dried matrix will cause such rapid generation of 
 steam that it cannot all escape before the metal solidities. Cast- 
 ing under such conditions usually results in imi)aired density 
 or deficient sharpness of the die. 
 
 CASTING THE DIE 
 
 Two ingots of Melotte's metal are placed in a small melt- 
 ing ladle and held over the Bun sen flame until a little more 
 than half of the mass is fused. The ladle is then removed 
 and the half-melted metal stirred with a small instrument or 
 flat wooden spatula, to disseminate the accumulated heat 
 throughout the mass until all is fused. Stirring also prevents 
 
TECHNIC OF CLASP CONSTRUCTION li.",? 
 
 liquatiun of tlie comiioueut metals, which, on aceouut of their 
 different specific gravities, gradually occurs. The film of 
 oxide which forms on the surface should be skimmed off be- 
 fore pouring. 
 
 By watching the surface of the fused metal at its margins, 
 it will be seen that the spherical appearance noticeable in most 
 metals when fused gradually disappears, and as the tempera- 
 ture is reduced the alloy will settle squarely against the ladle 
 wall. This appearance denotes that the metal, although some- 
 what reduced in temperature, is in its most fluid condition, and 
 when cast will adapt itself to the most irregular surfaces. 
 
 Usually in this class of work the casting is deferred until 
 the metal begins to lose its fluidity, or is on the point of 
 congealing, in which condition little or no steam will be gen- 
 erated, and a dense, sharp casting may be obtained. 
 
 As soon as the die has hardened it can be quickly chilled 
 in cold water, although it will be less brittle if allowed to cool 
 slowly. 
 
 When freed from the impression and cooled, the die should 
 be inspected for defects. These usually appear as excres- 
 cences, di;e to openings or spaces in the impression, caused 
 by loss of broken particles in assembling the impression and 
 into which the metal is cast. These defects are filed or chiseled 
 away so as to restore the tooth to correct form. The em- 
 brasures, when filled in, should he burred or chiseled out and 
 the die is ready for use. 
 
 CUTTING THE CLASP METAL TO SUITABLE 
 DIMENSIONS 
 
 A strip of No. (50 tinfoil, adapted to the tooth with the 
 fingers, and by burnishing if necessary, is cut to suitable 
 length, and slightly wider than the required clasp, to serve 
 as a pattern for cutting the strip of clasp metal. This pat- 
 tern is laid on a piece of clasp plate of the required thickness, 
 lengthwise of the lamina developed in rolling the ingot into 
 sheet form, and its outline marked with a sharp instrument. 
 Failure to parallel the clasp with the lamina of the plate 
 usually results in fracture of the clasp during construction or 
 under slight stress when in use. It also insures greater resil- 
 iency in the clasp. 
 
 When a stop is to he formed from the same piece of plate 
 it should be so indicated on the ]iatteni and the strip cut 
 wider at this point. 
 
258 TECHNIC OK CLASP CONSTRUCTION 
 
 Befoi'e beginning to conform the strip of clasp metal to 
 the die it should be carefullj^ and imiformly annealed at a 
 low, red heat. This reduces its stitTness but does not deprive 
 it of all of its resiliency. The full degree of elasticity may be 
 restored in the final polishing by subjecting the completed 
 clasp, after the final soldering, to the action of a stiff brush 
 wheel, on a high speed lathe, and Ity burnishing. 
 
 PRELIMINARY CONCAVING OF THE STRIP OF CLASP METAL 
 
 When the clasp strip has been cut as described, the first 
 preliminary step in adaptation is to concave it from 
 end to end with the hawkbill ])liers, on that side to 
 
 HAWKBILL PLIERS AS iVTrLIED l.\ COXCAVIXG THE STRIP OF CLASP METAL 
 
 be applied to the tooth. This concave depression em 
 braces the cone bases or greatest diameter of the tooth, 
 and permits the occlusal and gingival margins of the 
 clasp to rest in contact with the more or less convex axial 
 walls of the tooth as peripheral adaptation is carried on, step 
 by step. 
 
 The terminal end of the strip, which rests in the em- 
 brasure and where adaptation is to begin, should be rounded 
 
 APri.yiNG THE (TRVED END OF CLASP METAL STRIP TO TOOTH 
 
 on the gingival edge, curving it so as to parallel the gum 
 margin as it rises in the embrasure, where this end of the 
 clasp will rest. 
 
TECHNIC OF CLASP CONSTRX'CTION 259 
 
 Frequently the convexity of the .slrij) produeed by the 
 hawkbill pliers is greater than that of the axial walls of the 
 tooth. The central portion of the clasp will then stand away 
 from, while the occlusal and gingival margins will lie in con- 
 
 tact with the axial walls. This is an advantage rather than 
 a detriment, as light hammer blows, in subsequent steps, will 
 reduce the excess curvature and develop surface adaptation. 
 
 SECURING PERIPHERAL ADAPTATION OF THE STRIP 
 TO THE DIE WITH PLIERS 
 
 The i)eripheral ada])tation of a clasp to a die should be 
 developed by steps rather than by converting the strip at the 
 outset into a partial baud of general form by means of the 
 clasp benders. The latter method, although most commonly 
 followed, is less accurate at the start and in the end will result 
 in requiring greater care in securing adaptation than where 
 the former method is employed. The following procedure is 
 practical, accurate and rapid, when once the technic is under- 
 stood, and the required skill for carrying it out is developed. 
 
 The concaved strip, its angle rounded as described, is car- 
 ried into the embrasure where it is eventually to rest, and laid 
 closely against the axial surface of the tooth. By viewing it 
 oeclusally, the areas not in contact are readily noted. The 
 strip is then removed, held firmly with the fingers near the 
 end being adapted and with the hawkbill pliers applied to an 
 area not in contact, a positive bend is made in a direction to 
 secure the desired adaptation. It should again be returned 
 to the die and the change wrought by bending noted. One 
 or two additional beiids and trials may be required to effect 
 reasonably close adaptation of the strip against an area rep- 
 resenting about one-sixth of the tooth periphery. In the same 
 manner the strip is grasped somewhat further in from the 
 end already conformed, while other bends are similarly made 
 until the areas of the clasp not touching the die are brought 
 into reasonablv close contact. 
 
260 TKCHNIC OF CI.ASl' CONSTKrCTlON 
 
 When a torsional licnd in the clasp is required, as iu 
 turuing' the angles of a bell-erowued tootli, it can be accom- 
 plished by substituting a pair of pliers for the fingers for 
 holding the unadapted strip, the hawkbills being applied to 
 the adapted portion, while round or flat beak or another pair 
 of hawkbill pliers can be used on the unadapted portion, as 
 the contour of the surfaces requires. 
 
 To illustrate the steps as outlined, the adaptation of a 
 clasp to an upper first bicuspid will be described. The two 
 ends of the clasp will terminate, mesially. 
 
 The strip of concaved clasp metal is ai^plied to the mesio- 
 buccal angle of the axial surface of the tooth and the areas 
 not in contact noted. These are connected to the crest of the 
 
 buccal ridge, usually representing a linear distance of about 
 three-sixteenths of an inch. Adaptation should then be 
 secured between the buccal ridge and the disto-buccal angle 
 in like manner. Then the turn is made ai'ound this angle 
 and adai)tation secured across the distal surface, to the disto- 
 
 lingual angle. From this point the strip is bent against the 
 lingual surface to the center of this side. The final step con- 
 sists in turning the mesio-lingual end of the strip into place. 
 Thus the process of peripheral adaptation of a clasp consists 
 of five, or, in certain cases, seven distinct steps where the 
 terminal ends of the clasp require special adaptation in the 
 embrasures. 
 
 SECURING SURFACE ADAPTATION OF THE CLASP TO 
 DIE WITH HAMMER 
 
 Peripheral adaptation refers to the bending of the strip 
 into partial band form, so that it eiiibraces the ])eriphery of 
 
TECHNMC OF ('[.AST ("ONSTRCCTION 
 
 the tt)otli closely tiiroiiniumt its ciilirc li'iigtli. Peripheral 
 eontaet, however, does not imply that the entire inner surface 
 of the stri]) is in close adaptation to the die at all points or 
 throughout its entire occluso-gingival width. 
 
 Surface adajitation involves not only good peripheral 
 contact, but close approximation, occluso-gingivally of the 
 partial band to the axial walls of the tooth or die as well. 
 Peripheral contact is comparatively easy to develop with suit- 
 able pliers, but of itself does not afford the required stability 
 in the completed clasp. Surface adaptation is essential to 
 stability, Init is much moi-e difficult to secure, especially in 
 the thicker gauges of clas]) metal. The ]ireliminary concaving 
 
 KIVETING HAMMER 
 
 of the strij) with the liawkl)ill pliers aids greatly in securing 
 surface adaptation. 
 
 Since the concavity of the clasp is more or less uniform in 
 curvature from end to end and the axial walls of the tooth 
 constantly vary in curvature, it becomes necessary to de- 
 crease over some and increase over other areas the concavity 
 of the clasp. This is most easily accomplished with the small 
 riveting hammer. 
 
 The die, when" of the dinumsions jireviously mentioned, 
 serves the same purpose as an anvil and affords ample re- 
 sistance to hammer blows, so that heavy gauges of clasp metal 
 are readily conformed to its surfaces under such stress, ]u-op- 
 erly applied. 
 
262 TIOCHNIC Ol' CI.ASI' f'ONSTUt'CTlON 
 
 To (k'\i'lop sui'I'acc iulaiilatidii. Ilic siuiic oihUt of pro- 
 cedure as was followed with the ])liers is carried out witli 
 the liaimuer, the blows iK^iiif? first directed against the mesio- 
 buccal section of the clasj) and continued around to the op- 
 posite terminal. The ai)plication of the hammer and the horn 
 ])eni' mallet causes the clas]) to ojK'n, so that fi'om time to 
 
 llE[.OTTF/S HORN PEXE HAMMER 
 
 time it will be necessary to remove it from the die and reduce 
 its diameter with pliers and by finger jiressure, until it again 
 grasps the metal pattern firmly. 
 
 FINAL ADAPTATION OF THE CLASP TO THE DIE 
 
 When general surface adaptation between clasp and die 
 has been secured with the hammer, the final finishing touches 
 
TKCHNIC OF CLASP CONSTRUCTION 263 
 
 are given with tlie pliers. The clasp should grasp the die 
 tooth so firmly as to require considerable foi'ce to dislodge it. 
 Usually a clasp, when transferred from the die to the natural 
 tooth in the mouth, will fail to grasp it closely, even though it 
 may fit the die perfectly. This is due to the fact that the die 
 metal in cooling expands slightly, and therefore the die is in 
 reality a trifle larger than the tooth. Correction is easily 
 made in adjusting the clasp to the natural tooth in the mouth 
 by bending the two flanges slightly toward one another. 
 
 SOLDERING THE STOPS AND ANCHORAGE LUGS TO 
 THE CLASP 
 
 When the clasp is constructed without a stop, and it is 
 deemed advisable to attach one, the steps are as follows : Cut 
 a piece of 22 gauge clasp metal about 1-16 of an inch wide and 
 of suitable length to form the hook over the marginal ridge, 
 extend gingivally to the ridge and furnish attachment to the 
 metal or vulcanite liaseplate. The clasp is placed in position 
 on the die and with a pair of pliers the strip of metal is con- 
 formed as closely as may be to the clasp and die, the final 
 adaptation being secured with the hammer. 
 
 The clasp and stop are waxed together in proper relation 
 to each other on the die, removed, invested and soldered. 
 Final adjustment of the clasp to the die is now made, and the 
 position of l)oth the occlusal and gingival ends of the stop bar 
 corrected if necessary. That portion of the bar which forms 
 the anchorage lug should lie close to the crest of the border, 
 somewhat to the lingual so as not to interfere with the placing 
 of the artificial teeth. It is frequently necessary to reinforce 
 this iiortion of the bar so as to render it rigid and unyielding, 
 and thus obviate distortion of the relation between the clasp 
 and denture when subjected to stress. Many clasps, other- 
 wise well planned and serviceable, fail because the anchorage 
 lugs are weak, lack rigidity and bend under stress. 
 
 FINISHING THE CLASP 
 
 The ends and outer margins of the clasp should be round- 
 ed and beveled with files and engine discs, and finally polished 
 with felt wheels and polishing powders. Wlien properly fin- 
 ished, the tendency of the clasp margins to irritate the soft 
 tissues of the cheeks and tongue is obviated, and the liability 
 of food to accumulate around the appliance is reduced to the 
 minimum. 
 
2til TPX'HNIC OK CLASP CONSTRUCTION 
 
 Holding till' tiiiislied clasp i'ur a short tinu' against a stiff 
 brush wheel running at high speed will restore the elasticity 
 in the metal, which has become reduced as a result of solder- 
 ing operations. Eubhing vigorously with a burnisher will also 
 have a similar effect. 
 
 VARIOUS METHODS OF CLASP CONSTRUCTION 
 
 Other methods of clasp construction than those previ- 
 ously described are frequently employed to good advantage, 
 some of which will here be briefly outlined. 
 
 COMBINATION CLASP OF PURE GOLD WITH CLASP METAL 
 
 Secure an impression of the tooth to be clasped. From 
 this develop a model tooth in some good, hard investment com- 
 pound. To this model adapt a piece of pure gold of the form 
 of the clasp desired, of 32 or 34 gauge. The adaptation can 
 be readily secured first with pliers and finally ])y burnishing 
 to the model tooth. On this pure gold foundation apply a par- 
 tial band of clasi> metal, slightly narrower than the clasp is 
 to be when finished, and usually of 2G gauge. The adaptation 
 of the strip of clasp metal to the i^ure gold foundation clasp 
 should be reasonably close, but not necessarily perfect. Be- 
 tween the pure gold and the clasp metal strengthener flow 18 
 carat solder, contouring the outer surfaces of the clasp at the 
 same time, as conditions require. The soldering of the two 
 pieces is accomplished on the model tooth. This is necessary, 
 because if removed from the tooth the pure gold foundation, 
 which is practically devoid of resiliency, would in all probabil- 
 ity be permanently distorted. Final adaptation, which usually 
 consists in slighty reducing the diameter of the clasp, can be 
 accomplished in adjusting to the natural tooth. 
 
 The objections to a clasp of this type are, first, the gold 
 which embraces the tooth, because of its softness, will in time 
 be reduced by wear, and second, the resilient index of such a 
 clasp is low in comparison to its bulk. Platinum, or prefer- 
 ably iridio-platinum, being slightly harder, can be used to bet- 
 ter advantage for the foundation than pure gold. 
 
 CAST CLASPS 
 
 Clasps of any form desired, including stops and ane!ior- 
 age lugs, can be readily cast by the usual technic employed in 
 inlay work. Clasps of this type, however, are lacking in resil- 
 
TKCHNIC OF CLASP CO.VSTKIK'TIOX litif) 
 
 iciK-y, ami tui account of the more or less granular or crystal- 
 line characti'r llii' clas]i metal assiiincs when cast, are very 
 liable to break under stress. 
 
 THE WIRE LOOP CLASP 
 
 The oonsti'uction of a round wire clasj) is a conijiaratively 
 simple operation. It is essential that a Jiard, resistent die be 
 formed of Melotte's metal, amalgam or some of the cements, 
 to which the wire may he litte<l with jiliers and by light ham- 
 mer blows. 
 
 A plain wire loop clasp, which embraces a little more than 
 one-half of the periphery of a tooth, may be readily and quick- 
 ly conformed to the axial walls of the die as follows: 
 
 As a preliminary requirement in such cases, the teeth 
 )iroximatiug the one to be clasped should be eliminated in 
 forming the die so that the latter may stand alone. The wire, 
 bent in the form of an elongated looji, is conformed to the 
 l)eri])hery of the die tooth with pliers. Through the two ends 
 of the clasp a strii) of 28-gauge Gernian silver plate from 1-16 
 to V,s inch wide, depending on the distance apart it is deemed 
 advisable to ])lace the occlusal and gingival loops, is threaded 
 and doubled back ou itself so as to form a loop. With the 
 flat-n'osed ])liers the two ends of the strip are grasped and 
 twisted tightly together. The resulting tension draws the 
 wire loop clasp tightly around the die. A few light hammer 
 blows applied peripherally to the wires will permanently set 
 them to the form of the tooth. Stops and anchor lugs are 
 attached by soldering as jireviously described. 
 
 CONTINUOUS AND OPEN-LOOP CLASP 
 
 A number of new forms of continuous and open wire loop 
 clasps have been designed and presented to the profession by 
 Dr. F. E. Roach. In many cases clasi)s of the type imder con- 
 sideration are most useful and efficient and have the advan- 
 tage of extensive peripheral contact with the tooth, while the 
 area covered by the clasp is extremely limited. 
 
 A piece of 18-gauge clasp wii'e for open loop, and 19 or 
 20 gauge for continuons loop, is bent in staple form. This bend 
 or loo]), forms an occlusal rest or stop, when a proximating 
 tooth is present. Its principal purpose, however, is to connect 
 the buccal and lingual portions of the clasp, which, if not so 
 joined, would lack inherent strength. From the occlusal bend 
 both buccal and lingual wires drop into their respective em- 
 
2t;fi TECHNIC OF CLASP rONSTRl'CTIOX 
 
 bi'cisures to the gingival third of the tootii chisped when they 
 are eonfornied to the Iniccal and lingnal surfaces of the tooth, 
 joining on the opposite proximate surface to form the anchor- 
 age lug. A continuous loop clasp of this type can be converted 
 into an open loop clasp by soldering the two terminals to- 
 gether, which form the anchorage lug and severing the lahial 
 or buccal loop. The two terminals may be doul)led back upon 
 themselves and soldered for greater strength or to increase 
 the areal bearing of the clasp if necessary. The forms of 
 these clasps and their range of application seem limited only 
 by the ingenuity of the operator. 
 
 In api)lying clasps of any type to a partial denture the 
 fact should be borne in mind that clasps are not designed to 
 take up the stress of mastication, but merely serve to keep 
 the denture seated on its border in speaking and during mas- 
 ticatory effort. Thus it will be seen that clasps of this type 
 will, in very many cases, fulfill all the requirements efificiently. 
 
 SECURING THE RELATION BETWEEN CLASPS, THE 
 TEETH THEY EMBRACE AND THE BASEPLATE 
 
 When a ])artial clasp denture is finished and introduced 
 in the mouth it should bear evenly and comfortably on the 
 tissues and occasion the wearer no distress or inconvenience. 
 Kach clasji should embrace its respective tooth firmly and yet 
 subject it to no leverage, wedging or torsional strain. These 
 conditions can only be develojjed during the constructive 
 stages, with skillful technic, by securing the correct relation- 
 ship between the clasps, the teeth they embrace and the base- 
 plate or denture. The following method is practical and accu- 
 rate and should be carried out in the order detailed in most 
 cases. The clasps, having been conformed, preferably to 
 metal dies, are adjusted to the teeth in the mouth. This step 
 proves the acciiracy of their adaptation. Should they shift 
 in any manner or fail to grasp the tooth firmly, correction 
 must be made until satisfactory adaptation is secured before 
 proceeding further. They are then removed and the base- 
 plate is introduced when each clasp is returned to position on 
 its respective tooth. Should either clasiJ fail to go to correct 
 position, the baseplate or clasp, or both, should be filed away 
 at the points of interference until each factor can assume its 
 correct position without disturbing the other. 
 
 Usually the baseplate should fit snugly against all of the 
 teeth involved, including those clasped, the gingival margin 
 
TECHNIC OF CLASP CONSTRUCTION 267 
 
 of each clasp either resting on or clearing the periphery of the 
 baseplate, and occupying a iDosition to the occlusal of the lat- 
 ter. Variations from this rule are sometimes necessary, as 
 in case a tooth crown is extremely short, to insure grasping 
 properly it may be necessary to extend the gingival margin 
 of the clasp slightly under the free margin of the gum. In 
 such instances clearance for the clasp must be gained by filing 
 the baseplate to accommodate the former. Such relationship 
 between clasji and baseplate, although at times necessary, 
 should be avoided when possible because of the liability of the 
 clasp to set up gingival or peridental inflammation. 
 
 TAKING THE IMPRESSION OF THE CLASPS, TEETH 
 AND BASEPLATE 
 
 The clasps being in position on the teeth and the base- 
 plate tirmly seated on the tissues an impression is taken in 
 jtlaster. This need not be extensive, but should fully embrace 
 the clasped teeth, both bnccally and lingually, and the greater 
 l)ortion of the baseplate. 
 
 Dn removal of the inii)ression each clasp that is not re- 
 tained in and removed with it is removed from its tooth, 
 brushed free of particles and returned to position in its 
 matrix. The hinged trays mentioned elsewhere can be used to 
 good advantage in taking impressions in this class of work. 
 The ends of the clasp are now sprung apart by means of a 
 small peg of wood inserted between the liuccal and lingual 
 flanges to force them against the matrix walls in essentially 
 the same relation they occupied in the impression when on the 
 tooth. Neglecting to carry out this step usually results in per- 
 manently establishing an incorrect relationship between the 
 clasp and baseplate. In securing a cast fiiom the impression, a 
 clasp not properly forced against its matrix walls as outlined, 
 instead of embracing the axial walls of the tooth, will be found 
 l)artially imbedded within them. The extent to which it is 
 imbedded in the lingual surface of the plaster tooth represents 
 the linear movement bucally that has resulted from the recoil 
 of the clasp on removal from the tooth. When this error 
 occurs, if not corrected, and the clasp is permanently attached 
 to the baseplate in such relation, on introduction of the den- 
 ture the tooth clasped will be forced buccally, oftentimes to 
 such an extent as to render the i)resence of the denture un- 
 bearable. 
 
 The clasps having been adjusted as described, the base- 
 
26S TKCHNIC OK CLASP CONSTRUCTION 
 
 plate is st't in ])lac'e in the impression and Inted firmly witli 
 wax to hold it in place while secnring the east. When var- 
 nished the impression is filled with investment ('omi)onnd, and 
 the latter allowed time to set hard before removing the im- 
 pression. 
 
 SOLDERING THE CLASPS TO THE BASEPLATE 
 
 The attaehuieut of a clasp to l)aseplate is accomplished 
 by flowing- solder along the joint between the two. The extent 
 of attachment shonld be limited, nsnally to 3-16 of an inch, or 
 less. If joined to a much greater extent the clasp becomes a 
 rigid, nnyielding band and will not fulfill the purpose well 
 for which designed. The attachment should be made in as 
 nearly central a location between the two terminals of the 
 clasp as possible, so as to utilize and not destroy the greatest 
 grasping power of the clasp. 
 
 When clasp and baseplate are iu)t in contact, connection 
 should be made by inserting a strij) of clasp metal or a piece 
 of plate in the space between the two and fiowing solder over 
 all, so as to make a firm and rigid attachment. 
 
 Sometimes when the tooth clasped is long and the space 
 between the clasp and jilate is quite wide, a rigid wire ex- 
 tended lengthwise between the two, the connection being com- 
 pleted with solder, will afford a rigid, self-cleansing bond 
 of union. 
 
 The essential point to bear in mind in securing the correct 
 relationship between clasps, teeth and baseplate is that the 
 steps should be carried out as described by assembling the 
 appliances in the month and securing the impression first hand 
 from the tissues against which the denture is to rest. Assem- 
 bling the several jiarts of the denture on a model, while some- 
 times satisfactory, more often leads to error, sometimes so 
 marked as to require reconstruction, or at least reassembling 
 of the several parts. 
 
CHAPTER XVII 
 
 THE MASTICATORY MECHANISM 
 
 At the present time, more than ever before, the fact is 
 realized that the masticatory organs are of the most vital im- 
 portance in the maintenance and preservation of health. 
 Partial or complete failure of these organs to carry on their 
 important functions in the daily routine of life will, sooner 
 or later, result in the permanent impairment of other functions 
 as well. 
 
 When, through accident or by disease, a portion or all 
 of the teeth are lost, it is imperative that they be replaced 
 with artificial substitutes. Such substitutes should have the 
 appearance and perform the functions of the normally ar- 
 ranged natural teeth, and no effort should lie considered too 
 great in order to accomplish these ends. 
 
 The normal arrangement of the teeth in one arch in their 
 relation to each other and to the centers of rotation of the 
 mandible, insures normal occlusion and correct cusp clearance 
 in lateral movements with those in the opposite arch when 
 the latter are also so arranged. 
 
 A single tooth, however, when elongated, rotated, or out 
 of alignment, may impair the efficiency of the entire masti- 
 catory apparatus. It is therefore necessary to study care- 
 fully the normal human denture in detail, in both passive 
 and active states, to imderstand what is required in the re- 
 placement of the natural teeth with artificial substitutes. 
 
 THE MASTICATORY APPARATUS 
 
 The normal adult human masticatory apparatus consists 
 of four principal factors or groups of hard and soft tissues 
 which, when acting conjointly, and in unison on food, re- 
 duce it to a condition suitable for introduction into the di- 
 gestive tract. Ou6 of these factors is practically immovable 
 or passive in masticatory effort, except as the cranium itself, 
 of which it forms a part, moves. The other tliree groiips are 
 active or movable. They may be classed as follows: 
 
 First: The upper maxilla or immovable base. 
 
 Second: The mandible or principal moving factor. 
 
 269 
 
270 THE MASTICATORY MECHANISM 
 
 Third: The group of muscles which control and guide 
 the movements of the mandible. 
 
 Fourth: The group of muscles which control the po- 
 sition of the food and keep it within the working limits of 
 the teeth in masticatory effort. 
 
 THE UPPER MAXILLA 
 
 The two superior maxillary bones join at the median line 
 in a firm, strong suture to form the maxilla. This united 
 bone constitutes the anterior portion of the cranial base, 
 being directly and indirectly firmly united with all of the 
 other cranial bones except the mandible. 
 
 Since the maxilla moves only as the entire cranium is 
 subject to movement, it may justly be regarded as the base 
 or fixed factor of the masticatory apparatus. The upper 
 teeth are imbedded in its alveolar process, and against these 
 the food is forcibly carried in the process of reduction. 
 
 The body of the bone in general is composed of rather 
 thin, frail plates, but these are reinforced at various points 
 where stress is heavy by what are termed buttresses. 
 
 The alveolar process in which the teeth are imbedded is 
 especialh' heavy and resistant to stress. This process in 
 turn is reinforced by vertical ridges or columns running up- 
 ward and merging into the malar processes opposite the first 
 molars, while anterioi^ly the cuspid eminences pass upward 
 and merge into the nasal plates. The tuberosities are sup- 
 ported liy the thickened perpendicular posterior walls of 
 the maxilla itself. 
 
 Each maxillary bone has within its Iwdy a cavity known 
 as the maxillary sinus, or antrum.. The floor of this sinus 
 lies immediately over the roots of the second and third molar 
 teeth, some of which at times penetrate the bony plate. It 
 can thus be seen how easily oral infection may be transmitted 
 to the tissue lining the antrum when these teeth contain dis- 
 eased pulps. 
 
 The several plates composing the upper maxilla enter 
 into the formation of the floor and outer walls of the nasal 
 fossa, the palatal vault, floor of the orbit and spheno max- 
 illary fissure. 
 
 THE MANDIBLE 
 
 The mandil)le is the active working factor of the mas 
 ticatory apparatus. In its alveolar process the lower teeth 
 are imbedded, and through its movements they are brought 
 
THE MASTICATORY MECHANISM 271 
 
 in forcible contact with the npper dcntnre in the reduction of 
 food. 
 
 Wlieu all of the natural teeth are present in a healthy 
 
 condition and normally arranged, they constitute a powerful 
 
 , mill, capable of cutting, tearing, crushing and grinding all 
 
 varieties of food taken into the mouth as such, in a tlior- 
 
 ouglily efficient manner and with comparative ease. 
 
 The mandible is of peculiar form and especially strong 
 and rigid within itself, capable of a wide range of movement 
 and of fulfilling various fimctions. 
 
 AUXILIARY FUNCTIONS 
 
 The mandil)le has various functions and is capable of 
 many movements other than those concerned in masticatory 
 effort. Indirectly, it assists in iDhonation by enlarging or re- 
 ducing the size of the oral cavity, and by gauging the dis- 
 tance between the upper and lower teeth, the tongue is en- 
 abled to assume its proper position in modifying the vocal 
 tones as they issue from the larynx. By its vax'ious move- 
 ments, the mandible assists in giving expression to the face 
 in speaking, laughing, and in the exhibition of the various 
 emotions. In the lower animals, and occasionally in man, 
 when brute instinct dominates his intellect, the masticatory 
 a]iparatus becomes a weapon of otfence and defence. 
 
 GENERAL DESCRIPTION OF THE MANDIBLE 
 
 A lever is a rigid arm, capable of turning about a point 
 for transmitting force or motion or for applying power to 
 overcome resistcDice. 
 
 A device of this type is composed of three factors, viz : 
 a point or area where power is applied, designated as P; a 
 point or area whei'e that force is made available for work 
 or weight to be overcome, designated as W; and a point of 
 rotation or bearing called the fulcrum and designated as F. 
 
 Levers are divided into three classes, according to the 
 position or arrangement of their factors, as follows : 
 
 First Class, P F W 
 
 Second-Class, P W F 
 
 Third Class, W P F 
 
 The mandible is a double lever of the third class ; that is 
 to say. being double, it has two bearing points which may 
 move in unison, forward or slightly backward at the same or 
 
272 THIO MASTU'ATOltY MKCHANISM 
 
 (litTciciit liitc's dj' Speed, oi' one may tiiucl in a ileliiiite patli 
 and the other mei'ely act as a rotation center. 
 
 'I'he power is applied ))etween the working area and the 
 fulcrum or bearins' points. The peculiar form of the bone 
 permits of the application of great force, with but little ten- 
 dency to tip or become unbalanced in masticatory elTort. 
 
 The mandible consists of a body, a thick, flat bone, 
 curved on itself in the form of a U and of two perpendicular 
 portions, called the ramii, which form the extremities. Each 
 
 TTTE MAXDIELE 
 
 ramus is surmounted by two eminences, the anterior called 
 the coronoid process, to which the temporal muscle is attached, 
 and the posterior, called the condyloid process, which forms 
 the articular or sliding joint surface. The upper extremity 
 or head of the condyloid process is called the condyle, and 
 the constricted portion which connects it with the ramus is 
 called the neck. 
 
 The upper or articular surface of the condyle is convex 
 from before backward, as well as from side to side. It is 
 
THE MASTU'ATOI{Y MECHANISM 273 
 
 ellii»ti('al in ronn, the hm.i;' axis niiiiiiiii;' Croiii witliimt inward 
 and sliglitly liat'kward and downward. 
 
 In general proportions tlie niandilile resembles an equi- 
 lateral triangle. Konwill's researches led liim to believe that 
 the average distance from center to center of the condyles 
 and from the center of each condyle to the mesi-incisal angles 
 of the lower central incisiors was ap})roximately four inches, 
 these measurements forming an e(iuilateral triangle, and 
 hence this has been termed the Bonwill triangle. 
 
 On this basis of measurement he evolved his theory of 
 "anatomical articulation" and constructed his "anatomical 
 articulator." 
 
 MOVEMENTS OF THE MANDIBLE 
 
 Because of its jteculiar form and the manner of its at- 
 tachment to the base of the cranium, the mandible is capable 
 of, and subjected to, a great variety of movements. So free 
 and varied are these that r;nless carefully considered they 
 may appear to lack co-ordination. 
 
 Although callable of wide range of action, there are but 
 three definite movements of the mandible, however, that may 
 be considered as important in masticatory effort. These 
 should be carefully studied and thoroughly understood by the 
 prosthetist in order that the product of his hand, when con- 
 structed and subjected to masticatory action, may perform in 
 an efficient manner the same functions that are carried out 
 by the natural teeth. 
 
 The three important movements mentioned may be out- 
 lined as follows : First, a hinge-like movement emjjloyed in 
 opening and closing the mouth for the introduction, and also 
 to a limited extent for the crushing of certain varieties of 
 brittle food. 
 
 Second : A protrusive movement employed in the grasp- 
 ing and incision of food and in rearranging or changing the 
 position of food in the masticatory grooves in process of re- 
 duction. 
 
 Third: Eight or left lateral movements employed in the 
 reduction of fibrous, as well as all varieties of food. These 
 movements are the' most effective of any described, since by 
 their action food can be finely trituated with about one half 
 the expenditure of muscular energy that is required with the 
 hinge motion. 
 
 To appreciate these movements in detail it will be neces- 
 ary to consider the manner of attachment of the mandible to 
 
274 THE MASTICATORY MECHANISM 
 
 the eranial base, and the form of artii'ulation of the coudyles 
 with the temporal bones. 
 
 THE TEMPERO-MANDIBULAR ARTICULATION 
 
 Tlie condyles artieulate \Yith the temporal bones, being 
 received in elliptical concave depressions, called the glenoid 
 fossa?, and from which they travel forward ; in some eases, to 
 a limited extent slightly backward, and from side to side. 
 These depressions are situated immediately in front of the 
 auditory canals, from which they are separated by a tliin, 
 bony partition which limits the backward movement. In gen- 
 eral contour these fosste resemble, in reverse, the form of the 
 articular surfaces of the condyles, the adaptation of the two 
 surfaces to each other, however, not necessarily being exact. 
 
 Between each condyle and its dome-shaped socket is in- 
 terposed an inter-art icvilar fibro-cartilage, its upper surface 
 convex, its lower surface concave. Synovial sacs partially 
 enter between the cartilage and the condyle. The combined 
 thickness of the three layers of tissue seldom exceeds 3/32 of 
 an incli, and in many cases is less than 1/16 of an inch. 
 
 By bearing in mind the average thickness of these tis- 
 sues, the thickness of the bony plate separating the glenoid 
 fossa from the auditory canal and the antero-posterior diam- 
 eter of the condyle, which is risually about 14 of an inch, the 
 location of the outer end of the condyle in the living subject 
 can be determined with comparative accuracy. 
 
 The synovial sac contents lubricate the articular surfaces, 
 while the inter-articular fibro cartilage, being l)ut loosely 
 attached to and moving forward somewhat with the condyle in 
 its movement, reduces friction and acts as a cushion as well, 
 when the mandible is subjected to heavy stress. 
 
 At tlie anterior margin of the glenoid fossa is usually an 
 eminence formed by the middle root of tlie zygoma and called 
 the oiiiiieiitia articularis. 
 
 THE CONDYLE PATH 
 
 Viewed from the side, the general contour of tlie roof 
 of the glenoid fossa with that of the articular eminence at its 
 anterior margin and with which it imperceptibly merges, is 
 that of a compound curve. 
 
 The condyles, in the various opening, closing, protrusive 
 and lateral movements of the mandible, are guided by and 
 must take the general direction of this concave-convex roof 
 
THE MASTICATORY MECHANISM 275 
 
 throughout the extent traversed by them in each movement, 
 and hence this surface is called the condyle path. 
 
 The condyle path, as before stated, is usually curved, 
 being concave posteriorly and convex anteriorly. The cen- 
 tral portion is approximately a straight line. This portion, 
 the central one-half of the path, may be considered, and 
 actually is, the working surface which guides the condyle in its 
 movements in carrying the lower against the upper teeth, in 
 their protrusive and lateral excursions in masticatory effort. 
 
 For practical purposes, in denture construction it is 
 necessary to measure or record in some manner the angular 
 inclination of the central or straight portion of the path. 
 When, hereafter, it becomes necessary to refer to the in- 
 
 \ARTATIflNS IN COXDYl.K I'ATHS. ],EFT SIDE (TOMKS 
 
 IIDI.I.AMOUEI 
 
 cliiiatidii, angle of inclination, or pitch, of the condyle path, 
 these terms will refer to the central or woi-king surface just 
 described, unless otherwise specified. 
 
 VARIATIONS IN THE PITCH OF CONDYLE PATHS 
 
 The condyle paths vary in different individuals and fre- 
 quently in the same person, in their length, curvature and 
 angular inclination. 
 
 Walker, Christensen, Gysi and many others who have 
 investigated on the living subject, vary slightly in their con- 
 clusions. Gysi, whose work is perhaps the most thorough 
 because of more accurate methods emi)loyed, estimates the 
 average inclination of the condyle path at 35 degrees. 
 
 Variations ranging from horizontal to a pitch of 72 de- 
 grees, as recently recorded by the writer, have been noted. 
 It is not uncommon to find a difference of 10 degrees in the 
 pitch of the condyle paths of the same individual. 
 
276 THK MASTICATORY MECHANISM 
 
 The contour aud iucliuatiou of the condyle paths vary 
 in the same individual from infancy to old age, just as the 
 form of the mandible is itself modified by the lapse of time. 
 
 Such changes of the condyle path may be ascribed to 
 and are influenced by the partial or total lack or loss of the 
 teeth. Loss of all of the teeth will result in time in a possible 
 decrease in pitch of the condyle path, the change in the path, 
 however, occurring quite gradually. 
 
 The loss of a portion of the teeth may jiroduce a directly 
 contrary result. In a specimen in possession of the writer 
 the posterior teeth, except third molars on right, were lost a 
 number of years prior to the death of the subject. That side 
 
 A SKULL WITH ABNORMALLY DEEP GLENOID FOSSA ON LEFT SIDE. MANDIBLE THROWN 
 
 TO LEFT. TEETH IN WORKIXGT RELATION. BALANCING RELATION BETWEEN 
 
 THIRD MOLARS ON BIGHT. ALL BICUSPIDS AND MOLARS ON 
 
 RIGHT. EXCEI'T UPPER AND LOWER THIRD HAVING 
 
 BEEN LOST 
 
 of the mouth on which the loss occurred was useless for 
 mastication, and consequently it became the moving arm 
 of the mandible, or the balancing side of the masticatory ap- 
 paratus. The bicusjiids and molars on the opposite side were 
 all present and in good condition and occlusion, while the 
 condyle on this, the working side, merely rotated in its fossa. 
 Protrusive and lateral movements of the mandible on the 
 working side in the opi)Osite direction accomplished nothing. 
 So, nature, to maintain the masticatory function in as per- 
 fect a condition for as long a time as possible, increased the 
 depth of the glenoid fossa on the woi'king side by enlarging 
 the eminentia articularis and by reducing the pitch of the 
 
THK MASTRATOKY MECHANISM 277 
 
 condyle path on the opposite side, as the eusps and planes 
 of the various teeth were worn away. 
 
 It has been suggested that the registration of the condyle 
 paths and the construction of dentures in accordance with 
 such registration is unnecessary, since time and occlusal con- 
 ditions of the teeth modify the pitch and form of the paths. 
 
 This view is entirely unscientific as well as unwarranted 
 by results in practice. In no instance within the experience 
 of the writer has any marked improvement in the way of 
 additional lateral movements been observed with the lapse 
 of time, when such movements were not possible at first. It 
 is not r>easonable to suppose, except possibly in rare instances. 
 
 that any material change does occur, since the artificial 
 teeth in such cases are almost invariably arranged without 
 reference to future possible lateral mandibular movements. 
 Consequently, imless the teeth are so assembled as to permit 
 of anatomic movements other than simple occlusion at the 
 time of constructing the denture, the habit of confining mas- 
 ticatoi-y effort to the hinge movement alone, becomes perma- 
 nently fixed long before any perceiitible change occurs in 
 the condyle pjxths. 
 
 THE MUSCLES OF MASTICATION 
 
 The muscles which move the mandible in masticatory 
 effort, particularly those which close the jaw, are capable of 
 
:iTS THE MASTICATORY .MKCHANMSM 
 
 developing great jjower. lu tests made a uimiber of years 
 ago by Dr. Black, with his gnatho-dynamometer, and since 
 verified each year in class demonstrations, it was found that 
 a force ranging from 150 to oOO lbs. could be developed by 
 these muscles and delivered between the lower and upper 
 molars. 
 
 The two pairs of muscles, the masseters and temporals, 
 furnish most of the power. The internal pterygoids assist 
 in closing and also in protrusive movements. 
 
 THE MASSETER MUSCLE 
 
 The masseter muscle is composed of a superficial and a 
 deep portion. Each portion has a separate origin and in- 
 sertion, and since these vary in position, the direction of the 
 fibres of the two layers vary somewhat, and the action of each 
 portion is slightly ditTerent. 
 
 The superficial layer arises by a tendinous attachment 
 from the malar process of the superior maxilla and from the 
 anterior two-thirds of the lower border of the zygomatic arch. 
 The fibres pass downward and backward and are inserted into 
 the angle and lower half of the outer surface of the ramus. 
 Its action is to draw the mandible upward and forward. 
 
 The deep portion of the masseter arises from the inner 
 surface of the zygomatic arch and from the lower border of 
 the posterior third of the zygoma. It is inserted in the upper 
 half of the outer surface of the ranuis. Its fibres run perpen- 
 dicularly downward and its action is to draw the mandible 
 upward. 
 
 THE TEMPORAL MUSCLE 
 
 The temporal muscle arises from the tem]:)oral ridge 
 on the temporal bone, from the under surface of the temporal 
 fascia, and from the temjioral fossa. It is inserted in and 
 around the coronoid process of the ramus, some of its fibres 
 passing down the anterior margin of the latter as far as the 
 third molar. In general outline it is fan-shaped, its origin 
 representing a sweeping curve, its fibres converging to their 
 point of insertion in the coronoid process. Its action is to close 
 the jaw and to draw the condyle backward in its fossa when 
 protruded, as in unilateral or hilateral position. 
 
 THE EXTERNAL PTERYGOID MUSCLE 
 
 The external pterygoid muscle has two origins and two 
 insertions. The upper head arises from the pterygoid ridge 
 
THE MASTICATORY MECHANISM 
 
 A CUT SHOWIXG THE DLRECTION OP FIBRES OF VARIOHS SDPERFICIAL MUSCLES CON- 
 CER>rED IN FACIAL EXPRESSION (ECKLBY'S REGIONAL ANATOMY) 
 
2S0 THK MASTK'ATOKY MECHANISM 
 
 of the (inter and luidci- Mii-racc ol' llic nicatcr a!a of the sphe- 
 noid Ijoiie. Its insertion is in tlie anterior margin of tiie in- 
 terarticnlar iiln'o-oartilag'e, wliieli covers the arlienhir snrfaee 
 of the condyle. Its fnnetion is to draw the cartilage forward 
 in the protrusive movements of the mandible, tiins furnishing 
 a concave cap for the condyle to rest in as it is carried forward 
 onto the eminential articnlaris. 
 
 Eckley attributes the craclcing noise fre(iuently noticed 
 in the tempero-mandibular joint to partial or complete paraly- 
 sis of this portion of the pterygoid, whicli results in failure of 
 the muscle to draw the cartilage forward in unison with the 
 condyle and permits the latter, in its forward excursions, to 
 override the anterior rim of the cartilage. 
 
 The lower head of the external jiterygoid muscle has its 
 origin in the outer surface of the external pterygoid plate of 
 the si^henoid bone. It is inserted in the anterior surface of 
 the neck of the condyle. 
 
 The function of the muscle is extremely important. By its 
 action principally, the mandible is given a lateral movement 
 and with its mate on the opposite side protrusion is accom- 
 plished. These muscles are not large as compared with the 
 temporals and masseters, nor do they develop very great 
 power, since that is unnecessary. 
 
 The crushing of food is accomplished by the masseter. 
 temporal and internal pterygoid muscles in drawing the 
 mandible back to normal position, after having been carried 
 laterally or forward by the external pterygoids. 
 
 The combined action of the upper and lower portions of 
 the external pterygoid muscle is to draw the condyle and its 
 inter articular iibro-cartilege forward simultaneously. 
 
 THE INTERNAL PTERYGOID MUSCLE 
 
 The internal pterygoid has its origin on the inner surface 
 of the external pterygoid plate, from the tuberosity of the 
 palate bone. It passes downward and backward and is in- 
 serted in the inner surface of the mandible from the mylohoid 
 ridge and the inferior dental canal downward to the angle 
 of the ramus. Its action is to assist in closing the jaw and 
 bringing it back to normal frofn lateral position, in the latter 
 function assisting the posterior fibres of the temporal muscle 
 on the opposite side. 
 
THE MASTICATORY MKCHANISM 
 
282 THE MASTICATORY MECHANISM 
 
 MUSCLES WHICH DEPRESS THE MANDIBLE 
 
 The jaw is opened by the mylohyoid, genio-liyoid, genio- 
 hyo-glossus, digastric muscles and gravity. In fact, most 
 of the supra and infra hyoid muscles take part in the de- 
 pression of the mandible. Tlie hyoid bone acts as a movable 
 fulcrum when the jaw is opened widely. The supra hyoid 
 muscles contract and tend to lift the hyoid bone upward and 
 
 draw the mandible downward. This tendency is counter- 
 balanced by the action of the infra hyoid muscles, which de- 
 press or at least make rigid the hyoid bone, so that the upper 
 muscles may act effectively. 
 
 Depression of the mandible, which is equivalent to open- 
 ing the mouth, results in the drawing forward of the con- 
 dyles in their paths, as well as in a greater or less rotary 
 movement of their articular surfaces. 
 
THE MASTICATORY MECHANISM 283 
 
 111 other words, the centers of rotation in the hinge 
 action do not lie in the transverse centers of tlie condyles, 
 bnt are situated about three-fourths of an inch below and 
 sli^-htly back of the distal margins of the rami. Even this 
 location is variable in the same individual under different 
 conditions, depending on the distance the mandible is de- 
 pressed, and also whether it has been subjected to protrusive 
 as well as opening movements. 
 
 This is explained by Gysi as follows : 
 
 "If a man were susjieiided in the air by ropes attached 
 to each of his hands he could be pulled hither and thither by 
 tugging at either rope. His body would describe certain mo- 
 tions accordingly as force was applied to one rope or another. 
 If an architect were to chart the motions described by the 
 man's body, he would find them to be sections of curves, with 
 centers at tlic points where the opposing curves met, not at 
 the points to which the ropes were attached to the wrists. 
 When he found these imints. he would ])robal)ly call them 
 'centers of motion.' 
 
 "That illustration of the man suspended by ropes at- 
 tached to each wrist is not much unlike the suspension of 
 the jaw by ligaments attached to the heads and necks of the 
 condyles. The articulation of the condyles with their fossa? is 
 very loose; a sort of hanging attachment. Tlie jaw may be 
 pulled in any direction by tension of the proper muscles, and 
 when it moves it swings just as the man's body did, not tvith 
 its center at the condyles, but at the pointf^ ivliere opposing 
 pulls meet and balance each other." 
 
 Bowditch and Luce, in 1899, and Walker in 189-i, firsb 
 called attention to the fact that the head of the condyle moved 
 forward, and the angle of the ramus moved backward, in wide 
 ojien movements. Others have since verified the accuracy 
 of these first experiments. No special value attaches to the 
 registration of wide open jaw movements, since they have no 
 bearing on occlusion. Any movement of the mandible, how- 
 ever, which can be registered, increases the sum total of 
 knowledge of the human dental mechanism and aids in solving 
 this most intricate problem. 
 
 MUSCLES WHICH CONTROL THE POSITION OF FOOD 
 
 This group includes the lips, cheek, palatal and tongue 
 muscles, which when co-ordinating, control the position of 
 food and tend to keep it within tlie working limits of the 
 teeth. 
 
284 THE MASTICATORY MECHANISM 
 
 Sjiccilicall}', the buccinators on the sides and tlic orbicu- 
 laris oris in i'ront, confine tlie food to a great extent and pre- 
 vent it from being forced outward into tlie vestibule during 
 masticatory effort. Witliin the oral cavity proper the tongue 
 moves the bolus of food outwardly and as the mandible is 
 depressed, moved laterally, elevated and the teeth brought 
 together, the lingual marginal ridges shear off a portion, 
 which is caught, confined, and reduced in the masticatory 
 groove between the teeth as the mandible is returned to nor- 
 ma! from the unilateral position. 
 
 SUMMARY OF MUSCULAR ACTION ON THE MANDIBLE 
 
 Depression, or 
 opening of mouth 
 
 l^]levatiou, or 
 closure of month 
 
 Protrusion, 
 bilateral 
 
 Protrusion, 
 unilateral 
 
 Retrusion, 
 bilateral 
 
 Retrusion, 
 unilateral 
 
 Mylo-hyoid 
 Genio-hyoid 
 (lenio-hyo glossus 
 Infra-hyoid muscles 
 Digastric 
 Gravity 
 
 Temporals 
 Masseters 
 Internal pterygoids 
 
 External pterygoids 
 Internal pterygoids 
 Masseters — superficial fibres 
 
 External pterygoid ] ( )n protrud- 
 Interual pterygoid J ing side 
 Masseter — superficial fibres 
 
 Temporals — posterior fibres 
 Masseters — deep fibres 
 
 Temporal — posterior fibres 
 Masseter — deep fibres 
 Internal pterygoid on 
 opposite side. 
 
 THE MANDIBULAR LIGAMENTS 
 
 In addition to the muscles actuating the mandible, some 
 of which in a state of rest tend to hold the condyles in their 
 fossae, there are three pairs of ligaments, which limit its 
 range of movement and yet permit a variety of excursions 
 
THK .MASTICATORY MECHANISM 285 
 
 to be carried out with freedom. Tliese ligaments are as 
 follows : 
 
 The capsular ligament, divided into four parts — an an 
 terior, posterior, external and internal segment. 
 
 The spheno-mandibular, or long internal lateral ligament. 
 
 The stvlo-mandihular ligament. 
 
 THE CAPSULAR LIGAMENT, I'STEUXAI. \IE\V (DEA\ER) 
 
 THE CAPSULAR'LIGAMENT 
 
 Tlie anterior and posterior portions of the capsular lig 
 anient are composed of thin layers of loose, flabby fibres. An- 
 teriorly, these fibres are inserted into the anterior margin of 
 the interarticular fibro-cartilage, from which they extend up- 
 ward and downward. The upper fi])res are attached to the 
 
 X 
 
 ^^>-. 
 
286 THK MASTICATORY MECHANISM 
 
 front of tlu' cniiiientia artienlars, the lowci' (ibrcs to the 
 anterior margin of the condyle. 
 
 The posterior fibres are attached to the margin of tho 
 glenoid fissure and from there extend to and are inserted in 
 the posterior surface of tlie ramus below the neck of the 
 condyle. 
 
 Since the condyle movements to a great extent are for- 
 ward, it can readily be seen that the anterior and posterior 
 fibres of this ligament must be loose to give freedom of action 
 to the mandible. 
 
 THE EXTERNAL LATERAL LIGAMENT 
 
 The external lateral ligament forms the outer portion of 
 the capsular ligament, its tibres blending with the anterior 
 and posterior portions of the latter. Tliis ligament is the 
 strongest part of the capsule. It lias a broad attachment 
 above to the zygoma and is inserted in the outer surface of 
 the condyle neck. 
 
 THE INTERNAL LATERAL LIGAMENT 
 
 The short internal lateral ligament completes the cap- 
 sule. Its fibres are attached above to the inner margin of 
 the glenoid fossa and to the spine of the sphenoid lione. It 
 is inserted in the inner side of the condyle neck. 
 
 The four portions of the capsular ligament, by the blend- 
 ing of their tibres, encapsule the joint. Within this capsule 
 is enclosed the iuterarticular fibro-cartilage, the capsular 
 tibres being more or less closely attached to the cartilage 
 around its periphery. 
 
 THE SPHENO-MANDIBULAR LIGAMENT 
 
 This ligament is also called the luuci internal lateral lig- 
 ament to distinguish it from tlie short internal lateral liga- 
 ment, which forms a part of the capsule. 
 
 It Is attached to the spine of the s]ilienoid bone, from 
 which it extends downward and is inserted in the mandilnxlar 
 spine and a portion of the area immediately surrounding the 
 posterior dental foramen. 
 
 THE STYLO-MANDIBULAR LIGAMENT 
 
 The stylo-mandibular ligament is attached to the styloid 
 process of the temporal bone, its fibres passing downward to 
 
THE MASTICATORY MECHANISM 
 
 fiud insertion in the posterior border and angle of the ramus, 
 between the masseter externally and the internal pterygoid 
 internally. 
 
 These several ligaments being practically devoid of elas- 
 ticity, resemlile so many cables by which the mandible is 
 suspended from the base of the cranium. They limit the 
 action of the various muscles concerned in protrusion, lateral 
 
 LXTERXAI, VIEW OF TIIK SPHEXO-MANDIIiUI.AR AND ST\I,0-MA.\1JUUI-AR LIGAMENTS 
 (DEtVVER) 
 
 and wide-open movements. AVithout their restricting in- 
 fluence, the ]iossibilities of useless mandibular movements can 
 scarcely be conceived. 
 
 Usually, in" dislocations of the mandible, the posterior 
 fibres of the capsular ligament are broken by the excessive 
 strain to which they are subjected, and as they seldom if 
 ever again unite, recurrent dislocations in the same subject 
 are frequent. 
 
THE MASTICATORY MECHANISM 
 THE TEETH 
 
 The normal adnlt denture consists of thirtj'-two teeth, 
 sixteen in the iipper and a like numl)er in the lower jaw, 
 tile formula of which is as follows : 
 
 M. B. C. I. I I. C. B. M. 
 
 3 2122123 
 
 3 2 12 13 13 3 
 
 FKICTIONAL OK WORKING SURFACES OF THE TEETH. 
 
 Those surfaces of the bicuspids and molars in one arch 
 presenting toward those in the opposite arch are known 
 as occlusal surfaces, from occlude, which means to shut or 
 close together. 
 
 Those surfaces or edges of the incisors and cuspids in 
 one arch presenting toward those in the opposite arch are 
 called incisal surfaces or edges, from incise, which means 
 to cut. 
 
 Each cuspid tooth terminates in a i)oint or cusi), with 
 incisal edges, sloping away from it mesially and distally 
 to the mesio and disto incisal angles of the tooth. 
 
 OCCLUSAL SURFACE MARKINGS 
 
 The occlusal surfaces of the l)icuspids and molars are 
 made up of cusps, inclined i^lanes, grooves, pits and ridges, 
 displayed with more or less definite regularity. 
 
 THE CENTRAL SULCUS OR MESIO-DISTAL GROOVE OF THE 
 BICUSPID AND MOLAR TEETH 
 
 Traversing the occlusal surface of each bicuspid and 
 molar tooth, mesio-distally, is a general depression, or 
 sulcus, formed by the planes, which slope linguall.v from 
 the buccal, and buccally from the lingual, marginal ridges. 
 
 These planes meet at varying angles near the center 
 of the tooth, to form definite grooves. The grooves, which 
 cross the mesial and distal marginal ridges, are accordingly 
 named mesial and distal marginal grooves, and that which 
 divides the central portion of the tooth is called the cen- 
 tral groove. 
 
 In normal occlusion these general depressions or sulci 
 in the upper teeth receive the buccal cusps and marginal 
 ridges of the lower teeth, while the central sulci of the 
 lower teeth receive the lingual cusps and marginal ridges 
 of the upper teeth. 
 
THE MASTICATORY MECHANISM 289 
 
 THE BUCCO-LINGUAL GROOVES 
 
 III additiou to the central grooves mentioned, the vari 
 ons cusps, and planes sloinng away from them mesially 
 and distally, result in the formation of other grooves, which 
 traverse the occlusal surfaces of the teeth from buccal to 
 
 I)IA<iRA.\l SIK 
 
 SECTION" OF MANDIBLE AND MAXILLA SHOWING UPPER AND 
 LOWEB TEETH IN OCCLOSION. DISTAL VIEW 
 
 lingual. These .grooves run nearly at right angles to the 
 mesio-distal grooves, the buccal being slightly in advance of 
 the lingual end. 
 
 Each pair of cusps, as, for instance, the mesio-buccal 
 and mesio-Iingual cusps of the upper first molar, are situ- 
 ated approximately the same distance from the mandibular 
 
290 THE MASTICATORY MECHANISM 
 
 rotation center of tliat side of the arch. The phines, slop- 
 ing away from these cusps mesially and distally until they 
 meet in the central groove, and finally merging with those 
 from the adjacent pairs of cusps, enter into the formation 
 of grooves, which represent arcs of circles, also developed 
 from the same rotation centers. This arc-like or geomet- 
 rical bucco-liugual arrangement of cusps, ridges and grooves 
 of the upper teeth permits the cusps and sloping planes of 
 the occluding lower teeth, which bear a simihir relation to 
 
 NTKRKIIl VIKW 
 
 the rotation center, to be moved freely back and forth, in 
 the lateral swing of the mandible, without cusp interference. 
 
 THE MASTICATORY OR RECTANGULAR GROOVE 
 
 When the mandible is rotated laterally, so as to In'ing 
 the buccal cusps and marginal ridges of the lower teeth on 
 the pivotal side outward from the central sulci of the upper 
 teeth, and directly under the corresponding cusps and 
 marginal ridges of the latter, a fairly close and unbroken 
 line of contact between these wedge-like ridges is effected. 
 
 At the same time the lingual cusps and marginal ridges 
 of both lower and upper teeth on the same side are brought 
 into similarly close contact. A rectangular space is thus 
 formed, bounded above and below by the occlusal surfaces 
 of the upper and lower teeth, and laterally by their buccal 
 and lingual marginal ridges. This groove extends from 
 
THIO MASTICATORY MECHANISM 291 
 
 the iirst bicusind lo llie third molar, iiichisive, wlieu present, 
 and forms tlie receptacle in which food is held and crusheil 
 as the mandible is drawn back to noi'mal position. The 
 form and proi)ortions of this masticatory groove is of the 
 greatest irajjortance. The efficiency of tlie masticatory 
 apjjaratiis is largely dependent on the width of this space 
 bucco lingnally; the wider it is, within normal limits, the 
 greater the radial swing possible for the mandible and the 
 more efficient its effort in the reduction of food. 
 
 The detiniteness of the angles of the marginal ridges 
 which are formed by the junction of the buccal and lingual 
 surfaces of the teeth with the various planes sloping to 
 the central grooves is also important. These angles should 
 not be too sharp, as the tongue and cheek muscles arq^ liable 
 to be caught between them and injured in masticatory effort. 
 
 The closeness of apposition of the various occlusal 
 planes and marginal ridges of the lower to those of the 
 upper teeth, not onh^ in occlusion, but in radial movements 
 of the mandible as well, increases efficiency in both natural 
 and artificial dentures. When loosely approximated, or 
 possibly when only a few cusps or surfaces are in actual 
 contact, the food is merely punctured, and the fibers are 
 not torn asunder, as is the case when many planes and 
 cusps find contact with those of the opposite teeth. 
 
 ARRANGEMENT OF THE TEETH IN THE DENTAL 
 ARCHES 
 
 OCCLUSAL VIEW 
 
 Viewed occlusally, the arrangement of the teeth in each 
 dental arch presents the general appearance of a parabolic 
 curve, or in some cases that of a half ellipse, the central 
 incisors being at the outer extremity of the major half axis. 
 The size and outline form of the curve varies in different 
 individuals, according to structural build. 
 
 Since normally, the upper overlap the lower teeth to a 
 greater or less extent, the curve of the upper arch is slightly 
 larger than that of the lower arch. 
 
 THE ANTERIOR CURVATURE, INCISAL VIEW 
 
 The four incisors at their cutting edges iisually present 
 a symmetrically curved arrangement. The laterals may be 
 slightly in or out of a true curved alignment, or, when a 
 
292 Till': .MASTIC. \T()I;Y .MKCII.ANIS.M 
 
 tritie rottitcd, as is l'ic<|Ui'iitl\ tlic case, tlicir iiicsio-liu.nuo- 
 iiK'isal angles may overlap tiie (listolahial surfaces of the 
 central incisors. The variations noted, when not too pro- 
 nounced, are pleasinp; rather than other\vis<>, and give cliar- 
 acter and individuality to the denture. 
 
 The cutting edges of the cuspids usually are in sym- 
 metrical lahial alignment with the incisors. On account of 
 
 the greater convexity of the labial face of the cuspids, as 
 comijared with the incisors, these surfaces stand out more 
 or less prominently beyond the labial surfaces of the latter, 
 especially at their cervices. 
 
 The cuspids are the corners of the dental arches, the 
 labial curvature of the incisors merging here with the 
 straighter alignment of the posterior teeth. The general 
 
THE MASTICATORY MECHANISM 293 
 
 form, size and position of the (■iis{)ids, therefore, give tliem 
 greater jirominence than any of tlie anterior teeth. 
 
 ALIGNMENT OF THE POSTERIOR TEETH 
 
 Fi'om the cuspids, to and inohidiug the first molars, 
 the teeth are arranged in practically straight lines, which 
 in passing backward diverge. If projected, these lines 
 would usually fall within and below the inner ends of the 
 condyles. 
 
 The second and third molars frequently curve inward 
 somewhat to the lingual of these lines, an arrangement 
 which gives the general arch its parabolic or elliptical form. 
 This inward curvature of the second and third molars is 
 necessary to avoid contact of thin buccal surfaces with the 
 coronoid processes of the mandible in its lateral and wide- 
 open movements. 
 
 When viewed anteriorly, less tlian one-fourth of the 
 first bicuspids, taking their bucco-lingual diameters as a 
 basis, are visible back of the cuspids. The second bicuspids 
 exhibit about the same amount of surface as do the first 
 bicuspids. This retiring jjosition of the bicuspids adds 
 very much to the esthetic appearance of the denture, par- 
 ticularly in the u])per arch. 
 
 BUCCAL VIEW OF THE UPPER DENTAL ARCH 
 THE PLANE OF OCCLUSION 
 
 In normal occlusion tlie line of contact of the lower 
 with the upper bicuspids and molars is called the plane of 
 occlusion, for here tiieir occlusal surfaces meet in normal 
 closure as well as in lateral movements of the mandible. 
 
 The general direction and position of the plane of 
 occlusion is approximately parallel with, and about an inch 
 below, a straight line extending from the base of the nose 
 to the center of the condyle. 
 
 CURVATURE OF THE OCCLUSAL PLANE 
 
 In reality, however, the occlusal plane usually departs 
 from a straight 'line, the second bicuspid, first, second and 
 third molars curving upward toward the glenoid fossa, in 
 most cases, in a fairly well-defined arc, the convexity pre- 
 senting downward. 
 
 The amoimt of curvature of the occlusal plane varies 
 
294 THE MAS'l'K'A'I'OltV MICCHANISM 
 
 ill (lit'fcrciil iii<li\itUi;il,s, iiud rr(M|uciitly llicre is a notice 
 iihic <Iift'('reiice in tlic ]ilaiies cm the two sides of llio arch 
 ill the same subject. 
 
 The cvirvature varies from a wcll-deiincd arc in most 
 case's to a nearly or quite flat i»Uiiic in a few instances. A 
 few cases liave come under the notice of the writer where 
 the curvature of the occlusal planes was reversed. In 
 other words, instead of the convexity presenting downward, 
 the occlusal plane was conca^'ed upward. Such cases are 
 
 \L MKW OK 'I'lll': NATniAI. llENTtrU': 
 
 rare, however, and, within the writer's observation, only 
 occur when the occlusion is abnormal, the teeth in the lower 
 protruding beyond those in the upper arch. 
 
 RELATIONSHIP OF THE PLANES OF OCCLUSION TO 
 THE CONDYLE PATHS 
 
 The planes of occlusion and the condyle paths bear a 
 definite relationship to each other, as the following problems 
 will demonstrate : 
 
 First. On a jihotograph of a skull in which the teeth 
 are normally occluded, strike an arc intersecting the tips 
 of the buccal cusps of the bicuspids and molars. The 
 center from which this arc is developed nuist be located by 
 trial. This can easily be done when the curvature is pro- 
 nounced, as the center will lie in the region of the frontal 
 
THE MASTICATORY MECHANISM 295 
 
 promiueuees. It will Ix' more diffieult to locate the center 
 in those cases where the occlusal planes are nearly or quite 
 flat, because its position will lie higher up, beyond the range 
 of the ordinary dividers. 
 
 Second. Place one leg of the divider on the center 
 from which the occlusal arc was developed ; set ■ the other 
 leg on the margin of the middle half of the condyle path, 
 and strike an arc in this location. It will be fomid that 
 the arc last developed will coincide with the condyle patli 
 along its working area, and, furthermore, that it will be 
 parallel with the occlusal arc, since both are developed from 
 the same center. These arcs may coincide, or, as is more 
 commonly the case, be concentric, the condyle arc lying 
 above and witliin the one intersecting the tips of the teeth. 
 
 GOVERNING FACTORS IN MANDIBULAR MOVEMENTS 
 
 The mandibular movements which are of the greatest 
 importance to the jirosthetist are those which bring the 
 lower in contact with the upper teeth in some of their varied 
 lateral and protrusive excursions. 
 
 Any movement which, even to a slight degree, causes 
 separation of the entire lower from the upper denture 
 can have no bearing on occlusal conditions, and therefore 
 need not here be considered. The excursions of the con- 
 dyles in their paths in wide-open movements, however, are 
 of importance in certain technical procedures, which will 
 later be mentioned. 
 
 There are three definite and comparatively fixed factors 
 which guide the mandible in its protrusive movements. 
 These are the incisor path and the two condyle paths. 
 
 THE INCISOR PATH 
 Protrusion of the mandible carries the incisal edges 
 of the lower anterior teeth forward and downward against 
 the lingual surfaces of the corresponding upper teeth. If 
 projected sufficiently far forward their incisal edges will 
 occlude with those of the . upper teeth in an end-to-end 
 relation. The distance traversed by the incisal edges of the 
 lower teeth from the position of rest, or normal occlusion, 
 to that of edge-to-edge contact or incision is known as the 
 incisor path. It is obvious that this path controls the 
 movements of the mandible anteriorly, since, with the excep- 
 tion of the last molars in occlusion, the remaining bicuspids 
 
296 THE MASTICATORY MECHANISM 
 
 and molars in one ardi arc nut nsually in contact with 
 those in tlic oppowitc arch in protrnsive elt'ort. 
 
 THE CONDYLE MOVEMENT IN PROTRUSION 
 
 As the mandible is drawn forward in i)rotrusion, the 
 condyles, being lield in close contact with their paths ])y 
 the various mandibular muscles and ligaments, must follow 
 closely the direction of the condyle tracts, whatever may 
 be their form or })itch. It naturally follows that these 
 tracts determine the movements of the mandible posteriorly. 
 
 These three guiding factors in protrusive effort, the 
 incisor path and the two condyle paths, are located one at 
 each angle of thd equilateral triangle, to which attention 
 has previously been directed. 
 
 THE FUNCTION OF THE INCISOR TEETH IN PROTRUSIVE 
 EFFORT 
 
 Prehension, or the seizing hold of food liy the teeth, is 
 the first act in masticatory effort. 
 
 Incision, or the cutting off of a portion of suitable size 
 for reduction by the bicuspids and molars, is the second act. 
 
 These functions are performed by depressing, protrud 
 ing and raising the mandible while protruded, so as to bring 
 the anterior teeth together in edge-to-edge contact, with 
 final return of the mandible to normal position and the teeth 
 to normal occlusion. The final act of retrusion, as outlined, 
 shears off those portions of the morsel of food not com- 
 pletely severed by direct incisive effort. Only the anterior 
 teeth are concerned in the actual work accomplished. 
 
 Since, then, the focus of useful effort is confined solely 
 to the incisors and cuspids, there is no necessity for the 
 bicuspids and molars of the lower coming in contact with 
 those in the upper arch in the incisive act, except at the 
 extreme distal portion of the arches. Here the last lower 
 molars, which normally occlude (the second molars, usually 
 when the third molars are not fully erupted or are missing), 
 move forward in sliding contact with those in the upper 
 arch. Contact of the molars in this region does not increase 
 the field of effort or working area, since no food is being 
 reduced here. It serves the purpose, however, of steadying 
 or balancing the denture, and further of distributing or 
 equalizing the force of closure, thus avoiding the imdue 
 stress that would be exerted on the central portion of each 
 
THK MASTICATORY MECHANISM 297 
 
 lateral hall' of the maiulihle it' the incisur teeth ami condyle, 
 without such central bearing points, were required to sus- 
 tain all of the force of masticatory incisive effort. 
 
 LATERAL MOVEMENTS OF THE MANDIBLE 
 In actual masticatory effort the lateral mandibular 
 movements are the most important and effective of any 
 of those mentioned. By such movements the food is 
 crushed, torn asunder, finely triturated and insalivated as 
 it cannot be in any other manner or by any .other action. 
 Food subjected to the hinge action is merely punctured, 
 or at most slightly crushed. It cannot be torn and shredded 
 as when caught betweeu sliding contact surfaces, any more 
 than can wheat be reduced to flour by the lifting and drop- 
 ping of the upper upon the lower millstone. Flour is pro- 
 duced by the grains of wheat being caught and broken up 
 from contact with many sliding surfaces. So food, when 
 caught and confined in the masticatory groove, is torn 
 asunder by being brought in contact with the many sliding 
 planes of the opposing teeth. 
 
 To produce artilicial dentures that will fulfill the func- 
 tions of the natural masticatory organs it will be necessary 
 to study the radial swing of the mandible and the rela- 
 tion of the teeth in the lower to those in the upper arch 
 when subjected to such action. 
 
 ANALYSIS OF THE LATERAL MANDIBULAR 
 MOVEMENTS 
 
 In the lateral movements one condyle is drawn forward, 
 or protruded in its i)ath, while the other remains com- 
 jtaratively stationary, serving, in a general way, as a 
 pivotal or rotation center to guide the mandible in its 
 radial movements. 
 
 THE CENTERS OF MANDIBULAR ROTATION 
 
 The centers of the condyles may be, and frequently 
 are, the true centers of mandibular rotation. Oftentimes, 
 however, the rotatio'n centers are situated inside or outside 
 of the condyle centers at varying distances. Both actual 
 rotation centers may be inside, or both outside, of the con- 
 dyles, or one may be inside and the other outside, or, again, 
 one may be located in the true condyle center and the 
 other outside or inside of the opposite condyle. To deter- 
 
208 THE MASTICATORY MECHANISM 
 
 mine their exact location special appliances designed for 
 such iJurjjoses must he used, the most accurate as well as 
 convenient of wliicli are those suggested by Dr. Gj^si. 
 
 When the rotation centers are located between the con- 
 dyles the pivotal condyle has a slight l)ackward movement 
 as the other one is protruded. When the rotation centers are 
 located outside the pivotal condyle moves slightly forward. 
 
 Gysi's appliances indicate that the true rotation cen- 
 ters mav lie within two and three-fourth inches of each 
 
 other, and varj^ from that distance anywhere up to a trifle 
 over five inches apart. 
 
 The position of the teeth in the arches and of their 
 various occlusal surface markings in relation to the rotation 
 centers are of extreme importance. When the teeth are 
 incorrectly located co-ordinate movements between those 
 in the lower against those in the upper arch will be 
 inhibited. 
 
 RELATION OF THE LOWER TO THE UPPER TEETH ON THE 
 PIVOTAL SIDE 
 
 The working limit of the mandible in lateral masticatory 
 effort is reached when the buccal and lingual cusps and 
 
THE MASTK'ATORY MECHANISM 299 
 
 marginal ridges of the lower bicuspids and molars, on the 
 pivotal side, are directly under and in contact with the cor- 
 responding cusps and marginal ridges of the upi^er teeth. 
 The amount of side movement necessary to bring the 
 teeth in this relation to form the masticatory space was 
 designated the "differential limit" by the late Dr. T. W. 
 Pritchett. Used in this sense, it means the limit of side 
 movement of the teeth for doing, effective work, and is 
 a very appropriate term. "Differential" means a differ- 
 ence in rate or distances of movement of the parts of a 
 mechanism in a given period. In true rotary movements 
 of the mandible laterally the ])icuspids travel a greater 
 distance in the same jieriod than do the molar teeth, since 
 the former are situated farther from the rotation center. 
 
 SIDE MOVEMENTS OF THE MANDIBLE NOT CONTROLLED BY 
 THE ROTATING CENTERS 
 
 In reality the rotation centers do not absolutely contine 
 the mandible to an eiact radial swing at all times or rmder 
 all circumstances. Dr. Bennett of Tjondon has shown that 
 there is frequenth- a side movement of the entire mandible 
 independent of the ordinary rotation points. 
 
 In some experiments cari-ied out by the writer this 
 side movement was found to l)e involuntary, or automatic, 
 in some, and entirely volitional in other cases. In most 
 instances it is so slight as to be of little importance in 
 general masticatory effort, and need not be considered in 
 denture construction as a separate or vital factor. 
 
 A method of adapting artificial dentures to this side 
 movement, when present and involuntary, will later on be 
 described. 
 
 RELATION OF THE LOV/ER TO THE UPPER TEETH ON THE 
 PROTRUDED SIDE 
 
 The lateral movement of the mandible carries the lower 
 teeth on the protruded side lingually. During this move- 
 ment the disto-buccal cusp of the lower second molar moves 
 along the inclined planes leading from the central sulcus 
 to the lingual marginal ridge of the upper second molar, 
 and there finds contact with its mesio-lingual cnsii. This 
 is known as the hnlaucUifi covldcl. and this, the protruded 
 side of the mandible, is known as (he balancing side, in 
 contradistinction to the opposite, or pivotal, side, which 
 is the masticating or ivorking side. 
 
300 THK MASTICATORY MKCHANISM 
 
 Balaiicui.i^' contact, as just stated, is usually developed 
 between the lower and upper second molars. Similar con- 
 tact, however, may be developed between the lower and 
 ui)per third molars, when fully erupted, although it fre- 
 quently happens that these teeth, even after a lapse of 
 many years, fail to come into normal occlusion with each 
 other. For this reason, therefore, balancing contact is 
 most commonly develo])ed and remains most persistent 
 between the lower and u])per second molars. In radial 
 movements of the mandible no contact exists, nor is any 
 essential to the balancing of the masticatory apparatus, 
 from the second molar forward to the opposite central, or 
 even lateral, incisors. The actual work of mastication is 
 being performed on the opposite of the mouth, and there- 
 fore the close interlocking of planes and cusps on the pro- 
 truded side, exclusive of the balancing point, would tend 
 to disturb, rather than aid, masticatory effort. 
 
 THE COMPENSATING CURVE 
 
 As in-eviously stated, tlie tii)s of the buccal cusps of 
 the bicuspids and molars, when viewed bucally, assume a 
 curved arrangement, the convexity being downward. This 
 curved arrangement of the teeth in the upjier arch is called the 
 compensating curve. The reason for it being so designated 
 is as follows: 
 
 When the occlusal plane is flat, and the condyle path 
 is inclined downward and forward, separation occurs be- 
 tween the lower and upper bicuspids and molars in lateral 
 movement, the lower teeth being carried downward to the 
 lingual and away from the upper teeth on the protruded 
 side. Balancing contact, therefore, is not jiossible under 
 such conditions, because of incoordinate movements the 
 occlusal planes of the upper teeth oeing practically hori- 
 zontal while the occlusal planes of the lower teeth are 
 carried downward in an angular direction by the condylar 
 movements. When arranged on a proper curve, however, 
 the disto-buccal cusp of the lower second molar occupies 
 a higher position in the occlusal plane than the mesio- 
 lingual cusp of the upper second molar, which occupies 
 a position forward, downward and to the lingual in the 
 occlusal plane. In lateral movements the disto-buccal cusps 
 of the lower second molar moves downward, forward and 
 linguall}% in contact with the plane leading from the central 
 
THE MASTICATORY MECHANISM 301 
 
 groove to tlie mesio-]ingual eiisp of the upper second molar. 
 
 This balancing area is present, and the diso-buccal 
 cusp of the lower second molar, under normal conditions, 
 is in contact with it at some point throughout the entire 
 lateral excursion of tlie condyle, both out of and back to 
 its fossa. 
 
 The curved arrangement of tlic upper teeth, therefore, 
 compensaies for the dropping down of tlie condyle in its 
 path in radial and forward movements, and makes possible 
 
 DIAGRAil SHOWING PARAT.I.EL RELATION OF CONriVI.E PATH AND COMPENSATING CURVE 
 
 the contact just described. AVhile the compensating curve 
 represents a fairly accurate arc where it intersects the tips 
 of the buccal cusps of the bicusi)ids and molars, when 
 projected forward, it passes above the incisal edges of the 
 anterior teeth sometimes as high as the incisal third of the 
 central incisors. ' This is due to the overlapping of the 
 upper anterior over the lower teeth, there being a more 
 or less definite correlation existing between the curvature 
 of the teeth plane and the overbite. Variations as to 
 the amount of overbite naturally occur, one of the most 
 common being a deep overbite, with a comparatively shal- 
 
302 THK MASTU'ATORY MKCHANISM 
 
 low or flat conipensaling curve. In such cases some space 
 must be present, when the teeth are in occlusion, between 
 the lingual surfaces of the upper and the incisal edges 
 of the lower teeth, otherwise interference will occur with 
 normal lateral and protrusive movements. 
 
 THE CURVE OF SPEE 
 
 The lower teeth, including the incisors and cuspids, 
 usually present a very-well-defined arc-like arrangement 
 when viewed buccallv. This curved plane assumed by the 
 lower teeth is sometimes called the "Curve of Spee," be- 
 cause Graf von Spee, the G-erman anatomist, first called 
 attention to it, about 1890. 
 
 Spee says, in regard to tlie relation existing between 
 the condyle paths and the teeth planes : "In the forward 
 bite the teeth and condyles describe the same circular move- 
 ment. The steeper the ]iath of the condyle the more pro- 
 nounced the tooth cur\e will be, because both will have 
 the same radius." 
 
 This latter statement is incorrect, for, while the con- 
 dyle path and the teeth plane may both be arcs of circles 
 having a common center, their radii may vary, and the two 
 curves will often represent concentric arcs. 
 
 Spee's writings refer especiallj' to the curvature of 
 the lower teeth plane and its relation to the condylar move- 
 ments, and therefore the term, "Curve of Spee," should 
 not be applied to the upper teeth i)lane. 
 
 MODIFICATION OF THE COMPENSATING CURVE 
 
 Occasionally the occlusal surfaces of the upper molars 
 present a series of parallel planes, instead of assuming a 
 symmetrical curve, as described. The second molar is 
 slightly higher than the first, and the third slightly higher 
 than the second. The lower molars assume a similar 
 relation, with the result that the occlusal plane when analyzed 
 presents a step-like instead of a curved arrangement. 
 
 It is claimed by some that this is the logical manner 
 in which to arrange teeth in the construction of artificial 
 dentures. First, because balancing contact can be more 
 easily secured; second, that there is less liability of the 
 dentures becoming dislodged in masticatory effort. The 
 argument is that the force of muscular effort is delivered 
 upon the food more in the nature of an end thrust against 
 
THE MASTICATORY MECHANISM 303 
 
 right-angle surfaces, rather than against inclined planes; 
 third, that such an arrangement of the teeth is anatomical, 
 natural and more common than the curved arrangement. 
 
 It is the opinion of the writer, based upon the examina- 
 tion of many specimens, first, that the step-like arrange- 
 ment is the exception, and not the rule, or at least occurs no 
 more frequently than the curvcil arrangement; second, that 
 balancing contact can as readily l)e secured liy placing the 
 second molars in a relation similar to that which they 
 sustain in the natural denture, when the curvature is well 
 defined, as previousiy outlined; third, that the A'arying 
 planes on the occlusal surfaces of the intercusi^ating molars 
 tend to prevent displacement of the dentures in masticatory 
 effort; fourth, that better esthetic results can be secured 
 by arranging the teeth by the curved rather than by the 
 stepping method. However, either method is productive 
 of satisfactory results if due attention is given to details, 
 so it is largely a question of esthetics, in which neither com- 
 fort nor utilitv is concerned. 
 
CHAP T K R XVIII 
 
 CONSTRUCTION OF FULL DENTURES. 
 
 ANATOMIC METHOD 
 
 GENERAL REMARKS 
 
 In the eoiLstriictioii of good dentvires, as has ))een previ- 
 ously stated, the accomplishment of three objects is desirable, 
 necessary, and, in most cases, possible, when careful atten- 
 tion to detail is observed. These three objects — usefulness, 
 good looks and comfort — when attained in prosthetic, as well 
 as in all dental operations, represent that quality of service 
 which our patients have a right to expect, and which the ten- 
 ets of our profession impose upon us. 
 
 It is therefore the duty of every practitioner to perfect 
 himself in the liighest degree, not only in theoretical knowl- 
 edge, but in the acquirement of technical skill as well in all 
 that pertains to his calling, whether it be the general or a spe- 
 cialized field of dental practice. 
 
 Anatomic occlusion of artificial teeth consists in following 
 nature's plan of arrangement as observed in the normal 
 human masticatory apparatus. 
 
 Occasions arise, Jiowever, when this course is not pos- 
 sible, but such cases are rare. When occurring the causes 
 may be traced to some abnormality of the glenoid forste, usu- 
 ally the result of mandilmlar movements having since early 
 youth been restricted liecause of malocclusion or, in some 
 cases, to the sequela of temporo-mandibular inflammation. 
 
 Whatever the character of the abnormality an attempt 
 should be made to discern the cause and discover such useful 
 mandibular movements as are possible. With a thorough 
 knowledge of existing conditions and the application of an- 
 atomic methods far better service can be rendered a patient 
 than when such almormality is ignored. 
 
 By way of introduction to anatomic methods a brief re- 
 view of masticatory movements in general will he in order. 
 
 MASTICATORY MOVEMENTS OF THE CARNIVORA 
 
 The most effective masticatory movements of the carniv- 
 ora (flesh-eating animals) are hinge-like, no extensive lateral 
 movements of the mandible being possible for two reasons: 
 
 304 
 
CONSTRUCTION OF FULL UENTHRES 305 
 
 First, because of the t'orni oi' the temjjoro-iiuuKUbuhir artieu- 
 lation, which does not permit of much unihiteral action; aud, 
 second, because of the excessive length and relation to each 
 other of tlie upper and lower canine teeth. In general, the 
 posterior teeth of this class of mammalia liave strongly 
 marked cusps which intercuspate closely. Their function 
 is to tear and ciit food. 
 
 MASTICATORY MOVEMENTS OF THE HERBIVORA 
 
 In the herbivora (animals that live on herbs and vegeta- 
 tion), the effective mandibular movements are almost exclu- 
 sively lateral, or from side to side. The occlusal surfaces of 
 the teeth are not strongly cusped, but are ridged for grinding 
 food. 
 
 MASTICATORY MOVEMENTS OF THE OMNIVORA 
 
 In the omnivora or herbi-carnivora (subsisting on both 
 flesh and vegetation), the effective masticatory movements are 
 hinge-like as well as from side to side, or lateral. The occlu- 
 sal surfaces of the teeth consist of planes, ridges, grooves and 
 cusps, usually so arranged that in unilateral movements the 
 CUS13S of the lower may glide between those of the upper teeth 
 in definite paths, without interference. 
 
 Since man is omnivorous, the human masticatory ap- 
 l^aratus, while modified somewhat from that of the lower ani- 
 mals because of different habits of life, corresponds in gen- 
 eral to mammalia of tJiis class. A more complete general de- 
 scription of the human masticatory apparatus will be found in 
 the preceding chapter. 
 
 In the chewing of meats, tlie liinge action of the mandible 
 is most effective at first until the meat fibres have been more 
 or less torn and shredded by the cusps of the bicuspids and 
 molars, after which the lateral movements are just as essen- 
 tial in still further reducing the mass to a pulpy condition 
 suitable for action by the digestive fluids. 
 
 Cereals, fibrous vegetables and most all varieties of 
 starchy foods require active lateral movement for proper re- 
 duction. Dr. G. v.. Black in "Phvsical Characters of Hixman 
 Teeth" (Cosmo-s, 1895), states: 
 
 "In the mastication of cereal foods — those made from 
 grain of almost all kinds — the lateral or grinding motions are 
 largely employed. This is true also of all of the brittle foods 
 of whatever nature. Indeed, many of these are so difficult to 
 
306 CONSTRUC'PIOX OK FHI-L DENTTTRES 
 
 cnisli l)y dircci ]irossuf«' that it hcconics inipract ical)l('. Many 
 kinds of food will simply lie packed togethei- between the 
 teeth, and a stress of two or three hundred pounds will be 
 insufficient to crush it out as meats are crushed. Many of 
 the crusts from ordinary baker's bread, when subjected to 
 stress between the molar teeth, will not be cut through with 
 a stress of two hundred and fifty pounds ; and they are not 
 very hard crusts, either. They are readily broken up, how- 
 ever, with a much lighter stress combined with a little lateral 
 movement, especially as they become moistened with the 
 secretions. It seems probable, however, that many persons 
 unconsciously exert an enormous force upon such foods as are 
 inclined to pack between the teeth. I am no longer surprised 
 at the frequent breaking of frail teeth on In'ead crusts that, 
 are not very hard. It is but little wonder that porcelain fac- 
 ings on crowns and bridges are so often broken." 
 
 In carrying out a line of experiments to determine the 
 amount of direct stress required to crush various kinds of 
 food. Dr. Black used an instrument called a p)hago-d3"namome- 
 ter. The action of tliis instrument on the food tested was 
 practically identical with that exerted liy the natural teeth 
 on food wlien the hinye-like action of the mandil)le is em- 
 ployed. 
 
 Some years later Dr. Joseph Head carried out a line of 
 experiments to deterjnine the amount of force required to 
 reduce similar classes of food with lateral movements. He 
 used for this purpose a Imman skull in which the natural 
 teeth were present and occluded well. The following table 
 of comparison shows that it requires only about one-lialf the 
 effort to reduce food under lateral movem(>nts that is required 
 under the hinge action of the mandible: 
 
 Dr. Head 's 
 Meals Experiments 
 
 Corned Beef 18 -22 lbs. 
 
 Tongue 1 - 2 " 
 
 Tenderloin of Beef, very tender. 8 - 9 " 
 
 Round of Beefsteak, tough 38 -42 " 
 
 Eoast Beef 20 -.35 " 
 
 Boiled Ham 10 -14 " 
 
 Pork Chop 25 -30 " 
 
 Roast Veal 16 -30 " 
 
 Average 17 -20 " 3214-417/8 
 
 Dr 
 
 •.Black's 
 
 Ex, 
 
 >eriments 
 
 .",0 
 
 -35 lbs. 
 
 ;! 
 
 - 5 " 
 
 35 
 
 -40 " 
 
 60 
 
 -80 " 
 
 35 
 
 -50 " 
 
 40 
 
 -60 " 
 
 20 
 
 -25 " 
 
 35 
 
 -40 " 
 
CONSTRUCTION OF FULL DENTURES 307 
 
 Dr. Head's Dr. Black's 
 
 Vegetables. Experiments Experiments 
 
 Raw Cabbage 16 " 40 -60 " 
 
 Head Lettuce 16 " 25 -.30 " 
 
 Radish, whole broke at 20 -25 " 20 -25 " 
 
 Radish, i^ieces pulverized at. .. .10 -15 " 35 -40 " 
 
 Average 12V--16 '' 30 -383^" 
 
 (Dental Cosmos, 1906, P. 1191) 
 
 Dentures constructed on a plain line, or similar articula- 
 tor, or on an anatomical occluding frame, when all of the de- 
 tails are not carefulh- attended to. limit the wearer to the 
 hinge action of the mandible in the reduction of food. 
 
 The advantage of the anatomic system of denture con- 
 struction over the generally prevailing methods wherein 
 masticatory effort is limited to the hinge action of the mandi- 
 ble, have l)ecome an established fact. Dentures of the ana- 
 tomic type balance when in action, while those constructed 
 on plain line articulntors become readily unseated when 
 lateral movements are attempted. This fact alone is of suffi- 
 cient importance to warrant the adoption of anatomic meth- 
 ods, because of greater efficiency, as well as comfort, derived 
 by the patient from the use of dentures of this type. 
 
 The normal human denture, and the various relations the 
 lower sustain to the upi)er teeth in full and partial occlusion, 
 is the ideal working model for the jn-osthetist, although at 
 times departure from ideal conditions must be made. To 
 carry out the many steps of denture construction by this 
 method a knowledge of the mechanism of the masticatory 
 apparatus is the first essential, while the use of suitable ap- 
 pliances constitutes a second factor of equal imj^ortance. 
 
 MAIN FEATURES OF ANATOMIC METHODS 
 
 The essential practical features of anatomic denture 
 construction, therefore, aside from a knowledge of mandi- 
 bular movements, involve the use of special appliances and 
 require that certain steps be carried out in logical sequence. 
 The main factors Qf importance are as follows: 
 
 First — An -occluding frame capable of reproducing the 
 most essential masticatory movements of the mandible. 
 
 Second — A face bow, or caliper, for mounting the casts 
 on the occluding frame in correct relation to the lateral cen- 
 ters of rotation. 
 
 Third — Some means for registering the condyle path 
 
oOS CONSTRUCTION' OF FULL DENTURES 
 
 pitch of the i^atieut and of recording' the same on the occlud- 
 ing frame. 
 
 Fourth — The selection ot t<'eth of ai)pi-opriate size, shade 
 and anatomic forms to meet the requirements of each case. 
 
 Fifth — Ti'ial of the model dentures in the mouth under 
 masticatory movements to verify their efficiency and estlietic 
 appearance. 
 
 Sixth — Testing and correction of occhisiou of the jinished 
 dentures l)y means of carl)on paper and engine stones, to 
 compensate for variation of the natural lateral mandibular 
 rotation centers from those of the occluding frame on which 
 the teeth were arranged. 
 
 PRESENT METHODS OF TECHNIC IN ANATOMIC 
 DENTURE CONSTRUCTION 
 
 Two general methods of anatomic denture construction 
 are in vogue in this country at the present time, each of which 
 recjuires special appliances and the following of a rather 
 closely defined system of technic. 
 
 The two systems referred to are the Snow methods and 
 appliances, a logical outcome of, with improvements on, the 
 Bonwill and Christensen ideas, and the Gysi methods and ap- 
 pliances, which are based on similar principles but differ in 
 many important detail-^. Both systems in the hands of com- 
 petent prosthetists lead to the same desired results, viz., the 
 production of high-type dentures, which for efficiency and 
 comfort far surpass those produced by any other system in 
 which lateral mandibular movements are not considered. 
 Both methods involve the carrying out of many steps in com- 
 mon, in some of which the same technic is employed, while 
 in others considerable variation occurs. The essential details 
 of these two sj^stems will now be rendered sufficiently clear, 
 it is hoped, to enable a prothetist of average skill, who un(Jer- 
 takes the work, to secure satisfactory results. 
 
 THE SNOW APPLIANCES AND METHODS 
 
 The appliances used in the Snow method consist of an 
 occluding frame, or as it is termed, an "articulator," the 
 condyle or lateral rotation centers of which are four inches 
 apart, this being about the average distance from center to 
 center of the human condyles. '^Plie lateral rotation centers of 
 the frame are fixed at four inches and cannot be increased or 
 diminished. The condyle paths of the frame are capable of 
 
CONSTRUCTION' OF FULL DENTURES 3U9 
 
 adjiistuieiit and of being clamped at various angles, depending 
 npon the pitch of the condyle paths of the patient, as regis- 
 tered. The upper and lower bows of the occluding frame, to 
 which, when the casts are attached, represent the maxilla and 
 mandible, respectively, are adjustable for the accommodation 
 of thick or thin casts. The back spring, by its tension, holds 
 the mandibular portion of the frame in the back end of the 
 condyle slots, or in that jjosition representing the condyles 
 at rest in the glenoid fossa". 
 
 THE FACE BOW 
 
 The face bow is a measuring device or caliper designed 
 for registering the antero-posterior, as well as horizontal 
 plane relationship of tlie alveolar ridges to the condyles when 
 the latter are at rest in the glenoid fossje, as in normal closure. 
 It is used in conjunction with the wax bite, or with occlusion 
 models. This appliance is indispensable in order that the 
 casts may be mounted in true relation to the rotation centers 
 of the frame. By thus establishing the correct radial distance 
 of the casts from the hinges, the teeth, when occluded on the 
 frame and adjusted with clearance paths for the cusps of the 
 lower to traverse laterally between those of the upper teeth, 
 will follow the same lines of travel when the dentures are 
 completed and fitted in the mouth. Increasing or decreas- 
 ing the radial distance of the teeth on the frame from that 
 which they will occupy in the mouth, will cause cusp inter- 
 ference in lateral movements. 
 
 The face bow consists of a U-shaped frame, in the ex- 
 tremities of which are two graduated sliding rods to enable 
 the bow to be evenly balanced on the face. These are the 
 condyle rods, the inner ends of which, in adjustment, are to 
 be placed opposite the outer ends of the condyles and there 
 clamiied on points previously marked on the integument be- 
 fore adjusting the bow. The bow in its central portion carries 
 a universal clamp for receiving the bite rod after the latter 
 has been firmly fixed in the occlusion model and for clamping 
 it to the bow when proper adjustment of the condyle rods to 
 the face has been gecured. 
 
 THE BITE GAUGES 
 
 Two small flat plates of metal called hite gauges, having 
 the edges turned down to engage with the lower wax rim, 
 and with tapering pins projecting on the upper surfaces to 
 engage with the upper wax rim, are used for taking the pro- 
 
aiO CONSTRUCTION OF FULL DENTURES 
 
 trusive bite — the means by whicli the condyle paths are regis- 
 tered. The details for the application of these appliances 
 will be given in the following described case of full upper and 
 lower denture construction. 
 
 GENERAL CONSTRUCTIVE STEPS 
 
 The construction of full dentures anatomically involves 
 the securing of suitable impressions ; production of casts ; 
 development of wax contour models, first on the casts and 
 afterward in the mouth, to develop lost facial contour and 
 
 UPPER MODELING 
 
 establish the normal bite ; the mounting of the casts on an 
 anatomical occluding frame ; registration of the condyle paths 
 of the patient and the adjustment of the condyles of the frame 
 to correspond ; development of the compensating curve on 
 the wax occlusion model; selection of teeth of suitable form 
 and color to harmonize with anatomic and esthetic require- 
 ments of the patient, and their arrangement in upper and 
 lower arches so as to develo]i the greatest efficiency and pre- 
 sent the best appearance ; duplication in permanent materials 
 of the wax model dentures, and finally, the fitting and adjust- 
 ment of the dentures to the respective arches within the oral 
 cavity. 
 
CONSTRrCTIOX OP FULL DENTURES 311 
 
 Moi'f tliau one limidrcd iinliviilual stops must be carried 
 out in sequence in the production of full dentures of any type. 
 It is therefore imperative that the greatest care be constantly 
 exercised to arrive at satisfactory results, since a single 
 error in some particular step may minimize the efficiency, or 
 result in the total faiUire of the substitutes. 
 
 The technic of impression taking, east construction and 
 the formation of base plates of various kinds, has been pre- 
 viously presented. Also a brief description of the oral cavity 
 and the masticatory movements has been given. Tliese vari- 
 ous subjects should be thoroughly considered by the student 
 before undertaking the work now to be presented. 
 
 Assuming that suitable casts have been derived from ac- 
 curate iinjiressions of the mouth, tlie next step in the coustruc- 
 
 SIDE VIEW l)K IMl'RESSKJN" UKADV Fdl! FI1I!MIX( 
 
 tion of a full denture (upper and lower) is to form in wax, 
 or some easih" workable but comparatively rigid material, 
 models of the dentures to be constructed. These model -den- 
 tures, before being duplicated in permanent materials, are 
 tried in the mouth and tested as to occlusion, appearance and 
 comfort. Should any modification he required, such changes 
 as are necessary may be accomplished with less effort and loss 
 of time while the dentures are in a plastic condition than 
 subsequently. 
 
 The model dentures are developed in two stages: first, 
 base plates are fitted to the casts before the latter are mounted 
 on the occluding frame, and on these, rims of wax are ad- 
 justed to represent approximately- in depth and contour the 
 lost teeth and absorbed borders. These are ordinarily called 
 trial base plates. 
 
:512 (;ONSTRrC"IM().\ Ol' full DliNTrRES 
 
 Dr. G. II. Wilson suggests Ihc use of the tonus Dcrlusion 
 uud contour }iiodels, because by means of them ocelnsal rela- 
 tions are determined, while snbseqnently by additions to, and 
 trimming of the wax rims, the contour of the faeo is restored 
 
 \M) TltlM.MEI) 
 
 to normal outline. They also represent, in a crude way, 
 models of the dentures to be constructed. 
 
 The second stage i? developed as follows: After certain 
 sequent steps, to be described later, are carried out, sections 
 
 l.dWER CAST WITH BASEPLATE FITTED TO BORDER 
 
 are cut out of the wax rims, and in the spaces so formed the 
 selected teeth are adjusted, the lower to occlude with the up- 
 per. The gums are then carved in the wax and the surplus 
 material removed, which steps convert the wax occlusion and 
 
CONSTRUCTION OF FULL DENTURES 313 
 
 contour models into »v/.r Diodel dentures, by which term they 
 will be designated in this description of denture construction. 
 This term is appro] )riate l)ecanse they are the models by 
 means of which the matrices are produced in which the per- 
 manent dentures are molded. 
 
 OCCLUSION AND CONTOUR MODELS 
 
 In the construction of full dentures the upper and lower 
 occlusion models repiesent two masses of crude material 
 from which the prosthetist carves and shapes in outline and 
 
 DI.STAI. ^'IE^V (IF I'l'TER AND I^OWKR OCl'LISION MODEI^ 
 
 contour the forms of the permanent dentures, just as a sculp- 
 tor molds in clay the model of a ijermanent statue. 
 
 An occlusion model is usually developed in two steps 
 and may be composed of different classes of materials. 
 
 First, a base plate, either permanent or temporary, is 
 formed over a die or cast, derived from an impression of the 
 mouth. 
 
 Second, to the base plate a rim of plastic material, usually 
 wax, is tirmly attached and by trial in the mouth is carved 
 and molded to "the required contour of the future denture. 
 
 REQUIREMENTS OF A BASEPLATE 
 
 The base plate, of whatever class decided upon, should 
 be rigid and unyielding, capable of withstanding oral tern- 
 
314 CONSTRUCTIOX OF FULL DENTURES 
 
 perature without softening or bending under masticatory 
 stress. It should be olosely adapted to the oral tissues on 
 which it rests and should not become dislodged by its own 
 weight, or tip from the action of adjacent muscles. 
 
 The prospect of success of a permanent denture is slight 
 when the base plate ol the occlusion model fails to show an 
 equal amount of adhesion required in the finished denture. 
 The most exact technio, therefore, shoiild be carried out in 
 forming the base for an occlusion model, for by this means 
 the adaptation of the permanent denture can be determined 
 at a time when corrections can be made with little loss of time. 
 
 Wlien a permanent base plate of swaged gold, platinum 
 or aluminum fails to show good adaptation and adhesive prop- 
 erties in preliminary trials it should be reswaged over a new 
 die derived from a new impression, since in no case do sub- 
 sequent steps tend to improve defective adaptation, but rather 
 to increase it. The same holds true of vulcanite or cast 
 metal bases and of base plates constructed of the more rigid 
 temporary materials. Under no conditions should an elastic 
 substance or a material that readily distorts by heat or 
 pressure be employed in the construction of bases for oc- 
 clusion models, because distortion of the pattern denture 
 from any cause will result in similar errors in the permanent 
 denture. 
 
 REQUIREMENTS OF THE OCCLUSION RIM 
 
 The wax used in forming the occlusion rim must be of a 
 hard variety, not softening at oral tem]ierature or mashing 
 down under masticatory stress either before or after the 
 teeth are imbedded in it. The rim should not l)e built up in 
 layers as is frequently the case, but the wax should be kneaded 
 into a compact, solid mass before l)eing attached to the base 
 plate. A rim composed of a hard variety of^pink wax will 
 present a better appearance and enable the prosthetist to de- 
 velop a more esthetic temporary, or model denture, than 
 when yellow or l)rown waxes are employed. 
 
 CONSTRUCTION OF OCCLUSION MODELS 
 
 The base plate, of whatever material determined upon, 
 should be formed, introduced in the mouth and tested as to 
 its fitness in peripheral outline, stability on and adhesiveness 
 to the tissues. When found satisfactory in every respect the 
 occlusal rim is formed and attached to it as follows : 
 
CONSTRUCTION OP FULL DENTURES 315 
 
 Tlic wax tt) \)c used in forniiiig the rim is softened in 
 water not exceeding 130 degrees Fahrenlieit. When tlioi-- 
 oughly plastic it is kneaded into a compact mass with palm 
 and fingers, then transferred to a dry towel and the kneading 
 process continued until all moisture is eliminated. 
 
 The mass, while plastic, is then formed into a roll about 
 one-half inch in diameter and four and one-half inches long. 
 This roll is then bent around and placed upon the maxillary 
 portion of the base plate, against which it is only slightly 
 pressed. A heated spatula is passed along the line of junction 
 of the roll with the base plate on the labial, buccal and lingual 
 surfaces to melt the wax and cause it to adhere firmly to the 
 base plate throughout the entire extent of the border. The 
 angles are then filled in with melted wax until approximate 
 contour on all surfaces is developed. Considerable lieat is re- 
 quired to properly attach the wax rim to the base plate. When 
 the latter is composed of temporarj' material it should rest 
 upon the cast on which formed to prevent distoi'tion while ap- 
 plying the rim and melting the wax. 
 
 When the rim is firmly adherent and the wax has cooled 
 somewhat, the labial, buccal and lingual surfaces are devel- 
 oped api^roximately to the desired contour liy additions and 
 trimming as indicated. 
 
 APPROXIMATE DEPTH OF OCCLUSION RIMS 
 
 For ordinary cases, where an average amount of absorp- 
 tion of the borders has occurred, the rim should be about 
 three-eighths of an inch thick from maxillary to occlusal sur- 
 faces and about the same breadth from buccal to lingual. 
 The occlusal surface should be flat from before backward, 
 as well as from side to side. This may be accomplished by 
 paring otf the excess occlusal wax with a knife, softening this 
 area somewhat and pressing against any true flat surface as 
 a slab or the top of the bench. During this step the base plate 
 should rest upon its cast and the applied pressure should be 
 uniform to jirevent tln'nning the rim more on one side than 
 the other. 
 
 BUCCO-LINGUAL POSITION OF THE UPPER AND LOWER WAX 
 RIMS IN RELATION TO THE BORDER CRESTS 
 
 The rim should be set as nearly on the border as possible 
 to reduce to the minimum the tipping leverage, which increases 
 in direct proportion to the distance the teeth are placed labi- 
 ally or buccally from the maxillary ridge. 
 
;UC CONSTRUCTIOX OP FULL UKNTI'RKS 
 
 Tliero arc two iinjiorlaiit ract<irs, luiwcxci', which Uirgely 
 control tlio ]al)ial and l)iu'cal ])ot<itiou of the occlusal rim of 
 an npper occlusion model. First, the width of the lower arch 
 from buccal to buccal and its relation to the ui)per border; 
 and second, the extent of loss of the upper alveolar ridge on 
 labial and buccal surfaces b.y absorption. In h\l\ cases the 
 teeth in the lower must occlude with those in the upper, re- 
 gardless of the disparity in size of the two arches. When the 
 lower arch is excessively large and the upper is under size 
 in arranging the teeth on the iipper base plate they must be 
 placed out beyond the ridge, while the lowers must be set 
 inward as much as possible without interfering with tongue 
 
 1>ISTAI, VIKW Ol' Ul'l'KK AND l.OWKR OCCLUSION .MOIJKi.S 
 
 ITRI.U, PLATES), SHOWING THE UEI-ATFON Ol' WAX 
 
 niMS TO TITER AND I.OWEK llORDEIl CRKSTS 
 
 movements. A general rule to follow is to so adjust the wax 
 rims in full cases that the buccal and lingual surfaces of both 
 rims will be parallel with, and about an equal distance from, 
 a line drawn between tiie crests of tlie two borders. 
 
 The second factor, which must frequently be considered 
 in the development of the labial and Iniccal surfaces of an 
 upper occlusion model, is the extent of contour necessary to 
 develop on the rims to restore lost facial profile. The amount 
 of such restoration varies in different cases, being greatest in 
 those where the teeth were extracted early in life and dentiires 
 have been worn continuously for many years, the borders hav- 
 ing constantly become reduced in size. In such cases the best 
 judgment of the prothetist must be exercised to determine 
 just how far labially and buccally the upper teeth may be 
 carried beyond the fulcrum line, or crest of the border in re- 
 
CONSTHl'CTIOX OP FULL DENTURES 317 
 
 storiii.y' lost facial conlDur, witliout endangering the stability 
 of the substitute. Since anatomic methods have been devel- 
 oped, however, it is found that in most cases the teetli in 
 both arches can be lined up in accordance with esthetic re- 
 quirements, the tendency to tip l>eing practically overcome by 
 the balancing contact. 
 
 It is best, however, to establish the parabolic arch lines 
 conservatively — that is, within rather than at the extreme 
 outer position demanded by esthetics. Quite frequently in 
 these most difficult cases the arch lines of the teeth mav be 
 
 SIllK VIKW clI'" FIMSIIKII (ICI'I.USIOX IIOIIKI 
 
 kept within normal limits and yet the required facial restora- 
 tion may be accomplished by means of plumpers — reflections 
 of the upper peripheral margin of the base plate. The neces- 
 sity for this means of restoration cannot be determined be- 
 forehand and therefore in the preliminary formation of the 
 occlusion model it is not attempted. Trial in the mouth will 
 determine the position and extent of such reflected margins 
 and they can be developed accordingly. 
 
 All surfaces of the wax rim should now be smoothed up so 
 that when introduced in the mouth the patient may feel no 
 special discomfort, and further, so that the occlusion model 
 may present as good an appearance as possible. 
 
 The foregoing outline, although referring more particu- 
 larly to the construction of an u])per occlusion model, applies 
 in most essentials to the development of a lower model as 
 well. In lower cases the slant of buccal and lingual surfaces 
 
318 CONSTRUCTION OK FULL DKNTl'lUCS 
 
 of tli(_' oc'i'Iusioii rim is usually Id the lingual, t'roiii the border 
 crest ocdusally, in order that its periphery may coincide witli 
 tliat of tlie upper rim at tlie common occlusion plane. 
 
 TRIAL OF OCCLUSION MODELS IN THE MOUTH 
 
 The upper and lower occlusion models having' been de- 
 veloped to approximaie form, they are introduced in the 
 mouth. There are a number of important points to be consid- 
 ered and recorded by means of the occlusion models before 
 they are finally removed from the mouth, the usual order of 
 procedure being as follows : 
 
 First, testing the adaptation of the base plates to their 
 respective ridges. 
 
 Second, determining the correct occlusal plane. 
 
 Third, restoring disturbed facial profile and contour. 
 
 Fourth, marking the high and low lip lines on the wax 
 rims. 
 
 Fifth, marking the median line of the face. 
 
 Sixth, locating the ends of the condyles and marking 
 same on the integument. 
 
 Seventh, removing the upper contour model, inserting 
 and removing tlie bite rod. 
 
 Eighth, "taking the bite" and locking the contour models 
 together. 
 
 Ninth, applying, adjusting and clamping the face bow. 
 
 Tenth, removal of the occlusal models from the mouth. 
 
 TESTING THE ADAPTATION OF EACH BASEPLATE 
 TO ITS RIDGE 
 
 Each occlusion model is independently fitted to its border 
 and tested as to closeness of adaptation, freedom from muscu- 
 lar impingement and wliether or not it will retain its position 
 on the border under muscular action. 
 
 When the periphery of a base plate impinges on the 
 fraenum or muscular attachments, even tliough it may rest 
 firmly on the general surfaces of the ridge and vault under 
 pressure, yet displacement may readily occur when pressure 
 is discontinued and muscular tension is applied. Any points 
 of interference not previously disclosed during trial of the 
 base plate should lie relieved before proceeding with the sub- 
 sequent steps. 
 
CONSTRUCTION OF Fl'LL DENTURES :J19 
 
 DETERMINING THE CORRECT OCCLUSAL PLANE 
 
 Various plans are suggested for determining the correct 
 position of the occlusal plane between the two maxillary sur- 
 faces. One of these is to draw a line on the face extending 
 from tlie tragus of the ear to the ala of the nose and trim the 
 planes of occlusion piuallel with this line. AVhile perhaps 
 in the average case this rule might apply, variations are so 
 frequent that it cannot be relied upon. Many cases have come 
 under the writer's notice where, if this plan had been 
 adopted, the occlusal planes, while anteriorly correct, would 
 have intersected one or the other borders in the region of the 
 second molars, thus unequally dividing the space between the 
 crests of the two processes in which the teeth are subsequently 
 to be placed. 
 
 The following plan is accurate and easy of application : 
 P^irst determine the correct length of the occlusal rim of the 
 upper model auteriorly. In the largest percentage of cases 
 the anterior teeth in normal arches extend about one-sixteenth 
 of an inch below the ujjper lip when tlie latter is relaxed, as 
 can be seen when the lips are slightly parted. This amount 
 of margin of the upper occlusion model should be seen under 
 similar posing of the lips. Should the rim be too short an 
 addition is made, and when too long the excess is pared off 
 until the proper amount of wax is exposed. Whatever changes 
 may be made to the rim anteriorly should be followed by cor- 
 rections to the entire occlusal plane, keeping it flat and of uni- 
 form thickness antero posteriorly from incisal region to the 
 tuberosities, until subsetjnent changes are found necessary. 
 
 The length of the upper rim having been determined and 
 sucli changes as may be necessary effected, the lower model 
 is introduced and the patient instructed to close. Usually the 
 rims strike in the molar region, while anteriorly there is more 
 or less space between them. Instruct the patient to bring the 
 lips together and notice the amount of muscular effort re- 
 quired to effect their closure. 
 
 Both occlusion models are now removed and pared off 
 equally at their, contact points, being careful to preserve the 
 flat occlusal i^lanes by shaving off long bevel sliecs of wax. 
 The main point to kee]i in mind in this trimming process is 
 to preserve an equal thickness of wax on each side of each 
 rim from occlusal to maxillary surfaces, so that in occluding 
 the teeth they may be placed in the space thus provided. 
 
320 CONSTRUCTIOX OK FULL DENTl'RES 
 
 J->rii'tly stated, an cft'oft should be made to estalilish the 
 occlusal plane midway between the crests of the upper and 
 lower borders. Tlie only exception to this method is in those 
 cases where absorption of the borders has progressed un- 
 equally, the teeth in one arch having long been lost and in 
 the other having been extracted at a much later date. In 
 such cases the occlusal plane must be located nearer the 
 border showing the least absorption. 
 
 ESTABLISHING HEIGHT OF THE LOWER OCCLU- 
 SION RIM 
 
 The depth of the upper wax occlusion rim — that is, its 
 thickness from the maxillary surface of the border to the 
 occlusal plane — is to a very groat extent determined by the 
 length of the upper lip anteriorly, while posteriorly it com- 
 monly fills about one-half the space between the crests of the 
 two maxillary borders, the mandible being in nomal position, 
 which position usually j^laces it parallel with the upper max- 
 illary crest. 
 
 With these two factors as a basis it is a comparatively 
 simple task to develop the upper occlusion model. It is more 
 difificult, however, to develop a correctly proportioned lower 
 occlusion model, because of the absence of any fixed land- 
 mark, by means of which the height of the lower rim can be 
 established. 
 
 Let us consider the relation of the mandible to the max- 
 illa, first, with the natural teeth present and in occlusion, and 
 second, after the jaws become edentulous. In the first instance 
 the masticatory muscles bring the mandible upward until 
 when the teeth are in occlusion it is in a state of rest. In this 
 position the facial profile is normal; while the lips rest easily 
 against each other without apparent muscular tension, or 
 conscious effort on the part of the individual. Although while 
 it is possible for the ]:)atient to compress the lips and give 
 them a strained appearance it is purely a voluntary act of the 
 orbicular muscles, in which the mandibular muscles take no 
 part, since the teeth in occlusion arrest the approach of tiie 
 mandible toward the maxilla by contact of their normal 
 occlusion planes. 
 
 Could a registration of the normal profile be made when 
 the natural teeth are present and in occlusion, say by placing 
 one leg of a caliper on the under side of the mandible and the 
 other on the cranium on points that could afterward be located 
 
CONSTRUCTION" OF FULL DENTURES 321 
 
 and the distance between the two be recorded, this measure- 
 ment would enable the length of the face to be reestablished 
 after loss of the teeth. 
 
 This method is not practical, but the illustration shows 
 what we hope to and should accomplish liy means of occlusion 
 and contour models of suitable height. 
 
 Instead of the calipers the esthetic judgment of the pros- 
 thetist is the court of last resort. His eye should be so trained 
 as to detect defective profile or contour and restore his 
 patient's face to norm.al appearance. 
 
 THEORETICAJ. MEASUKEMBNT OP FACIAL PROFILE 
 
 In edentulous cases, there being no teeth present to ar- 
 rest the jirogress of mandible toward the maxilla, restoration 
 of the normal pose of the lips and the general profile and con- 
 tour of the face must be depended upon in establishing the 
 height of rim of the lower occlusion model. This can only 
 be done by repeated trial and testing, building up or reducing 
 the rim as facial contour and the pose of the lips indicate. 
 
 The depth of the upper rim having been determined by 
 the length of the upper lip, the height of the lower rim is 
 established at such point that the lower lip may rest easily in 
 contact with the upper without requiring muscular effort to 
 effect closure. Pursing out of the lip indicates that the rim 
 is too short, while muscular eft'ort in closing the lips indicates 
 that the rim is too high. 
 
322 CONSTRUCTION OF l^ULL DENTURES 
 
 When the rims have been developed correctly labially 
 the contour models should be tested posteriorly to determine 
 whether there is uniform and equal contact between them and 
 their respective borders. This test is made by having the 
 patient maintain moderate mandibular pressure while the 
 prosthetist endeavors to force the occlusion models apart, 
 first on one side and tlien on the other. If on moderate 
 pressure the two base plates separate while contact is main- 
 tained labially, it indicates that the occlusion rims are too 
 short where separation occurred, one or the other of the base 
 plates having tipped or left its border. Such imperfect con- 
 tact should be corrected by additions of wax to one or both 
 rims until uniform bearing on both sides of the mouth is 
 established. 
 
 In making such additions care should be taken to preserve 
 the flat plane areas of both occlusion models. 
 
 Should the upper plane be flat and the rim of proper 
 length the lower rim on the deficient side may be corrected by 
 adding a sheet of soft wax to the occlusal plane where defi- 
 cient, introducing in the mouth and having the patient exert 
 gradual and uniform pressure upon it. The lower model is 
 then removed and the surplus trimmed off to correct peri- 
 pheral outline. 
 
 RESTORING LOST FACIAL CONTOUR 
 
 One of the most important results of full denture con- 
 struction, when the steps are properly carried out, is the cor- 
 rection of disturbed facial contour. 
 
 The teeth, the borders in which they are imbedded, with 
 the overlying soft tissues in the natural masticatory ap- 
 paratus, when viewed anteriorly present a generally convex 
 appearance from side to side and a nearly perpendicular ar- 
 rangement from above downward. The labial and buccal sur- 
 faces of the teeth and alveolar arches support the lips and 
 cheeks and in tliis manner aid in giving form and contour to 
 the lower half of the face. 
 
 Wlien the teeth are lost and the alveolar borders absorb 
 to a greater or less extent from without inward, as well as in 
 height, the lips and cheeks lose their support and fall back- 
 ward and inward. The symmetry of the face is thus disturbed 
 to a marked degree and unless corrective measures are re- 
 sorted to the patient becomes disfigured for life. By the in- 
 troduction of suitably formed dentures disturbed facial profile 
 and contour can in a great measure be overcome. 
 
CONSTRUCTION OF FULL DENTURES 32S 
 
 The first stage in denture construction, where corrective 
 measures can be developed and tested, is during the trial 
 of the wax occlusion models in the mouth. Later on the final 
 test occurs with the introduction of the wax model dentures. 
 By molding and carving, varying the thickness of the labial 
 and buccal rims of the wax occlusion models, introducing them 
 in the mouth, having the patient close and bring the lips to- 
 gether in a normal relation, or state of rest, the prosthetist 
 can determine the measure of success attained. Repeated 
 modifications and trials are sometimes necessary to secure 
 satisfactory results, while in other eases but little difficulty 
 is encountered. 
 
 The occlusion rims, by their perpendicular height, estab- 
 lish the profile and length of the face. Their labial and buccal 
 surfaces lift out the sunken areas, particularly from the bi- 
 cuspids forward. 
 
 In order to correct the wrinkles which extend from the 
 alaB of the nose outward, over the angles of the mouth, it is 
 usually necessary to extend the periphery of the occlusion 
 model upward in the region of the cuspids. Such extensions, 
 however, should be neither too high nor too bulky, or they 
 will interfere with the movements of buccal and orbicular 
 muscles and displacement of the denture will result. 
 
 In those cases where considerable restoration is required 
 and the extension upward of the peripheral rim of the base 
 plate is limited by muscular attachment the required contour 
 can usually be developed by reflecting the peripheral margin 
 of rim, as previously mentioned, outward and downward in 
 the form of flanges, or so-called plumpers. The width and 
 slant of a flange of this type depends on the amount of re- 
 storation required and the tension of the muscles jDeripher- 
 ally. In all cases they must be so disposed as not to interfere 
 with freedom of muscular action or displacement will most 
 certainly occur. 
 
 The usual prominent features of an upper occlusion model 
 when developed are as follows : 
 
 The contour model is notched anteriorly, to allow free 
 play for the labial' frenum. 
 
 There should be slightly depressed areas between cen- 
 trals and cusiDids above the laterals, thus reproducing the in- 
 cisive fossae such as are noticeable in the maxilla. These de- 
 pressions allow freedom of movement of the alse of the nose. 
 Prominently contouring the labial rims above the lateral in- 
 
:;24 CONSTRUCTION OF FULI, DICNTUliKS 
 
 cisors ut'teiitimes restricts the size of the nasal urilice, inter- 
 feres with respiration and is generally uncalled for. 
 
 Prominent cuspid eminences to partially, but not usually 
 wholh', obliterate the wrinkles extending from the alae of the 
 nose outward over the angles of the mouth. A slight sug- 
 gestion of these wrinkles in persons of middle age, or past, 
 produces a more esthetic result than when completely obliter- 
 ated. 
 
 Peripheral margins, from median line to tuberosities 
 more or less notched, as indicated by the muscle-marking ex- 
 ercise carried out in impression taking. 
 
 MARKING THE HIGH AND LOW LIP LINES 
 
 The high and low lip lines are marked on the upper and 
 lower occlusion models respectively, to serve as guides in 
 determining the length of teeth to select for the case. 
 
 The upper central incisors should extend from the incisal 
 plane to the high lip line, or slightly above it, so that when 
 the artificial gum material is applied over the cervical ends 
 of the teeth, the highest curves of the gingival line coincide 
 with the high lip line. The same arrangement can be fol- 
 lowed in selecting and arranging the lower incisors and carv- 
 ing the gums, although the gums of the lower teeth seldom 
 show to the same extent as in upper cases. 
 
 The object in selecting teeth of the length indicated by 
 the high lip line is to avoid exposure of too much artificial 
 gum, as would occur when shorter teeth are used, and also 
 to obviate the monotony which is apparent when only the 
 jDorcelain is visible. 
 
 The patient is instructed to raise the upper and depress 
 the lower lip as in broadly smiling, and while in this position 
 the prosthetist marks on the occlusion models the lines of lip 
 perijiheries as they lie against the wax surfaces. 
 
 MARKING THE MEDIAN LINE OF THE MOUTH 
 
 The human face is seldom, if ever, symmetrical. Usually 
 the nose is bent to one side; one eye may be slightly higher 
 or nearer the median line than the other, or set at a different 
 slant; the general line of the lips from side to side may not 
 form a right angle with the perpendicular lijie of the face. 
 In fact, the most symmetrical faces, when studied closely, will 
 be found unsvmmetrical. 
 
CONSTRUCTION OI<^ FULL DENTURES 325 
 
 it is tliL'iH'l'urc ii tlil'licult, uiuUcr at times iu denture cou- 
 struc'tiou to determine just wliere the two ceutral incisors 
 should be placed because tliere is no fixed landmark to serve 
 as a basis, or to indicate the position once occupied by the 
 natural teeth. Usually the center of the philtrum of the lip 
 will serve as a guide, but when the nose, chin and other fea- 
 tures are out of alignment a general average must be struck 
 to arrive at hannoiiious results. This may be done by placing 
 a straight edge, or the edge of a card, flatwise against the face 
 extending from the center of the chin to a point located mid- 
 way between the inner ends of the eyebrows and making a 
 slight mark on the occlnsion models. The card is then re- 
 moved and a point directly under the center of the philturm 
 is marked. When there is much variation in the two lines a 
 third line midway between the two, yet favoring a location 
 near the philtrum, will give a harmonious median line. 
 
 When the correct position is determined a perpendicular 
 line extending across both base plates should be distinctly 
 marked in the wax. Care should be taken in subsequent steps 
 not to obliterate it until the arrangement of the teeth is be- 
 gun. 
 
 LOCATING THE OUTER ENDS OF THE CONDYLES 
 
 Previous to taking the bite the outer ends of the con- 
 dyles should be located and their exact position indicated by 
 dotting the integument directly over their locations with a 
 soft pencil. The outer ends of the condyles in most cases 
 approach the outer margins of the glenoid fossiB, sometimes 
 coming quite to the margins so as to be detected with little 
 difficulty. More frequenth', however, they are slightly over- 
 hung by the glenoid riras. When the integument is thick and 
 the interarticular fibrocartilages and cai^sular ligaments are 
 well developed it is sometimes difficult to locate them, either 
 at rest or when in action. 
 
 In the largest percentage of cases the condyle end will 
 be found about one-half inch in front of, and on a horizontal 
 plane with the upper jnargin of the external auditory meatus. 
 
 The index finger shoiild be placed perpendicularly against 
 the side of the face, .with that portion of the ball immediately 
 below the finger -nail resting on the immovable glenoid rim. 
 The patient is then instructed to open and close slightly with 
 the hinge motion. Wide open movements are confusing as the 
 condyle not only rotates but moves foi'ward in its path as 
 well. By applying steady pressure with the finger against the 
 
S26 CONSTRUCTION OK FULL DKNTIIKES 
 
 glenoid rim with slight opening and closing movements of the 
 mandible a point of iiereeptible movement will be detected 
 close n]5 along the glenoid margin and in about the same rela- 
 tion to the external auditorv meatus as stated. While varia- 
 
 GLENOID MARGIN 
 
 rOSlTIOX OF FINGER IX LOCATING rOXDVLE KXD 
 
 tions in position of the condyle ends occur in different indi- 
 viduals, and frequently in the same person, they will not be 
 very marked and usually are not difficult to detect. 
 
 The greatest care should be exercised in determining the 
 correct antero-posterior, as well as perpendicular position of 
 the condyle ends when at rest in their foss«, as the measure- 
 ment secured with the face bow becomes the basis of radial 
 movement of the casts when mounted on the occluding frame. 
 
 APPLICATION OF THE BITE FORK TO UPPER 
 OCCLUSION MODEL 
 
 The bite fork, with its crescent-shaped plate for insertion 
 into the occlusal model, is heated and the plate inserted in 
 the labial surface of the wax rim. The occlusion model is 
 
 UPl'EB OCCLUSION MODEL WITH BITE FORK IN POSITION 
 
 removed from the mouth during this step, since if carried out 
 in the mouth the melted wax caused by the insertion of the 
 heated fork is liable to burn the lips. 
 
 The fork while heated is pressed into the rim until its 
 
CONSTRUCTION OP FULL DENTURES 327 
 
 entire inner peri])hery engages with, and is firmly imbedded 
 in the labial surface. The rod should be jDarallel with the 
 occlusal plane and point as nearly forward, parallel with the 
 median line of the occlusion model, as possible, so that the 
 universal clamp of the face bow may grasp it firmly when 
 tightened. 
 
 After insertion it will be found most convenient to re- 
 move the bite fork from the occlusion model before taking the 
 bite, as its weight tends to dislodge the upper occlusion model. 
 When the latter step is carried out and the bite locks are in- 
 serted the fork is returned to the groove previously made for 
 it, the lip protected with a najikin and a hot spatula passed 
 around the upper surface of the fork to lute it firmly to the 
 occlusion model. 
 
 MEANING OF THE TERM, "TAKING THE BITE" 
 
 Tahiufi the bite refers to establishing the correct antero- 
 posterior, as well as perpendicular, relation of the mandibular 
 to the maxillary ridge. When the natural teeth are present 
 and in normal occlusion, the condyles are at rest in the glenoid 
 fossa?. Since in edentulous cases the occlusion rims, when prop- 
 erly formed, take the place of the natural teeth, they estab- 
 lish the correct perpendicular distance of the mandible from 
 the maxilla. The final step of taking the bite consists in hav- 
 ing the patient close the mouth normally, that is, so that the 
 condyles are at rest in the glenoid fossae while the occlusion 
 rims are in contact, ajid registering the relation of the occlu- 
 sion models to each other in this position. 
 
 DIFFICULTY ENCOUNTERED IN TAKING THE BITE 
 
 More or less difficulty is encountered in taking the bite 
 because of the tendency of patients to unconsciously protrude 
 the mandible, either uni- or bi-laterally. It is also a notice- 
 able fact that the more interested the patient is in this step, 
 and the greater effort he displays in giving a correct bite, the 
 greater is the liability of error resulting. It is therefore best 
 not to inform the patient of the importance of the step about 
 to be carried out, but merely instruct him at the proper time 
 what to do. 
 
 VARIOUS METHODS OF SECURING THE BITE 
 
 Various methods are adopted for securing a normal bite, 
 any one of which might prove successful in some cases and 
 
328 CONSTRUCTION OP FUI.L DENTURES 
 
 result ill failure in others. Some of these methods are as 
 follows : 
 
 First — Tlie patient is instructed to swallow and at the 
 same time close the mouth, the culmination of this muscular 
 effort being supposed to — and in some cases does — bring the 
 condyles back in their position of rest in the fossae. 
 
 Second — A small pellet of wax is attached to the distal 
 margin of the central vault portion of the baseplate. The 
 patient is instructed to touch the pellet of wax with the tip 
 of his tongue, and at the same time close the mouth until the 
 occlusion rims are in contact. 
 
 Third — A chin cup is applied to the meiitum, to which 
 straps are attached which jjass around the head. When these 
 straps are properly adjusted, tension is exerted on the mandi- 
 
 THE GAKBISON BITE GUIDE 
 
 ble to force it backward. Eepeatedly opening and closing of 
 the mandible will frequently, but not in all cases, result in 
 establishing the correct bite. An apparatus similar to the 
 one just described is known as Garrison's Bite Guide. 
 
 Fourth — Pressure may be exerted upon the point of the 
 chin, while the patient repeatedly opens and closes the mouth, 
 attention in the meantime being given to the relation the 
 occlusion rims sustain to each other when brought in con- 
 tact. 
 
 Fifth — It is a noticeable fact that when the masticatory 
 muscles are wearied by rapid and repeated exertion, they 
 draw the mandible backward until tlie condyles are in normal 
 resting position in the fossa?. 
 
 By combining the two methods last mentioned, a correct 
 bite may, in practically all cases, be secured. 
 
CONSTRUCTIOX OK FULL DENTURES 329 
 
 A PRACTICAL METHOD FOR SECURING A CORRECT 
 BITE 
 
 The jiatieiil isliuuld he instructed to open and close the 
 mouth rapidly many times, say for a period of one-half to one 
 minute, the operator in the meantime paying but little atten- 
 tion, further than to see that his instructions are followed. 
 He will then say to the patient, "Relax your muscles and let 
 me open and close your mouth. ' ' The point of the chin is then 
 grasped lightly with the tips of the fingers and thumb so as 
 not to displace the lower occlusion model, and the mandil}le 
 is moved up and down, the lips being raised to note position 
 in which the occlusion rims strike. Slight pressure may also 
 be applied on the mandible to force it upward and backward. 
 Undue pressure should be avoided, as it would result in com- 
 pression of the tissues in the temporo-mandibuiar joint, and 
 thus give a slightly backward or retruded bite. 
 
 Under the slight pressure exerted, together with repeated 
 opening and closing movements, the occlusion rims will finally 
 
 ^^^ 
 
 niiijii 
 
 ISITE LOCKS. LEFT, FORMED OF 
 
 WIRE RIGHT, 1)K. SNOWS 
 
 DESIGN 
 
 meet each time in the same relation to each other. The 
 patient is then instructed to "keep the mouth closed." The 
 bite locks are then warmed and forced into tlie upper and 
 lower occlusion models, about in the region of the bicuspid 
 teeth. Care should bo taken in placing them to avoid en- 
 croaching on the groove previously made for the bite fork. 
 A third bite lock is sometimes inserted in the labial region to 
 prevent possible change of relation between the baseplates in 
 removal from the mouth. 
 
 In some cases where the wax occlusion models are large 
 and the oral opening small, it is impossible to remove the 
 two models when ' locked together. By cutting cross 
 grooves in both occlusion rims opposite each other, one on 
 either side and one anteriorly, placing small pellets of warm 
 wax directly over them, and having the patient bite, the wax 
 will be forced in the grooves and will serve as guides in plac- 
 ing the models in correct relation to each other on removal 
 from the mouth. 
 
330 CONSTRUCTION OK FULL DENTURES 
 
 The bite lock having been inserted or the grooves cut as 
 described, the next step is to return the bite fork to position. 
 
 INSERTING THE BITE FORK IN THE UPPER OCCLUSION 
 MODEL 
 
 The bite fork is now warmed slightly, the lips opened 
 and the fork inserted in the groove previously made by it, 
 and from which it was removed previous to taking the bite. 
 To secure it firmly in place, a heated spatula should be passed 
 along the upper surface of the fork, the upper lip being held 
 up and the lower protected with a iia|)kin. When firmly fixed 
 the face bow can be applied. 
 
 ADJUSTING THE FACE BOW TO THE OCCLUSION 
 MODELS 
 
 As will be seen, the bite has been established, although 
 the occlusion models have not yet been removed from the 
 mouth. The face how is now applied so that when the hase- 
 
 ADJUSTIXG THE CONDYLE RODS 
 
 plates are removed from the mouth,, and the casts are in- 
 serted each in its respective baseplate and attached to the 
 occluding frame, their maxillary surfaces will bear the same 
 relation to the frame hinges that the natural ridges sustain 
 to the condyles ivhen the later are at rest in the glenoid fossae. 
 The condyle rods of the bow are now drawn outward so 
 as to allow them to pass on either side of the face without in- 
 terference. The universal clamp in the center of the bow is 
 carried over the projecting rod of the bite fork, and the back 
 
CONSTRUCTION OF FULL DENTURES 331 
 
 ends of the bow are dropped down nntil the condyle rods are 
 opposite the points previously marked in pencil to indicate 
 the condyle ends. The condyle rods are then pressed inward 
 until their ends rest on the points marked. 
 
 Care should be tiiken to see that the condyle rods show 
 the same number of gradations between their inner ends 
 which rest on the face and the inner sides of the bow. Should 
 the bow be unequally balanced when clamped, the casts will, as 
 a result, be mounted to one side instead of on the center of 
 the occluding frame, and their radii of movement will be in- 
 
 PATIENT TIGHTENING THE BITE FORK CLAMP 
 
 correct. When balanced, the clamps which lock the condyle 
 rods are tightened, the rods readjusted to the natural con- 
 dyle ends by springing the bow away slightly to allow the 
 integument to assume its normal position, then returned to 
 place and held in correct relation by the operator while the 
 patient, or assistant, is instructed to tighten the central clamp, 
 thus fixing the relation of the bite fork to the face bow. The 
 operator should forcibly tighten the clamp to insure against 
 any possible change from stress while removing the occlu- 
 sion models. The condyle rods are now released and drawn 
 outward, the patient instructed to open the mouth and the 
 occlusion models and face bow are removed, using the bite 
 fork as a handle. 
 
332 CONSTRUCTIOX OF FULL DENTIFRKS 
 
 ADJUSTMENT OF THE FACE BOW, WITH OCCLUSION 
 MODELS ATTACHED, TO THE OCCLUD- 
 ING FRAME 
 
 (Dn removal of contonr models from the mouth, the con- 
 dyle rods of the face bow are pressed inward their full ex- 
 tent, and tightly clamped. 
 
 OCCLDSIOX MODELS. ATTACHED TO FACE HOW. nEMO\ED FROM MOUTH 
 
 The sheet metal base is slipped on the lower bow of the 
 occluding frame, to prevent the latter tipping backward. The 
 occlusion models are carried between the upper and lower 
 bows of frame, the ends of the face liow sprung apart, and 
 
 FACE liOW, WITH OCCHSIOX .MODELS ATTAf'HED. AD.ILSTEJ) TO OCCLUDING FRAME 
 
 the condyle rods ai'e attacliod to tlie projectin.g lugs of the 
 frame hinges. 
 
 The face bow should be made parallel with the bench on 
 which the occluding frame rests. This may be done by plac- 
 
CONSTRUCTION OP FULL DENTURES 333 
 
 ing a cork, or small block of suitable thickness, under the cen- 
 tral clamp as illustrated. 
 
 ATTACHING THE CASTS TO THE OCCLUDING FRAME 
 
 The upper bow of the frame is thrown back, the upper 
 cast is seated in its baseplate and luted with wax, if neces- 
 sary, to hold it steadily in place. The bow is now dropped 
 
 IIIUoUN BACK TO RECEIVE UrPER CAST 
 
 UI'I'EK CAST SEATED IN ITS BASEPLATE 
 
 down on the base' of the cast, to which a mix of moderately 
 thin plaster is applied. The bow should be fully enclosed in 
 plaster and the latter i!iven time to set before mounting the 
 otlier cast. 
 
 The face bow and frame are now inverted, the sheet 
 metal base removed, the lower bow thrown back, the lower 
 
CONSTRUCTION OP FULL DENTURES 
 
 UPPER I'AST ATTACIlEIl TO FRAME BOW 
 
 OCCLUDING FRAME INVERTEP BOW THROWN BACK TO RECEIVE LOWER CAST 
 
 LOWBE CAST SEATED IN ITS BASEPLATE 
 
CONSTRUCTION OF FULL UENTLHF; 
 
 CASTS MOUNTED READY FOR REMOVAL OF FACE r.OXV 
 
 CASE «1TH FACE HOW. BITE FORK AND RITE LOCKS REMOXED. BUCCAL VIEW 
 
336 CONSTRTICTIOX OF FUL[. DKNTURKS 
 
 cast iusortc'tl and lute<,l to its baseplate, aud the mandibular 
 bow dropped down upon the base of cast. 
 
 By loosening the set screws of the mandibular bow, the 
 latter may be raised or lowered in the frame sockets until it 
 lays flat upon the base of the cast. When adjusted, the set 
 screws of the bows should all be tightened so that the rela- 
 tion of casts to frame hinges may not lie disturbed by slipping 
 of the bows in subsequent steps. The lower bow and cast are 
 united with plaster, as in the preceding step, the plaster al- 
 lowed to harden and the frame righted. 
 
 The face bow is 3-emoved first, then the bite fork, and 
 finally the bite locks, after which the surplus plaster is 
 
 LABIAL "ilBW OF MOnXTEU I'ASTS AND OCCLUSION MODELS 
 
 trimmed from the casts and occluding frame bows. This lat- 
 ter step, although apparently unimportant, adds to the ap- 
 pearance of the case, and where much surplus is present, 
 enables the frame to be handled more conveniently. 
 
 REGISTERING THE CONDYLE PATHS OF PATIENT 
 
 There are two fundamental steps of vital importance in 
 the construction of anatomic and scientific dentures that can- 
 not be ignored without lessening the quality and efficiency of 
 the substitute. 
 
 The first is mounting the casts in correct horizontal plane 
 relationship to, and radial distance from, the rotation cen- 
 ters of the occluding frame. This step just described is ac- 
 
CONSTRUCTION OF FULL DENTURFS 337 
 
 complished by means of the face bow or some similar device. 
 The second consists in registering the pitch of the con- 
 dyle paths of the patient, and setting the condyle paths of 
 the occlnding frame at corresponding angles. This may be 
 accomplished by two somewhat different methods, the very 
 simple Christensen-Snow plan and appliances, and the more 
 elaborate registration suggested by Gysi by means of his 
 Condyle Begister. The first method will be described here, 
 the second subsequently in connection with the Gysi appli- 
 ances. 
 
 CHRISTENSEN'S METHOD 
 
 Dr. Carl Christeusen of Copenhagen noticed that when 
 correctly formed occlusion models were introduced in the 
 mouth and the mandible was protruded, that in all cases where 
 
 4^ 
 
 
 the condyle paths inclined downward, the occlusion models 
 separated in the molar region, while anteriorly they remained 
 in contact. 
 
 He further noticed that the amount of separation of the 
 occlusal planes in the molar region increased in direct ratio 
 to increased pitch of the condyle paths. 
 
 He then conceived the idea that by rigidly fixing the occlu- 
 sion models together while in the mouth, in the separated re- 
 lation produced by mandibular protrusion, that on returning 
 them to the occluding frame and seating each cast in its re- 
 spective baseplate, the condyle paths of the frame, which pre- 
 
CONSTRUCTION OF FULL DENTURES 
 
 viously were released, would assume the same angular in- 
 clination as those of the patient. The condyle paths of the 
 frame thus automatically adjusted were then fixed in this 
 position. 
 
 While subject to errors from various causes, in the main 
 points the idea is practical. Christensen's efforts, there- 
 fore, have contributed much to solving the problem of ana- 
 tomic occlusion. 
 
 To hold the occlusion models in their separated relation, 
 he introduced rolls of soft wax in the molar region, instructed 
 the i)atient to protrude and close, after which the occlusion 
 models were locked together with staples or bite locks. By 
 exercising care in carrying out the steps, this method is accu- 
 
 CHRISTrNSE\ 1 
 
 lllh (ONDIXE 
 
 rate, but lack of precision on the part of the prosthetist will 
 usually result in a distorted relation between the occlusion 
 models in the various steps of removal from the mouth and 
 readjustment on the occluding frame. 
 
 Dr. Geo. B. Snow devised "bite gauges" to take the 
 place of the rolls of wax, and by means of these simple appli- 
 ances the liability of error occurring is greatlv reduced. 
 
 TECHNIC OF CONDYLE REGISTRATION 
 
 The occlusion models are now removed from their casts 
 on the frame, the two bite gauges heated slightly and pressed 
 downward into the occlusal surface of the lower wax rim 
 about five-eighths of an inch in front of the distal ends. The 
 
CONSTRUCTION OF FULL DENTURES 339 
 
 metal plate of the bite gauge should rest on the occlusal plane 
 of wax. 
 
 The object in i^lacing the bite gauges forward of the dis- 
 tal ends of the baseplate is to prevent the lower occlusion 
 model from sliding forward when the patient closes. Placed 
 in the position mentioned, the pressure on closure comes be- 
 tween the two extremities of the model. Before introducing 
 
 THE SNOW BITE GAnGES 
 
 in the mouth, the patient should be shown the occlusion 
 models, his attention called to the bite gauges, and a brief 
 explanation be made of what is expected of him. 
 
 The occlusion models are now introduced and the pa- 
 tient instructed to protrude the mandible, or "bite forward" 
 until the occlusion rims touch anteriorlj', while the pyramidal 
 pointed pins of the bite gauges presenting upward enter the 
 upper and keep the occlusion models apart at their distal ex- 
 tremities, in direct proportion to the drop of the condyles in 
 
 LOWER OCCLUSION MODEL WITH BITE GAUGES IN POSITION 
 
 their paths. The occlusion models are now locked together 
 with three bite locks, one on either side and one anteriorly, and 
 when firmly fixed are removed from the mouth. 
 
 LIMIT OF PROTRUSIVE MOVEMENT OF MANDIBLE 
 
 The extreme forward limit of mandibular protrusion 
 varies greatly in different individuals, the average distance 
 being about one-fourth inch. When the protrusive movement 
 
340 CONSTRUCTION OF FULL DENTURES 
 
 exceeds this amoimt. the condyle-beariiig surfaces in some 
 eases pass beyond tlie normal working slant of the condyle 
 paths, onto the more nearly horizontal surfaces of the articu- 
 
 TEitsi'icrTivK viF.u (ii- rrrioit and i,(i\vi:ii hcch sion mouei^s. i'i.umi'ers ox the upper 
 
 MODEL. TIIESIO Alil>lTlu.NS AUK USUALLY SITUATE11 51()I!E TO THE DISTAL 
 THAN AS SHOWN IN CUT 
 
 lar eminences, and an incorrect registration will result, the 
 l)itch of the condyle paths of the frame being less than in the 
 actual working area of the natural paths. 
 
 SCHEMATIC DRAWING OF WHAT OCCUBS IN TAKING THE PROTltUSIVE BITE AND ADJUSTING 
 THE LOCKED. PROTRUDED. OCCLUSION MODELS TO THE FRAME 
 
 On the other hand, a protrusive movement of one eightli 
 inch or less, while capable of being registered, will not be 
 suflScient to properh' adjust the condyle slots of the occluding 
 
CONSTRUCTION OP FULL DENTURES 341 
 
 frame, ou account of the short distance the hinge pin will 
 travel in the slot in adjustment of the casts to their occlusion 
 models. A slight amount of lost motion also contributes to 
 further error, the hinge pins being a trifle less in diameter 
 than the width of the slots. 
 
 It may be stated definitely that the amount of protrusion 
 should range between three-sixteenths and one-fourth inch, in 
 order that a correct record may be made on the occluding 
 frame. 
 
 Some patients cannot ])rotrude the mandible directly for- 
 ward to any extent, bi;t usually are capable of moving it to 
 
 SEATED IN THEIR RESPECTIVE 
 
 either side in lateral effort. In such case the bite gauges 
 are inserted as usual, and the patient is instructed to "bite to 
 one side." The bite locks are then inserted, the occlusion 
 models removed and returned to the occluding frame. The 
 condyle slot of the frame on the protruded side is adjusted 
 and locked, the clamps on both sides of the frame being re- 
 leased while seating the casts in their baseplates. The bite 
 locks are then I'emoved, the occlusion models returned to the 
 mouth, and the patient instructed to "bite sideways" in the 
 ()p])Osite direction. The occlusion models are again locked to- 
 gether, ]'emo\ed from the mouth, returned to the frame, and 
 the other condyle slot adjusted and locked as before. 
 
342 CONSTRUCTION OK KULL UENTUKES 
 
 ADJUSTING THE CONDYLE PATHS TO THE OCCLUDING 
 FRAME 
 
 The condyle slot clamps of the occluding frame are re- 
 leased and the back spring unhooked, as a preliminary step in 
 the adjustment of the casts to the occlusion models in their 
 protruded or unilateral relation. 
 
 The lower occlusion model is now set upon its cast, the 
 upper bow of the frame is moved backward until the upper 
 cast enters its baseplate and is accurately seated. 
 
 JIAJ>JNEK OF Al'PLYING rRESSUBE TO AVOID TIPPING IN' SEATING CASTS IN PBOTRDDED 
 AND LOCKED OCCLUSION MODELS 
 
 In seating the casts in their baseplates care should be 
 taken to direct the pressure upon them in line with their cen- 
 ters, to prevent tipping. Grasping the bows of the frame near 
 the hinges will unseat the casts anteriorly and reduce the 
 pitch of the condyle slots below that recorded by the pro- 
 trusive bite, while exerting pressure on the casts anteriorly 
 will increase the pitch of the paths. 
 
 The most accurate method of adjustment is to place the 
 thumb in the center of the base of the lower cast, the middle 
 finger in the center of the upper, and exert sufficient pressure 
 to firmly seat and hold the casts in their baseplates while 
 
CONSTRUCTION OF FULL UENTUKKS 343 
 
 adjusting and clamping the condyle slots. The casts being 
 seated and held firmly in their baseplates as described, the 
 projecting end of one condyle slot plate should be grasped 
 with the thumb and index finger of the other hand, and sub- 
 jected to gentle traction imtil a position of rest is found, 
 where neither side of the condyle slot impinges on the hinge 
 pin of the frame. When correctly adjusted, the condyle slot 
 plate is clamped in that position, and similar steps carried out 
 in adjusting the opposite condyle slot. 
 
 The condyle paths of the frame being adjusted in the 
 manner described, the bite locks and gauges are removed from 
 the occlusion models and the back spring again hooked on its 
 pin, the tension of which returns the hinge pins of the frame 
 to the distal ends of the condyle slots, the same position they 
 occupied when the casts were first mounted. 
 
 The occlusion models, therefore, sustain the same rela- 
 tion to each other as before. The only change effected by 
 adjusting the occlusion models in their protruded relation to 
 the unlocked frame is in the slant of the condyle paths which, 
 if the steps have been accurately carried out, now coincide 
 with the pitch of the condyle paths of the patient. 
 
 DEVELOPING THE COMPENSATING CURVES 
 
 Wliile it is not absolutely essential to the correct arrange- 
 ment of teeth anatomically, it will be found much more con- 
 venient for the beginner when the condyles move downward, 
 to change the occlusion rims from flat to curved planes, thus 
 indicating the alignment of the teeth from before backward. 
 When properly developed, these curved planes represent a 
 plane section of a convex sphere in the upper, and of a corre- 
 sponding concave sphere in the lower occlusion model, which 
 may be moved against each other in protrusive and lateral 
 effort without loss of contact. Theoretically, the working 
 area of the condyle paths also represent sections of a convex 
 sphere which have a common center with the occhisal sphere 
 sections. 
 
 In taking the protrusive bite, the condyles traversed a 
 distance along the condyle path sphere equal to the forward 
 movement of "the mandible. Tlie incisal plane of the lower 
 occlusion model traveled a like distance along the occlusal 
 sphere incisally. 
 
 Now since the condyle spheres are fixed factors, and the 
 incisal rim need not be modified, these areas become the basis 
 
344 CONSTRUCTION OF FULL DENTURES 
 
 Tor develupiiiK the compensating curves in tlie occlusion rims, 
 or in correcting tiie flal planes of the upper and lower occlu- 
 sion models so that they will remain in contact in lateral and 
 protrusive elTort. 
 
 FUNDAMENTAL PRINCIPLES OF DEVELOPING THE 
 COMPENSATING CURVE 
 
 While the following example is not exactly applicable to 
 developing the compensating curves, it will serve to illustrate 
 the fundamental principle involved. 
 
 Tn developing a cylindrical colunm from a S(|nare piece of 
 
 timber, when for any reason it cannot be turned in a lathe, 
 the woodworker will first square the ends of the material, and 
 on each end describe a circle of the same diameter as the col- 
 umn to be developed. Around these circles he will circum- 
 scribe polygons — usually octagons — the sides of which touch 
 the circles tangentially and are parallel to each other. By 
 drawing connecting lines from the angles of the polygon on 
 one end, to the corresponding angles of the polygon on the 
 opposite end, the surplus is marked off, which, when removed, 
 reduces the square timber to polygonal form. Accurate me- 
 chanical reduction of the remaining surplus may be accom- 
 plished by again drawing polygons having twice the number 
 
CONSTRUCTION OP FULL DENTURES 345 
 
 of sides, on each end of the timber, their sides also tangential 
 to the circles, connecting their angles and reducing the sur- 
 plus in a similar manaer. The remaining surplus is then re- 
 duced by planing off tlie line angles and testing with templets 
 of proper curvature as the work proceeds. 
 
 CONVEX AND CONCAVE SPHERE OCCLnSION MODELS. DIAGRAJQIATIC 
 
 In a similar manner the sculptor blocks out his statue in 
 the rough, and the lapidist grinds otf the rough and super- 
 fluous parts of gems, after which both apply the finishing 
 touches. 
 
 A simple yet comparatively accurate plan of blocking out 
 the compensating curves in the rough is as follows : 
 
 DIAGltAM OF STEI'S IN 
 
 ■UJXIJIUCAT> FIGIKE 
 
 The slight" protrusive mandibular effort required to bring 
 the teeth in working and balancing relation seldom exceeds 
 one-eighth of an inch. This distance represents the forward 
 movement of the protruded condyle in its path, which for all 
 jjractical purposes can be considered as a straight line tan- 
 
346 CONSTRUCTION OF FULL DENTURES 
 
 gential to the condyle path sphere. The slight deviation from 
 a horizontal line of th-.' lower occlusion model in the incisor 
 region in its protruded position is scarcely perceptible, there 
 being only one two hundred and fifty-sixth of an inch of sep- 
 aration, one-eighth of an inch from the labial surface of the 
 wax when the drop of the condyle in its path is one-eighth 
 of an inch. 
 
 The flat plane of occlusion in the incisor region may 
 therefore be considered as another line or plane, tangent to 
 the compensating curve. 
 
 Since the only object in developing the compensating 
 curve, aside from esthetics, is to secure balancing contact, 
 and since balancing contact is developed between the upper 
 and lower second molars, it follows that if a tangent can be 
 correctly located in the area to be occupied by the second 
 molars, the plane thus developed will serve as a guide in set- 
 ting the occlusal surfaces of these teeth. 
 
 The average distance from the condyle centers to the 
 mesio-incisal angles of the lower incisor teeth is four inches 
 in a straight line. The second molars are situated practically 
 half-way between these two points, but being below a straight 
 line, drawn between the points mentioned, they are usually 
 about two and one-fourth inches from the second molar 
 position. 
 
 The problem then mav be stated as follows : Given two 
 tangents of arcs developed from a common center from which 
 to develop a third tangent between the two, having a similar 
 angular inclination to each, or an angular mean between the 
 two. This is an extremely simple ]3roblem to solve on a sheet 
 of paper, and is accomplished as follows: 
 
 Project the two gixen tangents until they intersect. From 
 the point of intersection lav off a point on each tangent equi- 
 distant from the point of intersection and connect the points 
 so located with a strai2;ht line. If for anv reason the two tan- 
 gents cannot be extended to intersect, lines drawn parallel 
 to them, which will intersect, may be developed, and the line 
 of direction of the third tangent can easily be determined by 
 these construction lines. 
 
 Now the difficulty met with in developing the third tan- 
 gent on occlusion models is that the condyle path tangent if 
 projected may strike the occlusion tangent too far forward in 
 case of slight, or not at all in case of steep, pitch of the former. 
 Neither is there a flat surface on which to make the meas- 
 urements required. Yet with these difficulties encountered, a 
 
CONSTRUCTION OK FULL DENTURES 347 
 
 knowledge of a few fundamental facts will enable the pros- 
 thetist to develop the third tangent in a very short time. 
 
 The first fundamental fact to keep in mind is that under 
 any and all conditions the occlusal plane, whether flat or 
 curved, should be so located as to divide the space as equally 
 as possible between the crests of the two borders, in order 
 that there may be room for placing the teeth in each arch. 
 
 The second relates to how this space may be ap- 
 proximately divided evenly. Since the flat occlusal rims 
 have previously been formed in most cases so as to divide 
 the space between the borders equally, it follows that if the 
 flat plane is to be changed to a curved plane, the change must 
 
 LOCATING POINT A 
 
 be effected by modifying both occlusion rims, paring off the 
 upper and adding to tlje lower at the distal terminal, and re- 
 ducing the lower and adding to the upper in the bicuspid 
 region. 
 
 The third point is that the condyle path and the occlusal 
 plane represent short tangents of a common arc, or concentric 
 arcs having a common center, and therefore since they are 
 tangents of common or parallel arcs, the position of the third 
 tangent may be determined bj' developing one or more lines 
 parallel to the"m to find the angle of intersection. 
 
 The direction of the third tangent, or, as it may be called, 
 the second molar tangent, may be determined in several ways, 
 the simplest being to jiroject the occlusal plane backward be- 
 yond the point of intersection with the condyle path plane, and 
 
IMS CONSTIUICTION OF FULL DFNTIIRIia 
 
 liiscrt the included angle, (lie hisoctioii lino nivini;,- the direc- 
 tion of tile tliird tangent, hut tiie liiu; when developed may he 
 too far forward or back of llu' required positioiL 
 
 Again the line of direction of the second molar 
 tangent may bo determined by laying off equidistant points 
 from the point of intersection on both condyle path and 
 occlusal plane tangent, and connecting the two points, as 
 stated previously. This method places the position of the 
 second molar tangent above and at times too far forward or 
 back of the required position. 
 
 MAliKINXi LINE I!-C CONTINUOUS WITH OR P.iltALLKL TO TIIE CONDYLE PATH 
 
 The objections mentioned, together with the fact that 
 the point of intersection is often back of the distal ends of 
 the occlusion models, and therefore in space, frequently ren- 
 der both of these methods impracticable. 
 
 By the use of one or, in some cases, two parallel lines, 
 these objections are overcome and the second molar tangent 
 can be laid in its proper position without difificulty. The plan 
 is as follows: 
 
 PRACTICAL STEPS 
 
 Locate on the upper occlusion model at its distal termina- 
 tion point a, through which the compensating cnrve miist 
 and should pass. This point should be about one-sixteenth of 
 an inch above the flat occlusal plane since the latter, when 
 
CONSTRUCTION OF FULL DENTUKFS 34'J 
 
 changetl l<i a curved piano, must be so developed as to 
 divide the space between the upper and lower border crests 
 equally, or as nearly so as is possible with a cui'ved plane. 
 
 WI.IPERIXG 
 
 INDYT.K I.IN'E 
 
 LAYING OFF DISTAXCE A-F ON SUB-OOCLUSAL LINE 
 
 This is necessary, as before stated, in order that space may be 
 preserved for reception of the lower teeth. When the compen- 
 sating curve is developed so that its distal termination coin- 
 
:i60 CONSTRUCTION OK FULJ- DENTUKES 
 
 cides with the flat plane of occlusion, its curvature is devel- 
 oped at the expense of the lower occlusion model entirely. 
 
 Through point A draw line B, C, continuous or parallel 
 with the condyle paih, extending it diagonally across the 
 lower occlusion rim. With a pair of dividers scribe line 
 D, E, on the buccal surface of lower occlusion model, and 
 about one-fourth inch below the flat occlusal plane. This 
 subocclusal line intersects the projected condyle path line 
 at F. 
 
 Place one leg of a divider on F, the other on A, with this 
 as distance set off, F, G, on D, E. Draw line A, G, which rep- 
 resents a short tangent of an arc developed from the same cen- 
 
 CONNEOTING A-G. 
 
 ter as the comijensating curve and condyle path. At a point 
 one-fourth inch in front of the distal terminal of line A, G, 
 project a symmetrical, curved line forward, terminating it just 
 in front of the cuspid eminence. 
 
 The distal one-fourth inch of line A, G, represents the 
 second molar tangent, both in position and line of direction, 
 and is not changed in this blocking out of the compensating 
 curve. Later it may or may not be slightly modified in the 
 final correction of the curved occlusal plane. 
 
 With a condj'le path pitch of 35 degs., the compensating 
 curve will cut into the upper wax rim about one-sixteenth of 
 an inch, as stated, and in the lower occlusion model about the 
 same amount. When the condyle pitch is greater than the 
 
CONSTRUCTION OP FULL DENTURES 351 
 
 average, the curvature should be increased, and when less, 
 decreased proportionately. 
 
 With the exception of the second molar areas, the curved 
 line is developed with the eye. With a little experience a 
 
 COMPLETED DIAGRAM SHOWING ALL LINES EXCEI'T THE Cl.ll\E FROM SEC- 
 OND MOLAB FOKWABD TO MESLAl, OP CUSPID 
 
 just estimate of the correct curvature can be almost instantly 
 determined. 
 
 A thin, hot blade spatula is used to divide the wax along 
 line marked, from distal to cuspid terminals. That separated 
 
i!52 CONSTRUCTION' OP FULL DENTURES 
 
 from each occlusion model by the blade is transferred to the 
 opposite occlusal surface, and there attached with a hot 
 spatula. 
 
 Test the accuracy of the balancing area of the blocked- 
 out compensating curve by subjecting the occluding frame 
 to protrusive and lateral movements. 
 
 By warming the occlusal surfaces of the rims, and rub- 
 ing talcum power on them to ])revent adhesion when brought 
 
 COMPENSATING CURVE DE\ELOPED. Bl . 
 
 together, corrections can readily be made by subjecting them 
 to slight pressure in lateral movements of the occluding frame. 
 
 THE ULSAVER METHOD 
 
 Dr. E. S. Ulsaver suggests attaching a softened mass of 
 wax on the distal end of the lower occlusion rim, throwing 
 the frame forward on that side to a distance of an eighth of 
 an inch or jDossibly a little more, and closing the frame in this 
 protruded lateral position. 
 
 Separate the occlusion models and trim off the excess wax, 
 buccally and lingaiallj". On closing the frame, it will be seen 
 that the occlusion rims are prevented from striking by the wax 
 addition, which presents the form of an inclined plane, the 
 distal end being- the thickest. 
 
CONSTRUCTIOX OF FULL DENTUKKS ■So?. 
 
 The upper wax vim is now triimiied to accommodate itself 
 to the form of the built up, distal end of the lower rim. This 
 is doue by paring away with a knife, a little at a time, nntil 
 the two rims again occlude. 
 
 With this incline as a basis, which is really the beginning 
 of the compensating curve, it is a comparatvely simple matter 
 to develop symmetrical curves on both rims. The opposite 
 side is developed in a similar manner. The addition of talcum 
 powder to the rims iirevents the softened wax from sticking 
 in lateral and jirotrnsive movements. 
 
 L-I.l.SlclN .M( 
 
 in Air 111.. LABIAL 
 
 The only serious drawback to this otherwise excellent 
 method of developing the compensating curve is that the curve 
 is usually formed entirely at the ex])euse of the uiqier rim. 
 
 OMITTING DEVELOPMENT OF COMPENSATING CURVE 
 
 It is a fact that the teetli c;in be arranged to occlude, 
 and balance as well, without previously developing the com- 
 pensating curve on the occlusion models. To do so, however, 
 departure from the tint occlusal plane must be made, either in 
 the initial arrangement of the teeth or subsequently. This 
 change involves the development of a similar curvature of 
 the general occlusal sui'faces of the teeth to that developed in 
 the wax rims, as detailed. Comparison of the merits of the 
 two methods is largely in favor of preliminary development of 
 
354 CONSTRUCTION OP FULL DENTURES 
 
 the compensating curve in the occlusion models, both from the 
 standpoint of accuracy of result, and saving of time as well. 
 
 A method of developing balancing contact and which does 
 not require the changing of the flat occlusion rim to curved 
 planes has been suggested by Dr. G. H. Wilson. 
 
 This consists in stepping the upper second molar slightly 
 above the first and raising the lower second molar correspond- 
 ingly. In lateral movements, the mesial margin of the lower 
 second molar engages with the distal margin of the upper 
 first molar and in this manner balancing contact is secured. 
 In reality, this method of arrangement is a curve of steps. 
 
CHAPTER XIX 
 THE ESTHETICS OF TOOTH SELECTION 
 
 GENERAL CONSIDERATION 
 
 One of the most difficult problems of esthetics in pros- 
 thetic dentistry relates to the selection of teeth of such size, 
 form and color as will harmonize with the features of edentu- 
 lous patients. 
 
 Could the human race be classitied into a few, or even 
 many groupS; the face forms of the individual members of 
 each group being alike, or so closelj* similar that when the 
 peculiarities of one were known all of the other members of 
 that group would immediately be recognized, the problem 
 would be simple. As a matter of fact, the faces of no two 
 individuals in all probability were ever exactly alike in con- 
 tour, proportion, disposition of lines or color effects of the 
 complexion ; hence the difficulty of establishing an accurate 
 classification. 
 
 Numerous attempts have been made since Hippocrates' 
 time, 2,400 years ago, to classify the human race into groups 
 according to dominant characteristics. Practically all of these 
 classifications were based upon the form, color and activity of 
 the individuals. 
 
 In the older classifications, the cause of the differences 
 noted in various individuals was attributed to the influence of 
 four fluids, or humours, of the system, viz., the blood, phlegm, 
 yellow and black bile. These several fluids, it was supjDosed, 
 tempered or influenced both the form and habits of the indi- 
 vidual, according to their relative predominance and potencies. 
 
 The older classification of temperaments was given as 
 follows : 
 
 Sanguine (full blooded). 
 
 Phlegmatic (excess of watery fluids supposed to be elab- 
 orated in the brain). 
 
 Choleric (excess of yellow bile from the liver). 
 
 Melancholic -or atrabilious (black bile supposed to come 
 from the spleen). 
 
 Within the last century, when physiological functions be- 
 came better known, the fallacy of this ancient temperamental 
 basis was disclosed, and various writers on this subject have 
 
:!5(; TIIIO h:STllKTlCS OF TOOTH SIOLKCTION 
 
 at (lilTcrciit tinu's suggested nioditieatious. Auiuiig those most 
 promineiitl.y identified in tliis field may be mentioned Gregory, 
 Jacqiie, Laycock, Hutchinson and Spnrzheim. A classifica- 
 tion suggested by the latter is the best known of any at the 
 present time, and is here i^resented with an abbreviated table 
 in which the fundamental points of interest to the prosthetist 
 are outlined : 
 
 Sanguine (dominance ol' circuhitoiy system). 
 
 Nervous (preponderance of nervous element). 
 
 Bilious (excess of bile in system). 
 
 Lymphatic (superabundance of lym])h). 
 
 CLASSIFICATION OF TEMPERAMENTS 
 
 
 
 
 Teeth 
 
 merits 
 
 
 
 Color 
 
 Shape 
 
 Lymphatic 
 
 Pale blue or 
 gray 
 
 Fine and silky, 
 
 but without 
 
 luster 
 
 Pallid, opaque 
 or muddy yellov 
 
 Poorly shaped, 
 broad and flat 
 
 Sanguine 
 
 Blue, brilliant 
 and expressive 
 
 Blond-red or 
 chestnut, seldom 
 dark or black 
 
 Cream-yellow, 
 darker at neck 
 
 Well propor- 
 tioned, curved 
 and rounded 
 
 Nervous 
 
 Light gray or 
 
 blue, restless, 
 
 often morbidly 
 
 Ibrilliant 
 
 Fine, light and 
 soft 
 
 Peail-gray, or 
 blue tinge 
 
 iMng, conical 
 and rounded 
 
 Bilious 
 
 Blacli or brown.J Coarse, dark, 
 small and often black, 
 piercing and abundant 
 
 Strong, bronze 
 lyellow 
 
 Conical, long 
 and angular 
 
 That tile classification of temperaments just outlined, as 
 a basis for the selection of teeth, is not without glaring de- 
 fects, and very imperfect, cannot be denied; yet until quite 
 recently, although much has been written, lint little advance- 
 ment has l)een made in this field. 
 
 Dr. Hutchinson, as quoted by Dr. Ivy, says: "Are we 
 not obliged to confess that we have but little to guide us in 
 a classification excepting the conditions which ,go to make up 
 what we mean liy complexion? In complexion we include the 
 color of the hair and eyes, the state of the skin as regards 
 thickness, thinness or transparency, and the various degrees 
 of freedom of distribution of blood in the capillaries of the 
 face. It is easy to apply with tolerable accuracy such words 
 as blond, fair, dark, brunette, sallow, pale, florid, clear, muddy, 
 and the like, and these and many others are epithets aijpli- 
 cable to the complexion. Temjierament, however, although to 
 a large extent indicated by complexion, is generally held to 
 include sometliing more. If it did not, I fear we should find 
 it but a sorry basis upon which to build a knowledge of the 
 
THE ESTHETICS OF TOOTH SELECTION :J57 
 
 vital peculiarities of the individual. Yet again I ask what 
 have we to which we can make appeal! We may examine a 
 man's features, note the size of his bones, the shape of his 
 jaws, the brilliancy of his eyes, the coarseness or fineness of 
 his hair, his stature, his muscularity, his abundance or other- 
 wise of cellular tissue and fat; ln;t in observing all these 
 things we shall be reminded that some of them are simply 
 
 LyinpAatic 
 
 DIAOBAMMATIC 
 
 peculiarities of family or of race, and have little or nothing 
 to do with healtli, while others are conditions which may 
 vary much at different periods during the same life." (Amer- 
 ican System of Dentistry, p. 1031.) 
 
 Because of tlie comparatively rare occurrence of true 
 basal types of temperament as given, and the innumerable 
 variations from these types observed, the Spurzheim table 
 is extremely limited in its scope. That it has served a useful 
 purpose in a general way cannot be denied ; first, in suggest- 
 
358 THE ESTHETICS OF TOOTH SELECTION 
 
 ing the possibility of form and color harmony of teeth with 
 the individual, although lacking in adequate data for ac- 
 complishing the desired results; and, second, by keeping be- 
 fore the eyes of the dental profession the need of a better 
 and more scientific method for the selection of teeth. 
 
 With the recognized imperfections of the temperamental 
 table and the daily growing demands on the prosthetist in 
 the esthetic field, some solution of this most intricate problem 
 of tooth selection is not only desirable, but imperative. The 
 basis of the solution lies apparently in a proper application of 
 the laws of harmony of form and color, regardless of the age, 
 nationality, race or temporary physical condition of the in- 
 dividual. 
 
 HARMONY DEFINED 
 
 Harmony is defined as: "Completeness and perfection 
 resulting from diversity in unity; agreement in relation; or- 
 der; in art, a normal state of completeness and order in the 
 relation of things to each other; an essential in form as an 
 element of beauty; as the harmonies of nature; the harmony 
 of a plan well thought out; the harmony of a ship's lines." 
 (Standard Dictionary.) "Any arrangement or combination 
 of related parts or elements that is consistent or esthetically 
 pleasing; agreement of particulars according to some stand- 
 ard of consistency or the esthetic judgment." (Century Dic- 
 tionary.) 
 
 ESTHETICS DEFINED 
 
 Esthetics is defined as "The philosophy of the beautiful." 
 (Standard Dictionary.) "Esthetics, the science which de- 
 duces from nature and taste the rules and principles of art; 
 the theory of the fine arts ; the science of the beautiful, or that 
 branch of philosophy which deals with its principles ; the doc- 
 trine of taste." (Century Dictionary.) 
 
 INTUITIVE AND ACQUIRED ESTHETICS 
 
 We look upon certain recurring things in the material 
 world as right and natural, because we are accustomed to them 
 and because they are associated together. When one thing 
 is mentioned, other things which usually occur with it 
 are brought to mind. When mountains are spoken of, or 
 seen in the distance, wo immediately think of a range of them 
 varying in elevation, more or less covered with foi'ests, the 
 
THE ESTHETICS OF TOOTH SELECTION 359 
 
 home of flowers and birds and beasts, and through which 
 streams flow. 
 
 When a particular color is seen, as, for instance, green, 
 an artist will think of that color, its components, yellow and 
 blue, and its complementary color red. 
 
 Wlaen an architect, or one familiar with architecture, 
 sees a structure, say, of the Grecian Doric order, even at a 
 distance, he immediately recognizes it as such, and recalls to 
 mind its massive, well-proportioned columns, its plain sub- 
 stantial capitals, its undecorated architrave, the decorated 
 frieze, the cornice, the triangular ends of the structure — usu- 
 ally sculptured — called the pediment, bounded above by the 
 sloping cornice of the roof, and below by the horizontal cor- 
 nice of the entablature. Structures of this type, as the Parthe- 
 non at Athens before its partial destruction, are conceded to 
 be the most pleasing and perfect from an esthetic standpoint, 
 of anv that the hand of man has ever produced. 
 
 The production of such structures was rendered possible 
 only by the gradual a'rowth and development of the artistic 
 sense and esthetic judgment, beginning with the dawn of civ- 
 ilization — a growth in development of the sense of propor- 
 tions, harmonv and fitness of things. To combine in such a 
 structure as the Parthenon some of the more radical elements 
 of the BA'zantine or other dissimilar styles of architecture, 
 would detract from its dignity and grandeur, and shock the 
 esthetic sense of all beholders. 
 
 In these and innumerable other examples, the esthetic 
 judgment is a law unto itself. It cannot be formulated by rule, 
 but is dependent upon and has its origin in man's innate sense 
 of the fitness of things. This sense of harmony, although 
 totallv dormant in some and a natural gift in others, is capable 
 of cultivation, and in no profession or calling is there more 
 need for its enhancement than among the members of our 
 profession. The prosthetist must be able, not only to keenly 
 appreciate beautiful things and recognize them when har- 
 moniously arranged, but he must be able to execute them as 
 well. 
 
 These examples, although apparently abstract, have a 
 direct bearing on the subject under discussion — the selection 
 of teeth of appropriate size, form and color for each edentu- 
 lous patient who presents. Since, as is generally conceded, 
 the temperamental table affords only the most meager assist- 
 ance in this regard, some other means must be employed. 
 
360 THK KSTHKTICS OF TOOTH SELECTION 
 
 BASIS FOR TOOTH SELECTION 
 
 The basis of tootli sck'ctioii, as previously states 1, consists 
 in judging wliat size, form and color of teeth will hannonize 
 with the facial lineaments and color scheme of the individual. 
 Just as in architecture, the openings of a building, the lines 
 of its doors and windows must harmonize with the more mass- 
 ive lines of structure, so must the teeth, in their size and out- 
 line form, harmonize with tlie more massive lines of the face. 
 
 Again, in the decoration of a building, the color schemes 
 employed must harmonize. Violent contrasts are oppressive 
 and should be avoided, while lack of contrasts, or absence of 
 complementary colors, i)roduces a sense of dull monotony. • 
 
 In the selection of teeth, the first two factors, size and 
 form, are determined by the sense of proportion, the third 
 by color judgment. 
 
 The teeth occupy a comparatively central position in the 
 face, and since observation clearly shows that there is a gen- 
 eral similarity in form between face outline and tooth outline 
 in the same individual, a study of facial outlines is essential 
 as a basis in tooth selection. 
 
 FACIAL OUTLINES 
 
 In Dr. Wilson's ''Dental Prosthetics" is an illustration 
 reproduced from a work published 100 years ago on the "Sci- 
 ence of Beauty" by an English writer, Mme. Schimmelpen- 
 nick, and which, by his permission, has been here introduced. 
 The outlines of faces here shown are, of course, diagrammatic, 
 and conform too rigidly to geometrical forms ; yet they em- 
 brace practically all of the types of faces one sees nowadays, 
 with perhaps the exception of the ovoid, and even that is a 
 combination of the square with the round. Other combina- 
 tions are, of course, possible, as the tapering with the roimd, 
 or square or rectangular. 
 
 Naturally a tapering face indicates a tapering tooth. 
 Since the outlines of such a face converge from forehead to 
 chin and the taper of the tooth, when in position, is reversed, 
 harmonious results will be secured if color and size are 
 right. 
 
 An oval face calls for an o\al tooth — one with sides 
 slightly convex and angles rounded. 
 
 A square, or rectangular face, recjuires a tooth with 
 nearly parallel sides, and with moderately well-defined angles, 
 
THE ESTHETICS OF TOOTH SELECTION 361 
 
 sometimes sharply angular, as in cases where the incisal edges 
 are reduced to stimulate wear. 
 
 The width of a tooth should liear a similar relation to its 
 length as the correspoiidiiiii' dimensions of the face bear to 
 each other. 
 
 The prolilem of harmony in form and shade of teeth, with 
 the individual, is of vital interest to both yiatient and pros- 
 
 tanc/i 
 
 REPRODUCTION OK MADAME SCnrMMELPEXMC'K'S ■KAe^IAT. FORMS'- 
 
 thetist. To the patient, because the denture is a pari of him- 
 self, to be worn iir public and private life. To the prosthetist, 
 if inharmonious, the denture, like Banquo's Grliost, which 
 would not down, rises up at most inopportune times to remind 
 him of his deficient technic and lack of esthetic judgment. It 
 is furthermore, liguratively speaking, a standing monument, 
 
362 THE ESTHETICS OF TOOTH SELECTION 
 
 before the world at all times, of inartistic and misapplied den- 
 tal effort. 
 
 Since human faces vary in outline, form, contour and 
 general proportion, and since there are no fixed measurements 
 available, to indicate with precision the exact length and width 
 of teeth to select for edentulous cases, the necessity for culti- 
 vating the sense of proportion — esthetic judgment — -becomes 
 plainly apparent. 
 
 Every practitioner and student should interest himself 
 in the collateral studies of clay modeling, free hand drawing 
 and coloring, to acquire a rudimentary knowledge, at least, 
 
 
 TIIK TIIHEi: TVI'Al, F(II[.\IS (IF TKK'I II (DR. J. LEON \VIU.IAMS) 
 
 to serve as a working basis in this most esthetic branch of 
 dental science — prosthetic dentistr_v. 
 
 NATURAL TOOTH FORMS 
 
 Within recent years Dr. J. Leon Williams in his studies 
 of natural forms has shown quite conclusively that although 
 there are many variations in form and proportion in the teeth 
 of different individuals of many races, there are but three dis- 
 tinct typal forms. 
 
 While variation from these three types are of frequent 
 occurrence, such variations show certain characteristics com- 
 mon to the more distinctly marked t^^^es. Dr. Williams has 
 classified these three most persistent typal forms, together 
 with certain variations, as follows : 
 
THE ESTHETICS OF TOOTH SELECTION 363 
 
 r Mesial and distal sides straight and par- 
 Class or Type I.J allel for one-half or more of the length of 
 Square Type] crown from incisal edge toward the 
 I cervix. 
 
 CLASS I, FOKM 1. SEl'EREST MODIFICATION" OF THE SQUAKE TYPE 
 
 CLASS I, FOKM 4, SOFTEST MODIFICATION OF THE SQUARE TYPE 
 
 niooc, T TT r Mesial and distal surfaces comparatively 
 
 i^iass 01 J-Vpe ii. ^ • i ^ t i j • ; i 
 
 Taperino- Type. I '^^^'^^S'"* 'i"«"^' but converging toward 
 
 '^ \ each other from incisal edge cervicallv. 
 
 TRUBYTE FORM I CLASS n 
 SIZES AS MOULDS I L-IM - I N- IP- I R 
 
 ff?f!t 
 
 CLASS II, FOBM I. SE\ EKEST MODIFICATION OF THE TAPEBING TYPE 
 
THE li^STHIOTlCS OF TOOTH SKLhX'TlON 
 
 CI-ASS II. FOKM 4, SOFTEST MODIFICATION OF THE TAPERINt! TVI'E 
 
 Class or Tj'pe -III. 
 Ovoid Type 
 
 Mesial surface slightly convex, distal 
 surface a compound curve, convex in- 
 cisally, changing to concave as it passes 
 toward the cervix. 
 
 CLASS III, FORM 1. SEXHIilC Monil-ICATION OF THE OVOID T'iTE 
 
 CLASS III, F0R5I 4, SOFTEST .MODIFICATION OF THE OVOID TYPE 
 
 REPRODUCTION OF NATURAL TOOTH FORMS IN 
 PORCELAIN 
 
 Using Dr. Williams' data as a basis, the Dentists' Supply 
 Co. have reproduced in porcelain, from models carved by Dr. 
 Williams himself, the three typal forms of teeth enumerated, 
 in varying sizes, together witli a sufficient number of modified 
 types to meet average prosthetic requirements. 
 
 Class 1 contains five, Class II, four, and CUass III, four 
 modifications of form. Since each class and each modification 
 
THE ESTHETICS OF TOOTH SELECTION 365 
 
 is produced in several graded sizes, a large variety of sizes 
 are thus available for use. 
 
 Dr. Williams ' efforts have been devoted to the production 
 of typal forms and modifications of the anterior teeth, and 
 in this field he has arrived at most commendable and esthetic 
 results. 
 
 Dr. Gysi, whose distiuguislied work in the field of anatomic 
 occlusion is most widely and favora])ly known, has collaborated 
 with Dr. Williams in the designing of full sets of typal forms 
 
 of teeth in porcelain. The patterns for the bicuspids and 
 molars were furnished by Dr. Gysi. The upper and lower 
 teeth of these classes are so proportioned in their mesio-distal 
 diameters and their occlusal surfaces so formed that close- 
 locking occlusion can be secured with comparative ease. 
 
 Clearance paths for the cusps of the lower between those 
 of the upper teeth can be developed with Irat little, and in some 
 cases no change of form, thus leaving the occlusal surfaces, 
 which are strongly ridged and grooved, undistui-bed for the 
 more effective reduction of food. 
 
366 THE ESTHETICS OF TOOTH SELECTION 
 
 OBSERVED OUTLINES OF NATURAL TEETH IN 
 THE MOUTH 
 
 The fact should be borne in mind that in the living, hu- 
 man subject the typal forms of teeth, as illustrated, do not 
 show as distinctly as in extracted teeth, or in skull dentures, 
 from around the teeth of wliich the i>um tissues have been 
 
 removed, because these tissues, particularly in early life, 
 often cover some of the characteristic or determining class 
 lines. Later on, or when gingival absorption at any time oc- 
 curs, the class to which tlie teeth belong becomes apparent. 
 
 To know the typal forms of natural teeth is of vital im- 
 portance, and time spent in analyzing these forms and varia- 
 tions will be well expended. Such knowledge will enable the 
 prosthetist to produce esthetic effects not otherwise possible. 
 
 In the literature which the Dentists' Supply Co. furnish, 
 descriptive of these typal forms of teeth, are also illustra- 
 
 OCCLUSAL VIEW OF MOLAR Sl^RFACE MARKINGS 
 
 tions showing not only mold forms of the teeth themselves, 
 but of types of faces for which each mold is appropriate. 
 
 While a few of the illustrations referred to are here in- 
 troduced, a perusal of the literature and a study of the entire 
 series will prove most beneficial to the prosthetist in the selec- 
 tion of teeth of suitable forms for individual cases. 
 
THE ESTHETICS OF TOOTH SELECTION 367 
 
 The accompanying half-tones of noted statues in the 
 various galleries and museums of Europe and the United 
 States, illustrates quite plainly the types of faces to which 
 Madame Sehimmelpeunick called attention a century ago. 
 
 "Admiral Farragut," "Saphira," and "Vulcan" repre- 
 sent the square tj'pe and would require the parallel-sided tooth 
 of Class I. 
 
 ■ADMIRAL FAKEAGUT' 
 
THK KSTHKTICS OF TOOTH SELECTION 
 
THE ESTHETICS OF TOOTH SELECTION 309 
 
 "Cicero," the "\'estal \'iri;iii," and the statue of "A 
 Youug Woman" i-e]iv('sent the tapering face and would re- 
 quite taperina' teeth wcic ih'iitures to be supplied tlieni. Class 
 II. 
 
THE ESTHETICS OF TOOTH SELECTION 
 
 ■A MCSTAI. YIRi;lN" 
 
 ■•STATUE OF A YOUNG WOMAN" 
 
THE ESTHETICS OF TOOTH SELECTION 371 
 
 "Juno," "Aphrodite," and "David" represent the oval 
 type and would require the ovoid tooth of Class III. 
 
 ■APHRODITE" 
 
a72 THK ESTH1<]T1CS OK TOUTll SELECTION 
 
 "Nero" represents a circle, \cr\ iieai-ly, and cdnid he su| 
 plied with a sliort, wide tcmtli el' Class III. 
 
 The head of "A liNunan ijad\ 
 though liarmonious facial line. 
 
 shows a severely straight 
 
 •A HOMAN LATiy 
 
THE ESTHETICS OF TOOTH SELECTION 373 
 
 THE COLOR PROBLEM IN TOOTH SELECTION 
 
 The problem of selection of artificial teeth that will har- 
 monize with the general color scheme of the individual's com- 
 plexion is a vital factor in the production of dentures of 
 esthetic value. 
 
 That this subject is given too little consideration is appa- 
 rent from observing the prosthetic restorations seen in the 
 mouths of persons in all conditions of life. Many of these sub- 
 stitutes are out of harmony in color. The reason for this can 
 only be found in the prosthetist's lack of knowledge of color 
 principles. 
 
 The most logical means of avoiding such inharmoin- in 
 this line as is daily apparent is by a study of the rules of 
 harmony relating to colors, their complements and con- 
 tracts. 
 
 In Vander]>oel's "Color Problems," we find the follow- 
 ing: 
 
 "The relation of color to light is much the same as that 
 of music to sound. Color has its many hues, its long scales of 
 tints and shades, its true and false chords. Mere sound gives 
 us but little pleasure; when developed, however, into its high- 
 est form, music, we are thrilled, as by the song of a bird, a 
 favorite ballad, or a Beethoven symphony. So in light, our 
 enjoyment culminates at the glories of color in a flower or a 
 sunset, at the shadows that play over the hills, or at the varied 
 hues of a salt marsh. Hence, we may aptly term color the 
 music of light; and when we think of the wonderful ways in 
 which it has been used and combined liy painters and design- 
 ers for hundreds of years, it must seem strange to us that its 
 harmonies have not been as tlioroughly studied and classified 
 as those of sound." 
 
 It must not be inferred, however, from the above quota- 
 tion that a classified system of color science, capable of being 
 utilized by anyone who so desires, is not available. As a mat- 
 ter of fact, many valuable scientific works have been written, 
 some in the simplest language possible, in which the funda- 
 mental i)rinci]3les of color harmony are fully explained. 
 
 That these works have not been extensively recognized 
 and more generally utilized in the past, particularly in spe- 
 cialized lines, as in prosthetic esthetics, is largely due to pre- 
 vailing educational methods. 
 
 A brief outline of some of the principles of color har- 
 mony will now be given in the hope that it may not only be 
 
374 THE ESTHETICS OF TOOTH SELECTION 
 
 beneficial in a practical way, but prove an incentive to further 
 study in this most interesting field. 
 
 A SYNOPSIS OF COLOR PRINCIPLES 
 
 DEFINITIONS 
 
 "Color is the immaterial result of the decomposition of light. 
 A ray of light in passing through a triangular prism is 
 decomposed into a series of colors the same as a rain- 
 how. 
 
 " Paivt or Piginent is the material hasis which decomposes 
 light so as to reflect only some of its constituent colors. 
 
 "Shade refers to the chromatic composition of a color. Cobalt 
 and cerulium offer us different shades of hlue. 
 
 "Tint is the condition of a shade of color which arises from 
 its admixture with water or white. It becomes, thereby, 
 more or less intense without any change in its chromatic 
 composition. 
 
 "Tone is the condition of a color in which it appears other 
 than it is. A light blue under the effect of a bright or 
 dull light will appear a light blue, yet, in the representa- 
 tion of these different conditions, different shades must 
 be used; different tints would fail to convey a just idea 
 of the color. 
 
 "Harmony is the effect of a proper arrangement of colors in 
 a picture. 
 
 "Contrast is the etfect arising from different colors being 
 adjacent to one another, as red beside blue or yellow, etc." 
 — (Bacon). 
 
 COLOR 
 
 The i^rincipal source of terrestial light is the sun. Under 
 ordinary conditions, light emanating from this source is white, 
 or colorless. 
 
 By a process called dispersion, sunlight, as well as that de- 
 rived from artificial sources, can be resolved into a series of 
 different colors, known as spectrum colors. 
 
 Dispersion of light is accomplished by directing a ray of 
 sun or artificial light through a shutter, into a darkened room, 
 passing it through a horizontally-fixed prism, or over a dif- 
 fraction grating, and allowing it to fall upon a white screen. 
 
 By fixing the prism in such position that the light enters 
 it at a slant, the beam will be bent twice in its course, first on 
 entering, and second, on leaving the crystal. As a result, in- 
 
THE ESTHETICS OP TOOTH SELECTION 375 
 
 stead of showing as a spot on the screen it sliows as a perpen- 
 dicular band, or line, presenting a series of juxtaposed colors. 
 
 This indicates that certain colors, of wliieh white light is 
 composed, have different refractive indices, that is, the rays 
 of one color will be bent at a different angle from those of 
 another. 
 
 The colors and their order from above downward, as they 
 appear on the screen, are as follows: 
 
 Purple. 
 
 *Blue. 
 
 Green. 
 
 *Yellow. 
 
 Orange. 
 
 *Eed. 
 
 Purple. 
 
 Formerly the top color was rated as two colors, violet 
 and indigo, but in 1890 the discovery was made that indigo 
 was composed solely of blue and black, and as black is not a 
 component of sunlight, indigo is not a possible prismatic color. 
 
 Each pair of juxtaposed colors blend almost imiier- 
 ceptibly into each other so as to present different shades and 
 varying tints, just as they appear in the rainbow, yet tlie 
 center of each color is clear, distinct and unmixed. 
 
 A distinction must be made between white light, which is 
 immaterial or intangible, including the colors resulting from 
 its dispersion, and pigment colors, which are composed of 
 material substances. 
 
 Since we cannot distinguish the color of an object in the 
 dark it naturally follows that either sun or artificial light must 
 fall upon it to disclose its tint. 
 
 The reason why one object appears one color and another 
 object a different color in the same light and under similar 
 conditions is due to some inherent quality of the substances 
 themselves for absorbing certain spectral colors and reflecting 
 others. 
 
 For example, a red substance absorbs all the other colors 
 of the spectrum but red which is reflected. A green substance 
 absorbs all the spectrum colors but blue and yellow, which, 
 when mixed, produce green. 
 
 PRIMARY COLORS (PIGMENTS) 
 
 A primary color is one which cannot be formed by combin- 
 ing other colors. Blue, yellow and red are considered as 
 
:i7(i THE lOSTHlOTICS OK TOOTH SIOLKCTION 
 
 primaries, in lioili prismatic and pigment colors. From these, 
 b}' their admixture in proper proportions, practically all other 
 colors except white and black can be produced, and a very 
 close api)roximati()n to these are i»ossible. 
 
 SECONDARY COLORS 
 
 A secondary color is mailc by coinldiiing two primary 
 colors in ecpial parts. There are three secondary colors : 
 Green, orange and purple, wJiich are formed as follows: 
 
 Grreen — from blue and yellow. 
 
 Orange — from yellow and red. 
 
 Purple — from blue and red. 
 
 TERTIARY COLORS 
 
 A tertiary color is made bj' mixing two secondary colors 
 in equal parts. There are three secondary colors: Citrine, 
 russet and olive, which are formed as follows: 
 
 Citrine — from orange and green. 
 
 Eusset — from orange and purple. 
 
 Olive — from i^urple and green. 
 
 The formation of a tertiary color, by mixing two sec- 
 ondaries in equal parts, is equivalent to mixing two parts of 
 one primary to one each of the other two primaries. For 
 example, olive is formed from purple and green. Since pur- 
 ple contains one part of blue and one of red, and green is com- 
 posed of one part of blue and one of yellow it naturally fol- 
 lows that olive is composed of two parts of blue to one each 
 of red and yellow. 
 
 INTERMEDIATE COLORS 
 
 When a primary and a secondary color are combined in 
 equal parts they form what is known as an intermediate color. 
 These are named and formed as follows : 
 
 Sulphur (vellow-green), three parts yellow to one of 
 blue. 
 
 Saffron (yellow-orange), three parts yellow to one of red. 
 
 Nasturtium (red-orange), three parts red to one of yellow. 
 
 Graimet (red-purple), three parts red to one of blue. 
 
 Cami^anula (blue-purple), three parts blue to one of red. 
 
 Turquoise (blue-green), three parts blue to one of yellow. 
 
 By A^arying the proportions of the constituent pigments, 
 it is possible to jiroduce an almost endless variety of colors. 
 
THE ESTHETICS OF TOOTH SELECTION 377 
 
 COMPLEMENTARY COLORS 
 
 Certain colors are pleasing to the eye, or liarniovize, 
 when jolaced alongside each other, while others are displeas- 
 ing, or inharmonious. Those which are most pleasing are 
 termed complementary colors. Now, why is this so? 
 
 As has been shown, the most satisfying light to tlic visual 
 organs is simlight, subdued or diminished in its intensity to 
 such degree as the optic nerve can tolerate with comfort. The 
 same holds true of the more brilliant white varieties of artifi- 
 cial light. 
 
 Both natural and artificial light, as has been shown, when 
 passed through a prism or over a diffraction grating are 
 dispersed into the primary and secondary spectral colors. 
 
 It therefore follows that harmony in colors results from so 
 mixing them or placing them in juxtaposition that all are re])- 
 resented, as in white light, thougli not necessarily in balanced 
 proportions. 
 
 A complementary color is defined as one which sui)i)li('s 
 those colors tliat are lacking in another color. There are 
 various ways of producing complementary effects, some com- 
 plicated, and others quite simple. It is to tlie sim])lest of 
 these that attention will now be directed. 
 
 The complement of red is green, because green is com- 
 posed of blue and yellow, and, therefore, it sup]ilies these two 
 colors, which are lacking in red. Likewise the rule works 
 both ways, for red is the complement of green. 
 
 The complement of lilue is orange, and of orange, 
 lilue. 
 
 The complement of yellow is ])urple, and of ])urple, yel- 
 low. 
 
 As a general rule more harmonious results are produced 
 when the complementary color is less ]:)ronounced than the 
 principal color. When too conspicuous it lessens the ])roini- 
 nence of the main color. 
 
 COLOR FUNCTIONS OF THE VISUAL ORGANS 
 
 These statements in regard to colors and their comple- 
 ments are not arbitrary rules, promulgated for convenience, 
 but are based npou physiologic functions of the visual or- 
 gans, and can be demonstrated by anyone to his own satisfac- 
 tion. 
 
 For example, when one gazes intently at a red object foi' 
 two or three minutes, until the eyes become saturated with 
 
378 THE ESTHETICS OF TOOTH SELECTION 
 
 tliat folor, and then closes the eyes an image of the object will 
 still be seen, not in red, however, but in green. 
 
 If, instead of closing the eyes, one continues to gaze at the 
 same or other red objects, a greater or less sense of 
 monotony and visual fatigue is experienced, which is im- 
 mediately relieved on looking at something green.- The same 
 holds true of the other colors and their complements. 
 
 The tiring of the visual organs, when compelled to gaze 
 continuously at incomplete spectral colors, together with the 
 automatic foi'mation of complementary colors within the eyes, 
 clearly indicates that white light, which contains all of the 
 prismatic colors, is normally and naturally demanded by the 
 organs of vision. 
 
 When the principal color viewed is not intense, but rep- 
 resents a more or less dilute tint of a primary, secondary or 
 intermediate color, the corresponding complement will be pro- 
 portionately reduced. 
 
 Whatever the color scheme may be, the strength or tone 
 of the various colors should accord. "The note struck may 
 be high or low, but should be maintained throughout the color 
 scheme. A crude, strong color, though othei'wise harmonious, 
 will clash discordantlv among delicate tints of a notably 
 lighter tone." (Sanford.) 
 
 The question may arise in the reader's mind. "Of what 
 value is this discourse on the physics of light, and the harmony 
 of colors, to the prosthetist?" Simj^lv this: Without a rudi- 
 mentary knowledge of the physics of light, and the natural 
 laws of the harmonv of crude colors and their complements, 
 the selection of teeth of appropriate shade, or tint, becomes 
 a difPcult, and in some cases, an impossible task. 
 
 The artist, or artisan, can lighten or strengthen the prin- 
 cipals or complementaries of the color scheme he is creating, 
 and arrive at a just balance of harmony between the two. 
 
 The color scheme which presents to the prosthetist, 
 which he works with, and he cannot change, is the pa- 
 tient's face. Here the flesh tints of the complexion display 
 themselves in the integument according to the general char- 
 acteristics, habits of life and health of the individual. 
 
 The prevailing tones are gray and yellow, tinged with 
 red and brown. Now since gray consists of white and black, 
 the degree of grayness determines the tone of the complexion, 
 whether light or dark. The reds and browns always appear 
 in more or less attenuated form, and usually are modified by 
 
THE ESTHETICS OF TOOTH SELECTION 379 
 
 admixture with other colors to suggest secondaries or inter- 
 mediates. 
 
 The hair, to a marked degree, contributes to the general 
 color scheme of the individual. In color it may range from 
 white to black, including intermediate shades of yellow, red 
 and brown. As a rule, light hair and light complexions are 
 associated, while dark or black hair usually implies a more 
 strongly pigmented integument in which perceptible tints of 
 reds and browns more or less diluted, yet plainly apparent, 
 are noticeable. 
 
 The lips range in color from a gray, which at times is 
 scarcely distinguishable from the integument, through vary- 
 ing shades of pink, red, brown to purple, depending largely on 
 the vitality and age of the individual. They form the imme- 
 diate setting, or frame work, for the teeth. 
 
 In addition to the usually pronounced color of the lips 
 in which the teeth are framed, the shadows of the lips and 
 oral cavity must also be considered. These shadows tend to 
 soften the lighter teeth and blend them with the more darkly 
 shaded integument. 
 
 Dr. G. W. Clapp, who, with the aid of a color expert, ex- 
 amined many individuals, in an effort to determine the per- 
 centage of various colors present in natural teeth, gives the 
 following data of one case as follows : 
 
 Miss D. A. Wt. 119 lbs. 
 
 Ht. 5.6 In. 
 
 Eyes 
 
 Hair 
 
 UPPERS Skin 
 
 TT T. /-I i 1 ( Cervical 
 
 U. R. Central | j^^j^^j 
 
 COLORS FOUND IN NATURAL TEETH 
 
 According to Dr. Clapp 's analyses, many colors are to be 
 found in the natural teeth. With gray as a foundation, the 
 predominance of some one of the primary or secondary colors 
 gives the tooth its color individuality. He says: "Natural 
 teeth exhibit every color of the rainbow. The primary colors, 
 red, blue and yello.w, are found in every human tooth. At 
 least one of the- secondary colors, orange, green or violet, is 
 found in every tooth, generally with an excess of some prim- 
 ary color which gives to the tooth its recognized color as a 
 blue, a yellow or a pink. Gray teeth occur when there is no 
 excess of primary color." 
 
 Red Yellow Blue 
 
 Color Developed 
 Black Orange 
 
 17.5 43.0 16.0 
 
 16.0 
 
 1.5 25.5 yeL 
 
 Dead Black 
 
 
 
 4.1 3.0 .88 
 
 .88 
 
 2.12 1.1 red 
 
 1.1 1.4 .20 
 
 .20 
 
 .90 .3 yel. 
 
 1,1 1.35 .34 
 
 .34 
 
 .76 .25 yel. 
 
380 THE KSTHETICS OP" TOOTH SKLECTION 
 
 SUGGESTIONS 
 
 In the selection of teeth for a given ease no specific rules 
 can be laid down, because of the wide variation in color 
 schemes of different individuals. Persons with complexions 
 showing pronounced reds or browns, and with dark hair, re- 
 quire comparati\('1y dark teeth, in wliich orange or ]iink tints 
 predominate. 
 
 Persons are frequently seen whose general color scheme 
 is neutral, no pronounced primary or secondary colors appa- 
 rent. Either a very dark or a light tooth for such a case 
 would be inappropriate, by attracting too much attention to 
 the mouth. Teeth of gray shade or neutral tint should be 
 selected and of such dei)tli of tint as will coincide with the 
 complexion. 
 
 Fair or light complected persons recpiire correspondingly 
 light teeth, tinged with yellow or blue, sometimes almost 
 neutral as to primaries and secondaries. 
 
 White teeth are inappropriate in all cases, although pa- 
 tients frequently demand them. Natural teeth are never 
 white, the nearest approach being a light shade of gray. The 
 harmony and esthetic appearance of many otherwise good 
 dentures is frequently spoiled by the use of teeth of too light 
 shade. 
 
 As has been shown, the color scheme of an individual may 
 range from i^ronounced primaries or secondaries, through 
 imperceptibly attenuating gradations to neutral grays, in 
 which none of the prismatic colors are discernible. 
 
 This color scheme, painted by nature's hand, is the 
 prosthetist's canvas, in which he must place a central set- 
 ting, the teeth. How, then, can he hope to attain esthetic re- 
 sults without a knowledge of the laws of harmony of colors? 
 
 The physiologic color function of the eye, previously re- 
 ferred to, which automatically creates the complementary of 
 a pronounced color, is an aid, in the selection of teeth, to those 
 deficient in a knowledge of the laws of harmony. 
 
 In some individuals this infiiifioii, if it might be so called, 
 is an efficient, though unrecognized, guide in choosing teeth 
 that will "look well," while the results attained throiigli this 
 means are at times pleasing and harmonious. 
 
 More often, however, when the physiologic function is 
 imperfectly developed or totally lacking, as in the color blind, 
 most inharmonious selections result, a fact plainly apparent 
 to anvone in whom this facultv is not deficient. 
 
THE ESTHETICS OF TOOTH SELECTION 381 
 
 The selection of teeth for edentulous cases is not a prob- 
 lem of matcliing shades, Inxt of harmonizing colors by grada- 
 tions and complementaries, the general color scheme of the 
 patient affording the basis for such selection. 
 
 It is hoped that this discourse on color and form, brief 
 and imjiei'fect as it is. has disclosed its importance in the 
 field of dental prosthetics, and that it will create in the mind 
 of the reader an interest in and a desire for more extended 
 knowledge in the esthetic field. 
 
C H A P T E R X X 
 
 ARRANGING AND OCCLUDING THE TEETH 
 UPPER ARCH 
 
 ARRANGING THE SIX ANTERIOR TEETH 
 
 The full upper set of fourteen teeth should be first ar- 
 ranged, beginning witli the central incisors. A section of waN 
 is removed from the upper occlusion rim of sufficient width, 
 length and depth to r(;ceive a central incisor. Into the si^ace 
 so formed a central incisor is set, its mesio-labial angle in 
 line with the median line previously marked on the wax rin; 
 
 DIAGRAMMATIC CUT SHOWING SECTION OP WAX KEMOVED WITH TOOTH IN CORHECT 
 LAUIAL AND INCISAL POSITION 
 
 Its labial contour should coincide with the general labial con- 
 tour of the rim, the two undisturbed margins of wax on either 
 side of the space serving as guides in securing correct align- 
 ment. Its incisal edge is brought even with the incisal rim of 
 wax. When set, the tooth should occupy the space of and re- 
 store the disturbed contour occasioned by the removal of the 
 section of wax. In nearly all cases the long axes of the cen- 
 trals, when viewed labially, should diverge slightly from 
 incisal to gingival, away from the median line, the horizontal 
 alignment mesio-distally of the incisal edge serving as a 
 guide, or at least strongly indicating the amount of such 
 divergence. When in proper position, a hot spatula is passed 
 in back of the tooth so as to melt the wax, not only around the 
 pins, but against the entire lingual surface as well, and thus 
 firmly fix it in place. 
 
 In like manner a section of wax is removed and the lat- 
 eral incisor is set in position, the central just placed on its 
 
 382 
 
ARRANGING AND OCCLUDING THE TEETH 383 
 
 mesial side, and the undisturbed wax in the cuspid area on the 
 distal serving as g'uides for its correct labial alignment. The 
 cuspid is then set and fixed in similar manner. 
 
 VIEW OF rlM'ER LEFT CENTHAL INCISOR ADJUSTED IN OCCLUSION RIM 
 
 UPPER CENTRAI. LATEK^VL, AND CUSPID ARRANGED 
 
 It will usually be best to return to the median line and 
 place the other three anterior teeth in the order mentioned, 
 so that should rearrangement for esthetic reasons be neces- 
 
384 AKKANGINCI ANU OC'CLUDING THE TEETH 
 
 sary, it can he more readily aeeoiiiplislied now tiian after any 
 of the posterior teeth are phu-ed. 
 
 ARRANGING THE POSTERIOR TEETH 
 
 The first and seeouel iMcusjiids and lirst and seeond mol- 
 ars on one side are set in a similar manner in the order named, 
 followed by the arrangement of the teeth on tlie opposite side. 
 
 After remoA-ing the section of wax for each posterior 
 
 ^1X ANI'EHKII!.' 
 
 iKl) AMI \VAXEI> IN l'< 
 
 tooth, the walls of the matrix so formed should be thoroughly 
 softened with a hot spatula, the tooth pressed into buccal 
 alignment, and the frame closed. This Inings the occlusal rim 
 of the lower occlusion model up in contact with the tooth, 
 which, if longer than normal, establishes its correct incisal 
 or occlusal length. 
 
 If shorter tJiau required, it nuist Ije brought down in close 
 contact with the lower wax rim when closed. In fact, the tips 
 of the cusps of all of the npper bicuspids and molars should 
 be sunk one-half their depth in the lower occlusion rim. This 
 may readily be done by softening the wax slightly where the 
 cusps strike, as each tooth is placed. The reason for this is 
 that when the tips of the upper bicuspids and molars are not 
 imbedded as described, but are allowed to rest on the undis 
 
ARRANGING AND OCCLUDING THE TEETH 385 
 
 turbed lower wax rim, in arranging tlie corresponding lower 
 teeth they must be raised the full dei)th of their cusi)s, and 
 even higher, in order to bring them into occlusion with the 
 upper teeth. This raises the occlusal plane of the denture in 
 the bicuspid and molar region from one-sixteenth to one- 
 eighth of an inch above the line established by trial of the 
 wax occlusion models. 
 
 By following the plan outlined, the cusps of the upper 
 teeth pass slightly below, and those of the lower slightly 
 
 FULL UPPER DENTTRE OCCLUDED 
 
 abo\e, the wax occlusal plane, thus maintaining the normal 
 ])osition of the plane as previously determined. 
 
 ARRANGING THE LOWER TEETH IN OCCLUSION WITH 
 UPPER TEETH 
 
 The arrangement of the teeth in the lower arch should be- 
 gin with the lower second bicuspid because better interlocking 
 of the various planes and cusps can be secured with the occlud- 
 ing teeth than when the same order of arrangement is fol- 
 lowed as in the uppe'- arch, viz., centrals, laterals, cuspids, etc. 
 
 A section of wax is removed from the lower occlusion rim 
 directly opposite the distal one-half of the upper first and 
 mesial one-half of the upper second bicuspids. A heated spa- 
 tula is thrust deeply into the floor of the space, and the side 
 
■.iW ARRANGING ANIJ OCCLUDING THK TKBTH 
 
 walls, particularly toward the lingual, are thoroughly softened. 
 
 The lower second bicuspid is set in this softened matrix, 
 
 its occlusal surface considerably above normal position. The 
 
 LOWEB SECOND BICUSPID SET IN SOFTEKED WAX, BUT SLIGHTIiT ABOVE 
 
 POSITION. BY CLOSURE OF THE PRAJIE IT IS FORCED DOW'NWARD 
 
 AND IN APPROXIMATELY COSRECT OCI'LtTSION 
 
 CUT SIIOWINC PROPKR CONTACT I >E\i:i.OPEn BETWEEN' THE MARGINAL RIDGES 
 
 frame is then carefully and slowly closed, using reasonable 
 force if necessary to bring the ui^per teeth in contact with 
 the lower occlusion rim. The wax in which the upper teeth 
 are imbedded should be thoroughly chilled, previous to and 
 
AKKANGING AND OCCLUDING TH1<; TKETH 387 
 
 diiriug tins step, to prevent llicir (lis|i|;icciiii'nl iiihIci- Ihe ap- 
 plied pressure. 
 
 The closiug of the frame brings tlie upper bicuspids in 
 contact with the elongated lower second bicuspid, and forces 
 it down to place. If carefully carried out and the wax is suf- 
 ficiently plastic, the i^arious planes of the teeth will become 
 closely interlocked, as in normally occluded natural teeth. 
 
 Care should be taken to see that in closing the frame the 
 lower bicuspid is not forced outward gingivally. This will 
 most certainly occur on account of the slope of the ridge lap 
 
 KRAME THROWN TO LEFT TO TEST CONTACT OF BUCCAL MARGINAL RIDGES. IN THIS 
 
 CASE THERE IS IMPERFECT CONTACT BETWEEN MESIAL RIDGE OF LO«T,B 
 
 SECOND, AND DISTAL RIDGE OF TPPER FIRST BICUSPID 
 
 acting as an inclined plane, thus directing the tooth outward 
 as it settles into the wax, unless counter-pressure is applied 
 gingivally to keep it in proper alignment. 
 
 TESTING THE OCCLUSAL SURFACES FOR WORKING 
 EFFICIENCY 
 
 Before placing the next tooth the relation of the lower 
 second to the upper first and second bicuspids should be tested 
 as to its working efficiency. This is done by drawing the 
 lower portion of the frame outward on the side being tested, 
 so as to bring the buccal marginal ridge of the lower second 
 bicuspid outward and directly under the corresponding ridges 
 of the occluding teeth. 
 
 Usually, although in full occlusion the tooth maj' have 
 interlocked well with the opposite teeth, it will be found that 
 
.■!88 Al{KANGIN(i AND OCCLll DINC •rillO 'I'KKTH 
 
 while the mesial or distal slope of the buccal marginal ridge 
 linds contact with the opposite tooth, the other slope does not 
 strike, a space of greater or less width being apparent. 
 
 This defect may be remedied by holding the frame in lat- 
 eral position, and moving the lower bicuspid bodily forward 
 or backward, as required, until the planes are brought in 
 close contact and the wax surrounding the tooth chilled, when 
 the frame is allowed to spring back to position. 
 
 A piece of carbon paper inserted between the occlusal 
 surfaces will, imder pressure, disclose the points of interfer 
 ence in normal occlusion, which can be ground away with a 
 
 l.llWEI! iUClSrill IN 
 
 small engine-stone. The mesial and distal marginal ridges of 
 the opposing teeth ai'e usually the points needing correction. 
 Another method quite as efficient in some cases, particu- 
 larly where but little correction is required, is to soften the 
 wax in which the three teeth are imbedded so that with slight 
 pressure they may change their position. By carefully sub- 
 jecting the frame to lateral movements, at the same time ex- 
 erting slight pressure io keep the teeth in occlusion, the posi- 
 tion of both upper and lower teeth may be modified so as to 
 correct the defects mentioned, without much, if any, grinding. 
 
 SECURING CONTACT OF THE LINGUAL MARGINAL RIDGES 
 
 Now, while occlusal requirements may be perfectly de- 
 veloped and contact of the mesial and distal slopes of the 
 
ARRANGING AND OCCLUDING TIIK TEETH SS'J 
 
 buccal marginal ridges may he secured, it is frequently the 
 case that contact of the lingual marginal ridges is defective 
 or entirely lacking. Since the efficiency of the masticatory 
 apparatus depends upon close contact of both buccal and lin- 
 gual marginal ridges quite as much as upon good occlusal con- 
 tact, it is necessary to work out tlie required contact of the 
 lingual marginal ridges also. 
 
 Failure to develop contact lingually in the first steps of 
 arrangement is usually the resiilt of too long buccal cusps of 
 the lower, or too short lingual cusps of the upper teeth. When, 
 however, the teeth are well proportioned, lack of contact may 
 
 THE LEFT LOWER BKTSI'IDS AND MOLARS OCCLUDED 
 
 be due to inclining or lipping the teeth in one or both arches 
 too far lingually, that is to say, while tlieir cervical position 
 may l^e correct, their occlusal ends may incline too much to 
 the lingual. Correction may be made in the former case by 
 reducing the length of the cusps by grinding, and in the lat- 
 ter by changing the inclination of tlie teeth in the wax. The 
 time required for effecting such clianges as noted is very 
 slight, and when corrected as soon as discovered, and as each 
 tootli is set, usually obviates more general or extensive modifi- 
 cations later on. ' 
 
 A section of wax is now removed for the reception of the 
 lower first molar, the matrix walls softened, the tooth set in 
 a slightly elevated position, pressure exerted on its cervix, 
 and the occluding frame closed to force it into position as 
 
390 AltKANOlNO AND OCCLUDING THE TEETH 
 
 previously dcscrilH'd. In lil^c ruaiiiu'r siiiiilai' IcsIh aru ap- 
 plied, and (•(•ri'cdions madi' to iniiirovc occlusion and contact 
 between the buccal and lingual marginal ridges. Similar 
 steps are carried out iji adjusting tlie second molar and first 
 bicusi)id in the order named, after which the l)icuspids and 
 molars on the oi^posite side are arranged in similar order 
 and manner. 
 
 ARRANGING THE SIX LOWER ANTERIOR TEETH 
 
 The six anterior teeth can now be set in position. These 
 are placed in the wax rim in the following oi-dcr: cuspids, 
 laterals and centrals. 
 
 BDCCAI. VIEW OP FULL, DENTURE OCCLUDED. GUMS NOT CARVED 
 
 Should the teeth prove too narrow to fill the space when 
 aligned in proper curvature, a wider set of sixes should be 
 substituted, or if too wide, a narrow set can be used. When 
 only slightly excessive in width, correction may be made by 
 grinding the distal surfaces of the cuspids and the mesial 
 surfaces of the first bicuspids at their points of contact. This 
 procedure reduces the length of the arc described by the six 
 anterior teeth, and increases the distance between the first 
 bicuspids, so that teeth which at first glance appear too wide 
 to be practicable, can be utilized with very little effort. 
 
 As each tooth is set, the frame should be subjected to 
 lateral movements to test their incisal relationship. Fre- 
 quently by grinding the incisal edge of the lower teeth at the 
 
ARRANGING AND OCCLUDING THE TEETH oMl 
 
 expense of the labio-mcisal angle, clearance space may be 
 developed without shortening the teeth or placing them to 
 the lingual of their former position. 
 
 BIAGKAM SHOWIXC TUK HELATION OV LOWEK TO 
 UPPER MOLARS IX THE INITIAL ACT OF MAS- 
 TICATION. BALANCING SIDE ON BIGHT. WORK- 
 ING SIDE ON LEFT. 
 
 Where much overbite of the upper over the lower teeth is 
 deemed necessary, the arc descrilied by the latter must be 
 correspondingly reduced, in order to secure clearance space 
 in lateral movements. In ordinary cases an overbite of one- 
 sixteenth of an inch will prove sufficient for practical pur- 
 poses, and produce satisfactory esthetic results as well. 
 
 DEVELOPING BALANCING CONTACT 
 
 In the arrangement of the teeth, so far nothing has been 
 said of the balancing contact. This lias ]nirposely been left 
 
 DISTAL VIEW OF A FULL DENTURE SHOWINti RELATION OF TEETH ON WORKING 
 SIDE. LEFT. AND BALANCING SIDE. RIGHT 
 
 until the teeth have been occluded, since balancing adjust 
 ment must always be carefully developed in all cases as a 
 final step. Test is now made as follows: 
 
392 AKKANGINU AND OCCLUDING THK TEETH 
 
 Tlie frame is drawn to one side until tlie teeth on the 
 working side are carried to their differential limit, i. i'., the 
 l)uocal and lingual marginal ridges of the upi)er and lower 
 teetli are in contact. While in this position the relation of 
 the ujjper and lower second molars on the opposite side should 
 he observed. Tlie disto-buccal cusp of the lower second molar 
 should rest against the mesio-lingual cusp of the upper sec- 
 ond molar, or in the case of disproportion in the mesio-distal 
 diameters of the molar teeth, it sometimes finds contact with 
 the disto-lingual cusp of the upper first molar. 
 
 If on throwing the frame sidewise as described, the sec- 
 ond molars do not meet, an instrument should lie inserted 
 
 LEFT BUCCAL VIEW OF CASE. TKKTU IX WORKING RELATION 
 
 under the distal end of the lower second molar and the latter 
 raised until contact is established. The frame should now 
 l)e opened without distiirbing the molar in its raised position, 
 a heated s])atula passed under it to melt the wax and form a 
 new base on which to rest, and the wax allowed to cool. 
 
 The lower are now brought into occlusion with the upper 
 teeth by closing the occluding frame, if this can be done with- 
 out disturbing the lower second molar in its corrected position 
 and the position of the upper molar changed to occlude with 
 the lower. Wlien on testing the lower and upper teeth do not 
 occlude, being held apart by the modified i^osition of the sec- 
 ond molars, the wax under the upper molar should be softened 
 and the teeth brought together under pressure. The use of 
 carbon paper will also disclose points of interference. 
 
ARRANGING AND OCCLUDING THE TEETH 393 
 
 It should be kept in miiiil that baUiHciiiy contact is devel- 
 oped between the upper and lower second molars in almost 
 every instance, and when developed no other contact is re- 
 quired on that side between that point and the opposite lateral 
 or cuspid tooth. The teeth on tlie balancing side are not in 
 such relation to each other as to form a masticatory mill or 
 to hold food, the actual work being accomplished on the oppo- 
 site or working side. 
 
 It will be found by reference to the diagram that the gen- 
 (>r;d contact between the t(>etli in the two arches, in the initial 
 
 lilGHT BUCCAL VIEW OF (."ASE, SECOND .MOI 
 
 act of masticatory effort, i. e., the position where the teeth 
 begin their return to normal occlusion, is as follows : 
 
 The buccal and lingual marginal ridges of the lower and 
 upper teeth on the working side from the cuspid to the second 
 molars inclusive, are in contact. On tlie opposite side con- 
 tact exists between the second molars. These points, if con- 
 nected by imaginary lines, represent a triangle, the teeth 
 along the working side occupying the base, the second molars 
 on the opposite side the apex of the figure. 
 
 The fact that 'contact is thus ranged along the sides and 
 at the angles oi a three-sided figure no doubt gave rise to the 
 term three-point contacl. This term is misleading because, as 
 a matter of fact, there are, or should be, many points of con- 
 tact between the teeth on tlie working side of the mouth, but 
 not necessarily more tlian one on the balancing side. 
 
ARRANGING AND OCGLUDING TIIIC TlOI-nil 
 
 HUMAN DEXTUIIE SIIOWIXG BUOKEX CONTACT OF LOWER WITH Ul'I'EK 
 TEETH FBOM FIRST MOI,AnS TO CUSPIDS OF OPl'OSITE SIDE 
 
ARRANGING AND OCCLUDING THE TEETH 395 
 
 This is Nature's plan, as cau be seen by examiuiDg the 
 natural teeth in a normally arranged denture. Stress, there- 
 fore, is laid upon this fact because many in attempting to 
 occlude teeth anatomically, endeavor to secure close-locking 
 contact between the upper and lower bicuspids and molars 
 on the entire balancing, as well as working, side in lateral 
 movements. 
 
 FINAL TEST WITH CARBON PAPER 
 
 When the arrangement of the teeth has been concluded 
 and balancing contact has been secured, a final test of all sur- 
 faces with carbon paper is made, and the high points thus 
 disclosed removed with engine-stones. This test should be 
 
 DIAGR;U.I SHOWING HOW CONTACT ON WORKING AND 
 
 BALANCING SIDES OCCURS ALONG BASE AND 
 
 AT APEX OF A TRIANGLE 
 
 repeated until smooth- gliding contact in lateral and protru- 
 sive movements is developed. 
 
 DEVELOPING THE CONTOUR OF THE DENTURES IN WAX 
 
 Strips of wax are now placed on the labial and buccal 
 surfaces of the denture, one strip against and parallel with 
 the periphery, and another overlaying the cervices of the 
 teeth. The round end of the heavy burnishing spatula is 
 heated and passed rapidly back and forth along the strips to 
 soften and burnish them into close contact with, and cause 
 them to adhere to, the outer surfaces of the wax denture. 
 The wax should overlay the cervices of the teeth about one- 
 twentieth of an inch in depth and cover the gingival thirds 
 at this time, the idea being to apply a slight surplus every- 
 
396 ARRANGING AND OCCLUDING THE TEETH 
 
 where, from wliicli, by carving, the gum festoons and general 
 contours are developed to proper curvature and thickness. 
 
 It has been previousl}^ shown by the presentation of Dr. 
 Williams' work that tliere are three typal forms of Imman 
 teeth, each type presenting certain modifications. 
 
 To one who lias gi\en this subject any consideration, it 
 is a comparatively simple matter, according to the data, to 
 select teeth of appropriate form for any individual case, since 
 the manufacturers are supplying artificial teeth closely re- 
 sembling tlie tyjial forms of the natural organs. 
 
 Now, granting that teeth of correct form and size have 
 been selected and occluded, it does not follow that esthetic 
 results will inevitably follow their use. In fact, in the carv- 
 ing and festooning of the gums one class may be easily made 
 to resemble another, or any form may be so distorted as to 
 
 CARVING TOOL SUITABLE FOB IISi: IN WAX. \UIA'ANITE OR PORCELAIN 
 
 be unrecognizable. Clearly, then, it is the prosthetist and not 
 the manufacturer who finally detei'mines the class of tooth 
 the finished denture presents. 
 
 As an artist, the prosthetist should recognize the type of 
 tooth required. As a sculptor, he should be able to so mold 
 
ARRANGING AND OCCLUDING THE TEETH 397 
 
 the pliant materials around the rigid porcelain as to frame 
 them, as it were, to meet the esthetic requirements of the case. 
 
 It requires quite as much judgment to fashion the arti- 
 ficial gums around teeth of appropriate form in order not 
 to distort their type, as to develop reasonably appropriate 
 forms from types of teeth that do not strictly conform to the 
 requirements of a given case. In either case the prosthetist 
 nuist possess a well-developed esthetic sense to produce har- 
 monious results. 
 
 The advantage in using teeth of suitable typal forms is 
 that, although the prosthetist 's esthetic judgment must be 
 none the less well developed, the teeth themselves indicate 
 the form of the gum festoons, and therefore serve as pat- 
 terns in the carving of the case. When teeth are used which 
 do not strictly conform in typal outline to the case, the pros- 
 thetist must be able to see a mental picture of the require- 
 ments of the case, and develop those forms by the disposition 
 of his wax around the teeth. 
 
 As an artisan, the prosthetist must reproduce in per- 
 manent materials the modeled wax form of the denture and 
 maintain in clearness and purity during the finishing stages 
 the outlines of the typal forms of teeth he set out to develop. 
 
 The dentures at this stage are in the rough, as it were, as 
 slight surplus allowance of wax should be made for loss in 
 tinal finishing. They should, however, represent in general 
 detail, though roughly blocked, the typical outline forms of 
 the finished dentures, just as the work of a sculptor, as, for 
 example, the statue of Tolstoi, by Mucha, represents the 
 characteristic features of the man. (See page 398.) 
 
 The attainment of esthetic results along these lines, as 
 well as in the arrangement of the teeth, is of the utmost im- 
 portance. The denture which the prosthetist produces, and 
 which is fitted in the patient's mouth, is not like a garment 
 which can be worn at pleasure or put oft" for something more 
 attractive. It literally becomes a part of that patient's body, 
 to be worn for j^ears, or until further tissue loss or accident 
 requires renewal. It corrects impaired phonation, disturbed 
 facial contour, and by its use, when properly constructed, the 
 patient is enabled to. masticate and assimilate food, thereby 
 enabling normal lx)dily functions to be carried on. The health 
 of the patient, his well-being, comfort and good looks de]iend 
 upon the etiticiency of the prosthetist 's efforts. 
 
 He, therefore, who undertakes this specialty should have 
 the ambition, or be required, to develop more than (average 
 
398 AKKANGING AND UCCLUDING THK TEETH 
 
 skill, since conditious of sucli vital importance depend upon 
 the results of his efforts. 
 
 DEVELOPING THE GUM FESTOONS 
 
 When teeth of approximately the right form have been 
 selected and arranged, and the wax has been applied and bur- 
 nished against the labial and buccal surfaces of the denture 
 
 STATUE OP TOLSTOI (BY MUCHA) SHOWING CHjVRACTERISTIC LINES 
 WITHOUT FULLY DEVELOPED DETAILS (SEE PAGE 397) 
 
 slightly thicker than required, the gum festoons are developed 
 as follows: 
 
 With a sharp carving tool, or the pointed blade end of 
 the burnishing spatula, the surplus wax is removed from the 
 labial face of each tooth. The instrument, applied at right 
 angles to the surfaces of the tooth, should be held with the 
 pen grasp — thumb, index and middle fingers — the fourth and 
 
ARKANUING ANU OCCLUDING THK TEETH 39« 
 
 little tiugers rostiug at some couveiueul jioiiit on tlie ease so 
 as to control the movements of the bla<h'. 
 
 The gingiva of each tooth is then carefully outlined with 
 the blade, the surplus wax removed, and the correctness of 
 form noted. It is usually better to remove too little than too 
 much wax in the first outlining, since more time is lost in mak- 
 ing additions than is required in going over the case a second 
 time after inspection. The wax should be allowed to fill the 
 embrasures to as great an extent as is consistent with the 
 development of correct typal forms, to avoid the formation 
 of unnecessary food i30ckets. 
 
 This fact, however, should be kept in miml : When teetli 
 are selected for a given case whicli conform in length to the 
 distance between the incisal rim of wax and the liigh lip line, 
 and in typal form to the requirements of the case, they must 
 
 not be distorted and their esthetic value impaired by the ex- 
 cessive use of wax in gum festooning. 
 
 The round end of the spatula, or a similar carving tool, 
 is now used to develop the varying siirfaces of the gum fes- 
 toons above the embrasures and between the gingivae and 
 ]ieriphery of the denture. 
 
 It is not possible to describe accurately the outline of 
 these uniform, yet plainly marked, undulating surfaces swell- 
 ing out over the rounded labial and buccal curves of the teeth 
 and sinking into the embrasures and areas as between the 
 roots of the natural teeth, were they present. Many in the 
 attempt to reproduce the gum festoons and surfaces extend 
 grooves from the" embrasures toward the periphery. While 
 these are decidedly better from an esthetic standpoint than 
 mechanically rounded, convex ridges, they lack that inde 
 scribable and delicate variation — the imperceptible fading of 
 
400 ARRANGINC! AND OCCJLUDINfi THIC TKKTU 
 
 oue suvfju'c iii1(i iiiiollici- SO (it'toii seen ill iKiniiiil, licjiltliy ,ti;um 
 tissue. 
 
 One who is really interested in tliis work eau lind no 
 better ideals than can be gained by taking impressions of the 
 labial and buccal surfaces of the teeth and gums of normal 
 mouths, securing casts of the same, and studying the forms 
 and variations there represented. 
 
 TRIMMING THE PERIPHERAL OUTLINE OF THE DENTURES 
 
 When the festooning of the gums has been completed, and 
 frequently liefore, the excess peripheral wax should be re- 
 moved so as to disclose the general outlines of the dentures. 
 The attention should be directed to the form of the denture 
 as a whole, as well as to specific details, and by early outlining 
 them the proportion of the parts to the whole can be more 
 easily determined. 
 
 FINISHING TOUCHES IN CARVING 
 
 Attention has iireviously been called to certain prom- 
 inent points in the develoi)ment of the wax contour and occlu- 
 sion models. These will bear In-ief repetition, since the final 
 touches are given thern at this time before trial in the mouth. 
 
 The central notch providing for the unrestricted action 
 of the frenum is cleared of excess wax, and the margins 
 smoothly rounded. 
 
 The incisive fossae or depressions should be developed 
 above the lateral incisors. In most cases, in order to develop 
 these depressions, it will be necessary to set the cervices of 
 the laterals inward so that a straight edge applied to the 
 cervices of the central and cuspid on either side will clear 
 those of the laterals. This does not require that the incisal 
 edge of the lateral shall be set within the anterior curve of the 
 arch, but merely necessitates the slanting inward or liackward 
 of tlie long axis of the lateral. 
 
 When set directly upright the incisive fossae, if developed, 
 will form an abrupt, and usually an unsightly, depression, 
 while the monotonous curvature of the labial surfaces and 
 the parallel arrangement of the central, lateral and cuspid, do 
 not produce as fine esthetic effects as where the alignment is 
 varied. The cuspid eminence is usually plainly developed, 
 sometimes strongly marked, as conditions demand. It is 
 usually most prominent, though not always so, at the peri- 
 pheral margin, slightly concave from above downward, and 
 
ARRANGINC AND OCCLUDING THE TEETH 401 
 
 again proiuiiicnt as tlio ji'iiin tVsloon will ]ic!iuit at the ccivix 
 of the tooth. 
 
 Usually back of the euspid emiueiioe the periphery of the 
 denture drops down, frequently sufficient to form a decided 
 notch, to permit the free play of the buccal muscles. The 
 perijihery of the baseplate in the region of the tuberosities 
 should extend as high as tissue attachment will permit, to give 
 stability to the denture in masticatory eiTort. 
 
 It is best in all cases to so form the baseplate as to em- 
 brace practically all of the tuberosities, not only on the buccal 
 surfaces, but distally as well. When roiuided or somewhat 
 spherical, as the tuberosities frequently are, the baseplate, 
 when enclosing them, is prevented from sliding forward in 
 masticatory stress. 
 
 FINISHING THE LINGUAL SURFACES OF THE WAX MODEL 
 DENTURES 
 
 The excess wax should l)e removed from the lingual sur- 
 faces of the dentures and any depressions filled in to effect 
 the desired contour. 
 
 In many cases it is advisable to develop in wax the lin- 
 gual forms of the incomj^lete porcelain teeth so as to repre- 
 sent the forms of natural teeth. By applying tinfoil to the 
 palatine area and biirnishing it carefully against the lingual 
 wax contours of the various teeth, the work of final finishing 
 in vulcanite is reduced to the minimum. 
 
 t'are should be taken to see that the baseplate is not ex- 
 cessively thick at any point, and that the border portion is 
 not bulky or over-developed. Special care should be bestowed 
 on the correct development of the surfaces to the lingual of 
 the incisors. If unnecessarily thick, the patient's speech will 
 be thickened to a marked degree, while if deficient a whistling- 
 tone is apt to be produced. This is because in phonation the 
 tongue does not find normal contact with the denture, or, in 
 those cases where, in the production of certain tones, the 
 tongue does not touch the teeth or the baseplate, the space 
 through which the air passes is of abnormal outline. 
 
 Tests should be made as to the efficiency of the denture 
 in phonation during trial in the mouth. Frequently the re- 
 moval or addition of a li-ttle wax will correct what othei'wise 
 might prove a serious defect. Such changes are usually re- 
 quired to be made back of the incisor, and occasionally along 
 the lingual, surfaces of the bicuspids. 
 
402 ARRANGING AND OCCLUDING TlIK TKlflTH 
 
 THE DEVELOPMENT OF THE RUGiE 
 
 When the ruga? are plainly marked in the i)alale the\- 
 are easily reproduced in tlie denture by carefully adapting 
 the softened baseplate to the case in such manner as to force 
 it into the depressions between the folds, and yet not thin it 
 on the ridges. 
 
 In preparing an impression for the production of a cast, 
 the rugas should in most cases be slightly exaggerated by 
 scraping the bottom of the grooves impressed by the high 
 ridges with a discoid excavator. This not only allows the 
 denture to become more firmly seated on the vault tissues, 
 but clearly indicates the position and form of these folds so 
 that they may be easily reproduced in the baseplate when 
 desired. 
 
 Just what the function of the rugae may be is not known. 
 In the lower animals they aid in prehension. In man their 
 
 SECTION OP LOWER DENTURE SHOWING LINGUAL 
 
 SURFACE, A, CONCAVED TO INCREASE 
 
 TONGUE SPACE 
 
 roughened surfaces may assist in separating triturated from 
 imperfectly masticated food, and may result in a keener ap- 
 preciation of taste as well. 
 
 When ruga5 are developed in a denture special care must 
 be taken to have the baseplate of the exact thickness required 
 in the finished substitute, to cover the cast with thin tinfoil 
 before vulcanizing, and the lingual surface of the wax model 
 also before flasking the tin lining remaining in the matrix 
 side of the flask. This procedure forms an improvised metal 
 matrix between which the rubber is vulcanized, and when 
 carefully carried out, the surfaces of the vulcanite in contact 
 with the foil are practically finished when removed from the 
 flask. 
 
 The lower wax model denture is finished in much the 
 same manner as the upper, the prominent points of the lat- 
 ter, however, being developed to a lesser degree liecause the 
 
ARRANGING AND OCCLUDING THE TEETH 403 
 
 surface markings of the lower natural denture are not 
 strongly marked. Special care should be observed to avoid 
 unnecessary bulk of wax on the lingual of lower cases, for 
 unless remo\'ed in finishing the vulcanite, tongue movements 
 are liable to be impeded. When finished in the manner de- 
 scribed, the wax model dentures are ready for trial in the 
 mouth. 
 
 TRIAL OF THE DENTURES IN THE MOUTH 
 
 The following points should l)e observed in the trial of 
 the wax model dentures in the mouth : 
 
 First, occlusion. The patient is instructed to open and 
 close the mouth a number of times, and in doing so to avoid 
 the application of excessive masticatory force, which tends 
 to displace the teeth in the wax. 
 
 Observe the following: 
 
 Whether or not tlie teeth rest against each other, as in 
 normal occlusion. 
 
 See that they intercuspate properly. 
 
 That the overhang of the buccal marginal ridges of the 
 upper bicuspids and molars over the lower teeth is the same 
 on both sides. 
 
 Note whether the median lines of the upper and lower 
 dentures coincide. 
 
 Observe the pose of the lips when at rest and in smiling, 
 and finally, the profile and fullness of the face, to see whether 
 addition or reduction of wax in any area is required. 
 
 Second, lateral movements. The patient is instructed 
 to move the mandible from side to side to test the clearance 
 paths of the teeth. 
 
 Usually it is best at the beginning of this test to intro- 
 duce carbon paper between the occlusal surfaces of the two 
 dentures, and by this means iinder lateral movements the 
 high points are disclosed. These should be ground away with 
 engine stones. Repeated trials, followed by grinding, first 
 on one side and then on the other, should be made until the 
 cusps of the lower denture glide smoothly between those of 
 the upper teeth without interference. 
 
 When there is much variation of the lateral mandibular 
 rotation centers from those of the occluding frame, consider- 
 able grinding will be required. When the rotation centers 
 are approximately four inches apart, but few, if any, cor- 
 rections will be necessary. 
 
404 ARRANGING AND OCCLUDING THE TEETH 
 
 111 carrying out the lateral movemeiitss the patient should 
 be cautioned against exerting much force u^Don the teeth, 
 since hy these side movements they are much more readily 
 displaced than under direct stress. 
 
 The necessity for using hard wax tiiat will not soften 
 readily at oral temperature, for the rims in which to imbed 
 the teeth, becomes apparent at this stage of construction. 
 
 Tliird, balancing contact may be tested by placing car- 
 bon paper between the upper and lower second molars on 
 the protruded side. If porcelain is not discolored by the car- 
 bon, there is lack of proper contact. Correction is made by 
 removing the lower denture, raising the second molar dis- 
 tally, higher than the actual required position, melting wax 
 in the space underneath to serve as a foundation, returning 
 the denture to the mouth while the wax is still plastic, and 
 having the patient throw the dentures into balancing relation 
 and close. The elongated tooth will thus be forced down into 
 correct relation, the plastic wax underneath preventing the 
 tooth from settling to its former shortened position. 
 
 One other test still remains to be carried out. The change 
 of position of the lower second molar, particularly when ele- 
 vated as described, in order to develop balancing contact, 
 usually requires that the central groove and sloping planes 
 leading to it, of the upper second molar be deepened corre- 
 spondingly to receive the buccal marginal ridge of the lower 
 second molar when the teeth are in normal occlusion. This 
 test and the correction is made with carbon paper and stones, 
 or the wax under the upper second molar is softened, the 
 lower baseplate removed, chilled and returned to place, and 
 the patient instructed to close with sufficient effort to force 
 the upper molar into the softened wax a sufficient depth to 
 bring the remaining teeth into full occlusion. 
 
 The latter method, although practicable at times, fre- 
 (piently results in loss of balancing contact, because the point 
 of contact previously established by elevating the lower molar 
 is moved upward in gaining normal occlusion. Correction 
 by grinding, therefore, is preferable. 
 
 When satisfied that the various important requirements 
 of the dentures have been developed as outlined, tests of the 
 patient's aliility to phonate correctly should be made, as 
 previously mentioned. 
 
 It is difficult to correctly estimate the exact amoimt and 
 general form of contour in a denture required for the cor- 
 
ARRANGING AND OCCLUDING THE TEETH 4U5 
 
 rect artioiilatioii of sounds in all eases, except ))y careful 
 trial. In fact, in certain cases, as where the patient has never 
 before worn artilicial dentures, the use of any appliance hav- 
 ing a baseplate in excess of bulk of normal lost tissue will 
 cause a thickening of speech for some time after its intro 
 duction. 
 
 In all cases an effort should lie made to develop as nearly 
 as possible the normal surfaces seen in natural dentures by 
 avoiding either excessive hulk or deficient contour. 
 
 FINAL FINISHING OF THE WAX MODEL DENTURES 
 
 After the various tests and corrections have been car- 
 ried out as outlined until satisfactory results have been se- 
 cured, the dentures are removed from the mouth and returned 
 to the casts on the occluding frame. 
 
 If during trial in the mouth the position of any of the 
 teeth have been purposly changed, care should be taken to 
 avoid closing the frame with any degree of force or the cor- 
 rections made in the mouth are liable to be disturbed. 
 
 Each denture is now carefully inspected to see that the 
 gum festoons and general contour are as desired, or, if not, 
 corrected. 
 
 The surfaces of wax are carefully smoothed with a 
 burnisher and all minute fissures or holes obliterated, since 
 in subsequent flasking the plaster will enter them and show 
 as rough points on the matrix walls. 
 
 The surfaces of wax may be rendered very smooth by 
 carefully rubbing them with a pellet of cotton moistened with 
 chloroform. Since chloroform is a slow solvent of wax, care 
 should be taken to avoid covering the teeth with the dissolved 
 wax carried by the cotton. When this occurs the teeth will 
 readily loosen in the matrix in the removal of the wax. 
 
 The case is sometimes passed quickly through a Bunsen 
 flame to smooth the surfaces, but this method should not be 
 generally adopted, since the flame affects high points more 
 readily than depressions and finely-carved surfaces and deli- 
 cate festoons are qui.ckly obliterated. 
 
 Before removing the casts from the occluding frame care 
 should be taken to see that each wax model denture is firmly 
 attached to its cast. 
 
 This is done by placing a little extra wax at various 
 points around the periphery of the baseplate and with a hot 
 
406 ARRANGING AND OCCI>UDlNG THE TEETH 
 
 spatula melting it along the junction of the baseplate with 
 the cast. 
 
 REMOVING THE CASTS FROM THE OCCLUDING FRAME 
 
 With a sharp knife, the plaster which was built around 
 the bows and against the base of the cast in mounting, is pared 
 away so as to expose and undermine the bows, after which 
 the cast is easily detached. The adherent plaster is then 
 removed so as to reduce the cast to its original form before 
 attachment to the occluding frame. 
 
C H A P T I] K X X I 
 
 REPRODUCTION OF THE WAX MODEL DENT- 
 URES IN PERMANENT MATERIALS 
 
 The duplicatiou of the wax model dentures iu perma- 
 nent materials may be roiio'hly divided into tive stages, as 
 follows : 
 
 Flasking the wax model denture. 
 
 Packing the matrix witli rnbber. 
 
 Closing the flask. 
 
 Vulcanizing. 
 
 Finishing. 
 
 A wax model denture usually presents a very irregular 
 outline and many varying surfaces. It is also composed of 
 some of the permanent factors of the denture, viz., the teeth, 
 and sometimes the baseplate. The wax portion of the model 
 denture must be replaced with rubber applied in a plastic 
 condition and afterward hardened. The problem is how to 
 replace the wax with vi;lcauite without losing the relation 
 between the teeth and oast of the mouth. 
 
 SECTIONAL MOLDS 
 
 The reproduction of a pattern or model in metal or other 
 materials capable of being rendered plastic is usually ac- 
 complished by surrounding the object it is desired to repro- 
 duce with a sectional mold, so formed as to part from irreg- 
 ular surfaces without breaking, removing the model from th^ 
 mold, replacing the various sections, and filling the space 
 formed by the removal of the model, with the plastic material. 
 
 To carry out such work accurately some means must be 
 provided for holding tlie several parts of the sectional mold 
 in exact relation to each other after removal of the pattern 
 or model, and while filling the matrix. 
 
 Iron and brass founders use what is termed a flask or 
 molding box, consisting of two or more sections, iu each of 
 which a portion of the mold is formed. These various sec- 
 tions of the molding box are held in position by means of 
 accurately fitted guides, so that when separated and the model 
 is removed, the several parts of the mold can be reassembled 
 
 407 
 
408 KLASKINC WAX MODl^L OKNTUKKS 
 
 and held in the same iclalioi: tlicv (iccniii(Ml wiicri the pat- 
 tern was enclosed within. 
 
 When a pattern composed entirely of wax is used, and 
 the object is to be reproduced in metal, as an inlay, crown, 
 bridge or denture, the mold can be made in a single piece 
 and the wax model dissipated by heat, thus clearing the 
 matrix and obviating the necessity for forming the mold m 
 sections. 
 
 In prosthetic operations the reproduction of a wax model 
 denture is usually accomplished by forming of plaster a two- 
 piece sectional mold in a metal box termed a flask. Some- 
 times in complicated cases, as in the construction of obtura- 
 tors and artilicial vete, a three or four section mold is re- 
 quired, involving the use of flasks of special forms. 
 
 FLASKS 
 
 Vulcanite flasks used for dental purposes are made of 
 brass or cast iron. They usually cousist of a lower section 
 in which the base of the cast is invested, and an upper sec- 
 tion in which the mold containing the teeth and representing 
 
 in reverse the gum and lingual areas of the denture is 
 formed. The lower section may or may not have a removable 
 bottom, while the top of the upper section is always remov- 
 able, to facilitate the flashing of the case. 
 
 These varioiis parts of the flask are provided with pins, 
 or lugs, which fit into holes or slots in the corresponding op- 
 posite parts, for accurately guiding and holding them in cor- 
 rect relation to one auother while flasking, and during the 
 final closing of the packed case. 
 
FLASKING WAX MODEL DKXTURES 4oy 
 
 Two general styles of flasks are in oommou wae: 
 First — Flasks to whicli screw bolts are fitted, for clos- 
 ing and holding the packed case together during vulcaniza- 
 tion. 
 
 Second — Flasks which are closed and held together by 
 means of a spring clamp or ]>ress. 
 
 Cl'T SHOWING THE KLASK SlOI'AItATKl) 
 
 An appliance called a flask press is frequently employed 
 for closing packed cases, the bolts or clamps being used for 
 holding the flask together. 
 
 The usual methods followed in closing flasks and hold 
 ing them together- during vulcanization will yield satisfactory' 
 results if reasonable care is observed in carrying out the se\'- 
 eral steps. If carelessly performed, errors are liable to occur 
 during this o])eration which may result in destroying denture 
 adaptation. Attention will be called to these sources of error, 
 and means for obviating the same, under the heading. Clos- 
 ing the Packed Flcsk. 
 
 Most of the flasks offered by the supply houses are too 
 small to receive average and large sized casts. Since no ad- 
 vantage is gained in the use of small flasks, the larger sizes 
 should be used. 
 
410 
 
 PLASKING WAX MODEL DENTURES 
 
 FITTING THE CAST AND WAX MODEL DENTURE IN THE 
 FLASK 
 
 In uppei' cases the cast with wax model denture attached 
 is now set in the lower, or shallow, section of the flesk. If 
 too large peripherally to rest upon the bottom of the flask, 
 the margins of the cast should be pared away at points of 
 interference until it drops into position. Usually reducing 
 the distal end of a. cast, when trimming in this location is 
 permissible, will be all that is required. 
 
 The upper section of the flask is now set in position to 
 test the depth of cast and denture as compared to the depth 
 of the entire flask. Should the incisal ends or occlusal sur- 
 
 A Sl'ECIAI. SIZED FLASK KOK \U1.( AXIZIXG I.AUGE CASES 
 
 faces of the teeth project above the upper plane of the second 
 section, they will interfere with the top plate going to place, 
 and the teeth are liable to become disj^laced. This is obviated 
 by reducing the base of the cast sufficiently to lower the teeth 
 below the upper plane. 
 
 FLASKING THE WAX MODEL DENTURE 
 
 The upper portion of the flask is now set aside and the 
 cast and denture removed from the lower section. A mix of 
 plaster of medium consistency and containing no accelerator 
 is applied over the bottom and around the inside periphery 
 of the first section of the flask. 
 
 The east should be set in water for ;i sliori time just 
 previous to investment to partially fill the pores, then set in 
 position in the flask and pressed down into the soft plaster 
 
FbASKINC WAX .MODEL DENTURES 
 
 tu tlie positiou previously detenuiued. With a slioit, stifL' 
 blade spatula the plaster between the sides of the flask and 
 the peripheral line of the wax model denture is smoothed 
 down where high, and built in where deficient, so as to form 
 a continuous surface from the denture margin to the upper 
 plane of this first section. This surface of plaster forms the 
 dividing line between the two halves of the invested case. 
 
 Care should be taken to see that none of the gum por- 
 tion of the denture is imbedded in the plaster investment of 
 the first section, or the packing of the case becomes difficult. 
 Under no circumstances should the line of separation of the 
 two halves of the flask occur near the cervices of the teeth 
 or the basic rubber will most certainly find its way through 
 to, and mix with, the gum material. 
 
 DIAGRAM OF DPPEB WAX MODEL DENTURE INVESTED IN FIRST OR LOWER SECTION OF 
 
 FLASK 
 
 The plaster is built against the distal margin of the base- 
 plate, but not so as to overlay it at any point. When set, the 
 surplus plaster is trimmed off and the surfaces surrounding 
 the cast smoothed up with a piece of sandpaper. Particu- 
 lar attention should be given to removing all plaster from 
 the flask margins and from the holes or grooves which receive 
 the lugs of the second section. This is necessary in order that 
 the metal edges of the two sections may come together with- 
 out interference. Wlien smoothed up and the loose debris 
 is removed, the plaster surfaces are varnislicd with a good 
 separating medium and allowed to dry. 
 
 The second section of the flash is now set in j^osition, 
 into which plaster of medium consistency, too thick to pour, 
 is introduced with a spatula, placing it on the incisal and 
 occlusal surfaces of the teeth. By jarring the flask on the 
 bench, the plaster is vibrated down between the labial and 
 
412 FLASKINU WAX .\l(M)IOL DKNTURKS 
 
 liiiccjil sui'Taccs 1)1' llic ilcntiirc :iiiil ll;isk ;iii<l oxci- the liii.nual 
 iii'cas as well. 
 
 Special care slioiild he taken in lillini;' tlie upper liali" of 
 the flask to avoid eonliiiing tiie air in the embrasures, or any- 
 where throughout the plaster investment. When air spaces 
 are present, pressure of th(> surphis rubber in the matrix 
 is liable to force the teeth into them in closing the flask, or 
 result in uncontrolled loss of rubber from the matrix. Elon- 
 gation of the teeth from this cause is of frequent occurrence, 
 particularly when the matrix contains much surplus rubber. 
 
 To obviate this difficulty, a mcfal occlusion reiainer sug- 
 gested by Dr. rxreeno, is lieni to lay in contaet with the oc- 
 
 clusal surfaces of the teeth and extend over the labial and 
 buccal surfaces as well. In the second stage of flasking when 
 the plaster has assumed a level even with the occlusal sur- 
 faces of the teeth, the occlusion retainer previoiisly conformed 
 to the arch is quickly liiled with plaster, inverted and pressed 
 down until in contact with the teeth at many points. The 
 remaining space in the flask is now filled with plaster slightly 
 above its upper margin. 
 
 The top of the flask is now adjusted and pressure ap- 
 plied to force out the excess plaster while it is still plastic. 
 Care should be taken to see that the projections of the top 
 enter their respective guides of the flask. 
 
FLASKING WAX MODEL DENTURES 41:! 
 
 Siuce rubber is easily soiled from dirty lingers, and 
 siuce the flask as well as the rubber must be handled more or 
 less in packing the matrix, to obviate discoloration of the 
 rubber, the outer surfaces of the flask should be cleaned with 
 a scrub-brush and water. The holes and grooves which re- 
 ceive the bolts should also be cleared at this time, for if de- 
 ferred until the case is packed, some of the debris is liable 
 to become intermixed with the contents of the matrix. This 
 scrubbing and cleaning of the flask can be carried on while 
 the plaster is hardening. 
 
 From fifteen to twenty minutes' time should be given 
 the plaster in the upper portion of the flask is set, or a longer 
 time if necessary when slow-setting material is used. The 
 plaster must be thoroughly hardened before separating the 
 flask, to prevent displacement of tlie teeth. 
 
 SEPARATING THE FLASK 
 
 The flask and contents should he warmed to render the 
 wax soft, but not sufiiciently heated to melt it. This is neces- 
 sary so that the wax may part readily from the teeth with- 
 out dislodging them from the matrix. Heating is best ac- 
 complished in a warming oven, the temperature of wliich does 
 not exceed 120 degrees Fahrenheit. This method requires 
 but a short time, while the danger of melting the wax is en- 
 tirely obviated. In case the warming oven is not available, 
 the flask may be heated over a Bunsen stove. When so done, 
 it should not be allowed to rest in one position for any length 
 of time, particularly when the case is invested in a closed- 
 bottom flask. AVith a pair of flask tongs it may be turned 
 so that its various surfaces can all be heated without ovei- 
 heating any part. 
 
 The principal advantage of using dry heat in softening 
 the wax is that the plaster of both cast and matrix as well 
 is rendered harder and more resistant to stress than when 
 saturated, as it is by the usual method of placing in hot 
 water. 
 
 Since iilastei' is low in conductivity, sufficient time sliould 
 be allowed for the heat to penetrate the interior. When over- 
 heated and the wax is melted, it soaks into the plaster mat- 
 rix and cannot well be removed by the usual means. Its 
 presence impairs the quality of the vulcanite, frequently pre- 
 venting it from fuUv hardening, as well as modifying its color. 
 
114 FLASHING WAX MODICL DRNTURRS 
 
 OPENING THE FLASK 
 
 The lieated flask resting upon tlie beiieli is set edgewise 
 and with a folded towel steadied with one hand. The point 
 of a knife is inserted between the line of jinietion of the two 
 sections just sufficiently to gain a hold. A slight i-otary or 
 prying motion is applied until the sections show a slight line 
 of separation. The flask is then turned and the knife applied 
 to the opposite side. The sides of the flask by tlie guides, 
 especially when the latter fit closely, are the logical points 
 to apply the wedging ]jressure. 
 
 The force at the start should be very light and gradual, 
 to permit the wax to yield without endangering any over- 
 hang that may be present, either on the cast or matrix walls. 
 
 FIRST SECTION OF FLASK CONTAINING CAST. AFTER SErARATION 
 
 When the two sections show a line of separation around their 
 entire pei'ipheries, with a folded towel in each hand the flask 
 is picked up, and with a steady, rocking, manual force, the 
 lower and upper halves are gradually parted. 
 
 InsufiScient warming of the wax within the matrix, or 
 undue force exerted in separating the flask, frequently results 
 in fracturing the matrix, or the cast, or in dislodging some 
 of the teeth. 
 
 When separated, the cast will be found enclosed within 
 the lower section of the flask, and the teeth covered by the 
 wax in the upper section. 
 
 CLEARING THE MATRIX OF WAX AND BASEPLATE MATERIAL 
 
 When Ideal Baseplate, or any hard special material Is 
 used as a baseplate, it can best be removed by insei'ting the 
 point of a knife at the back under the central vault portion, 
 
FIvASKING WAX MODEL DENTURES 415 
 
 when by prying upward it may be readily fractured and the 
 broken pieces removed. 
 
 With a spoon-shaped instrument, such as a medium-sized 
 Kingsley Scraper, the wax enclosing the teeth can be started 
 at one tuberosity, and if of sufficient cohesiveness, can be 
 gradually released from the teeth and matrix, en masse. 
 
 When somewhat hardened, it should again be rendered 
 plastic or removed in sections; otherwise the teeth will be 
 displaced. When overheated, but not actually melted, a 
 dash of cold water will restore its cohesiveness without en- 
 tirely destroying its plasticity. When melted and partially 
 absorbed by the matrix, the entire elimination of the wax 
 is not possible without the application of dry heat sufficient 
 to lower the resistance of the plaster to stress; therefore 
 such means should not be used. 
 
 The bulk of wax having been removed, such smaller por- 
 tions as are adherent to the pins of the teeth and in the em- 
 brasures should be i)icked out with a delicate instrument, care 
 being taken not to mar the matrix or dislodge the teeth. 
 
 The flask is now set, tuberosities up, at an angle of about 
 45 degrees, in the sink, and a small stream of boiling water 
 allowed to fall from a height of ten or twelve inches against 
 the molar and bicuspid teeth on each side. A small teakettle 
 is very convenient for this purpose, the spout producing a 
 small stream which is easily directed where desired. A pan 
 with handle and having a sharp lip will answer the same 
 purpose. 
 
 To rid the matrix quickly of wax, and prevent excessive 
 absorption of water by the latter, the water must be boiling 
 hot, must fall from a considerable height, must be directed 
 where needed, the flask inclined so that the water will readily 
 flow from the matrix and carry the melted wax with it, and 
 the process carried out as quickly as possible and stopped 
 as soon as all wax is removed. The plan adopted by some, 
 of placing tlie flask section in a pan of water and bringing 
 to a boil, is an incorrect and careless procedure, resulting 
 in full saturation of the plaster with water and frequently 
 of a film of wax adhering to the flask, matrix surfaces and 
 teeth. 
 
 The matrix section is now emptied of the water in its 
 deeper parts, a thorough examination made to see that 
 the pins and embrasures are clear of debris and that the 
 plaster has not found its way into interproximate spaces 
 through crevices in the wax model denture while filling the 
 
416 FLASKING WAX MODEL DENTURES 
 
 second section. Slimild any he pn^sent, it is ])icke(l ont with 
 a delicate instrument, and tlie defective ])arts carved to cor- 
 rect form. 
 
 TOP VIEW OF PnEPAREn MATIilX P.EADY FOR PACKING 
 
 TOP VIEW OF FIRST SECTION OF FLASK CONTAINING CAST 
 
FLASKING WAX MODEL DENTURES 417 
 
 Auy delicate overhanging margins of the matrix sliould 
 be trimmed away to prevent fracture while closing the packed 
 case. Its removal only slightly increases the bulk of excess 
 peripheral vulcanite subsequently, while if allowed to re- 
 main, and fracture does occur, the broken pieces are liable 
 to become intermixed witli the rubber. Tlic correct order of 
 procedure is to remove the peripheral overhang of the matrix 
 margin before washing out the wax, since the latter step will 
 thus clear the matrix of the cuttings. 
 
 Should any teeth become dislodged, they may be ce- 
 mented in place by varnishing those surfaces which rest in 
 the matrix with liquid silex, and returning them to place un- 
 der pressure. 
 
 Should the case have become overheated before opening 
 the tlask and the wax melted, the order of procedure just out- 
 lined should be carried out. In addition and at this stage 
 the use of chloroform applied with tweezers and cotton 
 pellets will remove some of the superficial wax. 
 
 TREATMENT OF FIRST SECTION OF THE MOLD 
 CONTAINING THE CAST 
 
 Since plaster when dry is much more resistant to stress 
 than when moist, the application of water to the cast for the 
 removal of adherent wax should be avoided if possible. When 
 rigid baseplate material has been employed and the case is 
 not overheated, the cast is free from wax on all areas except 
 around the margins where the ]ieriphery of the baseplate has 
 been luted to it. A slight amount of wax in this location can 
 usually be removed by careful scraping, followed by wash- 
 ing of the areas so covered with chloroform. 
 
 PROVIDING FOR THE ESCAPE OF SURPLUS RUBBER 
 
 Since no two bodies can occupy the same space at the 
 same time, some means must be ]n-ovided for the reception 
 of the surplus rubber during the closing of the flask. When 
 no provision is made for the purpose stated, and any excess 
 of rubber is present in the matrix, then when the two sections 
 of the flask are brought together under pressure, compression 
 of some portioi> of the matrix will occur. The amount of 
 space so formed will be in direct lu'oimrtinn to the excess of 
 rubber retained within the flask. 
 
 To overcome danger of distortion of the cast or matrix, 
 a shallow depression extending from the inner wall of the 
 flask inward to within onc-sixteeiith of nil indi of the cast 
 
418 KLASKINO WAX MODEL DENTURES 
 
 margin should be made around the entire peripliery in the 
 first section of the flask. Tliis de]iression should not be con- 
 nected at any point with the matrix, the idea being- to leave 
 a narrow line of contact at the peripheral margin of the 
 denture between the surfaces of plaster in the two sections 
 when the flask is closed. 
 
 This line of contact retards the ready escape of the rub- 
 ber during the closing of the flask, and subsequently during 
 vulcanization. Furthermore, sliould much excess be present, 
 this peripheral line of contact being so much more limited in 
 area than the cast or matrix walls, will yield slightly and 
 l^ermit the surplus to escape into the groove, thus relieving 
 undue pressure within the matrix. 
 
 The cutting of waste gates leading from the periphery 
 of the matrix to the outer groove is unnecessary, and, in fact, 
 detrimental, as when ]iresent they permit the too ready 
 escape of surplus rubber. 
 
 The groove having been formed, the debris is brushed 
 off and this section is set aside until the matrix is packed 
 with rubber. 
 
 STEPS PREPARATORY TO PACKING THE MATRIX 
 
 Dental rubber, while more or less plastic and adhesive, 
 is not sufficiently so to be formed into a homogenous mass 
 as it is introduced into the matrix. In adding one piece of 
 pink rubber to another, or in introducing tlie basic material, 
 spaces are liable to result from the overlapping of one piece 
 on another. Unless these spaces are eliminated while pack- 
 ing, an intermixture of the pink and basic rubber will often 
 occur. Such mishaps alwa^'s detract from the esthetic ap- 
 pearance of the finished denture. 
 
 There are two methods in vogue for rendering the rub- 
 ber more plastic preparatory to packing, viz., first heating 
 the rubber before introduction, and second, heating the mat- 
 rix, by which means the rubber, although cold, is immediately 
 rendered plastic when carried to place. 
 
 HEATING THE RUBBER BEFORE INTRODUCING IT IN THE 
 MATRIX 
 
 This is usually accomplished by placing the pink aud 
 basic rubber on a plate, as it is cut in pieces of suitable size 
 for packing. The plate is placed over a pan of water and 
 the latter heated over a burner. The greatest amount of heat 
 l)Ossible to develop by this method will not exceed 212 degrees 
 Fahrenheit, not sufficient 1o injure the rubber, yet ample to 
 
FLrASKlNG WAX MODEL DENTURES 419 
 
 reuder it plastic and workable. Tlio ubjection to this method 
 lies in the fact that the rubber, although heated, is carried 
 to a cold matrix where it immediately becomes chilled, and 
 is almost as difficult to condense as though it had not been 
 so treated. 
 
 HEATING THE MATRIX PREPARATORY TO PACKING THE 
 RUBBER 
 
 The second and umch more practical method, when one 
 becomes accustomed to it, consists in heating the matrix side 
 of the flask to about 212 degrees Fahrenheit, or until steam 
 begins to escape from the plaster. A matrix so heated will 
 usually retain sufficient heat to permit the rubber to be con- 
 densed, but should the packing of the case prove tedious, it 
 may be re-heated without injury to the rubber already packed. 
 
 The advantages of this method are twofold, viz., first, 
 drying and hardening of the plaster matrix, rendering it more 
 resistant to stress, thus reducing its liability to distortion in 
 closing the flask ; and second, the absorbed heat of the matrix 
 not only softens the rubber as soon as placed, but keeps it 
 plastic so that it may be united into a homogeneous mass en- 
 tirely free from spaces, tlius obviating the danger of inter- 
 mixture of the basic and gum material. 
 
 The disadvantages of this method consist in danger ot 
 overlieating the flask, thus injuring the plaster, and the ne- 
 cessity for exercise of greater care in manipulation to avoid 
 burning the fingers. In all other respects this method of ren- 
 dering the rubber plastic is preferable to the former, and bj' 
 observing reasonable care the objections mentioned can be 
 obviated. 
 
 To prepare the matrix for packing by the second method, 
 the flask should 1k' placed on a metal plate or sheet of gauze, 
 over a Bunsen flame, and heat applied gradually so as not 
 to disintegrate the plaster in the bottom of the flask. Since 
 plaster is a poor conductor of thermal changes, the process 
 should be continued a sufficient time to heat the entire matrix 
 throughout. Care should be taken not to force the heat- 
 ing too strongly, or the rapid accumulation of steam next the 
 bottom and walls of .the flask may disturb the plaster contents. 
 In the meantime while the flask is heating, the rubber may 
 be prepared for packing. 
 
 PREPARING THE RUBBER FOR PACKING THE MATRIX 
 
 A good-sized sheet of clean paper is laid on the bench; 
 the i^acking instruments, a pair of ball .pointed pliers, a thin- 
 
420 KLASKIN(! WAX .\1()1)I01> I JlOXTIIIilOS 
 
 hliidc liiiniislicr, ;i sliiirp poiiilcd iiisl niiiiciil niid llic lieavv 
 wax burnisliiun' spatula are laid coiivcniciitly at hand. 
 
 Tlio muslin, (■(tvcrin^- both sidos of a slieot of granular 
 gum facing or jiink rulibcr, is strii)|H'd liiick so as to expose 
 
 THIS CUT SHOWS Till 1 si Nil \1 1( I 1 \ 1 1 I 111 LEU AAD lOllllM \I1I 
 
 THE INSTRUMENTS 1111(111111 II 111] IJll llll I I RUNf ULAU I 11 1 I s 
 
 OF PIMv OB ( KVMl \lt I \I Kl 1 1 HI ( N rill ltl< 1 1 1 SI III STRIPS 01 
 
 liASK Runi 1 R I (IWl 11 RI( IIT \SIMirilI I II I \sl RUB 
 
 HI R FOR (IM RI \^1N( lllr \ \l IT I ORTI<l\ dl' M \TRI\ 
 
 from oue-lialf to two-thirds of the sheet. Eight or ten strips 
 three-sixteenths of au inch wide are cut from across the slieet 
 and allowed to fall on the paper, but should not touch each 
 
 ^^ 
 
 other because of their tendency to adhere. From one or more 
 of these strips are cut about twenty-eight triangular pieces 
 for filling the embrasures between the teeth. These also 
 should be kept separate. 
 
FLASKINCi WAX .MODEL DENTURES 421 
 
 BASIC RUBBER 
 
 Several strips of the red, maroou or black rubber, which 
 is to constitute the base, are cut and laid to one side of the 
 pink. As tlie packing proceeds, wider strips will be required, 
 but they can lie cut as needed and of a width suitable to the 
 requirements of the case. The rubber being cut as described, 
 and the matrix side of the flask heated, the case is now ready 
 for packing. 
 
 PACKING THE MATRIX 
 
 Since the outer matrix wall of a vulcanite case, being 
 perpendicular or nearly so, is most difficult to adapt the rub- 
 ber to and hold in position until the flask is finally closed, this 
 portion of the matrix is packed first because more accessible 
 before the introduction of the basic material. 
 
 The one essential point to keep in mind during the pack- 
 ing of the rubber is to so place it as to avoid intermixture 
 of the gum material and the basic portion. The gum facing 
 must be applied piece by piece and formed into a solid homo- 
 geneous mass free from spaces. It miist lay in close contact 
 with the matrix walls and show no tendency to draw awaj' 
 from them. It must entirely fill the embrasures between the 
 teeth from the deepest portions represented by the interproxi- 
 mate spaces in the bottom to the extreme upi^er periphery of 
 the matrix. ', 
 
 PACKING THE GUM FACING 
 
 With the sharp packing instrument, or a pair of ball 
 pointed pliers, a triangular piece of granular gum or pink 
 rubber is carried, pointed end down, into the embrasure be- 
 tween two teeth, and with a suitable thin-bladed burnisher 
 is forced into the deepest and narrowest portion. Another 
 piece is carried to the adjoining embrasure and adapted in 
 a similar manner. The adjacent angles of the two are 
 pressed between the matrix walls and the labial cervix of the 
 tooth, and if sutlficiently long to meet, are united together 
 by pressure. If too short, a third piece can be laid above 
 the cervix of the tooth and the three united. 
 
 The other embrasures are similarly filled, each triangular 
 piece of rubber as it is added being closely conformed to the 
 walls and its upper end united with the adjoining piece al- 
 ready placed. The embrasures, interproximate spaces and 
 the space between the cervix of each tooth and the matrix 
 wall for an eighth of an inch above the teeth shoiild be filled 
 
•122 KLASKINC WAX MODKN DENTUHKS 
 
 solidly with triiiii,i;iilar pieces of gimi, mikI all well condensed 
 so as to eliminate all openings. 
 
 A strip of pink or granular facing rubber is now applied 
 against the lingual surfaces of the teeth, and pressed against 
 that which alread.y fills the embrasures. Its lower margin 
 should not approach the pins of the teeth closer than one- 
 sixteenth of an inch, nor should it ever enclose them, since 
 teeth anchored in pink vulcanite are gradually dislodged un- 
 der stress. 
 
 The strips of rubber, when cut crosswise of the sheet, are 
 not of sufficient length to pass around the matrix wall from 
 
 <KII IN TlIK 
 
 oue tuberosity to the other; therefore to complete the first 
 layer, a second strip is abutted or allowed to slightly overlap 
 the end of the first piece, after which it is adapted to the cor- 
 responding unfinished part of the matrix above the tooth pins 
 on the opposite side. In placing these and all other strips of 
 the gum material, care should be taken to avoid stretching 
 them, as the tendency of the mass of gum facing to leave the 
 matrix wall is very noticeable if the strips are stretched as 
 applied. 
 
 Another stri^D of facing is placed above that already 
 packed, its lower slightly overlapping the upper margin of 
 
PLASKING WAX MODEL DENTURES 423 
 
 the first. When by pressure — usually with the round end of 
 the burnishing spatula, slightly heated — it is adapted to the 
 matrix wall and underlying rubber, other strips are added 
 and pressed to place in like manner, one layer overlapping 
 another, until the entire wall of the matrix is covered. When 
 
 care has been exercised in carving the wax gums to correct 
 contour, two layers of pink rubber will furnish ample thick- 
 ness to obviate exposure of the basic material on the gum 
 surfaces in the final finishing of the case. 
 
 As a final step in the condensation of the gum portion, 
 a folded towel should be placed against the outer surface of 
 
 A CONVENIENT RUBBER I'ACKINO INSTIUMENT (IVORY) 
 
 the flask to protect the thumbs from the heated metal, and 
 finger pressure should be applied to the rubber built against 
 the matrix wall, the force exerted being outward and slightly 
 downward. 
 
 Some prosthetists. before introducing the gum material, 
 paint the matrix wall with a solution of pink chloro-rubber, 
 which serves to cement the layers of gum material closely 
 to the walls. When applied in a thin layer, and the chloro- 
 form is allowed to evaporate before packing, it serves a use- 
 ful purpose, but is more often harmful than beneficial, as at 
 times it seems to retard the hardening of the pink rubber in 
 vulcanizing. It is also liable to change the color of the outer 
 surfaces of the gum facing to a slight extent. 
 
■124 PLASKINti WAX MODEL DENTURES 
 
 PACKING THE BASIC RUBBER 
 
 The entire outer wall of the matrix having been packed 
 and condensed as described, the next step is to introduce the 
 basic rubber. 
 
 A narrow strip is laid in tiie bottom ot the matrix and 
 pressed under the pins of the teeth, care being taken not to 
 displace the gum facing which tills the deepest portions of 
 the interproximate spaces. This strip of basic material, al- 
 though placed under the pins, should lay to the lingual of the 
 gum facing. 
 
 A wider strip is now laid over the first one and pressed 
 solidly against it, so as to eliminate any s])aces that may be 
 
 THE CillM FACIV 
 
 present. The bottom of the matrix is filled in this manner 
 so as to represent in bulk the amount of wax and baseplate 
 material that formed the bulk of the wax contour model. 
 
 In upper cases the palatine portion is covered with one, 
 sometimes, though seldom, two, thicknesses of rubber cut so 
 as to overlay this area and extend on and attach to that fill- 
 ing the deeper part of the matrix. 
 
 A pattern can quickly be cut from the muslin removed 
 from the sheet rubber, and its size tested by placing in the 
 matrix. When properly formed, it is laid on the sheet of 
 rubber, a piece cut according to outline, the mu.slin removed, 
 and the rubber i^laced in position and firmly condensed at 
 
FIvASKING WAX MODKL DKXTUKKS 425 
 
 its margins to that already packed around and to the lingual 
 of the pins in the hottom of the matrix. A strip of basic 
 material wide enough to line the gum portion of the matrix 
 is cut and stretched to I'educe its thickness. This is then laid 
 
 THE TINS KNTIKKl.V CIlVERKll WITH IIA.SIC IUHHER 
 
 •At'I/T AREA CnVERKl) WITH A SINGLE LAYER OK liASIC ItUHKER 
 
 against the gum facing and firmly pressed against it. This 
 lining of basic material strengthens the gum portion, and fur 
 ther insures the entire palatine and border surfaces of the 
 denture, being composed of the same colored vulcanite, a 
 point of considerable esthetic importance. 
 
t2(i KLASKINC WAX .\l()|)i:i, lilOXTUKKS 
 
 A second layer ol' iuIiIxt, usually a strip about one-half 
 inch wide and long enougli to extend from anterior to pos- 
 terior limits of the matrix, is laid in the central palatine area, 
 to insui'e slioht surplus in this i-egion on closing the flask. 
 
 MATRIX PACKKD liKADY FOR CLOSING THE FLASK 
 
 When both basic rubber and gum facing have been introduced 
 and thoroughly condensed, the case is ready for the final 
 steps preparatory to closing the flask. 
 
 When diatoric teeth are used it is necessary, in packing 
 the matrix, to fill the central depressions of the bicuspids and 
 
 molars with small pieces of basic rubber. This is an essential 
 part of the packing process and is necessary in order that the 
 anchorage spaces within the teeth for the rubber may be per- 
 fectly filled in the final closing of the flask. 
 
PbASKING WAX MODEL DENTURES 427 
 
 GAUGING THE AMOUNT OF RUBBER REQUIRED 
 
 Tlie amount of basic material required is entirely de- 
 pendent on the extent to which absorption of the residual 
 ridge has progressed. AVhen extensive, more rubber will be 
 required than when the ridge is prominent. 
 
 A simple method of testing approximately the proper 
 amount of rubber required to till the matrix, is to collect all 
 of the wax and baseplate material removed from the matrix, 
 
 WATEK GAUGE FOR DETERMINING THE 
 
 VOLUME OF RUBBER REQUIRED TO 
 
 FILL THE SL\TRIX 
 
 work it up into a solid, compact mass and test its bulk by 
 displacement of water as follows : 
 
 A glass is filled to overflowing with cold water. Into 
 this the wax, held on the point of a small instrument, is im- 
 mersed, which, of course, displaces an equal bulk of water. 
 The wax is then removed, the required amount of gum fac- 
 ing — usually about one-half sheet — is placed in the glass, and 
 sufiScient basic material is added to again bring the water to 
 the point of overflow of the glass. A slight addition should 
 be made to compensate for the wax that adhered to the pins 
 and was lost by washing the matrix with hot water. 
 
 Dr. E. T. Starr suggested the use of a glass vessel hav- 
 ing two adjustable pointers attached to a perpendicular post 
 held by means of top and bottom bands. The top pointer 
 was set at high-water mark, as established by the introduc- 
 tion of the wax. The lower pointer was set at low- water 
 
428 FbASKING WAX MODEL DENTURES 
 
 mark, determined by removal of the wax. Sufficient rubber, 
 both facing and basic material, was added to raise the water 
 to the upper pointer. The use of this appliance obviated the 
 overflow of the water. 
 
 FLASK CLOSING 
 
 PRELIMINARY CONSIDERATIONS RELATIVE TO FLASK 
 CLOSING 
 
 Previous mention has been made of the crystalline char- 
 acter of plaster, its tendency to crush under pressure when 
 the modulus of resistance to stress of the crystals has been 
 reached, and of its greater resistance to stress when in a dry 
 condition than when saturated, or even slightly moistened 
 with water. 
 
 These facts are of vital importance in vulcanite denture 
 construction, for when disregarded, distortion of the cast, of 
 the matrix side of the flask, or of both, is very liable to occur. 
 When so occurring, the result is frequently a partial or total 
 loss of adaijtation of the denture to the tissues. 
 
 ESTIMATING THE FORCE EXERTED BY THE SCREW 
 
 Few prosthetists realize the enormous pressure capable 
 of being exerted on both the cast face and the opposite matrix 
 walls when the latter contain a considerable quantity of ex- 
 cess rubber, the flask being completely closed at a rapid rate 
 and under direct screw pressure. The rule for estimating 
 the force exerted by a screw is stated as follows : 
 distance between 
 P : W : : contiguous threads = ir X twice the length of 
 lever. 
 Explanation 
 
 P = power, indicates the amount of force exerted on 
 
 the end of the lever or wrench handle. 
 W = weight, indicates the load moved by the screw in 
 advancing through the nut or the force ap- 
 plied against the excess rubber. 
 Distance between contiguous threads of screw refers to 
 
 pitch of screw. 
 IT = pi, is the Greek letter used to indicate that num- 
 ber — 3.1416 — which, when multiplied by the 
 diameter of a circle = the circumference. 
 The lever or wrench represents the radius of the circle 
 described by the end of the handle in revolving the nut around 
 
FLASKING WAX MODEL DEXTUKES 429 
 
 the screw. To fiud the diameter of the circle, the radius must 
 be doubled. 
 
 Ill applying this rule to determine the force exerted by 
 the flask screws, the principal factors concerned are as fol- 
 lows: 
 
 First. The power delivered on the end of the wrench 
 handle by the hand. 
 
 The record of over two hundred tests made by pros- 
 thetists under the writer's observation, with a specially de- 
 
 DIAGItAlI SHOWING .Mil' DESC'IilBEI) ISY FLASK WRENCH 
 
 signed wrench capable of registering the pounds pressure ap- 
 plied, showed a range of from 15 to 80 pounds exerted on the 
 end of the four-inch handle. The low average of the total was 
 50 pounds. 
 
 Second. The ivcight, or second factor, represents the 
 force exerted )jy the surplus rubber against the cast in one 
 side, and the matrix walls and teeth in tlie opjtosite side of the 
 flask, as tli(! screw jiressure forces out the excess material. 
 This, of course, is an unknown quantity, but is determined I'y 
 the rules of proportion in the usual manner. 
 
430 PLASKING WAX MODEL DENTURES 
 
 Third. The distance between tivo continuous threads 
 represents the approach of the two halves of the flask to each 
 other in revolving the nut once around by means of the 
 wrench. The threads on the average flask bolts are 1-20 of 
 an inch apart, or, as ordinarily spoken of, the 'pitch of the 
 screw is 1-20. 
 
 Fourth. The fourth term of the proportion is deter- 
 mined as follows: Multiply the length of the wrench by 2, 
 which gives the diameter of the circle, in inches, traversed by 
 its outer end. This multiplied by .3.1 41G will give the circum- 
 ference of the circle in inches. 
 
 With three factors known, the fourth can easily be found. 
 The following example will serve to illustrate the enormous 
 force commonly delivered against the cast face in flask clos- 
 ing: 
 
 Number of pounds applied to the end of the 
 
 wrench handle -t inches long 50 
 
 Force exerted against cast face by excess rubber 
 
 under pressure X 
 
 Distance between two contiguous threads 
 
 1-20 of an inch 
 
 Circumference of circle described bv end of 
 wrench 3.1416 X 2 X4 = 25 +. 
 
 Formula, 50 : X : : 1-20 : 25 -f . 
 
 Multiplying the two extremes = 1250. 
 
 Dividing 1250 by 1-20 to determine the other 
 mean =25000.' 
 
 Deducting 2-3 for friction, gives 8333 pounds ex- 
 erted on cast face. 
 
 Accompanying tests made by tlie writer in a specially 
 designed compression dynamometer revealed the fact that a 
 face plate with one inch superficial area could be forced from 
 1-16 to l^ inch into hardened and comparatively dry plaster 
 at 2,000 pounds pressure, and 14 to % inch in well hardened 
 plaster, set four hours. It will thus be seen that distortion of 
 both cast and matrix may readilj'' occur under the pressure of 
 over four tons as ordinarily applied. 
 
 The only redemption from failure in denture construc- 
 tion in every case is due to the fact that the rubber is plastic 
 and does not resist the force of the screw, as would a hard, 
 unyielding material. When the closing of the flask is forced 
 too rapidly, however, with a large amount of excess rubber 
 present, the effect is practically equivalent to that produced 
 with a hai'd, unyielding material interi^osed. This is often 
 
PLASKING WAX .MODEL DENTURES 4ai 
 
 seen in fractured casts and distorted surfaces in the tinal 
 opening of the flask. 
 
 Five pounds of power on the end of the wrench handle 
 represents the maximum force that should he applied in flask 
 closing. Even this amount, limited as it is, yields a pressure 
 of over 800 pounds on fhr cast face. 
 
 TEST CLOSING OF THE FLASK 
 
 To insure a sufficient quantity of rubber in the matrix 
 and yet obviate distortion of the cast face and matrix walls, 
 
 as a result of undue force, the following method will be found 
 satisfactory : 
 
 The matrix should contain very little excess rubber. The 
 proper amount ma.v be determined with comparative accuracy 
 by means of the water glass test previously described. 
 
 The flask should be gradually raised in tempei'ature to 
 212 deg. F., dry heat, the two halves brought together by 
 tightening the bolt nuts slowly, being careful not to exceed 
 five pounds force on the wrench handle, and when closed the 
 bolts are removed and the flask separated. 
 
 To prevent adhesion of the rubber to the cast surfaces 
 a square of muslin slightly larger than the area of the matiix 
 should be interposed between the two halves of the flask. A 
 piece of the cloth removed from the sheet rubber, when freed 
 from the sizing or starch, will answer this purpose. On opening 
 
432 PLASKfN(i WAX AKJDKL DK.XTURKS 
 
 flu! closed lia.sk the imislin can readily be removed from the 
 condensed rubber within the matrix without distortinj^- the 
 latter by moistening it with a pellet of wet cotton. 
 
 Close examination should be made to see tbat the matrix 
 contains sufficient rubber, usually determined by observing the 
 perijijieral surplus and by ajjplying i)ressure interiorly. If 
 delicient. additional rubber should l)e placed wliere required 
 anil tlie flaslc closed without relieating. 
 
 TREATMENT OF THE CAST SURFACES FOR VULCANIZATION 
 
 Just before tlic linal closing of the flask the surfaces of 
 the plaster cast should be well saturated with liquid silex, a 
 thick coating being applied and allowed to remain undisturbed 
 for two or three minutes, when the surplus may be removed 
 with a cloth or pellets of cotton. This film of silex penetrates 
 the surface of the plaster to a slight extent, fills the minute 
 openings between the crystals as well as the smaller air 
 spaces and gives a smooth, hard finish to the cast. As a result 
 the vulcanite will present a much smoother surface than when 
 pressed and hardened against an untreated plaster surface. 
 
 Casts formed from Spence's plaster, which on account 
 of its greater resistance to stress is preferable to plaster, 
 should bo covered with a layer of thin tin foil, usually No. 4. 
 The foil is first applied to the cast surfaces with the fingers, 
 the surplus removed with shears and final adaptation secured 
 with a soft napkin or pellets of cotton and pressure. 
 
 When adapted the foil is removed, the surface of the cast 
 is coated with a film of LePage's glue, the foil returned to 
 place and by pressure and burnishing conformed closely to 
 all surfaces of the cast. Sandarac or shellac varnish may also 
 be employed. Whatever adhesive agent is used it should be 
 applied in a thin coat and allowed to become somewhat sticky 
 before returning the foil to the cast. 
 
 To aid in the removal of the tin foil from the vulcanized 
 case the former should be covered with a film of soap, either 
 lather or liquid, the surplus being removed with pellets of 
 cotton and the film allowed to dry before closing the flask. 
 
 In case the tin foil cannot be readily stripped from the 
 denture after vulcanization it can be removed by the applica- 
 tion of mercury, rubbing it into the tinned surfaces with 
 chamois leather. 
 
 Casts formed from magnesium oxy-chloride require no 
 coating or preliminary treatment, the surfaces being suffi- 
 
FLASKlXd WAX .\U)I)KI> DK.XTURKS 4S;} 
 
 cieiitly siiKMitli 1(1 iiii|iart a dense and jiolislicd surface to the 
 vulcauite. 
 
 The steps ha\iii,i;- lieeii earried eut as deserilied, tlie pUis- 
 tei' contents of the tiask are now in a eomparatively dry and 
 hardened condition, the matrix liUed ^Yithout distortion of 
 its walls or the east face. 
 
 To prevent the rapid saturation of the now dry piaster 
 investment in the flask during vulcanization, the latter 
 should be placed above the water in the vulcanizer, and 
 hardened in steam instead of under water, as is the usual 
 method. ( 'ases so manipulated often come from the vulcan- 
 izer with the plaster almost as hard and capable of resisting 
 stress as when first introduced. 
 
 SCREW PRESSES 
 
 Screir -presses are frecjuently employed for closing 
 flasks. These appliances have screws of different pitches, 
 ranging from 1-10 to 1-16. which with a sliort handle vield 
 
 DOUBLE HAXni.E FI.ASK CLOSING riU:SS 
 
 1 HEW 1 12 I'lTCH 
 
 less force than a screw of less pitch, as 1-20. The handles 
 of most flask jiress^s, however, are double, permitting the 
 use of both hands in closing, so that an equal, or gi-eater, 
 amount of force can be developed by means of the press with 
 double handle than with the flask wrench. 
 
 Spring devices, as the Donham or Wilson flask presses, 
 are designed for maintaining the partially closed over-packed 
 
KLASKINC WAX MOIJKL UKNTUKKS 
 
FbASKING WAX MODEL DENTURES 435 
 
 flask under continuous pressure until the elevation of tem- 
 perature within the vulcanizer renders the rubber sufficiently 
 plastic to escape into the space provided, without subjecting 
 cast or matrix to excessive pressure or crushing strain. 
 
 In the vulcanization of thick, bulky masses of rubber, 
 spring closing devices are of decided advantage, for the rea- 
 son that when excessive expansion of the mass occurs, the 
 spring yields, allowing the flask to open slightly, thus re- 
 lieving the matrix walls and east face from undue stress. 
 Later on when contraction sets in, the resiliency of the spring 
 will again force the flask together. 
 
C II A PT K If X XII 
 
 VULCANITE 
 
 In prostlietie operations, ndvaiilzathni is ilic process 1j\' 
 wliicli rubber as prepared for dental i)urposes is changed 
 from a plastic state to a hardened condition capable of re- 
 taining its molded form and of resisting stress. 
 
 Eubber so treated is termed vulcanite, and the apparatus 
 by means of which the i)rocess is carried out is called a vul- 
 canizer. 
 
 In order to have a clear understanding of the process of 
 vulcanization it will be necessary to learn something of the 
 origin and physical properties of both crude and manufac- 
 tured rubber, and of the chemical changes which occur dur- 
 ing the liardening process. 
 
 RUBBER 
 
 Eubber is a colloidal substance obtained by evaporating 
 the juice derived from various sjoecies of tropical trees, 
 shrubs, vines and creepers. The first importations of im- 
 portance of this material into Europe, in the form of bags 
 and bottles, occurred in the early part of the eighteenth cen- 
 tury, but its real origin was apparently unknown. From the 
 fact that it was foiind very useful in rubbing out lead-pencil 
 marks it was called rubber. The name India was applied to 
 it because the-early jshipments came from the West as well 
 as the East Indies. 
 
 Brantt states that "In 1735 La Condamine first discov- 
 ered that the substance was the dried milky juice of a tree 
 which the Indians on the coast of the Amazon River called 
 Caout-Chouc and from which, from time immemorial, they 
 had been making waterproof fabrics, shoes, vessels, etc." 
 
 CAOUTCHOUC 
 
 It is a long story — the history of investigation concern- 
 ing the physical and chemical properties of caoutchouc. More 
 than one hundred and seventy-five years have elapsed since 
 La Condamine first discovered that it was of vegetable origin. 
 Many eminent chemists have devoted a great deal of time to 
 
VULCANITE 437 
 
 investigating this natural product, and yet to-day there are 
 some problems arising from the necessary mixture of caout- 
 chouc with other substances for commercial purposes, but 
 partially solved. 
 
 Carl 0. Webber, Ph. D., Crumpsall, Eng., whose work 
 is perhaps the most logical and up-to-date, in "The Chem- 
 istry of India Rubber" (1909), says in regard to the diffi- 
 culties attending investigations of this material: 
 
 "No class of bodies otters such formidable manipulative 
 difficulties to the investigating chemist as the remarkable 
 group of colloids comprised under the collective name of 
 India rubber. These difficulties are physical rather than 
 chemical — that is to say, they do not so much consist in the 
 functional complexity of the molecules of India rubber as in 
 the circumstance that these molecules are, at any rate at pres- 
 ent, known only with the colloidal state superimposed upon 
 them. Matter in this state does not exhibit the abrupt 
 changes of physical condition which, in crystalloids, take the 
 form of melting points, boiling points and solution. The 
 physical changes induced in colloids by heat, or by solvents, 
 are perfectly continuous changes as long as the underlying 
 chemical molecule or configuration remains intact. As a 
 consequence the characterization and identification of the col- 
 loids and their derivatives, and their isolation and purifica- 
 tion from mixtures of them, offers frequently almost insuper- 
 able difficulties." 
 
 Crude caoutchouc as it comes to market is of varying 
 and uncertain composition. A lot produced in a given local- 
 ity will oftentimes differ slightly in composition from another 
 lot from the same species of trees in a nearby localitv. 
 
 The juice when it first issues from the tree is milklike in 
 appearance and is termed lafex. It consists of more than 50 
 per cent water. On exposure to the air it loses most of the 
 moisture, is reduced in bulk, turns brown and becomes more 
 or less elastic. 
 
 The rubber gatherer in the native forests dips a clay- 
 covered paddle in the collected latex, gives it a few turns and 
 subjects the adhering film to the heat and smoke of an open 
 fire to evaporate the moisture rapidly, repeating the process 
 many times unt^l a good sized oval mass, termed a "biscuit," 
 is formed. 
 
 In this as well as various other crude methods of prepara- 
 tion, sand, dirt and other foreign matter become incorporated, 
 while covering an imperfectly evaporated layer with a fresh 
 one causes the retention of excess moisture. 
 
r.K VULCANITE 
 
 Recent methods whereby the latex, when freshly col- 
 lected, is subjected to the action of chemicals for the extrac- 
 tion of nndesirable constituents, have resulted in the produc- 
 tion of rubber of a superior quality. 
 
 One formula for Para latex and another for the rubber 
 after evaporation of the moisture are given below: 
 
 Latex Evaporated Juice 
 
 Water 55.15 Caoutchouc 94.6 
 
 Caoutchouc 41.29 Resin 2.66 
 
 Proteids • 2.28 Proteids 1.75 
 
 Sugar 0.36 Ash 0.14 
 
 Ash (Salts) 0.41 Moisture 0.85 
 
 Loss 0.51 
 
 100.00 100.00 
 
 Caoutchouc of commerce is prepared for manufacturing 
 purposes by first shredding it and washing to remove the 
 contained soluble constituents and foreign matter. It is then 
 thoroughly dried and passed through heated rolls to render 
 it again homogeneous. Caoutchouc prepared in this manner, 
 although comparatively pure, is adaptalile to but few pur- 
 poses because of its tendency to stick to objects it comes in 
 contact with, or when folded on itself. It also deteriorates, 
 and in time loses its elasticity and liecomes hard. 
 
 The discovery of a method of rendering soft rubber less 
 adhesive and more permanent was made by Charles Goodyear 
 of Boston in 1839, and Thomas Hancock of England in 1842, 
 Goodyear iDatented his process in 1843. While the methods 
 of these men eliminated the stickiness and improved the qual- 
 ity, the rubber was not hardened appreciably. Nelson Good- 
 year discovered a process of hardening rubber in 1849, which 
 process was, and is still, termed vulcanization. 
 
 The hardening of all varieties of rubber is rendered pos- 
 sible by the addition of sulphur. In the actual process of 
 hardening, the rubber may be subjected to the action of heat 
 and usually moisture, in a specially designed boiler termed 
 a vulcanizer. "Thin articles may be vulcanized cold by dipping 
 them in a cold mixture of 100 parts carbon disulphide and 
 2V2 parts of bichloride of sulphur for from IV^ to 3 minutes, 
 according to the thickness of the articles." (Braunt.) 
 
 The first experiments with rubber in denture construction 
 were made by Mr. Bevan of the Goodyear Rubber Company, 
 in conjunction with Dr. Putnam of New York, and Dr. Mal- 
 lett of New Haven in 1853. Their vulcanizer weighed 1,200 
 pounds. (Harris, 1871.) 
 
VUIA'ANITE 431) 
 
 FORMULAS FOR DENTAL RUBBERS 
 
 The following formiilae for various colored rubbers used 
 for dental purposes are those furnished by Dr. Wildman: 
 
 Dark Dark Grayish Jet Ma- 
 
 Brown Red Pink White Black Black roon 
 
 Caoutchouc 48 48 48 48 48 48 48 
 
 Sulphur 24 24 24 24 24 24 24 
 
 Vermilion 36 10 30 
 
 White Oxide of 
 
 Zinc 30 96 
 
 Ivory or Drop 
 Black 24 48 6 
 
 Per cent of Caout- 
 chouc in mass. . 66 44 43 22.6 50 40 44 
 Various shades of red and pink rubber are produced by 
 modifying- the percentage of vermilion; maroon, by increas- 
 ing or decreasing the black pigment. 
 
 VULCANIZABLE RUBBER EMPLOYED FOR DENTURE 
 BASES 
 
 Red, maroon and black varieties of rubber of the best 
 quality, in addition to sulphur, contain a comparatively small 
 percentage of inert material usually represented by the col- 
 oring pigments employed. Because of their greater strength 
 and elasticity, the better grades of rubber should, as a rule, 
 be employed for baseplate purposes. 
 
 Cheap grades of basic rubber are heavilj- loaded with 
 foreign material to reduce the cost. When present in any 
 considerable quantity they reduce the elasticity of the finished 
 product and render it brittle as well. 
 
 The cheaper grades of rubber, however, show less tend- 
 ency to become porous in vulcanizing than do the better 
 grades because of the comparatively low percentage of caout- 
 chouc present, grayish white in the table of formulas, show- 
 ing only 22 per cent of rubber. 
 
 PINK RUBBER EMPLOYED FOR GUM FACING 
 
 Since the "oasis of all vulcanized rubbers is a combination 
 of sulphur and caoutchouc, and the color of this mixture is 
 brown, it follows that in order to produce a pink the base 
 must be lightened by the addition of a white pigment. Wliite 
 oxid of zinc, and sometimes kaolin are used for this purpose, 
 to which vermilion is usually added for producing a pink 
 
440 VUIA'ANITIO 
 
 tint. Varying shades of this color may be produced l)\' modi- 
 fying the proportions of tlie pigments. The best products, 
 however, are but poor imitations of the natural gum tissues, 
 being dense, opaque and flat. 
 
 In full cases where the gum tissues are not visible the 
 dissimilai'ity is not so striking as in partial cases where the 
 natural gums are exposed to view. When possible to avoid 
 it, pink vulcanite should not be a]3plied when the line of junc- 
 tion of the artificial gum with the natural tissues will be 
 plainly apparent. 
 
 To overcome the objection of the fiat, lifeless appearance 
 of pink vulcanite, various substitutes have been offered, one 
 of the most satisfactory of which is that known as Granular 
 Gum Facing. 
 
 PINK GRANULAR GUM FACING 
 
 This gum facing consists of many minute particles of 
 various colored rubbers, pink, white, red and possibly a little 
 yellow, the pink largeh^ predominating, so united as to form 
 a homogeneous mass, yet not so blended that the particles 
 lose their individual tints. 
 
 As prepared for use it is lighter than the natural tissues 
 but darkens slightly during vulcanization. Although opaque 
 it does not appear as flat as the ordinary pink vulcanite, on 
 account of the variegated colors of which it is composed. 
 
 When this material is used for artificial giim facing, the 
 carving and polishing having been properly accomplished, it 
 presents the very best appearance of any of the pink varieties 
 of vulcanite and should be used in preference to the latter. 
 
 If on vulcanizing it presents a darker appearance than 
 desired, it may be lightened or solarized by placing in a glass 
 vessel, covei'ing with alcohol and bleaching in the sun for one- 
 half to three-fourths of an hour. Pink viilcanite can also be 
 lightened in the same manner. The tint so imparted will in 
 time disappear, but the favorable impression produced on the 
 mind of the patient is well worth the time expended. 
 
 THE CHEMICAL CONSTITUENTS OF RUBBER 
 
 Caoutchouc is classed as a colloidal hydrocarbon. When 
 subjected to the action of the best-known solvents the greater 
 portion, about ninety-five per cent, is brought into solution, 
 while about five per cent remains insoluble. The chemical 
 formula of the soluble portion is CoHie, while that of the in- 
 soluble constituent is C3oH„„Oin. The percentage of carbon 
 and hydrogen in the insoluble portion is the same as in the 
 
VULCANITE 441 
 
 soluble portion, as is seen in the following: C3oHgsOio= 
 
 (C,oHio)a + 10H,O. 
 
 Webber, whose researches in this field are perhaps the 
 most elaborate of any, refers to the insoluble constituent of 
 rubber as follows: 
 
 "In brief I suggest that this insoluble compound is a link 
 between India rubber and the complex carbohydrates, the 
 celluloses in particular, which I am inclined to consider the 
 raw material from which the plant produces all the terpenes, 
 including India rubber." 
 
 There is, on the other hand, no doubt that India rubber 
 absorbs oxygen when exposed to the atmosphere, and this 
 oxygen absorption finally always results in the conversion 
 of the India rubber into a brittle resinous body, generally 
 described as Spiller's resin. Spiller has published an analysis 
 of this bodv and gives the following figures : 
 C— 64 
 H— 8.46 
 0—27.54 
 
 "It is interesting to note that these figures very exactly 
 agree with the composition of a body of the for- 
 mula GinHisOio, the relation of which to our insolu- 
 ble constituent, CaoHssOio, is obviously significant. Equal- 
 ly interesting to observe is the fact immediately de- 
 ducible from the above given percentage composition 
 of Spiller's resin, that this oxidation of India rubber consists 
 purely and simply in the addition of oxygen to the unsatur- 
 ated India rubber molecule, and that consequently the car- 
 bon-hydrogen ratio of India rubber — 10:16 — remains un- 
 affected in this process. " * * * " From this we maj^ infer 
 that the oxygen percentage of India rubber in its free resin 
 state of purity is due to two factors, one of which is the 
 presence of the insoluble constituent, CsoHcsOu,, the other to 
 the formation of oxygen addition products of India rubber." 
 
 He further states that the insoluble constituent does not 
 seem to be present in all varieties of rulilier, and when present 
 it occurs in very small quantities. 
 
 CHEMISTRY OF VULCANIZATION 
 
 Webber further sums up the observations and results of 
 many experiments in the vulcanization of rubber as follows : 
 
 "From these facts we are justified in drawing the fol- 
 lowing conclusions: 
 
 "First — The India-rubber hydrocarbon, polyprene CioH,,, 
 combines with sulphur without evolution of hydrogen sul- 
 
442 VULCANITE 
 
 ])lii(l('. The vulcanization jn'occss of India rubber is, there- 
 fore, an addition process. 
 
 "Second — The insoluble constituent of India rubber, 
 which forms only an insignificant jDroportion of the chemical 
 ])roduct, not exceeding five per cent of the total, combines 
 with sulphur under vulcanizing conditions at a very slow rate, 
 with the evolution of hydrogen sulphide and with the forma- 
 tion of a substitution product. 
 
 "The process of vulcanization consists in the formation 
 of a continuous series of addition products — of polyprene 
 and sulphur, with probably a polyprene sulphide CiooHic„S as 
 the lower and CmdHie^jSoi. as the upper limit of series. Phys- 
 ically this series is characterized by the decrease in distensi- 
 bility, and increase in rigidity from the lower to the upper 
 limit. Which term of the above series, i. e., which degree of 
 vulcanization, is produced is in every case only a function of 
 temperature, time, and proportion of sulphur present." 
 
 "There arises now, of course, at once the question as to 
 the nature of the process by which siilphur enters into com- 
 bination with the polj^orene, whether the polyprene sulphide 
 or sulphides formed are addition or substitution products. 
 Certainly what we already know respecting the chemical na- 
 ture of India rubber leads us to infer that the vulcanization 
 in'ocess consists essentially in the formation of an addition 
 ])roduct of sulphur and polyprene. This assumption, how- 
 ever, requires further support in view of the fact that quite 
 a number of writers, from Payen to most of the recent authors, 
 declare tliat vulcanization is accompanied by the evolution of 
 sulphuretted hydrogen, thereby implying that the process is 
 a substitution and not an addition process. Indeed, most of 
 the recent authors on this subject state this in so many words. 
 We shall therefore have to subject this point to a careful 
 examination. 
 
 "Assuming the compound of polyprene and sulphur, 
 which indisputably forms in the vulcanization process, to be 
 a substitution product, it follows with absolute necessity that 
 for each 32 parts of sulphur combining with the polyprene we 
 must obtain 34 parts of hydrogen sulphide. Now in the proc- 
 ess of vulcanization as practically carried out, we obtain on 
 an average, say, 2.5 per cent of combined sulphur. Conse- 
 quently, the vulcanization of one ton of India rubber, on the 
 above assumption, would be bound to yield very nearly 60 
 pounds of hydrogen sulphide, or approximately 18,000 litres. 
 Considering that in a number of factories the amount of India 
 
VULCANITE 448 
 
 rubber vulcanized daily largely exceeds one ton weight, we 
 should expect to iiud the vulcanizing rooms of these factories 
 reeking with this gas. As a matter of fact, however, there is 
 scarcely ever a trace of this gas to be discovered in the rub- 
 ber works atmosphere, and the very rare cases in which its 
 presence becomes noticeable may always be considered as an 
 indication of something 'having gone wrong.' " 
 
 Webber 's work may be briefly summed up as follows : 
 
 That the hardening of rubber by vulcanization is brought 
 about by a chemical union of CioHie or polyprene with sul- 
 phur, resulting in the formation of a series of polyprene sul- 
 phides, not bj^ the breaking up of the CioHio molecules, but 
 by the addition to them of sulphur; that the formation of 
 hydrogen sulphide during the process of vulcanization is not 
 an essential chemical reaction, necessary to the hardening 
 of rubber; that when formed it is due to the presence of the 
 insoluble constituent — CsoHcsOjo — in the rubber; that when 
 the process of vulcanization is properly conducted, such slight 
 amount of hydrogen sulphide as is formed does not seriously 
 interfere with the quality of the hardened product; and, 
 finall}', that when hydrogen sulphide is formed in excessive 
 quantity it is an indication that something "has gone wrong," 
 and the quality of the vulcanite is impaired. 
 
 While Webber's observations seem generally logical, 
 there are some peculiarities occurring in the vulcanization of 
 certain classes of cases that require further study. For ex- 
 ample, thick cases in which there is a large bulk of rubber 
 present, frequently come from the vulcanizer in a porous con- 
 dition and with a strong odor of hydrogen sulphide, an indi- 
 cation of something having gone wrong. The same grade of 
 rubber may be employed in thin or even medium thick cases, 
 vulcanized under the same conditions of temperature, time, 
 and moisture, or at the same time in the same apparatus, yet 
 show no porosity, nor will the odor of hydrogen sulphide 
 be perceptible. 
 
 The cause of this is not clear. If Webber's observations 
 are correct that the development of hydrogen sulphide is due 
 to the presence of -the insoluble constituent in the rubber,, and 
 the same grade of rubber is used in both cases, why should 
 not the case containing less bulk show at least a proportion- 
 ate amount of porosity, accompanied by an appreciable 
 amount of hydrogen sulphide? 
 
 Two hundred blocks of vulcanite, %x%x% inches, in all 
 
144 VULCANITE 
 
 oi' wliicli iiiartically the .same grade of rubber was used, when 
 sawed throTigh the center, sliowed tlie following results: 
 
 125 blocks, very ]Joroias. 
 25 blocks, slightly porous. 
 50 blocks, non-porous. 
 
 These cases were all vulcanized in the same apparatus, 
 and under as nearly the same conditions of time and tem- 
 perature as possible, yet seventy-five per cent were porous, 
 while twenty-five per cent were solid. The most porous blocks 
 were bulged out slightly, while some of the semi-i^orous and 
 all of the solid blocks showed some contraction. The above 
 tests were made for the purpose of illustrating the variation 
 in liorosity of the dilTerent blocks and were not tested for 
 dimensional change. 
 
 Wilson suggests that the expansion of the rubber in the 
 matrix, which occurs before and possibly continues for a 
 short time after the vulcanization point is reached, depletes 
 the matrix of some of the solid material. This having escaped 
 beyond the bounds of the matrix cannot return when con- 
 traction later occurs, being prevented from doing so, first, by 
 the natural sluggishness of the rubber, and, second, because 
 as soon as vulcanization sets in the rubber next the outer sur- 
 faces of the matrix forms a constantly hardening crust, which 
 effectually prevents its return, and, third, the surplus itself 
 being usually disposed in thin layers is quickly hardened by 
 the vulcanizing process. 
 
 Now, as vulcanization proceeds, the interior of the bulky 
 mass not yet hardened continually contracts, usually toward 
 the hardened outer shell, resulting in the development of many 
 internal spherical spaces, the formation of a partial vacuum, 
 and on account of the heat attained, the hydro-carbon may 
 be decomposed and unite with the sulphur to form sufficient 
 HoS gas to fill the space. 
 
 Whatever the cause, the fact remains that porous condi- 
 tions frequently develop during vulcanization, oftentimes to 
 such an extent as to require reconstruction of the denture. 
 
 POROSITY OF VULCANITE AND HOW TO OVERCOME IT 
 
 Any means, therefore, that can be employed for reducing 
 the excessive bulk of rubber without materially increasing the 
 weight or disturbing the required contour of the case might 
 be advantageously used for overcoming porosity. 
 
VUIA'ANITB 44G 
 
 Several methods, haviiis;- tliis end in view, will here he 
 mentioned : 
 
 Firf:f — The haseplate itself may be formed in wax so as 
 to represent one-half or more of the required bulk of the fin- 
 ished denture. This may then be vulcanized, after which the 
 teeth are occluded upon it, the deficient contour developed in 
 was and the case revulcanized. 
 
 This method is specially applicable to lower cases where 
 the alveolar border is almost completely absorbed and where 
 the establishment of normal profile and bite requires that the 
 teeth shall be set high above the border crest. It may also be 
 used to advantage in badly absorbed ridges in upper cases. 
 While this method does not reduce the bulk of rubber, the 
 process of vulcanization is divided into two stages, which in 
 practically every case will avert porosity. 
 
 Second — When for any reason the double vulcanization 
 method is not considered advisable, these and similar cases 
 may be carried out as follows : 
 
 The wax model denture is flasked in the usual manner. 
 Pink gum facing is applied to the labial and buccal walls of 
 the matrix. Tlie lingual wall of the matrix is lined with basic 
 material which sliould be carefully applied so as to leave no 
 open spaces in the lining. This leaves the central portion or 
 body of the matrix still unfilled. Into this space blocks of old 
 vulcanite, cut in such manner as to fit into the opening with- 
 out disturbing the packed rubber, are placed. The blocks 
 should not extend so high as to interfere with the alveolar 
 ridge of the cast when the two halves of the flask are closed. 
 
 Additional basic rubber is now laid over the blocks, ex- 
 tending from the inner to outer periphery of the matrix, thus 
 entirely covering or sealing them in, so that none of the old 
 rubber will be exposed to view when the case is finally fin- 
 ished. Sufficient excess should be present to insure all spaces 
 between the blocks and matrix walls being filled on closure 
 of the flask. 
 
 Third — Blocks of aluminum or tin may be employed in- 
 stead of vulcanite, the technic of application being similar to 
 that just described.- When a considerable space is to be filled, 
 aluminum is preferable to the tin on account of its lighter 
 specific gravity. When either of these or similar metals are 
 inclosed, the weight of the denture will increase. 
 
 Fourth — The interior of the matrix may be filled in with 
 pink or white rubber, each of which is heavily loaded with 
 
446 VULCANITIO 
 
 iiiorl I'oreii;.'!! inalciial, as tlic oxide ui' zinc or white kaoliu. 
 These rubbers, even in excessive bulk, seldom ever become 
 porous in vulcanization. 
 
 CLOSING FLASKS WITH SPRING PRESSURE 
 
 To compensate, in part at least, for the excessive con- 
 traction which occurs iu bulky cases during vulcanization, the 
 closing of the flask with spring pressure is advised. 
 
 The matrix is ]jacked in the usual manner, slightly in 
 excess of the amount actually required to fill the space. The 
 flask is set in a spring press of the Wilson or Donham type, 
 and the screw turned to develop sufficient tension in the spring 
 to force the flask together, as the rubber becomes semi-liquid 
 with rise of temperature. 
 
 Since closure of the flask is not accomplished immedi- 
 ately but is extended over a considerable period of time, in 
 
 FI,ASK WITH BOI-T SPRINGS IX TOSITION 
 
 many cases not until the hardening process begins, it is argued 
 that the expansion in the mass of rubber, due to heating, is 
 over before all of the excess is removed from the matrix. 
 Space is thus provided for some of the last excess by the eon- 
 traction of the mass of rubber which begins with the harden- 
 ing process. 
 
 Stated differently, some of the excess rubber is thus fed 
 into the constantly contracting mass until the hardening proc- 
 ess is well under way. The resulting vulcanite shows greater 
 density with less contraction than when the flask is completely 
 closed before introduction into the vulcanizer. 
 
 All forms of spring-flask closing devices are designed, 
 primarily, to partially compensate for excessive contraction in 
 the mass of rubber by prolonging the closing process through- 
 out the greater portion of the contractile period. Second- 
 arily, the use of springs obviates excessive stress on the 
 matrix walls and thus reduces the tendency toward distortion. 
 
VULCANITE 447 
 
 Dr. Geo. B. Snow suggests the use of small spiral springs 
 interposed between the nuts and flask top. When applied, the 
 flask need not be fully closed, but the springs must be com- 
 pressed so that as the rubber becomes plastic with rise in tem- 
 perature, the resiliency in the springs will effect complete 
 closure. 
 
 DIMENSIONAL CHANGES OCCURRING IN RUBBER DUR- 
 ING VULCANIZATION 
 
 EXPANSION 
 
 Two distinct changes occur in rubber during the vulcan- 
 izing process, viz., tirst, expansion, followed by contraction. 
 
 The expansive movement, which is very decided, begins 
 with the first application of heat and continues until shortly 
 after the hardening process sets in. The lowest point at 
 which rubber begins to vulcanize or harden is approximately 
 around 240 degs. F., while the highest point at which it may 
 safely be conducted, without causing detrimental chemical 
 change, is 320 degs. F. 
 
 During the initial heating of a ]iacked and closed flask, 
 up to the lowest point of vulcanization, the matrix having been 
 full and waste gates formed as described, the rubber flows 
 outward into the spaces so provided as a result of expansion 
 due to rise in temperature of the mass. 
 
 In case no waste gates are jn-esent and the flask, fully 
 packed, is closed before introducing into the vulcanizer, dis- 
 tortion of the matrix will usually occur, the amount depending, 
 first, upon the excess of rubber present, and second, upon the 
 tendency of the matrix walls to yield under stress or com- 
 pressive force, and third, upon the temperature of the applied 
 heat. 
 
 That the ex])ansive force of rubber is very positive and 
 powerful as well is frequently seen in the distortion of matrix 
 walls and cast surfaces, which distortion if wrought directly 
 would require the application of heavy mechanical force. 
 
 CONTRACTION OF RUBBER 
 
 The contractile movement sets in shortly after the rub- 
 ber begins to harden and continues throughout the vulcanizing 
 process in a moderately definite ratio, the amount depending 
 upon the functions of time and tem])erature of applied heat. 
 
 Since no appreciable amount of excess rubber, which from 
 anj' cause has been expelled, can return to the matrix, it natu- 
 
44S VULCANITE 
 
 rally follows that as contraction of the essential body of ma- 
 terial occurs, there being no means of replenishing it as it 
 becomes reduced in bulk, warpage of the baseplate is very 
 liable to occur since the mass no longer completely fills the 
 matrix space. 
 
 At times contraction of the rubber is so marked that 
 spaces develop between the vulcanite and the teeth, while 
 that enclosing tlie pins contracts in such manner as to almost 
 release the latter. When such a condition arises the teeth will 
 frequently he found loose, can rc^adily be moved in their 
 
 THIS CUT SHOWS A FLASK FORCED AND 
 HELD APART ONE-EIOHTH INCH BY THE EX- 
 PANSION OP RUBBER DURIXC VULCANIZA- 
 TION. THE SPRING EXERTED A PRESSURE 
 OF OVER 500 LBS. 
 
 matrices, and will be easily displaced under stress. When the 
 denture is subjected to use, the spaces become filled with food, 
 which, as it decomposes, gives rise to disagreeable odors. 
 Cases in which marked contraction occurs usually require re- 
 construction. 
 
 VULCANIZERS 
 
 The apparatus in which the flasks containing the packed 
 rubber are placed while hardening is called a vulcanizer. It 
 consists of a l)oiler usually large enough to hold two or three 
 flasks, and is commonl>- made of seamless hammered copjier, 
 the walls of which are about one-eighth of an incli tliick. 
 
VULCANITE 449 
 
 The top margin of the boiler is turned true and polished 
 and to this a cap or cover is fitted for confining the steam. 
 The cap is usually grooved to receive a packing of graphite, 
 steam-proof fiber or metallic lead, to seal the boiler tightly 
 and prevent the escape of steam during vulcanization. 
 
 Various method.s are employed for fastening the top to 
 the boiler, the most convenient of which is by means of a cross- 
 bar hinged to one side of the boiler. When the cover is ad 
 justed, the bar rests upon it and is bolted to the opposite side 
 with a single bolt. 
 
 As before stated, the boiler is usually made of hammered 
 or pressed copper, without brazed or soldered joints, so as 
 to resist the expansive force of steam to which it is subjected 
 during vulcanization. Cast boilers of copper, brass or iron, 
 unless made specially heavy, are liable to prove defective and 
 leak or burst with use. Explosions are by no means rare, and 
 such accidents are always dangerous. Every precaution, 
 therefore, should be taken to obviate them, first, in the selec- 
 tion and use of the most trustworthy and well-constructed 
 appliance it is possible to secure, and second, in bestowing the 
 proper care upon it while in use. 
 
 SAFETY DEVICES 
 
 To tlie lid of the vulcanizer is usually attached various 
 devices for registering temperature or indicating pressure 
 within the appliance, those most commonly employed being 
 the thermometer and the steam gauge. 
 
 THE THERMOMETER 
 
 An attached thermometer enclosed within a metal case 
 indicates the temperature. The base of the thermometer case 
 screws over a projection on the vulcanizer cover. 
 
 The center of the projection is bored out to make a reser- 
 voir for containing mercury. In this mercury bath the ther- 
 mometer bulb rests and by tliis means the thermometer has 
 a direct metallic connection with the interior of the vulcanizer 
 through the mercury and the metal cover. The metal casing 
 of the thermometer -should be removed from the vulcanizer 
 cap from time to ■+ime to see that the depression contains the 
 required quantity of mercury, i. e., sufficient to surround the 
 thermometer bulb. When the bulb does not rest in the mer- 
 cury bath the temperature reading will be much lower than 
 the temperature of the steam within the vulcanizer. The re 
 
■150 VULCANITE 
 
 suit in such cases is that if the temperature is raised to the 
 vulcanizing point as indicated by the thermometer, the con- 
 tents of the flask will in all probability be ruined by overheat- 
 ing. Deficient mercury in the depression oftentimes accounts 
 for the safety valve of the vulcanizer blowing off before the 
 thermometer registers the vulcanization point. 
 
 THE STEAM GAUGE 
 
 Since a definite ratio exists between steam pressure and 
 temperature, a steam gauge of ordinary type and connected 
 to the vulcanizer cover in the usual way may be used in con- 
 junction with or independent of other registering devices. 
 
 TABLE OF STEAM PRESSURE 
 
 The following table, showing the relation of temperature 
 to pressure of heated or unconfined, and superheated or con- 
 fined steam, is furnished by the Buffalo Dental Manufactur- 
 ing Co.: 
 
 Degrees Steam pressure 
 
 Fahrenheit per square inch 
 
 212 
 
 220 2 
 
 230 6 
 
 240 10 
 
 250 15 
 
 260 21 
 
 270 27 
 
 280 34 
 
 290 43 
 
 300 52 
 
 310 63 
 
 320 75 
 
 330 89 
 
 340 104 
 
 350 120 
 
 360 140 
 
 370 160 
 
 380 180 
 
 390 205 
 
 400 234 
 
 410 264 
 
 420 296 
 
 430 335 
 
VULCANITE 451 
 
 Degrees Steam pressure 
 
 Fahrenheit per square inch 
 
 440 375 
 
 450 410 
 
 460 455 
 
 470 515 
 
 480 565 
 
 490 603 
 
 500 663 
 
 510 721 
 
 520 798 
 
 530 864 
 
 540 937 
 
 550 1015 
 
 It will be noted that the elastic force of steam increases at 
 a rapid rate and not in direct proportion to rise of tempera- 
 ture. For example: 
 
 At 220° F. the pressure is 2 lbs. By steps of 50 degrees the 
 increase is very marked. 
 
 270° F. the pressure is 27 lbs., an increase of 25 lbs. 
 
 320° F. the pressure is 75 lbs., an increase of 48 lbs. 
 
 370° F. the pressure is 160 lbs., an increase of 85 lbs. 
 
 420° F. the pressure is 296 lbs., an increase of 136 lbs. 
 
 470° F. the pressure is 515 lbs., an increase of 219 lbs. 
 
 520° F. the pressure is 798 lbs., an increase of 283 lbs. 
 
 Without suitable means for controlling the temperature, 
 or without almost constant watching of the vulcanizer, over- 
 heating or burning of the rubber during the hardening process 
 is very liable to occur. 
 
 GAS REGULATORS 
 
 To avoid the necessity of constant supervision of the vul- 
 canizer when in use and still maintain a uniform and effective 
 working temperature, an appliance called a gas regulator can 
 be used for controlling the amount of gas supplied to the 
 burner. By proper adjustment of the regulator the gas sup- 
 ply to the burner will be reduced when the temiDerature rises 
 above the point of . vulcanization determined upon and at 
 which the pointer of the regulator was previously set. 
 
 TIME REGULATORS 
 
 To further reduce the responsibility of the prosthetist, a 
 time regulator can be attached to the gas supply pipes, which 
 
152 VUhCANI'I'K 
 
 will mitomatically out off the fuel at wliatevcr time tlie eluek 
 is set. By combining the gas regulator with the time regula- 
 tor, the prosthetist introduoes the flask, closes the vulcanizer, 
 turns on and lights the gas and leaves the apparatus to itself, 
 when, without furtlier attention, the case is vulcanized and 
 the gas automatically shut off. Before lighting the gas the 
 lever arm of the clock which controls the gas valve should 
 
 f 
 
 AUTOMATIC GAS BEGtLATOR 
 
 VULCAHIZER WITH GAS AND TIME 
 KEGULATOK ATTACHMENTS 
 
 be set on the threaded spindle of the hour hand at such point 
 as to allow time for the temperature to rise to vulcanizing 
 point and further to allow time for vulcanization to occur as 
 well. 
 
 Appliances of this type are not a luxury but a necessity 
 in every well equipped dental laboratory. 
 
 THE SAFETY VALVE 
 
 Every vulcanizer should have attached to it a device 
 called a safety i^nhe, which, when the pressure within the 
 
VULCAN' ri'K 
 
 boiler exceedb soiin^wliat the high vulcanizing picssiue, will 
 automatically open and release the steam. 
 
 The simplest device of this type consists of a tube screwed 
 into the top of the vulcanizer. The outer end of the tube is 
 fitted with a screw cap having a hole in the center. The open- 
 ing through the cap and tube leads directly into the 
 vulcanizer. By removing the cap, placing a disc of thin 
 copper foil over the end of the tube and replacing the cap 
 
 SAFETY VALVE AND BLllW OFF ATTAl'IIMEXT FOR A'ULCANIZER 
 
 Screw Cap 
 
 Brass Washer- 
 Safety Disk dgSB 
 
 Styd 
 
 DETAIL OF SAFETY VAL^•E 
 
 DETAIL OP HLOW OFF VALAE 
 
 tightly, the vulcanizer chamber is thus sealed. The copper 
 foil disc usiTally breaks when the pressure exceeds 350° F., 
 considerably above vulcanizing temperature, but well below 
 the tensile limits of the boiler, thus avoiding danger of 
 explosion. This- safety valve is independent of thermometer, 
 gas or time regulator or steam gauge and will work when 
 other means fail, providing, however, that reasonable atten- 
 tion is given it to see that the tube, both internally as well as 
 externally, of the disc does not become clogged. 
 
454 VULCANITIO 
 
 VULCANIZATION OF CASES IN WHICH AUTOMATIC 
 FLASK CLOSING DEVICES ARE USED 
 
 rractieally all doiitai riihlxTs are su compouiKled that 
 when heated to 320° F. and maintained at that temperature 
 for one hour thej- will vulcanize. From twenty-iive to forty 
 minutes are usually required to raise the temperature within 
 the apparatus to the vulcanizing point so that the actual time 
 consumed in the process of hardening the rubber ranges from 
 eighty-five to one hundred minutes. Bulky cases should be 
 vulcanized at the same temperature, but for a somewhat 
 longer period, since large masses of rubber naturally require 
 more time to harden than do those of less bi;lk. 
 
 It is the opinion of the writer, based upon many experi- 
 ments in the vulcanization of all classes of cases, bulky and 
 otherwise, that the use of automatic springs for closing the 
 flask in the preliminary stages of vulcanization will result, 
 first, in less dimensional change of the matrix; second, in a 
 thicker external shell being formed, and third, in a denser 
 quality of vulcanite when hardened. 
 
 These observations coincide very closely with extensive 
 experimental work carried on liy Dr. Gr. H. Wilson, and which 
 is described in detail in his work, Dental Prosthetics. (1914, 
 Lea & Febiger.) 
 
 When automatic closing devices are used, space should 
 be provided for the escape of surplus rubber. This should 
 be in the form of a groove of ample size, close to and extend- 
 ing entirely around the periphery of the matrix, but with no 
 gateway connections leading from the mati'ix to the space. 
 
 VULCANIZATION OF CASES IN WHICH THE FLASKS 
 
 ARE CLOSED AND BOLTED BEFORE PLACING 
 
 THEM IN THE VULCANIZER 
 
 To avoid excessive dimensional change in the matrix dur- 
 ing vulcanization, in those cases in which the flask is closed 
 and bolted before placing in the vulcanizer, the following con- 
 ditions must be observed: 
 
 The case should be treated as described under the head- 
 ing, "Test Closing of the Flask." 
 
 In this, as in all methods of vulcanization, the case should 
 be placed above water and the process conducted in an at- 
 mosphere of steam. 
 
 From thirty to forty minutes' time should be allotted in 
 raising the case to vulcanizing temperature, which, in this 
 instance, is lower than by the method just described. 
 
VULCANITE 455 
 
 Vulcanization should be conducted at a temperature rang- 
 ing from 290° F. to 300° F. and for a period varying from 
 two to two and one-half hours. 
 
 It is the belief of the writer that, although the rubber is, 
 in all probability, in the most liquid condition at the highest 
 temperature, it also exerts the greatest expansive force be- 
 tween 300° F. and 320° F. 
 
 If this assumption is true, it will thus be seen that by this 
 method the matrix is relieved of considerable expansive force, 
 which, if permitted to develop, would result in distortion. 
 
 SUMMARY OF FACTS OF IMPORTANCE IN REGARD TO 
 VULCANIZATION 
 
 The important facts in regard to vulcanization may be 
 summed up as follows : 
 
 When automatic flask-closing devices are used, cases may 
 be satisfactorily vulcanized at 320° F. for a period of one 
 hour, or, when bulky, at the same temperature for a longer 
 period. 
 
 When flasks are closed and locked before introducing in 
 the vulcanizer the process should be conducted at a tem- 
 perature not exceeding 300° F., preferably slightly lower, 
 and for a sufficient length of time to induce the proper de- 
 gree of hardness in the vulcanite. The time may range from 
 two to three hours, depending on the bulk of material and the 
 quality of the ru1)ber employed. The actual time can only be 
 determined by suitable tests for any particular rubber. Such 
 tests, when once made and recorded, serve as a basis for sub- 
 sequent operations. 
 
 REMOVAL OF THE FLASK FROM THE VULCANIZER 
 
 From ten to fifteen minutes should elai)S(', after vulcan- 
 izing a case, before opening the blow-off valve for the release 
 of the steam. It should then be opened but slightly so that 
 the pressure may be gradually reduced. Wiien opened widely, 
 so that the steam pressure within the vulcanizer is lowered 
 suddenly, before that within the flask, the contents of the lat- 
 ter will frequently -become distorted. 
 
 REMOVAL OF THE DENTURE FROM THE FLASK 
 
 On removal of the flask from the vulcanizer, and before 
 opening, it should be placed in cold water for another ten or 
 
456 VUbCANITK 
 
 lifteen inhiutcs, or until the jilaslcr and (Icnluri' ari' thor- 
 oughly C'hill(Ml. otlicrwise warpagc ol' the case will occur at 
 this stage. 
 
 When chilled, the bolts are removed and the fiask care- 
 fully pried apai't. Sometimes it is advisable, when the plaster 
 contents of the fiask have not become softened to any extent 
 in vulcanizing, to remove the top of the flask and with a knife, 
 carefully remove the plaster from the outer surfaces of liu' 
 denture, being careful while doing so not to mar the denture 
 base or fracture the teeth. 
 
 VULCANITE LATHE BUItS 
 
 The fiask is then separated, the plaster beneath the den- 
 ture nndermined and the cast and denture pried ont. Re- 
 moval of the surrounding plaster is a simple matter. The 
 case should then be thoroughly scjubbed with a stiff brush 
 to remove all remaining portions of i)laster when it is ready 
 for final finishing. 
 
 POLISHING THE DENTURE 
 
 With a coarse saw the suri)lus vulcanite is tiimnied from 
 the periphery of the baseplate. Further shaping of the mar- 
 gins to correct peripheral ontline can be done with the double 
 
VUIX'ANITIC 
 
 end vuleauitc lile and xulcanilc lallu' bars. The liiiul sniootli 
 iug of the margins and general surfaces can he ([niekly aeeoni- 
 plished witli emery hands on the lathe arbor. 
 
 A*^ 
 
 EMEI'.Y BAXII LATHE MANDKEL 
 
 When, in the final waxing of a denture, the correct gingi- 
 val outline is given the gums, so that they represent the type 
 of teeth recjuired for that particular case, hut little effort will 
 be required in finishing the vulcanite. 
 
 DIt. Ull.SON'S SET OK VII.L'AMTE FINISHERS 
 
 The right and left bevel chisels are used to true up the 
 gum festoons and develop clean, symmetrical, lingual margins 
 of vulcanite against these surfaces of the teeth. The set of 
 chisels and scrapers suggested by Dr. G. H. Wilson are excel- 
 
VUIX'ANITK 
 
 \ lew uF rrrKR and i,(i\vei', iikxtii'.i: siiowixi! lingi:ai. siufaces cif teeth de\T5E- 
 
 OPED IN VULCANITE. CONSTRUCTED FOR DR. JOHN BAWUNGSON. A NOTED 
 
 ENGLISH SURGEON. B^' DR. GENESE IN 1864. LOANED BY IIR. 
 
 SYKES OE C. ASH & SONS 
 
 BUCCAL VIEW OF THE RAWXINGSON CASE. THIS 
 
 SHOWS WELL-PROPORTIONED UPPER AND LOWER 
 
 TEETH AND FINE OCCLUSAL RELATIONS 
 
VUbCANITK 459 
 
 lent for this purjiose. This set contains a small pointed in- 
 strument for removing vulcanite from constricted spaces in 
 the embrasures and interproximate spaces. 
 
 It is frequently advisable to develop in vulcanite, the lin- 
 gual forms of the natural teeth, after the method introduced 
 by Dr. Genese, in 1860, and later described by Dr. Fine, in 
 1906. Three advantages are gained liy this manner of contour 
 development : First, the bulk of vulcanite is materially re- 
 duced without impairing the strength of the baseplate; sec- 
 ond, the teeth are given approximately their true lingual 
 forms and consequently feel natural and comfortable to the 
 
 SEl'TioNA!, Mi;\V (IK AX IPI'KR DENTURE. 
 
 LINGUAE SUnFACE.S OF THE TEETH DEVET.- 
 
 OPED IN VULI'ANITE (FINE) 
 
 SEUTIONAI. VIEW OF UPPEIl 
 
 DENTURE. SHOWING FORII OF 
 
 INSTRUIIF-NT USED IN CARVING 
 
 THE WAX 
 
 wearer; third, such a form of denture aids materially in cor- 
 rect phonation. The only objections are the time required in 
 the carving and the difficulty encountered in finishing the vul- 
 canite in the linguo-gingival angles and embrasures. 
 
 Bj' developing the lingual forms of the teeth in the final 
 carving of tlie wax and lining the vault portion of the wax 
 model denture with tinfoil before flasking the case, the finish- 
 ing steps are comparatively simple. The tinfoil margins next 
 the teeth should be turned away from the latter so as to be 
 caught in the plaster investment in the upper half of the fiask. 
 Wlien No. 30 foil ov heavier is used it can readily bo stripped 
 from the vulcanite or the thinner gauges can be quickly re- 
 moved bv rubbing with mercurv. 
 
■1()U VULCANITE 
 
 Kultlici- \ulcai]i/,c(l against tinfoil comes I'l-oin the liaslc 
 clean, poJisliecl and more dense than wlien vulcanized a.gainst 
 plaster, and when care is used in waxing a case hut little linal 
 ])olishin,<j' is re(|nired. 
 
 REPRODUCTION OF THE RUGAE 
 
 When re])r()(luction of the I'Ugac has been can'ied out, 
 small scrapers of the Kingsley type are most useful for fresh- 
 ening the depressions hetween these irregular ridges. If 
 proi^erly developed in wax, however, and the tinfoil is applied 
 as described, care being taken to burnish it into the dejires- 
 sions, the i^olishing wheels will complete the finish without 
 resorting to other means. 
 
 USE OF THE CALIPERS 
 
 To avoid iniduc thinning and conse(juent weakening of the 
 baseplate, the calipers should ))e ajiplied at various times 
 
 REIilSTEUlN 
 
 during the finishing process. The instrument shown in the 
 illustration is the type most commonly used. 
 
 FINAL POLISHING OF THE DENTURE 
 
 The general finish is given the vulcanite with various 
 grits of abrasive powders and water, in the form of a medium 
 paste, and applied with brush, felt and muslin wheels of vari- 
 ous sizes, on the lathe. For rajDid cutting, a rather coarse 
 grit, pumice stone, followed by a liner to remove the slight 
 scratches left by the former, is the usual method of reducing 
 the irregular surfaces and slight angles left by the chisels, 
 scrapers and emery bands. 
 
 The scratches left by the jiuniice powdei' are removed 
 with whiting and water. A still highei- polish may be given 
 the vulcanite by coating it with vaseline or heavy lubricating 
 oil, dipping it in dry plaster, and applying lightly to a soft 
 
VULCAiNlTK 
 
 bristle wheel, ruuuiug at high speed. The application of dry 
 plaster is continued until all of the nil has been removed from 
 the various surfaces. 
 
 FINISHING TOUCHES 
 
 The polished denture should be cleansed with soap and 
 water, applied with a medium stiff brush and afterward in 
 clear water. 
 
462 VULCANITE 
 
 It may then be ijlaced in a small glass vessel covered with 
 alcohol and set in the sun to solarize or lighten the pink vul- 
 canite when this step is considered necessary. About one hour 
 will be required to complete the bleaching process, the posi- 
 tion of the denture being changed from time to time so that 
 all surfaces may be of uniform color. After solarizing, the 
 denture should again be cleansed in water. 
 
 FINAL FITTING IN THE MOUTH 
 
 When the patient presents, the upper denture is intro- 
 duced and tested as to adhesion. When sealed, the finger 
 should be passed a number of times from front to back, apply- 
 ing considerable on the lingual surface of the baseplate. This 
 to a considerable extent forces the air from between the con- 
 tact surfaces, after which the patient is instructed to apply 
 the tonque to the baseplate and "draw the air" from beneath 
 it. 
 
 Should the peripheral margins impinge on the muscles or 
 soft tissues to any marked degree the denture should be re- 
 lieved at such points and the marred surfaces polished. 
 
 The lower denture is introduced and seated on its border 
 by drawing the lip and cheeks away from its lower margins 
 and by applying downward pressure to partially expel the air. 
 
 Tests of the excursions of cusps of lower against upper 
 teeth in lateral movements sliould be made, first without and 
 later with interposed carbon paper. The high points are re- 
 duced with engine stones until no interference can be de- 
 tected. The final finish is given the vulcanite mth whiting 
 and water applied with clean felt, muslin and brush wheels, 
 free from grit. All scratches should be removed and a highly 
 polished surface developed, not only in the lingual and outer, 
 but in the palatine areas as well. 
 
 FINISHING THE PALATINE SURFACES OF A DENTURE 
 
 To avoid subsequent irritation of mucous tissues against 
 which the denture will rest, the palatine surfaces should be 
 freed from all nodules, the roughened areas smoothed, and a 
 uniform polish given them. 
 
 Pumice stone applied with a stiff brush wheel, rmi at 
 high speed, using but little pressure, followed with whiting 
 and water, will accomplish desired results without in any 
 way interfering with denture adaptation. 
 
 Judgment must, of course, be used as to the amount of 
 
VTJIvCANITE i 463 
 
 pressui'f ai)plied to avoid cliangiiig the form of the palatine 
 or i)eriplieral surfaces. 
 
 Many avoid polishing the palatine and boi'der areas of 
 dentures, under the mistaken idea that such a step will im 
 pair adaptation. 
 
 The experience of the writer of twenty years or more, 
 together with that of many others, is offered as evidence that 
 the polishing of all areas of a denture, and particularly those 
 which l)ear the liurden of masticatory effort, is not only possi- 
 ble but imperative, and can be accom]ilislied without per- 
 ceptible interference to adaptation. 
 
 The use of tinfoil on the surface of casts reduces to the 
 minimum the amount of polishing required. The use of artifi- 
 cial stone for casts and the coating of cast surfaces with silex 
 aid in the product of smooth vulcanite surfaces. 
 
 A final, high polish can be given all surfaces by saturating 
 the denture in thick oil and applying dry plaster freely while 
 holding it against the soft bristle lathe wheel. The applica- 
 tion of the plaster must be continued until all oil is removed. 
 
 The regrinding of teeth in final trial in the mouth is of 
 utmost importance. Such procedure corrects errors of occlu- 
 sion occasioned by dissimilarity between mandibular and 
 occluding frame movements, as well as slight errors arising 
 from change in relation of teeth during flask closure and vul- 
 canization. 
 
 The prosthetist should keep in mind during the final trial 
 and adjustment of dentures to the mouth the three principal 
 objects he endeavored to accomi)lish when the case was under- 
 taken, viz., to give his patient dentures that would be useful, 
 look ivell, and feel comfortable. 
 
 CONSTRUCTION OF A FULL UPPER OR LOWER 
 DENTURE 
 
 With slight variation in technic, from that described for 
 full cases, either upper or lower dentures may be constructed 
 b}^ the anatomic method, the natural teeth in the opposite arch 
 being present. 
 
 The principal, departure is in the method of taking the 
 bite and in registering the protrusive bite. To illustrate, the 
 construction of a full upper denture will be outlined. 
 
 The impression, cast, and wax occlusion model for the 
 upper arch are formed as for an upper model in a full case. 
 
 Developing uniform contact of the wax rim with oeclud- 
 
Kii vui.cANi'ri': 
 
 illy teeth is esseutially the same as between two occlusion 
 models. The median and high lip lines are determintid in the 
 same manner, as is also facial contour. 
 
 The condyle ends are located and points marked on the 
 face. 
 
 The bite fork is inserted in tlie occlusion rim and removed. 
 
 An impression in compound is secured of the occlusal 
 half or more of all of the lower teeth, when it can be removed 
 without distortion, and from this a lower occlusion cast is 
 formed. 
 
 A layer of softened wax one-eighth of an inch thick is 
 now cut to the form of, and added to the occlusal surface of the 
 upper occlusion rim which should be chilled. The occlusion 
 model is introduced in the mouth, and, by trial, the normal bite 
 is determined, the patient biting into the softened, added layer 
 when instructed, until the natural teeth come in contact with 
 the chilled occlusion rim. 
 
 The bite fork is returned to position and tirmly h;ted in 
 the occlusion model, after which the face bow is adjusted in 
 position and the several clamps tightened. 
 
 The occlusion model, attached wax bite and face bow are 
 removed and the latter set in position on the occluding frame. 
 The upper cast is seated in upper occlusion model and at- 
 tached to the upper bow of occluding frame. The impression 
 is removed from the lower cast and the latter seated in the 
 wax bite, care being taken to see that the occlusal surfaces 
 of the plaster teeth rest flat on the corresponding surfaces of 
 wax bite. To be certain that this step may be carried out 
 accurately, the inner and outer margins of the wax bite should 
 be cut away so as to leave little more than the occlusal sur- 
 face markings of the natural teeth. 
 
 The lower cast is then attached to the lower bow of the 
 occluding frame and the face bow and wax bite are removed. 
 Since the bite locks cannot be applied in taking the protrusive 
 bite, the latter step may be carried out as Christiansen first 
 described it, viz., placing a roll of wax on either side between 
 the bicuspids and molars, and having the patient close the 
 mandible while in a protruded position. 
 
 The occlusion model should be notched in the molar region 
 so that on removal the protrusive wax bites will be correctly 
 guided to place. The condyle paths of the frame are released, 
 the back spring unhooked, the upper occlusion model set on its 
 cast, the two wax bites placed in their respective locations and 
 the final adjustment of the several factors accomplished by 
 
VUl.CANITK 4Gr, 
 
 exertiuy light Init sicady lux's^urc, tlirougli the ceutcr ol" 
 upper and h^wer casts, as in full cases. 
 
 When proper relation is established, the condyle paths 
 are clamped, the wax bites removed, the back spring hooked 
 and the case is ready for arrangement of the teeth, which 
 step is similar to the arrangement of teeth in full cases. 
 
 FULL LOWER DENTURES 
 
 In constructing a full lower denture, the upper natural 
 teeth being present, the stei)s are similar in detail, except that 
 the bite fork is attached to the lower occlusion model. In 
 mounting the casts, the occluding frame should lie inverted 
 and the lower cast mounted first. 
 
 THE GYSI SYSTEM OF ANATOMIC APPLIANCES 
 
 The Gysi System of appliances for anatomic denture con- 
 struction atTords means of registering certain movements of 
 the mandible, not possible by any other method. The appli- 
 
 THE GYSI ADAI'TABLE ARTICULATOR 
 
 ances consist of ffn articulator having adjustable condyle 
 paths, adjustable lateral rotation centers, an adjustable side 
 movement, and the ordinary hinge movement common to all 
 occluding frames ; also a condyle path register, a lateral con- 
 dyle path register, an incisor path register, and varioiis other 
 aceessoi'v appliances. 
 
4«G VULCANITE 
 
 APPLICATION IN DENTURE CONSTRUCTION 
 
 111 constructing dentures with these appliances, tiie steps, 
 up to the ap]ilication of the face bow, are practically the same 
 as detailed in the preceding chapters. Although the order of 
 procedure may be varied, tlie following will be convenient and 
 practical : 
 
 Eegister the condyle paths. 
 
 Take the bite. 
 
 Mount the casts on the articulator. 
 
 Adjust the condyle paths of tlic articulator. (Protrusive.) 
 
 Register the incisor path. 
 
 Set the rotation centers of the articulatoi-. 
 
 Eegister the lateral condyle i^aths. 
 
 Adjust the lateral condyle paths of the articulator. 
 
 REGISTERING THE CONDYLE PATHS, FORWARD MOVEMENT 
 
 The condyle path register records the downward and for- 
 ward movement of the condyles, and also fulfills the purpose 
 of a face bow in mounting easts on the occluding frame. It 
 is applied as follows: 
 
 The horseshoe plate is adjusted to the lower occlusion 
 model, the pins of the plate being forced into the wax rim 
 
 HORSESHOE I'LATE ADAPTED TO LOWER OCl'LUSIOX MODEL 
 
 until the plate rests flat upon its occlusal surface. The an- 
 terior portion of the plate should extend about three-eigbtbs 
 of an inch labially of the rim, so that later it may serve as a 
 table for recording the incisor path. 
 
 The occlusion models are now introduced in the mouth, 
 the condyle path register adjusted to the anterior projec- 
 tions of the horseshoe plate, and the pencils on the liori- 
 
VULCANITE 
 
 467 
 
 zoutal arms of the register brought iu eoutaet with face, 
 agaiust the previousl_v marked condyle ends. The adjustment 
 is accomplished by raising, lowering or rotating the pencil 
 posts in their sockets and locking them firmly with the set 
 screws; the pencils are moved inward by means of the rack 
 and pinion adjustment on the ends of the register. 
 
 A card, about two by three inches in size, is now inserted 
 and held firmly Ix'twoeii tlie ]i(Mi('il point and the face. Its 
 
 REGISTERING THE CONDYLE PATH 
 
 lower edge should be parallel with the horizontal arm of the 
 condyle register. 
 
 The patient is instructed to bite sidewise, so as to project 
 the condyle next the card. During this movement, the pencil 
 point moves synchronously with the condyle and marks on the 
 card the direction of its path. A card is now applied to the 
 opposite side of the face, and a similar registration of the 
 opposite path secured in like manner. 
 
 A straight edge is laid on the card, parallel with the 
 working part of the condyle path, and a line drawn along 
 it to the lower margin of the card. The protractor is then 
 
VULCANITE 
 
 applied to the card, by means of wliicli the inclination of the 
 condyle path in degrees is determined. The condyle paths of 
 the frame are set according to the readings obtained from the 
 two cards. 
 
 TAKING THE BITE 
 
 The bite is now taken as outlined in Chapter XIX, the 
 horseshoe plate being firmly affixed to the lower occlusion 
 model, for by this means the occlusion models are attached to 
 the condyle register for securing their correct relation to the 
 condyles in normal or resting position in the glenoid fossre. 
 
VULCANITE 469. 
 
 AVlien the normal bite is deteniiiued, the bite locks are 
 iutroduced, the condyle register adjusted as before, and the 
 occlusion models removed from the mouth. 
 
 In this sj'stem, it is found more convenient to seat each 
 cast in its baseplate and hold them in proper position by pass- 
 ing ]'ul)ber bands around both casts and occlusion models. 
 
 MOUNTING THE CASTS ON THE ARTICULATOR 
 
 The condyle register to which the occlusion models are 
 attached is set upon its base, the goose-neck rod being raised 
 or lowered as required to bring the pencil points opposite the 
 condyle points of the articulator. 
 
 Tlie iron stand, with condyle register and occlusion mod- 
 els attached, is now moved forward, clear of the articulator. 
 
 Plaster is applied around and over the lower bow, and the 
 iron base pushed back until the pencil points of the register 
 are opposite the condyle ends of the frame; further additions 
 may be made to the plaster around the lower cast, to firmly 
 attach it to the frame. 
 
 The upper cast is attached to the upper bow by applying 
 plaster in the usual manner. When set, the condyle register 
 and bite locks are removed, the rubber bands cut, and the 
 occlusion models removed from the casts. 
 
 REGISTERING THE INCISOR PATH 
 
 A pellet of cotton saturated in oil of cloves is ignited and 
 the anterior end of the horseshoe plate held over it to blacken 
 
VULCANITE 
 
 CASTS AND CONDYLE KEGISTER ADJUSTED TO ARTICULATOR 
 
 the surface. A thin film of wax is flowed over the smoked 
 surface to prevent its being rubbed off. 
 
 The incisor path register is now attached to the upper 
 occlusion model so that the pin will project slightly below 
 the occlusal surface. The register must not be set so low as 
 
 PENCIL FOR REGISTERING 
 
 LATERAL PATH OF LATERAL PATH 
 
 CONDYLE SET SCREW 
 
 RACK AND PINION 
 
 FOR LATERAL ADJUSTMENT 
 
 OF PENCILS 
 
 i;xi>i,ANATonv CUT showing the various adjustments of the gysi adaptable articulator 
 
VULCANITK 471 
 
 to obscure a view of tlie ]iiii iioiiit in its I'xoursions over the 
 waxed surface of the liorseshoe plate. 
 
 The occlusion models are uow introduced in the mouth 
 and the patient instructed to move the mandible sidewise, at 
 the same time holding the horseshoe plate in close contact 
 with the upper occlusion rim. 
 
 By this movement the pin of the register on the upper 
 occlusion model marks an arc on either side of the median 
 line of the horseshoe plate, the centers of which represent the 
 centers of rotation of the mandible. The logic of this is appa- 
 rent, for the condyles represent centers from which the arcs 
 
 KEGISTEItlXG THE IXCISOU PATH 
 
 are developed. Usually, several movements will be required 
 to mark distinct lines on the horseshoe plate. 
 
 When the record is sufficiently sharp, the occlusion models 
 are removed from the mouth, returned to the casts on the 
 frame, and the latter subjected to lateral movements. The 
 direction taken by the pin of the incisor register should be 
 closely observed. If it follows the arc, the rotation center of 
 the fra^e^is correct, and the latter may be fixed accordingly. 
 If not, the rotation center of the frame should be moved out- 
 ward or inward- as required, until the point accurately follows 
 the arc it made while in the mouth. The rotation center on the 
 opposite side of the frame is determined in like manner. 
 
 The object in carrying out the steps as described is 
 to insure correct lateral movements to the frame, so that when 
 
172 VinX'ANITK 
 
 tliL' teeth are aii;uij;('<l in the wax rims, tlie cusp (.'learauce 
 there devehjped will reiiuire but little chauge when tlie den- 
 tures are introduced in the mouth. It is a step nearer true 
 anatomic movements than can be secured from a frame, the 
 rotation centers of which are fixed the average distance apart. 
 
 REGISTERING THE LATERAL CONDYLE PATH 
 
 The lateral paths must not be confused with the lateral 
 rotary movements of the condyles. Naturally, when one con- 
 dyle is the actual center of rotation, the other condyle in mov- 
 ing forward describes an arc, the radius of which corresponds 
 to the distance between the two condyles. It is found, how- 
 ever, that the radius of the arc described by a projected con- 
 dyle is sometimes greater or less than the distance between 
 the condyle centers. 
 
 Again, in some persons, the mandible moves bodily, side- 
 wise, in the lateral rotary movements, and in some cases there 
 is a slight side movement, within certain limits, without any 
 percei^tible rotary movement. 
 
 The lateral path register has attached to each extremity 
 a glass plate ground on the under side, on which the perpen- 
 dicular pencil of the condyle path register records the lateral 
 movements of the mandible. 
 
 By use of the lateral condyle path register, these side 
 movements in individual cases may be recorded, and the artic- 
 ulator set to reproduce them to a fairly accurate degree. The 
 steps are carried out as follows : 
 
 The condyle ]3ath register is attached to the occlusion 
 models as in taking condyle registration, the perpendicular 
 pencils being turned so that they come opposite the outer ends 
 of the condyles. 
 
 The operator stands back of the patient and applies the 
 register', holding it at approximately the same inclination as 
 tlie pitch of the condyle paths, previously registered. The 
 ground glass plates should rest on the upturned pencil points, 
 and the arms be pressed in until the edges of the plates rest 
 firmly against the sides of the face. The patient is instructed 
 to move the mandible sidewise as before, which movement 
 marks on the under side of the glass, the line or arc described 
 by the moving condyle in its forward excursion. 
 
 To translate the lines recorded on the glass plates into 
 degrees, the following plan is adopted : 
 
 On a sheet of white paper as wide as the register bow, a 
 base line A B is drawn from side to side. A perpendicular 
 
VULCANITE 
 
 REGISTEUING THE LATERAL CONDYLE I'ATIIS 
 
 DETEIIMINING THE DEGREE OP INWARD INCLINATION ol' TTIE 
 LATERAL CONDYLE PATHS 
 
474 VULCANITK 
 
 C D is erected on the base line, near one edge of the sheet. 
 The lateral condyle path register is laid on the sheet, the 
 points on the ground glass plate which indicate the beginning 
 of forward movement of the condyle being placed at the junc- 
 tion of base with perpendicular line C, the base line. The 
 points should also be directly over the perpendicular lines. 
 AVith a straight edge placed beneath the ground glass, and 
 resting on the paper, its edge is brought in line with the 
 lateral path marked on the ground glass, and which can 
 
 L 17' . 16° K 
 
 A BECORD OF SIXTKK- 
 
 ANGULAB INCLlXATIi 
 
 SEVENTEEN" l>i:i 
 
 I'AIKS (I 
 \, l.\A\,\l! 
 
 r,i:i:s. i:i< 
 
 13° 
 
 iO° 
 
 33" 
 
 IS'' 
 
 ^Z<^ 
 
 -IS-" 
 
 18° 
 
 w 
 
 1S° 
 
 iZ" 
 
 Zo° 
 
 ZO' 
 
 3" 
 
 10° 
 
 10° 
 
 i1' 
 
 W 
 
 y^o 
 
 iZ" 
 
 r 
 
 nXDYLE PATHS. AVERAGE 
 II' LEFT CONDVLE PATHS. 
 1 . SIXTEEN' DEGREES 
 
 readily be seen tiirough the transparent plate. If properly 
 placed, its edge should coincide with the .junction of the per- 
 pendicular with the base line. 
 
 The register is removed and a line drawn along the 
 straight edge on the paper C E. This line usually forms an 
 angle with the perpendicular line, the apex of which is on the 
 base line. By applying the protractor to the angle, the num- 
 ber of degrees included may be read, and the lateral path 
 recorded accordingly on the articulator. 
 
VULCANITE 475 
 
 THE ANGULAR INCLINATION OF THE LATERAL 
 CONDYLE PATH 
 
 Dr. Gysi states that tlu- average angular inclination in- 
 ward, of sixteen pairs of condyles recorded, sliows 17 de- 
 grees for the left and 16 degrees for the right condyle. 
 
 This lateral movement of the mandible is evidently the 
 result of an unconscious or involuntary effort of the organism 
 to increase the occlusal function of the molars on the working 
 side, as well as to develop more effective balancing contact on 
 the protruded side. That it is less important than the for- 
 ward and downward condylar movement is self-evident, yet 
 both should ])o rockoiiod with in denture construction. 
 
 SUBSEQUENT STEPS OF DENTURE CONSTRUCTION 
 
 When the registrations have been determined as outlined, 
 and the articulator adjusted accordingly, the subsequent steps 
 of denture construction are carried out in practically the same 
 manner as detailed in the previous chapter. 
 
 Because of the liability of errors occurring, in carrying 
 out the various steps, the completed dentures should be tested 
 with carbon paper, to correct any c-nsp interference that may 
 exist and remove high points that, without such means of dis- 
 closing them, are not discernible to either prosthetist or 
 patient. 
 
CHAP T K R XXIII 
 
 CONSTRUCTION OF PARTIAL DENTURES 
 
 VARIOUS TYPES 
 
 A substitute wliicli replaces one or more, but not all of the 
 natural teeth in either arch, is commonly termed a partial den- 
 ture. This name is usually applied to a removable substitute 
 having a base plate which rests upon and is principally sup- 
 ported by the mucous tissues covering the bony substructure 
 of the dental arches, in contra-distinction of bridge work, 
 which fulfills essentially the same purpose but is attached to, 
 and mainly supported by some of the remaining natural 
 teeth or roots. A piece of bridge work, however, in the 
 broadest sense, is a partial denture, since it replaces a miss- 
 ing portion of the natural denture. The term bridge relates 
 to the manner of replacement, the bridging over of spaces 
 caused by loss of some of the natural teeth. 
 
 PLANNING A PARTIAL DENTURE 
 
 In planning a partial denture, aside from the general 
 routine steps involved, several factors of importance must be 
 determined, the dominant ones of which are as follows : 
 
 First — The materials of which the substitute is to be 
 constructed. 
 
 Second — The general outline form of the base plate. 
 
 Third — The means of retention to be employed. 
 
 Fourth — The class of teeth to be used and the manner of 
 their attachment. 
 
 BASEPLATES FOR PARTIAL DENTURES 
 
 The base plate is the foundation of a denture which rests 
 upon the oral tissues, and to which the substitute teeth are 
 attached. Through it, under normal conditions, the force of 
 masticatory effort is equalized and distributed to the mucous 
 tissues overlying the bony sub-structure in such manner as to 
 cause no injury to the tissues themselves and no inconveni- 
 ence to the patient. 
 
 Gold and vulcanite, either alone or in cojnbination, are 
 the materials most commonly* employed for partial denture 
 bases, preference in most cases being given the former be- 
 
 476 
 
CONSTRUCTION OK PARTIAL JJKNTURES 477 
 
 cause of its better appearauce, couduetivity auil greater 
 strength with least bulk as compared with vulcanite. How- 
 ever, there are many cases where vulcanite alone can be used 
 to good advantage, and other cases in which its use with gold 
 is indispensable, particularly where much restoration of bor- 
 der contour is required. 
 
 PARTIAL DENTURES OF VULCANITE 
 
 The outline form and size of a partial denture is governed 
 to a great extent at least by the position of the teeth to be 
 replaced. The manner of retention, however, has an impor- 
 tant bearing on the linear dimensions of the base plate. When 
 clasps or retaining appliances of similar character are used, 
 the terminals of the base plate should be extended beyond 
 these means of attachment when necessary, so as to develop 
 denture balance, as explained under the heading, "Indica- 
 tions and Contra-Indieations Governing the Application of 
 Clasps." 
 
 By drawing a line or laying a straight edge from one 
 clasp or attachment to the other, the linear extension, both 
 mesially and distally, necessary to secure correct denture bal- 
 ance, can readily be determined. 
 
 In upper partial dontui'es, when retention depends upon 
 atmospheric pressure and adhesion, the base ijlate should 
 cover a considerable portion of the palatine vault, but seldom 
 to such an extent as in a full deuture. 
 
 With the great variety of frictional appliances available 
 and improved methods of their construction the retention 
 of partial dentures is very much simplified, and the form 
 of upper dentures can be materially reduced in size over those 
 in which atmospheric pressure is employed. 
 
 In width, the base plate of an upper partial denture need 
 seldom exceed from one-fourth to five-sixteenths of an inch, 
 where it passes along the lingual surface of the natural teeth, 
 when retained in place by frictional appliances. 
 
 The base plate need only be considered as a frame-work 
 or splint for holding the teeth in position, the saddle, which 
 rests upon the border and supports the tooth., coupled with 
 but slight bearing, of the base plate proper upon the tissues, 
 u.sually affords ample resistance to masticatory stress. 
 
 The thickness of a base plate of vulcanite is, of course, 
 governed somewhat by its width, but not altogether, since a 
 thin, wide base plate will, under use, fracture more quickly 
 than a thicker but narrower one containing an equal or even 
 
478 CONSTRUCTION OK PARTIAh DKNTURES 
 
 less bulk of material. By actual measuremeut, a very nar- 
 row base plate, if constructed of a good quality of vulcanite, 
 need not exceed from one-sixteenth to one-twelfth of an inch 
 in thickness except when absorption of tissues requires a 
 greater amount for restoration of lost border contour. 
 
 TECHNIC OF CONSTRUCTION OF PARTIAL UPPER VULCANITE 
 DENTURES WITHOUT CLASPS 
 
 In all cases an accurate plaster impression of the teeth 
 and tissues involved should be secured in plaster. From this 
 impression a cast should be developed in magnesium oxy- 
 chlorid, or Spence's plaster, because of the greater hardness 
 of these materials. 
 
 When loss of but few teeth have occurred, these not being 
 contiguous, a mash bite of sufficient bulk to take an impres- 
 sion of the lower teeth and project labially so that the bite 
 stem of the face bow may be firmly imbedded in it, will usu- 
 ally jjrove satisfactory for mounting the upper cast in correct 
 position on the occluding frame, and for developing the lower 
 cast as well. Or an impression of the lower arch can be 
 secured, a cast developed from it and the special bite fork, 
 designed for partial cases, can be used for securing the cor- 
 rect relation between the mandible and maxilla, after which 
 the two casts can be mounted on the frame in a similar man- 
 ner to an edentulous case. 
 
 TAKING THE PROTRUSIVE BITE 
 
 Should it be deemed advisable to take a protrusive bite, 
 it is accomiilished as follows : Place two rolls of wax between 
 the bicuspids and molars, one on either side ; have the patient 
 l^rotrude and bite as in full cases where this step of condyle 
 registration is carried out. The two bites are removed from 
 the mouth and placed in position on the lower casts, the con- 
 dyle slots of the frame loosened and the back spring unhooked. 
 The upper cast is then moved backward and pressed down- 
 ward until the teeth take their proper position in the bite. 
 It is usually necessary to trim away the buccal and lingual 
 margins of wax before seating the casts, so that it may readily 
 be seen when they are in exact position. Care should be 
 taken not to distort the wax during the trimming process. 
 The condyle slots are now set tirmly as the wax bites indicate, 
 the wax removed, and the back spring again connected, when 
 the ease is ready for the selection of the teeth. 
 
CONSTRUCTION OF PARTIAL DENTURES 47'J 
 
 SELECTING AND GRINDING THE TEETH 
 
 When only a few teeth are missing, it is seldom necessary 
 to try the wax model denture in the mouth, therefore the use 
 of a hard, unyielding base jjlate, such as is used in full cases, 
 is uncalled for. A good quality of sheet base plate wax will 
 answer the purpose. 
 
 Teeth of suitable size and color are selected to fill the 
 spaces. When possible to do so, plain teeth should be selected 
 
 KEDUCTIOX Oi.- I'ltOXIJIATE Sirp.FACF.S 
 TEETH WHERE RT'ArE HAS BECOME 
 CONSTKICTEB 
 
 and ground to accurately tit the border, thus obviating the 
 application of artificial gum restoration. They should be of 
 sufficient length not to require tipping inward at their cervical 
 ends to meet the border and thereby be thrown out of 
 alignment. 
 
 When teeth adjoining a space have moved toward each 
 other, for example, a central and opposite lateral incisor, thus 
 reducing the space occupied by the lost central, it is often 
 advisable to disc away their proximating surfaces. This in- 
 
 ri.ATE TEETH BACKED. WITH LINGUAL EX- 
 
 TEXSIOX ADDED. FOB CLOSE 
 
 BITE CASE 
 
 creases the width of space and decreases the width of the 
 immediately adjoining teeth so that the replacement will more 
 nearly harmonize in form and proportion with the other in- 
 cisor than woujd be the case were such change not made. 
 
 By highl}- polishing the surfaces reduced, no injury to 
 the natural teeth is liable to result. 
 
 There is, however, a limit to the aiJplication of plain 
 teeth in partial cases. "Wlien gum restoration is required and 
 
■ISO CONSTRUCTION OF PARTIAL DENTURES 
 
 the line of junction of tlie artiticial with the natural gum tissue 
 is visible, a gum section tooth, or if two or more contiguous 
 teeth are missing, a gum section block which includes the 
 teeth required should be selected and ground to neatly fill 
 the space and restore the lost tissues with porcelain. When 
 
 such a block is not procurable, plain teeth may be selected and 
 a porcelain gum attached by baking as described under the 
 heading, "Special Uses of Porcelain." 
 
 In some cases it may be possible to apply "Protesyn" in 
 partial restorations, but since this material depends entirely 
 upon undercut spaces for its retention, it will be difficult to 
 develop the necessary anchorage in limited spaces. Pink or 
 granular gum restorations are the least desirable of any of 
 
 rini 
 
 the materials mentioned and when possible their use should 
 be avoided. 
 
 When two or more plain teeth, not requiring gum restora- 
 tion, approximate, "Fogg's Interstitial Gum Blocks" can be 
 used to advantage in filling the embrasures, thus avoiding the 
 display of vulcanite in these spaces. These also, together 
 
CONSTRUCTION OF PARTIAL UKNTURKS 
 
 with the method of application, ave deserilied under tht 
 of "Special Uses of Porcelain." 
 
 head 
 
 WAXING THE CASE 
 
 The teeth haviui;- been ground and waxed in position, the 
 base plate is applied to the lingual surfaces of the teeth and 
 given its desired outline form. The wax sliould be allowed 
 to extend occlusally on the lingual surfaces of tiie natural 
 teeth sufficiently to furnish a reasonably broad liearing for 
 tlie base plate, for retention i)urposes. A single thickness of 
 ordinary sheet wax will not afford enough Imlk of material 
 for the base plate and foi- loss of material as a result of fin- 
 ishing the vulcanite. Two sheets will reiuhM' the case too 
 I'ulkv. therefore the first sheet can be thickened scuiiewhat l)v 
 
 111 I or DL\TLRr IX \MIILII JIM ( ' 
 
 TrnsTiTi vr gim f\iings \k] 
 iM>r( \Ti n 
 
 hurnishing a sliglit addition of wax to it over all surfaces 
 and more where deficient contour requires. The wax should 
 extend well above the offset slioulder on tlie lingual surfaces 
 of the porcelain teeth so as to insure ample material for de- 
 veloping smooth surfaces in the final finishing. 
 
 FLASKING THE CASE 
 
 When plain teeth have been ground to the border, no 
 gum restoration having been required, the teeth may I)e im- 
 bedded in the tirst section of the flask with the cast of the 
 mouth. Frequently, in spaces where gum sections have been 
 fitted and absorption of the border is marked, so that con- 
 siderable space exists between the border side of the block 
 and the cast, gum sections may also be invested the same as 
 plain teeth. Special care must be taken in packing the case to 
 fill the space between tlie block and cast with rubber before 
 closing the flask, otherwise the vulcanite is lialile to lie de- 
 ficient from failure of surplus rubber being force<l intd the 
 
482 CONSTRUt'TION OK PARTIAL DENTURKS 
 
 space. When, however, tlie space between cast and block is 
 constricted, so that it will bo difficult to introduce the rubber, 
 the case should be invested so that the block will be cauglit 
 and hold by the plaster investment in the second half of the 
 flask. Tliis sini])liiios the ])ackin.n' of the case so that tlie 
 
 SECTIONAL VIEW 
 
 xn WITIIOl'T Gl'.M 
 
 vulcanite will flow freely back of and surround tlie block as 
 desired in the final closing of the flask. 
 
 Sometimes both methods of investing the teeth are adopt- 
 ed in the same case. . When the replaced teeth are on opposite 
 sides of the cast, the latter can be set more deeply in the 
 flask on that side occupied by the plain teeth without restora- 
 tion than on the other side where gum restoration has been 
 applied. This gives maximum strength with minimum bulk to 
 the plaster which supports the plain teeth. 
 
 Projecting plaster teeth should be trimmed even with the 
 lingual mai'gin of wax, and the outer surfaces of the cast 
 backed up with plaster and rounded down to the line of sep- 
 aration of the flask in such manner as to obliterate all under- 
 cuts. 
 
CONSTKUCTION OK PARTIAL DKNTIKIOS l.s:i 
 
 The points iiixohcd in Hiiskiui; aii.\' case are, lirst, to 8Ui)- 
 port the east under its base, so tliat it will not fracture under 
 the stress of closing; second, to construct a matrix in which 
 to mold the basic material which will not yield in forcing out 
 the excess rubber, not permit the teetli to become dislodged, 
 and. third, to so shape the invested case in the tirst half of the 
 flask that the second will readily separate from it without pro- 
 ducing fracture of the investment. 
 
 PARTIAL DENTURES OF VULCANITE WITH CLASPS 
 GENERAL CONSIDERATIONS 
 
 Wlien a partial denture of vulcanite is to l)e retained in 
 position with clasps, the order of procedure is as follows: 
 
 Take impressions of the teeth to be embraced by the 
 clasps, and from these develop metal dies. C'onstriict the 
 clasps as described under the heading, "Technic of Clasp Con- 
 struction." Attach the anchorage lugs to the clasps in such 
 position that they will neither interfere with correct align- 
 ment of the i^orcelain teeth nor require extra bulk of vulcan- 
 ite to cover them. 
 
 The clasps are now placed in position on the teetli in the 
 mouth and a mash bite secured, using the face bow if the 
 case calls for such procedure. Should the clasps come away 
 with the bite, they are returned to proper position on the 
 teeth. 
 
 An impression in plaster is now taken which should in- 
 clude all of the teeth involved in developing correct occlusion, 
 and all of the liorder surfaces to be covered by the substi- 
 tute. 
 
 On removal from tlie month, the broken parts of the im- 
 pression, if fractured, are replaced and firmly luted together, 
 the clasps adjnsted in correct position in their respective 
 matrices and wedged apart so that each wing rests in con- 
 tact with the matrix wall of the impression. Should any of the 
 plaster which flowed under the anchorage lug, next the border, 
 have become broken and lost in removal of the impression, a 
 little wax should be flowed over the lug and the general con- 
 tour of the impression be restored in this manner. When the 
 loss of impression in this area is extensive and cannot be re- 
 stored wdth comparative accuracy, a new impression should be 
 secured. 
 
 A cast is now develo]ied in the usual manner, using pref- 
 erably some of the harder materials for this i)nr]iose. When 
 
iSI COXSTKICTIOX ()!•' I'Airi'lAI, 1 IIONTI ' It KS 
 
 liartleiietl, lln' iiii|ircssi(iiL is cjii'i'l'iillx I'ciiKixcd lo iUdid ilis- 
 placing the clasps or ri'ac1iiriii,<; the tcctli. 
 
 The wax bite is now trinuned freely on that side that re 
 ceivcs tlie working cast, so that hotli teetli aii<l chisps iiia\ 
 occupy the same i)osition in the bite that the natural teeth 
 and clasps sustained to it, when in the moutii. 
 
 The steps from this point on are essentially the same as 
 those concerned in the i)rodnction of a partial vulcanite case 
 without clasps. 
 
 In case it is considered necessary to try the wax model 
 dentures in the mouth, which is sometimes done for the pur- 
 pose of testing occlusion, the base plate should be formed 
 around the clasp lugs in such manner that the denture may lie 
 released without disturbing the clasps from their position on 
 the teeth. Under no circumstances should the clasps be dis- 
 turbed from the time the impression is filled until the case 
 is vulcanized, in the class of dentures under consideration. 
 
 When, however, the base plate consists of metal, the 
 clasps are usually permanently attached to it in the prelim- 
 inary constructive stages, as will be explained later. In such 
 case they will come away from tlie cast with the l)ase plate. 
 
 In flasking the case, special care should be taken to cover 
 the exposed ends of the clasps with the plaster investment in 
 the first section of the flask, so as to hold them firmly in posi- 
 tion after the wax is removed and during the packing and clos- 
 ing of the case. 
 
 It is also frequently advisable, before ])acklng the matrix, 
 to jilace between the anchorage lug and the cast a small wedge 
 of vulcanite, of similar color to the basic rubber being used, 
 to prevent displacement of the clasp liy the rubber in the 
 matrix in the closing of the flask. 
 
 The wedge can be cut from an old base plate, should be 
 clean, and all surfaces freshened so as to insure close imion 
 of the new rubber with it. When neatly applied, no difference 
 in color will be noticealile, and practically all danger of clasp 
 dis])]acement will lie ol)viate(l. 
 
 PARTIAL LOWER DENTURES OF VULCANITE 
 
 The construction of i)artial lower dentures of vulcanite, 
 either with or without clasps, is much the same as for similar 
 upper cases. Attention should be given one important detail 
 which differs from upper partials, particularly in those cases 
 where the anterior teeth are px'esent, and the replacements 
 occur along the posterior borders. 
 
CONSTKICTIUN OK I^ARTIAL DKNTrUKS 485 
 
 While in upper partial cases the stress i)f mastication is 
 resisted directly by the saddle under the replaced tooth or 
 teeth, yet the comparatively flat or somewhat flaring sur- 
 faces of the lingual border base ])late, which rests upon the 
 mucous tissues, receives some of the stress also and imparts 
 general stability to the denture. 
 
 In lower cases but little if any suppoi-t is afforded the den- 
 ture by the lingual border surfaces of the base plate next the 
 teeth, because of the generally perpendicular relation of these 
 surfaces of the natural tissues. It is therefore necessary to 
 extend the base plate well up on the cingula? of the anterior 
 
 OCn.USAT, VIEW OF LOWEK PARTIAL MLCAMTH liASK PLATE, 
 
 SIIOWINC FINMSHING SHOI'LDERS FOR TilE SFCCOMI 
 
 AD111T10N OF RPliliER 
 
 teeth, otherwise if this is not done, irritation and absorption 
 of the lingual gingival tissues will occur in a very short time. 
 The application of stop clasps to the first bicuspids, or even the 
 second bicusiiids, when the replaced teeth are situated to the 
 distal of the clasps, will practically overcome the tendency of 
 lower partials to tip anteriorly. The use of clasps without 
 
lai; CONS'I'IU'C'I'ION Ol'' I'Airi'lAI, 1 )K.\TI ' ItKS 
 
 .stoi)s in the s;iiiir Im-jil imi .-iiid iiiiilci- llic same (•(iiiditidiis 
 usually iiuii'iiiciil the uiiilcsiralilc couditious lucntioiiL'd. 
 
 Frequently, in differenl cases, it is advisable to construct 
 the base of vulcanite tn wliich, a1 the s;une time, clasp may 
 be attached. This base plate is tiicn littrd in the mouth the 
 same as a gold base denture, a mash liite takeji and the teeth 
 selected, waxed, ground to meet requirements and vulcanized 
 to the ])reviously constructed base. 
 
 By forming finishing shoulders on the l)ase against which 
 the second addition of vulcanite will finish and using a slightly 
 different shade of rubber, very artistic results can be realized. 
 
 The introduction of the lingual bar of metal for lower and 
 the over-arch bar for upper cases combined with improved 
 forms of frictional retention a])pliances, have proven so satis- 
 factory that the teclmic of partial denture construction has 
 been practically revolutionized within the last few years. 
 
 MOUNTING THE CASTS ON THE OCCLUDING FRAME 
 
 When a mash bite has been taken, in conjunction with the 
 face bow, it is advisable in these, as in njany other similar 
 cases, to attach the face bow to the occluding frame and de- 
 velop the occlusion cast before adjusting the working cast or 
 that one to which the artificial teeth are to be fitted, in 
 the bite. The reason for so doing is that the bite which re- 
 ceives the working cast must be trimmed away freely so that 
 the occlusal surfaces of the teeth may rest perfectly on the 
 wax surfaces impressed by the natural teeth. This cannot be 
 determined accurately unless practically all of the buccal, 
 labial and lingual surfaces of the bite are ciit away sufficiently 
 to expose these occlusal areas to view, as has been pre\'iously 
 stated. Now, if an attempt is made to force the working cast 
 into the bite, or if the bite is trimmed before the occlusion cast 
 is developed, distortion of the wax will most certainly occur, 
 and later on, when the occlusion cast is developed, the rela- 
 tion between the two will be incorrect. 
 
 Summarized, the steps are as follows : 
 
 Apply face bow, with mash bite attached, to the occluding 
 frame. Fill the occlusion side of the bite with plaster, attach- 
 ing it to the bow of the frame. Trim wax bite to receive the 
 working cast, being careful not to injure the plaster teeth of 
 the occlusion cast while doing so. Adjust working cast in 
 trimmed wax bite and attach to occluding frame. When the 
 plaster has set warm the wax, open the fi-ame and remove the 
 wax from the occlusion cast. 
 
CONSTRUCTION OF PARTIAL DENTURES 4S7 
 
 REGISTERING THE CONDYLE PATHS IN PARTIAL CASES 
 
 Au ordinary protrusive mash l)itt', wlieu properly triminetl 
 so that the teeth of both oasts may correctly enter their 
 impressions, will serve to set the condyle paths of the oc- 
 cluding frame to coincide with tiiose of the patient. 
 
 ARRANGING THE TEETH 
 
 Teeth of suitable foi-m and color are selected and ar- 
 ranged as in full cases, the plaster teeth on the occlusion cast 
 serving as a guide in developing correct alignment and oc- 
 clusion. (*are must be taken, therefore, not to mutilate the 
 occlusion model by attempting to force the porcelain teeth 
 into imperfectly softened wax l)y closing the frame as in full 
 cases. Such procedure nearly always fractures the occluding 
 plaster teeth and destroys the only means of testing the ac- 
 curacy of occlusion in the constructive stages of the case. 
 
 When the very slight connection between the wax saddles 
 and anchorage spurs is considered it will readily be seen that 
 trial of the wax model denture in the mouth is impracticable. 
 Even when saddles of Ideal Base Plate are formed and firmly 
 luted to the anchor spurs, to serve as a foundation on which 
 to arrange the teeth, the benefits of a "try in" of the case is 
 questionable, because of the general distui'bance of relation 
 of the several parts to each otlier, wliicli coiiunonly occurs 
 during such procedure. 
 
 The points of interference between porcelain teeth and 
 those on the occluding cast should be noted and correction 
 made by grinding as each tooth is set in position.. When 
 the protrusive bite is taken, as outlined, the relation of the 
 lower and upper te"eth to each other in lateral movements 
 shoiild be tested and corrections made accordingly. The neces- 
 sity of developing perfect teeth on the occlusion cast and of 
 avoiding their fracture during the arrangement of the sub- 
 stitutes is, therefore, of extreme im|)t)rtance. 
 
 The case is waxed to the re(|uired outline form and given, 
 the desired surface develoiiment of th(> finislied denture, when 
 it is ready for flasking. 
 
 -FLASKING THE CASE 
 
 Partial cases of the type here described are flasked the 
 same as ordinary vulcanite dentures, except that the anterior 
 lingual surface of the cast should be filled with plaster in the 
 first investment of the case, so as to enclost' the exposed yior- 
 
488 CONSTRUCTION OK PARTIAI- DKNTURES 
 
 tioii of the lingual bar aud hold it rigidly duriug subsequent 
 procedures of flask separation, reinoval of wax, packing the 
 rubber, final flask closing and vulcanizing. 
 
 Since these steps, as well as finishing the case, are similar 
 to those of ordinary cases, the details need not be repeated. 
 
 LOWER PARTIAL GOLD BASE DENTURES 
 
 In replacing lower ])osterior teeth it is frec^uently advis- 
 able, and a common method of practice, to construct a gold 
 base and attach the substitute teeth to it with vulcanite, or 
 other means, as conditions require. 
 
 One of the older methods, which in favorable cases, has 
 I^roven very satisfactory, is carried out as follows : 
 
 A die and counterdie of the case are developed in the usual 
 manner, on which a gold base, usually of 28 or 29 g. and 20 k. 
 
 LOWER PARTIAL. SWAGED GOLD BASE WITH 
 DOUBLER A, BASE B. DOUBLER 
 
 DETAIL OF VULCANITE RIM 
 
 C. WIRE BEFORE SOLDERING 
 
 D. WIRE AFTER SOLDERING AND 
 SQUARING 
 
 is swaged. The lingual l)and of gold which connects the two 
 saddles should extend well up on the cingute of the anterior 
 teeth to prevent settling of the denture under stress as previ- 
 ously mentioned. The principal base should be reinforced with 
 a doubler, anteriorly, aud extending back of the teeth clasped 
 on either side, about one-half inch. This doubler may be of 
 29 or 30 gauge gold. The base plate and doubler are pickled, 
 polished and united with solder, trimmed to correct outline 
 and reswaged. Clasps are developed on independent metal 
 dies constructed for the purpose. Th.ese are fitted to the 
 
CONSTKICTIU.N l)K I'AKTIAI- I )K.\T I ' H K8 4S'J 
 
 teeth ill the mouth. The hase plate is triumiecl to take its 
 proper position on the border without interfering witli the 
 clasps. An impression is tlien taken of the teeth clasped, 
 preferably of one tooth at a time, with clasp in position, 
 and including the contiguous part of the base plate. The 
 base plate can thus be held in position while the plaster can 
 be applied in a small hinged tray. When set, the impression 
 is removed, the clasp and base plate adjusted in position, luted 
 firmly with wax and a small cast developed, which holds the 
 clasp and base plate in correct relation during soldering. 
 
 When united, the base plate is returned to the mouth and 
 an impression of the other tooth and clasp secured in like 
 manner. This clasp and the base plate are united as just 
 outlined. The metal structure is now i)ickeled, polished and 
 I'cturned to the mouth for final bite and iinjiression. 
 
 FORMING THE FINISHING SHOULDER FOR VULCANITE WITH 
 GOLD PLATE 
 
 In these, as in practically all cases of gold base dentures, 
 to which the teeth are attached with vulcanite, a shoulder 
 should be formed against which to finish the latter. This 
 may be done by cutting narrow, 2>arallel-sided strips of gold 
 plate of whatever curvature is required and applying and 
 soldering the same along the line on the base plate where the 
 \ulcanite should terminate. These strips are applied and 
 soldered neither at right angles to nor flatly against the base 
 plate, but usually somewhat slanting so as to form a ^"-shaped 
 groove interiorly, while the outer surfaces form a continuous 
 curve with the gold base and vulcanite. This method is not only 
 ])ractical and economical, but artistic as well. It is particu- 
 lai'ly applicable to those cases where border absorption has 
 progressed unequally and where, if correct contour be given 
 the case, the vulcanite will be disposed in unsymmetrical out- 
 line on the base. In such ease a strip of suitable width and 
 curvature can be cut, contoured, applied and soldered to the 
 iiase in such manner as to develop normal contour to the den- 
 ture, and symmetrical exposure of the vulcanite as well. 
 
 FORMING THE SHOULDER WITH WIRE 
 
 The most common method of developing the finishing 
 shoulder for the vulcanite is by soldering a wire along the 
 line on the base plate as indicated by the terminal margin of 
 the previously-contoured wax. That surface of the wire pre- 
 
■l!t(l CONS'l'UrC'I'ION Oh' I'AirriAL KKN'TlliKS 
 
 sciiliiig low.-inl llic \ iilr;iiii1r ;ui';i is s(|Uiin'il out with stones 
 and plu.n' liiiisliiiiii' Inii's, wiiiic liir oiitci- siirrarcs of wive ami 
 solder arc ,i;i\cii llic aii|ii'nxiiiiii1i' curxjiturc of tlic rniislic<l 
 case. 
 
 The wire not oiil>' atl'oi-ds a linisliiug slioultlcr for tlio 
 \'iilcaiiite, bvit when united to the gold base imparts rigidity to 
 the latter to almost any degree desinnl, de] lending on the 
 gauge used and the nniouiit of solder applied. 
 
 EXTENT TO WHICH THE WIRE IS APPLIED PERIPHERALLY 
 
 A shoulder wire is apjilied along those areas on a base 
 plate where loss of contour of the border becomes plainly 
 noticeable. This applies not only to lines parallel with the 
 border crest l)ut to the end or perpendicular lines as well. 
 In lower partial cases, of the type under consideration, the 
 wire wliicl) forms the anterior terminal shoulder will usually 
 be laid ])ai'allel with (lie distodingnnl line angle of the tooth 
 clasped, or at such point that when the vulcanite is applied 
 and the case finished, the general lingual contour of the case 
 is continuous witli that of the I)ase iilate along the lingual 
 surfaces of the natural teeth. 
 
 The wire should extend from the anterior lingual 
 shoulder margin, distally, along the Ungual border, curve over 
 the crest of the latter to the Iniccal side and pass forward along 
 the margin to near the anterior terminal of the base plate. 
 It should not rise perpendicularly as on the lingual side be- 
 cause the presentation of a line of gold in this area is un- 
 sightly and unnecessary as well. By trimming the base plate 
 a little scant at the anterior buccal terminal the artificial gum 
 .naterial can overrun the latter and thus oI)viate the display 
 of any gold. The ability to recognize lost border surfaces and 
 contours and lay the shoulder wires in correct ])osition 
 to restore them is an art that should be acqii.ired by every 
 prosthetist and one which, when developed, stamps him a 
 master of his calling. 
 
 LINGUAL BAR DENTURES 
 
 A very common and satisfactory method of replacing the 
 lower posterior teeth is by means of saddles either of gold or 
 of vvilcanite, combined with the lingual bar to serve as a 
 foundation for carrying the substitute teetli. Various methods 
 of retention are employed, the most fref|uent will now be 
 mentioned. 
 
CONSTRUCTION OF PARTIAL DKNTURES JStl 
 
 RELATION OF LINGUAL BAR TO ORAL TISSUES 
 
 In constructing lo^Yel■ lingual bar cases the assembling 
 of the several parts in correct relation to each other and to 
 the oral tissues must be carried out in a definite, systematic 
 and orderly manner. The position of the bar in reference 
 to the lingual border surfaces is particularly important. When 
 in the finished denture, if allowed to touch the soft tissues, or 
 to bear upon them with any degree of force, it will canse more 
 or less discomfort, sometimes so much so as to recjuire re- 
 construction of the case. On the other hand, the bar cannot 
 be placed too far from the border or too near the gingival 
 luargin of the gums, or tnugu(> movements will be interfered 
 with. 
 
 It is impossible to state definitely the exact position of 
 the bar as each case possesses peculiarities of its own. Usually 
 when placed from one-fourth to three-eighths of an inch below 
 the gingival margin, when the lingual muscles will permit. 
 
 and about one twenty-fifth of an inch from the border tissiies, 
 neither tongue movements will be interfered with nor will the 
 border tissues be impinged npon. 
 
 FORMS OF LINGUAL BARS 
 
 It is not possible to here describe all of the various forms 
 of bars used, nor the many general methods of construction 
 followed in these cases, but an outline of the principal steps 
 will be given to serve as a foundation in this work. A case 
 of rei^lacement of the posterior teeth involving a lingual bar, 
 stop clasps and \-ulcanite saddles will be described. 
 
 TECHNICAL' STEPS IN LINGUAL BAR CASES 
 
 F'irst, impressions of the teeth for clasp construction 
 should be secured, and these appliances developed in accord- 
 ance with steps previously described. 
 
 The clasps are placed in position on the teeth and a 
 
ty2 CONSTKlUrKJiN OK PAU'IMAI- OKN'I'l ItlOS 
 
 plaster impressidii secured of the liii.niial ai'ciiK oi' tlie l)ortlei' 
 next which the bar will rest, and of suflicieiil liorder areas hack 
 of the teeth clasped to indicate the iiiaiiiier in which the 
 terminal ends of the hnr can be bent to best advantage for 
 anchorage puriioses. The clasped teeth innst also be em- 
 hraced by the ini])ression. 
 
 To prevent marring of the cast while adapting the lingual 
 bar it should be formed fi-oni some of the harder materials, 
 as Spence's plaster or oxy-cliloride of magnesia. 
 
 The cast having been formed a measurement of the length 
 of wire to be used in making the bar is secured, usually 
 with a smaller wire which can be readily bent, or preferably 
 with a piece of 12 gauge electric fuse wire. The latter wire 
 is very pliable and can be formed to the exact shape of the 
 permanent bar, its ends flattened for retention purposes and 
 any peculiar bends which the case calls for can be discovered 
 before attempting to confonn the very rigid wire of precious 
 metal. This step will not be considered necessary by the 
 experienced wire liender, but will prove most useful to the 
 beginner. 
 
 High-grade clasp metal wire, or iridio-platinum, from 12 
 - tQ-34-gan ge~thickness. is usually used for the bar in orderTEat 
 it may stand the various stresses to which sulijected in the 
 constructive stages and in subsequent use, without bend- 
 ing. 
 
 Two pieces of 16-gauge wire are sometimes bent sep- 
 arately to the form desired and afterward united with solder. 
 This plan is followed by those who find difficulty in conform- 
 ing the heavier gauge wire. Care should be taken to fill the 
 V-shaped spaces between the two wires with solder. When 
 imperfectly filled, food lodges in them and the doubled wire 
 feels uncomfortable to the tongue. 
 
 To develop good anchorage in vulcanite saddles, it is 
 necessary to extend the bar back of the clasped teeth from 
 one-half to five-eighths of an inch. The bar should be bent 
 outward and upward, to the crest of the border, each terminal 
 end flattened broadly and a hole drilled through it, or a short 
 cross-head soldered on to prevent the gradual loosening of 
 the saddle imder stress. 
 
 The flattened ends of the bar should be warped to lie 
 parallel, but not quite in contact, with the border surfaces. 
 The ideal position for the terminal ends of the wire in the 
 finished case is in the center of the saddles. 
 
CONSTRUCTION OF PARTIAI. UKNTl'UKS 41t:! 
 
 VARIATION IN FORM OF CONNECTION BETWEEN LINGUAL 
 BAR AND CLASP 
 
 A conunuii and very ]>ractical lucthdil itf construt'ting tht^ 
 skeletou frame work for a lingual bar case is as follows: 
 
 The bar is coiiformecl anteriorly to the east, as previously 
 deseribed, but instead of being carried back of the teeth em- 
 braced by the clasps and terminating in the vulcanite saddle 
 it is bent upward and outward at the disto lingual angle of 
 each of the clasped teeth, in such position as not to render the 
 'lingual side of the ease bulky nor interfere with arrangement 
 of the substitute teeth. 
 
 This manner of connection of clasp and bar affords no 
 anchorage of metal framework to saddles. To supply such 
 attachment, a piece of clasp wire of the same gauge as the bar, 
 about one-half inch long, is flattened throughout about two- 
 thirds of its length, bent to conform to the curvature of the 
 border crest and distal surface of the tooth and clasp and 
 soldered to the latter. The better plan is to fit the anchor 
 spur in the angle between the turned-up end of the lingual 
 bar and clasp and form the connection principally between the 
 two wires, thus obviating too broad an attachment to the 
 clasp. Another method of anchoring the lingual bar to vul 
 canite saddles is as follows: 
 
 The bar is adapted to correct lingual curxature, as de- 
 scribed. The terminals, instead of being bent outward and 
 over the crest of the border, pass backward, ]mrallel with the 
 lingual periphery of the saddle on either side, or it may lie 
 somewhat above the peripheral margin of th(> saddle, so as 
 to be entirely enclosed with the vulcanite. 
 
 Two ribs of rigid metal are bent to the l)uceo-lingual con- 
 tour of the boi'ders and soldered to the lingual bar, one at the 
 distal extremity of the latter, the other midway between that 
 point and the clasped tooth. These ribs, as well as the Itar, 
 should be enclosed within the vulcanite. 
 
 SOLDERING THE CLASPS AND BAR IN CORRECT RELATION 
 TO EACH OTHER 
 
 The bar, when.jjroperly conformed, is blocked in position 
 on the cast by interposing a small pellet of wax under each 
 terminal end and one anteriorly. While the wax is soft the 
 bar is pressed to the exact position desired and luted by melt- 
 ing a portion of the wax lo both bar and cast. The excess 
 wax is then trinnncd awav. a small ainnunl of investment 
 
494 CONSTRUCTION OF PARTIAL DENTURKS 
 
 mixed and Howcd over the bar at these three points, leaving 
 the greater portion of metal exposed. 
 
 A strip of 20-gauge clasp metal, about one-eighth inch 
 wide, is titted between each clasp and the bar, the lower 
 end of the strip resting between the bar and east, the I'tpper 
 end extending above the gingival margin of tlie clasp so that 
 the solder may develop a broad attachment between the two. 
 No eifort need be made to fit the strip accurately to the cast, 
 since any slight space that may exist between the two will 
 later on fill with vulcanite. 
 
 Flux is now applied and the bar and clasj* on each side 
 are connected with solder, flowing it not only in the joints 
 but over the strip as well, to stiffen it and form a rigid con- 
 nection. This method, it will be seen, does not require the 
 removal of the clasps from their position on the cast, and 
 therefore the relation between them and the teeth they em- 
 brace is the same as when in the mouth. When soldered the 
 case is removed from the cast, picketed, polished and washed 
 and is now ready for the final bite and impression. 
 
 A sliglit variation from the above method is sometimes 
 carried out whereby the attachment of clasps and l)ar may be 
 made as described and stops developed on the clasps at the 
 same time. This refers to cases in which stops were not de- 
 veloped on the clasps or soldered to them during the con- 
 structive stages or before the impression was taken. 
 
 The strip which forms the connection between bar and 
 clasps, either of clasp ]ilate or half-round wire, is cut of suf- 
 ficient length to reach from the bar across the clasp and to the 
 point where the occlusal rest or stop should terminate. It is 
 then annealed and with pliers shaped to meet the recpiire- 
 ments of both standard and stop, when it is attached with 
 solder, as described. 
 
 Sometimes the location of the stop will be out of normal 
 alignment with position of the clasp and bar connection. In 
 such case the stop can be formed separately and soldered at 
 the time of connecting the bar and clasp. It will be found 
 most convenient, and accurate as well, to form the stops on 
 the clasps and unite them during the constructive stages, at 
 which time more ])erfect adaptation can be secured while the 
 clasps are on the metal dies. 
 
 TAKING THE WAX BITE 
 
 The bar, with clasps attached, is now introduced in the 
 mouth and its relation and that of the clasps to the tissues 
 
CONSTRUCTION OK PARTIAL DKNTCRKS 495 
 
 and Ici'tli xcrilicd. If (•(HTcct a wax iiiasli ))il(' is lakt'ii with 
 the api»liaiic(' in iiusitiuii, caiv l)(_'iiig takeu to iiichule all nec- 
 essary tooth, and the l)()vdor areas as well. In this, as in 
 practically all classes of extensive re])lacements, the face bow 
 shouid he a)ii)lied and the hite cavefuUy removed without dis- 
 tortion. 
 
 TAKING THE IMPRESSION 
 
 The final impression in all cases should he in plaster. In 
 cases of the class iinder consideration a full impression of the 
 border surfaces to be covered by the saddles, the teeth clasped 
 and the anterior teeth to slightly below' the gingival line is 
 essential. Lingually the impression should extend deeply 
 enougli to embrace the bar opposite the teeth clasped, but not 
 necessarily anterior to these locations. 
 
 Special care must be observed in taking hoth bite and 
 impression that undue stress is not brought upon the anchor 
 spurs posteriorly, or the lingual bar anteriorly of the teeth 
 clasped, otherwise the framework will l)e tipped and thrown 
 in an abnormal relation to the teeth and oral tissues. By en- 
 closing the terminal ends of each anchor spur in a small mass 
 of soft modeling compound, then pressing the bar down until 
 the clasps take their proper position on the teeth and the 
 bar its correct relation to the border, the framework can be 
 balanced and steadied while taking the impression. The com- 
 pound serves the i)urpose of temporary saddles and when 
 properly ap])lied to the border becomes a part of tlie im- 
 pression. 
 
 The impression usually fractures and comes away in 
 pieces. These should he cleared of debris, reassembled and 
 luted tirmly together, varnished and a cast of hard material 
 constructed on which to vulcanize the case. 
 
 ARTIFICIAL STONE 
 
 Recently there has l)een jilaced on the market an artificial 
 stone product which can be mixed with water and which will 
 harden in about four hours. It is dense and hard and will 
 stand rough usage. It softens somewhat during vulcanization 
 and is more readily removed from the vulcanite than is oxy- 
 chlorid of magiiesia. This ])roduct is specially useful in the 
 construction of partial, and, in fact, all cases where the 
 preservation of relations of several parts in constructive 
 stages is essential. The material referred to is "Weinstein's 
 Artificial Stone," prepared by C. A. Nielsen Co., New York. 
 
i:m; cons'I'1U'c"|'1(».\ oi'' i'aktial dkntukks 
 
 THE LINGUAL BAR COMBINED WITH GOLD SADDLES 
 
 In cases of this type, one of I he coniindii methods of con- 
 strnction is as follows: 
 
 Fii'st — Impressions of the teeth to be ehvsped are secured 
 and clasps constructed by methods previously oiitlined. 
 
 Second — A full impi-ession, in plaster, is secured of the 
 lower arch, including all of the ])arts concerned in the forma- 
 tion of saddles and lingual bar. In most cases the impression 
 should be scraped along the border crests slight 1\-, but the 
 r<'iier so afl'orded should iu)t extend to anterior or posterior 
 terminals. 
 
 The derived cast is trimmed and converted into a model, 
 so as to readily withdraw from the sand mati'ix, and a die 
 and counterdie formed. 
 
 Third — Saddles are swaged to the border surfaces and 
 trimmed to approximately correct peripheral outline. 
 
 Fourth — The lingual bar is adapted to the required con- 
 t(mr of the case, using the die as a model on whicli to do tlie 
 lifting. Tlae Benson Plier is particularly well adapted to the 
 work of bar bending, the wire being held in the concave de- 
 pression back of the beak contact. 
 
 In gold saddle cases, the terminals of the bar should lie 
 parallel with and rest against the lingual margin of the sad- 
 dles to which they are afterward soldered. By proper trim- 
 ming, the upper margin of the bar may lie formed into a finish- 
 ing shoulder for the vulcanite attachment of the teeth. 
 
 If any doubt exists as to the depth to which the lingual 
 border of the saddles can extend without impingement on the 
 tissues the safest plan will be to test the saddles in the montli 
 before uniting them to the bar. 
 
 Fiftli, after the saddles are trimmed to correct lingual 
 width they are returned to the die, the lingual bar adjusted as 
 described under the preceding heading, ''Lingual Bar Den- 
 tures," page 490. 
 
 The terminal ends of the bar are now firmly waxed to the 
 saddle margins, care being taken while adjusting it to avoid 
 springing the bar. It is frequently a good plan, after the bar 
 is perfectly adjusted to the two saddles, to unite one end 
 only with its saddle, remove from the die, invest and solder 
 the two together. The partially constructed frame is returned 
 to the die and careful adjustment secured between it and the 
 opposite saddle, after which they are invested and united as 
 in the first instance. 
 
CUN'STKrCTlOX oK I'AIM'IAI- HKiNTIKKS 497 
 
 Sixth, tlic slvL'lctuii (Iciilui'c is ijicklcd. clraiiscd and in- 
 troduced iu the mouth for llual ii('ri])licrnl triiniiiiiiii and gen- 
 eral adjustment. 
 
 Seventh, the chisps having been formed are adjusted to 
 the teeth, the denture base introduced, trinnned wliere inter- 
 ference witli clasps occur and the relation Ijetween clasps, 
 teeth and baseplate secured as ordinarily accomj^lished or by 
 the compression method describe<l, when sucli procedure is 
 indicated. 
 
 Eighth, when clasps and baseplate are united and the den 
 ture base cleansed; it is returned to the mouth for final im- 
 pression and bite. By usual methods, casts are ]iroduced and 
 mounted on the occluding frame. 
 
 Ninth, the teeth are occluded, and when deemed advisable, 
 cases of this type can lie removed from the cast for final trial 
 in the mouth. 
 
 Tenth, after flasking and separating the case, if the sad- 
 dles have not previously been spurred with a graver, this 
 step should be carried out before final closing of the packed 
 flask. In addition to this method of anchorage, small loops of 
 wire should lie soldered on the saddles and the latter coated 
 with a film of thin chloro-rubber to act as a cementing me- 
 dium between gold and vulcanite. 
 
 SETTLING OF DENTURES FROM USE 
 
 When a denture of any type is introduced in the mouth 
 and worn foi' even a sliort time the mucous tissiies on which 
 it rests will, under pressure, yield slightly, and as a result 
 the denture will settle, as it is commonly termed. The amount 
 of such settling varies in different individual mouths and fre- 
 quently in different areas of the same mouth, depending on 
 the thickness and condition of mucous tissues. 
 
 It is apparent, as a result of such settling, particularly in 
 partial dentures, that two and possibly three conditions ad- 
 versely affecting the usefulness of the denture may develop. 
 
 First, the maximum service of the denature will be im- 
 paired by the greater or less loss of occlusal contact which in- 
 variably occurs. SjBcond, when the substitute is fitted with 
 retention appliances, and no provision is made for settling of 
 the denture, undue stress may be brought upon the anchor 
 teeth. Third, as a result of the preceding condition peri- 
 dental inflammation of the roots of the teeth embraced by the 
 clasps, or to which the denture may lie anchored by other 
 
i'.iS CONS'rUICTKlX (>!•" I'AlfriAl, DKN'I'l'RKS 
 
 iiicaiis. is li;ililc' Id ciisiic. \',\ till' ilispliiy (if i-arcl'iil Jiidg- 
 nu!iit as 1(1 tlic iinilialilf aiiitMiiil llic tissues will yield under 
 workiu.n' conditidiis. and ran-yiui;' nut certain stej)S to c'()ni))(']i- 
 sate for sueli settlin.i;', the dil'liculties mentioned nui>' ho 
 ax'oided. Tliese stejis will now he hrietiy (letaile(l: 
 
 In tlie eonstniction ol' a part iai vulcanite denture to wliit'li 
 stop clasps are adjuste(l. a piece ol' cardboard should be i)laeed 
 lietween the stop and the occlusal area of the tooth on which 
 it rests, at the time of placing' the clasp on the tooth for final 
 impression. The area of the cardboard need not exceed that 
 of the occlusal area of the sto]). Its thickness should be 
 gauged by the extent it is estimated the denture will settle; 
 it may range from the thickness of a sheet of medium weight 
 writing ])a])er to that of a heavy visiting card. The piece of 
 card can be attach(>d to the sto}) l)y flowing between the two a 
 thin film of wax. After the impression is removed, and before 
 constrncting the cast, the cardboard should be removed from 
 the sto}). As a i-esnlt of interposing the cardboard as de- 
 scribed, the clas]) occupies a position on the tooth slightly 
 nearer the plane of occlnsion than it did on the die, during its 
 construction, or would occnpy if ])laced on the natural tooth, 
 without the inter])osition of the cardboard. 
 
 The final I'esnlt of snch proc(>dnre is that when the com- 
 pleted denture is i)laced in the nioutli the stop may project 
 slightly above the occlnsal snrface ui' the tooth it embraces. 
 After a short period of use, oftentiiues within twenty-four 
 lionrs, the settling of the denture will bring the stop in con- 
 tact with the tooth. 
 
 In occluding the teeth, in partial cases, it is advisable to 
 set the substitute teeth so that they strike strongly against the 
 opposite occlnding teeth to insure strong contact occlusally 
 when introduced in the mouth. 
 
 To further insure good contact l)etween the replaced 
 teeth and those in the opposite arch, after settling of the den- 
 ture has occurred, the teeth on the substitute should not be 
 ground to perfect occlusion on first introduction of the finished 
 denture in the mouth. This should be done, however, after a 
 lapse of twenty-four to forty-eight hours, provided the pa- 
 tient has Avorn the denture in th(» meantime. 
 
 COMPENSATING FOR SETTLING OF GOLD BASE SADDLES 
 
 The preceding method is also applicable to the adjust- 
 ment of clasps to a gold base denture, but the following plan, 
 when it can be carried out with accuracy, is to be preferred : 
 
CONSTRUCTION OF PARTIAL DENTURES im 
 
 The clasps are placed in ))ositioii on their respective teeth, 
 without interposing the cardboard, as described, and the 
 denture l)ase introduced and seated on the border. 
 
 .A suitable tray is selected and softened modeling com- 
 pound placed within, on each side, but not anteriorly, so as to 
 embrace a portion of the central area of each saddle Neither 
 the anterior teeth nor clasjis should l)e embraced by the com- 
 pound. Pressure is brought upon the tray to force the im- 
 pression material, not only on the border crests, but over the 
 buccal and lingual areas of the saddles as well. There should 
 be sufficient bulk to the compound so that the impressions of 
 the two sides may be secured without depressing the tray 
 below the level it should occupy in taking the final impression. 
 When chilled the impression may usually be removed withcmt 
 disturbing the ]JOsition of either baseplate or clasps. 
 
 Both anterior and posterior terminals oi each impression 
 are removed, by cutting, leaving a ridge al)out one-fourth inch 
 wide extending from Iniccal to lingual, across the tray. These 
 transverse ridges of compound, one on either side of the tray, 
 are actual cross-sections of the impressions and are designed 
 to force the saddles firmly in contact with tlie tissues while the 
 plaster impressions arc secured of the bas(> plate, the teeth 
 and the unattached clasps. 
 
 Each side of the tray is now filled with sufficient plaster, 
 of suitable consistency, to secure impressions of the desired 
 parts. When introduced and properly centered, pressure is 
 applied and the tray forced borderward until the ridges of 
 compound come in contact with the saddles. The pressure is 
 now increased to a very considerable extent, the idea being 
 to compress the mucous tissues to nearly the full extent of 
 their yielding capacity, after which casts are developed and 
 the clasps soldeued. 
 
 When the clasps are permanently attached to the base 
 plate and the latter is returned to the mouth, it will be seen 
 that the stops of the clasps usually stand slightly above the 
 occlusal surfaces of the teeth embraced. 
 
 By repeating the same steps for producing pressure on 
 the base, in taking the final impression, the t>eeth, when ground 
 and adjusted to the base plate as usual and later are perma- 
 nently attached' CO the denture, will strike the occluding teeth 
 strongly in occlusion. They should not, however, be ground 
 to perfect occlusion at first sitting, but time be given for the 
 tissues to yield before making final correction. 
 
 Dr. G-oslee suggests placing a small post of wood between 
 
sou CUNSTIUTTION OK l\\l{'l"IAI. DKNTliRIOS 
 
 the s;hI(II(' and occlusal surl'accs of llic oijpositc teeth, the 
 montli being open snt'ficiently tor the introduction of tray. 
 By means of this post the patient can coni])ress tlie tissnes 
 under the saddk' dnrinn' tlie hardening of the im])ression. A 
 lialf tray, sneli as is nsed in ])artial cases, by having its tloor 
 sU:)tted to aeconnnodate the post, is nsed foi' carrying tlie im- 
 in-ession material to place. 
 
 To relieve strain on anchor teeth, elliptical s])rings unit- 
 ing the clasps with base plate have been demonstrated by Dr. 
 L. J. Weinstein of New York, who ascribes the suggestion to 
 a Connecticut |)rac1itioner. 
 
 \NI) Fi.AT JIANI). OI'EN 
 
 With the se\eral fundamental iirinciples of partial den- 
 ture construction outlined, of both vulcanite and gold bases in 
 conjunction with stop clasps, the application of various other 
 forms of retention appliances will l)e outlined. 
 
 THE ROACH CONTINUOUS LOOP CLASP 
 
 TECHNIC OF CLASP CONSTRUCTION 
 
 An impression of the tooth which the clasp is to embrace, 
 and the proximating tooth also, is secured which should be 
 tilled with modelite, a very hard cement-like substance, w^iich 
 sets quickly and will withstand rough usage without marring 
 readily; or a die may be formed of Melotte's metal. A piece 
 of 18, 19 or 20 gauge, sixteen per cent platinized clasp metal 
 wire, about 2 inches long, is required for each clasp. The 
 
CONSTRUCTION OF PAKTIAI. UENTUKKS 5Ul 
 
 gauge dei)eiuls on tlie length of the h)()|i and hows and the 
 stress to whieli it will he snhjected. 
 
 The wire is annealed and hent in the middle to form a 
 close, i)arallel staple, after which it is opened slightly and 
 pressed down lietween the two proximatiug teeth, the ends 
 hent ontwavd and around the liuccal and lingual surfaces of 
 
 ROACH OPEN" COXTINUOUS LOOP CLASP. CLASP APPLIED TO LDWEH LINGUAL 
 
 BAR, GOLD SADDLE CAiSE. NOTICE FINISHING SIlOULDEIt FOH VULCANITE 
 
 FOBJIED liY SOLDERED WIRE TO SADDLE. ALSO BIB EXTENDING PROM LINGUAL 
 
 BAR. ONER BORDER CREST. FOR STRENGTHENING PURPOSES 
 
 I.dWKIi l'.\ltTl.\ 
 
 the tooth to form the hucoal and lingual spans so as to em- 
 hrace it closely. It must clear the gingival tissue at all points. 
 The adaptation is comjileted hy Ijeuding the buccal and 
 lingual terminals so as to form a projecting lug for attach- 
 ment to the baseplate, or by uniting with solder and turning 
 the extreme outer ends slightly apai't, they will serve for an 
 anchorage in vulcanite. 
 
502 CONSTRUCTION OK PARTIAL DENTURES 
 
 111 most eases, wlicii the cuilirasiirfs between tlic prox- 
 iiiiatiiig- teeth, in wliieli tlie vertical loop of the bow will rest, 
 are free from ,i<iii,iiival tissue, the wire on both buccal and 
 lingual sides sliould be ean-ied well iido these spaces and 
 comparatively chjse to the gingiva before turning it to form 
 the horizontal sjaans. By so doing the tendency of the dis- 
 tal end of the denture to leave its border is overcome. 
 
 li'i'iAr, I I'l'i.it AMI iiiwi.i: (.(11,11 i:\si, iu.nti iii.s 'iiii. i rri is inN'iii'.r is riTTi;i) 
 WITH sti;i;l facinc. v\ii i-'Lat iiaxd ci^vsrs Tin: i.ciwi.it ulnti hi. with 
 itiucii I'liXTiNi oi s i.dor Axr> flat ijand ci.a.sp 
 
 i.ixni'AT. \ii:w OF Tin-: riiFCEiiixT; cases 
 
 APPLICATION OF THE CONTINUOUS LOOP CLASP 
 
 The application of clasps of this type to a lingual liar gold 
 saddle ease is as follows : 
 
 The saddles and bar having lieen formed as previously 
 described, the baseplate is introduced and the clasps adjusted 
 to their respective teeth. The lugs of the clasps are bent so 
 as to rest on the saddles. An impression is now taken, using 
 the pressure method when advisable, when on removal and 
 
CONSTKl'CTIOX OV PAKTIAl. DKNTVUIOS 50:; 
 
 reassembling- ol' the parts a east of investment is developed 
 
 ami tlie clasps soldel'ed to the hase]ilate. 
 
 THE ROACH OPEN LOOP CLASP 
 
 The open loop clasp is constructed and applied in mncli 
 the same manner as the continuous loop clasp. When clasps 
 of this type are to be formed a heavier wire should be used, 
 since, not being continuous, as is the preceding clasp, it is 
 liable to be bent with use unless the wire is comiiaratively 
 riffid. 
 
 THE KOAfTT OPEX T.nOP CI-ASP 
 
 The outer end may he returned liack npon itself or be bent 
 in any manner to take advantage of a depressed area on the 
 tooth, thus adding to its stability. 
 
 The open loop clasp may lie formed, tirst, as a doul)le bow 
 clasp, the two terminals united with solder to form a rigid lug 
 for attachment and the outer loop severed and bent as condi- 
 tions indicate or they may merely be severed without bending. 
 
 The advantages of this type of clasp are manifold. The 
 long, linear contact of the wire, with varying surfaces of the 
 tooth insuring great clasping proi^erty, together with but lit- 
 tle superficial area of tooth surface covered, is tlie ]irincipal 
 one. 
 
 No provision need be made, as with stop clasps, for the 
 settling of the denture, since, with slight effort, the vertical 
 loop can be raised by bending the horizontal bows occlusally 
 when occasion requires. 
 
,",Ut CONSTIilC'I'IO.N OK I'AKTIAI, I )l':.\'l'l ' K ICS 
 
 Dciituri's littcd witli Inop clasps do not I'l'cl rigid and iiu- 
 yieldiiig, as is often the case wiien non-resilient clasps are 
 used, yet they are retained and rest firmly in position. 
 
 The loop clasp, by its form, obviates the necessity for a 
 stop in most instances, excepting when no proximating tooth 
 is present. 
 
 THE BALKWILL CLASP 
 
 A clasp similar in form to the open loop has been in use 
 in England for many years. A loo]i clasp, together with one 
 
 THE BAI.KWII.I, (II'EN 7. 
 
 of modified form, was described and illustrated by Balkwill 
 in his book on Mechanical Dentistry, edition of 1880. 
 
 The modified form of clasp referred to consisted in adapt- 
 ing a strip of clasp metal to the buccal surfaces of two prox- 
 imating teeth and connecting it with denture base on the lin- 
 gual side with a wire looj). 
 
 Still another form of retaining appliance is shown in the 
 Dental Cosmos, Vol. 56, page 1194, by Dr. Heinrickseu. 
 
 This appliance consists of a loop of clasp metal bent to 
 the curved contour of the gingival tissues, and having a ball 
 terminal which rests in the embrasure against the tooth on 
 
CONSTRUCTION OF PARTIAL DENTURKS 5U5 
 
 tilt' opposite side from the replacement. The wire is beut so 
 as not to impinge on the soft tissues nor does it touch the 
 tooth except at its terminal end. 
 
 To render the appliance effective there must he good 
 contact, in iioi-nial position, between the natural and prox- 
 
 TIIE JlEl.ViiUKSEX rAUTIAI. I.OOl' BAI.L-POIXTKIl 
 
 imating porcelain tooth on the denture, and the ball must be 
 placed close to the gingiva. If in the case illustrated the con- 
 tact of the ball was near the occlusal or incisal area and con- 
 tact between the teeth was defective or close to the gingiva 
 the action of the lnop would Ix' to unseat the denture at its 
 distal terminal. 
 
 THE ROACH BALL AND TUBE ATTACHMENT 
 
 This appliance consists of a ball with projecting spur for 
 anchorage purposes and a tube of lieavy clasp metal which re- 
 
 ceives the ball. The tube is slotted throughout one side to 
 accommodate the passage of the spur. 
 
 APPLICATION OF THE ROACH ATTACHMENT 
 
 The usual method of applying the ball and open tube at- 
 tachment is as follows : 
 
 The crown, inlay, Carmichael attachment, or whatever 
 means may be em])loyed, for securing anchorage to the natural 
 
5U6 CONSTRUCTION OK I'ARTIAI- UKNTURES 
 
 tooth or root is first constructi'd and tciiiiiorarilx set in place. 
 For c'onve'uiciice of des('ri])tioii, a ci-owii will he considered as 
 the means of attachment. 
 
 The position of tiic l)all. which should he close to tlie .2,'in- 
 giva", yet not touchin.i;' it, is mai'ked. To consci'V'c si)ac(' i'or 
 adjusting tlie suhstitutc teeth to the saddle, the ball should 
 be set somewhat to the lingual of the border crest, yet not so 
 far as to produce unnecessary hulk on the lingual side of the 
 finished denture. 
 
 Eemove crown from the mouth and drill a hole at point 
 marked for the reception of the ball stem. When applied to a 
 shell crown, the stem should be cut short, so as not to interfere 
 seriously with the inner periphery of the crown, '^riie shoulder 
 of the stem should rest fiat against the surface of the crown. 
 
 When soldered, the surph;s, if any is present, is removed 
 and the crown is returned to position on the root. A slot is 
 made in tlie saddle, directly beneath the location of the ball 
 to permit the free passage of the denture base to and from 
 position without interference. The denture is now seated on 
 its border. 
 
 An impression in plaster is taken, by the pressure method, 
 if indicated and when set, is removed, the crown usually com- 
 ing away with it. If not, the crown is remo\ed and ])laced 
 in the impression. The latter is now prepared, and partially 
 filled in with Modelite, into which one or two small wood 
 screws are inserted so as to leave the heads freely exposed 
 and projecting. The remainder of the impression is filled 
 with plaster or investment compound, and when hardened the 
 impression is removed. 
 
 The case now consists of a cast representing a portion 
 of the mouth carrying crowns with attached balls and saddles, 
 all in correct relation to each other. The next step is to at- 
 tach the tubes to the saddles in the correct relation to the balls. 
 The tube may be attached to the saddle by various means, but 
 the following method, suggested by Dr. Roach, is, for several 
 reasons, the most practical : 
 
 A piece of 15-gauge clasp metal wire, from one-half to 
 three-fourths inch long, is bent at right angles, flattened slight- 
 Ij^ on one side, the tube laid and soldered on the flattened sur- 
 face parallel with the vertical arm. This wire is called the 
 contact bar, because it not only affords attachment of the tube 
 to saddle, lint tlie vertical portion at its u])y)e]- extremity is 
 
CONSTKITTION OK 1'ART1AI> DKNTURKS 50? 
 
 In-lit t(i lie ill ('(intact with tlic aiiclidr ci-dwii. a1 iionnal con- 
 tact point. 
 
 The bar is now bent so as to briiii;' the liihc to a vertical 
 position snfliciently liigli so that the ball rests in its lower end. 
 
 The parts now sustain tiiis relation to each other: the 
 horizontal arm of tlie liar rests on and lies in contact with 
 
 I 
 
 niAGRAilMATIC CUT. SHO\VIN(i ItEI-ATIOX OF THE SEV- 
 ERAL PACTOKS OF ROACH APPLIANCE 
 
 TilE lUIACH ATT.' 
 
 lMlir.\Eli WITH STOP <'I,AS1' 
 
 saddle; the vertical arm, at its npper extremity, rests at point 
 of contact with the anclior crown; the tube, vertically placed, 
 contains the ball near its lower extremity. 
 
 When this adjustment has been perfected, the horizontal 
 arm is waxed tirmly to the saddle. A mix of investment is 
 applied around the tube, vertical arm, and anchor crown, a 
 
508 {'ONSTIU'CTIUN UK I'AKTIAI- IJKNTl'HRS 
 
 very small ainoiuit bciiii;- suliHcient to hold the |)art in correct 
 relation. The horizontal arm is now soldered tirmly to the 
 saddle. A similar adjustment and attachment is now made 
 Ix'tween tube, contact bar and saddle on tlie ojiposite side. 
 
 These a]>]>iianc('s, in favorable cases, when properly ad- 
 justed, afford most efticient means for retention. In addition, 
 slionld the denture settle, the tube follows without restriction 
 l)y the ball. The necessity for iixing the tube hii>h on the ver- 
 tical arm in the constmctive stage is apparent 
 
 RP 
 
 SM 
 
 W'lr 
 
 ^^V^^^l 
 
 ^Vi -0^ 
 
 ^4,. ^^H 
 
 ^m. *■ 1 
 
 A^ y ■ 
 
 
 
 AXTERIOIt RESTdRATlDX WITH ROACH ATTACHMENT ArPMED 
 
 When the denture is subjected to masticatory stress the 
 tube rotates on the ball, without subjecting the anchor tooth 
 to side stresses or strains. The contact bar, resting as it does 
 on the contact ])oint of the tooth, prevents the raising of the 
 
CONSTUrCTIUN OF I'AUTIAI. DKXTUKKS 509 
 
 distal ciiil (>r the (lenturc, \ct in im \va\' resists compressive 
 force. 
 
 By the exercise of a lilllc ingemuty, the ball and tube 
 attachments may be applied to advantage in many ways for 
 the retention of partial dentures in both arches. They may 
 also be combined with clasps of various types, or with the Gil- 
 more or other standard attachments in such manner as to re- 
 duce to the mininuun danger of injury to the remaining 
 natural tcetli. 
 
 THE MORGAN ATTACHMENT 
 
 This attachment consists of two parts, one of which tele- 
 scopes within the other. The outer consists of a flattened, open 
 loo]) or partial band, called the "keeper," and is attached to 
 
 the ci-owii or inlay of the anchor tooth. The other part, which 
 fits within the keeper, is termed the "anchor"' and is attache(l 
 to the substitute or denture base. 
 
 Tn api)lying these attachments to a denture it is necessary 
 thai they should be as nearly jiarallel as possible, so that the 
 
 WITH .M(lT!(!AX KETCPKIl ATTAI'llKll 
 
 appliance may. be introduced and i-emoved without diffi- 
 culty. 
 
 An appliance called a "soldering jack" is used for para- 
 lelling the keepers and for holding them in )iositi<ui against 
 the crown while soldering. 
 
•Ml) CONSTIU'C'riON OK I'AKTIAL I >l';\"r( ' ItlOS 
 
 TECHNIC OF APPLICATION 
 
 jVii iiui)rcssu)ii, with crowns in |Hisitii>n, is taken and re- 
 moved, the crowns cominc,' away willi i1. From this a cast of 
 investment material is formed ol' usnal size and yivoportions. 
 
 Mill Mill ( \X 
 
 UPIIWLI S 
 
 Tliis is set npon and clamped to tlie base of the soldering jack. 
 A keeper is adjusted to the peri)endicular arm of the jack. 
 
 The latter is moved so as to Itriiiii' tlic attaclmiont against the 
 
 crown surface at the correct angle and in proper itosition, 
 where it is united w^ith solder to the crown. Without changing 
 the perpendiculai- relation of the main post which governs the 
 direction of the arm, the set screw of the latter is released, 
 it is raised from the keeper already soldered: the other keeper 
 
CONSTRUCTION OP PARTIAL DENTURES ill 
 
 is adjusted to the arm. when it is rotated against the other 
 crowu and attached in a simihir manner. 
 
 The crowns may now be permanently set. The anchors 
 are next placed in position in the keei)ers for the final impres- 
 
 sion. When allowance is to he made for settling of the den- 
 ture a U-shaped piece of cardboard can be interposed between 
 the flange of the anchor and the occlusal end of the keeper. 
 The impression is now taken and removed, the anchors com- 
 
 ing away with it or, if dislotlged, an- remo\ed from the keep- 
 ers and returned to place in the impression. 
 
 A piece of heavy German silver plate, bent to resemble 
 the keeper l)ut about one-half incli long, is passed over each 
 anchor and the impression lilhMl with plaster or hard cast 
 
512 CONWTKIH'TION ()l<' l\\UTIAI. DKNTUKKS 
 
 material. 'I'hc (Tcniian >il\('r posts wliicli I'cccivc the Hauges 
 of the Ufeper prevent the distiirbaiicc of relation ot the hitter 
 to the cast. Loops siiould be sokh'i-cil on lhc extension of the 
 anchor for attachment in vulcanite work. 
 
 In case of a gold base denture, when tlie pi-ojeelion does 
 not tonch the base, a ])iece of heav.y plate mav l)e adjnsted be- 
 tween Ihe two and all united with solder. 'I'lie steps from 
 now on are can-ied ont as in an ordinarx- xuh-anite ease. 
 
 THE CONDIT ATTACHMENT 
 
 "^rhe Coiidil attachment consists of two ])ieees. the inner, 
 a chisp metal tube, o])en at the side and ends, which is at- 
 
 tached to the anchor crown, the ojien side toward the space to 
 be tilled. The outer part is a telescoping tube, open at the 
 side and one eud. To the other, or occlusal, end is attached a 
 floor, in the center of which is fixed a rigid post, the same 
 diameter as that of the inside of the inner tube. It will be 
 seen that tliis appliance possesses greater grasping property 
 than any of the other standard types descriljcd, since the inner 
 tube grasps the center post of the outer appliance, while the 
 latter grasps the outer surfaces of the inner tube. 
 
 The application of these appliances is similar to that of 
 the Morgan, just described, a paralleling device being neces- 
 sary for the proper adjustment of the inner tubes to their 
 respective crowns. 
 
CONSTRUCTION OF PARTIAL DENTURES 
 
 SMAl.I. IlESTORATIOXS SHOWINO VARIAa»IONS IN APPLICA- 
 TION OF CONDIT ATTACHMENT 
 
CONSTRUCTION OK PARTIAL DENTURES 
 
 Wlieu amplo oecluso-gingival space exists, these appli- 
 ances, when properly balanced and adjusted, serve a most 
 useful purpose. 
 
 THE GILMORE ATTACHMENT 
 
 This appliance consists of a U-shaped clip or clasp of 
 rig-id yet resilient metal, the tlauges of which receive a 14-gauge 
 wire. No paralleling device is needed other than the eye in 
 adjusting this attachment to a case, but at the same time when 
 
 E3 
 
 ENLARGED VIEW OF GILMORE 
 
 ATTACHMENT DESIGNED FOR 
 
 METAL OK VULCANITE 
 
 WORK 
 
 ENLARGED VIEW OF GILMORE 
 
 ATTACHMENT DESIGNED FOR 
 
 VULCANITE WORK 
 
 two or more are used in a denture they should be placed with 
 tianges as nearly parallel as possible with the line of direc- 
 tion of introduction to and removal from the mouth. 
 
 APPLICATION OF THE GILMORE ATTACHMENT 
 
 The application of the Gilmore attachment varies in dif- 
 ferent eases according to tlie position of the anchor teetli and 
 the spaces to be filled. 
 
CONSTRUCTION OP PARTIAL DENTURES 515 
 
 For example, in a lower partial denture in which the 
 posterior teeth, back of the cuspids or bicuspids, are to 
 be replaced, it is necessary to provide against the movement 
 of the denture away from the anchor teeth. The necessity 
 
 BARS BENT. AIM'LIEI) 
 
 FOR GILMORE 
 
 for this is apparent, since the attachment itself cannot resist 
 horizontal movement, under stress, of the denture along the 
 ridge. When the space to be filled is bounded anteriorly and 
 
 ANGLE B.Ul BENT TO SET 
 
 AGAINST CROWN AND 
 
 .\I,\EOI.AR BORDER 
 
 posteriorly by natural teeth, these prevent such movement 
 and the application of the appliance is simple. 
 
 The technic of application of the Gilmore appliance in 
 
 [- ,::^ ^_^\ 
 
 CROWN WITH BAR Al'I'LIED FOR 
 GILMORE ATTACHMENT. THE 
 VERTICAL ARM LIES TOO CLOSE 
 TO GINGIVAL jVHEA OF THE 
 CROWN, ALSO SHOULD fiXTEND 
 NEARLY TO OCCLUSAL SURFACE 
 
 CROWN WITH BAR APPLIED FOB 
 GILMORE ATTACHMENT. THE 
 BAB SHOULD NOT ENCROACH 
 TOO CLOSELY ON GINGIVAL 
 TISSUES NEXT TO CROWN 
 
 the first case mentioned, all of the teeth posterior to the sec- 
 ond bicuspids having been lost, is as follows : 
 
 Crowns are constructed for the second bicuspids and 
 placed in position, but not cemented to their respective roots. 
 
516 CONST'RIH'TIOX OF PARTIAI. DENTl'KKS 
 
 All imiJri's.sioii is secured and iciiiox cd, the ciowiis usu- 
 ally coining away witli it. Fruiii the impression, a east, com- 
 posed of investment material, is secured. To the distal sur- 
 face of each crown a piece of 14-gauge wire of iridio -phitinuni 
 or highly platinized clasp metal is adapte<l. 
 
 The wire should be bent so as to lie in contact with the 
 occlusal two-thirds of the crown; at the gingival third it 
 should leave the crown surface at a gradually increasing slant 
 to form a clearance sj^ace for the protection of gingival tis- 
 sue. The horizontal portion of the wire should conform to and 
 rest lightly upon the border, its position lieing usually slightly 
 to the lingual of the crest. At a distance not exceeding three- 
 eighths of an inch from the crown the distal end should be 
 turned up sharply at a right angle. The direction of this 
 vertical portion of the wire should be parallel with the line of 
 direction of introduction and removal of the denture. Its 
 height may vary from one-sixteenth to three thirty-seconds of 
 an inch. When the wire is properly conformed it is waxed 
 in position against the distal crown wall, and a mix of in- 
 vestment is made and applied over the bar along the ridge, 
 being careful to enclose the distal, vertical end. This is neces-. 
 sary to obviate jjossible lateral rotation of the end against the 
 crown wall in soldering. The wax is removed from the joint 
 flux applied and the bar is soldered to the crown. 
 
 It is frequently advisable to extend the solder somewhat 
 beyond the area of l)ar connection with the crown to render 
 the latter rigid. A l)etter ])lan is to adapt and solder a piece of 
 plate to the distal wall of the crown during the constructive 
 stages. The addition should be attached with high-grade sol- 
 der, so that the union may not later be disturbed in soldering 
 the bar. 
 
 When the bars are attached the rough surfaces of both 
 crown and bar are removed and given the final finish. The 
 crowns are again returned to position in the mouth and a bite 
 and final impression secured. The teeth are occluded, the 
 case carved, flasked and separated, and the matrix packed as 
 usual. 
 
 ADJUSTMENT OF CLASPS TO BARS 
 
 A strip of cardboard, cut to fit between the flanges of the 
 attachment, is pressed in place against the inner, curved sur- 
 face of the attachment, and the latter set in position on the 
 bow. This is to allow for sul)sequent settling of the denture. 
 
 The clasp should occupy a position about midway between 
 the crown and terminal end of the bar. It should be ranged 
 
CONSTRUCTION OF PARTIAL DENTURES 517 
 
 with Haiige.s parallel or as nearly so as possible, with those of 
 the opposite attaclunent ; tliat is, l)oth attachments shouhl ))(■ 
 placed so that the flanges stand ])eri)endicular. Furthermore, 
 
 REIATION OF GILMORE ATTACHMENT 
 TO BAR AND CAST. IN VULCANITE WORK 
 
 A. 14 G BAR 
 
 B. GILMORE ATTACHMENT 
 
 C. CARDBOARD 
 
 D. FILM OF PLASTER 
 
 DlACiUAMMATlL- CVT SHOWING DELA- 
 TION OF THE SEVERAL PARTS OP 
 A GILMORE ATTACHMENT 
 
 they should be forced as closely to the liar as the interposed 
 cardboard will permit. 
 
 The last step before closing the flask consists in obliter- 
 ating the s])aces between bars and borders so as to exclude 
 file lubber in closing tlie flask. This is necessary so that the 
 
 CASE IN WHICH IT IS L'NNECESSARY TO BEND TERMINAL 
 
 END OK 4SARS VERTICALLY FROM THE BORDER, 
 
 GILMORE ATTACHMENTS 
 
 bars and crowns may later be removed from the vulcanite 
 without mutilation. A thin mix of plaster is applied in the 
 space between the borders and bars, and along the outer sides 
 of the flanges as well, so that the surfaces are free from under- 
 
518 
 
 CONSTRUCTION OF PARTIAL DKNTUHBS 
 
 cuts. Tlie plastoi' should init ciitci- the (i]icniiios beneath 
 anchor lugs, nor surround the hitter. 
 
 Wlien the plaster has hardened, the tlask is closed and the 
 case vnleanized. On o])ening- and ch'ansiiiii- the denture, the 
 
 surplus vulcanite is removed. A thin t)lade instrument is 
 passed along on either side of the bar and flanges, to remove 
 as much as possible of the plaster which was built in under 
 the bar. With a little careful pressure and manipulation, the 
 bars will part from the vulcanite without difficulty, after which 
 the ease is finished. The margins of the groove which receives 
 
 LINGUAL \1E\V OF I'RECEDING CASES 
 
 the bar should be smoothed and a round bur of approximately 
 the diameter of the bar should be applied in the groove to 
 deepen it slightly and also to deepen the opening into which 
 the terminal end of the bar enters. This step is carried out 
 to provide for future settling of the denture. 
 
CONSTRUCTION OP PARTIAL DENTURES 519 
 
 Oftentimes two or three widely separated roots or teeth 
 can be utilized for supporting a denture. Roots should be 
 filled and post inlays, whieh extend neatly to the peripheral 
 
 ALVEOLAR BAK Sfl'PORTED BY TWO ROOTS ANll TWO IXLAT AT- 
 
 TA1-IIME\TS. THREE OR MORE (ilLMORES MAY BE AT- 
 
 TACIIEO AS REOrlREI) 
 
 margins, constructed for anchorage purposes. Such attach- 
 ments may be combined with crowns set on roots of teeth or 
 with inlays set within tootli crowns and all connected by a 
 
 border bar. It is frequently advisable, when only two or 
 three teeth remain, to remove the crowns and inlay the roots 
 as described. By this procedure there will be no break in the 
 
CONSTRUCTION OK I'AKTIAl. DKNTl'HKS 
 
 FULL DENTl'RE, I'ALATAL VIEW, SHOWING (iK()(>\ E 
 FOR AL\EOLAR BAR WITH (ilLMORE AP- 
 PLIANCE NEAR EXTREMITIES 
 
 ALVEOLAR BAR SIPPIIRTEH HV TWO CISPII) ROOTS. 
 
 A GILMORE ATTACHMIINT SHOULD BE PLACED 
 
 BACK OF IvACII lUlOT AND ONE IN 
 
 TIIK .\1 EI II AX LINE 
 
 SECTIONAL \ I E W OF 
 ROOT WITH DOWEL AND 
 INLAY TO WHICH ALVE- 
 OLAR BAR IS TO ATTACH 
 
 OCCLUSAL VIEW OF INLAY 
 IN POSITION ON ROOT. WITH 
 ALVEOLAR BAR ATTACHED 
 
CONSTRt^CTION OF PARTIAL DENTURES 521 
 
 aitilicial i>iini rt'stdvatioii, nor in tlic aliniinicnt of the sub- 
 stitute teeth. 
 
 Tins system, as well as the others previously deseribed, 
 are capable of a wide range of ap])lieation. Tn fact, they seem 
 limited only by the skill of the prosthetist. 
 
 GILMORE ATTACHMENT MOVEMENT 
 
 OF DENTURE DISTALLY PREVENTED 
 
 BT LOCKING AGAINST MESIAL OF 
 
 FIRST BICUSPID 
 
522 CONSTIUU'TION OF PARTIAL DKNTIIRES 
 
 THE PALATAL ARCH BAR 
 
 The palatal arch Ijar luliills a similar purpose in upper 
 partial dentures as the lingual bar in lower cases. The idea 
 of a bar is not to afford support by its bcarino- against the 
 
 LINGDAL BAB, GILMOBE APPLIANCES 
 
 tissues, but to unite widely divergent points of support by 
 means of a light yet rigid structure, and convert them into 
 what has been termed inuliiple anchoyage. This may be ac- 
 complished quite as efficiently in the upper as in lower arch. 
 Briefly stated, the system of partial denture construe- 
 
CONSTRUCTION OF PARTIAL DENTURES 523 
 
 tion as practiced to-day consists in developing light, rigid 
 structures, supported in tlie mouth in such manner as to cause 
 no injury to the remaining natural teeth, nor subject the 
 anchor teeth to undue strain or injury. 
 
 THE KELLY ATTACHMENT 
 
 The Kelly attachment consists of two small thimbles, each 
 closed at one end, which telescope one within the other, with 
 reasonably tight contact. 
 
 Retention of a denture, however, in which these appli- 
 ances are utilized, is not depended upon the closeness of 
 
 adaptation of tlic thimlile walls, but upon diverging or con- 
 verging the appliances in setting them upon the anchor teeth. 
 
 APPLICATION OF THE KELLY ATTACHMENT IN VULCANITE 
 WORK 
 
 Caps are formed and titted with dowels to prepared roots. 
 To these caps the inner thimbles are adjusted and soldered 
 so as to present from one-sixteenth to one- sixty-fourth inch 
 divergence from, or convergence to, each other. 
 
 The outer are set in position on the inner thimbles and an 
 impression secured. The cast produced from the impression 
 carries the two outer thimbles as projections above the border 
 surfaces. Freqneiitly a shell crown is constructed to telescope 
 loosely over the outer thimble, as its presence on the cast pre- 
 vents placing an ordinary vulcanite tooth in this location. 
 The vulcanite fills the space and forms the bond of union be- 
 tween the thimble ajid crown. The case is carried through in 
 the usual mani>er, the thimbles remaining with the cast in 
 flask separation, but they become a component part of the 
 denture. 
 
 Wlieu tinished, the margins around the opening of the 
 thimbles are slightly beveled and smoothly polished. 
 
524 CONSTRTK'TION OH PARTIAL DENTURES 
 
 In introducing- the denture, the yield of the peridental 
 membranes of the roots involved, together with some slight 
 spring in the dentui'c itself, ))ermits the inner thimbles to 
 enter the outer, altliongli not in perfect alignment. When 
 seated, however, no strain upon the anchor roots is noticcal)I('. 
 
 KELLY COMBINED WITH GILMORE ATTACHMENT 
 
 A. KELLY THIMBLE 
 
 B . 14 GAUGE BAR 
 
 C. GILMORE ATTACHMENT 
 
 These attachments, slightly modified, are frequently com- 
 bined with others, as, for instance, the Grilmore. They can 
 be applied in gold base dentures with even greater ease than 
 in vulcanite work, the outer thimlile being soldered to the base- 
 plate. The thimbles vary in size from three thirty-seconds 
 to one-fourth of an inch in diameter, or even larger. 
 
 THE GRISWOLD ATTACHMENT 
 
 This attachment consists of two triangular- shaped tele- 
 scoping tubes, the outer one open along the angle, the other, 
 or inner, being slotted through the middle of one side. 
 
 ENLABGED VIEW 
 OF GRISWOLD 
 ATTACHMENT 
 
 SKETCH OF GRISWOLD INNER TUBES IN POSITION 
 
CONSTRUCTION OF PARTIAL DENTURES 
 
 ll l.rAMI K AH I III. lit .Mil II lull 
 
 OR STRIP. DEXTIRE HVV- 
 
 PORTED I)Y FOUR CKIS- 
 
 WOLD .\TT.\1'HMEXTS 
 
 ri'PER ANTEBIOr. RESTORATION SADDLE 
 
 DEXTURE STIPP0R1E1J BY GRISWOLD'S 
 
 ON FIRST BICUSPIDS 
 
 The smaller is attached hy its a^ex to a crdwii or inlay, 
 while the other is soldered to the gold hase or enclosed within 
 the vulcanite. 
 
 FORMS OF PORCELAIN TEETH 
 
 Porcelain teeth as siip]ilied by the manufacturers are 
 divided into two classes, known as plai)i and giDii teeth. Each 
 of these classes can again be sulidivided into two classes, vul- 
 canife and phifc teeth. 
 
 PLAIN TEETH 
 
 A plain tooth represents the crown, or a portion of the 
 crown, of a natural tooth in porcelain. Since teeth of this 
 type are designed to take the place of lost natural teeth, they 
 represent, more or less jDerfectly, the anatomic forms of the 
 natural organs in general outline. The linguo-gingival areas 
 of most porcelain teeth are deticient, or lacking in contour, to 
 afford means for attachment to the metal or vegetable mate- 
 rial which forms the structure of the substitute. 
 
 MEANS OF ANCHORAGE 
 
 Metallic pins are most conuuonly used f^r anchorage pur- 
 poses, one end of each pin being enclosed and tixed in the 
 porcelain by fusion of the latter around it, the other end 
 projecting for attachment within the substitute material. A 
 plain tooth is usually supplied with two pins, vulcanite teeth 
 having headed pins while in plate teeth the pins are straight. 
 
526 CONSTRUCTION OF PARTIAL DENTUKKS 
 
 Another means of anchorage consists in (Ievelo])iug 
 within the porcelain some mechanical form of attatihment, as 
 dovetailed projections, or countersunk, depressed areas, with 
 small openings extending through the proximate surfaces, as 
 in diatoric and similar forms of teeth. 
 
 PLAIN TEETH FOR VULCANITE WORK 
 
 Teeth of this type are designed for use with plastic bases, 
 of vulcanite and celluloid, headed pin, and diatoric teeth being 
 the most common forms used. These are manufactured in 
 
 f^f\f%^ 
 
 SET OP NO. 28, PLAIN TKETH. \Tn,CANITB (S. S, W.) 
 
 great variety as to length, width and color, some in no wise 
 resembling natural tooth forms, while others approach very 
 closely to anatomic types. 
 
 Both platinum and alloys of base metal, usually nickel, 
 are used for pins of vulcanite teeth, the latter being employed 
 because of its cheapness. Unless protected by a film of non- 
 
 SET OP NO. 28, PLAIN TEETH, VULCANITE (JUSTI) 
 
 oxidizable metal as an electro-deposit of gold, base metal 
 pins are liable to disintegration with use in the mouth. 
 
 The oxidation of base metal pins during fusion of the 
 porcelain frequently causes discoloration of the latter, some- 
 times to such an extent as to render the product unfit for use. 
 This occurs most frequently in anterior teeth, where the bulk 
 of porcelain is limited. To overcome this difficult^^ thin 
 platinum tubes, the inner ends flanged, are baked in the teeth, 
 
CONSTRUCTION OF PARTIAL DENTURES 527 
 
 in the locatioii of the pius, aud the base metal plus are after- 
 ward soldered within the tubes. 
 
 ADVANTAGES OF PLAIN TEETH IN VULCANITE WORK 
 
 There are two principal advantages in the use of plain 
 teeth in vulcanite work as compared with gum teeth. 
 
 First, they are more easily arranged in anatomic align- 
 ment, and, if necessary, can be readily modified to meet usual 
 and unusual occlusal requirements. 
 
 Second, they can be placed in restricted locations and 
 spaces where gum teeth cannot be used. 
 
 V LJJJ 
 
 ^ R 
 
 VARIOUS SIZES OF rL.lIX TEETH. FOR \TI.C.i>.ITE OR CELLULOID. COXSTRICTED CERVICES 
 
 PL.ilX TEETH, VULCANITE. 
 
 TRANSVERSE CORRUGATIONS. 
 
 CONSTRICTED CERVICES 
 
 OBJECTIONS 
 
 The iirincipal objection to the use of plain teeth, where 
 gum restoration is necessary, is on account of the gum mate- 
 rial at present available. Pink vulcanite is oi)aque, and under 
 most favorable conditions affords but little resemblance to 
 living, healthy gum tissue. 
 
 The silicate cements are being tested, as to durability, 
 as a substitute for gum restorations. This material fulfills 
 esthetic requirements quite as well as porcelain. 
 
 . DIATORIC TEETH 
 
 Diatoric or pinless teeth are so formed as to afford 
 anchorage for plastic materials around and within the porce- 
 lain. Teeth of this type, when bulk of material is not too re- 
 stricted, and the mechanical retention forms are well propor- 
 
528 CONSTRUCTION OF PARTIAL DENTUHKS 
 
 tioiied, are cajiablc of witlistaiidiiig iiiasticatdry sifcss (inite 
 as well as pin teeth. In addition, they are much h'ss ex])en- 
 sive, a factor of some importance at times. 
 
 Diatoric molar and bicuspid teeth, when sliiihlly m(i<lilicd 
 by griiidiiis', ;ire fi-e(|iieiitl>- used iu cdnjunctidii with .yold, in 
 
 the construction of bridge work, the technic lieing similar to 
 that employed in the application of full or i^artial liorcelain 
 crowns, for such purposes. 
 
 COUNTERSUNK PIN TEETH 
 
 A countersunk pin tooth consists of a fully contoured 
 porcelain crown, in the base or cervical portion of which is a 
 depression from which projects a headed pin for anchorage 
 
 o mMi 
 
 COUNTERSUNK PIX TEETH. BISCUSPIDS 
 
 ^ 
 
 m 
 
 no 
 
 COUNTERSUNK PIN TEETH, ANTERIORS 
 
 purposes. The advantage of this type of tooth in denture con- 
 struction is due to the fact that the full lingual contour of each 
 tooth, which the basic material need not envelope to any ex- 
 tent, feels more comfortable, and enables the patient to speak 
 more distinctlv than when such contour is deficient. 
 
CONSTRUCTION OP PART1AI> DENTURES 529 
 
 ASH'S TUBE TEETH 
 
 A tube tooth consists oH a fully contoured porcelain crown, 
 having an opening extending entirely through it from cervical 
 base to occlusal surface or just to the lingual of the incisal 
 
 TUBE TEETH. BISCUSPIDS AND MO- 
 LARS (ASH'SI. SET ON GOLD CASTING, 
 JX WHICH IRIDU) I'LATINl M PINS 
 ABE ENCLOSED. SHOWING AI'IT.ICATION 
 IN BRIDGE WORK 
 
 edge. Teeth of this ty])e are occasionally used in conjunction 
 with vulcanite, a headed pin or wire, slightly smaller than the 
 opening, and longer than the crown being titted to each before 
 
 A B 
 
 B 
 
 D 
 
 E 
 
 4 1 
 
 F G 
 
 H 
 
 1 
 
 1 
 
 J 
 
 V.iRlOlS FORMS OK ASUS MINEUAE TEETH 
 A — Porcelain Tip with Pins for Anterior Restorations 
 B — Flat Back Repair Facing 
 C. D. E— Very Short Bite Molars. Dialorir 
 F. G— Dimelon- Faciiigs 
 H. I. .1— Tulie Teeth 
 
 packing the case. The head of the pin projects slightly 
 beyond the cervical end of crown. In closing the packed 
 flask, the rubber is forced into the vacant space in the tube 
 and around the pin head and thus firmly anchors the tooth 
 
530 CONSTRTTCTION OF PARTIAL DKNTURES 
 
 ill ])lac('. These teeth are capable of a wide range of applica- 
 tion ill crown and bridge restorations as well as in metal base 
 denture construction, but unfortunately are not easily pro- 
 cured or extensively used in this country. 
 
 I'ARTIAl, DEXTDBE. GOLD BASE. Tl'BE TEETH 
 
 (ASH'S) 
 PLAIN PLATE TEETH 
 
 A plain plate tootli consists of a veneer or partial crown 
 of porcelain. It is usually supplied with two straight, head- 
 less pins which project from the flattened lingual surface. 
 Teeth of this type are designed for use with metal, in crown, 
 bridge and denture work. Because of the liability of fracture 
 occurring in these teeth during soldering operations, and the 
 further difficulty of replacement, when fractured from any 
 cause, facings of the replacable type are gradually coming 
 into general use for the purposes mentioned. 
 
 VARIOUS FORMS OF PLAIN TEETH 
 
 There are various forms of ])lain teeth designed for spe- 
 cial purposes, among which may l)e mentioned the Dimelow 
 
 BACKING WITH STAPLE PINS 
 
 ADAPTED FOR DIMEI^flW 
 
 FACING 
 
 facing, consisting of a flat back veneer, having two holes in 
 the location usually occupied by the ]iins, and which slant 
 slightly, from lingual to labial, incisally. These holes receive 
 
CONSTRUCTION OP PARTIAL DENTURES 531 
 
 two pins, projeftiug at a corresponding angle from the substi- 
 tute. Mechanical anchorage is thus aftorded by the slant of 
 the pins as well as by the cement which serves as a bond of 
 
 OOOXD 
 
 SHORT AND LONG BITE BICUSPIDS AND MOLARS. DIMBLOW TEETH 
 
 union between the two factors. Tliis tooth is used principally 
 in repair work for crowns and 1)ridges. 
 
 ASH'S FLAT BACK REPAIR FACING 
 
 This tooth consists of a flat back veneer, having a trans- 
 verse, oblong, dovetailed opening in its lingual surface, for the 
 
 FLAT BACK KlOl'AII! FACING 
 
 USED PRLNCIPALLY IN CROWN 
 
 AND BRIDGE KEPAIHS 
 
 reception of a metal projection on the substitute and for the 
 cementing medium. It is used principally in repair work on 
 crowns and bridges. 
 
 ASH'S HELIX TOOTH 
 
 This tooth consists of a flat back veneer, having a cylin- 
 drical, threaded opening in its lingual surface, in the center 
 
 of which is a threaded metal pin. A slight collar surrounds 
 the opening, which may or may not be ground away as con- 
 ditions of adjustment demand. 
 
CONSTRUCTION OK I'AKTIAI. UKNTUKKS 
 
 Teeth of this lyi)c 
 where the .ilvoohir I'id 
 
 SADDLE BACK TEETH 
 
 ;nc iiitciuk'd for use in those cases 
 (■ is prouiinent, and space is con- 
 
 SIKIKT lUTE SADDLE llAl'K HllTSl'lD.S 
 
 strieted. Tliey arc intended principally for vulcanite work, 
 altiiough tliose sup])lied witli plain or headless pins are often 
 used in crown and ])rid"(' work. 
 
 CONTINUOUS GUM TEETH 
 
 The teeth used in continuous gum cases are of the plain 
 type, but differ from those described in having cervical ex- 
 tensions which resemble the outer surfaces of the roots. 
 
 These extensions serve two purposes. First, they afford 
 support to the tooth in its attachment to the iilatinum liase, 
 
 CONTlNIlOrS GUM TEETH 
 
 during fusion of the added i)orcelain, and second, being com- 
 l)0sed of high fusing porcelain, they supply a portion of the 
 recjuired Inilk or contoui' of the denture proper, thereby pro- 
 portionately reducing contraction in the bulk of continuous 
 gum body, due to fusion. 
 
 GUM TEETH FOR VULCANITE WORK 
 
 Gum teeth, as their name implies, have an extension root- 
 ward, which in contour and color represents the natural gum 
 tissue. They are made in single tooth sections and in blocks 
 of twos and threes for full dentures. Special sections of two, 
 three, and even four teeth are procurable, for use in partial 
 denture construction. Sections of this type are indicated in 
 
CONSTRIirTION OF PARTIAL DENTIRKS 
 
 SKT OF -NO. :;S GIM SECTION TEETH (S. S. W 
 
 THE IM \l Itl I \Tlo\ in VDIOIN 
 
 IXG BI.OIKS OF GUM SECTION' 
 
 TEETH BEFORE GRINDING 
 
 VAKIOCS FORMS OF ANTERIOR BLOCKS. NOTICE THE FESTOONS AND UNDULATING SUR- 
 FACES OF GUMS 
 
534 CONSTRUCTION OF PARTIAL DENTURES 
 
 cases where gum restoration is recniircd, and the joint be- 
 tween natural and artiticial gum is visible. 
 
 Because of the difficulty in developing anatomic occlusal 
 requirements in full dentures, gum section teeth arc not used 
 in such cases to any extent. 
 
 SPECIAL FORMS OF GUM KLOCKS FOR ANTERIOR REPLACEMENTS 
 
 GUM TEETH FOR METAL WORK 
 
 Since there is a wide range of ditference in contraction 
 and expansion of metal and porcelain the use of gum teeth in 
 conjunction with gold or other metals is contined to single 
 teeth or blocks. 
 
 Gum teeth designed for metal work have flat backs, and 
 straight or plain pins. Special care must be used in solder- 
 ing operations to avoid fracture of the porcelain, which occurs 
 from unequal distribution of heat, sudden changes of tem- 
 perature and ditference in expansion between teeth and metal. 
 
 PROPORTIONATE PARTS OF TEETH 
 
 In selecting a tooth for any given case attention should 
 be given to the shape and angle of its cervical end or "ridge 
 lap," the "shut" and the "bite." 
 
 RIDGE LAP 
 
 This term refers to the beveled surface of a tooth which 
 slopes lingually from its cervical portion to the lingual side. 
 The ridge lap varies in its length and angular inclination in 
 different teeth, although the shut and bite in the same teeth 
 
CONSTRUCTION OF PARTIAL DENTURES 535 
 
 may be alike. Likewise, either the shut, or bite, or both, may 
 vary, while the ridge lap will be the same. 
 
 When the alveolar ridge is prominent, liut little absorp- 
 tion having occurred, and the lip line is high, teeth with long 
 
 ridge lap are indicated. When much absorption has occurred 
 and but little, if any, of the ridge shows, when the lip is 
 raised, teeth with short ridge lap are indicated. 
 
 THE SHUT 
 
 The sliut refers to the space between the upper and lower 
 alveolar processes, or between the teeth of one arch and the 
 alveolar process of the opposite arch. The shut of an arti- 
 
 ficial tooth is indicated bj' the distance between its lingual 
 shoulder and the angle formed by its ridge lap with its lingual 
 surface. 
 
 THE BITE 
 
 The bite, or overhife, in artificial teeth refers to the dis- 
 tance between the incisal end of a tooth and its lingual 
 shoulder. 
 
 In selecting teeth, special care must be given this point. 
 When teeth with short bite are selected, and the case demands 
 considerable overbite of tlie upper over the lower teeth, the 
 lingual shoulders must be ground away to a greater or less 
 
536 CONSTRUCTION OF PARTIAI> DENTURES 
 
 extent, to secure the (icsircil rdatimi, wliich l'rei|iieiitl>' 
 weakens the porcelain. 
 
 Another case in wliicli lon^'-liite teeth sliouhl he used is 
 in h)wer anterior rephicenients. By tlie use of long-hite teetli 
 much less vulcanite is required to develop proper lingual 
 
 SHORT RIDGE 
 LAP 
 
 Long Simt. Mertiuin 
 Bite 
 
 MEDIUM RIDOE 
 liAT 
 
 Short Shut. Long 
 Hite 
 
 EXTRA LONG 
 RIDGE LAP 
 
 Short Shut. Mediiu 
 Bite 
 
 contour than when this ])()rtion of the crown is devoid of nor- 
 mal contour. 
 
 This portion of the tooth may be, and usually is, 
 described as having a }n\iq, vipdhrm or short bite. 
 
 THE TOOTH SHADE GUIDE 
 
 Most manufacturers of ])orcelain teetli j^i'ovide a shade 
 guide on which, in some manner, are displayed the different 
 shades or colors of teeth supplied by them. These guides 
 usually are composed of from twenty-five to forty sample 
 central incisors of average size, all differing in shade, tone 
 or tint. By means of a guide of this type, teeth of suitable 
 color may be selected with a reasonable degree of accuracy. 
 
 Some prosthetists without a special knowledge of the 
 laws of harmony are able to arrive at satisfactory results in 
 the selection of teeth of api)ropriate shades for any individual 
 case. 
 
 How they do it or why the results are satisfactory they do 
 not attempt to explain further than it is by guesswork or in- 
 tuition. 
 
 Intuition, however, in color science is not the result of 
 guesswork, but is due to a more or less conscious or uncon- 
 scious development of color function in the visual organs, as 
 has been explained. 
 
CONSTRUCTION OF PARTIAL DENTURES 537 
 
 APPLICATION OF THE TOOTH SHADE GUIDE IN PRACTICE 
 
 The patieut sliould hf seated facing- a direct liglit. The 
 face, eyes and hair shouUl be scanned as a whole, to deter- 
 mine the general color scheme of the complexion and to esti- 
 mate, as closely as ]5ossible, the eomplementaries of the tints 
 there displayed. 
 
 By carefnl observation, with a little experience, this 
 examination enal)les the prosethetist to select from the shade 
 guide a tooth of the general tints required. The first selec- 
 tion, even if possessing the fundamental tints indicated, may 
 not meet requirements. The tooth may be too light, or too 
 dark, or it may need the addition of some primary or sec- 
 ondary color of greater or less intensity, to develop the 
 necessary harmony. If not pleasing, other teeth are tested 
 until one is found that, by its presence in the mouth, creates 
 the impression of liarmony and is satisfying to the esthetic 
 sense. 
 
 Strong colors displayed in the complexion call for 
 strongly marked shades of teeth, within certain limits of 
 course, while a person having a complexion made up of weak 
 colors must be supplied with teeth of neutral tints, or highly 
 attenuated colors of a generally neutral tone. 
 
 Porcelain teeth are perceptibly darkened by the sliadows 
 of the lips and oral cavity, some more tlian others, depending 
 on their translucency or power of transmitting- light. 
 
 In selecting teeth, therefore, it is advisable to test them 
 not only in direct light but to change the position of the 
 patient so that the teeth may be subjected to both lip and oral 
 shadows, and the effect noted. When tested by direct light 
 only too light a shade of tooth is liable to be selected, with 
 the result that in the finished denture the teeth will appear 
 too dark. 
 
 When a suitable color of tooth has been selected a record 
 should be made of its number, and from tliis teeth of a cor- 
 responding color number are yirocureil. 
 
 A NEW GUM FACING 
 
 Protesyn, a silicate cement, has been recommended and 
 is being used to a limited extent, as a substitute for pink, or 
 granular jiink, sum facing, in vulcanite dentures. 
 
 It is semi-translucent in texture and compares favorably 
 in appearance with jiorcelain for gum restorations. The most 
 serious objection urged against this material is that a denture 
 to which it is applied must be kept moist at all times,, other- 
 wise the jirotesyn will contract and fi'acture. 
 
538 CONSTRUCTION OP PARTIAL DENTURES 
 
 The following illustrations, with descriptive text, have 
 been supplied by the L. D. Caulk Co., Philadelphia : 
 
 "There is scarcely a process in the pi'actice of dentistry 
 that is simpler than the making of a Protesyn denture. The 
 esthetic effect is striking, as it reproduces absolutely the ap- 
 pearance of the natural gum, giving a result not approached 
 with any other material. A package of Protesyn is sufficient 
 to make from six to ten dentures. The method of manipula- 
 tion has been carefully worked out l)y the manufacturers and 
 experienced dentists, and must be followed absolutely if the 
 liest results are to be secured. The successive steps in mak- 
 ing a Protesyn denture are ])i('tnr(Ml and described as follows: 
 
 I. One thickness of baseplate wax is placed on the cast 
 in the usual manner ; the teeth are set up and waxed up from 
 the palatine side. An undercut is left at the labial cervical 
 mai'gin for retention of the Piotesyn between the teeth and 
 vulcanite. 
 
 II. Putting on the rim. Cut and attach one or two strips 
 of wax (depending on the labial fullness desired), and attach 
 
CONSTRUCTION OF PARTIAL DENTURES 539 
 
 the strip or strips to the top of the plate, making an undercut 
 for Protesyn retention. 
 
 HI. A fully waxed u]) east ready to lie fliasked, packed 
 witli rubber and vulcanized. The itolislied and finished den- 
 
 ture will naturally be a duplicate; it is then ready for the 
 Protesyn. Mix a sufficient quantity at one time to complete 
 
 the denture. In making the mix, a large, strong agate spatula 
 is required. The consistency should be about the same as a 
 correct mix of Synthetic Porcelain. The mix, however, may 
 
540 CONSTRUCTION OK I'AKTIAL DRNTURES 
 
 be made with more dcliheiation than a mix of Synthetic, in- 
 asmiieh as Protesyn is sk)w setting, and therefore the operator 
 has ample time to secure the proper consistency witliont haste. 
 A period of from twenty to twenty-tive minutes is availal)le 
 from the time the mix is begun until the Protesyn is molded 
 and festooned, before the mass becomes too hard to work. 
 Wlien ready for the denture, tlie Protesyn must be a stiff, 
 homogeneous mass. 
 
 IV. The method ol' putting Protesyn on the plate. Small 
 successive quantities are taken on the spatula and forced into 
 the space provided for it. drawing the spatula across the front 
 rim of the denture, continuing until the whole space is filled 
 slightlv to excess. 
 
 V. Shaping the Protesyn. At this stage the mass is 
 ])atted and smoothed and forced fully into the undercuts. 
 The finger must be slightly anointed with the lubricant. Avoid 
 folds and laps of Protesyn. 
 
 ^'^I. Coating lightly with Protesyn lubricant prelimin- 
 irv to the molding. 
 
CONSTRtTCTION OF PARTIAT. nRNTT'RBS 
 
 VII. Using a tautaliini iiistnuiu'ut Id force back the 
 Protesvn and to clefino the gum niai'sins. 
 
 VIII. Finally smootliin.<i' and tinisliing the gum margins 
 with Protesvn brush No. 1. 
 
 IX. Forming the festoons, showing how easily and 
 artisticallv this mav be done with Protesvn. 
 
CONSTRUCTION OF PARTIAL DENTURES 
 
 X. Stippling witii brush No. 2. The area indicated at 
 the iJoint of the brush as shown in the picture is the only part 
 of the natural gum that shows a decided stippled effect. Uver- 
 stippling and excessive festooning, besides being unnatural, 
 render the denture less sanitary. 
 
 HH£ 
 
 ^^"^tJBB 
 
 bI 
 
 Pf^"^^ 
 
 Km 
 
 Hj^ 
 
 t ; 1 
 
 j^nph 
 
 ^^Ki. ,,' 
 
 ^tjr^ 
 
 XI. The completed denture coated with Protesyn Lubri- 
 cant. When the denture is finished and, five or ten minutes 
 later, the Protesyn sufficiently hardened, it must be immedi- 
 
CONSTRUCTION OF PARTIAL DENTURES 543 
 
 ately heavily coated with Protesyn Lubricant, exercising care 
 in its application not to mar or obliterate the festooning. 
 
 XII. A period of twenty-four hours must elapse after 
 the Protesvu denture has been finished, coated with lubricant 
 
 and laid away, before it is cleaned and placed in water. To 
 clean, use a brush, soap and water. 
 
 XIII. Method of removing Protesyn from a denture in 
 case repair of the vulcanite becomes necessary. This is done 
 after the denture has l)een repaired and otherwise finished. 
 We do not recommend the old Pi'otesvn to remain after it has 
 
 been through the vulcanizer. Use a knife-edge carborundum 
 wheel. Cut a longitudinal groove and chip the Protesyn away 
 with chisels or scalers. Then thoroughly remove all of the 
 old Protesyn and apply new. 
 
544 CONSTRUCTION OF PARTIAL DENTURES 
 
 XIV. An upper and a lower Protesyn gold denture ai'tic- 
 ulated. In these cases the Protesyn is extended to tlie under- 
 cut of the turned-up or wire-soldered rim, the teeth l)eing 
 anchored by the usual cleats and vulcanite attachment pala- 
 
 tally. Spurring on the labial face may also be resorted to 
 for added attachment, as in the case of vulcanite. 
 
 X^^. Here are shown a removable bridge and a lower 
 Protesyn denture. This suggests the wide use of Protesyn in 
 bridge-work. In tiiis lower denture (as also in No. 12, shown 
 
 
 in the bowl of water) the Protesyn is used conservatively, al- 
 lowing ample body of vulcanite margins for rim-titting, with- 
 out destroying the undercut for Protesyn. These cases also 
 show the Protesyn extended beyond the high lip-line. 
 
CONSTRUCTION OF PARTIAL DENTURES 545 
 
 In the making- of Protesyn dentures these requirements 
 must be observed. The mass must be mixed to the proper con- 
 sistency. The i^late when finished must be heavily coated with 
 lubricant and laid aside for twenty-four hours, when it is 
 cleaned and placed in water. Henceforth, it must always re- 
 main in water when not in the mouth of the patient. The 
 patient must be instructed on this point. 
 
 NATURAL DENTURES REPRODUCED IN PORCELAIN 
 TEETH AND WAX 
 
 The following series of cuts has been introduced to show 
 some of the commonly occurring variations in arrangement 
 of the natural teeth. These eases represent as nearly as pos- 
 sible, by means of porcelain teeth arranged in wax, the con- 
 ditions found in the mouths of living subjects. Most of these 
 illustrations have appeared in the past in the Dental Cosmos 
 and several of them appear in the American System of Den- 
 tistrv, 18SS, in an article on celluloid and zvlonite l)v Dr. 
 W. W. T<]vans. 
 
 I. Ai)pearance of teeth of person i)ast middle life, gum 
 recession, strongly mai'l^cd meciianical alirasioii. 
 
 II. Teeth of a woman of thirty to tliirty-flve. There is 
 ratlier long overbite, and the chamferiiisi- of tlie edges of the 
 
546 CONSTRUCTION OF PARTIAL DENTURES 
 
 lower incisors is i)lainl.v seen. Tlie right central overlaps 
 the left. Two teeth are lost from these arches, the right 
 upper first bicuspid and the left lower first molar. The upper 
 denture is provided with ])lnmp('rs to restore disturl)ed facial 
 contour. 
 
 III. The denture of a man past fifty years of fige. The 
 teeth are inclined well forward, with end to end occlusion. 
 The effect of wear is seen on the incisal edges of the lower 
 incisors, and indicated by the squaring of those of the upper 
 lower incisors separated, as is often seen; gums receded. 
 
 IV. The denture of a girl of twelve or thirteen years of 
 age. The cuspids are not yet fully erupted, and the incisors 
 show a ver}^ marked example of the cusplets which adorn 
 them when first erupted. 
 
 V. The denture of a man between twenty-five and thirty 
 years of age. Teeth are fully developed, large, with a long 
 overbite. The upper cuspids are elongate and incline slightly 
 inward. The lower incisors are considerably crowded and 
 inclined. The upper right first bicuspid and lower left first 
 
CONSTRUCTION OK PARTIAL DENTURES 547 
 
 molar have been lost. Two tillings are shown in tlie upper 
 central incisors. 
 
 VI. The denture of a young woman between eighteen 
 and twenty years of age. All of the teeth are fully eruiited, 
 
 and the little' cusps of the incisors are nearly effaced. Every 
 tooth is in a healthv condition. 
 
 VII. The denture of a man between forty and fifty 
 years of age. Occlusion almost end to end. Some recession 
 of the gums. Plumpers to restore disturbed facial contour. 
 
CONSTKIU'TION OF PARTIAI- niONTUUES 
 
 VIII. Denture of a man between fift.\- and sixty years 
 of age. The teeth show wear from use. 
 
 IX. Teetli of a man ahont fifty years old. Left npper 
 lirst bicuspid lost. Teeth show incchanical abrasion. 
 l'lum|)('i-s. 
 
 X. Overlap])ino' lateral ineisors. Gnms are prominently 
 ridged, indicating position of roots. 
 
CONSTRUCTION OF PARTIAL DENTURES 
 
 XI. T(>eth arrangod with close bite, considerable over- 
 lap, lateral rotated. 
 
 XII. Central incisors rotated outward distally. Laterals 
 rotated inward distallv and slislitlv within the arch. 
 
 XIII. Centrals inclined inward, hiterals overlapping, 
 cuspids i^rominent. 
 
 XIV. Centrals V-shaped. All incisors diverging 
 strongly from incisal edges apically. 
 
CONSTRUCTION ()K PAKTIAI. DENTURKS 
 
 XV. Incisors (mt of ;ili,n'iiincnt. 
 
 XVI.' Plain teeth a,ronnd to liorder. Gmn restoration 
 from cuspids backward. 
 
C If AFTER XXI \^ 
 
 CELLULOID DENTURES 
 
 Of the plastic vegetable bases used in dentiare construc- 
 tion, celluloid presents the most natural appearance, closely 
 approaching porcelain in the translucent, live-tissue color of 
 the gums and mucous membrane. 
 
 It is not generally as durable as vulcanite, freciuently 
 discoloring and rapidly disintegrating in some mouths, while 
 again it ]iroves satisfactory in other cases. Its value as a 
 denture base is largely dependent upon the manner of manip- 
 ulation of the material during construction, as well as on 
 the care bestowed upon it by its possessor. 
 
 DISCOVERY OF CELLULOID 
 
 In 1855 an Englishman by the name of Parks invented 
 the material now known as celluloid, and which he named 
 parksite or zylonite. In 1859 a man by the name of Mack- 
 intosh, also in England, patented the material called collo- 
 dion, from which he constructed denture bases. This sub- 
 stance was improved upon by Dr. McClelland of Louisville, 
 Ky., in 1860, who gave it the name of rose pearl. The denture 
 base was made from sheet collodion, moistened in alcohol and 
 ether sufficiently to render it plastic for securing adaptation 
 to the cast. The teeth also were attached with additions of 
 the same material, similarly softened. Dentures so con- 
 structed showed a decided tendency to warp in drying out. 
 
 The Newark Manufacturing Company, organized in this 
 country in 1869, began, and for a number of years conducted, 
 a series of experiments to determine the possibilities and 
 limitations of this material. After the lapse of a number of 
 years and the expenditure of large sums of money, during 
 which time many almost insurmountable difficulties were met 
 and overcome, a product of stable character was finally 
 evolved, capable of application to innumerable purposes. 
 
 COMPOSITION OF CELLULOID 
 
 Celluloid is made from pi/ru.rijlin, or the woody filler of 
 plants. This material is treated with nitric and sulphuric 
 
 .551 
 
552 CELLULOID DENTURES 
 
 acids, after which it is known as nitro-ceUulose, or (pincotton, 
 a highly explosive substance. 
 
 The proportions of this material with other substances, 
 as used for dental purposes, are about as follows : Guncotton, 
 100 parts; camphor, 40 parts; white oxide of zinc, 2 parts; 
 vermilion, .06 part. 
 
 Zylonite is made by first dissolving the guncotton in 
 ether, or methyl alcohol, and then combining it with the other 
 ingredients. Celluloid is made by effecting the union of the 
 several ingredients by means of heat and pressure, without 
 first dissolving the guncotton. 
 
 MANUFACTURE OF CELLULOID 
 
 The following abbreviated description of the manufac- 
 ture of celluloid appeared in the Dental Cosmos, January, 
 1875, being a reprint from an article in the American Ar- 
 tisan: 
 
 "After the pulp is ground in the beater engine, and the 
 camphor and whatever coloring matter may be desired are 
 thoroughly incorporated with it, the substance being kept, 
 meanwhile, at the proper temperature, the superfluous water 
 is removed by pressure and absorption, a peculiar porous 
 material, made especially for the latter purpose, being em- 
 ployed. 
 
 "During the process of drying under pressure and ab- 
 sorption, the material becomes nearly converted, so that it 
 is no longer nitro-cellulose, but imperfect celluloid. In so 
 far as conversion has taken place, its properties have under- 
 gone a total change. All that remains to convert it into the 
 various articles referred to is manipulation under heat and 
 pressure, during which the chemical combination is com- 
 pleted. 
 
 "For some qualities of the material desired to be pro- 
 duced, a small percentage of alcohol is added in the subse- 
 quent manipulation. As evidence that there is a perfect 
 chemical combination, and not a mere mechanical mixture 
 of the materials, the fact may be stated that camphor in its 
 uncombined state is an extremely volatile substance when 
 exposed to the air; in its combination with nitro-cellulose it 
 loses this property altogether. An enumeration of the prop- 
 erties of the material, which we shall give anon, will be fur- 
 ther proof of the chemical combination. 
 
 "When the material is properly converted, comparatively 
 no shrinkage takes place. There is no escape of the cam- 
 
CELLULOID DENTURES 553 
 
 phor, uuless au excess has been employed, and in that case 
 the excess of camphor will escape from the surface of the 
 celluloid; but whatever uncombined camphor remains in the 
 interior, it is so closely imprisoned by the solid surfaces that 
 it cannot escape. By varying the proportion of the excess of 
 camphor, different degrees of solidity and flexibility are ob- 
 tained. . . . 
 
 ADVANTAGES CLAIMED FOR CELLULOID 
 
 "Without the admixture of coloring matter it has a pale 
 amber color. If it is desired to make the material white, like 
 ivory, oxide of zinc is used, and for other colors various 
 mineral pigments are incorporated with it, or dyes soluble 
 in alcohol, or any of the analine dyes, may be caused to per- 
 meate the matei'ial to give it any desired color. It is hard 
 and elastic, having a hardness ranging from horn to that of 
 ivory. It is as tough as whalebone. In elasticity it greatly 
 exceeds ivory. . . . 
 
 "Celluloid is also a very fair non-conductor of heat and 
 electricity, not quite so much so as hard rubber, Init approxi- 
 mating the latter very closely in this particular. . . . 
 
 "While it is so good a non-conductor, it is not perceptibly 
 electric. . . . 
 
 "But perhaps the most remarkable property of this 
 otherwise very remarkable material is the fact that it be- 
 comes plastic at a temperature of from 250 to 300 deg. F., 
 and this property enables it to be molded with facility into 
 a great variety of forms for ornament and utility. Pure 
 celluloid has a specific gravity of about 1.4. 
 
 "A profitable and successful industry, based upon these 
 l)roperties of celluloid, is the manufacture of dental plates. 
 The material can be made precisely the color of the palate 
 and gums. 
 
 COMPARATIVE STRENGTH OF CELLULOID AND VULCANITE 
 
 "It is much stronger than rubber and has a perfectly 
 clean surface. It may be more easily manipulated than rub- 
 ber, as it does not require to be vulcanized. It possesses all 
 the valuable qualities of rubber for dental purposes with 
 none of its defects. It requires only about 1/60 as much 
 vermilion to give the proper color to celluloid as is required 
 to impart the usual color to rubber. The danger of saliva- 
 tion, which sometimes occurs in the use of rubber for dental 
 purposes, is, therefore, obviated. The difificulties encoun- 
 
554 OBbLULOIl) DRNTURES 
 
 tered in tlio application of celluloid to dental plates have 
 been very great, and many failures were at lirst experienced, 
 but with untiring perseverance the inventors have pursued 
 the subject until, during the last year or two, they claim to 
 have produced an article possessing all the requirements de- 
 sired, not a single failure having been experienced through 
 any fault of the material made within a twelvemonth past." 
 The foregoing claims are somewhat exaggerated in sev- 
 eral respects, but, taken as a whole, the description of this 
 material is an admirable one. Just about the time celluloid 
 came into use, much litigation was in progress between the 
 Groodyear Rubber Company and members of the dental pro- 
 fession, who refused to pay a royalty to the above-named 
 company for the privilege of using vulcanizable rubber for 
 dental purposes. At that time celluloid was welcomed and 
 widely used, but owing to the fact that its properties were 
 not fully understood, and that the methods of manipulation 
 were not perfected, many failures have been recorded against 
 it. These failures will now be mentioned and the causes ex- 
 plained. 
 
 DISADVANTAGES OF CELLULOID AS A DENTURE BASE 
 
 First. — In some cases these seems to be a gradual solu 
 tion of the substance by the fluids of the mouth. Such action 
 results in thinning and the consequent weakening of the 
 baseplate. The material around the pins of the teeth is 
 gradually worn or dissolved away, thus allowing the latter 
 to become displaced under the stress of mastication. 
 
 Second. — When used for some time, in many instances a 
 very disagreeable odor develops, so objectionable that the 
 denture cannot be worn with comfort. 
 
 Third. — ^The baseplate often becomes badly discolored, 
 assuming a dirty, brown appearance, and, in the case of 
 smokers, a black film, extremely difficult to remove, forms on 
 the surface. 
 
 Fourth. — Liability of the cast to become distorted in 
 molding the celluloid blank over it. When this occurs, failure 
 to secure adaptation to the oral tissues results. 
 
 Most of these objectionable features mentioned are 
 largely due to faulty technic, and can be obviated to a great 
 extent by exercising care. When the blank is molded over 
 the cast in the presence of oil, steam or glycerine, the vola- 
 tile constituents are not eliminated as they should be, but. 
 on the contrary, the celluloid seems to take up some of the 
 
CELLITLOID DENTURES 555 
 
 liqi^ids and becomes reduced in density and less resistant to 
 the action of the finids of the montli. 
 
 GENERAL METHODS OF MANIPULATION 
 
 The best results are attained by pressing celluloid in a 
 dry chamber, at high temperature, continuing the process 
 as long as may be consistent with the work in hand. By 
 this method the volatile constituents are driven off, the ma- 
 terial rendered more dense and compact, while its elasticity 
 will be increased and its color improved over the product 
 resulting from the moist process. 
 
 Steam, oil or glycerine softens the plaster cast and flask 
 investment as well, rendering them more susceptible to com- 
 pressive force and consequent distortion in closing the flask. 
 When dry heat is employed, the flask contents become hard- 
 ened by the evaporation of the moisture before the com- 
 pression force is applied, and consequently there is less lia- 
 bility of warpage or distortion occurring than by the moist 
 method. 
 
 The chief objection to the dry method is due to the dan- 
 ger of burning tlie blank during the process of pressing. 
 By cutting ample waste gates in the plaster investment sur- 
 rounding the matrix, so that no surplus material comes in 
 contact with the metal flask, this danger is largely overcome. 
 An extra large sized flask for investment purposes is neces- 
 sary in order to afford the needed space for deep and wide 
 gates. 
 
 The flask should be of the same general form as a vul- 
 canite flask, but larger and hea^'ier throughout. The gTiide- 
 pins should be strong and long enough to hold the two halves 
 of the flask in proper relation to each other when separated 
 by the introduction of the unpressed blank. 
 
 CONSTRUCTION OF THE WAX MODEL DENTURE 
 
 The construction of the wax model denture for a cellu- 
 loid case differs in no essential particulars from that for a 
 vulcanite case. The wax contour model is constructed and 
 fitted in the mouth to establish the bite and the direction of 
 the condyle paths. ' On this the teeth are occluded and tried 
 in the mouth for appearance, alignment, occlusion and bal- 
 ancing contact, after which it is returned to the cast, the lat- 
 ter detached from the occluding frame, and the case is ready 
 for investment in the flask. 
 
CELLULOID DENTURES 
 
 FLASKING 
 
 Upper eases should he invested iu the shallow half of 
 tlie flask; lower cases in tlie deeper portion, in order to con- 
 sei've space. In upper cases the anterior part of the cast is 
 elevated, more or less, to insure a parallel relation between 
 the several surfaces of the east and the guide-pins, or the 
 line of direction in which the two halves of the flask must 
 travel in closing. Sliould undercuts be present, the material 
 may fail to find its way into them on account of the matrix 
 
 rEI.LUI.dID FLASK 1 IK.SICNEll 1!V 1>I1. H C MIM.ER c IF FORTLAND, ORB. 
 
 margins preventing; hence the necessity for elevating the 
 cast, as suggested. 
 
 Coarse plaster should be used for investment purposes, 
 as it withstands high pressure, without perceptible yielding, 
 much better than impression plaster. 
 
 CUTTING THE WASTE GATES 
 
 Deep and wide waste gates should extend entirely 
 around the matrix, these being cut in the side of the flask 
 containing the cast, for if cut in the opposite, or matrix, side, 
 the walls of the latter would be weakened and probably 
 crushed under the pressure required to force out the excess 
 material. The outer margin of the gate should be at least 
 an eighth of an inch from the inner margin of the flask to 
 
CELLULOID DENTURES 557 
 
 prevent any possibility of the surplus celluloid coming in 
 contact with the heated metal. It is a peculiar fact that com- 
 bustion of celluloid almost invariably occurs when brought 
 in contact with metal lieated to 300'' F. or above, while if 
 enclosed entirely in plaster the temperature may be raised 
 fifteen to twenty degrees higher before the material will burn. 
 The inner margin of the gate should approach very close to 
 the matrix margin, so that the surjilus material may flow 
 out readily after it once passes the matrix periphery. The 
 plaster between the two margins of the gate outline is cut 
 out in V-shaped form, sufficiently deep to afford ample space" 
 for any surplus present. 
 
 CLEARING THE MATRIX OF WAX AND DEBRIS 
 
 The gates having been formed, the wax is removed from 
 the interior of the flask, the latter cleansed with boiling water, 
 the sharp, angular margins of the matrix are trimmed off 
 to prevent them fracturing and mixing with the celluloid in 
 closing the flask. 
 
 The face of the cast should be covered with a tilm of 
 collodion to give smoothness to the surface of the denture 
 pressed against it. 
 
 SELECTION OF THE BLANK 
 
 Celluloid, as prepared for dental purposes, comes in 
 the form of blanks, blocks having the general form of a 
 denture baseplate, but considerably thicker than the finished 
 denture will be, so as to suj:)ply the necessary surplus to fill 
 the matrix under pressure. 
 
 The blanks come in various sizes and are numbered as 
 follows, beginning with the smallest: No. 21/2, 3, 31/0, 4, 41/2, 
 5, 5^^, 6, 6I/0. These are sufficiently thick to insure a sur- 
 plus of material for ordinary cases. Wben a large amount of 
 absorption has occurred, it is sometimes necessary to use a 
 thicker blank than those mentioned. For such purposes a 
 series of extra-thick blanks are supplied and numbered as 
 follows: 2i/,a, 3a, Sy.a, 4a, 4i/.a, etc., up to ev^a. 
 
 When using upper blanks of this variety it will invaria- 
 bly be necessary to reduce the palatine portion to a reason- 
 able thickness with a lathe burr, shown elsewhere. If not 
 I'educed, the matrix, and frequenth^ the cast, is distorted in 
 forcing out the excessive surplus, oftentimes to such an ex- 
 tent as to destroy denture adaptation. 
 
 Frequently it will be necessary to modify the form of a 
 
558 CELLULOID DKNTURES 
 
 blank before introducing and pressing, so that, in a general 
 way, it will conform to the face of the cast. This is done 
 by placing it in boiling water until thoroughly heated, and 
 with pliers bending the outer rim to the required form, or if 
 the vault portion, as in flat-arch cases, needs modifying, lay 
 the blank on a flat surface, and with a round-end wood handle 
 depress the central area until the outer rim settles down 
 over and encloses the labial and buccal surfaces of the cast. 
 It may be necessary to heat the blank three or four times in 
 order to give it the proper form, but time devoted to this 
 preliminary adaptation is well spent, as it reduces the lia- 
 bility of the celluloid folding on itself, of the matrix failing 
 to fill, and also of the latter becoming distorted from the 
 application of unequal pressure. 
 
 Usually during this preliminary adaptation the blank 
 will become more or less soiled. This may be corrected by 
 scraping the soiled surfaces and also rubbing the blank with 
 a clean piece of muslin moistened with spirits of camphor. 
 The application of the latter will also prevent the tendency 
 of the celluloid to flake or crack during the pressing process. 
 The blank is now set upon the cast, and the upper half of 
 the flask set in position to engage with the guide-pins of the 
 opi^osite side, then carefully let down until the matrix mar- 
 gins are in contact with the blank. Care should be taken to 
 see that the latter is not displaced during this step. 
 
 PRESSING THE CASE 
 
 A dry-chamber press should be used, for reasons pre- 
 viously mentioned. The flask is set on the bedplate of the 
 press, matrix side down, so that in ease any of the teeth be- 
 come loosened in the dry heat, gravity will retain them in 
 position. The three screws which draw the bedplate up 
 against the lid of the press should be tightened evenly, so 
 that the guide-pins may at all times travel in a perpendicu- 
 lar direction and parallel with the screws. No jiressure 
 should be put upon the blank until the latter is thoroughly 
 heated to a tem]ierature of at least 300° F., at which point 
 it should be maintained during the pressing process. At 
 least twent.y-five minutes should be allowed for raising the 
 temperature in the interior of the press up to tliis point. 
 
 When the proiDer temperature has been attained, the 
 bolts are gradually tightened, and, as before suggested, care 
 should be taken to kee]i the bedplates iiarallel at all times 
 with the top of the press, so that the guide-pins will not be 
 
CELLULOID DENTURES 559 
 
 bent. The case should be lifted out of the press from time 
 to time for examination, to determine the progress of the 
 closure, but should be returned to the chamber as quickly as 
 possible to prevent cooling. 
 
 Too much pressure should be avoided. Celluloid, even 
 when plastic, is rather sluggish and flows slowly If forced 
 too rapidly, or faster than the normal flow the matei'ial will 
 warrant, distortion of the matrix and face of the cast will 
 occur, and a misfit will result. 
 
 When the flask is closed, the source of heat is cut off and 
 the case allowed to cool for ten or fifteen minutes or longer, 
 if time permits. This permits the molecules of the material, 
 under the continued heat and pressure, to adjust themselves 
 to each other, and lessens the danger of warpage which some- 
 times occurs when pressure is relieved too suddenly. In every 
 case the flask and contents, whether suddenly or quickly 
 chilled, must he perfectly cold before the press bolts are 
 loosened, otherwise distortion may result. 
 
 REMOVAL OF THE CASE FROM THE FLASK 
 
 In removing a case from the flask it will be found that 
 the plaster is extremely hard and difficult to cut. The desire 
 to pry the flask apart suddenly, or use a hammer to knock 
 the investment out of the flask, is great, but if these methods 
 are emploj^ed some of the teeth will very likely be fractured. 
 It is, therefore, best, even though more tedious, to saturate 
 the case in water, pry off tlie top and bottom plates, and re- 
 move the content of the flask by cutting close to the inner 
 periphery of the flask. 
 
 FINISHING 
 
 No special directions are necessary for finishing cellu- 
 loid cases, as this material is susceptible to the same methods 
 of polishing as vulcanite. Should there be a decided odor of 
 camphor present when the case is finished, it may be re- 
 moved by immersing the denture in a 10 per cent solution 
 of sulphuric acid for a few minutes. If allowed to remain 
 in the acid for a long time, or in a strong solution for a short 
 time, solution of the celluloid will occur. 
 
 GENERAL REMARKS 
 
 As before stated, celluloid is not as durable a material 
 as vulcanite, but it certainly deserves some consideration 
 as a serviceable and inexpensive base for dentures, as well 
 
560 CELLULOID DENTURES 
 
 as for its beauty and dost' rfsciiihlaiicc to the natural gum 
 tissues. 
 
 Celluloid is peculiar, aud its physical properties must 
 be well understood in order to derive the best results from 
 its use in denture construction. It forms an admirable base 
 for temporary, and under favorable conditions for perma- 
 nent dentures also. Celluloid does not serve well as a base 
 for partial dentures, for the reason that single or isolated 
 teeth are more readily displaced from a base of this material 
 than from one of vulcanite. 
 
 CASTS FOR CELLULOID CASES 
 
 Since the principal source of error in celluloid denture 
 adaptation is due to compression and consequent distortion 
 of the cast in pressing the material, and since the pressure 
 applied cannot well be reduced imder that usually employed, 
 on account of the sluggishness of the material, even under 
 high temperature and pressure, the remedy lies in the use 
 of a harder substance than plaster for casts. Any of the 
 three materials previously mentioned in connection with cast 
 construction are applicable for this purpose, viz., oxy- 
 chloride of magnesium, Spence's plaster, and tin, although 
 when the latter is used great care must be exercised to avoid 
 overheating and consequent burning of the celluloid. 
 
CIIAPTKR XXV 
 
 REPAIRING VULCANITE DENTURES 
 
 The materials of whieli vulcauite deuturew are composed 
 are susceptible to wear and breakage under stress, and since 
 dentures of this, as well as of all types, are subjected to 
 more or less heavy masticatory effort, accidents of various 
 kinds frequently occur to both the vulcanite base and the 
 porcelain teeth. The accidents which are of most frequent 
 occurrence, with methods for repairing such cases, will now 
 be outlined. 
 
 FRACTURE OF THE VULCANITE BASE 
 
 Fracture of the baseplate may be caused by the appli- 
 cation of sudden or undue stress in handling while cleans- 
 ing, or from a fall ; or, in case unequal absorption of the 
 alveolar process occurs after the denture is introduced, under 
 heavy masticatory stress the baseplate breaks from the re- 
 sulting imdue torsional strain, due to lack of support over the 
 absorbed areas. 
 
 Under such conditions a fissure usually makes its ap- 
 pearance at some point along the margin of the baseplate, 
 and, unless corrected, extends more deeply into the vulcanite, 
 finally resulting in fracture of the denture into two or more 
 pieces. Occasionally complete fracture of the baseplate will 
 occur suddenly from undue strain, as from the sudden crush- 
 ing of a hard morsel of food, as well as from some of the 
 causes previously mentioned. 
 
 Usually the plan of repair of a denture is easily deter- 
 mined. Occasionally, however, the natiire of the accident 
 and the causes leading up to it clearly indicate that recon- 
 struction, instead of repair, will prove most serviceable. 
 
 It should be noted that the preceding outline covers a 
 common class of accidents, due to two different causes — 
 first, those resulting from sudden undue stress, as in care- 
 less handling or from a fall ; and, second, those resulting from 
 torsional or bending strain in masticatory effort. 
 
 In all cases where, up to the time of the accident, the 
 adaptation of the denture to the tissues has proven satis- 
 factory, repairs are generally indicated. In those cases 
 
 561 
 
562 REPAIRING VULCANITE DENTURES 
 
 wliere the primary cause of the fracture is due to imperfect 
 adaptation of denture to oral tissues, reconstruction of the 
 case is, in most instances, indicated, since by the usual meth- 
 ods of repair tlie g-reatest efficiency cannot be realized. 
 
 REASSEMBLING A FRACTURED BASEPLATE 
 
 In repairing a fractured denture, the first consideration 
 is to assemble and hold the several i^arts of the baseplate in 
 correct relation to each other while preparing the joints and 
 splicing the fractured pieces together with new material. This 
 is best accomi^lished by constructing a cast, not in the usual 
 way, by taking an impression of the mouth, but by reassem- 
 bling the broken pieces of the denture and filling in the 
 maxillary or border side with plaster to serve as a cast. 
 
 TECHNIC OF SECURING A CAST FROM THE BASEPLATE 
 
 The broken parts of the baseplate are pressed together 
 until the fractured surfaces show perfect contact, and, while 
 in this relation, sticky wax is applied to the lingual surfaces 
 on either side of and across the fracture line, but, for ob- 
 vious reasons, not on the border or palatine areas. The 
 wax should be applied in sufficient bulk, so that when chilled 
 it will hold the several broken pieces firmly and accurately 
 while the cast is being formed. 
 
 The border and palatine sides of the denture are now 
 coated with a thin film of oil, and the material of which the 
 cast is to be constructed is aijplied in the same manner as 
 in an impression and allowed to harden. 
 
 Sometimes the relation of the several parts of the den- 
 ture can be best maintained, while securing the cast, by im- 
 bedding them to a slight extent in modeling compound, care 
 being taken to maintain the correct relationship of the frac- 
 tured surfaces until the compound has hardened somewhat. 
 This method is especially applicable to holding in correct 
 relation the two halves of a full lower denture, fractured in 
 the incisor region. When sticky wax alone is used in such 
 cases, slight pressure on the outer sides of the denture while 
 handling is liable to disturb the correct relation of the frac- 
 tured surfaces before the cast is secured. This danger can 
 be obviated, in most cases, by laying a small piece of wood, 
 as a match or a rigid wire, between the distal ends of the 
 
REPAIRING VULCANITE DENTURES 563 
 
 baseplate and attaching each end tirraly to the ]3late with wax 
 before forming the cast. 
 
 The method frequently followed of assembling the frac- 
 tured parts of a baseplate on a cast derived directly from 
 an impression of the month is objectionable, because it is 
 inaccurate. The cast, being hard and unyielding, will not 
 permit the baseplate to settle to position, as it does on the 
 soft and yielding areas of the mouth, and when the repair is 
 accomplished with the several parts thus sustaining an in- 
 correct relation to each other, even though the distortion 
 
 may be slight, a misfit usually results, or the occlusion of the 
 teeth is impaired. 
 
 Repairs occasionally present, usually in partial dentures, 
 however, where the broken pieces can be placed in the mouth 
 and an impression secured which will give a more accurate 
 relation of the parts to each other than is possible to obtain 
 by adjusting the fractured surfaces together and applying 
 wax, as outlined. 
 
 METHODS OF JOINING THE FRACTURED PIECES 
 
 A long bevel joint, if properly formed, will present the 
 best appearance and prove the strongest and most satisfac- 
 tory manner of repairing a fractured vulcanite base of any 
 of the methods in vogue. The practice of cutting a series of 
 dovetailed spaces on either side of the fracture line for the 
 reception of the new material, in most cases, tends to weaken 
 the old \^ilcanite, and when the base is composed of other 
 
564 REPAIRING VULCANITE DENTURES 
 
 than black, basic material, the repair, when completed, will 
 present a very unsightly — or, at least, noticeable — appear- 
 ance, because of the variation in the color of new and old 
 vulcanite, as well as on account of the irregular outline 
 margins of the patch. 
 
 A cabinetmaker who desires to produce the strongest 
 possible union between two pieces of wood — a joint that will 
 resist both torsional strain and end pull — will make a long 
 
 bevel joint instead of halving each piece and abutting the 
 halved ends against the corresponding shoulder of the oppo- 
 site piece. Tests show that the bevel joint is the strongest of 
 the two methods outlined, not only in wood, but in vulcanite 
 as well. 
 
 The dovetailed method of repairing a simple fracture is 
 based upon the principle that some positive form of mechani- 
 cal anchorage is essential, even though it be gained at the 
 expense of weakening the old vulcanite, and in areas not 
 previously involved in the break; it accords too much value 
 to the dovetail, a joint calculated to resist end pull and not 
 torsional strain, and not enough in the lap joint, which, with 
 practically perfect union of surfaces between new and old 
 vulcanite, will resist both torsional strain as well as end 
 pull. The fact does not seem to be generally well under- 
 stood that under proper conditions new rubber will unite 
 tirmly and permanently with old vulcanite. The necessary 
 requisites for serviceable union between the old and new 
 vulcanite are as follows : Fresh, clean surfaces to the old 
 base, produced by tiling, scraping or burring; the covering 
 of these surfaces with a thin tilm of rubber cement before 
 adding the new rubber, and the maintenance of pressure 
 upon the newly added material during vulcanization ; also 
 freedom of the joint from wax, grease or dirt. 
 
 The rubber cement should correspond in color with the 
 vulcanite or the fresh rubber between the surfaces of which 
 it is interposed, to avoid imjiarting a variegated appearance 
 to the joint. 
 
 The commercial rubbei'-tire cement, which is nearly in- 
 visible when applied to, or used in connection with, any color 
 
REPAIRING VULCANITE DENTURES 565 
 
 of vulcanite, may be used, or a cement maj^ be made by dis- 
 solving red, pink or black rubber in any solvent, such as 
 benzine, bisulphide of carbon or chloroform. When the lat- 
 ter is used the solution is called "chloro-rubber. " The three 
 colors should bo kejit in stock, in the laboratory, in tightly- 
 
 stoppered bottles, for use as occasion requires. Excessive 
 application of cement to a joint, without removal of the sur- 
 plus, will result in jjorosity of the newly-added material. 
 
 FORMING THE BEVEL JOINT 
 
 Two shallow grooves, about one-sixth the thickness of 
 the baseplate in depth, are cut, one on either side of the frac- 
 
 SECTIONAL VIEW OP BASEPLATE, 
 SHOWING OUTLINE OP BEVEL OF 
 OLD VULCANITE. THE CENTRAL 
 BEVELED PORTION IS TO BE RE- 
 MOVED 
 
 ture line, and approximately parallel with it on the lingual 
 side of the baseplate. These grooves limit the area of the 
 old base to be covered by the new vulcanite and determine 
 the outline of the patch, as it might be called. When the 
 fracture line is very irregular, the position of the limiting 
 
566 REPAIRING VULCANITE DENTURES 
 
 marginal Hues may be varied, if by so doing a more sym- 
 metrical balancing of the new witli the old vulcanite can be se- 
 sured. 
 
 The relative position of these lines to the fracture line 
 may be modified by inci'easiug or dimiuisliing their distance 
 from the latter uniformly; or, if the conditions of the case 
 re(}uire, the.y may be laid in curved or diagonal directions. 
 The result of varying the position of the marginal lines will 
 be to vary the length and pitch of the bevel, but this will in 
 no way interfere with the strength of the repair. The main 
 object of varying the outline margins of the freshened area, 
 as before stated, is to give a symmetrical form to the newly- 
 added vulcanite, and when good judgment is displayed in 
 planning the repair, very presentable, and at times quite 
 artistic, results are realized. In most instances the average re- 
 pair is an unsightly, and often an unsatisfactory, operation, 
 when in practically every instance where a repair is indi- 
 cated, both satisfactory and esthetic results are possible when 
 proper steps are taken. 
 
 SUMMARY OF THE TECHNICAL STEPS FOLLOWED IN 
 
 REPAIRING A MEDIAN LINE FRACTURE, 
 
 FULL DENTURE 
 
 Assemble and unite the fractured pieces firmly, as pre- 
 viously outlined; secure tlie cast; with a pencil, sketch on the 
 
 DENTURE WITH COMPLETE PRACTUIIE. EX- 
 TENDING ENTIRELY THUOnGH PALATINE AND 
 LABIAL GUM PORTIONS 
 
 lingual surface of the baseplate, as symmetrically as possi- 
 ble, the position of the marginal lines which limit the area 
 to be covered by the new vulcanite; cut the grooves along 
 these lines to the depth previously indicated; bevel off the 
 
REPAIRING VULCANITE DENTURES 567 
 
 old vulcanite from the bottom of these grooves to the oppo- 
 site or palatal surface of the baseplate, terminating the bevel 
 in feather-edge along the fracture line. This entirely re- 
 moves the inner wall of each groove and converts the outer 
 wall into a shoulder against which the new vulcanite tinishes. 
 
 When the break extends through the labial portion of 
 the denture, the outer surface of the pink gum should be 
 beveled in a similar manner to the alveolar border joint 
 surface. In all cases of pink vulcanite gum repairs, where 
 the fracture occurs anteriorly, or anywhere between the cus- 
 pids, the marginal lines of the repair sliould be laid back 
 of the cuspids, so as to render invisible, if possible, the line 
 of junction of the old with the new vulcanite. This is impera- 
 tive on account of the unsightly discoloration noticeable in 
 joint areas on pink gum after vulcanization. 
 
 In preparing the joint, the beveling is most easily ac- 
 complished by applying those areas of the baseplate to be 
 
 LAIUAI. VIEW OF I'ltKCKIllNCj 
 
 reduced against the emery band on the lathe mandrel. Con- 
 stricted areas that cannot be reached by this means can be 
 reduced with large fissure or round burs in the engine. 
 
 After beveling, the fractured pieces are returned to the 
 cast, a piece of sheet wax is applied to the freshened areas 
 on the lingual surface of the denture", and with a hot spatula 
 burnished, but not melted, down to the required contour of 
 the finished ease. 
 
 METHOD OF FLASKING A REPAIR CASE 
 
 It is seldom possible to flask a full denture so that the 
 matrix side of the flask can be withdrawn from that con- 
 taining the baseplate, to which the teeth have previously been 
 permanently attached, without injuring the matrix, especially 
 those portions of it which fill the embrasures. Therefore, in 
 repairs involving the labial or buccal gum surfaces, as well 
 as lingual portions of a denture, provision must be made for 
 
5«S REPAIRING VULCANITK DKNTURES 
 
 plrU'iiin- the iuMk'i- on the gum surfaces in such manner as not 
 to he disturhed in the tinal eloshig of the flask. 
 
 'I'his may be accomplished in two ways. First, by cover- 
 ing tlie prepared and waxed portion of gum repair with the 
 plaster in the first, half of the flask, and by means of one or 
 more suitably located connecting gates removing the wax from 
 the gum surface, packing the matrix through these openings, 
 and with an excess of rubber in the gates condense that form- 
 ing the gum rejjair in the partially enclosed matrix in the 
 final closing of the flask. 
 
 Second, the following method, when carefully carried out, 
 involves less time and is (juite as effective as the first and 
 can, in most cases, be followed. The details are as here out- 
 lined : 
 
 When the beveling of the several surfaces involved in 
 the repair is completed and the parts are adjusted to the cast, 
 the lingual surface is waxed as before described. Instead of 
 waxing the gum areas they are coated with a thin film of rub- 
 ber cement, well rubbed into the freshened surfaces with a 
 pellet of cotton. 
 
 A strip of pink, or granular, rubber, large enough to 
 neatly cover the entire area of removed old gum, is applied, 
 and with a large, hot burnishing spatula is pressed firmly 
 against the freshened areas until perfect contact and firm ad- 
 hesion is develojjed. Smaller pieces are added and burnished 
 against that already placed until the required g-um contour 
 is developed and a compact homogeneous mass results. 
 
 When the pink gum restoration has been liuilt up as de- 
 scribed, the case is ready for flasking, and herein lies the 
 
 ODM FACING APPLIED TO FRESHENED I.AIilAI, AREAS 
 
 advantage of packing the gum repair as outlined, since com- 
 plications in flasking and subsequent packing are avoided. 
 
 A mix of plaster is made and the case invested in the 
 lower half of the flask just as though no gum surfaces were 
 involved ; that is to say, the entire labial and buccal portions, 
 
REPAIRING VULCANITE DENTURES 5,69 
 
 including the gum surfaces just packed, the teeth and the 
 lingual surface of the baseplate not included in the repair 
 area in this location, are covered or entirely enclosed within 
 the plaster investment in the first half of the flask. The pink 
 gum, packed as above described, is thus entirely enclosed 
 within a matrix. No provision need be made for producing 
 pressure on the pink rubber, for, if properly packed, the ex- 
 pansion of the mass of pink rubber in vulcanizing is sufficient 
 to hold it firmly in contact with the old vulcanite and cause it 
 to unite firmly with the latter. 
 
 When the plaster in the lower half of the flask is 
 smoothed up and varnished, the upjter half of the flask is ad- 
 justed, filled, and when hardened, separated, the wax removed 
 with hot water, the surfaces of freshened rubber covered with 
 a film of rubber cement, well rubbed in, some l)asic ruliber of 
 appropriate shade is applied to the cut-out area, slightly in 
 excess of the actual bulk required, so as to insure pressure 
 in vulcanizing, the two halves of the flask are adjusted, and 
 while cold the bolts are tightened with finger power only, the 
 case is warmed with dry heat and finally closed in the usual 
 manner. Vulcanization is carried out as for ordinary cases. 
 
 REPLACING A DISPLACED TOOTH 
 
 When a tooth has been forced from the denture base, its 
 pins having itulled out of the vulcanite, or as sometimes oc- 
 curs, when a small section of vulcanite enclosing the pins 
 fractures and comes away with the tooth without injuring or 
 in any way impairing the usefulness of the latter, replace- 
 ment of the same tooth can in most cases be effected liy very 
 simple methods. The following means for replacing bicus- 
 pids and molars are both simple and serviceable. 
 
 First, adjust and wax the tooth in its correct position in 
 the vulcanite base, enlarging the old pin holes if necessary, 
 to let the tooth in place. The periphery of the vulcanite 
 socket in which the tooth rested before displacement should 
 be disturbed to the least possible extent at this time, as it 
 guides the tooth to proper place. 
 
 Second, oil the labial or buccal surfaces of the teeth and 
 gums, including, the displaced tooth and extending a short dis- 
 tance mesially and distally from it. 
 
 Third, make a matrix of plaster by building it against 
 these oiled surfaces. This is necessary in order that the dis- 
 placed tooth can be returned to correct position after the sup- 
 
570 REPAIRING VULCANITE DENTURES 
 
 porting vulcanite on the lingual side is removed preparatory 
 to adding new vulcanite for the repair. 
 
 Fourth, remove the matrix and the tooth, and with a vul- 
 canite tile or a large engine bur form a dovetail space in the 
 basei^late, to the lingTial of the tooth displaced, as wide as the 
 latter and deep enough to entirely obliterate the old pin holes. 
 
 Fifth, return and hold the tooth in correct position on the 
 baseplate by means of the matrix, and apply wax in the dove- 
 tailed space around the pins and against the i^orcelain, build- 
 ing it out to the required contour of the finished denture. 
 
 Sixth, remove the matrix, invest the case in the lower 
 half of the flask, entirely enclosing the denture in plaster ex- 
 
 DENTUKE BASE PREPAKED FOR REPLACEiMEXT OF 
 
 ONE TOOTH. SHOWING FOBMjVTION OF 
 
 DOVETAIL SPACE 
 
 cept a small surface immediateh' surrounding and including 
 the waxed repair area. The tooth itself should remain in 
 position in the baseplate, and be covered sufificiently with 
 plaster to obviate its being raised on forcing the rubber into 
 the dovetailed space and vinderneath the tooth in closing the 
 flask. Smooth the upper surfaces of plaster, tapering the 
 margin around the repair area so that the plaster in the upper 
 section maj' separate readily, varnish, complete the invest- 
 ment in the upper half of the flask, and allow time for plaster 
 to set. 
 
 Seventh, separate flask ; pick out as much wax as possible 
 and use hot water for the removal of the last traces of it. 
 
 Eighth, apply a thin film of rubber cement, being very 
 careful to avoid excess, since as before stated a surplus will 
 
REPAIRING VULCANITE DENTURES 571 
 
 cause porosity iu the uewly added rul)lier in vulcanizing-. Cut 
 and apply some small jiieces of basic rubber of appropriate 
 shade, usually slightly darker than the denture base, as the 
 latter will darken somewhat with each vulcanization. With a 
 warm, round end rubber packing instrument the pieces should 
 be fairly well condensed in the dovetailed space and around 
 the pins, and a little surplus added to insure slight pressiire 
 on the mass when the flask is closed and during vulcanization. 
 Ninth, close the flask, vulcanize and finish in the usual 
 manner. When the pink gum margin has been fractured and 
 requires restoration, the surfaces are freshened and small 
 pieces of pink rubber are built up to the required contour, 
 condensing them with a hot instrument. This should be done 
 before flasking the case, the pink rubber being enclosed in the 
 first half of the investment as previoush' outlined in repair- 
 ing a fractured baseplate. Usually, however, on account of 
 the unsightly discoloration at the line of junction of the new 
 with the old pink vulcanite, visible areas needing repairs 
 should be extended to such point that the discolored joints are 
 invisible, and only new pink vulcanite will show. This often 
 necessitates carrying the beveling back as far as the second 
 bicuspid on each side. 
 
 REPLACING A DISPLACED TOOTH BY THE CASTING 
 METHOD 
 
 When the displaced tooth is situated between two proxi- 
 mating teeth as in a full denture, and rests in a vulcanite 
 socket or matrix having a complete periphery, attachment of 
 a new tooth may be made by casting. The advantage of this 
 method is that vulcanization is obviated, a process wLich, 
 when resorted to as is usual in repair cases, while the plaster 
 is "green," soft and yielding, often results in warpage and 
 consequent loss of adaptation of the denture to the oral 
 tissues. 
 
 The steps are as follows : 
 
 The vulcanite which enclosed the pins is freely cut away 
 and in addition a cavity, having a decided undercut, is formed 
 in the sides and battom of the vulcanite matrix in which the 
 tooth rests. Care must be taken not to disturb the peripheral 
 outline of the matrix, or if unavoidably disturbed, of restor- 
 ing in wax the lost portion after the tooth is finally set in 
 place. A positive connection of the wax so applied with the 
 interior of the matrix is essential so that the metal, when cast. 
 
572 KKFAIIUNG VULCANITIO DENTURES 
 
 will flow t'rniii 1lic interior outwardly and talcc the place ol' 
 the wax. 
 
 Now at a point well within one of the lingual embrasures 
 drill a hole connecting with the undercut cavity, as nearly 
 parallel with the long axis of the tooth as possible. A broken 
 engine bur converted into a drill of the full diameter of the 
 shank produces a hole of convenient size. Later on the bur, 
 l)y reversing, will assist in forming the sprue. 
 
 The tooth is now returned to position in its matrix and 
 waxed externally, if necessary, to hold it in place, thus leaving 
 the undercut space free from wax or debris. 
 
 A .093 wire (the diameter of an engine bur shank) is now 
 passed into the sprue previously drilled in the baseplate, or 
 
 KEPLACING A TOOTH BV THE CASTING METHOD 
 
 the drill may be reversed and used for this purpose, a mix of 
 investment or plaster is made, tilled in the palatine or border 
 side of the denture, to form a base to prevent the denture 
 tipping, carried out against the buccal or labial surface, over 
 the occlusal or incisal surfaces, and down on the lingual sur- 
 face of the denture surrounding the sprue wire. 
 
 While the plaster is yet soft, a small cup, similar to or 
 made from a common thimble, having a hole drilled in the 
 bottom, is slipped over the sprue wire and pressed down into 
 the plaster sufficiently deep to support it when the wire is 
 withdrawn, and to insure its stability under the pressure of 
 casting. 
 
 When the plaster has hardened, the sprue wire is with- 
 drawn, thus forming a sprue connecting the thimble with the 
 
REPAIRING VULCANITE DENTURES 
 
 573 
 
 iiiuiercut space under the tooth. Fiisi})k' metal is melted and 
 ])oured into the thimble, from which it is forced into the space 
 by means of Melotte's moldiue, contined within a ring or cup 
 somewhat larger than the diameter of the thimble. Forcing 
 the metal in the undercut under pressure causes it to fill the 
 
 MOLDINE 
 
 SPRUE 
 FORMER 
 
 ri'*~~-~ 
 
 
 ) 
 
 
 — ^'^ 
 
 
 
 ~^DOVE 
 SP 
 
 TAILED 
 ^CE 
 
 ]>1AG1!AMMAT1C VIEW OF THE INVESTED I'AKE. THIMBLE 
 
 IN rOSITION. AND MOEDINE rARKIER. SPUUE 
 
 FORMER NOT YET REMOVED 
 
 entire s))ace and enclose the heads of the pins perfectly, thus 
 making a very serviceable repair. When finished, the only 
 metal showing -is that which tills the sprue, which, when 
 dressed down and polished, is scarcely noticeable. 
 
 Dr. A. C. Alexander of Kahoka, Mo., first called the writ- 
 er's attention to this method of repair two years ago, and 
 since that time it has been applied satisfactorily in many 
 
574 KEI'AIKING VULCANITK DENTURES 
 
 practical eases. In geiipval, the principle is similar to the 
 metliod suggested by Dr. J. P>. P)('an in ISdl) foi' attaching gum 
 sections to east ahimiiiiini Imscs l)\- roruiin,^- an undercut in 
 
 the baseplate and casting tin into the space so formed and 
 around the pins of the section ; described in Harris, Ed. 1870. 
 
 ANOTHER METHOD OF REPAIR BY MEANS OF 
 FUSIBLE METAL 
 
 Cut a decided dovetail in the lingual surface of the den- 
 ture, as for an ordinary vulcanite repair, but greater care 
 must be exercised in developing positive mechanical anchor- 
 age in the space in repairs of this type than where vulcanite 
 is employed, since in the latter case the union is an adhesion 
 of molecular material and not merely a mechaiucal anchor- 
 age, while in the repair under consideration the union of the 
 metal with the base is mechanical. 
 
 Fill the palatine or border surface of the denture with 
 plaster to form a base, extending it out over the outer sur- 
 faces of the gums and teeth to serve as a matrix for holding 
 the displaced tooth in position. 
 
 The ease should be set at such an angle in the investment 
 that gravity will assist in tilling the undercut space when the 
 molten metal is poured. 
 
 The case being properly invested as described, some Mel- 
 lotte's or other easily fusible metal is melted in a small ladle 
 and poured into the dovetailed space. As it begins to congeal, 
 
REPAIRING VULCANITE DENTURES 575 
 
 a little surplus is added, and with a pad of blotting paper 
 folded three or four times, pressure is made on the mushy or 
 semi-hardened metal to force it into all parts of the space and 
 around the pins of the tooth. AVheu hardened, the excess is 
 trimmed off and the surface polished to proper contour. 
 
 REPAIRING BY MEANS OF AMALGAM 
 
 A very common method of attaching a displaced tooth is 
 to form the dovetailed space as just described, adjust the 
 tooth in position and form a matrix in such manner that it 
 will not become displaced nor allow the tooth to be forced out 
 of position imder the pressure of i^acking the amalgam. A 
 mix of amalgam of moderate consistency is made and quickly 
 forced into the space prepared for it and around the tooth 
 23ins, using small-pointed pluggers to pack it into the deeper 
 portions of the dovetail. 
 
 Repairs made in this manner, although at times quite 
 satisfactory, are ixsually temijorary in character, the amal- 
 gam around the pins fracturing under masticatory stress and 
 allowing the tooth to be dislodged. 
 
 By forming a loop of fine tinned iron wire, such as is 
 used for root measurement, twisting it around the pins and 
 weaving it back and forth between the two, three or four 
 times, additional anchorage of the tooth to the denture will 
 be gained over that afforded by the pin heads alone. This 
 method is very applicable in amalgam or fusible metal re- 
 pairs, where the tendency' of the pin heads to pull out or the 
 amalgam to readily fracture under stress is very marked. 
 The loojj should be well embedded in the amalgam. It can 
 readily be seen that if a little tension is placed on the loop 
 to take up the slack, and it is well surrounded with metal, that 
 the tooth or pins will most likely fracture before displace- 
 ment will occur. (See wire loop on tootJi pins, i^age 572.) 
 
 Still another method of increasing anchorage is by sold- 
 ering to the pins a smalUloop of wire of suitable form to fit 
 within the dovetailed space and be entirely enclosed within 
 the metal. 
 
 REPAIR INVOLVING THE SUBSTITUTION OF 
 ANOTHER TOOTH 
 
 When in addition to being forced from the baseplate the 
 tooth is fractured and rendered useless as well, another tooth 
 must be selected for the repair. Since the chance is slight 
 
576 REPAIRING VULCANITE DENTURES 
 
 of finding a substitute of tlie same size, mold and occlusal 
 form as the fractured tooth, the steps just outlined, although 
 in the main applicable, must be varied somewhat to insure 
 correct alignment and satisfactory occlusal conditions in the 
 completed repair. 
 
 In the methods previously outlined, the position for and 
 occlusion of the displaced tooth was found by returning it 
 to the vulcanite socket in which it rested before displacement 
 and of holding it there with wax, if necessary, while a satis- 
 factory matrix was secured. This plan is not applicable in 
 case a new tooth is used, because it will seldom fit in the old 
 socket. In full denture cases, and in some partials as well, 
 the denture is returned to the patient's mouth and a wax or 
 modeling compound mash bite is secured, involving the space 
 to be filled, the proximating and occluding teeth. 
 
 In case of complicated occlusion, the denture and bite 
 should be transferred from the mouth to the occluding frame 
 with the face bow, mounted, and the bite filled with plaster to 
 develop the occluding teeth, after which the bite material is 
 removed. 
 
 In uncomplicated cases the bite may be filled in with 
 plaster and an extension at the same time be made ligually 
 so as to cover definite areas on the lingual surface of the den- 
 ture, or it may even extend across the entire baseplate, the 
 point of importance being to have a sufficient number of 
 guides to bring the occluding plaster teeth into normal rela- 
 tion with those of the denture when the bite material is re- 
 moved. 
 
 The old socket is now burred out in its interior, and the 
 lingual side cut away to receive the new tooth. Care should 
 be taken not to disturb the gum margin and further compli- 
 cate the repair. In fitting the substitute tooth in place the 
 porcelain itself can, in many cases, be ground to fit the socket 
 on the gum side of the denture. Usually, however, a little 
 careful trimming of the vulcanite socket, together with a little 
 grinding of the tooth, will develop a satisfactory joint, that 
 will not recjuire the addition of new gum material. 
 
 PRELIMINARY DOVETAILING OF A DENTURE BASE 
 
 In partial dentures, where an isolated tooth is to be re- 
 l)laced, it is frequently advisable to prepare the dovetail form 
 on the baseplate for the reception of the new rubber before 
 taking the bite. By so doing the danger of mutilating or 
 
REPAIRING VULCANITE DENTURES 577 
 
 breaking the proximating plaster teeth when the cast is run 
 up will be obviated. 
 
 A small wax bite is now taken, involving the space to be 
 filled, the proximating teeth and the opposite occluding teeth. 
 The denture and bite should be removed, if possible, to ob- 
 viate danger of distorting the latter. If for any reason the 
 bite and denture are separated in removal, they should be 
 carefully fitted together and held firmly by melting some of 
 the bite wax at various points against tlie denture. 
 
 The cast is now formed in tlie united denture and wax, 
 and when hardened, the opposite side is run up. The occlu- 
 sion cast should extend over onto the palatal surfaces of the 
 denture so that it may be guided to place when the wax bite 
 is removed. 
 
 On removal of the wax a suitable tooth is selected, waxed 
 in place, and the case flasked, packed and vulcanized in the 
 usual manner. 
 
 Sometimes the neck or vulcanite connecting an isolated 
 tooth with the denture base must, on account of the occluding 
 teeth, be so reduced in thickness as to invite ready fracture 
 
 A PLATE TOOTH BACKED 
 WITH GOLD. TO \VHICH A 
 CLASP METAL EXTENSION 
 IS APPLIED FOB ENCLOS- 
 URE WITHIN THE VULCAN- 
 ITE 
 
 under stress — an accident which frequently occurs — in partial 
 dentures carrying upper anterior teeth. To repair such a 
 case, one of two methods must be adopted, either the opposing 
 tooth must be shortened to make room for greater bulk of 
 vulcanite, or a plate tooth must be selected, ground to posi- 
 tion, backed with gold and a strip of heavy clasp metal 
 abutted against the backing to which it is attached with solder. 
 This strip should lie close against the maxillary surface, yet 
 not quite in contact with it, and extend lingually so as to be 
 enclosed in the vulcanite. Two or three holes should be 
 punched in the extension, or its edges should be notched with 
 
578 REPAIRING VULCANITE DENTURES 
 
 a file to afford anchorage in the vulcanite whioli encloses it. 
 The clasp metal strip must be sufficiently broad and thick to 
 withstand heavy masticatory stress without bending, or, if of 
 light gauge, it may be stiffened by flowing solder over it. 
 
 This plan of backing a tootli with metal and attaching 
 to it a lingual extension in close bite cases is often resorted 
 to in the initial construction of the denture when the bite is 
 exceptionally close. 
 
 SUBSTITUTING ARTIFICIAL FOR LOST NATURAL 
 TEETH IN PARTIAL CASES 
 
 It frequently occurs that when a partial denture has been 
 worn for some time, one or more of the remaining natural 
 teeth, through accident or as the result of disease, are lost. 
 
 If the adaptation and general requirements of the den- 
 ture are satisfactory, aside from the conditions noted, re- 
 
 placement of the lost with artificial teeth may be readily ac- 
 complished by the following method: 
 
 With a file or engine burs form a dovetail in the base- 
 plate to the lingual of the space to be filled. In case the bor- 
 der in which the natural teeth were situated has absorbed, 
 the baseplate should be cut back to a i^oint where its maxillary 
 surface rests upon the mucous tissues, thus permitting the 
 new vulcanite to join the old baseplate and form a continuous 
 bearing surface over the absorbed area. In such cases a long 
 
REPAIRING VULCANITE DENTURES 579 
 
 bevel splice will prove more serviceable than the dovetail 
 method. 
 
 The denture, having been cut out as described, is re- 
 turned to the mouth and a mash bite is taken, being careful 
 to press the wax or compound firmly against the labial or 
 buccal absorbed areas, and to secure an accurate impression 
 of the occluding teeth. 
 
 On removal of the bite and denture they should be care- 
 fully adjusted and luted together, and the subsequent steps 
 carried out as described under the "repair of partial den- 
 tures." 
 
 REPAIRING GUM SECTION CASES 
 
 When one of the sections of a gum section denture has 
 been fractured beyond the possibility of further usefulness, 
 a new block must be selected that will conform as perfectly 
 as possible to the broken section in form, size, color, length of 
 bite and curvature of the labial or buccal surface. 
 
 Usually this is a difficult matter unless the prosthetist is 
 fortunate in securing a block of the same manufacture, mold 
 and shade. In repairs of this class the vulcanite in which 
 the old pins are enclosed should be freely cut away, the den- 
 ture introduced in the mouth and a bite taken. The case is 
 then mounted on the occluding frame and the block selected 
 and ground to fit the ends of the proximating sections. The 
 block, if thick, may need grinding or dressing down on the 
 surface that approximates the baseplate, or the vulcanite it- 
 self, if of sufficient thickness, can be reduced with burs to 
 permit the block to settle into correct labial or buccal 
 contour position. Special care should be taken in grinding 
 the joints to hold the block in correct alignment when testing. 
 
 Subsequent steps are carried out as outlined in the re- 
 pair of a single tooth. 
 
 SUBSTITUTION OF A BASEPLATE 
 
 Although the adaptation of a denture may be satisfac- 
 tory, and its occlusion correct, yet, because of frequent re- 
 pairs which have detei'iorated the quality of the vulcanite, or 
 because of some peculiar fracture which renders impossible 
 a satisfactory repair, a new baseplate may be substituted for 
 the old vulcanite In- tlie matrix method in much shorter time 
 than is required to reconstruct the case in the usual way. 
 The procedure is as follows : 
 
580 REPAIRING VULCANITE DENTURES 
 
 CONSTRUCTION OF THE MATRIX 
 
 The baseplate, if fractured, should he reassembled and 
 the several parts held in proper relation by means previously 
 described, "Eei^airing a Fractured Baseplate." 
 
 Oil the denture with a thin him of vaseline and develop 
 a cast sufficiently deep to raise the peripheral margin of the 
 denture about three-eighths of an inch above the base bottom 
 and smooth its outer surfaces. 
 
 Countersink the buccal walls of the cast at two points on 
 each side so that the matrix, when formed and removed, may 
 be returned to projjer position again. Varnish the outer sur- 
 faces with separating medium. 
 
 Oil the outer surfaces of the teeth and gum restoration; 
 make a mix of and aj^ply plaster to the buccal and anterior 
 walls of the cast and denture surfaces, extending from the 
 median line to the tuberosity on one side and from the base 
 up over the incisal and occlusal surfaces of the teeth. This 
 addition, which, when completed, forms one-half of the matrix, 
 should be about three-eighths of an inch in thickness. 
 
 When the plaster forming this portion has set, the me- 
 dian end is squared up, a countersunk depression made in the 
 planed surface, the latter varnished, and a second application 
 of plaster is applied in a similar manner extending back to 
 the tuberosit}^ on the opposite side. 
 
 When hardened, the outer surfaces of plaster are 
 smoothed up, and with a few light taps of the hammer on the 
 sides and base of the matrix, it will come away in two pieces. 
 
 REMOVAL OF THE TEETH FROM OLD BASEPLATE 
 
 The teeth are now removed from the old vulcanite, one at 
 a time, being careful to card them on wax in regular order 
 so as to avoid confusion in their arrangement. 
 
 Each tooth is now thoroughly cleaned, the old vulcanite, 
 if any remains, is removed from around the pins and returned 
 to its position in the matrix. 
 
 Should any tooth become disturbed or fall out of place in 
 raising the matrix to an upright position, a little liquid silex 
 touched to the labial or buccal surfaces will, on returning the 
 tooth, under pressure, retain it firmly in place. 
 
 FORMING THE WAX BASEPLATE 
 
 A sheet of wax is now applied to the cast surfaces and 
 trimmed peripherally so as not to interefere with the matrix 
 being carried to exact position against the cast surfaces. 
 
REPAIRING VULCANITE DENTURES 581 
 
 Each half matrix is tlien returned to position against 
 the sides of the cast and brouglit in contact anteriorly, being 
 guided and lield in place by the projections of the matrix fit- 
 ting into the countersunk holes of the cast. Usually a string 
 is woimd several times around the matrix and cast and tied 
 tightly to hold all firmly together, or a heavy rubber band ap- 
 plied peripherally will be more convenient to a]3ply and serve 
 the purpose equally well. 
 
 The teeth, each one in its individual matrix, and the two 
 halves of the matrix in correct position against the cast, now 
 bear the exact relation to the cast surfaces that they did be- 
 fore removal of the vulcanite. 
 
 Softened wax is pressed into the space between the teeth 
 and cast to, and the general contour of the case developed as 
 it was before the removal of the old base. 
 
 A heated spatula is now passed under the pins and along 
 the ridge lap of each tooth, as well as into the interproximal 
 spaces and embrasures, to firmly cement the teeth to the wax 
 base, so that they will not be disturbed or come away with the 
 matrix when the latter is removed. 
 
 Care should be taken not to touch the matrix walls with 
 the heated spatula, or in any manner melt the wax against 
 these surfaces. Should this occur not only the adherent wax, 
 but some of the teeth are liable to come away with the 
 matrix. 
 
 To obviate the union of the wax with the matrix, the lat- 
 ter can be coated with a thin film of oil after the teeth are in 
 place and just before assembling the parts of the matrix to 
 the cast. Care should be taken not to apply any oil to the 
 teeth. 
 
 The string or band is now removed and the matrix is 
 gradually and carefully worked free, so as not to disturb the 
 position of the teeth in the wax. Each tooth should now be 
 tested to see that it is still firmly adherent to the wax. A 
 further test can be applied by returning the matrix to its 
 former position. 
 
 The wax model denture is now smoothly finished, flasked, 
 l^acked, vulcanized and finished in the usual manner. 
 
 In planning the reconstruction of the case, should it hv 
 deemed advisable to test the denture in the mouth, ideal or 
 some unyielding baseplate should be applied to the cast in- 
 stead of the ordinarv wax. 
 
582 UKPAIRING VULCANITE DENTURES 
 
 MODIFIED METHODS OF RECONSTRUCTION 
 
 A somewhat simpler, but less accurate, method of sub- 
 stituting a new for an old baseplate frequently resorted to is 
 as follows: 
 
 Thoroughly clean the denture, oil the palatine surface 
 aTid secure a cast. 
 
 MOUNTING CAST AND OLD DENTURE ON THE OCCLUDING 
 FRAME 
 
 Mount the cast and denture on the occluding frame in as 
 nearly the normal position as possible without the use of the 
 
 Url'ER DENTURE MOUNTED ON OCCLUDINU FRAME. TEETH EMBEDDED IN PEASTER MATRIX 
 
 face-bow. An occluding frame with an incisor guide pin is 
 preferable, as such an appliance obviates springing of the 
 bows in the subsequent steps. 
 
 FORMING THE MATRIX 
 
 Turn back the upper bow on which the case is mounted 
 and apply a mix of plaster to the lower Iww, building it up 
 sufficiently high for the teeth of the denture to enter. 
 
REPAIRING VULCANITE DENTURES 583 
 
 Drop tlie upper bow down and press the teeth into the 
 plaster so that all exposed portions of porcelain are covered. 
 It may be further extended against the labial and buccal gum 
 svirfaces, although this is not usuallv necessarv. The set 
 
 PRECEDING CASE WITH OLD BASEPLATE KEMOVED AND TEETH RETURNED TO THEIR 
 RESPECTIVE MATRICES 
 
 screw at the back of the frame, or the incisor guide, should 
 l)e firmly tixed so as to hold the upper and lower bows a 
 fixed distance ajjart after removal of old baso]jlate. 
 
 FORMING THE WAX BASEPLATE 
 
 When the plaster has set, carefully separate, remove the 
 teeth from the old baseplate and return them to their respec- 
 tive positions in the matrix. 
 
 A baseplate with roll of wax is adapted to the cast, the 
 wax warmed slightly, and the upper bow of the frame closed 
 so as to force the wax against the teeth in the matrix. 
 
 That portion of the matrix enveloping the outer surfaces 
 of the teeth is cut away, so as to allow the teeth now attached 
 to the baseplate to part from the matrix without interfer- 
 
584 REPAIRING VULCANITE DENTURES 
 
 ence, after which the case is waxed and the suhsccjucnt steps 
 are carried out as usual. 
 
 The weak point of this method is in the lialulity of tlie 
 frame springinti' in pressing the teeth into the wax and thus 
 
 shortening the bite. Such an error cannot well occur when 
 the incisor guide pin is used. 
 
 CORRECTING IMPERFECT ADAPTATION BY SUBSTI- 
 TUTION OF A NEW BASE 
 
 When the adaptation of a denture has become impaired, 
 but the teeth which it carries occlude and interlock well with 
 those in the opposite arch, adaptation may be restored by sev- 
 eral methods, the first of which is as follows : 
 
 Thoroughly clean the denture with a stiff brush wheel 
 and pumice stone. Remove from the entire palatine and bor- 
 der surfaces a thin layer of the old vulcanite by means of a 
 small lathe bur or a large surgical bur in the engine. 
 
 Apply a thin laj^er of well-mixed, but rather thin, im- 
 
REPAIRING VULCANITE DENTURES 585 
 
 pression plaster over the entire interior of the vault and bor- 
 der surfaces. 
 
 Introduce in the inoutii and instruet patient to bite 
 intermittently at tirst, then with steady, maintained pressure 
 to compress the tissues, bring the denture into correct occlu- 
 sion and force out all excess plaster. 
 
 When hardened, trim off perijiheral excess, relieve pres- 
 sure over hard areas by scraping, coat impression with sepa- 
 rating medium, secure a cast and mount it on the occluding 
 frame in the usual manner. 
 
 P^ither one of the methods previously described may be 
 adoi^ted for securing the correct relation between the teeth 
 and cast, so that on removal of the old vulcanite the aligii- 
 ment and occlusion of the teeth in the wax model may be cor- 
 rectly established. 
 
 When the matrix for the teeth is formed, the denture is 
 tirst removed from the latter, then from the cast, the surfaces 
 of which are then cleared from any remaining jiortious of the 
 plaster impression. 
 
 The steps from this point forward are the same as those 
 already outlined under the head of "Substitution." 
 
 CORRECTING ADAPTATION BY ADDITION OF NEW 
 RUBBER TO OLD BASE 
 
 When the impression has been secured in the manner de- 
 scribed aliove and the cast secured, the case may be flasked 
 immediately ; when the investment plaster has set, the flask is 
 separated, the plaster is removed from the impressed areas, 
 and the exposed palatine and border surfaces of the denture 
 thoroughh' freed from all debris. 
 
 All exjjosed areas of the baseplate not previously already 
 freshened, and to which new vulcanite is to be added, should 
 be renewed by scraping, these areas covered with a thin film 
 of rubber cement ; a sheet of new rubber is cut to correct size 
 and carefully pressed against the old baseplate, being careful 
 not to confine the air between the two surfaces. 
 
 The two halves of the flask are now adjusted, the screws 
 tightened slightly and the flask contents heated to about 200 
 degrees F., dry. heat, when gradual, but not excessive pres- 
 sure is applied to force out the excess rubber. 
 
 When closed the flask is separated, the muslin removed 
 and the result of the work so far accomplished noted. Should 
 there be an insufScient amount of rubber, more is added and 
 
586 REPAIRING VULCANITE DENTURES 
 
 the flask finally closed and vnleanizcd and the case finished 
 as usual. 
 
 Previous to the ajjplication oi' the rubber cement, an am- 
 ple waste gate should be cut close to and around the entire 
 periphery of the denture, but not connected with the margin 
 of the matrix at any point, to receive the excess rubber. 
 
 CORRECTING ADAPTATION BY MEANS OF RUBBER 
 PASTE 
 
 Bur out and freshen the surfaces of the baseplate as 
 above outlined and apply a film of Bridgeford's rubber paste, 
 a solution of rubber heavily loaded with powdered aluminum. 
 Thickness of the film applied varies, depending on the amount 
 of old vulcanite removed and the extent of absorption of the 
 border that has occurred, but usually from one to one and a 
 half millimeters will be sufficient. 
 
 The denture with paste applied is immersed in cold water 
 for an instant to chill it slightly and also to prevent it adher- 
 ing to the oral tissues. 
 
 On introduction into the mouth, the denture is pressed to 
 place for a moment, removed, the excess around the margins 
 brushed otf, the case dipped in cold water and again returned 
 to the mouth for further adaptation bj^ closure on the part 
 of the patient, as well as reapijlied pressure on the palatine 
 areas by the operator. 
 
 These steps are repeated three or four times, or until 
 satisfactory adaptation is secured, when the denture is re- 
 moved, freed from excess and set aside for a short time to al- 
 low the volatile constituents time to evaporate, when the ease 
 is flasked in a single investment and vulcanized. 
 
 TO RENEW THE ADAPTATION OF A DENTURE BY 
 MEANS OF FURLONG'S PLASTIC RUBBER 
 
 Prepare the palatine and border surfaces of the denture 
 by freshening as outlined in the first method described. 
 
 Apply to these surfaces a sheet of Furlong's Plastic Im- 
 pression Rubber, pressing it well against the old vulcanite, 
 being careful not to confine any air between the surfaces. 
 
 The plasticity of this rubber is increased and its impres- 
 sion quality improved by immersing it in warm water for an 
 instant before introducing in the mouth. Apply pressure as 
 when using Bridgeford's paste. When satisfactory adhesion 
 
REPAIRING VULCANITE DENTURES 587. 
 
 has beeu developed, the excess is removed and the denture is 
 flasked in a single investment, vulcanized and finished in the 
 usual manner. 
 
 TO CORRECT OCCLUSION WHEN DENTURE ADAPTA- 
 TION IS SATISFACTORY 
 
 It sometimes occurs that a patient may persistently main- 
 tain an incorrect bite in trial of the contour models and of the 
 wax model denture in the mouth, and the error only be dis- 
 covered when the cases are tinished. 
 
 The result is that the occlusion is incorrect, the teeth of 
 one of the dentures occupying a position a little forward in 
 iipper and backward in lower cases, or to one side of the nor- 
 mal alignment. 
 
 The best plan, as a rule, is to reconstruct one or both 
 dentures, beginning with a new impression and carrying out 
 the usual steps in such cases. 
 
 When, however, the adaptation of the denture to be re- 
 constructed is in every way satisfactory, equally good results 
 may be attained, with minimum inconvenience to both patient 
 and operator by adopting the following method : 
 
 With a small engine bur cut the vulcanite from around 
 the pins and remove the teeth. 
 
 By means of a vulcanite file and the emery cloth band on 
 the lathe, sufficient vulcanite is removed to permit the shift- 
 ing of the teeth to proper position without interference. The 
 entire outer gum surfaces should be removed so that in the 
 completed case no joints or lines of junction will be visible, 
 a layer of new material having replaced the old. 
 
 The case now presents the same conditions as does the 
 one in which the double vulcanization method is followed, the 
 old base, denuded of teeth and surrounding vulcanite, serving 
 as a foundation on which to construct the wax contour model. 
 On this base the teeth are waxed and occluded and the subse- 
 quent steps carried out in the usual manner. 
 
C II A I"!' \'] \l \ X \' 1 
 
 CONTINUOUS GUM DENTURES 
 
 From an esthetic, as well as Jiygienic standpoiut, coii- 
 tiuuous gum dentures fulfill most perfectly the requirements 
 of substitutes for the lost natural teeth. They are most 
 strongly indicated in full cases, although at times partial den- 
 tures of this type will prove very serviceable. 
 
 ADVANTAGES 
 
 Continuous gum dentures possess two important ad- 
 vantages over dentures of any other type. 
 
 First, they are absolutely impervious to moisture, exempt 
 from chemical action to which they are ordinarily subjected 
 in use, and afford but little opportunity for the lodgment and 
 retention of food; consequently they are easily kept clean 
 and free from decomposing food and from the odors of ptyalin 
 of retained saliva. 
 
 Second, the gum surfaces, being composed of glazed por- 
 celain enamel tinged with pink, present an unbroken or con- 
 tinuous gum surface free from joints, tissures, or cracks of 
 any character, and which is united to the underlying vitrified 
 porcelain, the teeth, and to the peripheral margins of the 
 baseplate by fusion. 
 
 When the denture is proijerly constructed and the gum 
 enamel artistically a]>plied, it is impossible in most cases to 
 detect the fact that the substitute is artificial. 
 
 DISADVANTAGES 
 
 The principal objections urged against dentures of this 
 type are as follows: 
 
 First, excessive weight, particularly in upper cases where 
 much absorption of the border has occurred. 
 
 Second, difficulty in construction, from warpage of the 
 entire denture due to shrinkage of mass in fusing the silicious 
 material around the teeth and to the base; to the formation 
 of fissures in the underlying body and in the enamel in the 
 final baking; to the tendency of the mass of porcelain to be- 
 come porous at any stage of fusion after the first baking. 
 
 Third, dentures of this type are liable to fracture if care- 
 
 588 
 
CONTINUOUS GUM DENTURES 589 
 
 lessly handled, because of their excessive weiglit and tlie fria- 
 bility of the materials of which composed. 
 
 Fourth, the expense of time and material involved place 
 them beyond the reach of persons of limited means. 
 
 In regard to the first objection, when good adaptation of 
 the dentures is secured and the teeth are arranged anatomi- 
 call}^, the weight of the denture is seldom noticeable to the 
 patient. 
 
 The second objection can be overcome by patient attention 
 to details on the part of the prosthetist. 
 
 The third objection more especially concerns the patient, 
 who, however, if ]n"operly instructed, can usually avoid acci- 
 dent. 
 
 The fourth disadvantage is an important one to both pa- 
 tient and prosthetist. The patient must of course decide 
 whether a denture of this type is within his means. The 
 prosthetist, on the other hand, must exact such fee as will 
 cover the cost of the materials and recompense him well for 
 all possible time involved in constructing the case. Oversight 
 in this ]iarticular is responsible for many failures in the class 
 of work under consideration, the tendency being to rush the 
 constructive details to their detriment, or turn the case over to 
 someone who may prove incompetent. 
 
 In no department of prosthetics is there an opportunity 
 for the display of greater skill, or the realization of finer 
 esthetic results, than in the planning and construction of 
 dentures of this type. There is first, the development of a 
 well trussed, yet light, platinum baseplate; second, the ar- 
 rangement of the teeth anatomically, as well as esthetically ; 
 third, their attachment to the baseplate by soldering, and 
 bracing when necessary, in such manner as to remain un- 
 changed during the contraction of the porcelain in fusing; and 
 finally, the application of the porcelain body, and subse- 
 quently, the enamel so disposed as to represent nature's best 
 efforts in contour gum effects and vault irregailarities. 
 
 Formerly dentiires of porcelain were constructed without 
 metallic bases, but on account of the shrinkage which invari- 
 ably occurred in baking, adaptation was seriously interfered 
 with, or entirely destroyed. As a result corrections had to be 
 made by the method mentioned elsewhere of securing a new 
 cast of the mouth, pigmenting its surface, and by repeated 
 trials of the denture to the cast, locating the high points, which 
 were then ground away imtil close adaptation was secured. 
 The grinding of the glazed surfaces exposed many minute 
 spaces, and left the porcelain more or less rough and porous. 
 
590 CONTINUOUS GUM DENTURES 
 
 A further objection to the all-porcelain denture was that 
 unless formed thick and somewhat bulky, it was lial)le to frac- 
 ture under usage in the mouth. 
 
 About 1855 Dr. John Allen of New York, introduced tlie 
 method of attaching- the teeth to a platinum base and fusing 
 the porcelain around them. By this means warpage of the 
 denture during baking was to a large extent obviated. This 
 is essentially the method in vogue today, the constructive de- 
 tails of which are as follows : 
 
 FORMING THE PLATINUM BASEPLATE 
 
 From an impression of the mouth a model is secured. A 
 die and counterdie are formed in the manner elsewhere de- 
 
 PLATINtlM BASEPLATE. SWAGED AND TRIMMED TO 
 
 APPROXIMATELY CORRECT PERIPHERAL 
 
 OUTLINE 
 
 scribed, and a pattern of the baseplate obtained. Usually pure 
 platinum No. 28 gauge, is used, since a thinner plate unless 
 heavily reinforced, will not furnish a sufficiently rigid founda- 
 tion to prevent warpage of the porcelain during baking, or 
 obviate fracture of the finished denture under stress. 
 
 In the swaging of a platinum baseplate special care should 
 be taken to avoid the formation of folds in any location, since 
 if subsequently corrected by flowing solder into them, and re- 
 ducing the excess by grinding, an unsightly area is left due to 
 difference in color of solder and baseplate. 
 
 FITTING THE BASEPLATE IN THE MOUTH 
 
 When swaged and trimmed peripherally, the base should 
 be introduced in the mouth and tested as to general adaptation 
 
CONTINUOUS GUM DENTURES 591 
 
 aud stability. All margins which impinge on the muscles or 
 frenum should be corrected, and the peripheral outline of the 
 baseplate trimmed to as nearly the exact outline of the finished 
 denture as possible. This is necessary in order to avoid the 
 unsightly appearance caused by grinding away the metal rim, 
 often into the porcelain, to relieve impingement when the fin- 
 ished denture is introduced — a condition frequently seen in 
 cases where proper care has not been exercised in pei'ipheral 
 trimniing of the baseplate. 
 
 REINFORCING THE BASEPLATE 
 
 Since porcelain in thin layers is easily fractured, the 
 metal framework of dentures and bridges which are to be 
 overlaid with this material should have sufficient inherent 
 
 DISTAL SHOULDER WIRE AD.U>TED TO PLATINUM 
 
 JiASEPLATE. THIS WIRE SHOULD BE iu TO 22 
 
 GAUGE, AND TERMINATE ABOUT THE 
 
 CENTER OF EACH TUBEROSITY 
 
 strengtii, exclusive of the added porcelain, to withstand all 
 stress to which they may be subjected. 
 
 A platinum base may be strengthened in several ways, the 
 most common methods of which will now be given : 
 
 First, to strengthen an upper baseplate, a platinum wire 
 of 22 to 2-t gauge is adapted and soldered to the lingual side 
 of the baseplate near its distal margin. It should be laid in a 
 symmetrical curve, and advanced further forward in the vault 
 portion than at either side. The object in placing the two ends 
 near the margins at their terminal points on the tuberosities 
 is to afford some space for a graceful curve to the porcelain 
 in its extension distally from the second molars. 
 
 Over this wire a second strip of platinum, usually 31 or 
 32 gauge, is swaged to the plate. The anterior margin of this 
 
CONTINUOUS GUM DENTURES 
 
 strip should overlap the wire anteriorly, and the posterior 
 margin extend slightly beyond the distal margin of the base- 
 plate, to afford a shoulder on whioh to lay the solder. When 
 
 I'l.ATE AMI UIRK 
 
 swaged, the anterior margin of tlie strip is trimmed to the an- 
 terior surface of the wire and the two ends cut so as to termi- 
 nate on the tuberosities and even with the underlying wire. 
 
 In addition to the doubler just described, a second doubler 
 is sometimes swaged and trimmed as illustrated, to overlay 
 the border and extend into the palatine area. It should not 
 
CONTINUOUS GUM DENTURES 593 
 
 extend much beyond tlic crest of the border either labially or 
 incisally; first, because it is not necessary for strength; sec- 
 ond, the space it would occupy if extended can be best con- 
 served for increasing bulk of poi'celain ; third, unnecessary 
 metal adds to the weight of the denture. 
 
 Instead of the doubler just described, some prefer to 
 adapt and solder a piece of 1(i or 14-gauge iridio-platiniun 
 
 I)Orm,EB TltlMMEII AND SOLUEBBD TO BASEl'LATE 
 
 wire along the crest of the border in such position as not to in- 
 terfere with correct tooth alignment. 
 
 The doubters, of whatever form, should l)e firmly attached 
 to the baseplate with high-grade platinum solder, and the base 
 reswaged to correct any warpage that may have occurred. 
 
 FORMING THE FINISHING SHOULDER FOR THE PORCELAIN 
 
 It is necessary in order to avoid fracture, to form a right- 
 angle shoulder around the entire periphery of the base, 
 against which the porcelain may settle in fusing. The anterior 
 margin of the doubler and underlying wire, when squared out 
 with small stones and burs, constitute tlie distal shoulder, 
 while that on the labial and liuccal periphery is formed on 
 these surfaces by soldering a wire of about 18 gauge to the 
 baseplate. 
 
 One end of the peripheral wire should abut the doubler 
 and wire on oilo tuberosity, and be bent to lie in contact with 
 the baseplate rim for a distance of about an inch anteriorly. 
 It is then clamped in position and attached with solder 
 throughout a portion of this distance, and the plate cooled. 
 The adaptation of the wire and attachment with solder should 
 
594 CONTINUOUS GUM DENTURES 
 
 proceed in sections, rather than to attempt to adapt and elanip 
 it around the entire periphery at the start. 
 
 The wire should be parallel with the periphery of the 
 baseplate rim, but be placed about one-sixteenth of an inch 
 from it, so that subsequent trimming, if necessary to relieve 
 muscular 'impingement, may be accomplished witliout en- 
 croaching on the porcelain. 
 
 Extensive contouring of the solder in the space on tiie 
 l)eripheral side of the wire should not be attempted, as pits 
 are liable to develop in bulky masses of platinum solder dur- 
 ing the fusing of the porcelain. The angle, however, should 
 
 BASEPLATE WITH PERIPHERAL WIRE ATTACHED. 
 
 ALSO A STRENGTHENEK ADAPTED TO 
 
 BORDER AREAS 
 
 be filled in to develo}) a uniform, but slightly tapering or con- 
 cave surface. 
 
 The angle between wire and baseplate presenting toward 
 tlie crest of the border should not be filled to any extent with 
 solder, since this surface of the wire must subsequently be 
 squared out in forming the shoulder. 
 
 Small square-edged carborundum stones are now applied 
 to the wire to develop a square shoulder against which the 
 porcelain may be fused. Plug-finishing burs are also useful 
 for this purpose. The shoulder should jjresent a definite angle 
 around the entire periphery of the base, for if left round at 
 any point a crease may form by the contraction of the porce- 
 lain, or the latter may overlap the rounded surface as a thin 
 edge and the latter be fractured in handling. 
 
 The soldering is best accomplished by means of nitrous 
 oxid and gas blow-pipe, or when pure gold is used as a solder 
 
CONTINUOUS GUM DENTURES 
 
 595 
 
 the ordinary gas blow-pipe may be employed. Platinum solder 
 is preferable to pure gold, as it is not dissipated during the 
 several bakings of the porcelain as is pure gold, the latter 
 being absorbed by the platinum at high temperatures. Fre- 
 
 THE TURNER ALCOHOL liLOWPrPE. ^\^TICH 
 
 DEA'ELOPS AN INTEN.SB PLAJIE SUITjVBLE 
 
 FOR FU.SINr, PLATINUM SOLDER 
 
 ([uently joints united with pure gold as a solder pull apart 
 during baking, or under slight stress when the finished piece 
 is introduced in the mouth. 
 
 RESWAGING AND CLEANSING THE BASEPLATE 
 
 The doubter and peri]iheral shoulder wire having been 
 attached by soldering, the baseplate should be reswaged to 
 correct the warpage that may have occurred during this op- 
 eration. 
 
 To prevent the baseplate from becoming lodged in the 
 counterdie in swaging, due to the peripheral shoulder wire 
 being driven into the sides of the latter, a few layers of damp 
 newspaper can be interposed between the two. The die and 
 counterdie sliould at all times be kept oiled to prevent con- 
 tamination of the platinum by the base metals. In addition 
 to this precautionary measure the baseplate should be boiled 
 in dilute acid and .thoroughly polished on the lathe with a 
 stiff brush wheel and pumice stone, to prevent any possible 
 danger from this source. 
 
 DEVELOPING THE OCCLUSION AND CONTOUR MODEL 
 
 The baseplate is now in condition to receive the rim of 
 wax, by means of which the occlusion and facial contour is 
 
596 CONTINUOUS GUM DENTURES 
 
 established. The steps from now on are exactly similar to 
 those described under the head of J-^iill Denture Construction 
 np to that of permanently attaching the teeth to the baseplate, 
 with the exceptions resulting- fi'oni the use of a special type of 
 tooth for these cases. 
 
 CONTINUOUS GUM TEETH 
 
 Teeth intended for continuous gum woi*k differ from 
 vulcanite teeth in having gingival extensions resembling roots. 
 
 A SKT IIF NO. 
 
 rONTixuors r:uM teetti. 
 
 These extensions are flattened somewliat on their lingual sur- 
 faces to obviate excessive grinding in aligning the teeth on 
 the baseplate. 
 
 These root extensions serve two very useful purposes ; 
 first, being composed of high-fusing porcelain which is unaf- 
 
 tMiUiiiiimui 
 
 I'ENTRAL. AND BICUSPID. TURNED 
 
 fected by contractile changes dui-ing vitrification of the con- 
 tinuous gum body, the bulk of the latter required for the case 
 is materially lessened, and shrinkage of the denture mass is 
 proportionately reduced ; second, in addition to the long pin 
 attachment of the tooth to the baseplate, the extension serves 
 to increase stability by resting upon the baseplate, thus ob- 
 
CONTINUOUS GUM DENTURES 59T 
 
 viatiug- the danger of displacement due to contraction of tlie 
 body during baking. 
 
 When but slight absorption of the I'idge has occurred, 
 it is frequently necessary to grind away a portion or all of 
 the extension, thus bringing the body of the tooth directly in 
 contact with the baseplate, mucb as the ridge lap of an ordi- 
 nary vulcanite tooth is frequently set in contact with its base- 
 plate, or sometimes upon the cast itself. 
 
 In other cases when excessive absorption of the ridge 
 has occurred and the correct labial, buccal and occlusal align- 
 ment of the teeth have been secured, these extensions may 
 fail to touch the baseplate at any point. It then becomes nec- 
 essary to interpose blocks of high-fusing porcelain, as pieces 
 
 CASE KEQUIRING CONSIDER 
 ABLE BEDnCTION OF LIN- 
 GUAL SIDE OF BOOT 
 
 t'ASE REQUIRING ADJUST- 
 MENT OF BROKEN PIECES 
 OF PORCELAIN BETWEEN 
 TEETH AND BASEPLATE 
 
 of broken teeth, between the baseplate and the extensions not 
 in contact, or to truss them in proper position with platinum 
 wire or plate. In addition to the difference noted, continuous 
 gum teeth are supplied with a single platinum pin, larger and 
 longer than those ordinarily used in other types of teeth. 
 
 SELECTION AND ARRANGEMENT OF TEETH 
 
 Teeth of suitable form, size and shade to meet the recjuire- 
 ments of the case having been selected, they are let within 
 the wax rim by successively cutting out sections of the latter 
 of sufficient depth- to permit each tooth, with its extension, 
 to assume propVr alignment. No attention need be given the 
 relation of the extension end of the tooth to the baseplate 
 during arrangement, except when its length or lingual surface 
 interferes with correct placing of the tooth, when it may be 
 reduced by grinding, or entirely excised, as conditions require. 
 
598 CONTINUOUS GUM DENTURES 
 
 The steps of arrangement and occlusion of full upper and 
 lower cases of this type are carried out in other respects the 
 same as for full dentures in general. When the teeth are 
 occluded the denture should be waxed up labially and buccally 
 to represent the natural gums, with such added contour as 
 may be required for facial restoration. This step is seldom 
 carried out, but more esthetic results can be produced by 
 following this plan than by developing the contour without 
 definite guidance. 
 
 TRIAL OF THE WAX MODEL DENTURE IN THE MOUTH 
 
 When properly contoured, the denture is tested in the 
 mouth, first as to normal occlusion; second, as to clearance 
 ]iaths in lateral movements; thii'd, balancing contact; and 
 fourth, general esthetic results. When corrections have been 
 made, if necessary, and the prosthetist is satisfied that all re- 
 quired conditions have been fulfilled up to this stage of con- 
 struction, the next step is to prepare a guide for testing the 
 labial and buccal contour of the case at various stages of 
 construction. 
 
 DEVELOPING THE CONTOUR MATRIX 
 
 The entire labial, buccal and palatine surfaces of the 
 wax model denture are now coated with a thin film of oil, a 
 mix of plaster made, and a cast of ordinary form developed 
 
 
 l^'^J 
 
 ■^^^^H 
 
 
 FOUR PIECE MATRIX, AM. I'AIiTS IN CURRENT Ar'l'OSrriON 
 
 l)y filling in the palatine and border svirfaces of the baseplate. 
 This cast should be about %-inch thick in the vault region, 
 or sufficiently deep to raise the peripheral margins of the 
 baseplate about one-fourtli inch above the base of the cast. 
 The sides of the cast should he trimmed smooth, converging 
 slightly from the base upward, to the outer peripheral line of 
 the wax. At several points on the labial and buccal surfaces 
 of the cast shallow countersunk depressions are made to 
 
CONTINUOUS GUM DENTURES 599 
 
 develop pro.jcctiinis on the several sections of the labial and 
 buccal matrix. This is necessary in order that any section of 
 the matrix may be returned to position independently of the 
 other pieces. The side of the base is varnished with shellac, 
 which, when dry, is coated with a thin film of oil. 
 
 Plaster is now applied to one of the buccal surfaces and 
 built against the base of the cast, the wax and outer surfaces 
 of the teeth. It should not extend over the buccal marginal 
 ridges or incisal edges of the teeth. This first section includes 
 the area from the tuberosity back of the second molar to the 
 middle of the cuspid tooth. It should be about three-eights 
 
 FOUn-riECE MATRIX FOB LOWER CASE. USED FOB TESTING CONTOUU Of CASE 
 DURING CONSTBUCTION STAGES. PARTIALLY SEPABATED 
 
 of an inch in thickness, its outer surface parallel with the buc- 
 cal surface of the cast base and denture. When hardened the 
 anterior end of this first section is squared up, varnished and 
 oiled. 
 
 Another mix of plaster is now applied to the incisor area, 
 building against the squared end of the first section and 
 extending to the opposite cuspid tooth. When set, this section 
 of plaster is trimmed, varnished, oiled, and the third piece cor- 
 responding to the first on the opposite side is constructed. 
 
 When the plaster has set the three sections are tapped 
 slightly to loosen, then removed, and the wax model denture 
 is detached from the cast. These are now set aside until after 
 the ai)plication of the body in the second baking, when the 
 baseplate is returned to the cast and the several labial and 
 buccal areas are tested as to required fullness, or excess of 
 apiilied body, by returning each section to position against 
 the cast base. By sawing partly through any section at one or 
 more points, cutting from without inward, it may be cleanly 
 fractured into any numl)er of required pieces, any one of 
 which may be used for test purposes over its own particular 
 area. 
 
600 CONTINUOUS GUM DENTURES 
 
 It is possible by caliperiiig a number of prominent areas 
 of the waxed case, and recording the same, to arrive at com- 
 paratively accurate results in the disposition of the gum body. 
 The time required for measuring, recording, and later for 
 reference, usually aggregates more than that required for 
 forming a matrix, while the latter when suitably fractured will 
 determine quickly the accuracy of many gingivo-peripheral 
 surface contour lines. 
 
 These various steps having been completed, the case is 
 now ready for investment, ]iroparatovy to attaching tlie teeth 
 to the baseplate. 
 
 INVESTMENT OF THE WAX MODEL DENTURE 
 
 In continuous gum cases the teeth must be rigidly at- 
 tached to the baseplate by soldei'ing and trusting to prevent 
 their relation, as established in the wax rim and by trial 
 in the mouth, from becoming distorted by the contraction of 
 the porcelain while fusing the latter. The steps are carried 
 out as follows: 
 
 The wax representing the labial and buccal surfaces of 
 the gums is removed from these areas and from between the 
 embrasures and root extensions as well, so as to permit the 
 investment to partially surround and hold the teeth when 
 lingual support is removed. A mix is made of some standard 
 investment material which possesses considerable hardness 
 when set. A portion of the investment, about one-lialf inch 
 
 IIM TKETH ARRANGED ON 
 \sn-I.ATE. WAX REMOVED 
 l;\srltES TO ALLOW IN- 
 r MATERIAL TO ENTER 
 THESE SPACES 
 
 thick and a little larger than the area of the baseplate, is 
 placed on a sheet of paper on the bench. Another portion is 
 filled in the palatine side of the platinum base and the latter 
 pressed down upon that resting on the paper, until it ap- 
 proaches within three-eighths of an inch of the bench. The 
 investment is then worked into the embrasures and over the 
 
CONTINUOUS GUM DENTURES 601 
 
 occlusal and incisal surfaces of the teeth. . To resist the more 
 or less rough usage it will receive in applying the truss bars 
 and soldering, the investment should be about three-eighths 
 of an inch thick througli the side walls. All overhanging por- 
 tions should be removed from the occlusal and incisal surfaces, 
 
 FROM I.INCIAI. 
 
 to permit of ready access in bending the i)ins and soldering 
 them to the truss or baseplate. 
 
 When hai'deued the rough excess of investment is trimmed 
 away, the wax surrounding the lingual surfaces of the 
 teeth in which the pins are imbedded is thoroughly warmed 
 and removed — care being taken not to dislodge the teeth — 
 the final trimming of all excess investment accomplished and 
 the case thoroughly cleansed with a stream of hot water. 
 
 FITTING AND APPLICATION OF THE METAL SUPPORT TO 
 THE TEETH 
 
 Occasionally cases present where the long pins of the 
 continuous gum teeth can be directly applied and soldered to 
 the platinum baseplate in such manner as to give all necessary 
 support to the t_eeth. More frequently, when much absorption 
 of the border has occurred, it is necessary to extend some kind 
 of metal support from the border crest to the angle of junction 
 of the pins with the porcelain. The Allen method, although 
 not the best, is most frequently resorted to, and is as follows: 
 
G02 CONTINUOUS GUM DENTURES 
 
 The platiniiiii pins are straightened ont at I'ight angles 
 to the long axes of the teeth. A strip of cardlioard abont four 
 inches long is cut like the illustrated pattern, subject of 
 course, to such modifications of form as tlie slant from the 
 
 SUri'ORTIXC TRfSS MAY 
 
 border to the iiins and to the varying width of the space be- 
 tween the same at different points. (See cut on page 603.) 
 
 This cardboard pattern is corrected by trial, and recon- 
 structed if necessary, until when finally fitted it exactly repre- 
 
 SECTMINAI, VIKW OF TOOTH. 
 BASEPI.ATE JIBTAI. SUP- 
 PORT AND INVESTMENT 
 
 sents the form of metal strip to cut for the proper support of 
 the teeth. The pattern as shown usually represents the seg- 
 ment of an ellipse. A metal duplicate of 30 or 31 gauge iridio- 
 platinum plate is now made and bent to place. Marks are now 
 made at various points on its lingual surface between the teeth, 
 
CONTINUOUS GUM DENTURKS 
 
 to indicate the position for punching the holes, the idea lieing 
 to so place the holes that the pins when bent and soldered to 
 the strip will not close them. The holes, usually about ten 
 or twelve in number, should be located about midway lietween 
 tlie border crest and the pin margin of the strip and should 
 
 rAI'ER I'ATTKUX UF METAL Siri'OliT KOU THE TEETH 
 
 be about cue-sixteenth of an inch in diameter. At various 
 l)oints along the margin which rests on the border, crescent- 
 shaped notches are cut in the strip. Through these various 
 openings the labial and buccal ]iortions of porcelain become 
 more or less firmlv united and under stress of mastication 
 
 METAL SLl'lMJUT, 
 
 splitting of the denture is not so liable to occur as is the case 
 when the openings are omitted. 
 
 It will readily be seen that a support so formed mechani- 
 cally divides the denture into two portions, and is therefore 
 a source of weakness, which after consti'uction of the case, can- 
 
CONTINUOUS GUM DRNTURRS 
 
 not be overcome. More recent and bettei- methods will be 
 shown for trussing and holding tiie teeth in position. 
 
 The holes having been punclied and the notches cut as 
 described, the striji is returned to position and the pins bent 
 
 down in contact with it, and the baseiilate also if the space is 
 not too wide. 
 
 The invested case is now placed on a Bunsen stove to 
 thoroughly dry and become heated. Medium fusing platinum 
 
 SECTION SHOWING PIN 
 
 ADAPTED TO METAL SOP- 
 PORT. AND. IN THIS CASE. 
 TO THE BASEPLATE AS 
 WELL 
 
 solder is cut in small pieces preparatory to the final union 
 of the many parts. When thoroughly heated, the invested 
 case is placed on a solder block in such position that gravity 
 will retain the solder in jjcsition in certain areas to wliieh 
 
CONTINUOUS GUM DENTURES 605 
 
 it is now applied. The nitrous oxid and gas blow-pipe previ- 
 ously mentioned is now directed on the solder placed, and 
 when fused the position of the case is changed. The process 
 is repeated until all of the teeth are firmly united to the strip 
 and the latter to the baseplate. The use of excessive amounts 
 of solder should be avoided, as it only increases the weight 
 of the denture without materially adding strength. 
 
 Pure gold is often used as a solder in this class of work, 
 and while commonly safe, there is danger of it being absorbed 
 b}' the platinum and the joints becoming disconnected. 
 
 In all soldering operations of the class under considera- 
 tion, certain essentials should be kept in mind. These may 
 be summarized as follows : 
 
 Close, clean joints. 
 
 Strong, yet not too bulky, investment. 
 
 Plenty of preliminary, as well as blow-pipe, heat. 
 
 Small pieces of platinum solder laid just where 
 they are needed. 
 
 Avoid the use of too concentrated or long-con- 
 tinued flame on any one tooth. 
 
 Depend on gravity for retaining and carrying 
 the solder in position when fused. 
 
 Avoid the use of flux, since the metals do not 
 oxidize and its presence, if allowed to come in contact 
 with the porcelain at high temperatures, is certain 
 to check the latter. 
 
 SUPPORTING THE TEETH WITH WIRE 
 
 When the distance between the border crest and the pin- 
 porcelain junction of the teeth does not exceed one-fourth of 
 an inch, a No. 18 gauge iridio-platinum wire can be bent as 
 shown in the illustration, to afford a comparatively rigid sup- 
 port for the teeth, while the tendency to divide the porcelain 
 into an outer and inner portion is obviated, or at least greatly 
 reduced. The technic of application-fitting and trying is so 
 simple that it need not be here detailed. 
 
 When the amount of absorption is excessive and the teeth 
 must of necessity be raised a considerable distance from the 
 baseplate, the foll6wing plan can be adopted. 
 
 Two wires of 16 gauge iridio-platinum are bent to con- 
 form to the arch. One is laid on the border crest, not neces- 
 sarily in close contact, but touching, the baseplate at the distal 
 extremities and at several intermediate ]ioints. The other 
 
606 CONTINITOUS GUM DENTURES 
 
 wire is bent to lie in close contact witli the pins and porcelain 
 at their junction. The extremities of this wire are carried 
 from the pins of the second molar in a sloping direction, down 
 alongside of, and in contact with, the wire on the border 
 crest. 
 
 WIRE TRUSS. 
 
 Five or six iridio-platinnm posts are now cut and fitted 
 so as to reach from the baseplate to the wire under the pins. 
 They should also touch the wire on the border crest. The 
 pins are now bent around the upper wire and the frame-work 
 when soldered forms a rigid truss, capalile of withstanding 
 all ordinary strains. 
 
 In these cases of excessive absorption, the teeth are fre- 
 quently so placed that their cervical extensions do not touch 
 the baseplate, nor can the border wire of the truss at all times 
 be bent in such manner as to afford them necessary support 
 without reducing the efficiencv of the truss. 
 
CONTINUOUS GUM DENTURES 
 
 By blocking in tlie space between the baseplate and the 
 porcelain roots with broken pieces of old porcelain teeth, or 
 even whole teeth, so placed as not to interfere with proper 
 contouring of the gum body, the danger of distortion in fusing 
 is ol)viated. The presence of tlie blocks of liigh-fusing porce- 
 
 lain is not in the least objectionable, biit rather an advantage, 
 since the bulk of gum body required will be proportionally 
 reduced. The soldering of the wires is carried out in a man- 
 ner similar to that followed in attaching the teeth by means 
 of the metal strip. 
 
 When the teeth, by whatever method adopted, are at- 
 tached to the baseplate, the investment is allowed to cool. It 
 
 is then placed in \yater to soften and finally carefully removed 
 so as not to disturb the position of the teeth. The latter, al- 
 though firmly fixed to the truss bar or strip by the pins, can 
 be rotated or bent under stress until rigidly fixed by fusion 
 of the first application of body. 
 
608 CONTINUOUS GUM DENTURES 
 
 In some cases it may be advisable after soldering to try 
 the skeleton denture in the month to test the occlusal relations 
 of the teeth. Frequently some slight change, as rotating a 
 tooth or modifying its axial alignment at this time will ob- 
 viate what might later on prove a glaring defect. 
 
 The skeleton denture is now boiled in dilute HCl, thor- 
 oughly washed and the palatine and outer surfaces of the 
 platinum base roughened by passing a sharp-pointed blade 
 over them in various directions to afford some slight hold 
 for the porcelain. The case is now ready for the application 
 of the continuous gum body. 
 
 CONTINUOUS GUM BODY AND ENAMEL 
 
 Under the description of porcelain will ))e found the gen- 
 eral formula' of confimious gum body, and giDii etiawel. These 
 materials, supplied hy the manufacturers for denture con- 
 struction, come in powder form, usually in one-ounce pack- 
 ages. They are commonly referred to as hodij and enamel. 
 The body is almost white in powder form; during fusion it 
 assumes a yellowish tint much resembling dentin. 
 
 The enamel is a delicate pink, which on fusing assumes 
 varying shades ranging from almost imperceptible pink to 
 a pinkish purple, depending on the thickness of the layer and 
 the amount of heat applied. 
 
 The body supplies the necessary bulk and contour to the 
 case, and is usually applied and fused two times. The enamel 
 supplies the color and is fused once, although at times two 
 applications are necessary. 
 
 PREPARATION OF THE BODY 
 
 As a preliminary requirement in successful porcelain 
 work the strictest care as to cleanliness must be observed. 
 This includes clean hands, instruments, materials and a room 
 free from dust. 
 
 About one-half the contents of the box of body is placed 
 upon a flat glass or porcelain slab four inches square, or even 
 larger. With a drop tube sufficient distilled water is added 
 to the powder to make a medium plastic mass. 
 
 The specific gravity of titanium oxid is 4.2; of silex, 2.66; 
 and of kaolin, 2.6. It is apparent that in a thinly-fluid mix 
 of body the coloring matter will gravitate below the other 
 ingredients if much time elapses before taking up the surplus 
 moisture. While the quality of such mass when fused may not 
 
CONTINUOUS GUM DENTURES 609 
 
 be impaired it will not be of exactly uniform color. To avoid 
 separation of the constituents mentioned the pasty mass 
 should be thoroughly spatulated and the excess moisture ab- 
 sorbed by immediately pressing a clean linen towel or napkin 
 over it. 
 
 APPLICATION OF THE BODY TO THE TEETH AND BASEPLATE 
 
 With a moderately broad spatula the body is applied to 
 the lingual surfaces of the teeth, and vibrated to i)osition by 
 
 drawing a knurled instrument against the side or back of 
 the baseplate. 
 
 The skeh>ton denture should be held l)y i)iacing the tinnnli 
 against the iieripheral rim or within the maxillary portion of 
 the basei^late and the index linger on the occlusal surfaces 
 of the teeth. Now, by applying the middle finger against the 
 buccal surfaces of the teeth and extensions and holding the 
 baseplate edgewise the body will be prevented from dropping 
 through the open spaces. The excess moisture which is forced 
 out by the settling of the granules together is taken up with 
 
610 CONTINUOUS GUM DENTURES 
 
 tlie napkin and anotlicr mass oi" ))ody applied in liko manner 
 until the greater bulk of lingual contour re(piired is developed. 
 It will l)e found most convenient to apply tlie bulk of 
 body to the lingual space in three sections; first, from the 
 cusjjid to the tuberosity on one side, vil)rating and absorbing 
 the moisture; second, from cuspid to cuspid ineisally; third, 
 from cuspid to tuberosity on the opposite side. Each addi- 
 tion as it is applied and vibrated to place should be relieved 
 of the surface moisture. In dentures requiring excessive 
 restoration, it sometimes becomes necessarv to further 
 
 CONBEXSING THE BODY WITH CARVING TOOL 
 
 eliminate the moisture by passing the case a few times 
 rai3idly through the Bunsen flame, to prevent the flowing of 
 the adapted body while vibrating subsequent additions to 
 place. Should further additions of body to areas which have 
 been rendered comparatively dry, be necessary, such areas 
 should be moistened before making the adBitiou, so that the 
 two will intimately unite. When this precaution is neglected 
 the comparatively dry body will absorb the moisture from 
 the mass last added so rapidly that the latter cannot be vi- 
 brated into a dense, compact state. 
 
 The lingual contour is developed roughly to approximately 
 the required thickness of the finished case, as are the laliial 
 
CONTINUOUS GUM DENTURES 
 
 and buccal surfaces also. C*are should be taken to avoid ex- 
 cess of material in any area, for if present in excess, removal 
 by grinding would be necessary, while any deficiency may be 
 corrected in the second application of the body. 
 
 [<)X BEFORE BAKING 
 
 Tlic denture should be brushed free from all particles of 
 the body that may be lodged upon the platinum baseplate or 
 the teeth where not actually required, as during fusion they 
 will become firmly attached to either platinum or teeth and 
 must subsequently be removed with discs. 
 
 Special care should be given to the exposed jiortion of 
 the teeth to see that proper gum curvature is outlined. Dr. 
 
 THE CASE READY FOR FIRST BAKIXd. CON- 
 
 TIXIIOCS GUM BODY DIVIDED WITH THIN 
 
 BL.VDE INSTRUMENT 
 
 L. P. Haskell recommends for this purpose an ordinary quill 
 toothpick sharpened to a neat, smooth blade-like point. A 
 delicate spatula will answer the same purpose. This step is 
 followed by applying a delicately-pointed camel 's-hair brush. 
 
612 CONTINUOUS GUM DENTURKS 
 
 moistened first, afterward drying and removing every particle 
 of body not required from the gingival curvatures. 
 
 Since porcelain contracts from one-sixth to one-fifth its 
 bulk in vitrifying when applied in the manner described, unless 
 preventive measures are used the teeth are liable to be 
 warped out of i)osition from the contraction of the material 
 between and around the root extensions. To obviate this diffi- 
 culty a thin spatula should be passed through the body to the 
 baseplate on both external and vault surfaces. Each tooth 
 previously fixed by its pin to the truss or stay wire thus be- 
 comes a fixed center toward which the body composing that 
 section will contract. 
 
 The case should finally he inspected to see that all sur- 
 faces are free from excess material before introducing in the 
 furnace. 
 
 SUPPORTING CONTINUOUS GUM CASES WHILE FUSING 
 
 To obviate danger of war})age of the denture during 
 baking, it must be supported at widely divergent points. One 
 of the most convenient methods consists in bending a 16-gauge 
 platinum wire in the form of a V, bending the angled end and 
 
 the two terminals upward so as to form three legs of sufficient 
 height to raise the denture clear of the muifle slab. The two 
 terminals support the case at the tuberosities, and the angular 
 • leg anteriorly. These three points of contact give uniform 
 support to the case at all times and effectually prevent warp- 
 age. 
 
 This form of support is also of advantage because it does 
 not absorb the radiated heat as does a support composed of 
 fibre asbestos and investment material commonly employed. 
 In case a support of the latter class is used it should be re- 
 duced to the smallest possible dimensions consistent with 
 strength. 
 
CONTINUOUS GUM DENTURES 
 
 PORCELAIN FURNACES 
 
 Electric furnaces of various types are almost universally 
 used at the jn-esent time for the fusing of porcelain in pros- 
 thetic procedures. The Custer and the Hammond represent 
 
 DENTURE IX rOSITIOX. ELECTRIC FURNACE (CUSTER TYPE) 
 
 two of the most serviceable forms, although there are others 
 almost, if not quite, equally as dependable. 
 
 The principle involved in the generation of heat depends 
 upon the resistance offered by a fine platinum wire to the 
 passage of a current of electricity. When a 110-v. current of 
 low amperage is passed through a 28-gauge wire the resist- 
 
614 CONTINUOUS GUM DIONTUKKS 
 
 ance ofiVrcd to the passage ol' the current is manifested by 
 the wire becoming heated to high temperature of varying de- 
 gi'ees, depending on the length of wire and the time of current 
 flow. 
 
 When a <'(in(Uictor oft'ers resistance to the passage of a 
 current to such an extent that lieat is manifested the voltage 
 of the current is reduced. By interposing outside resistance, 
 as a rlieostat in wliicli the resistance can he graduallv reduced 
 
 or entirely cut out, the amount of heat generated within the 
 furnace is easily controlled. This is an important advantage 
 in the fusing of porcelain, for if heated too rapidly, bulky 
 pieces contract unevenly, while the quality of the fused product 
 is impaired. 
 
 Time is a most important factor in the fusing of porce- 
 lain. Practically all of the high-fusing bodies, with the excep- 
 tion of tooth bodies, can be fused under 2,000 deg. F. if srab- 
 jected to long continued heat. The quality of porcelain so 
 fused is denser and its color better than when subjected to 
 
CONTINUOUS GUM DENTURES 615 
 
 rapid fnsiou. However, very satisfactory results may be 
 secured hy adoi:)ting' the plan of fusing at a temperature about 
 midway l)etween the lowest possible point of vitrification and 
 that required for the shortest time for the particular body 
 used. 
 
 FIRST BAKING OF THE CONTINUOUS GUM CASE 
 
 The case is now introduced into the furnace, teeth upward, 
 and placed on its sup])ort. The latter, whether of wire, as 
 suggested, or composed of investment materials, should rest 
 on a fire-clay slab to afford protection to the slightly imbedded 
 fiirnace wires. This is necessary to obviate short circuiting of 
 the current, and also to prevent any small flakes of porcelain 
 which might become detached from falling to the furnace floor 
 and there fusing to the fire-clay lining, or over the nearly- 
 exposed wires. 
 
 The muffle is closed, the rheostat arm set on the first but- 
 ton and allowed to remain there a sufficient time to expel all 
 moisture. This usually requires from 8 to 10 minutes. If 
 this step is crowded too rapidly, the body will flake off as a 
 result of the sudden generation of steam within the mass. 
 
 Several methods are in vogue in the baking of porcelain, 
 any one of which will give good results if carefully carried 
 out. The following method, and one preferred by the writer, 
 is to gradually increase the temperature in uniform steps as 
 follows : 
 
 When the moisture has lieen expelled, which can readily 
 be seen by the chalk.v appearance of the case, the rheostat arm 
 is moved from first to second button, where it is allowed to 
 remain until the maximum heat of that section is developed. 
 This usually retpiires from 15 to 20 minutes. The arm is now 
 moved on, allowing five-minute interval between each change. 
 In extra-lmlky cases the interval may be safely extended one 
 or two minutes longer. 
 
 With a new or strange furnace, preliminary tests should 
 always be made to determine the length of time required, and 
 the particular button at which fusion will occur. The time 
 of fusion will vary somewhat with the intensity of the current 
 and various other conditions. If in a position where a strong 
 di'aft of air strikes the furnace fusion is retarded. 
 
 The liody should not l)e glazed during the first leaking, but 
 carried to the point of fusing the most fusible ingredients, yet 
 stopped before the granular surface is entirely lost. This 
 stage is called "biscuit bake." It presents a semi-granular, 
 
616 CONTINUOUS GUiM UFINTURKS 
 
 yet partially ulazcd aiii)paran('e, while the ])(iicclain is dense 
 and darkened. 
 
 When tlie fusing stage is reached the interior of the fur- 
 nace and contents present a bright red appearance, so that it 
 is sometimes difficult at first to distinguish the outlines of 
 the case. By carefully viewing the Imccal surfaces of the 
 denture in line with the back of the furnace, the roughly 
 granular surface can be seen to gradually disappear. The 
 fusion should be stopped at this stage by reversing the rheo- 
 stat arm, opening the switch and the case allowed to cool. If 
 removed and cooled suddeul}% fracture of the porcelain is 
 almost certain to occur. 
 
 SECOND BAKING 
 
 The gum body should now be freshly spatulated, adding 
 water and absorbing it as previously described. The case 
 is dipped in cold water, the surplus shaken out, fresh body ap- 
 plied to the fissures purposely formed before the first baking 
 and all others that may have developed in any location from 
 contraction in baking. The body should be actiially com- 
 pressed in these fissures when possible to reduce to the mini- 
 mum the slightly greater contraction that must occur over 
 these areas than will be noticeable where the freshly added 
 material is thinner. 
 
 The case should now be developed to full contour on all 
 surfaces and the labial and buccal areas tested with the con- 
 tour matrix previously formed. If deficient, more body should 
 be added, and if too full the amount reduced as required. 
 
 Palatine rug,-? should be developed somewhat stronger 
 than the natural marking, as some detail will be lost in fusing. 
 
 Again, all surplus body must be carefully brushed from 
 the teeth and baseplate, the moisture expelled, and the case 
 returned to the furnace for the second baking. This step 
 is carried out as before, except that less time is required 
 on first button — usually about 10 minutes, and the fusion 
 stopped at the semi-granular stage. Since time of exposure 
 to heat is an important factor in fusing porcelain care must 
 be taken not to over-fuse the case. 
 
 In the second baking the body last applied is not alone 
 affected. That first fused is also advanced from the biscuit 
 to the glazed stage. It also contracts to a very slight extent, 
 although the greatest contraction has previously occurred in 
 the first fusing. 
 
CONTINUOUS GUM DENTURES 617 
 
 \\'Ir'11 the seeuud appliccitioii of body lias been biscuited, 
 fusion is stopped as in the first halving and the case allowed 
 to cool, when it is ready for the tliird bake. 
 
 PREPARATION OF THE CASE FOR THE THIRD BAKING 
 
 The case should now be thoroughly inspected for fissures 
 that may have formed during the last baking. These usually 
 are found at the junction of the body with the lingual surfaces 
 of the teeth, and around the periphery of the base, although 
 they may occur in any location. When not extensive they may 
 be filled with another mix of the gum body and the case enam- 
 eled. The overlying enamel, although not requiring a tem- 
 l)erature for fusion sufficiently high to fuse the body last 
 added, will intermingle and unite with it to form a compact 
 mass. 
 
 APPLICATION OF THE GUM ENAMEL 
 
 The gum enamel is now mixed with water, spatulated, 
 and the surplus moisture absorbed as in the preparation of 
 the body. It is applied to the case in a thin uniform layer 
 about 1-32 of an inch thick. Since slight variation in shade 
 of the pink enamel is desirable in the finished case this et¥ect 
 may be produced by varying the thickness of the layer of 
 enamel as it is api^iied. Care sliould be taken to distribute 
 it uniformly over the rngje and avoid tilling in the depressions 
 between the ridges, the tendency being for it to settle into 
 depressed areas. By pressure and burnishing, the gum 
 settle into depressed areas. By pressure and burnishing, the 
 gum enamel while slightly moist can be distrilnited and con- 
 densed so that when fused it will display a very lif elite color. 
 Since it is almost transparent if not applied in sufficient thick- 
 ness, the enamel when fused will frequently present an an- 
 ipmic and uusiglitly appearance. On the other hand, if applied 
 too tliickly, the color will be abnormally dark. 
 
 Particular attention should be given the gum festoons to 
 have them of proi)er curvature and distinctly developed. 
 Every particle of surplus should be swept clear of exposed 
 tooth surfaces, the baseplate, and from the lingual, labial and 
 buccal embrasures, where its presence as a pigment would 
 prove unsightly. 
 
 Briefly summed up, the teeth should stand out clean and 
 prominent, the gum festoons and other surface markings 
 should be sharply, or at least plainly, defined, and the base- 
 plate free from all adherent particles. 
 
618 CONTINUOI'S (!I'M DIONTL'KRS 
 
 The moi.sluic is now giadually evaporated by passing 
 the case througli a current of heated air above a Bunsen 
 flame, in preference to placing in the furnace to dry, so that 
 if any of the gum enamel Hakes off in drying it may l)e cor- 
 rected before halving. 
 
 FUSING THE ENAMEL 
 
 The denture is now introduced into the furnace and lieat 
 applied as before. Gum enamel fuses at a considerahly lower 
 temperature than gum hody, so wlien the furnace becomes 
 well heated the case shoiild lie watched very closely to avoid 
 overfusing and bleaching the color. 
 
 The enamel should be perfectly glazed so that it may 
 easily be kept clean, will look well, and not prove irritating 
 to the mucous tissues as a result of roughened surfaces. 
 
 Being able to distinguish the outlines of the denture when 
 in the furnace and highly heated, and to determine the in- 
 stant when the enamel is perfectly glazed, is one of the es- 
 
 sential points in porcelain technic, and comes only with ex- 
 l^erience and careful observation. 
 
 When fused, the current is shut otT, the furnace opened, 
 and the case examined to see that glazing has been accom- 
 plished. If satisfactory, the furnace is closed and the denture 
 allowed to remain within until perfectly cold. Sudden chill- 
 ing or drafts of cold air striking the porcelain when heated 
 will almost certainly check it, sometimes in a very unsightly 
 manner. 
 
CONTINUOUS GUM DENTURES 619 
 
 FINISHING THE DENTURE 
 
 The enamel surfaces, if properly fused, require no fin- 
 ishing. The peripheral margins, palatine vault of the platinum 
 base, and the lingual surface of the doubler are first polished 
 as in gold denture construction with felt wheels and pumice 
 stone, following with the finer j^owders. 
 
 The fact sliould be kept in mind that when porcelain bod- 
 ies are brought to a state of fusion, continued heat, even 
 though the tem]X'rature is not elevated, will gradually rendei- 
 
 LAlllAI. VIEW OK FIN'ISHEI) IlEXTrRE 
 
 them glasslike, friable, porous, l)leach the color, and render 
 them weak and devoid of usefulness for prosthetic restora- 
 tions. Much better and more certain results, therefore, can be 
 attained by subjecting the case to only three bakings — two 
 for the body and one for the enamel — than are possible when 
 a greater numl^er of bakings are required. 
 
 SPECIAL USES OF PORCELAIN 
 
 Oftentimes in the construction of dentures for partial 
 cases some of the spaces to be supplied with teeth are in a 
 conspicuous position. When but slight absorption of the 
 ridge has occurred, plain teeth may be neatly fitted against 
 the natural tissues in such manner as to escape detection. 
 This may be done by first grinding the ridge lap of each tooth 
 to conform to the irregularities of the ridge, and afterward 
 paring away on the cast the area on which it rests. This step 
 advances the teeth slightly beyond the palatine and border 
 surfaces of the baseplate, so that with use they become 
 slightly imbedded in the tissues and thus present about the 
 same appearance as do natural teeth surrounded with their 
 gingivae. 
 
 INTERSTITIAL BLOCKS OF PORCELAIN 
 
 When two or more contiguous teeth are missing and they 
 are replaced by plain teeth without giim restoration, it is fre- 
 
020 CONTINUOUS GUM DENTURES 
 
 queiitl} (lifliciilt to obviate tlie display of vulcanite in the em- 
 brasures of the artiticial teeth. 
 
 Recently there has been placed on the market Fogg's in- 
 terstitial porcelain blocks, which, when properly applied, over- 
 come the difficnlty mentioned. These pieces of porcelain are 
 
 i k k k k i k 
 
 UkkkU. 
 
 wedge-shape in form and slightly concaved on their mesial 
 and distal areas to embrace the proximating surfaces of the 
 teeth. Their exposed surfaces are overlaid with pink gum 
 enamel. 
 
 By selecting blocks of suitable length and grinding their 
 proximating surfaces, as well as those of the teeth, these 
 points may be so nicely adjusted that they have the appear- 
 
 ^i^^P 
 
 ance of natural gum tissue in the embrasures. They are 
 ground and fitted in position before flasking the ease, invested 
 as though a part of the teeth, and become firmly attached by 
 means of the flowing of the vulcanite in closing the packed 
 flask. 
 
 GUM SECTIONS 
 
 Gum section teetli, either single or in blocks, can often be 
 used to advantage in partial cases, particularly when border 
 absorption is marked. 
 
 By grinding the margins of the block to a thin edge where 
 it joins the gum tissue, very natural restoration of the lost 
 gum tissue can be accomplished. The block should be reduced 
 at the expense of the lingual or border side, since if reduced 
 from the labial or buccal margins the pink enameled surface 
 
CONTINUOUS GUM DENTURES 
 
 is destroyed and a liglit colored line of demarcation shows at 
 the junction of the block with the soft tissues. 
 
 Gum section teeth are used to a limited extent only, at the 
 present time, in full cases because of the difficulty in develop- 
 
 ilM BLOrK OF THREE TEETH 
 
 iug anatomic relations. Oftentimes when care is used in con- 
 structive steps and the condyle path pitch is not excessively 
 steep, most esthetic results may be secured with gum section 
 teeth combined with vulcanite or irold and vulcanite bases. 
 
 .IDINTS CROUND 
 
622 CONTINUOUS OVM DKNTUUES 
 
 They are very useful in i)artial cases in tlie repliiccineiit of 
 teeth in conspicuous positions. 
 
 It is sometimes difificult to secure porcelain sections Tor 
 special cases other than the usual three-tootli anterior and 
 two-tootli posterior stoclv blocks. Stoclv blocks are frequently 
 applicable when the number of teeth thej' include corresponds 
 to, or is greater than, the number of teeth to lie replaced in 
 the space, the extra teeth being easily cut away, hut unfortu- 
 nately the loss of teeth does not occur with regularity. V\n- 
 example, two centrals and a lateral may be missing, or a 
 cuspid and two bicuspids. In these and many other cases, 
 stock blocks will not fulfill the requirements without the use 
 of two l)Iocks and the grinding of a joint. 
 
 CONSTRUCTION OF GUM BLOCKS FOR SPECIAL CASES 
 
 Various methods have been suggested for baking single 
 blocks to meet the requirements of unusual cases, but because 
 of the friability of blocks so formed, few undertake their con- 
 struction. Dr. Walter M. Bartlett of St. Louis has produced 
 some very artistic work in this line, and by a comparatively 
 simple method of teclmic. TTis method is practically as fol- 
 lows: 
 
 An impression is secured from which a plaster cast is 
 derived. Plain vulcanite or ordinary long pin facings are 
 
 TWO ri.Aix Ti:i:i'ii ahapteh to 
 
 PLATINUM FOIL ru\ EitED CAST 
 
 BEADY FOB AI'PLICATION OF 
 
 GUM BODY 
 
 selected and ground, when necessary, to bring them in proper 
 alignment in the usual manner. The teeth are now removed 
 and a piece of platinum foil is burnished to the cast over the 
 area to be covered by the block. The foil base should be so 
 formed as to be easily released without distortion. When 
 properly adapted and trimmed to suitable outline, it is re- 
 tained on the cast uniil the model block is formed. 
 
CONTINUOUS GUM DENTURES 623 
 
 The teeth are now roturueil to the cast aud wax flowed 
 between them and the foil to hold them in position. The 
 future block is now modeled in wax to the exact outline de- 
 sired, and when hardened, the teeth, wax and foil are removed 
 as one piece. Care should be taken to avoid covering the 
 pins of the teeth with the wax, since in introducing the porce- 
 lain paste it will fill all spaces caused by the removal of the 
 wax, and the pins would thus be obscured. 
 
 The block is now invested, pins and border side down, in 
 tenax. The investment should be as small as possible to be 
 consistent with strength. When set, the wax is thoroughlj' 
 removed with hot water, and continuous gum body, or the 
 regular high fusing crown and bridge porcelain, is filled into 
 the space between the foil aud the teeth. The gum is now 
 carved to tlie desired contour and the entire case carefully 
 dried, when it is ready for fusing. 
 
 In simple cases one application and baking of the body 
 will be all that is required, the slight shrinkage which occurs 
 being compensated for and covered over by the layer of 
 enamel which follows. 
 
 When fused, if much contraction of tlie l)ody has oc- 
 curred, a second application should be made and fused, fol- 
 lowed by the application and fusing of the gum enamel. 
 
 By scraiaing the cast slightly around the periphery of the 
 gum block, so that the latter may fit the tissues closely, and 
 
 CASE BAKED. LABIAL VIEW. 
 
 BLOCK CONSTRUCTED FOR SPECIAL 
 
 CASE. (DR. G. W. SCHWARTZ) 
 
 l)y l)riiiging the body and enamel to a gradual rather than an 
 abrupt termination around the margins, the block when fitted 
 in place in the molith can be scarcely distinguished from the 
 natural teeth aiid tissues. 
 
 The platinum foil is now peeled off and the sharp margins 
 of the periphery removed with fine discs, when the l)lock is 
 readv for iise. 
 
CONTINUOUS GUM DENTURES 
 
 Another luctliod cuiisists in swaging a thin phite of plat- 
 inum in the form of a saddle, to cover the ridge and serve as 
 a foundation for the liaek of the gum portion. To this saddle, 
 long pin facings are soldered and addilional attachments 
 
 I-LATINLM BASE WITH UlNli PIN 
 
 TEETH ATTACHED FOIt BE<:EI'TIOX 
 
 OP PORCELAIN BODY 
 
 added for vulcanite anchorage, when advisable. The porce- 
 lain is applied and baked as in the ]n-evious ease. By this 
 method the platinum is not removed, liut becomes a part of 
 the section. 
 
C H A P T E I{ X X ^' 1 1 
 
 CROWN WORK 
 PRELIMINARY CONSIDERATIONS 
 
 When tlirongh accident, or as the result of caries, the 
 crown of a natural tooth has been impaired so that operative 
 procedures will not fully restore it to usefulness, an artificial 
 crown, when conditions are favorable, can be constructed to 
 replace it. Oftentimes the perfectly formed natural crown 
 of a healthy tooth is reduced in size, or entirely removed, and 
 an artificial siibstitutr" placed over it or on the root, to serve as 
 an abutment or jjier for a bridge. 
 
 Such a i)rocedure, when necessary, is considered good 
 practice and justitiable in well-selected cases, the benefits in 
 improved masticatory function and esthetic appearance re- 
 sulting from the replacement of missing teeth, more than com- 
 pensating for the sacrifice of the natural tooth crown. 
 
 The successful crowning of teeth requires a thorough 
 knowledge of several correlated subjects, viz., histological 
 and physiological structures of the teeth and tissues involved; 
 oral pathological conditions; therapeutic methods of treat- 
 ment of diseased conditions ; anatomatic and esthetic forms of 
 the teeth; hygienic requirements of crowns; technical pro- 
 cedures. 
 
 STRUCTURES OF THE TEETH AND INVESTING 
 TISSUES 
 
 The grosser structures of wliicli a tooth is composed are 
 as follows: 
 
 Dentine, whicli constitutes the larger portion of both 
 crown and root, and within which the pulp chamber is sit- 
 uated. 
 
 Enamel, which envelops the crown portion of dentine, and 
 gives the crown its anatomatic form. 
 
 Cementum, which covers the root portion of dentine, and 
 furnishes attaclmient to the fibres of the peridental membrane. 
 The cementum at the cervix of a tooth comes to the enamel 
 margin and, in some cases, slightly overlaps the latter. 
 
 The Peridental Membrane, composed of fibrous tissue, is 
 interposed between the root of a tooth and its bony socket or 
 
 625 
 
626 CROWN WORK 
 
 alveohis. The fibres of this meinln-aiie extond from the socket 
 walls to the eementum covering the root, most of them running 
 in an apical direction as well as tangentally. The tooth is re- 
 tained in position princiijally by the network of fibres which 
 pass in various directions through the gingival tissue. 
 
 The attachment of the peridental fibres to the tooth termi- 
 nates with the gingival termination of the eementum. They 
 do not, however, terminate at the margin of the alveolus, but 
 continue on incisally or occlusally into tlie glngivus, forming 
 a sort of fibrous network or band which liolds the gum tissues 
 firmly in contact with the axial surfaces of the tooth. By 
 passing through the interproximate spaces and across the em- 
 brasures from tooth to tooth, they unite the lingual with the 
 laljial giugivi and buccal, and form what is termed the dental 
 ligament. 
 
 Now, since the eementum comes to, or slightly overlaps, 
 the gingival margin of enamel, and since the peridental fibres 
 are attached to the extreme gingival margin of the eementum, 
 extending outward from this point and interlacing to form 
 tlie dental ligament, in those cases where the peripheral ring 
 of enamel is entirely removed for the reception of a crown 
 band, more or less cutting and laceration of the peridental 
 fibres in this region occurs from the use of the cleavers, files, 
 discs and stones. These severed fibres may, or may never, 
 again re-unite with the eementum, depending on the extent of 
 injury done, the general tonicity of the parts and the character 
 of the joint between the crown band and the root periphery. 
 
 In line with this idea, Di'. F. B. Noyes in his Dental Histi- 
 ology, page 189, says: "That the tissues (peridental mem- 
 brane) may be re-attached to the surface of a root is both 
 theoretically possible and clinically demonstrable, but for it 
 to occiir, biological laws must be observed and the conditions 
 are very difficult to control, especially with the old methods 
 involving the excessive use of strong antiseptics. It is well 
 to remember that a dentist can never cure a suppurating 
 pocket along the side of a tooth root, but if the conditions can 
 be controlled the cells of the tissue may form a new layer of 
 eementum, re-attaching the tissues, and so close the pocket. 
 It is a biological problem, not a matter of drugs, except as 
 they are a means of i^roducing a cellular reaction. In view 
 of its function, therefore, the eementum becomes not the least 
 but the most important of the dental tissues, for no matter 
 how perfect the crown may be, without firm attachment the 
 tooth becomes useless and is soon lost." 
 
CROWN WORK 627 
 
 One of the gravest dangers resulting from traumatic in- 
 jury to the peridental fibres and their failure to again re- 
 attach themselves to the root, is in the loss of tension of the 
 dental ligament at or near the site of injury. In such cases 
 the formation of a pocket is almost certain to occur, and into 
 this food finds its way, is difficult to remove, decomposes, and 
 pathological conditions arise, which in many cases from infec- 
 tion eventually result in phagedenic pericemeutitis or other 
 troubles. 
 
 It will thus 1)6 seen that while a crown may restore the 
 function of mastication, accomplish desired esthetic results, 
 and, by wedging, maintain proximate contact which has been 
 lost i^revious to its application, yet pathological conditions 
 may be induced througli imi)roper technic and an imperfectly 
 adapted band. 
 
 ^lany prosthetists, either through carelessness or to avoid 
 traumatic injury to the peridental membrane, fail to remove 
 all of the peripheral enajnel ring from the root when prepar- 
 ing it for a band, with the result that the latter, when applied, 
 presents a shoulder which not only invites the lodgment of 
 food, but proves a constant mechanical irritant to the gingival 
 tissues as well. The greatest care should therefore be ob- 
 served to remove all of the enamel in cases where indicated, 
 and yet avoid excessive injury to the peridental membrane 
 and gingival tissues in general. 
 
 PHYSIOLOGICAL RELATIONS 
 
 The pulp of a tooth occupies tlic central chamber, or what 
 is termed the pulp chamber and root canal. It is largely com- 
 posed of embryonal connective tissue in which very few con- 
 nective tissue fibres are present. It contains nerve filaments 
 and minute blood vessels which enter through the apical fora- 
 men of the root. 
 
 The primary function of the pulp is a dentine builder, 
 the outer layer of columnar cells, called odontoblasts, receiv- 
 ing from the blood and depositing from without, inward, the 
 calcific materials of which the dentine is composed. The den- 
 tinal fibrils, occupying the dentinal tubuli, are the remnants of 
 the odontoblastic c^lls which have become reduced in diameter 
 and withdraw inward as calcific dentinal deposit progresses. 
 
 The secondary function of the pulp is that of a sensory 
 organ, as it is very responsive to thermal changes, to chemical 
 action on, and traumatic injury to the tooth. 
 
fi28 CROWN WORK 
 
 111 tilt' prc|)ar;iti()ii ol' u vital tooth I'or I lie r('cc|i1ion of 
 a crowu, the friction caused by engine stones and iliscs is 
 often exceedingly painful, even though the site of the opera- 
 tion is far removed from the pulp. Since the dentinal iibrils 
 are devoid of nerve filaments, external irritation when notice- 
 able, is, without doubt, conveyed to the pnlp by molecular vi- 
 bration of the contents of the tubuli, and the heat caused by 
 friction as well. 
 
 U.sually it is customary to devitalize a tooth before adapt- 
 ing a shell crown, for two reasons; first, so as to reduce to 
 the minimum the pain resulting from the use of stones and 
 cleaners in the root preparation, and second, to avert possible 
 ]iathological conditions subsequently arising from death of 
 the pulp, either from the shock of denuding the crown of its 
 enamel, or from thermal variations. 
 
 When this practice is resorted to, the pulp removed, and 
 the root apices perfectly filled, it is a most excellent procedure. 
 The danger of following this plan in every case lies in the 
 fact that frequently teeth have multiple roots or multiple 
 canals — more than the normal number — and some of these 
 are liable to be overlooked in the treatment and filling. Again, 
 the roots of teeth may be deformed, and the canals so tortuous 
 and minute that by the most ]iatient and conscientious effort 
 it is impossible to clear and fill them. These conditions are 
 frequently met with in peg-shaped lateral incisors, third 
 molars, and occasionally in the lower anterior as well as other 
 teeth. Should indications point to abnormalities, the X-ray 
 will disclose their nature, and the prosthetist can then govern 
 himself accordingly. When pathological conditions do not 
 require treatment or devitalization, the safer plan in these 
 abnormal cases is to crown the tooth without removing the 
 pulp, even though the tooth or root preiiaration may occasion 
 some pain. 
 
 ORAL PATHOLOGICAL CONDITIONS 
 
 The prosthetist should be able to recognize any abnormal 
 or pathological conditions present in the mouth, and be famil- 
 iar with recognized and proven methods of treatment. 
 
 The most frequently occurring abnormal conditions which 
 ]iresent in practice are cases in which one or more of the teeth 
 liave lost their crowns, or the teeth themselves are missing. 
 Stieb loss, if of long standing — usually the result of a substi- 
 tute crown not having been applied — almost always entails 
 the loss of proximate contact of some, if not all, of the remain- 
 
CROWN WORK 629 
 
 iug natural teeth. The spaces thus formed invite the hidg- 
 ment and retention of food. As stated elsewhere, phagedenic 
 troubles have their origin in such mouths under these and 
 similar conditions, and unless corrective measures are resorted 
 to, the loss of all the teeth will sooner or later occur. 
 
 When the axial surfaces of the teeth in general have not 
 suffered from caries, and proximal contact has been lost 
 through loss of the crowns of one or more teeth, the roots of 
 which are in condition to carry substitute crowns, contact may 
 frequently be restored between teeth considerably removed 
 from the space to be supplied, by a slow wedging process. 
 The substitute crowns should be constructed of sufficient di- 
 mensions to maintain the space gained in wedging. 
 
 Hyperaemic or putrescent pulps should be removed, and 
 the root canals of all pulpless teeth rendered aseptic and 
 their apices filled, before attempting the preparation of roots 
 for crowns. Pus pockets and alveolar abscesses connected 
 with, or located near, the site of operation, must be eradicated. 
 Inflammation of the gingival tissues and peridental mem- 
 branes shoiild be allayed, and when possible, restored to 
 health, before extensive crowning operations are undertaken. 
 In some cases complete restoration to normal conditions may 
 not be effected, since the irritation occasioned by food wedg- 
 ing on the tissues in unprotected locations — as in the em- 
 brasures and interproximal spaces — may continue until af- 
 forded protection by suitably formed and well adapted crowns. 
 Special care should be given to the removal of the excess ce- 
 ment, which in setting is forced out at the periphery of a 
 crown. When this is not entirely removed inflammatory con- 
 ditions frequently develop which may result not only in im- 
 mediate discomfort to the patient, but later on in the forma- 
 tion of a permanent gingival pocket. 
 
 The prosthetist should endeavor ))y every possible means 
 to temporarily and permanently correct all pathological con- 
 ditions present, and to so form the substitutes, of whatever 
 class, that they may in no way give rise to a recurrence of 
 diseased conditions, or initiate others of a different character. 
 
 THERAPEUTIC METHODS OF TREATMENT OF 
 DISEASED CONDITIONS 
 
 It is taken for granted that the student is pursuing the 
 study of, and has access to, textbooks dealing with the therapy 
 of the teeth and oral tissues. Therefore it is unnecessarv to 
 
t;;!o CROWN work 
 
 recount the various methods of trcatiuent and tlie many gen- 
 eral agents employed, except wliore they arc of s]ieeial interest 
 to the prosthetist. 
 
 LOCAL ANESTHETICS 
 
 Local anaesthetics in some cases are invaluable, as for 
 instance in the removal of pulps, the excision of hypertro- 
 phied gum tissue, the curetting of necrosed process, the scaling 
 of roots in deep-seated alveolar pockets, and at times in the 
 preparation of roots of teeth for the reception of crowns. 
 
 Solutions of cocaiu, eucain, novo-cain and various similar 
 agents, either alone or combined with other drugs, are used 
 for this purpose. Such agents may be applied superficially 
 or injected at or near the site of operation, in which case the 
 peripheral nerve endings are influenced by the anaesthetic. 
 Novo-cain and suprarenin dissolved in Ringer's solution are 
 frequently employed, especially in conductive ana'sthesia. 
 By this method the main nerve trunk back of the site of opera- 
 tion is anfesthetized, the anjesthesia being more or less com- 
 plete along the peripheral branches to the nerve endings, ex- 
 cept where the tissues are also supplied with other nerve fila- 
 ments coming from some other than the trunk anaesthetized. 
 In such case an additional local injection at the site of opera- 
 tion is sometimes resorted to, to complete the ana?sthesia. 
 
 In the use of antesthetics of any character, and particu- 
 larly when used by the injection method, extreme care should 
 be exercised in the sterilization of the instruments, a])pliances 
 and the agent itself, and in rendering aseptic the tissues to 
 which the aniesthetic is applied, or through which the needle 
 is inserted. 
 
 Unless scrupulous care is observed in removing the peri- 
 pheral ring of enamel from the root of a tooth, the adjacent 
 tissues having been anfesthetized, serious traumatic injury 
 to the dental ligament and gingival fibres of the peridental 
 membrane is liable to occur, since the nerves are imresponsive 
 and can give no warning of the extent of injury being in- 
 flicted. Wlien possible to do so, the use of anaesthetics in 
 such operations should be avoided for the reason stated. 
 
 Low per cent solutions of cocain or similar drugs, com- 
 binded with pressure, usually produce effective anaesthesia in 
 removal of pulps, when the solution and the unvulcanized rub- 
 ber, by means of which pressure is usually applied, can be 
 confined, as within a four-walled cavity, or one that may be 
 so formed by means of a matrix. 
 
CROWN WORK 631 
 
 TREATMENT AFTER SETTING A CROWN 
 
 After setting a crown, the excess cenient having been 
 removed, the tissues should be massaged, syringed witii warm 
 normal salt solution, and where pain is experienced an appli- 
 cation of tincture of iodine, or a saturated solution of iodine 
 in beechwood creosote, should be applied under the free mar- 
 gin of the gum around the root crowned. This method of 
 treatment is frequently of value as an aid in relieving tender- 
 ness in the jjeridental tissues. 
 
 Hot water alone, when properly applied and continued a 
 sufficient time, will very frequently reduce inflammation or 
 abort an abscess in the incipient stage. The method is as fol- 
 lows: 
 
 A surgical tank used for irrigation purposes, holding a 
 gallon or more, should be filled with water heated to about 
 135 deg. F., or even higher if the patient can tolerate it with- 
 out scalding the tissues. A nozzle with a very fine opening 
 should be applied to the irritating tube, the nozzle of the bulb 
 water syringe or a glass dropper tube with curved point being 
 suitable for this purpose, the curvature permitting the water 
 to be directed against the gingivae in the embrasures and in- 
 terproximate spaces of the teeth affected. 
 
 The patient should sit with head inclined over the foun- 
 tain cuspidor, and usually with a little instruction can, without 
 assistance, irrigate the parts thoroughly. The application 
 should be continued for fifteen or twenty minutes continu- 
 ouslj', the efficiencv of the method depending upon contraction 
 occasioned by heat of the arterioles and capillaries, thus re- 
 ducing the flow of blood to the i)arts and enaliling the tissues 
 to recover their normal tone. 
 
 The tank may require refilling once or twice in severe 
 cases, and the stream of water should be directed not only 
 around the gingivae of the tooth affected, but along the labial 
 or buccal and lingual surfaces of the border of all of the teeth, 
 so as to control the circulation of blood in the entire arch. 
 The writer has in many instances effecti;ally applied this 
 method of treatment for the relief of conditions mentioned, 
 and in various other forms of painful troubles as well. 
 
 ANATOMIC AND ESTHETIC FORMS OF TEETH 
 
 The anatomic form of an artificial crown is governed by 
 its position in the arch, and usually corresponds with the class 
 of crown carried by the root which will support it. Variations 
 
632 CROWN WORK 
 
 from this rule occur at times, exam])les of wliicli aie seen in 
 tlie following instances: 
 
 A lateral incisor has been lost and the space it occupied 
 has been nearly, or quite, obliterated by the movement toward 
 each other of the teeth on either side. In case the cuspid root 
 requires crowning, a wide lateral incisor placed upon its roots 
 would in all jM-obability fill the space and be more in harmony 
 with tiie proxinuiting teeth than would a cuspid crown. 
 
 Sometimes it becomes necessary to vary the form and 
 Ijroi)ortions of an artificial crown for hygienic reasons, to 
 raise or lower, omit or add. a cusp to meet occlusal require- 
 ments, or to secure contact with proximating teeth. 
 
 In many instances a tooth has lost all or a portion of its 
 crown long before tlic patient presents for a substitute. Fre- 
 quently proximate contact of the remaining natural teeth 
 has been disturbed by such loss. Before crowning the root, 
 the lost space should, to as great an extent as possible, be 
 regained by wedging, which in turn will frequently restore 
 knuckling contact at other points where spaces have de- 
 veloped from the movement toward each other of the teeth 
 proximating the missing crown. In many instances the wedg- 
 ing oi)eration will not only regain the lost space, but may, 
 with benefit to the other teeth, tighten up all lost contacts, 
 when this can be done without disturbing the occlusion. The 
 crown when constructed to fill the space may, therefore, be 
 somewhat greater in its mesio-distal diameter than was the 
 original one it replaces. 
 
 When the root of a tooth, capable of can-ying a crown, is 
 slightly out of alignment labio or bucco-lingually, should 
 orthodontic measures be deemed inadvisable for bringing it 
 into position, an offset crown may be constructed, and by skill- 
 ful root preparation and assembling of the several parts, the 
 crown, although not of anatomic form, will present a good 
 appearance and fulfill useful requirements. 
 
 In the construction of crowns of any class, variations in 
 form from true anatomic types are frequently necessary. The 
 usual conditions calling for modified forms are exceessively 
 wide or narrow spaces, abnormal occlusal surfaces of the op- 
 posite teeth, movement of the remaining teeth from their 
 normal position with loss of contact, and various other 
 causes. 
 
 A study of the axial surfaces of typical natural teeth 
 should be made, and a reproduction of these surfaces carried 
 out whenever possible in crown construction. The convexity 
 
CROWN WORK 633 
 
 of tl)e buccal and lingual axial surfaces of the bicuspids and 
 molars, aside from the esthetic value of such forms, serves a 
 most useful purpose. The bulging mid-crown forms of these 
 teeth, together with constricted crevices, afford efficient pro- 
 tection to the free margin of the gums against the excursions 
 of food tliat may be forced beyond the occlusal surfaces of 
 the teeth in masticatory effort. 
 
 As crowns are frequently constriicted, their liuccal and 
 lingual axial surfaces are either parallel with each other, or 
 converge from the gingivae occlusally, thus preventing in- 
 clined planes fin- directing food toward, instead of away from, 
 the gum margin. A crown so formed invites the lodgment 
 of food, the formation of gingival pockets, and infiammatory 
 conditions which will eventually residt in loss of the tooth. 
 
 FLARE OF THE AXIAL SURFACES OF BICUSPIDS AND MOLARS 
 
 An examination of many bicuspids and molars with a 
 view of determining the average flare occlusally of their gin- 
 gival cones was made as follows : 
 
 A strip of No. 60 tin foil was cut al)()ut l-'A of an inch 
 wide, slightly curved to more readily adai)t it to this portion 
 
 CROWN OF ri'PER FIRST MOLAR. 
 WITH TINFOIL HAND APPLIED 
 
 TO (ilNClVAI. CONE 
 
 of the tooth. It was then bent around and burnished to the 
 gingival cone of the tooth, the shorter, or concave, margin of 
 the strip being applied gingivally. The ends were brought 
 squarely together and cut at the angles of junction. The strip 
 
634 
 
 CROWN WORK 
 
 was then straightened ont, one cud laid parallel with tlic 
 straight edge of a cardboard, and a line drawn along, and 
 parallel with, the opposite end, running toward and intersect- 
 ing the margin of the cardboard. Tlie angnlar divergence 
 of llic ends was read by means of a pi'otractor. From fifty 
 
 MESI.U- VIEW IPF UI'l'ER FIRST MOLAR. TIN' HITCAI, \ii;\\ ii|- 1 iM-ii: 1 HIST Mill, All TIX- 
 
 FOIL STRIP AISOVE Foil. STItir KH.MOMOIi. SI Rl'l.L S TRIM.MED 
 
 FROM ENDS AND OCCIA'SAI, M,UtGIN 
 
 to one hundred teeth of eacli class were measured in this man- 
 ner, the reading of which are as follows : 
 
 Least Greatest 
 
 Divergence Divergence Average 
 
 Deg. Deg. Deg. 
 
 Upper first bicuspids 21 33 27 
 
 Upper second bicuspids. .. . 18 32 27.75 
 
 Upper first molars 19.-i 31 25.5 
 
 Upper second molars 16 28 24 
 
 Lower first molars 28 40 32 
 
 Lower first bicuspids 24 43 30 
 
 Lower second bicuspids .... 20 35 32 
 
 Valuable assistance has been received in this work from 
 Dr. J. F. Wallace of Canton, Missouri, who made many 
 measurements of teeth by this method. His work, while 
 varying slightly from that of the writer, coincides closely, 
 personal equation accounting for the difference in findings. 
 
CROWN WORK 635 
 
 CUTTING MOLAR AND BICUSPID CROWN BANDS BY THE 
 CONIC SYSTEM 
 
 The piaotical application to orowu work of the measure- 
 ments seen in the table will now be shown. 
 
 AVhen a molar or bicuspid crown band is cut to approxi- 
 mately the form of the tin foil pattern produced as above 
 described, it represents, when the ends are united, a frustum 
 of a cone instead of a cylinder, as would be the case when 
 the ends of the band are parallel. The small end of the cone 
 represents the gingival margin of the band, while the large 
 end, although excessive in peripheral outline, represents the 
 occlusal margin. Keproduction of the occlusal cone to cor- 
 rect form can easily and quickly be accomplished with the 
 hawkbill or Benson pliers, using the latter without exerting 
 excessive force, and when properly contoured the axial walls 
 of the band will present a similar appearance to those of the 
 natural tooth. The advantages of this method are that the 
 band walls are not reduced in thickness at any point in con- 
 touring, while proximate contact can be secured without the 
 usual narrowing of the band in its mid-crown, bucco-lingual 
 diameter. 
 
 The method of diverging the ends of a crown band from 
 gingival to occlusal, has long been followed by careful pros- 
 thetists for reasons above given. A few have even cut the 
 band to represent the section of a cone instead of a cylinder, 
 as is most frequently the case, but no definite rule has been 
 evolved capable of application to the development of bicuspid 
 and molar bands in general. 
 
 By referring to the table of measurements previously 
 shown, it will be seen that the average flare of a conic crown 
 band of an upper first molar is 25.5 deg., while the average 
 peripheral gingival measurement of this class of teeth is 
 29.92 m. m. 
 
 To cut a conic crown band by this system the only ap- 
 pliance required aside from the regular laboratory equipment 
 is a pair of ordinary 6-inch dividers, a piece of cardboard and 
 a straight edge. The method is as follows: 
 
 Measure the prepared root with wire in the usual manner 
 and cut the loop opposite the twist. 
 
 Draw a stlaight perpendicular line on the cardlioard 
 l)arallel with and near the edge, or the edge of the card can 
 be used. 
 
 Mark iioints on line A and B, 314 inches apart. 
 
 Mark width of band B— C. 
 
(136 CROWN WORK 
 
 Lay a piece of gold plate; from wiiidi the hand is to be cut 
 on the line, the upper corner at C. 
 
 Set divider points at A — B, radius. 
 Hold plate firmly on card and descrilx' arc B D. 
 Extend divider to reach from A to C 
 Describe arc (' (}. 
 
 
 
 / 
 
 CARDBOARD 
 
 / 
 
 Lay root measurement slightly curved along arc B D and 
 mark length of band B E. 
 
 Lay ruler edge on points A and E and draw A F. 
 
 B C E H represents the band which is cut with the shears. 
 The band when bent around and the ends soldered, in the 
 usual manner, represents the section of a 'cone instead of a 
 cylinder, the smaller being the gingival end. 
 
 In trimming the gingival end of the band to correspond 
 to the gum festoon, the inner diameter of the band is increased 
 as the gingival periphery is sheared away, and consequently 
 
CROWN WORK 637 
 
 is larger than the root. This may be corrected in two ways ; 
 first, by reducing the gingival periphery with the pliers, and 
 second, by cutting the band sliglitly shorter than the wire 
 measurement, when laying it out. 
 
 By extending the line along the straight edge to the 
 center. A, and reading the included angle, it will usually be 
 found to range from 22 deg. to 28 deg. This reading, how- 
 ever, is unnecessary for practical purposes. The variations 
 noted in a number of readings are due to variations in peri- 
 pheral root measurements, long measurements showing 
 greater, and short measurements less, divergence of the l)and 
 ends. 
 
 In those cases where for exami)le, the space in which the 
 crown is to be placed has become constricted by the leaning 
 toward each other of the proximating teeth, the contact points 
 of the remaining teeth in the arch lieing good, this method, 
 for obvious reasons, is not applicable. 
 
 In cases of normal or excessive width of spaces, it is the 
 very best method to follow in the construction of two-piece or 
 band and swaged cus]) crowns. Its range of application can 
 be extended to include band and cast, cusp, and other varieties 
 of crowns. 
 
 The band of a crown cut to represent a cone, when cut 
 gingivally to correspond with the festooning of the gums, 
 is enlarged slightly since the smaller end of the cone is cut 
 away. To compensate for such enlargement, the band can 
 be cut from Vo to 1 m. m. shorter than the root measure- 
 ment. If, when festooned, the band is too small to be driven 
 to i)lace, it can be stretched slightly by placing on a round 
 numdrel and tapping lightly with a riveting hammer. When 
 too large, it can be reduced with contouring pliers. 
 
 Any wide crown band, as for a molar or bicuspid, can be 
 tightened gingivally, and its perfect peripheral adaptation 
 insured, the root having been properly prepared, when, after 
 fitting and axial contouring have been accomplished, its 
 gingival margin is reduced as above outlined, after which it 
 can be finally driven to place. A gingival shoulder on the 
 natural tooth or root would preclude this plan of final adapta- 
 tion. 
 
 Badly decayed teeth, to which shell crowns are to be 
 adapted, should in all eases have their axial surfaces restored 
 by means of well anchored amalgam fillings or alloy cast- 
 ings, placed before the final preparation of the tooth or root 
 is accomplished, so as to obliterate all gingival shoulders. 
 
638 CROWN WORK 
 
 When a tiufoil envelope is adapted to any of the twelve 
 anterior teeth, the ends of the strip cut at their junction, and 
 the strip flattened, the two ends will l)e approximately parallel, 
 and when again united in hand form would form the section of 
 a cylinder. Anatomically; the anterior teeth represent wedges 
 or cylinders flattened at one end to form incisal edges. 
 
 STRESS 
 
 The amount of stress and the direction of its ap])lication 
 are of the greatest importance in crown, hridge and denture 
 construction. 
 
 A crown, or a prosthetic appliance of any tyi)e, may be 
 anatomical in form, yet when introduced into the mouth may 
 become displaced, or rendered useless, tlirough some abnormal 
 condition present, as elongated cusps of teeth in the opposite 
 arch. 
 
 The sloping occlusal surfaces of the various cusps of a 
 tooth, when brought into contact with occhiding surfaces of 
 opi)osite teeth, act as inclined planes, and tend to force the 
 tooth of which they are a part forward or backward, or in or 
 out of aligTiment, unless such tendency is counterluilanced by 
 proximating teeth or by contact planes of occluding teeth 
 sloping in a contrary direction. 
 
 The greatest care, therefore, should be observed in the 
 development of cusps to so form them that displacement from 
 undue force on sloping planes cannot occur. Oftentimes the 
 occlusal surfaces of the opposite teeth must be modified by 
 grinding to meet new occlusal requirements arising from the 
 introduction of ])rosthetic substitutes. The use of both single 
 and double surface carbon paper will readily disclose points 
 of interference between occluding planes and cusps, and cor- 
 rections can be made accordingly. 
 
 In constructing a crown with porcelain facing, care should 
 lie observed to so protect the incisal edge of the facing from 
 direct stress, either by beveling and tipping it with gold, as 
 will hereafter be shown, or by avoiding contact with opposing 
 teeth, under any and all conditions, otherwise the pins will be 
 sheared off, or the porcelain itself fractured. 
 
 A number of tests conducted by the writer, in which the 
 facings of various manufacturers were employed in the con- 
 struction of porcelain faced crowns with unprotected, as well 
 as protected, tips, disclosed the following: That (>0 pounds' 
 .stress will fracture the strongest facings, or shear off the pins, 
 while others will become dislodged at a pressure of 12 pounds. 
 
CROWN WORK 639 
 
 Protected facings were not affected l)y stress and remained 
 intact nntil snfficient force was apiilied to bend the metal 
 structure wliicli constituted the metal tip, after wliicli, with 
 slight additional stress, they were dislodged. 
 
 Gnatho-d}Tiamometer tests show that the masticatory 
 muscles can deliver a stress of from 20 to 90 pounds in the 
 incisor, and a much greater amount in the bicuspid and molar 
 region. The necessity for protecting facings from stress in 
 some manner is therefore imperative. 
 
 HYGIENIC REQUIREMENTS OF CROWNS 
 
 In order that the health of the oral tissues may be main- 
 tained, a crown should be so constructed as not to prove an 
 irritant, either by directing food to and under the free margin 
 of tlio gums and holding it there, or by presenting rougli, im- 
 iinislied surfaces to the tissues, and by this means setting up 
 mechanical irritation. The first of these conditions arises 
 from faulty contour, the second from too large or too wide 
 a band. 
 
 In a bandless crown, imperfect peripheral adaptation of 
 the crown base to the root face will result in shoulders on 
 either the root or the crown. Such shoulders may or may 
 not prove mechanical irritants, but in any case they afford 
 lodgment for food, which through decomi)osition will give rise 
 to chemical irritation, with recession of the gingivse and fre- 
 quently recurrent caries of the root. 
 
 Correct occlusal forms should be developed in order that 
 the usefulness of substitutes may be realized, that undue side 
 stresses may be obviated, and that the crown may not be sub- 
 jected to extra heavy direct stress. When possible to do so, 
 firm kuuckling contact with the proximating teeth should be 
 established, and between neighboring teeth when such loss of 
 contact is occasioned by movement of the teeth toward the 
 space which the sulistitute occupies. 
 
 These several requirements, although previously men- 
 tioned, are again in order under this heading, since, if neg- 
 lected, the hygiene of the mouth cannot be preserved. 
 
 In introducing substitutes of any character into the mouth 
 the dominant idea should lie to so form them that with reason- 
 able care on the part of the ])atient they may be kept clean; 
 that they may not injure the remaining natural teeth or oral 
 tissues; that the function of mastication may be restored; 
 that the esthetic requirements may be fulfilled; and withal, 
 that thev mav be worn with comfort. 
 
(;40 CROWN WORK 
 
 PORCELAIN-FACED CROWNS FOR THE ANTERIOR 
 TEETH 
 
 By the coninioii iiictliods in vogue, it is possible and ])i-ac- 
 ticable to construct many classes and varieties of porcelain- 
 faced crowns for the anterior teeth. It is not, however, ad- 
 visable, in a work of ibis character, to attempt to describe 
 all or even a comparatively limited number of such substitutes 
 in extensive detail. 
 
 One type of crown, in which a hirgc luimbcr of the con- 
 structive steps are familiar and ai'('('])ted methods of ])rac- 
 
 tice, and applicable to many other similar types of crowns, 
 will therefore be described in detail. Consequently, in men- 
 tioning variations from the type of crown about to be de- 
 scribed, rehearsal of details as hei'e presented need not be 
 repeated. 
 
 The crown selected for this description is a left, upper, 
 central incisor, this being one of the most prominent teeth 
 in the month, and one for which a substitute crown is fre- 
 quently required. 
 
 The same steps as here detailed are applicable to the 
 crowning of all of the upper anterior teeth, and in most in- 
 stances, to the corresponding teeth in the lower arch as well. 
 
CROWN WORK 641 
 
 The student, therefore, is advised to become intimately 
 familiar with every detail as here presented, with the assur- 
 ance that when he has mastered the technic as outlined, he 
 has laid a substantial foundation for further progress, and 
 has mastered many details appli('al)l(' to the construction of 
 various other classes of crowns. 
 
 TECHNIC OF CONSTRUCTION OF A PORCELAIN-FACED 
 
 UPPER, CENTRAL INCISOR CROWN 
 
 GENERAL STEPS 
 
 Devitalization, treatment and filling of root canal. 
 
 Eemoval of remaining portion of natural crown. 
 
 PreiDaration of root — removal of enamel. 
 
 Measurement of root. 
 
 Cutting and soldering of baud. 
 
 Scribing and fitting baud to root. 
 
 Reducing root face. 
 
 Construction of root cap. 
 
 Fitting cap to root, and itorfovatiug for reception of 
 
 dowel. 
 Adaioting and soldering dowel to cap. 
 Taking bite and impression. 
 Selecting and grinding facing. 
 Backing the facing. 
 
 Assembling and waxing the facing and cap. 
 Removal and investment of the assembled crown. 
 Soldering. 
 Finishing. 
 Setting. 
 
 These steps will now be taken up in order and the vari- 
 ous details explained as clearly, yet briefly, as possible. 
 
 DEVITALIZATION, TREATMENT AND FILLING OF THE 
 ROOT CANAL 
 
 It is assumed that the prostlietist is familiar with the 
 treatment of vital and non-vital teetli, their peridental mem- 
 branes and adjacent tissues. Therefore, it is unnecessary to 
 dwell extensively- on this subject further than to emphasize 
 the importance of adopting correct therapeutic measures and 
 finally in sealing of the apical end of the root with a pei-ma- 
 nent filling before proceeding with the preparation of the 
 root for the reception of the cap. 
 
fi42 PROWN WORK 
 
 REMOVAL OF THE REMAINING PORTION OF THE NATURAL 
 CROWN 
 
 To avoid unuecessaiy injury to the dental ligament and 
 soft tissues which surround the tooth cervix while adapting 
 
 GROOVING THE ENAMEL OF A 
 
 CROWN WITH CARBORUNDUM 
 
 STONE FOR APPLICATION OF 
 
 EXCISING FORCEPS 
 
 PRELIMINARY STEP IN REMOVING CROWN. HOLES DRILLED 
 
 the band, the remaining portion of the natural crown should 
 not be reduced beneath the gum margin until after the 
 peripheral ring of enamel has been removed, the wire meas- 
 
CROWN WORK 
 
 643 
 
 uremeut secured, the band scribed and trimmed to correct 
 gingival outline and is finally driven to place on the root. 
 
 When a considerable portion of the natural crown re- 
 
 DIAGRAMMATIC VIEW OF 
 
 CROWX PERFORATED WITH 
 
 DRILL 
 
 DIAGRAMMATIC VIEW OF 
 CROWN PARTIALLY REMOVED 
 
 mains, the excising forceps can be used for its removal. 
 Grooves should be cut through the enamel and well into the 
 dentin in the gingival third area, on both labial and lingual 
 surfaces, with a knife-edge carborundum stone. In these 
 
 iVrPLICATION OF STONE IN REIUi 
 
 ;IN(;IVAL SECTION OF CROWN 
 
 grooves the beaks or blades of the forceps are set, when, 
 with the application of a little force, the crown can be frac- 
 tured. 
 
644 CROWN WORK 
 
 Auotlicr mi'tliod, (luite as convenient as that described, 
 consists in drilling several holes through the crown at right 
 angles to the long axis of the tooth and removing the inter- 
 vening tooth structure between the holes with cross-cut fis- 
 sure burs. The drill should be introduced in the cavity and 
 the holes cut from within outward, when possible, or the 
 enamel surface can be notched with a carborundum stone as 
 described, and the drill entered in the groove. A bi-bevel 
 drill made by flattening an inverted cone bur on two sides 
 and beveling the point is most efficient for this purpose. 
 
 After the bulk of the crown is thus removed, the remain- 
 ing stump is reduced with engine stones to within about one- 
 sixteenth of an inch of the gingiva, after which the enamel 
 can be removed. 
 
 REMOVAL OF THE ENAMEL 
 
 The most effecti\(' instrument for removing the enamel 
 is the Case cleaver, or some modification of it of which there 
 
 CASE ENAMEL CLEAVEUS 
 
 are several on the market, notably the Ivory and the Weaver. 
 A selection of these instruments with both straight and con- 
 tra-angle shanks should be on hand for this purpose. These 
 
 WEAVER ENAMEL CLEAVER 
 
 instruments have a side blade, terminating in a sharp, rather 
 bulky point for strength, and are tempered very hard so as 
 to readilv break the enamel. 
 
CROWN WORK 
 
 The point of the iiistriuneiit is ai)plie(l to the euamel, 
 under the gum margin, pressure exerted and the point drawn 
 incisally. This step is repeated many times, the position of 
 
 ENAMEL CLEA.\'ERS OF VARKIUS FORMS 
 
 the point being shifted each time, until as much of the periph- 
 eral ring as it is possible to reach with the point has been 
 so treated. The enamel will seldom come away as a result 
 of application of the point in this manner, l)ut the cohesion 
 
 BOOT SHOWING PERIPHERAL POSITION OF CLEAVER I'OINT A !■ 1' L I C A T ION OF SIDE 
 ENAMEL RING TO HE IN FRACTURING ENAMEL BLADE OF CLEAVER IN 
 
 REMOVED SURFACES REMOVING ENAMEL 
 
 of the rods will be disturbed by the many fracture lines de- 
 veloped. 
 
 The cleaver is now passed beneath the free margin of the 
 gum, the side blade near the point being laid in contact with 
 the enamel. The instrument should be held with the palm 
 grasp, the thumb on the adjacent tooth to serve as a rest, 
 and with a forward and outward movement incisally, the 
 instrument is rotated from beneath the free margin of the 
 gum. With the application of moderate force applied to a 
 great extent in a tangential direction the enamel can readily 
 be removed from the labial and lingual surfaces and from 
 well into the four embrasures. 
 
 Wlien the interproximal spaces are constricted the 
 enamel must be removed by other means, since the cleaver 
 points are too Imlky to enter these spaces to any great extern. 
 
 A very small tissure bur can frequently be passsed into 
 the embrasure, and under proper control will fracture the 
 
646 CROWN WORK 
 
 remaiiiiug ouamel so that it eaii be reiuovt'd with the root 
 files. Care must be taken to avoid injuring the dental liga- 
 ment, the peridental membrane and the proximating tooth 
 
 CUT SHOWING I-11U\1.\1AT1.M, 10(1111 L«tli AS A TIU MB BEST IN 
 CLEA\1>."G ENAMEL 
 
 with the bur, also to avoid notching the root margin from the 
 bur working beneath the enamel and into the dentin. 
 
 SMOOTHING THE ROOT PERIPHERY WITH FILES 
 
 A pair of right and left diagonally-cut, thin-l)laded files, 
 such as designed by the writer, or others of similar type, will 
 be found very useful for i:)laning and smoothing the periphery 
 of the root after the cleavers have removed the Inilk of 
 enamel. These files are designed to be used in a tangential 
 direction, much the same as the cleavers, and are held with 
 the palm grasp. They pass without difficulty in constricted 
 embrasures. 
 
 The entire periphery of the root, from its face end to 
 as far imder the free margin of the gum as the crown band 
 is to extend, must be made smooth and free from all irregu- 
 larities. 
 
CROWN WORK 
 
 ENAMEL FILES FOK SMOOTH- 
 ING ROOT PERIPHERY. 
 (PROTHERO) 
 
 E.NCIM: KOUT I'Kl.M.MEIt Kc IK 
 
 PERIPHERAL SMOOTHING 
 
 OF ROOT 
 
 APPLICATION OF THE liclOT FILES IN PERIPHEISAI, TltlMMINC OF HOOT 
 
648 CROWN WORK 
 
 GENERAL FORM OF THE PREPARED ROOT 
 
 'l^lic ])cri[)li('ral form of a iircpari'il I'oot should he tliat 
 of the fri;stnni of a cone, the large end .situated under the 
 free margin of the gum at the terminal location of the crown 
 band, the smaller end terminating at the face of the root. 
 The flare of the sides of the cone should not be excessive, 
 
 DIAGRAM OF THE CONIC FORM 
 
 A ROOT SHOULD BE GIVEN 
 
 FOR RECEPTION OF BAND. 
 
 LABIAI, VIEW 
 
 PROXIMATE VIEW OF TOOTH 
 
 SHOWING GENERAL REDUCTION 
 
 OF ROOT FOB BAND 
 
 not more than five degrees nor less than two degrees. A 
 root prepared with too much flare affords but little reten- 
 tion for the band in fitting, while if not flared at all, as when 
 the periphery is not given a cone shape, the band when 
 fitted will usually present a gingival shoulder under the free 
 margin of the gnm of more or less prominence, depending on 
 
 PEUIPHERY 
 
 the failure of the prosthetist to produce a true flare or con- 
 striction on all surfaces, from gingival toward the incisal 
 area. 
 
 The exact fitting of the band of a crown to the root un- 
 der the free margin of the gum is of vital importance, for 
 regardless of how carefully subsequent steps are carried out. 
 
CROWN WORK 649 
 
 an imperfect form of I'oot preparation will iuvariably result 
 in the production of a shoulder, either on the root itself or 
 from too large a hand. 
 
 TESTING THE FLARE OF THE ROOT SURFACES 
 
 Since a considerable portion of the root surfaces to which 
 the baud will be applied is obscured by the gum tissues, it 
 is sometimes difficult to determine with the eye when proper 
 form is developed. One test that may be applied is to place 
 the point of a delicate instrument, as an explorer, on the 
 side of the root, near the face end, and pass it carefully 
 toward the apex, observing closely the direction it travels, 
 or whether its line of movement changes as would be the case 
 when it passes over a ridge and gradually or suddenly drops 
 into a depression. 
 
 By applying the instrument first on one, then on the 
 opposite side of the root, comjjaring the line of movement 
 each time with the same fixed surface, as the axial surface 
 of a proximating tooth, it can soon be determined whether 
 or not the proper flare to the root sides has been developed. 
 
 A second test may be observed in the wire root measure- 
 ment, which, when tightly twisted, if it can be readily sep- 
 arated from the root without stretching or untwisting, indi- 
 cates that the gingival portion of the root is the largest. 
 When it becomes necessary to cut or untwist the wire meas- 
 urement to effect its removal this is positive proof that the 
 sides of the root have not been reduced to a conical form, 
 nor even brought to a ijarallel relation with each other. Fur- 
 ther reduction of the root becomes necessary under such con- 
 ditions. 
 
 In general form, a root should be sufficiently cone-shaped 
 so that as the band is forced apically it tightens. 
 
 SECURING THE MEASUREMENT OF THE ROOT 
 
 A piece of 36-gauge, annealed iron wire, about three 
 inches long, is bent in the form of a loop, and fixed in a denti- 
 
 A DENTIMETER FOR HOLDING AXD APPLYIXG THE WIRE MEASUREMENT TO ROOT 
 
 meter or an ordinary broach holder. The loop is then passed 
 over the projecting end of the root, the handle turned until 
 the wire engages loosely with the root surfaces. Careful ad- 
 
CItOWN WORK 
 
 justnicnl ol' the loop is now iiiade so that it occupies a place 
 even with or slightly under the free mari^iu of the gum. Un- 
 der no condition should it be carried ajiically to the extreme 
 limit of tlu' cone base, as such a measurement would usually 
 
 result in a loose-iitting band. The fundamental idea to keep 
 in mind is the production of a band slightly smaller than the 
 section of root cone wliere its apical end will terminate when 
 finally fitted. As the metal is driven under the free margin 
 
 il'lM.lEll TO HOOT IN THE 
 
 of the gum, the conic form of the root will cause it not only 
 to assume correct peripheral adaptation, but stretch it sufifi- 
 ciently to take its proper position. By adopting this method 
 of fitting the band, together with correct root preparation, 
 gingival shoulders are avoided. 
 
CROWN WORK 651 
 
 MEASURING AND CUTTING THE BAND FOR THE ROOT CAP 
 
 After removal of the wire measurement from the root, 
 it is cut opposite the twist and the two halves are straightened 
 out, care being taken not to \;ntwist the wires, as such a mis- 
 hap would increase the length. 
 
 The straightened measurement is now laid on a piece of 
 gold plate, usually 29 g. and 22 k. The lamina of the gold 
 should run lengthwise of the band for greatest textile 
 strength. One end of the measurement is placed exactly even 
 with the edge of the plate, and with a thin, sharp blade, a 
 
 LOOF JUiASUUEMENT SE\ EBliD. 
 
 STBAIGHTEXED, AND LAID ON 
 
 GOU) PLATE FOR MAHKINO 
 
 LENGTH OF CROWN' BAND 
 
 mark is made on the gold exactly even with the other end of 
 the wire. This indicates the length of the band. 
 
 The width of the band should be slightly greater than 
 the apico-incisal curvature of the gingiva. Usually one- 
 eightli of an inch in width is ample, but when the curvature 
 is very marked a wider band will be required. 
 
 The length and width of the band having Ijeen marked, 
 the gold strip is cut with a pair of plate shears, being specially 
 careful to cut it the exact length. 
 
 Another method consists in making a lap joint to the 
 band and after soldering reduce the excess thickness, the 
 idea being that such a joint is stronger as well as less liable 
 to become unsoldered in subsequent steps. 
 
 When a lap joint is to be formed the measurement is 
 taken as described and the gold marked accordingly. An 
 amount equal to the width of the lap is now added to the 
 
652 CROWN WORK 
 
 original band Icii.^lli as dcteTniined by tlic wire nicasurcnR'nt 
 and the band cnt that much longer. 
 
 In forming- the band, one end of the strip overlaps the 
 other an amount equal to the excess length ])reviousl_y marked. 
 
 FORMING AND SOLDERING THE BAND 
 
 The band is now bent in the form of a ring or ferrule 
 and compressed so that the two ends of the strip pass each 
 other slightly. When later adjusted, the ends will be held in 
 contact by the resiliency of the metal. 
 
 The band is now sprung a])art and the ends abutted 
 scfuarely against each other between which there should be 
 absolute contact, otherwise it will be difficult to unite them 
 perfectly with solder. Should either or both ends have been 
 cut irregularh' they must be corrected by filing. By observ- 
 ing care in cutting the band the application of the file will be 
 unnecessary. 
 
 A piece of 36g, annealed, untiiuu'd, iron wire is bent 
 around the ring and t\^isted to form a loop, the twist opposite 
 the joint. This twist serves as a plier grasp for holding the 
 band while soldering, while the loop itself prevents the ends 
 from springing apart. When tinned iron wire is used as a 
 binder, the tin unites with the gold during soldering, to form 
 a low fusing alloy, and frequently as a result the band will be 
 partially melted. 
 
 A little flux (pulverized borax and water, or soldering 
 flux paste) is applied on the inside of the band along the joint, 
 being careful to place it oiilii where needed, since the solder 
 will spread imnecessarily on the band if the flux is applied 
 carelessly or in excess. 
 
 When the joint between the two ends of the band is close, 
 as it should be, an almost inconceivably small amoiint of sol- 
 der, properly placed and fused, will effect a perfect imion. 
 An excess of solder, which, when fused, extends any distance 
 on either side of the joint, stiffens the band and renders its 
 perfect adaptation to the root difficult if not impossible. 
 
 Usually a piece of solder one m. m. long and one-half 
 m. m. wide, will prove ample for any ordinary band joint. 
 
 The piece of solder is now laid on the inside of the band 
 and across the joint, each end of the solder resting on a dif- 
 ferent end of the band, the joint space being thus bridged 
 over. As the solder fuses, being already in contact with the 
 two ends of the band, gravity causes it to settle to place in 
 the joint. 
 
CROWN WORK 663 
 
 The twisted ends of tlie loop are grasped with a pair 
 of soldering pliers and the hand is carried close to the Bun- 
 sen flame, but not into it, until the moisture has all been 
 driven from the borax. Tlus should be carefully done or the 
 evaporation of the moisture from the paste, and later the driv- 
 ing out of the water of crystallization from the borax, during 
 which the latter swells, will displace the solder before it fuses. 
 
 SOLDERING THE BAND JOINT. 
 NOTICE THE PIEt'E OF SOLDEB 
 CROSSES THE JOINT jVND RESTS 
 ON liOTH ENDS OF THE BAND 
 
 The band is now carried into the tlanie and held in the 
 reducing flame until the solder is fused, when it must be in- 
 stantly removed, as the gold itself is liable to fuse at the joint 
 if only slightly overheated. 
 
 The wire is now removed and tbe liand contoured to the 
 general form of the root. "When the convexity of the alveolar 
 border is very marked, the liand can be cut out slightly on 
 its mesial and distal sides and from the gingival border, to 
 partially approximate the required curvature, after which 
 the final fitting can best be done on the root. The joint of the 
 band is usually placed to the lingual side of the root, some- 
 times to the mesial or distal in certain bridge cases, but never 
 to the labial. 
 
 SWEATING THE BAND (AUTOGENOUS SOLDERING) 
 
 The higher caVats of gold can readily be autngrnouslij 
 soldered, or, as it is commonly expressed, .^ircafed. This 
 process consists in maintaining the parts to be united, as the 
 ends of the band, in intimate contact* and bringing the gold 
 along the margins of the joint to such a state of fusion that the 
 
654 CROWN WORK 
 
 molecules of the two pieces will intermingle. Though appa- 
 rently a difficult process, with a keen vision and a steady 
 hand, it can readil.y be accomplished. 
 
 The essentials to success are a high grade gold that will 
 not readily oxidize, close contact of the surfaces to be united, 
 a limited application of clean flux along the joint, a strong 
 but not large reducing flame, so that the heat may be con- 
 centrated along the desired line of union, and finally the 
 removal of the piece from the flame the instant fusion 
 occurs. 
 
 This method of joining pieces of gold without the inter- 
 position of solder is applicable, not only to the forming of 
 bands, but to the attacliment of discs to bands in the produc- 
 tion of root caps as well. 
 
 SCRIBING THE BAND TO GINGIVAL OUTLINE 
 
 In fitting a crown band of any class to the root or re- 
 maining portion of the crown of a natural tooth, its cervical 
 end should be so shaped that as it is passed into position it 
 will touch the gingival gum margin at the same time. When 
 trimmed in this manner, this will insure a uniform width of 
 band under the free margin of the gum, when it is finally 
 driven to place. 
 
 The most convenient method for marking this trimming 
 line on the band is by means of a pair of jeweler's spring 
 dividers. In mechanics, this process is known as scribing. 
 The method is carried out as follows : 
 
 The band is passed over the root until its mesial and 
 distal margins are in contact with or are carried slightly 
 
 UNTRIMMED BAND APPLIED 
 TO PREPAKED ROOT 
 
 under the gingival tissues in the interproximate spaces. A 
 space usually shows on the labial view of the root, between 
 the gingival end of the band and the highest curve of the labial 
 gingiva. This space indicates the distance apart at which 
 
CROWN WORK 
 
 655 
 
 the points of the dividers must be set, one point being placed 
 in contact witli the gnm margin, the other jnst resting on the 
 gingival margin of the band. 
 
 The dividers are now drawn along root and gold band 
 from the center of the labial surface, first mesially then dis- 
 tally, the point on the plate marking a line as the other fol- 
 lows the gingival gnm curvature. 
 
 The dividers should not be rotated as in drawing an 
 arc, but be held so that a line extending from one point to the 
 other is at all times parallel with the long axis of the tooth. 
 
 Since the dividers cannot conveniently be used within 
 the oral cavity, for marking the lingual trimming line, an ex- 
 plorer can be used for this purpose, keeping its point as far 
 removed from the lingual, gingival curvature as the divider 
 point which rested on the gold was removed from the labial 
 gum margin while marking the labial surface of the band. 
 
 When both labial and lingual trimming lines are thus 
 marked, the band i's removed, and with a pair of small, curved 
 beak, crown shears, trimmed accordingly. The margins are 
 now smoothed with a half round, fine cut file, so that they 
 will not irritate the soft tissues in the subsequent steps of 
 fitting to the root. 
 
()5U CROWN WORK 
 
 FITTING SCRIBED BAND TO THE ROOT 
 
 The band, with its gingival end niodihed as described, is 
 returned to the root and jiressed cervically until al)out in con- 
 tact with but not quite l)eneath the free gum margin. A close 
 examination is now made to see whether the gingival margin 
 of the band is parallel with that of the gum tissue. If not, 
 the band margin should be corrected by reducing with a tile, 
 the points which first touch the tissues, until the paralleling 
 or approximation of the two margins is accomplished. There 
 are cases where it is necessary to carry the gingival band mar- 
 gin farther beneath the gum at one point than another, as 
 
 BAND SCBIBED. THIMMED AM) liLTJ I!\EII TO ROOT. NOTICE 
 
 ITS GINGIVAL MARGIN t-OIN<'Il)KS WITH CIRVE 
 
 OF THE GUMS 
 
 where the free flap of the gum tissues varies in its width, or 
 liecause of hypertrophy or some previous injury it is not of 
 normal curvature or depth, or where a pocket may be present, 
 and it is considered best to extend the band to line of attach- 
 ment of the peridental fibers to the root. Such conditions 
 should be noted and the band formed at this time to meet the 
 requirements of the case. 
 
 The band is now carefully and lightly driven beneath the 
 free margin of the gum, usually to the depth of one to one and 
 one-half millimeters when conditions are normal. The cer- 
 vical margin of the band should approach, but- never encroach 
 
CROWN WORK 657 
 
 Oil the attiU'limcnt of the peridoiital lilicrs to the root, nor 
 should it ever pass beyond the base of the root cone developed 
 by the cleavers and files. Should this occur, the result will 
 be the formation of a shoulder under the free margin of the 
 gum, which will prove a mechanical irritant to the soft tis- 
 sues from the moment the crown is permanently set. Later, 
 when food tinds its way beneath the tissues and lodges on the 
 shoulder, as decomposition sets in, chemical irritation aug- 
 ments the nicchauical. and loss of the root will eventually 
 occur. The most painstaking and conscientious effort should 
 be bestowed not only upon the preparation of the root, but 
 in the fitting of the band as well, in order that the sultslitntc 
 crown may prove permanent and conifortal>le when set. 
 
 TRIMMING BAND TO PROPER WIDTH 
 
 The band being driven to place as described, its cervical 
 margin in close contact with the sides of the cone base and 
 the proper distance under the free margin of the gum, is still 
 
 TERVICAL AND INCISAJj 
 ENDS OF BAND REDUCED 
 TO PROPER OUTLINE. BAND 
 DRIVEN TO PLACE UNDER 
 FREE GUM MARCIX 
 
 only partially formed The opposite end of the band or thai 
 portion which projects beyond the free margin of the gum 
 must be reduced to such length that when the root cap, of 
 which it forms a part, and on which the porcelain facing rests, 
 is completed, no gold will be visible on the labial surface. 
 
 With a sharp pointed instrument a line is marked on the 
 band close to and following the gingival curvature of the gums, 
 around its entire peri^jhery, labially, lingually and in the 
 embrasures as well. 
 
 The liaud is then removed from the root and with a pair 
 of curved shears cut to the line marked on labial, mesial and 
 distal surfaces, but not necessarily on the lingual surface, 
 since a wide band in this area is desirable, affording greater 
 resistance to outward stress than a narrow band. 
 
CROWN WORK 
 
 CDRVBD BLADE CROWN SHEARS SUITABLE FOR TRIMMING BAND MARGINS 
 
 STRAIGHT BLADE CROWN SHEARS FOR GENERAL USE 
 
CROWN WORK 
 
 The baud is returned to tlie root, driveu to place, aud the 
 projecting- eud of the root reduced to the gum margin on the 
 mesial and distal, slightly beneath on the labial and near to 
 but not beneath on the lingual surface in order, as before 
 
 STONE APPLIED FOR FINAL RE- 
 DUCTION OF ROOT FACE. ARROW 
 INDICATES DIRECTION STONE 
 SHOULD REVOLVE TO AVOID IN- 
 JURY TO FREE GUM MARGIN 
 
 stated, that the band may be wider to better resist the stress 
 of the oiDposing teeth. 
 
 The general form of the face end of the root should be 
 convex from labial to lingual and straight or slightly con- 
 cave from side to side, depending on the depth of the labiai 
 curvature of the gingiva. The root may also be ground to 
 present two planes, one sloping from the pulp chamber 
 labially, the other from the pulp chamber lingually. This 
 
 OTTOLENGUI ROOT FACER AS 
 
 APPLIED IN REDUCING EXCESS 
 
 OF ROOT " 
 
 form of preparation, which is common, will usually require 
 less grinding of the ridge lap of the facing than when the root 
 face is decidedlv convex. 
 
66(1 CROWN WORK 
 
 Tlu' loot may he raced willi an engine slune about three- 
 fourths of an inch in diameter and one-eighth inch face, or 
 witli the Ottoleugui root facers, the various sizes of which 
 afford the selection of one suitable to different sizes of roots. 
 
 The Roach root facer can be used to advantage in reducing 
 the ])rojecting end of the root. This appliance has a central 
 loose pin which keeps it within the root periphery. 
 
 In facing the root with the stone it should revolve from 
 the root toward the free margin of the gum to avoid laceration 
 of the soft tissues. 
 
 The root should be faced even with but not shorter than 
 the band, for when the disc which forms the end of the cap 
 is attached it should rest directly upon the root end. Care 
 
 TlIK ROACH BOOT FACER. 
 
 WITH MOVABLE CENTER 
 
 GUIDE PIN 
 
 should be taken, therefore, in facing the root, not to reduce it 
 below the baud margin or in driving the finished cap to place, 
 the cervical end of the band will be forced too far apically. 
 
 CONSTRUCTING THE ROOT CAP 
 
 The root cap consists of the band formed as described, to 
 which is attached a disc of metal, designed to rest upon the 
 root face and which forms the foundation for the crown. The 
 constructive steps are as follows : 
 
 The band is removed from the root and a disc of 24 k. 
 or 22 k. 30 g. gold, slightly larger in diameter than the band, 
 is adapted to its incisal end. General adaptation may be 
 secured by placing the cervical end of the band on the ball of 
 the thumb, adjusting the disc correctly against the other end 
 and with the ball of the finger forcing it in contact with the 
 
CROWN WORK 
 
 baud margins. While pressure is thus maiutained, a tliin 
 blade burnisher is applied between the ball of the tinger and 
 the disc to conform it accurately at all iioints to the band edge. 
 By scratching the side of the luiiid and adjacent surface of the 
 
 KIRST STEP IX ADAI'TING GOLD 
 
 PLATE TO COMPLETED BAND IN 
 
 FORMING BOOT CAP 
 
 disc at two or three points, the two parts may later be re- 
 adjusted in exact relation as they must be when soldering. 
 
 When closely adapted, which means positive contact of 
 the disc with the baud around its entire periphei'al edge, the 
 two are separated, a thin tilm of flux is applied to the disc 
 surface on which the band will rest, a little to the band edge 
 also, and the outer margin of the disc is caught in the beaks 
 of a pair of self -locking soldering pliers. A very small piece 
 
 PLATE BCRXISHER FOR ADAPTIX<; liACKIXG TO FACIXG (PKl ITII ICIil I 
 
 of solder is cut and set endwise, one end resting on the disc, 
 the other against the outside of the band, care being taken to 
 see that the band and disc are in exact relation to each other, 
 as previously marked. 
 
 SOLDERING THE BAND TO THE DISC 
 
 The disc with band and solder in i)!ace is quickly passed 
 back and forth through the flame a few times, to gradually 
 expel the moisture and water of hydration from the flux and 
 thus obviate displacement of the band, after which it is held 
 in the reducing, flame until the solder fuses, when it is quickly 
 withdrawn. When the adaptation between disc and band is 
 perfect, the solder should flow around the entire joint peri- 
 ]ihery. Frequently, however, the solder will fail to flow along 
 the joint immediately in front of the plier beaks because the 
 
CROWN WORK 
 
 conduction of heat l\y the latter, away from the gold in tliat 
 particular area, lowers the temperature below the fusing point 
 of the solder. By grasping the opposite side of the disc with 
 
 SOLDERING THE BAND AND 
 PLATE. NOTICE TWO SMALL 
 PIECES OF SOLDEK ON OPPO- 
 SITE SIDE FROM PLIER BEAKS. 
 ONE PIECE IS DSnALLY SUF- 
 FICIENT 
 
 the pliers and again introducing in the flame, complete union 
 of band and disc can usually be effected without addition of 
 more solder. 
 
 TRIMMING OFF THE PERIPHERAL EXCESS OF THE DISC 
 
 The flat side of the shear blade is applied against the 
 side of the band, and the excess margin of the disc removed. 
 Further reduction should be made with the file, care being 
 taken to avoid rounding the disc margin, but leave it square 
 and flush with the band. In some cases it is advisable to allow 
 
 it to extend slightly beyond the outer surface of the band, 
 particularly on the labial surface, when proper alignment of 
 the facing requires that it be set to the labial of the band 
 surface. 
 
 CONSTRUCTING CAP BY THE INDIRECT METHOD 
 
 In making a cap by the indirect method, the excising of 
 the crown, removal of the enamel and smoothing up of the 
 root cone is the same as by the direct method, in which the cap 
 
CROWN WORK 663 
 
 is constructed of two pieces, as described. The steps vary, 
 however, from this point on. 
 
 In the indirect method, tlie root must be faced to tlie final 
 form desired, the labial portion being reduced beneath the 
 free margin of tlie gnms the full extent before the impression 
 is secured. Counter-sinking the canal orifice should also be 
 done so that this depression may be reproduced on the die. 
 
 TAKING IMPRESSION OF ROOT 
 
 A seamless copper band, slightly larger than the root, is 
 contoured to its general peripheral outline, and the con- 
 toured end trimmed to ai^proximate the curve of the gingiva. 
 The band should be slightly longer than the proximating teeth 
 for convenience in handling. 
 
 The band is filled slightly in excess with softened model- 
 ing compound, then introduced between the proximating teeth. 
 
 BAND FlI.Lrn WITH MODELlNf; 
 
 COMPOl M) I'KI l'\RlTOEY TO 
 
 TAKINf! IMPBESSION OF ROOT 
 
 FAfE AND PEBiniERY 
 
 and evenly centered over the root. Pressure is now applied 
 to force the compound against the root face and at the same 
 time telescope the band over the root periphery so as to con- 
 fine the compound and press it closely against the sides of 
 the root. The thumb or finger should be placed over the 
 outer or open end of the band to prevent the compound escap- 
 ing in this direction. The Ivory impression cups, a number of 
 varying sizes of which are suyiplied, which fit into a universal 
 handle, are well adapted to this work. 
 
 When properly carried out, the gum margin is pressed 
 apically and aft imjiression of the face end of the root and of 
 the sides as well can bo secured. Because of the limited com- 
 pressibility of the gum tissues, an impression of the root 
 sides, as far apically as the band will eventually extend, can 
 
664 CROWN WORK 
 
 seldom be securcil, but sufficient of the root surfaces can be 
 embraced so that the die when developed can be filed away 
 to represent a longer root. Wlien tliis plan is followed care 
 sliould be taken to jireserve llic original flare of tlie root cone. 
 
 CONSTRUCTING THE ROOT DIE 
 
 Any excess impression material tiiat may have been 
 forced out beyond the periphery of the impression band is 
 removed. A section of rubber tubing which neatly fits the 
 outside of the band is slipped over it and allowed to project 
 aliout oue-eighili iudi beyond flic im])i-ession, to confine the 
 
 nUBBER BIM> VIl'IIFD TO IM 
 
 I'RESSION I I Rll>lil HI lit COX 
 
 UNF THI VMiU.VM 
 
 amalgam or cement and thus increase the depth of the die. 
 A mix of amalgam, such as is used for die pui'poses, is 
 made and carefully worked into all inequalities of the im- 
 pression, being careful while doing so not to mar any of the 
 surfaces. Not only the impression, biit the rubber ring is 
 filled to give sufficient base to the die to resist the stress of 
 .swaging and that it may be well anchored in the swaging ring. 
 
 IMBEDDING THE DIE IN THE SWAGING RING 
 
 The die, when hardened, is removed from the impression 
 by warming the latter, and set in a base of modeling com- 
 pound in the swaging ring, placing it well al»ove the margin 
 
 of the ring, so that the counterdie material may press the 
 gold against the sides of the root. 
 
 Should any change of form of the die lie indicated, as in- 
 creasing" the length of the root apically, it can be made at this 
 time. In practically all cases such change should be made, 
 
CROWN WORK 
 
 even to the extent of iuereasiun' the length of the root hci/oiid 
 what is required. The band of the cap when swaged will 
 naturally be wider than necessary, but in fitting to the root it 
 
 DIE IMBEDDED IN KING WITHIN SWACiEI! 
 
 can readily be reduced to correct width, while if too narrow 
 the form of the die must be changed as outlined and the cap 
 reconstructed. 
 
 SWAGING THE ROOT CAP 
 
 The swaging I'ing is now placed in the base of the swager, 
 a disc of pure gold, of 34 or 36 gauge, slightly larger than 
 will be required to form the face and sides of the cap, is oiled 
 on both sides and adapted by finger pressure and burnishing, 
 to the die. The general outline of the cap can thus be defi- 
 nitely determined and the surplus gold removed practically 
 to the band margins. 
 
 The swager is set in position, niivulcaiiiz(Ml rubl)er or 
 moldiue being interposed between the iilunger and the root 
 
666 CROWN WORK 
 
 cap, and with two or three heavy Mows of tlie swaging ham- 
 mer the cap is swaged. 
 
 The band margins are now trimmed to as near the correct 
 width as possible before trial in the mouth, and the cap re- 
 swaged to correct the distortion from trimming. Since a die 
 formed in the manner described shows distinetlv the entrance 
 
 SWAGED CAP. IN POSITION ON 
 
 DIE. SURPLUS NOT TET 
 
 HEMOVED 
 
 to the root canal, and this is indicated by a depression in the 
 cap, the hole for the dowel may be punched before the last 
 reswaging. 
 
 The cap is boiled in acid to remove any adlierent amalgam 
 and cleanse the surfaces, then washed to remove the acid, 
 when it is ready for fitting to the root. 
 
 FITTING THE CAP TO THE ROOT 
 
 The principle fitting to the root consists in trimming the 
 band to proper width. The cap is placed on the root and 
 light pressure applied. If any obstruction is met the loca- 
 tion and cause are ascertained and correction made. The usual 
 change necessary is to shorten the cervical end of the band 
 so that it will not encroach on the tissues around the root 
 cervix. When the cap can be firmly seated without impinge- 
 ment on the tissues, a thin, flat burnislier is applied under 
 the gum margin and the band burnished into close contact 
 with the root periphery. While doing so the cap must be held 
 in close contact with the root face. 
 
 From now on, the steps are similar to those described 
 for the two-piece crown, the next step being securing the rela- 
 tion between cap and dowel and attaching them as previously 
 described. In flowing the solder which unites cap and dowel, 
 the entire cap should be covered at the same time with a 
 thin layer of solder to give it rigidity. 
 
CROWN WORK 667 
 
 ENLARGING ROOT CANAL FOR RECEPTION OF THE DOWEL 
 
 If the root canal liys not already been prepared to receive 
 the dowel, it must be at this time, since the following steps 
 relate to the fitting and adjustment of the dowel to the root 
 and cap. 
 
 The reaming out of a root canal is a comparatively simple 
 step when the prosthetist himself has treated the root and 
 lilled the apex. When, however, the case presents, the root 
 having previously been filled by another operator, an eit'ort 
 should be made to determine the probable length of the root 
 and its position in the border. If any doubt exists as to its 
 anatomic form, its position, or the thoroughness of the root 
 filling, a skiagraph should be secured to determine as accu- 
 rately as possible the existing conditions. 
 
 Examination of the labial tissues overlying the root will 
 frequently disclose a slight elevation of the mucous membrane 
 and underlying alveolar plate, which will indicate the position 
 of the root in the process. If no visible evidence is present, 
 pressure with the ball of the linger, particularly in the apical 
 region, will frequently locate the direction of the root. It is 
 of the utmost importance that the general trend of the root be 
 known before attempting to ream out and enlarge the canal. 
 When for any reason it is impossible to determine it, the great- 
 est care should be observed in keeping the cutting instrument 
 within the canal and pointed in the right direction or serious 
 injury is liable to occur. 
 
 A rigid, inflexible drill, bur or root reamer, having a 
 cutting point, is a dangerous instrument in the hands of an 
 unskilled or careless operator. Perforation of the side of the 
 root is very liable to occur as a result of the instrument point 
 leaving the canal and boring its way through the dentin and 
 into the alveolus. The tissues injured as a result of such acci- 
 dent seldom ever recover their normal tone, the root having a 
 feeling of chronic soreness, while frequently its extraction in 
 a short time becomes necessary. 
 
 The safest method of removing a root filling and enlarg- 
 ing the canal to the required diameter, or to such size that a 
 reamer may with safety be used, is by means of various sizes 
 of round engine burs. The technic is as follows : 
 
 Determine, if possible, the general direction of the root, 
 and keep this constantly in mind at all times until the initial 
 reaming of the canal to proper depth has been accomplished. 
 
668 CROWN WORK 
 
 Place a No. V2 round l)ur in the liandiiiccc and iatroduee 
 the point in tlie extrauoe to the eanal. 
 
 Line the handpiece up to conform to the general direction 
 of the root, hokling it loosely with tlie pen grasp. 
 
 Start the engine and apply light pressure with tiie point of 
 the bur, removing it frequently to l)ring out tlie guttapercha 
 cuttings and keep the canal clear. 
 
 Do not attempt to guide the point ; it will follow the canal 
 if the handpiece is held loosely and in proper alignment, and 
 the cuttings are removed frequently. 
 
 Since a dowel should extend as far apically as the crown 
 extends incisally, it will be necessary to ream out the canal 
 to this dei3th when the length of root will permit. 
 
 As soon as the bur begins to bind, and the feel or vibra- 
 tion of the handpiece indicates that the bur is cutting dentin 
 instead of root filling, an examination should be made with a 
 straight explorer to determine whether the bur is leaving the 
 canal and if so, the cause. 
 
 Should the tapering shank of the small bur jam against 
 the sides of the canal before the latter has been opened to re 
 quired depth, a No. 3 round bur can be substituted and the 
 canal slightly enlarged from without inward for a short dis- 
 tance, thus making room for the smaller bur with which the 
 opening of the canal can be completed to the required depth. 
 
 The No. 3 bur is now used in the manner as described for 
 No. % bur, holding the handpiece loosely and allowing the bur 
 to make its own way in the now open canal as far as the lat- 
 ter has been opened by No. \'2. 
 
 The canal can now safely be enlarged to the required size 
 for the reception of the dowel with either Nos. 4 or 5 round 
 burs, depending on the diameter of the dowel to be used. Any 
 of the ordinary forms of reamers can also with safety be used, 
 since there is little danger, except when grossest carelessness 
 is displayed, of perforating the side of the root. 
 
 Great care should be taken to avoid passing the small 
 round bur through the apical end of the root, or of disturlnng 
 that portion of the filling which closes the terminal of the 
 canal. Pressure on the Inir nuist be extremely light at all 
 times, but particularly so in the final steps of removing the 
 root filling. 
 
 COUNTERSINKING THE CANAL OPENING 
 
 To give rigidity to the cap and a firmer attachment to it 
 of the dowel when soldered, the entrance to the root canal 
 
CROWN WORK 
 
 slionld be slightly countersunk with a No. 10 round bur, and 
 into this depression the cap disc is depressed. 
 
 LABIAL VIEW OF KOOT SHOW- 
 ING CANAL ENTRANCE SLIGHT- 
 LY ENLARGED 
 
 PROXIMATE VIEW OP ROOT 
 
 SHOWING ENL,\KGED CANAL 
 
 ENTRANCE 
 
 INDENTING THE CAP IN COUNTERSUNK AREA 
 
 The cap is now returned to position on the root and the 
 small end of the large egg Ijuruisher is applied to its central 
 area with sufficient force to press it into the depressed area. 
 
 BOOT CAP IN POSITION. NOTICE 
 THAT LABIALLT THE BAND IS 
 BENEATH GDM MARGIN. WHILE 
 L I N G U A L L Y IT PROJECTS 
 SLIGHTLY- BEYOND 
 
 Usually, when the burnisher is somewhat pointed, the gold 
 will be forced slightly beyond the countersunk area and into 
 the entrance of the root canal itself, thus giving the exact 
 location of the hole in the cap for the dowel. 
 
 PERFORATING THE ROOT CAP FOR THE DOWEL 
 
 A heavy instrument, witli a sharj) ))oint, the diameter of 
 which is slightly less than the dowel, is now forced against 
 the cap directly over the opening in the root, and the gold 
 punctured. A small engine drill may be used for the same 
 purpose, or the ca'p can be removed and the hole punched 
 with the plate punch. The opening, as before stated, should 
 be smaller than the dowel, so that when the latter is forced 
 through it the margins of the disc may ht tiglitly against and 
 hold the dowel firmly in position. 
 
t;70 CROWN WORK 
 
 FORCING THE DOWEL THROUGH THE CAP INTO THE ROOT 
 
 The dowi'l, usually of 16 or 15 g. iridio-platinum, or clasp 
 metal wire, is cut slightly longer than the actual depth of 
 the reamed canal so that it may project beyond the root cap 
 and be surrounded by the solder which forms the lingual con- 
 tour of the crown. Its apical end should be slightly reduced 
 so as to readily enter the hole iu the root ca]i. Better reten- 
 
 FOKCING THE DOWEI 
 
 \l, THROUGH ROOT CAP 
 
 tion, however, will be afforded the crown if the sides of the 
 dowel are not tapered as is the common practice. 
 
 With a pair of parallel jaw pliers, the dowel is grasped 
 firmly, the reduced apical end outward. This end is entered 
 in the opening in the root cap, the dowel brought in alignment 
 with the root canal, and forced through the cap and into the 
 root, the full depth of the reamed out portion. 
 
 As the dowel is forced into the root through the con- 
 stricted opening in the cap, the margins of the latter will be 
 
CROWN WORK 
 
 enlarged and carried into the entrance of the canal, and tlie 
 bearing of the gold against the dowel be much increased. 
 
 DIAGRAM OF INTRODUCTION OF 
 
 DOW-EL THROUGH CAP. WITH 
 
 PARALLEL JAW PLIERS 
 
 ROOT CAP WITH ATTACHED 
 DOWEL IN POSITION ON BOOT 
 
 MAINTAINING CORRECT RELATION BETWEEN DOWEL AND 
 CAP WHILE REMOVING FROM ROOT 
 
 The cap and dowel are now ready for attaching together 
 with solder. To preserve the exact relationship which they 
 now sustain to each other, on the root, during the soldering 
 process, a piece of wax or modelling compound which will 
 enter the space of the missing crown, is softened, pressed 
 against the projecting dowel and root cap and chilled. A 
 small G-2-23 hoe, or iuotrument of similar shape, is carefully 
 passed under the free margin of the gum, labially or lingually, 
 hooked over the cervical margin of the band and the cap 
 loosened. 
 
 Should the cap and dowel cling to the root and fail to 
 come away witli the impression as it is removed, they can be 
 released and set in position without difficulty. 
 
 Frequently, wli.en the dowel fits tightly in the cap open- 
 ing, and the ca|> and dowel release easily from the root, they 
 can be removed from position, a little sticky wax applied to 
 and melted on the cap and against the dowel, after which they 
 are returned to the root to correct any disturbance of align- 
 ment of the dowel that mav have occurred in removal. The 
 
672 CROWN WORK 
 
 wax is now (^liilk'd and the two, now tiruily held together in 
 correct relation, are removed and invested for soldering. 
 
 At times the dowel may be held so tirmly by the cap that 
 (he two mav be removed and sol(hT('(l without investment. 
 
 SOLDERING CAP AND DOWEL SOLDEMNG CAP AND DOWEL 
 
 WITHOUT INVESTMENT, PER- WITHOUT INVESTMENT. HORI- 
 
 PBNDICULAR POSITION OF ZONTAI, POSITION OF DOWEL 
 
 DOWEL. NOTICE REFLECTED 
 MARGIN OF DISC AROUND 
 DOWEL 
 
 Althoiis'li r<'(iuirin,i>' a little longer time than by the method 
 just mentioned, it is much the safest plan to take the small 
 impression and invest the two for soldering. 
 
 INVESTING THE CAP AND DOWEL FOR SOLDERING 
 
 A small mix of investment material or plaster alone, be- 
 cause of its greater rapidity in setting, is prepared and ap- 
 plied to the root side of the ca]) and around the dowel, build- 
 ing it up the full length of the latter and squaring it off to 
 form a base on which to rest while soldering. 
 
 CAP ANT) DOWEL INVESTED FOB 
 SOLDERING. THIS PLAN IS 
 PREFERABLE TO THE T«'0 PRE- 
 CEDING METHODS 
 
 When set, the investment is reduced to small size to facil- 
 itate soldering, the wax and moisture removed, a little flux 
 applied over the surface of the cap and around the dowel 
 where it is desired the solder should flow, a piece of solder is 
 
CROWN WORK 673 
 
 ap]ilied, one eud rt'stiiig on the cap, the otlier against the 
 dowel, and with the blowpipe flame is fused. 
 
 The investment is now removed, the cap pickled in acid 
 to cleanse, and thoroughly washed in water to remove the acid, 
 when it is ready to return to the mouth for final impression. 
 
 TAKING THE BITE AND IMPRESSION 
 
 Although there are many ways by which an acciirate 
 relation may be secured between the backed facing and cap 
 in assembling the crown for final soldering, without taking 
 an impression and bite and constructing casts, the safest plan 
 for the beginner at least is to carry out the steps as now 
 outlined. 
 
 USE OF THE FACE BOW IN CROWN WORK 
 
 To secure esthetic results, it is essential that at least two 
 teeth on either side of the s^iace in which the crown is to be 
 
 ADJUST.ME^'T OF WAX 
 
 THE UlTE 
 
 placed should be reproduced on the cast, in order that correct 
 alignment and length of crown may be determined acciirately, 
 therefore the bite should include from five to six teeth. It 
 
B74 CROWN WORK 
 
 is also essential that llie crown be so constructed as not to 
 interfere with the teeth in the opposite arcli in lateral as 
 well as incisive movements. The use of the face bow will 
 enable the prosthetist to so construct the crown that sul)se- 
 cjuent changes by grinding will not be required. 
 
 In crown work the bite should be secured before the im- 
 pression is taken, for the reason that when the impression 
 is taken in plaster, as in most cases it should be, the project- 
 ing end of the dowel, being imbedded in the plaster, will bring 
 the cap away from the root with the impression. In case the 
 impression is taken first and the cap comes away with it, the 
 cap must be removed and replaced on the root before taking 
 the bite or the latter will be useless or at least unreliable. 
 
 Some prosthetists take a combined bite and impression in 
 modeling compound, which in simple cases, where there are no 
 
 SECTIONAL ^■IE\V OF COMBINED 
 
 IMPRESSION AND BITE. BOOT CAP 
 
 AND DOWEL IN POSITION 
 
 undercuts present, will answer for the separate bite in wax, 
 and impression in plaster. 
 
 DETAILS OF TAKING THE BITE 
 
 The cap is set in position on the root, care lieing taken 
 to see that it is firmly seated. 
 
 A piece of wax is formed into a compact mass, about 
 1/2x1x2 inches, introduced between the teeth and the patient 
 instructed to close. The wax should extend sutKiciently far 
 labially of the teeth to receive and firmly hold the bite fork 
 of the face bow, which is now applied and the face bow ad- 
 justed in the usual manner. 
 
 While the wax is still soft the patient is instructed to 
 press it against both upper and lower teeth with the tongue 
 
CROWN WORK 
 
 SO as to secure as accurate an iiupressiou of them as possible. 
 Stress should be laid on forcing the wax against the loiver 
 as well as the tipper teeth, otherwise the tongue will raise it 
 against the upper teeth only. 
 
 APPEAKANCE IN MOUTH 01'' ROOT CAP WITH PROJECTING 
 
 DOWEL. EXTREME LABIAL MARGIN OF BAND IS 
 
 OBSCURED UY GUM MARGIN 
 
 The wax is now chilled, the condyle rods of the face bow 
 released, the patient instructed to open the mouth, and the 
 bite attached to the face bow is removed and laid aside until 
 the cast is secured. 
 
 A bite fork, modified by having the inner edge of each end 
 reduced by grinding to increase its inner arc, will serve the 
 purpose better than one of regular form. 
 
Cuo runwN work 
 
 Still anotlior modiiicutiun which will be found very use- 
 ful for taking side bites, as for cuspids, bicuspids and the 
 first molar, can be made as follows : Saw off one of the fork 
 prongs next the stem, to the other, lit a sleeve wliich will slide 
 freely along the fork, but which can be firmly fixed with a 
 set screw at any point desired. The inner margin of the 
 sleeve is supplied with a projection for extending into the 
 space of a missing tooth. A firm hold is secured in the bite 
 by having sufficient bulk of wax outside the arch to enclose 
 the inner margin of the fork. The projection of the sleeve 
 should be set so as to enter the space of the missing crown. 
 
 When the root cap comes away with the bite, as is fre- 
 quently the case, it must be removed and returned to the root 
 before taking the impression. 
 
 DETAILS OF SECURING AN IMPRESSION WITH PLASTER 
 
 In crown work it is just as imi)ortant to secure an accu- 
 rate impression of that part of the mouth involved as in full 
 denture construction. When much irregularity of surfaces 
 exists, as in teeth witli constricted cervices, or when the em- 
 brasure spaces are open as a result of tissue absorption, the 
 impression should always be in plaster. 
 
 In order to preserve the essential parts of such an im- 
 pression, so that the teeth involved may be reproduced as 
 perfectly as possible, it will be necessary to fracture it, care- 
 fully remove the pieces, and re]ilace them in proper order for 
 the production of the cast. 
 
 Any one of three methods may be adopted, as follows : 
 
 First, a tray of suitable size is selected and oiled to pre- 
 vent the plaster from adhering to it. Plaster sufficient to 
 secure an impression of the teeth involved is placed in the 
 tray, introduced in the mouth and given sufficient time to thor- 
 oughly harden. The tray is then carefully removed so as not 
 to disturl) the impression. With the point of a knife an incisal 
 groove is cut in the plaster to weaken it. The groove should 
 extend well into the space of the missing crown. Pressure on 
 the ends or the extreme border surface outward will fracture 
 the labial portion, which will usually come away intact. With 
 careful manipulation the lingual portion may be released 
 and removed without further fracture. The tray and frac- 
 tured surfaces of the impression are now cleared of all par- 
 ticles of debris, the pieces replaced in the tray, luted firmly 
 with wax and the cast secured in the usual way. 
 
 Second method : A piece of cardboard is cut in the form 
 
CROWN WORK 677 
 
 of a square about IVoxlVo inches, and the four corners 
 rounded slightlj'. 
 
 Two opposite sides, each a littk' less than one-half inch 
 wide, are turned up at right angles to form an improvised 
 impression tray, the bottom of wliicli is a little more than one- 
 
 half inch wide. The sides and floor of -the tray may be varied 
 in width to confoi*m to any special requirements, as a greater 
 or less curvature of the arch or a deep or shallow alveolar 
 border. 
 
 The plaster is mixed to medium thick consistency, placed 
 in the tray carried against the teeth so as to divide it about 
 equally labially and lingually, and pressed borderward until 
 the iueisal edges of the teeth touch the tray floor. 
 
 Since the sides of the tray are not rigid, they should be 
 supported with the thumb and fingers while introducing the 
 plaster and until it has begun to set. 
 
 When the plaster has set, it is unnecessary to remove the 
 tra>' from the impression, since the cardboard will be easily 
 Ijent along the line where fracture will occur. Neither is it 
 necessary to groove the impression, for when the tray is car- 
 
 mXGE TRAY OI-EN 
 
 ried borderward until its floor comes in contact with the teeth, 
 the plaster is already practically divided into two sections and 
 will readily break along the incisal line with the application 
 of slight force. Furthermore, the cardboard serves the same 
 purpose as a hinged tray, for by removing the particles of 
 
1)78 CROWN WORK 
 
 debris from the fi-acturcd surfaces, the two luilves of the im- 
 pression can be brought together in exactly tlie right relation 
 to each other, and on hitiiig with wax or wrapping a strand of 
 tine binding wire around the outside, is ready for the produc- 
 tion of the cast. 
 
 Third method: A very serviceable and permanent tray 
 may be constructed of an ordinary brass hinge, so bent as to 
 present a floor and sides of about the same dimensions as 
 those of the cardboard tray. The joint of the tray is in the 
 center of the floor, while the hinge projects a little below and 
 serves as a handle, or fiiiyer hold in introducing the tray. 
 
 PRODUCTION OF CAST FROM THE IMPRESSION 
 
 The impression having been secured, and the fractured 
 pieces correctly adjusted, it is coated with separating medium 
 and allowed to dry. 
 
 Usually when an impression is fractured in removal, the 
 cap will remain in position on the root. It may, however, 
 come away, but its position in the impression will usually be 
 disturbed. 
 
 Before replacing it, the several parts of the impression 
 are first placed together and firmly attached with sticky wax. 
 The cap is then cleaned and a thin film of wax flowed over 
 the dowel and inside the cap to obliterate any undercuts that 
 may be present. The object of this is to permit the ready 
 removal subsequently of the cap from the cast, without break- 
 ing the latter. Before the backed facing is finall)' attached 
 to the cap, the latter is heated slightly to soften the wax, after 
 which it is carefully removed from the cast, the wax cleared 
 away and the cap returned to position, the outer periphery 
 and dowel opening guiding it accurately to place on the cast. 
 Then when the facing is attached with sticky wax, in the exact 
 and final relation it should sustain to the cap, the assembled 
 crown can be removed for investment without danger of dis- 
 turbing the relation so estalilished. 
 
 The cap is now returned to its exact position in the im- 
 pression where it is luted firmly with a little wax applied to 
 the outside of the lingual band surface. 
 
 Plaster is then mixed and the impression filled as for any 
 partial case, special care being taken that no air is confined 
 in the deeper parts of the impression. 
 
CROWN WORK t>79 
 
 ATTACHING THE CASTS TO THE OCCLUDING FRAME 
 
 When the face bow has been applied in taking the bite as 
 described, the most convenient as well as accnrate method 
 of monntiug the casts ou the occluding frame is to mount the 
 bite and produce the occlusion cast first. 
 
 The face bow with bite fixed to the fork is attached to the 
 frame and the latter inverted. The lower bow is thrown back- 
 ward out of the way, the interior of the bite coated with a 
 thin film of oil and filled with plaster, building it well above 
 the bite margins. The bow of the frame is brought down in 
 position and plaster applied around it to unite it with that in 
 the bite. 
 
 When the plaster has hardened, the face bow and bite 
 fork are removed, and both labial and lingual portions of the 
 bite in which the upper cast is to be fitted are pared down 
 so as to permit the teeth to enter freely. The labial side of 
 the bite should be cut away so as to expose the imprint made 
 l)y the incisal edges of the natural teeth in the wax, so that 
 in placing the cast in position it can readily be seen when 
 the plaster teeth are in contact with the deepest portion of 
 the bite. Sufficient wax, however, should be left to guide the 
 cast into correct vertical ])osition. 
 
 FUU. I'ASTS MOrXTED ON OCCLUDING FRAME. CAI" IN POSITION. 
 DSCALLY ONLY P.iRTIAL CASTS ABE DEVELOPED 
 
 The upper cast is now set in the bite, the upper bow of 
 the frame dropped down upon its base, and plaster applied 
 to attach the two firmly. When the plaster has set the wax 
 is thoroughly warmed to prevent breaking the teeth and is 
 
680 CROWN WORK 
 
 then removed. The case is now ready for the scsh'ction and 
 grinding of tlie facing. 
 
 SELECTION OF THE FACING 
 
 By means of the shade guide, the tints displayed in the 
 natural teeth of the patient can he determined, the number of 
 the shade required noted, and a facing of corresponding color 
 and of suitable form selected. 
 
 The form of the facing selected should correspond to the 
 type of proximating natural teeth. In case such a tooth is not 
 procurable, one of the correct shade but sliglitly larger than 
 required can be selected and by grinding be modified to meet 
 the requirements. The ground surfaces, when the proper con- 
 tour is developed, can be finished with fine discs, and after- 
 ward given a fine glaze with putty powder on a hard felt lathe 
 wheel. 
 
 The facing should be wide enough to fill the space and 
 restore strong proximate contact with the adjoining teeth, 
 unless for some special reason this is not advisable. 
 
 Usually the facing selected should be slightly longer than 
 required, since both incisal edge and ridge lap must be re- 
 duced to required form by grinding. 
 
 Since the pins afford tlie only anchorage of the porce- 
 lain to the metal structure of the crown, a facing should be 
 selected having the pin« located as close to the incisal edge as 
 possible, so as to bring the anchorage near the point of stress. 
 
 GRINDING THE FACING TO THE ROOT CAP 
 
 To facilitate the soldering of the backed facing to the root 
 cap, the ridge lap of the facing is beveled from its cervico- 
 
 RIDGE LAP AND INCISAL EDGE 
 OF PORCELAIN PACING GROUND 
 AND ADJUSTED TO ROOT CAP 
 
 labial margin to the lingual surface. This leaves a V-shaped 
 space of greater or less width between the base of porcelain 
 and the root cap. 
 
CROWN WORK 
 
 In grinding the cervical end of a facing to the required 
 form, care should be taken to develop a distinct line angle be- 
 
 CUT SHOWING DIREPTION STONE 
 
 SHOULD ROTATE IN GRINDING 
 
 TO OBVIATE CHIPPING MAB- 
 
 GINS OF PORCELAIN 
 
 tween the ridge lap surface and the laliial surface to avoid a 
 defective joint between the porcelain and backing. 
 
 The stone should revolve from the labial surface lingually 
 to prevent fracture of the margins. 
 
 BEVELING THE INCISAL EDGE OF THE FACING 
 
 The incisal edge of the facing should be ground to har- 
 monious alignment with the proximating teeth, the facing, 
 however, being shortened slightly to allow for the thickness 
 of the gold tip to be added, and also for the backing, which 
 must cover the ridge lap. 
 
 The inciso-lingual line angle should be reduced to about 
 30 degrees with the lingual surface taken as a base. This is 
 somewhat less than is usually recommended, but when so 
 formed will result in a metal tip of equal or greater strength 
 with less labial exposure of gold than where the porcelain is 
 beveled at an angle of 45 degrees. Special care should also 
 be observed in developing the bevel to avoid fracturing the 
 labial margins of porcelain with the stone. 
 
 CHANGE OF COLOR IN PORCELAIN DUE TO METAL BACKING 
 
 Different metals are used and various methods are in 
 vogue in backing facings in crown and bridge work. The 
 technic of applying the various metals is similar, but the color 
 elTect on the porcelain of the metal employed as a backing 
 should be known in order to avoid luidesirable change of tint 
 in the facing of a finished crown. 
 
 Pure gold imparts a slightly yellowish tint to very light 
 porcelain, and increases or darkens the tint of yellow porce- 
 lain, particularly when the facing is thin. 
 
(;82 CROWN WORK 
 
 AlloWHiiee, therefore, should be made in the selection of a 
 facing when pure gold is to be used as a backing by choosing 
 one having the correct basic color, but slightly lighter than 
 the shade desired, the variation depending on the thickness 
 of the facing selected. 
 
 When 22 k. gold is used, a similar effect is produced, but 
 to a lesser degree, because of its less pronounced yellow color. 
 
 Coin gold perceptibly darkens thin, translucent facings of 
 any shade. 
 
 Platimun imjiarts a bluish tint to light porcelain, in some 
 cases darkening it perceptiltly. 
 
 A greenish yellow tint can be imparted to light yellow 
 Ijorcelain by using an 18 k. alloy known as "green gold," com- 
 posed of 18 parts of pure gold and 6 parts of pure silver. 
 This gold is almost as soft and easily worked as pure gold. 
 
 BACKING THE FACING WITH GOLD 
 
 Pure gold is most generally used as a backing because of 
 the ease with which it can be adapted to irregular surfaces. 
 When conformed to a surface it shows but little tendency to 
 warp or spring away as does gold of the lower carats. 
 
 Two general methods are in vogue for applying the back- 
 ings to teeth, first, by burnishing, and, second, by swaging, both 
 of which will be outlined. 
 
 PERFORATING THE BACKING FOR THE PINS 
 
 Spread a thin film of wax over the surface and near the 
 corner of the piece of plate. Place the facing, pins resting 
 on the wax, so that a slight margin of gold shows at the end 
 
 METHOD OF MABKING CORRECT POSITION 
 
 OF HOLES, ON BACKING, FOR TOOTH 
 
 PINS 
 
 and along the side. Press the pins into the wax to indicate the 
 location of the holes for the pins. Punch the holes as marked 
 in the wax. Apply the facing and with a sharp instrument 
 mark the outline of the tooth on the backing, allowing a little 
 surplus all around, particularly at the cervical and incisal 
 ends. The gold is then cut to the outline marked. 
 
CROWN WORK 683 
 
 Another method is to puiieh one hole near the edge of the 
 plate for the outer pin. Apply the facing, entering the pin in 
 the hole already punched, and rotate the tooth. Remove the 
 facing and punch the other hole, its inner margin or tliat next 
 the first hole heing on the rotation line. 
 
 Whatever method is employed, care should be taken to 
 punch the holes the proper distance apart to avoid straining 
 the porcelain as the gold is forced over the pins and against 
 the facing. When the space between the pin holes is either too 
 wide or narrow, such an accident is liable to occur. 
 
 The holes should be of the exact diameter of the pins or 
 slightly smaller, but never larger, to obviate the danger of 
 fracture in final soldering, from the flux and solder being 
 drawn into and through the holes next the pins, thereby com- 
 ing directly in contact with the porcelain. 
 
 THE MASON SPACING CALIPER 
 
 The Mason spacing calipers and auxiliaries, consisting of 
 a pointed puncli and an engine burnishing tool, was designed 
 to and does effectually obviate the liability of both too large 
 
 APPLICATION OF .MASON SPACING CAI/Il'ER IN PEIIFORATING THE BACKING 
 
(i84 CROWN WORK 
 
 or iucorrectly located holes. The directions for using the 
 appliances are as follows: 
 
 "The pins of the facing are placed in tiie holes on the 
 side of the caliper which have guide slots to guide the pins into 
 the holes ; this accurately spaces the holes, which register with 
 pins of the tooth, held in that position by the thumb nut; the 
 backing is then marked or pierced by the hardened points, 
 which gives the exact spacing for the pins; now place the 
 backing thus marked on a piece of lead; then with the pointed 
 punch the metal or gold is pierced, throwing u]) a lip, giving 
 an a]3erture the same size as the pins; the backing thus 
 pierced is placed on the tooth, the lips extending on the pins; 
 finally, to burnish this lip of gold to the pin, the lathe tool is 
 used ; this has an aperture in the end which fits over the 
 
 THE MASON SPACING CALIPER AND ACCESSOKIES 
 
 pin; with a high speed engine or lathe the gold is tightly 
 burnished around and slightly raised against the sides of the 
 pins . . . ." 
 
 The writer's experience with this appliance has proven 
 it to be a most valuable addition to the laboratory equipment. 
 
 THE YOUNG PLATE PERFORATOR 
 
 This is another convenient appliance by means of which 
 the tooth serves as a gauge for setting the double end punch 
 
 TTTE YOUNG PLATE PERFOHATOR 
 
 so that both holes are punched at the same time and at exact- 
 ly the proper distance apart. 
 
CROWN WORK 685 
 
 ADAPTING THE BACKING TO THE FACING BY BURNISHING 
 
 The backing, cut slightly larger than the surfaces it is 
 to cover, and with holes punched, is applied to the facing and 
 adapted as closely as possible to the porcelain with finger 
 pressure. By means of the contra-angle burnisher or one of 
 the Wilson type, general surface adaptation is secured, after 
 which the borders are gradually worked into close contact 
 with the margins of the facing. The gold should be removed 
 and annealed occasionally to reduce the hardness developed 
 by burnishing. Finally, when as close adaptation as possible 
 has been secured by burnishing, the backing is removed, an- 
 nealed, returned to place and the facing pressed, pins down, 
 with backing interposed, into a broad cork that has previously 
 been grooved to the general lingual contour of the facing. A 
 piece of wood about the size of a lead iieneil, concaved on the 
 
 ADAPTING THE BACKING TO 
 
 FACING AGAINST COKK WITH 
 
 I.K;UT IIAMIIEB BLOWS 
 
 end. is set on the facing and with both jn-essure and light ham- 
 mer blows final and close adaptation of the gold to the porce- 
 lain is secured. 
 
 Previous to this final adaptation, the surplus gold extend- 
 ing over the margins of i^orcelain should be reduced with a 
 file, applied so as to force the backing toward rather tlian 
 away from the facing As before mentioned, a slight surplus 
 of the backing should be allowed to remain on both incisal 
 and gingival margins, until the final finishing of the crown, so 
 that the solder may be drawn outward to the full extent de- 
 sired. Under no circumstances should the backing on these 
 two ends be reflected over and onto the labial surface, as frac- 
 ture of the porcelain will occur, due to contraction of the 
 applied lingual solder. 
 
 It is absolutely essential that the backing be brought into 
 close and positive contact with the porcelain, not only at the 
 margins, but on the lingual surfaces as well, to avoid the 
 formation of a space between the two, into which organic mat- 
 ter will gradually find its way. When food accumulates in 
 
686 
 
 CROWN WORK 
 
 such spaces it gives rise to disagreeable odors, and as it de- 
 composes and darkens will inddil'y the shade of the ])orcelain. 
 
 SWAGING THE BACKING 
 
 When the backing lias been cut to proper size, the holes 
 inmehed for the pins, and general adaptation secured with a 
 burnisher, the facing is invested, labial face down, in modeling 
 compound, in the swaging ring. 
 
 UNVULCANIZED 
 RUBBER.-- 
 
 MODELING 
 COMPOUND^ 
 
 ADAPTING THE BACKING TO FACINC IN S. S. W SWAOER 
 
 SIMILAR METHOD OF 
 ADAPTING FACING TO 
 BACKING IN AJAX SWAGER 
 
 It should set well above the ring margins so as to freely 
 expose the beveled incisal tip on one end and the ridge lap on 
 the other. The com])ound should be trimmed so that the mar- 
 gins of the facing are freely exposed to permit the gold being- 
 forced in close contact by the unvulcanized rubber. 
 
 When the thinner gauges of gold or platinum are used, as 
 34 or 36 g., two or three light blows on the plunger will set 
 
CROWN WORK 687 
 
 the backing in close contact witli tlie facing. Heaviei' gauges 
 of metal will require more force. When swaged, the backing 
 is removed and trimmed to desired correct outline, and the 
 backing returned to the facing and reswaged to correct any 
 distortion that may have occurred. 
 
 FIXING THE BACKING TO THE FACING 
 
 When final adaptation has been developed between facing 
 and backing, the latter should be firmly fixed to the porcelain 
 so that the close and essential relation between the two may 
 not be disturbed while assembling and soldering the crown. 
 
 A common practice is to bend the pins over in contact 
 with the backing. As a result, however, the porcelain is sub- 
 jected to undue strain, and if not fractured immediately, as is 
 frequently the case, is very liable to be in the subsequent sol- 
 dering process. 
 
 A much safer and quite as effectual method is to apply 
 a sharp blade or chisel to the side of pin and turn a light 
 shaving of the platinimi down upon the backing. Tliis puts no 
 strain upon the porcelain and holds the gold firmly in place. 
 The Eeese Pin Shaver, a small, cylindrical, hollow mandrel, 
 the Oldening in which is slightly larger than the diameter of a 
 tooth pin, can also be used for shaving the pin and burnishing 
 the shaving down in close contact with the backing. The in- 
 strument is passed over the pin in a slightly diagonal direc- 
 tion, and as it is forced along the pin toward the backing, the 
 sharp inner margin of the tool cuts and carries a shaving of 
 platinum down in contact with the gold. 
 
 FITTING THE BACKED FACING TO THE ROOT CAP 
 
 The facing now having its backing conformed and at- 
 tached as described is ready for adjustment to the root cap, 
 A small piece of soft wax is placed over the projecting dowel 
 and on the lingual half of the cap, and the facing pressed 
 against it so as to secure proper aligiiment with the prox- 
 imating teeth. 
 
 If in adjusting the facing the labial surface of the dowel 
 interferes with its labial alignment, the dowel may be partially 
 ground away. Sometimes it is necessary, when the facing is 
 thick or the •labio-lingual diameter of the root is short, to 
 remove the greater portion of the i^rojecting dowel. When 
 the root is countersunk and the cap has been burnished into 
 it as previously described, the removal of the dowel projection 
 
688 CROWN WORK 
 
 will not ap!>rfci;ihl>- wciikcii I lie attachiiiciil ol' llic ddwd to 
 tlie finished crown. 
 
 It is sometimes iulxisaldc to ream out tlic liiii;ual side of 
 tlie root canal, so that in adjusting the dowel it may be bent 
 slightly to the lingual, and thus give more space for the facing. 
 
 Special care should be observed to set the cervical mar- 
 gin of the facing in line with the labial surface of the band. 
 It may even project slightly if tlie alignment of the facing 
 recjuires, but should never be set to the lingual or the labial 
 band surface, or a jn-ojecting shoulder of gold, wliicli cannot 
 be obliterated, will result. 
 
 The long axis of the facing must be set at a similar angle 
 of divergence from the perpendicular line of the face or, in- 
 ciso-apically, as the corresponding tooth on the opposite side 
 of the arch, the line of direction, however, being reversed. 
 
 In most cases the backing which covers the ridge lap of 
 the facing can be slightly reduced in thickness by filing, and 
 that portion of gold on the root cap against which the facing 
 rests may also be thinned by grinding. The object of this 
 is to bring the porcelain in as close contact as possible with 
 
 LINGUAL SIDE OP BOOT CANAL 
 
 REAMED TO RECEIVE 
 
 BENT DOWEL 
 
 the root face, and thereby reduce the width of the labio-gin- 
 gival margin of gold in the finished crown. By this step, in- 
 stead of two thicknesses of gold being interposed between the 
 face end of the root and facing there is the equivalent of only 
 one. When the facing is adjusted in the exact desired relation 
 to the cap, the point of a heated instrument is passed into the 
 wax supporting it and the two are firmly united. 
 
 INVESTMENT OF THE ASSEMBLED CROWN FOR SOLDERING 
 
 The crown is now carefully removed and its full lingual 
 contour developed in wax. Special care should be taken to 
 flow wax into the space between the backing and root cap 
 around the labial surface to exclude the investment in which 
 crown is later on inclosed for soldering. 
 
CROWN WORK 689 
 
 The crown is now assembled, but all of the several parts 
 are not yet permanently united. It must therefore be enclosed 
 in some material capable of resisting heat without perceptible 
 change, that will hold the cap and facing in correct relation 
 to each other after renio\ al of the wax and during the solder- 
 ing i^rocess. 
 
 Anj' of the standard investment materials prepared and 
 sold for this ynirpose may be employed, or one can be com- 
 pounded in the laboratory. One of the best "home made" 
 investments for soldering purposes consists of a mixture of 
 two-third coarse ground asbestos (short cut fibre), and one- 
 third plaster. 
 
 The two ingredients sliould be measured out in proper 
 proportions and "dry mixed," thfen placed in the bowl, a suf- 
 
 BACKED FACING AND CAP AS- 
 SEMBLED AND HELD WITH 
 WAX, BEADY FOR INVESTMENT 
 
 ficient quantity of water added to make a rather stiff mass, 
 and spatulated thoroughly. 
 
 An oiled slab should be prepared or a piece of paper 
 placed on the bench. On this the investment is placed, build- 
 ing it up to an inch or more in thickness. The crown cap is 
 completely filled with investment before enclosing in the mass 
 to subsequently exclude the solder. 
 
 The crown is now pressed into the plastic mass, being 
 careful to keep its labial face at least one-half inch above the 
 base of the investment, so that the latter may not be fractured 
 when subjected to heat, as is frequently the case when the bulk 
 of investments is too limited. The investment is now built 
 around the sides of the facing and even with, but not above, 
 the incisal end. 
 
 The crown should be settled into the plastic mass in a 
 diagonal position rather than horizontally. This is to bring 
 the linguo-gingival edge of the root cap and the incisal end of 
 
690 c:ro\vn work 
 
 the facing on a level, so that in flowing the solder gravity will 
 assist in gi\ing the lingnal snrface its proper contour. 
 
 TRIMMING THE INVESTMENT PREPARATORY TO SOLDERING 
 
 It is necessar}', in order that the flame may be readily ap- 
 plied to all essential parts of the crown and the solder read- 
 ily fused where needed, that the surplus investment be re- 
 moved and the investment reduced to the smallest possible 
 dimensions consistent with strength and the protection of the 
 porcelain. 
 
 First, the sides of the investment are trimmed close to 
 the mesial and distal surfaces of the facing, leaving a suffi- 
 cient thickness, however, to protect the porcelain. 
 
 Second, the ends are reduced close to but not so as to ex- 
 pose the incisal edge of porcelain or the dowel at the oppo- 
 site end. 
 
 Third, an opening should be carefully made from one 
 side to the other so as to expose the labial surface of band 
 
 fROWN INVESTED FOR SOLDERING. 
 
 NOTIC^ THE JOINT IS ENTIBELY 
 
 EXPOSED. WHILE PORCELAIN IS 
 
 PROTECTED 
 
 and margin of backing which projects beyond the ridge lap 
 of the porcelain, but not the facing. 
 
 The investment along the sides of the facing and extend- 
 ing down to the labio-cervical opening is now beveled so as 
 to freely expose the entire backing and joint area. The in- 
 vestment next the incisal tip should be removed so that the 
 solder may be freely drawn to the outermost limits of the 
 backing and thus stiffen the gold which forms the incisal tip 
 of the crown. 
 
 By so forming the investment the entire joint between 
 the backing and root cap is exposed to view, so that in flow- 
 ing the solder it can readily be seen when i^erfect union and 
 required contour has been effected. 
 
 REMOVAL OF THE WAX 
 
 The investment, trimmed as described, is cleared of de- 
 bris, the wax warmed and removed with a small instrument. 
 
CROWN WORK 691 
 
 That in the more coustrieted space can be entirely cleared 
 away witli a fine streani of hoijins' water. 
 
 APPLYING THE FLUX 
 
 A thin film of thick borax paste, made by grinding crystal 
 borax with water on a ground glass slab, is now applied to 
 the backing and root cap on those surfaces to be covered by 
 the solder. With a thin wooden spatula or toothpick it should 
 be carried into the constricted V-shaped opening between the 
 ridgelap and the root cap, and along the cervical joint. 
 
 The flux should not be spread on the investment along 
 the margins of the backing, where it can come in contact with 
 the porcelain during the soldering, nor be applied so plenti- 
 fully that it will overflow on these margins when heated. 
 
 Should this occur, fracture of the porcelain is liable to 
 result, due to difference in contractility of porcelain and borax, 
 which, under heat, unite. When an oily soldering paste is 
 used instead of one composed of borax and water, the same 
 care should be observed in keeping it away f i-om the porcelain. 
 
 DRYING OUT AND HEATING THE CASE FOR SOLDERING 
 
 The investment is now set on a sheet of gauze, near the 
 edge or slightly above the Bunsen flame, to gradually drive 
 off the moisture and thoroughly heat it preparatory to sol- 
 dering. 
 
 When dry and thoroughly hot it is transferred to the 
 soldering block, where the blowpipe flame is applied around 
 the base and sides until the investment is red hot, when the 
 solder can be applied and fused. 
 
 DEVELOPING THE LINGUAL CONTOUR OF THE CROWN WITH 
 SOLDER 
 
 It is common practice to cut the solder into small pieces, 
 apply a number of them at a time to the backing, and when 
 fused to discontinue the flame until more is added, then re- 
 apply the flame, continuing this process until the desired lin- 
 gual contour is developed. 
 
 Wliile this method is effective so far as developing the 
 required contour of the crown is concerned, it frequently re- 
 sults in fracture of the facing, due to repeated change of tem- 
 perature and consequent repeated expansion and contraction 
 of the porcelain. 
 
 By far the quickest, most convenient and safest method 
 of applying the solder is to cut it in thin strips about one- 
 eighth inch wide and from three to six inches in length. All 
 
(!!I2 CROWN WORK 
 
 surfaces should bo covered with a tliiu iiliii of ilux before 
 use. One of these sti'ips is clamped in the beaks of the sol- 
 dering pliers, and when the investment is thorona,hly heated 
 and red, the point of the strip is directe(l intn llic deepest 
 part of the V-shaped opening. 
 
 The flame of the blowpipe is now applied to that area, 
 when the solder will be instantly fused. As it settles into the 
 
 joint more of the strip is fed into the molten mass, until the 
 proper contour is developed. 
 
 Special care should be observed in lliickening the back- 
 ing over the incisal tip and also allowing the solder to over- 
 
 THE STIVER BLOWPrPE 
 
 flow the lingual surface of the root cap. When the lingual sur- 
 face of the crown is developed to resemble the natural cingu- 
 lum of the tooth, much better protection will be afforded the 
 
CROWN WORK 693 
 
 gum margin than where this surface presents an inclined 
 plane. 
 
 The blowpipe flame should never be directed against the 
 platinum pins of a facing until the porcelain itself is thor- 
 oughly heated and well expanded. The reason for this is 
 obvious: porcelain is f liable and easily broken; the platinum 
 pins expand quickly when heated, and when highly heated 
 exert great force, within certain limits ; this limit of expansive 
 force is greater than the porcelain can stand without fractur- 
 ing unless itself first expanded. 
 
 The three principal causes of fracture of porcelain facings 
 have now been mentioned, viz., contact with and fusing of 
 borax to the porcelain, expansion of the platinum pins, sud- 
 den changes of temperature or the intermittent application 
 of the flame. 
 
 FINISHING THE CROWN 
 
 After the soldering has lieen completed, the investment 
 should be allowed to cool down gradually, or again fracture 
 of the facing is liable to occur. The investment should be pro- 
 tected against strong, cold drafts of air by placing over it 
 an inverted cup or plaster bowl until the temperature is re- 
 duced to such point that it may be comfortably handled with 
 the fingers. 
 
 The investment is then broken away, the crown examined 
 to see that no accident has happened, and that the desired 
 contour has been developed. Should contour be deficient at 
 any point the crown must be reinvested and corrections made 
 as needed. 
 
 The crown is now pickled in acid to loosen any adherent 
 investment and flux. A convenient method is to boil it in acid 
 in a test tube, after which it should be thoroughly washed 
 to remove the acid. 
 
 The sur])li]s gold can lie economically removed with a 
 file, the filings being caught in the gold drawer or on a sheet 
 of paper. The finer finish is accomplished with engine stones 
 and discs, followed by the use of fine pumice stone first and 
 afterward rouge, applied with felt wheels on the lathe. Every 
 
694 CROWN WORK 
 
 file mark and all scratclios iirodiiccd by the coarser polishing 
 powders must be removed and the metal parts polished as 
 well as the finest piece of jewelry. The cervical margin of 
 the band must be beveled and slightly roimded so that it may 
 not prove an irritant to the gingival tissues or for'm a shoulder 
 for the lodgment of food. 
 
 Too much care cannot be bestowed on the finish of the 
 cervical band margin, for on this, together with restoring close 
 ])roximate contact with tlie adjoining teeth, will depend the 
 future service and comfort of the substitute. 
 
 SETTING THE CROWN 
 
 One of the most essential requirements in the setting of a 
 crown is to thoroughly dry the root and adjacent parts and 
 keep them so until the operation is completed and the cement 
 well set. 
 
 Since the rubber dam cannot be applied, the lip should 
 be raised with a cotton roll to prevent the oral fluids from in- 
 terfering with the immediate and subsequent steps. 
 
 The general moisture is removed from the mucous tissues 
 and root face with pellets of cotton, from the canal with cot- 
 ton on a brooch and small cotton or bibulous paper points. 
 
 Finally, with blasts of air from the chip blower or the com- 
 pressed air point, the parts are thoroughly dried and made 
 ready for the reception of the crown. The crown itself should 
 be dry, clean and free from polishing ]iowder, grease or wax. 
 
 A previously tested crown cement should be mixed to 
 thin-medium consistency and thoroughly spatulated. 
 
 With a root canal plugger, a small portion of the cement 
 is carried into the canal and worked against the sides and to 
 the apex, continuing this until the entire opening is filled. A 
 
CROWN WORK 695 
 
 thin layer should be worked over the face end of the root. 
 The crown cap is now partially tilled with the cement, a little 
 smeared on the dowel and the crown is qnickly pressed into 
 position on the root. 
 
 Heavy but intermittent pressure should be exerted at hrst 
 and afterward steady pressure to force out the excess cement 
 contined within the cap and root canal, and which, if not ex- 
 pelled, would elongate the crown to a greater or less extent. 
 Mallet blows are much less effective in seating a crown than 
 heavy maintained pressure, because the cement being more 
 or less plastic and sluggish and closely confined within the 
 cap, is scarcely affected by heavy, sudden blows, while main- 
 tained pressure causes it to flow as long as there is any open- 
 ing through which it can escape. 
 
 REMOVAL OF THE EXCESS CEMENT 
 
 When the cement has set reasonably hard, which usually 
 requires from fifteen to twenty-five minutes, the excess ce- 
 ment wluch can be removed without danger of disturbing the 
 crown should be cleared away, first with pellets of cotton, fol- 
 lowed by the use of the blunt explorer. When time is limited 
 it is advisable, as soon as the excessive surplus is removed, 
 to dismiss the patient until the cement is thoroughly hardened, 
 or after the lapse of two or three hours, when the removal of 
 the remainder can be effected without danger of loosening the 
 crown. 
 
 When satisfied that every trace of the cement has been 
 removed from beneath the gingival tissues, the jsarts should 
 be syringed with warm normal salt solution, and the gums 
 massaged to restore normal circulation and tone. 
 
 Finally before dismissing the patient a close examination 
 should be made to see that the opposite teeth do not strike the 
 crown in either occlusion or lateral movements. Should such 
 be the case, correction must be made b}^ grinding away the 
 points of contact on either the crown or natural teeth or both, 
 as good judgment dictates. 
 
 SETTING A CROWN TEMPORARILY 
 
 Sometimes it may be deemed advisable to set a crown tem- 
 porarily in order to test its efficiency or for other reasons. 
 This may be done as follows: 
 
 A piece of gutta percha bas(^plate matei'ial is cut and 
 formed into a roll or cylinder which will approximately fill the 
 
l)9G CROWN WORK 
 
 root camil. The riuial, root, and adjoiniug tissues are tlior- 
 oughly dried, the canal moisteend with oil of cajaput, or 
 eucalyptus, the cylinder of gutta-percha is warmed and in- 
 serted in the canal. The crown itself is gradually heated, 
 particularly the dowel, and a blast of hot air from the syringe 
 directed against the gutta-percha. The crown is then forced 
 to place on the root, or when it cannot be perfectly seated is 
 quickly removed and the cause determined. 
 
 The cause may be due to too much material or to the gutta- 
 percha not being sufficiently plastic. Removal of some of the 
 material and the application of more heat, with quick action 
 and heavy pressure, will usually result in success on second 
 trial. 
 
 REMOVAL OF A TEMPORARY CROWN OR A BRIDGE SET WITH 
 GUTTA-PERCHA 
 
 Since the easiest way of removing a crown set with gutta- 
 percha is by the application of heat, and since the heat must be 
 sufficient to soften the gutta-percha, the appliance now to be 
 described will be found most efficient. 
 
 Remove the bulb from a chip-blower. Pass a common 
 twine string, large enough to fit closely, through the nozzle of 
 the pipe, to form a wick. Pour a few drops of alcohol into the 
 pipe and cork the large end. This forms an alcohol lamp, the 
 wick projecting from the small end. Trim the wick short so 
 that it projects but slightly from the nozzle. A flame varying 
 from one-half inch in length to one no larger than a pin-head 
 may be produced, depending on the projection of the wick. 
 
 With this lamp a small flame is applied to the crown. The 
 heat thus applied is transmitted through the dowel to the 
 gutta-percha in the canal, which, when sufficiently softened, 
 will release the crown. 
 
 DIFFERENT METHODS OF APPLYING PORCELAIN FAC- 
 INGS AND REPLACEABLE TEETH IN SINGLE 
 CROWNS, AND DUMMIES FOR BRIDGES 
 
 Porcelain is utilized in various ways, other than that de- 
 scribed, as a veneer or partial crown in single crown work, 
 and bridge construction as well. 
 
 Since a bridge is nothing more or less thau an assemblage 
 of full crowns, combined with partial crowns called dummies, 
 some of the various methods of construction of the different 
 factors of bridges will now be considered. 
 
CROWN WORK S9T 
 
 INTERCHANGEABLE TOOTH FACINGS 
 
 To obviate fracture in soldering and facilitate repairs of 
 facings in crowns or bridges, various forms of interchangeable 
 or replaceable porcelain facings are used instead of regular 
 long pin plate teeth. 
 
 Replaceable teeth and facings of different forms are now 
 procurable and in many cases are useful, not only in repair 
 cases, but are coming into general use in crown and bridge 
 construction. 
 
 The three most common forms of flat back teeth, or fac- 
 ings of this type, are the Steele, the Evslin and the Dimelow. 
 In addition to these, a number of types of partial crowns of 
 the replaceable class, for both anterior and posterior teeth as 
 well, are now available. 
 
 Among these partial crowns may be mentioned the Gos- 
 lee, Gardiner, Merker and posteriors of Steele and Evslin 
 
 STEELE'S INTERCHANGEABLE TOOTH 
 
 This consists of a facing of porcelain and a backing of 
 metal. In the back of the facing, beginning at the ridge lap, 
 a hole extends into the porcelain, toward hut not to, the incisal 
 
 edge. This hole is slotted lingually to receive a projection 
 from the backing. The backing consists of a piece of flat 
 metal plate, to which is affixed a tubular post which enters the 
 hole in the facing, and forms the attachment between facing 
 and crown or bridge. 
 
 APPLICATION OF THE STEELE FACING 
 
 The application of a Steele facing to a central incisor 
 crown, as just described, is as follows : 
 
 The cap havi-ng been constrvicted and in position on the 
 cast, a facing is selected and ground to fit the root cap. The 
 backing is then adjusted and the surplus trimmed to the mar- 
 gins of porcelain, leaving the incisal edge longer than the 
 porcelain. 
 
698 CROWN WORK 
 
 Sliould tlu' (uliular ])(ist ol' tlic hacking- extend beyond tlie 
 porcelain at the ridge laj), it is ground flush witli the latter. 
 
 The facing and backing are now ad,iust(>d to the cap. 
 Sticky wax is applied to the backing and melted against the 
 root cap, being careful to keep it from flowing on the porcelain. 
 
 STEELE FACING WITH BACKING 
 
 TBUUrED AND IN POSITION 
 
 ADJUSTED TO ROOT CAP 
 
 The assembled crown is now renioviMl from the cast and the 
 facing slipped from the backing. 
 
 A thin film of Anti-Flux is applied to backing on that 
 surface against which the porcelain rests. This is necessary 
 to prevent the solder or borax flowing over the backing, as the 
 slightest amount of either, if adherent to this surface, will 
 prevent the facing i^assing to place. 
 
 The metal parts of the crown are now invested and sol- 
 dered as usual. 
 
 To clean the metal structure and remove the borax after 
 soldering, the crown should be heated and dropped in a pickle 
 of 30 per cent H. CI. If boiled, as is usually the case, the metal 
 of which the tube is composed will be corroded or honey- 
 combed. 
 
 The facing is slipped in position on the backing, and the 
 surplus gold reduced with stones and discs. The incisal edge 
 of gold should be continuous with the labial contour of porce- 
 lain for a short distance to afford protection to the latter 
 against incisal stress. When the metal parts are polished, the 
 facing is set in position with cement and the crown is ready 
 for setting on the root. 
 
 STEELE'S INTERCHANGEABLE TOOTH— TECHNIC FOR 
 POSTERIOR CROWNS 
 
 Bicuspid and molar teeth of the Steele type can be em- 
 ployed in crown construction, although they are more often 
 
CROWN WORK 699 
 
 used as dummies in bi'id.ne work. The method of procedure 
 is as follows : 
 
 The root is prepared, a root cap constructed and dowels 
 extendiug into the root canals are fitted and attached to the 
 cap by soldering. At the same time the cap should be stiff- 
 ened by flowing solder over it. Casts should be constructed 
 and mounted on the occluding frame. 
 
 A porcelain tooth of suitable size is selected and ground 
 to proper length, allowing for the interposed backing of gold 
 over the ridge lap. 
 
 The backing is then fitted to the porcelain in the usual 
 manner. To its cervical end is attached an extension of 22 or 
 24k. gold 13'ate, to cover the ridge laj) and extend slightly 
 beyond the buccal margin of the tooth. 
 
 The backed tooth is now set in position on the root cap 
 and waxed in proper relation to the latter, after which the 
 assembled crown is removed from the cast, the porcelain re- 
 moved from position, Anti-Flux applied to the buccal surface 
 of the backing, the metal structure invested and developed to 
 proper contour with solder. By using inlay wax in assembling 
 the crown, the cap and backing may be united and the lingual 
 contour develo]3ed liy the casting method. 
 
 STEELE INTERCHANGEABLE TOOTH, TECHNIC FOR CAST 
 DUMMIES 
 
 A facing is selected and ground to the cast. The backing 
 is then applied and trimmed to correct peripheral outline. 
 
 Inlay wax is now applied to the lingual surface of the 
 backing and the desired contour of the tooth is developed by 
 carving. 
 
 BICUSPID DUMMY CONSIST- 
 ING OP STEELE PACING. 
 BACKING. OCCLUSAL SUR 
 FACE. PARTIAL LINOITAI. 
 CONTOUR DEVELOPED . IN 
 IKL.\T WAX 
 
 RACKING AND WAX WITH 
 STEELE PACING RE- 
 MOVED 
 
 THE DUMMY. MINUS PORCE- 
 LAIN. INVESTED FOR CAST- 
 ING 
 
 The facing is now removed, a sprue former attached to 
 the wax in such manner that when invested the gold will enter 
 the matrix at the highest point. 
 
700 CROWN WORK 
 
 The case is invested and cast t)y usual methods of ijro- 
 cedure. 
 
 CONSTRUCTION OF DUMMIES WITH SWAGED CUSPS 
 
 When it is deemed advisabk> to construct the dummy with 
 swaged occlusal surface the larocedure is as follows : 
 
 A tooth of suitable size is selected, ground and backed 
 as previously described. A cusp is carved in plaster or some 
 medium by means of wliich a counterdie may be secured and 
 a cusp swaged. 
 
 This is trimmed and fitted to the backing, the facing is 
 adjusted and the assembled dummy tested as to its occlusal 
 relations witli the opposite teeth. When satisfactory, the fac- 
 ing is removed, and the metal structure is invested and sol- 
 dered. 
 
 REFLECTING THE BACKING OVER THE CERVICAL MARGIN 
 OF PORCELAIN 
 
 In some cases it may be considered advisable to reflect 
 the extension which is added to the principal backing of a 
 Steele tooth or facing over the gingival margin of porcelain. 
 The object in doing this is to form a socked or gingival cup 
 
 WlLltum lUtlLHjE I U.Ml'USED 
 OF STEELE FACINGS. CEN- 
 TRAL INCISOK KEMOVED 
 
 for the better protection of the porcelain against stress. When 
 this plan is followed the cervical margin of the porcelain 
 should be beveled slightly at the expense of the labial or buc- 
 cal surface. This permits the reflected gold being finished 
 flush with the porcelain without eliminating the shoulder. 
 
 UTILIZING LONG PIN PLATE TEETH FOR REMOVABLE 
 FACINGS 
 
 One of the main considerations in the use of replaceable 
 facings of any type, in addition to ease of repair when frac- 
 tured with use, is to avoid danger of fracture of porcelain dur- 
 ing soldering operations. 
 
 A long pin facing, or ordinary plate tooth, is often util- 
 
CROWN WORK 701 
 
 ized as a removable facing for the same reason that special- 
 ized forms of interchangeable teeth are employed. 
 
 One of the common methods of procedure is as follows: 
 
 The facing is ground to correct form and Ijacked witli gold 
 
 in the usual manner. The pins must be parallel with each 
 
 LONG PIN TOOTH GROtTND. 
 
 BACIUNO ADAPTED ANB 
 
 WAXED IN POSITION ON ROOT 
 
 CAP. FACING 11EM0\"ED 
 
 PROXIMAL VIEW OF RE 
 
 MOVED FACING. SHOWING 
 
 I'INS BENT GIXGIVALLY 
 
 ASSEMBLED BICUSPID DUM- 
 MY. FACING REMOVED. CAR- 
 BON POINTS INSERTED 
 
 other, but not necessarily at right angles to the inciso-gingival 
 plane of the lingual surface of the facing. Usually the pins 
 are bent slightly toward the ridge lap to give them a hook- 
 like contact with the backing. 
 
 LONG PIN FACING GROUND 
 
 AND BACKED FOB BICUSPID 
 
 DUMMT 
 
 FACING BACKED. LINGUAL 
 
 CONTOUR DEVELOPED IN 
 
 WAX 
 
 FACING REMOVED FROM 
 DUMjn'. CARBON POINTS 
 INSERTED THROUGH BACK- 
 ING IN WAX 
 
 The backed facing is waxed in correct relation to its root 
 cap, or if for a dummy its lingiuil contour is developed in 
 wax to the desired form. 
 
 The facing is carefully removed and in the openings in 
 the wax formed by withdrawal of the pins, small pieces of 
 carbon are inserted, the ends of which should project from tlie 
 
702 CROWN WORK 
 
 backing. This is necessary in order that they may be caught 
 in and held by the investment. 
 
 The assembled metal parts are now united by casting 
 or soldering. The carbon points are broken off and that 
 enclosed within the gold is drilled out to receive the pins. 
 
 The facing is then fitted to the metal and when correctly 
 adjusted the pins are slightly roughened and the facing set 
 with cement. 
 
 THE EVSLIN INTERCHANGEABLE TOOTH 
 
 This tooth is made of porcelain in the form of facings for 
 anterior replacements and with fully contoured bucco-occlusal 
 surfaces for posterior replacemeiits. 
 
 A posterior tooth of this type, in its general contour, is 
 deficient on the lingual surface. In this surface a dovetailed 
 sjjace exists for receiving a lug of clasp metal of correspond- 
 ing shape, which forms a part of the metal structure of the 
 crown or dummy, box or socket. 
 
 In this, as in practically all other types of replaceable fac- 
 ings, the porcelain serves as a veneer for obscuring the essen- 
 tial metallic structural parts of a crown or bridge. 
 
 The dovetailed lug which is attached to the socket, and the 
 opening in the porcelain are so related that, in adjusting the 
 two parts together, the facing is not brought into close con- 
 tact with the backing until the two are in nearlv correct rela- 
 
 tion to each other. Stated differently, the facing approaches 
 its normal position or seat against the backing and base of 
 the crown in an inclined direction and does not jam or become 
 tightly wedged until practically seated. For this reason the 
 incisal edge of an anterior facing may be beveled at an angle 
 and the backing adapted accordingly, which, when reinforced 
 with solder, forms a tip or metal protection for the porcelain 
 against stress. 
 
 Backings of 24 k. 34-gauge gold with lugs attached may 
 be procured or tlie prosthetist may attach the individual lug 
 to any gauge and carat of gold he desires to use for the 
 backing. 
 
CROWN WORK 703 
 
 EVSLIN FACINGS— TECHNIC FOR ANTERIOR CROWNS 
 
 Construct the root cap by either direct or indirect method, 
 adapt and solder dowel. Place on natural root, take bite and 
 impression and mount easts on occluding frame. Select fac- 
 ing of suitable form and color and grind to position. Bevel 
 incisal edge of porcelain at an angle of about .35 degs. to lin- 
 gual siirface. The facing should be slightly shorter than the 
 required length of crown to allow for extension of backing 
 over ridge lap and for the thickness of the metallic incisal tip. 
 
 Anneal backing with lug attached and adjust to facing, 
 passing the square end of the lug into the slot incisally. Bur- 
 nish and swage backing directly against the tooth, annealing 
 
 and reswaging until i)erfect adaptation is secured. Trim 
 backing flush with mesial and distal surfaces of facing, but 
 allow it to project slightly beyond both cervical margin and in- 
 cisal edge. 
 
 Apply film of sticky wax over lingual surface of backing 
 while the latter is still on the facing and chill it. This is to 
 prevent distortion of the backing while removing the facing. 
 Heat a piece of stickj^ wax and apply to the labial surface of 
 the facing. This serves as a handle in separating it from the 
 backing. The separation of the facing and backing at this 
 time is necessary to see that the two have not become wedged 
 or jammed by tlie rough edges of the backing left by the file. 
 
 When this test has been carried out the sticky wax is 
 removed from the facing, the latter is returned to the back- 
 ing, the two are set in correct relation to the proximating 
 teeth on the root cap and the backing firmly luted in position 
 with sticky wax." 
 
 The assembled crown is now removed from the model, 
 the facing again removed from its position, and tlie liacking 
 and lug coated with Anti-Flux to prevent the solder from flow- 
 
CROWN WORK 
 
 iiig Oil those surraccs against whicli tlic iiorcclahi comes in 
 contact. 
 
 When the dniiiiny is constructed witli an individnal sad- 
 dle, tile backing should extend over the ridge lap of the facing 
 
 SEGTIONAI, ^•IE^V OF FAf- 
 ING. LUG, AND BACKING 
 
 Arl'EARANCE OF FINISHED 
 CROWN 
 
 to the labial or buccal surface. The disc of gold which forms 
 the saddle is adapted to the alveolar border and extended 
 labially or bucally to meet the backing on these surfaces. 
 When assembled, tlie lingual contour of the dummy is com- 
 pleted with wax. Usually the surface of the plaster cast cov- 
 ered by the saddle is scraped slightly before assembling and 
 waxing the two parts together, to insure firm bearing of the 
 completed dummy upon the ridge when the bridge is perma- 
 nently set. 
 
 EVSLIN TEETH— TECHNIC FOR POSTERIOR CROWNS 
 
 The root cap having been constructed, impression 
 and bite taken, casts secured and mounted on the occluding 
 frame, the construction steps are as follows : 
 
 A posterior tooth of suitable form and color is selected 
 and ground to suitable length. The mesial and distal surfaces 
 
 EVSLIN MOLAR 
 
 should be beveled by grinding from the ridge lap occlusally. 
 This is essential so that the sides of the gold socket may pass 
 along these surfaces without ]:)rodncing unnecessary bulk in 
 
CROWN WORK 705 
 
 the iuterproximate space. Furthermore, the socket iu wliich 
 the porcelain rests can thus be made in boxlike form and will 
 atford better retention for the tooth. 
 
 A backing with lug attached is adjusted and burnished to 
 the porcelain. The surplus is then cut away, the tooth im- 
 bedded, occlusal and buccal surfaces down in moldine in the 
 swaging ring and the backing swaged into close contact with 
 the porcelain. 
 
 Remove the tooth and backing from the swager, flow 
 sticky wax over the backing and separate. Correct any over- 
 hang of the gold margins, return tooth to ])lace and wax back- 
 ing to root cap, building the lingual contour out as desired. 
 
 The assembled crown is now removed from the model, 
 the porcelain removed, Anti-Flux applied to the buccal sur- 
 face of the backing, the case invested, as usual, for soldering. 
 
 The wax is now removed from between the root cap and 
 the socket which receives the liase of the tooth, the case heated 
 
 and solder flowed in to complete the lingual contour of the 
 crown. 
 
 Pickle in acid wash and return the facing to position, 
 being careful not to use much force. If obstructions, as 
 nodules or excess solder, are present, remove them with a file 
 or engine burs. 
 
 The surplus gold at the margins is removed with files, en- 
 gine stones and discs. 
 
 The direction of movement in filing, grinding and polish- 
 ing should always be from the gold toward the porcelain. 
 
 When the metal part of the crown is roughh^ contoured 
 and moderately well smoothed u]), the facing is cemented in 
 place. 
 
 The final polishing on the lathe should be deferred until 
 the facing is cemented in position, or the square margins of 
 the metal next the porcelain will l)e lounded and thus leave a 
 visil^le groove between the two. 
 
TUG CROWN WORK 
 
 EVSLIN TEETH— TECHNIC FOR ANTERIOR DUMMIES IN 
 BRIDGE WORK 
 
 The abutment crowns of the bridge having been con- 
 structed, they are set in position on the roots in the mouth 
 and a bite and an impression secured. The casts are then 
 formed and mounted on the occluding frame. 
 
 Evslin facings of suitable color and form to meet the re- 
 quirements of the case are selected and ground, as when long 
 
 THESE fUTS SHOW PROTECTION AFFORDED INCISAI, 
 
 EDGE OF PORCELAIN. ALSO FORM OF BACKING SOME- 
 
 TIMES EMPLOYED FOR ANTERIOR FACINGS 
 
 pin, flat back facings are used, tlie ridge lap of the facing 
 being ground to fit the irregularities of the border. 
 
 The facing is then backed as for a crown except that 
 usually the backing does not extend onto the ridge lap. 
 
 The extent to which the backing covers the porcelain, 
 however, depends upon the type of dummy bein.g constructed, 
 as it is sometimes extended over the ridge la]) to form a socket. 
 
 INTERCHANGEABLE TEETH 
 
 Removable, replaceahle and hiterchaugeahle teeth of vari- 
 ous forms have been designed for use in crown and bridge 
 work, the object of which is to obviate subjecting the porce- 
 lain to soldering operations and thereby avoid danger of frac- 
 ture from this cause. 
 
 In the use of teeth of this type, the metal structure is 
 built around and adapted to the porcelain, and after comple- 
 tion the teeth are cemented in position. 
 
 A distinction should be made between removable flat bach 
 facings and certain types of removable or replaceahle teeth. 
 A replaceable facing usually has within the body of porce- 
 lain a slotted opening which receives a correspondingly shaped 
 lug of metal projecting from the crown or bridge structure. 
 A replaceahle tooth usually has, in addition to this or some 
 similar means of anchorage, a standardized base composed of 
 planes, so disposed as to aid in resisting displacement under 
 masticatorv stress. 
 
CROWN WORK 707 
 
 A tooth formed with a standardized base of the character 
 described can thus be readily replaced in case of fracture. 
 
 Replaceable teeth represent more nearly the anatomic 
 types of natural teeth than do facings of any class. Not only 
 are the labial surfaces of the anterior teeth represented, but 
 a portion of the lingual surfaces are reproduced, while in the 
 posterior teeth, the buccal, occlusal and a portion of the lin- 
 gual surfaces are developed in porcelain. 
 
 Among the well-known teeth of this type, as well as new 
 forms which have recently appeared, are the Goslee, the 
 Steele and Evslin posteriors, the Gardener and the Merker. 
 A brief description of the Steele and the Evslin teeth has 
 already been outlined. 
 
 THE GOSLEE TOOTH 
 
 This consists of a partially contoured porcelain crown, 
 deiicient in its lingual areas. Within the lingual side, and at 
 
 right angle to the long axis of the tooth, is developed a flat 
 seat. In this seat is a cylindrical opening, extending incisally 
 
 □ 
 
 A GOSLEE INCISOR FACING 
 SHOWING BASAL. SEAT OPEN- 
 ING FOR DOWEL AND FLAKING 
 LINGUAL SURFACES 
 
 or occlusally into the body of the tooth, for the reception of 
 a dowel which forms a part of the metal structure. The sides 
 
708 CliOWN WOriK 
 
 Hare (Uilwai'dly, and (iccliisally or iiii-isall.\ , I'l-oiii tlu* seat. 
 Tji the hic'usiiids and iiidlars, the Hai'iiii;- sides tcniiiiiatc within 
 
 and form a depressed shoulder just beneath the mesial, distal 
 and lingual surfaces of the crown. 
 
 TECHNIC OF APPLICATION OF THE GOSLEE TOOTH IN 
 CROWN WORK 
 
 Prepare a root cap, preferably by the indirect metho<l, 
 using 36 gauge platinum or pure gold i)late. By forming a 
 depressed area in the central portion of the root, the walls of 
 which are but slightly divergent, the root periphery may be 
 decidedly beveled so that in the completed crown no peri- 
 pheral shoulder will be present. In forming the cap, it is 
 swaged into the depressed area and thus forms a shoulder 
 for guiding the cap to and holding it in correct position on the 
 root. 
 
 Through openings in the cap, dowels are introduced into 
 the root canals. The relation between the dowels and cap is 
 secured and their subsequent attachment b>" soldering is ac- 
 complished by methods previously described. At the time of 
 attaching the dowels, high grade solder or 22k. plate should 
 be flowed over the root cap to stiffen it and till the depressed 
 central area. 
 
 The cap, with dowels soldered in place, is now returned to 
 the root and the perijiheral margin of the band corrected by 
 burnishing. 
 
 An impression and bite or a bite-impression is secured, 
 removing it from the mouth with the face bow. 
 
 A film of wax is flowed over the dowels and inside the 
 root cap to facilitate removal of the cap from the cast later on. 
 
 The cap is placed in position in the imjiression and casts 
 developed and attached to the occluding frame. 
 
 A Goslee tooth of suitable size is selected and ground, if 
 necessary, to meet requirements. 
 
CROWN WOJtK 
 
 It is then imbedded, occlusal end down, in modeling com- 
 pound, in the swaging ring. The surfaces to which the gold is 
 to be applied should be above the ring margins, so that the 
 rubber in the swager mav force the gold against all areas. 
 
 GOSLEE TOOTH INVESTED IX SWAGING RING. I'REPARA 
 
 TORY TO ADAPTING SOCKET. TOOTH SET IN A DIA(!ONAI. 
 
 POSITION FOR SWAGING 
 
 A disc of 36 g. pure gold, or platinum, somewhat larger 
 than the areas to be covered, is applied to the crown base, and 
 with finger pressure and burnisher adapted to the porcelain. 
 
 When reasonably close adaptation has thus been secured 
 and the excessive surplus removed, final adaptation is de- 
 veloped by swaging. 
 
 GOSLEE TOOTH SET IN UPRIGHT 
 POSITION FOR SWAGING SOCKflT 
 
 BACKING OR SOCKET ADjiPTED 
 
 TO GOSI.EE TOOTH. DOWEL IN 
 
 POSITION 
 
 An opening in the gold socket is now made for the re- 
 ception of the short dowel, which may be of regular form 
 and headed on one end, or a piece of 14 g. clasp metal wire, 
 sufficiently long to project slightly beyond the socket, may 
 be used. With dowel in position, the cap is reswaged. 
 
CKOWN WORK 
 
 Wax is applied in the ddwcl and ai;aiiist tlic gold, the two 
 removed and nuited witli liish gvade solder. The gold should 
 also be stiffened l)y flowing a film of solder over its general 
 surfaces, hut not nloiig the margins. 
 
 ^M 
 
 METAL SOt'KET. SWACKIi, Willi liOWEL ATTAIIIEI). 
 
 GOSLEK TOOTH. FORM (IK HOOT CAP ISIAl.NV KM- 
 
 I'l.OYED KOIl MllLAR TEETH 
 
 The socket is now returned to the porcelain for final 
 swaging, after which the tooth is removed from the moldine. 
 
 The tooth in its socket is now adjusted to the root ca]i and 
 waxed in position. 
 
 Previously, however, the root cap is heated slightly to 
 soften tlie wax around the dowel, removed, freed from wax, 
 and returned to position on the cast. 
 
 TROWN WITH SOIKET, All 
 
 .USTED TO miOT CAP. RE.II)\ 
 
 FOR WAXIXr, TOfiETIiER 
 
 The assembled crown is waxed to the desired contour, 
 removed from the cast, tlie porcelain removed from its socket 
 and the metal structure invested for completing the required 
 contour, either by soldering or casting. 
 
 The Goslee tootli is capable of a wide range of applica- 
 tion in bridge work, when sufficient space is present in which. 
 
CROWN WORK 
 
 r.osi.EE nRinnic ix position- on cast 
 
712 CROWN WORK 
 
 in addition to the porcelain icplaccint'iits, a ri^id iiii'tal stnie- 
 ture may be introduced. 
 
 The individual saddle is ol'tcn a]i|ilicil in connection with 
 teeth of this type to very n'reat hygienic advantanc 
 
 THE GARDINER REPLACEABLE TOOTH 
 
 This tooth is supplied for both anterior and posterior 
 replacements. In form, it is somewhat novel, having a 
 broader base than occlusal area. 
 
 Instead of liaving an opening within tlie body of the 
 crown for the reception of a lug, the l)ase of porcelain pre- 
 sents a square or rectangular projection, which is received 
 by and enclosed within a corresjiondingly shaped depression 
 in the socket. 
 
 To give the crown additional stability and resistance to 
 stress, the base is composed of flat planes, placed at varying 
 
 CERVICAI. \IEW. SHOWING DIS- PROXIMO-CERVICAL \1EW OF 
 
 POSITIONS OP THE VARIOUS OAKDINER TOOTH. SHOWING 
 
 BASAL, PLANES ANCHORAGE LUG OF PORCELAIN 
 
 angles. These planes are so disposed as to tend to seat the 
 crown firmly in its socket under masticatory stress. 
 
 Because of the extremely constricted bulk of porcelain 
 entering into the construction of the tooth, it can be applied 
 in many eases in limited spaces without requiring appreciable 
 modification of form. 
 
 The planes are so disposed as to give uniformity of thick- 
 ness to the occlusal body of porcelain. The projecting lug is 
 placed directly under the lingual cusps, thus giving support 
 to an otherwise weak area of porcelain. 
 
 TECHNIC OF APPLICATION OF THE GARDINER TOOTH 
 
 The root cap is formed by any of the previously described 
 methods, an impression secured, casts developed, and mounted 
 on the occluding frame. 
 
CROWN WORK Ti:; 
 
 A tooth of 8uital)l(' form and color is selected and titted 
 to the root cap, due allowance beiiij;- made in its lengtli for 
 the interposition of the socket. 
 
 The tooth is then imbedded, occlusal end down, in mold- 
 ine, in the swaging ring, and a 36 gauge i)ure gold or platinum 
 socket developed by burnishing and swaging. 
 
 When adapted, the margins of the socket are trimmed so 
 as to form a collar around the entii'e peripheral margins of 
 
 the tooth, as should be the case in practically all types of 
 replaceable teeth. 
 
 To prevent distortion in handling and soldering, a film 
 of high grade solder should be flowed on the under, or cervical, 
 areas of the socket, but not over tlie peripheral margins. 
 
 When this plan is adopted, the margins should be rebur- 
 nished to the porcelain before investment. 
 
 The socket, with crown in position, is now adjusted to the 
 root cap, the two united with wax, the assembled crown re- 
 moved from cast, the porcelain removed from socket and the 
 metal parts invested for soldering or casting. 
 
 APPLICATION OF THE GARDINER TOOTH IN BRIDGE WORK 
 
 Teeth of suitable form and width are selected to fill the 
 space between tlie abutment supixirts. Sockets are formed 
 
 LABIAL VIEW O^F IIETAL 
 STRITTIRK OF BRIDGE 
 
 in the manner described. These should be stitTened 
 with a solder or plate that will not fuse in the final assembling 
 and soldering of the bridge. 
 
CROWN WOUK 
 
 Before pennaiieiilly altacliini;' ]i()rcelaiii teeth to their 
 sockets with eenieiit. the surfaces to he covered hv the hitter 
 
 OUT SHOWING MANXEB OF 
 PLANOINi; THE METAI, SOCKETS 
 TO INCREASE PORCELAIN AN- 
 CHORAGE 
 
 should be etched with iiydro-tiuoric acid, or tlie glaze removed 
 with discs. 
 
 THE MERKER REPLACEABLE TOOTH 
 
 This tooth, comparatively new, possesses two points of 
 interest. The base is com]iosed of two flat planes disposed at 
 
 PBOXIMAL VIEWS OF MERKER ANTERIOR 
 
 AND POSTERIOR TEETH. SEATED ON 
 
 METAL BASES 
 
 right angles to the long axis of the tooth. A small, rather 
 deep opening in each plane extends occlusally for the recep- 
 
CROWN WORK 
 
 715 
 
 tiou of two iridio-phitiiiiiin anchor dowels, whicli, during con- 
 stnictive stages, are adjusted to llie metal socket. 
 
 ^^^l 
 
 ANTERIOH BRinnii COML'OSEl) l)F MKRKElt 
 REPI.ACEARLE TEETH. TWO CENTRAL IN- 
 CISORS OF WHICH ARE REMOVED FROM 
 POSITION 
 
 The application of tliis e 
 is practically identical to tin 
 crown. 
 
 iwn in crown and bridge work 
 steps outlined for the Goslee 
 
 THE DIATORIC USED AS A REPLACEABLE TOOTH 
 
 Diatoric ])osterior teeth are often nsed as replaceable 
 teeth in bridge structures. When utilized for such purpose 
 the basal periphery is usually reduced so as to permit the 
 
 POSTERIOR IMlllMlE FETTED WITH DIA- 
 TORICS AS REPLAC'EAm.E TEETH. A 
 I.1)N(i PIN. CUSPID PLATE TOOTH AP- 
 PLIED AS A REPLACEABLE PACINC, 
 
 formation of a collar around the socket. In addition to the 
 anchorage afforded by the ]ieripheral collar, during the swag- 
 ing of the socket, the gold is carried into the central opening 
 of the crown base. This forms a projection on the metal 
 
71U CROWN WOKK 
 
 structure and fulfills the jjurpusc of a dowel. In some cases 
 .short, grooved dowels are adapted to the socket, as in the 
 Goslee crown. 
 
 FULL CONTOURED PORCELAIN CROWNS 
 
 Crowns composed of porcelain and metal, although ad- 
 mirably adapted to and indispensable in some cases, are fre- 
 quently deficient in esthetic effects, the tinge of porcelain being 
 adversely affected by the presence of the metal. 
 
 To overcome this very decided objection, full contoured 
 porcelain crowns are very often used when conditions as to 
 mesio-distal and occluso-gingival space will jjermit. 
 
 Crowns of this type are supplied by the manufacturers, in 
 great variety of forms and shades, and when well selected and 
 skillfully applied to natural roots, are not distinguishable 
 from natural teeth. 
 
 Full contoured porcelain crowns may be divided 
 into two general classes, viz., fixed doivel crowns and detached 
 dowel crowns. The principal advantage of a detached dowel 
 crown over one having a fixed dowel is that the porcelain base 
 of the former can be readily adapted to the root face, the 
 absence of the dowel permitting unrestricted grinding on 
 areas that interfere with close peri])heral adaptation. 
 
 FIXED DOWEL CROWNS 
 
 The Logan, Twentieth Century and Johnson tJc Lund are 
 types of the attached dowel crown, the dowel l)eing enclosed 
 
 vAKioi s \ir:«.s OF tiii: r.iicAN 
 
 within the body of porcelain, and the latter fused around it. 
 Since the technic of application of crowns of this type is sim- 
 ilar, a description of one will answer for all, whether plain 
 or combined with a root cap or cast base. 
 
CROWN WORK 71? 
 
 TECHNIC OF ADAPTING A PLAIN LOGAN CROWN TO A 
 NATURAL ROOT 
 
 It will be assumed that the apex of the root to be crowned 
 has been sealed with a permanent tilling". 
 
 The remaining portion of the natural crown is reduced by 
 means of stones and Ottolengni root facers, slightly beneath 
 the gum margin, being careful while doing so to avoid un- 
 necessary injury of the soft tissues. 
 
 The root canal is iirst enlarged with graded sizes of 
 round burs as previously described, omitting the use of No. 
 
 10 and substituting therefor a tissure bur, the diameter of 
 which is slightly larger than the mesio-distal thickness of the 
 dowel, next the crown base. 
 
 By means of the fissure bur the canal is enlarged labially 
 and lingually sufficiently to receive tbe dowel at its greatest 
 diameter, while the mesial and distal dentin walls of the root 
 are not materially reduced and consequently weakened as is 
 the case when a taper reamer is emplo^^ed. 
 
 From a stock of crowns one of suitable form and color is 
 selected. In size it should be slightly longer than required, 
 since both base and incisal edge must be modiiied by grinding, 
 the first to secure necessary adaptation, the second for esthe- 
 tic reasons. The width of the crown should be sufficient to 
 afford strong knuckling contact with proximating teeth. The 
 periphery of the crown base should slightly exceed that of the 
 root face, since a subsequent step reduces the excess of porce- 
 lain until it coincides with the root periphery. If too small, a 
 shoulder is formed which cannot be obliterated, the root pro- 
 jecting beyond the crown base. 
 
 ADAPTING THE CROWN TO THE ROOT 
 
 The crown is now applied to the root and the points re- 
 quiring gross reduction are removed with suitable stones. 
 Close adaptation is developed by interposing a disc of carbon 
 
718 CRCnVN WCJKK 
 
 paper between the crown l)asc and root face to mark the high 
 points. These are groiiml away and the steps repeated until 
 close 23eripheral adajitalion between crown and root is secured. 
 
 Care should be observed while making these tests to see 
 that the crown is in correct alignment labio-lingually, which 
 may be done by bending the dowel. 
 
 When close adaptation of crown base to root face has 
 been developed, the incisal edge or other areas of the crown 
 are modified with stones and discs, to coincide with tlie type 
 
 LOGAN CROWN APPLIED TO 
 ROOT BEFORE ADAPTING TO 
 ROOT PACE HAS BEEN ACCOM- 
 PLISHED 
 
 CARBON PAPER INTERPOSED 
 
 BETWEEN CROWN BASE AND 
 
 ROOT FACE. TO DISCLOSE 
 
 POINTS OF INTERFERENCE 
 
 of proximating teeth. When these show wear or ridged sur- 
 face markings, similar surfaces and markings should be de- 
 veloped on the crown. 
 
 Sometimes the jiroximating natural teeth show unusual 
 colors in or beneath the enamel, and which cannot be removed 
 by any means employed. The setting of a porcelain crown 
 or replacement of any type between teeth so marked, unless it 
 is of closely corresponding color, is unsightly. Porcelain 
 stains, both oil and water colors, are procurable, by means of 
 which a tooth or crown can be made to match the most unusual 
 shades found in natural teeth. The technic of application of 
 such colors is simple. The tooth to be stained is thoroughly 
 cleansed and washed in alcohol, a pigment of the desired 
 shade is mixed with water or one of the essential oils as cloves 
 or glycerin, and applied with a small brush by painting it 
 over the surfaces or stippling, the degree of color being de- 
 pendent upon the layer of pigment applied. 
 
 When applied, the colors should be slowly dried, moderate 
 heat accellerating the evaporation of the liquid. It is then in- 
 troduced in the furnace and vitrified, the tooth resting on a 
 bed of pulverized silex, on the slab, and face upward. The 
 colors glaze at a temperature varying from 1100 degs. F. to 
 
CROWN WORK 719 
 
 1500 degs. F. A little experience with these stains will en- 
 able the prosthetist to produce most beautiful esthetic results. 
 In case a suitable shade of Logan or any of the types of 
 crowns mentioned cannot be procured, the.y should be stained 
 to coincide with the colors observed in the natural teeth. 
 
 SECURING PERIPHERAL ADAPTATION OF CROWN BASE 
 TO ROOT 
 
 The final step in adaptation consists in removing the ex- 
 cess or overhang of porcelain over the root, and line the two 
 peripheries up until they form continuous surfaces. The steps 
 are as follows: 
 
 A disc of white baseplate gutta percha, slightly larger 
 than the crown base, is punctured in its center and passed 
 over the dowel and against the porcelain. Moistening the sur- 
 
 GlITTA PERCHA INTERPOSED 
 BETWEEN CROWN BASE AND 
 ROOT FACE TO DISCLOSE EX- 
 TENT OP PROJECTING PORCE- 
 LAIN OVER ROOT MARGINS 
 
 face of the disc next the crown base with oil of cajaput will 
 cause the gutta percha to adhere flrmlv to the porcelain. 
 
 The crown and disc are warmed and the crown forced to 
 place on its root. Under pressure, the gutta percha being 
 forced against the root, an impression of not only the face but 
 of the periphery as well is secured. A blast of cold air 
 directed on the disc will chill it so that removal can be ef- 
 fected without distortion. If the steps have been properly 
 carried out a distinct impression of the root periphery will 
 be seen in the gutta percha. 
 
 A coarse, large size engine stone, running at a high 
 speed, is lightly applied to the surplus gutta percha, and the 
 latter removed until the stone comes in contact with the pro- 
 jecting shoulder of porcelain. The grinding is continued until 
 the porcelain is reduced to the peripheral margin of the root 
 
720 CIJOWN WORK 
 
 as indicated in the gutta perciia impression. During the grind 
 iiig [)roeess tlie crown and disc slionld he inunorscd in cold 
 water from time to time to ol)viat(> distortion of the gntta 
 perclia from frictional heat of the stone. 
 
 During lirst grinding tlie prosthetist shouhl not attempt 
 to develop correct axial contour to the crown, but merely to 
 
 ATPLICATION OK STONE TO 
 
 RKMOVE EXCESS PERITHERAI. 
 
 PORCELAIN 
 
 remove tlie projecting shoulder, after which the gutta perclui 
 may be removed and axial contour developed with suitable 
 stones. The tinal polish on surfaces which have been ground 
 and disced, is accomplished with putty powder, applied with 
 a soft wood or hard felt wheel, running at high speed. 
 
 The crown, having been ground to correct outline form, 
 its base shaped to coincide with the root periphery, its sur- 
 
 faces polished, and, if necessary, stained, it is ready for 
 mounting on the root. 
 
 SETTING THE CROWN 
 
 Cotton rolls should be jjlaced under the lip or in such 
 location as to guard against moisture during the setting of 
 the crown. The root canal and root face should be thoroughly 
 dried with cotton points and warm air. Cement of medium 
 consistencv is thoroughlv mixed and worked into the root 
 
CROWN WORK 721 
 
 canal and applied oxer the root face. The dowel and crown 
 base is also covered with a thin tihn, and if a depression is 
 present in the base of the crown it shonld also he filled. The 
 crown is now set in position, considerable force l)eini;- recpiired 
 to seat it and expel the excess cement. 
 
 Pressiire should lie maintained upon the crown until the 
 cement has set, which usually requires from eight to ten min- 
 utes. Further time should he given the cement to thoroughly 
 harden before removing the peripheral surplus. A small, 
 angular blade instrument like a gold knife, used in finishing 
 the margins of gold fillings, can be used in removing the sur- 
 plus cement which should be cut or shaved rather than broken 
 from along the joint. 
 
 When loosened and the particles ai'e removed as well as 
 can be witli cotton and pliers, the gum tissues should be 
 syringed with warm water and the crown tested as to its in- 
 cisal or occlusal relation with opposite teeth. If satisfactory 
 the patient is dismissed with instructions to avoid subjecting 
 the crown to any stress for several hours, in order that the 
 cement may not be disturbed until thoroughly crystallized. 
 
 THE BANDED LOGAN CROWN 
 
 The technic of construction of a l)anded Logan crown is 
 as follows: A root cap is constructed by methods previously 
 outlined under the heading, "Construction of a Porcelain 
 Faced Crown" (page 641). The enlargement of the root canal 
 for the reception of the rectangular dowel of the Logan crown 
 is essentially the same as detailed for a plain Tjogau crown. 
 
 ADAPTING THE LOGAN CROWN TO THE ROOT CAP 
 
 Before jierforating the root cap for the reception of the 
 dowel the root canal should be enlarged and the crown adapted 
 to the root face by grinding. The lingual side of the crown 
 base sliould he reduced to form a V-sbaped space, which later 
 on is filled with solder. 
 
 The general ada]itation of the crown to root face having 
 been developed, the root caj) is set in position on the root 
 and with a burnisher indented to indicate the location and ex- 
 tent of the opening for dowel. A series of small holes can 
 be drilled through the cap while in position on the root, or it 
 can be removed and the holes punched with plate punch. In 
 either case the several holes are connected by passing a fine 
 fissure bur through the intervening divisions. 
 
722 
 
 CROWN WORK 
 
 The dowt'l is now forced through the more or less irregu- 
 hir slot, the excess gold being forced into the entrance of the 
 root canal, the margins of gold thus fitting tightly against the 
 dowel. 
 
 PREPARED ROOT WITH CAP. 
 
 NOTICE FORM OF OPENING IN 
 
 CAP REQUIRED FOR DOWEL 
 
 CROWN liESTINO (IX ROOT CAP. 
 DOTTED LINE SHOWS LINGUAL 
 REDUCTION OF PORCELAIN RE- 
 QUIRED 
 
 A disc of gold, slightly larger than the crown base, is 
 perforated with a corresponding rectangular slot, placed on 
 a large corjv and the dowel forced through it until the crown 
 base rests upon the disc. By repeated burnishing and an- 
 nealing the disc is closely adapted to the porcelain. 
 
 The i^eripheral excess of the disc is removed, close to, 
 but not exactly even with the crown periphery, a slight sur- 
 
 plus being necessary to insure the solder being drawn out to 
 full contour. 
 
 The cap, disc and crown are now assembled on the root 
 and their relation noted. Particular attention should be given 
 the labial alignment of the crown and band. Wlien the crown 
 sets to the lingual of the labial band surface, it may be brought 
 forward by bending the dowel to the lingual and extending 
 the slot in the cap to the labial, it being necessary in some 
 cases to ream the root canal also for the accommodation of 
 the dowel. When the crown extends to the labial of the band 
 
CROWN WORK 
 
 surface and its labial aligiinient is approximately correct, the 
 solder ma.y be drawn through so as to till the space between 
 the disc and labial band surface, and the gold and porcelain 
 
 SECCRING RELATION BETWEEN 
 
 CBO\VN. DISC. AND ROOT CAP. 
 
 \VITH WAX 
 
 dressed smoothly to form a continuous surface in the final 
 finishing of the crown. 
 
 Two thicknesses of gold plate, the disc and cap top, are 
 interposed between the root face and crown base. Both of 
 these may be reduced somewhat to bring the crown closer to 
 the root, and lessen the display of gold on the labial surface of 
 the finislied crown. 
 
 ASSEMBLING THE SEVERAL PARTS OF THE CROWN 
 
 The cap, disc and crown having been fitted in correct rela- 
 tion to each other on the natural root, they are assembled as 
 follows : 
 
 The crown and disc are removed, all of the parts dried, 
 sticky wax is a])plied around the dowel and a,gainst the disc 
 and softened with a hot spatula. The crown is then forced 
 
 THE ASSEMIil.ED PARTS RE- 
 MOVED, READY FOR INVEST- 
 MENT 
 
 against the cap, the inter]iosed wax pressing the cap against 
 the root, and the disc against the crown base. AVlien the wax 
 is chilled, the three parts, now firmly united, are removed from 
 
724 CKOVVN WORK 
 
 the root, tlie surplus wax trimmed away and auy openings 
 between cap and disc tilled in with wax, when tlie crown is 
 ready for investment. 
 
 INVESTING THE BANDED LOGAN FOR SOLDERING 
 
 The investment of a banded Logan crown for soldering 
 is essentially the same as the investment of a porcelain-faced 
 crown. The joint surfaces between disc and root cap must 
 be entirely exposed to prevent the confinement of air in con- 
 
 L-RO\VN INVESTED FOR SOLDER- 
 ING. NOTICE SMALL WEDGE OF 
 METAL TO BE INSERTED BE- 
 TWEEN ROOT CAP AND DISC 
 TO PREVENT DISPLACEMENT OF 
 THE LATTER IN SOLDERING 
 
 stricted spaces, and further, so that in soldering it may read- 
 ily be seen when the joint is filled. 
 
 When the investment has hardened, the surplus trimmed 
 away, and the joint surfaces freely exposed, the wax is re- 
 moved by pouring a fine stream of boiling water into the space. 
 Care should be taken to remove every particle of wax, for if 
 any is left and flux is ajjplied, it will act as a carrier for the 
 latter, for when heat is applied the wax will melt and pass 
 beyond the gold surfaces and onto the porcelain, thus invit- 
 ing fracture of the crown. 
 
 SOLDERING THE CROWN 
 
 The joint areas to be soldered are covered with a thin film 
 of thick borax paste, a thin piece of wood, as a delicate, wedge- 
 shaped toothpick, being most useful in introducing it in con- 
 stricted spaces. 
 
 When fluxed, the invested case is set on a gauge, over a 
 Bunsen burner, and thoroughh^ heated, until the base of the 
 investment is red, when it may be removed to the soldering 
 block and the blow-pijie flame aj^plied to bring it to suitable 
 temperature for soldering. 
 
 The solder, in the form of a long strip, is applied in the 
 
CROWN WORK 725 
 
 deepest part of the joint area, and as it melts is fed into tlie 
 fused mass lantil proper contour is attained. 
 
 To obviate the tendenoy of the disc being drawn away 
 from the crown base by the contraction of the solder in cool- 
 ing, a wedge of plate metal should be inserted between the 
 cap and disc, before placing the case on the Bunsen burner. 
 
 FINISHING THE CROWN 
 
 When cooled, tlie investment is broken away, the crown 
 placed in a test tube and boiled in a jjickle of 25 per cent H CI, 
 
 after which it is finished in the usual manner with stones and 
 discs, the final polishing being accomplished with fine pow- 
 ders on the lathe wheel. 
 
 THE DAVIS CROWN 
 
 The Davis is a fully-contoured porcelain crown, having a 
 central cavity within its base for the reception of an anchor- 
 age dowel. 
 
 The dowel, which accompanies the crown, and of which 
 there are varying sizes, consists of a pin having a shoulder 
 
 SECTIONAL VIEW OK DAVIS CROWN BEFORE AND 
 AFTER THE BASE HAS BEEN MODIFIED. SPECIAL 
 CARE MUST BE OBSERVED TO PRESERVE THE SHOUL- 
 DEIJ DEPRESSION IN CROWN BASE FOR RECEPTION 
 OF DOWEL COLLAR 
 
 near the crown end. From the shoulder, one portion tapers 
 apically for insertion in the root, while the other is parallel 
 sided for insertion in the crown base. The dowel is grooved 
 
726 ("ROWN WORK 
 
 in several places tlirouniiout its Iciintli t(» at'i'ord better anchor- 
 age within the cement. From 13 to ](j gauge iridio-platimun 
 or clasp metal wire may be used as dowels if desired. 
 
 There are three general methods of applying crowns of 
 this type to the roots of natural teeth, the crowns so applied 
 being designated as plain, cast base, and ha-mled. 
 
 APPLICATION OF THE PLAIN DAVIS CROWN 
 
 A Davis crown without cap or metal base may l)e applied 
 to the I'oot of a tooth in several ways, the following of which, 
 if carefully carried out, will yield good results. After the 
 root has been properly treated and filled, the remaining por- 
 tion of natural crown is reduced slightly beneath the gum 
 margin. 
 
 The root face should usually be given a distinct labio- 
 lingual convexity sufficiently marked to guide the crown base 
 to position without any tendency to rotate. 
 
 ROOT REAMKIi 
 
 DOWEL IN LANAL 
 
 The root canal is opened up first with small burs and 
 afterward enlarged with a reamer corresponding in taper with 
 
 the dowel. To avoid excessive enlargement of the root canal, 
 the dowel should lie inserted from time to time and tested as 
 to closeness of adaptation to the canal walls. The shoulder 
 
CROWN WORK 727 
 
 should rest s(iiiart'ly upon the root face, while the sides of the 
 dowel lit closel}' within the canal. This latter requirement, 
 however desirable, cannot always be realized, it being neces- 
 sar.y at times to incline the dowel in some direction to bring 
 the crown in alignment with proximating teeth. 
 
 A crown should be selected slightly longer than required 
 and with base a little larger than the root face. 
 
 The dowel is now remo\-ed from the canal and the crown 
 base adapted to the root, first removing the grosser points of 
 contact with moderately coarse stones. 
 
 Close adaptation is developed by returning the dowel 
 to the root canal, placing a disc of carbon paper over it and 
 applj-ing the crown to the root face, the interposed carbon 
 indicating the points of interference. 
 
 In all of these tests, care should be taken to hold the 
 crown in correct alignment with the proximating teeth be- 
 fore applying pressure against the carbon ]3a])er. 
 
 The points indicated on the base of the crown by the car- 
 bon are ground away and the tests repeated until close adap- 
 tation, particularly peripherally, is obtained. 
 
 In some cases it may lie found necessary to hem\ the 
 dowel slightly to bring the crown into correct alignment with 
 the proximating teeth. In other cases an offset dowel may be 
 
 THREE SIZES OF OFFSET DOWELS 
 
 required, and again it may be necessary to ream the canal 
 wall away, thus permitting the dowel to move liodily, in the 
 direction indicated. 
 
728 CHOVVN WORK 
 
 Special care sliould lie cihscrvcd to sec that tlic slidulder 
 of the dowel rests in tlic depression in tlie crown liase. When 
 it fails to rest within the dejjression in the i)orcelain designed 
 for it, the attachment of crown to dowel will be weakened 
 because of the shorteninn- of the latter. 
 
 REDUCING THE PERIPHERAL SHOULDER 
 
 Apply a disc of white baseplate gutta percha to the crown 
 base, having first moistened the disc with oil of cajaput and 
 warmed the porcelain slightly to develop adhesion. Perforate 
 the disc in its central area to allow the dowel to pass through. 
 
 PLAIN DAVIS. AD.iTTED TO 
 ROOT PAl'E, EXCESS PERIPH- 
 ERAL SHOULDER NOT YET RE- 
 MOVED 
 
 Moisten the face end of root with water. Direct a blast of 
 hot air on the gutta percha and force the crown to place. A 
 few drojis of cold water will chill the gutta percha, and on 
 removal of the crown it will adhere to and come away with 
 the latter. 
 
 The excess porcelain is now ground away to the line of 
 root periphery as indicated in the gutta percha impression. 
 The steps are similar to those of correcting the base of a 
 plain Logan crown. (See page 719.) 
 
 GENERAL MODIFICATION OF THE CROWN BY GRINDING 
 
 The incisal or occlusal relation of the crown is tested and 
 any modification as to length or general contour corrected. 
 All surfaces so modified should be polished with tine discs, 
 followed with putty powder on the lathe wheel. 
 
 SETTING THE CROWN 
 
 The crown, dowel, root face and canal are thoroughly 
 dried. A mix of cement of medium consistencv is made and 
 
CROWN WORK 
 
 introduced in the canal and in tiie opening in crown, after 
 wliicli more is added to the crown base. The crown is now 
 
 forced to place and held iirnily until the cement has liardened, 
 when the surplus is carefully removed. 
 
 THE DAVIS CROWN IN BRIDGE WORK 
 
 The Davis crown can often he aiiplied to advantage in 
 bridge work. When so utilized, the base of the crown selected 
 for the dunnny must be reduced sufficiently to give space for 
 
 S\\Ai;lXt: DISl' AGAINST CROWX BASK AND IIOXVKL COLLAR 
 
730 
 
 CROWN WORK 
 
 ROOT CAPS WITH PERrENDICULAR RIBS, DESIGNED TO UNITE WITH CORRESPONDING RIBS 
 OF DUMMY SOCKET. FIRST VIEW REMOVED. SECOND VIEW IN POSITION 
 
 the metal structure. It is also advisable to groove the prox- 
 imating surfaces of crowns and swage base caps or sockets, 
 the sides of which are conformed to and tit within the prox- 
 imal grooves. These perpendicular ribs add greatly to the sta- 
 
 IXTERPROXIMAL EXTENSIONS. 
 INOISAIJA'. OF GOLD IN SMALL 
 URIDGE STRUCTURE FORMED BY 
 GROOVING DAVIS CROWNS ON 
 THEIR MESIAL AND DISTAL 
 SURFACES. OB.IECT, TO RESIST 
 TENDENCY OF CROWNS TO TIP 
 BUCALLY OR LINGITALLY UNTJER 
 STRESS 
 
 THE CO»n"LETED IiniDGE 
 
 READY FOR PERMANENT 
 
 SETTING 
 
 bility of the i^orcelain, tending, as they do, to resist torsional 
 strain. The principal anchorage is secured by means of short 
 dowels set within the sockets, to whicli they are attached dur- 
 ing the consti'uctive stages of the individual dummies. 
 
 3USTI CROWN SHOWING CRESCENT OPEN- 
 ING FOR DOWEL. ALSO CROWN WITH 
 DOWEL IN POSITION 
 
CROWN WORK 731 
 
 THE CAST BASE DAVIS CROWN 
 
 The prostlietist who cau grind a perfect joint between 
 crown base and root face will find only occasional need for 
 interposing a cast base between crown and root. 
 
 A cast base as ordinarily constructed neither obviates 
 splitting of the root nor displacement of the crown under 
 stress. 
 
 The insertion of short dowels, of iridio-iilatinum, in lin- 
 gual areas of the root face, to the mesial or distal of the root 
 canal, or beveling the lingual peri))hery of the root so that the 
 projecting lip of the cast base may engage with it, will largely 
 reduce the tendency of a root to split under stress. 
 
 These and other similar means of obviating root splitting, 
 although simple and efficient, are often ignored in the class of 
 work under consideration. 
 
 Cast bases are most strongly indicated in those cases 
 where consid(>ral)le loss of root structure has occurred, and 
 when the fitting of a peripheral band would be difficult, if not 
 impossible. 
 
 CONSTRUCTION OF A CAST BASE DAVIS CROWN 
 
 After tlie apex of th<' root is filled the remaining portion 
 of the natural crown is remo\-ed. In case the crown has been 
 
 ROOT I'REl'ARED WITH IN- 
 SIDE SHOULDER DEPRES- 
 SIOX. SHOWING LABIAL V- 
 SHAI'ED NOTCH 
 
 lost through extensive caries, all leathery decay should lie re- 
 moved and the root margins rendered smooth and firm. 
 
 A crown is now selected and ground to meet requirements. 
 
 When the root has not suffered loss of structure from 
 caries, space for the cast base is gained at the expense of 
 grinding both root and lingual areas of the crown base. 
 
732 
 
 CROWN WORK 
 
 When space Id he occupied l)y the cast l)ase is limited it 
 is advisable, in order to impart rigidity to tlie wax pattern, 
 to extend a V-sliapod groove I'loiii the canal to the labial sur- 
 face of the root. NotcJiin.n' of the crown base will also prove 
 beneficial, but the notcli should terminate within the labial 
 periphery. 
 
 Such notches t'()r)n streii,i;theiiiii_i>- I'ilis in the wax pattern 
 and prevent distortion while handling and investing. 
 
 The crown having been ground to requirements, the root 
 face prepared, the canal reanu'd and dowel fitted, the next 
 step is to form the wax pattern. 
 
 The crown base is coated with a thin film of oil, the dowel 
 inserted in the crown, a piiece of softened inlay wax passed 
 over the dowel and against the crown base. The crown is 
 
 DAVIS CROWN IN POSITION 
 
 ON BOOT WAX MODET, FOR 
 
 CAST BASE INTERPOSEn 
 
 CROWN AND UNITED WAX 
 
 BASE AND D0m5L REMOVED 
 
 FROM ROOT 
 
 now forced firmly against the root face, being careful to keep 
 it in proper alignment with the proximating teeth. 
 
 When chilled, the surplus wax is trimmed away, even with 
 root and crown peripheries. This step must be carefully 
 carried out or the peripheral nuirgins of the iiattern will be 
 disturbed. 
 
 The crown is now removed, which usually is easily accom- 
 plished if the base was previously oiled. 
 
 The wax pattern is removed by grasping the projecting 
 end of the dowel lightly with the pliers, being careful not to 
 rotate or oscillate it. 
 
 If satisfactory, the oil is removed with a camel 's-hair 
 brush and soapy water, or its surfaces can be cleansed with 
 a spray of acetone, which will dissolve the oil without aflfect- 
 ing the wax. 
 
CROWN WORK 
 
 A sprue foniicr is now iittai-lii'd in the thickest poiiitm 
 of the lingual area, usually at right angles to the dowel, and 
 it is ready for investment in tiie easting ring 
 
 THE BANDED DAVIS CROWN 
 
 The following method of applying a Davis crown to a 
 banded or ca]iped root is comparatively simple and satis- 
 factory : 
 
 After treatment and filling of the canal, the remaining 
 portion of natural crown is removed, the peripheral ring of 
 enamel cleaved away, and the root faced, practically at right 
 angles to its long axis. To this the cap is fitted in the usual 
 manner and perforated in line with the root canal, previously 
 reamed, for the reception of the dowel. 
 
 The crown is now selected and ground away on its lin- 
 gual side to form a V-shaped opening with the cap. 
 
 In the base of the crown a shallow, yet distinct, V -groove 
 should be cut, extending from the lingual surface to the cen- 
 tral area. The gold, when forced into this groove, forms a 
 ril) which guides the crown into proper position on the base. 
 
 The crown, base upward, is now imbedded in moldine, in 
 the swaging ring. A short dowel is inserted in the crown and 
 a disc of 36 gauge pure gold, perforated in the center, is 
 passed over the dowel and against the base of the crown. 
 
 The disc is now adapted to the crown base with burnish- 
 ers and the adaptation comiileted by swaging Care should 
 be taken to force the gold into the V-shaped groove in the 
 crown base. 
 
 The peripheral surplus is now removed and the disc, if 
 distorted, is reswSged. 
 
 The short dowel is formed by excising the apical four- 
 fifths of a dowel of regular size. It is used so that a place 
 may be made in the disc for the regnlai" dowel, which is now 
 substituted. 
 
CROWN WORK 
 
 The several parts are asseinblod in the following order: 
 The cap is set in position on the root, the dowel inserted in 
 crown base, and the disc passed over the dowel until it rests 
 against the porcelain. A pellet of softened wax is placed on 
 
 DAVIS CROWN. MODIFIED. 
 
 I.V POSITION ON BOOT. DISC 
 
 AND CAP INTERPOSED 
 
 CROWN, DISC. INTERPOSED 
 WAX. DOWEL AND ROOT 
 CAP. REMOVED PBOM ROOT 
 
 FINISHED BANDED DAVIS 
 AS IT iVPPEARS ON ROOT 
 
 the root cap, the dowel inserted in the wax and the crown 
 and disc forced to position on the root. 
 
 If the parts are free from moisture and the wax suffi- 
 ciently plastic and adhesive, the assembled crown can be re- 
 moved without difficulty. 
 
 To obviate disturbance of relation, a hot spatula should 
 be applied to the wax at several points between disc and 
 cap. 
 
 All spaces should be filled in with additional wax where 
 needed, and the structure contoured to desired form. 
 
 The crown is now removed and the assembled metal parts 
 united either by casting or soldering. 
 
CHAPTER X X A" 1 1 1 
 THE GOLD SHELL CROWN 
 
 (MORRISON CROWN) 
 
 The two-piece, gold shell crown, as ordiuaiily constructed, 
 consists of an axial band and a swaged occlusal surface, both 
 developed from plate gold, so contoured and united as to 
 represent the anatomic form of the lost natural crown it is 
 designed to replace. 
 
 ADVANTAGES 
 
 A crown of this type is strong, economical and efficient. 
 The constructive details, although requiring care in their 
 execution, are comparatively simple. Because of the ease 
 with which sheet gold can be wrought in this method of crown 
 construction, most beautiful esthetic forms can be produced 
 by "the man who knows" anatomic tooth forms, and technic 
 as well. 
 
 DISADVANTAGES 
 
 The color of .gold as compared with porcelain for tooth 
 replacement, is objectionable, therefore gold crowns should 
 not be placed in conspicuous locations. 
 
 WHERE INDICATED 
 
 Gold shell crowns are most commonly indicated in the 
 restoration of badly decayed molars in either arch, occasion- 
 ally in second bicuspids, and sometimes but rarely in first 
 bicuspids, when filling operations are likely to prove unsatis- 
 factory. In bridge work, when oecluso-gingival space is too 
 limited for the combined use of metal and porcelain, a shell 
 crown of the type under consideration, or some modification 
 of it for an abutment is practically indispensable. 
 
 MODIFICATIONS OF THE METAL SHELL CROWN 
 
 There are many modifications in constructive details of 
 the metallic shell crown, consisting principally of the manner 
 of obtaining axial contour of the band and of forming and 
 attaching the cusp surfaces to the axial section. 
 
 A sufficient knowledge for practical purposes of these 
 various types of crowns, can be gained from a full description 
 
 73.5 
 
736 THE GOLD SHELL CROWN 
 
 of llic two-])i('('(> Morrison crown, as now constructed, to- 
 gether with a hrief description of the cast crown. 
 
 TECHNICAL DETAILS OF GOLD SHELL CROWN 
 CONSTRUCTION 
 PRELIMINARY PREPARATION OF THE TOOTH OR ROOT 
 The preliminary work of most ini])ortance in tliis as in 
 all classes of crown constnietion is the proper treatment and 
 successful tilling of the root canals. This shcmld, in prac- 
 tically all cases, be completed before attempting the peripheral 
 reduction of the tooth oi' root. 
 
 RESTORING A BADLY DECAYED NATURAL TOOTH FOR 
 ANCHORAGE PURPOSES 
 
 When most of the natural crown has been lost from any 
 cause, it is imperative that a considerable portion of it be 
 restored by operative procedures, to afford firm anchorage for 
 the substitute crown. This may be accomplislied in two ways: 
 first, with amalgam, and second, by means of a suitaVily shaped 
 casting, usually of Weston's metal or silver. 
 
 THE AMALGAM METHOD OF RESTORATION 
 
 When the roots have been properly filled, the canals are 
 reamed out to receive one or more anchorage posts, deiiending 
 on the requirements for snch means of anchorage. The wire 
 posts should extend deeply in the canals to avoid danger of 
 loosening when the crown is set and later subjected to stress. 
 The How anchor screw post is most useful for such purpose. 
 Also a special form of screw made by the Blue Island Spe- 
 cialty Co. By this method both root canal and post are thread- 
 ed, and when, in setting the post, a little cement is applied 
 around it, firm anchorage of the post within the canal of the 
 root is insured. 
 
 After posts are set, a soldered copper band constructed 
 to fit the root is adapted to its periphery and trimmed suffi- 
 ciently short to clear the occlusal surfaces of the opposite 
 teeth. Into this matrix amalgam is packed and the patient 
 dismissed for twenty-four hours or longer, so that the amal- 
 gam may harden, and will not be disturbed in removal of the 
 matrix or in subsequent root preparation. 
 
 On removal of the matrix, iisually acconqilished by cut- 
 ting with a shar]> chisel, the amalgam stunqi is treated as if it 
 
THE GOLD SHELL L'KOWN 737 
 
 wert' tooth stiuctuii', and rediu-ed with stones, discs and files 
 in conjunction witli the iieriiilieral ring of enamel. 
 
 RESTORATION BY MEANS OF A CASTING 
 
 To restore a delcftive cniwn with a casting, the root 
 canals should be enlarged as prcx 'musly mentioned. When 
 two posts are to supply the anchorage, the canals which re- 
 ceive them should be reamed i>arallel with each other, so that 
 the posts may come away with tiie wax model without dis- 
 torting their relatioiu If this is not possible, one good-sized 
 
 g g Q g g g 
 
 s . i I 
 ? f f f 
 
 g g gi 
 
 IIULAR ROOT BANDEll, AN- 
 
 CllOll SIREWS SKT IN ROOT 
 
 CAN'AI.S. MATRIX IN I'OSI- 
 
 TION 
 
 MOLAR RESTORED WITH 
 AMALGAM. BAND STILL IN 
 POSITION. FOR CROWN RE- 
 STORATION THE BAND 
 SHOULD NOT BE CONTOURED 
 NOR TIIE OCCLUSAL SUR- 
 I'WCES DEVELOPED 
 
 post, deei)ly seated, in conjunction with such additional 
 anchorage as may be developed l)y s(|uaring out the pulp 
 chamber will usually fullill re(purements. 
 
 The posts are set in jjosition in the canals, after wliicli 
 inlay wax is applied and built to re(pured form. The wax 
 model is then removed — the post, or posts, coming away with 
 it — invested, cast, and set in position with cement. 
 
 The object in making such restoration is to increase the 
 hold of the crown to the uatural root, as well as afford a 
 solid foTindation for the crown when subjected to masticatory 
 stress. Without such means the attachment of the srrbstitute 
 to the natural crown, when the latter is badly decayed, is 
 liable to pi-ove unstable. 
 
738 THE GOLD SHELL CROWN 
 
 CASES IN WHICH EXCESSIVE ROOT RESTORATION IS 
 REQUIRED 
 
 Cases frequently ])i'cseiit in wliidi the axial walls of a 
 tooth may be partially or wholly decayed oi- broken away be- 
 neath the gum margin. In sndi ease peripheral root prepara- 
 tion cannot be undertaken williout forcing back the soft tis- 
 sues and freely exposing the loot face and margins. 
 
 When the pulp chamber is open and of such form as to 
 afford anchorage, baseplate gutta percha can be packed into 
 it and over the face end of the root, of sufficient thickness 
 wlien compressed, to "overflow" and force the soft tissues 
 beyond the root perii^hery. The packing should be left in 
 position for twenty-four or forty-eight Inmrs. If, on re- 
 moval, the root face is not sufficiently exposed, the packing 
 should be renewed so as to still further force the tissues out- 
 ward beyond the root periphery. 
 
 Should the ])ul}"> chamber anchorage provt^ insufficient to 
 hold the gutta percha in position, a small, flat-head screw, 
 about one-fourth to three-eighths of an inch long, or longer if 
 necessary, may be screwed into the root canal, and the pack- 
 ing material built around the projecting head. In case the 
 root canals have not yet been treated and filled, extreme care 
 should be exercised not to force any putrescent matter 
 through the a]iex. It is also usually best to puncture the gutta 
 percha with a small instrument to permit any gas that might 
 accumulate in the pulp chamber to escape during the com- 
 pression process. 
 
 When sufficient clearance sjiace has been gained in the 
 manner described a matrix should be applied and adapted 
 to the root periphery. The entire band is then filled with 
 cement, which is allowed to set, when an opening may be 
 drilled through the center, into the pulp chamlier, through 
 which the canals may be treated and filled. 
 
 The matrix must remain in position during the entire 
 treatment of the root to prevent return of soft tissues. After 
 treatment is completed the cement is removed from the matrix 
 and amalgam substituted, as previously outlined. 
 
 WEDGING 
 
 When the teeth adjoining the space the crown is to occupy 
 have moved toward each other, thus reducing it, they should 
 be forced a]iart by wedging, so that interproximal space next 
 the crown, both mesially and distally, may be restored. 
 
THE GOLD SHELL L'ROWN 739 
 
 A wedge, shaped from palm wood (the handle of a palm 
 leaf fan) should be inserted tightly between the inclined teeth, 
 its base resting on the stump of root to be crowned. The 
 fibers of wood should run bucco-lingually. When inserted 
 dry the wood tibers will swell and gradually force the teeth 
 apart, usuallj' without much inconvenience. While the process 
 is slow, requiring a week or more of time and insertion of 
 progressively larger wedges as space is gained, it is an essen- 
 tial step and should in all cases, when possible, be accom- 
 plished by this or other effective means. 
 
 PREPARATION OF THE TOOTH OR ROOT FOR THE BAND 
 
 The same general principles of root preparation previ- 
 ously outlined in the porcelain-faced anterior crown, of con- 
 verting the remaining portion of natural tooth into a slightly 
 tapering cone, the base beneath free margin of gum at point 
 of termination of crown band, apex pointing occlusally or in- 
 cisallv, apply with equal force in preparing posterior teeth 
 for the reception of shell crowns. 
 
 REDUCTION OF OCCLUSAL SURFACE OF THE CROWN 
 
 The preparation of a root or tooth for the reception of 
 a shell crown does not involve the shortening of the natural 
 crown when present to the same extent as is required for 
 anterior porcelain-faced restorations. In fact, the natural 
 crown is left as long as possible to furnish anchorage and 
 obviate displacement of the substitute crown under lateral 
 stress. Sufficient reduction, however, must be made to afford 
 space for a thick, well-reinforced occlusal cap to the shell. 
 About one-sixteenth of an inch space, seen from the buccal, 
 when the teeth are in occlusion will usually be ample. Should 
 this not prove sufficient, the face of the root may be readily 
 reduced later on when fitting the band. The occlusal surface 
 is cut away to the required extent with a five-eighths to three- 
 fourths inch, coarse carborundum stone. Care should be taken 
 not to mar the proximating teeth. 
 
 REDUCTION OF. THE AXIAL WALLS OF THE TOOTH 
 
 A thin edge carborundum stone is used to reduce the 
 mesial and distal surfaces. The wheel is allowed to touch the 
 tooth lightly, yet must be held firmly and under perfect con- 
 trol of the operator to avoid injury to the lips, cheeks, tongue 
 
TIIK COM) SUKIJ, CltOWN 
 
 iiiMl .ituiiis. 'I'hc lirst cut is liciiuii sli;;litl\ inside (if (ir at the 
 (-U'litd-ciiaiiicl ,iuiictii)ii, and liic stone so held (lial ils cdnc will 
 come llii-oui;li to tlic p|-ipxiniatc surface of cnanii'l at the ixlu- 
 gival line. A second cut is usually re(|uii-ed on liotli mesial 
 
 and distal surfaces, to complete the rou,i;ii hlockiii.ii,' off of 
 these surfaces. 
 
 The buccal and lin,i;ual surfaces are reduced with rather 
 small square-faced stones so a|i])lied as to a\oid injury to the 
 
 ^ 
 
 iW] 
 
 DIAGRAMMATIC WF.W OF rOSI- 
 
 TION OF STONE. CtlTTINT! AT 
 
 EXPENSE OF MOLAR TOOTH 
 
 cheeks and tongue. The removal of enamel with these stones 
 cannot usually be carried below the gingival line. 
 
 With small knife-edge stones and discs the peripheral 
 ring of enamel just under the gum margin can be partially, 
 and in some areas entirely, removed. It is frequently a diffi- 
 cult task to rejuove the enamel from those locations where the 
 
■PHE GOLD SHIiLL t'ROWN 741 
 
 surfaces turn t'l-oin Imccal and lingual into tlir mesial and 
 distal embrasures. Small rubber and earbonuidum wIuh'Is 
 carried in the port polisher, ai)plied so that tlieir outer sur- 
 faces or euds can reaeli the constricted areas will be found 
 very useful in reducing the root to symmetrical form. 
 
 The enaiTiel cleavers of ordinary form are of but little 
 service in removing enamel from molar teeth, since it is not 
 
 .VPPtlCATION OF SMALL STONE IN 
 RIGHT ANGLE HAND PIECE TO 
 DISTOLINGUAL ANGLE OF CROWN 
 
 possilile to ai)ply the necessary force effectively back of the 
 bicuspids. 
 
 Dr. W. K. Harper has (h'signed a contra-augle handle 
 which holds a variety of short shank, regular and other forms 
 of cleavers and tiles. These can be used to advantage in the 
 
 LEFT CUT SHOWS API'I.ICATION OF STONE 
 INBEMOVAL OF BUCCAL ENAMEL. DOTTED 
 LINE, THE USUAL AMOUNT OP TOOTH 
 STP.UCTURE REMOVED. RIGHT CUT. OUT- 
 LINE OF PREPARED TOOTH 
 
 removal of enamel in difticult locations, where the ordinary 
 forms of cleavers are ina])plicable. 
 
 By carefully introducing carborundum ])aper discs and 
 warping them around the angles, much of the final prepara- 
 tion can be accomplished without serious injury to the soft 
 parts. 
 
 The root iiles can be used to advantage, ])articularly in 
 the emlirasures. When the instrument is held in the right 
 hand, the thumb of the left is placed against the buccal border 
 
742 THK CUM) SllKLL CKOVVN 
 
 surface, the iudex finger to the liug'uaJ. The thumb is used 
 as a fulerum with the result tliat greater and mure direct force 
 can be applied against the enamel in the interproximate spaces 
 than is ]i()ssih]e with any othei' position. 
 
 GENERAL FORM OF THE PREPARED ROOT OR TOOTH 
 
 The flare of axial sui'faees should be plainly noticeable, 
 bnl not too marked; that is, the convergence of peripheral 
 
 GENEHAL FOHM OF REVEKSEIl (DM: AKTKI! r,KM(l\AI. (II' EXAMEI, 
 
 surfaces from the base of the cone under free margin of the 
 gum outward or occlusally siiould range from two to five 
 degrees. 
 
 Certain facts must be kept continually in mind during 
 root preparation, viz., the gingival cone of the natural tooth 
 
 CDT SHOWING RELATION OF 
 PREPARED TOOTH TO OCCLUD- 
 ING TEETH 
 
 must in all cases be reversed; the base of the new cone must 
 be extended apically as far or even slightly beyond the point 
 where the cervical end of the band, when permanently set, 
 will rest; the formation of shoulders or grooves, or any 
 
THE GOLD SHELL CROWN 743 
 
 irregular surfaces that will interfere with the correct fitting 
 of the band, must be avoided. 
 
 TESTING THE CORRECTNESS OF ROOT PREPARATION 
 
 The two tests previously mentioned under root prepara- 
 tion for a porcelain-faced crown are applicable for proving 
 the correctness of root preparation for shell, as well as other 
 classes of crowns. The first of these — passing a delicate in- 
 strument apically — is dependent quite as much on tactile sense 
 as on the eye, for revealing irregular surfaces, grooves, shoul- 
 ders or any remaining portions of enamel, and for determin- 
 ing whether the sides have the proper flare. 
 
 The final test is in the root measurement itself, which, 
 if easily removed, indicates that the remaining portion of 
 the tooth between the position of measurement and its occlu- 
 sal end converges or becomes smaller. 
 
 TAKING THE PERIPHERAL MEASUREMENT OF ROOT FOR 
 BAND 
 
 The wire loop is formed, placed in a holder, applied to 
 the root and tightened. The loo]i shonkl seldom ever be 
 pressed under the free margin of the gum, unless the root is 
 
 excessively cone-shaped, the idea being to form the band 
 slightly smaller than actually required and drive it to place 
 in fitting, thus insuring a close and accurate adaptation to 
 the root periphery. On removal of the measurement, the loop 
 
744 THE GOLD SHELL CROWN 
 
 is ciil (i)i]>()si1(' the twist, in II I laid aside until t lie ini'asurcinciil 
 I'di- the liaiid width is dhtaiiu'd. 
 
 DETERMINING WIDTH OF BAND 
 
 As a uuittt'i- of ('coiKiiuy, the hand should he cut of ap- 
 proximately correct width. The width may be determined by 
 measuring' the distance lietween the deepest curve of the gin- 
 giva of the root to be crowned to the tips of the cusps of the 
 opposing teeth. Should the dip of the gingival gum curva- 
 ture approach the root apex more closely on one side than 
 the other, the greater width must be used for the band meas- 
 urement. For example, when marked tissue absorption ex- 
 tends apioally, exposing more or less of the surface of the 
 
 lingual root of an upper first molar, the band should be wide 
 enough to cover the entire exposed area. There are better 
 methods, however, of adapting crowns to teeth around which 
 gingival absorption has occurred to a considerable extent 
 than by the application of a band. In such cases the shoulder 
 crown in which no overlapping of gold on the root occurs, is 
 far more hygienic and serviceable than any- type of banded 
 crown. 
 
 A piece of ordinary cardboard, cut on a taper with the 
 narrow end squared, serves as a convenient gauge. If too 
 wide, the sides of the card are reduced, wliile if too narrow 
 the end is cut away until tlie width coincides with the distance 
 designated. A pair of dividers may also be used for securing 
 the measurement. The length and width of band havino- been 
 
THE GOLD SHKLL CROWN 745 
 
 dctcriiiiiicd. the next step is to lay it out, and cut it t'ruui the 
 piece of gold plate. 
 
 CUTTING THE BAND ACCORDING TO MEASUREMENT 
 
 As has been previously pointed out, the outer envelop of 
 the average posterior natural tooth represents two cones, an 
 occlusal and a gingivah revei-sed, and with their bases meet- 
 ing in a coinnion plane in the mid-crown region. 
 
 SCIlIlilXG THE CERXICAL END OP AXIAl, CONE HAND. THE OUTEll ARC REPRESENTS 
 
 THE OCCIA'SAI, END OF THE BAND. THE DlSTAXl'E BETWEEN THE TWO ARCS IS 
 
 DETERMINED liV THE CARDHOARD iMEASl'REMENT 
 
 'I'o reproduce sucli an enxclop in gold, one of two plans is 
 followed: first, form the band as a cylinder and by swelling 
 and stretching, gain contact with proximating teeth, in- 
 crease the mesio-distal diameter of the band at the occlusal 
 surface, and the bucco-lingual diameter in its mid-crown area 
 to represent the axial contour of the natural tooth. Second, 
 form the band as a section of a cone, representing the flare 
 
746 Tllh; (;()I,I) SIIKLL CKOVVN 
 
 ol' the iivcrnnc, naluial gingival cone, and reduce tlie occlusal 
 end by compression contouring to the required dimensions. 
 Of the two methods, the latter is much the simpler and better 
 in every way. 
 
 By referring to anatomic forms of teeth on page G34 it 
 will be seen that the average flare of the gingival cone of 
 molars is 25 degrees. Unless the space which the crown will 
 occupy is constricted, a cone having this flare sliould l)e used. 
 
 CUTTING A CONE BAND 
 To cut a liand liy this method, the dividers are placed at 
 the edge of the card oi- piece of gold jdatc, the iioints set at 
 
 314 inches apart and an arc is struck, somewhat longer than 
 the root measurement. The radius is then increased the 
 width of the band, as determined by the cardboard measure- 
 ment, and from the same center a second arc is struck, rep- 
 resenting the occlusal end of the band. 
 
 When curvature of the gingival gum margin, around the 
 
THE GOLD SHELL L'ROWN 
 
 root being crowned, is very marked, as is frequently the ease, 
 the cervical end of the cone band must be reduced by scribing 
 and trimming, to conform to such curvature This naturally 
 reduces the lieiglit of the cone, entirely at the expense of its 
 
 smaller end, and enlarges its cervical diameter or peripheral 
 length proportionately. 
 
 On returning the band to the root it will usually be fonnd 
 entirely too large. And while reduction of its cervical diame- 
 ter may be effected with contouring pliers, anatomic outlines 
 of the axial surfaces will be disturbed. 
 
 When it is evident that much reduction of the cervical 
 end of the cone must be made, the band should be marked 
 
748 THIO COLD SHKLI. CROWN 
 
 and ciil Irciiii one to tlncc thirty-sccoiitls of ;m inch shortci' 
 than tlic root measurciiiciit. 
 
 The measurement is h-iiil olT on tiir L^ohl phitc ami tiie 
 hand cut as follows : 
 
 Tlie wire measnrcnicnl is mrxcd In r(iiTcs|i(ind with 
 the gingival arc on which i1 is now laid, one end of the wire 
 l.ieing bronghl e\'en with the ontcr margin of the gohl ])late. 
 The other end of the hand is iMark<'d cxcn witli the wire meas- 
 
 LIXK URAWX WITH nul.E TO INUICATK l)lVEI!<;ENrE 111'- IX.NEll KNh 
 
 OF BAND. THE OUTER END OF THE BAND AT THE EDGE OF PLATE 
 
 IS CORRECT. UPPER LEFT CORNER SHOWS FORM OP BAND 
 
 urement, or in case of decided gingival enrvature, ])roi)or- 
 tionately shorter, in accordance with the slight or pronounced 
 curvature of the gingival tissues. 
 
 Liay a rule against this point and the center from which 
 the arc was develojied and mark the end of the band. When the 
 gold plate is placed parallel with the outer edge of the card the 
 opposite or outer end of the band will have the proper flare. 
 The gold is cut and bent in the form of a cone, the two ends 
 abutting squarely against each other. 
 
THE tJOLD SHELL CROWN 
 WIRING THE BAND 
 
 'I'he hand ends should be held in contact with binding wire, 
 for. although they may be soldered without the use of the 
 binder, they will usually spring apart, at one or the other edge 
 of the band, and the union l)e imperfect. 
 
 IIAXI) ENDS ABUTTED AND 
 
 HEM) WITH CROSSED BIND- 
 
 IN'Ci WIRE 
 
 Since the wire will not keep its position on the cone as 
 ordinarily applied it should be crossed and carried around the 
 band occluso-gingivally and t^nsted tightly, the surplus being- 
 placed on the 0])posite side of the cone, from the joint. 
 
 SOLDERING THE BAND 
 
 Borax is applied to the joint, a small piece of solder laid 
 across, and the band ends united in the usual manner. 
 
 FITTING THE BAND TO THE ROOT 
 
 The band is conformed to the general outline of the root 
 and pressed down until in contact with the gingiva. The 
 scribing tool is a]iplied and the gingival line marked on the 
 Imccal surface. Usually, because of difficulty in applying the 
 scriliing instrument to the lingual surface an explorer can be 
 substituted and the lingual curvature approximately marked in 
 this manner. It is advisable to mark too close rather than too 
 far from the gingiva and cut accordingly to avoid shortening 
 of the band width. After trimming off the gross surplus a 
 second application of band to root will disclose the points 
 needing further reduction. 
 
 Naturally, when much curvature is pi'esent the band, 
 when trimmed, will become enlarged. This may be compen- 
 sated for in two ways: first, by cutting the band slightly 
 shorter than the measurement at the start, and second, by 
 reducing the gingival ]ieri])hery with suitable contouring 
 pliers of the Peso or I'cuson txpc 
 
 CONTOURING THE BAND 
 
 In forcing the liaiid to place its bncco-lingual diameter 
 will be somewhat increased bevond true anatomic dimension. 
 
THE (iOI.L) SHKLL I'ROWN 
 
 This distortion, however, can be readily corrected by apply- 
 ing the round beak of the Benson plier inside the band about 
 the middle, occluso-gingivally, and with careful pressure on 
 the outer side with the flat beak the occlusal cone can be re- 
 duced to proper form. No appreciable pressure should be 
 
 REDUCING THE OCCLUSAL END l)K BAND WITH BENSON PLIERS 
 
 exerted on the handles to force the beaks together, as this, 
 by thinning the gold, would increase the diameter and contour 
 of the band in the mid-crown area. 
 
 The Benson pliers are designed primarily for effective 
 contouring of bands in any location where convex surfaces 
 are required, the heavy handles and short beaks being spe- 
 cially adapted for developing great force. One beak is flat, 
 the other round, the latter acting on gold plate as a ball pene 
 hammer does against metal on an anvil. 
 
 The accompanying cut shows an extensively contoured 
 crown, formed with these pliers by Dr. Benson, the axial band 
 
 SKCOND MOLAR INCLINED FORWARD 
 FROM LOSS OF FIRST JIOLAB I'BOWN 
 CONTOURED TO FORM PROXIMAL 
 CONTACT WITH SECOND BICUSPID 
 (BENSON) 
 
 lilCrSI'ID BANDS CONTOURF.D. 
 STRIP AT BOTTOM SHOWS DOTT- 
 BLEB ATTACHED TO MAIN 
 BAND. NOTICE FLAKING ENDS 
 OF LATTER (BENSON) 
 
THE GOLD SHELL CROWN 751 
 
 being expanded in order to develop contact with a tootli some 
 distance removed. lu this case, a piece of gold was sweated 
 against tlie sti'aight baud to give additional material for ex- 
 l)anding and tlms obviate weakening of the crown walls. 
 
 The thickening of the band walls is essential where ex- 
 tensive contouring is carried out. It is not essential when the 
 band is developed to represent the section of a cone except in 
 unusual cases. 
 
 FORCING THE BAND TO PLACE ON ROOT 
 
 When properly contoured, it should be forced to position 
 under the free margin of the gum, usually about one-twentieth 
 of an inch, in some cases a little more, when the peridental 
 attachment will permit. 
 
 By placing a flattened piece of wood on the occlusal sur- 
 face of the liaud, the ])atient can assist in setting it liy biting 
 
 CONTOURING AND BAND-EXrANDING PLIERS DESIGNED BY WRITER 
 
 on the wood. Test of the length of band is made by closure of 
 the teeth, and any points of interference are reduced bj^ trim- 
 ming. The occlusal end of the band should be squared with 
 the flat side of a file so that the cusp when developed and 
 similarly treated will form a close joint with the band. 
 
 TESTING THE BITE 
 
 The band, having been fitted to the root, a wax bite should 
 be taken with the band on its root, together with the proximat- 
 ing teeth. The mass of wax should be large enough to re- 
 ceive and firmly hold the bite fork of the face bow. It should 
 also be of the hard variety, so that when chilled it will re- 
 tain its shape, and not become distorted in subsequent han- 
 dling. 
 
752 THIC (!()l,l) SIIKI.L CltOW.X 
 
 Tlie l)ito fork is insci'lcd in llic \\;i\. (d 1hc outside, in 
 such nianiicr as nol Id intrrrci-c with (iccliisidii. the wax iii- 
 ti-(>ilnri'(l ill ilic iiioiitli anil the haticnt iiist nii-t('(| td ddsc. 
 
 OCCLCSAL VIEW OF Till! rdXTOl'HEn BAMI IN POSITION 
 
 The face bow is adjusted to tlie bite fork, and over the con- 
 dyles, the several clamps tig'htened, and the bite, attached to 
 the bow. removed from the mouth. 
 
THE COLD SHKLL CROWN 
 
 All iiiipn'ssioii of tlu' liaiid mi its root is olitaiucil, tonctlicr 
 witli two or three of the .-Kljoininn' tcelli on citlicr side. Kroiu 
 tliis n east is developeil, whidi, wlicii iciiiox-ed and tiinnned. 
 
 BITE MOl'NTEI) OX OCl'l.l l)IX<i KllAMK. I.dWEK CAST DEVlOr.orEI) 
 
 is fitted to tlie wax bite and attaelied to the upper bow of the 
 frame. The sides of the wax bite should be trimmed as previ- 
 ously deseribed to permit tlie oechisal siirfaees of the teeth to 
 become seated against the wax. 
 
754 THE (;OI>I) SlIKM. CliOVVN 
 
 MOUNTING THE BITE ON THE OCCLUDING FRAME 
 
 The face bow is ad.juKted to the occluding frame, the wax 
 bite oiled, and that side which is to form the occlusion cast 
 is tilled with plaster, and at the same time attached to the bow 
 of the frame. When hardened, the cast carrying the band is 
 
 fitted in its bite and attached to the opposite bow. After 
 removal of the bite, the occlusal surfaces of the occluding 
 teeth opposite the band are coated with separating medium. 
 
 "developing the cusps OF THE CROWN IN PLASTER 
 
 When the occlusal surface of a crown is to be swaged, it 
 is necessary to develop a pattern of the form desired, in plas- 
 ter or some medium, by means of which a suitable counterdie 
 can be constructed. One of the most common methods of 
 carrying out this step is as follows : 
 
 A mix of plaster is made and applied in the occlusal end 
 of the band, slightly in excess of the amount required for the 
 cusps. While soft, the two casts are occluded, the surplus 
 plaster being forced buccally and lingiaally. On separating 
 the casts it will be seen that the central groove of the occlusal 
 surface to be carved has been fairly well developed by the 
 buccal marginal ridges of the lower occluding teeth. The 
 groove, however, should be deepened slightly, and some small, 
 unnecessary ridges on the occlusal surface reduced, to bring 
 
THE GOLD SHELL CROWN 755 
 
 out the general anatomic form of the tooth. The peripheral 
 surplus is trimmed even, and continuous witli the axial walls 
 of the band at this time, but later on nmst be rounded in to 
 form the marginal ridges. 
 
 The frame should be subjected to lateral movements and 
 the iJoints of interference noted and trimmed accordingl.y. This 
 step might be termed development of clearance paths. The 
 trimming of tlie peripheral margins of the plaster to represent 
 the marginal ridges of the crown should be carefully carried 
 out, since these boundaries of the occlusal surface give char- 
 acter and individuality to the substitute. 
 
 Finall}', the developmental lines and finer surface mark- 
 ings are carved in tlie occlusal surface. To do this well, the 
 prosthetist should have a knowledge of typical forms of the 
 teeth. 
 
 TYPICAL FORMS OF NATURAL TEETH 
 
 A number of sketches of natural teeth have been care- 
 fully drawn, showing various surfaces, among them the occlu- 
 sal surfaces of seven types of teeth that the crown and bridge 
 worker should be thoroughly familiar with, able to draw in 
 
 DIAGRAMMATIC 
 
 pencil, carve in wax or plaster, or model in clay. These are 
 not presented in reverse, it being taken for granted that famil- 
 iarity with one type of tooth will enable the prosthetist to 
 carve it for either right or left side. 
 
'I'Hli; COI.l) SHKLl, CKUWN 
 UPPER RIGHT FIRST MOLAR 
 
 oci'i.rsAT- 
 
 LOWER RIGHT FIRST MOLAR 
 
THE GOLD SHELL CROWN 
 
 LOWER RIGHT SECOND MOLAR 
 
 LINGUAL MESIAL 
 
 UPPER LEFT FIRST BICUSPID 
 
 IircCAL LIXULAL 
 
 <i> 
 
 occi.rsAL 
 
THE GOl^U SHELL CROWN 
 
 UPPER RIGHT SECOND BICUSPID 
 
 LOWER LEFT FIRST BICUSPID 
 
THE GOI>D SHELL OROWN 
 
 LOWER LEFT SECOND BICUSPID 
 
 OCCLUSAL 
 
 REPRODUCING THE CUSP SURFACES IN GOLD 
 
 Two general methods are in vogue for forming the oeclu- 
 sal surfaces of a crown. First, by swaging the cusps, and sec- 
 ond, by casting them. When swaged, a counterdie is con- 
 structed and in this the cusps are formed. When east, the 
 cusps are carved in wax, in tlie gold band, the two invested, 
 and the cusps cast directly to the axial band. 
 
 CONSTRUCTING THE COUNTERDIE— DIRECT METHOD 
 
 A common procedure in forming the counterdie is as fol- 
 lows : The cusps having been developed in plaster, the crown 
 
 CROWN IJANJi l.MIU;l')iEl> IN MOLDINB. 
 CABVBD I'USrS HXPOSKD READY FOR 
 PLACING THE SWAGING BING AND CAST- 
 ING THE COUNTERDIE 
 
 band with cusps attached is removed from the cast and im- 
 bedded, cervical end down, in moldine to the line of junction 
 
TBO 'llll': liOl.li SHKIJ. CltOWN 
 
 <tl' llic ,i;()l(l willi llic piaslrr, tlnis Icaxiii.i; <>i\\y llic cusps ex- 
 IHiscd. A small rulihcr liii.n'. or llic iiidal i-iu!; of a swaging 
 
 (lc\icc, is (•entered oxer tl nsjis, on llie iiioldiiie, and fusible 
 
 metal iioiireil in Hie ring and o\-er the cusp surfaces in suffi- 
 cient quantity to form a resistant counlerdie. Wlien chilled, 
 tlie moldiiie and crown are removed and the matrix, it' satis- 
 factory, is oiled, tile gold annealed, and swaged into the cus]i 
 depressions. 
 
 V^ery often thi' cusp sui-faces of the connterdie m.itrix will 
 he defective, as a lesult of iiouring the heated metal over tJie 
 imperfectly dried i)]aster carving. Tliis may lie largely over- 
 come hy eliminating all moisture from the plaster before im- 
 bedding the crown in moldine. Two or three very small holes 
 may be drilled througii the plaster cusps and after the crown 
 is imbedded in the I'ing a small wire is introduced through the 
 holes and passed entirely through tlie moldine base, to form 
 free vents for the downward escape of steam The disturb- 
 ance of (he molten metal wliile hardening is tluis, in most 
 cases, averted. 
 
 CONSTRUCTING THE COUNTERDIE— INDIRECT METHOD 
 
 A very excellent method of constructing a connterdie 
 without casting directly to the carved surfaces, and which will 
 yield a dense casting, is as follows: 
 
 It is well known that dense castings of fusible metal, free 
 from porosity or surface imperfections, can lie successfully 
 cast against moldine, liecause the latter contains no moisture. 
 Neither does the glycerine, with which moldine is mixed, to 
 render it plastic, volatilize under the fused metal. Therefore, 
 by reproducing the reverse of the desired connterdie surfaces 
 in moldine a dense connterdie will result from casting fusible 
 metal against such surfaces. 
 
 The cusjis art' carx'ed in the same maimer as i)reviously 
 described. By this method hard wax or modeling com])onnd 
 will serve quite as well as plaster as a medium in which to 
 carve the cusps. 
 
 When carved, remove the crown from cast, make a mix 
 of plaster and spread on a piece of paper, forming a flat mass 
 about three-eighths inch thick and one and one-half inches in 
 diameter. With the point of a knife or a brush fill in the in- 
 equalities of the carved surfaces and quickly press the crown, 
 occlusal end down, in the soft plaster. The cusps should be 
 fully imbedded to the band margin. Remove the surplus plas- 
 ter from around the crown. When plaster has set, remove 
 
THE GOLD SHELL CROWN 7G1 
 
 erowii and carving. Trim the margins ol' tlic matrix to elim- 
 inate nndercnts. The plaster with oiisp depression now repre- 
 sents the essential surfaces of a eounterdie. This must be re- 
 produced in metal whicli can be accomplished as follows : 
 Dust the cus]) surfaces and plaster slab with talcum powder 
 and brush oft' the surplus. Press a small mass of moldine in 
 the cusp depressions and a larger mass over the upper surface 
 of the plaster slab. The two masses of moldine should tirmly 
 unite, which will occur if surfaces are fresh and sufficient pres- 
 sure is applied. The upper surface of the moldine should be 
 flat, to afford a firm ])ase on which to rest when, later on, 
 it is inverted. 
 
 The plaster and moldine are carefully sei)arated to avoid 
 distorting the latter. On the surface of moldine. which was 
 pressed against the plaster, will be seen a raised occlusal sur- 
 face of exactly the same size and form as the plaster pattern. 
 The moldine is set on the bench, a casting ring centered over 
 the cusps and tilled with fusible metal. 
 
 When the metal has hardened and the ring and moldine 
 are separated, the eounterdie surfaces will he found dense, and 
 with finest details reproduced. Since the steps are carried out 
 quickly while the plaster is damp, the surface of the moldine 
 may absorb a little moisture from the latter. This can be re- 
 moved before casting, by dusting freely with talcum iiowder 
 and removing the suriilns with n soft brnsli. 
 
 DEVELOPING A COUNTERDIE WITH METALLINE COMPOUND 
 
 Mcfdiliiii' ( 'iiiHjioifiiil is a moderately hard substance, hea\'- 
 ily loaded with graiihite, somewhat resembling modeling com- 
 pound in that it becomes plastic with heat and hardens (piickly. 
 Fusible metal can be cast direi'tly against it without distorting 
 its surfaces, since a higher temperature is re(|uired to soften 
 it than modeling compound. 
 
 It can be carved readily, and if, in carving, too much is 
 removed, more can be added with a hot spatula and the sur- 
 faced corrected. By its use a most excellent eounterdie can 
 be quickly formed as follows: With the casts mounted on the 
 occluding frame and the band in position on its cast, a jtellet 
 of Metalline C'omjiound, slightly larger than that required for 
 the cusps, is ijoftened, placed in the occlusal end of the band 
 and Ihe casts occluded. When hard, the cusps are carved as 
 usual. With a small bui'uisher the cusp surfaces are rendered 
 perfectly smooth. 
 
 The Metalline car\iiig is carefully lifted ont of the band, 
 to prevent distoi'tion, and thai ]iorti(in wliicli cntei'ed H\o 
 
762 THE GOI.D SHELL CROWN 
 
 l»;ui(l is pared away with a sliarp kiiifp, even with the impres- 
 siou of its occlusal end. This converts the Metalline carving 
 into an occlusal form of exactly the right depth for the cusps. 
 It now resembles in form one of the Ilollingsworth metal cusp 
 l)atterns. 
 
 The upper or occlusal surfaces are now coated with a 
 thin film of glycerin, and all surplus removed with absorbent 
 cotton. 
 
 A small iK'lict of soft moldine no larger than a pin-head 
 is thinly sjiread on a flat surface of polished steel. On 
 this the metalline carving is set and pressed lightly against 
 the moldine, to cause the cnsj^s to adhere to the steel. The 
 object in cementing the cusp to the steel is to prevent its dis- 
 placement by the metal in casting. If the cusp carving is not 
 adherent to the steel, the fusible metal, because of its greater 
 specific gravity, will settle under and cause it to rise to the 
 surface. Another method of obviating displacement of the 
 carving is to press it against the steel with a small wire while 
 pouring the metal. The steel should be moderately cool, so 
 as to chill the fusible metal quickly before the cusp forms 
 are softened. 
 
 A ring is centered over the cusp and the fusible metal 
 cast into it. When the steps are properly carried out, a sharp, 
 well defined counterdie is obtained. 
 
 SWAGING THE CUSPS IN AN OPEN COUNTERDIE 
 
 A piece of soft wood about four inches long and one-half 
 inch square is shaped, on one end, to the general outline of the 
 cusp depression and driven into it and the counterdie is oiled. 
 
 DISC OP GOLD WITH SOFTWOOD 
 IN POSITION READY FOR SWAG- 
 ING IN COUNTERDIE 
 
 A disc of 31 or 32 gauge, 22 carat gold plate is annealed, 
 evenly centered over the cusp depression, the conformed end 
 of the stick set squarely on it and given a sharp blow with 
 the hammer. 
 
THE GOLD SHELL CROWN 
 
 Any folds that have hegiui to t'onii around the margins 
 are corrected with pliers, and the swaging process continued 
 until general adaptation is secured. The finer lines and sharp 
 ridges of the cusps are developed witli a blunt-pointed hick- 
 
 DEVI I <I1MN(. I III I l\l It (M'C'Lr- 
 
 SAL SURFACE MVItKIVCS WITH 
 
 HARDWOOD POINT 
 
 cry stick, or a rather small but round edge chaser, using light, 
 rapid hammer blows. Finally, liy applying the piece of soft 
 wood with heavy hammer, the gold is driven against all sur- 
 faces of the matrix. The gold is pickled in acid, polished with 
 pumice to remove all traces of base metal, when it is ready 
 for the final step of fitting. 
 
 REMOVING PERIPHERAL SURPLUS OF GOLD 
 
 With a pair of shears the marginal surplus of gold is 
 removed, and the surfaces of the cusp to l)e united with the 
 band are flattened with a file. 
 
 ADAPTING THE OCCLUSAL CAP TO THE BAND 
 
 By placing a pellet of soft wax in the band to steady 
 the cusps and returning the latter to position, from time to 
 time, on the band, both length and occlusal relations may be 
 determined and corrected as required. 
 
 The cusp margins should rest flat upon the occlusal end 
 of the axial band, while the peripheries ot both should coin- 
 cide. 
 
 When trimmed to correct length, so that in lateral move- 
 ments the cusp planes do not interfere with the opposite 
 occluding teeth, the crown can be removed from its cast and 
 the two permanently united by soldering. 
 
 DEVELOPING THE. MARGINAL RIDGES OF THE CROWN ON 
 THE AXIAL BAND 
 
 A most excellent method of developing the cusp eleva- 
 tions on a ei'own, and which largely reduces the difficulties 
 of carving the occlusal surface, is as follows: 
 
764 TIIK liOl.l) Slll':i,l, CliOWN 
 
 'I'lic axial band is roriiictl as wide or cncii sliiililly wider 
 than I he oeclusu-ccrvical height of the liiiished crdwii. 
 
 The steps of fitting oi" liaiid lo rcmt and contdniiiig of 
 axial surfaces are carried out as prcN ioiisly desciilied. Since 
 the length of hand will not permit the teeth to occlude, a bite 
 cainiot l)e taken until the occlusal band margins are corrected. 
 
 instead of Irinnning this end of the band to re])resent a 
 lioi'izonlal jilane, as is usually done and as luis been pre- 
 
 TIIE AXlAr. I'lillWN I'.ANII NdTI'lIKII T( 
 
 ■l.rllK WITH 
 
 ■-111 II hTH 
 
 viously described, it is utitched to represent tlie xarious cusp 
 elevations and sloping planes of the marginal ridges. 
 
 The mesial and distal occlusal margins must also be 
 notched to receive the opi)osite occluding cusps which rest 
 in the central groove. 
 
 This can easily and quickly lie carried out in the mouth, 
 the general alignment of the cusps of proximating' teeth and 
 the cusps of the occluding teeth serving as guides while trim- 
 ming the band margin. 
 
 The patient should subject the mandible to lateral move- 
 ments to test the correctness of clearance jmths. 
 
 When trimmed so that the occlusal band margins inter- 
 cuspate properly, not only in occlusion, but in lateral mandib- 
 ular movements as well, the bite may be taken as usual, casts 
 developed and the crown finished by any of the ordinary meth- 
 ods desired. 
 
 If the cusps are to be cast, inlay wax may l)e a])])lied and 
 carved in the mouth, the ci'own and carving removed and in- 
 
THE GOLD SHKLL t'ROWN 765 
 
 Vfi^tt^'d (lirt'ctly, witlunit tnkiiii;- an iiiii)rcssi()ii or bite or de- 
 veloping easts. 
 
 Carving tlic cusps is a \cry simple operation, since the 
 cusp elevations and depth of grooves are already established 
 and the central groove is clearly indicated by the cusps of the 
 occluding teeth in the l)ite. 
 
 DEVELOPING THE CUSP SURFACES IN A SWAGER 
 
 ("I'own swagers are \cry coinnionly used in dental labora- 
 tory jirocednres, and for many jiurposes are most useful and 
 convenient. A swager, however, is not as etTeetive in the 
 development of cusp surfaces from thick gold plate as the 
 method previously outlined, 'riierefore, when the swager 
 alone is employed, the cusps must be developed from light 
 gauges of gold i)late, or when a heavy gauge is used, which 
 in all cases is more desirable, the two methods may be com- 
 bined. The following plan is ]iroductive of good results: 
 
 Before placing the counterdie in the swager its surfaces 
 are oiled. A disc of HO or ."il gauge 22 carat gold plate is 
 annealed and c<'ntered oNcr Ihe depression, into which it is 
 
 I'OrNTEBDIE IN I'dSlTKIN IN SW.' 
 
 swaged by means of the soft and hard wood i)unches, as pre- 
 viously described. 
 
 Remove the excessive ]ieri])heral surplus, pickle and an- 
 neal the partially developed caj), return it to the counterdie, 
 place the latter' in the swager, and with a heavy rawhide mal- 
 let drive the gold into the matrix. ITsually it will be neces- 
 sary to develop the finer surface markings of the cusps with 
 the lilunt hardwood point, or fine-pointed steel chaser. Final 
 
7(JG THE (iOI.I) SHKLI. CROWN 
 
 adaplatidii ami i-ciii(i\al of wariianc ai-<' ai'r(iiii])lisli('(l in tlu; 
 swagcr. 
 
 Fitting the occlusal cap to llic axial hand is accomplished 
 as previously outlined. 11 should he pickled in acid, cleansed 
 and ])olished to remove all traces of base metal. 
 
 ASSEMBLING AND SOLDERING THE BAND AND 
 OCCLUSAL CAP 
 
 Remove the band from tlie cast, jiickle in acid and cleanse 
 in water. Apply boi-ax to the inner cusp surfaces and the 
 occlusal end of the band. 
 
 Adjust the occlusal cap and band in proper relation to 
 eacli other as indicated by the coincidence of their peripheries, 
 and bind together with untinned binding wire, bringing the 
 ends over the cervical end of tlie crown, to form a loop for 
 
 holding while soldering. The wires may be crossed, if neces- 
 sary, to hold the occlusal cap in proper relation. 
 
 The occlusal cap and band may be held in proper relation 
 to each other without wiring by means of the Kerr soldering 
 tweezers. One beak of this appliance is bent at right angles 
 to the handle. Opposite this point and attached to the other 
 beak is a loose, three-prong table. The crown is held by set- 
 ting the cervical end of the band on the adjustable table, while 
 the right angle point rests in the central area of the occlusal 
 cap. 
 
 Small pieces of fluxed solder are placed within the crown, 
 the latter carried to and held within the Bunseu flame, occlu- 
 sal end down, where it is carefully and uniformly heated until 
 the solder fuses. Sufficient solder should be applied to form 
 a thick, rigid, occlusal cap, three or four times thicker than 
 the swaged cusps. Care should be taken to see that not only 
 the joint areas are perfectly united, but that the solder has 
 been drawn up slightly along the inner margins of the liand 
 
THE GOLD SHELL CROWN 
 
 767 
 
 as well. The solder, when so disposed, strengthens the oceln- 
 sal surface and obviates the danger of it wearing tlnoiigh 
 under masticatory stress. 
 
 FINISHING THE CROWN 
 
 The finishing of the crown is accomplished with engine 
 stones and discs, and the final |)olish developed with felt 
 and brush wlieels on the lathe. 
 
 A piece of wood about four inches long and three-eighths 
 inch in diameter, reduced at one end so as to fit loosely within 
 the crown, will serve as a handle for holding it while polish- 
 ing. The handle is applied by ]ilacing a pellet of heated model- 
 ing comi)ound on the reduced end, iiressing it into the crown 
 
 CROW^ HOLDER 
 
 CUOWX IIOI.nEK APPLIED 
 
 and chilling. When the crown is ])()lished, by warming it 
 slightly to soften the comi^ound, the handle may be removed. 
 A convenient appliance designed for holding crowns con- 
 sists of a group of divergent steel springs, set in a handle. 
 When compressed inwardly, and introduced in the crown, the 
 springs press outward and Iiold it firmly wliile polisliing. 
 
 SETTING THE CROWN 
 
 Wiien finislied and the ])(ilishing powder is removed, the 
 crown is washed in alcohol and laid aside while the tooth is 
 cleansed and dried and the cement mixed. 
 
 Cotton rolls may be used to guard against the encroach- 
 ment of saliva, during the earlier stages of setting the crown 
 and imtil the cement begins to set. 
 
 The cotton may be held in various ways, one of the most 
 convenient being to apply a clamp to a proximating tooth, 
 and place cotton rolls under its lingual and buccal bows. 
 
THK (iOLU SHKLL CROWN 
 
 A eonvenioiit type o[' cottnii roll holder, s|irciiilly dcsiiiiicd 
 for such purpose, tlu' Ivory, is here illustrated. 
 
 Oue objection to tiie use of any clamp in this o|icriitioii 
 is that when ap])lie(l before the setting of the crown. I he occhi- 
 
 ^V 
 
 THE IVClltl ('(ITTCJN 11(11. 1. HOLDER 
 
 sion cannot be tested, the clanip bows interfering;' with closure 
 of the opposing teeth. 
 
 After forcing the crown to place, a clani|) may be a])piii'<l 
 to advantage. 
 
 The usual order of ])i()ce(lure is to ajiply cement within 
 the crown somewhat in excess of the amount required, and 
 quickly carry it to place. 
 
 It should lie forced in position with tinger pressure, after 
 which the ])atient is instructed to bite the crown to place. 
 Usually a piece of soft wood is inserted lietween the occlusal 
 
 THE COTTON UOEI, HOI.IJEK Al'I'MED TO TEETH 
 
 surface of the crown and the opposing teeth to act as a 
 cushion on which to bite. 
 
 This procedure will force out the excess cement if the 
 latter is of suitable consistency to tlow. If too stitT to flow 
 under steady pressure, mallet blow^s will be even less effective, 
 although the latter method is frequently adopted, usually to 
 the injury of the peridental membrane. 
 
THE GOLD SHKLL CROWN 769 
 
 When seated and tlie eenient has set, tlie sni-jilns sliouhl 
 he removed, the gums syringed with warm, normal salt solu- 
 tion, and massaged to relieve the general discomfort resulting 
 from the operation. 
 
 CASTING THE CUSPS 
 
 The occlusal surface of a crown may 1k> cast directly to 
 the axial band. This method, in some cases, obviates the con- 
 struction of a counterdie, as well as the necessity for form 
 ing casts of the mouth. Technical procedures of this method 
 of develojiing a crown vary considerably, but the general lu'in- 
 ciples are similar. TIic following is a sinijile and conunon 
 method of procedure: 
 
 Form, fit and contour the axial liaiid to the tooth as de- 
 scribed. Apply a block of softened inlay wax to the occlusal 
 end of the tooth, within the band. Instruct the patient to close 
 in simple occlusion. Trim oft" peripheral surplus of wax 
 and instruct the patient to bite sideways and in various direc- 
 tions. This step develops clearance ]iaths for the cusps of 
 opposite teeth. With small carving instruments, the fine 
 lines and sui-face markings are developed in the wax, and the 
 occlusal surface given its desired form and contour. 
 
 Eemove the band and carxing fi-oni the tooth. Usually 
 the bulk of wax within the band is greater than necessary to 
 reproduce in gold. It may lie removed by chilling the wax 
 and scraping from the interior of the crown with a discoid 
 instrument. The wax may be reduced to a layer of uniform 
 thickness, over the entire occlusal area, by holding the crown 
 against a strong light while scraping away the excess. The 
 transmission of light through the wax clearly indicates the 
 thick and thin areas. This method was suggested by Dr. J. 
 W. Birkland a number of years ago. Another method of re- 
 moving the wax is as follows : 
 
 A small metal tube with a receptacle for holding the 
 melted wax is heated and passed against the interior of the 
 crown. As the wax melts it is withdrawn by suction, a small 
 rubber hose, attached to the metal tube, being held in the 
 mouth. This is a design of Dr. F. E. Eoach and is called a 
 wax suclier. 
 
 A sprue foi'mer is attached to the cusp surfaces at some 
 convenient point, the crown invested in a casting ring, so that 
 the wax occupies as nearly a central position as possible in 
 the ring. Casting is accomplished in the usual manner. 
 
770 'I'HE GOLD SilKLL CHOWN 
 
 Sometimes the cast ciisiis I'liil lo unite perfectly with the 
 axial band at all points, and in some instances not at all. 
 When this occurs, the casting may be soldered to the band. 
 
 To obviate the failure of union mentioned, the occlusal 
 end of the band may be notched with the shears, and the den- 
 tated edges bent slightly before ajiplying the wax and carving 
 the cusps. This method develo])s positive mechanical anchor- 
 age between the band and casting. 
 
 CAST CROWNS 
 
 Various other methods are in vogue for casting crowns, 
 either whole or in part, which have proved more or less sat- 
 isfactory. 
 
 One of these methods consists in prejiaring the root de- 
 cidedly cone shaped or so that tlie band, wiien adajtted closely 
 to it, will withdraw. 
 
 The band is now formed to fit the root closely, so that 
 when driven on it will cling to the axial walls firmly. It may 
 have a disc soldered to the occlusal end, thus converting it 
 into a deep cap, or the occlusal end may l)e left open. 
 
 Inlay wax is applied to the axial walls and occlusal sur- 
 face of the cap and the crown developed to the desired con- 
 tour by carving. 
 
 Since it is difficult to adapt the wax to tlie cap in the 
 mouth, an imjiression-bite should be taken with the band or 
 root cap in position. From this casts are developed and 
 mounted on the occluding frame. The f)and is then carefially 
 removed from its cast, being careful not to disturb its cervical 
 matrix. Inlay wax is now applied to and melted against its 
 outer surface and over its occlusal end. It is uow returned to 
 position on the cast, the occlusal area softened and the 
 occluding teeth pressed into it, after which the cusps are 
 carved to desired form. The axial outlines of the crown are 
 developed by removing surplus or making additions of wax 
 as required. 
 
 The waxed crown can be returned to the mouth if neces- 
 sary for testing its occlusal adaptation, length, general con- 
 tour, etc. 
 
 When satisfactory, it is invested and cast in tlio usual 
 manner. 
 
 Oftentimes in casting a crown of this ty])e, the contrac- 
 tion of investment within the liand walls is sufficient to per- 
 
THE CJOI.D SHKLL CKOWN 771 
 
 mit the gold to cuter, thus intei-t'eriiig with tlie fit of closely 
 adapted bands. 
 
 Dr. Weinsteiu suggests the insertion of a closed end cop- 
 per thimble, slightly smaller than the interior of the crown. 
 The crown is first tilled with investment, and the thimble in- 
 serted, closed end first, so as not to tonch the crown walls. 
 
 THIMBLE INSERTED IN CKOWN 
 TO PREVENT EXCESSIVE CON- 
 TRACTION OF INCLOSED IN- 
 
 \E.STMENT 
 
 The interior of the thimble is also filled with investment, after 
 which the crown may be invested in the nsnal manner. 
 
 The contraction of investment between interior crown 
 walls and thimble is so slight that no gold will enter in casting. 
 
 THE SHOULDER CROWN 
 
 The SltDiildt'r Cnniii is designed to oliviate the overlay- 
 ing" of a band against the peripheral surfaces of a tooth. The 
 joint junction between tooth and a crown of this type being 
 continuous, is similar to that of an inlay w'ith adjacent tooth 
 surfaces. The advantages of such a crown, therefore, when 
 well adapted, are obvious. 
 
 PREPARATION OF THE NATURAL TOOTH 
 The axial surfaces of the tooth are prepared so as to 
 converge more or less uniforml.v cervico-occlusally. Instead 
 of terminating cervically, in a cone, the base of which is more 
 or less indefinite, the axial surfaces should terminate in a dis- 
 tinct cervical shoulder. This shoulder should be formed at 
 right angles to the long axis of the tooth. Should be about 
 one thirty-second of an inch wide, more or less, and should 
 follow the curve of the gingival gum tissues. 
 
 When possible it should be located under the free gum 
 margin, but if inconvenient to so locate it, the hygienic value 
 of the crown will not be impaired, since, as before stated, the 
 surface of the crown with that of the tooth is continuous. 
 
772 THE (iOI.I) SHKLL CROWN 
 
 CONSTRUCTION OF THE CROWN 
 
 'I'ln' usn.-il iiictluxl dl' ciinsl nictinii foiisisis in tiiking an 
 impression (<\' tlic |iic|i;iic(l Idnlli in an open end l)and, fillwl 
 with softcncil inodcliii.ti' conipdniiil. This is lilicd with aiiial- 
 .ii'iitn. roi'iiiini;- (he liasc sullicicnt l\' wi<h' and deep to I'csist 
 st fcss of swaying. 
 
 Wlicii separateil from the impi-cssion the die is imhcddcd 
 in moldine, in tlie swaging ring, and a cap fitted to it. A ligiit 
 gauge, '22 carat gold, seandess thimble, slightly longer than 
 the eervico-oceliisal length of the prepared tooth, is adapted 
 to the metal die, first with tlic iiorn pene mallet and afterward 
 ))y swaging. The cervical end of the cap should he reflected 
 against the shoulder and its outer margin trimmed to coincide 
 with the root periphery. The cap may lie formed of a band, 
 and its occlusal end closed with a disc 
 
 Heavy platinum or gold foil is sometimes used, being 
 conformed to the die, first by burnishing and afterward by 
 swaging. The folds or wrinkles, which naturally result from 
 this method of adapting the foil, in no way seriously interferes 
 with the adaptation of the crown. 
 
 When the cap is developed it is returned to the root for 
 an impression-bite, from which casts are developed. 
 
 Inlay wax is now applied to the outer surfaces of the 
 cap and the crown carved to meet occlusal and esthetic re- 
 quirements, after which it is cast in the usual manner. 
 
 SEAMLESS GOLD CROWNS 
 
 A seandess crown is formed from a single disc of gold 
 plate, and is therefore devoid of soldered joints. 
 
 With mandrels of gradually decreasing size, the disc is 
 forced through a series of holes in a device much like a draw 
 plate, and is thus converted into a thimlile. From this thimble 
 the crown is developed by swaging. 
 
 Thimbles are comparatively simjile to construct, but most 
 prosthetists use the maimfactured thimbles which the su|)ply 
 houses carry in stock in various sizes and gauges of gold. 
 
 Although there are many variations in detail, there are 
 only two general methods of constructing seamless gold 
 crowns. 
 
 First, by swaging the thimlile within a matrix, and sec- 
 ond, by swaging it over a die. By' either method a model or 
 pattern of the desired form of crown must first be foi'uied, 
 in order to construct the matrix or die. The construction of 
 
THE GOLD SHKLL CROWN 773 
 
 the iiattcni is practically the same in citlu'r case except that 
 ill the die method the pattern iiiiisl he sligh.tly smaller than 
 the proposed crown is to be, since the gold is adapted over or 
 outside of the die. and is tlieret'ore larger than the latter, or 
 the pattern from which the die is (h'Vel()[ied. 
 
 THE MATRIX METHOD 
 
 First, the tooth is prepared as for an ordinary shell 
 crown. To this is fitted a seamless or soldered copper band 
 of the same gauge as the gold thimble to be used. The band 
 should be scribed and fitted niuler the gingival margin of the 
 gums exactly the same as a gold band is fitted. 
 
 Its axial walls should be contoured to the desired form, 
 its occlusal end notched to represent the cusp elevations. 
 
 The occlusal surface is filled in with softened metalline 
 compound and when caixcd to correct form, the band and 
 carving are removed from tiie tooth. 
 
 Fill the inside of the band with moldine, flush with its 
 gingival margin, and within this insert a small wood or metal 
 peg, allowing it to project about one-fourth inch, to serve as 
 an anchorage for the pattern in casting the counterdie. 
 
 Form some moldine into a cake about two inches in diam- 
 eter and one-half inch thick, giving its upper central surface 
 a slightly convex form. 
 
 Set the crown on this convex surface, cervical end down, 
 the projecting ]>eg entering the moldine base. AVith the point 
 
 LEKT CIT SHOWS PATTERN CROWN SET ON MOLDINE SL.\B WITH 
 
 CAROHOARU SET IN POSITION TO DIVIDE THE SIETAI. AS IT IS POURED. 
 
 IIIOHT CIT snows SWAGING RING READY TO APPLY OVER CROWN, 
 
 ON MOLDINE BASE 
 
 of a knife adai)t the moldine neatly to the cervical margin of 
 the band, being careful not to imbed the latter in the clay. 
 The ui)]ier surface of moldine on Avhich the cervical end of 
 the crown rests gives form to the cer\ ical margin of the coun- 
 
774 THK liOLI) SHELL CROWN 
 
 Ici'die, and siiic<' tlic ,i;iii;;i\al ciirNatiirc as well us length of 
 crown (lc|icii(ls u[iiin lliis margin of the conntcrtlie, care 
 should !)(' taken Id carry (Hit this step accurately 
 
 A siieciul riii.i;-, (it which there are two genei'al tornis, is 
 used in wliicli to cast the counterdie matrix. Both forms of 
 rings liave tapered openings extending through them so that 
 counterdies, wlien cast, will part readily from them. In one 
 ring there are two slots formed in the inner wall and opposite 
 each other for holding a U-shaped piece of cardboard, for par- 
 tially dividing the metal in casting. In the other, there are 
 two metal ribs extending centrally toward the ])attern, which 
 fulfill the same purpose as the cardboard. A plain, heavy- 
 walled ring with a taper opening will, however, answer the 
 jmrpose equally as well. 
 
 The U shaped cardboard is now cut and fitted in the ring 
 slots, the central portion of the card being removed, and the 
 opening made sufficiently large to avoid eucroachuient of the 
 card margins on the pattern crown. 
 
 The ring should be so centered over the i^attern that tlu- 
 card edges are opposite its greatest diameter, so that when 
 
 \(, TUNC, KRSTING ON MOLDING 
 HI M)\ rOB TTin ( OI NTEItnlE 
 
 east and the counterdie is split, both halves wil' be readily re- 
 leased from the ^lattern. 
 
 Fusible metal is now cast into the ring, around and over 
 the model crown. When hardened, the casting is removed, 
 the lilade of a knife is inserted in the slot made by the card- 
 board, and with a sharp hammer blow the die is split in two 
 pieces. 
 
 The ])attern is now removed and the counterdie, if sat- 
 isfactory, is trimmed, oiled, and returned to the casting ring. 
 
THK COM) SHKLL CROWN 
 
 775 
 
 SWAGING THE CROWN 
 
 A gold tliiiuhlc is selc'ctcd, slightly loiigiT than the dciitli 
 of matrix and which tits closely into it. The interior of the 
 thimble is filled with baseplate gutta ])ercha, a square end. 
 steel mandrel, which will i)ass into the thimble and lit it closely, 
 is pressed against the gutta percha and given two or three 
 blows with the hammer. 
 
 The thimble is now remoxcd and examined, to note the 
 result of the tirst swaging. The ]irincii)al accident liable to 
 
 occur during swaging is tearing of the gold. By thoroughly 
 cleaning the crown, ])olishing, annealing and continuing the 
 swaging process slowly, the gold can be forced out against the 
 matrix walls and partially into correct occlusal form. 
 
 Development of the fine occlusal lines u-<nally reciuires 
 the a]i])lication of a hardwood ])oint or a small, somewhat 
 round-i)ointed steef mandrel. At no time during the swag- 
 ing process can the gold be forced too rapidly, or splitting of 
 the walls will most likely result. When developed to correct 
 form, tlie cervical surplus of the crown is removed even with 
 the cervical margin of the matrix. 
 
776 THK (JOLU SHIOLL CKOVVN 
 
 Usuallx' ;i little (•(in-cctioii i)\' tlii> end ol' liic ci-dwii with 
 the eontoiiriiii;- jilicrs is rciiuii'cd. 
 
 Tlie inner ciis]) snrl'ai'es sliduld he tliickeiicd hy lIowiuK 
 solder inside the crown. 
 
 Sometimes, to avoid daiiger of the nin^ival end of a 
 seamless erowii stretching, when set and sul)jected to stress, 
 a tihn of high grade solder is flowed around its entire oTiter 
 periphery'. AVhen ^lolished, snch addition will not \n' 
 noticeable. 
 
 The steps of linishing and setting the einwii ai'e similar 
 to those of any gold shell crown. 
 
 SWAGING A SEAMLESS CROWN BY THE DIE METHOD 
 
 When the crown is to he swaged o\-er a die, the ])attern 
 must, as before stated, be smaller timn the required crowu by 
 an amount equal to the thickness of the walls of the gold thim- 
 ble, otherwise when completed the finished crown will be cor- 
 respondingly larger than the pattern. 
 
 A convenient and accurate method of forming the ]iattern 
 is as follows: 
 
 A copper band of the same gauge as the gold to be used 
 is fitted to the root, as previously described. The a.xial walls 
 should be contoured and the occlusal end notched or occluded 
 with the opjiosite teeth. The cusps are carved in plaster and 
 when the crown is removed the inner walls of the band are 
 coated with a thin film of oil. 'I'lie remaining interior space 
 is filled with plaster, wdiich should unite with the cusp carv- 
 ing. The plaster last added should also extend about one- 
 eighth inch beyond the cervical end of tlie crown to form a 
 pedestal for the pattern. 
 
 The band is now carefully divided with a tine fissure bur 
 usually applied on the lingual side, being careful not to mar 
 the jilaster while doing so. The ends are then bent outward 
 and the band carefully removed, leaving a pattern of the tooth 
 in i^laster. 
 
 The plaster cusps overhang the axial surfaces an amount 
 equal to the thickness of the band walls. 
 
 This overhang should be carved away so that the sur- 
 faces are continuous. No reduction of the occlusal surfaces 
 is necessary, as the slight amount in extra length of the crown 
 (about 1-100 of an inch) can be removed from the cervical 
 end in final fitting. The pedestal or cervical extension should 
 be trimmed so as to show a slight shoulder, to outline the 
 termination of the cervical end of the crown. 
 
THE (iOI.D SHELL t'KOWN 777 
 
 'I'lic [»;itl('rii, now \vlioll>' (•(iinpost'd of jilastcr, is coated 
 with separating medium. 
 
 A small mix of plaster is made and spread on a siieet of 
 palmer. It should be about three-eighths inch thicli and one 
 and one-fourth inches square, flattened on its upper surface. 
 
 Into tliis the varnished pattern is jjressed, so as to imbed the 
 occlusal area and some of the axio-occlusal jteriphery, usually 
 about one-eighth inch of the occlusal end of the pattern. When 
 hardened, the ))laster is trimmed smoothly, small depressions 
 made in the four angles to serve as guides for the subsequent 
 pieces to be constructed, and its surface varnished. 
 
 Another mix of ])laster is now made and applied to one- 
 half the crown and pedestal. This should embrace approx- 
 
 imately one-half the pattern, the line of greatest diameter 
 indicating the amount of surface to cover. Its ends and 
 sides should be squared up, and the surfaces extending from 
 the pattern outward, trimmed perpendicularly. Guide depres- 
 sions sliould also be made in these surfaces. 
 
77S -PUK liOl.l) SIIKIJ, CUOWN 
 
 W'licii liiinlciicil, llic fi-csli areas of |iiaslcr ai'c \'ariiislu'd 
 and auotlicf mix inailc and applied a.i^aiiisl the opjto.site side 
 of the pattern, Iniihlinn il np in conjunctioii witli tlie other 
 two ]iiocos to I'diin a reelani;ulai- lihick, in the top of which 
 I he liase ol' 1 he lieileshd is seen. 
 
 PI.ASTEU MATRIX rdMIT-ETE, liUT NOT 
 SEI'AltATKll 
 
 MATJtlX Si;i'AIlATi:il 
 
 I'ATTKHX I'KCIVVX KHMIIVEH 
 
 When hardened and squared up, a few light hammer 
 lilows will loosen the several pieces and the pattern is removed. 
 
 On placing the three pieces together, a matrix will lie 
 formed, representing in reverse the form of the pattern. 
 
 The external ojiening is now beveled slightly, the block 
 bound together witli rubber bands or binding wire, tlie ring 
 
THE GOI.U SHELL CKOVVN 
 
 779 
 
 of a swaging de\ioe is set on top of the block and e\('nly 
 centered over the opening. 
 
 Fusible alloy is now melted and cast into the matrix and 
 ring. 
 
 When cold, and the jilastei- is remoxcd, a die of the tooth 
 witli a cervical extension will he seen, attached to and stand- 
 
 The rongh margins of the die are smoothed up, the latter 
 
780 'nil': (!()l,l) SHIOLI. CliOWN 
 
 oiled, and a lliinihlc scliM-tcil that will tclcscdiic o\ci- the die 
 loolli and cxlciid 1(1 its cervical line or slii;lilly lielow. 
 
 SWAGING THE CROWN 
 
 The thinilile and nppei- surface ol' the die are now co\'- 
 ercd witli tissue i)a])('r, to i)re\-ent the swag'ing material of 
 wliatever kind from iinding its way between gold and die. 
 
 The ring is placed in the swager, the outer ban-el set 
 over it and with one heavy hanunei- blow tlie ada])tation of 
 gold to die is beiiun. An examination of llie thimble is now 
 
 ■rniMHT.E ix t'osition on dm; 
 
 made. Invariably, after the first swaging, one or more folds 
 of gold have begun to form around the cervical constriction. 
 These can be obliterated without removing the thimble from 
 the die by means of light blows with the horn pene mallet or 
 the small riveting hannner. 
 
 When corrected, the gold is again subjected to another 
 single, heavy hammer blow in the swager, and wrinkles or 
 folds removed as l)efore. 
 
 This process is repeated until the gold is constricted gin- 
 givally so that folds cannot develop. 
 
 The occlusal surface, in the meantime, has become only 
 partially conformed. With the riveting hammer and a small 
 
THE GOI.U SHKLI> ([{OWN 
 
 steel luaiiilrcl. the orclusiil surracc lines arc developed, after 
 which the erowii is om-e more i-etiini(Ml Id the swager for final 
 adaptation. 
 
 Since in practically every case the crown pattern, and 
 consequently the die, are bell-shaped, the gold cannot be 
 removed from the die during the swaging process. 
 
 It is finally removed l)y placing the die with crown at- 
 tached, in water and bringing it to l)oiling point, at which 
 temperature the fusible metal melts. This method prevents 
 
 contamination of the gold by the base metal, which usually 
 occurs when the die metal is melted in the open flame. 
 
 By this method of construction the crown walls are thick- 
 ened, while in the matrix method the walls are to a greater 
 or less extent reduced in thickness. 
 
 FINISHING THE CROWN 
 
 The gingival surplus is trinnned to the line of .iunction 
 of crown with pedestal, the crown boiled in acid and polished. 
 The occlusal or incisal ends should be stiffened interiorly, and 
 the cervical end covered exteriorly with a thin film of high- 
 grade solder. 
 
 GENERAL REMARKS 
 
 In all cases of pattern construction, a copper band should 
 l)e carefully scribed and fitted to the natural tooth. This may 
 be wide or narrow, deiiending on how the pattern is to be 
 formed. On or within this band, the wax, plaster or other 
 material is built and carved as required. 
 
 It will be seen' that since the pattern is at no time sub- 
 jected to heat, it may be formed of wax or any material suffi- 
 ciently resistant to carve well and retain its form in handling. 
 
 One who can carve well can produce very satisfactory 
 forms of crowns by this method. One who cannot carve 
 
782 THK LiOLD SHELL CROWN 
 
 slioiikl not attempt this niothod of construction, for he will 
 most cortainly be disappointed with esthetic results. 
 
 Certain mechanical aids, however, can be resorted to, 
 which will relieve one of most of the carvinsj-, but not of nice 
 adjustment of the several ]iarts of the wlioh'. 
 
 REPRODUCING NATURAL TOOTH FORMS IN INLAY WAX 
 
 One of these mechanical aids that may be applied in vari- 
 ous ways consists in pressing the crown of a natural tooth, or 
 a typically formed artificial tooth, into moldine, the surface 
 of which should be dusted with talcum i)owder. On removal, 
 a distinct matrix is seen, into which melted inlay wax is 
 poured. Since this wax cools quickly, and when cool is quite 
 hard, the reproduction may he carved to any desired form. At 
 any rate, it furnishes a very good basis on which to Ijuild the 
 form desired. 
 
 This method is often adopted in forming dummies in wax 
 that are to be reproduced by casting. 
 
 In the hands of the writer the swaging of crowns over a 
 die has proven very satisfactory. 
 
CHAP ^1^ K R XXIX 
 
 BRIDGEWORK 
 
 ENGINEERING PRINCIPLES 
 
 In scientific fields it is a recognized fact tliat the use of 
 exact terms encourages tlie development of exact methods. It 
 is therefore of advantage to the student to become familiar 
 with the terms connuonly used in dental hridgeworl^, and their 
 concise meaning as understood and applied in engineering, 
 from which field these terms have been selected and adapted 
 to dental purposes. 
 
 A bridge is a structure which spans a space, and which 
 is designed for sustaining or supporting not only its own 
 weight, but additional loads or stresses that may be brought 
 upon it. 
 
 A bridge consists of a substructure and a superstructure. 
 The substructure of a bridge is the supporting foundations, 
 while tlie superstructure is that part which rests upon the 
 foundation supports, spans the space and carries the load. 
 
 The term abutment is defined as "the terminal mass of a 
 bridge, usually of masonry, which receives the thrust of an 
 arch or the end weight of a truss; in distinction from a pier 
 which carries intermediate points. . . ." (Century Dic- 
 tionarj'.) 
 
 APPLICATION OF STRESS TO THE SUBSTRUCTURE OF A 
 BRIDGE 
 
 There are five principal types of bridges recognized in 
 engineering, differentiated l)y the manner in which the weight 
 of the superstructure and load is sustained by the foundation 
 supports. 
 
 First, the arch bridge of masonry, in which the abutments 
 must not only support vertical stress, but end thrust as well. 
 In a bridge of this type the arch is not a complete factor in 
 itself, but is dependent upon constant end compression be- 
 tween opposing abutments for maintainance of form and 
 capacity for sustaining load. This end compression, which 
 tends to force the abutments apart, is usually provided for by 
 broadening the end terminals of the abutments with flaring 
 walls, and filling the inclosed space between these abutting 
 
 783 
 
I!i;iih;k\v()i;k 
 
 walls and the iiriiiripal foinMlat inii with I'artli or lork. Tb(^ 
 L'lid abiitiiR'iit lliercrdrc dciiv-'s its iiaiiu; t'ruiii thu fad tliat it 
 (ibuts the bank. 
 
 A STONE ABCH BBIDGE 
 
 The weight of the structure and applied load exerts down- 
 ward vertical stress and an outward ])ush against the abut- 
 ments. 
 
 GIRDER OF TRUSS BRIDGES 
 
 Second. The finder, or tniss bridge, is one in which the 
 structure which bridges the space between the two abutments, 
 or wlien consisting of more than one span, between an abut- 
 ment and a pier, is a complete factor in itself, rigid, and 
 capable of sustaining its own weight and of the applied load 
 as well. The span may be solid, consisting of simple, solid 
 girders of wood or iron, or it may consist of several members 
 so united as to act as a solid beam. As an example, the Howe 
 Truss is composed of an up]ier and a lower chord united by 
 
 A HOWE TRUSS BRIDGE 
 
 vertical and diagonal web members. This truss is so framed 
 that the upper chord is always in compression, the lower al- 
 ways in tension, the vertical members under tensile strain, 
 and the diagonal under compressive stress. The weight of the 
 truss an^ load exert a downward vertical stress upon the abut- 
 ments and piers. 
 
BRIDGE WORK 
 
 SUSPENSION BRIDGES 
 
 Third. A SKspcnsion bridge consists of a ])latform, liuiig 
 on cables which span the space and ai-e snpi)orted by abut- 
 
 A SUSPENSION BRIDGE 
 
 ment towers. The weiglit of the structure and the load it 
 carries exert a vertical stress and an inward pull upon the 
 abutments. 
 
 PONTON BRIDGES 
 
 Fourth. A ponton bridge consists of a platform super- 
 structure, supported by shallow vessels, or boats which float 
 upon, and are anchored in a stream of water. Bridges of this 
 type have no solid or tixed abutments or piers, except the ter- 
 minal banks, each boat carrying its proportion of weight of 
 the immediate superstructure, and yielding under the immedi- 
 ate load imposed, according to its capacity for displacement of 
 water. 
 
 The term "pontic" has been suggested as a substitute for 
 "dummy" in describing a bridge tooth replacement. The term 
 seems scarcel}' appropriate, since practically all fixed bridges 
 are of the rigid truss type. • 
 
 THE CANTILEVER BRIDGE 
 
 Fifth. A cantilever bridge is a structure consisting of 
 two or more rigid trusses which span a space, each of which is 
 sui)i)orted in or near its center by a foundation pier. That 
 portion of the truss extending from the foundation pier to the 
 abutment bank is called the shore arm, wliile its opposite end 
 is called the river arm. 
 
 In a structure of this type, consisting of two trusses which 
 bridge a river, the length or weight of the shore arm is in- 
 creased over that of the river arm. To counteract the eti'ect 
 of load applied at the terminal end of the river arm, the 
 shore arm is tied down to the bank al)utment. This is neces- 
 sary, since the terminal end of the river arm is unsupported 
 and its stability under load depends upon the rigid 'ty of the 
 entire truss structure. 
 
BRIIKJKVVOKK 
 
 l''()i- tlic |iiii|i(is(' (iT (Miiializiiii;' stress iis well as for coii- 
 vciiiciicc in consl ruction, particiilai'ly wiicii the space to lie 
 bridged is wide, an independent truss is interjiosed hetween 
 and supported liy the tei'niinal ri\'ei' anus. 
 
 A CANTILEVER BRIDGE 
 
 Tlie stress upon the central foundation of a cantilever 
 bridge is downward, while that upon the bank abutment, when 
 the weiglit of the river arm, together with its load, exceeds 
 the weiglit of the shore arm, is upward. 
 
 DENTAL BRIDGEWORK 
 
 Bridgework, in its dental meaning, refers to the replace- 
 ment of some of the lost natural teeth by means of substitutes 
 or dummies, which are attached to and held in position by 
 some of the remaining natural teeth or roots. The teeth or 
 roots so utilized, according to the nomenclature ]irevionsly 
 outlined, are termed ahiitmoits and piers. 
 
 GENERAL CLASSIFICATION OF BRIDGES 
 
 Bridges naturally fall into two classes, fixed and reinov- 
 ahle. Both types mentioned are capable of division into sub-' 
 classes, generally similar in form, yet varying in detail, ac- 
 cording to the means of retention or attachment employed, 
 the forms of the individual factors or dummies of which they 
 are composed, and the class and arrangement of the materials 
 entering into their construction. 
 
 DISTINCTION BETWEEN FIXED AND REMOVABLE 
 BRIDGES 
 FIXED BRIDGES 
 A fixed bridge is so designated because, when perma- 
 nently set, it cannot be removed by the patient. As ordinarily 
 constructed, a fixed bridge cannot be removed by the operator 
 
BRIDGEWORK 787 
 
 without more or less mutilation of some of its parts. Occa- 
 sionally, when a l)ridge has previous!}' been partially loosened 
 through disturbance of the cementing medium, as from stress 
 of mastication or other causes, it may be removed without 
 mutilation. 
 
 FIXED BRIDGES SO CONSTRUCTED AS TO BE REMOVABLE 
 
 It is possible, and practicable as well, to construct a bridge 
 of the fixed or stationary type, wliich can readily be removed 
 and replaced by the operator, but not by the patient. This is 
 a decided convenience, for in ease of repair, or if the roots 
 forming the substructure require treatment, removal may be 
 made without mutilation of the substitute, or injury to the 
 supporting roots, and the bridge later returned to and set in 
 position. 
 
 A bridge in which the "Corcoran" block and screw is 
 applied is a representative of this type. (See page 835.) Vari- 
 ous other attachments have been suggested and successfully 
 used. One of the most practical of these consists of a projec- 
 tion extending from a crown or inlay, wliich is received in a 
 correspondingly shaped socket in the substitute. An opening- 
 extends througli both bridge and projection and in this a dowel 
 or screw is fitted. 
 
 By reference to "Application of stress to tlie substructure 
 of a bridge" it will be seen that fixed bridges come under the 
 second classification, viz., rigid truss, A-ertical stress, no end 
 thrust on abutments. 
 
 FIXED SADDLE BRIDGES 
 
 Fixed bridges are sometimes constructed with saddles to 
 rest upon and cover the border to a greater or less extent. 
 By some it is thought that two advantages are gained by the 
 use of a saddle in a fixed bridge. 
 
 First. It is claimed that the saddle affords some resist- 
 ance to stress, and thereby relieves the sub-structure or abut- 
 ments and piers, of some of the exti'a load they must neces- 
 sarily sustain, in performing their own work and that of the 
 substitute crowns as well. 
 
 Second. That by the use of a saddle, better gem-ral con- 
 tour can be given the individual members of the bridge, and 
 the formation of constricted spaces between the structure and 
 the border, in which food will accumulate, can to a great ex- 
 tent be obviated. 
 
788 KKIIKIEWOKK 
 
 It is the oitinioii (it (he wi'itcr', hased on oljsoi'vation and 
 experience, tliat the iirst of tliese so-called advantages is ex- 
 tremely doubtfnl. A saddle wliicli bears so firmly upon the 
 mucous, and indirectly upon the bony tissues when in a state 
 of rest as to yield support under the slight movement of the 
 abutment roots in their peridental membranes, will sooner or 
 later result in absorption of the bony tissues. The constant 
 pressure exerted may or may not result in absorption of the 
 mucous tissues. In any event, the slight resistance to stress 
 afforded by these tissues, even though they may not be per- 
 ceptibly absorbed, is not worth considering. 
 
 The second advantage, that of better contour afforded the 
 substitute teeth, however, is unquestionable in those cases 
 where a saddle is applicable. Wide saddles are always objec- 
 tionable and should never be applied. Even with a narrow 
 saddle, it is sometimes impossible for the patient to maintain 
 correct hygienic conditions around the structure because of 
 the difficulty in removing food particles which find their way 
 beneath it. Discrimination, therefore, should be observed 
 in the application of saddles of any fyjie in fixed bridge work. 
 
 INDIVIDUAL SADDLES 
 
 More than thirty years ago. Dr. H. H. Keith of St. Louis 
 advocated the use of individual saddles; that is, an individual 
 saddle for each dummy, not greater, usually less in area, than 
 the normal cross-section at the border, of the natural tooth 
 replaced. Within recent years this method has been revived, 
 and is being used by many with very satisfactory results. 
 
 The advantages of an indi\idiud saddle are threefold, 
 viz: first, more esthetic form may be given the dummy; sec- 
 ond, the structure feels more comfortable to the tongue, the 
 dummy being given the approximate lingual contour of the 
 natural tooth, and, third, there is less tendency for food to 
 accumulate in bulk, or become as tightly wedged as when the 
 dummies approach close to or rest against the labial or buccal 
 border surfaces only. 
 
 As before stated, a saddle, either continuous or of the 
 individual type, cannot afford any appreciable resistance to 
 masticatory stress, in fixed bridge work, and should not be 
 applied in those eases where the abutment teeth are inherently 
 weak and unable of themselves to withstand the stress. In 
 such ease a bridge is contra-indicated. 
 
BKIDCKWORK 
 
 SANITARY BRIDGES 
 
 A type of iixed Iji-idiic, (•(HiiiiKuily known as a .s(tiiitari) 
 bridge, is frequently constriK'tcd. in lnwer restorations ot" 
 bicuspids and molars partieulai-I> . wlicn absorption of tbe 
 ridge lias progressed to a eonsiderahli' extent, and when tbe 
 detieient portion of tbe substitute is not visible wben tbe 
 moutb is opened as in speaking or laugbing. 
 
 A bridge of this type consists of an ocdasal platfunii, 
 attacbed to abutment crowns or inlays. Tbe buccal and lin- 
 gual margins of tbe dummies are I'ounded in and terminate in 
 a more or less convex surface ]iresenting toward tbe border. 
 Not more than one-tbird, usually less, of tbe buccal and lin- 
 gual surfaces are deve]o])ed to anatomic form, tbe idea being 
 to preserve as mucb space as possible between ridge and dum- 
 mies, so that food may be readily removed. In most cases 
 these bridges are constructed entirely of metal. Certain types 
 of replacable porcelain teeth may, however, l)e utilized in such 
 structures when conditions are favorable. 
 
 EXTENSION BRIDGES 
 
 An extension bridge is purely and simply a cantilever 
 bridge. The cantilever princi])le is often misapplied in bridge 
 work, one abutment root having to carry one, or even two, 
 ))roximating teeth without any additional anchorage, furtbei- 
 than that afforded by contact of the terminal dummy with a 
 proximating tooth. This principle is wrong under any circum- 
 stance, even in the attachment of a single dmnmy to a single 
 root. 
 
 When two proximating roots are available as aljutments, 
 if it is possible to so rmite them that the structure will not 
 impinge upon the soft tissues, and it can be kep^t clean, this 
 principle may at times be emjiloyed to advantage. 
 
 Again, in bridges of considerable length, where teeth or 
 roots and spaces alternate, an extension dummy can be ap- 
 plied to fill tbe terminal space at one or the other end of tbe 
 structure, thus reducing the nunilx'i' of su])]iorting crowns 
 without curtailing necessary sup]U)it. 
 
 Practically the only advantag<' of an extension bridge 
 under any conditions is in obviating the crowning or inlaying 
 of a sound and useful tooth. Tlie problem tbe in'ostbetist 
 must determine is whether a rigid, well-supported, sanitary 
 structure can be introduced without a terminal sn]iport at 
 each extremity. 
 
790 liUlDliKWOKK 
 
 IMPORTANT FACTORS TO BE CONSIDERED IN PLANNING 
 FIXED BRIDGES 
 
 Tlie eiigiiiccr, in |ilaiinin,ii' and constructing a lii'iilgc, can 
 select the material and Imild tlic foundations for the structure 
 in wliatever location is best calculated for its support. 
 
 The prosthetist cannot Iniiltl 1 he foundation for the bridge 
 he constructs. He must select f loni among- the teeth and roots 
 present those which, in his judgment, are most favorably 
 located and best calculated to i)erform, not only their own 
 work, but sustain the extra stress thrown upon them by the 
 added masticatory area of the teeth supi)lied. 
 
 ABUTMENTS AND PIERS 
 
 No engineer will ])lau or construct a bridge truss with 
 lateral curvature. In case a curve in the road is required 
 he will either construct short, straight trusses with piers at 
 
 GltOUND I'LAN OK A CfBVEI) riUSS SI TI'dUTED IIY ONl.V TWO Am TMKNTS, 
 CORKECT BECAUSE WHEN UJAl) IS Al'I'MED TO OITKRMOST CLRVE 
 THE TENDE.VrV «dr[,l) HE TO ROTATE 
 
 TIIL SAME TRISS SUl'I'ORTEl) IIV 
 
 \1UTMENT IN THE CENTKl! 
 
 each end, and dispose them in curved alignment, or plan 
 somewhat longer trusses of greater breadth on which the 
 required curve of roadbed may be laid out. In any case, 
 change of direction requires that the outermost curve shall 
 have a firm foundation to support it or the structure will fail. 
 
BRIUGEWORK 791 
 
 Again, ill engiiit'i'iiiii;' the t'oinidations of a bridge rest upon 
 bedroclv or its equivalent, and the abutments are not sviscepti- 
 ble to any marlved lateral stress or vibration. Neither does 
 the substructure suffer materially under direct stress, being 
 capable of successfully sustaining not only the weight of the 
 constant suiierimposed structure, but many hundred times 
 more than the heaviest intermittent load that will be applied. 
 
 .V bridge designed and built in a manner, or of such ma- 
 terials, that the dividing line between safety and disaster is 
 indelinite, would subject the designer to severest criticism, if 
 not criminal ijrosecution. 
 
 In the construction of dental bridges, the prosthetist is 
 confronted with more serious problems than arise in the engi- 
 neering field. The foundations of a dental bridge are not firm 
 and unyielding. They are su))ject to depression under direct 
 and a much greater degree of movement under lateral stress. 
 
 The power of resistance to stress, without injury, of the 
 peridental membranes of teeth, varies in dift'erent individuals. 
 The dividing line between the amount of stress ordinarily 
 delivered upon the abutment roots under a bridge, and that 
 which will cause permanent injury to the peridental mem- 
 brane is very indefinite, so close, in fact, that frequently in- 
 jury beyond repair occurs before the patient is aware of it. 
 
 The amount of stress actually delivered upon a bridge 
 to the supporting roots is directly dependent upon two fac- 
 tors; first, the habitual masticatory effort of the individual, 
 and second, the occlusal area of the bridge involved. 
 
 This stress cannot be determined, or at least only ai> 
 proximatel}', nor can the power of resistance of the peridental 
 membrane to withstand stress, without injury, be estimated. 
 The necessity, therefore, of selecting sound, healthy roots 
 or teeth, in sufficient number, and properly located for sup- 
 porting a bridge, is obvious. 
 
 Since the vital factors which determine the possibility 
 of placing a successful bridge depends upon the position and 
 condition of health of the abutments and piers, the utmost 
 care should be observed in their selection. 
 
 Long span bridges, extending, for exami)le, from cuspid 
 or first bicuspid to third molar, inclusive, without an inter- 
 mediate pier, are", as a rule, unsatisfactory. In such case 
 the abutment teeth or roots are required to perform not only 
 their own functions, but siistain the stress delivered ui»on the 
 intervening teeth as well, for which, jihysiologically, they are 
 not capable. 
 
7!»2 liKlliCKWOliK 
 
 A r;i\(ii';ilil(' rouiidnlidii for siicli a. span would !)(', cusiiul 
 and third molar for alintniciits, and serond liicnspid or lirst 
 JiK.lar for a pier. 
 
 in case no ititcrxcning pier is present, tlie prostlielist 
 cannot Iniild oiu' as can the engineer. A saddle will not i'ul- 
 lili the requirement, thcrcFoi-e some form of removable den- 
 ture of the saddle iy['<' should be considered, in which the 
 border will receive the burden of stress, the terminal teeth 
 serving principally to retain the a])pliance in i)osition. 
 
 A simple anterior bridge in which the two lateral incisors 
 are to be replaced, the two central incisors serving as abut- 
 
 Sl.MI'l.E AXTEIUOIt. ('A:NTI- 
 LEVEI! BRIDGE 
 
 ments, will frequently i)rove successful. A structure of this 
 tyioe is classed as a cantilever bridge. 
 
 A simple anterior bridge, involving the replacement of 
 the four incisors, the two cuspids serving as abutments, is 
 not usually successful, when the anterior curvature is con- 
 siderable, even though the incisive stress is moderate. In 
 
 such case the line of force against the abutment roots is 
 outward, instead of apically as it should be. 
 
 The cantilever principle, however, can fre(|U('ntly be em- 
 ployed to advantage by extending the bridge distally at each 
 end. to include the first bicuspids. When extended, the cuspid 
 and bicuspid crowns should be so united as not to impinge 
 on the soft tissues. This may be done by joining them at 
 their contact surfaces, leaving the inter]n-oximal space free 
 and open. 
 
 Again a frequent combination consists of cuspids and 
 second bicuspids utilized as supporting roots, the four an- 
 terior and the two first bicuspid teeth being replaced. This 
 
BKIUliKWOKK 
 
 is a complex bridge of stahlc t'oi'iii liascd on the cantilever 
 priuciple and when eoiiditioiis aic faxorahle will prove suc- 
 cessful. 
 
 SAMr-: imiDCK .\s ox rBErEDix<; 
 
 PACK EXTENDKD TO INl'LUOE 
 
 EiusT urcrsriDs. Tnrs formixo a 
 
 (.'OMIM.EX STIUCTtRE 
 
 (_'O.Ml>I.EX BKIDGE, OF THE ('AXTILE\ER 
 TYl'E, OP THE CUSPID AND SBCOXU BI- 
 CUSPID SERIES 
 
 A com])lex bridge, extending from the first bicuspid on 
 one side to the corresponding opposite tooth, with a sound 
 and healthy central incisor present to serve as a pier, might 
 possibl.v prove successful if the stress of occlusion is light. 
 Under these conditions, however, a fixed bridge is usually 
 contraindicated. 
 
 Frequently the space resulting from the loss of one tooth 
 or of two teeth that proximated, can be successfully filled 
 by a fixed bridge of the cantilever type, that is, having only 
 one fixed abutment. To suj)iiort the extension, a lug is at- 
 tached to and carried beyond the terminal end of the dummy, 
 on a line with or slightly below ils occlusal surface. This 
 lug rests in a depression, in an inlay carried by the proxi- 
 mating tooth. Such an attachment converts the extension 
 bridge into one of the regular type, since the tooth carrying 
 the inlay, although not attached, serves as an abutment. 
 
 A very connnou type of simple ])osterior rejilacement con- 
 sists in utilizing the cuspid and first molar as abutments, the 
 two bicus])ids being su]iiilied. 
 
 I'.rcrAL AMI I.IXCIAI, VIEW OK SIMri.E rosTi: 
 
 lilOR IlIUlJliE. IX THIS CASE THE S1'A<'E OCIT- 
 
 PIEI) BY THE SECOXD BICUSPID HAS WIDEXKI) 
 
 AXD A MOLAR DUMjrV IS SUBSTITUTED 
 
 A SIMIM.E. POSTERIOR BRIDGE. 
 KIltST UiCUSlMD AXn SECOND 
 MOLAR SERIES, IX WHICH SADDLE 
 HACK TEETH ARE UTILIZED FOR 
 THE SUBSTITUTES 
 
 Sometimes the cuspiil and second molar are used as alnit- 
 ments, the two bicuspids and first molar dunnnies being swung 
 between. Tn this case the cusjiid and second molar must sus- 
 
liKIDCKWORK 
 
 lain not only their own load, lint (■a<'ii |)crl'oini the work of 
 uiie and uiu'-liall' additional teeth. In many instanees a liridj^e 
 of this type will pi-oxc iiiisiiceessrnl. 
 
 . k .jilL^lvJPii^ 
 
 \ SIMIM I I'OSILRKIR FltllM I 111 
 
 IHF IISPII) AND &E <)\II Mill Mi 
 
 bERILb. IIIATORIC TEIiTH IU1I,1/L1I 
 
 FOR SUBSTITUTES 
 
 A type of stnicture called an interrnpted l)rid^e is some- 
 times construeted to avoid involving sound ]iroxiniatino- teeth, 
 '{'he lividge is converted into a rigid structure l»y joiniui!,' the 
 
 A COMPLEX CANTILEVER BRIDGE I'OKMKH in IMT- 
 ING A CENTRAL AND CUSPID SERIES WITH A CUSPID 
 AND SECOND MOLAR SERIES 
 
 several factors with lieavy iridio-)ilatinuin wire, l)ent to lie in 
 contact with the tissues, yet so as to avoid contact with the 
 teeth not involved. This tyjx' of bridge was suggested I)y Dr. 
 
lililDCKWORK 795 
 
 ,1. l.cdii W'illiiiius iilimit ISSli and illustrated in the Dental 
 L'osnio8 of that year. 
 
 Occasionally a i'nll denture liritlge is constrneted in which 
 practically all of the miissing teeth and the natural teeth |»res- 
 ent are united to form a rigid structure. 
 
 ITsually bridges of this type are unsatisfactory. First. 
 because of constrictive difficulties encountered; second, he- 
 cause of danger of fracture under masticatory sti'ess, and. 
 
 third, the lial)ility of the almtment and pier roots giving way 
 under the excessive strain to which subjected. 
 
 Some form of removable denture will, in most cases, 
 ]n'ove very much more satisfactory than a structure of this 
 type. 
 
 PREPARATION OF ABUTMENT ROOTS AND PIERS 
 
 The al)utment and pier attachments of a bridge which 
 rest upon the supporting roots usually consist of crowns. 
 Since these differ in no essential detail from individual 
 crowns, the preparation of roots and teeth for their reception 
 differs but little from the outlines previously given under 
 "Crown Construction." There is, however, one imjiortant 
 consideration in bridge work that does not apply to individual 
 crowns which must be carefully observed. 
 
 When the supporting crowns of a bridge which rest upon 
 the roots consist of either shell or dowel crowns, the axial 
 surfaces of the teeth involved must be parallel as nearly as 
 l)ossil)le. This is ;iecessary in order that the abutment and 
 pier pieces may be withdrawn from and returned to position 
 on their respective roots without hindrance. 
 
 Tn some cases excessive reduction of the axial surfaces 
 of divergent or convergent natural crowns is required to 
 
Tilti Bi;il>(iK\V()l{K 
 
 liriii.n' lliciii in |i;ir;illcl ivljiliuii. I''i-c(|iicn1 1>', iilso. the ciuial, 
 of a root oiil of i;i'iicral ali,i;iiiiii'Mt. imist he rcaniiMl I'l-oin its 
 race end, a|iically. Id I he ln(•^ial or ilistal, t(i release and re- 
 ceive the dowel of the Miper imposed crown. 
 
 When such ])rocednres ai'e necessary, extreme caution 
 must be observed 1o a\did, Hrst, the i'ormatiou of cervical 
 shoulders on suiiportim;- teetii or projecting margins on the 
 substitute crowns, and second, to avoid weakening a root to 
 too great an extent by excessive lateral reaming of its canal. 
 
 Various methods have been suggested for overcoming the 
 difficulties of the class just mentioned, one of the simplest 
 and most practical of which can be illustrated in a case shown 
 by Dr. C. L. Anderson of Tomah, Wis. (See page 840.) 
 
 This case consisted of an upper bridge extending from 
 cusjiid to first molar inclusive. The divergence of the roots of 
 the two abutments, apico-incisally and occlusally, was so 
 marked that excessive reaming of the cuspid root canal and 
 reduction of the distal surface of the molar would be required 
 to permit the introduction of the bridge. The case was con- 
 structed as follows: 
 
 The molar tooth was prepared and a shell crown con- 
 structed for it by the usual method. A close-fitting cap, extra 
 heavy, was constructed foi- the cuspid root, in the center of 
 which and in alignment witii the root canal was an oijening. 
 A lingual half-band disc was conformed to the root cap and 
 on this base a cuspid dowel crown was constructed, being 
 adapted to but independent of the root cap. The bicuspid 
 dummies were luiited to the molar crown and root cap. 
 
 The bridge was set by cementing the molar crown and 
 cap on their respective roots, and inunediately forcing the in- 
 dependent cuspid crown in position, its dowel passing into the 
 root canal through the central opening in the root cap. 
 
 Another method consists in removing the crown of the 
 inclined tooth constructing a cap for or adapting an inlay to 
 the root. The appliance in either case should be supplied with 
 dowels of suitable size and length for anchorage purposes. 
 
 On the cap or inlay is fitted and soldered a vertically in- 
 clined block, of the Corcoran or Pleddy type. It should be 
 l)laced parallel with the line of axial surfaces of the other 
 involved teeth or roots. To this block is fitted a removable 
 jacket, around and over which a crown, of the anatomic form 
 required, is constructed. By means of an occlusal screw pass- 
 ing through the ci-own and into the block, or a set-screw pass- 
 
BRIDGEWORK 797 
 
 iug throiigli the axial wall of tlie erown and against the Ijlock, 
 the removable crown may be tirmly locked in position. 
 
 Various types of paralleling devices are procurable, with 
 which the aligmuents of the several canals aud tooth surfaces 
 involved may be tested. An instrument made by the J. W. 
 Ivory Company is very convenient for general paralleling 
 purposes, although possibly not sutiSciently exact for com- 
 plicated eases of removable bridgework in which the structure 
 is attached to several widely separated roots or teeth. 
 
 INLAY ABUTMENTS 
 
 Inlays are frequently used as abutment and pier sup- 
 ports in bridgework. There is a tendency to utilize this form 
 of attachment in extensive cases, oftentimes with disastrous 
 results. The most frequent accidents which occur are dis- 
 lodgement of the inlay or splitting of the tooth under side 
 stresses. 
 
 DISPLACEMENT OF INLAYS 
 
 The fact should be kept in mind that the stresses and 
 strains to which an inlay l)ridge abutment is subjected vary 
 radically from the stress to which the same inlay in tlie same 
 tooth will be subjected when not so involved. 
 
 First, torsional stress is very marked as when the inlay 
 occupies a comparatively central position in the mesial or 
 distal axial surface of a tooth while buccal and lingual luar- 
 ginal ridges of the dummies occupy a position to the outside 
 and inside of the jjerpendicular line or anchorage of the inlay. 
 
 In masticatory effort, the resulting torsional strain in- 
 vites not only dislodgment of the inlay, but fracture of the 
 tooth itself, i^articularly in case of weakening of the tooth 
 from caries. 
 
 Second, when two inlays carry one or more (.lummies, aud 
 the roots of the teeth diverge or converge relatively to each 
 other, the yielding of either tooth in its socket or the synchro- 
 nous movement of the two under direct stress exerts a lev- 
 erage either in the gingival or occlusal areas on the inlays, 
 which, unless very firmly anchored, will result in their dis- 
 placement. 
 
 These observed facts have proven conclusively that the 
 use of inlays as abutments must l)e confined to favorable cases, 
 and that in practically every instance some form of pin an- 
 chorage should be emjiloyed. 
 
 Various forms of modi lied iulavs or oiilaiis are made use 
 
798 UKllHilOVVORK 
 
 III' for al)u1niciil purposes, aiiuinii' which may Ix' mentioned 
 the ('aimiehael Attaehment, applieahle more iiaitienlarly to 
 the euspids, and a modified form of altachment for bicuspids 
 as well as cuspids suggested by Di-. iv A. Kennedy. 
 
 In this latter attachment the tooth is pi'epared and the 
 inlay attached to its mesial or distal half instead of the lingual 
 half of tlie tooth as in the ( 'armicliael Attachment. 
 
 A CLASSIFICATION OF FIXED BRIDGEWORK 
 
 Dr. A. J. Bush, Professor of C'i'own and Bridge Work in 
 the Ohio University, Dental Department, of Columbus, pre- 
 sented a paper before the National Dental Association at 
 liochester, N. Y., in 1914, on "A Classification of Fixed 
 Bridgework. " In Jamiary, 1915, a similar paper was also pre- 
 sented by the same essayist before the National Association 
 of Dental Teachers at Ann Arbor, Midi. (C^opyriglited by 
 Dr. Bush.) 
 
 In these papers Dr. Bush expressed his views of the 
 fundamental principles on which the present system of fixed 
 bridgework is or should be leased. That these principles are 
 logical and in general accordance with tlie views of the most 
 thoughtful men in the profession is conceded. 
 
 The essayist's idea was not to encourage tlie more ex- 
 tended application of denture restorations by means of fixed 
 bridgework, but to call attention to those principles which, if 
 properly considered and applied, will lead to success in this 
 field. 
 
 By means of a series of charts Dr. Bush has shown that 
 according to location, bridges naturally are resolved into three 
 well-defined classes — simple, compound and complex. 
 
 These are further subdivided into series according to the 
 teeth which serve as abutment supports, as central and cuspid 
 series, cuspid and third molar series, etc. 
 
 This does not constitute a new system of bridgework, but 
 is a presentation in clear and concise form of commonly con- 
 structed simple bridges and combinations which have not 
 heretofore been classified. 
 
 It is the writer's opinion that for teaching and general 
 descriptive purposes, this classification of fixed bridgework 
 will prove of great value, not only for teacliing and general 
 descrijitive purposes, but will encourage more careful consid- 
 eration of the underlying pirinciples which lead to success in 
 the field. 
 
BRIUGEWORK 799 
 
 Pfrniissioii for the following reiirint of the subject mat- 
 ter and the reiiroduction of tlic charts has kindly lieen granted 
 b}' Dr. Busli to the writer for use in this ))ook. 
 
 CLASSIFICATION OF FIXED BRIDGEWORK 
 
 . . . "Because of the rapid advancement in the prac- 
 tice of crown and bridge work during the last half century and 
 in ■\'iew of the phenomenal develojunent of bridgework in the 
 last decade especially, most teachers in this tield no doubt have 
 foimd it difficult to preserve the student's mind free from con- 
 fusion in about the same ratio as the various methods and 
 numerous modifications of procedures have been multiplied. 
 
 "While much has been accomplished toward the formula- 
 tion of principles and requirements governing their indica- 
 tions, contra-indications, adai»tation and construction in an 
 effort to place crown and bridge work on a more scientitic and 
 teachable basis, yet confusion still confronts our efforts in 
 this direction and the reason becomes very ayiparent when 
 we stop to consider that every teacher of crown and Inidge- 
 work in the average dental college essaj's to teach the average 
 student the principle and requirements, indications and con- 
 tra-indications and methods of construction of any one of 
 fifty thousand or more possible bridge replacements that may 
 present for solution in any one oral cavity. 
 
 MULTIPLICITY OF METHODS 
 
 " 'Multiplicity of Methods,' therefore, is no longer an 
 empty phrase and its significance liecomes more apparent 
 when it is known that, according to my unabridged classifi- 
 cation, one method alone is flexible enough, under ordinary 
 conditions, to be applicable to any one or more 4,410 different 
 conditions which may be present in any one mouth. 
 
 "In view of these considerations, we may safely assert 
 that the teaching of crown and bridgework in the modern den- 
 tal college is a task which has resolved itself into a proI)lem of 
 no small proportions and one wliich seems of enough moment 
 to demand that every teacher of this subject should at least 
 have given it enough serious consideration to justify his 
 possession of a viewpoint. 
 
 PRIME OBJECT OF CROWN AND BRIDGE APPLICATION 
 
 "In gixing you my \iew, I assume two things, both of 
 which I believe may be accepted as facts without argument. 
 First, that crowns and bridges are employed in the effort to 
 
800 HKllHiKWOKK 
 
 iiici'cnsc llic iiscfuiiH'ss of the (Iciitiil ;i| i) ini'iitus wliicli lias 
 hccii iriiiiaiicil l)y l|ic partial iir total loss of a few tcotli, and 
 second, that the practice n\' ciciwii and liridncwork should bo 
 taus'ht in accordance witii tlie coricct ]irinciiiles and re(|uire- 
 nieiits \vhi<'li iioxcrii Ihcir eiii|iln\ incut. 
 
 "It is ()l)\i(ilis, (liercfni-c, that the teaciiiiiii' of the priii- 
 ci]ih's and rei|uireinents l)ee(nne of lirst inipoi-taiice and serves 
 as the oidy possihh^ f()nn(hiti()ii npoii which methods of 
 restoration nia_\' he coi-icctiv taui^ht. 
 
 THE BASIS OF SUCCESS 
 
 "Every student should he taui^'ht tliat success can be 
 aclneved oidy thronnh a stiict compliance with the principles 
 and requirements and conversely that failures are invariably 
 the direct result of their non-observance; that crown and 
 bridgework should not be practiced with tlie thought of 
 rendering a service to his patients by increasing the functional 
 efficiency of the dental apparatus through the nu'chanical 
 requirements alone; but furthermore, that tlie jihxsiological 
 and hygienic requirements mnst also be observed, lest this at- 
 tempt to increase the functional efficiency of the dental ap- 
 paratus be more than offset by establishing conditions which 
 may prove far more serious to the patient than would be 
 caused by the impairment of the dental apparatus through 
 the physical loss of the few teeth he is striving to replace. 
 
 "The greatest proposition that confronts the teacliers of 
 crown and bridgework in oui- dental colleges today, is the 
 problem of teaching a more lively respect for the require- 
 ments, to instill into the student's mind a more thorough re- 
 gard for their importance, a more intelligent conception of 
 their true significance and to bring the student into a fuller 
 realization tliat the most valuable lesson that can be learned 
 regarding the five requirements is the fact that only one of 
 the five is mechanical. 
 
 "My viewpoint relative to tliis )ihase of the subject may 
 be best stated by saying that humanity, enlightened by the oral 
 hygiene and iirophylaxis propaganda, will sooner or later 
 demand that all of the requirements be observed in the ])rae- 
 tice of crown and bridgework and that sooner or later teachers 
 in this field will be compelled by a long-suffering public to 
 place less emphasis upon the mechanical and esthetic require- 
 ment, exce]it as a means to gain an end, and devote more time 
 to the teaching of those requirements, which, from a humani- 
 tarian standpoint are more vital and which in fact constitute 
 the essential consideration underlying the physical diagnosis 
 
BKIDGEWORK 801 
 
 of oral conditions wliieii demand the execution of these me- 
 chanical prescriptions as applied to living tissues, namely the 
 physiological and hygienic. 
 
 "A practical knowledge of the correlated sciences of 
 anatomy, physiology, physics, metallurgy, orthodontia, and 
 oral jiathology and ))hvsiology as viewed and comprehended 
 by the periodontologist, is presupposed as subjects which are 
 fundamental to the study of the requirements and through 
 the combined consideration of which we form our conceptions 
 regarding indications and contraindications, and, according 
 to my viewpoint, these correlated subjects are so fundamental 
 to the scientific teaching of crown and bridgework that this 
 fact alone would justify our giving them a prominent position 
 in the dental corriculum, even in the absence of any other con- 
 sideration. 
 
 "My viewpoint relative to tiie teaching of the princijiles 
 which govern the employment of fixed bridgework, and my 
 idea regarding the best plan of teaching metliods, are incor- 
 porated in the following classification of fixed bridgework 
 based upon a ]iroposed law or rule which has been formulated 
 in accordance with accepted principles of practice. 
 
 ADVANTAGES OF CLASSIFYING FIXED BRIDGES 
 
 "In attempting to classify fixed bridgework T have en- 
 deavored, first, to broaden the foundation upon which the su- 
 perstructure of our present conception thereof rests, an<l to es- 
 tablish more thoroughly our comprehension of the principles 
 and their a])))lication which constitutes the very superstruc- 
 ture of the foundation itself; second, to systematize and facili- 
 tate the teaching of fixed bridgework in accordance with the 
 accepted principles of practice which govern tlieir employ- 
 ment ; and third, to formulate a law that embodies the princi- 
 ples which modern practice has approved, a law which will 
 assist in teaching the proper selection of abutments, accord- 
 ing to princijile, for the support and retention of fixed bridge- 
 work, and one which will likewise, impose restrictions to the 
 employment of those types of construction which are, from 
 the standpoint of principle, indefensible 
 
 "The tcniihioloffi/ used in the classification is simply a 
 correlation of terms selected from our nomenclature, that 
 constant usage has rendered familiar, and which have been 
 selected because they seem to be the most expressive of any 
 terms available. 
 
802 UKIDCKWOKK 
 
 "Most writers of (Iciitistry, in icrcriiiiii- to tcetli of certain 
 position in tlie ai'eli, liiive nsed the teiiiis anterior teetli and 
 posterior teetli as best calculatetl to convey the idea of the 
 association between object and position, likewise anterioi' and 
 posterior have l)een used as the most expressive terms in 
 referring to bridge replace)nents tliat su])ply a missing tooth. 
 or group of teeth, in either of tiiese locations. 
 
 "Accordingly, then, tixed Ijridgework a))iilie(l iiiid conlined 
 within these limits may be divich-d into tnifcriin- hridges and 
 posterior bridges. 
 
 "In referring to Plate 1 (i)age <S07) illustrating possible 
 tixed bridge replacements, it will be observed that the l)ridges 
 represented as applicable to the various positions arrange 
 themselves into well-defined groups that are characterized by 
 the teeth chosen for abutments in connection with the tooth 
 or teeth supplied. Accordingly, therefore, anterior bridges 
 may be subdivided into a central and lateral series and a cen- 
 tral and, cuspid series; likewise, ]iosterior bridges may lie sub- 
 divided into a cuspid and third molar scries, and a first bi- 
 cuspid and second molar series. 
 
 SIMPLE BRIDGES 
 
 "A single bridge of any one of the above series may be 
 said to form a simple bridge. 
 
 COMPOUND BRIDGES 
 
 "Any bridge that can be effected by connecting unilatcr- 
 ally, any one of the simple bridges forming either of the an- 
 terior series, with any one of the simjile bridges formuig 
 either of the i)Osterior series, may lie said to form a compound 
 bridge. 
 
 COMPLEX BRIDGES 
 
 "Any bridge that can l)e effected by connecting bilater- 
 (dly, any one of the simple bridges forming either of the an- 
 terior series, with any one of the simple bridges forming 
 either of the posterior series, may be said to form a compter 
 bridge. 
 
 "To recapitulate, first, fixed bridgework may be divided 
 according to extension, into simple, compound and complex 
 bridges ; second, simple bridges according to location, may be 
 divided into anterior and posterior bridges; third, according 
 to attachment and teeth snp])lied, simple anterior liridges 
 niav lie sulxlivideil into a central and lateral series, and a 
 
BRIDGEWORK 
 
 central and cuspid scries; and simple posterior bridges may 
 be subdi\ided into a cuspid and third molar series, and a 
 first bicuspid and second molar series; and fourth, the simple 
 bridges of the anterior series when joined unilaterally and 
 bilaterally to the simple bridges of the posterior series, form 
 compound and complex bridges respectively. The adjectives 
 
 
 
 Central and Lateral Serie» 
 
 
 Simple 
 
 Anterior 
 
 Central and Cuspid Series 
 
 
 Bridges 
 
 Cuspid and 3rd Molar Series 
 Posterior 
 
 1st Bicuspid and 2nd Molar Series 
 
 Class,fi 
 
 
 , _ Cuspid and 3rd Molar Series 
 Central and Lateral Series "^ 
 
 cation 
 
 Compound 
 
 joined to Right or Left ,^j g ^_^j 2nd M. Series 
 
 of 
 
 FIXED 
 
 BRIDGE- 
 
 Bridges 
 
 „ , . „ J c ■ Cuspid and 3rd Molar Series 
 Central and Cuspid Series 
 
 joined to Right or Left , ^^ g ^^^ jnd M. Series 
 
 WORK 
 
 
 
 R. and L. Cuspid and 3rd M. Series 
 R. andL. 1st B.and 2nd M. Series 
 
 
 
 Central and Lateral Series 
 
 R. Cuspid and 3rd M. Series with 
 
 
 
 connecting 
 
 L. 1st B. and 2nd M. Series. 
 L. Cuspid and 3rd M. Series with 
 
 
 Complex 
 
 
 R. 1st B.and 2nd M. Series. 
 
 
 Bridges 
 
 
 R. and L. Cuspid and 3rd M. Series 
 R. and L. 1st B. and 2nd M. Series 
 
 
 
 Central and Cuspid Series 
 
 R. Cuspid and 3rd M. Series with 
 
 
 
 connecting 
 
 L. 1st B. and 2nd M. Series 
 
 PLATE 
 
 n 
 
 
 L. Cuspid and 3rd M. Series with 
 R. 1st B.and 2nd M. Series 
 
 Upper and lower, right and left, are used as prefixes and com- 
 plete the terminology. 
 
 "Again referring to Plate 1 (page 807), it will l)e noticed 
 that all simi)le bridges are of comi)arativcly straight align- 
 ment and have at least one sup])ort or attachment at each end ; 
 and furthermore, that all the simple bridges of the various 
 series, in heing joined or connected to form compound and 
 complex bridges form extended bridges of curved alignment 
 with one or more intervening i)iers or attacliments. 
 
 ■'In view of this fact, therefore, it seems litting and much 
 more in accord with the scientitic ])hase of this class of work, 
 that a general law be ado]ited that will furnish a safe plan 
 for teaching the application of all fixed bridgework in general, 
 and which will serve the same jiurpose as the various rules 
 that have been formulate(l from time to time to cover a com- 
 
S04 BRIDGEVVORK 
 
 paratively small number of cases, more or less typical, all of 
 which are fmidamentally based upon the same principles. 
 
 PROPOSED LAW 
 
 "The hnv propo.sed is as follows: J// /i.trd hri/lficiiniL (if 
 tttiaiyht aligiunoit should he attached to, or supported Ijij, 
 one or more abutments at each end, and should receive addi- 
 tional attachment and support from one or more intervening 
 abutments or piers ivhen of curved alignment. 
 
 "In accordance to the classification and law proposed, 
 the following definitions are derived. 
 
 SIMPLE BRIDGE DEFINED 
 
 "A simple fi.xcd bridge may be defined as a bridge used to 
 replace one or more teeth missing from the anterior or 
 
 posterior positions of the arch, attached to or supported by 
 at least one or more abutments at each end and are of com- 
 paratively straight alignment. 
 
 COMPOUND BRIDGE DEFINED 
 
 "A co)up(iin/(/ liridf/e may Ik* defined as an extended 
 bridge effected by a simple anterior Ijridge joined iniilaferallii 
 
 to a simple posterior bridge to suj^ply two or more missing 
 teeth from the anierior and posterior ]iortions of the arch, at- 
 
BRIDGEWORK 805 
 
 tacbed to or sii^jported by one or more abutments at eacb end 
 and one or more additional attaelmients or supports from one 
 or more intervening abutments or piers, and are of carved 
 alignment. 
 
 COMPLEX BRIDGE DEFINED 
 
 "A cdiuplc.i: jixed bridge may be depued as an extended 
 bridge effected by connecting a simple anterior bridge hi- 
 laterally with a simple posterior bridge to supply four or 
 more missing teeth in the arch and are attached to or sup- 
 
 ported by one or more abulnicul^. at each end and one or more 
 additional attachments or supports from one or more inter- 
 vening abutments or piers, and are of curved alignment. 
 
 ARGUMENT IN SUPPORT OF THE CLASSIFICATION 
 AND LAW PROPOSED 
 
 ''In support of the proposed classitication and in defense 
 of the law which embodies the principles upon which the classi- 
 fication is largely based I wish to quote the following, taken 
 from a former paper : 
 
 POSSIBLE MASTICATORY STRESS 
 
 " 'If the muscles of mastication are capable of exerting a 
 stress of 275 pounds upon the first molars and if the support- 
 ing tissues of the first molars have lieeu capable of developing 
 a structure which will safely bear such a strain, it must be 
 concluded that the development of the muscles and the sup- 
 porting tissues of the teeth are co-incident and in accordance 
 with physiological laws. 
 
 " 'It is also" true that this muscular power is normally 
 intended to be exerted within physiological directions, and 
 that the supporting tissues of the teeth are developed and 
 
sdi; i!i{ii)(;io\V()i!K 
 
 |ili\ siologically (IcsigiMMl hi rccciNc and supiiorl lliis strain 
 only wlicii this niusciilar stress is I lansniitted to them iu a 
 nninial direction and accoidinn to physiological principles. 
 
 •' 'Tlie woiKh'rl'nl power that the muscles of mastication 
 are capable of exerting, and the wonderful plan upon which 
 Nature has constructed the human teeth iu order to utilize 
 this energy in the mastication of food, and the wonderful de- 
 sign of the tissues wJiich support the teeth while performing 
 these functions, all seem to be iu perfect accord with the 
 nuu'velous schemes of Nature. Yet, it must be remembered 
 that this muscular energy is intended to be exerted only within 
 certain limitations, bounded by the normal, and the design of 
 the teeth render them etificacious in performing their functions 
 only when nuiscular energy propels them normally, and that 
 the tissues which support the teeth wiiile performing their 
 functions are capable of yielding normal support only when 
 the nuiscular stress of mastication is normally directed. 
 
 " 'Therefore, it would not be in accordance with physio- 
 logical laws to expect a lirst molar which, if normally capable 
 of withstanding a stress of 1275 pounds, and the suppoi'ting 
 tissues normally capable of resisting the stress, to physiologic- 
 ally resist this stress if the direction of the stress be per- 
 verted, and the supporting tissues compelled to receive the 
 stress contrary to the direction that they are normally de- 
 signed to receive it. 
 
 " 'Hence, it seems oljvious that if lixeil lu'idgework be con- 
 structed with occlusal and incisal masticating surfaces after 
 Nature's plan and iu accordance with physiological law gov- 
 erning normal articulation and occlusion, and if the stress as 
 received by the abutments is normally directed, that such 
 bridgework may be successfully attached to tiie roots of teeth 
 without inviting pathological manifestations." 
 
 "But, on the other hand, // p.rrd hridficivoil; be con- 
 st lucted without due rrr/did for thesr principles, and the occlu- 
 sal or incisal surface be so niodc. as to (tlninnnnltu direct tlie 
 restdtant force to the utiutuicnl tcrth. nr thr cniitloi/nient of 
 abutments he such as to subject them la stress perverted 
 through leverage, then will the supportiufi tissues surrounding 
 the root fail to render support, just in })nip(irtion as the stress 
 is perverted, and the support iur/ tissm-s ore oliliged to offer 
 resistance in a direction u'hich tlnti n-erc never intended to 
 furnish. 
 
 "Unquestionably, there are many fixed bridges outside the 
 scope of this proposed law and classification which are a]i- 
 parently giving good service, and which, by reason of this n\^- 
 
BRIUGEWOKK 8« 
 
 pareut st'rvice, aud their coiitiuued eiuijloymeut, have th;is. 
 seemingly, been sanctioned as good practice nevertheless, 
 the soundness of the iirinciples underlying the proposed law 
 cannot he questioned, neither can it be denied that these same 
 bridges in question might have rendered a still greater serv 
 ice had they been elTected more strictly in accordance with the 
 principle involved. 
 
 CLASSIFICATION OF FIXED BRIDGES 
 ACCORDING TO LOCATION 
 ATTACHMENT AND TEETH SUPPLIED 
 
 9765432112343678 
 
 ANTERIOR , 
 BRIDGES \ 
 
 1 
 
 POSTERIOR , 
 BRIDGES \ 
 
 [ 
 
 
 
 
 
 A 
 
 • X 
 
 •' 
 
 
 
 
 
 
 i central and 
 /lateral series 
 
 > central and 
 ^ cuspi d seri e3 
 
 , cuspid and 
 ^ 3"molar series 
 
 itbicuspid and 
 / 2mmolar series 
 
 
 
 
 
 B 
 
 • X 
 
 X •! 
 
 
 
 
 
 
 
 
 
 
 c 
 
 X • 
 
 • X 
 
 
 
 
 
 
 
 
 
 
 
 D 
 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 E 
 
 X 
 
 • 
 
 
 
 • 
 
 X 
 
 F 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 A 
 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 B 
 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 C 
 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 D 
 
 
 X 
 
 • 
 
 X 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 E 
 
 
 X 
 
 X 
 
 • 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 F 
 
 
 X 
 
 • 
 
 • 
 
 X 
 
 
 
 - 
 
 
 
 
 
 
 
 
 G 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 
 
 
 
 
 
 
 
 
 H 
 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 • 
 
 X 
 
 X 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 J 
 
 
 X 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 K 
 
 • ••;x 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 L 
 
 • IX 
 
 X 
 
 X 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 M 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 N 
 
 
 
 • 
 
 X 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 O 
 
 
 
 
 • 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 A 
 
 
 
 N 
 
 
 X 
 
 • 
 
 
 
 
 
 
 • IX 
 
 X 
 
 •;b 
 
 
 
 o 
 
 
 X 
 
 X 
 
 • 
 
 
 
 
 • X • X 
 
 • c 
 
 
 
 p 
 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 • X X X 
 
 • D 
 
 
 
 
 
 
 X 
 
 X 
 
 X 
 
 • 
 
 
 
 XX • X 
 
 • E 
 
 
 
 R 
 
 
 X 
 
 • 
 
 X 
 
 X 
 
 
 
 X • X X 
 
 • 'F 
 
 
 
 s 
 
 
 X 
 
 X 
 
 • 
 
 X 
 
 
 
 X • • X 
 
 • Q 
 
 
 
 T 
 
 
 X 
 
 • 
 
 • 
 
 X 
 
 
 • X XXX 
 
 • H 
 
 
 
 u 
 
 
 X 
 
 X 
 
 X 
 
 X 
 
 
 
 X • X • 
 
 X 1 1 
 
 
 V 
 
 X 
 
 • 
 
 X 
 
 • 
 
 X 
 
 
 
 X • X • 
 
 J 
 
 
 
 w 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 
 
 X 
 
 X 
 
 X 
 
 • 
 
 
 K 
 
 
 
 X 
 
 
 • 
 
 X 
 
 X 
 
 X 
 
 
 
 X 
 
 X 
 
 • 
 
 
 
 L 
 
 
 
 r 
 
 
 
 • 
 
 X 
 
 X 
 
 
 
 X 
 
 • 
 
 
 
 
 M 
 
 
 
 z 
 
 
 
 
 • 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 
 A 
 
 
 
 H 
 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 B 
 
 
 
 1 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 C 
 
 
 
 J 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 X 
 
 D 
 
 
 
 K 
 
 X 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 • 
 
 X 
 
 • 
 
 
 
 E 
 
 
 
 L 
 
 
 
 • 
 
 X 
 
 • 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 
 F 
 
 
 
 M 
 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 • 
 
 X 
 
 Q 
 
 
 
 N 
 
 X 
 
 • 
 
 
 
 
 
 PLATE I 
 
 
 
 "Showing series classification of simple bridges according 
 to location, attachment and teeth supplied. The incompleted 
 bridges E and F of the Central and Lateral Series, also G 
 
808 BRIDGEWORK 
 
 and N of the First Bicuspid and Second Molar Series, when 
 joined, form simple bridges E(t and FN, and are classitied as 
 anterior I)ridges and enumerated as belonging to the Central 
 and Cuspid Series — both, however, retain tlieir identity when 
 used to form other combinations and are so enumerated as 
 illustrated in charts 3, 4, 7, 8, 9, 10, 12, 13 and 14. 
 
 "The incompleted bridge C of the Central and Lateral 
 Series is not classilied as a simple bridge, but when joined bi- 
 laterally to the simple bridges of the posterior series it assists 
 in the formation of complex bridges and is so enumerated as 
 illustrated in charts 9 and 10. Likewise, incompleted bridges 
 I and V of the Cuspid and Third Molar Series and B, D, F 
 and I, K, M of the First Bicuspid and the Second Molar Series 
 are not classified as simple bridges, but when joined uni- 
 laterally and bilaterally to the simple Ijridges of the anterior 
 series they assist in the formation of compound and complex 
 bridges and are so enumerated as illustrated in charts 3, 4, 
 7, 8, 9, 10, 11, 12, 13 and 14. 
 
 "The two groups of simple bridges comprising the two 
 Anterior Series effect eight different combinations when 
 joined unilaterally with the four groups of simple bridges com- 
 prising the two Posterior Series, thus forming eight groups of 
 compound bridges. Likewise the two groups of sinii)le bridges 
 comprising the two Anterior Series, effect eight different 
 combinations when joined bilaterally with the various groups 
 of simple bridges which comprise the two Posterior Series, 
 thus forming eight groups of complex bridges. 
 
BRIDGEWORK 
 
 
 COMPOUND BRIDGES 
 
 FORMED BY 
 
 876545;! 1:345678 
 
 
 
 
 
 
 
 B 
 
 • X 
 
 X •! 
 
 
 
 
 
 
 LEFT 
 
 CUSPID 8i 3rd molar 
 
 SERIES 
 
 SERIES 
 
 
 
 
 
 D 
 
 • 
 
 X •, 
 
 
 
 
 
 
 
 
 
 
 
 
 
 M • 
 
 X • 
 
 
 
 
 
 
 
 
 
 
 
 O • 
 
 X X • 
 
 
 
 
 
 
 
 
 
 
 
 P • 
 
 X • X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 Q • 
 
 X X X • 
 
 
 
 
 
 
 
 
 
 
 "!• 
 
 X • X X • 
 
 
 
 
 
 
 
 
 
 
 S!« 
 
 X X • X • 
 
 
 
 
 
 
 
 
 
 
 Ti» 
 
 X • • X • 
 
 
 
 
 
 
 
 
 
 
 u,« 
 
 X X X X • 
 
 
 
 
 
 
 
 
 
 
 V 
 
 X 
 
 • 
 
 X 
 
 • 
 
 X • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 E 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 w 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 X 
 
 
 • 
 
 X 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 87654321 12345678 
 
 
 
 
 
 
 A 
 
 
 • X 
 
 • 
 
 
 
 
 
 
 
 
 CENTRAL 8t LATERAL 
 SERIES 
 
 
 
 
 B 
 
 
 • X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 • X 
 
 • a' 
 
 
 
 
 
 
 
 
 
 
 • XX 
 
 • B 
 
 
 
 
 
 
 
 
 
 ~i« X • X 
 
 • c 
 
 
 
 
 
 
 
 
 
 
 • X X X 
 
 • D 
 
 
 
 
 
 
 
 
 
 RIGHT 
 
 • X X • X 
 
 • E 
 
 
 
 
 
 
 
 
 
 CUSPID at 3rd molar 
 
 • X • X X 
 
 • F 
 
 
 
 
 
 
 
 
 
 SERIES 
 
 • X • • X 
 
 • G 
 
 
 
 
 
 
 
 
 
 
 • X X X X 
 
 • H 
 
 
 
 
 
 
 
 
 
 
 • X 
 
 • X • 
 
 X, 1 
 
 
 
 
 
 
 
 
 
 
 PLATE m 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 •" 
 
 X 
 
 
 !E 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 • 
 
 x» 
 
 
 J 
 
 
 
 
 
 
 
 
 
 
 • X XX* 
 
 
 K 
 
 
 
 
 
 
 
 
 
 
 1 1 1 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 "Showing bridges formed by Central and Lateral Series 
 joined unilaterally to Left Cuspid and Third Molar Series, 
 also Central and Lateral Series joined unilaterally to Right 
 Cuspid and Third Molar Series. 
 
niui)('.i;\\()i{i< 
 
 
 COMPOUND BRIDGES 
 
 FORMED BY 
 
 8765432112345678 
 
 
 CENTRAL a LATERAL 
 SERIES 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 LEFT- 
 IST BICUSPID a 
 2nd MOLAR 
 SERIES 
 
 
 
 
 
 B 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 D 
 
 
 
 • 
 
 x|« 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 F 
 
 
 
 
 
 
 
 
 
 
 
 
 N X 
 
 • 
 
 
 
 
 
 
 
 
 
 1 X 
 
 • X • 
 
 
 
 
 
 
 
 
 
 
 'K|X 
 
 • lX|X|«; 
 
 
 8765432112345678 
 
 
 RIGHT 
 
 
 
 
 
 
 
 1 
 
 
 
 
 
 
 CENTRAL a LATERAL 
 SERIES 
 
 
 
 
 
 A 
 
 • X 
 
 • ! 
 
 
 
 
 
 
 
 
 
 
 B 
 
 • X 
 
 X • 
 
 
 
 
 
 
 
 
 
 
 E 
 
 X • 
 
 
 
 
 
 
 
 
 j 1ST BICUSPID a 
 
 • 
 
 X G 
 
 
 
 
 
 
 
 
 2ND MOLAR 
 
 • X • 
 
 X B 
 
 
 
 
 
 
 
 
 
 SERIES 
 
 • XX* 
 
 XiD 
 
 
 
 
 
 
 
 
 
 i 
 
 PLATE w: 
 
 
 
 ' * Showing compound bridges formed liy Central and Lat- 
 eral Series joined unilaterally with Left First Bicuspid and 
 Second Molar Series; also Central and Lateral Series joined 
 unilaterally to Right First Bicuspid and Second Molar Series. 
 
BRIDGEWOKK 
 
 1 
 
 COMPOUND BRIDGES 
 
 FORMED BY 
 
 87654321 12345678 
 
 
 RIGHT 
 
 CUSPID & 3RD MOLAR 
 
 SERIES 
 
 
 
 
 |A 
 
 • {x|« 
 
 1 
 
 
 
 
 
 
 
 CENTRAL a CUSPID 
 SERIES 
 
 
 
 
 |B 
 
 • XX 
 
 • 
 
 
 
 
 
 
 
 
 
 
 c 
 
 • X • 
 
 X • 
 
 
 
 
 
 
 
 
 
 
 D 
 
 • X • 
 
 X X 
 
 • 
 
 
 
 
 
 
 
 
 
 |E 
 
 • XX 
 
 • X 
 
 • 
 
 
 
 
 
 
 
 
 
 F 
 
 • X • 
 
 • X 
 
 • 
 
 
 
 
 
 
 
 
 
 iG 
 
 • • X 
 
 • X 
 
 • 
 
 
 
 
 
 
 
 
 
 H 
 
 • X • 
 
 X • • 
 
 
 
 
 
 
 
 
 1 
 
 • • X 
 
 X X • 
 
 
 
 
 
 
 
 
 IJ 
 
 • X X 
 
 X • • 
 
 
 
 
 
 
 
 
 
 IK 
 
 • • X 
 
 X • 
 
 • 
 
 
 
 
 
 
 
 
 
 L 
 
 • X;X 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 A 
 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 B 
 
 
 
 
 
 
 
 
 
 
 • X • X 
 
 • c 
 
 
 
 
 
 
 
 
 
 
 • X X X 
 
 • D 
 
 
 
 
 
 
 
 
 
 
 • X X • X 
 
 • E 
 
 
 
 
 
 
 
 
 
 
 • X • X X 
 
 • F 
 
 
 
 
 
 
 
 
 
 
 • X • • X 
 
 • G 
 
 
 
 
 
 
 
 
 
 
 • X X X X 
 
 • ,H 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X|«|XI« 
 
 
 J 
 
 
 
 
 
 
 
 
 
 
 • 
 
 xixlx • 
 
 
 K 
 
 
 
 
 
 
 
 
 
 
 PLATE 3z: 
 
 
 
 "Showing compound bridges formed by Central and Cus- 
 pid Series joined unilaterally to Right Cuspid and Third 
 Molar Series, 
 
lilUlHiEWOltK 
 
 
 COMPOUND BRIDGES 
 
 FORMED BY 
 
 87654321 12345678 
 
 
 CENTRAL a CUSPID 
 SERIES 
 
 
 
 
 
 D 
 
 • Xl* 
 
 X X • 
 
 
 
 
 
 
 LEFT 
 CUSPID & 3RD MOLAR 
 SERIES 
 
 
 
 
 
 E 
 
 *'X'X 
 
 • <xl* 
 
 
 
 
 
 
 
 
 
 
 F 
 
 • X • 
 
 • X • 
 
 
 
 
 
 
 
 
 
 
 G 
 
 • • X 
 
 • X • 
 
 
 
 
 
 
 
 
 
 
 H 
 
 • X • 
 
 X • • 
 
 
 
 
 
 
 
 
 
 
 1 
 
 • • X 
 
 X X • 
 
 
 
 
 
 
 
 
 
 
 J 
 
 • XX 
 
 X • • 
 
 
 
 
 
 
 
 
 
 
 K 
 
 • • X 
 
 X • • 
 
 
 
 
 
 
 
 
 
 
 L 
 
 • XX 
 
 XX* 
 
 
 
 
 
 
 
 
 
 
 M 
 
 • X 
 
 • X • 
 
 
 
 
 
 
 
 
 
 
 N 
 
 
 
 • 
 
 X 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 O 
 
 
 
 
 • 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 N 
 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 p 
 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 X 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 R 
 
 
 X 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 s 
 
 
 X 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 T 
 
 
 X 
 
 • • 
 
 X • 
 
 
 
 
 
 
 
 
 
 
 u 
 
 
 X 
 
 XXX 
 
 • 
 
 • 
 
 
 
 
 
 
 
 
 
 
 w 
 
 
 • X •,x 
 
 
 
 
 
 
 
 
 
 
 X 
 
 
 • xjx x{* 
 
 1 PLATE 3ZE 
 
 
 
 "Showing compound bridges formed by Central and Cus- 
 pid Series joined unilaterally to Left Cuspid and Third Molar 
 Series. 
 
BRIDGEWURK 
 
 
 COMPOUND BRIDGES 
 
 FORMED BY 
 
 87654321 12345678 
 
 
 RIGHT 
 
 1ST BICUSPID ft 
 
 2ND MOLAR 
 
 SERIES 
 
 
 
 
 A 
 
 .lx|. 
 
 
 
 
 
 
 
 
 
 CENTRAL ft CUSPID 
 SERIES 
 
 
 
 
 B 
 
 • XX 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 C 
 
 • X • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 ,D 
 
 • |X • 
 
 X X|« 
 
 
 
 
 
 
 
 
 \" E 
 
 • XX 
 
 • X • 
 
 
 
 
 
 
 
 
 
 P 
 
 • X • 
 
 • X • 
 
 
 
 
 
 
 
 
 
 
 G 
 
 • 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 H 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 • 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 • 
 
 X 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 • XX 
 
 Xi*^ 
 
 
 
 
 
 
 
 
 
 K 
 
 • • X 
 
 X • • 
 
 
 
 
 
 
 
 
 
 |L 
 
 • x,x 
 
 x,x,» 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 
 A 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 c 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 
 F 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 M 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 G 
 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 B 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 X 
 
 D 
 
 
 
 
 
 
 
 
 
 PLATE 3zn: 
 
 
 
 "Showing compound bridges formed by Central and Cus- 
 pid Series joined unilaterally to Right First Biscupid and 
 Second Molar Series. 
 
BKIDtiEWOHK 
 
 
 COMPOUND BRIDGES 
 
 FORMED BY 
 
 876?•4:^^l 12345678 
 
 
 CENTRAL a CUSPID 
 SERIES 
 
 
 
 1 D 
 
 • X* 
 
 X X • 
 
 
 
 
 
 
 LEFT 
 
 1ST BICUSPID a 
 
 2ND MOLAR 
 
 SERIES 
 
 
 
 i F~ 
 
 • XX 
 
 • X • 
 
 
 
 
 
 
 n iP 
 
 • x« 
 
 • X • 
 
 
 
 
 
 
 !G 
 
 • • X 
 
 • X • 
 
 
 
 
 
 
 
 
 H 
 
 • X • 
 
 X X • 
 
 
 
 
 
 
 
 
 1 1 
 
 • • X 
 
 X X • 
 
 
 
 
 
 
 
 
 J 
 
 • XX 
 
 X • • 
 
 
 
 
 
 
 
 
 |K 
 
 • • X 
 
 X • • 
 
 
 
 
 
 
 
 
 
 
 L 
 
 • XX 
 
 X X • 
 
 
 
 
 
 
 
 
 
 
 M 
 
 • X 
 
 • X • 
 
 
 
 
 
 
 
 
 
 
 N 
 
 • 
 
 X X • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 H 
 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 J 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 M 
 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 C 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 N 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 K 
 
 X 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 PLATE Ami 
 
 
 
 "Showing compound bridges formed by Central and Cus- 
 pid Series joined unilaterally to Left First Bicuspid and Sec- 
 ond Molar Series. 
 
BRIIIGRWORK 
 
 
 COMPLEX BRIDGES 
 
 FORMED BY 
 
 CENTRAL a LATERAL SERIES 
 
 87654321 I234567B 
 
 
 RIGHT 
 
 CUSPID a 3RD MOLAR 
 
 SERIES 
 
 
 
 
 
 B 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 LEFT 
 
 CUSPID a 3rd MOLAR 
 
 SERIES 
 
 
 
 
 
 C 
 
 
 X 
 
 • 
 
 • 
 
 X 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 X 
 
 1 
 
 
 
 N 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 O 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 P 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 q!» 
 
 X 
 
 X X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 R • 
 
 Xi* XX* 
 
 
 
 
 
 
 
 
 
 
 S'» 
 
 x\x • X • 
 
 
 
 
 
 
 
 
 
 T • 
 
 X • • X • 
 
 
 
 
 
 
 
 
 u • 
 
 X X X X • 
 
 
 
 
 
 B 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 
 1 
 
 
 
 
 
 
 C 
 
 
 X 
 
 • 
 
 • 
 
 X 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 
 A 
 
 
 
 V 
 
 X 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 • 
 
 X 
 
 X 
 
 
 B 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 
 C 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 X 
 
 X 
 
 
 D 
 
 
 
 
 
 
 
 
 
 
 ,• X iX • X 
 
 
 E 
 
 
 
 
 
 
 
 
 
 
 • X • X X 
 
 
 F 
 
 
 
 
 
 
 
 
 
 
 • ><J» • X 
 
 
 G 
 
 
 
 
 
 
 
 
 
 
 • X 
 
 X X 
 
 X 
 
 
 H 
 
 
 
 
 
 
 
 
 
 
 • X 
 
 • X 
 
 # 
 
 X 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 87654521 12345678 
 
 
 RIGHT 
 
 1ST BICUSPID a 
 
 2ND MOLAR 
 
 SERIES 
 
 
 
 
 Ib 
 
 • 
 
 X 
 
 X • 
 
 
 
 
 
 
 
 LEFT- 
 IST BICUSPID a 
 2ND MOLAR 
 SERIES 
 
 
 
 
 c 
 
 !x 
 
 • 
 
 • X 
 
 
 
 
 
 
 
 1 
 
 
 • 
 
 X|G 
 
 
 ;NiX 
 
 • 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 XIB 
 
 
 1 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 X D 
 
 
 K X 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 PLATE IX 
 
 
 
 "Showing complex bridges t'ornicd l>y ( V'liti'al and Lateral 
 Series joined bilaterally to Bight and Left Cuspid and Third 
 Molar Series; also complex bridges formed by Central and 
 Lateral Series joined bilaterally to Rigiit and Tjcft Bicuspid 
 Series. 
 
BRIIXJEWORK 
 
 
 COMPLEX BRIDGES 
 
 FORMED BY 
 
 CENTRAL a LATERAL SERIES 
 
 87654321 12345678 
 
 
 
 
 
 
 B 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 LEFT 
 
 1ST BICUSPID a 
 
 2ND MOLAR 
 SERIES 
 
 
 
 
 
 c 
 
 
 X 
 
 • 
 
 • 
 
 X 
 
 
 
 
 
 
 " 
 
 
 
 
 • 
 
 X 
 
 
 A 
 
 
 
 N 
 
 X 
 
 • 
 
 
 
 
 
 
 • 
 
 X 
 
 X 
 
 
 B 
 
 
 
 1 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 RIGHT 
 
 - 
 
 • 
 • 
 
 X 
 
 • 
 
 X 
 
 
 c 
 
 
 
 K 
 
 X 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 CUSPID a 3rd molar 
 
 x 
 
 X 
 
 X 
 
 
 D 
 
 
 
 
 
 
 
 
 
 
 SERIES 
 
 
 X 
 
 X 
 
 • X 
 
 
 E 
 
 
 
 
 
 
 
 
 
 
 
 
 X 
 
 • 
 
 X 
 
 X 
 
 
 F 
 
 
 
 
 
 
 
 
 
 
 
 ^ 
 
 X 
 
 xi 
 
 • 
 
 • 
 
 X 
 
 
 G 
 
 
 
 
 
 
 
 
 
 
 X 
 
 X 
 
 X 
 
 
 H 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 X • 
 
 X 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 87654321 12345678 
 
 
 RIGHT 
 
 1ST BICUSPID a 
 
 2ND MOLAR 
 
 SERIES 
 
 
 
 
 
 B 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 LEFT 
 CUSPID a 3RD MOLAR 
 SERIES 
 
 
 
 
 
 
 
 
 X 
 
 • 
 
 • 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 G 
 
 
 
 N 
 
 
 X 
 
 • 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 B 
 
 
 
 O 
 
 
 X 
 
 X 
 
 • 
 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 X 
 
 D 
 
 
 
 P 
 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 Q 
 
 
 X 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 R 
 
 
 X 
 
 • 
 
 X 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 S 
 
 
 X 
 
 X 
 
 • 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 T 
 
 
 X 
 
 • 
 
 • 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 U 
 
 
 X 
 
 X 
 
 X 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 V 
 
 X 
 
 • 
 
 X 
 
 • 
 
 X 
 
 
 PLATE ZX: 
 
 
 
 "Showing complex bridges formed by Central and Lateral 
 Series joined liilateralh' to Eight Cuspid and Third Molar 
 Series and Left First Bicuspid and Second Molar Series. 
 Also complex bridges formed by Central and Lateral Series 
 joined bilaterally to Left Cuspid and Third Molar Series and 
 Right First Bicuspid and Second Molar Series. 
 
BRIDGE WORK 
 
 COMPLEX BRIDGES 
 
 FORMED BY 
 
 CENTRAL a CUSPID SERIES 
 87654^21 12345673 
 
 
 i 
 
 RIGHT 
 
 
 
 
 D 
 
 • Ix]. 
 
 x|x|« 
 
 
 
 
 
 LEFT 
 
 CUSPID a 3RD MOLAR 
 
 SERIES 
 
 
 
 
 E 
 
 • X X 
 
 • X • 
 
 
 
 
 
 
 
 
 F 
 
 • X • 
 
 • X • 
 
 
 
 
 
 
 
 
 G 
 
 • • X 
 
 • X • 
 
 
 
 
 
 
 
 
 
 1h 
 
 • xj* 
 
 x» 
 
 • 
 
 
 
 
 
 
 
 
 
 h 
 
 • MX 
 
 XX 
 
 • 
 
 
 
 
 
 
 
 
 
 ■J 
 
 • xx 
 
 X • 
 
 • 
 
 
 
 
 
 
 
 
 K 
 
 • • X 
 
 X • • 
 
 
 
 
 
 
 
 
 L 
 
 • XX 
 
 X x* 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 A 
 
 
 n'» 
 
 X 
 
 • 
 
 
 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 B 
 
 
 o • 
 
 X X • 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 C 
 
 
 p • 
 
 X • X • 
 
 
 • 
 
 X 
 
 X 
 
 X 
 
 • 
 
 D 
 
 
 Q • 
 
 X X X • 
 
 CUSPID & 3rd molar 
 
 • XX • X 
 
 • E 
 
 R • 
 
 X|» X X • 
 
 SERIES 
 
 • X • XiX 
 
 • r 
 
 s • 
 
 X X • X • 
 
 • X • • X 
 
 • G 
 
 T • 
 
 X • •y • 
 
 
 • X X X X 
 
 • H 
 
 u • 
 
 X X X X • 
 
 
 • X • X • 
 
 J 
 
 w 
 
 • X • X • 
 
 
 
 X 
 
 X 
 
 X 
 
 • 
 
 
 K 
 
 
 
 X 
 
 
 • 
 
 X 
 
 X|X|« 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 c 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 V 
 
 X 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 M 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 X 
 
 1 
 
 
 
 
 
 
 
 
 
 
 PLATE 31 
 
 
 
 "Showing complex bridges t'oniicd Ijv Central and Cuspid 
 Series joined bilaterally to Right and Left Cuspid and Third 
 Molar Series. 
 
S18 
 
 liI!ll)f!K\VORK 
 
 
 
 COMPLEX BRIDGES 
 
 
 
 
 FORMED BY 
 
 CENTRAL a CUSPID SERIES 
 87654321 12345678 
 
 
 RIGHT 
 1ST BICUSPID a 
 2nd molar 
 SERIES 
 
 
 
 
 
 D 
 
 .X. 
 
 x[xi» 
 
 
 
 
 
 
 LEFT 
 1ST BICUSPID a 
 
 2nd molar 
 
 SERIES 
 
 
 
 
 
 E 
 
 • fxtx 
 
 • ix'* 
 
 
 
 
 
 
 
 
 
 
 F 
 
 
 X • 
 
 • X • 
 
 
 
 
 
 
 
 
 
 
 G 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 H 
 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 • 
 
 X 
 
 X 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 J 
 
 
 X 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 K 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 « 
 
 
 
 
 
 
 
 
 
 
 L 
 
 
 X 
 
 X 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 
 A 
 
 
 
 H 
 
 •;x'«' 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 c 
 
 
 J 
 
 • XX* 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 
 F 
 
 
 
 M 
 
 X • X • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 c 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 
 A 
 
 
 
 N 
 
 X 
 
 • 
 
 
 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 C 
 
 
 
 1 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 
 A 
 
 
 
 K 
 
 X 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 M 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 G 
 
 
 
 H 
 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 B 
 
 
 
 J 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 X 
 
 D 
 
 
 
 M 
 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 PLATE 3ir 
 
 
 
 "Showing ('om]ilex hridgcs forunMl liy (V'litial and (.'ns])id 
 Series joined bilaterally to Rigiit and Left First Bicuspid and 
 Seeond Molar Series. 
 
BRIDGEWORK 
 
 819 
 
 
 COMPLEX BRIDGES 
 
 FORMED BY 
 
 CENTRAL a CUSPID SERIES 
 
 87654321 12^45678 
 
 
 
 
 
 
 D 
 
 • X • 
 
 X x|« 
 
 
 
 
 
 
 LEFT 
 1ST BICUSPID & 
 
 2ND MOLAR 
 SERIES 
 
 
 
 
 Ie 
 
 • XX 
 
 • x|» 
 
 
 
 
 
 
 
 
 
 F 
 
 • X • 
 
 • X • 
 
 
 
 
 
 
 
 
 
 G 
 
 • • X 
 
 • X • 
 
 
 
 
 
 
 
 
 
 H 
 
 • X • 
 
 X • • 
 
 
 
 
 
 
 
 
 
 
 1 
 
 • • X 
 
 X X • 
 
 
 
 
 
 
 
 
 
 
 J 
 
 • X X 
 
 X • • 
 
 
 
 
 
 
 
 
 
 
 K 
 
 • • X 
 
 X • • 
 
 
 
 
 
 
 
 
 
 
 L 
 
 • XX 
 
 X 
 
 X • 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 Ai 
 
 
 H 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 • 
 
 x 
 
 X 
 
 • 
 
 e 
 
 
 J 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 M 
 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 • 
 
 X 
 
 X 
 
 X 
 
 * 
 
 D 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 XX 
 
 • X 
 
 • 
 
 E 
 
 
 
 
 
 
 
 
 
 
 RIGHT 
 
 • X • X X 
 
 • 
 
 F 
 
 
 
 
 
 
 
 
 
 
 CUSPID a 3RD MOLAR 
 
 • X • • X 
 
 • 
 
 G 
 
 
 
 
 
 
 
 
 
 
 • X XjX X 
 
 • H 
 
 
 
 
 
 
 
 
 
 
 
 • X • X • 
 
 
 J 
 
 
 
 
 
 
 
 
 
 
 
 • X XiX • 
 
 
 K 
 
 
 
 
 
 
 
 
 
 
 
 n 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 c 
 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 • 
 
 X 
 
 
 A 
 
 
 
 N 
 
 X 
 
 • 
 
 
 
 
 
 
 
 • X 
 
 X 
 
 
 B 
 
 
 
 1 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 • 
 
 X • 
 
 X 
 
 • 
 
 C 
 
 
 
 K 
 
 X 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 
 "•XX 
 
 X 
 
 X 
 
 
 D 
 
 
 
 
 
 
 
 
 
 
 
 • X 
 
 
 E 
 
 
 
 
 
 
 
 
 
 
 
 • X • X X 
 
 
 F 
 
 
 
 
 
 
 
 
 
 
 • X • • X 
 
 
 G 
 
 
 
 
 
 
 
 
 
 
 • X X X X 
 
 
 H 
 
 
 
 
 
 
 
 
 
 
 • X,« X • 
 
 
 J 
 
 
 
 
 
 
 
 
 
 
 •ix|x|xi« 
 
 
 K 
 
 
 
 
 
 
 
 
 
 
 PLATE xnr 
 
 
 
 "Showing complex bridges formed by Central and C'usiiid 
 Series joined bilaterally to Right Cuspid and Third Molar 
 Series and Left First Biousjiid and Second Molar Series. 
 
i!inii(;K\voKK 
 
 1 
 
 COMPLEX BRIDGES 
 
 FORMED BY 
 CENTRAL a CUSPID SERIES 
 
 87654321 t .^ •< 4 5 6 7 a 
 
 
 1 
 
 RIGHT 
 
 1ST BICUSPID & 
 
 2ND MOLAR 
 
 SERIES 
 
 
 
 
 
 D 
 
 • lx'« 
 
 XX • 
 
 
 
 
 
 
 LEFT 
 
 CUSPID a 3rd molar 
 
 SERIES 1 
 
 
 
 
 
 E 
 
 • XX 
 
 • X • 
 
 
 
 
 
 
 
 
 
 
 F 
 
 • X • 
 
 • X • 
 
 
 
 
 
 
 
 
 
 
 G 
 
 • • X 
 
 • X • 
 
 
 
 
 
 
 
 
 
 
 H 
 
 • X • 
 
 X • • 
 
 
 
 
 
 
 
 
 
 
 1 
 
 • •x 
 
 X X • 
 
 
 
 
 
 
 
 
 J 
 
 • XX 
 
 X • • 
 
 
 
 
 
 
 
 
 K 
 
 • • X 
 
 xk •, 
 
 
 
 
 
 
 
 
 n 
 
 
 L 
 
 
 X 
 
 X 
 
 XIXj^ 
 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 
 A 
 
 
 In^^ 
 
 X 
 
 • 
 
 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 
 C 
 
 
 o;^ 
 
 X 
 
 X 
 
 • 
 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 
 F 
 
 
 p • 
 
 X • 
 
 x^ 
 
 
 
 
 
 
 
 
 
 Q!^ 
 
 X X xi^ 
 
 
 
 
 
 
 
 
 
 R • 
 
 X • X X • 
 
 
 
 
 
 
 
 
 
 S • 
 
 XX • X • 
 
 
 
 
 
 
 
 
 
 T • 
 
 X.*.*|X|^ 
 
 
 
 
 
 
 
 
 
 U 
 
 • 
 
 X 
 
 X 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 W 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 r 
 
 
 • 
 
 X 
 
 X 
 
 X 
 
 • 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 M 
 
 
 • x 
 
 • X • 
 
 
 
 
 
 
 
 
 
 
 • 
 
 X G 
 
 N • 
 
 X 
 
 • 
 
 
 
 
 
 
 • 
 
 X 
 
 • 
 
 X 
 
 B 
 
 
 O • 
 
 XlXj 
 
 • 
 
 
 
 
 • 
 
 X 
 
 X 
 
 • 
 
 X 
 
 D 
 
 
 P,» 
 
 X • X 
 
 • 
 
 
 
 
 
 
 
 
 
 
 q'^ 
 
 XXX 
 
 • 
 
 
 
 
 
 
 
 
 
 
 |R • 
 
 X •jX^ 
 
 X 
 
 
 
 
 
 
 
 
 
 
 S • 
 
 X x'» 
 
 X 
 
 
 
 
 
 
 
 
 
 
 lT|^ 
 
 X •• 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 u • 
 
 X 
 
 X X 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 w 
 
 • 
 
 x« 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 X 
 
 • 
 
 XXX 
 
 
 PLATE XIV 
 
 
 
 "Showing complex bridges formed by Central and Cns])id 
 Series joined bilaterally to Left Cuspid and Third Molar 
 Series and Right First Bicnspid and Second Molar Series. 
 
BRIDGE WORK 
 
 
 TOTAL NUMBER OF FIXED BRIDGES, UPPER & LOWER, 
 
 ACCORDING TO SERIES CLASSIFICATION AND 
 
 LAW GOVERNING THEIR APPLICATION. 
 
 SIMPLE BRIDGES 
 Ccnlr^ ^d L.lcrid Scrlc. 6 
 Central and Cuipid Seriei 34 
 Cutpid and Third Molar Serie. 48 
 Ut Bicutpid and 2nd Molar Strict 12 
 
 COMPOUND BRIDGES 
 Central and Lateral Seriei joined to 
 
 Cuipid and 3rd Molar Serie* . 80 
 Central and Lateral Scriei joined to 
 
 Ut Bicuipid and Second Molar Scriei 36 
 Central and Cu.p.d Senei joined to 
 
 Cn-pid and 3rd Molar 5er.e< 480 
 Central and Ciupid Serie* joined to 
 
 lit Bicuipid and 2nd Molar Serie. _IS6 
 
 COMPLEX BRIDGES 
 Central and Lateral Serie. ronnecLn, 
 
 Right and Left Cu.pid and 3rd Motar Serie. 68 
 Central and Lateral Serie. conneeting 
 
 Right and Left Pint Bicuipid and 2nd Molar Seriei 36 
 Central and Lateral Seriei connecting 
 
 Right Cuipid and 3rd Molar Serici with 
 
 Left lit Bicuipid and 2nd Molar Seriei 108 
 Central and Lateral Seriei connecting 
 
 Right lit Bicuipid and 2nd Molar Seriei 108 
 
 Right and Left Cuipid and 3rd Molar Sariei IS40 
 Central and Cuipid Seriei connecting 
 
 Right and Left lit Bicuipid and 2nd Molar Seriei 198 
 Central and Cuipid Seriei connecting 
 
 Right Cuipid and 3rd Molar Seriei with 
 
 Left 1 It Bicuipid and 2nd Molar Serie* 600 
 Centra] and Cuipid Seriei connecting 
 Uft Cuipid and 3rd Serici with 
 
 Right lit Bicuipid and 2nd Molar Seriei ^00 
 
 Total numher of combination ^MIO 
 
 
 PLATE jca: 
 
 
 "Sliuwiug the total number of fixed bridges upper and 
 lower, according to proposed classification and law governing 
 their application. 
 
 "Wliilo this classification will render no material assist- 
 ance in teaching the requirements which are fundamental to 
 teaching of fixed bridgework, and which should be regarded as 
 essential regardless of the plan pursued, still it will, no doubt, 
 prove of great lielp in teaching tlie principles of fixed bridge- 
 work and prove to he of still greater assistance in the teach- 
 ing of method,s. 
 
 "To illustrate: the classification recognizes tliree divisions 
 of fixed bridgework, namelj', simple, compound and complex. 
 Therefore, if tbe student is tau,ght the construction of each 
 according to any one method, be will have been taught accord- 
 
822 BRIDCEWOHK 
 
 iiiii' to tlic ('lassilicatioii, tlic const I'liction i>\' 4.41(1 ixissililc 
 bridge replacements. 
 
 "Ill a like iiianiicr the coiistructiDii and application of all 
 of the varions metliods may l)e taught, and liy thus systematiz- 
 ing our efforts a\'oid the occasions for confusion." 
 
 APPLICATION OF FIXED BRIDGEWORK 
 
 Success in tlic liehl of lixcd hi-idgework, to a very large 
 extent, is de]>endent npon the correct application and con- 
 strnetion of full and partial crowns to the roots, or remain- 
 ing portions of crowns of natural teeth which, by reason of 
 their position, have been selected to serve as abutment and 
 pier supports for the completed truss or superstructure. 
 
 The same general requirements governing the successful 
 application of crowns to individual roots or teeth apply with 
 equal force to those employed as supports for a bridge. 
 
 In addition to this, certain hygienic requirements must be 
 observed in bridge construction, in the a])plication of dum- 
 mies or substitutes for the lost natural teeth, to so form and 
 assemble them that not only the tissues upon which they rest, 
 or approximate, but those around the adjacent crowns may 
 be maintained in a condition of health. 
 
 The union of a dummy Mith a crown in such manner as 
 to form a constricted space or ]X)cket, difficult of access to 
 cleansing ai)i>liances, is one of the common causes of failure 
 in fixed bridgework. 
 
 Therefore, gingival iuterproximate spaces, and particu- 
 larly the embrasures between crowns and dummies, should 
 be left as free and o]ien as is consistent with esthetics, and 
 the required strength of the structure. 
 
 A dummy fitted with an individual saddle which rests with 
 tirmness npon the border is, in many cases, preferable to a 
 dummy applied to the labial or buccal surface of the border 
 in such manner as to form a deep, constricted. V-shaped space 
 between the two. A ligature passed under the saddle will re- 
 move debris from both structure and border, while neither 
 ligature nor toothbrush will ]>rove efficient in the V-shaped 
 space. 
 
 Since the function of an in<lividual saddle is not to afford 
 support to a tixed bridge, but to develo)) reasonable lingual 
 contour to the dummy to which attached, its bearing on the 
 tissues should be restricted to the smallest possible area con- 
 sistent with desired contour. 
 
HRIDGEWOUK S23 
 
 l)y means ui' the iirt-ccdiiiii' •'("lassilicatiuii of Fixed 
 Jirid.i-es" it can he shown that it is possiljh:- to eoustnict more 
 than tifty-fonr thousand different varieties of fixed hridges. 
 To attemi)t to exi)lain in detail tlie technical methods em- 
 ployed in the construction of each would be a well-nigh im- 
 l)ossil)le task, and entirely uncalled foi- in a treatise of this 
 character. Fundamental })rinciples for all, however, are es- 
 sentially the same, therefore, when the student has mastered 
 these principles, which are comparatively few, he should be 
 capable of undertaking the coiistrnction of ordinarv, as well 
 as complicated, cases. 
 
 TECHNIC OF BRIDGE CONSTRUCTION 
 
 By way of illustrating some of the preceding ]>rinciples 
 outlined, tlie technical procedures involved in the construction 
 of a simple, fixed bridge, extending from right lower cuspid 
 to second molar, inclusive, the second bicuspid present to 
 serve as a pier, will now be described. 
 
 In examining the mouth and noting the I'elation of the 
 teeth to each other in this particular case, it is deemed advis- 
 able to iilace on the abutment and iiier teeth the following 
 crowns: 
 
 Cuspid root, jwrcelain face, banded crown. 
 
 Second bicuspid and second molar roots, shell crowns, 
 because of restricted space occluso-gingivally. 
 
 Tt is further assumed that the teeth have lieen devitalized 
 and their roois filled, if such procedure is considered ad- 
 visable. 
 
 The enamel is removed from the axiai surfaces of the 
 three roots, as previously described for crowns of the type 
 indicated. 
 
824 BRIDCRWORK 
 
 111 addition to reversing the cone form of Hie roots, tlicir 
 mesial and distal, axial surfaces must not diveri;e. Imt 
 rather couverge, from gingival to occlusal surfaces. The 
 necessity for establishing this relation is obvious, since 
 divergence of these surfaces will |>rc\cn1 \\\f rciiio\al of the 
 several crowns with the impression, ny tin' rdnni of the fin- 
 ished bridge to place. 
 
 The line of direction of the canal of the cuspid root must 
 also be considered. When not in parallel alignment with the 
 axial surfaces of the bicuspid and molar, a like difficulty will 
 be encountered as that mentioned. Since, however, reaming 
 tlie canal to any extent will weaken the root, in order to estab- 
 lish parallel relationship, it is a better plan to bring such 
 axial surfaces of the bicuspid and molar as diverge from the 
 general direction of the root canal into alignment with it 
 rather than ream the canal to the extent of weakening it. 
 
 In practically all other respects, tlie preparation of tlie 
 three roots is essentially the same as has been previously out- 
 lined for crowns of similar types as tliose used in the present 
 case. 
 
 When root preparation lias been completed, the crowns 
 are constructed individually, keeping in mind their correct 
 alignment buccally and the reservation of proportionate 
 spaces for the first bicuspid and first molar dummies. 
 
 The crowns are roughly finished, set on their respective 
 roots, a wax bite taken, the face bow applied, the bite mounted 
 on the occluding frame and. the occlusion cast developed. 
 
 If, in taking the bite, the crowns are disturbed, they are 
 returned to position on their respective roots and a plaster 
 impression secured. Usually, in such case as is being de- 
 scribed, the impression can be removed without fracture, the 
 crowns coming away with it. When fractured, however, the 
 broken j^ieces are assembled, the crowns set in their respective 
 matrices, and all luted firmly with wax. 
 
 The object in taking a bite and an impression as well, in- 
 stead of an impression-bite combined, in modeling coni])Ound, 
 as is frequently done, is to secure an accurate relation of the 
 crowns to each other. While it is possible, in some cases, to 
 remove the crowns from their respective roots without chang- 
 ing their relation to each other witli a combined bite and im- 
 pression in modeling compound, disturbance of relation is 
 liable to occur, and therefore plaster should always be used 
 in preference to a material which is liable to distort under 
 stress. 
 
BRIDGEWORK 825 
 
 From the impression, a east is formed whieli, when iiard- 
 ened, is fitted in the hite and attached to the occluding frame. 
 
 By flowing a film of wax in the interior of the shell 
 crowns and in the cap and around the dowel of the cuspid 
 crown, before filling the imjjression, the bridge, when assem- 
 bled and waxed together, can readily be removed from its 
 cast without mutilating the latter. The wax within the crowns 
 should be thoroughly removed before investment of the bridge. 
 
 REQUIREMENTS OF THE DUMMIES 
 
 For esthetic reasons, the first bicuspid dummy should be 
 of porcelain, or at least be porcelain-faced. When consider- 
 able absorption of the alveolar border has occurred and the 
 cervical half of the dummy will not be exposed to view in 
 laughing or speaking, a space may be left between this end of 
 the dummy and the ridge for hygienic reasons. 
 
 The application of a short dunnny in such location leaves 
 the gingival tissues next the crowns which proximate the 
 space, more or Jess exposed and accessible to the toothbrush 
 and other cleansing devices. 
 
 In case it is deemed advisable to extend the dummy to the 
 alveolar border, or saddle the latter, as is frequently done, 
 it should be uniformly reduced on its proximal surfaces, so 
 as to leave the interproximate spaces in the gingival half 
 areas free and accessible for cleansing purposes. 
 
 Too often the union between crowns and dummies extends 
 from the occlusal points of contact to the gingiva?, thus pre- 
 cluding the possibility of proper cleansing of the tissues and 
 appliance. 
 
 CONSTRUCTION OF THE BICUSPID DUMMY 
 
 A dummy may be constructed by any (if tlie several meth- 
 ods outlined, using facings or teeth of the removable type, or 
 a long pin, plate tooth may be employed. 
 
 By this latter method a facing of suitable form and color 
 is selected to fit within tlie space between the cuspid and sec- 
 ond bicuspid crowns. 
 
 Reduce tht mesial and distal surfaces so as to taper some- 
 what from occlusal to gingival. 
 
 Bevel the buccal marginal ridge, or that ]3ortion of the 
 facing which corresponds to the incisal edge of an anterior 
 
826 liKIUCiEWORK 
 
 tooth, to allow for an ext(Misiou of Warkinn lo the huccal mar- 
 gin for protection from stress. 
 
 The cervical eml of the dummy ma>' he liiiishcd in thi'cc 
 ways : 
 
 First, it may simply be rounded and swing clear of the 
 border, so as to leave a self-cleansing space between the bor- 
 der and the strncture. 
 
 I'ORL'EI.AIX F A (• K O DUMMY 
 
 FORMED WITH lERVlL'AL 
 
 L'I,EARANCE SPACE 
 
 Second, it may be adapted by grinding to lay in close 
 contact with the border at its cervico-laiccal margin, with 
 more or less of a V-shajied space, opening lingnally. 
 
 rORl'EI.AIX V A I' E D DUMMY 
 WHICH RESTS ON liUCCAi 
 SURFACE OF THE BORDER 
 
 Third, a saddle may be adapted to the cervical end, which, 
 when closely fitted to the border, ])ermits the lingual contour 
 of the dummy to be developed, and obviates the formation of 
 the objectionalile space referred to. 
 
 l'OBCEl,AlN FACED DUMMY 
 
 WITH SADDLE WHICH RESTS 
 
 UPON THE BORDER 
 
 The type of dummy suitable for each individual case can 
 be determined l)y setting it in correct buccal alignment with 
 the proximating crowns and noting the relation of its cervical 
 end to the border. 
 
BRIDGKWORK 827 
 
 Jn this case, a (huinny, tn wliicli a saiMIc is apiilicil. will 
 be euusidered the most appin|irialc. 
 
 The facing shoulil be groiiiul at its eervioal eud to tit the 
 inequalities of the border, and its l)uc('al marginal ridge bev- 
 eled as i3revii)usly deNcribed. 
 
 A baelving is now applied to its lingual surface, extend- 
 ing from the ridge lap to, or slightly beyond, the bucco-occlu- 
 sal margin. When the ridge lap of the porcelain does not tit 
 closely to the border except at its cervico-buccal margin, the 
 backing should extend bnccall\', so as to cover it, usually slight- 
 ly beyond the cervico-bui'cal margin. 
 
 A jiiecc of thin, pure gokl or i)latinum is burnished to 
 the border, innnediately on the area on which the dummy 
 will rest, and is trimmed to the approximate outline of the 
 dummy base. 
 
 The facing to wliicli the backing is attached is set in cor- 
 rect alignment with the ])roximating teeth on the saddle, and 
 the two are attached Avith wax. 
 
 Sufficient bulk of wax is now added, in which the occlu- 
 sal surface of the dumm.v can be carved. 
 
 When carved to desir(>d form, a counterdie can be con- 
 structed by the indirect method by casting over moldine as 
 desei'ibed. 
 
 Develop the cusp l)y swaging in the usual manner. Trim 
 peripherally, soften the wax and adapt to the dummy, return 
 the latter to the cast and by trimming and adjustment de- 
 velop correct occlusal relation. 
 
 Remove the dummy from the cast and wax to the desired 
 axial form. 
 
 The facing is now removed from the assembled dummy, 
 carbon points are inserted in the holes left by the withdrawal 
 of the pins and the dummy, minus the facing, is invested in a 
 casting ring, and the ojieration completed liy the casting 
 process. 
 
 By using a heavier gauge of metal for the saddle, to 
 prevent warpage or contraction in fusing the metal, the lin- 
 gual contour of the case can be developed by soldering. 
 
 When this plan is followed the mesial and distal margins 
 of the saddle should project slightly l)eyond the wax so as 
 to be caught iij the investment. 
 
 After the metal structure is completed, the carbon points 
 are drilled out, the facing titted ready for cementation in 
 position, after the lu'idge is com]ileted. The i)ins of the fac- 
 
S2S BRIDGEWORK 
 
 iiig slioiild, ill all cases, he r(mi;|iciic(l hcl'drc (■ciiiciitation to 
 afford inaxiiiiiiiii aiicli(ira,i;c in llic rciiiciit. 
 
 The duiimiy is now rough drcsst'd to the tlesired form, re- 
 turned to place between cnsind and second bicuspid crown 
 and waxed in ]iosition. 
 
 VARIATIONS IN THE FORMS OF DUMMIES 
 
 Various other forms of dummies can be applied with 
 ecjual facility to the case under consideration. For example, 
 a Steele, or an Kvslin facing, or a partial crown of either 
 type, may be used. Again, a Goslee, or a Gardiner partial 
 crown are equally apjilieable, either with or without a saddle, 
 providing sufficient .space exists to ])ermit the introduction of 
 a rigid metal structure beneath. 
 
 CONSTRUCTING THE MOLAR DUMMY 
 
 To illustrate still another tyjic of dummy fre(|iu'utly used, 
 the technic of an all metal i-e)ilaccm('iit for tlie first molar will 
 be described. 
 
 A mass of casting wax is warmed and pressed into the 
 space between second bicuspid and second molar, and the 
 occlusion developed in the usual manner. 
 
 The gingival half of the block of wax is excised, the occlu- 
 sal portion being carved to correct peripheral outline. 
 
 Since the object in applying a dummy of this type is to 
 gain space for cleansing purposes, the buccal and lingual sur- 
 faces of the dummv should be rounded inward, so as to form 
 
 ALL METAL MOLAK DUMMY. A 
 T\T>E OF PUMliy FRKQUENTLY 
 USED IN -'SANITARY BRIDGES" 
 
 a convex, or even V-shape, to the surface which looks toward 
 the border. By avoiding the formation of a flat, or a slightly 
 convex surface, to this portion of the dummy, practically all 
 parts are rendered accessible to the toothbrush and cleansing 
 appliances. 
 
 When carved to correct outline form, the wax is removed, 
 invested and cast in the usual manner. 
 
 Another method whereby practically the same form of 
 dummy may be i^roduced is by carving the cusp in some suit- 
 able medium, developing a counterdie and swaging the occlu- 
 
BRIDGEWORK 829 
 
 sal surface and occlusal third i)cri]ilH'ry from gold ]>latc in 
 the couuterdie. 
 
 This is trinnued to i)roper depth, the border inargius con- 
 toured inward slightly with pliers, the interior of the partial 
 crown tilled in with plate scrap, huilding it high in the form of 
 a mesio-distal ridge, and tilling in the voids with solder to the 
 required contour. 
 
 After developing the dummy, by whatever method em- 
 ployed, it is rough finished, and fitted in position between the 
 second bicuspid and second molar crowns. 
 
 ASSEMBLING THE BRIDGE 
 
 Before the linal waxing of the several parts of the hriclge, 
 the dummies are laid aside, the three crowns warmed suffi- 
 ciently to soften the film of interior wax, and removed from 
 the cast. By observing care in removal, their cervical 
 matrices on the cast will not he appreciably disturbed. The 
 wax is cleared from the interior of the crowns, after which 
 they should be boiled in acid, washed thoroughly, and re- 
 turned to position on the cast. A little sticky wax, applied 
 at two or three points along the gingival margins, will hold 
 them firmly in position while assembling the bridge. 
 
 The dummies are now adjusted and luted firmly with hard, 
 sticky wax, applying it in sufficient quantity to firmly unite 
 them to the crowns. 
 
 Before final removal from the cast, the occlusion should be 
 tested, the general aligmnent of the crowns and dummies 
 noted and the assembled bridge, as a whole, inspected, to 
 see that every part is in exact relation. 
 
 In grinding and adjusting porcelain facings in a bridge, 
 special care should be taken, that a very slight space exists 
 between them, or between the porcelain and proximating 
 metal crowns. The metal backings of the facings, however, 
 should, whenever possible, i-est in close contact with each other 
 and with adjacent metal crowns. 
 
 This is necessary, in order that shortening of the bridge 
 may not occur as a result of contraction of l»oth investment 
 and solder., as the latter cools. 
 
 On removal of the bridge from the cast the joints between 
 the several dmnmies should be flushed with wax to prevent 
 the ingress of the investment material the result of which is 
 to exclude the solder, and thus weaken the union lietween the 
 several ]iarts of the structure. 
 
f>au HRIIK'.EWOKK 
 
 I'^iuallx' Ihc cnspid I'aciiin' is iciiKivcd tVoiii the crown ami 
 laiil aside until al'tci' llic several |iarls ai'e soldered. 
 
 INVESTING THE BRIDGE 
 
 A mix of medium consistciiey of some tlioroughly tested 
 investment material should he maile. This is placed on a 
 slali or piece of paper on the hench, Iniilding it ujj to one inch 
 or slightly more in thickness, ai)pi()xiniately the same width, 
 and somewhat longer than the bridge. 
 
 With the point of a small inslrument some of the invest- 
 ment is carefully applied to the interior of the cap of the cus- 
 ])id crown, in the pin holes left l)y removal of the facing, and 
 in the two shell crowns as well. 
 
 The bridge is now laid, buccal side down, on the invest- 
 ment, into which it is gradually settled, to within about one- 
 half inch of the bottom of the mass. If pressed too deeply, the 
 investment, when trimmed, will ))e weak and is very liable to 
 fracture during soldering. 
 
 When hardened, the surplus inxcstnient is trimmed away, 
 being specially careful to clear away all obstructions from 
 around the teeth and dummies which might interfere with 
 the direct api>lication of the flame to the solder in the various 
 joints. 
 
 The wax is removed, first by picking out the bulky portion, 
 and afterward applying boiling water for the removal of that 
 in the deepest parts. 
 
 A thin film of thick borax paste is applied to all parts on 
 which it is desired that the solder should flow, and the invest- 
 ment jjlaced on a gauze over the Bunsen flame. 
 
 When heated to a dull red heat along the base of the in- 
 vestment, the case is transferred to the soldering block, the 
 blow-piiie flame aiii^lied and strip solder fused and fed into 
 the lingual surfaces and embrasures imtil the required con- 
 tour is attained. 
 
 FINISHING 
 
 The finishing of a bridge of this tyjie is similar to that of 
 a single crown. In bridgework, however, particular care 
 should lie taken to finish the metal smoothly in the inter- 
 ])roximal spaces. Rough surfaces in any location invite the 
 lodgement of food. Therefore, all file marks should be re- 
 moved with fine discs, and the finer scratches left by these 
 i-emoved by coarse, followed by fine ])olishing powders, with 
 felt and lirush wheels, on the lathe. 
 
BRIUGEWORK 
 
 SETTING THE BRIDGE 
 
 The bridge when finished is adjusted in jiosition on tlie 
 natural roots to test its eorreetness of form, and proliable 
 fultilhneut of function, after whicli it is washed, dried, and 
 laitl asitle while tlie mouth is prepared for its reception. 
 
 The mouth should be syringed with warm normal salt 
 solution, cotton rolls applied to dam against the encroach- 
 ment of moisture, and the teeth and roots tlioroughly dried. 
 
 From a thoroughly mixed mass of mediinn thin cement, 
 the shell crowns are ])artially tilled and some applied around 
 the dowel and on the root ca]). Tiie root canal is also filled, 
 using for this ]iui-]iose a small pinggci- ]>()int. or the regular 
 root canal plugger. 
 
 The bridge is now quickly set in position and forced to 
 place with heavy, steady ])ressure, and the jiatient instructed 
 to close the teeth with foi-ce. If occlusion is correct, the 
 
 BRIDGE IX POSITION ON" CAST. SHOWING CONSIDERABLE 
 
 INTERPROXIMAL SPAfE TO THE MESIAL AND 
 
 DISTAL OF KIRST BKTSPID DUMMY 
 
 mouth is 0])eued and the parts guarded from moisture until 
 the cement has had time to become fairly hard. 
 
 Removing the excess cement requires care and close at- 
 tention not only from beneath the gingival, but from the 
 various surfaces of the structure against which it may have 
 become lodged. If not removed at this time it may remain 
 adherent for a long time, particularly in jirotected locations, 
 as in the interproximal spaces, where, although it may not 
 prove a direct irritant, will invite the accumulation of food. 
 
 Finally tltc bridge is tested with carlion paper to dis- 
 close any points of interference in lateral maudebular move- 
 ment. If any are present they are reduced with stones and 
 the roughened surfaces again ixilislied. 
 
S32 BRIDGEWORK 
 
 THE CARMICHAEL ATTACHMENT 
 
 An attachment often applied to good advantage in fixed 
 hridgework is that known as the "Staple Half Crown," 
 "Carmiehael Attaclnnent, " and nnder various other names. 
 
 This attachment is in reality a shallow inlay, covering a 
 considerable area of tooth surface from wliicli the cniimcl ;uid 
 a superficial layer of denture has been renio\ed. 
 
 Anchorage of the attachment to the tooth is secured by 
 means of interior, peripheral ribs in the metal structure, 
 formed during constructing, which fit within corresponding 
 grooves in the prepared tooth surface or shallow cavity. 
 
 The particular advantages of this attachment, when prop- 
 erly constructed and applied, are as follows : 
 
 First, it can be applied to the lingual surface of a vital 
 tooth without endangering the pulp. 
 
 Second, a secure attachment to the tooth can be devel- 
 oped without involving much of the labial or buccal sui'face. 
 
 Third, the joint between the attachment and cavo-surface 
 angles is the same as in ordinary inlay work, or gold foil fill- 
 ings, thus obviating the formation of a shoulder, which, in 
 many cases, particularly in constructed locations, invites the 
 lodgment of food and, subsecjuently, caries. 
 
 Attachments of this type are most applicable to cuspid 
 teeth, although they may at times be applied to central in- 
 .cisors. When slightly modified they may lie ap]ilied to very 
 great advantage to the bicuspids. 
 
 The name Staple Half Croivn was given this attachment 
 because formerly an iridio-platinum wire staple was applied 
 in the groove in the tooth, a gold or ]ilatinuni matrix adapted 
 to the tooth and staple and the two attached. The staple thus 
 formed the interior rib alluded to. 
 
 CONSTRUCTION 
 
 To illustrate the constructive steps, the application of a 
 Carmiehael attachment to a cuspid tooth will be described: 
 
 With suitable stones and discs the jilate of enamel is re- 
 moved from the entire lingual and proximal surfaces of the 
 tooth; except at the cervical periphery, and the incisal edge 
 beveled at the expense of the lingual surface. 
 
 Usually, for subsequent protection of the tooth, removal 
 of enamel on proximal surfaces is carried slightly to the 
 labial of the contact points. 
 
BRIDGEWORK 833 
 
 A gingival shoulder is formed by moans of square-end 
 burs. This should be carried either under the free gum 
 margin, or terminated a short distance to the incisal of it, 
 to avoid the formation of a joint at the margin. 
 
 With a fissure bur, grooves are cut on the proximal sur- 
 faces, next the labial plate of enamel, from gingival seat to 
 incisal edge, converging slightly, incisally. 
 
 PROXIMAI- VIEW OF CUSPID LINGUAL VIEW OF SAME INCISAL VIEW OF SAME 
 
 PREPARED FOE A CAR- 
 MICHAEL ATTACHMENT 
 
 These grooves are iinited Ijy another transverse groove 
 located as close to the incisal edge as possible in order to de- 
 velop anchorage for the resistance of labio-lingual, torsional 
 strain. 
 
 All surfaces, margins and grooves should be so corre- 
 lated that, when formed, removal of the wax model may be 
 accomplished without distortion. 
 
 This requires that all overhanging or rough margins and 
 sui'faces be smoothed and all undercuts obliterated before 
 forming the model. 
 
 A modeling compound impression enclosed within a band 
 or half thimble cup is secured, of surfaces and margins of the 
 tooth involved. 
 
 From this an amalgam, or a modelite, die is developed, 
 which, when hardened, is smoothed, and on this the pattern 
 is developed in inlay wax. 
 
 The wax should be forced into all grooves and against 
 all cavit}' surfaces, ]5articular care being taken to adapt it 
 closely to the margins and against the beveled incisal edge. 
 It is then carved to restore the tooth to its original form. 
 
 Usually it is best to test the wax model on the natural 
 tooth to see that it fulfills requirement, when, if found satis- 
 factory, it is invested and cast, preferably in a good grade of 
 platinized gold. 
 
BRIDGEWORK 
 
 FINISHING 
 
 AVhen cast, it is washed, heated and dropped in acid, the 
 nodnlar surfaces corrected, after wliicli it is fitted to tlie tootli 
 and tlic iiKi ruins disced to coiiicich' with llie tootli surfaces. 
 
 CARMICHAEL COMPLETED, 
 
 BEADY FOB ATTACHMENT 
 
 TO imincE 
 
 Wiien the other ahutnicut and i>ier structures are com- 
 pleted, all are placed in position, an impression and bite se- 
 cured and the Carmichael attachment is treated in the same 
 maimer as of full crown. 
 
 MODIFIED TECHNIC 
 
 Another method of construction consists in applying a 
 piece of 34 or 36 gauge gold or platinum to the die, and by 
 burnishing, form a matrix which fits accurately within 
 grooves and against the reduced surfaces of the tooth. 
 
 When perfectly ada]ited and trimmed to correct periph- 
 eral outline, sticky wax is flowed over the lingual side of the 
 matrix to prevent distortion, after which the latter is re 
 moved, invested, the wax burned off and liigh-grade solder 
 flowed on the gold to develop required lingual contour. 
 
 Still another method consists in applying inlay wax to 
 the burnished matrix, developing the wax to correct form, 
 investing and casting against the matrix. By this method 
 the surfaces which rest against the tooth are free from 
 nodular imperfections, resulting from casting the entii'e ap- 
 pliance. 
 
BRIDGEWORK 835 
 
 MODIFIED CARMICHAEL APPLIED TO CUSPIDS AND 
 BICUSPIDS 
 
 An application of the Carmicliacl attaehnuMit applit^d to 
 cuspids and bicuspids, suggested l)y Dr. E. A. Kennedy, is as 
 follows : 
 
 The enamel and a layer of dentin is removed from a 
 portion of the lingual, i)roximal, and labial or buccal surfaces 
 of the tooth, extending from incisal, or occlusal, to gingival 
 areas. In bicuspids, an (irchisnl step, having a decided dove- 
 
 MODIFIED 
 CARMICHAEL 
 ATTACHMENT 
 
 TOOTH PREPARATION FOR MODIFIED CAR- 
 MICHAEL FOR BICUSPID 
 
 MODIFIED CjUIMICHAEL IN, AND 
 REMOVED FROM, POSITION 
 
 tail shape, is formed, while the giiigixal area terminates in a 
 right-angle shoulder. 
 
 The axial surfaces of the tooth should present a slightly 
 conical form to permit the removal of the wax pattern. 
 
 Grooves are now cut in the lingual and labial, or buccal, 
 axial surfaces in the dentin, for anchorage purposes. The 
 process of forming the wax pattern, casting, fitting and tin- 
 ishing is the same as described in the construction of a Car- 
 michael attachment. 
 
 This attachment can be applied to vital teeth and, when 
 l)roperly constructed, affords an anchorage for small bridges 
 equal to that of tlie average crown. 
 
 THE CORCORAN ATTACHMENT 
 
 The Corcoran attachment is applied to aliutment crowns 
 in those cases where it is desirable that a liridge of the fixed 
 type be removed from time to time for cleansing, or for 
 treatment of the supporting teeth and adjacent tissues. 
 
 This attachment consists of a gold block, threaded in- 
 ternallv. and which receives a threaded bushing. The bush- 
 
836 
 
 BRIDGEWORK 
 
 ing also is threaded to receive a lioadcd screw, by means of 
 which the crown is anchored. 
 
 In case of wear, both bushing and screw may be replaced 
 with new ones, the parts being interchangeable. 
 
 CONSTRUCTION 
 
 The root is jtrcpared as previously descriliod, with dis- 
 tinctly conical peri])hery, and having an interior shoulder. 
 
 IMPRESSION CUP AS AP- 
 PLIED IN TAKING MODEL- 
 ING COMPOUND IMPRESSION 
 OP ROOT FACE AUD PERIPI!- 
 ERY OF MOLAR TOOTH 
 
 ROOT CAP CONSTRUCTED 
 
 CORCORAN ATTACHMENT 
 SHOWING COMPLETED 
 
 CROWN. BLOCK AT- 
 TACHED TO ROOT CAI'. 
 WITH BUSHING AND 
 SCREW IN POSITION. BUT 
 NOT SCREWED TO PLACE 
 
BRIDGEWORK 
 
 837 
 
 An open band impression is secured in modeling com- 
 pound, from which an amalgam die is formed. 
 
 Over this die a root cap is swaged, through which dowels 
 are passed and attached with high-grade solder. 
 
 The central shoulder depression should be filled at the 
 same time, and the cap stiffened by flowing solder over its 
 entire area. 
 
 A Corcoran block is now set in position on the cap and 
 attached to the latter with a lower fusing solder than that 
 previously applied. 
 
 The sides of the block slioukl be parallel with the long 
 axis of the tooth, or the line of direction of introduction and 
 removal of the bridge. 
 
 A URIDGE ANCHORED liV THE COIirORAN ATTACHMENTS HEIIOVED 
 
 FROM ITS MULTIPLE ANlHORAflE, WHICH. IN THIS CASE. 
 
 CONSISTS OF PI\E ROOTS. THREE OF WHICH 
 
 CARRY BLOCKS 
 
 A solid metal crown can be formed on the root cap and 
 around the Corcoran block by applying and carving inlay 
 wax to the desired form and casting. 
 
 A countersunk opening, directly in line with that in the 
 block, made through the occhisal surface of the crown, re- 
 ceives the headed screw which anchors the crown to the root 
 cap. 
 
BRIDGEWORK 
 
 By setting the block somewhat to tlie lingual, a porcelain- 
 faced crown can be constructed in the usual maimer. 
 
 To obviate the tediousuess of final fitting of the crown 
 to the block, which in all cases must be done in cast work, a 
 
 BRIDGE SET IX PCSLTICIN AMI TIKI, I) in TIIKKE SrRKWS. THE TWO 
 DISTAL ROOTS I'AIUtV KKI,1,V ATTA<MIMENTS AND ONE ON 
 LEFT A BAH Folt <ilLMOItE ATTACHMENT. EN- 
 CLOSED WITHIN PARTIAL DENTURE 
 
 boxing, composed of ])latinum or high fusing gold, is first 
 formed and fitted to the block on the root eaj). 
 
 Over this the crown is built in any manner that the con- 
 ditions of the case demand, after which it is removed from 
 the cap, the box covering the block coming away with the 
 pattern crown, and the solder flowed, or gold cast against it. 
 
 The crowns and bridge showing application of the Cor- 
 coran appliances were kindly loaned for illustrations by Dr. 
 H. F. Methven. 
 
 Still another modification is sometimes carried out; a 
 disc of gold or platinum, to serve as a crown base is per- 
 forated, fitted around the block and swaged to accurately 
 conform to the root cap. To this the boxing, which encloses 
 the block, is soldered, and on this metal base the crown is 
 built. 
 
BRIDGEWORK 
 
 839 
 
 SIDE VIEW OF liRIPGE ON CAST. WITH rARTIAT. DEN- 
 TURE ABOVE 
 
 BRIDGE AND DENTURE IN POSITION ON CAST 
 
840 BRIDGEWORK 
 
 On page 79(5 reference is made to a bridge eonstructed by 
 Dr. Anderson, in which the substitute, altJiough composed 
 of two pieces, is of the fixed type when set. 
 
 BRIDGE rONSTRIUTED I!Y TiR. C. h. AND- 
 ERSON. FOE DESCRIPTION, SEE 
 PAGE 796 
 
 Mueller of Zuricli, Switzerland, suggests a similar method 
 of anchoring a removable bridge in position. 
 
 He constructs a root cap fitted with a tube, near the apical 
 end of which a slight rib is attached to one side. The dowel 
 of the crown is split, and sprung apart slightly at its apical 
 end. A groove is formed in the dowel at a point which, when 
 the latter is in jjosition in the tube, will fit over the rib in the 
 tube. The split dowel as it passes the rib is sprung together, 
 and as the crown is seated the notch of the dowel receives 
 the rib, and in this manner the crown is latched in position. 
 
 The structure is composed of a perforated root cap, 
 through which the independent doweled crown passes. 
 
 A telescoping crown or heavy stop clasp is fitted to the 
 other supporting root and the two connected by a saddle, to 
 which the teeth are attached. 
 
 THE HEDDY ATTACHMENT 
 
 The Heddy attacliment consists of a metallic lilock simi- 
 lar in form to tlie Corcoran attachment, differing, however, 
 in being solid. 
 
BRIDGEWORK 
 
 841 
 
 The general steps of root cap constrnction, as well as 
 that of the crown, are similar to those just outlined. Anchor- 
 age of the crown to the block attached to the root cap is se- 
 
 HOOT CAP IN POSITION. 
 
 CROWN COMPLETED. BUT 
 
 NOT SEATED 
 
 cured by cutting a V-shaped groove transversely across the 
 block, about midway between cap and occlusal end. 
 
 An opening is made througli one of the axial surfaces of 
 the crown. This is threaded to receive a set-screw having a 
 beveled point. 
 
 The crown is locked in position by setting the screw 
 firmly into the V-shaped groove of the central block. 
 
 REMOVABLE BRIDGES 
 
 A removable bridge, in the ordinary acceptation of the 
 term, refers to a substitute for lost natural teeth, which is 
 held in position and-supported by some of the remaining natu- 
 ral teeth or roots, and which can be removed from position 
 and replaced by the patient at will. 
 
 For hygienic as well as esthetic reasons, bridges of this 
 type are usually supplied with saddles. These may or may 
 
842 BRIDGEVVORK 
 
 not rclicvt' llic almtiiicnt and pier roots of a certain amount 
 of masticatory stress. As i)revioiisly stated iii structures 
 whieli conform to bridge engineering princijiles, whether fixed 
 or removable, the abutment aiul pier roots must resist prac- 
 tically all masticatory stress, regardless of the presence of 
 saddles. 
 
 When the structure is so jiianned tliat the saddle will re- 
 ceive the burden of stress, the abutment and pier roots being- 
 utilized principally for retention purposes, it should be classed 
 as a ])artial denture. 
 
 REMOVABLE BRIDGE ATTACHMENTS 
 
 The Roach, Gihuore, Morgan and similar ajjplianees are 
 frequently used in cases of so-called removable l)ridge work, 
 when, in reality, the structures should be classed as partial 
 dentures, since resistance to masticatory stress devolves 
 upon saddles, and not on the ai)i)liances themselves. 
 
 Various forms of attachments and many peculiar and 
 ingenious devices have been designed for the retention and 
 support of removable bridges. Many of these, because of 
 the exacting care required in their construction, or of certain 
 weaknesses which developed with use, have been discontinued. 
 
 The forms of attachments which have proven most satis- 
 factory and capable of resisting masticatory stress consist 
 of rigid telescoping devices, as cap crowns and crowns fitted 
 with heavj' dowels which are received within, and accurately 
 fitted to. tubes enclosed within the roots of natural teeth. 
 
 Dr. F. A. Peeso of New York, who is a recognized author- 
 ity in the field of removable bridge work, ai)plies this princi- 
 ple, or some slight modification of it, in practically all cases 
 where removable work is indicated. Although most satisfac- 
 tory, these forms of attachment require the use of compara- 
 tively rigid gold, and very exact technic in their production, 
 otherwise unsatisfactory results attend their application. 
 
 When a removable bridge structure is supported by two 
 or more roots, or teeth, these must be so prepared that the 
 attached crowns or retention devices may sustain a parallel 
 relation to each other. 
 
 This is necessary, as before stated, iii order that the 
 bridge may be readily removed and replaced by the patient 
 without special care or annoyance. 
 
 In addition, a bridge sustained by abutment and pier sup- 
 
BRIDGEWORK 
 
 843 
 
 IDorts not ill parallel ali.£>iimeiit must sooner or later, in many 
 cases at least, cause irritation of the enveloping structures of 
 the supporting roots. 
 
 "^tilV.-MlnMl, 
 
 PABALI^ELIXG DEVIl'E FOR rSE IX CROWN AND ISltllXiE WORK (IVORYl 
 
 Various devices have been suggested for deteriniuing 
 whether, in root preparation, the axial surfaces and root 
 canals are being shaped to meet the requirements. 
 
 A simple appliance is here shown, with which the general 
 alignment or parallelism of the surfaces and canals invohed 
 mav be tested. 
 
 ''"'■l'H||rfi;j, 
 
 WITH DISTAL SL'RFACK OF 
 
 When two- or more removable crowns with dowels are 
 emijloyed — the dowels fitting accurately within tubes in the 
 root canals — the necessity for establishing accurate parallel 
 alignment of the removable with the stationary parts to which 
 they are adapted is obvious. 
 
844 nRIDGEWORK 
 
 THE TELESCOPING CROWN 
 
 Tliis form of crown is applicalilo to l)icuspid and molar 
 teeth, when such teeth are properly aligned, or when they can, 
 by suitable preparation, be brought in correct alignment with 
 the other teeth involved. 
 
 Briefly, the general steps of constructing a crown by this 
 method are as follows: 
 
 The tooth is prepared as for a shell crown, its axial sur- 
 faces being slightly but uniformly tapered, and its occlusal 
 end reduced to a flat plane sufficiently to provide ample space 
 between its face end and the occluding teeth for not only the 
 inner cap, but for a thick, heavy, occlusal end to the outer or 
 telescoping crown. 
 
 The root cap, as before stated, should be tapered uni- 
 formly from gingival to occlusal plane, so as to present the 
 form of a more or less true frustum of a very slightly taper- 
 ing cone. 
 
 Its cervical end is accurately scribed to the gingival mar- 
 gin and in fitting is driven beneath the latter to the full extent 
 permissible by the peridental attachment, terminating it, 
 however, on the still flaring, conical, axial surfaces of the 
 tooth. 
 
 The occlusal margin is trimmed even with the flat tooth 
 plane. To this a disc is soldered, and its margins trimmed 
 even with the axial surfaces of the band, which step com- 
 pletes the assembling of the root cap. 
 
 The cap is now mounted on a wooden mandrel, with mod- 
 eling compound, and its outer surface wrought into a perfectly 
 true cone by means of a fine cut, flat file, after which it is 
 smoothly polished. 
 
 On removing the cap from the mandrel, its inner surfaces 
 are covered with a thin film of whiting and water, in which a 
 little gum arable is dissolved, to cause the whiting to adhere 
 closely to the metal. 
 
 The cap is now imbedded in moldine, occlusal end down, a 
 swaging ring centered over it, and a die cast directly into the 
 cap and ring. By tapping the cap lightly on its sides with a 
 mallet the die is released. 
 
 Over this root cap an outer or telescoping cap having the 
 same taper as the latter is closely fitted. It should, in fact, 
 be driven onto the root cap, thus insuring close adaptation 
 between the two. 
 
 Its gingival end is trimmed so as to terminate close to, 
 but not pass beneath, the gum margin. Its occlusal end should 
 
BRIDGEWORK 845 
 
 be covered with a disc similar to that which completed the root 
 cap. 
 
 When in position and its inner surfaces are in friction- 
 tight contact with the axial surfaces of root cap, its occlusal 
 end should not rest upon the latter, a space of about one- 
 sixty-fourth of an inch between the two being reserved for 
 the bridge to settle as the contact surfaces become worn. This 
 insures close gripping contact between the root cone and the 
 inner walls of the telescoping crown under continued use. 
 
 The root cap is returned to position in the month, a bite 
 and im^jression taken and casts developed and mounted on 
 the occluding frame. 
 
 The occlusal end and axial surfaces of the outer cap are 
 covered with inlay wax, melting it on to insure close union. 
 
 The wax on the occlusal end is now softened and the 
 occluding teeth pressed into it and subjected to lateral move- 
 ments as well, after which these surfaces are carved to re- 
 quired form. 
 
 The axial surfaces are developed by addition or reduction 
 of wax as indicated and the crown given its anatomic form. 
 
 The outer cap, or crown proper, is now removed from 
 the root cap, and after smoothing the wax, is invested and 
 cast the same as ^ny ordinary cast crown. 
 
 THE SPLIT DOWEL CROWN 
 
 The split dowel crown, combined with a tubed root cap, 
 is frequently employed in conjunction with the telescoping 
 crown in removable bridge work. 
 
S4G I'.IJIIHilOVVCJIlK 
 
 C-rowns of this t\|ic arc iiioi'c i)articiilarl\' apiilicaliU; to 
 cuspids and large-si zt-d, siiigie-i-oot teeth. Tiiey may, how- 
 ever, be applied to roots of any class, under favorable condi- 
 tions. The general constructive steps are as follows: 
 
 The root is prepared as for an ordinary cap crown, ex- 
 cept that the lingual side is not reduced to the margin of the 
 gum. In fact, it sliould jiroject one-sixteenth of an inch be- 
 yond the margin, so Ihaf tlic lialf band of the crown base may 
 not encroach n])()ii Ihc hitlci'. 
 
 A band, usually of coin gold, or i)late etiually as jiard 
 and high fusing, is formed and fitted beneath the gum margin. 
 The incisal end of the band is ti-imiiicd even with the face end 
 of the root, to whicli a disc of gold of similar character is 
 attached, either with high fusing solder or by sweating. 
 
 The cap is perforated for the reception of a tube whidi 
 serves the double purpose of anchoring the cap to the root, 
 and for the reception of the crown dowel as well. 
 
 The size of the dowel having been decided upon, a hard- 
 ened steel mandrel of corresponding diameter is selected, and 
 around this a piece of coin gold ])late is formed into a tube 
 and soldered with high grade solder. 
 
 A reamer of the exact size as the dowel is now passed into 
 the tube and its inner walls reamed true, and to exact size. 
 
 One end of the tube is closed with a small disc of gold 
 plate, the peripheral surjilus trimmed even with the outer sur- 
 faces of the tube, and its corners chamfered or roun<le(l 
 slightly. 
 
 The dowel is formed from half-round clasp metal wire, 
 as follows : 
 
 A piece of half-round wire, slightly larger than the dowel 
 and about one and one-half inches long, is bent in the form 
 of a loop, the two ends bent to lie in close contact from their 
 terminals inward, for about one-fourth inch, the remainder 
 of the loop being open. 
 
 A little coin gold is now ai>plied in the V-shaped space, 
 next the contact area, and the two ends united by fusion. It is 
 necessary to use coin, or equally high fusing gold, to effect 
 this union, to avoid the split portion of the dowel from being 
 united in subsequent soldering operations. 
 
 The loop portion of the half-round wire is now carefully 
 
BRIDGEWORK 847 
 
 battered down with a small rawhide mallet, in a half-round, 
 grooved anvil, until the flattened surfaces of the wire are iu 
 contact. 
 
 The dou])l(Hl wire, with ends united, now presents the 
 appearance of a round wire, about three-fourths of an inch 
 long. This is passed through gradually decreasing holes in 
 the draw plate, until it is brought to very nearly the reipiired 
 diameter to enter the tube. 
 
 The final reduction to exact size is accomplished by plac- 
 ing the wire in a pin vice, resting it in a grooved block, and 
 with a fine cut, flat file carefully reducing it under rotary 
 action. 
 
 It should be tested from time to time in the tube, and 
 when it just begins to enter the latter, the tile marks are re- 
 moved with fine flour of emery cloth or crocus. The soldered 
 end of the dowel may be placed iu a true running lathe chuck, 
 and the final finish given by api:)lying the fine polishing cloth 
 against it by means of a flat stick, or by laying it on the flat, 
 fine file and running the lathe at high speed. 
 
 The dowel should fit the tulie with friction-tight contact, 
 yet not so tightly as to iirccludc its ready introduction and 
 removal. 
 
 ASSEMBLING THE PARTS 
 
 An opening is made in the root cap for the reception of 
 the tube, as before stated. This opening, although in some 
 cases it may be located directly in line with the canal, is usu- 
 ally made a little to the lingual, and the canal reamed accord- 
 ingly, so that the dowel may not interfere witii proper adjust- 
 ment of the facing. 
 
 In this case, as in that of all cap and dowel crowns, the 
 entrance to the root canal can be reamed out slightly and the 
 margins of the cap around the tube opening dei)ressed into the 
 countersunk area. This adds strength to the attachment be 
 tween cap and tube, and further permits tlie tube opening to 
 be countersunk for the more ready introduction of the dowel. 
 
 The cap is set in position on the root, the tube passed 
 through it, into the root canal, which previously has been en- 
 larged to receive it, and an impression taken to secure the re- 
 lation between the two. 
 
 When secured^ and a small investment model formed, the 
 two are united in the same manner as an ordinary cap and 
 dowel. The tube should be filled with investment previous to 
 soldering to prevent its becoming filled with solder during this 
 operation. 
 
848 BRIDGEWORK 
 
 CONSTRUCTING THE CROWN BASE 
 
 Usually a lingual, lialt'-band c-a)) is adapted to the root 
 cap to serve as a crown base and to which the split dowel is 
 attached. Such a caj) affords resistance to outward displace- 
 ment, and obviates the presence of a second band beneath the 
 gum margin. 
 
 For convenience in constinu-iion a full band is adapted to 
 the periphery of the root cap, to which a disc, or floor, is con- 
 formed and the two united with high grade solder on the lin- 
 gual, but not on the labial half of the cap. 
 
 After uniting the band and floor of the telescoping cap 
 and completing its adaptation to the root cap, the floor is per- 
 forated for the reception of split dowel of the crown. This 
 should be in perfect alignment with the opening in the tube 
 of the root cap. 
 
 The telescoping cap, or crown base, is adjusted to the root 
 cap, the dowel having been cut to suitable length, its free or 
 divided end is inserted in the tube to full depth, a small im- 
 pression taken to secure correct relation between the two, and 
 in which they are placed previous to running up the cast in 
 investment. 
 
 Since subsequent soldering operations must follow, the 
 union between cap and dowel should be made with high grade 
 solder, or the special plate recommended for this purpose in 
 the section on metallurgy. 
 
 The labial half of the band is removed and the terminals 
 of the lingual half neatly finished against floor. This may be 
 easily accomplished if, when soldering, care was observed to 
 prevent the labial joint area from filling with solder. Wein- 
 stein suggests notching the incisal edge of the band before 
 soldering, the break in the continuity of surfaces thus pre- 
 venting the solder being drawn to the labial. 
 
 When the several steps have been carried out accurately, 
 the floor of the crown base will rest firmly on the root cap, its 
 
 A BAND, NOTCHED TO PREVENT 
 
 SOLDER FLOWING TO LABIAL 
 
 HALF OF BAND 
 
 lingual half band in close contact with that of the cap over 
 which it telescopes, while the dowel fits with almost friction- 
 tight contact within the tube. 
 
BRIDGEWORK 
 
 On this base a crown of any desired type is built to meet 
 the requirements of the case, which, when completed, would 
 be called a half hand, split dowel crown. 
 
 HALF BAND, SPLIT DO^VEL 
 CBOWN. PARTIALLY KEMO^TED 
 PKOM POSITION OX HOOT CAP 
 
 CONSTRUCTING THE SADDLE 
 
 The saddle may be swaged by methods outlined under 
 partial denture construction or a wax model of the desired 
 form may be developed and cast. When the latter plan is 
 followed, ample though not very large sprues should be pro- 
 vided for the ingress of gold into the matrix, two or three 
 being sufficient for the purpose. 
 
 "When constructed, the saddle is adjusted to the border, 
 the two complete crowns being in position on their respective 
 roots, and an impression taken by the pressure method as de- 
 scribed on page 499. 
 
 The crowns should come away with the impression, or, 
 if not, they are set in their respective matrices and a cast of 
 some reliable investment material formed. 
 
 The saddle and crowns are now firmly united, and if not 
 previoiisly provided for, attachments should be made for vul- 
 canite anchorage. These attachments, however, are omitted 
 when the structure is to be composed entirely of metal and 
 porcelain. 
 
 The now assembled and uiiited metal framework is re- 
 turned to the mouth for final bite and impression. The metal 
 structure is correctly placed in its matrix in the impression, 
 
850 BUHKnOWORK 
 
 the I'oot caps rciiuiNcd and set in llicir n'sjx'ctivc (Tdwiis and 
 a cast oi' one of tlic liai'd materials t'ornicd. 
 
 ATTACHING THE TEETH 
 
 Plain or giun section teeth may lie ,i;i-ound to position and 
 attached to the saddle in the usual manner, or some of the 
 replaceable type of teeth are frequently used. When this plan 
 is followed, gold sockets are adapted to the bases of the sev- 
 eral teeth, the teeth with sockets attached, waxed in position, 
 the porcelain removed, the case invested and the union of 
 sockets to saddle accom|)lished by flowing- plate or high grade 
 solder between and to complete tlie contoui- of the case. 
 
 FINISHING THE CASE 
 
 The steps of iinishing are similar to those followed in 
 regular bridge or partial denture work, the idea being to 
 remove all surplus material, remove sharp margins that may, 
 by their presence, produce irritation, and finish the case as 
 smoothly and perfectly as the most finished ]iiece of jewelry 
 ever produced. 
 
 SETTING THE ROOT CAPS 
 
 In cases of the tyjie under consideration, setting the root 
 caps is ])ractically the last operation. This is purposely de- 
 layed until this time, so that, should any warpage occur in the 
 
 <i- % 
 
 BRIDGE OOMPOSED OF HALF BAND. 
 SPLIT DOWEL BICUSPID CBOWTJ, A 
 TELESt'OPINO MOLAR CROWN AND TWO 
 Dl'MMIES COMPLETED, ROOT CAPS IN 
 POSITION 
 
 final assembling and soldering of the structure, the exact rela- 
 tion between root caps and their telescoping crowns may be 
 preserved. 
 
BRIDGEWORK 851 
 
 The caps are set as follows: 
 
 Tiie interior of the telescoping crowns is coated with 
 a thin tilm of oil, the root caps cleansed and dried and set in 
 position in their respective crowns, cement applied in their 
 interior and to the roots, and the entire strnctnre carried to 
 position and forced to place, first with direct pressnre and 
 immediately tested with the occluding teeth to see that it is 
 correctly seated. 
 
 GENERAL REMARKS 
 
 The details of this most excellent system of removable 
 bridge work has been presented in book form by Dr. F. A. 
 Peso, a man most eminently qualified by years of successful 
 experience to present it in a clear, logical and practical man- 
 ner. He is, in fact, responsible for the development of the 
 finer and more accurate details, a neglect of which would re- 
 sult in indifferent success, or total failure. 
 
 Coin gold, because of its hardness and comparatively high 
 fusibility, is recommended for root caps, tubes and telescop- 
 ing caps as well, and highly platinized gold for split dowels. 
 
 In initial operations, when possible, the joints are siveated 
 to obviate danger of fusion in subsequent operations. When 
 union cannot lie thus effected the highest fusing solder pos- 
 sible to use on tlic jilale with safety is (■mi)l()yed, for reasons 
 before stated. 
 
 THE INLAY CLASP ATTACHMENT 
 
 A combined inlay clasp attachment, suggested by Dr. II. 
 J. Goslee, can at times be used to advantage in removable 
 bridge work when stress of mastication is not excessively 
 heavy. This can best be illustrated by descriliing the applica- 
 tion of such an attachment to a crown, in this case a lower 
 first molar. 
 
 The tooth is i)rei)ared slightly cone shape, to which a 
 deep root cap or thimble is fitted, similar to that used in the 
 telescoping crown. Tnlay wax is now applied to the occlusal 
 and axial surfaces and carved to meet anatomic and occlusal 
 requirements. 
 
 From the axia-occlnsal third of the ci'own, tlie wax is re- 
 moved from the axial surfaces to form a shoulder depression 
 for the reception of the clasp. A dovetail depression, similar 
 to an occlusal step cavity, is cut in the occlusal surface of wax. 
 The axial walls of both inlay step and outer surfaces of re- 
 
852 BRIDGEWORK 
 
 duced portion of the crown are rendered parallel or slightly 
 convergent to permit the withdrawal of the wax pattern for 
 the clasp attachment later on. 
 
 The crown, minus the portions removed, is cast, and fin- 
 ished. Wax is filled in the removed areas and carved to com- 
 plete the anatomic form of the crown, after which it is care- 
 fully separated, invested and cast. When made sufficiently 
 rigid and wide, and the walls of the crown which it embraces 
 are formed practically parallel, this attaclmient grasps the 
 crown very firmly. 
 
 An attachment of this type may be combined with an- 
 other of similar style, or combined with the telescope, or the 
 half band dowel crown, in the construction of small bridges. 
 
 A tube attached to the inlay seat of the crown, extending 
 toward or into the pulp chamber, for the reception of a split 
 dowel anchored in the inlay, will add greatly to the stability 
 of the appliance. 
 
 THE SPLIT DOWEL, LINGUAL HALF CROWN 
 
 This attachment is really a removable Carmichael attach- 
 ment, combined with a split dowel, applied to a partial, arti- 
 ficial crown. The writer is unable to state who first suggested 
 
 LINGUAIi VIEW OF CKOWN. 
 
 CERVICAI, VIEW OF LINGUAL 
 
 HALF CBOWN 
 
 BUCCAL VIEW OF CROWN. 
 
 CERVICAL VIEW OF HALT 
 
 CROWN, SHOWING SPLIT DOWEL. 
 
 SLIGHTLY MODIFIED 
 
 it as a removable bridge anchorage. When accurately con- 
 structed, in well-selected cases, it is a very rigid and service- 
 able attachment. It is particularly applicable to bicuspids 
 and molars. 
 
BRIDGEWORK 853 
 
 CONSTRUCTION OF THE HALF CROWN 
 
 The crowu, or remaining portion, is reduced to the gin- 
 gival, the peripheral ring of enamel removed and the root end 
 prepared decidedly cone shape, and for which a root cap is 
 swaged, by metliods previonsly outlined. By preparing the 
 pnlp chamber walls with a slight flare oiitwardly, an inside 
 shoulder may be developed on the root cap, which will hold 
 the latter in position, regardless of the pronounced flare of 
 the root periphery. 
 
 One or more dowels are passed through the cap and into 
 the root canals and attached as in any similar case. 
 
 Usually a porcelain facing is ground, backed and applied 
 to the root cap in proper alignment with the proximating 
 teeth. The backing should be extended so as to protect the 
 buccal marginal ridge of porcelain from stress. 
 
 Inlay wax is melted against the backing and on the root 
 cap in excess of what will be required to form the lingual 
 shoulder, and when hardened is carved somewhat in the form 
 of a half cylinder, or very slightly tapering cone, or rectangu- 
 lar block, the axis of which lies parallel with the long axis of 
 the tooth. 
 
 The backing itself would be thickened with wax, specially 
 the beveled portion extending over the marginal ridge. Usu- 
 ally the outer half of the buccal cusps are developed in this 
 wax. 
 
 The sides of the cylinder terminate within the mesial and 
 distal surfaces of the crown, the angle between the backing 
 and half cylinder being grooved to form a sort of dovetail, by 
 means of which the lingual attachment is locked in position. 
 
 The occlusal end of the cylinder is reduced sufficiently to 
 allow space for the thick occlusal cap to the attachment. 
 
 The gingival end of the cylinder is squared and a fiat 
 cervical shoulder is thus formed on which the lingual half of 
 the crown may rest. 
 
 The cylinder, as before stated, should converge some- 
 what from gingival toward occlusal areas, to permit the pat- 
 tern for the lingual half crown to be removed. 
 
 A closed end. tube, of suitable size to receive the split 
 dowel, and somewhat longer than required, is heated and 
 pressed into the occlusal end of the wax cylinder, until its 
 closed end rests on the crown base. Care should be taken to 
 adjust it parallel with the line of direction, of introduction 
 and removal of the half crown. 
 
854 BRIDGRWORK 
 
 The facing' is now removod and cai'ljon jioiiits inserted in 
 the pin holes, the case invested and cast, after wliich it is fin- 
 ished with phig finishing burs, stones, discs, etc. 
 
 The carbon points are drilled out, the facing fitted in 
 position, its pins roughened, when it can be tem])orarily set 
 in position with gutta percha while finishing the crown. This 
 is essential, for if the metal parts are ])olished without the 
 facing being in position, the joint area lu'tween porcelain 
 and backing will be impaired. 
 
 Later on in soldering the assembled bridge, the facing 
 is removed when, after comi)letion of the metal structure, it 
 is permanently set with cement. 
 
 CONSTRUCTION OF THE LINGUAL HALF CROWN 
 
 A Split dowel, slightly longer than required, is adjusted to 
 tlie tube within the cylinder, the surfaces of gold against which 
 the lingual half crown rests are coated with a thin film of oil 
 and inlay wax applied in sufficient bulk to complete the re- 
 quired contour. By means of a metal matrix slightly longer 
 than th« crown, an excess of softened inlay wax can be ap- 
 l)lied and forced into every angle, groove and irregularity. 
 On removal of the matrix the excess can l)e carved off and 
 the crown developed to required anatomic form. 
 
 The carved model of the half crown is carefully removed, 
 care being taken to bring the dowel away with it without dis- 
 torting the relation lietween the two. Should it become loos- 
 ened, the wax immediately around it must be melted and the 
 model returned to the metal parts for final adjustment, when 
 it may be removed, invested and cast. 
 
 FINISHING THE ATTACHMENT 
 
 The natural contraction, together with the more or less 
 nodular surfaces i)resent, demands the exercise of the greatest 
 care in finishing, to avoid cutting away unnecessary gold, be- 
 fore the actual points of interference are discovered. 
 
 When an amalgam die has lieen formed on which to con- 
 struct the root cap, the crown can be returned to it, and bj^ 
 tapping the lingual half crown in the direction of the long axis 
 of the tooth and removing, burnished spots will disclose the 
 points of Interference. 
 
 These attachments are used in conjunction with and with- 
 out saddles, if conditions demand their application in such 
 manner. 
 
BRIDGEWORK 855 
 
 MODIFICATION OF THE TELESCOPING MOLAR CROWN 
 
 A modification of the telescoping, shell molar crown, 
 combined with si)iit dowel crown, is sometimes employed in 
 extensive bridges of the compound or complex types. It is 
 not adaptable to simple liridges for the reason that the abut- 
 ment being in nearly straight alignment, torsional strain will 
 unseat the ap])liance. 
 
 Instead of a deep root cap with a telescoping cap of prac- 
 tically the same de'jith adapted to it, the molar root is reduced 
 to within a short distance of the gingiva and fitted with a 
 doweled cap having practically parallel sides. 
 
 On the top of the cap a Gilmore attachment is soldered, 
 the flanges presenting occlusally. 
 
BRIDGBWORK 
 
 A crown is constructed the base of which rests upon the 
 root cap and telescopes over it sliglitly. 
 
 In the central portion of the crown base is a recess which 
 receives the flanges of the (rihuore attachment, while extend- 
 
 'AL VIEW OF CAST AND BRinCE 
 
 ing across the recess and fixed withiu the body of the crown 
 is a IJr-gauge bar. 
 
 This bar is so adjusted that, when the crown is seated on 
 the root cap, the flanges of the Gilmore attachment grasp it 
 and thus aid in retention of the appliance. 
 
 The appliance here illustrated is the work of J. B. Rideout 
 of Minneapolis, who kindly loaned it to the writer. 
 
 Still other combinations of the various attachments men- 
 tioned are possible, depending upon the ingenuity of the 
 prosthetist and his skill in carrying out the ideas conceived. 
 
 REPAIRING CROWNS AND BRIDGES 
 
 The most common accidents which occur to crowns and 
 bridges, when permanently set and subjected to use, are frac- 
 ture of the porcelain teeth or facings and fracture of some 
 portion of the metal structures. 
 
 When a crown or bridge can be removed from the sup- 
 porting roots or teeth, without injury to itself or to them, re- 
 pair can be most easily accomplished out of the mouth. 
 
 Since, as is most frequently the case, removal of a crown 
 or bridge is accompanied by more or less mutilation of the 
 metal parts, or subjecting the foundation supports to undue 
 strain, the general method of procedure is to repair such cases, 
 if possible, without removal. 
 
BRIDGEWORK 857 
 
 Tlie replacement of dislodged facings can frequently be 
 accomplished quite as well in the mouth as by removal of the 
 substitute, with some of the available repair outfits. Some of 
 the common methods of repair will now be outlined. 
 
 REPLACING PORCELAIN FACINGS— THE ASH, FLAT BACK 
 REPAIR FACING 
 
 One of the simplest methods of replacing a flat back 
 porcelain facing where the pins of the fractured facing re- 
 main with and project from the old backing is accomplished 
 by grinding and fitting to the metal parts, an Ash flat back 
 repair tooth shown under "Various Forms of Teeth." 
 
 When the pins are short and practically headless, they 
 may be threaded and a small washer attached to each to in- 
 crease their hold in the cement which fills the dovetail space 
 within the porcelain. 
 
 In case the tooth pins have broken or are weak, with suit- 
 able drill and tap, threaded holes may be made in the labial 
 or buccal face of the old backing to coincide with opening in 
 the porcelain and screw wire of iridio-platinum or platinized 
 gold inserted for anchorage purposes. The pins should be as 
 long as the depth of dovetail space in the porcelain will re- 
 ceive, or they may be cut somewhat long, and after being 
 inserted in the backing, bent inwardly toward each other to 
 form a sort of staple anchorage. 
 
 When the pins are adjusted, cement is applied to both 
 backing and facing, and the latter forced and held in place 
 until the cement has hardened, after which the surplus is 
 removed. 
 
 THE DIMELOW FACING 
 
 A facing of this type is applied in repair work as fol- 
 lows: 
 
 The porcelain, if any remains of the old facing, and the 
 pins, are removed from the backing. 
 
 A facing is selected and ground to meet requirements. A 
 very small quantity of wax is m.elted on the old backing in that 
 area which corresponds to the position of the pinholes in the 
 facing. 
 
 While the wax is soft, the facing is moistened and pressed 
 firmly against it. ' On removal, the position for the pinholes 
 will be indicated by the raised points of wax which entered 
 the holes. These points are carefully marked on the backing 
 with a sharp-pointed instrument. A bi-beveled drill is selected, 
 corresponding in size with the openings in the porcelain, and 
 
858 BRIDGEWORK 
 
 witli this llic holes aic (li'ilhMl in a liiii^uo-gingival diroclion to 
 porrcspoud witii tlie an.niilar iiu'liiiatioii of tho holes in th(! 
 facing. 
 
 Two small pins made of threaded clasp metal wire, which 
 will fit the holes closely, are cut of suitahle length, extending 
 to the full depth in the holes of both backing and facing. 
 
 Cement is applied in the holes of both backing and facing 
 and over the contact surfaces, the pins set in ])osili((n in the 
 backing, the facing adjusted and forced to ]>la('e. 
 
 THE STEELE REPAIR OUTFIT 
 
 This set of a])pliances, consisting of drills, ta])s, headed 
 screws, and a screwdri\'er, is intended to be used in conjunc- 
 
 tion with the Steele facing in repair work. The method of 
 application is siiuple. 
 
 II.D IMXS REMOVED 
 
 The old pins and any of the old facing present are re- 
 moved and a Steele facing of suitable form and color selected 
 
BRIDGEWORK 859 
 
 and grouud to meet requirements. It will usually be found 
 more convenient, and a better rejiair can be made by select- 
 ing a facing slightly wider and longer than the space it is to 
 fill, and adapting it by grinding rather than to select one that 
 will drop in position without titting. A little wax is applied 
 in the central area of tlie ))a('king extending from the crown 
 I)ase to near tlie incisal ciliic. 
 
 Tliis should be melted against the l)acking, and while soft 
 the selected facing, having been ground, is pressed tirmly 
 against it being careful to see that it is in correct alignment. 
 
 JlKI.TINt; THE WAX IIX THE BACKINO 
 
 IN'ST THE 
 
 On remova-1 of the facing a ridge will be seen on the wax 
 where it entered the slotted groove of the porcelain. 
 
 With a sharp-pointed instrument two points are marked 
 on the backing, one near the ciown l)ase, the other the incisal 
 
S60 
 
 BRIDGEWORK 
 
 termination of tlie wax ridge. These points indicate the posi- 
 tion for the pins. The; ineisal point should be marked slightly 
 witliin the ridge. 
 
 FAfINd KEIKIVKD. SlIOUINC TIIK RIDGE 
 
 OP WAX WHERE IT ENTERED THE 
 
 GROOVE OP THE PACING 
 
 Holes are now drilled for tlic rc('(']>ti(»ii of tlic licaded 
 screws at the points indicated. 
 
 Since the holes must be very small and the drills corre- 
 spondingly so, special care must be exercised to avoid break- 
 ing the drill in the backing, an accident which is very liable 
 to occur. 
 
 WAX RUKiK I'EUFUKATlvD TO INDICATE 
 POSITION FOR THE SCREWS 
 
 DRILLING THE HOLES IN BACKING 
 
 The holes are now threaded with the tap for the reception 
 of the screws, and the latter set in position. 
 
 The facing is applied, passing it over the screws from an 
 incisal direction. If, in its passage to place, interference 
 occurs, locate the cause, which is proliably due to setting tlie 
 
BRIDGEWORK 
 
 screws too deeply in the backing, thus bringing their heads 
 too close to the interior wall of the slot of the facing. 
 
 Till, lliil.l.: 
 
 If too long, they may prevent the facing resting against 
 the backing. The screw heads should be so set as to permit 
 the backing sliding readily to place yet close enough to avoid 
 any labial move of the facing from the backing when once 
 seated. 
 
 THE FAflXl! SET IN I'OSITIOX ON ISACKINCi 
 
 Cement is now applied around the pins, over the backing, in 
 the groove of the facing, and the latter is forced in position. 
 
 THE BRYANT REPAIR OUTFIT 
 
 This set of appliances consists of threaded taps, a taper 
 reamer, a split end, screw driver, and taper nuts, which, in the 
 replacement of a flat back, porcelain facing, are used as 
 
 follows: 
 
nRIDGIOWORK 
 
 Tlic old jiins aro removed, a layer of wax is applied to 
 tlic hacking, into wliich the i)iiis of tiie selected facing are 
 ])ressed, to indicate the position for drilling the holes. 
 
 'I'iie holes are drilled entirely through the l)acking with 
 a bi-heveled drill a little Ini-ger than the diainetei- of the 
 ])latinum pins. 
 
 The facing, which should lie slightly larger than actually 
 reijuired. to ]iennit of icduction foi' exact fitting, is gi'ound 
 to place. 
 
 Tile lingual ends of the holes in the l)acking are enlarged 
 with the taper reamer by means of tlie riglit angle liand piece. 
 They should be large enough to receive the taper nuts so that 
 the small ends of the latter may approach close to, but not 
 project through, the labial surface of tlie backing. Should the 
 small ends pass through tlie labial of tlie backing, tliey must 
 be reduced by grinding, or the facing cannot lie drawn tightly 
 against the backing. 
 
 THK liK\l\l UH \1I{ (II HIT. SH(l\VIX(i TAPS, KKAMEIt. SCREWDRIVEK. XUTS. ETC. 
 
 Threads are cut on the pins, using first No. 1 tap, which 
 cuts a partial thread, and followed by No. 2 tap, wliicli cuts 
 the thread to full depth. 
 
 The pins should be oiled and the taps applied carefully 
 to prevent the ]iins being twisted off during the cutting of tlie 
 threads. 
 
 Cement is now applied to the backing, and the facing 
 adjusted in position. 
 
 A nut is dro])ped into the small sleeve of the screw driver, 
 small end outward, applied to one of tlie pins and tightened, 
 after which tlie other is applied in like manner. 
 
 This step should be carried out quickly, liefore the cement 
 has perceptibly hardened, otherwise the nuts cannot be forced 
 into close contact with the backing and the facing will soon 
 become loosened. 
 
BRIDGEWORK 863 
 
 The facing should be held by positive mechanical anchor- 
 age, developed by jamming the nut tightly against the walls 
 of the opening in the backing, on the lingual side, while the 
 porcelain should rest firmly against the backing labially. 
 
 The cement is used only as a sealing agent, to close the 
 space between porcelain and metal. 
 
 When hardened, the surplus cement is cleared away, the 
 projecting ends of the nuts on the lingual surface reduced 
 with stones, and tlic rough surfaces polislied with fine discs. 
 
 LONG PIN FACINGS USED IN REPAIRS 
 METHOD OF REPLACEMENT SUGGESTED BY DR. R. W. STARR 
 
 When the backing of a crown, or a bridge dummy is ex- 
 ceptionally thick, so that the pins of the facing will not readily 
 engage with the Bryant nuts, as ordinarily applied, the mode 
 of attachment may be varied as follows : 
 
 Place a piece of i)latinum foil lietween and around the 
 pins, and bend the latter down in close contact with it, so 
 that they lie parallel and touch each other. 
 
 Invest the porcelain and unite the pins with solder. Flat- 
 ten them somewhat by filing, and square u]) the sides of the 
 rectangular pi'ojection which they now form. 
 
 Eemove the old pins from the backing, apply wax and 
 press the jjartially prepared facing into it to secure an im- 
 pression of the ridge formed by the united pins. 
 
 A groove is cut in the backing, of the same dimensions 
 as outlined in the wax, of sufficient depth to receive the 
 folded pins and let the facing rest firmly against the backing. 
 
 The facing is now ground to correct position, which previ- 
 ously could not be done, because the facing was prevented 
 from coming in contact with the l)ai'king on account of the 
 pins. 
 
 Drill a hole through the backing, locating it in the center 
 of the groove which receives the pins. 
 
 Apply a thin film of oil to the backing, in the bottom of 
 the groove, and to the sides of the opening through the backing. 
 
 Melt a little sticky wax to the pins, opposite the opening 
 in the backing, and set the facing in position. 
 
 A piece of iridio-platinum or clasp metal wire, about 16 g., 
 preA'iously threaded, and slightly longer than required, to 
 pass throng]] the backing, is heated, and passed through the 
 opening, from the lingual, until it enters the wax and rests 
 against the pins. 
 
BRIDGRWORK 
 
 The heated screw wire melts the wax, which, wlien cold, 
 unites it with metal ridge of the pins, and the two may be re- 
 moved in a labial direction in correct relation to eacli other, 
 after which they may be invested and soldered 
 
 LEFT. PINS BENT AND SCREW ATTACHED, 
 RIGHT, ItArKING SLATTED AND DRILLED 
 
 FOR heception of facing 
 
 LEFT, PACING IN POSITION. SURPLUS 
 SCREW AND NUT REDUCED AND POLISHED. 
 RIGHT. LABIAL APPEARANCE OF FACING 
 
 The lingual end of the hole in the backing is enlarged with 
 a taper reamer, to receive a taper nut, formed to fit the screw. 
 
 Attachment of the facing to backing and reduction of sur- 
 plus screw and nut are accomplished in a similar manner as 
 described under the Bryant System. 
 
 RIVETING THE FACING TO BACKING 
 
 When the pins of the new facing are long enough to ex- 
 tend through the old backing and permit of spreading, the 
 facing may be attached by riveting. 
 
 Mark position on backing, and drill holes which corre- 
 spond closely with the diameter of the pins, countersinking 
 their lingual ends slightly. 
 
 Grind facing to meet requirements, and if the jains are 
 excessively long, cut them so that they will extend but slightly 
 beyond the lingual surface of the backing. 
 
 The ends of the pins should be squared and their centers 
 depressed with a delicate, bi-beveled drill, to jirevent the point 
 of the riveting punch from slipping when applied. A sleeve 
 
 drill, designed for this purpose, can be used to good advan- 
 tage, and is, in fact, indispensable. 
 
 The Shriver riveting punch, one beak of which is sup- 
 plied with a cup for holding a rubber pad, or modeling com- 
 pound, for producing pressure on the porcelain, the other 
 
BRIDGBWORK 
 
 fitted with a round end and a pointed end punch for com- 
 pressing and spreading the pins is used as follows : 
 
 Cement is spread over the backing and the facing pressed 
 to place. The padded beak of the punch is applied to the 
 
 Tr]}~7» 
 
 RIVETI^& PL\(_H SHOWING cvr 
 
 BEVK A^D TWO RH ETI^G 
 
 POINTS (SHKIVEB) 
 
 facing, the round punch applied to the pin, being careful to 
 center it so that the pin may not be bent to one side, and pres- 
 sure made to compress the pin upon itself. This step shortens 
 the pin but increases its diameter and causes it to fill the 
 
 BACKINGS OF CUSPID CROWN 
 
 AND CENTRAL DUMMY DRILLED 
 
 FOR RECEPTION OF LONG PIN 
 
 FACINGS 
 
 hole in the backing, just as a rivet is compressed endwise, to 
 fill the hole before the head is formed. 
 
 The pointed punch is ajiplied to spread the end and form 
 the head of the rivet, after which the round end is again ap- 
 
866 BRIDGEWORK 
 
 plied to smooth any rouglinoss raised l)y t\w point, while 
 any surplus that remains is removed with discs. 
 
 When modeliii!^" compound instead of rubber is used as a 
 pad, it should be softened, placed in the cup, the punch ad- 
 justed in ]iosition and slight pressure applied to secure an 
 impression of the labial surface of the tooth, when it is re- 
 moved and chilled, after which the steps are carried out as 
 described. 
 
 An ordinary plate punch, modified as suggested by Dr. 
 George Evans, may be used instead of the Shriver Punch if 
 desired. To the beak in which the hole is located, a lead block 
 
 OKDINAKY PLATE I'UNtH CON\ERTED 
 INTO A RIVETING PUNCH BY APPLICA- 
 TION OF LEAD BLOCK TO BIGHT AND 
 HEAVY PIN TO LEFT BEAK 
 
 is applied for producing pressure against the facing, while a 
 larger pin replaces the ordinary pin in the other beak. The 
 method of application is similar to that described. 
 
 With either method, in addition to gripping the handles 
 while compressing the pin, pressure should be made lingually 
 to keep the facing firmly seated against the backing. 
 
 A slight side to side movement of the handles will aid in 
 compressing and heading the pin as well. 
 
 REMOVING A BANDED, DOWEL CROWN 
 
 When, for any reason, it becomes necessary to remove a 
 banded, dowel crowm which is to be reset, care should be taken 
 to avoid mutilating the root cap. 
 
 The most convenient method is to release the crown from 
 the dowel which constitutes the main anchorage. This may be 
 done by drilling through the lingual surface of the crown, in 
 an apical direction, to the root face, alongside the dowel. 
 
BRIDGEWORK 
 
 "With a fissure bur, tlie first opening is enlarged, cutting 
 around the dowel in such manner that the latter will project 
 bevond tlie root face, thus facilitating its removal later on. 
 
 LINGUAL VIEW OF SAME TOOTH, PROXI- PROXIMAL VIEW OF CERVICAL VIEW OF 
 
 fENTRAL. SHOWING MAL VIEW. DOTTED INCISOR. RELEASE OF CROW N PROXIMAL 
 
 OPENING THROUGH LINE SHOWS DIREC- DOWEL FROM LABIAL VIEW OF BOOT 
 
 WHICH DOWEL H.\S TION OF OPENING SIDE SHOWING PROJECT- 
 
 BEEN RELEASED ING DOWJX 
 
 When the facing is fractured, release of the crown can be 
 most readily accomplished by entering the crown base from 
 the labial surface and cutting around the dowel as described. 
 
 A single crown, when thus freed from its dowel, can be 
 removed without difficulty, but when attached to a bridge the 
 other abutment crowns must also be released before removal 
 can be effected. 
 
 REPLACING A FACING ON A CROWN REMOVED AS 
 DESCRIBED 
 
 The best and quickest methotl of replacing a facing on a 
 crown is by removal of the bulk of old backing, grinding and 
 backing a new facing, adjusting and waxing it in position, 
 investing and soldering in the usual manner. 
 
 Usually, after the backing is removed, the root cap should 
 be returned to position, a new dowel fitted, an impression to 
 secure correct relation of the two taken, or the two waxed to- 
 gether, removed, invested and soldered, after which the fac- 
 ing is adjusted. 
 
 When the facing of tlie removed crown is present, the lat- 
 ter having been removed by releasing the dowel from the lin- 
 gual side, a dowel is fitted, the incisal end being allowed to 
 project beyond the opening, after which it is waxed in correct 
 relation, the crown removed, invested, and the two united 
 with solder 
 
 Before investing the crown, the o]iening around the dowel, 
 in the crown base, should be covered with a small disc of 
 
868 BRinOEWORK 
 
 platiinim foil, to complete tlie floor of the root cap, and form 
 a metallic surface a.^ainst which the solder may flow. 
 
 REMOVING DOWELS FROM ROOT CANALS 
 
 Various devices have been suggested for removing dowels 
 from root canals. When applicable, appliances of this type 
 relieve the tooth from both excessive cutting and strain. 
 
 LITTLE GIANT POST PULLER 
 
 The Little Giant Post Puller, designed by Dr. F. H. Skin- 
 ner, consists of a clamp, having thin yet strong beaks, for 
 
 SHOULDER FIN OF POST PULLER 
 
 grasping the dowel, together with a shoulder post for resting 
 npon tlie root face. 
 
 By turning the screw, the shoulder post is brought in 
 contact with the root face, while the clami^ and dowel are 
 moved incisallv. 
 
 LITTLE GIANT POST PULLER 
 
 To a]>]jly the device, the entrance to the root canal must 
 be enlarged sufficiently to permit the clamp licaks to enter and 
 grasp the sides of the dowel firmly. 
 
 THE S. S. WHITE CROWN REPAIR OUTFIT 
 
 The devices in this outfit, intended for removal of dowels 
 from root canals, consist of trephines for gaining space around 
 the dowel within the root, and at the same time reducing the 
 dowel to a definite size to correspond with the opening in a 
 threading die. 
 
 After space is gained, threads are cut on the projecting, 
 formed end of the dowel, to which the inner barrel of a de- 
 vice, much like a jack screw, is applied. By turning the milled 
 
BRIBGEWORK 
 
 nut of the outer barrel until it rests agaiust the face end of 
 the root, the inner screw, which is attached to the dowel, is 
 moved incisally, bringing the dowel with it. 
 
 (.■RO\\'N POST PUIjLER. (S. S. WHITE) 
 
 REMOVAL OF A DOWEL FROM THE DEEPER PORTIONS OF 
 A CANAL 
 
 When a dowel is fractured within the canal, some distance 
 from the face of the root, the appliances described are un- 
 suited for its removal, and some other means must be 
 employed. 
 
 A method which will result in but little sacrifice of tooth 
 structure consists in squaring the end of the dowel, applying 
 a delicate bi-beveled drill to its center and drilling inward a 
 short distance, removing the drill, and with a square end bur 
 reducing the periphery of the dowel by end cutting. 
 
 These steps are repeated until, by careful cutting, the 
 entire dowel is removed. Careful manipulation is required 
 to prevent the drill cutting from center to periphery of the 
 dowel. 
 
 When the dowel is very small, a fine fissure bur can be 
 passed around it, dividing the cutting as much as possible be- 
 tween tooth structure and metal to avoid weakening the root 
 and excessively enlarging the canal, or in some cases the dowel 
 itself may be gradually cut away with small fissure burs. 
 
 This is a most unsatisfactory method of removing a dowel, 
 3'et at times it is the only means of clearing the canal. 
 
 REMOVING A SHELL CROWN BY SLITTING 
 
 The quicket method of removing a shell crown is by slit- 
 ting one of its axial walls, introducing an instrument in the 
 
870 BRIDGEWORK 
 
 opening and prying the crown walls away from tlie tooth, 
 thus break the adhesion of the cement. 
 
 A fine fissure Imr may be used for cutting the slot from 
 gingival to occlusal areas. This method results in loss of sub- 
 stance of the crown wall, and where the crown is to be re- 
 placed must be filled in with a strip of gold of corresponding 
 width of the slot, or the crown when joined will be too small. 
 
 By means of a croivn slitter, the walls may be divided 
 without loss of gold, and when properly contoured and sol- 
 dered the crown will fit as before. 
 
 This appliance is a plier-like device, one beak carrying 
 a sharp, cutting blade, the other being somewhat broadened 
 
 CBOWN SLITTER FOR REMOVING SHELL CROWNS 
 
 and curved, for resting upon the occlusal surface of the 
 crown. 
 
 By introducing the point of the blade against the cervical 
 margin of the crown, the other beak on the occlusal surface, 
 and closing the handles, the wall is readily slit. 
 
 REMOVING A SHELL CROWN BY LEVERAGE FORCE 
 
 A shell crown can, in most cases, be removed without much 
 mutilation by the following method : 
 
 Drill a hole at a convenient point, just beneath the occlu- 
 sal surface of the crown, extending it through to nearly the 
 opposite side. 
 
BRIDGEWORK 871 
 
 lu this hole, which should be about the size of an engine 
 bur wire, a long-handled instrument is inserted to serve as a 
 lever. 
 
 Brace the tooth with the linger, on the opposite side from 
 the opening, and exert pressure on the handle in an occlusal 
 direction. This forces the inner point against the end of the 
 tooth, or body of enclosed cement, breaks adhesion and re- 
 leases the crown. 
 
 REPAIRING CROWNS THAT HAVE BEEN SLIT IN THE MAN- 
 NER DESCRIBED 
 
 When, in removal, a crown has been mutilated by slitting 
 or by cutting with a bur, the tirst step in its repair is to remove 
 all cement by boiling in acid. Such portions as fail to come 
 away readily by this means should be removed by scraping and 
 the crown again treated with acid as before. 
 
 This is necessary, because, if not removed, the oxide of 
 zinc in the cement will, under heat of the blowpipe, be re- 
 solved into metallic zinc, which will unite with the gold, 
 forming a low alloy, and cause the latter to fuse, or hum, as it 
 is usually expressed. 
 
 After cleansing as described, the band ends, or axial 
 walls, are contoured to correct form, wax flowed in any exist- 
 ing space between the ends, trimming it to exact internal con- 
 tour, the interior of the crown filled with investment, the wax 
 removed, flux applied and solder flowed into and over the joint. 
 
 The same method may be employed in closing the drill 
 hole near the occlusal surface, or when waxed, invested and 
 the wax removed, a piece of platinum foil may be pressed in 
 the opening in the crown to the investment, and solder applied 
 to fill the depression and restore axial contour. 
 
 REPAIRING A FRACTURED BRIDGE 
 
 When a bridge is fractured at some point between its 
 abutments, it may be repaired in two ways : 
 
 First, remove the parts, saw otif the intervening dum- 
 mies, replace the abutment crowns in position, secure a bite 
 and impression, construct and moi;nt casts on the occlud- 
 ing frame, readjust'and wax the dummies in position, remove 
 and invest the assembled bridge, and solder. 
 
 Second, when fractured in only one place, remove the 
 broken parts, cleanse thoroughly, iiress some softened model- 
 ing compound on the border between the abutment crowns, 
 
BRIDGEWORK 
 
 return the two parts to position, pressing the dummies into 
 the modeling com])ouud interposed between their cervical ends 
 and the border; instruct the patient to close, thus biting the 
 bridge into correct occlusal relation. 
 
 SANITAHT BRIDGE. TO SECURE RELATION OP 
 PABTS. WHEN STRnCTURE IS FRACTURED AT 
 A. INTERPOSE MODELING COMPOUND BE- 
 TWEEN A AND B 
 
 Pressure should be made on the buccal surface of the 
 bridge to prevent outward displacement while the patient is 
 forcing it to place. 
 
 When compound is chilled, secure an impression of the 
 bridge in its reassembled relation, remove, invest, and solder. 
 
CHAPTER XXX 
 
 PORCELAIN CROWN AND BRIDGE WORK 
 PORCELAIN CROWN WORK 
 
 In addition to the many varieties of crowns it is possible 
 to construct by means of facings, partial and full crowns of 
 porcelain as shown, still another type of crown can be con- 
 structed and applied in certain cases to advantage. This is 
 ordinarily known as the baked porcelain croivn, because it is 
 subjected to the process of fusion or baking by the prosthe- 
 tist in his laboratory. 
 
 Crowns of this type may be subdivided into three general 
 classes, viz. : 
 
 First — A crown supported by and built upon a perma- 
 nent substructure of metal, usually composed of a cap and 
 dowel of platinum, to which a facing is attached, the lingual 
 portion of porcelain being applied and fused to the cap and 
 affixed facing by the prosthetist. 
 
 Second — A crown supported by, and built upon, a per- 
 manent platinum cap or base, the entire crown portion being 
 built up and contoured in porcelain body and afterward 
 fused. 
 
 Third — A crown built upon and around a cap of platinum 
 foil, which when the crown is fused is removed. 
 
 The two former crowns are usually designated as banded, 
 baked porcelain crowns, the latter as a porcelain jacket 
 crown. 
 
 The introduction within recent years of many new and 
 excellent forms of replaceable facings and partial crowns of 
 porcelain, together with improved methods of technic, has 
 to a great extent rendered unnecessary the baking of crowns 
 and bridges, except in special cases. 
 
 As a preliminary consideration the fact should be kept 
 in mind that porcelain is strong only in bulk; therefore, in 
 constricted spaces it is liable to fracture under stress. 
 
 Again, the porcelain used in inlay, crown, bridge and 
 continuous gum and denture construction is less dense and 
 more friable than that of which porcelain teeth is composed; 
 therefore the former material will not stand the stress, bulk 
 
 873 
 
S74 PORCELAIN CROWN AND BRIDGE WORK 
 
 for liulk, (hat tooth body will resist, without danger of 
 fraeture. 
 
 Occasionally, however, cases present wliere a specially 
 baked substitute will fnllill esthetic requirements more satis- 
 factorily than will one constructed by any other method. 
 
 INDICATIONS FOR USE 
 
 Baked porcelain crowns can be successfully applied in 
 any location where sufficient space is present for a reasonable 
 bulk of porcelain and where the metal structure can be well 
 adapted to the supporting roots. 
 
 Crowns of this type are, however, specially indicated when 
 departure of the ordinary anatomic form the tooth is required, 
 provided such departure will not tend to weaken the crown 
 when constructed. 
 
 The porcelain jacket crown is admirably adapted to peg- 
 shaped lateral incisors and frequently to other classes of teeth 
 as well. The placing of a crown of this type on a vital tooth 
 in no way endangers the pulp, providing, of course, proper 
 tooth i:)reparation can be successfully accomplished without 
 serious inconvenience to the patient. 
 
 THE BANDED, BAKED PORCELAIN CROWN 
 
 This crown consists of a rigid root cap of platinum or 
 iridio-platinum, a dowel of iridio-platinum, a tooth facing ap- 
 plied to the dowel by soldering, while its lingual contour is 
 developed by application and fusing of porcelain to facing 
 and root cap. 
 
 CONSTRUCTING THE ROOT CAP 
 
 Methods vary as to root-cap construction for crowns of 
 this type. The following technic is adopted bj^ many because 
 the metal band on the labial or buccal surface may be entirely 
 obscured by the facing and applied porcelain. 
 
 Prepare the root as for an ordinary cap crown described 
 on page 600. 
 
 Construct a band of 29 or 30 gauge iridio-platinum. 
 Platinum may be used, but it is liable to stretch under stress. 
 
 Cut the strip about 1-20 of an inch longer than the actual 
 root measurement, to allow for a lap joint. 
 
 Bend one end at right angle to the band, turning over the 
 amount of surplus allowed. The other end is then brought 
 under the bent portion and butted tightly against both the 
 
PORCELAIN CROWN AND BRIDGE WORK 
 
 tuniod portion and band end proper. Solder with high-fus- 
 ing platinum solder. 
 
 Place on a round mandrel and tap lightly to tiatten and 
 form a continuous, curved inner surface to band, being care- 
 ful not to stretch or elongate the metal. 
 
 Reduce the excessive thickness of the joint, from the 
 outside, by tiling or with engine stones. 
 
 Fit the band to root, scribing and trimming the cervical 
 end until perfectly and uniformly adapted to the gingiva, 
 when it is driven to correct position under the gum. 
 
 Trim the iucisal end of the band to coincide with gingival 
 curvature, allowing it, however, to project slightly beyonid 
 the gum margin, lingually. 
 
 DETAllS OP PORCELAIN CROWN. A SHOWS LABIAL BEVEL OP CAP; 
 BCD. LAP JOINT: E, RIDCE LAP OF PACING CON- 
 CAVED: P O. PARTS ASSEMBLED 
 
 Drive the band to position on the root, and face the latter 
 to the iucisal end of the band. 
 
 Eemove the band and further reduce the outer or labial 
 third of the root face to a point about where the cervical mar- 
 gin of the band will rest. 
 
 Thin the band by grinding, along the labial area corre- 
 sponding to the reduced root, being careful, however, to leave 
 its exti'eme cervical margin full thickness. 
 
 Return it to the root and with a square end plugger in 
 the automatic mallet, reflect the thinned labial portion over 
 against the root face. 
 
 Adapt a disc of 30-gauge iridio-platinum plate to the iu- 
 cisal end of the band, being careful to develop a perfect joint 
 between the two. 
 
 Perforate the cap for reception of the dowel, locating 
 the opening far enough to the lingual to avoid interference of 
 the facing from the projecting dowel. When the opening 
 does not coincide -with the root canal, ream the latter to cor- 
 respond. 
 
 No. 16 or 15 gauge iridio-platinum, round wire, is usually 
 employed for dowels in central and cuspid teeth, while 17- 
 gauge is used in upper laterals, lower incisors, and when two 
 dowels are applied, in bicuspid teeth. 
 
876 PORCELAIN CROWN AND BRIDGE WORK 
 
 The opening in the root cap should be slightly smaller 
 than the diameter of dowel, the entrance to canal counter- 
 sunk slightly, the dowel forced through cap as previously de- 
 scribed, relation between the two secured with wax, after 
 which they are removed from root, invested and soldered with 
 medium or high-fusing platinum solder. 
 
 Pickle and cleanse the cajo and by grinding reduce the 
 labial portion of the cap along the angle, between band and 
 disc, so as to produce a decided bevel in this area. This is 
 necessary in order that the facing, when reduced to a thin 
 edge by grinding, may cover the labial surface of the cap. 
 
 Eeturn cap to root, take impression and bite, remove, de- 
 velop casts and mount on occluding frame. 
 
 Select a facing slightly lighter in color than the natural 
 teeth, yet containing the proper basic colors, because, when 
 thickened by the addition of lingual porcelain, its depth of 
 color will be increased. 
 
 Grind the ridge lap of the facing somewhat concave, so 
 that it may clear the cap at all points, except along the ex- 
 treme labial margin, which should be brought to a thin, deli- 
 cate edge, to rest closely in contact with the cervical margin 
 of the band. 
 
 Flatten the pins so that the flattened surfaces lie parallel 
 with the dowel in order that they may present a broad sur- 
 face bearing when adapted to the latter. 
 
 A 
 
 Pm BENDING AND CnTTINQ PLIERS 
 
 The pin bending and cutting pliers here shown is a most 
 useful instrument for this and many other purposes in crown 
 work. 
 
PORCELAIN CROWN AND BRIDGE WORK 877 
 
 Set the facing in correct alignment and wax in position. 
 Test its length under lateral movements of the frame and 
 if interference occurs grind away the points of obstruction. 
 
 When ground to meet requirements, the facing is again 
 returned to the cap, the flattened pins adapted closely to the 
 dowel, wax applied, the assembled parts removed, invested, 
 and soldered with medium or low-fusing platinum solder. 
 
 Care should be taken, in removing the assembled cap and 
 facing, to avoid marring the cast, since, during constructive 
 stages, the crown must lie returned to it, from time to time, 
 for testing contour development. 
 
 CAP. DOWEL AND PACING 
 ASSEMBLED. KEADY FOR AP- 
 PLICATION OF THE PORCE- 
 LAIN 
 
 Since the ]5oreelain cannot be perfectly protected from the 
 blow-pipe flame, the investment should be raised to a full red 
 heat before soldering the pins to dowel, otherwise fracture of 
 the porcelain is very liable to occur. 
 
 When soldered, the crown should be boiled in acid and 
 thoroughly washed, after which the dowel is grasped in a pin 
 vice to serve as a handle when it is ready for the application 
 of the body. 
 
 APPLICATION OF THE PORCELAIN BODY 
 
 A small quantity of well mixed croivn and bridge porce- 
 lain body, of medium thick consistency, is taken up on the 
 point of the spatula and placed on the end of cap close to the 
 ridge lap of facing. 
 
 Draw a serrated instrument across the pin vice, when the 
 vibration thus produced will cause the granules to settle 
 closely together, and as the water is expelled from the mass 
 it is absorbed by a clean linen napkin or with bibulous paper. 
 
 Special care should be taken to fill the space between 
 
878 PORCELAIN CROWN AND BRIDGE WORK 
 
 ridge lap of facing and cap (lniiii<;- the first apijlioation of body, 
 for if not packed densely at this time it may be im])ossible to 
 introduce it after the first baking. 
 
 The crown may be develojied to practically the required 
 contour during the first application of the body. When fused, 
 additions ai^e made where needed to correct loss of contour 
 occasioned Ijy shrinkage of the mass in first baking. 
 
 An effort should l)e made to complete the crown in two 
 fusings. When a third or fourth baking is required the quality 
 of the porcelain rapidly deteriorates. 
 
 Dr. F. T. Van Woert has found that by compressing 
 plastic, comparatively dry porcelain to a certain degree by 
 means of a screw press, shrinkage of the mass during the first 
 bake is reduced to one-tenth instead of one-fifth, as usually 
 occurs. 
 
 By means of a metal matrix slightly larger than the crown 
 is to be, in which the root cap is placed, the porcelain is ap- 
 plied to it, nnder pressure, and condensed. 
 
 The actual dimensions of the crown having l)een previ- 
 ously determined, a doiible end caliper, the beaks on one end 
 of which register one-tenth more than the others, is applied 
 to the crown from time to time, while carving the compact 
 mass to form. 
 
 The crown, when carved, ready for the first bake, is one- 
 tenth larger than actually requii-ed, but in the first fusing is 
 reduced to actual dimensions. 
 
 It is possible by means of these ingenious devices to com- 
 plete a crown in one baking, while another advantage of great 
 importance is that there is less distortion and greater den- 
 sity of the mass when fused. 
 
 The details of fusing porcelain will be given under Porce- 
 lain Bridgework. 
 
 Finishing the crown consists in polishing such portions of 
 the cervical margins of the platinum cap as may be exposed 
 after fusion of the porcelain is completed. 
 
 In setting crowns of this type, special care should be 
 taken to avoid the use of the mallet, as a sudden blow is liable 
 to fracture the porcelain. 
 
 MODIFIED FORMS OF PORCELAIN CROWNS 
 
 Various modifications of the baked porcelain crown are 
 constructed, some of which are as follows: 
 
 A lingual half band crown, the dowel and facing being 
 attached to a half band diaphragm, instead of the regular form 
 of root cap. 
 
PORCELAIN CROWN AND BRIDGE WORK 879 
 
 A bandlcss crown built upon a disc of platinum; usually 
 the root is faced so as to jiresent a decided labial and a lin- 
 gual plane. The dowel and disc are united, while the facing- 
 is ground to rest upon the cervical margin of the disc and is 
 soldered to the dowel. 
 
 Bicuspid and molar crowns are frequently constructed 
 bj' capping the roots as described and fitting dowels in the 
 
 ESSEN'TIAI. TARTS OF AN 
 UPPER FIRST BKUSriD 
 CROWN ASS1':J1I!I,ED. READY 
 FOR AI'PLUATION OF BODY 
 
 root canals; to the outer or projecting ends of which the fac- 
 ings are attached. In such cases it is advisable to solder some 
 auxiliary projections on the root caps in the form of loops or 
 pins to afford additional anchorage for the porcelain. 
 
 Frequently entire crowns, without facings, are thus built 
 up on root caps so constructed. 
 
 PREPARATION OF A MOLAR 
 TOOTH FOR A FULL BAKED 
 PORCELAIN' CROWN THE FOIL 
 CAP IS CONSTUITTKO AND THE 
 PORCELAIN A 1' 1' 1. I E D 
 
 AND 
 
 SIMILAR MANNER 
 
 TO THE STEPS JUST DESCRIBED 
 
 BAKED IN 
 
 PROXIMAL FLANGES OF 
 IRIDIO PLATINUM ADDED 
 FOR STREN(!THENINC, CROWN 
 AND AIDING IN HOLDING 
 CONTOUR OF PORCELAIN 
 DURING BAKING. SUG- 
 GESTED BY DR. C. A. WHITE 
 
880 PORCELAIN CROWN AND BRIDGE WORK 
 
 J^^laiiges of iridio-platinum are applied to the root cap, 
 extending- incisally or occlnsally, to give additional strength 
 to the porcelain and assist in developing contour. 
 
 THE PORCELAIN JACKET CROWN 
 
 The porcelain jacket crown, as before stated, is specially 
 indicated in the restoration of peg-shaped lateral incisors. 
 
 The reason for this lies in the fact that an anomaly of 
 this type usually has a small, sometimes distorted, root, in 
 which the placing of a suitable dowel is questionable. Often- 
 times it is impossible to successfully remove the pulp and fill 
 the root canal in a satisfactory manner. The crown, also 
 being undersized, requires but little preparation for the re- 
 ception of a shell crown of porcelain. 
 
 CASE SHOWING PEG-SHAPE 
 LATEBAI, INCISOR BEFORE 
 PKBPABATION 
 
 This form of crown can be successfully applied to various 
 other classes of teeth, both vital and non-vital, and when prop- 
 erly constructed and permanently set, fulfils esthetic require- 
 ments in the highest degree. 
 
 LABIAI, VIEW OF PREPAKED 
 
 TOOTH. SHOWING GINGIVAL 
 
 SHOULDER 
 
 TECHNIC OF CONSTRUCTION 
 
 Prepare the tooth so that it presents a perceptible cone 
 form, thinning it on labial and lingiial surfaces so as to give 
 space for a uniform layer of porcelain. 
 
PORCELAIN CROWN AND BRIDGE WORK 881 
 
 The mesial and distal surfaces need not be reduced to 
 the same extent as the labial and lingual surfaces, yet they 
 must also converge slightly from gingival to incisal areas. 
 
 The sides of the cone should terminate in a distinct cer- 
 vical shoulder, located just beneath the free gum margin. 
 
 TAKING IMPRESSION OF TOOTH 
 
 Construct a reasonably close litting copper band suffi- 
 ciently long to handle easily, and adapt to the periphery of 
 the tooth. It sliould not encroach on the peripheral shoulder 
 at any point nor upon the gum margin, but should pass be- 
 tween the two. 
 
 PROXIMAL VIEW OF TOOTH. 
 
 UIPKESSION TAIiEN AND 
 
 EEMOVED 
 
 Fill with softened modeling compound and apply to the 
 prepared tootli, at the same time closing the incisal end of the 
 band witli tlie finger to prevent escape of impression material. 
 
 A^jply sufficient force to secure an impression, not only 
 of the axial surfaces of the tooth, and flattened cervical shoul- 
 der, but of the root periphery as well. 
 
 Chill the comijound, remove the impression and trim off 
 gingival surplus. 
 
 CONSTRUCTING THE DIE 
 
 Apply a section of rubber tubing to the band periphery 
 and pack the impression with amalgam, building it up suffi- 
 
 ciently to afford a firm base for attachment to the cast, 
 plaster base. 
 
882 PORCELAIN CROWN AND BRIDGE WORK 
 
 Modelite may be used to advantage instead of amalgiini ; 
 in which case, before liardening, a small wood screw should 
 be inserted in the base for anchorage purposes. 
 
 OF THE 
 
 Secure an impression in plaster and a bite in wax of 
 the prei>ared tooth and of the two proximating teeth also and 
 set aside for later use. 
 
 Iml)ed the die base in modeling compound in a swaging 
 ring and trim so as to freely expose the gingival shoulder. 
 
 FORMING THE PLATINUM CAP 
 
 Cut a triangular piece of 1-1000 platinum foil of sufficient 
 dimensions to encircle the cervical periphery, and extend 
 somewhat beyond the incisal end of the die tooth. 
 
 Anneal the foil and cut ot¥ the excess points from the 
 cervical ends of the triangle, as indicated in cut F. 
 
 Apply the foil to the die to form a cone, the base of which 
 should extend beyond the cervical shoulder. 
 
 Slit the foil near the apex, so that the sides of the triangle 
 maj be wrapped around the die. 
 
 Before closing the two sides together, the apex of the 
 triangle should be turned over the incisal edge of the die so 
 as to lie beneath them and thus close the incisal end of the 
 cone cap. 
 
 With a pair of foil carriers the two sides are grasped and 
 brought together against the lingual surface of the die and 
 there folded together to form a lap or stove-pipe joint. 
 
PORCELAIN CROWN AND BRIDGE WORK 883 
 
 At the time of making the folded joint, care should be 
 taken to see that the cone base is embracing the root periphery. 
 
 Burnish the now closed cap to the die, carrying the bur- 
 nisher along the axial surfaces and downward in a cervical 
 direction. 
 
 h. 
 
 SECTIONS SHOWING PABTIAl. 
 AND COMPLETE FORM OF 
 
 JOINT 
 
 Trim off excessive surplus, both iucisally and eervically, 
 and with a large pellet of absorbent cotton or punk, enclose 
 the entire cap and apply pressure with the fingers from all 
 sides against the axial surfaces, and in a cervical direction 
 as well. 
 
 Care should be taken to avoid undue force at all times 
 or the foil will be torn. 
 
 PLATINXIM CAP ADAPTKl) TO 
 DIE AND TRIMMED TO COR- 
 RECT OUTLINE FORM 
 
 When the foil cap is perfectly adapted and its cervical 
 margin trimmed close, but not quite, to the peripheral cervical 
 shoulder, it should be carefully removed and laid aside until 
 the body is applied. 
 
 Since the porcelain must be applied and the crown carved 
 so that its incisal edge will come in correct alignment with the 
 proximating teeth, it should be formed on a cast in whicla these 
 proximating teeth are present. 
 
 CONSTRUCTING THE CASTS 
 
 The die is now removed from the swaging ring or base 
 in which it was imbedded, the gingival portion of the impres- 
 sion trimmed somewhat freely to admit the die, the latter 
 placed in its matrix and a cast developed in the usual manner. 
 
 The bite is applied to the cast, the latter mounted on the 
 occluding frame and the occlusion cast developed. 
 
 Trim the plaster from around the cervical end of the die 
 tooth, so as to freely expose the shoulder and permit the foil 
 cap to be set in proper position without interference. 
 
884 PORCELAIN CROWN AND BRIDGE WORK 
 
 Make a small cylinder of oiled writing paper and apply 
 around the platinum cone, holding it in position with a loosely 
 tied ligature. This is to assist in condensing the porcelain. 
 
 APPLICATION OF THE PORCELAIN 
 
 High-fusing tooth body (2560 degs.), of suitable shade to 
 match the tooth, is now mixed ready for application. 
 
 Usually two shades, sometimes three, are selected and 
 mixed, the darkest being applied to the gingival third, the 
 medium to the middle, and the lightest to the incisal third of 
 the cylinder. 
 
 The body should be mixed to medium consistency, and 
 as each portion is applied it should be vibrated to place. 
 
 When of medium consistency the sharp lines of demarka- 
 tion of the two or three colors will disappear during vibra- 
 tion and when fused will show gradual blending of the colors. 
 
 As the incisal portion is added, the paper cylinder is flat- 
 tened mesio-distally to give correct alignment to the incisal 
 portion. 
 
 Absorb the moisture that comes to the surface with bibu- 
 lous or blotting paper, and when compact and reasonably dry 
 remove the ligature and oiled paper. 
 
 THE OrTEE DOTTED LINE SHOWS 
 APPROXIMATELY HOW MUCH 
 LARGER THE CROWN SHOULD BE 
 FORMED IN THE BODY TO COM- 
 PLETE IT IN ONE BAKING 
 
 The body is now carved to the required form and such 
 additions made as are necessary. 
 
 Particular attention should be given the cervical end, to 
 see that the body comes flush with, but does not overlap, the 
 peripheral root portion of the matrix. 
 
 Smooth up all surfaces with a fine sable brush, carefully 
 remove and set on a soapstone base, carved to the general 
 form of the die, but slightly smaller. 
 
 The interior point of the support should be sufficiently 
 long to afford a rest for the erowii without its weight being 
 thrown on the cervical end. 
 
PORCELAIN CROWN AND BRIDGE WORK 885 
 
 BAKING THE CROWN 
 
 Dry out the moisture in the body very carefully, to pre- 
 vent flaking, and when ready introduce the crown in the fur- 
 nace, heat slowly, and bring to a semi-glazed condition. 
 
 Since in these cases tooth body is used, a longer time will 
 be required to vitrify the material than is required for con- 
 tinuous gum body. 
 
 THE FINISHED CROWN 
 
 When fused, the crown is returned to position on the 
 cast, its relations to the other teeth noted, correction made 
 by addition of body to such areas as need further contouring, 
 and the case is returned to the furnace, usually for the final 
 baking, this time bringing the porcelain to a glaze. 
 
 If by trial on the cast it is found correct, the crown is 
 moistened, the matrix carefully peeled out of the interior, 
 rough margins are smoothed and the crown is ready for 
 setting. 
 
 THE "LAND JACKET CROWN" 
 
 Dr. C. H. Land of Detroit was probably the first to in- 
 troduce a system of practical technic for the jacket crown. 
 
 The following outline presents the essential steps of the 
 Land system : 
 
 PREPARATION OF THE TOOTH 
 
 Bemove all of the enamel and prepare the tooth cone- 
 shaped, without cervical shoulder, but in other respects much 
 the same as required for the preceding crown. 
 
 CASE SHOWING A PEG-SHAPE LATERAL 
 INCISOR BEFORE PREPARATION 
 
886 PORCELAIN CROWN AND BRIDGE WORK 
 
 CONSTRUCTION OF THE CAP 
 
 Construct and adapt a wide band of 30-gauge platinum 
 to the tooth, scribing and fitting it carefully under the free 
 gum margin as for any banded crown. 
 
 The band should extend from the cervix to a short dis- 
 tance beyond the incisal end of the prepared tooth. 
 
 Bevel cuts are now made in both mesial and distal sur- 
 faces of the band, in line with the labial and lingual planes 
 of the tooth, extending from incisal edge to near the cervical 
 margin. 
 
 Bend both labial and lingual sections outward to give 
 space for adapting and liurnisliing the mesial and distal sec- 
 tions of platinum against these surfaces of the tooth. 
 
 PLATINUM BAND ADAPTED 
 
 TO TOOTH. THE DOTTED 
 
 LINES SHOW WHERE BEVEL 
 
 CUTS ABE TO BE MADE 
 
 LABIAL AND LINGUAL SEC- 
 TIONS BENT OUTWARD. 
 PROXIMAL SECTIONS 
 
 ADAPTED TO THE TOOTH 
 
 When close adaptation of these sections is secured, the 
 edges of the triangular margins may be reduced with discs to 
 permit the other sections of platinum being brought in close 
 contact with the tooth at along the joints. 
 
 Bend and adapt the lingual section of platinum against 
 this surface of the tooth, removing the excess so that it over- 
 
PORCELAIN CROWN AND BRIDGE WORK 887 
 
 laps the mesial and distal margins of platinum to a slight 
 extent only. 
 
 Burnish the joints closely and solder with high-fusing 
 platinum solder. 
 
 Adapt and trim the labial section to the sides, and solder 
 in like manner. 
 
 THE CAP COMPLETED 
 
 After soldering, the four angles of the cone cap may be 
 rounded off with discs, to reduce the platinum to uniform 
 thickness. 
 
 TAKING BITE AND IMPRESSION 
 
 Take an impression and bite of the proximating teeth with 
 cap in position. 
 
 Flow a film of wax inside the cap, develop casts, and 
 mount on the occluding frame. 
 
 Warm the cap, remove, clear its interior of wax and re- 
 turn to the cast. 
 
 SELECTION AND GRINDING OF FACING 
 
 Select a facing of desired shade and form and grind to 
 proper alignment. 
 
 This step usually requires the concaving of the facing on 
 its lingual side, to a very considerable extent, and the reduc- 
 tion of its ridge lap to a thin margin. 
 
 METHOD OF GBOOVING THE 
 PORCELAIN FACING 
 
 Frequently, the porcelain must be grooved from cervical 
 near the incisal areas carrying the groove between the pins. 
 In some cases the pins themselves are ground away in order 
 
888 PORCELAIN CROWN AND BRIDGE WORK 
 
 to bring the facing into correct labial alignment. When this 
 is necessary, however, it is best to form a shoulder in the 
 porcelain to rest ujioii tlie incisal end of the cap. 
 
 I'ROXIMAJ- 
 
 When ground to correct labial alignment, the pins, if 
 present, are bent in close contact with the cap, the facing and 
 cap waxed in correct relation, when they are removed from 
 the cast, invested, soldered, pickled in acid and washed. 
 
 APPLICATION AND FUSING OF PORCELAIN 
 
 High-fusing porcelain is now applied around the mar- 
 gins of the facing, next the cap and with vigorous vibration 
 worked into the entire space between the two. 
 
 Additions are now made where needed to develop required 
 contour, all surfaces smoothed and with a tine sable brush 
 all particles are removed from the labial surface of the fac- 
 ing and exposed root cap. 
 
 Frequently during the application of the body some of it 
 may become lodged in the interior of the cap, and, if so, should 
 be removed before fusing. 
 
 THE FINISHED CROWN 
 
 Set the crown on a soapstone base having a projection 
 for entering the cap of suiEcient height to support the crown 
 in an upright position. 
 
PORCELAIN CROWN AND BRIDGE WORK 889 
 
 Eemove the moisture l)y gradually applied beat, introduce 
 the crown in the furnace and raise the temperature gradually 
 to fusing point, stopping the fusion while the porcelain is in 
 a semi-glazed condition. 
 
 . Cool slowly and, when in condition to handle, additions 
 of body are made to fill any tissnre that may be present, and 
 develop contour where required. 
 
 THE CROWN IN POSITION 
 
 Since, in a crown of this type, the bulk of porcelain is 
 comparatively slight, and contraction jsroportionately so, two 
 bakings are usually sufficient to develop required contour, 
 therefore the porcelain should be fully glazed during the sec- 
 ond fusing. 
 
 PORCELAIN BRIDGEWORK 
 
 As preyiously stated, there is less necessity at the pres- 
 ent time than formerly for the construction of porcelain 
 bridges by the baking process. 
 
 This is due to the introduction of various types of re- 
 placeable, full and partial crowns, which, when properly com- 
 bined with metal, fulfill esthetic requirements, in many cases, 
 quite as well as do baked porcelain bridges. 
 
 Bridges composed of metal, and to which replaceable teeth 
 are adapted, have a decided advantage over those of the for- 
 mer type, in that they are easily repaired in case of fracture 
 of the porcelain parts. 
 
 However, cases present when a baked porcelain bridge 
 will fulfill esthetic requirements where one of another type 
 would prove inadequate. 
 
 GENERAL CONSIDERATIONS 
 
 Most of the failures recorded against porcelain, when 
 used in bridgework, are due to its injudicious application. 
 
890 PORCELAIN CROWN AND BRIDGE WORK 
 
 Certain conditions are often foinid in tlie moiitli wliich pre- 
 clude tlie introduction of a bridge of tliis cliaracter. 
 
 Porcelain is strong only in bulk. In thin, attenuated 
 plates it is friable and l)reaks readily under stress. The truss 
 or platinum framework nmst be depended upon primarily, to 
 furnish the necessary strength to resist stress. A truss may 
 be constructed that fulfills this requirement and the case still 
 be unsuitable for porcelain if the remaining spaces not occu- 
 pied by the metal structure, is so limited that the porcelain 
 will be spread over the framework in thin layers, especially 
 on occlusal surfaces. The constantly repeated force of mas- 
 tication, directed against the cusps of porcelain, will fracture 
 and break them away from the truss, even though the latter 
 may be rigid enough to retain its form. 
 
 In addition, therefore, to having sufficient space for a 
 rigid truss, there must be sufficient additional space remaining 
 to apply the porcelain in ample bulk to resist stress. It is 
 impossible to state just how wide this space should be. A 
 great deal depends upon the hal)its of the patient, the amount 
 of force exerted by tlie muscles of mastication, the length of 
 span and the number and position of abutments and piers. 
 
 It may be stated that, as a general rule, there nmst be a 
 minimum s]3ace of at least 5 mm. between the alveolar border 
 and the occlusal surfaces of the opposite teeth in short spans, 
 while longer spans will naturally require more space, since 
 the truss itself must be more bulky. 
 
 The length of span is a matter of great importance and 
 should be closely studied. In long spans, where much curva- 
 ture in the bridge will be required and where only two abut- 
 ments afford supjoort, a porcelain bridge would most certainly 
 prove a failure. If, however, there is an intervening pier, 
 with sufficient space to insure bulk of porcelain, the case 
 would be suitable for an appliance of this character. 
 
 The points to be carefully observed and studied are: 
 
 First — The number, position and condition of the roots 
 or teeth that are to serve as supports for the bridge. 
 
 Second — The length of span to be covered by the truss. 
 
 Third — The amount of space between the alveolar border 
 and the occlusal surfaces of the opposite teeth. 
 
 Fourth — The habits of the patient as to the care of the 
 teeth. 
 
 Fifth — The amount of force exerted by the muscles of 
 mastication. 
 
PORCELAIN CROWN AND BRIDGE WORK 891 
 
 Sixth — Study carefully, whether a substitute of any other 
 character might be equally as serviceable if not more effi- 
 cient than porcelain. 
 
 PORCELAIN BRIDGE CONSTRUCTION 
 
 The various steps involved in the construction of a porce 
 lain bridge may be arranged in the following order: 
 
 First — Preparation of the abutment or pier roots or teeth. 
 
 Second — Construction of caps or shell crowns for same. 
 
 Third — Taking bite and impression, and mounting casts 
 on occluding frame. 
 
 Fourth — Locating position of, and constructing and sol- 
 dering saddle to caps and crowns. 
 
 Fifth — Locating position of, and fitting truss bars in 
 position. 
 
 Sixth — Investing and soldering same to caps and crowns. 
 
 Seventh — Attaching facings to metal framework. 
 
 Eighth — Application of body. 
 
 Ninth — Baking. 
 
 Tenth — Finishing. 
 
 Eleventh — Setting the bridge. 
 
 PREPARATION OF ROOTS OR TEETH 
 
 The preparation of the roots or teeth for the reception 
 of caps and crowns which are to serve as abutments and piers 
 for bridges differs in no essential particular from the instruc- 
 tion previously given under the heads of porcelain cro^vns and 
 shell crouvs, therefore it is unnecessary to enter into the de- 
 tails of this procedure here. 
 
 CONSTRUCTION OF CAPS AND SHELL CROWNS 
 
 When the abutment and pier crowns are to be of porce- 
 lain, the construction of the caps is similar to, or identical 
 with, the methods outlined under the head of porcelain 
 crowns. 
 
 When platinum shell crowns are constructed for the bicus- 
 pids or molars, as is frequently advisable, the details differ 
 in a few essential particulars, from the methods followed in 
 ordinary shell cr.own construction. 
 
 The cusps of crowns, when platinum is used, are more 
 difficult to swage in this material than from 22 k. gold of equal 
 thickness. Therefore, in order to have the needed bulk of 
 platinum in the occlusal surface of a crown, to withstand attri- 
 
892 PORCELAIN CROWN AND BRIDGE WORK 
 
 tioii; two thicknesses of platinum are swaged, separately at 
 first, and then together and solidly attached by soldering. 
 
 This is necessary since the interior of such crowns can- 
 not be reinforced with solder, as is done in ordinary crown 
 work, as the latter would be more or less dissipated by the 
 heat necessary to fuse the porcelain. 
 
 Special care should be taken to contour the occlusal 
 margin of the band and the corresponding margin of the cusps 
 until they coincide perfectly, then true both contact margins, 
 first with a flat file, following this by dressing on an oil 
 stone until perfect contact is secured, thus obviating the use 
 of much solder in attaching the two pieces together. 
 
 The method of constructing a crown of this class in the 
 ordinary manner, and afterward swaging a second piece to the 
 interior to stiffen up the occlusal surface, allowing the mar- 
 gins of the second piece to overlap the joint between the band 
 and cusp, is frequently resorted to with satisfactory results. 
 
 To give additional strength to the crown, at the point 
 where the saddle and truss bars join it, a second piece of 
 
 ON LEFT. DRESSING DOWN OCCLUSAL Cj\P AND AXIAL BAND 
 
 ON OIL STONE. ON RIGHT. OCCLUSAL CAP, COMPOSED OP 
 
 TWO THICKNESSES OF PLATINUM PLATE 
 
 platinum plate is often adapted and soldered to this surface, 
 on the outer side of the crown. 
 
 The caps and crowns having been constructed and fitted 
 in their respective places, an accurate bite and an impression 
 are secured, the casts constructed, and mounted on an occliad- 
 ing frame. 
 
 CONSTRUCTION OF SADDLE 
 
 The saddle, although not universally, is frequently used 
 to give the porcelain proper contour on both labial or buccal 
 and lingual surfaces. 
 
 Formerly broad saddles were recommended and much 
 used, as previously mentioned, but for reasons already stated 
 their use has been discontinued. 
 
 Saddles, therefore, when indicated, should be as narrow 
 as possible, yet sufficiently wide to fulfill the requirements of 
 proper contouring of the case. 
 
PORCELAIN CROWN AND BRIDGE WORK 893 
 
 The position as well as outline for the saddle can be best 
 determined by waxing the facings in position and trimming 
 the wax to correct form, then marking on the line thus 
 indicated. Another method frequently followed is to 
 make the saddle broader than necessary, and after the first 
 application and making of the body, cut away the surplus 
 margins. This gives good results, lint entails considerable 
 waste of material. 
 
 Tlie saddle should la}) well over caps and against crowns, 
 to insure secure attachment of the several parts. It is cut 
 to proper length and width as indicated by the outline on the 
 cast, and either burnished and conformed to it, or swaged on 
 Melotte's metal die. Wliere the surfaces on which the saddle 
 is to rest are very irregular, the latter method is an excellent 
 and accurate one. 
 
 When swaged or conformed perfectly to the cast or die, 
 it is attached to the caps and crowns by soldering and the 
 several connected parts are fitted in the mouth for final ad- 
 justment of the saddle to the natural tissues. A large round 
 end burnisher, or one of the contra-angled form designed 
 by the author, can be used for this purpose. The saddle should 
 be pressed uniformly against the soft tissues until a slight 
 blanching of the gum is noticeable. This should disappear 
 in tliree or four minutes and tlie tissues regain their normal 
 appearance. Too great pressure will produce hypertrophy of 
 the tissues and finally atrophy and absorption, while under a 
 properly adjusted saddle they will usually remain in a healthy 
 condition and in contact with it for a varying period. 
 
 At this time the partially constructed framework is in 
 position in the mouth, and the soft tissues in a more or less 
 com])ressed condition. If removed and placed on the original 
 cast, the saddle would be distorted, since the cast, unlike the 
 gum tissue, is unyielding. Therefore it becomes necessary to 
 take a new bite and impression, and mount tlie cast as before. 
 
 LOCATING AND FITTING TRUSS BARS 
 
 In short spans a single bar of 16 or 15 gauge round iridio- 
 jilatinum wire is usually sufficient to furnish the needed rigid- 
 ity and support to the bridge. Longer spans frequently re- 
 quire two bars of 16-gauge, or a single bar of 14-gauge. 
 
 The position for the truss bar is found by grinding the 
 facings accurately to place and waxing them in position. Var- 
 nish the outer surface of the cast with separating medium and 
 build a matrix of plaster against the labial or buccal surfaces 
 
894 PORCELAIN CROWN AND BRIDGE WORK 
 
 of tlie teeth and cast. When set, remove from t!ie cast, and, 
 if the facings have remained with tlie framework, remove 
 and jilace them in their respective positions in the plaster 
 matrix. 
 
 The wax is all removed and the plaster matrix carrying- 
 the teeth returned to the cast. Tiie truss bar is then bent and 
 conformed to the lingual surfaces of the facings, usually occu- 
 pying a position between the pins and the ridge lap. By plac- 
 ing in tliis position, more space is afforded for the porcelain 
 and the liability of its breaking away under stress will be 
 much less than if the bar was placed between the pins and 
 the occlusal or incisal margins of the facings. 
 
 Broad surface contact should be secured between the bar 
 and dowels and the several parts held in absolute contact while 
 soldering, so as to insure the greatest possible amount of 
 strength. 
 
 The attachment of the bar to a shell crown is usually 
 made by splitting the abutting end and adapting the split por- 
 tions to the reinforced section of the crown before mentioned ; 
 or a hole may be drilled through the axial wall of the crown 
 and the bar bent so as to pass up the inner side of the wall and 
 across the occlusal surfaces, a groove being cut in the tooth, 
 if necessary, for the accommodation of the bar. This affords 
 a firm anchorage to the crown and one that will not pull away, 
 as frequently occurs when the contact of the bar with the crown 
 is superlicial. 
 
 Eound or oval are preferable to square bars, since the 
 sharp angles on the latter seem to induce fracture in the 
 porcelain, under stress. 
 
 If square wire is used the sharp angles should be rounded 
 off to obviate this difficulty. 
 
 When the bar is accurately adapted, the ends are waxed 
 to the dowels and crown attachments. 
 
 In the series of drawings shown in Cut I from a former 
 edition of this text, the construction of a two-bar truss of 
 square wire is illustrated. In 31 d the bar next to the saddle 
 is first fitted and attached to cap, dowel and shell crown. 
 The second bar nearest the occlusal surface is next fitted, 
 bending it so as to lie in close contact with the lingual sur- 
 faces of the facings as shown in .32 e. It can be bent to 
 pass over the pins if necessary, but when jjossible should 
 pass under them, for reasons before stated. It can be bent 
 irregularly to follow the line of the pins, should they be \va- 
 even. The ends of the bars connected with the dowel can be 
 
PORCELAIN CROWN AND BRIDGE WORK 895 
 
 notched as indicated in 3-1 and the reduced portion bent 
 around it, as shown in 35. 
 
 Thirty-three shows imperfect contact of post and bar ; 37, 
 a condition in which there is not space enough between the 
 labial side of the dowel and the lingual surface of the facing 
 to receive the truss bar, and, to overcome the difficulty, both 
 dowel and bar are notched. In some cases both bars lie on the 
 same side of the dowel, one upon the other, as indicated in 
 31 c, and again there are cases whei'e, if arranged in this 
 manner, the outer one would l)e thrown too far occlusally. 
 
 JA^ 
 
 CDTS SHOWING VARIOUS STEPS IN THE FITTING OK SADDLES, TRUSS BARS. AND TEETH 
 
 OP A PORl'ELAIX BRIDGE. IN THIS CASE THE MOLAR IS A SHELL 
 
 PLATINUM CROWN 
 
 One is then placed on the lingual side of the dowel and the 
 other one on the opposite side, as in 38. 
 
 In 36 the method of splitting the bar and bending the 
 split ends so as to partly encircle the shell crown is illustrated. 
 When bicuspid and molar roots carry full porcelain crowns 
 the bars are attaclied to their caps and posts in the manner 
 described. 
 
 The bars, when fitted, are connected by braces, which are 
 cut and accurately fitted in position. Both ends can be notched 
 as shown in 31 /. 
 
896 
 
 PORCELAIN CROWN AND BRIDGE WORK 
 
 CDT II CUT 111 
 
 URIDGE ItEFOKB AND AFTER DUPLICATION AND FUSING 
 
 OF THE PORCELAIN BODY 
 
 Cut II shows a single bar truss, with short posts soldered 
 on the molar cap and at intervals along the truss bar, to afford 
 firmer attachment to the lingual body of porcelain. 
 
 FRAMEWORK OF AN UPPER. FOUR-TOOTH 
 BRIDGE, SHOWING HEAVY TRUSS BAR AT- 
 TACHED TO DOWELS OF CUSPID AND 
 FIRST MOLAR CROWN. FITTED WITH 
 NARROW SADDLE 
 
 Cut III shows the \neee after the porcelain has been ap- 
 plied and baked. 
 
 SOLDERING 
 
 The several parts having been accurately fitted they are 
 waxed together, the facings removed, the cap, crown, saddle 
 and truss removed from the cast and invested so that the in- 
 vesting material extends over the bars and holds them firmly 
 in position after the wax is removed. When soldered, the 
 frame is returned to the model and the facings returned to 
 place, waxed in position, the piece removed, again invested, 
 the pins, after having been flattened, bent in actual and close 
 contact with the bar and soldered. 
 
 The essential points to he observed in constructing the 
 framework for a porcelain bridge are: 
 
 First, be accurate in every detail. Second, develop close 
 joints Third, flow solder into and between all junctions so as 
 to perfectly unite the several parts together. 
 
 APPLICATION OF THE BODY 
 
 Before applying the porcelain body, the framework should 
 be pickled, cleansed and roughened on those surfaces against 
 
PORCELAIN CROWN AND BRIDGE WORK 897 
 
 which the porcelain is to be fused to afford some additional 
 attachment of the porcelain to the metal framework. 
 
 As mentioned in connection with crown work, a pin vice 
 can be used to good advantage in handling the piece while 
 applying the body. 
 
 The body is built on the lingual surfaces of the facings 
 and against the saddle a little at a time, the piece vibrated 
 to settle the granules of powder close together, the moisture 
 is taken up as it appears on the surface, and a rough contour 
 given the piece for the first baking. 
 
 All particles of body should be removed from the labial 
 or buccal surfaces of the facings, for if carried through the 
 furnace they become attached and can only be removed by 
 discing or grinding, which destroys the fine glaze on the 
 porcelain. 
 
 FUSING THE PORCELAIN 
 
 The directions, beginning on page 615, with reference to 
 the fusing of continuous gum body apply with equal force in 
 the fusing of porcelain in bridgework. Uusually, the piece, 
 being smaller, can be fused in somewhat shorter time than a 
 
 SMALL ELECTRIC KCRNACE SCITARLE FOIt PORCELAIN 
 
 CROWX, HRIDOE. AND INLAY WORK 
 
 (HAMMOND) 
 
 full denture, and since less time is required, greater care must 
 be observed in the latter stages of baking, to prevent over 
 fusion. 
 
 When possible to do so, the bridge should l)e completed in 
 two bakings to avoid friability of the material, which char- 
 acteristic, as well as a tendency to liecome porous, develops 
 rapidly after the second fusion. 
 
S9S PORCELAIN CROWN AND BRIDGK WORK 
 
 FINISHING AND SETTING THE BRIDGE 
 
 Pinisliing and setting a porcelain bridge differ in no 
 essential particulars from the steps involved in the finishing 
 and setting of porcelain crowns, the details of which have been 
 given. As previously mentioned, however, the use of the 
 
 SMALL, GASOLLNE FURNACE SUITABLE FOB PORCELAIN CBOWN. 
 BRIDGE. AND INLAY WORK (TURNER) 
 
 mallet, either hand or automatic, should be avoided in the set- 
 ting of baked crowns of porcelain, combined with metal, be- 
 cause of the very great danger of fracture. 
 
 VARIOUS TYPES OF METAL STRUCTURES 
 
 The principal thought to keep in mind in planning a 
 porcelain bridge is to form a rigid metal structure, capable of 
 sustaining all stress to which the bridge may be subjected, 
 without depending upon the applied porcelain. 
 
 Therefore, the forms of trusses may be varied according 
 to conditions, as space occluso-gingivally, length of span, posi- 
 tion of abutments, width of alveolar border, etc. 
 
 Frequently, in the replacement of a single tooth, a truss 
 of the cantilever type may be united with a single crown, the 
 opposite end terminating in a projection for resting in a 
 grooved inlay in the proximating tooth. 
 
 In other cases, instead of a saddle being adapted to the 
 bordei', a half-round wire is fitted close to, or in contact with, 
 
PORCELAIN CROWN AND BRIDGE WORK 899 
 
 tlie border crest, against which tlie Iniccal and lingnal surfaces 
 of ai»plicd porcelain may terminate. 
 
 FRAMEWORK OF AN EXTEN- 
 SION BRIDGE, WITH SUP- 
 PORTING LDO TO REST IN 
 GROOVED INTiAY IN CUSPID 
 TOOTH 
 
 FRAMEWORK OP A LOWER FOUR-TOOTH 
 BRIDGE. HEAVY TRUSS BAR FOR SUPPORT- 
 ING TEETH. HALF-ROUND WERE TO REST ON 
 BORDER CREST, AND AGAINST WHICH BOTH 
 BUCCAL AND LINGUAL SURFACES OP PORCE- 
 LAIN WILL TERMINATE 
 
 FR.AME\VORK OF AN UPPER. FOUR-TOOTH 
 
 BRIDGE FITTED WITH SADDLE, TO WHICH A 
 
 LINGUAL FLiVNGE IS APPLIED FOR SUPPORT 
 
 OF PORCELjUN 
 
 Again a flange of platinum is adapted and attached to 
 the lingual border of the saddle or wire to add strength to the 
 framework and afford a matrix for supporting tlie porcelain 
 under stress. 
 
900 PORCELAIN CROWN AND BRIDGE WORK 
 
 The Peeso and Bensou pliers, because of their short beaks 
 and heavy handles, are partifiilarly nsofnl for coiitonrins' of 
 
 THE TEESO CONTOUBINO PLIERS 
 
 THE liEN'SOX CONTOllRIXd PI.IERS 
 
 plate and bending of wires in this, as in many other classes of 
 crown and bridge work. 
 
CHAPTEE XXXI 
 
 INLAYS 
 
 PORCELAIN AND METALLIC 
 PORCELAIN 
 
 Porcelain, or "cliiiunvare, " was imported into Europe 
 principally by the Portugese, who gave it the name of porce- 
 lain, from its resemblance to the nacre or lining of the sea- 
 shell Porcellana (C'yprea). The shells of this species derive 
 their name from their supposed resemblance to the back of a 
 hog (Porcus). It was at first su^jposed that porcelain con- 
 sisted of pulverized egg shells, fish scales and fish glue. 
 
 The first authentic record we can find of porcelain being 
 used for dental purposes appears in the "Art of Dentistry," 
 published by Fauchard in 17:28. In this he says: "I have 
 thought that advantage might be derived from a regular and 
 unaltei'able coloration from enamel artificially composed. I 
 have also thought that I might from this not only perfectly 
 imitate the enamel of the teeth, but the gum in cases where it 
 is necessary to replace the teeth in whole or in parts of sets. 
 I have consulted the most able enamelers, and by conversa- 
 tions which I have had with them I have rendered practicable 
 tiiat which I believe no one else has ever thought of; the teeth 
 or dentures made of enamel will endure a very considerable 
 time, since the enamel is a substance scarcely susceptible of 
 change or alteration." 
 
 EARLY APPLICATION OF PORCELAIN IN DENTURE 
 CONSTRUCTION 
 
 The development of porcelain in its application to den- 
 tistry is a most interesting story, an outline of which will be 
 found in the chapter on the "History of Prosthetic Den- 
 tistry. ' ' 
 
 The efforts of the pioneers in the porcelain field until 
 Fonzi's time, 1808, were directed principally to the produc- 
 tion of full and partial dentures in a single piece, yet but 
 little progress .was made in this class of work until about 
 1850, when Dr. John Allen introduced the continuous gum 
 denhire. His work consisted in improving the character of 
 the porcelain then in use, reducing its fusing point and con- 
 
 901 
 
902 INLAYS 
 
 tractile tendency, improving tlie color of the gum enamel, 
 and of baking the denture on a platinum base to which the 
 teeth were previously attached by soldering. The use of the 
 platinum base obviated the warpage, which invariably oc- 
 curred when the porcelain was fused on a silex and plaster 
 form. 
 
 CORRECTION OF WARPAGE IN THE ALL-PORCELAIN 
 DENTURE 
 
 Previous to Allen's improvement, it was necessary, after 
 the denture was baked, to secure an accurate cast of the 
 mouth in plaster, paint the areas to be covered by the denture 
 with red lead or similar pigment, and apply the denture to the 
 cast ; the areas of contact between denture base and cast were 
 colored on the base with the pigment, and on removal were 
 ground with small stones. This process of trial and grinding 
 was repeated until finally the entire denture surfaces which 
 rested upon the oral tissues showed color, when pressed ujjon 
 the cast. The same general technic was followed in securing 
 adaptation to the oral tissues, of the old-time dentures carved 
 from the elephant or hippopotamus ivory. 
 
 Dentures constructed by this method, while occasionally 
 showing good adaptation and stability, usually recjuired the 
 aid of springs for their retention under masticatory stress. 
 
 BASIC INGREDIENTS OF PORCELAIN 
 
 The basic ingredients in most of the porcelain bodies of 
 today consist of kaolin, silex and feldspar in proportions 
 varying according to the purpose for which the material is 
 intended. The porcelain used for tooth bodies is the highest 
 fusing of any used for dental purposes, the point of vitrifica- 
 tion ranging from 2,440° to 2,600° F. 
 
 KAOLIN (Al,H,(SiO.)-H,0 
 
 The word kaolin is a corruption of the Chinese word 
 Kauling, which means a high ridge, and is the name of a hill 
 near Jachau Fu, China, from which a great deal of this ma- 
 terial is derived. A tine variety of clay is also found in 
 Germany. Both of these varieties of elaj" are practically free 
 from iron oxide and other deleterious imirarities and are used 
 almost exclusively in the compounding of dental porcelains. 
 
 Kaolin is a tine pure variety of clay, or aluminum sili- 
 cate. It is formed by the disintegration and decomposition 
 
INLAYS 903 
 
 of granitic and feldspatliic rocks tlirougli weathering, or con- 
 tinued freezing and thawing. Tliese rocks being granular, 
 take up moisture, and this when expanded by freezing spilts 
 oft" the outer surfaces of the rock. The rain in time dissolves 
 out some of the constituents and washes away the small par- 
 ticles, which, as they are carried down the stream, grind upon 
 each other and become still more finely divided until all sem- 
 blance of their original form is lost. These particles, mixed 
 with sand, float or are washed down stream and settle in beds. 
 Some of these clay beds are at tlie present time high above 
 the water line, having been deposited ages ago and placed in 
 their present location by volcanic upheavals. 
 
 PREPARING THE CLAY FOR USE 
 
 The clay is prepared for use by mixing with water in a 
 tank, agitating and allowing the sand and heavier particles to 
 settle, after which the water is drawn otf into another tank, 
 while the finer j^articles of clay are still held by it in solution. 
 
 These finer particles are allowed to settle in the second 
 tank, and when the water becomes clear it is carefully drawn 
 off and the clay allowed to dry. The slab of dry clay is then 
 turned over and the coarser particles which settled to the bot- 
 tom as the first preciiiitate are scraped off, when it is ready 
 for use. 
 
 FELDSPAR (KAlSi.OO 
 
 Feldspar is a double silicate of aluminum and potassium 
 known as Orthoclase. It occurs crystallized in rhombic prisms. 
 There are many varieties of this mineral, but only those that 
 are free from soda or lime are used in compounding porce- 
 lain. It is yellowish pink in color in its natural state, but 
 transparent and colorless when fused. 
 
 A variety of this mineral suitable for tooth bodies is 
 found in many parts of the United States. The principal de- 
 posits snital)le for the compounding of porcelain are found 
 near Wilmington, Del. 
 
 PREPARING THE FELDSPAR FOR USE 
 
 Feldspar is prepared for use by heating to redness, drop- 
 ping in water while hot, to break it up into small pieces, 
 ground to powder in a special pulverizing machine or with a 
 large mortar and pestle, and under water, to facilitate the 
 grinding. The powder is then run through a No. 10 bolting 
 sieve, placed in closed vessels to keep dry and free from im- 
 
purities until needed for use. Pulverizing too finely detracts 
 from the translucency of the porcelain when fused. 
 
 SILICA (SiO.) 
 
 This mineral is a silicic oxide, ordinarily known as 
 quartz. It is one of the constituents of granitic rocks ; it also 
 occurs free in large masses in many parts of the United 
 States, as well as in many parts of the Avorld. 
 
 PREPARING THE SILICA FOR USE 
 
 Silica is prepared for use l),y grinding to a liue powder 
 in a powerful mill constructed especially for this class of work. 
 It is extremely hard and fuses only at very high tempera- 
 tures, about .3,500° F. 
 
 These three materials, kaolin, silex and feldspar, as be- 
 fore stated, are combined in varying proportions to form 
 tooth bodies, and the more fusible continuous gi;m and inlay 
 bodies. 
 
 PROPERTIES OF THE BASIC CONSTITUENTS OF 
 PORCELAIN 
 
 Kaolin imparts plasticity to the tooth body, enabling it 
 to be luolded into the desired form before baking. It also 
 contracts somewhat in fusing, and as a result draws together 
 the more infusible constituents, thereby imparting density to 
 the mass. 
 
 Silex, on account of its infusible property, tends to keep 
 the form into which it is molded, whether inlay, tooth, crown, 
 bridge or denture, from melting down in the heat of the fur- 
 nace. 
 
 Feldspar imparts translucency and also acts as a flux, 
 closely uniting the kaolin and silex. By varying the propor- 
 tion of this material in compounding the l)ody, a number of 
 porcelains differing in texture and fusibility can be pro- 
 duced. 
 
 APPROXIMATE PROPORTIONS OF INGREDIENTS IN 
 PORCELAIN 
 
 The manufacturers do not publish the formulas of their 
 tooth or other porcelain bodies of the lower fusing types de- 
 signed to be used in continuous gum and other classes of 
 work. Since it is not necessary for the prosthetist to com- 
 pound his own porcelain materials, as the pioneers in this 
 
INLAYS 905 
 
 field were required to do, still it is essential that he know 
 the elementary constituents and their physical properties 
 in order that the best results may be derived from their use. 
 
 The names of Wildman, Hunter and Allen are insepara- 
 bly connected with the history of continuous gum work and 
 carved block teeth in this country, and to them the profession 
 owes mucli for im^^rovements in porcelain bodies and tech- 
 nical methods. The period of greatest activity of these early 
 porcelain workers extended from 1835 to 1860. Since the 
 latter date the carving and baking of single and block teeth 
 in the dental laboratory, as was the prevailing custom in 
 their time, has been discontinued because of the continually 
 advancing improvements in these lines of the manufactured 
 products. Continuous gum dentures, however, cannot be 
 made in a factory. The prosthetist, therefore, should be 
 capable of selecting the best material and of manipulating 
 it in tlie best possible manner to secure ai'tistic and perma- 
 nent results in the construction of dentures of this type. 
 
 The following formulas will show, in a general manner, 
 the proportions of the basic ingredients used in compound- 
 ing some of the many iiorcelains : 
 
 Dr. Wildman's fonnnla for toDth bodi/: 
 
 No. 1. Kaolin 1 oz. 
 
 Silex 3 ozs. 
 
 Feldspar 18 ozs. 
 
 Titanium oxide 65 grs. 
 
 Titanium oxide imparts a yellowish tint to porcelain. 
 The oxides of some of the other metals are used for produc- 
 ing various tints, as required ; they are mixed in and thor- 
 oughly incorporated with the porcelain in process of manu- 
 facture, the latter often, after the addition of the metallic 
 oxide, being fused, crushed and pulverized, to more thor- 
 oughly disseminate the tint. 
 
 OXIDES OF THE METALS USED IN TINTING PORCELAIN 
 
 Gold in a state of minute subdivision Eose red 
 
 Oxide of gold Bright rose red 
 
 Purple of Cassius (double oxide of tin and gold . Purplish red 
 
 Sponge platinum and filings Grayish blue 
 
 Oxide of cobalt. . : Bright blue 
 
 Oxide of manganese Purple 
 
 Oxide of uranium Greenish yellow 
 
 Oxide of silver Lemon yellow 
 
 Oxide of zinc Lemon yellow 
 
 Oxide of titanium Bright yellow 
 
906 I^a,AYS 
 
 The formula for continuous gum body is similar to that 
 of the Wildnian tooth hody, previously given, except that more 
 kaolin and feldspar are added to reduce the fusing point ; this 
 is necessary in order that the teeth, which have previously 
 heen attached to the platinum base, will not be fused and lose 
 their shape or color while vitrifying the continuous gum body. 
 
 THE CONSTITUENTS OF GUM ENAMEL 
 
 The continuous gum body, when applied around the 
 teeth and over the metallic base, gives form and contour to 
 the denture; in color it does not resemble the natural gums, 
 being white, or, when oxide of titanium is present, slightly 
 yellow; the denture must be tinted to give it a natural ap- 
 pearance. A material called gtim enamel, purplish pink or 
 red in color, is distributed in a thin, more or less uniform 
 layer, over those surfaces representing the mucous tissues 
 and fused to the continuous gum body, thus giving the re- 
 quired color and the proper glaze, to the surfaces of the 
 denture as well. 
 
 Gum enamel is made by combining certain compounds in 
 definite proportions with feldspar. These compounds are 
 known as frits and fluxes, the formuke of which are similar to 
 the following: 
 
 No. 2. Flux. 
 
 Carbonate of potassium 1 oz. 
 
 Fused borax (powdered) 1 oz. 
 
 Quartz 4 oz. 
 
 These materials are fused together, then crushed and 
 ground to a tine powder, to prepare them for combining with 
 the following: 
 
 No. 3. Gum frit. 
 
 Purple of Cassius 16 grs. 
 
 Feldspar 700 grs. 
 
 Flux (as per Formula No. 2) . . .175 grs. 
 This gum frit is fused, crushed and ground to a tine 
 powder, preparatory to the final compounding of the pink 
 gum enamel. 
 
 No. 4. Gum enamel. 
 
 Gum frit (as i^er Formula No. 3) 1 oz. 
 
 Feldspar 3 oz. 
 
 This also is fused, crushed and ground, wlien it is ready 
 for use. Fortunately, both continuous gum body and gum 
 enamel of excellent quality are procurable at the supply 
 houses, which, by mixing into a paste with water, is ready 
 
for immediate use. From the preceding formulas a vague 
 idea can be formed as to the amount of study and effort it 
 has taken to develop suitable materials for use in dento- 
 ceramic art. 
 
 CROWN, BRIDGE AND INLAY PORCELAINS 
 
 The porcelain most commonly used in crown, bridge and 
 inlay work closely resembles in composition and physical 
 properties that prepared for continuous gum work, except 
 that it is ground a little finer and fuses at a slightly lower 
 temperature. Crown, bridge and inlay porcelain is also pre- 
 pared in a variety of colors, in order to match the varying 
 shades of teeth in and next to which it may be placed. 
 
 HIGH AND LOW FUSING PORCELAIN BODIES 
 
 The fusibility of porcelain separates this material into 
 two general classes, the fusing point of pure gold being the 
 dividing line. Those fusing at or above this point are called 
 high fusing, and those fusing under this point are denomi- 
 nated lotv fusing porcelain. 
 
 The following table, from Dr. W. A. Price's tempera- 
 ture scale, gives the approximate temperatures required to 
 vitrify the principal bodies and enamels, also the fusing point 
 of gold and coiDperas registered liy the same scale: 
 
 Consolidated tooth body 2630-F. 
 
 S. S. White's tooth body 2515-F. 
 
 Dental protective tooth body 2440-F. 
 
 Justi's tooth bodv 2440-F. 
 
 Sibley's tooth body 2410-F. 
 
 White's porcelain (crown and bridge) .2300-F. 
 
 Close's bodv 2300-F. 
 
 Ash's tooth body 2260-F. 
 
 Whiteley's porcelain 2210-F. 
 
 Brewster's bodv 2210-E\ 
 
 Consolidated high fusing 2200-F. 
 
 Brewster 's enamel 2080 F. 
 
 Moffitt's porcelain 2050-F. . 
 
 Copper 1980-F. 
 
 Gold 1950-F. 
 
 Ash's high- fusing 1900-F. 
 
 Downie-'s 1550-F. 
 
 Jenkins' 1550-F. 
 
 Ash's 1550-F. 
 
 Brewster's low 1500-F. 
 
COMPARATIVE VALUE OF HIGH AND LOW FUSING 
 PORCELAINS 
 
 Experience has shown that lii.uli i'usini'- jiorcehiin is a 
 stronger and more permanent material for use in the montli 
 than is the low-fusing porcelain. Foi' this reason, therefore, 
 it has almost entirely displaccMJ the latter, especially in 
 crown and bridge construction, and in inlay work where the 
 filling will be subjected to any considerable stress. 
 
 The principal advantage of low-fusing porcelain for in- 
 lay work is in the ease witli which it may be fused, and in 
 certain cases because of its more opaque texture, better color 
 results in the matching of the natural teeth are possible 
 than with high-fusing bodies. In the hands of the inexpe- 
 rienced it is doubtful whether the low fusing will yield as 
 good results as will the iiigh-fnsing ))odies. 
 
 PORCELAIN INLAY WORK 
 
 The system of inlay work most generally in vogue at the 
 present time consists in preparing the tooth cavity, conform- 
 ing a matrix of platinum or pure gold to it, or a reproduc- 
 tion of it, fusing the inlay material into the matrix thus 
 formed, removing the matrix from the fused filling and set- 
 ting the latter in the cavity with cement. Like all classes 
 of filling materials, porcelain has its advantages and disad- 
 vantages. 
 
 ADVANTAGES 
 
 With care, skill and experience, porcelain inlays may, 
 in many cases, be so accurately constructed, and the shades 
 of the natural teeth in which they are placed so perfectly 
 matched, that it will be impossible to detect these restora- 
 tions from the natural tooth structure, except by the closest 
 scrutiny. The esthetic properties of this material, there- 
 fore, place ])orcelain above that of any other filling material 
 for the artistic restoration of natural teeth. Its insolubility 
 places it above the synthetic cements. 
 
 Second, porcelain is a poor thermal conductor, and for 
 this reason, inlays may be placed in cavities of teeth, the 
 pulps of which are sensitive to sudden temperature changes, 
 where metallic fillings could not be tolerated. 
 
 Third, patients are relieved from long and tedious sit- 
 tings in the chair, when for any reason they are physically 
 unfit for lengthy operations. 
 
Fourth, the strain upon the operator is much less than in 
 ordinary filling operations. 
 
 OBJECTIONS 
 
 The principal disadvantages resulting from inherent de- 
 fects in the material itself, or from use in the mouth, may 
 be stated as follows : Friability, constructive difficulties, 
 shadow problem and retention. 
 
 FRIABILITY 
 
 In thin, attenuated plates, porcelain is frial)le and very 
 easily broken. It is strong only in bulk, and, therefore, the 
 utmost care should he exercised in the preparation of cavi- 
 ties to so shape them that the inlay, when set, may be sub- 
 jected to but little, if any, stress. Cavities involving an 
 incisal edge or the proximo-occlusal surfaces of a bicuspid 
 or molar should be so formed that the inlay will have strong, 
 well-defined margins and ample bulk to withstand masti- 
 catory action without fracturing. When conditions preclude 
 the formation of cavities in this manner, porcelain is contra- 
 indicated. 
 
 DIFFICULTIES MET WITH IN CONSTRUCTION 
 
 Among the most important difficulties which arise dur- 
 ing the construction and in the a]5plication and use of porce- 
 lain inlays, the following deserve careful consideration: 
 
 First, inlay retention, or developing retention form in 
 the cavity, so that the inlay, when formed and set, may not 
 become displaced under stress. 
 
 Second, securing correct adaptation of tlie matrix to 
 cavity walls. 
 
 Third, avoiding warpage of the matrix during the fusing 
 of the porcelain. 
 
 Fourth, the selection, ajjplication and fusing of the sev- 
 eral tints of porcelain in proper succession, so that the 
 finished inlay will coincide in color with the natural tooth in 
 whicli it is to be placed. These constructive problems will 
 now be briefly considered. 
 
 INLAY RETENTION 
 
 The walls of cavities intended for the reception of in- 
 lays of any class must show slight divergence from within 
 outward in order that the matrix, or wax model, may be 
 
910 INLAYS 
 
 released without distortion. This applies to both gold and 
 porcelain inlays. 
 
 A cavity should be so shaped that when the inlay is 
 constructed and set, the forces to which the latter is sub- 
 jected will tend to drive it into the cavity rather than out of 
 position. Where an inlay is solely dependent upon cement 
 for retention purposes, particularly when subjected to any 
 appreciable stress, its permanence and value as a filling are 
 questionable. 
 
 The usual means of retention capable of being developed 
 in the formation of the cavity are: parallel or slightly di- 
 vergent, opjiosing walls, flat seats, and grooves so formed as 
 to permit not only the ready removal of tlie matrix without 
 distortion, but to allow the inlay, when completed, to go to 
 place without interference. 
 
 As a means of retention for porcelain inlays, Dr. F. H. 
 Skinner suggests the following: 
 
 Drill one or more small retention pits in gingival wall 
 or incisal step of the cavity, in line with tlie direction of re- 
 moval of the matrix. 
 
 When the matrix has been conformed to the cavity, that 
 over the retention pits is pimctured and the margins turned 
 into the opening. 
 
 Each pit is now lined with a small cylinder of foil made 
 by cutting a strip slightly wider than depth of pit and a little 
 more than three times longer than its diameter. 
 
 This strip is formed into a cylinder, slit at three or four 
 points around tlie periphery, so that the sections of foil be- 
 tween may be reflected outward. 
 
 The cylinder is passed through the opening in the foil, to 
 the bottom of the pit, the slit sections of the opposite ends 
 turned down on the foil covering the gingival wall, or incisal 
 step of the cavity, and there closely adapted to the matrix. 
 
 The cylinder which lines the pit should be pressed out- 
 ward against its walls so as to form a clear opening into 
 which the porcelain may later find its way. 
 
 Sticky wax is now softened and pressed into the cavity, 
 against all matrix walls, and when hardened the foil can be 
 removed without distortion. 
 
 The matrix is invested in high-fusing investment material, 
 and when set the wax is removed and the porcelain applied 
 for first bake. 
 
 If, in applying the wax, care is taken to fill the small 
 
cylinders in the retention pits also, to exclude the investment, 
 the porcelain will flow into and fill them. 
 
 When the inlaj- is fused, and the foil is removed, the small 
 projections of porcelain which are seen will fit into tlie reten- 
 tion pits of the cavity and prevent displacement. 
 
 WARPAGE OF THE MATRIX 
 
 Patinum foil 1/1000 of an inch thick is most commonly 
 used for matrix construction in porcelain work. Thicker 
 foil, say 1/500 of an inch, while naturally more rigid, when 
 stripped from the completed inlay, results in too much space 
 between the latter and the cavity walls; again, it is more 
 difficult to adapt to small or complex cavities than the 
 lighter gauges. On the other hand, 1/2000 foil, occasionally 
 used, is too easily distorted, both in handling and through 
 contraction of the porcelain in fusing, to be depended upon 
 as a reliable matrix material. 
 
 NECESSITY FOR ANNEALING THE FOIL 
 
 Unless thoroughly annealed before beginning, kept soft 
 by occasional reheatings throughout the steps of adaptation, 
 and given a thorough final annealing, followed by final pres- 
 sure swedging with spunk, camphor gum or sticky wax, ))e- 
 fore applying the porcelain, any of the platinum foils ordi- 
 narily used in matrix construction are very liable to spring 
 away from the cavity walls, either before or during the fusing 
 process, and thus present from the very start an imperfect 
 matrix in whicli to fuse the porcelain. 
 
 WARPAGE RESULTING FROM IMPROPER SUPPORT OF THE 
 MATRIX 
 
 Warpage of the matrix may also result from its im- 
 proper support in the furnace while baking the porcelain. 
 Before final adaptation of the foil to the cavity is secured, 
 excessive overlapping jjeripheral margins and long, angular 
 points must be removed ; otherwise one or more of such 
 points may prevent the matrix proper, with the added weight 
 of the porcelain, from resting uniformly upon the muffle slab. 
 Under ordinary .temperatures no mishap would occur, but 
 with the platinum highly heated and somewhat soft, con- 
 traction occurring in the porcelain contained within it, to- 
 gether with more or less adhesion, developed and active, be- 
 tween the latter and the metal, warpage is most certain to 
 
occur. A mufflo tray or slab for supporting and carrying 
 tile matrix, having a slight dejjression in its npper surface, 
 can be used to advantage in the fusing of inlays of compli- 
 cated form. In the depression of the slab, some granular 
 silex is placed, building it higher in the center, if necessary, 
 to meet and support the matrix. On this granular bed the 
 matrix is carefully placed, moving it just sufficiently to de- 
 veloj) support at several divergent itoints, particularly in the 
 center. 
 
 WARPAGE DUE TO CARELESS HANDLING 
 
 In addition to these causes of warpage mentioned, a 
 matrix may be distorted through careless handling in re- 
 moval from the cavity^ or in any of the manipulative proced- 
 ures u]) to the time the porcelain is fused within it. The 
 necessity for exercising constant, ever-watchful care in the 
 production and manipulation of the matrix and in applying 
 and fusing the materials is one of the principal reasons why 
 porcelain is not used more extensively than it is at the pres- 
 ent time. 
 
 FAVORABLE LOCATIONS FOR PORCELAIN INLAYS 
 
 Porcelain inlays are indicated in all cavities exposed to 
 view, Avhen proper retention can be secured, and the fillings, 
 when constructed, will have sufficient bulk to withstand stress. 
 
 The classification of cavities, ranging from those in which 
 porcelain is most strongly indicated, to those in which it is 
 least required, may be stated as follows : 
 
 First — Gingival third cavities in the anterior teeth. 
 
 Second — Proximal cavities in the anterior teeth, not in- 
 volving the angles. 
 
 Third — Proximal cavities in the anterior teeth, involving 
 the angles. 
 
 Fourth — Cavities in bicuspids and molars, involving a 
 visible axial and occlusal surface. 
 
 Fifth — Occlusal cavities in the posterior teeth. 
 
 GENERAL RULES IN REGARD TO CAVITY PREPARATION 
 
 Cavity walls should be formed at right angles to the sur- 
 faces in which they are located. 
 
 Opposing axial walls should be formed as nearly parallel 
 as possible, yet be sufficiently divergent to permit the matrix 
 to be withdrawn without distortion. 
 
 Gingival and pulpal walls should be flat, and at right 
 angles to the long axes of the teeth. 
 
Cavo-surface angles sliould be planed true, but not per- 
 ceptibly beveled as for gold foil or amalgam tillings. This is 
 to avoid the formation of a frail margin to the porcelain. 
 
 Cavities occurring in occlusal surfaces should, when prac- 
 ticable, have the cavo-surface angle of their walls laid be- 
 yond points of contact or occlusion with the opposite teeth. 
 
 This will greatly reduce the liability of margins to frac- 
 ture under stress. 
 
 When an inlay is pro^jerly set, under pressure maintained 
 while the cement is crystallizing, the minutest space between 
 the cavo-surface angles and the periphery of the inlay is filled 
 with condensed cement. This supports both enamel margins 
 and those of the inlay, and since condensed cement maintains 
 its integrity much better and solution occurs more slowly than 
 when introduced as an ordinary filling, it is reasonable to sup- 
 pose, and observation has shown, that cavity margins, though 
 only slightly beveled, will stand for a considerable length of 
 time. 
 
 DETAILS OF CAVITY PREPARATION 
 
 GINGIVAL THIRD CAVITIES IN THE ANTERIOR TEETH 
 
 In cavities of this class, as well as in all others, the prin- 
 ciples of ertensinn for prevention should be carried out as 
 fully as possible. 
 
 Undermined enamel should be broken down and the cav- 
 ity outlines made s\Tnmetrical. 
 
 The walls should be as nearly parallel as conditions will 
 permit to insure retention of the filling. 
 
 SQIUUIB END, PAKALUa. SIDE. 
 
 Braia, USEFUL IN CAVITY 
 
 PBEPABATION 
 
 \ ARIOUS KORMS OF SMALL 
 ARKANSAS STONES, SOMPTIMBS 
 USED IN SMOOTHING MARGINS, 
 
 In surfaces where much curvature exists a parallel con- 
 dition of the walls may be secured, partially at least, by squar- 
 ing out the dentine slightly below the dento-enamel jmiction. 
 
 The angle formed by the junction of the axial with other 
 walls should not be squared out too definitely. 
 
 The cavo-surface angles should be sharp and well defined 
 
and Init sliglitly beveled, if at all, in order that the perii)heral 
 margins of the inlay will not be frail. 
 
 PROXIMAL CAVITIES IN THE ANTERIOR TEETH NOT 
 INVOLVING THE ANGLES 
 
 In cavities of this class it is necessary to separate the 
 teeth before beginning operations. Tliese cavities must be 
 
 formed without undercuts. They should be so shaped that 
 the matrix when burnished in position can be removed without 
 distortion. The location of the cavity will determine the direc- 
 tion in which the matrix can be most readily removed, whether 
 labially or lingually. If the cavity of decay has progressed 
 more to the labial than to the lingual, the cavity preparation 
 should be made to allow the removal of the matrix labially. 
 If decay has progressed to a greater extent lingually, the prep- 
 aration of the cavity should be made accordingly to meet this 
 condition. (See Cut I.) 
 
 The gingival and incisal walls should be made as nearly 
 
INLAYS 
 
 915 
 
 parallel to each other as practicable. When the cavity is 
 formed for the introduction of the matrix from the lingual 
 side, the labial margin should be carried far enough labially 
 to insure the porcelain being well exposed to view. This will 
 partially obviate the shadow problem that arises in this loca- 
 tion. The cavo-surface angles should be prepared as outlined 
 in cavities of the previous class. 
 
 BUCCAL CAVITIES 
 
 The pi'eparation of cavities of this class is similar in 
 most respects to those of the first class mentioned, and the 
 rules there laid down apply with equal force to the class under 
 consideration. 
 
 PROXIMAL CAVTTIES IN THE ANTERIOR TEETH INVOLVING 
 THE ANGLES 
 
 The pre]iaration of cavities of this class requires much 
 thought and skill, since the completed fillings are exposed to a 
 greater or less amoixnt of stress in mastication. 
 
916 INLAYS 
 
 The g'iiinixal wall or seat should he made Hat and at ri.u'ht 
 angles to the h)ng axis of the tootli. 
 
 The iuti'oduction of" inlays in cavities of this class must 
 naturally be in a labial, lingual or incisal direction, therefore 
 tlie labial and lingual cavity walls must be formed at least 
 parallel with the long axis of the tooth. 
 
 In the tijjper anterior teeth, when the cavity does not 
 
 extend far on the labial surface, iireparation can he made as 
 follows : 
 
 Square the gingival wall. Cut away the labial and lingual 
 walls to pei-mit of the ready removal of the matrix. Cut a 
 step on the lingual surface of the tooth, extending from the 
 incisal edge to the gingival wall. 
 
 This is done by removing a section of the lingual plate 
 of enamel, as shown in Cut II. 
 
 Cut a groove at the junction of the linguo-axio-mesial or 
 distal walls, as the case may be, extending from the gingival 
 
wall to the iiicisal edge, and bevel the several cavo-surfaoe 
 angles slightly. 
 
 It is usually best to out away the labial plate of enamel 
 at the ineisal edge to the same extent that the lingual has been 
 carried back (Cut II), to avoid a long irregular line of junction 
 occurring on the ineisal edge. 
 
 Cut III illustrates a cavity prepared as directed and tlie 
 inlay baked around a post whicli extends into the root canal, 
 
 thus furnishing additional anchorage. Note that there is a 
 labial shoulder to prevent outward displacement. 
 
 CAVITIES IN BICUSPIDS AND MOLARS INVOLVING AN AXIAL 
 AND AN OCCLUSAL SURFACE 
 
 The same general principles followed in the prepara- 
 tion of cavities for the reception of gold or amalgam fillings 
 applv in inlav work with a few exceptions, which will be noted. 
 (See Cut IV!) 
 
 First — The cavity must l)e formed without imdercuts. 
 
 Second — The axial, buccal and lingual walls sliould 
 
918 INLAYS 
 
 slightly diverge, from gingival to occlusal, to allow the ready 
 removal of the matrix in an occlusal direction. 
 
 Third — When the line of junction of the cavity wall and 
 the periphery of the inlay comes within a contact area of a 
 tooth in the opposite arch, fracture of one or both margins is 
 liable to occur. Therefore cavity walls should be laid beyond 
 such points of contact to prevent stress on the periphery of 
 the inlav- 
 
 Cut V represents a method of restoring the angle of an 
 incisor tooth. The cut shows a lingual view of the cavity, with 
 the inlay rotated to the left. The labial shoulder, flat seat and 
 slight groove in both seat and shoulder furnish needed resist- 
 ance to displacement. The preparation for lower incisors 
 should be reversed. 
 
 RESTORATION OF INCISAL EDGES 
 
 Cut VI illustrates a method of restoring a notched incisal 
 edge. A lingual view of the cavity is presented. The shoulder 
 prevents outward displacement. In lower incisors the shoul- 
 
der should be lorepared in the labial plate to prevent lingual 
 displacement by the iipper teeth. 
 
 The preparation of the cavities as outlined is similar in 
 most respects to the methods recommended and taught by Dr. 
 A. E. Peck, who deserves much credit for the interest he has 
 
 displayed along this line. Those who are familiar with his 
 system will note the points of difference as they occur. 
 
 PRODUCTION OF THE MATRIX 
 
 The conformation of the ])latinum foil to the cavity is a 
 step requiring skill, patience and experience. Two methods 
 are followed at the present time, both of which are reliable if 
 proper care is exercised. The first consists in burnishing the 
 foil directly into the cavity with pellets of cotton or spunk 
 
920 INLAYS 
 
 carried in the pliers aud by the use of suitable Ijiiriiishers of 
 ordinary and special shapes. 
 
 The other metliod consists in forming the matrix against 
 an impression of the cavity or a model derived from an im- 
 jtression, with a suitable swaging device. 
 
 BURNISHING THE MATRIX 
 
 The rubber dam should be applied in all cases and the 
 cavity dusted with soapstoue to prevent tearing the foil. 
 
 A piece of platinum foil, thoroughly annealed, should be 
 cut of sufficient size to extend beyond the cavity margins when 
 pressed into place. This is centered over the cavity and held 
 in position with the fingers, while a small piece of spunk car- 
 ried in a pair of ball-pointed pliers is pressed against the cen- 
 ter of the foil to force it against the floor of the cavity. 
 
 Special care should be taken to obviate the wrinkling 
 of the foil against the cavity walls, to prevent its tearing while 
 being forced to place, or its perforation by the pliers or burn- 
 ishers. Wherever a wrinkle or fold appears it represents 
 three thicknesses of foil at that point, and while the bulk of 
 material may be thinned down somewhat in burnishing, it 
 cannot be reduced to any great extent. The result is that 
 when the inlay is completed a very perceptible space exists 
 where the fold occurred, which must be filled with cement. This 
 is objectionable on account of the color of the cement and be- 
 cause of its ready dissolution under such conditions. 
 
 The foil, having been carefully forced to the floor of the 
 cavity, is held there by a burnisher resting on a pellet of 
 spimk. Another pellet is taken up with the pliers and forced 
 into the cavity, carefully adapting the foil to the entire floor 
 first, before making any attempt to adapt it to the walls. 
 
 A ligature or strip of thin tape passed through the inter- 
 proximate spaces and against the matrix will oftentimes assist 
 in holding it in place while securing adaptation of the foil to 
 the various surfaces. 
 
 The adaptation to the walls is secured by pressing a small 
 pellet into the cavity near the floor and drawing it outward, 
 producing pressure toward the wall at the same time. The 
 entire floor of the cavity should be covered with spunk, held 
 with some suitable instrument during the operation. 
 
 Some prefer to use various shapes of rubber points for 
 this i^urpose, and very good results are secured in this way, 
 but as the spunk and cotton are always conveniently at hand 
 and pellets of any size can be formed quickly, these materials 
 are perhaps more commonly used than the rubber points. 
 
INLAYS 
 
 & 
 
 BALL-POINTED PLIERS FOR 
 
 APPLYING COTTON OR SPUNK 
 
 TO THE MATRIX 
 
 CARVING TOOL WITH COR- 
 RUGATED SIIA^^<. WHICH. 
 BV DRAWING ACROSS THE 
 TWEEZERS, VIBRATES AND 
 CONDENSES THE PORCELAIN 
 BODY 
 
 SJIALL SPATULA FOR MIX- 
 ING AND APPLYING THE 
 PORCELAIN TO THE MATRIX 
 
922 INLAYS 
 
 Buruishers of various forms, as tlie Thompson or Reeves 
 selections, may be used to advantage in securing adaptation 
 of the foil to the cavity walls and angles. 
 
 When fairly close general adaptation has been secured 
 tlie entire matrix is filled with spunk and pressure applied with 
 an instrument which will force the foil against the floor and 
 walls of the cavity at the same time. 
 
 The adaptation of the foil to the outer surfaces of the 
 tooth can be accomplished with spunk in the manner outlined, 
 drawing the pellet from the cavo-surface angle outward in all 
 direction until the foil lies flat upon the tooth surface. 
 
 The adaptation of the foil to the cavo-surface angle yet 
 remains to be done. This is one of the most important steps 
 in the whole operation. Securing perfect adaptation at this 
 point, with sharp angle definition, without folds in the foil, in- 
 sures practically perfect margins to the inlay. 
 
 The entire interior of the matrix should now be filled 
 with spunk and a piece larger than the cavity applied over all. 
 Pressure with a suitably shaped instrument slightly larger 
 than the cavity or with the finger, when this is possible, is 
 made against the spunk to force the matrix into all parts of 
 the cavit.y, against the cavity margins and the tooth surfaces 
 at the same time. 
 
 REMOVAL OF THE MATRIX 
 
 The spunk should then be removed and the matrix lifted 
 out. the surplus, if excessive, trimmed away and the foil thor- 
 oughly annealed and returned to tlie cavity for adaptation. 
 
 NECESSITY FOR FINAL ANNEALING 
 
 When metal plate is swaged, hammered or burnished the 
 relation of the molecules to each other is changed. This is 
 especially true of platinum foil used in matrix construction. 
 By repeatedly annealing and returning the matrix to the cav- 
 ity for final adaptation the foil can he made to lie "dead flat" 
 without change under high temperature. 
 
 SELECTION, APPLICATION AND FUSING OF THE 
 PORCELAIN 
 
 SELECTION OF SHADE 
 
 As porcelain powders are now supplied by the manufac- 
 turers they appear to be white, or but slightly tinted with 
 yellow or brown. No definite idea can be formed from looking 
 at the powder, or when made into a paste with water, as to 
 
INLAYS 923 
 
 what its tint will be when fused, as its true color is only de- 
 veloped by vitrifying. 
 
 To select a suitable porcelain for an inlay to match the 
 shade of a natural tooth small sticks of fused porcelain, each 
 made of a particular single shade, are supplied by the manu- 
 facturers. These sticks are made from, and numbered to cor- 
 respond with, the numbers of the powders supplied. In de- 
 termining the shade of porcelain to use in a given case, one 
 of these fused j^ieces is placed alongside of the tooth for 
 which the inlay is to be constructed and the similarity or dif- 
 ference in shade noted. This process is repeated until a satis- 
 factory shade has been found to match the tooth, or some 
 portion of it, against which the inlay is to rest. 
 
 It is fro(inently necessary to select two, sometimes three, 
 shades of porcelain for a proximo-incisal inlay when the tooth 
 presents marked variation in shade from gingival to incisal 
 areas. In ai)plying these vari-shaded porcelains to the matrix 
 they are not blended on the slab but are applied in the matrix 
 in the particular location where indicated. By drawing a 
 rough instrument across the pliers with which the matrix is 
 held the vibration so caused will blend the several colors at 
 their margins sufficiently to obviate a sharp line of demarka- 
 tion of tints. Usually after fusing the primary colors selected 
 a neutral shade of porcelain is applied and fused to complete 
 the contour and still further soften and blend the more pro- 
 nounced underlying tints. 
 
 MIXING THE PORCELAIN 
 
 The proper colors having been selected corresponding 
 l^owders are placed separately on a clean glass slab and with 
 a drop tube, sufficient distilled water is added to form each 
 into a mass of medium plasticity. The powder and water 
 should be well spatulated to thoroughly incorporate the sev- 
 eral ingredients in each shade. To prevent the heavier from 
 settling and forcing the lighter particles to the top of the 
 mass when well mixed, a linen napkin, or piece of bibulous 
 paper, should be pressed against the paste to take up the ex- 
 cess moisture. 
 
 APPLICATION OF THE PORCELAIN TO THE MATRIX 
 
 The matrix is grasped with a pair of K tweezers at some 
 point on the surplus margin in such manner as not to distort 
 it, yet with sufficient hold to sustain not only the matrix but 
 the porcelain to be added as well. A small amount of the 
 
924 INLAYS 
 
 paste, usuallv of a yellowish liii,i;;e. 1o serve as a foundation 
 body, is transferred from the shib to the matrix, api)lied to 
 the hitter without ijressure and the serrated surface of the 
 earving tool drawn over the tweezer beaks to vibrate the 
 porcelain in position. More is added in like manner until the 
 matrix is from one-half to two-thirds full, leaving the labial 
 portion deficient in order to add the proper colors later. The 
 
 partially filled matrix is now carefully passed above a Bnnsen 
 flame, or placed near the entrance of the furnace, to gradually 
 expel the moisture, after which it is placed on a muffle tray, 
 introduced and fused. 
 
 When removed, the various tints are applied in their re- 
 spective locations, this time filling the matrix to its margins 
 and vibrating as before so as to blend the sevei-al colors. 
 Any excess paste which overflows is carefully brushed off with 
 a dampened sable brush, thus avoiding thin overhanging 
 margins in the finished inlay. 
 
 Should the colors be too pronounced when fused, a thin 
 layer of gray or neutral tint may be overlaid and fused, as 
 before suggested, to tone them down. 
 
 Usually in simple cavities two applications of the body 
 and two fusings will be sufficient to produce a satisfactory 
 inlay. In complicated cases, however, three, or possibly 
 four, fusings may be required. It must be kept in mind, how- 
 ever, that each additional fusing not only produces contrac- 
 tion in the porcelain last added, but in the entire mass, thus 
 increasing the danger of warpage and a misfit. The fewer 
 times required for fusing and finishing a piece of porcelain 
 of any class, the better the quality of the material and the less 
 contraction and warpage will occur. 
 
 When slightly overfused, or when the vitrifying process 
 is continued too long, both the texture of the porcelain and its 
 color is impaired. Long continued low temperature, just suf- 
 ficient to vitrify porcelain, will produce better results as to 
 texture and color than when the process is carried on rapidly 
 and at a higher temperature. 
 
FURNACES FOR FUSING PORCELAIN 
 
 Various tj'pes of furnaces are used for fusing or "bak- 
 ing" porcelain, as this process is usually termed. The most 
 common method of developing the required temperature is 
 
 MUFFLE TKAY TONGS, FOR INTRODUCTION AND 
 
 REMOVAL, OF THE TRAY DURING THE STEPS 
 
 OP FUSION OF THE PORCELAIN 
 
 by passing an electric current through a fine platinum wire 
 imbedded to a slight depth within the fine clay muffle walls. 
 The resistance of the wire to the passage of the current de- 
 
926 INLAYS 
 
 velops an intense heat within tlie wire when fine, which in tiirn 
 is transmitted to the fire-clay lining of the furnace. 
 
 The amount of heat capable of being developed within a 
 mufJie is dependent upon the length and sectional area of the 
 wire, the depth it is imbedded in the fire-clay lining and the 
 intensity of the current which flows through it. Furnaces of 
 tills type are called "electric furnaces," and as a rule are 
 capable of developing a considerably higher temperature than 
 that required to fuse the common porcelain bodies. In most 
 cases a rheostat is employed to control the flow of the cur- 
 rent and keep the temperature within working range. In some 
 cases furnaces are fitted with pyrometers for indicating the 
 point of fusion of the porcelain. 
 
 To Dr. L. E. Custer belongs the credit of having first con- 
 structed a practical electric furnace suitable for fusing porce- 
 lain (1894). At the pi-esent time a number of excellent electric 
 furnaces are procurable. Gas, gasoline, oil and coke furnaces 
 are also manufactured which, from a practical standpoint, are 
 applicable to porcelain work. The electric furnace is prefer- 
 able in dental opei"ations because of its compactness, ease of 
 manipulation and freedom from gases which always accom- 
 pany the use of the fuels mentioned. 
 
 The temperature usually required to fuse the various 
 inlay, crown and bridge, porcelain bodies is given under the 
 heading of "High and Low Fusing Porcelain Bodies." 
 
 FUSING THE PORCELAIN 
 
 The moisture having been expelled from the porcelain, 
 the matrix is placed upon the muffle slab and introduced in 
 the furnace. Care should be taken to see that the body of the 
 matrix rests upon the fire-clay slab, or that a sufficient number 
 of marginal points touch to afford ample support and prevent 
 warpage. When the form of the matrix is complicated some 
 granular silex should be placed upon the slab and the matrix 
 settled carefully down upon it. 
 
 When a furnace having no pyrometer is used, a pellet of 
 pure gold is usually placed alongside of the matrix to serve 
 as a guide in determining the point of vitrification. A little 
 device made of soapstone or fire clay, having a small imder- 
 cut groove with slightly enlarged extremities, is cut in the 
 concave face of the block. In the upper extremity of the 
 groove a pellet of gold is placed and when fusion of the latter 
 occurs it disappears by falling to the lower extremity, much 
 as the sand in an hour glass flows from upper to lower com- 
 
INLAYS 927 
 
 partment. When the temperature is reduced and the gold solid- 
 ifies, by inverting the block the gold is again at the upper ex- 
 tremity of the groove and in position for another test. 
 
 The matrix and test block being in position, the current 
 is turned on by moving the rheostat arm from its initial po- 
 sition of rest to the first contact, where it should be allowed 
 to remain for five minutes, when it can be moved to the second 
 contact. Tlie arm should remain on each contact about the 
 same length of time before moving to the next in order to re- 
 duce to the minimum ihe strain on both platinum wire and 
 fire-clay lining, and also so that the porcelain may not be 
 subjected to sudden increase of temperature. In most fur- 
 naces the rheostats are supplied with five or six contacts. 
 When the arm is moved at five-minute intervals the iDorcelain 
 will usually bo near the point of fusion by tlie time the arm is 
 transferred to the last contact. The gold must be closely 
 watched and the instant it fuses the time should be noted. 
 
 By iireviously determined tests, the difference in time 
 between the melting of the gold and the biscuiting, as well as 
 glazing of the porcelain, is known, and this time should be 
 allowed according to the degree of fusion required. This 
 period varies usually from forty seconds to six or seven 
 minutes, depending on the intensity of the current, the class 
 of porcelain used and the type of furnace employed. 
 
 The first bake should be carried to the "biscuit" stage, 
 i.e., where vitrification has occurred but the granular surface 
 has not disappeared. 
 
 The rheostat arm is now returned to the second contact 
 to conserve time, and heat as well, by not allowing the furnace 
 to become cold, the muffle opened and the slab partially with- 
 drawn, allowed to cool somewhat and, finally, the matrix is 
 picked up with tlie K tweezers and the result of the first liake 
 noted. If free from porosity, of good color and not overfused 
 the second application of body is made as at first. When an 
 effort is made to complete the inlay in two liakes the second 
 application of porcelain should be very carefully executed, 
 developing very slightly fuller contour than required to com- 
 pensate for final contraction that always occurs on fusing. 
 
 When two or more colors are required to match the tooth 
 shade they are applied at this time and blended as before de- 
 scribed. 
 
 SECOND BAKING 
 
 The contour of the second application of body having 
 been completed, surplus removed from the margins and the 
 
928 INLAYS 
 
 moisture expelled, the matrix is again returned to the furnace. 
 The temperature is gradually raised as before until the sur- 
 face of the inlay is glazed and perfectly free from granules, 
 the idea being to give it such a surface as will not require the 
 application of discs or polishing powders. Porcelain inlays 
 baked under ordinary conditions are liable to be slightly 
 porous under the glazed surface, and these porous sjjaces are 
 frequently disclosed on grinding. Since reglazing does not 
 always remove the ])its. and if more is added to correct the 
 defects the additional fusion will induce further dimensional 
 changes in the inlay itself, it is best to avoid grinding and 
 polishing if possible to do so. 
 
 DELETERIOUS EFFECT OF OVERFUSING THE PORCELAIN 
 
 Special care should be taken to not overfuse the jiorce- 
 lain. Some of tlie defects arising from this mishap are bleach- 
 ing of the porcelain, friability, undue contraction and warp- 
 age and the development of porosity — sometimes to such an 
 extent as to render the inlay useless. 
 
 THE SHADOW PROBLEM 
 
 Comparatively little difficulty is encountered in selecting 
 porcelain of suitable translucency and color, which when fused 
 to proper form and introduced in the cavity without cementa- 
 tion will harmonize with tooth structure. 
 
 The discouraging feature connected with porcelain inlay 
 work, however, is in the variation in shade observed between 
 the natural teeth and inlay when the latter is finished and 
 set with cement. All varieties of cement used in the setting 
 of inlays are opaque. Light will not readily pass through 
 even thin, attenuated layers of this material. Therefore, un- 
 less the light which falls upon a tooth filled with a cemented 
 inlay is directly parallel with the exposed cavity walls a 
 shadow will be cast upon either tooth or the inlay, de]:)ending 
 upon which is nearest the source of light. 
 
 For example, in a distal cavity in a central incisor involv- 
 ing the angle, when the light falls upon the tooth first — the 
 direction of the rays slanting toward the inlay — a shadow 
 will be observed in the latter next to the line of junction, 
 owing to the cutting off of the light by the film of interposed 
 cement. When the light comes from the opposite direction, 
 striking the inlay first, the shadow will appear in the tooth, 
 but to a less extent because of a more or less general diiifasion 
 
of light in the greater l)ulk of tooth structure. lu the upper 
 teeth the overhang of the upper lip will often oast a shadow 
 in the gingival portion of an inlay, though the light may be 
 comparatively direct and well diffused. 
 
 To overcome, or at least reduce somewhat, the shadow 
 caused by indirect rays of light on an inlay, the labial walls of 
 cavities in the anterior teeth sliould be carried well to the 
 labial. The result of such cavity formation is to increase the 
 bulk of porcelain in the inlay and permit diffused light to 
 enter through the porcelain, thus reducing the depth of shadow 
 cast in inlays of limited labial exposure. The necessity for 
 this line of procedure is evident when the form and position 
 of an inlay, in proximal cavities, is considered. On one side 
 the inlay is limited by an ojiaque layer of cement, and on 
 the other by the proximating tooth, both of which tend to 
 restrict the uniform diffusion of light through the porcelain 
 except under the most favoralile circumstances. 
 
 Again, the color of the cement used in setting an inlay 
 may modify the shade of both the restoration and the tooth 
 next to, and for a short distance away from, the cavity walls, 
 lightening or darkening both according to the inherent tinge 
 of the cement. The remedy for tlie latter defect is overcome 
 to a great extent by using a cement which in color coincides 
 as nearly as possible with the shade of the natural tooth. 
 
 It has been suggested that the use of an opaque, low- 
 fusing porcelain of the Jenkins tyjie, in which color effects are 
 not so much dependent upon translucency as is the case in the 
 higher fusing porcelains, may be applied to overcome the 
 shadow effects noted. An inlay constructed of an opaque 
 porcelain having the essential, component colors of the tooth 
 brought to the labial surface is but slightly affected by light 
 striking it at various angles. The tooth in which it is placed, 
 however, is subjected to shadow variations to the same ex- 
 tent as wlicn higli fusing i)orce]ains are employed. 
 
 REMOVING THE MATRIX 
 
 Wlien the fusing of the inhiy is comi)leted the platinum 
 foil matrix must be removed. This may lie accomplished by 
 carefully grasping the surplus margin with the beaks of the 
 K tweezers and with a rotary movement roll the foil awav 
 from the margins of the porcelain, using special care to avoid 
 fracturing the latter. By wetting the inlay and matrix the 
 danger of fracture is greatly reduced. Usually the matrix 
 can be peeled off by grasping the surplus margin between 
 
930 INLAYS 
 
 the thumb nail and the ball of the index finger, the latter 
 acting as a resilient cushion on which to rotate the inlay. 
 In case the matrix tears, the adherent portion being devoid 
 of free margins, it must be chiseled, scraped or ground away, 
 as when allowed to remain it will interfere with the correct 
 seating of the inlay. 
 
 ETCHING THE CAVITY SURFACES OF THE INLAY 
 
 To break up the glaze and afford better retention of the 
 cement to the porcelain the cavity surfaces shoiild be etched 
 with hydrofluoric acid. The labial, and, in fact, all the exposed 
 surfaces of the inlay, must be protected from the action of the 
 acid by covering them with wax, the acid having no effect on 
 the latter material. The wax should be formed into a roll, 
 the end heated and the inlay pressed against it, being careful 
 to see that all surfaces on which the glaze is to be preserved 
 are perfectly covered. 
 
 With a pencil of wax, or a toothpick, the acid is applied 
 to the cavity surfaces, the application renewed once or twice 
 until the glaze is removed. The acid is then washed otf with 
 water and neutralized with a solution of bicarbonate of soda, 
 again washed and dried, when it is ready to set. 
 
 SETTING THE INLAY WITH CEMENT 
 
 The rubl)er dam should be applied to the tooth involved, 
 and the proximating teeth as well, and the cavity thoroughly 
 cleansed and dehydrated. 
 
 Cement of suitable shade mixed to medium consistency is 
 quickly applied to both inlay surfaces and cavity walls, the 
 inlay introduced and forced to place under gradual, 
 heavy, maintained pressure. In proximal cavities, this pres- 
 sure may he applied by forcing between the inlay and the 
 proximating tooth a ]ireviously-prepared wedge of orange 
 wood. Care should be taken to see that in forcing the wedge 
 in place the inlay is not displaced or unseated at any point. 
 
 The force capable of being exerted by a thinly-tapered 
 wedge is enormous, therefore caution must be exercised to 
 avoid undue force in its application. The mallet should never 
 be used in setting a porcelain inlaj', as the instantaneous blow 
 will scarcely produce flow in cement of medium consistency, 
 while the impact is liable to fracture the porcelain. 
 
 A piece of pine stick a little larger than a lead pencil, 
 with one end trimmed to suitable size and slightly concaved to 
 
fit snugly against the inlay, affords a most convenient means 
 of producing and maintaining pressure upon the restoration 
 until the excess cement has heen expelled and crystallization 
 has set in. Pressure on the inlay should usually be main- 
 tained from five to eight minutes, dei)ending on the rapid 
 setting qualities of the cement used. 
 
 In setting inlays in proximal cavities, a strip of rubber 
 dam about six inches long and one-fourth inch wide can be 
 passed between the inlay and the proximating tooth, the two 
 ends of the strip placed together and the ruljber stretched 
 almost to its limit, in a direction at right angles to the long 
 axis of the tooth. The resilient rubber forces the inlay into 
 the cavity and condenses the cement in the joint line as 
 well. 
 
 When hardened, the excess cement is removed from the 
 joint and adjacent surfaces, the rubber dam removed, the parts 
 syringed with warm water, and the occlusion verified to see 
 that in setting it has not been modified by the cementing me- 
 dium. If so, it should be corrected by grinding and polishing 
 until clearance space is gained, to avoid fracture from stress 
 of oijposing teeth. 
 
 GOLD INLAYS 
 
 The production of gold inlays may be occomplished in 
 various ways. With one or two exceptions, all of the many 
 methods in vogue may be groiiped into two general classes, 
 viz., the matrix method and the casting process. A descrip- 
 tion of both methods will follow cavity preparation. 
 
 CAVITY PREPARATION FOR GOLD INLAYS 
 
 The general princij)les followed in cavity formation for 
 gold foil or amalgam fillings apply with equal force to those 
 designed for the reception of inlays of any class. Briefly 
 stated, these princi])les, as laid down in Black's Operative 
 Dentistry, are as follows : 
 
 First — Obtain the required outline form. 
 
 Second — Obtain the required resistance form. 
 
 Third — Olitain.the required retention form. 
 
 Fourth — Obtain the required convenience form. 
 
 Fifth — Remove any remaining carious dentin. 
 
 Sixth— Finish the enamel wall. 
 
 Seventh — Make the toilet of the cavity. 
 
OUTLINE FORM 
 
 To secure the ooncct outline i'oi-ui involves the breaking 
 down of unsound overhiingiiig enamel walls, the removal of 
 practically all undercuts, the opening up of tissures when re- 
 quired, extension for prevention of all margins to immune 
 areas, and further extension of margins, if necessary, for 
 convenience of introduction and removal, without distortion, 
 of tlie wax model, or the I'dil matrix. 
 
 RESISTANCE FORM 
 
 Resistance form refers to the development of flat gingival 
 and jtulpal walls so as to withstand the stress of mastication, 
 thus obviating the tendency of the inlay to slide from or rotate 
 out of position under direct stress. 
 
 RETENTION FORM 
 
 In the preparation of a cavity for an inlay, the walls that 
 lie parallel with the line of direction of introduction of the 
 inlay should be formed at an angle of divergence of at least 
 one degree from perpendicular to the base, to obviate distor- 
 tion of the wax model in removing from the cavity. A greater 
 amount of divergence may be permissible in some cases, but 
 firmer and better retention follows with slight than with ex- 
 cessive divergence of the walls. 
 
 AVliile cement is employed for the retention of all classes 
 of inlays, this means alone will prove ineffectual against side 
 stresses and strains, particularly when the inlays are to be 
 utilized as abutments in biidgework. 
 
 Since, for obvious reasons, neither undercuts nor parallel 
 walls are permissible in the finished cavity, and since cement 
 is unreliable under heavy stress, some more positive means 
 of retention must be developed in practically all cases; this 
 may be accomplished in several ways, depending on the form 
 and location of the cavity. 
 
 In cavities involving an axial and an occlusal surface, 
 flat pidpal and gingival seats afford resistance to direct stress, 
 while a dovetail on the occlusal surface will prevent the tip- 
 ping stress. 
 
 When more than one axial surface is involved, and it is 
 deemed advisable to connect the cavities and thus construct 
 the inlay in one piece, the proper flare of the walls, to avoid 
 undercuts, should be constantly kept in view, so as to obviate 
 distortion of the wax model in removal from the cavity. 
 
INLAYS 933 
 
 Frequently when two or more axial surfaces are involved, 
 and the preparation of the cavity so as to permit the release 
 of the matrix would recjuire excessive sacrifice of good tooth 
 structure, an interlocking inlay constructed in two pieces can 
 be used to advantage. In such case one inlay having a dove- 
 tailed sjiace to receive the interlocking spur of the adjacent 
 piece or complement, is first cast and set, after which the wax 
 model of the other is formed and cast in like manner. By 
 this sectional method of construction, maximum resistance to 
 displacement of the inlay is gained, with the sacrifice of tlie 
 mininuun amount of tooth structure. 
 
 Oftentimes a slightly divergent groove can be formed in 
 the puli)al wall of the cavity in such manner as to release the 
 wax, the resulting shoulder of which on the inlay will effectu- 
 ally prevent it from tipping. 
 
 In obtaining retention form in cavities in the anterior 
 teeth, an incisal step with a notch in the lingual plate of en- 
 amel will etfectually counteract the tendency to displacement 
 from tipping stress. 
 
 Frequently, by stripping both labial and lingual plates 
 of enamel away so as to ex])oso the dentine, the latter may be 
 
 VARIOUS FORMS OF CAVITIES IN WHICH DENTIN SHODLDERS AND LINGUAL GROOVES 
 ARE DEVELOPED FOR RETENTION I"ITRI'0SE.S (ST. .TOHNI 
 
 used as a shoulder or hook, as it were, ovei' which the inlay 
 may be formed, and which will e1Te<-tually counteract the 
 tendency to tip. This form of cavity iirei)aration was recom- 
 
mended many years ago by Dr. I. ('. St. John of St. Paul, for 
 the reception of gold foil fillings. In eeitain eases it lias 
 proven very serviceable for inlays. 
 
 PIN ANCHORAGE FOR INLAYS 
 
 The application of pins for the retention of inlaw's, and 
 in obviating displacement under heavy stresses, has proven 
 of great value, particularly when the inlays are utilized as 
 abutments for bridges. 
 
 The form and location of the cavity and the condition of 
 the tooth, whether vital or pulpless, govern the size and length 
 of the pin. 
 
 The usual manner of developing a pin anchorage consists 
 in drilling a hole in the gingival or pulpal wall of the cavity 
 entirely within the dentine, in such location as not to inter- 
 fere with the pulp. The direction of the hole should corre- 
 spond with the line of removal, or at least not interfere with 
 the release of the wax model from the cavity. The diameter 
 of the hole should be but slightly larger than the pin to be 
 employed. Before introducing the wax, the pin, cut slightly 
 longer than the depth of the hole, is inserted and as the wax 
 presses to ])lace it surrounds the projecting end of the pin. 
 When the wax model is removed, the pin is removed with it 
 and caught in the investment and the gold cast around it. 
 
 CONVENIENCE FORM 
 
 Convenience form relates to such modifications in pre- 
 pared cavities as will admit of the most perfect as well as con- 
 venient placing of the filling. In gold foil operations this re- 
 fers to cutting away a wall or some area that interferes with 
 proper instrumentation or the development of slight under- 
 cuts in certain locations to aid in holding the filling material 
 until the general retention form can be made effective. 
 
 These points do not directly apply to inlay work, but 
 indirectly the shaping of the cavity so as to permit the ready 
 removal of the wax model and the introduction of the inlay 
 come under this head. When the general form of a cavity has 
 been developed, it is frequently found that some slight under- 
 cut within the dentine will seriously interfere with removal of 
 the wax model. The removal of the undercut by reshaping 
 the cavity may result in weakening an otherwise firm cavity 
 wall when by carefully filling the depression with cement, the 
 difficulty may be overcome. As a general rule, however, the 
 
best plan is to eliminate all nndercuts in the development of 
 the ontline form, and not depend upon cement for such pur- 
 pose. 
 
 REMOVAL OF ANY REMAINING CARIOUS DENTINE 
 
 It is just as important, in cavity preparation for inlays 
 as for other classes of fillings, that all decayed dentine be 
 removed to obviate recurrent caries. 
 
 Some prefer to leave a layer of leathery, decayed dentine 
 in the pulpal or axial walls of deep cavities, under the mis- 
 taken idea that tlie transmission of thermal changes will be 
 impeded and the vitality of the pulp be conserved. 
 
 This is, in nearly every instance, an incorrect procedure, 
 for in cavities which encroach so closely on the pulp as to 
 need a protection of this character, the varjnng thermal 
 changes transmitted by a large gold inlay will very soon set 
 up hyperemia conditions, and the pulp will die. 
 
 FINISH OF THE ENAMEL WALLS 
 
 In gold inlay as well as in gold foil operations, the cavo- 
 surface angles should be beveled for the protection of the 
 exposed enamel rods. This is carried out as in general opera- 
 tive jirocedures by carefully planing outer cavity margins 
 with sharp chisels and gingival margin trimmers. 
 
 The method of using stones on the margin and in smooth- 
 ing up the walls of cavities is bad practice and to be. deplored. 
 The method cannot be made effective in, nor is it universally 
 applicable to, all classes of cavities, and where applicable the 
 tendency is to weaken frail walls and obliterate definite re- 
 tention surfaces. The only possible advantage resulting from 
 this method is in reducing to a slight degree the discomfort 
 to the patient, in those cases where the tooth structure is sen- 
 sitive to the application of the bur. 
 
 TOILET OF THE CAVITY 
 
 The removal of all chips and debris, not only from the 
 cavity but from the mouth as well, is important and can best 
 be accomplished by use of the water syringe and wiping the 
 cavity thoroughly with pellets of cotton before forming the 
 wax model. 
 
 In forming the wax model, as will be seen later, a lu))ri- 
 cant is used to facilitate the ready application and adaptation 
 of the wax to all cavity surfaces. This lubricant, whatever its 
 class, should be thorouglily removed, the cavity dried and 
 
936 INLAYS 
 
 packed willi a .n'ooil (|iialit>' of .i^ntta jXTclia until tlic time 
 of setting- of tlic inlay. 
 
 SOME SPECIAL METHODS OF CAVITY PREPARATIONS 
 
 I'rnxiinal caNirics in the anterior teetli, in which gold 
 inlays are to b(^ placed, require special attention. In case a 
 tooth proximates tlie one in which the cavity occurs and the 
 angle is involved, the cavity must be formed so as to release 
 the wax model usually lingually or incisally. 
 
 Provision must he made to prevent the inlay when set, 
 from becoming dislodged under ti]:)ping stress. Several meth- 
 ods are resorted to for accomplishing this object. These usu- 
 ally consist of a dovetail or some form of step in the lingual 
 surface of the tooth involved, some of wliich will be illustrated. 
 
 TUO VIEWS OF TOOTH IMlErAREO WITH AN INCISAL HOOK OF DENTIN 
 (ST. JOHN) 
 
 The first of these, the St. John method of cavity prepara- 
 tion, jireviously alluded to, consists in stripping off the plates 
 of enamel so as to expose sufficient solid dentine to form a 
 hook for incisal anchorage. A gingival seat takes up the in- 
 cisal stress. 
 
 A method of forming a dovetailed space in the lingual 
 surface of the tootli as near the incisal edge as possible, to 
 provide for tipping as well as outward displacement. 
 
 A method of forming a step along the linguo-incisal edge, 
 involving principally the lingual ])late of enamel. The bottom 
 of the steji may be grooved slightly, and near its farthest 
 extremity from the cavity a small hole is drilled in tlie dentine 
 to receive an iridio-platinum post. The line of junction of 
 the inlay with the labial ]ilate of enamel, occurring on the in- 
 
937 
 
 eisal edge, invites displaeenient of the inlay as well as frac- 
 ture of the labial plate of enamel under stress. 
 
 A method of step preparation, similar to the above, but 
 with the labial plate rediu>ed sliojitly so that tlie inlay will 
 
 PR0X1M.VL VIEW OF DISTAL 
 
 CAVITY IN CUSPID TOOTH. 
 
 SHO«nNG I.IXGUAL STEP 
 
 LINOUAL VIEW. SHOWING 
 DOVETAIL, OP STEP 
 
 LINGDAL VIEW OP 
 BOTH, SHOWING IN 
 CISAI, STEP CAVITY 
 WITH PIN IN STEP 
 
 UISTO-I.IXOUAL VIEW 
 
 OF PRECEDING 
 
 TOOTH 
 
 LABIAL VIEW OP 
 
 TOOTH WITH INI.AY 
 
 JX POSITION 
 
 I-INGUAI, VIEW OF 
 INCISAL STEP CAV- 
 I T V , S H O W I N G 
 GROOVE RETENTION 
 
 LABIAL VIEW OP 
 
 TOOTH WITH INI.AY' 
 
 IN POSITION 
 
 LABIAL. DISTAL ANt) INCISAL VIEW OF 
 
 CAVITY IN CUSPID PREPARKO WITH 
 
 DO\ETAILED ANCHORAGE COMBINED WITH 
 
 PIN. 
 
 form a tip of gold over the two plates of enamel. This form 
 of cavity preparatipu is preferal)le to the preceding. 
 
 A method ef forming a step similar to the above, but in- 
 stead of the pin anchorage, a drop of the step gingivally, in 
 the lingual plate of enamel and the dentine as well, furnishes 
 the resistance to tipping stress. 
 
A method of auelioriug a large contour filling in a pulp- 
 less tooth by means of a pin extending into the root canal. 
 
 A method of forming in the labial or buccal surface of 
 the wax model, a cavity with undercuts, in which, after the 
 inlay is set, a synthetic cement filling is placed to avoid the 
 display of gold. 
 
 I'ROXIMAI. VIEW OF LINGUAL VIEW O 
 TOOTH WITH MESIO- THE PRECEDING 
 
 INl'lSO-DISTAL CAV- 
 ITY PKEPiVBED 
 
 LINGUAL VIEW OF 
 
 TOOTH WITH FILLING 
 
 IN POSITION 
 
 LABIAL VIEW OF 
 
 TOOTH WITH FILLING 
 
 IN POSITION 
 
 A method of preparation for a mesio-inciso-distal cavity 
 in an anterior tooth, formed with a grooved step, cut princi- 
 pally at the expense of the lingual plate of enamel. The in- 
 cisal edge of the tooth is rediiced so that it may be tipped with 
 gold for its protection. 
 
 THBEE VIEWS OF THE WAX MODEL FOR A MESIO-INCISO-DISTAL INLA\' 
 
 In casting fillings of this type, a piece of iridio-platinum 
 wire should be bent so that it will not interfere with the mar- 
 gins of the inlay. This is inserted in, and as close to the 
 cervical terminal of the wax model as possible to prevent 
 change of relation due to contraction. 
 
INLAYS 939 
 
 A straight piece with square ends will serve this purpose 
 equally as well, if inserted between the axial surfaces of the 
 mesial and distal sections. 
 
 A mesio-oeclusal, grooved cavity in an upper molar. The 
 pulpal wall is grooved to provide against tipping stress. This 
 
 THEEE \IE\VS OF TTIE CO^!^LETED IXLAY 
 
 form of cavity preparation is frequently employed when the 
 inlay is to serve as a bridge abutment. 
 
 A loose pin anchorage for an inlay to lie used as an abut- 
 ment for a bridge. A square iridio-platinum bar, from 32 to 
 
 SECTIONAL VIE\V OF A MOLAB. 
 
 SHOWING GROOVED STEP FOB 
 
 (ItlARDING AGAINST TIPI'ING 
 
 STRESS 
 
 SIMPLE MESIO-Ot'CH'SAL. 
 
 DOVETAIL STEP CA\ITy 
 
 IN MOLAR 
 
 14 gauge, is imiformly tapered on the four sides, extending 
 back about three-fourths of an inch from one end, and reduced 
 sufficiently to enter the enlarged root canal the required depth 
 for anchorage purposes. Around the tapered portion and in- 
 
volviiii;- tlic ai'cn wliicli will rest within 1lic inlay, is wrapped 
 a band of 1 100(1 platiinnn foil wliieli slionid lap on itself about 
 one-half tnin of the wire. The taper pin is withdrawn and 
 the square tube of foil is tacked with a little pure gold solder 
 to prevent it from opening. It is returned to the pin and re- 
 ada])ted to coi-reet any change that may ha\(! occurred in 
 soldei'ing. 
 
 The wax model is carved to proper contour, and the pin 
 without the sleeve is warmed, passed throTigh the wax and to 
 position in the root canal and withdrawn. It is now heated to 
 burn off the adherent wax and oiled to ])re\'ent the sleeve be- 
 
 coming fast. The sleeve is again returned to position, pin 
 warmed and the two are passed through the opening in the in- 
 lay and into the canal to projier position. A small heated in- 
 strument is passed around the sides of the tube so as to cause 
 the wax to adhere to it, but not to the pin. The latter is now 
 withdrawn, wdiile the tube remains in the wax. The tube should 
 be long enough to project beyond the upper and lower sur- 
 faces of the wax, so as to become inclosed in the investment. 
 On removal of the wax model, the tube is first filled with in- 
 vestment, after which the model is invested in the usual man- 
 ner. When cast, the projecting ends of the tube are reduced 
 to the level of the inlay surfaces, the opening cleared for the 
 
reception of the i^in, the inlay finished and set and while the 
 cement is still soft the pin is forced to place. Care should be 
 taken to avoid the excessive use of cement which might be 
 forced into the canal from which it would bo difficult to expel 
 it. 
 
 This attacliment is intended to be used in conjunction with 
 bridge work, and as the setting of the bridge is of itself a 
 particular operation, the following plati could be adopted : 
 
 Fill the root canal, or the outer portion of it, with tem- 
 porary stopping, being careful not to encroach on the base 
 of the cavity. Set the bridge in the usual manner, and when 
 the cement has hardened, with a small, rough, heated instru- 
 ment remove the temporary stopping, and free the canal from 
 all debris, after which the pin may be set independently and 
 the ijrojecting end reduced with stones to the level of the in- 
 lay. This method was suggested anci has been successfully 
 used ])y Dr. A. L. Le Gro of Detroit, Mich., who has demon- 
 strated it at various times within the past few years. 
 
 A metliod of utilizing short pins for anchorage purposes, 
 placed in various locations in cavities prepared in vital teeth, 
 has been extensively applied by Dr. M. L. Ward of Ann 
 Arbor. Mich. In this system he makes use of one or more 
 pins or a two-point staple, the bent ])ortion of which is en- 
 closed in the inlay. 
 
 The main points to keep in mind in api>lying this system 
 of anchorage to inlays are to arrange the pins parallel with 
 the line of direction in which the wax model is withdrawn 
 from the cavity, and in drilling the holes to avoid encroaching 
 on the pulp. 
 
 A method of shoulder anchorage, applicable to axio-occlu- 
 sal cavities in vital bicuspid and molar teeth.. In this system 
 a groove is cut at the extremity of the steyi farthest from the 
 axial wall involved and of sufficient deptii to prevent radial 
 rnovement of the inlay outward. Usually from one to one and 
 one-half millimeters in width and depth will be ample dimen- 
 sions for the groove. 
 
 A simple method of dovetailed anchorage, applicable to 
 axio-occlusal cavi-ties in vital teeth. This cavity preparation 
 ditifers but little from that followed in gold foil operations, 
 except that all axial walls must flare slightly from gingival 
 and ])ul]ial surfaces, from one to two degrees. 
 
942 INLAYS 
 
 THE MATRIX METHOD OF INLAY PRODUCTION 
 
 The preparation of cavities intended for the reception of 
 inlays formed in a matrix is essentially the same as for in- 
 lays of any class, viz., the development of flat seats, and 
 slightly flaring walls, to permit release of tlie matrix without 
 distortion. The subject of cavity preparation will lie found 
 on page 931. 
 
 The matrix of gold or platinum may l)e formed in two 
 ways, by the dirrrf, or by the indirect method. 
 
 DIRECT METHOD OF PRODUCING A MATRIX 
 
 The direct method consists in adapting a piece of 24- 
 carat gold, or platinum foil, to and against the cavity sur- 
 faces of the natural tooth. The steps are as follows : 
 
 Cut a piece of foil somewhat larger than the cavity and 
 from 1 1000 to 1-500 of an inch thick, the thicker foils, while 
 being more difficult to adapt, are less liable to distort in sub- 
 sequent steps. 
 
 Anneal the piece, center it over the cavity, and with spunk 
 or pellets of cotton, in the ball-pointed pliers, press it against 
 the cavit\' floor and gradually adapt it to the cavity walls and 
 margins. 
 
 Since the steps are practically^ the same as in forming a 
 platinum matrix for a porcelain inlay further details may be 
 found on page 920. 
 
 When general adaptation of the foil to the cavity surfaces 
 has been secured, the peripheral excess is trimmed away, a 
 narrow margin, however, being left to outline the cavity mar- 
 gins and prevent the gold, in fusing, from being drawn out- 
 side to the cavity surfaces of the matrix. 
 
 Finally, the matrix should be annealed and readapted to 
 the cavity with spunk or cotton, applied under heavy pressure, 
 to correct warpage. 
 
 In simple cases the matrix is carefully removed, laid on 
 the solder block, some small squares of plate or pellets of pure 
 gold, previously spheroided and fluxed, placed in the interior, 
 and high-grade solder fused iiitd the matrix and around 
 them. 
 
 During the fusing of the solder the pure gold pellets or 
 pieces are not fused, consequently there will be less contrac- 
 tion and less danger of warpage of the matrix than when 
 solder alone is used. 
 
 Sufficient gold is added and fused to develop desired con- 
 
tour, the inlay pickled in acid, washed and returned to the 
 cavity for final reduction with stones and discs. 
 
 It is then cemented in position and the final polish applied 
 as vvith a gold foil filling. 
 
 VARIATION IN METHOD 
 
 In compound cavities, it is frequently advisable to force 
 slightly softened wax in the matrix while in the cavity, being 
 particularly careful to adapt it to the margins. 
 
 The matrix is then removed and its cavity surfaces im- 
 bedded in some good investment material. When hardened, 
 the wax is removed, the matrix fluxed, case heated, and solder 
 applied as above described. 
 
 FORMING THE MATRIX BY THE INDIRECT METHOD 
 
 An impression of the tooth is secured in modeling com- 
 pound. One of the cup pattern trays, suggested by Dr. Eoach, 
 may be used or one can be improvised from thin aluminum 
 plate by the method described by Dr. Van Woert. (Items of 
 Interest, 1913.) 
 
 The impression is dusted witii talcum powder and the 
 surplus carefully brushed from the deeper portions. This is 
 to serve as a separating medium. 
 
 Modelite or a good quality of cement is mixed to medium 
 thick consistency, applied and forced into every joortion of the 
 impression, building it up in sufficient bulk to withstand the 
 stress of matrix adaptation, without fracturing. 
 
 When the cement has hardened, the modeling compound 
 is removed, and the cement tooth partially imbedded in model- 
 ing compound for support, or it may be set in a ring of the 
 swaging device. 
 
 In either case, the cement reproduction of the tooth should 
 be so placed that its axial walls will be supported to resist side 
 stress. Most of the force of matrix adaptation should be ap- 
 plied vertically, downward. 
 
 The matrix may be adapted, either by burnishing or 
 swaging, or by both methods combined. 
 
 When possible to do so it is advisable to test the adapta- 
 tion of matrix -to tooth cavity before contouring with gold. 
 
 When the matrix method is carried out accurately, com- 
 paratively perfect adaptation of an inlay to tooth and cavity 
 surfaces can be secured. 
 
CAST GOLD INLAYS 
 GENERAL REMARKS 
 
 To be reasonably siiecesst'iil iu the easting of inlays and 
 of prosthetic restorations in general, it is necessary to know 
 something- of tlie physical properties of the materials em- 
 ployed. 
 
 Casting operations involve the nse of waxes, investments, 
 and the metal of whicli the restorations are to be made, usu- 
 ally gold. These materials, within certain limits, are subject 
 to the same law as are nearly all solid substances, viz., that 
 heat expands and cold contracts, the amount of dimensional 
 change being generally dependent on temperature varia- 
 tions. 
 
 In the various steps, from the formation of the wax model 
 to its reproduction in metal by casting, the materials under 
 consideration are subjected to widely varying temperature 
 changes. These changes, as the work is carried forward, tend 
 to produce errors, by increasing or decreasing the size of the 
 model, the form of the investment, and, finally, reduction in 
 size, or in warpage of the metal casting itself, which changes 
 are oftentimes sufficient to render it worthless. 
 
 AVhile no absolute line of procedure, for avoiding error in 
 the casting process has been determined, certain facts of im- 
 portance are known, wliich, if observed, will minimize the tend- 
 ency to error. 
 
 PHYSICAL PROPERTIES OF THE MATERIALS EMPLOYED 
 IN CASTING 
 
 With few exceptions, the physical law, as previously 
 stated, that heat expands and cold contracts, ajjplies to solids, 
 liquids, and gases alike. The standard of measurement of the 
 linear, superficial, or cubical change, occasioned by raising 
 the temperature of a given substance, is based on the increase 
 noted in elevating the temperature of that substance from 
 to 1° C. The amount of such increase is termed the co-effi- 
 cient of expansion. 
 
 Between and 100° C, the co-efficient of expansion in a 
 metal, an alloy, or any substance of standard character, is 
 comi^aratively constant for that or any like class of substances. 
 When metals are alloyed, or when the composition of sub- 
 stances is modified, their co-efficients of expansion change, 
 sometimes to a remarkable degree. The following four alloys 
 
INLAYS 945 
 
 of nickel and iron, although instances of the extreme type, 
 serve to illustrate this fact. 
 
 Mean co-efficient of expansion 
 Nickel. Iron. between O and 100 deg. C. 
 
 No. 1 28 72 .000015 
 
 No. 2 36 64 .0000015 (Known as "invar") 
 
 No. 3 .45 55 .0000088 
 
 No. 4 GO 40 .000012 
 
 Varying the proportion of nickel and iron only 8 per cent 
 reduces the co-efficient of expansion of the invar to one-tenth 
 that of the first alloy. Combining the same two metals in the 
 proportions as shown in the fourth alloy, results in increas- 
 ing the expansive index to within .OOOOOo that of the first. 
 
 EXPANSIVE AND CONTRACTILE FORCES 
 
 When metal is expanded by heat, a certain amount of 
 energy is develojjed which becomes apparent on restricting its 
 free movement. According to Joule's data, when a pound of 
 iron is raised in temperature from to 100° C, it expands one- 
 two-humlred-and-eightieth of its bulk. The energy or force 
 of this expansion is sufficient to raise seven tons one foot in 
 height. 
 
 A bar of iron 10 inches long will expand 1/200 of an inch 
 with a raise in temperature of 45° C. The force of this ex- 
 pansion is equivalent to 50 tons. 
 
 A bar of malleable iron, of one inch sectional area, is 
 stretched 1/10000 of its length by a weight of one ton. Raising- 
 its temperature about 9° C. will elongate it to the same 
 extent. 
 
 When bodies have been heated to a high temperature, the 
 force produced by their contraction in cooling is equivalent 
 to the force wliich is needed to compress them to the same 
 extent by mechanical means. (Ganot's Physics.) 
 
 The relation of these examples of expansive and con- 
 tractile forces to inlay work, particularly to investments, will 
 be brought out later. 
 
 PRINCIPAL SOURCES OF ERROR IN INLAY CONSTRUCTION 
 
 The three principal classes of materials used in inlaj' con- 
 struction, as previously stated, are waxes, refractory invest- 
 ments and gold of varying carats. In manipulative proced- 
 ures these materials are subjected to dimensional changes 
 which vary according to the composition of the substances 
 used, and the technical methods employed. The many varie- 
 ties of wax exhibit a wide range of difference in their hard- 
 
946 INLAYS 
 
 ness, adhesivoiioss, cohcsiveness, expansive tendenoy, liabilit.y 
 to warp, and general susceptibility to thermal changes. 
 
 Investment materials vary greatly in composition, density 
 and porosity. Some maintain their integrity at high tempera- 
 tures without crumbling, crushing, or flaking, while others are 
 more or less disintegrated. 
 
 Gold of varying carats and compositions show different 
 exjaansive indices, and more or less variation in fluidity, as a 
 general rule, when fused. The higher the carat of gold used, 
 the sharper will be the casting, while less contraction will 
 occur in cooling. There are, however, exceptions to this in 
 some of the more recent alloys of gold. 
 
 Two or more men using identically the same materials, fol- 
 lowing the same technic, and working under as nearly the 
 same conditions as possible, will not produce identical results. 
 Duplicate pieces produced by the same individual, even when 
 extreme care is taken to follow the same methods, vary more 
 or less. 
 
 This fact, together with variations in the physical prop- 
 erties of materials employed, render impossible the produc- 
 tion of perfect inlays. A near approach to good adaptation 
 and general requirements, however, may be secured by using 
 carefully selected materials, and by exercising care in tech- 
 nical details. 
 
 WAXES 
 
 The basis of most of the inlay waxes is beeswax. In its 
 natural condition beeswax is not siiitable for inlay models. It 
 is too soft and bends too easily to retain its form in handling. 
 Beeswax consists of three principal substances, first, Myricyl 
 palmitate, CauH„i CjoHsiOo; second, Cerotic acid, C^jHsiOo, and 
 Cerolein, a waxy organic compound. 
 
 Beeswax melts at 63° C. (145° F.), Sp. Gr. .960. Wlien 
 melted on a plaster slab it is gradually absorbed, and if pure 
 leaves no residue. On applying increased heat it is volatil- 
 ized. It is quite adhesive when pressed firmly against an 
 object. This is a detrimental quality, as it tends to stick to 
 cavity walls. Beeswax lacks cohesiveness and consequently 
 its molecules do not cling together firmly. For this reason it 
 is brittle, and in carving, thin margins tear away easily. 
 
 PARAFFIN 
 
 Paraffin is a natural, wax-like substance, usually com- 
 posed of two or more members of the paraffin series of hydro- 
 
INLAYS 947 
 
 carbons. Its formula varies soniewiiat, dppcndiug on its der- 
 ivation, but corresponds generally with the following: 
 C.jr.,s C..H„o a„H„.. It melts between li:'. to 149° F., depend- 
 ing on the source from which procured, and on cooling forms 
 a white, rather hard, compact crystalline mass. It is quite 
 cohesive, but not very adhesive in a cold state. 
 
 EFFECT OF COMBINING WAX AND PARAFFIN 
 
 By combining beeswax with iniraffin, frequently having 
 a very considerable excess of the latter, the product is less 
 adhesive, more cohesive, and somewhat harder than when 
 uncombined. Some of the resins are frequently added to the 
 foregoing combination, to give increased liardness. Such 
 ])rodncts sometimes fail to volatilize, leave a residue in the 
 matrix, and are usually detrimental. 
 
 ESSENTIAL REQUISITES OF A WAX 
 
 Briefly stated, the necessary qualities of an inlay wax are 
 as follows : 
 
 First, it must have a low coefficient of expansion. 
 
 Second, it should l)e strongly cohesive, but not percept- 
 ibly adhesive. 
 
 Third, when cold, it should break before bending. 
 
 Fourth, it should be hard enough at body temperature to 
 carve well. 
 
 Fifth, it should become plastic at a reasonably low point 
 above body temperature. 
 
 Sixth, it should be dark in color and translucent, so that 
 in carving, tooth surfaces may be seen through thin layers of 
 it. " 
 
 In practice, a wax should be selected, as previously stated, 
 which, on testing, leaves no residue. If so, it should be dis- 
 carded, as its use would result in rough and imperfect sur- 
 faces to the inlay. The next most important quality in a wax 
 is a low range of expansion. It must be borne in mind that 
 the wax is forced into the cavity in its most expanded condi- 
 tion The higher the temperatui'e required to render it plastic, 
 the greater its expansion, and, conseciuently, the more con- 
 traction will occur in cooling to room temperature. While in 
 this contracted state, the investment of the model is usually 
 accomplished. It is therefore smaller than when first adapted 
 to the cavity walls. "While, in the subsequent steps of cast- 
 ing, the investment and ring expand under heat, and i^ossibly 
 
948 INLAYS 
 
 the matrix itself may become sliglitly enlarged, such changes 
 are beyond control. They may correct, partially or wholly, 
 the error of contraction in the wax, or they may lead to still 
 greater error, through unequal expansion, since the crucible 
 portion of the ring is much hotter than the bottom, at the 
 moment of casting. 
 
 ELASTIC PROPERTIES OF WAX 
 
 When a roll of wax is rendered plastic by heat, bent in 
 the form of a ring, and chilled, the ends being unattached, it 
 will remain in that form so long as the temperature is not 
 raised. In bending, the molecules on the outer periphery of 
 the ring are elongated, while those along tlie inner y)eripliery 
 are compressed. 
 
 In most materials, and in wax as well, the tendency of 
 molecules, when stretched or distorted, is to return to norma! 
 
 n I A G R A M M A T I (' DRAWING 
 SHOWING MOLECULAR AB- 
 
 RANGEMENT OF WAX WHEN 
 MELTED ASn RIN IN BAR FORM. 
 DIAGRAM OF TOOTH WITH liAR 
 BEXT INTO A MESIO-OIVHiSO- 
 DISTAL CAVITY- NOTICE THE 
 BI.ONGATION OF THEORETIl^iL 
 MOLECrLE.S ON THE OUTER 
 PERIPHERY AND THE COM- 
 PRESSED CONDITION OF THOSE 
 IN THE INNER PERIPHEHY" 
 
 form and relation to each other, when the stress which dis- 
 torted them, or the force which holds them in abnormal form 
 and position, is removed. Chilling the wax hardens it, and 
 renders inert the tendency of the molecules to return to nor- 
 mal form. By subsequently raising the temperature of the 
 wax, the force which locks the molecules in their strained rela- 
 tion is partially overcome, and, to a limited extent, they re- 
 turn to their original form, causing the ends of the wax ring 
 to separate. The temperature at which the inherent tendency 
 of the molecules of wax to recover their form becomes per- 
 
INLAYS 949 
 
 ceptible varies according- to the comiiosition of the material. 
 It is evident that some waxes, hard enough to carve at body 
 temperature, change form on removal from the mouth, while 
 others apparently do not exhibit such tendency. Time, and 
 fluctuating temperature, without doubt, encourage warpage, 
 therefore, to avoid excessive dimensional change and warpage, 
 the wax model should be invested as soon as possible. 
 
 INVESTMENT MATERIALS 
 
 The refractory basis of most investment materials, used 
 for casting purposes, is pulverized silex, of varying degrees 
 of fineness, and in some cases graphite. Plaster of paris 
 serves as a binder, or cementing medium, and fills the voids 
 between the granules of silex. Various other substances are 
 added to control the time of setting, prevent contraction, and 
 impart smoothness and density to the mass when mixed. 
 
 EXPANSION OF INVESTMENT RING AND INVESTMENT 
 MATERIAL 
 
 The coefficient of expansion of l)rass of which most casting 
 rings are made is .000018, between and 100° C, that of quartz 
 between and 1000° C, .00000055. (Ganot's Physics.) The 
 expansion of the brass is therefore thirty-three times greater 
 at only one-tenth the temperature, than that of quartz. The 
 coefficient of expansion of graphite is .0000078 (Ganot's 
 Physics), or about 14 times greater than that of quartz, but 
 perce];)tibly less than brass. Its effect, when combined with 
 quartz in an investment, is to increase the coefficient of ex- 
 pansion. Some of the liest investments procurable contain a 
 considerable percentage of graphite incor])orated for this pur- 
 pose. The coefficient of expansion of the materials mentioned 
 is variable, according to composition, variety, etc. 
 
 Since the investment ring ex]iands on heating, the invest- 
 ment itself should also expand and follow the walls as closely 
 as possible, first, to counteract the internal force brought upon 
 the matrix walls in casting the gold under pressure, thus pre 
 venting the investment from cracking or Inilging outward in 
 thin places, and second, to prevent the investment dropping 
 from the ring in handling; third, to enlarge the mold slightly, 
 thus compensating to a slight extent for contraction of the 
 gold. Expansion of the investment, therefore, is a neces- 
 sary quality. 
 
 Some investment materials show a tendency to contract 
 toward several common centers when overheated. When this 
 
occurs, ci-ack'iiii;' of the investment follows and the si:eneral 
 surfaces of the matrix are warped. 
 
 Some investment materials are sul),)ect to varyin.i;' dimen- 
 sional changes on the apitlication of heat, depending on the 
 quantity of water used in mixing. Thin mixes, as a rule, show 
 a greater tendency to contract and warp than thick mixes of 
 the same material. Taggart's investment is an exception to 
 this rule, as it has a high coefficient of expansion when mixed 
 thin enough to l)e poured. 
 
 ESSENTIAL PROPERTIES OF AN INVESTMENT MATERIAL 
 
 'J'lie essential ])roi)erties of an inlay investment material, 
 briefly stated, are as follows: 
 
 First, it should not contract in setting, even when mixed 
 thin. 
 
 Second, it should be dense and free from perceiitible 
 porosity when set. 
 
 Third, it should be hard, resistant to stress, and show no 
 tendency to crack when heated to casting temperature. 
 
 Fourth, it should possess a high expansive index, and a 
 low co-efifieient of conductivity under heat. 
 
 Fifth, it should not be fused, by the molten gold, in cast- 
 ing the latter. 
 
 Since there is no cohesion whatever between the granules 
 of refractor^' materials themselves, a binder must be incor- 
 porated, which in practically all cases is plaster of Paris. As 
 has previously been shown, this material is a crystallized, 
 di-hydrate of calcium sulphate, which decomposes to a greater 
 or less extent at 190° C. The crystals do not immediately 
 crumble on being heated, but are greatly weakened, so that 
 the application of slight force is sufficient to disintegrate 
 them. That the matrix walls of overheated cases do not flake 
 away more readily than would at tirst api:)ear from the disin- 
 tegration of plaster is due to the mechanical interlocking of 
 the granules of the various materials of which the invest- 
 ment is composed, and which lie in more or less close contact. 
 Decomposition of the binder from overheating is largely re- 
 sponsible for the roughening and bulging outward of the 
 matrix walls under the ]3ressure of casting. 
 
 As an example, casts and investments composed of plaster 
 alone, although at first expanded with slight rise in tempera- 
 ture, when heated to high temperatures, contract, crack and 
 distort very quickly. Plaster, therefore, should not be used to 
 
excess in inlay investments or tlie qnality of tlie latter will be 
 impaired in proi)ortion to the excess of this material present. 
 By using but little more than an amount sufficient to till the 
 voids between the granules of refractory materials, contrac- 
 tion is, to a great extent, obviated and the tendencj^ to crack 
 and warp is greatly reduced. Roughly estimated, the propor- 
 tion of plaster to refractory materials ranges from 25 to -iO 
 per cent. 
 
 Further valuable discussion of this subject will be found 
 under the heading, "Refractory Materials," by Dr. Wein- 
 stein, page 1040. 
 
 DIMENSIONAL CHANGES IN GOLD, DUE TO TEMPERATURE 
 CHANGES 
 
 When gold changes from a fused to solid state and normal 
 temi)erature, its cubical contraction, according to Dr. W. A. 
 Price's tindings, is about 6.75 per cent of volume. 
 
 Linear, being one-third that of cubical contraction, is, 
 therefore, about 2.25 per cent. In an inlay one-fourth inch 
 wide, or long, the linear contraction of that surface would 
 show a deficiency of about .005 of an inch. 
 
 While heavy pressure, api)lied during and after injection 
 of the molten gold into the mold, might, by the compressive 
 force exerted, reduce to a slight extent the percentage of 
 contraction noted, such method is impracticable, because of the 
 comparative non-resistance of the investment materials to 
 heavy pressure. 
 
 Contraction of the gold, therefore, is a constant source of 
 error in the production of castings of exact dimensions. 
 
 COMPENSATING FOR ERRORS DUE TO CONTRACTION OF 
 GOLD 
 
 Various means have been suggested for minimizing the 
 errors arising from the contraction of gold in cooling, a few 
 of which will now be mentioned. 
 
 First, the use of an investment which will expand on heat- 
 ing, thus enlarging the matrix to a slight extent. This method, 
 however, is subject to error, for unless the investment is lani- 
 formly heated it will not be equally expanded, and as a result 
 the mold walls will be distorted. 
 
 Second, heating the wax model somewhat above body tem- 
 perature by investing in warm, instead of cold, investment, 
 thus expanding it slightly before the investing medium hard- 
 ens. Error may or may not occur when this method is fol- 
 
952 INLAYS 
 
 lowed; if the wax is under niolcciilar slraia, yet rigid at room 
 or body temperature, investing it in a warm medium may re- 
 lease the tension and result in warpage of the model before the 
 investment hardens. When not subjected to molecular tension, 
 expansion without distortion will occur, thus favorably in- 
 creasing the dimensions of the matrix. 
 
 Third, tlie use of sufficient gold to insure a considerably 
 larger residual button in the crucil)le than the bulk of gold in 
 the casting. Naturally, the casting, being smaller, and the 
 matrix walls in a less heated state than the crucible, the con- 
 tents of the mold will solidify first. When the sprue is of 
 sufficient size and its length not excessive, as contraction of 
 the gold within the matrix sets in, the pressure on the more 
 highly heated residual gold in the crucible forces it in and 
 feeds the contracting mass within the mold until it solidifies. 
 
 The necessity for the unequal balancing of the gold as 
 suggested is apparent for the following reasons: 
 
 To produce sharp castings it is necessary that the gold be 
 in a su]3erheated condition, considerably above its actual fus- 
 ing point. The contraction of superheated gold may be 
 divided into two stages, first, that which occurs in passing 
 from its highest heated, and most expanded condition to the 
 freezing state, and second, from the point of congealing to 
 normal temperature. 
 
 Now, if gold, in a superheated condition, be cast into 
 either a hot or cold matrix, and no provision is made for re- 
 plenishing the contracting, fluid mass, the casting will be de- 
 fective, and in case of inlays the margins will be rounded. 
 
 RESULT OF CONTRACTION OF GOLD IN INLAY ADAPTATION 
 
 The result of contraction of gold in inlay construction is 
 that; in a simple cavity, the inlay will fail to fill the cavity per- 
 fectly, a more or less open space showing around the margins, 
 while the axial surface usually sinks slightly below that of the 
 tooth. 
 
 Since, as has been previously shown, the contractile force 
 exerted by a casting, in cooling, is equivalent to the mechanical 
 force required to compress gold, of similar bulk, an equal 
 amount by mechanical means, it therefore follows that in 
 mesio-occluso-distal inlays the investment interposed between 
 the mesial and distal flanges of the inlay will be compressed 
 and distorted to a greater or less extent. 
 
 As a result of such contraction, the inlay frequently fails 
 to go to place. To seat it, the tooth may be reduced, the inner 
 
walls of the matrix enlarged or the oeelusal portion of the in- 
 lay stretched snffieieutly to permit its being driven to place. 
 
 Dr. Price suggests two means for overcoming the diffi- 
 culty; first to cast the inlay against a reproduction of the 
 tooth, develoi^ed in a special artificial stone, or to cast the in- 
 lay around a threaded iridio-platinuni liar, extended through 
 and beyond the occlusal body of the inlay, sufficiently to gain 
 a firm hold in the investment. 
 
 Still another method, suggested by a member of the pro- 
 fession in Wisconsin, whose name the writer cannot recall, 
 consists in drilling a hole through the occlusal portion of the 
 inlay, inserting a fine saw and cutting l)uccally and lingually 
 almost, but not quite, to the walls to weaken the gold, introduc- 
 ing the inlay and driving it to i)lace. As a result the gold is 
 stretched and the inlay lengtheneti. Care should be taken to 
 see that the gingival ends are not bent outward, or, if so, to 
 readjust them, after which wax is filled in the hole and saw 
 cut, the inlay invested and the opening filled with solder. 
 
 Since ordinary investments, used in casting, are unable 
 to resist the force of contraction of the gold, practically the 
 only means left is to select a material that expands perceptibly 
 during the heating and casting process. 
 
 TECHNIC OF CAST GOLD INLAY CONSTRUCTION 
 FORMING THE WAX MODEL 
 
 Tnlay waxes are prepared in stick form and are also sup- 
 plied in the form of cones and various irregular shapes suit- 
 
 ••Attll«t 
 
 VARIOUS FdRMS OF IN'l.AV. WAX JU.OI'KS 
 
 able for introduction into different classes of cavities, with- 
 out bending. - 
 
 These blocks and sticks are formed by melting the wax 
 and casting into molds. They are, therefore, free from mole- 
 cular tension. 
 
954 INLAYS 
 
 Select a wax form of approximately the sliape, Init larger 
 than is required to fill the cavity. 
 
 If the cavity is irregular as one of the mesio-occluso-dis- 
 tal class, a form should be carved, of the desired shape, from 
 a large block, or two forms may be joined by melting their 
 contact surfaces, and the reqiiired form carved from the 
 united pieces. 
 
 Soften by placing in hot water, the temperature of which 
 should range from US'" to 139° F., according to the variety 
 of wax used. 
 
 Price's wax becomes workable at 115° P., Peck's at 120° 
 F., Cleveland Dental at 127° F., S. S. Wliite at 128° F., Con- 
 solidated at 130° F., Goslee's at 135° F. and Taggart's and 
 Klewe's at 139° F. 
 
 The wax should be entirely immersed in the water, re- 
 maining there a sufficient time to become uniformly heated 
 throughout. Dry the cavity and apply a thin film of oil to 
 l^revent wax adhesion. Introduce wax in the cavity, and with 
 ball of the thumb or finger apply steady, positive pressure in 
 such direction as will force the wax info and affohhst cavity 
 walls and margins. 
 
 Avoid changing direction of pressure, or rolling the ball 
 of the finger over the wax. When change of direction of 
 pressure, from any cause, occurs, the wax is liable to be- 
 come unseated, or moved away from the cavity walls. Then, 
 when contraction of the wax occurs, as is invariably the case, 
 errors in adaptation are still further increased. 
 
 Continue pressure until wax has cooled to body tempera- 
 ture. Heat a spatula and soften the occlusal surfaces. Instruct 
 patient to subject the wax to the action of opposing teeth, 
 not only in full occlusion, but to lateral movements as well. 
 
 Remove peripheral surplus of wax and carve to desired 
 form. The carving tool should be applied so as to cut parallel 
 with the line of junction of wax with cavity margin or be 
 drawn diagonally across the junction from wax to tooth. 
 When drawn from tooth to wax, the latter is liable to be torn 
 or drawn away from the cavity margin and thus result in a 
 defective margin of the wax model. 
 
 A smooth finish may Iie given axial surfaces by means of 
 silk strips, moistened with oil of cajeput. Flat surfaces may 
 be smoothed with pellets of cotton, slightly moistened with 
 the oil. 
 
 Remove the wax model carefully with small instrument, 
 and attach sprue former. 
 
In all cases the attacliinent of the sprue to the wax should 
 be at the highest point of the matrix, when the ring is set in 
 projier position for casting. 
 
 AVhen any portion of the matrix is higher than the point 
 of entrance of the gold into the latter, air frequently becomes 
 
 WAX MODEL OP INI.AY ATTACHED 
 
 TO SI'RUE FORMER. READY 
 
 FOR INVESTMENT 
 
 WAX MODEL OF SMALL SADDLE. 
 READY FOR INVESTMENT. THREE 
 WAX SPRIE FORJIERS LEAD FROM 
 METAL SPRUE FORMER TO EX- 
 TREMITIES AND CENTER OF MODEL 
 
 confined or the gold becomes chilled and fails to perfectly fill 
 such high areas. 
 
 A small strip of gold plate may be heated sufficiently to 
 melt its way into the wax, and when cold this will serve as a 
 plier grasp in removing the model. It may be allowed to 
 remain in the wax when invested, and when the inlay is cast, 
 the projecting end will facilitate handling the inlay while 
 fitting- After serving its purpose it may be removed by cut- 
 ting and the surfaces polished smoothly. Suggested by Dr. 
 T. L. Pepperling. 
 
 The sprue former is now heated and applied at the point 
 of proximate contact. It must be imbedded sufficiently to ob- 
 tain a firm hold upon the model so that displacement will not 
 occur during investment. 
 
 The wax around the sprue former should be smoothed 
 properly and a slight amount added, if necessary, to insure 
 strong proximate contact. 
 
 INVESTMENT OF THE WAX MODEL 
 
 The sprue former with wax models attached, is now set in 
 the opening of the crucible former and the wax washed with 
 a soap}' water solution and afterward clear water, applied 
 with fine brush, to remove the oil. 
 
 A mix of investment of medium consistency is now made 
 and with a fine brush the surfaces of the wax are carefully 
 coated with a film of it. The investment ring is now set in 
 
956 INLAYS 
 
 ])ositi()ii, the rounded iiuirgiii down, ajitl ilic space around tlie 
 model entirely iillod with investment. 
 
 (!are sliould be taken, both in coating the wax and in till- 
 ing tlie ring with investment, to avoid tlie fornuition of air 
 spaces. 
 
 When the investment has hardened, the surplus project- 
 ing from the open end of the ring is squared off, the crucible 
 former removed, the sprue former heated sufficiently to melt 
 tlie wax at its inclosed end, after which it is carefully removed. 
 
 Remove from the crucible and the spru.e any particles of 
 investment that may be present, so that when ready to cast 
 the mold may lie clear. 
 
 DRYING OUT THE INVESTMENT AND ELIMINATING THE WAX 
 
 Place the investment ring al)out three inches above a low 
 Bunsen flame for five minutes, that it may become gradually 
 heated. 
 
 Lower the ring and raise the flame imtil the latter touches 
 the investment, and continue the heating process for five or 
 ten minutes longer. 
 
 Increase the flame until it passes up, surrounding the 
 sides of the ring. Continue the heat at this higher tempera- 
 ture until the investment is freed from all moisture and the 
 gas has been driven off. At no time should the heat be applied 
 so rapidly as to boil the wax and force it through the sprue. 
 
 Test by holding a piece of cool glass close to upper end 
 of ring. 
 
 When all gas has been expelled, the ring is set aside and 
 allowed to cool before casting. 
 
 VARIATION IN THE METHOD OF PREPARING THE MOLD FOR 
 CASTING 
 
 When investment has hardened, the ring is placed about 
 six inches above a medium-sized Bunsen flame and allowed 
 to remain in the current of heated air until all moisture is 
 expelled. 
 
 This may require from ten to twenty minutes, and during 
 the process the temperature will be raised somewhat above 
 212° F. It should not at any time be raised much above that 
 point. 
 
 Now, since wax melts at about 150° F., it will be absorbed 
 by the investment as the moisture is expelled from the latter. 
 A film of wax, however, will remain on the matrix walls. 
 
 The ring may be set aside to cool, before casting the gold, 
 
INLAYS 957 
 
 or the button of gold may be placed in the crucible, fused and 
 cast immediately, if desired. 
 
 The film of wax in no way interferes with the production 
 of a sharp casting. In fact, when the gold is sufficiently super- 
 heated and injected into the mold, under proper conditions, 
 a sharper and cleaner casting can be produced by this than by 
 the former method. 
 
 The instant the gold is forced into the matrix its tempera- 
 ture is considerably above 2000° F. All gas and air in the 
 matrix is forced outward through the walls into the invest- 
 ment, the film of wax is instantly carbonized and prevents the 
 oxygen in the air, forced out, from coming in contact with the 
 gold, the result being a clean, bright casting. 
 
 The greatest advantage, however, is that the binder in 
 the investment has not been disintegrated by previous heat- 
 ing, and as a result the matrix walls are firm and compara- 
 tively unyielding. The roughness, therefore, so frequently 
 seen on cast gold surfaces, when the investment is previously 
 highly heated, is not noticeable in a casting produced by the 
 method just described. 
 
 Credit for this method of treatment of the invested case 
 belongs to Dr. Chas. B. Meade of Rockford, 111., who first dem- 
 onstrated it at a clinic of the Chicago Dental Society. 
 
 THE CASTING OF GOLD 
 
 Under the most favorable circumstances a certain amount 
 of time unavoidably elapses between the discontinuance of the 
 heat applied in fusing the gold and its injection into the mold. 
 
 The instant the flame is discontinued the temperature of 
 the gold begins, and continues to drop, resulting in change 
 from a fluid to a pasty and finally a solid state. 
 
 When gold is brought to a fused condition only, and the 
 flame is discontinued, these changes occur very quickly, so 
 rapidly, in fact, that in introducing it in the mold, even under 
 heavy pressure, the latter will seldom be filled perfectly, be- 
 cause of the changes mentioned. 
 
 Therefore, to insure sharp castings, gold must be super- 
 heated considerably above its actual fusing ijoint in order 
 that it may not only enter the mold, but be sufficiently fluid, 
 after injection, to conform to all irregular surfaces of the 
 matrix under the compressive force applied. 
 
 The most imi^ortant contribution of Dr. Taggart to the 
 casting process was the discovery that in order to cast sharply, 
 gold must be superheated considerably above its fusing point. 
 
Tliis lie aceonii)lisli('(l icmlily liy iiiciiiis of a slij.;lit iiiodilica- 
 tion of tlie Kua]!)) nitrous oxide and gas l)lowpipe. 
 
 When all moistnre has been eliminated, the ring is placed 
 in the casting device, a button of gold considerably larger than 
 required is placed in the crucible, brought to a superheated 
 condition and as quickly as i^ossible forced into the matrix 
 under pressure. 
 
 With the Taggart a])pliances tlie gold may he quickly 
 brought to a suix'rhcafed condition ))y means of the nitrous 
 
 oxide and gas blowpij^e and the casting quickly accomplished 
 by forcing the sealing cap down tightly upon the ring margins. 
 
 With the R. & K. vacuum machine, the chamber should 
 be emptied of air before fusing the gold, when, after this has 
 been accomplislied, by opening the valve, the gold is drawn 
 into the matrix by suction. 
 
 Further details of gold, reducing fluxes, investments, etc., 
 of practical value will be fcnuul in the section on metallurgy, 
 under the general topic, "Alloys of Gold," etc., by Dr. Wein- 
 stein. 
 
 ROUGH FINISHING THE CASTING 
 
 On removal of the casting from the investment, it should 
 be washed, boiled in acid, and again washed, to remove the 
 acid. 
 
 The button is now removed from the casting, the rough 
 points removed with discs, being careful while doing so not 
 
959 
 
 to mar the margins, and in proximo-occlusal inlays to pre- 
 serve a strong contact point. 
 
 Should nodnles be present in any of the inlay surfaces 
 which proximate cavity walls, they should he smoothed down 
 
 THE RANSOM & RAXDOI.I'H \ACUUM CASTING MACHINE 
 
 with chisels; discs or stones or reduced in any manner most 
 convenient. Wlien present, they prevent proper seating of 
 the inlay. 
 
 SETTING THE INLAY 
 
 When, b}' test, the inlay can be perfectly seated, it is re- 
 moved, the cavity rendered thoroughly dry, cement mixed and 
 applied in the usual manner, and the filling set imder con- 
 tinued, heavy pressure. 
 
 FINISHING 
 
 Wlien the cement has thoroughly hardened, the margins 
 of the inlay are now given their final finish with discs, strips, 
 and polishing powders. 
 
 Previous to the final setting, however, the contact and 
 adjacent areas of the filling are polished, thereby reducing 
 danger of loss of proximate contact, which frequently occurs 
 in final finishing, unless separation of the teeth is previously 
 made. 
 
CHAPTER XXXII 
 
 AN OUTLINE OF METALLURGY 
 
 The science of metallurgy deals with the extraction of 
 metals from their ores, with their physical properties when 
 free and nncoral)ined, and with the changed conditions 
 brought about by alloying the individual metals, or by the 
 presence of some other substances, either in the form of im- 
 purities or that maj^ have been added for some definite jiur- 
 l^ose. 
 
 Metallography deals more particularly with the structural 
 form of metals and their alloys, the study in this compar- 
 atively new field in physics being carried on chiefly with the 
 microscope. It is closely related to the chemistry of metals, 
 and yet it covers a field not occupied, and yields information 
 not obtainable, In^ ordinary chemical analysis. 
 
 In the i^ractice of prosthetic dentistry, aliout fifteen of 
 the metals are used to a greater or less extent, either in their 
 pure state, or in the form of alloys. To handle these various 
 metals intelligently and economically, so as to secure the best 
 results, the prosthetic dentist sliould have an intimate knowl- 
 edge of general and metallurgical chemistry, as well as of the 
 collateral sciences. In the description of the metals now about 
 to be considered an effort will be made to point ont those 
 essential physical and chemical ijroperties and peculiarities 
 which, if overlooked or misunderstood by the prosthetist, may 
 result in mishaps of a more or less serious character. 
 
 All of the material substances of the universe with which 
 we are acquainted consist of elements alone or in combinaticm 
 with each other. 
 
 An element is a substance which cannot be siilit uj) or 
 decomposed into dissimilar substances by any means now 
 known, and differs from a compound, which may be split up 
 or separated into dissimilar substances. 
 
 At this time there are about eighty elements known, 
 fifty-two of which are metals. It is possible that some of these 
 substances which are now considered elements may prove to 
 be compounds. 
 
 960 
 
AN OUTLINE OF METALLURGY 961 
 
 FACTS, HYPOTHESES, THEORIES AND SPECULATIONS 
 ELEMENTS 
 
 An element is a substance which cannot be decomposed 
 into simpler substances by any method now known. Stated 
 differently, "an element is a distinct species of matter which 
 has not been shown to be composite." 
 
 At the present time, so far as is known, there are about 
 eighty elements in the universe. The physical properties of 
 most of these are well understood, but a few, because of their 
 scarceness and the difficulties attending their examination, 
 have but sparse accumulated data. It is not only possible but 
 quite probable that other elements now unknown may be dis 
 covered, and that some of those now classed as elements may 
 prove to be compounds. 
 
 DISCOVERY OF ELEMENTS BY MEANS OF THE SPECTROSCOPE 
 
 The spectroscope has aided materially in the detection 
 of some of the elements, and by means of it their presence in 
 the universe was recognized before they themselves were iso- 
 lated. As an illustration, in 1868 a bright line was noticed 
 in the spectrum of the sun's atmosphere which differed from 
 that of any element then known. Lockyer and Frankland, be- 
 lieving it to be a new element in the sun, called it helium, from 
 the Greek, meaning the sun. Twenty-seven years later Sir 
 William Ramsey discovered in the spectrum of cleveite, a line 
 corresponding to that of helium, which was still unknown 
 except by its spectrum. On further examination this new 
 element proved to be a gas, a constant component of the 
 earth's atmosphere, and, as will be shown later, an end 
 product of radio active substances under certain conditions. 
 Because of its spectroscopic position it received the name of 
 helium. For many years the spectrum of the Aurora Borealis 
 was a subject of puzzling investigation. This light shows in 
 it a peculiar, greenish yellow line, unlike that of any other 
 element known. The discoverey of krypton solved the prob- 
 lem, its spectrum showing the identical line found in that of 
 the "Northern Lights." 
 
 THE MUTABILITY OF MATTER 
 
 There is a growing belief among physicists that some, 
 possibly all substances now known as elements, may be trans- 
 mutable or capable of being changed from one to the other. 
 The change, however, appears to be one of degradation. 
 
9G2 AN OUTLINE OF METALLURGY 
 
 No laws have been discovered by which this mutability of 
 matter can be brought about at will or among the elements 
 indiscriminately. Certain facts, however, have been observed 
 and verified time and again, beyond the question of doubt, 
 that under definite conditions degradation of elements occurs. 
 The character of the element before such change occurs can 
 be recognized, the intense energy exhibited while decomposi- 
 tion is going on can be noted and even measured to a certain 
 degree, and the character of the substance into which the 
 original element is finally resolved can 1)0 determined. 
 
 BRIEF OUTLINE OF RECENT DISCOVERIES 
 
 To make these facts more plainly ai)i>ar<'iit, a statement 
 of some of the discoveries in physical and chemical fields in 
 the last twenty years, together with their bearing on the sub- 
 ject under discussion, will be in order. 
 
 ELEMENTAL GASES 
 
 In 1894 Lord Eayleigh discovered in the atmosphere a 
 new and hitherto unsuspected gaseous element. Because it 
 would not combine chemically with any other substance except 
 at intensely high temperatures, and in other ways seemed 
 generally inert, it was named "argon" which means "lazy." 
 It closely resembles nitrogen in its physical i^roperties, is 
 slightly heavier and extremely difficult to separate from the 
 latter gas witli which it is associated in the atmosphere. 
 
 In 1895, Sir AVm. Ramsey discovered four other elemental 
 gases in the air, viz., helium, neon, krypton, and xenon, all of 
 which have similarly inert i^roperties to argon. These five 
 gases have all been "won out of the hidden places in the air," 
 and as will be seen later, the presence of most of them in this 
 medium can he accounted for. 
 
 DISCOVERY OF THE X-RAYS 
 
 In the same year Prof. William Konrad Roentgen dis- 
 covered the peculiar penetrating power of the rays from an 
 induced electric current when passed through a vacuum. 
 These rays are now known as Roentgen, or X-rays, and their 
 power of penetrating opaque substances and affecting light 
 proof photographic plates is well understood and made use of 
 in innumerable ways, particularly in the medical and dental 
 fields, for diagnostic purposes. 
 
AN OUTLINE OF METALLURGY 963 
 
 DISCOVERY OF RADIO-ACTIVE SUBSTANCES 
 
 In 1896, Becqnerel discovered that all compounds of 
 uranium emitted a radiation capable of penetrating opaque 
 objects similar to Init not with the same energy or rapidity 
 displayed by the X-ray. Uranium com])(nmds are derived 
 from pitchlilende, a complex mineral containing many other 
 elements. The residue left after extracting practically all of 
 the uranium is the source from which radium is derived. 
 The Curies noticed that this residue possessed considerable 
 radio-activity. In an effort to locate the true source of the 
 emanations, they found that after separating the residue into 
 its constituent parts, so far as could be done at that time, that 
 most of the radio-activity was concentrated in the chloride of 
 barium. On sul)jecting the barium chloride to further reduc- 
 tion, the barium was finally eliminated and a substance which 
 proved to be radium chloride was secured. Radium, the 
 element, has only recently been isolated by Madame Curie. Its 
 salts RaCL and EaBr^ are commonly prepared and employed 
 for experimental and other jiurposes. The spectrum of 
 radium and its chemical relations to other elements indicate 
 that it should be classed among the metals of the alkaline 
 earths. 
 
 There are about twenty-five substances which possess, 
 in varying degrees, distinct radio-active properties. The salts 
 of radium mentioned exhiliit this property more strongly 
 than any of the others. 
 
 DECOMPOSITION OF RADIUM COMPOUNDS 
 
 The peculiar feature of the radium compounds is that 
 they decompose, rapidly at first, then more slowly, until finally 
 practically nothing remains of the original salt. The intense 
 energy displayed in their decomposition is half spent in the 
 first four days after the preparation of the salt, but in that 
 time there has been emitted, proportionately, three million 
 times inore heat than will result from any other chemical ac- 
 tion known. 
 
 There are three principal types of rays emitted by radio- 
 active substances, designated as alpha, beta, and gamma rays. 
 The ali)ha raj's are electro-positive particles or electrons of 
 atomic size which fly through space at the amazing velocity of 
 twenty thousand miles per second. A little radium brought 
 near a screen of zinc sulphide produces brilliant, scintillating 
 stars of light. Each star is the result of impact of an alpha 
 
i)B4 AN OUTLINE OP METALLURGY 
 
 particle or atom against the screen. The beta rays act most 
 readily on photographic plates. The gamma rays possess 
 the greatest penetrating power, readily passing through a 
 lead jjlate seven centimeters thick. The principal dilTerenee 
 aside from the effect of the several rays seems to be one of 
 velocity, the alpha rays having the greatest and the gamma 
 rays the least speed. 
 
 CHARACTER OF THE EMANATION FROM RADIO-ACTIVE 
 SUBSTANCES 
 
 Dorn has proven that the emanations from radio-active 
 substances is a gas, which, under dry atmospheric conditions, 
 eventually breaks down or decays into helium. 
 
 Later Ramsey, in an effort to utilize or conserve some 
 of the enormous energy which is manifested during and is 
 apparently the result of its debasement, placed the radium 
 compound in water. Instead of decaying into helium as it 
 does in dry atmosphere, it is finally resolved into neon, the 
 second of the elemental gases mentioned. 
 
 When copper sulphate is dissolved in the water in which 
 the radio-active substance is placed neither helium nor neon 
 are found, but argon is the final product. 
 
 Prof. Duncan sums up these facts as follows: "It ap- 
 pears then, that this gas, this radium emanation, whicli, it 
 must be said, has a good claim to the name of element, decays 
 or becomes transmuted, not into one other element, but into 
 three, according to its surrounding circumstances." 
 
 THE DEGRADATION OF COPPER 
 
 Ramsey's researches further led him to believe that the 
 action of the radium emanations on the copper sulphate broke 
 down or changed some of the copper into lithium. He bases 
 his deduction on the following: At the beginning of his ex- 
 periments lithium was not present in the water, in the copper, 
 in the emanations, in the air, nor in the glass apparatus with 
 which the experiments were conducted, but the final results 
 showed loss of copper and the presence of lithium. Every- 
 thing else could be accounted for but the loss and additions 
 noted, and those only on the basis of the degradation of cop- 
 per into lithium through the influence of radio-activity. 
 
 DEBASEMENT OF VARIOUS SUBSTANCES INTO HYDROGEN 
 
 Still another fact of extreme interest was observed, viz. : 
 that water in the presence of radium emanations breaks up 
 
AN OUTLINE OF METALLURGY 965 
 
 into oxygen and hydrogen, not in the usual proportions of two 
 volumes of hydrogen to one of oxygen, but the resulting un- 
 combiued gases show from 10 to 20 per cent too much 
 hydrogen. 
 
 Prof. J. J. Thompson has shown that in the energetic elec- 
 trical field generated in a Crookes tube, various substances 
 give off particles charged with positive electricity, that these 
 particles are independent of or differ in character from the 
 gas from which they originate, that they are of two kinds, one 
 to all appearances identical with the hydrogen atom, the 
 others resembling in every respect the alpha particles which 
 emanate from radio-active svibstances. All of the substances 
 with which he experimented were decomposed, in part, into 
 the element hydrogen. 
 
 These experiments of Thompson's, conducted in a differ- 
 ent field with unlike apparatus without employing any of the 
 so-called radio-active substances, serve to confirm most forci- 
 bly the work of Ramsey and others, and establish the fact that 
 hydrogen results from the debasement of other elements when 
 conditions are favorable. 
 
 SUMMARY OF THE STATEMENTS PRESENTED 
 
 From present knowledge it appears evident that uranium 
 is transmuted into radium; that radium may be transmuted 
 into helium, neon, or argon, depending on surrounding condi- 
 tions ; that copper, under the influence of the alpha rays, may 
 be debased into lithium; that the energizing influence of the 
 alpha as well as the X-rays, acting on inert substances, cause 
 them to break down into hydrogen, and finally, that the 
 radium emanations are themselves the product and evidence 
 of elemental change and decay. 
 
 The atomic weight of copper is 63.6 and that of lithium 
 is 7.03. In every case the substance resulting from the deg- 
 radation of an element stands lower in the atomic scale than 
 that from which it was derived, copper and lithium being 
 examples of what is seen in all of the other elements in which 
 such changes have been noted. 
 
 In reference to ' ' The decay of an element, ' ' Prof. Alexan- 
 der Smith, Directoi: of General and Physical Chemistry, Uni- 
 versity of Chicago, says: "The phenomena of radio-active 
 substances lead undeniably to the startling conclusion that 
 some, if not all, of the element are capable of spontaneous 
 decofnposition." 
 
itCC AN OUTLINK OK METALLURGY 
 
 The following table from "Scientific Ideas of Today," by 
 Charles E. Gibson, shows the progress of chemical discovery 
 of the elements in the last 4(i4 years. 
 
 THE ELEMENTS IN ORDER OF THEIR DISCOVERY 
 
 A.D. Elements Discovered by 
 
 1450 Antimony Valentino (German alchemist) 
 
 1450 Bismnth \^alentiue (German alchemist) 
 
 1520 Zinc Paracelsus (Swiss chemist) 
 
 1694 Arsenic Schroder (German) 
 
 1733 Cobalt Brandt (German) 
 
 1738 Phosphorus Brandt (German) 
 
 1751 Nickel Cronstadt (Russian) 
 
 1766 Hydrogen Cavendish (English) 
 
 1772 Nitrogen Rutherford (English) 
 
 1774 Manganese Gahu (Swedish) 
 
 1774 Oxygen Priestley (English) 
 
 1780 Uranium Kla])roth (German) 
 
 1781 Timgsten d'Elihujar (Spanish) 
 
 1782 Molyodenum Hjelm (Swedish) 
 
 1782 Tellurium Reiclienstein (German) 
 
 1785 Titanium Klaproth (German) 
 
 1798 Chromium Vauquelin (French) 
 
 1901 Tantalum Hatchett (English) 
 
 1801 Cerium Berzelius and Hisinger 
 
 (Swedish) 
 
 1801 Vanadium Del Rio (Spanish) 
 
 1803 Osmium Tennant (English) 
 
 1803 Palladium Wollaston (English) 
 
 1804 Iridium Tennant (English) 
 
 1804 Rhodium Wollaston (English) 
 
 1807 Potassium Daw (English) 
 
 1807 Sodiimi Davy (English) 
 
 1808 Barium Davy (English) and Berzelius 
 
 (Swedish) 
 
 1808 Strontium Davy (English) 
 
 1808 Boron Davy (EngUsh) and Gay-Lusac 
 
 (French) 
 
 1808 Magnesium Davy (English) 
 
 1808 Calcium Davy (English) and Berzelius 
 
 (Swedish) 
 
 1810 Chlorine Davy (English) 
 
 1810 Fluorine Ampere (French) 
 
AN OUTLINE OF METALLURGY 967 
 
 A.D. I]lenients Discovered by 
 
 1811 Iodine Conrtois (French) 
 
 1817 Selenium Berzelius (Swedish) 
 
 1817 Lithium Arfvedson (Swedish) 
 
 1817 Cadinm Herman and Stromyer (Grerman) 
 
 1823 Solicon Berzelius (Swedish') 
 
 1824 Zirconium Berzelius (Swedish) 
 
 1826 Bromine Balard (French) 
 
 1827 Berylium Wohler (German) 
 
 1828 Alumium Wohler (German) 
 
 1828 Thorium Berzelius (Swedish) 
 
 1828 Yttrium Wohler (German) 
 
 1841 Lanthanum .Mosander (Swedish) 
 
 1843 Terbium Mosander (Swedish) 
 
 1843 Erbium Mosander (Swedish) 
 
 1844 Ruthenium Clans (German) 
 
 1846 Columbium Rose (English) 
 
 1860 Caesium Bunsen and KirchlotT (German) 
 
 1862 Thallium Crookes (English) 
 
 1863 Indium Reich and Richter (German) 
 
 1868 Helium (in tlie Sun).Lockyer (English) 
 
 1868 Rubidium Bunsen (German) 
 
 1875 Gallium Boisbaudran (French) 
 
 1878 Ytterbium Marignac (French) 
 
 1879 Thulium Cleve (Swedish) 
 
 1879 Scandium Nilson (Swedish) 
 
 1879 Samarium Boisbaudran (French) 
 
 1885 Praseodymium Welsbach (German) 
 
 1885 Neodymium Welsbach (German) 
 
 1886 Gadolinium Marignac (French) 
 
 1886 Germanium Winkler (German) 
 
 1894 Argon Rayleigh and Ramsay (English) 
 
 1895 Helium (On Earth) .. Ramsay (English) 
 
 1897 Krypton Ramsay and Travers (English) 
 
 1898 Xenon Ramsay (English) 
 
 1898 Neon Ramsay and Travers (English) 
 
 1898 Radium Curie (French) 
 
 THE ELEMENTS IN THE ORDER OF THEIR ATOMIC 
 WEIGHTS 
 
 1. Hydrogen 1.008 4. Glucinuni 9.1 
 
 2. Helium 4.00 5. Boron ILO 
 
 3. Lithium 7.03 6. Carbon 12.0 
 
AN OUTLINE OP METALLURGY 
 
 7. Nitrogen 14.04 
 
 8. Oxygen 16.0 
 
 9. Fluorine 19.0 
 
 10. Neon 20.0 
 
 11. Sodium 23.05 
 
 12. Magnesium 24.36 
 
 13. Aluminum 27.1 
 
 14. Silicon 28.4 
 
 15. Phosphorus .... 31.0 
 
 16. Sulphur 32.06 
 
 17. Chlorine 35.45 
 
 18. Potassium 39.15 
 
 19. Argon 39.90 
 
 20. Calcium 40.1 
 
 21. Scandium 44.1 
 
 22. Titanium 48.1 
 
 23. Vanadium 51.2 
 
 24. Chromium 52.1 
 
 25. Manganese 55.0 
 
 26. Iron" 55.9 
 
 27. Nickel 58.7 
 
 28. Cobalt 59.0 
 
 29. Copper 63.6 
 
 30. Zinc 65.4 
 
 31. Gallium 70.0 
 
 32. Germanium .... 72.5 
 
 33. Arsenic 75.0 
 
 34. Selenium 79.2 
 
 35. Bromine 79.96 
 
 36. Krypton 81.8 
 
 37. Rubidium 85.4 
 
 38. Stroutimn 87.6 
 
 39. Yttrium 89.0 
 
 40. Zirconium 90.6 
 
 41. Columbium 94.0 
 
 42. Molvbdium 96.0 
 
 43. 
 44. 
 45. 
 46. 
 47. 
 48. 
 49. 
 50. 
 51. 
 52. 
 53. 
 54. 
 55. 
 56. 
 57. 
 58. 
 59. 
 60. 
 61. 
 62. 
 63. 
 64. 
 65. 
 66. 
 67. 
 68. 
 69. 
 70. 
 71. 
 
 74. 
 
 75. 
 76. 
 
 77. 
 
 78. 
 
 Ruthenium 101.7 
 
 Rhodium 103.0 
 
 Palladium 106.5 
 
 Silver 107.93 
 
 Cadmium 112.4 
 
 Indium 114.0 
 
 Tin 119.0 
 
 Antimony 120.2 
 
 Iodine 126.85 
 
 Tellurium 127.6 
 
 Xenon 128.0 
 
 Ca?sium 132.9 
 
 Bariimi 137.4 
 
 Lanthanum 138.9 
 
 Praseodvmii;m . 140.5 
 
 Cerimu ' 140.25 
 
 Neodymium .... 143.6 
 
 Samarium 150.0 
 
 Gadolinium 156. 
 
 Terbium 160.0 
 
 Erl)ium 166.0 
 
 Thulium 171.0 
 
 Yitterbium 173.0 
 
 Tantalum 183.0 
 
 Tungsten 184.0 
 
 Osmium 191.0 
 
 Iridium 193.0 
 
 Platinum 194.8 
 
 Gold 197.2 
 
 Mercury 200.0 
 
 Thallium 204.1 
 
 Lead 206.9 
 
 Bismuth 208.5 
 
 Radium 225.0 
 
 Thorium 232.5 
 
 Uranium 238.0 
 
 THE KINETIC CONSTITUTION OF MATTER 
 
 Matter is composed of or at least presents itself to our 
 senses in three distinct forms, viz., solids, liquids and gases. 
 The molecular theory of matter, as believed in and taught 
 by the physicists of today, may be briefly stated as follows: 
 
 Matter consists of units called molecules; these in turn 
 
AN OUTLINE OF METALLURGY 969 
 
 are composed of still smaller units of elements called atoms; 
 atoms are made up of still smaller units consisting of ele- 
 mentary charges of negative electricity, called electrons, each 
 of which probably has a nucleus or center of positive elec- 
 tricity. 
 
 THE VIBRATION OF MATTER 
 
 It is believed that the electrons move about or vibrate 
 within the atom; that the atoms vibrate within the molecule, 
 to a lesser degree ; and that the molecules move about within 
 the mass of matter, freely when the matter is gaseous, re- 
 stricted in movement when solid or liquid, but still possess- 
 ing movement. 
 
 The infinitesimal particles of gold in a colloidal state, al- 
 though much larger than the estimated size of electrons, when 
 viewed through that wonderfully sim^jle but simply wonder- 
 ful instrument, the ultra-microscope of Zsigmondy, enables 
 one to form some slight conception of the vibration of mat- 
 ter. Here is his own desci'iption of what may be seen: 
 
 " * * * The small gold particles no longer float, they 
 move — and that with astonishing rapidity. A swarm of danc- 
 ing gnats in a sunbeam will give one an idea of the motion of 
 the gold particles in the hydrosol of gold. They hop, dance, 
 jump, dash together and fly away from each other, so that it is 
 difficult in the whirl to get one's bearings. 
 
 "This motion gives an indication of the continuous mix- 
 ing up of the fluid; and it lasts for hours, weeks, months, and, 
 if the fluid is stable, even years. 
 
 "Sluggish and slow in comparison is the analogous 
 Brownian movement of the larger gold particles in the fluid, 
 which are the transition forms of ordinary gold that settles. 
 
 ' ' The smallest particles which can be seen in the hydrosol 
 of gold show a combined motion, consisting of a motion by 
 which the particle moves from 100 to 1,000 times its own 
 diameter in one-sixth to one-eighth of a second, and a motion 
 of oscillation of a considerabh^ shorter period, because of 
 which the possibility of the presence of a motion of oscillation 
 of a higher frequency and smaller amplitude could not be de- 
 termined, but is probable." (Colloids and the Ultra-Micro- 
 scope, Zsigmondy).. 
 
 The foUowir.g comparison will give an idea of the size of 
 the smaller gold particles: 
 
 The limit of visibility of an ordinary high power micro- 
 scope is about one-fourth micron, or one-four-thousandth of a 
 
!)70 AN OUTLINP: op METALLURGY 
 
 luilliiiictci', a iiiicroii hciiij;' oiic-oiie-thoiisaiKltli ot" a milli- 
 meter, or about one-twenty-Hve-tliousandtli of an inch. 
 
 Under favoral>le conditions, particles of one one-mil- 
 lionth millimetei's in diameter can readily be seen with the 
 nltra-microscope. Some of the smaller particles of gold are 
 barely visible with this instrument, and it is believed that 
 still smaller particles exist. 
 
 When planed surfaces of gold and lead are brought in 
 contact and held together firmly for several weeks, on ex- 
 amination it will be found tliat particles of gold have made 
 their way into the lead, likewise particles of lead can be found 
 within the gold, thus showing that molecules of solid sub- 
 stances vibrate or move about not only in the mass of like 
 material, but wander away into unlike substances. 
 
 Prof. A. Wilmer Duff, of the Worcester Polytechnic In- 
 stitute, after citing this and similar instances of dift'nsion, 
 states: "There are many other reasons for believing that 
 the particles of matter are in all cases in motion. This 
 hypothesis is called the hypothesis of the kinetic constitution 
 of matter." 
 
 In reference to electrons, Sir William Ramsey has ex- 
 pressed himself as follows: "Electrons are atoms of the 
 chemical element electricity; they possess mass; they form 
 compounds with other elements; they are known in the free 
 state, that is, as molecules." (Trans. Chemical Society, 
 Great Britain, 1908.) 
 
 THE UNEQUAL DISTRIBUTION OF ELEMENTS 
 
 "More than 99 per cent of terrestrial material is made up 
 of eighteen or twenty elements, of which the quantities of the 
 first eleven, as estimated by F. W. C-larke, are given in the 
 following table: 
 
 Oxygen 49.98 Sodium 2.28 
 
 Silicon 25.30 Potassium 2.23 
 
 Aluminum 7.26 Hydrogen 0.94 
 
 Iron 5.08 Titanium 0.30 
 
 Calcium 3.51 Carbon 0.21 
 
 Magnesium 2.50 
 
 99.59 
 
 "The evidence of the spectroscope shows that the sun and 
 stars contain many of the very same elements as does the 
 earth." — Alexander Smith. 
 
 "Recent researches have thrown a flood of light upon 
 these questions (the unequal distribution of elements). It is 
 
AN OUTLINE OF METALLURGY 971 
 
 now believed that the elements are not tlie changeless sys- 
 tems that they were once thouglit to be, bnt rather systems 
 in slow but incessant mutation. 
 
 "According to Prof. J. J. Thompson, all of the elements 
 represent successive condensations of one primary stuff, 
 whose atoms, called electrons or corpuscles, weigh less than 
 the 1/1,000 part of an atom of the lightest known terrestrial 
 element, namely hydrogen. This primary stuff is negative 
 electricity, which is therefore a true chemical element." — 
 Geoffrey Martin, in Triumphs and Wonders of Modern 
 Chemistry. 
 
 ELEMENTS AND THEIR ATOMIC RELATION TO EACH 
 OTHER 
 
 Tile elements when studied collectively, although differ- 
 ing in many respects from each other, as, for instance, in 
 their atomic weight, specific gravity, valence and physical 
 appearance, have many peculiar properties in common. 
 
 (Jbservation has shown that certain definite relations 
 exist between the elements, particularly when arranged in 
 series or groups. The gradual and almost uniform increase 
 in the atomic scale, beginning with hydrogen, the lowest, and 
 progressing up to uranium, the highest, in the atomic series, 
 has long attracted attention and given rise to the idea that 
 such orderly progression is not the result of chance, but of 
 some so far undiscovered law. 
 
 Hydrogen, discovered by Cavendish in 1776, is the light- 
 est known terrestrial element. Until recently its atom has 
 been rated as 1 of the atomic scale, but for reasons subse- 
 quently to be stated, it is now accorded the value of 1.008. 
 When the atomic weights of the other elements are computed 
 on the basis of 1 for hydrogen, it is found that several are 
 whole numbers and many more a]i]iroximate whole numbers. 
 
 PROUT'S HYPOTHESIS 
 
 Just one hundred years ago William Prout, an English 
 physician, observing that the atomic weights of many of the 
 elements were either exactly or approximately whole num- 
 bers, advanced the idea that all of the other elements were 
 composed of hydrogen atoms in various stages of condensa- 
 tion, and that therefore their atomic weights must be even 
 multiples of that of hydrogen. Th(> fact that some of the 
 
972 AN OUTLINE OF METALLURGY 
 
 atomic weights as then determined terminated in decimals, 
 he regarded as the result of errors in calculation. 
 
 Chemists lined up in support of, or in an effort to dis- 
 prove, Front's theory, and for a time great diversity of 
 opinion prevailed, due largely to the fact that the atomic 
 weights of some of the various elements had not been deter- 
 mined accurately. 
 
 The brilliant work of Stas, a Belgian chemist, in the 
 period between 1855 and 1865, in accurately computing the 
 atomic weights of many of the elements, cleared up much 
 of the existing confusion. As a result of his etforts, the even 
 multiple theory of Prout was proven incorrect. Later it was 
 shown that the atomic weight of oxygen was not 16, as Prout 's 
 hypothesis called for, but 15.879, which, however, was within 
 Ys of 1 per cent of a whole number. 
 
 Further, it was foimd that by allotting to oxygen the 
 atomic weight of 16, and computing the atomic weights of all 
 of the other elements on this basis, a much larger percentage 
 of them were resolved into whole numbers than when calcu- 
 lated on the basis of 1 for hydrogen. By this system of com- 
 putation, which is the accepted one at present, the atomic 
 weight of hydrogen is 1.008, as before stated. Considering 
 the atomic weight of oxygen as 16, the atomic weights of 
 fifty-five elements are foimd to be either whole, or within 
 1/10 of 1 per cent of whole numbers. 
 
 Now since it is clearly shown that the atomic weights of 
 more than five-eighths of all Imown elements are approxi- 
 mately whole numbers, much interest in chemical and phys- 
 ical fields has been aroused, and efforts have been made to 
 determine, if possible, the laws governing the atomic, as 
 well as other interesting relations discernible in the ele- 
 ments. This interest, which is greater at present than ever 
 before, first found tangible expression in the hypothesis of 
 Prout, although the theory of the unity of matter is one of 
 very ancient origin. 
 
 THE TRIADS OF DOBEREINER 
 
 In 1827 Dobereiner called attention to the fact that 
 among the elements then known, there occurred here and 
 there groups of three having remarkably similar chemical 
 properties. These groups have since been termed the 
 "Triads of Dobereiner." 
 
AN OUTLINE OF METALLURGY 
 
 The following will serve to illustrate some of the vari- 
 ous triads observed : 
 
 Atomic Weight. 
 
 Calcium 40.1 
 
 Strontium . . . 87.7 
 Barium 137 4 
 
 Atomic Weight. 
 
 Sulphur 32.1 
 
 Selenium 79.2 
 
 Tellurium . . .127.5 
 
 Atomic Weight. 
 Chlorine .... 35.4 
 Bromine .... 80.0 
 Iodine 126.8 
 
 The first group is composed of alkaline earth metals. 
 They are white in color, about as soft as lead, and decompose 
 water at ordinary temperatures, resulting in the formation 
 of hydroxides with the liberation of hydrogen. In most com- 
 pounds these metals are divalent. 
 
 The second group, consisting of Sulphur, which is very 
 abundant, and Seleniinn and Tellurium, which are compara- 
 tively rare, forms a series of similar compounds. 
 
 The third group are sometimes called the halogens (pro- 
 ducers of sea salt), because they are found in sea water. The 
 first is a greenish-yellow gas, the second is a red liquid and 
 the third is a purplish-black solid. They are monovalent in 
 their compounds with hydrogen, and when combined with the 
 latter, form acid gases soluble in water. 
 
 The most remarkable characteristic noted, however, was 
 in the ratio existing between their atomic weights. Dobe- 
 reiner noticed that when the atomic weights of the first and 
 third element of anj' triad were added and the sum divided by 
 two, the resulting mean coincided very closely with the atomic 
 weight of the intermediate element of the triad, as is shown 
 below : 
 
 Calcium . .Atomic Weight. . 40.1 
 Barium . . .Atomic Weight. . 137.4 
 
 Strontium ..Atomic Weight. 
 
 Sulphur .. . .Atomic Weight. 
 Tellurium ..Atomic Weight. 
 
 Selenium . . . Atomic Weight . 
 
 2/177.5 
 
 
 88.7 
 87.7 
 
 ■.V2.1 
 127.5 
 
 mean 
 
 2/159.6 
 
 
 79.8 
 79,3 
 
 mean 
 
AN OUTLINE OF METALLURGY 
 
 Chlorine .. .Atomic Woiii,lit. . '.]^)A 
 Iodine Atomic Weight . . liiG.H 
 
 2/162.2 
 
 81.1 mean 
 Bromine ...Atomic Weight.. 80.0 
 
 While in no ease is the resulting mean exactly equal to 
 the atomic weight of the second memlier of the triad, it is so 
 close in each instance as to suggest the possibility of an un- 
 discovered law which, if known, might clear up the discrep- 
 ancies. The work of Dobereiner and others since his time 
 has resulted in the discovery of many other interesting and 
 peculiar correlated properties of the elements. 
 
 THE OCTAVES OF NEWLAND 
 
 In 1863 Newlands called attention to the fact tiiat when 
 the elements were arranged in the order of their atomic 
 weights, beginning with the lowest, hydrogen 1, running 
 through the entire list of the elements then known and ending 
 with uranium 240, at regular intervals, every eighth element, 
 in most instances, bore a striking resemblance in certain 
 Ijroperties to the preceding eighth below, or the succeeding 
 eighth element above. This method of classification is known 
 as the Octaves of Newlands. While the discovery of New- 
 lands was remarkable, be failed to realize its great impor- 
 tance, or work out the full details of it, being unable to clas- 
 sify all of the elements satisfactorily. 
 
 THE PERIODIC SYSTEM OF MENDELEEFF 
 
 In 1869 two chemists, Dimitri Mendeleeff, a Russian, and 
 Lothar Meyer, a German, working independently, presented 
 almost simultaneously what is known as the Periodic System 
 of the Elements. Priority in this manner of classifying the 
 elements has been accorded Mendeleeff, although Meyer's 
 work, which was almost identical, was performed without 
 knowledge of Mendeleeff 's efforts. The periodic system, as 
 presented by Mendeleeff and Meyer, was based on the Octaves 
 of Newlands, but differed from the work of the latter by in- 
 cluding all of the then known elements. Previous to his 
 death in 1907, MeudeleelT revised the periodic table, modify- 
 ing it to include all of the more recentlv discovered elements 
 (1903). 
 
AN OrXLIXE OF METALLURGY 
 
 Group VIII 
 
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 Ruthenium Hliorlium Palladium 
 Ru = 101,7 Rh = 103.0 Pd = 106.5 (Ag) 
 
 Osmium Iridium Platinum 
 Os=191 Ir = 193 Pt=194.9(Au> 
 
 
 
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y76 AN OUTLINE OF METALLURGY 
 
 A fliart of the periodic system of the elements consists 
 of 13 horizontal columns called series, numbered from zero to 
 12, inclusive, subdivided into 9 perpendicular columns called 
 groups, numbered from zero to 8, inclusive. The elements 
 are arranged in the series from left to right in the order of 
 their atomic weiglits, and in the perpendicular grouji col- 
 umns according to their chemical properties. 
 
 It will be noticed that certain spaces are unoccupied by 
 elements because of breaks in the regular progression of the 
 atomic weights, and which, if closed up, would throw the re- 
 maining elements out of their natural groups. I'rom this 
 the inference is drawn that elements may yet be discovered 
 to fill these vacant spaces. 
 
 When Mendeleeff first devised the table there was a 
 space in series 4, group III, another in series 5, group III, 
 and still another in series 5, group IV. Two years later, in 
 1871, he declared his belief that elements would be found to 
 occupy these spaces. He described their properties and 
 atomic weights, and named them eka-alumiuum, eka-boron 
 and eka-silicon. In 1878 Boisiiaudrau, a French chemist, dis- 
 covered gallium, eka-boron; in 1879 Nilson, a Swedish chem- 
 ist, discovered scandium, eka-aluminum, and in 1886 Winkler, 
 a German chemist, discovered germanium, eka-silicon, all of 
 which corresponded to Mendeleeff 's predictions as to proper- 
 ties, and fit exactly in the vacant spaces. 
 
 NEW ELEMENTS 
 
 In Mendeleeff 's latest table he includes two new ele- 
 ments, neither of which, so far as is known, have a place 
 among the terrestrial elements. These two head the list and 
 are designated as x and y, both supposed to be gases and 
 lighter than hydrogen. 
 
 Coronium, found in the spectrum of the sun's highest at- 
 mosphere, beyond the tips of the sun's flames and highest 
 protuberances, is believed to coincide with y, whose atomic 
 weight is estimated by Mendeleeff at 0.4, or possibly less. 
 
 X is called Newtonium, after the famed English physicist. 
 This gas element, according to Mendeleeff 's calculations, has 
 an atomic weight of probably 0.000001. Arrhenius states 
 that "its atoms ought, therefore, to be about 500 times lighter 
 than electrons." Now since electrons are 1,000 times smaller 
 than the hydrogen atom, it naturally follows that it would re- 
 quire 500,000 Newtonium atoms to equal one of hydrogen. 
 
 Mendeleeff further believed that the element x, or New- 
 
AN OUTLINE OF METALLURGY 977 
 
 tonium, is the substance from which the luminit'erous ether, 
 which pervades all space, is formed. 
 
 THE ELEMENTS CONSIDERED IN GROUPS 
 
 The zero group of elements is composed of the gases of 
 the helium family. These are all mouoatomic and generally 
 inert, forming no compounds with other elements. On ac- 
 count of their scarcity, obscure nature and lack of combining 
 power, their presence among the terrestrial elements was for 
 a long time unknown. It is only within recent years that 
 they have been isolated. The original periodic table, there- 
 fore, contained no zero group, because all but one of the ele- 
 ments now embraced in it had at that time not yet been dis- 
 covered. Helium was known by its spectrum only as a sun 
 element. Because of their atomic weights, they naturally 
 precede Group 1, but their presence in nowise invalidates the 
 periodicity of the other elements. In fact, their discovery and 
 position only confirms the previous findings. 
 
 Take, for instance the first triad of Series 4, argon, at. 
 wt. 38, calcium, at. wt. 40.1 = 78.1 divided by 2 = 39.5. The 
 atomic weight of potassium, the middle factor of the triad, 
 is 39.1. Observe, again, the first triad of Series 8, xenon, 
 at. wt. 128, bariimi, at. wt. 137.4 = 265.4 divided by 2 = 132.7. 
 The atomic weight of caesium, the middle factor, is 132.9. 
 
 When the elements in any group are considered closely 
 it will be seen that while their atomic weights increase rap- 
 idly from above downward, and they differ in other respects, 
 yet there is in most cases a marked resemblance as to chem- 
 ical properties. 
 
 Prof. Duncan calls attention to the fact that each group 
 may be arranged in two sub-groups, the elements embraced 
 in each of which are very closely related. G-roup 2 is taken 
 as an example. 
 
 The elements in the order of their atomic weights are: 
 Beryllium, magnesium, calcium, zinc, strontium, cadmium, 
 barium, mercury and radium. By the sub-group arrange- 
 ment the elements having the greatest number of common 
 pro})erti(>s are l>rought together as follows: 
 
 Siih-f/ioup A. _ Siih-group B. 
 
 Calcium. Beryllium. 
 
 Strontium. Magnesium. 
 
 Barium. Zinc. 
 
 Radium. Cadmium. 
 
 Mercury. 
 
978 AN OUTLINIO OF MKTALLURGY 
 
 THE ELEMENTS CONSIDERED IN SERIES 
 
 As before stated, the clciiiciits ai-ianged in liorizontal 
 rows are termed series. 
 
 Hydrogen is unlike any otlier element, because it is an 
 essential component of all acids, and it, therefore, forms a 
 series by itself. 
 
 While there is a general similarity between the elements 
 in one series to tliose in another, there is a marked and pro- 
 gressive variation between the elements in the same series. 
 First, the atomic weights rise from left to right, or from 1 
 to 7, in comparatively regular gradations. Second, in each 
 horizontal row the first element of the series is a well-marked 
 metal or base-forming element, while the succeeding ones 
 gradually merge from metallic into the non-metallic class, or 
 acid-forming elements, with the exception of manganese, the 
 seventh element of the fourth series. 
 
 Third, in every series the valence toward oxygen ascends 
 from 1 to 7, while the valence toward hydrogen or chlorine 
 ascends from 1 to 4, and then uniformly descends to 1. 
 
 The elements in Group 8 belong to the metallic class, 
 have similar properties to each other, but do not fit in the 
 scheme of the octaves, as their presence in the beginning of 
 the succeeding series would disarrange the grouping of the 
 remaining elements, according to their chemical group simi- 
 larities. They are, therefore, placed in Group 7, outside of 
 the octave system, although their valences are continuous 
 with those of the regular table. 
 
 From the many correlated facts observed, the periodic 
 latv has been formulated as follows: The properties of ele- 
 ments are periodic functions of their atomic weights. 
 
 Many other interesting relations have been disclosed, the 
 details of which can be found in various works on advanced 
 chemistry, particularly Dr. Gordin's Inorganic Chemistry, 
 in which will be found a clear and concise statement of the 
 periodic correlations of the elejnents and of the imperfec- 
 tions of the system as well. These few crudely-stated facts 
 have been introduced with the idea of creating a desire for 
 further knowledge in this most interesting field. 
 
 The following works have been consulted and largely 
 utilized in the presentation of the foregoing facts: 
 
 Gordin's Inorganic Chemistry. 
 
 Smith's General Chemistry for Colleges. 
 
 Levy and Willis, Radium. 
 
 Arrhenius' Theories of Chemistry. 
 
AN OUTLINE OF METALLURGY 979 
 
 Gribson's Scientific Ideas of To-day. 
 Martin's Trimnphs and Wonders of Modern Chemistry. 
 Kennedy Duncan's Some Chemical Problems of To-day 
 and the New Knowledge. 
 Duff's Physics. 
 Ganot's Physics. 
 
 METALS 
 
 Of the fifty-two metals, al^out fifteen are used in the arts 
 and sciences in their true metallic condition, as well as in com- 
 bination with each other and with the non-metallic elements. 
 
 A metal is an opacjue elementary substance which, with 
 the single exception of mercury, is solid at ordinary tempera- 
 ture ; is a good conductor of heat and electricity ; has a metallic 
 luster; has the property of replacing hydrogen in acids form- 
 ing salts, and is electropositive as compared with the non- 
 metallic elements. 
 
 METALLOIDS 
 
 Certain of the non-metallic elements, iodine, arsenic, 
 jihosphorous, silicon, sulphur and carbon, possess to a greater 
 or less degree the properties attributed to metals, especially 
 the power of reflecting light, and which is known as metnUic 
 lustre. 
 
 They are all more or less opaque, while carbon is a conduc- 
 tor of both heat and electricity, which properties, with the ex- 
 ception just noted, are confined exclusively to the metals. This 
 group of elements, therefore, while not metals, are called 
 Dicfalluids, from their resemblance in some respect to the 
 metals. 
 
 FORMS OF MATTER 
 
 Matter, as previoi;sly stated, presents itself to our senses 
 in three distinct forms, as solids, liquids, or gases. These 
 forms, in most instances and under proper conditions, are 
 snscei^tible of change. 
 
 For example, a metal liquifies when subjected to heat. 
 
 Water vaporizes under heat and solidifies at low temper- 
 atures. 
 
 Hydrogen at extremely low temperature and under high 
 pressure liquifies and can be solidified on further reduction of 
 temperature and increase of pressure. 
 
 OCCURRENCE OF METALS IN NATURE— MINERALS 
 
 Most of the metals are found in combination with some of 
 the non-metallic elements, as oxides, sulphides, or carbonates, 
 etc. 
 
AN OUTLINE OF METALLURGY 
 
 Usually the combinations are of such nature as to entirely 
 mask their metallic character and render them unrecognizable 
 as metals, and, when so occurring, are called minerals. 
 
 NATIVE METALS 
 
 Gold, silver, coj^per, platinum, mercury, bismuth, anti- 
 mony and iron frequently occur in nature in their true metallic 
 condition, and are known as native metals. Those just men- 
 tioned are about the only ones so occurring. 
 
 ORES 
 
 When a mineral is found which contains a particular 
 metal in sufficient quantity to pay for its extraction on a com- 
 mercial basis, it is called an ore of that metal. 
 
 NOBLE METALS 
 
 Metals included under this head are those whose com- 
 jDounds with oxygen are decomposable by heat alone at a tem- 
 perature not exceeding redness. The following comprise the 
 list of noble metals : 
 
 Grold, silver, platinum, palladium, rhodium, ruthenium, os- 
 mium iridium, mercury. 
 
 BASE METALS 
 
 Under this classification are included the metals whose 
 comi^ounds with oxygen are not decomposable by heat alone, 
 but retain oxygen at high temperatures. 
 
 PHYSICAL PROPERTIES OF METALS 
 
 Since there are properties common to all metals, these 
 properties will be briefly explained before taking up the study 
 of the individual metals. 
 
 Some of these propei'ties, common to all, but which, of 
 course, vary, according to the individual metal, are atomic 
 weight, specific gravity, melting point, malleability, ductility, 
 tenacity, conductivity of heat, and electricity, specific heat, 
 color, etc. 
 
 ATOMIC WEIGHT 
 
 The atomic weight of an element is the weight of one 
 of its atoms compared with the weight of an atom of hydrogen. 
 
 Hydrogen is the lightest of all known substances, and is 
 taken as the unit or 1 of the atomic scale. Atomic weight. 
 
AN OUTLINE OF METALLURGY 981 
 
 therefore, may be considered as the proportion by weight in 
 which elements unite chemically. 
 
 SPECIFIC GRAVITY 
 
 The sjjecihc gravity of any substance, whether solid, 
 liquid or gas, is the measure of its density. The standard or 
 unit of measurement of solids and liquids is water, and that 
 of gases is hydrogen. 
 
 The specific gravity of a solid or a liquid of a given bulk 
 is its relative weiglit to a like bulk of water under like condi- 
 tions of temperature and pressure. 
 
 In order to find the specific gravity of any solid, it is first 
 weighed in air, then in water, and its weight in water deducted 
 from its weight in air. The weight in air is then divided 
 by the difference thus obtained, and the result represents 
 the specific gravity of the substance. A convenient formula 
 for determining the specific gravity of solids and liquids is 
 as follows : 
 
 ■ Let W=weight of substance in air. 
 
 Let Wi^weight of substance in water. 
 
 Let sp. gr.=specific gravity. 
 W 
 
 Then ^r_-^Y~ "= ^P' ^^'• 
 
 The specific gravity of most metals can be somewhat 
 increased by hammering, rolling, wire drawing or cold pres- 
 sure. 
 
 The specific gravity of aluminum, it being the lightest 
 metal of commercial importance, is 2.5, while osmium, which 
 is the heaviest, is 22.47. 
 
 Comparing two cubes of equal size of aluminum and os- 
 mium, the first would weigh 2.5 and the latter 22.47 times 
 more than an equal bulk of water. 
 
 MELTING POINT 
 
 When an element or substance is changed from a solid 
 to a liquid state as the result of thermal increase, the point 
 at which such change occurs is called its "melting" or "fus- 
 ing" point. 
 
 When a liquid is reduced to a solid state by lowering its 
 temperature, the point where such change occurs is called 
 its "freezing" point. 
 
 The melting point and the freezing point of a metal 
 usually approach each other very closely, but are never quite 
 
»82 AN OUTLINE OF METALLURGY 
 
 tlie same. Tliey are so close at times as to be incapable of 
 registration by tbe tlierinonieter. 
 
 Some substances expand on being melted, while others 
 contract. When a substance expands on being melted, and 
 it is subjected to increase of i)ressure above normal during 
 the fusion process, the effect is to raise its melting point. 
 On the other hand, a substance which contracts on melting, 
 when subjected to increase of pressure, has its fusing point 
 decreased. By reversing the pressures, opposite results are 
 obtained. 
 
 The range of fusibility or the melting points of the 
 various metals differs greatly. Mercury melts at — .39 deg. C, 
 and, consequently, is liquid at ordinary temperatures. Bis- 
 muth, tin, lead, zinc and antimony melt below a red heat; 
 aluminum requires a red heat ; gold, silver and copper a bright 
 red heat; iron and nickel, an intense white heat, while plat- 
 inum and i:ialladium are still more refractory, fusing only in 
 the electric arc or the oxyhydrogen flame. 
 
 Some metals, when heated beyond their melting points, 
 readily vaporize, zinc, antimony and mercury being the most 
 common examples of this class. As a matter of fact, all of 
 the metals can be volatilized if subjected to a sufficiently high 
 temperature. 
 
 Most of the metals pass from the solid to the liquid state 
 under the influence of heat and under increased temperature 
 volatilize. Osmium, however, is an exception to this rule, 
 as it passes from the solid to the volatile condition without 
 assuming the liquid state. 
 
 The following table, by Pouillet, will give an idea of 
 temperature as displaved bv color: 
 
 °C. °F. 
 
 Incipient red corresponds to 525 977 
 
 Dull red corresponds to 700 1292 
 
 Incipient cherry red corresponds to 800 1472 
 
 Cherry red corresponds to 900 1652 
 
 Clear cherry red corresponds to 1000 1832 
 
 Deep orange corresponds to 1100 2012 
 
 Clear orange corresponds to 1200 2192 
 
 White corresponds to 1300 2372 
 
 Bright white corresponds to 1400 2552 
 
 Dazzling white corresponds to 1500 2732 
 
 Most metals expand when heated, and contract on cooling. 
 Within certain limits the expansion is proportional to the 
 degree of heat to which they are subjected. There are, how- 
 
AN OUTLINE OF METALLURGY 983 
 
 ever, certain exceptions to tliis rule. Aiitimonj' expands at 
 the moment of becoming solid, and bismuth occupies more 
 space in the solid than in the liquid state. This property ren- 
 ders these metals particularly useful in alloys of type and 
 fusible metals, where sharp, well-defined castings are de- 
 sirable. 
 
 MALLEABILITY 
 
 Mallealnlity is that property of metals by which they 
 may be beaten out or otherwise extended into thin sheets 
 without a break in the continuity of their surfaces. This prop- 
 erty varies in different metals, some possessing it to a marked 
 degree, while in others it is almost entirely absent. 
 
 Gold is the most malleable of all of the metals. It can 
 be beaten out into extremely thin attenuated sheets, 1/300000 
 of an inch tliick. In other words, it would require 300,000 
 sheets laid one upon the other to measure an inch in thick- 
 ness. Gold, therefore, is taken as the standard or unit of 
 measurement of the degree of malleability of metals, and is 
 rated "first rank." 
 
 This property is seriously impaired l)y the presence of 
 impurities, and also by heat, although the latter tends to in- 
 crease the malleability in zinc. This metal, when cast, is 
 crystalline and brittle, but when heated to about 150°C., it is 
 capaltle of being rolled into thin sheets, and these retain their 
 malleability to a considerable degree when cold. 
 
 Metals of a crystalline structure are almost totally de- 
 void of this property, while those of a soft and tenacious 
 character are the most malleable. 
 
 DUCTILITY 
 
 Ductility is that property possessed by metals by means 
 of which they may be drawn out into wire or rods, by lateral 
 compression, without breaking. 
 
 Gold liossesses this in the highest degree, since it can be 
 drawn out into the most delicate wire ; a piece one mile in 
 length having been drawn from less than one gram 
 weight. 
 
 The softness and tenacity of a metal control the degree 
 of ductility. 
 
 Ductility is affected by heat, which increases this property 
 in some metals and decreases it in others. 
 
 Lead is the least ductile because of the slight tenacity by 
 which the molecules are held together. Bismuth and anti- 
 
984 AN OUTLINE OF METALLURGY 
 
 iriony are examples of metals in which this property is almost 
 wholl}' absent because of their crystalline structure. 
 
 Steel is extremely ductile, and is now being drawn into 
 wire 1/1000 of an inch in diameter for commercial purposes. 
 
 Ductility is modified by mechanical working, the latter 
 affecting metals to such an extent at times as to render them 
 unworkable until this ])roperty is again restored by an- 
 jiealing. 
 
 ANNEALING 
 
 This process consists in heating metals and cooling, slowly 
 in some cases, and rapidly in others. 
 
 Annealing changes metals from the hardened condition 
 produced by hammering, rolling, wire-drawing, burnishing 
 and polishing, to a soft, pliable condition. 
 
 It is sui^posed that the molecules in a metal, changed 
 by the i^rocesses mentioned, are under a greater or less degree 
 of tension which, while not of sufificient force to do so, tends 
 to return them to their former relation. Under the influence 
 of heat, and, as before stated, in the case of some metals, fol- 
 lowed by sudden chilling, as when plunged into cold water 
 while hot, the tension referred to is destroyed and the mole- 
 cules are brought to a normal relation to each other under 
 the changed conditions. 
 
 The degree of hardness developed in metals h}^ mechan- 
 ical woi'king is dependent upon the character and amount of 
 force applied within and up to certain limits. In other words, 
 a moderate amount of manipulation will jiroduce a moderate 
 degree of hardness, while an excessive amount of working will 
 produce the extreme degree of hardness capable of being pro- 
 duced in a particular metal. 
 
 If a metal be worked to its extreme limit of hardness, 
 and is then annealed, a greater or less amoimt of warpage is 
 noticeable. This is apparent in swaging metal plates. The 
 base, when swaged, may lie in absolute contact with the die, 
 yet, when annealed, the adaptation will be found to have 
 changed. A slight amount of swaging will again restore the 
 adaptation, and, if annealed again, very little, if any, change 
 Avill be noticeable. 
 
 This fact renders it imperative that matrices of platinum 
 or gold foil, when adapted to cavities for inlay work, should 
 be annealed thoroughly, and a final adaptation secured before 
 introducing the porcelain for baking. By observing this sug- 
 gestion, misfits traceable to this cause are obviated. 
 
AN OUTLINE OF METALLURGY 985 
 
 Intentional or accidental alloying of the metals also 
 modifies their degrees of ductility, sometimes increasing, and 
 again diminishing, this property. The slightest trace of lead, 
 zinc, bismuth or antimony in gold impairs its ductility to a 
 marked degree, hence the necessity in dental laboratory pro- 
 cedures of keeping gold perfectly free from these baser metals. 
 
 TENACITY 
 
 Tenacity is that property of metals which enables them 
 to resist stress or dead weight when applied to rods or wires 
 in the direction of their length. 
 
 This property, as well as those of malleability and duc- 
 tility, is greatly affected and readily influenced by the pres- 
 ence of other metals or impurities, and bj^ heat, which in 
 some cases increase and in others decrease these various 
 properties 
 
 The tenacity of iron, for instance, is greatly increased by 
 the addition of a small per cent of carbon, while the presence 
 of silicon diminishes it. 
 
 In addition to the ordinary or comparative tests of te- 
 nacity of a metal, several other kinds should be considered, 
 and these are classified according to the externally acting 
 force. 
 
 Ordinary tenacity, as before stated, relates to resistance 
 to traction or direct pull ; relative tenacity, resistance to frac- 
 ture; reactive tenacity, resistance to crushing; shearing te- 
 nacity, resistance to lateral displacement; torsional tenacity, 
 resistance to twisting. 
 
 When metal bars are subjected to a certain amount of 
 tension, permanent elongation occurs. If the tension is nor 
 sufficient to produce this result, the bar will return to its orig- 
 inal length. This line of division is called the elastic limit. 
 
 In machine construction, when wires or rods are used, it 
 is essential that such parts be composed of metals of suitable 
 kind, and be of sufficient size, to withstand stress without 
 passing beyond the elastic limit. 
 
 TENSILE STRENGTH 
 
 The tenacity or tensile strength of metals and alloys is 
 tested by placing a bar of the metal of one inch sectional area 
 in a suitable testing machine and applying stress sufficient to 
 fracture it. The following table will convev an idea of the 
 
986 AN OUTLINE OP METALLURGY 
 
 wide ratine of (lirrci-cncc in tciiacity of vai'ious inctals and 
 
 iilloys. (From ( "a i-n chic's liaiifllxiok.) 
 
 Average, 
 Pounds. 
 
 Brass 18,000 
 
 Brass, wire 49,000 
 
 Bronze or "unnieial ."JG.OOO 
 
 Copper, cast 19,000 
 
 Copper, bolts ;!6,000 
 
 Copper, wire 16,500 
 
 Iron, cast 16,500 
 
 Iron, wrouglit 53,000 
 
 Iron, wire 70,000 to 100,000 
 
 Lead, sheet 3,300 
 
 Steel 50,000 to 80,000 
 
 Tin, cast 4,600 
 
 Zinc 7,000 to 8,000 
 
 ELASTICITY 
 
 This property refei-s to tlie amount of force wliieh can 
 be resisted by metals under stress without permanent de- 
 formation or "set" being i^roduced. 
 
 The "modulus of elasticity" is the force that would be re- 
 quired to double the length of a bar if its elasticity remained 
 perfect. The "modulus" is an index of the stretching capacity 
 of a metal. 
 
 FLOW 
 
 Metals which in a solid state can be shaped into any 
 required form by pressure are said to possess the property of 
 flowing. 
 
 Stamijings, lead ])ipe, rods, coins, medals, etc., are ex- 
 amples of what can be accomplished through this property. 
 The flowing property depends upon a combination of other 
 qualities, such as malleability, ductility and toughness, to- 
 gether with a siitificient amount of tenacity to permit the mole- 
 cules of metals to roll over each other without adhesion being 
 destroyed. 
 
 CONDUCTIVITY OF HEAT 
 
 Conductivity of heat refers to the property of different 
 substances for transmitting heat. The degree of rapidity of 
 heat transmission varies greatly in different substances, 
 metals being the best conductors. This property also varies 
 
AN OUTLINE OF METALLURGY 987 
 
 in the different metals, silver being the best, and it is, there- 
 fore, taken as the standard of measurement, and is rated 100. 
 
 CONDUCTIVITY OF ELECTRICITY 
 
 Conductivity of electricity refers to the capacity of metals 
 for receiving- and transmitting a current of electricity. Silver 
 in this case also is the best conductor, and is taken as the 
 standard of comparison, being rated 100. As a general thing, 
 the best conductors of heat are also the best conductors of 
 electricity. There are, however, exceptions to this. 
 
 Those metals ranking low in the scale of conductivity 
 of electricity oiTer resistance to the passage of a current. This 
 resistance is very apparent in platinum, iron and nickel, and 
 as resistance to the passage of a current is marked by a rise 
 in temperature, these metals, as well as the alloy known as 
 German silver, are used for rheostat and electric furnace 
 construction. 
 
 The electric furnace, commonly used in poreclain work, 
 consists of a metal case lined with fireclay, so shaped as to give 
 a muffle form to the interior, in which the piece to be baked 
 is placed. In the inner walls of the fireclay is imbedded fine 
 platinum wire, and as the current passes through this, it be- 
 comes heated, and the temperature in the interior of the fur- 
 nace is gradually raised to the iioint of fusion of the porcelain, 
 usually about 1200° C. 
 
 The following table gives the comparative conductivity 
 of heat and electricity of fourteen metals, and, as before 
 stated, silver heads the list in both tallies: 
 
 Heat. Electricitv. 
 
 Silver 100 Silver ." 100 
 
 Copper 85 Copper 97.8 
 
 Gold 53.2 Gold 76.7 
 
 Aluminum 31.3 Aluminum 65.5 
 
 Zinc 28.1 Zinc 29.6 
 
 Cadmium 20.1 Cadmium 24.4 
 
 Tin 15.5 Iron 14.6 
 
 Mercurv 13.5 Platinum 14.5 
 
 Iron ." 11.9 Tin 14.4 
 
 Nickel Nickel 12.9 
 
 Lead 8.5 Lead 8.4 
 
 Platinum '. 8.4 Antimony 3.6 
 
 Antimony 4.0 Mercury 1.8 
 
 Bismuth ' 1.8 Bismuth 1.4 
 
 The conductivity of a substance, as a rule, diminishes 
 with a rise in temperature. 
 
988 AN OUTLINE OF METALLURGY 
 
 EXCEPTION TO THE GENERAL RULE OF CONDUCTIVITY OF 
 ELECTRICITY 
 
 One important exception to this might be mentioned here. 
 The oxides of some of the metals, especially when combined, 
 exliibit the opposite quality, viz., being non-conductors when 
 cold and conductors when heated. This principle is made use 
 of in the construction of pyrometers or instruments for mea- 
 suring heat units and applied to porcelain furnaces. 
 
 Two methods are employed. In one ease a thermopile, 
 an apparatus consisting of two or more plates of dissimilar 
 metals, which upon being heated generate a mild current of 
 electricity, are built in the back of the furnace. As the fur- 
 nace gradually rises in temperature, the current in the thermo- 
 pile increases, which is indicated by a mila-voltmeter modified 
 to correctly register the fusing point of the various por- 
 celains. 
 
 In the other case, a Nernst glower, a small rod composed 
 of the oxides of zirconium and yttrium, which when cold is a 
 non-conductor, but which when heated readily transmits a 
 current, is placed in the muffle and connected with an inde- 
 pendent dry cell current. 
 
 As the furnace temperature rises the dry cell current 
 finds its way through the glower and is registered by an ap- 
 paratus similar to the one before described. 
 
 Profs. Dewar and Jenkins, in determining the conduc- 
 tivity of metals and alloys at very low temperatures, found 
 that the resistances of pure metals decrease in such ratio as 
 to convej' the idea that, if absolute zero could be obtained, 
 all resistance would vanish. The resistance of alloys, how- 
 ever, does not diminsh in the same ratio. For example, at — 
 200° C. the alloys — platinoid, German silver, platinum silver 
 and phosphor bronze — show nearlv the same resistance as at 
 0° C. 
 
 An illustration of the wide range of conductivity of the 
 metals can be presented by making a chain composed of al- 
 ternative links of platinum and silver wire of the same size 
 and passing a current of electricity through it. The platinum 
 links will become heated, while the silver links will remain 
 normal except at their junction with the platinum, where the 
 heat from the latter is transmitted by contact. 
 
 SPECIFIC HEAT 
 
 It has been found that different metals are capable of 
 absorbing different amounts of heat when subjected to the 
 same degree of temperature. 
 
AN OUTLINE OF METALLURGY 989 
 
 The amount of heat necessary to raise one kilogram of 
 water through one degree of temperature, from 4° to 5° C, 
 is taken as the unit or standard of specific heat, and this is 
 called the thermal unit. 
 
 The quantitj' of heat necessary to raise a kilogram of mer- 
 cury through one degree C. is only 0.033 of the heat unit, and 
 this fraction expresses the specific heat of mercury relatively 
 to water. It, therefore, follows that the same quantity of heat 
 required to raise one kilogram of water through one degree 
 of temperature would produce an equal increase in temper- 
 ature in about 30 kilograms of mercury. 
 
 The greater the specific heat of a substance, the greater 
 the heat necessary to raise the temperature through any given 
 degree, and conversely, the less the specific heat, the smaller 
 quantity of heat required. 
 
 TABLE OF SPECIFIC HEAT 
 
 Mercury 0.03332 Silver 0.0570 
 
 Gold ." .0.03244 Cadmium 0.0567 
 
 Iron 0.1138 Tin 0.0562 
 
 Nickel 0.1086 Antimouv 0.0508 
 
 Cobalt 0.1070 Lead 0.0314 
 
 Zinc 0.0956 Palladium 0.0308 
 
 Copper 0.0952 Platinum 0.0311 
 
 Palladium 0.0593 : 
 
 EXPANSION 
 
 It is a well-known law of physics that substances ex- 
 pand when heated. 
 
 This movement is particuarly marked in metals, since 
 they are good conductors of heat. 
 
 THE CO-EFFICIENT OF EXPANSION OF SUBSTANCES 
 
 The co-efficient of expansion of any substance is the 
 amount which the unit of length (surface or volume) expands 
 in passing from 0° to 1° C. 
 
 The co-efficient of expansion is constant in metals crystal- 
 lizing in the regular systen). In the others, the expansion 
 varies according to crystallization, this movement occurring 
 in the direction of the various axes. Such metals are usually 
 tested by compressing their powders. 
 
 In the industrial field a thorough knowledge of the ex- 
 l)ansion of different material is essential so that provision 
 
990 AN OUTLINE OF MRTALLURGY 
 
 may bo madt" Toi- compensating' for it in the construction of 
 buildings, bridges, and large pieces of machinery. 
 
 In assembling bridges in the dental laboratory it is es- 
 sential that an investing material be used whose co-efficient 
 of expansion is about equal to that of gold. 
 
 If one is employed whose co-efficient of expansion is much 
 greater, the assembled pieces will l)e moved apart as the in- 
 vestment expands under heat, and while in that changed re- 
 lation become fixed by the solder, the result being that the 
 bridge is lengthened. 
 
 The following table gives the linear expansion occurring 
 in metals when raised from a temperature of 0° to 100° C, 
 The fraction represents the ratio of linear expansion per 
 length of rod : 
 
 Cadmium OO.SOfi? or 1/326 
 
 Lead 002932 " 1/342 
 
 Zinc 002915 " 1/313 
 
 Aluminum 002307 " 1/432 
 
 Tin 002232 " 1/448 
 
 Silver 001930 ' ' 1/518 
 
 Copper 001()72 " 1/598 
 
 Bismuth 001620 " 1/617 
 
 Gold 001451 " 1/689 
 
 Nickel 001270 " 1/787 
 
 Iron 001070 " 1/934 
 
 Antimonv 001050 " 1/952 
 
 Platinum 000900 " 1/1123 
 
 COLOR 
 
 Most metals are gray or wiiite in color, these colors 
 merging into ])luish tinges in some cases. Gold is a rich 
 yellow color in masses, but transmits a greenish tinge in thin 
 attenuated sheets. Copper is of a decidedly red color. The 
 color of most metals is changed by alloying with other metals. 
 
 Gold alloyed with silver is changed to a greenish tinge, 
 and when alloyed with copper a decidedly red color is im- 
 parted to it. By combining silver and copi^er in proper pro- 
 portions, gold may be reduced in fineness without material 
 change in color. 
 
 WELDING 
 
 This i^rocess consists in uniting two ]iieces of metal to- 
 gether by pressure so as to form one compact piece. The 
 requisites of a metal necessary to successful welding are that 
 
AN OUTLINE OF METALLURGY 991 
 
 it must be clean, soft, and that it should possess cousiderable 
 malleability and toughness. 
 
 In the case of iron, some of these properties are devel- 
 oped only at a higli temperature, in which condition it is in 
 a pasty state. The surfaces to be united are cleaned and cov- 
 ered with borax to remove any oxide that may be present 
 and prevent further oxidation, or sand can be used also, which 
 by combining with the iron forms a fusible silicate, and which, 
 under the lilows of the hammer, is forced out from the contact 
 surfaces. 
 
 When subjected to hammering or pressure, the mole- 
 cules of metal are capable of interpenetrating or diffusing into 
 and among each other so as to form a continuous piece. 
 
 Steel must be welded at a considerably lower temperature 
 than iron because of its lower fusing point. The carbon also 
 is liable to burn out when overheated, and its quality thus be- 
 come impaired. Because of the difference in the melting 
 points, and for the reason just stated, it is difficult to weld 
 iron and steel together. 
 
 Gold is an example of a metal which can be welded cold. 
 In the form of foil, pure gold is rolled into pellets or folded 
 into small pieces and packed into tooth cavities by mallet 
 force or hand pressure. Under favorable conditions it can 
 be worked into a mass seemingly as solid as though it had been 
 cast. 
 
 In electric welding, the pieces to be united are placed in 
 a suitable device for holding them in proper contact and re- 
 lation to each other, and a powerful current of low tension 
 is passed from one piece to the other. The high resistance at 
 the junction, caused by imperfect contact, develops an intense 
 heat at this point, and when heated sufficiently the surfaces 
 are jammed together and union occurs. 
 
 The metals which weld most readily are gold, silver, tin, 
 lead, iron and nickel. 
 
 As a matter of fact, a number of the metals, when pow- 
 dered and subjected to intense pressure, can be welded cold. 
 
 The following table, by Professor Spring, shows the 
 amount of compression required to unite those listed into a 
 solid mass : 
 
 Tons per 
 sq. inch. 
 
 Lead 13 
 
 Tin 19 
 
 Zinc 38 
 
992 AN OUTLINPJ OF METALLURGY 
 
 Aiitiiiiony 38 
 
 Alumiiniiii 38 
 
 Bi.simith 38 
 
 Copper 33 
 
 Lead flows at 33 
 
 Tin flows at 47 
 
 WELDING COPPER TO IRON 
 
 A remarkable yet simple method of tveldivg eoi^per to 
 iron is being employed for many purposes in the industrial 
 fields. The copper and iron objects it is desired to unite are 
 bound in contact, placed in a crucible, and finely ground retort 
 carbon, moistened slightly with sugar water to make it ad- 
 hesive, is packed closely around them. The crucible is then 
 heated in a furnace for half an hour at a temperature about 
 midway between the melting point of copper and iron, when 
 perfect fusion of the two metals will occur, the welded joint 
 being tougher than either of the two metals. 
 
 A peculiar fact concerning this process is that the sur- 
 faces of the metals to be united need not be prepared, cleansed 
 or fluxed in any manner, the graphite and sugar taking the 
 place of the ordinary fluxes, clearing away any oxide that 
 may be present, and preventing the atmospheric oxygen from 
 getting to the joint. The molecular cohesion is as strong and 
 perfect between copper and iron as between the molecules of 
 the individual metals; such a weld is not to be compared to 
 the ordinary brazed joint, which is merely an imperfect super- 
 ficial surface union. 
 
 The process is utilized in welding steel teeth to cast iron 
 wheels, in joining pieces of wrought iron where ordinary 
 welding operations are not practicable, in the construction 
 of large gun projectiles, in ship construction, in the electrical 
 and many other fields where an absolute union between pieces 
 of similar as well as dissimilar metals is desirable. Professor 
 Simpson, of London, is given credit for this remarkable 
 method of welding copper to dissimilar metals. 
 
 ALUMINOTHERMY 
 
 From 1760, when Moreau, a French chemist, named the 
 white substance he obtained by calcining alum, "alumina," 
 because he believed it to be the oxide of a metal, until Wohler 
 isolated it in 1827, rejjeated but futile efforts were made by 
 many to discover some means of reduction of aluminum from 
 its ores. 
 
AN OUTLINE OF METALLURGY 993 
 
 The strong atSnity of alumiuiim for certain non-metallic 
 elements, particularly oxygen, is very marked. It is only 
 through the action of a powerful electric current together 
 with suitable fluxes that the oxide of aluminum is decomposed. 
 When freed from oxygeu, however, aluminum under ordinary 
 conditions is not readily oxidized, but under favorable con- 
 ditions the two elements most energetically unite, with the 
 evolution of intense heat. 
 
 This places aluminum amoug the most powerful of tlie 
 reducing agents, since many metallic oxides which cannot be 
 broken up with carbon are readily reduced by it. Professor 
 Goldschmidt, of Essen, Germany, in 1904, discovered this fact 
 and applied it to industrial purposes. So effective has it 
 proven that "alumino-thermics," as the process is called, 
 occupies a unique and iireviously unfilled place in high tem- 
 perature chemical, metallurgical, and industrial fields. 
 
 The process is comparatively simple and easy of applica- 
 tion. Finely granular, metallic aluminum together with the 
 oxide of iron and some substance to act as a flux, as fluor spar, 
 are placed in a suitable receptacle. Some magnesium filings 
 mixed with barium or sodium peroxide — a mixture highly 
 combustible — are thrown on top to "kindle the fire," or start 
 chemical action. 
 
 Almost instantly there is a flash, the development of a 
 temperature of more than 3000 C, and in the bottom of the 
 crucible lies a little button of iron with a film of slag, the oxide 
 of aluminum, covering its surface. 
 
 A mixture of granular alumini;ra and oxide of iron is 
 sold for industrial purposes under the name of "thermit." 
 This mixture when placed in a very simple hopper-like appa- 
 ratus from which it is fed to the point desired, constitutes a 
 most powerful, portable blacksmith shop. It is used for unit- 
 ing the ends of street car rails, welding them together to 
 form a "continuous rail." Large castings of iron or steel 
 when broken can l^e perfectly welded by this means, and, as 
 before intimated, the oxides of many of the metals can be 
 easily and quickly reduced without the annoying combinations 
 of metal with carbon that so frequently follow ordinary fuel 
 reduction processes. 
 
 TEMPERATURES, COMMON AND EXTRAORDINARY 
 
 Although most of the metals can be welded cold, under 
 heavy pressure, it is found more convenient as well as econ- 
 omical to render the surface to be united jDlastic by heat, so 
 
994 AN OUTLINE OK MBTALLUIUiY 
 
 that the molecidos may more readily iiitcriioiiotrato and 
 molecular xmion be established. 
 
 The degree of heat necessary to apply in successful weld- 
 ing operations coincides closely with the fusing points of the 
 metals to be united, and in soldering operations with the 
 fusing point of the solder employed. 
 
 The following list indicates some of the temperatures 
 ordinarily employed in soldering and welding operations, as 
 well as some developed for special purposes. Comparative 
 heat of the sun and hottest stars as indicated by the spectro- 
 scope is also given. 
 
 180 to 200 C soft soldering operations. 
 
 1000 to 1200 C hard soldering, as silver and the varioiis 
 alloys of gold. 
 
 1800 C is about the highest temperature attainable in a 
 fuel furnace on account of the fire clay lining fusing at this 
 point. 
 
 2000 C represents about the temperature of the oxy- 
 hydrogen flame. 
 
 3000 to 3300 C. Thermit. 
 
 3400 C oxv-acetvlene blow-pipe. 
 
 3500 to 4000 C. "electric arc. 
 
 5000 C. cordite, confined and exploded exerts a pressure 
 of 50 tons per square inch. 
 
 6000 C. estimated temperature of the sun. 
 
 30000 C. estimated temperature of some of the hottest 
 stars (Lockyer). 
 
 The last of these records can, of course, be only approx- 
 imate, since time, space, refraction of light, and other possible 
 sources of error, detract from the accurac.y of the spectro- 
 scopic scale, by means of which temperature readings of 
 celestial spheres are determined. 
 
 Even Lockyer 's temperature estimates, astonishing 
 though they seem, pale into insignificance when compared 
 with those of Arrhenius, who suggests a possible temperature 
 of 7,000,000 C. in some of the larger stellar bodies, which, 
 of course, consist of elements in a highly rarefied gaseous 
 state, and in an intensely heated and active condition. 
 
 SOLDERING 
 
 Soldering consists in uniting the surfaces of metals to- 
 gether by heat without pressure. This is usually accomplished 
 by the interposition of another metal or alloy, called a solder, 
 
AN OUTLINE OF METALLURGY . 995 
 
 that fuses at a lower temperature than the metals to be 
 united. 
 
 Soft soldering is accomplished l)y using a solder that fuses 
 below a red heat, and liard sohlcriiif/ l)y means of one that 
 fuses above a red heat. 
 
 Autogenous soldering is a process of uniting metals by 
 direct fusion of their contact surfaces, and is used principally 
 in plumbing operations. In crown and bridge work this 
 method is sometimes employed for uniting the two ends of a 
 gold band together without the interjiosition of solder, and 
 is commonly termed sweating. 
 
 In all three methods of soldering it is essential that a 
 flux be used. This prevents oxidation of the solder and sur- 
 faces to be united, and also dissolves any oxide that may be 
 present. In hard soldering and sweating operations, borax 
 or a solution of boracic acid is used most frequently. For 
 soft solder, chloride of zinc, to which a little sal ammoniac 
 is sometimes added, is most frequently used. 
 
 Eosin is also used for this purpose, and in plumbing op- 
 erations where lead joints are to be united, stearin, or tallow, 
 is often employed. 
 
 CONDITION ESSENTIAL TO SUCCESSFUL SOLDERING 
 
 The conditions necessary to successfid soldering are as 
 follows : 
 
 1. Close contact of the surfaces to be united. 
 
 2. Exposure of clean, bright surfaces over which the 
 solder is to flow. 
 
 3. Use and proper distribution of a suitable flux. 
 
 4. A solder which will fuse at a slightly lower tempera- 
 ture than the metals on which it is to be used, and which 
 will flow freely. It should also conform, as closely as possible, 
 in color and fineness to the metals to be united. This is a 
 necessary consideration in gold dental substitutes. 
 
 5. There should be a gradual and uniform application 
 and distribution of heat, and in dental operations involving 
 the use of i)orcelain facings, the flame should be directed 
 around the base and sides of the investment to drive off the 
 moisture, heat the porcelain and allow it to expand before 
 the platinum pins are heated, otherwise fracture of the por- 
 celain is likely to occur. 
 
 6. The reducing flame should be used to prevent oxi- 
 dation of the solder and the sufaces to l>e united. 
 
AN OUTLINE OF METALLURGY 
 
 THE STRUCTURE OF FLAME 
 
 To solder successfully, it is necessary to understand the 
 structure of flame. A common candle flame will serve as an 
 illustration. A flame of this character consists of four parts: 
 (1) a dark central zone or supply of unburned gas surround- 
 ing the wick; (!') the Inininous zone or area of incomplete 
 
 OUT OF CANDLE FLAME 
 
 I SEMI-HiMIXOrS FLAME 
 
 II LUMINOUS FLAME 
 
 III UNBURNED GAS ZONE 
 
 IV CARBON MONOXID PIxAME 
 
 combustion immediately outside the inner zone; (3) the outer 
 or non-luminous zone, or area of complete combusion; (4) a 
 deep blue flame at the base which extends only a slight dis- 
 tance upward, consisting of cai'bon monoxide gas. The cen- 
 tral zone of unburned gas is generated by the heat of the 
 flame acting on and decomposing the fat, and is highly charged 
 with carbon. In the luminous flame the particles of carbon 
 in the inner zone float outward and become heated and incan- 
 descent, imperfect combusion occurring, since the supply of 
 oxygen is insufficient to form CO^. 
 
 In the outer zone the supply of oxygen from the surround- 
 ing air is sufficient to produce complete combustion. 
 
 The small, deep blue part at the base of the flame con- 
 sists of carbon monoxide gas. 
 
AN OUTLINE OF METALLURGY 997 
 
 THE BUNSEN FLAME 
 
 In the Bunsen flame the gas is admitted into the base 
 of the burner, and passes up through a tube to the point of 
 ignition. Near the bottom of the tube are openings for admit- 
 ting air. As the gas passes upward, the air is drawn in also, 
 and mixes with the gas; and when ignited the flame burns 
 without himinosity, but with intense heat, because the admitted 
 air furnishes the necessary amount of oxygen for complete 
 combustion. 
 
 THE BLOWPIPE FLAME 
 
 The blowpipe usually consists of two tubes — a large 
 outer one for conducting the gas, and a small inner one for 
 admitting the air — and so shaped as to be convenient to 
 handle. (See page 998.) 
 
 "Oxiduin^ Flame. 
 --Reducin| Flame 
 
 "Mi.-xed Gas and Air 
 
 E 
 
 ■ -Inlet for Air. 
 
 BUNSEN FLAME 
 
 When in operation the air is forced in the center of the 
 flame through the inner tube by compression, and the requisite 
 amount of oxygen for complete combustion thus supplied. 
 
 The blowpipe flame consists of three zones, an inner one 
 of mixed unburned gas and air; a middle zone of bluish tinge, 
 
998 AN OUTLINE OF METALLURGY 
 
 and an outer zone, sligiitly yellowish in color. Just beyond 
 the tip of the inner blue flame is a point termed the reduc- 
 ing flame. If this flame be directed upon the oxidized surface 
 of a metal, for example, a copper coin, the surface is immedi- 
 ately brightened, and tlie oxide removed. This is due to the 
 presence of particles of carbon in excess in this part of the 
 flame uniting with the oxygen in combination with the copper, 
 and under the influence of heat COo is formed, and passes off 
 as a gas, leaving the metal clean and untarnished. 
 
 When the flame is removed, however, the oxygen from the 
 air immediately re-combines with the copper again, unless 
 some means, such as a flux, like borax, is used to prevent it. 
 
 Near the extremity of the outer cone is a point known 
 as the oxidizing flame, so-called because, when applied to 
 
 ..J^/pe for air. 
 Space for -4 as . 
 
 Air blast. 
 
 '/ieduciriif flame . 
 Oxydiz in4 f/'^''ne ■ 
 
 BLOWTIPE FLAME 
 
 metallic surfaces, regardless of how bright and clean, they 
 immediately become oxidized by the action of the external 
 air. 
 
 In all soldering operations, therefore, care sliotild be taken 
 to cover the solder and the surfaces over which it is to flow 
 ivith flux, and apply the reducing flame. 
 
 When solder is applied in considerable bulk, as in back- 
 ing crowns and dummies, in bridge work, the flame of the 
 blowpipe should be continued some little time upon the fused 
 solder, to jiermit the flux in the deei)er parts to find its way 
 to the surface. If this precaution is not observed, the re- 
 tention of the flux in the solder causes pits to form through- 
 out the mass, and in grinding down and finishing the piece 
 these are frequently exposed. When this condition occurs, 
 the case requires resoldering, or the exposed pits must be 
 filled by plugging with material of essentially the same char- 
 acter as that of which the piece is constructed. 
 
AN OUTLINE OF METALLURGY 999 
 
 MICRO STRUCTURE OF METALS 
 
 The study of the structure of metals under the micro- 
 scope is a field apart from that of general metallurgy, and may 
 more properly be included in the science of metallography. 
 
 It is impossible to obtain sections of metals transparent 
 enough for examination in the ordinary manner under the 
 microscope, therefore they must be studied by reflected light. 
 
 The surfaces of specimens to be examined are first 
 ground, and then highly polished. 
 
 This is accomplished by the use of stones and emery 
 paper of gradually increasing fineness, and aftenvards fin- 
 ishing witli fine polishing powder. 
 
 Tlie polished surface is then etched with very dilute 
 nitric acid. A mixture of equal parts sulphuric acid and bi- 
 chromate of potassium, with ten times its bulk of water, is 
 frequently used for this purpose. 
 
 The etching process brings out the structure of the metal 
 or alloy being examined, so that nnder the microscope it is 
 readily determined whether the structure is crystalline, gran- 
 ular, or amorphous. 
 
 In the examination of some steels by this method it has 
 been observed that they are not homogeneous throughout, but 
 composed of imperfectly crystallized grains called ferrite, 
 crystals of iron and carbon called cemenite, and a combina- 
 tion of ferrite and cementite, called pearlite. This method 
 of examining metals and alloys has proven of great practical 
 value in the industrial world, for by it the means of producing 
 the best qualities of crude and finished material have been 
 determined, and data established by means of which stock 
 material already manufactured may be selected for a given 
 ])urpose. 
 
 ALLOYS 
 
 Most of the metals can be united with one another in 
 various proportions by the aid of heat. The product of such 
 a combination is termed an alloy. 
 
 Alloys cannot be regarded as chemical combinations, al- 
 though it is probable in some instances that chemical com- 
 binations may occur. 
 
 MATTHIESSEN'S THEORIES AS TO THE NATURE OF ALLOYS 
 
 Mattliiessen expressed the belief that an alloy of two 
 metals may be : 
 
 First, a solution of one metal in another. 
 
1000 AN OUTLINE OP METALLURGY 
 
 Second, a chemical combination. 
 
 Third, a mechanical mixture. 
 
 Fo^irth, a solution or mixture of two, or all of those men- 
 tioned, or a perfectly homogeneous diffusion of one body in 
 another. 
 
 AFFINITY OF METALS FOR EACH OTHER 
 
 The affinity of metals for each other is variable, and con- 
 sequently they will not alloy uniformly. A good example of 
 this is seen by melting lead and zinc together. When melted 
 and agitated they may be diffused through each other, but if 
 allowed to cool slowly, they separate, the zinc, being lighter, 
 rising to the top, while the lead will settle to the bottom of the 
 crucible. 
 
 LIQUATION 
 
 This tendency of metals to separate on cooling is known 
 as liquation. In some cases it can be overcome, and in others 
 partially so, by breaking up the ingot and remelting it. 
 
 OBJECT IN ALLOYING METALS 
 
 The prime object in alloying metals is to fit them for 
 some special application for which in their pure state they 
 are unfitted. 
 
 Some of the results of alloying may be tabulated as fol- 
 lows : 
 
 1. To increase strength, elasticity and tenacity. 
 
 2. To harden. 
 
 3. To reduce the melting point. 
 
 4. To modify the color or structure. 
 
 5. To facilitate the production of sound and workable 
 castings. 
 
 6. To resist corrosion or oxidation. 
 
 Examples : Grold is alloyed with copper and silver to 
 harden it ; its fusing point reduced and its color modified 
 according to the proportions of the metals used. 
 
 Silver is rendered harder and its color modified by the 
 addition of copper. 
 
 Copper is hardened by the addition of zinc, its touglmess 
 reduced, and its reddish color changed to yellow, as is appa- 
 rent in the many-colored brasses produced. Its strength, 
 tenacity, and elasticity are enhanced by the addition of nickel. 
 
 By the addition of tin to copper an alloy known as bell 
 
AN OUTLINE OF METALLURGY 1001 
 
 metal is produced, in wbicli is developed a quality of sonor- 
 ousness not present in either of the uncombined metals. 
 
 As a general rule, the alloying of one metal with another 
 reduces the melting point of the most difficultly fusible, and 
 sometimes reduces the fusing point of the alloy below that 
 of the least fusible. 
 
 In making alloys, if the fusing points of the metals being 
 combined are widely separated, it is best to melt the most 
 refractory first, and then add the lower fusing constituents. 
 This will prevent to a great extent, at least, the tendency of 
 the latter to volatilize. The union of the low with the high 
 fusing metal should be effected at as low a temperature as 
 possible. 
 
 EUTECTICS 
 
 When two or more metals are fused, and combined by 
 heat, on cooling down, or freezing, certain portions of the 
 molten alloy frequently exhibit a tendency to crystallize be- 
 fore the entire mass solidifies. Such behavior indicates that 
 the union by fusion of the component metals has resulted in 
 not one, but a series of alloys, differing in fusibility and usu- 
 ally in physical properties. 
 
 The most liquid portion of the alloy, or that which solidi- 
 fies last, is called a entectic alloy, from en, well, and teko fuse, 
 meaning well fused. (G-r.) 
 
 The formation of eutectics may be partially obviated by 
 stirring the molten alloy until it begins to congeal. 
 
 When metals are alloyed in certain i^roportions for some 
 definite purpose, as in the compounding of solders and dental 
 amalgam alloys, the formation of eutectics is a disadvantage 
 because the component metals will not be uniformly diffused 
 throughout the mass. 
 
 AMALGAMS 
 
 An amalgam is an alloy of two or more metals, one of 
 which is mercury. 
 
 A dental amalgam alloy usually consists of tin and sil- 
 ver, to which is sometimes added a small percentage of other 
 metals, such as platinum, gold, zinc, copper, etc., for the sup- 
 posed improvement of color, edge strength, hardness and 
 resistance to stress. 
 
 As a matter of fact, any amalgam alloy will in time dis- 
 color in the mouth, while as to resistance to stress, edge 
 strength, etc., it has been demonstrated that an alloy of silver 
 and tin in the proportion of 72.5 to 27.5, when properly tern- 
 
1002 AN OUTLINE OF METALLUIUIY 
 
 pered and amalgamated, i'ullils the requirementH as well as 
 most of the alloys containing additional metals. 
 
 Dental amalgam alloys are finely comminuted, being 
 either in the form of filings or of shavings, in order to fa- 
 cilitate their amalgamation with mercury. 
 
 Copper amalgam consists of pure copper and mercury 
 usually brought into combination with the galvanic current. 
 It softens when heated and hardens again on cooling. It is 
 used very often in the tilling of temporary teeth. On account 
 of its tendency to discolor, oftentimes becoming lilack, it is 
 not extensively used for permanent operations. 
 
 SPECIFIC GRAVITY OF ALLOYS 
 
 The specific gravity of an alloy, as a rule, differs from 
 the mean of the specific gravities of its constituents. In case 
 of contraction occurring, the density of the mass has in- 
 creased, and when expansion occurs, the reverse condition 
 prevails. It is thought probable that, when the density of an 
 alloy is greater than the mean of the specific gravities of the 
 metals involved, chemical combination has occurred. 
 
 The following table, by Thenard, illustrates the varia- 
 tions of density in a number of alloys: 
 
 Alloys of greater specific Alloys of lower specific grav- 
 gravity than the mean ity than the mean of their 
 
 of their constituents. constituents. 
 
 Gold and zinc. Palladium and Ijismuth. 
 
 Gold and tin. Gold and silver. 
 
 Gold and bismuth. Gold and iron. 
 
 Gold and antimony. Gold and lead. 
 
 Gold and cobalt. Gold and copper. 
 
 Silver and zinc. Gold and iridium. 
 
 Silver and lead. Gold and nickel. 
 
 Silver and tin. Silver and copper. 
 
 Silver and bismuth. Copper and lead. 
 
 Silver and antimony. Iron and Insmuth. 
 
 Copper and zinc. Iron and antimony. 
 
 Copper and tin. Iron and lead. 
 
 Copper and palladium. Tin and lead. 
 
 Copper and bismuth. Tin and palladium. 
 
 Copper and antimony. Tin and antimony. 
 
 Lead and bismuth. Nickel and arsenic. 
 
 Lead and antimony. Zinc and antimony. 
 Platinum and molybdenum. 
 
AN OUTLINE OF METALLURGY 
 
 
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1004 AN OUTLINE OF METALLURGY 
 
 GOLD 
 
 Gold has been known and nsed from the remotest an- 
 tiquity, and its value as a medium of exchange recognized by 
 civilized and uncivilized peoples in all ages. 
 
 Alchemy was defined as the art of transmuting the base 
 metals into gold and silver, and the ancient alchemists ex- 
 perimented with this end in view. Their labors, however, 
 while not accomplishing the discovery of this much desired 
 process, did i-esult in the discovery of many curious scientific 
 truths on which the foundation of modern chemistry stands, 
 and thus gold has played a very important part in the ad- 
 vancement of science and civilization. 
 
 There is, perhaps, no other metal whose intrinsic value 
 has remained so permanent as has that of gold. Its compara- 
 tive scarceness, its beautiful, rich, yellow color, the ease with 
 which it can be worked into different forms, together with 
 the fact that it does not readily tarnish or oxidize under ordi- 
 nary conditions, may account for the high regard in which 
 gold is held. As before stated, it has been used from time 
 immemorial as a medium of exchange, and in most coun- 
 tries to-day is the basis or standard of the monetary systems. 
 
 OCCURRENCE AND DISTRIBUTION 
 
 Although comparatively scarce, gold is found qiiite wide- 
 ly distributed over the earth. It occurs native or in metallic 
 condition, and also combined with silver, lead, tellurium, or 
 with sulphides. It is obtained from two very different 
 sources; first, from placer or alluvial deposits of rivers and 
 streams, both ancient and modern, and, second, from veins 
 in rocks. 
 
 PLACER DEPOSITS 
 
 The placer deposits are the result of the weathering arid 
 disintegration of the rocks carrying the vein gold, and as 
 these fall to pieces they are washed down stream with the 
 sand, gravel and soil and settle in the beds of rivers. In time 
 the channels of the streams change, and the beds of gravel 
 or placer, bearing the gold, ai'e left high and dry sometimes 
 miles from any water. The vast placer deposits on the west- 
 ern slopes of the Sierra Nevada mountains are supposed to be 
 the beds of ancient rivers long since obliterated. 
 
 Placer gold is usually in the form of small pellets, flake^ 
 or rounded grains, the larger pieces, those weighing i/o ounce 
 or more, being called nuggets. The largest mass of gold ever 
 
AN OUTLINE OF METALLURGY 1005 
 
 found in one piece was taken from the placer deposits of Vic- 
 toria, Australia, and weighed 183 poimds, its value being over 
 $40,000. Another one, the "Blanch Barkley" nugget, also 
 found in Australia, weighed 146 pounds. A nugget was found 
 in Prussia in 1842 which weighed 96 pounds, and in Califor- 
 nia a number of pieces have been found which weighed 20 
 pounds or more. These, however, are rare instances of gold 
 occurring in large masses, the usual form being, as before 
 
 
 PANNING PLACim COLD 
 
 stated, in small flakes and grains, and frequently as fine dust, 
 the particles being so small as to be indistinguishable without 
 the aid of a lens. 
 
 PLACER MINING 
 
 Gold is obtained from placer deposits in several ways, the 
 most simple of which is by means of the "pan." This con- 
 sists of a shallow vessel, usually of sheet iron, about 14 or 16 
 inches in diameter and two or three inches deep, in which the 
 
AN OUTLINE OF METALLURGY 
 
 soil bearing the gold is placed. This is then held in water 
 and the pan given a rotary and side-to-side motion, which 
 washes out the soil and sand and leaves the gold in the bot- 
 tom of the pan. 
 
 ^^ ^ --^vV ,J-^- ^.^ -X 
 
 WASHING I'LAVEIt i;()I,ll IN 
 
 The cradle is a similar device, constructed on a some- 
 what larger scale, for washing larger quantities of soil. 
 
 The sluice is a convenient means of washing still larger 
 quantities of soil where running water is convenient. It con- 
 sists of a long flat-bottomed trough set on a slight incline so 
 that the water mav readilv run through it from end to end. 
 
 WASHING PlyACER GOLD IN A SI.L'IC'E 
 
 Across the bottom, sti'ips are placed parallel with the 
 water current, and others are placed at right angles to these, 
 thus forming a series of small comi)artments which con- 
 tain mercury. Since mercury has a strong affinity for gold, 
 the smallest particles are saved in this manner. The soil 
 
AN OUTLINE OF METALLURGY 1007 
 
 is thrown into the upper end of the shiice and the current 
 washes it down over the ridges, the lighter particles being 
 thus carried off, leaving the gold amalgam in the bottom. 
 
 At regular intervals the mercury charged with the gold 
 is removed, placed in retorts and subjected to heat. This dis- 
 tills off the mercury and leaves the gold. The mercury is re- 
 covered by conducting its vapor into suitable condensers, 
 when it is again ready for use. 
 
 These sluices vary from a few feet to several hundred in 
 length, those used in hydraiilic mining often being a mile long. 
 
 In the small sluices the soil is thrown in with shovels, 
 while in hydraulic mining it is loosened by a large forcible 
 stream of water directed against the bank or hill of gravel by 
 means of a hose with nozzle. The water used for tearing 
 down the soil is directed into the sluices and is utilized for 
 washing the gravel. 
 
 VEIN GOLD 
 
 When gold is found in veins in rocks, the rock or min- 
 eral with which it is associated is first mined, then crushed to 
 reduce it all practically to a powder. This is accomplished by 
 first crushing the rock into small pieces, and then stamping 
 tlic l)i-oken pieces of special machinery called a stamp mill. 
 
 EXTRACTION OF GOLD FROM ORES 
 
 More or less variation exists in the construction and 
 operation of stamp mills, depending principally on the char- 
 acter of the ore to be reduced. Stamp mills are usually built 
 on a side hill or inclination having a fall of at least 30 feet in 
 the length of the mill. For economical reasons they should be 
 situated convenient to both fuel and water. 
 
 The inclination of the ground enables the various pieces 
 of machinery to be placed so tliat gravity carries the crushed 
 ore from one to the other without difficulty. In the highest 
 part of the mill is placed the platform, which receives the ore, 
 and from which it is shoveled into the crusher. This breaks 
 the mineral into pieces ?i inches or less in diameter, in which 
 condition it is carried down to the stamp mill. 
 
 The stamp mill consists of large, flat-bottomed iron mor- 
 tars, into which are fitted heavy iron pestles, each weigliing 
 from 500 to 1,000- pounds. These are lifted by cam devices, 
 keyed on a revolving horizontal shaft, and fall by their own 
 weight. Stamps are usually ranged in line, in groups of five 
 stamps each, operating in a connnon mortar box. A stream 
 
1008 AN OUTLINE OF METALLURGY 
 
 of water carries tin? pulverized material against amalgamated 
 copper plates, placed in the sides of the mortar, the mercury 
 ou which retaius llic gold, wliilc tlie earthy couslitucuts are 
 washed away. 
 
 At intervals, before the mercury has become saturated 
 with the gold, the plates are removed and scraped, and the 
 amalgam thus collected subjected to powerful pressure in 
 leather bags. This squeezes out the excess of mercury 
 through the pores of the leather. The thick amalgam remain- 
 ing is then placed in retorts, subject to heat, and the mer- 
 cury distilled off. 
 
 The gold remains in the retort in a spongy state, and is 
 usually quite free from other metals, with the exception of 
 silver. It is then melted with suitable fluxes, cast into bars 
 and shipped as bullion. 
 
 CHLORINATION PROCESS 
 
 Gold ores can be reduced and the gold freed by means 
 of chlorine gas. The process is as follows : 
 
 The ore is first crushed, then roasted to expel sulphur, 
 arsenic, antimonj^ or other volatile substances that may be 
 present. The roasted ore, slightly dampened, is then placed 
 in wooden vats having false bottoms. 
 
 When the vats are charged, close-fitting covers are placed 
 over them and chlorine gas is introduced under the false bot- 
 tom. This in time rises through the false bottom and into the 
 moistened ore, converting the gold into a soluble chloride, 
 which is afterward removed by washing. From this solution 
 the gold can be precipitated by the sulphate of iron. 
 
 CYANIDE PROCESS 
 
 This iDrocess is much in favor in many parts of 
 the world because of its cheapness and from the fact that 
 low-grade ores which cannot be worked economically by other 
 processes can be reduced profitably by this method. 
 
 The advantage of the cyanide over the chlorination pro- 
 cess lies in the fact that in the method under consideration 
 it is unnecessary to roast the ore. 
 
 The process is as follows : The ore is first crushed, and 
 in this condition is placed in vats with false bottoms sim- 
 ilar to those used in the chlorination process, but deeper. 
 Water containing a small percentage of c}'anide of potassium 
 is then added to the contents and allowed to slowly percolate 
 through the mass. This process is known as lixiviation. The 
 
AN OUTLINE OF METALLURGY 
 
 gold is dissolved by the cyanide and carried out in solution, 
 when it is afterward precipitated by zinc shavings. 
 
 PHYSICAL PROPERTIES 
 
 The fusing point of pure gold is 106-1 deg. C, its specific 
 gravity 19.4, malleability and ductility first rank, tenacity 
 seventh rank, conductivity of heat 53.3, electricity 76.7, and 
 specific heat .0324. 
 
 PREPARATION OF PURE GOLD 
 
 In the dental laboratory gold scraps and filings accumu- 
 late, and these can be refined, the base metals eliminated and 
 the pure gold reduced to the desired carat by alloying with 
 pure metals in proper proportions. 
 
 Filings should be spread on a paper and a liorsesboe mag- 
 net passed back and forth through them to remove any par- 
 ticles of iron that may be present. They should then be 
 treated with acids, to remove such of the baser metals as are 
 not actually alloyed with the gold. 
 
 The gold is now placed in a flat-bottomed flask that may 
 be subjected to heat without breaking and covered with aqua 
 regia. This is composed of two parts of concentrated hydro- 
 chloric to one part of nitric acid. Heat is then applied and 
 additions made to the acid from time to time until the gold is 
 all in solution. 
 
 The solution is then weakened with water and filtered. If 
 any silver is present, it will be retained on the filter paper. 
 The solution should be further dihited until only very slightly 
 acid. A clear solution of ferrous sulphate is now slowly add- 
 ed and time allowed the gold in solution to precipitate. This 
 usually requii'es several hours. The clear liquid is then 
 drawn off and the brown precipitate of metallic gold is heat- 
 ed several times with dilute hydrochloric acid to remove iron. 
 The precipitate is then thoroughly washed to remove every 
 trace of acid, dried out, the filter paper carrying the gold 
 folded and placed on charcoal block or in furnace, borax and 
 saltpeter added and the metal fused. 
 
 TREATMENT OF SCRAP PLATE 
 
 When the clippings from plate of the same carat are 
 allowed to accumulate and kept separate, these may be simply 
 remelted, cast into the ingot mold and rolled out into plate 
 of the required thickness without the necessity of refining. 
 
mUl AN OITTLINI'; OF MKTALLUKGY 
 
 ALLOYING GOLD 
 
 For most dental purposes, with the exception of foil for 
 filling and plate for backing porcelain facings, gold is reduced 
 in fineness. That in most common nse for crowns and bridges 
 is 22 C. and 21.6 C. (coin gold) ; 20 and 18 C. gold is used for 
 dentures. 
 
 The term carat, used in this connection, indicates the 
 nunilier of parts of pure gold there is in an alio}'. Pure gold 
 is called 24 carat, and may be regarded as 24-24ths pure; 
 22 carat is 22-24ths pure, or 22 parts pure gold and 2-24 alloy; 
 20 carat is 20-24ths pure and 4-24 alloy, etc. 
 
 REDUCTION OF GOLD 
 
 The dentist can make his own gold plate and solder of 
 any desired carat, if ordinary skill is exercised. 
 
 Gold plate of a known carat can be increased or decreased 
 in fineness by the. addition of pure gold, or of gold plate of a 
 higher or lower carat. This process, whether raising or low- 
 ering, is called rcchtcf'wn. 
 
 BOSER'S RULE 
 
 A general rule that answers for l)oth methods is that 
 known as Boser's rule. "The difference betiveen the carat of 
 gold used to reduce with and the required carat, is to the dif- 
 ference betiveen the required carat and the carat of gold to 
 be reduced, as the iveight of the gold to he reduced is to the 
 iveight of reduction metal required. The iveight of the entire 
 mass, when alloyed, may be found by adding the iveight of 
 gold reduced to the weight of reduction metal required." 
 
 U. S. gold coin is 90 per cent pure gold and 10 jjer cent 
 alloy (silver and copper), or 21.6 carat fine. This is fre- 
 quently employed in crown and bridge work. It is a little 
 darker in color than 22 carat gold because of the percentage 
 of copper contained, and is more difficult to work, since it is 
 harder and stiffer; 22 carat gold is, perhaps, most generally 
 used in crown and bridge work, and 20 carat and 18 carat in 
 denture construction. 
 
 Pure gold is frequently used for backing teeth because 
 of its softness and ease of adaptation to the porcelain. 
 
 An alloy of 75 parts pure gold and 25 parts pure silver 
 (18 carat) is sometimes used for backing teeth when it is 
 necessary to impart a greenish tinge to the porcelain. Tliis 
 alloy is known as green gold. 
 
AN OUTLINE OF METALLURGY 
 
 GOLD SOLDERS 
 
 Most solders contain a trace of zinc or cadmium to re- 
 duce the fusing point of the gold so that solder of a given 
 carat may be fused upon plate of tlie same carat without 
 danger of melting the latter. 
 
 Dr. Dorrance gives the following alloy as a practical one 
 for making good colored gold solders : 
 
 Pure silver 1 part 
 
 Pure zinc 2 parts 
 
 Pure copper 3 parts 
 
 These are melted together to form an alloy, the coppei 
 and silver being melted first, after which the zinc is added 
 quickly in small pieces and the mass stirred to insure thor- 
 ough mixing of the metals, then poured into water to granu- 
 late it. 
 
 If 20 carat solder is desired, it can be made by taking 4 
 parts of this alloy and 20 parts pure gold; 18 carat gold 
 solder may be made by taking 6 parts of the alloy and 18 parts 
 pure gold, etc. 
 
 The proportion of the zinc in most solders is 1 to 21 parts 
 of the entire alloyed mass. 
 
 Dr. W. H. Trueman recommends the following solders as 
 being of good color, easy flowing, and as tough as gold plate. 
 An excess of zinc is added to compensate for some slight loss 
 from volatilization : 
 
 22 Carat Solder. 18 Carat Solder. 
 
 Pure gold 22 Gold 18 
 
 Copper 1 Copper 2 
 
 Zinc 114 Silver 3 
 
 Zinc 11/2 
 
 TABLE OF MIXED CARATATION 
 
 Tlie following table gives the proportions of the various 
 metals used in jewelers' gold plate: 
 
 Carats. Copper. 
 
 23 1/2 
 
 22 1 
 
 20 2 
 
 IS 3 
 
 IG .' 5 
 
 15 r 6 
 
 14 7 
 
 12 SV2 
 
 10 10 
 
 8 10% 
 
 Silver. 
 
 Gold. 
 
 V2 
 
 23 
 
 1 
 
 22 
 
 2 
 
 20 
 
 3 
 
 18 
 
 3 
 
 16 
 
 3 
 
 15 
 
 3 
 
 14 
 
 SVa 
 
 12 
 
 4 
 
 10 
 
 5% 
 
 8 
 
lOllJ AN OUTLINE OK METALLUKGY 
 
 Gold i)late may be made l)y using all copper, or all silver, 
 as the alloying agent, Init its color is materially changed in 
 either case, becoming darker when alloyed with the former, 
 and lighter or of a green tinge when alloyed with the latter. 
 
 As before stated, pure gold may be reduced in tineness 
 without material change of color l)y the use of silver and cop- 
 per in pro]ior proportions. 
 
 CLASP GOLD 
 
 Platinum is added to gold to impart elasticity to it, and 
 when gold is so alloyed it is called clasp 'metal. The follow- 
 ing formula is one recommended by Harris : 
 
 20 carat clasp gold : 
 
 Pure gold 20 dwt. 
 
 Coijper 2 dwt. 
 
 Silver 1 dwt. 
 
 Platinum 1 dwt. 
 
 Clasp gold is usually made of 26, 24 and 22 gauge, the 
 thickness of plate required for a given case depending on the 
 length of teeth to be clasped, long teeth requiring thin, and 
 short teeth thick, plate. (See Clasp Metals, ])age 1033.) 
 
 PLATINUM SOLDER 
 
 Formerly jolatinum base plates, dentures and the metal 
 parts of porcelain crowns and bridges were soldered with pure 
 gold, but this method was not satisfactory, because the gold 
 diffused itself into the platinum and formed a brittle, crys- 
 talline alloy, incapable of resisting much stress. For this 
 reason the use of pure gold as a solder for platinum has been 
 abandoned and an alloy of gold and platinum substituted by 
 which the difficulty mentioned is obviated : 
 
 No. 1. 
 
 Pure gold 75 parts 
 
 Pure platinum 25 parts 
 
 No. 2. 
 
 Pure gold 80 parts 
 
 Pure platinum 20 parts 
 
 No. 3. 
 
 Pure gold 85 parts 
 
 Pure platinum 15 parts 
 
AN OUTLINE OF METALLURGY 1013 
 
 SOME RECENT WORK CONCERNING GOLD ALLOYS 
 
 The following section, from page 1013 to 1063, is the result 
 of a series of recent researches in gold alloys and kindred 
 subjects., by Dr. L. J. Weinstein of New York, the copyright 
 of which he holds. 
 
 This section was written specially for and will appear in 
 Dr. F. A. Peeso's work on "Bemovable Crown and Bridge 
 Work," now in press. 
 
 The author of this valuable contribution has kindly 
 granted the writer the privilege of its presentation in this 
 Ijook. 
 
 AUTHOR'S PREFACE 
 
 "In the preparation of this contribution, it has been the 
 aim of the author to present a brief and practical rather than 
 an academic discussion of the subject. 
 
 "In addition to a consideration of the gold alloys, it was 
 found advisable to include a section on the closely allied and 
 important sul)jects of refractory materials and fluxes used in 
 connection with gold, during soldering or casting operations. 
 
 "The series of investigations, upon which this contribu- 
 tion is based, was started during the year 1908, when the 
 author experienced considerable difficulty in attempting the 
 execution of removable bridge work along the lines laid down 
 by Dr. Peeso. 
 
 "In attempting to use the coin gold and modifications of 
 same in the form of solders, he was seriously handicapped by 
 the comparatively low melting point of the coin gold and the 
 inadequacy of the other gold alloys usually obtainable, which, 
 to the man of exceptional skill, is not so apparent as to one 
 of average, or even less than average, skill. 
 
 "In view of the well-known fact that platinum is a metal 
 that could be alloyed with gold to increase the melting point 
 of the latter, a number of experiments were made to produce 
 a formula for a gold alloy sufficiently high in melting point 
 so that it could be used as a substitute for coin gold and 
 thereby eliminate the process of "sweating," which, in the 
 hands of the author and many other novices, was a more or 
 less hazardous procedure, and instead, soldering the resultant 
 high fusing gold with other gold of a melting point equal to 
 that of 24 or 22k., and thus obtaining a strong union that 
 would withstand the subsequent, and often numerous, solder- 
 ing operations required for the completion of the case. 
 
1014 AN OUTLINK OF METALLURGY 
 
 "The alloys finally (Icvclopcd wore found so satisfactory 
 that it is not too mucli to say that even in the hands of the 
 most skilled operator these alloys will prove of considerable 
 value, if for no other reason than the very great difference in 
 the melting- point between the highest and lowest fusing alloys 
 in the series and the consequent increased facility and safety 
 during the necessary subsequent soldering operations. 
 
 "In the author's efforts to obtain information from which 
 to formulate alloys he was greatly handicapped, inasmuch 
 as there were no dental publications bearing to any extent on 
 the subject. After a thorough study of the then recently re- 
 vised books on dental metallurgy, a number of experiments 
 were made, the results of which did not appear to correspond 
 with the data in the text books. A number of works on general 
 metallurgy were consulted and found to differ materially with 
 the dental text books in a great many instances, particularly 
 on data concerning the properties of the binar.y alloys of gold 
 and silver, gold and platinum, etc. In order to establish a 
 definite foundation upon which to base further researches, the 
 author proceeded to make a series of binary alloys and from 
 the resultant data was enabled to proceed with the develop- 
 ment of more complex alloys. 
 
 "The resultant formute given herein have been in prac- 
 tical use for a period ranging from two to five years, and while 
 the author does not claim that his is by any means the last 
 word on the subject, he trusts that the results of his research 
 will prove of some immediate benefit to both advanced students 
 and practitioners. ■ . ' ' 
 
 INTRODUCTION 
 
 The elements following gold have been divided into four 
 groups. This division is an arbitrary one, and made solely 
 for the purpose of facilitating future references. (See table 
 1, page 1015.) 
 
 BINARY ALLOYS 
 
 It is a well-known fact that pure gold has but a limited use 
 in the construction of various dental appliances and that it 
 is necessary to alloy it with various other metals in order to 
 increase its durability, hardness, tenacity and to vary the melt- 
 ing point above or below that of pure gold, as may be re- 
 quired. The metals in common use for this purpose have been 
 
AN OUTLINE OF METALLURGY 
 
 copper, silver and platinum, the latter to a Hunted extent; 
 also zinc, cadmium, etc., for solders, which, of course, require 
 a considerably lower melting point than the gold upon which 
 thev are to lie used. 
 
 NECESSITY OF A KNOWLEDGE OF BINARY ALLOYS 
 
 A thorough knowledge of the properties of the simple 
 binary alloys is of paramount importance, because these prop- 
 erties almost invariably give an indication of what may be 
 expected from more complex alloys. 
 
 It is generally accejjted by metallurgists that l)inary alloys 
 of gold and silver, copper, platinum or palladiiuii form solid 
 
 TABLE NO. 1. 
 THE MELTING POINTS* AND DENSITIES OF METALS. 
 
 
 Name of Metal 
 
 Symbol 
 
 M.P.'F 
 
 M.P.'C 
 
 Density 
 
 
 GOLD 
 
 Au 
 
 1945 
 
 1063 
 
 19.3 
 
 GROUP 
 
 I 
 
 Silver 
 
 Copper 
 
 Platinum 
 
 Palladium 
 
 Ag 
 Cu 
 Pt 
 Pd 
 
 1761 
 1981 
 3190 
 2820 
 
 960 
 1083 
 1755 
 1550 
 
 10.5 
 8.9 
 21.5 
 11.4 
 
 
 Iridium 
 
 Ir 
 
 Os 
 Rh 
 
 4170 
 4900 
 3525 
 
 2300 
 2700 
 1940 
 
 22.5 
 22.5 
 12 1 
 
 GROUP 
 11 
 
 Osmium 
 
 Rhodium 
 
 
 
 Zn 
 Cd 
 
 Sn 
 Al 
 
 787 
 610 
 460 
 1218 
 
 420 
 321 
 232 
 658 
 
 8 6 
 7.3 
 2.7 
 
 GROUP 
 
 
 III 
 
 Tin 
 
 Aluminum 
 
 GROUP 
 
 Nickel 
 
 Cobalt 
 
 Manganese 
 
 Chromium 
 
 Tantalum 
 
 Ni 
 Co 
 Mn 
 Cr 
 Ta 
 W 
 Mo 
 
 v 
 
 Ti 
 
 2646 
 2714 
 2237 
 2750 
 5160 
 5430 
 450n 
 31.50 
 3450 
 
 1452 
 1490 
 1225 
 1510 
 2,S50 
 3000 
 2500 
 1730 
 1900 
 
 8.9 
 8.7 
 7.4 
 6.9 
 
 14 5 
 
 15 7 
 8,6 
 6.1 
 4.5 
 
 IV 
 
 Tungsten 
 
 Molvbdenum 
 
 Vanadium 
 
 
 
 "From Circular No. 35, U. S. Bureau of Standards. 
 
 solutions. That is, solutions of one metal in another, if in 
 proportions within certain limits. Such binary alloys as will 
 be discussed, form solid liomogeneous solutions except when 
 otherwise noted. 
 
 It is therefore unnecessary to enter into an academic dis- 
 cussion of the possible molecular affinity existing among vari- 
 ous elements or of eutectics formed between the metals in 
 the binary alloys that will be considered, because such com- 
 pounds or mixtures do not occur in such alloys as may be con- 
 sidered fit for use in the mouth. For example, alloys of gold 
 and copper in the proportion of 82 per cent gold to 18 per cent 
 copper (by weight) form a eutectic, which is tlie lowest fus- 
 
1016 AN OUTLINK OF METALHTRGY 
 
 ing of the gold copjaer series, and wlicu more than 18 per cent 
 copper is present the copper is not in uniform solution and 
 segregates. As the alloys containing over 15 per cent copper 
 are extremely brittle and lack uniformity, no binary alloys 
 containing more than 10 to 12 per cent copper will be consid- 
 ered. In other words, alloys of gold and coppei", where cop- 
 per does not exceed 12 or 13 per cent, do not form any com- 
 pounds with special characteristics. 
 
 To simplify the references to ternary, quaternary or 
 more complex combinations of metals, alloys of only two 
 metals will be termed, as is customary, "binary," but the 
 alloys composed of three or more metals will be termed "com- 
 plex" alloys. 
 
 SECTION I. 
 
 GOLD AND SILVER 
 
 Silver is commonly utilized as an alloying element with 
 gold. It is used, to a considerable extent, as part of the alloy 
 in dental golds, and, as will be shown later, principally as a 
 cheapening agent. 
 
 EFFECT OF SILVER UPON GOLD 
 
 There seems to prevail generally an erroneous concep- 
 tion regarding the properties of silver-gold alloys. It has 
 been stated* that silver is used to harden and to lower 
 the melting j^oint of gold. This deduction is distinctly con- 
 trary to the results obtained by the author. After making a 
 number of binary alloys, it was proven that even the maximum 
 percentage that may be used in dental work, say 25 per cent 
 of silver to 75 per cent gold, does not confer any perceptible 
 hardness upon the gold, neither does it lower the melting 
 point to such an extent that the difference could be measured 
 with a pyrometer. 
 
 Practically the only effect silver (even if present to the 
 extent of 25 per cent) has upon gold is to discolor the gold, 
 making it greenish, and lower the specific gravity, thus in- 
 creasing the volume. It will thus be seen that silver confers 
 no special benefit upon gold, except cheapening it and acting 
 as a color modifying agent. On the other hand, it may prove 
 detrimental, as a considerable proportion of silver may inter- 
 fere with the action of other alloying elements when attempt- 
 
 *Essig's Metallurgy (Koenig's revision), p. 163. 
 ♦Hodgen's IVTetallurgy (Milberry's revision), p. 
 
 278. 
 
AN OUTLINE OF METALLURGY 1017 
 
 ing to produce a complex gold alloy, and also on account of the 
 strong affinity that oxygen and other gases possess for silver. 
 It will thus be readily seen that small percentages may some- 
 times be used to advantage as a color modifying agent, but 
 a large percentage of silver is distinctly contraindieated. 
 
 Silver, in such proportions as may be needed for dental 
 golds, alloys uniformly and without difficulty and may be de- 
 pended upon to remain in uniform distribution. 
 
 The author has found that gold alloys, with a high j^er- 
 centage of silver, when remelted and cast, show in the casting 
 a considerable variation of the silver content which indicates 
 that a partial separation takes ]ilace. This lii^s not been in- 
 
 Melting Points Or Alloys 
 Of Gold And Silver. 
 
 
 PERCENTAOE WEIGHT Or SILVER 
 
 5% Ag. M.P 1945"^. 1063°C. 
 
 10% •• 
 
 15% ■• ■■ 1943° r. loez'-c. 
 
 30% •■ ■• 1942^. 1061° C, 
 
 vestigated further for the reason that castings of gold with 
 a high percentage of silver have no practical application. 
 As stated before, small percentages of silver have practically 
 no effect upon the gold and this fact has been taken advan- 
 tage of for a considerable period of time by at least one manu- 
 facturer who alloys pure gold with from one to two per cent 
 of silver and sells it as 24k. This alloy appears so similar to 
 pure gold that the ordinary eye is deceived and the unprinci- 
 pled manufacturer is the gainer. 
 
 Fig. 1 illustrates the melting point curve of gold-silver 
 alloys. 
 
 Practically the same determination appears in very re- 
 cent works on metallurgy.* 
 
 ♦Penchel's Metallurgy. 
 
1018 AN OUTLINE OF METALLURGY 
 
 Hilvor-platimim alloys have been used to a considerable 
 extent for crown posts, dowels, backings, etc. As a rule, 
 alloys of this character (20 to 30 per cent) are extremely un- 
 satisfactory, both during their manipulation and in ultiiuate 
 service, and their use should be avoided. They are somewhat 
 improved with higher percentages of platinum, but the alloys 
 are extremely non-uniform and still quite solui)le in acids and 
 apt to discolor and corrode. The cost with more platinum 
 is considerably higher, and even then the alloys are not equal 
 to a fair grade of alloyed gold, either in usefulness or 
 economy. 
 
 GOLD AND COPPER 
 
 Copper is one of the most commonly used and most use- 
 ful alloying elements. It confers hardness and elasticity 
 upon gold, but is detrimental when used in large proportions 
 on account of its great tendency to lower the melting point of 
 the alloy and the strong oxidation and brittleness of the alloys 
 when the copper is in high proportion. It is, however, a most 
 useful, and, in fact, an indispensable alloying element if em- 
 ployed judiciously. Alloys of gold and copper, such as U. S. 
 coin gold (An. 90 Gu. 10), have been used with most satis- 
 factory results, both from the standpoint of durability and 
 resistance, against action of the oral fluids, and an alloy of 
 this character is ideal for crown work, except for the disad- 
 vantage of its low melting point, which is caused by the cop- 
 per content, and its range of usefulness is therefore limited 
 even in the hands of the skilled operator. This inadequacy, 
 as will be shown later, can be corrected by substituting pla- 
 tinum, etc., for some of the copper, tlms raising the melting 
 point and reducing oxidation without changing the valuable 
 properties the coin gold possesses, namely, strength and dur- 
 ability. 
 
 Fig. 2 illustrates the melting point curve of gold-copper 
 alloys. 
 
 As will be seen from the chart, the melting point of pure 
 gold drops rapidly upon the addition of copper; 5 per cent 
 copper lowers the melting point about 100 degs. F., 10 per 
 cent copper lowers the melting point of gold about 200 degs. 
 F., 15 per cent copper lowers the melting point about 250 degs. 
 F., and 18 per cent causes a drop in melting point of about 
 300 degs. F. As will be seen from the illustration, the lowest 
 melting point between gold and copper is when 18 per 
 cent cu. is present. The addition of more than 18 per cent cu. 
 
AN OUTLINE OF METALLURGY 1019 
 
 causes a rise in melting point until the melting point of cop- 
 per, 1980 degs. F., is reached. 
 
 As mentioned previously, it is advisable to limit the total 
 copper content to 10 or 12 per cent. Consequently, if the 
 melting i^oiiit of an alloy of gold and copper of requisite 
 strength and hardness is too low, it is necessary to use 
 platinum or palladium to bring it to the point desired. 
 
 The valuable properties of copper as a hardening agent 
 have ajiparently been underestimated by writers, but taken 
 
 
 
 
 Melting Points Of Alloys 
 Of Gold And Copper. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 \ 
 
 
 
 
 
 
 
 
 / 
 
 / 
 
 
 \ 
 
 
 
 
 
 
 
 
 / 
 / 
 
 / 
 
 
 
 \ 
 
 
 
 
 
 
 
 / 
 
 
 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 \ 
 
 
 
 ^ 
 
 /' 
 
 
 
 
 
 leso 
 
 
 V 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 PERCCNTACt WEI6MT OF COPPER 
 
 5% Cu. 
 
 10% •■ 
 
 15% " 
 
 18% ■• 
 
 1840^. 
 1735°F. 
 1690°F, 
 166 IT, 
 
 1004"'C. 
 946°C 
 9E1°C. 
 905''C. 
 
 advantage of by manufacturers, as will be noted in the com- 
 position of commercial clasp metals. 
 
 GOLD AND PLATINUM 
 
 Platinum is being used to some extent as an alloying ele- 
 ment with gold principally for clasp metal, etc. It has been 
 stated that platinum confers great elasticity and hardness 
 upon gold, which appears correct, only to a limited extent. 
 The author's experiments have indicated that platinum has 
 comparatively little effect as a hardening agent upon gold. It 
 does, however, raise the melting point considerably, as will 
 be shown later. 
 
AN OUTLINE OF METALLURGY 
 
 Platinum is much inferior to copper as a hardening agent. 
 This is readily proven upon an examination of a binary alloy 
 of gold and copper containing 10 per cent cojaper and a binary 
 alloy of gold and platinum containing 25 per cent platinum 
 (so called platinum solder). A comparison of two pieces of 
 equal dimensions will show that the gold-copper alloy, with 10 
 per cent copper, is fpiite as hard and elastic as the gold alloy 
 
 Melting Points Of Alloys 
 Of Gold And Platinum 
 
 
 
 
 
 / 
 
 ^7- 
 
 
 
 
 
 
 
 
 
 / 
 / 
 / 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 /' 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 / 
 
 r 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 S 
 
 100 
 
 percentage: weight of platinum 
 
 5% Pt. 
 10% " 
 15% ■• 
 20% •■ 
 
 BOIS-F, 
 2085°F, 
 2165°F, 
 2260"^. 
 
 1102°C. 
 1141°C. 
 1165°C 
 1228°C 
 
 with 25 per cent platinum, and more uniform. It is there- 
 fore evident that platinum is not the most suitable hardening 
 agent and its range of usefulness as an alloying element is 
 therefore limited. 
 
 Platinum, however, is an excellent adjunct to copper, as 
 it tends to raise the melting point, which is lowered sensibly 
 by any considerable ijercentage of copper. 
 
 Fig. 3 illustrates the melting point curve of gold- 
 platinum alloys. 
 
AN OUTLINE OF METALLURGY 1021 
 
 Large percentages of platinum cannot be alloyed uni- 
 formly with gold, and in order to insure a uniform alloy it is 
 not advisable to use more than 5-10 per cent in a binary alloy 
 and 10-15 per cent in a complex alloy. In the latter the other 
 alloying elements help to hold the platinum in uniform dis- 
 trihution. If it is desired to raise the melting point of an 
 au.-cu. alloy higher than 5-10 per cent platinum makes pos- 
 sible, it is advisable to use palladium, which combines per- 
 fectly in both the binary and complex alloys that will be con- 
 sidered. 
 
 GOLD AND PALLADIUM 
 
 Palladium is as yet a comparatively rare metal. It has 
 been used to some extent in the industries and arts, but prac- 
 tically to no extent in dental golds. Palladium is a metal 
 very similar to platinum except for its specitic gravity, 11.4, 
 which is considerably lower than platinum and its melting 
 point, which is also considerably lower than that of platinum. 
 
 TABLE 2 
 MELTING POINTS OF BINARY ALLOYS 
 
 GOLD, 
 
 1945° F, 1063° C 
 
 GOLD, 
 
 1945° F, 1063° C 
 
 SILVER, 1761° F, 960" C 
 
 PLATI 
 Gold 
 
 NTUM, 3190° F, 1755° C 
 
 Gold 
 
 95%— Silver 5% 
 
 95%— Platinum 5% 
 
 
 1945° F 
 
 
 2015° F 
 
 
 1063° C 
 
 
 1102° C 
 
 Gold 
 
 907c— Silver 10% 
 
 Gold 
 
 90%,— Platinum 10% 
 
 
 1945° F 
 
 
 ' 2085° P 
 
 
 1063° C 
 
 
 1141° C 
 
 Gold 
 
 85%— Silver 15% 
 
 Gold 
 
 85%— Platinum 15% 
 
 
 1943° F 
 
 
 2165° P 
 
 
 1062° C 
 
 
 1165° C 
 
 Gold 
 
 70%— Silver 30% 
 
 Gold 
 
 80c;— Platinum 20% 
 
 
 1942° F 
 
 
 2260° P 
 
 
 1061° C 
 
 
 1228° C 
 
 GOLD, 
 
 1945° F, 1063° C 
 
 GOLD, 
 
 1945° P, 1063° C 
 
 COPPER, 1980° F, 1083° C 
 
 PALLA 
 Gold 
 
 DIUM, 2820° P, 1550° C 
 
 Gold 
 
 95% — Copper 5% 
 
 95%— Palladium 5% 
 
 
 1840° F 
 
 
 2060° P 
 
 
 1004° C 
 
 
 1127° C 
 
 Gold 
 
 90%,— Copper 10% 
 
 Gold 
 
 90%— Palladium 10% 
 
 
 1735° F 
 
 
 2145° F 
 
 
 946° C 
 
 
 1174° C 
 
 Gold 
 
 85%— Copper 15% 
 
 Gold 
 
 85':;— Palladium 15% 
 
 
 1690° P 
 
 
 2250° P 
 
 
 921° C' 
 
 
 1232° C 
 
 Gold 
 
 82%— Copper 18% 
 
 Gold 
 
 80',— Palladium 20% 
 
 
 1661° F 
 
 
 2340° P 
 
 
 905° C 
 
 
 1282° C 
 
1022 AN OUTLINE OF METALLURGY 
 
 It has been stated that palladium makes gohl brittle. 
 This is contrary to the author's findings. More than twenty- 
 five different alloys were made containing from 1 to 30 per 
 cent palladium. All of them api)eared perfectly uniform and 
 remarkably malleable, ductile and tenacious. 
 
 Palladium also forms excellent uniform alloys with co])- 
 per, silver, etc., and it is a very valuable adjunct to i)latinuni 
 
 2500 
 2450 
 
 
 
 Melting Points Or Allots 
 Of Gold And Palladium. 
 
 
 
 
 
 
 
 , 
 
 --'' 
 
 ■' 
 
 
 
 
 
 
 
 *' 
 •^ 
 
 
 
 
 
 
 
 2350 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 3 2 
 
 i 
 
 4 
 
 5 
 
 6 
 
 7 
 
 9 S 
 
 3 
 
 P 100 
 
 plrcentage; weight or palladium 
 
 5% Pd. MP 
 10% •■ 
 15% •• 
 
 20% •• 
 
 2060°F. 
 2145-F. 
 2250°F. 
 2340-?. 
 
 U27»C. 
 1174»C. 
 
 1282''C 
 
 in complex gold alloys. Its use, however, is limited on ac- 
 count of the fact that it exerts a strong decolorizing action 
 upon gold, 3-5 per cent turning gold sensibly lighter and 15 
 to 20 per cent almost white (platinum color). 
 
 Fig. 4 illustrates the melting point curve of gold-pal- 
 ladium alloys. 
 
 Another remarkable and most valuable property that pal- 
 ladium possesses is the fact that, although the melting point, 
 
AN OUTLINE OF METALLURGY 1023 
 
 2820 degs. F. (1550 degs. C), is considerably lower tliau that 
 of platinum, a given percentage of palladium (by weight) 
 will increase the melting point of gold more than an equal 
 amount of platinum, and in view of the fact that platinum in 
 considerable percentages does not alloy uniformly with gold, 
 it is well to use palladium, as it alloys uniformly with gold in 
 all proportions. Therefore, in alloys where color is no object, 
 palladium may lie incor]iorato(] to very great advantage. 
 
 GOLD AND METALS IN GROUP II 
 IRIDIUM 
 
 Iridic platinum is usually employed in place of pure 
 platinum on account of its greater hardness and dui-ability. 
 When experimenting with the series of binary alloys previ- 
 ously discussed, it naturally occurred to the author that gold 
 alloyed with iridic platinum instead of pure platinum would 
 prove superior to gold alloyed with pure platinum. A number 
 of alloys were attempted and the results obtained were found 
 invariably inferior to alloys of gold and pure platinum. The 
 unsatisfactory results should have been anticipated because 
 it is well known that iridium will not alloy with gold uniform- 
 ly, but segregates on account of its extremely high melting 
 point and high specifie gravity. It is quite certain that in 
 attempting to make the alloy, the following occurred : When 
 the iridio-platinum was brought into the gold, the heat used 
 was sufficient to melt the ])latinum and set free the particles 
 of iridium which did not go into solution with the gold plat- 
 inum mixture, but susyjended and then segregated in the same 
 way as if free iridium were added to gold without the pres- 
 ence of the platinum. 
 
 The experimental alloys were made of pure gold and 15 
 per cent iridio-platinum and compared with alloys made of 
 pure gold and 15 per cent platinum. On rolling both to equal 
 gauge, polishing and etching, the gold-platinum alloy was 
 found quite uniform, whereas some sections of the gold iridio- 
 platinum alloy (?) were harder and higher fusing, while 
 other sections were softer and lower fusing than the gold- 
 platinum alloy. In addition, all the gold-platinum-iridiura 
 mixtures appeared, streaky and non-uniform, even to the naked 
 eye, while the-g'old-platinmn alloys appeared almost perfect, 
 even under the microscope. 
 
 Numerous other ex]ieriments were made along these lines, 
 and in spite of the fact that some have advocated the use of 
 
1024 AN OUTLINE OF METALLURGY 
 
 iridio-platiniim instead of pure platinum in alloys, it is the 
 autlior's conclusion that pure platinum is far superior to 
 iridio-))latinuin as an alloying element with gold. 
 
 OSMIUM 
 
 No attempts have yet been made to form alloys with 
 osmium, as it is even higher fusing than iridium and therefore 
 poor results may be anticipated. The author expects, how- 
 ever, to experiment with osmium shortly to determine if there 
 is any possible benefit to be derived from it, because alloys of 
 Os. per cent are claimed to be superior to alloys of Ir. per 
 cent.* 
 
 RHODIUM 
 
 Rhodium is a metal of the platinum group that will prove 
 of considerable benefit if sufficient of it can be obtained at a 
 moderate cost. It is quite similar to palladium. It also has a 
 low specific gravity, 12.1, and is considerably higher fusing 
 than platinum (according to U. S. Bureau of Standards). 
 
 The author has not experimented with it in the pure state, 
 but procured a quantity of it in the form of platinum con- 
 taining 10 per cent rhodium. This platinum-rhodium alloy 
 was used for a considerable time instead of pure platinum. 
 The alloys were quite satisfactory, but the advantages over 
 pure platinum as an alloying agent are so slight and the cost 
 so high that it appeared advisable to discontinue its use at 
 the time. 
 
 GOLD AND METALS IN GROUP III 
 
 A discussion of gold and metals in Group III will be found 
 in the section on Gold Solders, page 10o6. 
 
 GOLD AND METALS IN GROUP IV 
 
 Some time after the introduction of recent casting proc- 
 esses, it became apparent that in order to utilize such proc- 
 esses to advantage, alloys other than ordinarily obtainable 
 would have to be made in order to insure satisfactory results. 
 The ordinary plate golds obtainable when cast in small bulk 
 were too soft and frail, and the sections had to be cast larger 
 and heavier than normal and were therefore objectionable. 
 
 A number of experiments were made in attempting to cast 
 the various clasp metals and the results obtained were very 
 unsatisfactory. At this time began to appear literature re- 
 
 *F. Zimmerman, Alloy of Platinum and Osmium, U. S. Patent No. 
 1055119. 
 
AN OUTLINE OF METALLURGY 1025 
 
 garding- industrial alloys, both ferrous and non-ferrous, with 
 the so-called rare, or little known, metals, such as nickel, 
 cobalt manganese, tungsten, vanadium, etc., enumerated in the 
 table of elements under group 4. 
 
 Some remarkable results were obtained in various indus- 
 trial steels, brasses and bronzes and it was not unreasonable 
 to expect that some of these rare metals could be utilized to 
 advantage in the formation of gold alloys for casting pur- 
 poses. 
 
 In view of the fact that there was no precedent to follow 
 and no literature on the relation of these metals to gold ob- 
 tainable, it can readily be understood that the author's at- 
 tempts to alloy these rare metals with gold were more or less 
 empirical and the results obtained wei'e no better than should 
 have been anticipated. Meeting with such poor success, the 
 author proceeded with the series of researches into both the 
 binary and complex alloys of gold with the elements in groups 
 one, two and three, and the resultant formulte developed are 
 given in the following pages. 
 
 Since then a number of experiments have been made by 
 other investigators in attempting to utilize some of the rare 
 metals, such as nickel, tungsten, molybdenum, titanium, etc., 
 as substitutes for iridio-platinum. The resiilts so far have 
 not proven successful. 
 
 This non-success will not appear strange to those familiar 
 with both the chemical and physical characteristics of the ele- 
 ments mentioned. Unless some radical method of handling 
 these metals is evolved iridio-platinum will continue to retain 
 the position it occupies. See "elastic" gold under clasp 
 metals.) 
 
 The author has not hy any means given up hope of the 
 possible utilization of some of the "rare" elements in connec- 
 tion with alloys for casting. He is now engaged in a series 
 of experiments which have already shown promising results 
 and he hopes to have data of importance available for pub- 
 lication in the near future. 
 
 SECTION II 
 A NEW SERIES OF ALLOYS 
 
 From the ]ireceding data on the properties of the binary 
 alloys of gold wilIi the metals in group one, certain conclu- 
 sions may be drawn and data obtained and it then becomes 
 a comparatively simple matter to form complex alloys for 
 our requirements. Before proceeding to formulate a com- 
 
1026 AN OUTLINE OF METALLURGY 
 
 plex alloy, it will be well to consider again the hardness con- 
 ferred upon gold by the metals in group one. 
 
 As will be seen from Fig. 5, pure silver has practically no 
 effect on gold as far as increasing the hardness. Palladium 
 has some hardening properties and it is well to bear that in 
 mind when formulating an alloy. Platinum has considerably 
 
 100% Au 
 
 90% Au-|0%A^. 
 
 90%Au-|0%Pd. 
 
 90%Au.-IO%Pt 
 
 Comparative Haedne$s Or Binary Alloys 
 Of Gold With 10% Ag.. Pd, Pt.. and Cu. 
 
 FIGURE 5 
 
 more hardening jiower than palladium and is a factor, but cop- 
 per is the most valuable agent of them all and in proceeding 
 to formulate the complex alloys we must consider the copper 
 as the principal hardening agent and the others as adjuncts. 
 
 GOLD FOR CROWN. BRIDGE AND PLATE WORK 
 
 Bearing in mind the hardening power and the effect on 
 melting point produced by the alloying elements, let us con- 
 sider such a formula as the following: 
 
 Fonmila of Gold Plate No. 1 
 
 Per Cent 
 
 Gold 88.0 
 
 Platinmn 7.5 
 
 Palladium 2.5 
 
 Silver 2.0 
 
 Total 100.0 
 
 Melting point, 2075 degs. F., 1135 degs. C. 
 
 This alloy is equivalent in hardness to ordinary 22k. gold, 
 containing 91.6 per cent gold, 3.5 to -t per cent copper and 4.5 
 to 5 per cent silver — 100 per cent. Now, as the co]iper is the 
 acti\'e hardening agent in the 22k. gold, and as we know from 
 the preceding data that jilatinum and palladium exert some- 
 what less than half of the hardening influence of copper, it 
 will be seen that the total of 10 parts platinum and palladium 
 
AN OUTLINE OF METALLURGY 1027 
 
 are about equal in liardeuing loower to the 3.5 to 4 parts of 
 copper usually present in l22k. gold, and thus we get an 
 alloy equivalent in hardness to the ordinary 22k. plate. 
 
 The silver content, 2 parts, is no factor whatever, except 
 as a color modifying agent, because it is an object to adhere 
 to a certain standard of color throughout the whole series of 
 alloys. As there is no copper present in this alloy, it is abso- 
 lutely non-oxidizable, but the great advantage that an alloy of 
 this character possesses over ordinary 22k. plate is the fact 
 that its melting point is much above that of ordinary 22k. gold, 
 approximately 225 degs. F to 250 degs. F. higher, and instead 
 of sweating a band and floor it may be very easily soldered 
 with pure gold or 22k. plate and resoldered with the same or 
 lower grade plate gold innumcralile times without any dan- 
 ger of burning or blistering. 
 
 Any, or all, of the alloys in the series following plate No. 
 2 may be safely used as solders on plate No. 1, thus permit- 
 ting many soldering operations tcifhoiif dauger of hurning the 
 gold, as may occur in sweating, or the danger of the solder 
 (if poor quality) burning into and alloying with the gold, as 
 often occurs when using the so-called "easy flowing" solders. 
 It is evident, therefore, that this alloy offers a great many 
 advantages over the ordinary 22k. plate gold. 
 
 GOLD PLATE NO. 2 
 
 As has been impressed by Dr. Peeso. it is absolutely 
 essential to use for removable bridge work a hard, durable 
 gold such as U. S. coin gold. It may be well at this time to 
 state that U. S. coin gold contains 90 per cent pure gold and 
 30 per cent copper, whereas the so-called coin gold obtainable 
 from most supph" houses contains, as a rule, some silver, 
 which softens it and makes it icork more easily, and it there- 
 fore does not possess the strength and durability required. 
 
 The following formula replaces coin gold most satisfac- 
 torily : 
 
 Formiihi of Gold Plate No. 2 
 
 Per Cent 
 
 Gold 84.5 
 
 Platinum 8.5 
 
 Palladium 2.0 
 
 Silver .- 0.5 
 
 Copper 4.5 
 
 Total 100.0 
 
 Melting point, 1975 degs. F., 1080 degs. C. 
 
1028 AN OUTLINE OF METALLURGY 
 
 In this formula, in order to obtain the equivalent hard- 
 ness of coin gold, it is necessary to use copper. We can again 
 readily see just how the hardening properties of the alloying 
 elements are utilized. We have 4.5 per cent copper and the 
 platinum and palladium replace the rest of the copper, thus 
 giving us an alloy equal to U. S. coin gold. This oxidizes, 
 of course, to a slight extent, but the oxidation is not objec- 
 tionable, and this alloy can be used to replace coin gold prac- 
 tically for every purpose and may be soldered with other al- 
 loys in the series which have the same color. When soldered 
 with casting gold, B or C, the attachment of the floor to a 
 band cannot open up during the final soldering unless de- 
 liberately abused, because the soldered junctions are actually 
 higher in melting point than ordinary gold plate. 
 
 The fusing point of this alloy is approximately 225 degs. 
 F. higher than coin gold, and it possesses all the advantages 
 over coin that the No. 1 formula has over 22k. gold. 
 
 These alloys, Nos. 1 and 2, can be utilized to great ad- 
 vantage in the construction of swaged plates, both full and 
 partial, especially where it is desired to make the plates of 
 two or three thin layers, on account of the high melting point 
 of the alloys which permits of thorough soldering of the 
 laminfE without danger of burning. When used in conjunc- 
 tion with the other alloys in the series, these golds enable the 
 operator to produce dentures far superior to those made from 
 the golds ordinarily employed on account of increased 
 strength, minimized bulk and perfect color harmony through- 
 out the whole structure. 
 
 It should be borne in mind that high fusing golds, such as 
 these, cannot be "sweated" advantageously. This is a char- 
 acteristic of all gold alloys high in platinum metals, on account 
 of the total absence of or minimum oxidation. The "sweat- 
 ing" of an alloy such as coin gold is facilitated by the fact that 
 the high oxidation of the copper content helps to prevent tlie 
 flow of areas not fluxed. 
 
 ALLOYS FOR PROSTHETIC CASTING 
 
 As has been previously stated, in order to cast sections 
 of bridge work, saddles, partial plates, etc., it is essential to 
 have alloys that are rigid in the cast form to obviate the 
 necessity for increased bulk. Again, the value of the harden- 
 ing properties of the allojdng elements becomes apparent, as 
 in the following : 
 
AN OUTLINE OF METALLURGY 1029 
 
 FoDiiitIa of Castiiiq Gold "B" 
 
 Per Cent 
 
 Gold 80.0 
 
 Platinum 9.5 
 
 Palladium 2.5 
 
 Silver 1.0 
 
 Copper 7.0 
 
 Total 100.0 
 
 Melting point, 1900 degs. F., 1035 degs. C. 
 
 We have here 7 per cent copper and a total of 12 per cent 
 of the platinum metals which makes an alloy considerably 
 harder than coin gold. When cast, this alloy is about mid- 
 way in hardness between rolled coin gold and clas^D metal. 
 The melting point of this alloy is about 50 degs. F. below pure 
 gold. It is intended for use with the nitrous oxide blow-pipe 
 and should be melted with same, if a considerable quantity of 
 gold is to be cast. Sufficient quantities for small castings can 
 be melted with the ordinary blow-pipe. The copper content 
 being comparatively low permits of the use of the nitrous- 
 oxide blow-pipe without any material change or deterioration 
 of the alloy, if a suitable reducing flux is used in connection 
 with it. 
 
 This alloy corresponds in color with plates Nos. 1 and 2 
 and may be used to cast cusps or cusps and contours directly 
 to bands of either plate No. 1 or plate No. 2. It makes a 
 particularly suitable gold for cast occlusal surfaces on account 
 of its hardness and durability. 
 
 The next formula is a modification of "B" and brings out 
 an interesting point in connection with the effect of copper 
 and the platinum metals on the decrease and increase of melt- 
 ing points. 
 
 Fonintla of Castiiu/ Gold "C" 
 
 Per Cent 
 
 Gold 80.5 
 
 Platinum 6.5 
 
 Palladium 2.0 
 
 Silver 2.0 
 
 Copper 9.0 
 
 Total 100.0 
 
 Melting point, 1800 degs. F., 980 degs. C. 
 
 We note in this fornmla an increase of two parts of co]i- 
 per and a decrease of a total of 3.5 parts platinum and pal- 
 
1030 AN OTITLINE OF METALUTnOY 
 
 liulium, tlie conscKjucnce being that tlic melting- point is 
 <li()])ped ))y tlie increase of copp(;r and by tlie decrease of the 
 j^latinnni inetals. The melting i)oint is droi)ped about 100 
 degs. F. and brought down to a))])roxiniately that of 22k. gold. 
 This lowering of the melting point permits this alloy to be 
 melted readily for large or small eastings with an efficient 
 illuminating gas and air blow-pipe. It is identical in strength; 
 hardness, color, etc., with casting gold "B" except the fusing 
 point and resistance to the nitrous-oxide blow-pipe flame. If 
 the latter is used, precaution must be taken to use a reducing 
 flux and not superheat the metal. This applies to coin gold, 
 too, if same is cast. Excessive heat, if applied with the ni- 
 trous-oxide blow-pipe, and lack of a suitable reducing flux will 
 permit the oxidation of considerable copper and the dissem- 
 ination of oxide throughout the casting. 
 
 GOLD FOR INLAY CASTING 
 
 Since the introduction of the casting process, pure gold 
 has been generally advocated for cast fillings, etc., on account 
 of its supposed minimum shrinkage, softness and malleabil- 
 ity and consequent ease with which the margins could be bur- 
 nished to eliminate the cement line of an inlay. 
 
 A good many operators have failed to cast pure gold sat- 
 isfactorily and claim that they can cast inlays with scrap gold 
 and produce better and sharper margins. To those who have 
 not experienced this difficulty it may appear very strange, but, 
 nevertheless, it is a fact that alloyed gold, when properly 
 alloyed, and under fair casting conditions, invariabl.y casts 
 with sharp,, true margins, whereas pure gold has very often 
 failed to accomplish the purpose, both at the hands of the 
 aiithor and many others. 
 
 It may be well to consider that the casting of scrap gold 
 of indefinite composition is rather a hazardous and usually 
 unsatisfactory ^^I'ocedure, and a great many operators recog- 
 nizing that fact are using 22k. gold, coin gold, etc., with bet- 
 ter results than they have been able to obtain with pure gold. 
 
 It is a well-known fact that pure platinum, pure palla- 
 dium and pure silver absorb hydrogen, oxygen and other gases 
 while in the molten state and retain some of the gases upon 
 solidification. It is not generally known, but nevertheless 
 true, that pure gold absorbs nitrogen, hydrogen and oxygen, 
 and retains a considerable percentage of one or more of the 
 absorbed gases upon solidification.* This tendency on the 
 
 *T. K. Rose (in Metallurgy of Golci), quoting Roberts-Austen. 
 
AN OUTLINE OF METALLURGY 1031 
 
 part of the metals meutioued to absorb gases is minimized 
 and sometimes entirely eliminated by alloying and a small 
 percentage of copper, palladinm or platinnm will materially 
 alter the behavior of pure gold upon solidification. Castings 
 made with a slightly alloyed pure gold will be found to pos- 
 sess sharp margins and practically equal to pure gold in 
 color, ductility and facility of burnishing, but comparativel>' 
 free from cavities or blow-holes, such as are often found in 
 the unalloyed gold castings. 
 
 A number of eases under observation have shown that fill- 
 ings of slightly alloyed gold do not, after a period of wear, 
 present the same pitted surface so characteristic of east pure 
 gold fillings under the same conditions. 
 
 The rounding of the margins in cast pure gold fillings is 
 usually accompanied by a separation of the residue button 
 from the casting, which takes place just prior to the comple- 
 tion of solidification. This occurs particularly when a com- 
 paratively large sprue is used and more especially when a 
 large residue button is used at the same time. An explanation 
 of this occurrence may reasonably be attributed to the follow- 
 ing: If the sprue is quite large and the gold residue button 
 large, the residue remains fluid for a considerable period of 
 time after the casting pressure has been applied and there 
 appears to be a tendency for the large button to draw to it the 
 gold of the casting through the medium of the large gate (the 
 sprue). A large button of gold very often draws only part 
 of the sprue to it, thus separating the connection between the 
 residue button and the casting and arresting the exercise of 
 the casting pressure which would otherwise be transmitted 
 from the button to the sprue and then to the casting proper. 
 For those who wish to use pure gold for casting it is suggested 
 that the quantity of gold used in the casting operation should 
 not exceed more than three pennyweights above the amount 
 actually required for the casting proper, and also that the 
 sprue be no larger than 16 gauge B. and S. This will serve to 
 lessen the area of connection between the casting and residue 
 button so that this area (the sprue) may solidify more rapidly 
 and in conjunction with the smaller button, which naturally 
 freezes more rapidly, tend to prevent the separation previ- 
 ously discussed. 
 
 Another ]ioint' that is well to consider is the fact that 
 alloying of gold reduces the surface tension and cohesion of 
 the molecules while in a molten state and increases the fluid- 
 ity, thus facilitating the flow of the metal, requiring less 
 
1032 AN OUTLINE OF METALLURGY 
 
 pressure to force the gold into the mold, and consequently 
 lessening the danger of distorting the mold. (See investment 
 compounds for casting.) 
 
 Fonmihi of ('asliiig (jold "A" 
 
 Per Cent 
 
 Gold 97.0 
 
 Platinum 1.5 
 
 Palladium 0.3 
 
 Silver 0.3 
 
 Copper 0.9 
 
 Total ..100.0 
 
 Melting point. 1945 (legs. F., 1063 degs. C. 
 
 This alloy makes an efficient substitute for pure gold, as 
 the comparatively small amount of alloy does not harden the 
 gold sufficiently to prevent burnishing, nor does it affect the 
 color perceptibh'. Copper is the most suitable agent for in- 
 creasing the fluidity and the small percentage used does not 
 materially harden the gold. The drop in melting point is 
 compensated for by the platinum, and the small percentage of 
 silver counteracts the coloring effect of the copper on the 
 gold, the consequent alloy possessing practically the same 
 melting point as pure gold and producing, almost invariably, 
 sound castings without the special precautions which must be 
 taken when pure gold is used. 
 
 This alloy will be found suitable for use in teeth close to 
 others, with fillings or inlays made of pure gold, in order to 
 maintain color harmony. 
 
 As all the alloys in the series, excepting the casting gold 
 A and the elastic alloy described later, are practically of a 
 uniform color and somewhat lighter (grayish red) and less 
 conspicuous than pure gold or coin gold, it has been found 
 advisable to also formulate an alloy for casting inlays to 
 harmonize in color with the rest of the series. 
 
 Foiiniihi for Casting Gold " D" 
 
 Per Cent 
 
 Gold 95.0 
 
 Palladium 3.3 
 
 Silver . . '. 0.4 
 
 Copper 1.3 
 
 Total 100.0 
 
 Melting point, 1945 degs. F., 1063 degs. C. 
 
AN OUTLINE OF METALLURGY 1033 
 
 In this alloy, the palladium decolorizes the pure gold and 
 raises the melting point. The copper brings it back to the 
 pure gold standard and by the addition of the small percent- 
 age of silver to counteract the reddening effect of the copper 
 a color elTect is obtained in perfect harmony with the rest of 
 the series. 
 
 This gold is quite soft and malleable and may be bur- 
 nished with ]3ractically the same facility as pure gold. This 
 question of burnishing margins of inlays is rather a more or 
 less indefinite procedure. It is the author's opinion that very 
 little effective burnishing (spinning) can be done on inlay 
 margins and that only after the margins are stoned down to 
 an extremely thin edge. Experience has shown that it is 
 advisable to use hard and duralile alloys for inlays, especially 
 those intended to aid in supporting liridge work and then only 
 when supplemented with posts or dowels. 
 
 This alloy D can be combined with B or C to obtain 
 harder alloys, with no difficulty and no change in color, thus 
 enabling the operator to obtain practically any degree of 
 hardness for special requirements in inlay casting. 
 
 SECTION III 
 CLASP METALS 
 
 The alloys known as clasp metal, or platinized gold, as 
 ordinarily obtainable, have been used, with poor results, for 
 casting sections of bridge woi'k, etc., and are being used to a 
 large extent and with but mediocre results as a substitute for 
 iridio-platinum for crown posts, dowels, etc. The ordinary 
 clasp metal is also used to a considerable extent for posts or 
 dowels in the construction of cast base crowns, with usually 
 poor results on account of its brittleness, especially after it 
 has been cast again. There appear to be about four distinct 
 types of clasp metal obtainable at the supply houses. 
 
 The following formula are nearly exact and types one and 
 two readily indicate the particular role that copper plays as 
 a hardening agent. 
 
 Typo one represents a class of clasp metals of which there 
 are several on the market. They contain a trace of platinum, 
 so that they may legally be called platinized gold, and a very 
 high percentage of copper. The copper content confers a 
 high degree of hardness and elasticity upon the alloy, lint 
 during subsequent heating (soldering and annealing) and 
 
AN OUTLINE OF METALLURGY 
 
 working, the alloy softens considerably and loses a good deal 
 of the original elasticity and sometimes becomes very brittle, 
 especially when overheated.* As the melting point is quite 
 low, soldering with even a eominvratively low fusing solder 
 
 COMPOSITION OF CLASP METALS. 
 
 CONSTITUENT 
 METALS. 
 
 TYPE 
 
 1* 
 
 TYPE 
 
 2* 
 
 TYPE 
 I!* 
 
 TYPE 
 
 4" 
 
 ■ELASTIC" 
 GOLD 
 
 GOLD 
 
 (i3 
 14 
 21 
 
 65 
 15 
 13 
 
 fi3 
 17 
 7 
 13 
 
 05 
 f) 
 
 18 
 4 
 
 64 
 1.5 
 7.(1 
 
 11 
 
 16.5 
 
 SILVER 
 
 COPPER 
 
 PLATINUM 
 
 PALLADIUM 
 
 COMPARATIVE 
 MELTING POINT 
 
 1600°F 
 870''C 
 
 1725°F 
 n40°C 
 
 1S60°F 
 1015°C 
 
 I9G()°F 
 1070<'C 
 
 2100°F 
 1150°C 
 
 is apt to endanger the integrity of the alloy more often than 
 not. 
 
 Type two represents a class of clasp metals which con- 
 tain a larger percentage of platinum and less copper. This 
 alloy, while not qnite as elastic before annealing, retains its 
 elasticity after annealing or soldering, better than type one, 
 and makes a quite satisfactory material for clasps for vul- 
 canite work, etc., if not excessively heated and otherwise 
 abused. 
 
 Neither of the two alloys is suitable for work requir- 
 ing repeated soldering operations. Posts or dowels made of 
 these alloys and cast against usually show a partial fusion, 
 and although this fusion is not always evident, the posts if 
 cast against break away (at the junction) ultimately. These 
 alloys are absolutely unfit for the making of split pins. 
 
 Type three offers a much better material. It contains 
 still less copper and more platinum, but has not sufficient 
 strength and elasticity. For want of a better material it has 
 been used for the construction of split pins for a number of 
 years. In addition, the fusing point, although higher than 
 that of types one and two, is too low, and when attempting 
 
 *Gold-silver-copper alloys containing over 15 per cent copper are quite 
 brittle, very non-uniform, and variable in behavior upon annealing. 
 
AN OUTLINE OF METALLURGY 1035 
 
 to solder the solid portion of a split pin with coin gold, the 
 metal is apt to fvase partly, becoming granular and brittle, and 
 the finished pin is apt to give out in use. The t>iJe three clasp 
 metal has been cast against with fair results, but the danger 
 of burning it is imminent. 
 
 In the three types of clasp metals, under discussion, is 
 demonstrated the value of copper and its superiority over 
 platinum as a hardening agent and the value of platinum in 
 raising the melting point lowered by the copper. 
 
 A number of experiments were made to improve the type 
 three clasp metal and it can readily be seen from formula of 
 type four how comparatively simple it was to do so, having 
 established the i^roperties of the binary alloys as a founda- 
 tion. By raising the platinum to 18 points, the melting point 
 and the elasticity were increased somewhat. Even at this 
 stage the advance in melting point appeared insufficient, and, 
 as it was deemed advisable to avoid more platinum on account 
 of the danger of its not alloying uniformly, palladium, which 
 alloys readily, was added and the melting point increased to 
 a total of app. 100 degs. F. above type three. No more pal- 
 ladium was used on account of its decolorizing action. With 
 the comparatively small content (4 per cent), the color of 
 the alloy is still quite goldlike. 
 
 This alloy has been used with uniformly good results. 
 It may be soldered safely with coin gold (for split pins) and 
 may be cast against safely if a comparatively heavy gauge 
 of wire (above 16 g. B. & S.) is used. 
 
 In view of the fact that for split pins, dowels for cast base 
 crowns, etc., color is no object, it was deemed advisable 
 to raise the melting point even above that of type four and 
 the elastic gold was formulated, using a considerable percent- 
 age of palladium. The palladium, of course, decolorized the 
 alloy completely, but raised the melting point very consider- 
 ably, and, in conjunction with tlie copper and the considerable 
 percentage of platinum, produced an elasticity even beyond 
 that of type four and a melting point very considerably 
 higher. 
 
 This alloy can be soldered with perfect safety with pure 
 gold or anything below that in melting point. It may be 
 cast against with perfect safety (except very thin wire) and 
 retains its strength and elasticity after any reasonable num- 
 ber of soldering operations that it may necessarily be sub- 
 jected to. It may he soldered veri/ readily and nnth better 
 union that iridio platinum. It is much more rigid than ordi- 
 
1036 
 
 AN OUTLINE OF METALLURGY 
 
 iKiiji ii'idiii jildlhinni (iihI possesses elasticity that is prac- 
 tically absent in all of the iiidio platinum alloys, and it may 
 therefore replace tlic hilhr and ordinary clasp metal for a 
 great many purposes. 
 
 In the making of split posts of the elastic gold it is advis- 
 al)le to solder the area that is intended should remain solid 
 with coin gold, as it offers a strong color contrast to the com- 
 paratively white elastic gold. 
 
 The line of demarkation between the solid and the split 
 13ortions of the post will be then readily distinguished. As 
 the coin gold is of sufficiently high melting point it will not 
 reflow during later soldering operations. 
 
 The comparative hardness and the elasticity of the four 
 types of clasp metals and the "elastic" gold is approximately 
 as illustrated in the following: 
 
 COMPARATIVE ELASTICITY AFTER 
 ROLLING AND ANNEALING ONCE 
 
 Type 
 One 
 10 
 
 Type 
 
 Two 
 
 9 
 
 Type 
 
 Three 
 
 8 
 
 Type 
 Four 
 
 9 + 
 
 "Elastic" 
 Gold 
 
 10 + 
 
 
 Fig. 7 
 
 
 COMPARATIVE LOSS OF ELASTICITY AFTER 
 SOLDERING AND ANNEALING THREE TIMES 
 
 Type 
 One 
 2-3 
 
 Type 
 Two 
 1-2 
 
 Type 
 Three 
 
 1 + 
 
 Type 
 Pour 
 
 1 
 
 "Elastic" 
 Gold 
 .5-1 
 
 Types one and two become very brittle if overheated dur- 
 ing soldering. Type three is subject to same to a lesser de- 
 gree, and type four only rarely. The "Elastic" gold appears 
 practically immune to temperatures below the melting point 
 of pure gold. 
 
 Clasp metal should always be annealed before use, as 
 manufacturers often neglect to do so after the rolling or 
 drawing operations. 
 
 SECTION IV 
 
 GOLD SOLDERS 
 
 In order to obtain the desirable uniformity of color in a 
 denture without subsequent gold "washing," it was neces- 
 sary to formulate solders to correspond in color with the 
 
AN OUTLINE OP METALLURGY 1037 
 
 other alloys. Ineideutally, it is well to consider the imposition 
 that has been practiced upon the profession by some of the 
 unscrupulous manufacturers of gold solders. 
 
 For many years a great many in the profession have 
 been under the im23ression that gold solders stamped 18k. 
 were actually 18k. (75 per cent gold) in fineness. This was 
 not so, and a number of the manufacturers were producing, 
 and are still producing, solders marked 18k., etc., anywhere 
 from two to six karats below the mark. In addition, the sol- 
 ders mentioned are not only deficient in gold content, but con- 
 tain man.v deleterious alloying elements, such as high per- 
 centages of cadmium, iron, etc., in order to complete the re- 
 quired total content of metals in the solders. 
 
 On the other hand, the reputable manufacturers have con- 
 sistently stated that their solders were approximately two 
 karats below the mark and intended for use on that karat of 
 plate. The reputable manufacturers have recently started to 
 stamp the actual fineness on their solders and the others have 
 followed suit; but some manufacturers still persist in the 
 practice of misrepresentation by not actually furnishing the 
 gold content indicated by the fineness stamp on the product. 
 
 ALLOYS OF GOLD WITH METALS IN GROUP 3 
 
 Besides zinc, the other three metals in Group 3, namely, 
 cadmium, tin and aluminum, are being used to a very large 
 extent as alloying elements in making gold solders. Cadmium, 
 if used in large percentages, debases the alloy very consid- 
 erably and renders it practically unfit for use in the mouth. 
 
 Tin is also used to a considerable extent, as it lowers the 
 melting point of gold very considerably, but it renders the 
 gold quite brittle and aids materially in the tendency of the sol- 
 der to burn into the work, which property is characteristic of 
 all the so called easy flowing solders. The term "easy flowing" 
 is undoubtedly a misnomer. Bather, these solders melt 
 "easy," but do not flow easy. They ball up and stick and if 
 the heat is forced to induce flow, they burn into the work with 
 consequences too well laiown to require fui'ther discussion. 
 
 The volume of aluminum as a constituent of gold solders 
 is yet to be proven. It is a constituent of most of the patent 
 commercial alloys used by jewelers in compounding their 
 solders. 
 
 Solders made according to the following formula? will 
 be found satisfactory in color, strength and fusing point, al- 
 though higher in fusing point than the so-called easy flowing 
 
1038 AN OUTLINE OF METALLURGY 
 
 solders for which there seems to be a "popnUir" demand. 
 They will be foimd to flow readily if the work on which they 
 are to be used is brought up to the proper temperature. 
 
 FORMULA FOR GOLD SOLDERS 
 SOLDER NO. 84 
 
 TGoW 84.09^ 1 
 
 M. P. 1650° F, 900° C-^ SHver ITv f "^ KsiTut fine. 
 
 Izinc 3.0% J 
 
 SOLDER NO. 76 
 
 rGoId 76.0% 1 
 
 M. P. 1550° F, 840 C g°/^'g^'" '^8'5% ( ^** ^^''^^ ""^' 
 
 Izinc 4.07pJ 
 
 SOLDER NO. 68 
 roold 68.07f,-| 
 
 M. P. 1450° F. 785° C"^ ^"P^®'" It'lt? [ ^^V- Karat fine. 
 
 Sliver 12.5% ( 
 
 I Zinc 5.0% J 
 
 The first and second, 84 and 76, will be found sufficiently 
 low in melting point for all ordinary operations, and where 
 Dr. Peeso recommends the use of his No. 21 and No. 19 solder. 
 The number 68 solder, although higher in actual gold content 
 than the best so-called 18k. solder obtainable, is still too low 
 a grade to be used in general work, especially in fixed bridge 
 work, but may be used in connection with removable bridge 
 work or plate work, because in that work or repair work there 
 is I'equired at times a lower fusing solder. 
 
 SECTION V 
 COMPOUNDING OF GOLD ALLOYS 
 
 Although the new series of alloys, made with practically 
 no deviation from the formula? which are given herein, may 
 be purchased from the supply houses, the author considers it 
 well to give a number of directions to those who may desire 
 to compound the various alloys. 
 
 It is not practical to make a small quantity, especially if 
 for plate gold or solder, which is to be poured into an ingot 
 mold and rolled. The higher the melting point of the alloy, 
 the more necessary it is to have a comparatively large quan- 
 tity and it is well not to attempt less than five ounces for plate 
 gold and three ounces for solder. The elastic alloy should be 
 made in even larger quantity, as it freezes very rapidly. 
 
 It is practically impossible to alloy platinum or palladium 
 with gold in the small blast furnace which the practitioner is 
 
AN OUTLINE OF METALLURGY 1039 
 
 likely to have in his laboratory. For all alloys with platinum 
 metals (made on the small scale previouslj^ mentioned) it is 
 well to alloy the gold and the platinum metals (rolled very 
 thin) first on a charcoal block, using the nitrous oxide and 
 illuminating gas blow-pipe, or preferably the oxygen and 
 illuminating gas blow-pipe. A number of the alloyed nuggets 
 can then be placed in a crucible on top of the required silver 
 and copper content, covered with a suitable I'educing flux and 
 melted, poured into an ingot mold and rolled or drawn. 
 
 When copper is to be used, it is essential that same be 
 chemically pure and especial precaution must be exercised to 
 prevent oxidation as far as possible, which latter can be ac- 
 complished by the use of a strong reducing flux. (See under 
 fluxes.) 
 
 A slight excess of copper should always be added to allow 
 for some loss which invariably occurs. 
 
 If the alloy that it is intended to make is to be used for 
 casting purposes, the procedure is the same as previously de- 
 scribed, excepting that the metal, when properly molten, can 
 be poured into a pail of water and thus granulated. This pro- 
 cedure saves the labor of rolling the ingot and the granulated 
 form of gold is as convenient to use for casting as any other. 
 
 In all cases, just before pouring the contents, the crucible 
 should be well shaken to insure a thorough admixture of the 
 metals. 
 
 Some writers advocate the preparation of alloys for cast- 
 ing in the following manner: Melt the gold, feed the platinum 
 (very thin) into the molten gold and then add copper, etc. It 
 is impossible to make a uniform alloy in this manner, espe- 
 cially if copper is used, because a considerable amount of the 
 copper is oxidized on account of direct contact with the blow- 
 pipe flame and in the author's hands the directions previously 
 given have been found to work out admirably. 
 
 In compounding solders where zinc and copper are the 
 constituents it has been advocated that brass which contains 
 copper and zinc be used in order to prevent the loss of zinc 
 through oxidation and volatilization. This is a very danger- 
 ous practice and the results are very unsatisfactory, because 
 it is impossible to obtain a commercial brass that does not 
 contain a considerable percentage of lead, tin, and traces of 
 antimony, etc., ^t^hich are all very harmful substances and 
 invariably teiid to make the solders brittle. It is therefore 
 necessary to first make an alloy of chemically pure zinc and 
 chemically pure copper in a proportion of, say, one part zinc 
 
1040 AN OUTLINE OV METALLURGY 
 
 and two pai'ts copper. Tliis alloy, when properly melted, 
 is granulated by ijouring into water and then, if carefully 
 gathered, dried and weighed, the loss of zinc can be deter- 
 mined. The necessary additional copper to make the required 
 alloy is then calculated and added when compounding the 
 solder. 
 
 It is well, of course, to make a considerable cpiantity of 
 the copper zinc alloy, as the cost is slight and the prepared 
 alloy is then available when wanted. It has been stated that 
 zinc volatilates very readily from solders. This is quite con- 
 trary to the author's findings. The small percentage of zinc 
 as given in the formulas herein is quite stable after remelting 
 several times. The authors who claim this strong volatiliza- 
 tion of zinc may have been dealing with a solder of unknown 
 constitution in which they suspected zinc, but which probably 
 contained a high percentage of cadmium, which volatilates 
 quite readily. 
 
 SECTION VI 
 
 REFRACTORY MATERIALS 
 
 INVESTMENT COMPOUNDS FOR SOLDERING 
 
 The normal contraction of gold from the molten to solid 
 state is approximately 2 per cent. The contraction of gold 
 solder is practically the same, although some of the constitu- 
 ents have a higher contraction than gold, but when combined 
 in an alloy the movement is practically the same. 
 
 While possibly there may be a slight difference between 
 the contraction of solder and gold, a considerable contraction 
 occurs nevertheless and is the cause of a great deal of trouble. 
 
 A number of soldering investment compounds on the 
 market are claimed by the manufacturers to possess neither 
 expansion nor contraction and therefore perfect. Granting, 
 for the sake of the argument, that such is the case, we still 
 have the contraction of solder to contend with and how are we 
 to produce a soldered bridge or denture that will tit and go 
 into place accurately when a number of the units in the work 
 have been drawn together by the contraction of the solder? 
 
 Unfortunately, we have not merely the contraction of the 
 solder to contend with, but we have a much more prolific cause 
 of disaster. For example, we have a number of completed sec- 
 tions, such as castings, to join together where but a very 
 small quantity of solder is to be used, and yet after soldering 
 we find that the finished piece is contracted and distorted and 
 
AN OUTLINE OF METALLURGY 1041 
 
 will not go into position. The fact of the matter is, that prac- 
 tically all the commercial compounds shrink upon heating 
 when brought up to the proper temperature for soldering. 
 
 In some commercial investment compounds, the shrinkage 
 is extremely high, fully six or seven per cent,* so it is evident 
 that the principal cause of the troiible lies not so much in the 
 actual contraction of the solder as it does in the great contrac- 
 tion of the average investment, even before the case is quite 
 hot enough to apply the solder. 
 
 Fig. 8 shows an ordinary simple bridge assembled and 
 read}^ for investment. The porcelain facings are spaced as 
 
 FIGURE 
 
 per instructions from time immemorial. Fig. 9 shows the 
 case invested and the distinct spacing of the backings. 
 
 The case is then heated, and if an examination of the 
 investment is made with a magnifying glass, just before plac- 
 ing it on the soldering block, it will be noticed that the units 
 have been drai''n together, as in Fig. 10, and when the case is 
 
 *See papers of J. G. Lane in Dental Cosmos and Dental Digest, 1910-14. 
 Also M. A. Ward in Dental Cosmos. These contributions are very inter- 
 esting and tlie most valuable that have appeared pertaining to the subject. 
 
1042 AN OTITI.INK OF METAIJATRGY 
 
 soldered and cooled, tlie facings are very apt to be checked on 
 account of having been brought together into very strong 
 contact. 
 
 When attempting to place back on the cast, difficulty is 
 encountered, but as the plaster yields, the bridge is forced 
 
 down and then becomes evident tlie loss of the contact points, 
 as illustrated in Fig. 11. 
 
 This discrepancy will not be considered by some oper- 
 ators as a serious factor. In fact, those who solder directly 
 on the cast destroy the evidence for the time being. If it is a 
 fixed bridge, it is forced home some way or other and let go 
 at that, but, on the other hand, if a removable bridge, even as 
 small in dimension as the one illustrated, it is practically 
 impossible to place it in position and the matter is a most 
 serious one, as a good many operators have found. 
 
 Some writers advocate completing the dummies and then 
 placing them in perfect contact to prevent the shrinkage of 
 the solder used to unite the sections. This is practically im- 
 possible, because the metallic units are infinitely stronger than 
 
 the investment and expanding under heat will invariably split 
 the investment (see Fig. 12), and thus often cause a serious 
 distortion in the soldered piece. 
 
 There seems to have been, as a search of the literature 
 has shown, absolutely no consideration given to the movement 
 of the refractory mass that holds the parts in situ during the 
 preliminary heating and final soldering operations. 
 
AN OUTLINE OF METALLURGY 1043 
 
 The author's aim in experimenting has been not merely 
 to produce an investment compound that would not shrink, 
 but one that would actually expand, move in unison with the 
 solid invested metal, and spread the units sufficiently so that 
 when a reasonable amount of solder is flowed to connect the 
 units, the contraction of the total piece loould he neutralized 
 by the expansion of the investment. 
 
 Before attempting to formulate an investment compound 
 possessing such properties, it is necessary to consider the 
 chemical and physical properties of refractory materials which 
 may be employed in the compounding of investment materials. 
 
 In one of the well-known books on crown and bridge 
 work.* the following appears. 
 
 "Many substances may be used in combination with plaster of 
 Paris, which is necessarily the basis because imparting the property 
 of crystallization, and which must be incorporated to the extent of 
 at least 50%. 
 
 "The remaining proportion may be then composed of such ma- 
 terials as will, by virtue of their characteristics and physical prop- 
 erties, meet such requirements. The following are serviceable: 
 Powdered Silex, Pulverized Pipe Clay, 
 
 Pine Asbestos, Powdered Fire Brick, 
 
 Beach Sand, Magnesium Oxide, 
 
 Marble Dust, Pumice Stone. 
 
 "A combination of any of these ingredients in varying propor- 
 tions with the proper quantity of plaster will usually possess the 
 necessary qualities, etc., etc." 
 
 Before even considering a compound of expanding prop- 
 erties, it is well to thoroughly understand the properties of 
 plaster of paris and the other materials enumerated in the 
 list of suitable refractories in order to see if it is possible to 
 even produce an investment compound that will at least not 
 shrink under heat. 
 
 PLASTER OF PARIS 
 
 Plaster of paris, Ca SO4 (calcium sulphate), is made by 
 burning gypsum rock. In the process of burning, most of the 
 water is driven off. The phenomena of recombining with 
 water and crystallizing is well known and need not be discussed 
 here. It is universally employed as the binder for all in- 
 vestment compounds used both for soldering and casting. It 
 shrinks very strongly upon heating, but for want of a better 
 material must be employed. 
 
 The more plaster used in an investment compound, the 
 harder the resultant mass will be and the more shrinkage will 
 take place. As will be shown subsequently, any such propor- 
 tion as the 50 per cent mentioned by the author quoted is abso- 
 
 •Goslee's Principles and Practice of Crown and Bridge Work, pp. 36-37. 
 
1044 AN OUTLINE OF METALLURGY 
 
 lutely out of question, because it has been found, so far, im- 
 possible to compensate for this contraction of the binder by 
 the addition of any other material, even if possessing the 
 property of expansion. 
 
 POWDERED SILEX 
 
 Silex is the commercial term applied to silicon dioxide 
 (Si Oo), which is the main constituent of rocks, stones, clays 
 and many other minerals. A great deal of it is also found 
 in a free state and in the form of quartz, rock crystal, flint, 
 opal, chalcedony, etc. The so-called silex is often practically 
 pure Si O2. However, different varieties of silicon dioxide 
 exist, and although all of a similar chemical composition they 
 possess varying physical properties. 
 
 Silica obtained from quartz or rock crystal consists of 
 sharp crystalline particles and possesses a high specific grav- 
 ity, 2.6 to 2.8. It expands considerably upon heating, but 
 loses this property gradually upon reheating frequently or 
 fusing completely.* The melting point of pure silica is ap- 
 proximately 3,200 degs. F. 
 
 Another variety of silica that exists quite as frequently as 
 the crystalline is an amorphous form which possesses a lower 
 specific gravity, 2.2 to 2.4. It has very little expansion upon 
 heating and some varieties of the same type do not expand at 
 all.** ' 
 
 Still a third variety exists in a tabular form and is ex- 
 tremely light and porous. It is known as diatomaceous earth 
 or kieselguhr. Its specific gravity is 1.6 to 1.8. It is mined 
 in very great quantities and used very extensively as a heat 
 insulating agent, but contracts very strongly and therefore is 
 totally unfit for use as part of a dental refractory compound. 
 
 As stated before, these various forms of silica can be ob- 
 tained in almost a pure state and are alike chemically, but 
 the term "powdered silex" means nothing unless a particu- 
 lar type is specified, and the individual who is not conversant 
 with tlie matter is as likely as not to purchase and use a 
 grade of least expansion. The crystalline variety, of high 
 
 *Utensils made of fused silica are replacing platinum ware to a great 
 extent in chemical work. As the coefficient expansion is very small 
 (.00000054 per ° C) it is possible to subject crucibles, casseroles, etc., to 
 rapid changes of temperature without danger of breakage. Apparatus suit- 
 able for dental purposes is manufactured by the Thermal Syndicate, Ltd., 
 of New York. 
 
 **Both surface and volume expansion of silica must be considered in 
 selecting the grades of silica to be used. 
 
AN OUTLINE OF METALLURGY 1045 
 
 specific grarifij, expands coiisiderabltj under heat, and in this 
 fact lies tJie solution of the whole problem. 
 
 A mixture of 50 per cent plaster of paris and 50 per cent 
 silica, even if the latter is of the variety possessing the highest 
 expanding properties, contracts very considerably when 
 bronglit np to the temperatnre required for soldering or cast- 
 ing oi^erations. 
 
 In order to be brief, the author will state that all the 
 otlier items in the list of suitable materials have a positive 
 shrinkage, with the exception of beach sand. The objection 
 to the latter is the fact that it is often quite impure and the 
 iron and alkalies that form the major portion of the impuri- 
 ties usually act as a flux and thus lower the melting point. 
 
 It is well to state that magnesium oxide and marble dust, 
 which latter is, of course, calcium carbonate, are subject to a 
 particularly strong contraction under heat. 
 
 Fig. 13 illustrates the comparative shrinkage of one of the 
 best commercial compounds olitainable. A considerable space 
 
 will be noted between the mass of investment and the rim of 
 the metallic ring in which it was placed after mixing, permit- 
 ted to set and heated to soldering temperature. 
 
 Fig. 14 (in cross-section) shows even more clearly the con- 
 traction, after heating, when a straight edge is placed across 
 the top of the flask. 
 
 To summarise the whole proposition, the author will state 
 that in order-to produce an investment compound that merely 
 does not shrink, but actually expands siifficiently to follow the 
 movement of a red hot ring, that it is necessary to use a grade 
 of silica as pure as possible and of the highest expansion, 
 
AN OUTLINE OF METALLURGY 
 
 ii'liich mediis of course a fjrade silica from the quarts group 
 and. a grade of plaster of paris of the least contraction* As 
 previously mentioned, any such proportion as 50 per cent 
 plaster cannot he used, because the expansion of the best sil- 
 ica, great as it is, is not sufficient to compensate for even the 
 slirinkage of the plaster, hence a loiver percentage of plaster 
 and a higher percentage of silica must be used. 
 
 Formula for Inresf)nent Compound {Soldering) 
 
 Per Cent 
 Plaster of paris (Excelsior Brand No. ?>) . .Parts 33 
 
 Silica (fine) (F. F. F.) Parts 45 
 
 Silica (coarser) (M. C.) Parts 22 
 
 Total 100 
 
 A componnd made according to this formula will be found 
 to expand upon heating to soldering temperature sufficiently 
 to fill a red hot ring, as in Figs. 15 and in. 
 
 FIGUEE IC 
 
 This property of expansion is sufficient to counteract the 
 contraction of a normal bulk of solder. Furthermore, this 
 expansion is sufficient to follotv the movement of invested 
 metallic sections that have been previously completed. This 
 compound sets promptly and is sufficiently strong to hold the 
 invested parts in situ firmly. It will withstand the action of 
 boiling water (when washing out the wax) without disintegra- 
 tion. 
 
 *It is, no doubt, well known that fine plaster contracts more than coarse 
 plaster when subjected to heat. Most of the coarse building plasters are 
 rather non-uniform and do not possess the binding power of the finer plasters. 
 The grade selected is quite uniform and not too coarse to prevent efficient 
 binding of the mass. 
 
AN OUTLINE OF METALLURGY 1047 
 
 Dr. Peeso has long ago demonstrated the great impor- 
 tance of not soldering Avork directly on the cast. The work 
 should be so assembled that the waxed up structure could be 
 lifted off the east, which is made of plaster of paris or a more 
 durable material such as "Artificial Stone" (made from the 
 author's formula) and then transferred to the investment 
 compound. After soldering, the work could be placed back 
 on the cast, which is intact, and required corrections could be 
 made by grinding or trimming where necessary before the 
 structure is even tried in the mouth. 
 
 Of course, the author has made numerous and exhaustive 
 experiments to determine the properties and behavior of vari- 
 ous refractory materials and it is important that the grades 
 of silica and plaster specified be used. 
 
 As the reader can deduct from the preceding, the terms 
 silica and plaster of paris mean very little, because while the 
 different grades of silica are practically alike chemically, they 
 differ very materially physically. To the author's knowledge, 
 it is possible to purchase at least three or four himdred dif- 
 ferent brands of plaster and over a thousand distinct grades 
 of silica with varying percentages of impurities and varying 
 sizes of particles.* There is no intention to claim that this 
 is the last word on the subject. No doubt, other experiment- 
 ers will succeed in producing as good or even a better com- 
 pound with other grades of material. 
 
 INVESTMENT COMPOUNDS FOR CASTING 
 
 The elements of error caused by the physical behavior of 
 the metallic alloys and the refractory materials utilized in 
 the casting process are cjuite analogous to the conditions that 
 exist in the soldering process. Gold, no matter how alloyed, 
 as far as present knowledge of the subject indicates, does con- 
 tract in the transition from the fluid or plastic state to the 
 solid or frozen state, and an inlay investment compound that 
 possesses the property of expansion will at least in a measure 
 compensate for the contraction of gold. 
 
 It is not the author's aim here to exhaustivelj' discuss 
 casting problems in general. He simply wishes to suggest a 
 
 *The materials used in the formulae given were obtained from W. B. 
 Daniels, 252 Front street. New York City, who is a dealer in minerals and 
 chemicals. He will supply the ingredients for both the soldering and casting 
 compounds in quantities suitable for the requirements of the practitioner. 
 Of course it must be remembered that such comparatively cheap materials 
 are, as a rule, sold by the ton or carload. Hence, Mr. Daniel's willingness 
 to furnish these materials in small (luantities at a moderate price deserves 
 commendation. 
 
1048 AN OtTTLINE OF METALLURGY 
 
 fonuula for what lie considers a better investment compound 
 than is inireliaseable and to point out some of the physical phe- 
 nomena of existing conditions. Before discussing the formula, 
 it is well to first consider some of the conditions that have 
 to be dealt with. We have not only the contraction of gold 
 to contend with, but we also have the contraction of the wax, 
 and that is a most serious factor indeed. The contraction of 
 wax is usually productive of a greater degree of error than 
 the actual contraction of gold. 
 
 This subject has been covered most thoroughly by Dr. C. 
 S. Van Horn of Bloomsburg, Pa., in his articles in the Den- 
 tal CosmoS;* and his conclusions are yet to be controverted. 
 
 The conditions which he successfully corrects are the fol- 
 lowing: After the removal of a wax pattern from the mouth 
 at body temperature, it contracts considerably upon reaching 
 room temperature and still more when invested with cold 
 water. His method consists of investing the pattern at ap- 
 proximately 110 degs. F., which increase in temperature not 
 merely compensates for the contraction of the wax, but also 
 expands the wax to almost completely counteract the shrink- 
 age of the gold. 
 
 In addition, he uses an expanding investment (made 
 from the author's formula) and the total expansion of the 
 wax, coujiled with the expansion of the investment, enables 
 Dr. Van Horn to produce the most accurate fitting inlays the 
 author has ever seen. 
 
 A study of Dr. Van Horn's technique will amply repay 
 anyone who is desirous of obtaining better results. 
 
 Dr. James G. Lane of Philadelphia was among the first 
 to point out the value of silica as an ingredient of inlay in- 
 vestment compounds, on account of its expansion and conse- 
 quent ability to counteract the contraction of plaster of paris 
 (the binder). The formula that he used (plaster 25 per cent 
 and silica 75 per cent) expands considerably. Dr. Lane was 
 also among the first to point out the fact that a hot mold was 
 stronger than one that was heated and allowed to cool. 
 
 In the utilization of the casting process, there are a great 
 many important factors to be considered, among them the fus- 
 ing point of the investment compound ivhich constitutes the 
 mold; the relation of this degree of fusibility to the tempera- 
 ture of the mold at the time the molten metal enters it; the 
 temperature of the molten metal at the time it enters the mold 
 and the pressure used, to force the molten metal into the mold. 
 
 *1911, pp. 664, 472, 1109; 1912, pp. 890, 973; 1914, p. 940. 
 
AN OUTLINE OF METALLURGY 1049 
 
 The fusing point of an inA'estment compound, made of 
 plaster of paris and pure silica, is under 3000 degs. F. Some 
 of the commercial investment compounds, which are made 
 with impure silica containing a considerable percentage of 
 iron and feldspar, which latter contains alkalines, such as 
 sodium and potassium, are often considerably lower fusing, 
 consequently when superheated gold is cast into such a com- 
 paratively fusible investment a partial vmion is bound to take 
 place, with the consequence that the gold partly unites with 
 the investment and the resultant casting is quite rough and 
 inaccurate. 
 
 The strong jjossibility of such a condition as described 
 leads the author to state his opinion on that apparently never 
 ending controversy regarding the casting of gold in a liot or 
 cold flask. This point has been argued time and time again, 
 some operators claiming that they obtain better results by 
 casting into a hot fiask and others maintaining the reverse. 
 In order to discuss the subject intelligently, we must also bear 
 in mind the degree of heat that is utilized for melting the 
 metal to prepare for its entrance into the mold. 
 
 Let ns first consider the following: 
 
 HOT OR COLD MOLD— USING ILLUMINATING GAS AND 
 COMPRESSED AIR BLOW-PIPE 
 
 We will discuss this phase first, because the great major- 
 ity of castings are accomplished by using the ordinary gas and 
 air blow-pipe. The maximum temperature that it is possible 
 to produce with artificial gas and compressed air is approx- 
 imately 2450 degs. F. The temperature of the investment in 
 the casting ring when red hot is about 1300 degs. F. If this 
 "red hot" flask is placed on the casting apparatus and a quan- 
 tity of gold, say, 5 dwts., placed in the ci'ucible, it will take 
 about two and a half minutes' exposure to an efficient blow- 
 pipe flame to bring the gold to the proper state of fluidity to 
 enter the mold. In the meantime, the "red hot" mold (on the 
 casting apparatus) has cooled considerably and the actual 
 temperature of the cavity in the mold at the time the gold 
 enters it can be safely calculated not to exceed 900 degs. F. 
 Therefore, casting into a "red hot" flask with an ordinary 
 gas and air blow-pipe is done with the mold not red hot, but 
 at a temperature approximately 900 degs. F. 
 
 In casting into a so-called "cold" flask, using the same 
 blow- pipe and quantity of metal, it will be found that it takes 
 longer, say four minutes, to bring the metal into a state of 
 
lono AN OUTLINE OF METALLURGY 
 
 fluidity, and altlion,i;li llic flask is at room temperature when 
 the process of melting the gokl is started, the subjection of the 
 mold to the flame of tiie efficient blow-pipe for a period of 
 approximately four minutes raises the temperature of the 
 mold to an extent of nearly 700 degs. F. Therefore, when it 
 is attempted to make a casting with the ordinary gas and air 
 blow-pipe in a so-called "cold" flask, the temperature of the 
 mold at the time the gold enters it is approximately 700 degs. 
 F. 
 
 Upon considering both conditions and comparing the tem- 
 peratures of the molds, namely, 900 degs. and 700 degs., it 
 will be readily seen that there is comparatively little difference 
 between the tivo at the actual time that the casting is done, 
 and consequently both the "hot mold" and "cold mold" advo- 
 cates are right, strange as that may appear, providing, of 
 course, that the ordinary gas and air blow-]iipe is em- 
 ployed. 
 
 The author's experiments along this line have shown con- 
 clusively that it is hardly possible to superheat the gold with 
 an ordinary gas and air blow-pipe or bring the gold to such a 
 temperature that it will unite with the investment at any stage 
 of the procedure, and it is the author's firm opinion that in 
 the hands of the careless or inexperienced operator, the ordi- 
 nary gas and air hloiv-pipe is a positive insurance against 
 superheatifig the gold, and therefore insures a casting satis- 
 factory, at least as far as errors consequent to the superheat- 
 ing of gold are concerned. 
 
 HOT OR COLD MOLD— USING ILLUMINATING GAS AND 
 NITROUS OXIDE OR OXYGEN BLOW-PIPE 
 
 Here we have a totally different and quite often a dan- 
 gerous condition to contend with. While the ordinary gas 
 and air blow-pipe is capable of producing temperatures only 
 somewhat beyond 2400 degs. F., it is possible to obtain, with- 
 out difficulty, 3400 to 3500 degs. F. from nitrous oxide and 
 illuminating gas and over 4000 degs. F. from pure oxygen 
 and illuminating gas. It may be well at this time to call at- 
 tention to the fact that the often used term "Oxyhydrogeu" 
 is incorrect when used in connection with illuminating gas 
 because of the fact that in order to produce an oxyhydrogen 
 flame it is necessary to have both oxygen gas and hydrogen 
 gas, whereas ordinary illuminating gas contains less than 
 half of its volume of hydrogen and the balance is principally 
 methane (carbon, etc.). 
 
AN OUTLINE OF METALLURGY 1051 
 
 II is rather dillicnlt to avoid superheating gold when ap- 
 pl\ iug such extreme temperatures and extreme caution must 
 he exercised hy the operator. 
 
 As a rule, the cold flask is indicated when using extreme 
 temperatures for melting the gold, because the gold melts 
 very rapidly (15 to 20 seconds), and comparatively little heat 
 is transmitted to the mold. The mold is then comparatively 
 cool, and even if somewhat sujoerheated gold is cast it is not 
 so apt to unite with the investment as when both the gold 
 and the mold are superheated. 
 
 The author has very often made failures of castings on 
 account of superheating the gold and he wishes to impress 
 strongly the fact that extreme caution must he exercised in 
 this connection. 
 
 The nitrous oxide or oxygen and gas blow-pipe offers ad- 
 vantages over the ordinary gas and air blow-pipe as a means 
 of producing heat rapidly, but the maximum temperature 
 attainable with the ordinary gas and air blow-pipe acts as a 
 sort of an insurance against superheating and, in fact, if 
 efficiently used, produces satisfactory casting results in all 
 ordinary operations. 
 
 One of the most prolific causes, in fact, probably the great- 
 est cause that is productive of faulty castings, is the excessive 
 pressure used in forcing metal into the mold. The principal 
 reason for this is due to the fact that in the majority of cast- 
 ing apparatus, there is no provision for obtaining a definitely 
 measured and indicated amount of force. It takes just so 
 much and no more pressure to force gold into a given mold 
 and hold it there until solidification begins. Excessive pres- 
 sure will not, lander ordinary conditions, prevent the normal 
 contraction of gold, because the mold into which the gold is 
 cast yields and hence vnll distort in the same proportion as 
 excessive pressure is applied. It may be true that a pressure 
 of 2,000 pounds per square inch may totally prevent contrac- 
 tion, hut ivhere is the mold, that will stand that pressure? 
 
 It is unfortunate that more operators do not realize the 
 true value of an efficient casting apparatus, such as the Tag- 
 gart, and the false economy resulting from the use of an in- 
 trinsically faulty ©r makeshift device. 
 
 By using a grade of silica of maximum expansion and a 
 grade of plaster of minimum contraction, it is possible to pro- 
 duce an investment compound as follows: 
 
1052 AN OUTLINE OF METALLURGY 
 
 Formula for Investment {Casting) 
 
 J^laster (Excelsior Brand No. 3) Parts 2!) 
 
 Silica (Fine) (F. F. W.) Parts 71 
 
 Total 100 
 
 The plaster is the same as is used in the soldering invest- 
 ment. The silica is similar to the tine grade ntilized in the 
 soldering investment fornmJa, bnt it is purified and combines 
 with water readily withont releasing dirt, scum, etc.,* and 
 consequent bnlibles. An investment made from this formula 
 will be found to expand slightly more than Dr. Lane's formula, 
 although the plaster of paris content is higher and, for the 
 same reason, somewhat stronger and more resistant to ex- 
 cessive pressure. 
 
 COMPOUNDING OF INVESTMENT MATERIALS 
 
 It is a well-known fact that very few commercial invest- 
 ment comiiounds are uniform in composition. In other words, 
 although manufacturers claim that their formulae are adhered 
 to, there appear variations in batches purchased at different 
 times. This is due to the fact that insufficient attention is 
 paid to testing the different batches of raw material and also 
 to the faulty compounding due to the large quantities mixed 
 at a time. One commercial preparation has been found, on 
 the contrary, quite uniform, for the simple reason that the 
 manufacturer pays especial attention to the testing of the raw 
 materials and compounds the mixture in comparatively small 
 quantities (200 to 300 lbs. to the mix). 
 
 In mixing the plaster of paris and silica, it is not neces- 
 sary to do anj' sifting, because the specified materials may 
 be obtained evenly and definitely graded. All that is required 
 is a thorough mixture without excessive trituration. 
 
 A very efficient small mixing apparatus may be obtained 
 from J. H. Day Co., Cincinnati, Ohio. It is known as the 
 "Hunter" (experimental size) and will handle from seven 
 to eight pounds of material. The ingredients are weighed 
 out, placed in the container and the apparatus revolved slowly 
 for 25 to 30 minutes. This produces a uniform and intimate 
 mixture without crushing or grinding the plaster. This point 
 is very important, and if smaller quantities are mixed in a 
 mortar, it is important to use very light pressure in order not 
 
 *Bubbles and froth produced upon attempting to combine investment 
 compound and water are often caused by dirt or sucli impurities as mica, 
 etc., contained in the silica. 
 
AN OUTLINE OF METALLURGY 1053 
 
 to crush the plaster particles. The mixed material, of course, 
 should be properly stored and protected against moisture. 
 
 INVESTMENTS, DIRECTIONS FOR USE 
 
 The soldering investment should be mixed quite thick. 
 The thicker, the better, up to a certain limit, of course. If 
 mixed too dry, the i:)laster of paris content does not obtain 
 sufficient moisture to crystallize properly and act efficiently. 
 A good consistency is 41 to 42 grammes powder to each 15 
 c.c. water or 26 dwts. (Troy) to one-half fluid oz. water. 
 
 The inlay investment should be mixed in a proportion of 
 32 grammes powder to 15 c.c. water, or 20 dwts. (1 Troy oz.) 
 powder to i-^ fluid oz. water. This quantity is sufficient to 
 fill an ordinary inlay fiask. 
 
 These proportions produce a mixture tliat allows ample 
 time for manipulation, provided considerable time is not spent 
 in adding a little more water, a little more powder, etc. Tlie 
 setting time of the plaster naturally controls the setting time 
 of the whole mixture, and as the action of retarding agents 
 added to control the set of plaster is sometimes indefinite and 
 often harmfid, it is advisable not to attempt to interfere ivith 
 the normal setting time of the plaster. 
 
 The compound, if mixed without any unnecessary delay, 
 sets sufficiently slow for all ordinar.y operations. It is the 
 author's i^ractice to have on hand a number of cork-stoppered 
 bottles containing the dry compound (weighed) and a num- 
 ber of rubber-stoppered vials containing water (measured). 
 The accurately measured powder and water are thrown sim- 
 ultaneously into the mixing bowl and having no bubbles or 
 froth (as with graphite compounds*) to contend with, the 
 mix can be made ready for use in from 30 to 40 seconds, thus 
 allowing ample time for coating the pattern and imbedding in 
 flask. This method is superior to using the automatic weigh- 
 ing apparatus furnished by some of the compound manufac- 
 turers, as they are often either inaccurate or not sufficiently 
 "flexible." 
 
 It is not advisable to attempt to invest more than one 
 pattern at a time. When a larger mix is to be made for a 
 
 *Most of the compounds that contain flake graphite are very difficult 
 to mix on account of the air content in the flaltes and their tendency to 
 "float." Such a compound requires a considerable period of time to mix, 
 and therefore a retarded plaster is usually employed. Nodules, or "ghosts," 
 on castings occur- frequently because the material is not "dormant" until 
 "set." A manufacturer of such a compound claims that it is the plaster 
 and not the graphite that causes the bubbles. This statement appears 
 quite contrary to the facts. Kerr's "Graphite" Investment is made with 
 previously treated graphite and it is the best commercial preparation that 
 the author knows of. 
 
1054 AN OUTLINE OF METALLTTROY 
 
 liii'gor flask, throe to five per cent more powder than a given 
 quantity of water demands is not only permissible, but 
 advisable. 
 
 Another advantage in using measured and stored water 
 lies in the fact that it is, when used, at room temperature and 
 not at hydrant temperature, and the room temperature water 
 does not induce a further coufrdcHtni of the wax pattern dur- 
 ing the process of investing. 
 
 HEATING OF INVESTMENTS 
 
 The soldering investment may be heated quite ]n-omptly 
 upon setting. Boiling water does not atTeet it materially and 
 the wax may be washed out thoroughly, the case fluxed and 
 immediately placed on the heat, moderate at first and then 
 brought up quite rapidly to a good red heat prior to the actual 
 soldering operation. 
 
 It is the inefficient and insufficient lieatinc/ of the invested 
 work that is partly to blame for the "popular" demand for 
 "easy floiving" solders. Properly heated investments facili- 
 tate the floiv of normal or even high fusing solder. 
 
 A small quantity of potassium sulphate or sodium chlo- 
 ride may be used to hasten the setting of the investment, but 
 that is rarely, if ever, necessary, because it sets quite promptly 
 if mixed to the proper consistency. 
 
 The inlay investment should be permitted to set for at 
 least thirty mimites to insure a fair crystallization (so-called 
 "initial set") of the plaster. The flask should then be placed 
 over a low heat and kept there until the moisture disappears 
 and the wax begins to dit¥use and carbonize. The heat is in- 
 creased somewhat during the latter part of this operation 
 and still further increased until the mold is brought up to 
 either a dull red heat (for cold mold) or a bright red lieat 
 (for hot mold). 
 
 The initial stages of heating must be a temperature that 
 will not permit the wax to run out of the mold, as it is im- 
 portant that the wax be absorbed in the mold. Forced heat- 
 ing and a generation of steam during the initial stages of the 
 drying process will force the wax out of the mold and pro- 
 duce a rough interior which in turn will show its etfects upon 
 the casting, the resultant casting being rough, incorrect, and 
 usually unfit for use. It is, of course, essential to confine and 
 concentrate the (higher) heat in order to bring the mold to 
 the proper temperature within a reasonable period of time. 
 
 Prolonged heating of the investment is even more dan- 
 
AN OUTLINE OF METALLURCtV 1055 
 
 gerous than iinderheating, as plaster of paris, which is the 
 binder, shrinks in proportion to the time that it is exposed to 
 heat. The total heating operation for an ordinary mold (in- 
 lay, etc.) should not exceed fifty minutes, or an hour at most. 
 It may be divided into three periods, say twenty-five to thirty 
 minutes for low drying heat, then increased somewhat for ten 
 to fifteen minutes, and finally subjected to the highest heat for 
 not more than from ten to fifteen minutes. 
 
 It is permissible not to heat a case imtil two or three 
 hours after the investment has been mixed, but if it is per- 
 mitted to stand for a day or two and loses all moisture, if then 
 heated and cast, the resultant casting is apt to be very poor. 
 It is hard to determine the actual principle involved, and it 
 is not important to do so, but the fact does exist. In addition, 
 under such conditions, the investment is very apt to crack or 
 split upon heating. The author usually heats and casts into 
 "green" molds, but has found that a dry mold, if moistened 
 prior to heating, appears to behave almost as well as a 
 "green" mold. If the mold is only a few hours old it is moist- 
 ened slightly, but if it is more than a day old it is placed in 
 water until saturated to the extent of a "green" mold. 
 
 Both the soldering and casting investment compounds 
 are practically immune to "checking" or "cracking" even 
 under the most severe heating conditions.* 
 
 SECTION VII 
 
 FLUXES 
 FLUXES FOR SOLDERING AND CASTING 
 
 For sweating, soldering or melting metals in the construc- 
 tion of bands, crowns, bridges or castings, the selection and 
 use of the proper flux or fluxes is a matter of the utmost im- 
 portance, especially if the metals or alloys used are oxidizable 
 or volatile when subjected to heat. 
 
 Ordinary borax, or calcined borax, has been the principal 
 flux used for this purpose. It has been almost rmiversally 
 used by jewelers and the dentist has followed suit. There is, 
 
 *This fault is inherent in most investment compounds, the causes are 
 numerous and principally due to the producers ignoring the physical laws 
 governing the selection and compounding of materials for the purpose. 
 One of the principal errors in this connection is the attempt to form a 
 "concrete-like" mass without realizing that there is a very great difference 
 in the behavior of dental investment compounds and concrete used in build- 
 ing operations. 
 
105G AN OUTLINR OF METALLURGY 
 
 liowever, a consideral)le difference between the dass of work 
 that the jeweler and tlie dentist perform. 
 
 In dental soldering, we use higher grade solders and a 
 considerably higher heat, during the various operations. As 
 ordinary borax melts at a comparatively low temperature, it 
 does not act as efficiency during the higher temperature stages 
 as the requirements demand. The tendency of borax when 
 considerable heat is applied is to liquefy strongly and run 
 down to the deep portions, leaving the otlier portions, that 
 it is desired to solder, insufficiently protected. Dr. Peeso 
 recognized this long ago by using a combination of borax and 
 boric acid, which combination melts at a higher temperature 
 than borax alone, does not liquefy so readily, stays on the 
 surface and protects the work longer and is more efficient in 
 every way. 
 
 An efficient flux that has served verj^ satisfactorily in the 
 author's hands for a considerable period of time is the fol- 
 lowing: 
 
 Formula for Soldering Flux 
 
 C. P. Borax Glass (fused) Parts 55 
 
 C. P. Boric Acid (not fused) Parts 35 
 
 C. P. Silica Parts 10 
 
 Total 100 
 
 The ingredients are placed in a clean clay or sand cruci- 
 ble and brought to a fair red heat. They combine quite read- 
 ily and when quite fluid the mistiire is poured into cold water. 
 As this glass is quite soluble, it must be removed from the 
 water as soon as possible, dried and pulverized to pass an 
 80-mesh sieve. It may be pulverized without difficulty, as the 
 particles are very frail and brittle. 
 
 This flux may be used either in the powdered form or 
 compounded with "vaseline," to form a i^aste, or dissolved in 
 Iroiling water and the saturated solution used. In the liquid 
 form, it will be found suitable for all general operations where 
 the work can be heated so as to drive off the moisture and 
 thus leave a coating of the flux, as in bands, crowns, etc. When 
 the work is in an investment, the grease flux will be found most 
 useful, as it may be applied just after the case is waslied out 
 and still warm. The carrier (vaseline) flows down into the 
 deep portions and crevices, carrying the particles of flux 
 along. The powdered dry flux can be used on invested work 
 under the blow-pipe when more flux is required. Strips of 
 
AN OUTLINE OP METALLURGY 1057 
 
 solder can, of courso, be coated with either tlie liquid or the 
 grease flux and heated ))rior to use. 
 
 This soldei'hui /hu ni a ponvleii'd form inU also he used 
 as the base for both flic reducing and ().ridr::iii() flii.res to be 
 discussed. 
 
 It is important that the forms of borax and boric acid 
 specified be adhered to because of the variable amount of 
 water that these materials contain when purchased. 
 
 The formula of borax glass is Na2B40;, whereas ordinary 
 borax, either powdered or crystals, contains a considerable 
 jiroportion of water which is evident from the formula 
 Na.BiOj + 10H,( ). Therefore the borax glass is preferable to 
 the ordinary borax containing water because it occupies much 
 less space and is therefore more convenient to handle in small 
 crucibes. However, if ordinary borax is used the water con- 
 tent must be calculated and provided for in weighing out the 
 ingredients. The lioric acid used does contain water, as will 
 i)e seen from the formula lIsBO;,, because it is more stable than 
 the fused boric acid BJ)^ and more readily obtainable. The 
 silica should be pure and in the form of a fine powder so that 
 it may combine readily.* 
 
 REDUCING FLUX 
 
 In connection with the casting process, it is necessary to 
 treat buttons of gold, both during casting and before recasting, 
 with a flux that will take care of the accpiired impurities. Very 
 often there have apjieared statements to the effect that a mix- 
 ture of potassium nitrate and borax be used to cleanse but- 
 tons before recasting. This statement has been, in a good 
 many cases to the author's knowledge, misunderstood. Potas- 
 sium nitrate is an excellent oxidizing agent and does remove 
 base metals, but its use in treatment of casting buttons is con- 
 tra-indicated, because generally when casting gold alloys con- 
 taining copper, etc., it is desired to retain the base metal, the 
 copper, ill a reduced metallic form and not in an oxidized form. 
 Consequently, if a fiiix is to be used it must be of a distinctly 
 reduciiifi nature. 
 
 Reducing fluxes are used extensively in assaying and 
 smelting operations and their properties are well known. In 
 the case of casting, it is rather difficult to utilize all the benefit 
 that mav be derived from a reducing flux on account of the 
 
 ♦The grade (P. P. W.) used in inlay casting investment is quite suitable. 
 
1058 AN Ol'TLINK OF METALLURGY 
 
 difficulty of applying same to the molten metal which is ex- 
 posed to the blo\v-i)ipe Hame which drives off the flux almost 
 as fast as it is api)lied. Therefore, to obtain any considerable 
 benefit from a reducing flux, it is necessary to not merely 
 apply same while the gohl is fluid under the blow-pipe, but 
 also to sprinkle an additional amount in the manner described 
 in the following: After placing flask on casting apparatus, 
 place button or nuggets of gold into crucible, melt without flux 
 until the mass of gold assumes a spheroidal form and coni- 
 l)letely covers the s])rue hole. Then api)ly some flux by sprin- 
 kling, continue melting until the gold is in a projicr state of 
 fluidity for casting, then remove flame, add some more flux 
 and instantly apply the casting pressure. 
 
 Formula for Rcdiic'nig Flux 
 
 Soldering Flux ( Base) Parts 40 
 
 Borax Glass Parts 30 
 
 Argol Parts 25 
 
 Animal (."harcoal Parts 5 
 
 Total 100 
 
 Argol is the commeicial term for crude postassium bi- 
 tartrate, KHC4H4O0 (cream of tartar), and has a higher re- 
 ducing power than pure cream of tartar. If the latter is used 
 it should be increased to about 25 parts and the soldering flux 
 and borax glass content reduced in proportion. 
 
 A flux of this character will practically prevent the bring- 
 ing into the casting of oxidized material and can be used to 
 advantage in remelting and cleansing buttons of gold for 
 recasting. 
 
 The author's procedure for this operation is as follows: 
 After a casting is made, the residue button is placed into 
 hydrofluoric acid for 15 or 20 minutes, removed and melted 
 with the blow-pipe in a charcoal block, using the reducing flux, 
 which, in addition to reducing the oxidized copper in the but- 
 ton, combines with the silica, traces of which may still adhere 
 to the button. After the button is melted and the flux used 
 has segregated into a globule, the hlow-pipe is removed and 
 a small quantity of ammonium chloride is sprinkled on the 
 button. As soon as the button has solidified, and while still 
 red. it is plunged in dilute hydrochloric or sulphuric acid. 
 Most of the glass formed by the flux will splinter off. If any 
 
AN OUTLINE OF METALLURGY 1059 
 
 considerablo quantity adlicrcs, it may he rt'iiioNcd l)y boiling 
 in the same acid. 
 
 OXIDIZING FLUX 
 
 Potassium nitrate is a most excellent oxidizing agent and 
 removes base metals, the only objection being the strong fumes 
 which are given off during the melting ])rocess. Although tlie 
 operator should rarely attempt to do refining, it is well to 
 have a suitable oxidizing flux that will not give off the objec- 
 tionable fumes characteristic of potassium nitrate. 
 
 Formula for Oxidizing Flux 
 
 Soldering Flux (base) Parts 55 
 
 Potassium Chlorate Parts 20 
 
 Sodium Perborate Parts 25 
 
 Total 100 
 
 This flux will be found useful for revivifying buttons of 
 gold which are contaminated. It is sufficiently powerful to 
 volatilize such impurities as tin, cadmium, liismuth. etc. It 
 will combine with adherent investment comi>ound and not at- 
 tack copper very strongly, so that a button of gold that has 
 been used several times and is quite sluggish and dirty can be 
 usually brought into good shape without diflicult\'. 
 
 A button treated with this flux should be cleansed in acid, 
 as previouslj' described, and then remelted trith the reducing 
 fltix prior to use for casting. 
 
 In cases of refining, where a stronger action is recjuired, 
 the potassium chlorate and sodium perborate can be increased 
 to obtain the same efficiency that a high percentage of potas- 
 sium nitrate would give without the objectionable fumes char- 
 acteristic of the latter. 
 
 It is expected that pre^sared flux made according to the 
 formulas given will be very shortly available from the sup- 
 ply houses. Until such time, a modification of the soldering 
 flux formula, which also acts as a base for tiie reducing* and 
 oxidizing fluxes, is given herewith for the benefit of those 
 who have not the facilities for fusing and pulverizing the 
 material. These ingredients make a flux which appears to 
 
 *There are a number ot better reducing agents than those suggested 
 by the author used industrially. They are not mentioned because of either 
 difficulty of application under casting conditions, or on account of not being 
 obtainable in small quantities. A study of the methods used in deoxidizing 
 copper, brass and bronze is suggested to those particularly interested. 
 
]060 AN OIITLINK OF METALLnuCY 
 
 woik imich iiioic satisfactorily lliaii (udiniiix hdiax or any 
 (it llic sccri't lircjiarations ])iir('liasal)lc. 
 
 FoiiiiiiIk fur Suldcriii// Flux (Snhsl il iilc) 
 
 C. P. Borax Glass Parts 50 
 
 C. P. Boric Acid Parts 43 
 
 C P. Siidiuin Silicate (i\vy pmvd.) Parts 7 
 
 Total , 100 
 
 Tliis is mixed tliorouglil)' in a niorlar and mnst be fine 
 eiiougli to pass an 80-mesli siexc 
 
 The author trusts that his icmarks ni)on the importance 
 of producing castings with all the metal in a reduced form and 
 not in a partially oxidized form will be given some considera- 
 tion by the reader, as this probhnii, on an immeasurably larger 
 scale, has been and is one of the most important ones in the 
 api)lication of industrial alloys, and is being coped with suc- 
 cessfully. 
 
 TABLE 4 
 MELTING POINTS OF THE NEW SERIES OF 
 ALLOYS AND STANDARD DENTAL GOLDS 
 
 "F Alloy °C 
 
 2100 *"Elastic" Gold 1150 
 
 2075 *Plate No. 1 1135 
 
 1975 *Plate No. 2 1080 
 
 1960 Type 4 Clasp 1070 
 
 1945 Pure Gold 1063 
 
 1945 *Casting Gold "A" 1063 
 
 1945 *Casting Gold "D" 1063 
 1945 "Green" Gold [App. Au. 80',; — Ag. 20c; ] 1061 
 
 1900 *Casting Gold "B" 1035 
 
 1900 Light 22K Plate 1035 
 
 1860 Medium 22K Plate 1015 
 
 1860 Type 3 Clasp 1015 
 
 1825 Dark 22K Plate 995 
 
 1800 *Casting Gold "C" 980 
 
 1760 Light 20K Plate 960 
 
 1735 Coin Gold (21.6K) 946 
 
 1725 Type 2 Clasp 940 
 
 1650 *Gold Solder No. 84 900 
 
 1625 Gold Solder for 22K 885 
 
 1600 Type 1 Clasp 870 
 
 1550 *Gold Solder No. 76 840 
 
 1525 Gold Solder for 20K 820 
 
 1450 *Gold Solder No. 68 785 
 
 1425 Gold Solder for 18K 770 
 
 The ten alloys marked * constitute the new series. They 
 are all uniform in color with the exception of "Elastic" Gold, 
 which is similar to ]ilatinum in color, and Casting Gold "A," 
 which is similar to pure gold in color. 
 
AN OUTLINE OF METALLURGY 1061 
 
 SOME OF THE APPLICATIONS OF THE NEW SERIES OF 
 
 ALLOYS IN THE PEESO SYSTEM OF REMOVABLE 
 
 BRIDGEWORK 
 
 As will he seen from the preceding table, tbe series of 
 alloys offers a wide range of variation in melting point over 
 the ordinary alloys, tlms facilitating the performance of suc- 
 cessive soldering operations. 
 
 CONSTRUCTION OF BANDS, FLOORS AND INNER CAPS 
 
 As has been ju'evionsly stated, coin gold is the most suit- 
 able alloy for the construction of bands, floors, etc. It is 
 therefore necessary to use its equivalent in the new series of 
 alloys. The band should therefore be made of the No. 2 plates 
 (M. P. 1975 degs. F., 1080 degs C), and united* by soldering 
 with the next lowest fusing alloy, namely, Casting Gold "B" 
 (M. P. 1900 degs. F., 1035' degs"c.). 
 
 The band is also prepared of No. 2 plate and attached 
 with Casting Gold "B" (the pliers grasping the band at pre- 
 viously joined portion). 
 
 The method will make, for all intents and purposes, a 
 seamless cap. The melting point of the soldered junctions 
 will be still considerably above that of coin gold. The tube 
 may be then attached with the No. 84 solder. 
 
 Outer caps for telescope crowns are made in exactly the 
 same manner. As the hardness and tenacity of the No. 2 plate 
 is the same as that of coin gold, the same gauges of plate are 
 to be used as with coin gold. The casting gold, if used as 
 solder, should be of practically the same thickness as ordinary 
 gold solder, app. 27 or 28 gauge B. & S., or preferably thinner 
 (30 to 32 g.). 
 
 OUTER HALF BANDS AND TELESCOPE CROWNS 
 
 After completing the inner cap, the outer half band and 
 floor are made of suitable gauge No. 2 plate and the split pin 
 is attached and the half band united to the floor with the No. 
 84 solder. 
 
 For telescope crowns, the outer band is made of the No. 
 2 plate and the joint soldered with Casting Gold "B." The 
 wings are made of No. 2 plate and soldered to the band with 
 Casting Gold '.'C." The cusp is swaged of No. 1 plate (higher 
 fusing than pure gold), filled with Casting Gold "C" in the 
 same manner as a pure gold cusp is filled with coin gold and 
 "See Dr. Peeso's method of band preparation for sweating. 
 
1062 AN OUTLINK OF MKTALLUIUIV 
 
 attac'lied to the previously ('(iinplctcd outer liaml and wiugs 
 with No. 84 solder. 
 
 If tlie cusp is to be cast, C'asting Gold "B" or "('" should 
 be selected according' to the blow-pipe used and attached to 
 the contoured band with No. 84 solder. 
 
 As all of the alloys of the series used in this operation 
 are of the same color and the No. 84 solder is actually liOk. tine, 
 there will be no line of deniarkatiou evident in the finished 
 work. 
 
 INLAY ABUTMENTS 
 
 The shell for the inner inlay may be cast with Casting 
 Gold "D" and adapted to the cavity by burnishing. The 
 tube is then soldered and completed with No. 84 solder. The 
 outer inlay matrix can then be made, using the comparatively 
 soft but high fusing plate gold No. 1 and Casting Gold "C," 
 instead of pure gold and coin gold. 
 
 CONSTRUCTION OF SADDLES 
 
 The saddles, if swaged of platinum, may be reinforced 
 with Casting Gold "B" or "C," instead of coin gold, or the 
 saddles may be swaged of No. 1 plate (softer than No. 2) and 
 reinforced with Casting Gold "C." If the saddles are to be 
 cast; Casting Gold "B" or "C" should be selected according 
 to the blow-pipe used. 
 
 CONSTRUCTION OF DUMMIES 
 
 In constructing the dummies (if all porcelain), the bases 
 and dowels may" be cast with either "B" or "C" and attached 
 to the saddles with the 84 or 76 solder. 
 
 They may also be made by burnishing .34 g. pure gold 
 backings to the prepared porcelain crowns, fitting and sol- 
 dering dowels made of "Elastic" gold or type four clasp 
 metal to the backings (or boxes) and attaching the com- 
 pleted backings to the saddles with 84 and 76 solder. 
 
 REMARKS 
 
 The author cannot close without calling attention to the 
 fact that a broad conception of the scientific principles in- 
 volved in the chemical and ]ihysical behavior of the various 
 materials utilized in connection with the construction of 
 prosthetic restorations is a most potent factor toward the 
 attainment of the ideal. 
 
 He has been aided materiallv in arriving at the conclu- 
 
AN OUTLINE OF METALLURGY 1063 
 
 sions presented herein by the kindness of Mr. H. C. Ney, 
 president of the J. M. Ney Co., who unstiutingly placed at 
 the author's command all the facilities of their metallurgical 
 research laboratory in Hartford. ("Dental Metallurgy," 
 Weinsteiu.) 
 
 IRON 
 
 Iron, like gold, has hecn known and used since the earliest 
 times. It is almost uni\ersally distributed over the earth in 
 some form or other. The oxide of iron in the form of red 
 and yellow ochre is the principal coloring pigment in clay, 
 sand and rocks. The ores of iron are also found in abnost 
 every country on the face of the globe. These are in the form 
 of oxides, carbonates and sulphides, and their name and 
 chemical composition, according to Bloxam. are given in the 
 table below : 
 
 Common Xaiiie. CJteiiiicdl Nmiic. Coiiiposiiio)/. 
 
 Magnetic iron ore. Protosesquioxide of iron. Fcs O4. 
 Bed haematite. Sesqnioxide of iron. Fe, 0:,. 
 
 Specular iron. Sesqnioxide of iron. Fe^ O.,. 
 
 Brown haematite. Ilydrated sesqnioxide of 
 
 "iron. 2 Fe, ( ), 3IL O. 
 
 Si)athic iron ore. Carbonate of iron. Fe CO^. 
 
 Clay iron stone. Carbonate of iron with 
 clay. 
 
 {Carbonate of iron with 
 clay and bituminous 
 matter. 
 Iron i)yrites. Bisulphide of iron. Fe Sa. 
 
 Iron very rarely occurs native, owing to its strong atlinity 
 for oxygen and other non-metallic elements. It is found na- 
 tive in meteorites and in minute particles in basaltic rocks, 
 but not in quantity sufficient to be of recognized value. 
 
 Magnetic iron ore is the protosesquioxide of iron, and is 
 commonly called lodestone when strongly magnetic, and pos- 
 sesses the property of attracting small ]iarticles of iron 
 similar to a horseshoe magnet. It furnishes a most excellent 
 quality of iron, examples of which are the Wootz steel and 
 the Swedish iron. . 
 
 Red haema'iie, so called from its dark, blood-red color, 
 is a sesquioxide of iron. It is a remarkably abundant ore, 
 being found all over the world, and contains about 70 per 
 cent iron, 30 per cent oxygen. 
 
1064 AN orTLINIO OP" MKTALLtTRrrY 
 
 The scsqnioxidc sometiuios occurs us a steel-gray iiiin- 
 eral, and it is then called specular iron ore. 
 
 Brown haematite is also a very common ore of iron, and 
 is the hydrated sesqxiioxide of iron, containing ahout 15 per 
 cent water. It is sedimentary in character and is often mixed 
 with' wood, clay and sand. The lahe ores of Europe and this 
 country are of this variety. 
 
 Spathic iron ore is the carbonate of iron and occurs crys- 
 tallized in veins and beds, and also in glol)ular masses. When 
 first mined it is yellow, but soon turns brown on exposure 
 to air. Most of the iron used by the Krup]i iron works of 
 Essen is derived from this ore. 
 
 Clay ironstone is the carbonate of iron with clay, and 
 contains about 34 per cent of iron. It often occurs with or 
 accompanies coal formations, of which it is the characteristic 
 ore. 
 
 Black band. When clay ironstone contains more than 
 10 per cent coaly matter it resembles shale, slate or cannel 
 coal, and is a valuable ore for the reason that the coal it con- 
 tains is sufficient to burn or roast it. 
 
 Iron pyrites is the bisulphide of iron and is of a bright 
 yellow, crystalline structure, with a distinct metallic luster. 
 It is largely used in the manufacture of sulphuric acid, but is 
 not, to any extent, of value as an ore of iron. 
 
 REDUCTION OF IRON ORES 
 
 Most iron ores containing carlion dioxide or sulphur are 
 roasted to drive off these elements or combinations and to 
 reduce the ore to an oxide. The ore is then mixed with cer- 
 tain proportions of calcium carbonate (limestone), which 
 acts as a flux, and with coal, charcoal or coke, and thrown into 
 a blast furnace. Under the influence of heat and the blasts 
 of air which are directed into the bottom of the furnace the 
 fuel is converted into CO,. As this ascends in the furnace 
 it x^asses over the red-hot fuel in the liigher portions and is 
 converted into CO. 
 
 The carbon monoxide thus formed reduces the ore to the 
 metallic state by combining with the oxygen with which the 
 iron is united and becomes CO2 gas, which is thrown out of 
 the furnace, leaving the iron free and uncombined. This 
 sinks through the slag (the calcium carbonate which has 
 united with the earthly impurities of the ore) to the bottom 
 of the furnace, where it is retained in a fluid condition until 
 sufficient quantity has accumulated, when the furnace is 
 
AN OUTLINE OF METALLURGY 1065 
 
 tapped. The slag from time to time is removed through open- 
 ings placed higher iu the furnace than that from which the 
 iron is drawn. 
 
 The metal is drawn off from the furnace and conducted 
 into a ditch or trough formed in the sand, and from this into 
 lateral oj^enings in the form of half cylinders, called pigs. In 
 this condition it is crude cast iron, and can l)e used in this 
 form for many purposes or be refined by sulisequeut opera- 
 tions and reduced to the imrer condition of steel or wrought 
 iron. 
 
 For general purposes iron is used in three distinct forms, 
 as cast iron, steel and ivroiight iron, all consisting of iron 
 with more or less carbon. 
 
 Cast iron contains the largest percentage of carbon, the 
 quantity varying from 11/2 to 7 per cent. Steel contains from 
 1 to 11/2 per cent of carbon, and wrought iron contains the 
 smallest percentage of the three varieties, having less than 
 1/4 of 1 per cent. 
 
 PRODUCTION OF WROUGHT IRON 
 
 Wrougltt iron is produced from cast iron by extracting 
 most of the carbon present. This is accomplished by remelt- 
 ing pig iron and directing a lilast of air upon the heated sur- 
 face of the molten metal to remove some carbon and other 
 impurities that may be present, after which it is cast into 
 molds, and is now known as plate metal. 
 
 The second step is designed to more fully free the metal 
 from its carbon, and this is done by the process called pud- 
 dling. The ingots of plate metal are introduced into a rever- 
 beratory furnace, and again melted. At a certain stage oxide 
 of iron is added to the molten metal and the mass mixed, or 
 puddled, as it is called, with long iron bars, until the oxide of 
 iron is diffused through the molten metal. 
 
 Under continued heat the oxygen in the last mass added 
 unites with the carbon in the i^late metal and forms COo, 
 which escapes as a gas. After a time the mass assumes a 
 i:)asty condition, when it is divided into balls of about 90 
 pounds each, removed from the furnace and subjected to in- 
 tense pressure by rolls and converted into bars or blooms. 
 
 Two or three ' of these blooms are again heated and 
 welded together, and the rolling process repeated once, twice 
 and sometimes three times, depending on the quality of the 
 iron desired. In this changed condition it is tough and fibrous 
 and elastic, its malleability, ductility and tenacity has in- 
 
AN OUTLINK OF MRTALLITRCY 
 
 creased, and it is now caiiaMc of hciiii;- wcIiIimI, a proiicrty 
 which cast ircm docs nol possess. 
 
 PRODUCTION OF STEEL 
 
 Steel is maih' in two ways, first by direct process from 
 cast iron, wliicli is known as the Bessemer pn/cess. and I'l-oni 
 wrouglit iron by tlie cevinitation process. 
 
 THE BESSEMER PROCESS 
 
 Tlie Bessei)icr /^roce.s.s consists in melting cast iron in 
 large crucibles called converters, capable of liolding several 
 tons, and when in a molten condition, directing a blast of cold 
 air upon its surface. The oxygen in the air unites with the 
 carbon in the molten metal and frees the iron from car- 
 bon in this manner to a greater or less extent, depending on 
 the length of time the process is continued. The best results 
 are attained by purifying the iron to as great a degree as 
 possible, and afterward adding a given quantity of cast iron 
 containing a known iiercentage of carbon. 
 
 THE CEMENTATION PROCESS 
 
 Tlu: cemeiildfioii. pri)cess consists in placing bars of 
 wrought iron in fire brick muffles, together with alternate lay- 
 ers of charcoal, and sealing the charge in so as to exclude the 
 air. Heat is then applied to the exterior of the muffle and 
 maintained for 7 or 8 days. 
 
 Upon examination it will be found that the fil)rous struc- 
 ture of the iron has become granular and that its hardness, 
 elasticity and sonorousness has increased. 
 
 It is more brittle and less malleable and ductile than be- 
 fore. Its surface is covered with blisters, and in this condi- 
 tion is known as blister steel. By arranging it in bundles, 
 subjecting it to heat and the l)lows of a trip hammer, it is 
 rendered dense and comi)act. 
 
 This reduces it to a condition known as shear steel. This 
 process is sometimes repeated, and it is then known as double 
 shear steel. When blister steel is remelted and cast into in- 
 gots it is known as cast steel. 
 
 HARDENING AND TEMPERING STEEL 
 
 Steel possesses the property of being rendered so hard 
 that no tools of ordinary form or composition will affect its 
 surface. This is accomplished by heating it to a full (cherry) 
 
AN OUTLINE OF METALLURGY 1067 
 
 red, and suddenly chilling it by plunging in water or some 
 medium that will rapidly conduct away" the heat. This is 
 called full hardening. For many purposes steel in this condi- 
 tion is too hard for use, and its hardness must be reduced or 
 tempered to meet the required purposes. 
 
 When instruments are shaped to proper form they are 
 first full hardened. The surfaces are then polished so that the 
 colors which appear on subsequent heating, and which indi- 
 cate the varying degree of hardness, may be accurately ob- 
 served. 
 
 The polished steel is now i)assed back and forth ihrougli 
 a Bunsen flame or heated in any other manner, if more con- 
 venient, until the jiroper color appears, when the instrument 
 .sliould be suddenly cooled to prevent further reduction of its 
 hardness. Sometimes an alloy of tin and lead, which melts at 
 a known temperature, is used for drawing the temper to the 
 required point. 
 
 Bessemer steel usually contains such a small percentage 
 of carbon that it is not possible to render it full hard, and, 
 consequently, it cannot be tempered. 
 
 All dental instruments, especially edge tools, should be 
 made from the finest tool steel. 
 
 The following table indicates the various colors as they 
 appear on steel when drawing the temper, the yellows appear- 
 ing first. It also indicates the alloy that may be used for 
 securing any given temper: 
 
 TEMPERING STEEL. ALLOYS FOR TEMPERING 
 
 Color. Temper. Lead. Tin. Melting 
 
 points. 
 
 Very faint yellow to Lancets, razors, surgical in.struments, 
 
 pale straw color. . enamel chisels 7 85 4 215°— 232° C 
 
 Full yellow Excavators, very small cold chisels 10 4 243° C 
 
 Brown Pluggers, scissors, pen kniyes 14 4 254° C 
 
 Brown with purple Aires, plain irons, saw^s, cold chisels — 
 
 spots large. 19 4 265° C 
 
 Purple Table kniyes, large shears 30 4 276° C 
 
 Bright blue Swords, watch springs 48 4 287° C 
 
 Full blue Fine saw.s. augers 50 4 293° C 
 
 Dark blue Hand and pit saws. Boiling oil. 315° C 
 
 PLATINUM 
 
 Platinum was discovered in 17;]5 in the province of 
 Choco, Columbia, South America, in the sands of the river 
 Pinto. The credit of this discovery belongs to Antonio de 
 Ulloa, a Spanish naval officer and explorer. Six years later 
 an Englishman, a Mr. Wood, who was traveling in Jamaica,, 
 secured some specimens of this metal and presented them 
 to Watson, a noted chemist at that time, who recognized in 
 them the presence of an unknown metal, Some years later 
 
 Temp 
 
 era- 
 
 ture 
 
 !15°— 232°C 
 
 243° 
 
 C. 
 
 254° 
 
 (• 
 
 265" 
 
 
 
 276° 
 
 T 
 
 287" 
 
 ■V. 
 
 293" 
 
 v. 
 
 315" 
 
 c 
 
1068 AN OUTLINK OF METALLUFtGY 
 
 ScluifTci-, wlio was iwaiiiiiiiiiu- tlu' new iiiclal. (Icclait'd it to be 
 "wliite gold." Ill Spain it was called "piatina del Piuto," 
 whifli, translated, moans "little silver of the Pinto," and from 
 wliicli tlie present name, phitiiniiii, was derived. 
 
 In ISO.') Wollaston discovered two other metals associated 
 witii platimnn, viz., palladium and rhodium. 
 
 About the same time Tennant discovered iiidiiun and 
 osmium. 
 
 In 1828 Berzelins analyzed pohixi^ne, the Siberian plat- 
 inum mineral, and found it contained platinum, iron, pal- 
 ladium, iridium, rhodium, osmium and coi)])er. With the ex- 
 ception of iron and copper, these metals lariiely constitute 
 what is known as the platinum group. 
 
 DISTRIBUTION 
 
 Platinum is found in many parts of the world. South 
 America, Australia, Canada, United States and Mexico — all 
 yielding moderate amounts. 
 
 Eecently some discoveries of vein platinum in Wyoming 
 have been made which promise to be very productive. 
 
 The largest bulk of the world's supply comes from Rus- 
 sia, whose i)latinum placers and mines have 1)ecome world 
 renowned. 
 
 The total production in that country from 1824 to the 
 present time amounts in round numbers to 250,000 pounds. 
 
 Platinum was used as money in Russia from 1828 to 1845. 
 During this period the volume of coinage amounted to 4.250,- 
 000 roubles, or about $3,000,000. 
 
 The production of platiniim during the i)eriod of its coin- 
 age was greatly stimulated, which, however, almost entirely 
 ceased when it was demonetized. 
 
 The great demand for platinum in recent years for elec- 
 trical, chemical and general scientific purposes has been so 
 marked that the metal is being as eagerly sought for as is gold 
 in all of the principal productive fields of the world. On 
 account of the great demand and limited supply, it ranks in 
 value very much above gold. 
 
 OCCURRENCE 
 
 Platinum usually occurs in nature in placer deposits, sim- 
 ilar to gold, frequently accompanying the latter in the allu- 
 vial deposits of rivers. 
 
 The mother lode, from which the placer de])osits are de- 
 rived, consists usually of serpentine or magnesium iron 
 silicate, which is closely related to chrysolite. 
 
AN OUTLINE OF MKTALLUHr,Y 1069 
 
 PliK'cr pijitiiiuiii usually dccurs in roiindcd n'raiiis, tinkers 
 or pellets, nccasidiially nuggets of iiicdiuin size are t'ound, 
 and ill two (ir tliicc iiistaiiees large (uics weighing from 15 to 
 21 poniids lia\c liccn discox'ered. Tlic largest one ineiilioned 
 is preserveil in the Demidoff innseinn. 
 
 PHYSICAL PROPERTIES 
 
 Pure platinum is a very soft metal, tin white in color. 
 It is not readily acted on by acids, witli the exception of nitro- 
 niuriatic, in which it is readily dis.solved. It does not oxidize 
 even at very high temperatures, and for this reason lills a 
 ]>lace in the arts and sciences for which the oxidizahle metals 
 are unsuited. 
 
 MALLEABILITY 
 
 Platinum is \<'ry malleable, and can be beaten out into 
 extremely thin foil, in which form it is used for many pur- 
 poses. It ranks sixth in this quality among the other metals. 
 
 DUCTILITY 
 
 'Phis metal can be drawn into exti'emely fine wire. Dr. 
 Arendt states that a cylinder of platinum 5 inches long and 1 
 inch in diameter can be drawn into a wire sufficiently long to 
 encircle the globe. The fine wire used in microscopic ej^e- 
 ])ieces is made by coating platinum wire with silver and draw- 
 ing this composite wire to the finest possible state, then dis- 
 solving off the silver with nitric acid. 
 
 TENACITY 
 
 In point of tenacity platinum occupies third rank. This 
 pi()])erty is so marked in ])latinum as to render it es])ecially 
 valuable for dowels in crowns and for the truss work in porce- 
 lain bridges. The addition of from 10 to 15 per cent of 
 iridium greatly increases its tenacity, as well as its liardness, 
 elasticity, infusibility, and resistance to chemical action. 
 
 SPECIFIC GRAVITY 
 
 The specific gravity of ])latinum is 21.4, two others hav- 
 ing greater density — osmium 22.47 and indium 22.40. These 
 three are the heaviest of the metals. 
 
 CONDUCTIVITY OF HEAT 
 
 Platinum is low in heat conductivity. Compared with 
 silver at 100, it ranks 8.4. Its co-efficient of expansion is low, 
 
1070 AN OUTLINE OF METALLURGY 
 
 being only .OOOi). For this reason it is especially valuable for 
 the ])ins of i)or('elain teeth, sinee the expansion of botli the 
 metal and jioreelain is nearly the same, and consequently 
 there is less liability of fracturing the porcelain in baking. 
 
 CONDUCTIVITY OF ELECTRICITY 
 
 Compared with siivci', which ranks 100 in conductivity 
 of electricity, i)latinuni ranks 14.5, or, in other words, this 
 metal offers about seven times more resistance to the passage 
 of a current than does silvei'. 
 
 FUSING POINT 
 
 Platinum fuses at 1779 deg. C, the oxyhydrogen blowpii)e 
 or the electric arc being required to effect it. 
 
 Dr. L. Fj. Custer of Dayton, Ohio, has devised a simple 
 yet effective method of fusing platinum scrap, the outline of 
 which is here given : 
 
 The first method consists in fastening the ])ositive end 
 of a wire capable of carrying a 110-volt current into a carbon 
 block. ^Vn ordinary battery plate will answer the purpose. 
 To the negative pole is attached an electric light carbon of 
 ordinary size. A resistance coil, lamp or electric furnace 
 should be included in the circuit capable of furnishing from 
 8 to 12 ohms resistence to prevent the fuses from blowing out. 
 
 It is necessary to make the positive and negative connec- 
 tions as described, as when so arranged the fusing can be ac- 
 complished more rapidly and with less noise than when re- 
 versed. 
 
 With 12 ohms resistance from 6 to 8 pwts. can be fused at 
 once, while with 8 ohms an ounce can be melted at one time. 
 By keeping the edge of a bulk heated and adding a fresh 
 supply, the mass can be elongated indefinitely. As much as 10 
 ounces have been melted in this manner in the form of a rod, 
 and the rod afterward drawn into a fine wire. 
 
 Platinum fused in this manner is harder than new plat- 
 inum, the cause assigned being due to a small per cent of 
 carbon uniting with the platinum. 
 
 To obviate this hardness a second method was devised, 
 which is as follows : 
 
 A piece of heavy platinum wire is attached to the posi- 
 tive terminal, and this is laid on a block of lime so shaped as 
 to serve as a receptacle for the scrap. The other terminal 
 consists of a brass rod five-eighths of an incli in diameter and 
 8 inches long, covered most of its length with wood to insulate 
 
AN OUTLINE OF METALLURGY 
 
 it. In Ihe exposed eml a slit is made, in whicli a nn.nget of 
 ])latinnni of at least one-half oz. weight is fastened. Too small 
 a piece would fuse in the are. The scraps are laid on the 
 platinum wire forming the positive terminal, which is placed 
 in the depression in the lime hlock. The arc is established by 
 interposing a stick of carbon between the negative pencil and 
 the scrap, and, when established, quickly removing it. Tliis 
 step is necessary to prevent the scrap fusing to the nugget 
 on the negative end. 
 
 The eyes sliould be protected by wearing glasses of the 
 darkest variety, as the arc light is intensely brilliant. This 
 
 _-Wboti HcLTi^le. 
 
 ,,BrdssRodL. 
 
 Pla^iMum Point. 
 'Platinum Wire 
 
 -pole.. 
 
 metliod of fusing iilatinum is recommended as practical for 
 dental laboratory procedures. 
 
 In a fused condition platinum absorbs oxygen, and when 
 cooling "spits" as the gas is given off, none of it being re- 
 tained or occluded when cold. 
 
 When a jet of hydrogen is directed on spongy i)latinum, 
 the latter begins to glow, and the gas ignites. 
 
 Platinum black is formed by adding platinum chloride 
 solution to a boiling mixture of 3 parts of glycerine and 2 
 parts of caustic soda. The platinum is thrown down as a 
 black powder. In this form it absorbs about 800 times its 
 volume of oxygen from the air. 
 
 USES 
 
 Platinum is used for many purposes in dentistry, espe- 
 cially in combination with porcelain. It is used as base plates 
 
1072 AN OlITLINIO ()!•' MKTAI.LtTRGY 
 
 I'di' (■(i)i(iiiii(ius i;iiiii ilciitui-cs, the iiiclal piii'ts and trusses in 
 continuous i;uni dcnlui'cs, llic metal pai'ts and trusses in 
 jJorcH'hiin crown and hridii'e work, as a matrix nuiterial in 
 inlay work, for pins in poicelain teeth and I'or electric fur- 
 nace constriu'tioii. It is also used in combination with gold 
 in the form of foil, foi' tillins' teeth, heini;,- harder and more 
 neutral in color than ]aire gold. It requires more care in 
 condensation than pure gold, however, to develop its welding 
 property in the highest degree. 
 
 In the chemical, electrical and sci entitle fields, it has a 
 wide range of usefulness, being utilized in many instances for 
 purposes for which no otliei- metal is ada])ted. 
 
 ALLOYS 
 
 Its ]3rincipal alloys for dental ])ur])oses are its combiiui- 
 tions with iridium, for hardening and increasing its tenacity, 
 and gold in the composition of solders for platinum, and for 
 clasp metal. 
 
 It is also comhined with silver, the resulting alloy being 
 harder than either of component metals and less oxidizable 
 than silver. This alloy is known as dental alloy, and is used 
 to a considerable extent in Europe as a base for artificial 
 dentures. 
 
 DENTAL ALLOY 
 
 Silver 70 or 80 
 
 Platinum 30 or 20 
 
 Gold solder can be used in conjunction with this alloy. 
 
 PLATINUM SOLDER AND CLASP METAL 
 
 These formulas are given in connection with the alloys of 
 gold. 
 
 IRIDIUM 
 
 Iridium is one of the metals of the platinum group, and 
 resembles the latter in some respects, but is much harder. 
 When combined with ])latinum, the resulting alloy has greater 
 tenacity and hardness than platinum, and, therefore, for this 
 quality alone it is valuable for dental uses. 
 
 The specific gravity of iridium is :2:].40, atomic weight 
 192.65, and fusing jtoint 2200 deg. 
 
 On account of its hardness, it is used alone and in com- 
 bination with osmium for watch and compass bearing, the 
 knife edges of delicate balances, and for the nibs of gold pens. 
 It ranks in value somewhat higher than platinum. 
 
AN OUTLINE OF METALLURGY 1073 
 
 SILVER 
 
 Silver is fuiiiul in iiiany parts of tlie world, but the West- 
 ern Continent has the richest and most extensive deposits 
 known. 
 
 It is im]iossihle to l)riefly enumerate the many practical 
 uses found for this metal. 
 
 It is brilliant white in color, very soft, malleable and 
 ductile, and moderately tenacious. Its speciiic gravity is 
 10.53, specitic heat .056, and it fuses at 960 deg. C. It is the 
 best known conductor of heat and electricity, and is taken as 
 the standard of measurement of all of the metals in these 
 properties, being rated at 100. 
 
 ORES OF SILVER 
 
 Silver sometimes occurs luiiire, but is more often asso- 
 ciated with other metals and with non-metallic substances. 
 One of the in-incii)al ores of silver is the sulphide Ag. S, 
 called argeiitite. This is grayish black in color, and is read- 
 ily fusible. It contains about 87 of silver. Pyrargyrite Ag,, 
 Sb S3. Silver copper glance (Ag Cu)2S. Stephanite Ags Sb 
 S4, with lead as argentiferous galena and in several other 
 combinations. 
 
 REDUCTION 
 
 The reduction of silver is accomplished by three princi- 
 pal methods. 
 
 First. Amalgamation. 
 Second. By the wet method. 
 Third. By' the lead method. 
 
 AMALGAMATION 
 
 In the first process, the silver, after being reduced to a 
 chloride, is amalgamated with mercury, from which it is re- 
 covered by distilling the latter off. There are three different 
 methods of recovery of silver by amalgamation, each of whicli 
 is more or less complicated, and in this treatise it is not ad- 
 visable to enter into the details of them. 
 
 WET METHOD 
 
 There are several wet i)rocesses, all of which depend 
 upon the solubility of the sulphide and chloride of silver in 
 water, or some other solvent, from which the silver is thrown 
 down by a precipitant, usually copper. 
 
AN OUTLINIO OK MRTALLUUfiY 
 
 THE LEAD METHOD 
 
 By this iiu'tliod the .silver is eouceiitratcd in a (|uaiitity 
 of k'ad, from whicli it is recovered by cupellatioii. 
 
 Cupellation consists in heating an alloy of silver and lead 
 in a porous cupel, or shallow crucible, made from i)re))ared 
 bone ash. Under the influence of heat, the lead is oxidized 
 and absorbed by the ])or()us cupel, while the silver remains 
 in the crucible. 
 
 USES IN DENTISTRY 
 
 Silver occupies a ])rominen( ])lace in the dental office and 
 laboratory. It is the principal metal used in the compounding 
 of dental amalgam alloys. It is iised as an alloying agent with 
 copper and gold in the various gold plates and solders used in 
 the laboratory. 
 
 Were it not for the fact that sulphur has such a strong 
 affinity for silver, as to readily discolor it, the latter would 
 have a much greater range of usefulness. For the reason 
 mentioned, although it possesses most of the necessary re- 
 quirements, silver is not suitable as a base for artificial den- 
 tures, nor for crowns and bridges. Before the introduction 
 of vulcanite, however, it was used extensively as a base i>late 
 because of its cheapness as compared with gold or continuous 
 gum dentures. 
 
 It is not possible to attach teeth to silver base plates with 
 vulcanite, because the suli)hur in the rubl>er acts on the silver, 
 forming silver sulphide. It disintegrates the rubber to such 
 an extent that all attachment of vulcanite to base plate is de- 
 stroyed or never effected. 
 
 Silver is not readily acted upon by oxygen, but when 
 fused it mechanically absorbs about 22 times its volume of this 
 gas. The "spitting" so noticeable when fused silver solidi- 
 fies, is due to the forcing out or escape of the oxygen, nearly 
 all of which is expelled. 
 
 This peculiar affinity between oxygen and silver in a 
 fused state renders the jn-oduction of sharp castings of this 
 metal a difficult matter. 
 
 ALLOYS OF SILVER 
 
 U. S. coin silver is composed of 90 parts silver and 10 
 copper. The latter is added to harden the silver, which, un- 
 alloyed, is almost as soft as pure gold. 
 
 In Great Britain and Europe the profession is using an 
 alloy composed of silver and jilatinum for dental purposes. 
 
AN OUTLINE OF METALLURGY 1075 
 
 It does uot discolor quite so readily as silver alone, but is 
 not by any means free from the action of snlplmr. It is more 
 rigid than coin silver, and in some months can be worn for a 
 long time without discoloring. 
 
 In compounding this alloy, the rule commonly followed 
 of melting tlie highest fusing ingredient first is reversed. The 
 platinum is rolled into a very thin ribbon, the silver melted, 
 and the platinum gradually fed into it. The two metals will 
 unite at a temperature far below the fusing point of platinum. 
 
 Silver solders are composed of silver and copper, with 
 some other ingredient, usually zinc, to reduce the fusing 
 point. The following are standard formulas for some of the 
 solder used in the dental laboratory and by jewelers : 
 
 Low fusing. High fusing. 
 
 Silver 6 Silver (J 
 
 Copper 3 Copper 2 
 
 Zinc 2 Zinc 1 
 
 A method followed by jewelers is to take a silver coin, 
 add one-half its weight of spring brass wire, and fuse under 
 a flux. Solder prepared in this manner usually flows readily. 
 Purple of Cassius, a jngment used to impart a pink- 
 color to porcelain enamel, is formulated as follows : 
 
 Silver 432 grs. 
 
 Gold 48 grs. 
 
 Tin 36 grs. 
 
 The gold, silver and tin are melted together in the order 
 named, and granulated by pouring into cold water, repeating 
 the process several times to insure through mixture of the 
 metals. 
 
 The granulated alloy is then treated with nitric acid to 
 remove the silver, the residue is a brown powder of unknown 
 composition, but containing gold and tin, which is called 
 Purple of Cassius, and which, as before stated, will produce 
 varying shades of pink in porcelain, according to the amount 
 used. It may also be prepared by adding a solution of stan 
 nous and stannic chlorides to auric chloride. 
 
 THE CHEMISTRY OF PHOTOGRAPHY 
 
 Some of the salts of silver, as the bromide and the iodide, 
 are exceedingly sensitive to the influence of light, and when 
 ('X])osed to it are readily reduced to black metallic silver on 
 being subjected to the action of various reducing agents. 
 
1076 AN OUTLINE OF METALLURGY 
 
 Pliotographio plates or liluis ai'e eoal('(l with a layci- of 
 gelatin eiuulsiou, coutaiuiiig one or both ol' tlie salts men- 
 tioned. The emulsion is applied to one side of the i)lates 
 oidy, in the dark, or with ruhy light, allowed to dry, after 
 which they are wrapped in light-proof paper, packed and 
 sealed in boxes or packages, in wliich condition they nnist be 
 kept until ready for use. 
 
 When a plate so prepared is i)laced in the plate-holder 
 of the camera and light is transmitted to it through the lens, 
 the various areas of the plate are atTected in different de- 
 grees by the light which falls i;pon them, according to the 
 depth or intensity of the shadows and lights of the view re- 
 flected and the time of exposure. Where no light falls, the 
 silver salt is unaffected. Medium shadows produce moderate 
 decomposition, while bright light atfects the silver salt most 
 intensely. When an exposed plate is examined under ruliy 
 light, no visible altei'aticm in the film can be seen until ))rought 
 to view by develophtg. 
 
 To develop the latent inuige and make it visible, the plate 
 is immersed in a licjuid developer. The silver salt upon 
 which the strongest light was directed is first and most read- 
 ily decomposed by the develo^jer, being resolved into metallic 
 silver. The portions not so strongly affected by the light 
 are acted uiaon more slowly, and on developing sliow corre- 
 spondingly lighter shadows. When the image shows up dis- 
 tinctly and clearly, the development must be stopjied imme- 
 diate!}'; otherwise the plate will liecome fogged from the 
 action of the developer on the less affected portions of the 
 silver, which will in time be reduced. 
 
 The development is arrested and the plate cleared up 
 l)y immersing it in a solution of ln'])osulphite of soda, which 
 dissolves out the unreduced silver bromide, but does not act 
 readily on the metallic silver. The heavy shades and shad- 
 ows are formed by the reduced or metallic silver, which is 
 held in suspension in the film of gelatin and thus accounts 
 for the varying degrees of intensity of the negatire. 
 
 The hypo, as it is called, must be removed by thorough 
 washing before the negative is exposed to the light, other- 
 wise the silver salt which is dissolved by it, but not yet re- 
 moved, will thicken the shadows and the transparency of the 
 jilate be affected. 
 
 Many kinds of developers are in use, each having some 
 peculiar quality which renders it specially adapted for some 
 particular purpose. The following expresses in a general 
 
AN OUTLINE OF METALLURGY 1077 
 
 way the chemical action which occurs in the use of any of 
 the standard developers : 
 
 SAgCl + 3FeS04 = 3Ag- + FeCh + Fe,(lSU,). 
 
 The negative is a reverse of the object photographed, the 
 light shades being dark and the dark tints light. To obtain 
 a positive or true likeness, a similar process is carried out, 
 the silver salts again being the sensitized factor in the paper 
 on which the picture is to be ])riuted. In printing, tlie dark 
 areas of the negative produce light tints on the i)aper, and 
 tlie light, dark, according to the facility with which the liglit 
 passes through negative and decomposes the silver in th.e 
 sensitized paper. 
 
 Ag.I., the iodide Ag.Br. bromide, and Ag. CI., tlie chlo- 
 ride, are used in photography. 
 
 COPPER 
 
 Copper was one of the first metals known to the ancients, 
 probably because it is found so widely distributed over the 
 earth. From it weapons, ornaments, and useful implements 
 of all kinds were made. The ancients employed a method of 
 tempering edge tools made from this metal, which is now con- 
 sidered a lost art. 
 
 Copper is distinguished from all other metals by its red 
 color. It is very soft, mallealile, ductile and tenacious. It 
 fuses at lOS-l^C, or a little below pure gold. Copper is an 
 excellent conductor of electricity, ranking 97, silver being 
 100. Its specific gravity is 8.95, sjiecific heat .09.3 and atomic 
 weight 63.6. 
 
 Copper is not readily oxidized in dry air at ordinary tem- 
 lierature, but is easily affected under tlie influence of heat. 
 In moist air a green carbonate is quickly formed, and whea 
 acted u])on l)y acid fumes, it oxidizes rai)idly. 
 
 ORES 
 
 Copper frequently occurs native in large masses, par- 
 ticularly in the Lake Superior region. The most common 
 ores of copper are tabulated below : 
 
 Cu O2 — cuprite, or red oxide. 
 
 Cu — Melaconite, or black oxide. 
 
 Cu Fe S.. Chalcopvrite — copper p\Tites. 
 
 Cu CO. Cu H, d.,— Green malachite. 
 
 (2 Cu CO3 Cu H, 02)— Blue malachite. 
 
 Cu; S — Chalcocite — Copper glance. 
 
AN OUTLINIO OF METALLURGY 
 
 REDUCTION 
 
 Tlie ores of copper are reduced ))>• two principal metli- 
 ods, known as the dry and the wet method. In tlie dry metliod 
 the ore is snljjected to treatment in the reverheratory furnace, 
 which drives oif impurities and leaves it free as a sulphide. It 
 is then strongly heated with sand, which reduces it to an ox- 
 ide. Tlie oxide is then mixed with some form of carbon and 
 sul)jected to a very high temperature. The oxygen, in com- 
 bination with the copi)er, unites with the carbon to form CO.. 
 which escapes, leaving the metal free. 
 
 When the wet method is employed, the ore is mixed with 
 rock salt and calcined, which converts the copper into a sol- 
 uble cupric chloride. The calcined ore is then lixiviated with 
 water, and from the resulting solution the copper is thrown 
 down in a metallic state by the addition of scrap iron. 
 
 USES 
 
 Copper is used for many purposes, and in great quan- 
 tities, unalloyed, especially in the electrical field. On land, 
 and under the sea, hundreds of thousands of miles of copper 
 wire are laid, and by means of the telephone and telegraph, 
 communication with most parts of the civilized world is pos- 
 sible in a few minutes or hours' time at most. 
 
 In every dynamo and motor, copper wire is used, and in 
 numberless instances a single machine contains many miles 
 of wire. 
 
 It is used in the manufacturing and chemical industries, 
 and occupies a field no other metal can fill. 
 
 ALLOYS 
 
 Cojiper forms the basis of two prominent classes of al- 
 loys — l)rasses and bronzes — and occupies a minor but imjior- 
 tant place in the composition of many other useful and val- 
 uable alloys, particularly in the compounding of gold plate 
 and solder. 
 
 BRASS 
 
 Under this head may be included most of the alloys of 
 copper and zinc. Brasses, with a wide range of strength 
 and color, can be produced by alloying copjter and zinc to- 
 gether in varying proportions. 
 
 Name and Color. Copper. Zinc. 
 
 Pinchbeck (reddish vellow) 88.8 11.2 
 
 Sheet brass (yellow) 84 16 
 
AN OUTLINK OF METALLURGY 1079 
 
 Nfiinc and ( 'olor. ('(ii>pcr. Ziiie. 
 
 Similor (yellow) 80 '20 
 
 Brass wire (bright yellow) 70 30 
 
 White brass (very light ) o4 (>() 
 
 Common brass (full yellow) (54 '.Uj 
 
 Machine brasses, bearing metal, iiumj) valves, steam 
 whistles, cog wheels, etc., usually contain some tin, in addi 
 tion to copper and zinc. 
 
 BRONZES 
 
 Bronzes are metallic alloys, composed principally of 
 copper and tin. They cast with great clearness of outline, and 
 are therefore extensively used in making statues, medals, 
 busts, and were also formerly much used in making cannon 
 and field ordnance. 
 
 P h o s - 
 Copper. Tin. ]ihorous. Zinc. 
 
 U. S. ordnance bronze 90 10 
 
 Phosphor bronze ()0.;14 8.90 .7(i 
 
 Statuary bronze 84.42 4.30 11.28 
 
 Speculum metal 66.66 33.34 
 
 Bell metal 72-85 28-15 
 
 Aluminum bronze consists of: Coi)per, 90; and alumi- 
 num, 10 ])arts. This alloy very much resembles gold in color, 
 is not readily tarnished, has pronounced elastic property, can 
 be turned and engraved, and fuses at about 860° C. 
 
 ALUMINUM 
 
 Although aluminum is the most abundant metal in the 
 earth's crust, it never occurs native. It forms the basis of 
 the feldspar rocks, which when disintegrated by the action 
 of the elements, lose their potassium and sodium. The residiie 
 is silicate of alumiimm, or common clay, which is found almost 
 everywhere. Clay containing impurities and coloring mat- 
 ter as iron oxides is known as sienna, umber, ochre. Fuller's 
 earth, etc., according to composition. 
 
 It also enters into the composition of slate rocks, mica, 
 jumiice stone, and is found in many other forms too numerous 
 to mention. 
 
 It occurs in crystalline form as an oxide, and among the 
 many interesting and curious results of this combination, may 
 be mentioned the ruby, garnet, sapphire, emerald, topaz and 
 amethvst. Corundum and emery, substances in crystalline 
 
1080 AN OUTLINIO OF METALLTTROY 
 
 I'oriii and cxtrciiic liardiicss, used for ni'iiiditiu' and pulishiiig 
 j)Ui'))()S('s, ai'c also iriflndcd in this class of oxides. 
 
 REDUCTION 
 
 Must, oi' the aliiuiinuni at the [tresent time is produced at 
 the gigantic electrical works at Niagara Falls, N. Y., and is 
 o])tained by the electrolytic process. 
 
 The i)rinciple of reduction depends u])on the i)o\ver, the 
 fused double fluoride of aluminum and i)otassiuni or sodiinii 
 has of reducing the ores of aluminum. The apparatus con- 
 sists of a large iron box, lined with carbon, in which there is 
 a receptacle for the ore about -i^'-^ feet long by L'Vo feet wide 
 and G inches in depth. 
 
 The carbon lining acts as the cathode. Tliere are usually 
 40 anodes, consisting of carbon cylinders 3x10 inches, sup- 
 ported above the pot in which the ore is placed, their lower 
 ends resting in the bath of fused fluorides. The heat is de- 
 veloped by the resistance of the fluoride to the passage of 
 the current from the anode to the cathode. The ore to be 
 reduced is ]jlaced in the bath of fluoride, and renewed from 
 time to time as that in the pot becomes reduced. 
 
 The resistance, and consequently the heat, increases as 
 the ore is reduced, which, by means of an incandescent lamp 
 attached to the furnace, becomes apparent to the furnace at- 
 tendant by the brightening of the lamp, when he immediately 
 reiilenishes the charge. 
 
 The ore introduced in the furnace is an oxide, and the re- 
 action under heat is due to the oxygen in combination with the 
 metal uniting with the carbon of the anodes forming COo, 
 which escapes, leaving the metal free. The process is con- 
 tinuous, being carried on day and night. The metal is drawn 
 off every twenty-four hours, 100 pounds per furnace being 
 the usual amount reduced in that length of time. As there 
 are more than 100 of these furnaces in operation in a plant, 
 the yield per day is about 10,000 pounds. A current of 20 
 volts and 1700 amperes is required to effect the reduction. 
 
 PHYSICAL PROPERTIES 
 
 Aluminum is a white metal, with a slightly bluish tint, 
 reseml)ling zinc in color. It is soft and workable, capable of 
 taking a high polish, and does not discolor appreciably on 
 exposure to air, moisture or siilplnir. It is not readily acted 
 upon bj' nitric or sulphuric, but can readily be dissolved in 
 hvdrochloric acid or solutions of caustic potash or soda. 
 
AN OUTLINE OF METALLURGY 1081 
 
 Alumimun is very malleable, ductile and (juite tenacious, 
 ranking eighth in respect to the latter property. It is a mod- 
 erately good conductor of heat and electricity, ranking about 
 half way between silver and platinum. 
 
 Its si:)ecific gravity is 2.6, the lightest of all of the metals 
 except magnesium. Its atomic weight is 27.1, specific heat — , 
 and its melting point 700° C. 
 
 Aluminum is soft, and in working it, files soon clog. It is 
 best to use single rather than cross-cut files, and when clogged 
 they may l)e cleaned by dijjping in a solution of caustic soda 
 and wasiiing in hot water. In annealing, aluminum should not 
 be heated above 200° C. The proper heat is attained when n 
 soft wood stick will leave a brown streak when di'awn across 
 the heated surface. 
 
 SOLDERING 
 
 It is very difficult to solder successfully, although this 
 operation can be accomplished under proper conditions. The 
 difficulty is supposed to be due to a film of oxygen adhering 
 to the surface, which by means of the known fluxes can only 
 with difficulty be removed. 
 
 Many formulas for fluxes and solders have been ])vo- 
 posed, some of which are successful when applied with skill. 
 The following solder and flux is recommended as being suc- 
 cessfully used in the manufacture of aluminum jewelry: 
 
 Zinc 80 or 85 or 90 
 
 Al 20 or 15 or 10 
 
 The soldering iron is dipped in a mixture of copaiba 
 balsam 3 parts; Venetian turpentine, 1 ]iart; lemon juice, a 
 few drops. 
 
 Another method recommended by Page and Anderson 
 consists in spreading ])owdered silver chloride along the joint 
 to be united, and applying common solder with a l)lowpipe. 
 
 USES 
 
 Aluminum can be applied in many ways in dentistry. It 
 makes an excellent base for dentures, 16 or 18 gauge plate 
 l)eing recommended, and the teeth attached with vulcanite. 
 Although not as lasting as some other bases, on account of 
 the action upon it of the fluids of the mouth, its lightness, 
 cleanliness and good conductivity commend its use. 
 
 Basei)lates are frequently cast over models of investment 
 nuiterial, which to a limited extent are satisfactory, but as 
 the density of such casting is fr(M|uciitly imi)erfect, the action 
 
1082 AN OUTLINl': OF MIOTALLURGY 
 
 of tlio fluids ol' the inoutli is iinirc rapid tliaii updii swa^c*! 
 base-plate.s. 
 
 On account of its extreme liglitness, aluminum is em- 
 ployed to a considerable extent in tlie manufacture of physical 
 apparatus of all varieties. It is especially valuable for light 
 balance weights, instrument handles, etc. In powder form 
 it is used as a paint, wliich is not readily acted upon by the 
 air or moisture. 
 
 ALLOYS 
 
 As mentioned elsewhere, aluminum with copiHT makes 
 an excellent bronze, which is used for many ))urposes. It 
 also unites with zinc to form alloys used as solders for the 
 metal itself. 
 
 Silver and aluminum unite readily, and produce alloys 
 of commercial importance. 
 
 The silicate of aluminum, or kaolin, the double silicate, 
 feldspar and the oxide of silicon, form the basis of porcelain 
 teeth, and the porcelain bodies used in continuous gum, crown, 
 bridge and inlay work. 
 
 It is not generally known that aluminum can be used as 
 a whetting agent, like the ordinary oil stone. A keen, smooth 
 edge, not possible to secure with fine oil or water stones, can 
 be developed on fine edge instruments, and especially razors, 
 by using a true ])lane slal> of ahnuinum and oil. 
 
 Combined with magnesium, a very important alloy known 
 as magnalium is formed. It is used in the making of fine 
 instruments, such as mathematical instruments, balances, etc. 
 
 ZINC 
 
 The ancients were familiar with the ores of zinc, since 
 they were able to compound brass, liut the separation of the 
 metal itself from its ores is of comparatively recent date. 
 
 ORES 
 
 The carbonate, sulphide, silicate and oxide are the prin 
 ci]ia] ores of this metal, the formulas of which are as follows : 
 Zn CO;; — calamine or carbonate. 
 Zn S — zinc blend or suli^hide. 
 Zn Si O2 — willemite or silicate. 
 Zn — red zinc ore or oxide. 
 
 REDUCTION 
 
 Those ores, other than the oxide, are reduced by roast 
 ing to an oxide. In this form the ore is mixed with coke or 
 
AN OUTLINE OF METALLURGY 1083 
 
 cliarcoal, and lieated in a retort. Tlie carhon imitcs witli tlu' 
 oxygen of the ore to form COj and the zinc volatilizes and is 
 condensed in receivers. 
 
 Usually some slight amount of oxide passes over with the 
 zinc, which can be removed by remelting. 
 
 PROPERTIES 
 
 Zinc is bluish white in color. It tarnishes readily in 
 moist air or when heated, an oxide being formed on the sur- 
 face. When exposed to the vapor of, or fiuids containing, 
 carbonic acid, a film of zinc carbonate is formed. It is sol- 
 ulile in most of the acids, and is readily acted upon l)y alkaline 
 solutions. 
 
 Its fusing point is 433° C. Specific gravity, 7; atomic 
 weight, 64.9, and specific heat, .0956. It ranks low in malle- 
 ability, ductility, and tenacity, on account of its crystalline 
 character, which renders it brittle at ordinary temperatures. 
 When heated to a temperature between 100° and 150° C. it 
 can be rolled and drawn into wire, becoming both malleable 
 and ductile, and retaining these properties in a degree when 
 cold. 
 
 Considerable contraction occurs in jiassing from the fused 
 to the solid state. 
 
 USES 
 
 For many years zinc was about the only metal in use 
 for constructing dies for swaging baseplates, but Babbitt's 
 metal has largely taken its place. The advantages claimed 
 for it were its hardness and ability to stand the stress of 
 swaging without the face of the die becoming mutilated, and 
 that its contraction in cooling compensated for the expansion 
 in the plaster model. It does not seem possible, however, that 
 uniform contraction without warpage can readily occur, and 
 therefore, it is best to compensate for the expansion of the 
 plaster model by scraping properly and use a die metal that 
 will not perceptibly contract, such as Babbitt's metal. 
 
 When zinc is used for dies, lead can be used for coun- 
 terdies, as there is enough variation in their respective melt- 
 ing points to obviate the melting of the zinc by the lead when 
 the latter is i)oured upon the die. 
 
 A coating of whiting and alcohol painted over the ex- 
 posed surface' of the die will further tend to prevent the 
 fusion of the zinc and union of the two metals in counterdie 
 construction. 
 
1084 AN OtlTLINh: OF MRTALLITUnY 
 
 Tlic oxide of zinc oilers into the coiiiposit ion of oxy- 
 pli()si)licite and oxycliloi-ido dental cements. In fact, the pow- 
 der of these cements is nothing more than the retined oxide 
 of zinc, citiiei- pui-e, oi- containiiii;' some piiiincnt to slightly 
 color it. 
 
 The li(iuid constituent of the oxyphosi)hate consists of 
 glacial phosi)horic acid in distilled water, reduced to a syrup- 
 like consistency by e\'aporation. 
 
 The oxychloride licjuid is made 1)\- adding one-half ounce 
 of crystalline chloride of zinc to two drains of distilled water, 
 allowing it to stand for two or three days, then drawing off 
 the clear liquid. Both liquids should be kept in tightly stoji 
 pered bottles to prevent deterioration. 
 
 Zinc has a wide range of aj^plication in the chemical, 
 scientific and industrial fields. In recent years there has 
 been an increasing demand for it as a precipitant of gold in 
 the cyaniding process of recovery. Its vise in the electrical 
 field for cheap and efficient battery work is fully as great 
 as ever, while in foundry work there seems to be a greater 
 demand for zinc than ever in the compounding of brasses, 
 some of the formulas for which are given in connection with 
 copper. Zinc is used for coating iron to prevent oxidation 
 (galvanized iron), in the development of hydrogen gas, and 
 for very many other useful purposes. 
 
 CADMIUM 
 
 Cadmium is usually found associated with zinc as a sul- 
 phide, and is recovered in the refining of zinc. As it is more 
 volatile than the latter, the vapor first given off is directed 
 into a separate chamber and condensed, the product being 
 cadmium with some zinc and oxides. 
 
 Redistillation further refines it. 
 
 Cadmium resembles tin in color, and is capable of taking 
 a high polish. It is subject to slow oxidation on exposure to 
 air. It is malleable, ductile and slightly tenacious. It fuses 
 at 320° C, has a specific gravity of 8.6, and specific heat of 
 .05(37. Its principle ore is greenockite. 
 
 ALLOYS 
 
 Cadmium enters into the composition of a numl^er of 
 alloys, among which might be specifically mentioned one fre- 
 
AN OUTLINE OF METALLURGY 1085 
 
 (liK'iitly used in cast l)ase lower dentures, iustead of Watt 
 metal, the foiinuhi ol' which is as t'oUows: 
 
 Tin, 16. 
 
 Cadmium, 1. 
 
 Cadmium also is one of the component metals of "Wood's 
 Alloy." 
 
 LEAD 
 
 Lead might he called an ahundaut metal, yet the constant 
 and increasing demand for it for old as well as new purposes 
 is so great that its value is constantly heing enhanced. 
 
 It occurs in nature in several forms, the principal ones of 
 which are here mentioned: 
 
 (Pb S) — Galena or sulphide. 
 
 (Pb COa) — White lead or carbonate. (Cerussite.) 
 
 (Pb Or 64) — Crocoesite or chromate. 
 
 (M Oi Pb)— Wulfenite. 
 
 (Pb So.)— Sulphate. 
 
 Lead ore carrying silver is designated as argentiferous 
 galena. 
 
 REDUCTION 
 
 The ores are first roasted to reduce them to oxides and 
 sulphates. Upon raising the temperature of the furnace these 
 two compounds react on themselves, as indicated, lead and 
 SO, resulting: 
 
 2Pb O+Pb S=S0,+3 Pb and 
 
 Pb SO.+Pb S=2SO.+2 Pb. 
 
 PROPERTIES 
 
 Lead is a bluish gray metal, so soft that it can be readily 
 cut or scratched, quickly tarnishes in the air, forming a 
 suboxide, but is not readily acted on by water, hence its ex- 
 tensive use in plumbing operations. 
 
 Its fusing i)oint is 326° C. Specific gravity, 11.4 Atomic 
 weight, 206.47, and speciiic heat, .0314. It is quite malleable 
 and ductile, Imt is deficient in tenacity. 
 
 USES 
 
 The prinrijial use of this metal in the laboratory is for 
 counterdies, being used unalloyed with zinc, and in the propor- 
 tion of 1 of tin to 7 of lead with Babbitt's metal dies. 
 
1086 AN Or'J'LINIO Ol' MIOTALU'KCY 
 
 ALLOYS 
 
 Coinnioii tinners' solder eonsists of lead and tin in vary- 
 ing i)roi)ortions, those having the most tin being considered 
 the best. 
 
 (xrade Tin Lead 
 
 Fine 2 1 
 
 Common 1 1 
 
 Coarse 1 - 
 
 Another series of valual)le alloys in whieh lead plays an 
 important part is gi\('ii in the section on bismntli. 
 
 The alloj's given in the section on tempering steel also 
 form an important series in which lead is the principal metal 
 employed. 
 
 TIN 
 
 Tin occurs usually as a native oxide, Sn O. in crystals of 
 quadratic form, usually colored by manganic or ferric oxide. 
 
 REDUCTION 
 
 The ore is first washed and stami^ed, then roasted to 
 drive off any arsenic or sulphur tliat may be present, at a tem- 
 perature that will not fuse the ore. It is then mixed with 
 fine anthracite coal and smelted for five or six hours, when, 
 after thorough stirring the melted metal is drawn off. The 
 reaction during the process is as follows : 
 
 Sn 0,+2 C=Sn+2C0. 
 
 PROPERTIES 
 
 Tin is a white, soft, lustrous metal, quite malleable, some- 
 what ductile, but with very little tenacity. It fuses at 232°C., 
 and is not perceptibly volatilized at ordinary temperatures. 
 It does not oxidize readily, and for this reason is largely 
 used as a coating or protection for iron plates. In this form 
 it is known as the sheet tin of commerce. 
 
 When a bar of tin is cut, it apiiears to be devoid of crys 
 talline structure, but if tlie surface is etched with dilute acids, 
 its crystalline cliaracter becomes apparent. When a bar of 
 tin is bent, it emits a peculiar crealcing sound, known as the 
 tin cry, and whicli is undoubtedly due to the sliding or rear- 
 rangement of the crystalline facets. 
 
 The specific gravity of tin is 7.3, and its spcific heat 
 0.0562. 
 
AN OUTLINK OF METALLURGY 
 
 USES 
 
 Tiu is used in the dental office and laboratory in the 
 form of foil for filling teeth and for covering jjlaster models 
 in vulcanite work, to give a finished surface to rubber. After 
 being vulcanized, the foil is removed. It is questionable 
 whether this is a good plan to follow, since the model is en- 
 larged by the addition of the foil, which must impair the 
 close adaptation of the denture to the tissues. 
 
 Tin is also one of the principal ingredients in the compo- 
 sition of dental amalgam alloys, from 'I'l to 35 per cent l)eim': 
 used with 77 to fi5 ]iev cent of silver. 
 
 HASKELL'S BABBITT METAL 
 
 It is also used in the composition of fusible alloys and 
 counterdie metal, and forms in conjunction with copper and 
 antimony a hard and practically non-contractile die material, 
 known as Babbitt's metal. 
 
 The formula for Haskell's P>abl)itt metal is Cu 1, anti- 
 mony 2, tin 8 parts. 
 
 The coiniterdie metal used in conjunction with Ba))bitt's 
 metal is: Lead 7, tin 1 part. Tlie tin is added to reduce the 
 melting i)oint of the lead. Babbitt's metal melts at 260°C., 
 while the fusing point of lead is .S25°C. If lead is poured upon 
 a Babbitt metal die, the heat is sufficient to fuse the latter, 
 and union of tlie two will very likely occur. 
 
 This undesirable result is obviated by the addition of tin 
 to lead in the proportions before mentioned, which gives an 
 alloy with a fusing point of about 225°C. 
 
 MERCURY 
 
 Mercury sometimes occurs in nature free, though it is 
 commonly found as the red sulphide Hg. S., called cinnabar. 
 It is fi'equently found forming an amalgam with silver, and 
 also in the form of a protochloride or native calomel. 
 
 DISTRIBUTION 
 
 Mercury is found in Spain, Corsica, Mexico, California, 
 Peru and China. 
 
 At the present time California itroduces a greater bulk 
 tlian any other country in the world. The ore is very rich 
 in mercury, yielding as higli as 70 per cent, while the oi'e from 
 
1088 AN OUTLINE OF METALLURGY 
 
 tilt' Spuiiisli iiiiiics, the next largest ]»i'()(lnccrs, yields only 
 38 per eeiit. 
 
 COMBINATIONS 
 
 Mei'L'ury forms two oxides, inercurons oxidis ll^-O, 
 and mercuric oxide, trig (). It ;dso forms two chlorides of 
 prominence, HgCL — corrosive .^iihUnidfc — a powerful disin- 
 fectant, and Hg, CL, called calnnicl. 
 
 Vermilion — or mercuric sulphide, JJg. S. — a brilliant red 
 color, is used extensively as a ])igment in paints and for the 
 coloring agent in the manufacture of red and i)ink rubber and 
 celluloid. 
 
 As is well known, mercury is extensively employed for 
 thermometers, barometers, etc., and for many other useful 
 purposes in the arts and sciences. 
 
 ALLOYS OF MERCURY 
 
 Mercury uniti's with many of the metals to form amal- 
 gams. It is used very extensively with (h-ntal alloys for the 
 filling of teetli. 
 
 PROPERTIES 
 
 Mercury is silver white in color, tarnishes slightly in 
 air, but is not acted upon by water. It is tasteless and odor- 
 less. It is liquid at ordinary temperature, boils at 357. 3°C., 
 and can be soliditied by subjecting it to a temperature of 
 — 39.5° C. It contracts noticeably in passing from tlie liquid 
 to the solid state, and assumes a crystalline form. When 
 solid it can be flattened out under hammer blows, thus prov- 
 ing that it is malleable. In this condition it can also be 
 welded, and can be cut into shavings with a knife. 
 
 The specific gravity of mercury is 13.6, specific heat .032, 
 and its atomic weight 200.6. 
 
 EEDrCTION 
 
 Mercury is obtained from the native sulphide in two 
 ways. The first method consists in crushing the cinnabar ore 
 and mixing with lime. The mixture is then placed in cast- 
 iron retorts, which are connected with earthenware receivers 
 l)artially filled with water. Upon the application of heat the 
 sulphur coml)ines with the calcium and forms calcium sulph- 
 ide, while tlie mercury is distilled over and condensed in the 
 receivers. 
 
 4HgS + 4Ga() = 3CaO + CaSO, + 4Hg. The second 
 method of recovery consists in exposing the ore directly to the 
 
AN OUTLINE OF METALLURGY 1089 
 
 oxidizing- flame, aiul conductiiiii,' the nuTeurial vapor witli 
 suitaMe aiiparatns into condensers. 
 
 NICKEL 
 
 Nickel is a silvery wliite metal, witli a brilliant luster, 
 which does not tarnish readily in air. It is as tenaeioi;s as 
 iron, is ductile, hard, and somewhat malleable. It is slightly 
 magnetic, resembling iron somewhat in this respect. Its spe- 
 cific gravity is 9, increased by hammering to 9.93. Specific 
 heat 0.1086." Atomic weight 58.68, and fuses at about 1500° C. 
 Nickel is used extensively with copper to form german silver 
 — an alloy which, on account of its color, hardness, tenacity, 
 and many other good qualities, is used in large quautities for 
 innumerable purposes. 
 
 A coiumon formula for german silver is : Co])per 55, 
 zinc '2b, nickel 16 parts each. 
 
 The hardness and strength of steel is increased by the 
 addition of a small \^er cent of nickel. This allow is known as 
 armor |i]ate, and is used in the const ruction of warships. 
 
 USES 
 
 This metal is made use of to a great extent for plating 
 purposes, since it does not readily tarnish, is not easily ox- 
 idized, and can be quickly and firmly dejiosited upon iron, 
 steel, brass, german silver, and copi»er, by electro-deposition. 
 
 BISMUTH 
 
 Bismuth is a crystalline metal of a gray-white color, 
 with a decidedly reddish tinge. On account of its highly crys- 
 talline character it can be easily jmlverized. It is almost 
 totally lacking in the qualities of malleability, ductility, and 
 tenacity. Its specific gravity is 9.75, and specific heat 0.0308. 
 Fuses at 270". Atomic weight 208. 
 
 Bismuth is the most diamagnetic eh'Uient known, a sphere 
 of it when suspended close to, is repelled by a magnet. 
 
 Bismuth is very useful in the composition of fusible al- 
 loys, reducing the fusing points of the more difficultly fusible 
 ingredients, and imiDarting clearness and sharpness of outline 
 to castings made from such alloys. 
 
 In conjunction with tin and h^ad, it forms a number of 
 alloys which are in constant use in the dental hdtoratory. The 
 following is a partial list of such alloys: 
 
Name 
 
 
 HiSMllltll 
 
 Tin 
 
 I>ea(i 
 
 Hodgen's 
 
 metal 
 
 S 
 
 3 
 
 5 
 
 Mellotte's 
 
 
 S 
 
 5 
 
 ."! 
 
 Essig's 
 
 
 3 
 
 r. 
 
 :', 
 
 Darcet's 
 
 
 4 
 
 1 
 
 :! 
 
 Rose's 
 
 
 2 
 
 1 
 
 1 
 
 Newton's 
 
 
 8 
 
 
 r, 
 
 Onion's 
 
 
 5 
 
 2 
 
 :i 
 
 Wood's 
 
 
 4 
 
 1 
 
 2 
 
 Lipowitz's 
 
 
 15 
 
 4 
 
 ,s 
 
 Darcet's 
 
 
 2 
 
 1 
 
 1 
 
 1090 AN OtTTLINfO OK MRTALLUKOY 
 
 FUSIBLE ALLOYS 
 
 Melting 
 
 11 Merciir\- A ril iniMii\' Point 
 
 2 105° C. 
 
 100° C. 
 
 96° C. 
 
 96° C. 
 
 95° C. 
 
 94° C. 
 
 92° C. 
 
 65° C. 
 
 63° C. 
 
 10 45° C. 
 
 In eoiii])onn(lin,n- alloys (if this cliai'actcr they sliduld lie 
 melted under chai'coal to prevent oxidation, and stirred with 
 a stick of soft wood just before pouring, to prevent the load 
 from separating. 
 
 When cadmium or mercury are incoriioratcd, the other 
 metals should ))e melted tirst, and these added just before 
 ]iouring', to prevent volatilization. 
 
 ANTIMONY 
 
 Antimony usually occurs as a sulphide, and with other 
 metals, as silver, iron and cop]ier. It is reduced liy heating 
 the sulphide with scra]i iron, ii-on sulphide being formed and 
 the antimony set free. 
 
 PROPERTIES 
 
 It is extremely low in malleability, ductility and tenacity, 
 being crystalline in structure and very brittle. The atomic 
 weight of antimony is 120.2, fusing point 632^(_'., specific grav- 
 ity 6.71, specific lieat .0508. 
 
 Its principal uses in dentistry are as a component of 
 Haskell's Babbitt metal and for certain low-fusing alloys. It 
 is also used extensively in the manufacture of ty]>e for print- 
 ing, as alloys containing antimony expand in cooling, thus in- 
 suring sharp castings. 
 
 Primarily common Balibitt metal is an anti-friction al- 
 loy, and that intended for such purpose contains a larger 
 percentage of copper and antimony, while it is softer and more 
 easilv defaced than that prepared after the formula of Dr. 
 Haskell. (See page 1087.) 
 
 Britannia metal is an alloy used for making spoons, tea- 
 pots, trays, etc., and is composed of several metals and in 
 different proportions. 
 
AN OUTLINE OF METALLURGY 
 
 Tlie followiug- is oiio of the formulas nnicli used : Copper 
 1.85, tin 81.90, antimony 16.25. Zinc, lead and bismuth are 
 also used in some of the formulas of this alloj". 
 
 TUNGSTEN 
 
 Tungsten occurs combined with ferrous oxide in the 
 mineral called wolfram, or wolframite, FeWOi. also with 
 calcium in the mineral called scheelite, CaAVOj. These are 
 called the tungstates of iron and calcium, respectively. 
 
 Its principal use imtil recently was as a mordant in dye- 
 ing and a fireproofing material for cotton goods. It has also 
 been iised as a hardening component for steel, usually in the 
 l^roportion of from 5 jjer cent to 9 per cent. 
 
 PHYSICAL PROPERTIES 
 
 The fusing point of tungsten is sliglitly over 3000 C. 
 Atomic wt., 184. Specific gravity, 19.2. Acids have but 
 slight effect upon the metal at ordinary temperatures. It 
 is very difficult to convert the powder, in which form it is 
 usually sold commercialI>', into a solid, on account of its ex- 
 tremely high fusing point. By heavy compression into 
 definite form, and the application of an electric current of 
 high amperage, coiipled with careful swaging, the rod or bar 
 of compressed powder is gradually rendered compact and 
 the granules sufficiently coherent to enable it to be drawn 
 out into wires of various sizes, even as fine as the 1/1000 of 
 an inch. 
 
 At high temperatures it is readily oxidized, unless pro- 
 tected from the air. This deleterious property, however, does 
 not inhibit its use for electric lamp filaments, since it is 
 placed within a ^•acuum globe or one filled with nitrogen. 
 In either case the oxygen is excluded, and consequently oxida- 
 tion does not occur. 
 
 USES 
 
 Dr. Weston A. Price of the Scientific Research Commis- 
 sion of the N. D. A. presented a paper on metals and alloys 
 at the meeting in Rochester, N. Y., in July. 1915, in which some 
 of the valuable points of this metal were disclosed. In that he 
 showed that the hi-gh fusing point of tungsten, its low range 
 of expansion. Its great rigidity and hardness rendered it 
 extremely vahiable in prosthetic operations. 
 
 A bar of this material, threaded, coated with ])alladium 
 
1092 AN Uiri'LINIO UK MP^TALLIJIUIY 
 
 or S'old to prcxciil oxidnlioii. iiiid imcstcd in ii matrix for 
 a complex iiil;i\', the wire cNlciHliiii;' iiicsin-dislall) llirou^h 1 lie 
 easting, i)ra('tically inliiliits the cnnl ractidii of liic ?;(ild on 
 itself, wliicli, witlidiil sucli coiitnil, al\va>s dccurs in coDliii!;'. 
 its rigiditx', couiilcd witii great tensile strength. rend<'i's it 
 specially \alual»le I'or dowels in crowns and inla>s. 
 
 The principal disadvantages are its oxidation at solder- 
 ing and casting temiierntni'es and the difficnlty in t'nsing 
 any of the metals to it in the oiien air becanse of such oxida- 
 tion. 
 
 The solntion offered was to coat the wire with an alloy 
 of Pd-An or PdAg., after which gold may be cast or soldered 
 to it readily. 
 
 To illustrate its hardness, mention was made of the fact 
 that a phonogra))hic needle of tungsten will outwear two 
 hundred of the standard hard-steel points in common use. 
 The iDossibilities of this metal for use in cutting instruments 
 was suggested, when the methods of working it are better 
 developed. 
 
 THE MEASUREMENT OF PLATE AND WIRE 
 
 In all scientilic and meclianical fields, the accurate deter- 
 mination of weights, dimensions and strength of materials, 
 when such measurements are called for, is a recognized ne- 
 cessity; the same holds true in prosthetic procedures, for 
 without a reasonably accurate knowledge of the strength of 
 the various materials entering into the structure of re]iIaco- 
 ments, the prosthetist's efforts will often jn'ove inefficient. 
 
 Gold, platinum, and various other metals, are reduced 
 from ingot form to plate by means of a device called a rolling 
 mill. This may be done in the dental laboratory with pi'oper 
 equipment. 
 
 More often, however, the prosthetist obtains the ])recions 
 metals in plate form, direct from the supply liouses. 
 
 In either case, it is essential that the laboratory be 
 ecjuipped with suitable measuring devices for testing the dif- 
 ferent gauges of material used. 
 
 Tlie measurement of the thickness of gold and platinum 
 plate and the gauging of the diameter of wire in an intelli- 
 gent manner — that is, so that a just estimate may be formed 
 of the relative thickness and strength of the materials being 
 used — aids materially in the planning and construction of 
 successful prosthetic substitutes of all classes. 
 
AN OUTLINE OF METALLURGY 1093 
 
 AVitli tliis end in view, the pvosthetist ^^honkl lieconie 
 familiar witli, and can to advantage apply in practice, the 
 methods and instruments nsed by scientists and artisans in 
 otlier lines of work. 
 
 Various measnrini;- devices are in use for determining 
 the tliickness of plate and the diameter of wire, as well as 
 
 A COMMON TYPE OF ROI.LINI! MILL 
 
 for sundry other measurement readings. These instruments 
 are known under the common name of c/dKC/es, calipers, etc., 
 the forms of which vary, depending upon the jmrposes for 
 which thev are desioned. 
 
 THE UNIT OF MEASUREMENT OF GAUGES 
 
 The unit cf measurement of gauges used in England 
 and the United States is generally the fractional jjart of an 
 inch and of tiic millimeter. 
 
1094 AN OUTLINK OF METALLURGY 
 
 LACK OF UNIFORMITY OF THE VARIOUS GAUGE SYSTEMS 
 
 With exceptions to be noted, most of the various gauge 
 systems do not show a uniformly decreasing ratio from thick 
 to thin measurements, Imt llic stejis between tlie various 
 gauge numbers appear tti ha\e been ai-bitrarily established, 
 without following any fixed standard. 
 
 THE BIRMINGHAM GAUGE 
 Tliis is true of the li'u iii'uKjhatii, also known as the Eiuj- 
 lisli Standard, and again as Stub'a Soft Iron Wire Gauge, 
 so called to distinguish it from Stub's Steel Wire Gauge. 
 The discrepancies noted are plainly apparent in this gauge, 
 as will be seen by examining the first few largest numbers. 
 
 DISCREPANCIES OF THE BIRMINGHAM GAUGE 
 
 No. 0000 = .454 of an incli. No. = .340 
 No. 000 = .425 No. 1 = .300 
 
 Difference .029 Difference .040 
 
 No. 000 = .425 No. 1 = .300 
 
 No. 00 = .380 No. 2 = .284 
 
 Difference .045 Difference .016 
 
 No. 00 = .380 No. 2 = .284 
 
 No. = .340 No. 3 = .259 
 
 Difference .040 Difference .025 
 
 To summarize, the difference between the first seven 
 numbers of the Birmingham gauge is as follows: .029 — 
 .045— .040— .040— .016— .025. 
 
 The Birmingham gauge was for years used extensively, 
 but not exclusively, in this country, in machine-shop i)ractice 
 and various other fields. Some wire and plate manufacturers 
 used one gauge, some another. More or less confusion and 
 misunderstanding naturally resulted, since no one gauge sys- 
 tem was accepted as standard and each varied slightly from 
 the others. 
 
 THE BROWN AND SHARP GAUGE 
 
 To correct the discrepancies noted, the Brown & Shar]^ 
 Manufacturing Company of Providence, R. I., designed a 
 gauge having approximately the same range of measure- 
 
AN OUTLINE OF METALLTTRGY 1095 
 
 iiieut as the Birmiiiiiiiani, hut the various gauge numbers, 
 from the largest downward, decrease in a definite ratio. 
 
 This gauge has proven so satisfactory that it has been 
 generally adopted in this country, and is now known as the 
 America)! Standard Gauge. It should not, however, be con- 
 founded with the United States Standard Gauge, which was 
 designed for, and approved by, Congress in 1893, and is used 
 in determining duties and taxes levied by the United States 
 Government on sheet and plate iron and steel. 
 
 The principle on which the Brown & 81iar]i gauge is 
 constructed is as follows: Two straight bars of steel are 
 fitted together at one of their ends, and permanently fixed 
 in such manner as to form a divergent space between the 
 two, about one-half inch across at the outer end of the gauge. 
 The gauge numbers are marked on the inner edges of the 
 arms, next the divergent space. The general form of tliis 
 gauge is similar to the jeweler gauge. (See page 1096.) 
 
 No. 0000, or .-46 of an inch, is the largest dimension of 
 the gauge, and from this all of the other gauge dimensions 
 are, either directly or indirectly, derived. 
 
 The next lowest dimension — No. 000 — is obtained by 
 nuiltiplying its predecessor, .-1-6, by 0.890522, which is equiva- 
 lent to deducting 10.9478 per cent. Placii succeeding lower 
 number is obtained in a similar manner, by nuiltiplying the 
 last determined gauge length, or thickness, cstablislKMl, l)y the 
 decimal above given. 
 
 It will thus be seen that any gauge number under 0000 
 is approximately 10 jjer cent less than the preceding higher, 
 or greater than the succeeding lower number. The steps 
 between the various gauges represent gradual and uniform 
 decrements as the gauge numbers, although rising numeri- 
 cally, become thinner. The last gauge of the scale is No. 40, 
 or .003144 of an inch thick, although still thinner numbers 
 can be correctly formulated l)y the plan given. 
 
 FORMS OF GAUGES 
 
 THE JEWELER'S GAUGE 
 
 The jeweler's gauge is liased u])oii the same general 
 princijile as the Original Brown & Sharp gauge, viz., two 
 rigidly fixed, cliverging arms. These are graduated on the 
 inner margins so as to read in nniltiples of one-thousandths 
 of an inch. 
 
lOiifi AN OUTLINE OK M lOTALLURGV 
 
 .Mlliouyli tlic I'oriii dl' _!;an,i;(' Just (Icscrilicd is siiilalilc 
 and very t'oiiwiiiciit t'oi inciisurinn wire and small rods, it is 
 not well adapted for gaiis^-iiiii,- plate, hecause tiie edge of the 
 latter is very fi'e(|ueiitly inari-eij in shearinu. so that a niar- 
 ginal readiiin', in such cases, will seldom he aeeurate. Some 
 
 A JEWELER'S GAUliE liKAl>I> 
 TO THE 1/1000 OF AX IXIII 
 
 form of appliance capable of passing beyond the margin of 
 the plate, and calipering nndistnrbed surfaces, is, therefore, 
 neeessarv for securing accui'ate in(^asurements. 
 
 THE PLATE AND WIRE GAUGE 
 
 One of the most connnon forms of plate and wire gauge 
 in use consists of a steel disc about two and one-half inches 
 in diameter and one-eighth of an inch thick. In the perii)hery 
 of this disc are accuratelv cut and nninbei'ed slots, which 
 
AN OUTLINE OF METALLURGY 1097 
 
 represeut tlie tliickiicss ut' tlif various .naiigc muiiher.s of the 
 system used. To measure a piece of i)late or wire, the various 
 slots of the gauge are applied to the piece until a ueat fit 
 is obtained, or, in case the piece being measured is not of 
 exact gauge thickness, the two proximating gauges are found, 
 one of which is larger and the other smaller than the wire 
 or plate being calipered. This form of gauge, as before 
 
 AN ORDINARY FDRJ! 1JI-- i:\I lii: Full I'l.ATI- 
 
 stated, is satisfactory for measuring standard thickness of 
 plate and wire, but is not ada]ited to accurate and imiversal 
 readings, when the materials are not standardized. 
 
 THE MICROMETER CALIPER 
 
 An instrument of this type consists of a U-shaped steel 
 frame, the arms of which are parallel. One arm is threaded 
 and contains the adjustable screw, by means of which read- 
 ings are made. The other arm holds an adjustable stop, 
 which is never moved except for adjustment purposes, when 
 the instrument is worn or sprung. The face of the stop and 
 the end of the screw, presented toward it, form exactly 
 jiarallel planes. Tiie object to lie gauged is ])]aced, one side 
 against the face of the stop, while the screw in the other arm 
 is brought in contact with the opposite side. The reading is 
 made on the, screw spindle and on the hub, or nut, through 
 which it passes. In the foHowing description, the micrometer 
 graduated to read to the 1/1000 of an inch, will be used as 
 an example of tliis general type. Some of the more recent 
 
AN OUTLINE OF METALLURGY 
 
 forms li;i\c i\ \cniicr attarliinciit, liy iiicaiis of which read- 
 ing's can be made as line as tlie l/iUUUU of an incli. 
 
 The screw spindle has a lioUow head in tlie furni of a 
 deep sleeve, whidi telescopes over the cylindrical extension 
 of the nut of Ihc frame. As the screw is turned toward or 
 away from tlie stoj) in the o])posite arm, the sleeve rotates 
 and travels with it. The inner end of the sleeve is beveled 
 and graduated into 25 ecjnal parts, and nmnbered 0, 5, 10, 
 15, 20, while 25 is reached on the complete revolution to 0. 
 When the screw is closed and in close contact with the stop, 
 the of the sleeve stands opposite the on the nut. The 
 screw pitch is 40 — that is, there are 40 threads to the inch 
 on the spindle. By multiplying the divisions on the sleeve 
 by the number of threads to the incli on the sjiindle, it will 
 
 A MICROMETER GACUE BEADING TO TIIE 1 /I.OUd OF AX I 
 
 be seen that 1,000 divisions must pass the longitudinal line 
 on the hub in moving the screw outward one inch. Each 
 division, therefore, registers the 1/1000 of an inch move- 
 ment of the screw toward or away from the stop in the op])o- 
 site arm. To facilitate rapid readings of pieces of consider- 
 able thickness, the hub is also graduated. The space between 
 the gradations on the hub, or nut, is equal to the distance 
 between contiguous threads. As the screw is turned once 
 around, in opening, an unexposed gradation api^ears on the 
 hull under the edge of the sleeve, showing tliat the screw 
 has been moved 25/1000 of an inch. Every fourth gradation 
 on the hub is accordingly numbered, the beginning or closed 
 position of screw being 0, the fourth division 1, or 100/1000; 
 the second 2, or 200/1000, etc. 
 
 In using this gauge three sources of error must be kept 
 in mind, viz., imperfect paralleling of the piece being meas- 
 
AN OUTLINE OP METALLURGY 1099 
 
 ured, with the i'at'e of the st'Vew; excessive i)ressure will 
 spring the frame and give imperfect results; slight variation 
 in the pitch of the screw, clue to wear. 
 
 No dust or dirt should adhere to the screw, stop or piece 
 being gauged. A spring ratchet is frequently applied to the 
 extreme outer end of the screw to insure against excessive 
 force being applied in making measurements. 
 
 VARIOUS SYSTEMS OF WIRE AND PLATE GAUGES AND 
 
 THEIR EQUIVALENTS IN THOUSANDTHS 
 
 OF AN INCH 
 
 For convenience in finding any required gauge, the wii-e 
 and plate gauge numbers are given on the right and left 
 sides of the table. 
 
 
 
 Difference 
 
 
 
 
 
 
 
 
 No. ot 
 Wire 
 Oauge. 
 
 Brown & 
 
 Sharp 
 American 
 Standard. 
 
 between 
 Consecu- 
 tive 
 Numbers 
 
 in 
 Decimals. 
 
 Birming- 
 ham or 
 Stub's 
 Wire. 
 
 Wash- 
 burn & 
 MoenCo, 
 Wire. 
 
 Imperial 
 
 Wire 
 Gauge. 
 
 Stub's 
 .Steel, 
 Wire. 
 
 U. fg. Stand „ 
 ard for ^ 
 Plate. c 
 
 &M. 
 Wire 
 auge. 
 
 No.ol 
 Wire 
 Gauge. 
 
 000000 
 
 
 
 
 .464 
 .432 
 .400 
 
 
 .46875 
 .4375 
 .40625 
 
 0095 
 010 
 Oil 
 
 000000 
 
 00000 
 
 
 
 
 
 00000 
 
 0000 
 
 ^46 
 
 
 ^454 
 
 .3938 
 
 0000 
 
 000 
 
 .40964 
 
 !65036 
 
 
 .3625 
 
 .372 
 
 
 .375 
 
 012 
 
 000 
 
 00 
 
 .3648 
 
 .04484 
 
 ^38 
 
 ..3310 
 
 .348 
 
 
 .34375 
 
 0133 
 
 00 
 
 
 
 .32486 
 
 .03994 
 
 .34 
 
 .3065 
 
 .324 
 
 
 .3125 
 
 0144 
 
 
 
 1 
 
 .2893 
 
 ,03556 
 
 
 ,2830 
 
 ,300 
 
 ■■:227 
 
 .28125 
 
 0156 
 
 1 
 
 2 
 
 .25763 
 
 .03167 
 
 ^284 
 
 ,2625 
 
 .276 
 
 .219 
 
 .265625 
 
 0166 
 
 2 
 
 3 
 
 .22942 
 
 .02821 
 
 .259 
 
 .2437 
 
 .252 
 
 .212 
 
 .25 
 
 0178 
 
 3 
 
 4 
 
 .20431 
 
 .02511 
 
 .238 
 
 .2253 
 
 .232 
 
 .207 
 
 .234375 
 
 0188 
 
 4 
 
 5 
 
 . 18194 
 
 .02237 
 
 .22 
 
 .2070 
 
 ,212 
 
 .204 
 
 .21875 
 
 0202 
 
 5 
 
 6 
 
 . 16202 
 
 ,01992 
 
 ,203 
 
 .1920 
 
 ,192 
 
 .201 
 
 .203125 
 
 0215 
 
 6 
 
 7 
 
 .14428 
 
 .01774 
 
 ,18 
 
 .1770 
 
 .176 
 
 .199 
 
 .1875 
 
 023 
 
 7 
 
 8 
 
 .12849 
 
 .01579 
 
 ,165 
 
 .1620 
 
 .160 
 
 .197 
 
 .171875 
 
 0243 
 
 8 
 
 9 
 
 .11443 
 
 .01406 
 
 ,148 
 
 .1483 
 
 .144 
 
 .194 
 
 . 15625 
 
 0256 
 
 9 
 
 10 
 
 .10189 
 
 .01254 
 
 ,134 
 
 .1350 
 
 ,128 
 
 .191 
 
 .140625 
 
 027 
 
 10 
 
 11 
 
 .090742 
 
 .01105 
 
 12 
 
 .1205 
 
 ,116 
 
 .188 
 
 .125 
 
 0284 
 
 11 
 
 12 
 
 .080808 
 
 .00993 
 
 m 
 
 .1055 
 
 ,104 
 
 .185 
 
 . 109375 
 
 0295 
 
 12 
 
 13 
 
 071961 
 
 .00885 
 
 095 
 
 .0915 
 
 ,092 
 
 .182 
 
 .09375 
 
 0311 
 
 13 
 
 14 
 
 .064084 
 
 .00788 
 
 ,083 
 
 .0800 
 
 ,080 
 
 .180 
 
 .078125 
 
 0325 
 
 14 
 
 15 
 
 .05768 
 
 .00702 
 
 072 
 
 .0720 
 
 ,072 
 
 .178 
 
 .0703125 
 
 0343 
 
 15 
 
 16 
 
 .05082 
 
 .00625 
 
 065 
 
 .0625 
 
 ,064 
 
 .175 
 
 .0625 
 
 0359 
 
 16 
 
 17 
 
 .045257 
 
 .00556 
 
 ,058 
 
 0540 
 
 ,056 
 
 .172 
 
 .05625 
 
 0378 
 
 17 
 
 18 
 
 .040303 
 
 ,00495 
 
 ,049 
 
 .0475 
 
 ,048 
 
 .165 
 
 .05 
 
 0395 
 
 18 
 
 19 
 
 .03589 
 
 .00441 
 
 ,0(2 
 
 .0410 
 
 ,040 
 
 .164 
 
 .04375 
 
 0414 
 
 19 
 
 20 
 
 .031961 
 
 .00393 
 
 ,0.35 
 
 .0348 
 
 ,036 
 
 .161 
 
 .0375 
 
 043 
 
 20 
 
 21 
 
 .028462 
 
 .00350 
 
 ,032 
 
 .03175 
 
 ,032 
 
 .157 
 
 ,034375 
 
 0461 
 
 21 
 
 22 
 
 .025347 
 
 .00311' 
 
 ,028 
 
 . 0286 
 
 ,028 
 
 .155 
 
 ,03125 
 
 0481 
 
 22 
 
 23 
 
 ,022571 
 
 .00278 
 
 025 
 
 .0258 
 
 .024 
 
 .153 
 
 ,028125 
 
 0506 
 
 23 
 
 24 
 
 .0201 
 
 .00247 
 
 ,022 
 
 .0230 
 
 .022 
 
 .151 
 
 ,025 
 
 0547 
 
 24 
 
 25 
 
 .0179 
 
 .00220 
 
 02 
 
 .0204 
 
 .020 
 
 .148 
 
 ,021875 
 
 0585 
 
 25 
 
 26 
 
 .01594 
 
 ,00196 
 
 ,018 
 
 ,0181 
 
 .018 
 
 .146 
 
 ,01875 
 
 0626 
 
 26 
 
 27 
 
 .014195 
 
 ,00174 
 
 ,016 
 
 ,0173 
 
 .0164 
 
 .143 
 
 ,0171875 
 
 0663 
 
 27 
 
 28 
 
 .012641 
 
 ,00155 
 
 014 
 
 ,0162 
 
 ,0149 
 
 .139 
 
 ,015625 
 
 0719 
 
 28 
 
 29 
 
 .011257 
 
 ,00138 
 
 ,013 
 
 ,0150 
 
 ,0136 
 
 .134 
 
 0140625 
 
 076 
 
 29 
 
 30 
 
 .010025 
 
 .00123 
 
 ,012 
 
 ,0140 
 
 ,0124 
 
 .127 
 
 or25 
 
 080 
 
 30 
 
 31 
 
 .008928 
 
 .00110 
 
 ,01 
 
 ,0132 
 
 ,0116 
 
 .120 
 
 ,0109375 
 
 
 31 
 
 32 
 
 .00795 
 
 .00098 
 
 ,009 
 
 ,0128 
 
 ,0108 
 
 .115 
 
 ,01015625 
 
 
 32 
 
 33 
 
 .00708 
 
 .00087, 
 
 ,008 
 
 ,0118 
 
 ,0100 
 
 ,112 
 
 ,009375 
 
 
 33 
 
 34 
 
 .006304 
 
 .00078 
 
 , 007 
 
 ,0104 
 
 ,0092 
 
 ,110 
 
 ,00959375 
 
 
 34 
 
 35 
 
 .005614 
 
 ,-00069 
 
 005 
 
 ,0095 
 
 ,0084 
 
 .108 
 
 ,0078125 
 
 
 35 
 
 36 
 
 .005 
 
 ,00061 
 
 004 
 
 ,0090 
 
 ,0076 
 
 .106 
 
 ,00703125 
 
 
 36 
 
 37 
 
 .004453 
 
 ,00055 
 
 
 
 ,0068 
 
 .103 
 
 ,006640625 , 
 
 
 37 
 
 38 
 
 .003965 
 
 ,00049 
 
 
 
 ,0060 
 
 .101 
 
 .00625 
 
 
 38 
 
 39 
 
 .003531 
 
 ,00043 
 
 
 
 ,0052 
 
 ,099 
 
 
 
 39 
 
 40 
 
 003144 
 
 ,00039 
 
 
 
 ,0048 
 
 ,097 
 
 
 
 40 
 
1100 AN OIITMNE OF METALLURGY 
 
 TABLES OF SOME OF THE VARIOUS GAUGE SYSTEMS 
 IN USE 
 
 The tabic ol' gauges wliicli is liei'c apiK'ndcd will enable 
 any one to determine aceurately, by means of a micrometer 
 gauge, the relative tliiekiiess of plate and wire, regardless 
 of what system of gauging lias been used b\' llie manufacturer 
 in its prodnction. 
 
 Attention is s])eci;dly cjdied to tlie table of piano-wire 
 gauges, as it is at variance with the other systems tabulated. 
 The diameters, or thicknesses, of the gauges in this system 
 increase as the numbers rise numerically. Since piano wire 
 is used extensively in orthodontic operations, those engaged 
 in this specialty will find the table of assistance in judging 
 the relative thickness of the various sizes of wire employed. 
 
 Practically all supply houses use the American Stand- 
 ard, also called tlu' Brown & Sharp gauge, for gauging the 
 precious metals. For this reason, therefore, distinction 
 should be made between the American Standard gauge, which 
 is almost universally employed for the purpose mentioned, 
 and the United States Standard gauge, the principal use of 
 which, as before stated, is in the measurement of iron and 
 steel plate, and is seldom used in prosthetic operations. 
 
(Ml APT!-: II XXXIII 
 A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 All t'xact and detailed history of the treatment of dental 
 lesions, spanning the period from very ancient to modern 
 times, liowever interesting and instructive it might prove, 
 has not been and never can be written, because of lack of 
 accurate and consecutive data. 
 
 Many of the I'ecords of earlier times on this subject 
 are incomi^lete, or sadly lacking in detail ; some have been 
 lost; and still others now in existence are only copies of 
 manuscripts having a much earlier origin. 
 
 Some of the original old records now remaining, rest in 
 government archives of Old World countries, or in the li- 
 braries of their universities. 
 
 To the uninitiated student of dental lore, many of these 
 historic treasures, written in a foreign, dead, or almost imde- 
 cipherable and forgotten language, have been until recently 
 as completely out of his reach as though they never existed. 
 
 The efforts of a number of men, fitted by training and 
 experience, and conveniently located near to these manu- 
 script depositories as well, have been directed to clearing 
 up and collating such ancient and median-al historical data 
 of medicine and dentistry as are available. Notable among 
 these the names of Prof. George Ebers, a celebrated German 
 Egyptologist, and Dr. Mncenzo Guerini, of Naples, Italy, 
 stand out most prominent. 
 
 THE EBERS PAPYRUS 
 
 In 1873 Professor Ehers obtained from "an inhabitant 
 of Luxor, Up]ier Egypt," a manuscript written in hieratic 
 characters on pa])yrus paper, which u})on deciphering 
 proved to be the most complete, as well as probably the most 
 ancient of the early records relating to tlie treatment of 
 disease, both general and dental. 
 
 Two translations of this manuscript have been made, one 
 by Professor Ebers in 1875, and the other by Dr. Heinrich 
 Joachim in ]8n(). 'Quoting from Guerini, the sco])e and an- 
 tiquity of tliis manuscript is made apparent: 
 
 "Lepsius, and with him the greater part of Egyptol- 
 ogists ai*e of the opinion that the Ebers papyrus is not an 
 
 1101 
 
11(12 A liKII'^F IlISTOliY OP I'ROSTlllOTU; DKNTISTRY 
 
 original wdik at all, l)iit simply a copy of medical writings 
 of still earlier date, belungiiig to diffci'eiit epochs, and which 
 were collected and reunited lo form a kind of manual on 
 medicine. 
 
 ANTIQUITY OF THE PAPYRUS 
 
 "From some indications existing in the papyrus itself, 
 Ebers has been able to argue, with quasi certainty, that the 
 papyrus was written toward the year 1550 B. C. But some 
 parts of it have their origin in a far more remote epoch; 
 they go back, that is, to thirty-seven centuries or more be- 
 fore the Christian era. In fact, at page ciii of the lObers 
 papyrus one reads : 
 
 " 'Beginning of the book about the treatment of the 
 uxeda in all the members of a person, such as was found in 
 a writing under the feet of the god Anubis, in the city of 
 Letopolis; it was brought to His Majesty Usaphais, King 
 of Upper and Lower Egypt.' Now as Joachim remarks, 
 the Usaphais herein named was the fifth king of tlie first 
 Egyptian dynasty, and he reigned toward 3,700 years before 
 the Christian era. Hence, it may be argued that some, at 
 least, of the writings from which the Ebers papyrus was 
 taken were composed in the very remote epoch to which we 
 have just alluded, or perhaps still farther, for it is impossi- 
 ble to know whether the book, deposited by unknown hands 
 at the foot of the statue of the god Anubis, had been written 
 biit a short time previous or at a much earlier epoch." — 
 Guerin. 
 
 This suggests a possible age of 5,600 years for some of 
 the prescriptions offered for the relief of pain. The \ixeda 
 mentioned literally means a painful swelling, and might 
 ajjply to inflammatory conditions, accompanied by swelling, 
 in any part of the body, alveolar abscess included. In fact, 
 specific mention is made in several places, of remedies for 
 the cure of "growth of the uxeda in the teeth (alveolar ab- 
 cess?) and also "bennut blisters in the teeth," the latter 
 supposed to mean small fistulous ojienings to abscesses of 
 dental origin. 
 
 No reference of any sort in regard to prosthetic oper- 
 ations is found in the papjyrus. It does not follow, however, 
 that prosthesis was not attempted in very ancient times. 
 In fact, positive evidence exists to prove that replacement 
 of one or more teeth was a recognized, although ]ierhaps 
 not common method of practice, almost or quite 3000 years 
 ago. Mention of this will be made later. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1103 
 
 GUERINI'S HISTORY OF DENTISTRY 
 
 Within recent years, tlie most tiiorongh, exliaustive, 
 and painstaking inquiry in ancient and mediaival liistory of 
 dentistry ever undertaken by one individual, lias been car- 
 ried out by Dr. Vincenzo Guerini, of Naples, Italy. It repre- 
 sents an effort on the part of this distinguished gentleman, 
 quoting his words, to "contribute to the diffusion of exact 
 historical knowledge as to the origin and gradual develop- 
 ment of dentistry." 
 
 The results of his labours, which represent a vast 
 amount of researcli work and much financial outlay as well, 
 he has generously jn-esented to the profession in America, 
 through the National Dental Association, as a token of his 
 appreciation of American progress in dental science and de- 
 velopment. 
 
 That the results of Dr. Guerini 's efforts are appreci- 
 ated, not only by tlie profession of America, but of the world, 
 goes without saying. His work is frequently quoted by 
 writers on historical dental subjects, and with a feeling of 
 security as to fact, hitherto noticably lacking in mucli of the 
 previously avaihible data, because of its questiona))le au- 
 thenticit.v. Much of the contents of the present chapter is 
 based eitlier directly or indirectly upon Guerini 's work. 
 
 The facts as presented in Guerini 's History lead to the 
 belief that the origin of dentistry was coeval with that of 
 medicine; that in all probalnlity, in very ancient times, 
 dentistry as a specialty was not recognized as such, and 
 therefore the treatment of dental lesions came properly 
 within the domain of the medical practitioner. 
 
 Although the statement has repeatedly been made that 
 teeth filled with gold and various substances, and prosthetic 
 pieces of different forms, have been found in the sarcophagi 
 of mummies, in the pyramids and necroiJoli of Egypt, the 
 fact has not been substantiated. Schmidt, Ebers, Virchow 
 and Mummery, all of whom devoted considerable effort to 
 this phase of research, failed to find authentic specimens 
 of the classes of work mentioned. Neither has Guerini, in 
 his examination of ancient specimens or in historical re- 
 search found anytliing to indicate that the very early Egyp- 
 tians knew "how to insert gold fillings, and still less to 
 apply pivot teeth." He further states, however, that, al- 
 though the direct proof may be lacking, he beliercd the 
 Egyptians knew how to apply artificial teetli. 
 
 He bases his deduction on the following: "And even 
 
1104 A liKIWF IIISTOKY OK i'UOSTUKTU' DKNTISTUY 
 
 tliouuli it in;i>- iiol lie |i(issihlc tii dciiioiist r;il c this by tlii'cct 
 prddl', (iiic is (M|ii.'illy prdiic to atliiiit it when one coiisidcvs, 
 on tlic one hand, the remarkable ability of tlic ancient K.nyi"- 
 tians in all j)lasti(' arts, and, on the other hand, the great 
 importance they attril)uted to beantii'yiug the human body; 
 so much so, tliat even in so ancient a document as the Fibers 
 l)apyrus, one tinds formula' for medicaments against bald- 
 ness, for lotions for the liair, and other kinds of cosmetics. 
 Is it not likely, therefore, that so refined and ingenious a 
 people should not have found the means of remedying the 
 deformity resulting from the loss of one or more front 
 teeth!" " 
 
 THE PHCENICIANS 
 
 The ancient Phu-nicians, a race of Semitic origin, were 
 a thrifty nation of maritime traders. Their country, the 
 nortliern Palestine Mediterranean coast land, ^afterwal''ds 
 known as Canaan, consisted of a strip about 15 miles wide 
 and 150 long. It lay between the Lebanon Mountains and 
 the sea, on the borders of which were situated the populous 
 cities of Tyre, near the center, and Sidon to the north. All 
 of the principal ports of the world were known to, and vis- 
 ited by her merchantmen, whose bartering excursions and 
 voyages of discovery lirought them in contact with the trad- 
 ers, artisans, and scholars of many lands. 
 
 EFFECT OF EGYPTIAN CIVILIZATION ON PHCENICIA 
 
 P>eginning about 17()(i P. (". Kgypt assumed a protector- 
 ate over Phoenicia, which was maintained for about three 
 hundred years. This political bond, coupled with mutual 
 commercial exchange, brought the ])eople of the two coun- 
 tries into close business and social relations with each other. 
 
 Since the beneficent influence of Egypt's advanced civili- 
 zation was felt and recognized in the known remote cor- 
 ners of the earth in those times, it naturally followed that 
 Phoenicia, l)y reason of the connection noted, must have 
 benefited thereby, and ai)propriated to herself some of the 
 advanced ideas of the older country in culture, fine arts and 
 medical science. 
 
 ONE OF THE MOST ANCIENT SPECIMENS OF PROSTHETIC ART 
 
 Now, although she has left no papyrus scrolls, no pyra- 
 mids, no obelisks to commemorate important historical events, 
 Phamicia has left what P]gyi)t has not, viz., a well preserved 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY IIO.J 
 
 speeimeu of ancient prosthesis. How old this piece may be 
 no one can tell, but that it is very ancient there can be no 
 doubt. The outline of Guerini's history of it is about as 
 follows : 
 
 In 1862, Dr. Gaillardot. (•(iniicclcd with Kenan's Syrian 
 Exploring P]xpedition, found in tlie most ancient part of 
 the necropolis of Sidon. a part of the upper jaiv of a woman, 
 in which the six anterior teeth were united together with 
 gold wire. A central and ])roximating lateral incisor appear 
 
 I'HiEXiciAX .U'ri,i^o;c-E found at 
 
 SIDON, AS RErRESENTED IN A CUT OF 
 RENAN'S MISSION DE THENICE 
 
 (GUERINI) 
 
 THE SAME FIGURE RE\ERSED. AS IT 
 
 OUGHT TO HE IF THE PIECE FOUND 
 
 AT SinON BELONGED TO A LOWER .TAW 
 
 IGI'ERINII 
 
 to have belonged to another person, and from the manner 
 of their attachment were sul)stitnted for lost teeth. This 
 piece is now in the Louvre in Paris. In addition to this 
 prosthetic piece there were also found in the same grave 
 two copper coins, an iron ring, a vase of most graceful out- 
 line, a scarab, and twelve very small statues of Egyptian 
 deities, probalily a necklace judging by the holes bored in 
 them. 
 
 Concluding his remarks on "Dental Art Among tht 
 Egyptians," Guerini says: 
 
 "The remains discovered in many of the Plia?nician 
 tombs would of themselves alone be sufficient to demonstrate 
 luminously, the enormous influence exercised by the Egyp- 
 tian civilization on the life and customs of that people. Now, 
 if there were dentists in Sidon capable of applying false 
 teeth, it may reasonably l)e admitted that the dentists of the 
 great Egyptian metropoli, Thel)es and Memphis, were able 
 to do as much and more, the level of civilization being with- 
 out doubt higher there than in Tyre or in Sidon, or in other 
 non-Egyptian cities." 
 
 THE ETRUSCANS 
 
 The I'ltniscaiis were a iKMiplc who iiihahited TT]ip('r 
 Central Italy from' about 800 15. C. to -JS:'. 15. C., when they 
 wore conquered by the Romans. One author has said of 
 them: "Ancient writers concur in rei)resenting the Etrus- 
 cans as the most cultivated and refined peo])le of ancient 
 
1106 A BnilOP HISTORY OF PROSTHETIC DENTISTRY 
 
 Italy, ami as especially skillt'iil in (ii-]iaiiiental and useful 
 arts, in which 1 he ideas and patterns used singularly re- 
 semhh' those dl' I'lgypt." — "They made groat progress in 
 architecture, sculpture, and i)ainting, and es])ecially in 
 bronze work and gold jewelry." — "They excelled in agricul- 
 ture, navigation, engineering, and in useful jMililic works." 
 ( Universal J^ncyclopedia. ) 
 
 Guerini says: "They were a laborious and courageous 
 race, not only active in agriculture, in art and commerce, 
 but also brave warriors and hardy navigators. In tlieir 
 long sea voyages tlie Etruscans frequently visited Egypt 
 and Phoenicia, trading especiall.y in the more flourishing 
 cities, which were at that time Memphis, in Egypt, and Tyre 
 and Sidon in Phoenicia. On the other hand, the PlKPnicians, 
 who were also active merchants and navigators, not only 
 visited Etruria and other regions of Italy very frequently, 
 but also established numerous colonies in many islands of 
 the Mediterranean, and especially in those nearer Italy. 
 
 "This continual intercourse between I^truscans on one 
 side, and Egy))tians and Pluimicians on the other, accounts 
 for the great influence exercised by the Egyptians and Phoeni- 
 cian civilization upon the later developed Etruscan culture 
 — an influence manifesting itself very distinctly in the works 
 of art of the latter, whicji often have an altogether Oriental 
 character, and not seldom re])resent scenes drawn from the 
 domestic life of the Egy]itians and Phcenicians. 
 
 ETRUSCAN DENTAL ART 
 
 "As to what concei-ns dental art, everytliing leads up 
 to the belief that it was ])racticed by tlie Egyptians and 
 Plioenicians earlier than l)y the Etruscans, whose civiliza- 
 tion, as already hinted, is certainly less ancient. Neverthe- 
 less, in comparing the dental appliances fovmd in the Etrus- 
 can tombs with the sole and authentic dental appliance of 
 Phoenician workmanship known at the present day, we can- 
 not but be struck with the greater superiority of the Etrus- 
 can appliances. It is therefore probable that the Eltruscans, 
 although they had learned the dental art from the Egyptians 
 and Phoenicians, had subsequently carried it to a much higher 
 degree of perfection than it had aiMi\-ed nt in Egypt or in 
 Phoenicia." 
 
 A number of specimens of ancient prosthetic appliances 
 of Etruscan workmanship have been found within recent 
 years, the genuineness of which are unquestioned. Most of 
 these specimens are preserved in various Italian museums. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1107 
 
 Some of them arc illustrated in Dr. Guerini's admirable 
 work, a few of which are here reproduced. 
 
 In an excavated tomb at Valsiarosa, near the ancient 
 Falerii, was found an ap]>lian('e consisting of four gold rings 
 
 HTlirSl'AX AI'l'LlAXOB FOUND 
 AT VALSLiVBOSA. DESTINED TO 
 SUPPORT AN ARTIFICIAL BICUS- 
 PID, NOW DISAPPEARED 
 ((iUEKINI) 
 
 soldered together and fitted to the cuspid, tirst bicuspid, and 
 first molar. The ring over the site of the second bicuspid, 
 the missing tooth, had a rivet extending through it from 
 buccal to lingual, evidently intended for holding the sub- 
 stituted tooth, which, however, was lost. 
 
 ETRUSCAN AI'PLIANCE FOR SUPPORTING THREE 
 
 ARTIFICIAL TEETH. TWO OP WHICH WERE MADE PROM 
 
 ONE OX TOOTH (CIVIC MUSEUM OF CORNETO) 
 
 (GUEMNI) 
 
 *5 
 
 THE SAME APPLIANCE REVERSED 
 
 Guerini suggests that the substitute tooth may have been 
 made of some destructible material, and had disintegrated, 
 or that it might liave been slotted at its base to pass on 
 
11(18 A i!i;ii':i'' HISTORY OK ruos'riii'n'ii' I)iontisti{Y 
 
 eitlu!!' side of llu' I'ix'cl, jiikI not haviiin' hccn i-i,i;i(lly lixcd 
 within tlie ring, was dislodged jind losl during the cxcaN'atioii. 
 Tliis appliance is now in the iiuisiMiiii (if i'upc -liilius, in llonu'. 
 
 Two appliances similar in character to the one just de- 
 scribed will serve to illustrate the general type of the an- 
 cient prosthetic pieces found in other Etruscan tombs, and 
 which are supposed to be about 3000 years old. Botii of 
 these specimens repose in the civic museum of Corueto, the 
 ancient city of Tarquinii. 
 
 The first of these s]:)ecimens to be described, consists of 
 bands of pure gold, soldered together and fitted to the cus- 
 pid and lateral on the right, and to the cuspid, first bicuspid, 
 and first molar on the left side. A band of gold con- 
 taining a rivet extending through it from buccal to lingual, 
 occupies the site of the missing natural second bicuspid, 
 and served for the attachment of its substitute, the latter, 
 however, having become disintegrated or in some manner, 
 lost. A single, elongated band of gold, occupying the space 
 of the three missing anterior teeth, extends from the right 
 lateral to the left cuspid. Fitted within this band and filling 
 the entire space, was a wide ox tooth, grooved longitudinally 
 in its center to represent two central incisors. The space 
 once occupied by the these three teeth, having closed slightly, 
 no effort was made to reproduce the lateral incisor. This 
 block was firmly fixed in position by means of two rivets. 
 (Page 1107.) 
 
 Whether the dentist in this case, recognized the prophy- 
 lactic advantage of keejiing the gingival ends of the bands 
 as far removed from the gun line as possible, or was merely 
 
 ETRrsc w \i-n I wii: inu si-r- 
 rOETIw: 'I'wn i\si:i;ti.ii ihmaN 
 TEETH. ilXi. IIK W llhll IS NOW 
 WANTI.NC icnic .Ml SKI .\1 OF 
 fOliXKTOl (GlEIUXI) 
 
 actuated through moti^'es of convenience in fitting and at- 
 taching the appliance, cannot of course, be determined, but 
 the fact is apparent that the bands occupied a position well 
 toward the incisal and occlusal third areas of the anchor 
 teeth. 
 
 The second s]teciinen consisted of two strips of rolled 
 gold, adapted, one labially and the other lingually to the 
 
A BRIKF HISTORY OF PROSTHIOTIC DKNTISTRY llUli 
 
 rL'maiuiiig autL'iior tei'tli, and soldfred at their extremities 
 to form an elongated band. Four small sections of gold, 
 spaced and soldered within this elongated l)and, divided 
 it into five square spaces. Three of these s))aces were oc- 
 cupied by supporting natural teeth. The otlier two spaces 
 served as sockets to carry the sulistitutes, which in this 
 case were natural teeth, one of wliich was missing. The 
 same method of anchorage as previously described — the 
 rivet — was used for attaching the snlistitute teeth to the gold 
 structure. 
 
 ETRI'SCAX .\P 
 
 TEXDED TO A \ i 
 EFFECTS OF I (IN 
 PERHAPS. Tn 
 PURELY nl;\ \ \l 
 FICIAI. K' I'.si I r 
 OF COXTI I'l:! ■ 
 
 xi:' 
 
 Tliese methods of wiring and banding together, with 
 gold, loose natural teeth, and of applying the same means 
 for the retention of substitutes for missing teeth, in the 
 manner described, represent C[uite fully the lirst etfoi'ts of 
 the earlv dentists in bridge construction. 
 
 The addition of a saddle to rest ui>on the border, and 
 thus furnisli greater support and security to the substitute 
 than was affordeu by ligating or ))anding to tlie proximat- 
 ing, and adjacent teeth, was evidently not conceived until 
 a much later period. 
 
1110 A BRU'W mSTOIlY OF PROSTHETIC DKNTISTUY 
 
 ANCIENT CROWN WORK 
 
 The first and only specimen of ancient gold crown work 
 so far known was found within recent years, at Satricum, 
 near Rome, and is now in the museum of Pope Julius. This 
 crown consists of two pieces of gold, stamped to represent 
 
 ROMAN APPLIANCE FOUND AT THE SAME SEEN FROM liBf.OW 
 
 SATRICCM. CROWN OF ' LOWER (GUERINI) 
 
 INCISOR MADE OP C.mA) 
 
 the labial and lingual surfaces of a lower central incisor, 
 and united along the mesio-inciso-distal surfaces witli solder, 
 just as the Hollingsworth two-piece anterior crown is joined 
 together. It was held in place by an elongated band which 
 embraced the proximating and adjacent tootli on either side 
 of the crown. The attacliment of the band was close to the 
 gingival margin of the crown. 
 
 FIRST REFERENCES IN HISTORY TO PROSTHESIS 
 
 Although these ancient specimens of dental prosthesis 
 have been found, and somewhere near the probable time of 
 their construction determined by deductive reasoning, no 
 written records of such or similar work appears until about 
 the beginning of the CHiristian Era. 
 
 In Edersheim's "Life and Times of Jesus, the Mes- 
 siah," according to Dr. W. C. Miller, in Dental Cosmos, 
 December, 1905, the following statement is found: "Speak- 
 ing of things purchasable in Jeruslaem in the time of Herod 
 the Great, 40 to 4 B. C, 'And then the lady visitor might 
 get anything in Jerusalem, from a false tooth to an Arabian 
 veil, or a Persian shawl, or an Indian dress.' " 
 
 Martial, a Latin poet, who lived in Rome during the 
 first century A. D., in a number of his epigrams mentions 
 artificial teeth. Gruerini says: "There is therefore, not the 
 least doubt that in the days of Martial, artificial teeth were 
 in use; and that these, as may be seen from the epigram 
 just qiioted, were made of ivory and bone; we do not know 
 whether they were formed of other substances. The ques- 
 tion, however, arises; In those days did they manufacture 
 movable artificial sets, or was the dental art then limited 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1111 
 
 to tixiug the artificial teeth immovably to the neighboring 
 firm teeth, by means of silk threads, gold wire and the like ? 
 The answer to this question may be found in anotlier epi- 
 gram of Martial, where the latter ridicules a wanton old 
 woman, telling her, among other things still worse, that 
 she at night lays down her teeth just as she does the silken 
 robes. 
 
 "It is, therefore, beyond all doubt that, at that period, 
 the manner of constructing movable artificial sets was 
 known; and most i)robal)ly not only partial pieces were made, 
 but even full sets. In fact, from the verse quoted above 
 we have justly the impression that the poet means a whole 
 set rather than a few teeth. From the words of Martial, 
 it may also be concluded that these dentures could be put on 
 and off with the greatest ease; or, as we may say, by a 
 iiiancuvcr as simple as that of removing any articles of wear- 
 ing apjiarel; they must, therefore, have been extremely 
 well constructed." 
 
 DENTISTRY AMONG THE ANCIENT HEBREWS 
 
 In Dr. Koch's "History of Dental Surgery" is found the 
 following from the pen of Dr. H. L. Ambler: "The ancient 
 Hebrews did not have any large amount of mechanical in- 
 genuity, and dentistry with them was in a state of semi- 
 cultivation, but they replaced natural teetJi with false ones 
 more than two thousand years ago. A law of the Talmud 
 allowed the women 'to go out on the Sabbath with their 
 false golden or silver teeth.' Some rabbis allowed their 
 ])eople 'to wear the false silver teeth, since these appeared 
 natural, but the use of golden false teeth on the Sabbath 
 was ])roliibited.' Many teeth were made of wood, and later 
 on from the ivory of the elephant's tusk." 
 
 SLOW PROGRESS OF DENTAL PROSTHESIS IN THE 
 MIDDLE AGES 
 
 Passing down through the centuries but little progress 
 seems to have been made in denture construction until within 
 the last one hundred and fifty years. It is true that various 
 monographs on medical and dental subjects jirevious to the 
 date last mentioned,, contain frequent references to teeth 
 carved from bone.- or ivory, or hippopotamus tusks, but it is 
 more than likely that most of these were partials, held in 
 ]ilace with ligatures of silk or gold wire, in the manner al- 
 readv described. 
 
1112 A liHlEF HISTOKV OK i'ROSTH lilTIC DKXTISTKY 
 
 'I'lic coiistriiclidii dl' siitisract(u-y I'lill upper mid lower 
 dentures imist liave been u coiiHiderahie undertaking in the 
 olden time, considerin.i'' tlie manner in which impressions 
 of the moulh weic secured and casts wei'e derived from them, 
 and finally the de\-el(ipnient i>\' a(hii)tation of the block of 
 hone or i\'ory to tlie cast by carxiui;- and scra]Mni4'. 
 
 FIRST REFERENCE TO THE USE OF MODELS 
 
 Brief as it is, the outline of technic of full denture con- 
 struction as given by Aratthias Gottfried Purmaim, of Bres- 
 lau, 1fi48 to 1721, is the most complete description found 
 u]) to his lime, lie was the lirst to refer to the use of models 
 in dental i)rostliesis, but he does not state how they were 
 obtained. Here is his outline as given by Guerini : 
 
 "The front teeth, or pronouncing teeth, ought, when 
 they are wanting, to lie substituted by artificial ones, in 
 order to avoid the defects of |jronunciation, as well as to 
 obviate deformity of the mouth, and this is carried out in 
 the following manner : One has other teeth made of bone, 
 or of ivory, according to the number, the size, and the pro- 
 portions of those wanting; for which purpose one may 
 previously have a model executed in wax, reproducing the 
 particular conditions of the teeth and jaws, in order after- 
 ward to make and exactly adjust the whole on the pattern 
 of it; then when the base of these teeth is well fitted on 
 the jaw and small holes have been made in the artificial 
 teeth and also in the natural ones next to them, one applies 
 the artificial teeth in the existing void and fixes them as 
 neatly as possible with a silver wire by the help of pnn- 
 cers. " 
 
 Because he advised the perforation of the natural teeth 
 for the passage of the silver wire, a method which would 
 prove exceedingly painful, and invite pathological complica- 
 tions as well, Guerini concludes that Purmann simply de- 
 scribed, "and not even accurately, a prosthetic method al- 
 ready in use among specialists of that period. * * * 
 On examination of the passage cited above, which, how- 
 ever is not so clear as might be desired — it would appear 
 that the models of which the author speaks were most prob- 
 ably' quite different from those in use now. It is almost 
 certain that the specialists of those days first made a sketch 
 of the prosthetic part to be constructed, using for the pur- 
 pose a piece of wax, which they modeled jiartly with the 
 hand and partly carved ; and after having tried on this model 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1113 
 
 until it fitted ]>('rt'ectly in tlic inontli, and was iu every way 
 satisfactory, they probably |)assed it on to a craftsman to 
 make an exact re]n'odnction of it in bone or ivory." 
 
 FIRST REFERENCE TO FULL LOWER DENTURES 
 
 The first reference to a full lower denture is found in 
 the writings of Anton Nuek, an eminent Dutch surgeon and 
 anatomist, 16M to l(i92. He says, "In the case of all of the 
 teeth of the lower jaw being wanting, the entire dental arch 
 ought to be framed in with a single piece of ivory or tusk 
 of hipi^opotamus. " From this we infer that full upper 
 dentures, being more difficult to retain, were not frequently 
 constructed, else they also would have been mentioned in 
 this connection. 
 
 Nuck further recommends that artificial teeth be made 
 of hippo])otamus tusk, specially favoring the whitest, which 
 he estimated would preserve its color for seventy years, in 
 preference to ivory, which turned yellow from the action of 
 food, drink, and the saliva. 
 
 FIRST RECORD OF APPLICATION OF MINERAL SUBSTANCES 
 FOR DENTURES 
 
 Pierre Dionis, a surgeon and anatomist of Paris, in 
 1690, states that artificial teeth are generally made of ivory, 
 but may be made of ox bone, which will retain its color bet- 
 ter than ivory. He also states that Guillemeau constructed 
 artificial dentures from a composition made by fusing to- 
 gether white wax. gum elemi, ground mastic, and powder of 
 white coral and of pearls. 
 
 On this Guerini remarks: "This fact is, as everyone 
 can see, most important, for it constitutes the first step to- 
 ward the manufacture and use of mineral teeth. Dionis 
 tells us that the teeth made of Guillemeau 's composition 
 never became yellow, and that it was also very good for 
 stop])ing decayed teeth. It would seem, therefore, that it 
 could be used as cement is now used." 
 
 RETENTION OF PARTIAL DENTURES WITHOUT THE USE OF 
 LIGATURES OR WIRES 
 
 While it is i)ofsible, and in fact quite probable, that 
 partial dentures'liad been constructed and used, which were 
 not dependent on the use of the ligatures for their reten- 
 tion, yet no clear statement of this fact has so far appeared. 
 
1114 A HIUKF HISTORY OK I'ROSTHKTK' DKNTISTRY 
 
 The first attempts to construct easily I'ciiiovable pieces, .in 
 all probability, consisted in longitudinally i^rtxjving the ends 
 of tbe partial deulure so as to partially embrace tlie prox- 
 imating teeth, just as the nativ(>s of the Orient now do in 
 their prosthetic restorations. II will therefore be interest- 
 ing to mention tlie first record of such practice. 
 
 Lorenze ITeister, a celebrated surgeon, in 1611 first rec- 
 ommends the use of movable jirosthetic appliances of ivory 
 or liippopotamus tusk without special means for fixing tliem, 
 and further, that they should be removed at night and not 
 be returned to the mouth again until well cleansed. 
 
 Johann Adolph Goritz, in 1725, recommended that tlie 
 natural teeth be preserved by every possible means. He 
 discouraged the use of prosthetic appliances where only a 
 few natural teeth were lost, but suggested that in the worst 
 cases, to avoid defective "pronunciation, or for some other 
 reason (presumably unsightliuess) it may lie filled by an 
 imitation in soft wood." 
 
 Heinrich Bass of Bremen, 1690 to 1754, iirofessor of an- 
 atomy and surgery in Halle, recommended the application 
 of "whole dental sets, even in the upper jaw, so long as 
 there be two natural teeth existing to fix the prosthetic piece 
 to." From this we again infer that the construction of full 
 upper cases was not frequently attempted, on account of the 
 difficulty* in securing adequate adaptation and guarding 
 against the force of gravity and masticatory stress. 
 
 FAUCHARD'S WRITINGS 
 
 Pierre Fauchard, born in Brittany, 1690, died in Paris 
 in 1761, has been called the "founder of modern scientific 
 dentistry." He published a work in 1728, entitled "Le 
 Chirurgien Dentiste, " consisting of two volumes, which 
 was by far the best exposition on dentistry that up to that 
 time had ever been written. 
 
 In olden times, down to a ])eriod within the memory of 
 some of the members of the profession still living, there was 
 a tendency on the ]iart of many practitioners to jealously 
 guard with secrecy their methods of practice, especially 
 prosthetic operations, and thus jireveiit comjietitors from 
 profiting thereby. 
 
 Fauchard 's writings cover a wide range of dental sub- 
 jects and in i^rosthetic operations he is particularly explicit. 
 He recognized the existence of the petty jealousies alluded 
 to, but was able to rise above them, as his descriptive details 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1115 
 
 plainly show. In roference to tliis he says: "I have per- 
 fected and also invented several artificial pieces, both for 
 substituting a part of the teeth and for remedying their 
 entire loss, and these pieces substitute them so well that 
 they serve perfectly for the same uses as the natural teeth. 
 To the prejudice of my own interests I now give the most 
 exact descriptions possible of them." 
 
 "While Fauchard did perfect some of the prevailing 
 forms of artificial sulistitutes and invent others, the greatest 
 benefit he rendered the profession and posterity consisted in 
 having collected and included in his work "the whole doc- 
 trine of dental art, theoretical as well as practical, thus set- 
 ting in. full light the importance of the specialty, and giving 
 it a solid scientific basis." (Guerini.) 
 
 Interesting as all of Fauchard 's writings are, only a 
 few of the ])iiiici])al methods he describes can lie here in- 
 troduced. 
 
 TRANSPLANTATION OF NATURAL TEETH 
 
 He mentions that iu transplanting a tooth, whether re- 
 cently extracted or not, its root should be grooved hori- 
 zontally, so that when ligated firmly in position, the alveolar 
 process would eventually be built in the depressions so 
 formed, and as he expressed it, "the tooth will remain mor- 
 tised and may be preserved for a considerable length of 
 time. ' ' 
 
 He describes several methods in detail for replacing the 
 loss of two, three, or more contiguous teeth. One of these 
 consisted in carving from ivory, hippopotamus tusk, or bone, 
 each tooth, individually, to be replaced and fixing them to- 
 gether in a single piece by drilling holes and ligating with 
 wire. This was then bound to the natural teeth with gold 
 or silver wire, or silk or linen thread. Another method, in- 
 stead of ligating the substituted teeth together, consisted of 
 applying a strip of gold fitted into a horizontal groove 
 formed in the lingual surfaces of the carvings, and to which 
 each tooth was attached by means of two rivets. Again, the 
 teeth to be re]ilaced were sometimes carved from a single 
 block of the materials commonly used and attached in the 
 manner ])reviously mentioned. 
 
 CROWN WORK IN FAUCHARD'S TIME 
 
 Crowns were attached to roots of teeth by means of a 
 metal pivot extending into the root, which in ease of enlarged 
 
IIIG A BRIEF HISTOKY OK I'KUSTHETU', DKNTlSTItY 
 
 canal had ])revioiisl\ hcoi lillcd with lead. A hole drilled 
 in llio load i-eceivcd the root end of tiic pixnt, while I lie crown 
 was attached to the iirojectin.n' end of I he |ji\ol with a cement 
 
 J"- fu 
 
 c 
 
 i-'ArniAitii-s ii.i.rsTitATiox df a riiowx ok 
 
 noitV DIt IIIIM'OI'OTAMIS TUSK 
 WITH METAL IJOWEI, 
 
 composed of gnni lac, \'enice tnrjientine, and jiowdered white 
 coral. The crown of a natural tooth was frequently em- 
 ployed in such cases. 
 
 MEDIEVAL BRIDGEWORK 
 
 The first mention of fixed bridgework, although not so 
 designated, is made by Fauchard, wherein he describes how 
 a prosthetic piece may be held in position, in case the crowns 
 of the teeth had been losl but the roots were ])resent. Two 
 
 BBIDGE CAR\ED FROM nf)RV. RETAINED 
 
 BY TWO SCREWS FITTED IN ROOTS OF 
 
 I,\TEUAI, INCISORS (FAUCHARD) 
 
 holes were made in the substitute, corresponding to and in 
 alignment with the canals of two roots, through which pyra- 
 midal screws were introduced and screwed firmly into the 
 roots. 
 
 FULL DENTURES 
 
 Full lower dentures were recommended, with the sug- 
 gestion that the piece should be so formed as to fit the irreg- 
 ularities of the arch perfectly, when, with the aid of the 
 
A BRIEF HISTORY OP' PROSTHETIC DENTISTRY 1117 
 
 tongue interiorly and the cheek and lower lip exteriorly, the 
 substitute would be held steadily in place and the patient 
 would be able to masticate with it after becoming accus- 
 tomed to its ])resence. 
 
 CONSTRUCTION OF FULL DENTURES BY FAUCHARD 
 
 Although full upper dentures were constructed long be- 
 fore Fauchard's time, it is evident that thev were seldom 
 
 AN I I'l'Klt DENTLRE Kl I'l'OliTEl) BV SriilXGS FIXED Til A 
 
 COED APPLIANCE WailCII EMBKACES THE NATIRAI. 
 
 TEETH OP THE LOWER JAW (FAUCHARD) 
 
 (GUBRINI) 
 
 satisfactory. One case is mentioned which illustrates the 
 helplessness and inaliility of some who were considered other- 
 wise well qualiS.'^d in llie construction of full upper cases. 
 Pauchai'd says: "In 17;!7 a huly of high rank, of about the 
 age of sixty, who had not lost any of her lower teeth, Init 
 
1118 A BRIKF illSTOKY OF IMiOSTHETIC DENTISTRY 
 
 "was deprivcil entirely nl' llie upper mies, jipplied to M. 
 Caperon, dentist to the Kiiii;-, who was riidst ahh' in his pro- 
 fession, in the liope that he ini^lit he alih' to furnish her 
 mouth witli an upper set. But lie said that, 'no tooth what- 
 ever being left in existence, every possible point of attacli- 
 ment was wanting, and it would therefore be as difficult to 
 do this thing as it would he to huild in the air.' " M. Caperon 
 referred her to Fauchard, who after some delil)ei-ation "suc- 
 ceeded in devising a means of applying an upper set of teeth 
 which, in fact, entirely satisfied the wishes and wants of his 
 client." (Gruerini.) 
 
 The apjiliance in this case did not include the full com- 
 plement of teeth, some of the posterior space being occupied 
 by the springs, by means of which, in conjunction with a 
 double bow frame of gold lifted around the lower teeth, the 
 denture was retained in ]iosition. 
 
 Mention is also made of three successful cases of full 
 upper dentures which were retained without the aid of 
 springs. Several points of interest are seen in Fauchard 's 
 own description of these cases, which is as follows: 
 
 "One can adapt an entire set of teeth to the upper jaw 
 of much greater sim]ilicity than those described, and which 
 
 r^ 
 
 
 
 m ^/^ 
 
 
 P-^iJW 
 
 B. ■ W, A 
 
 41^ 
 
 Li^^S 
 
 
 
 
 is maintained in its ]>lace by tlie sole support of the cheeks 
 and the lower teeth. It must be very light indeed and serves 
 almost solely to improve the appearance and the pronunci- 
 ation ; but when the individual gets used to it, he can also 
 masticate with it. A set of teeth of this kind ought to ad- 
 here well to the gums and to be constructed in such a man- 
 ner that the cheeks may afford if sufificient ]iressure and 
 
A BRIEF HISTORY OP PROSTHETIC DENTISTRY 1119 
 
 support, together with the aid of the k^wer teeth. These 
 latter sometimes bring it baclv into its place without anyone 
 perceiving the movement except the wearer liimself. Not 
 long since I had occasion to renovate a set of teeth of this 
 kind made by me more than twenty-four years ago and 
 worn by the owner to the greatest advantage. I have since 
 made two others which have proved most useful to the per- 
 
 UPPER DENTUKE IX IVORY. AT THE END OF THE ErcHTBENTH CEN- 
 TURY, roR A CASE IN WHICH THE LAST MOLARS AND THE FRONT 
 TEETH WERE PRESENT (GUERINI'S COLLECTION) 
 
 sons wearing them. Tt is true that tliere are few mouths 
 adapted for wearing tliese sets, so much so that, excepting 
 the three referred to, I have never made any others. To be 
 able to construct similar sets successfulh', the dentist must 
 be possessed of skill and ingenuity. Apart from this, they 
 are tlie most suitable for poor persons wlio cannot sjicnd 
 niiu'li, as they cost less to make." 
 
 SUMMARY OF FAUCHARD'S WORK 
 
 Fauchard made use of both flat steel and coiled gold wire 
 springs for the retention of both full and partial dentures. 
 
 Summed up briefi.y, tlie main facts of prosthesis which 
 Fauchard elaborated upon are as follows: 
 
 The transplantation and replantation of natural teeth. 
 
 The application of both carved and natural crowns to the 
 roots of teeth l)y means of metal pivots, or by binding tliem 
 to proxiraating natural teetli with ligatures of gold or silver 
 wire, or silk or linen thread. 
 
 The ap])lication of a crude form of bridgework consisting 
 of a carved replacement rigidly fixed to two natural roots l)y 
 
1120 A RHIIOF HISTORY OF rROSTHKTIC DENTISTRY 
 
 means of two tapcriiis;' screws passiiit;- tln'ouiili llie siilislitut.e 
 into the root canals. 
 
 Tlie carving- of jiailia I and I'lill deiitiii-es fioni ivory, hip- 
 poyiotanins tnsk, or hone, 1oi;e1 her with a desci'iption of means 
 
 OOMPI.ETl! DKN'TtlRES IFAlTHAHDl. F' RKl'ItESEN'TS AX ENAM- 
 ELED DENTURE WITH ARTIFICIAL GUMS. F< AND F- STEEL 
 SrniNGS (GUERINIl 
 
 of attachment witli liii-atnres, springs and metal cril)s, and 
 adhesion. 
 
 The enameling of artificial teeth to represent the varia- 
 tions in color of the natnral teeth, and the staining or enam- 
 eling of the gnm portion to reju-esent the color of the mucous 
 tissues. 
 
A BRIEF HISTORY OF PROSTHKTU' 11KNTISTRY 1121 
 
 'IMic coiistructioii <>( (ilil uijitnis I'nr (•(in-cclinu- tlclVcls of 
 the palate. 
 
 Finally, the suggestion Init iiul the ilc\('li)|)incnt ami nsi', 
 of ])oivelain for teeth ami dentures, as not(Ml in the clia])!!-!- 
 on ]iorcelain. 
 
 DD 
 
 A SPRING DEXTIRE FOB A lASE I.N WHICH THK LOWER FRONT 
 TEETH STILL EXIST. FIfiS. 1 TO II ILLI'STRATE \'ARIOUS PARTS 
 OF THE APPARATUS IFAUrilAROI ((H'ERIXI) 
 
 BENEFICIAL INFLUENCE OF FAUCHARD'S WRITINGS UPON 
 . THE PROFESSION 
 
 rndouhtedn , the exanijile of Fauchard in giving freely 
 and uustintingly to tlie profession, the henetits of his knowl- 
 edge, experienee and im])rovements, exei'ted a widespread and 
 
1122 A liUlICK HlSTOJtY OK J>l{OSTHKTIG DKNTISTKY 
 
 beneiicial iiitluciicc oii his coiilcinporarics aiu! llic mi'ii who 
 followi'd. This is cNidi^'iit I'l-oiu tiie sijarsciicss oT ilctail in 
 previous writings and tho marked tendency oT suhscciiiciit 
 writers to more fnlly clalxiratc tlicir ideas. 
 
 Tliat till' work ot l''iui<'har(l was up to date and in some 
 respects in advance of Ihc tiiiics is apparent from the fact 
 that altliough other works appcai-ed at about that time and 
 at intervals afterward, none of importance was presented 
 until eighteen years after the i)nl)lication just reviewed. 
 
 FIRST WORK CONFINED EXCLUSIVELY TO DENTAL 
 PROSTHESIS 
 
 In 1746 Mouton i)iil)lished the first work of record con- 
 fined to dental prostiiesis. Most of the methods detailed by 
 Fauchard were included in this later publication, and some 
 new ideas were introduced, among which may l)e mentioned 
 the application of gold crowns to badly decayed front and 
 back teeth, the front crowns being enameled to correspond in 
 color with the natural teeth. 
 
 For the first time mention is also made of the use of 
 spring clasps for the retention of partial dentures. 
 
 FIRST MENTION OF PLASTER 
 
 In 1756 Philip Pfaff, dentist to Frederick the (Ireat, in 
 a work confined to dental subjects, first describes the use of 
 plaster models. Guerini remarks: "It is therefore to two 
 Germans — Pfaff and Purmann, the latter who, as we have 
 already seen, used wax models — that one of the greatest pro- 
 gressive movements in dental prosthesis is indebted; that is, 
 the method of taking casts and making models, of which 
 method one finds no trace whatever in the authors of anti(|uity, 
 and which, it would appear, was not known even to Fauchard 
 himself. The wax casts of an entire jaw were taken by Pfaff 
 in two pieces, one of the right half of tlie jaw, the other of 
 the left, which were then reunited, and one thus avoided spoil- 
 ing the cast in removing it from the month." 
 
 FIRST MENTION OF GOLD BASES 
 
 In 1757 Bourdet described the use of gold bases for 
 resting upon the aheolar process, to which the replaced teeth 
 were attached )iy means of small pins and the whole base 
 overlaid with flesh colored enamel, similar to the continuous 
 gum pieces of today, lie also described another dentui'e in 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1123 
 
 wliicJi he carved the three back teeth on either side from tlie 
 same block of hippopotamus tusk, which formed the base, 
 while the ten anteriors were human teeth fixed to the carved 
 base by means of rivets. 
 
 IMPLANTATION OF TEETH 
 
 The first mention of imiilantation of teeth is made by 
 Bourdet, which is related Ity Guerini as follows: "This sel- 
 ebrated author inveighs bitterly against charlatans and quack 
 dentists, and throws light on all their impostures. It appears, 
 however, that in the midst of this despicable class, so justly 
 condemned by him, there existed a courageous though unscien- 
 tific operator, to whom posterity would have attributed due 
 honor had his name been handed down, for he was the first, 
 in all probability, to try the implanting of teeth in artificial 
 alveoli. This is, at least, what we deduce from a passage in 
 one of Bourdet 's works, in which we read that a charlatan 
 sought to impose on the public the belief that he could make 
 a hole in the jaw bone and plant therein an expressly pre- 
 pared artificial tooth, which in a brief space of time would be- 
 come firm and as useful as a natural one. Bourdet adds that 
 an attentive investigation led to the recognition of said tooth 
 being sim])ly that of a sheep. It would appear, therefore, that 
 the operation had been in reality performed, it matters but 
 little whether with the tooth of a sheep or with one of another 
 kind." 
 
 Adam Anton Brunner, a (reinuui, in 1766, described a 
 method of applying pivot teeth by screwing the pivot into the 
 base of the crown, then enlarging the root canal just enough 
 to tightly embrace the root ])ortion of the ]nvot Light ham- 
 mer l)lows directed against the crown forced the pivot into 
 the root canal and held it firmly without the aid of cement. 
 
 BERDMORE'S REFERENCE TO ARTIFICIAL DENTURES 
 
 Thomas Bcnlnioic, dentist 1o Oeorge ill of England in 
 17()H, makes this statement in regard to artificial teeth: "Al- 
 though artificial teeth are evidently ornamental, although they 
 give a juvenile air to the countenance, imi)rove the tone of the 
 voice, render pronunciation more agreeable and distinct, help 
 mastication, and. preserve the o]iposite teeth from growing 
 prominent, yet many are prejudiced against them on account 
 of some inconveniences which are often fduiid to attend the 
 use of them. For thev are said to become very soon yellow 
 
11^4 A imilOK IIIS'I'OKY OK I'UOSTI 1 KTIC DKNTISTKY 
 
 ami tlirtv', to .i;i\(' a stiiikiiii;- hrcatli, not to lit easy on the 
 i!,'uiiis, selciom to slaml linn, and to loosen after some time 
 the rieis>'hhc)rin,s>' teeth to wliieli they are t'asteneil, or the hafd 
 lij^'atiire, which i^ connnonlx nscd. is often seen to ent \-ei\v 
 deo]) into the soimd teeth." Il<' la\s tiiese dil'tienlties to the 
 fa nit of the "artist," the ne^li.ii'enee of the patient, or the want 
 of proper instrnetions. lie reeonmiemh^d the frei|nerit nse 
 of the brush with suitable iiowders, aud to axoid the use of 
 red wines and stainiu,<>- hKiuors, and the use of silk twist in 
 stead of wii'c ligatures. 
 
 "A whole set of artilieial teeth ma>' he made for one oi' 
 hotli jaws, so well litliMJ to admit of the ueeessar> motions, 
 and so eonvenientiv retained in the proper situation li>' the 
 hel]i of spring's of a ih'W aud peculiar consti'uetiou tiiat they 
 will answer e^•ery purpose of natural teetli. ami can he taken 
 
 ^^^BSi^ 
 
 out, cleaned and rejtlaced by the ])atient himself, with the 
 greatest ease. I say si)i-ings of a peculiar construction, he- 
 cause they are totally different in shape and action from 
 those whieli have Ijeen used by my predecessors, because they 
 follow all the various motions of the jaw very freely, aud be- 
 cause the ])ressure which they give is always e(|ual and gen- 
 tle, whether the mouth be shut oi- not." He further states 
 that dentures made from soft hone or ivory discolor readily, 
 but may be made of more durable materials which will retain 
 their ])olish and whiteness for a long time. Further, that the 
 gum ]»ortion ma>- lie stained so ])erfectly that "nobody in 
 common conversation can distinguish the artificial from the 
 natural gums," 
 
 Jourdain, in 17S4, descrihed a full ujiper and lowei' den- 
 ture sustained in ])i)sition by means of four springs, the idea 
 of which, he states, was conceixcd, hut ]irol)ahlv not developed, 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1125 
 
 by Massez in 177"_'. Because tliis means of retention was com- 
 ])lieated and dil'licult to atlapt, it did not eome into i^eneral use. 
 
 PRINCIPAL MATERIALS USED AS DENTURE BASES 
 
 The principal materials so I'ar mentioned and used as 
 substitutes for natural teeth were hone, ivory, hippopotamus 
 tusk, wood, gold, silver, white wax, mother of ])earl, human 
 teeth and those of animals, all more or less i»ei-ishable except 
 the metals mentioned. 
 
 The effort of (Tiiillemeau, mentioned hy Dionis, in KilMI, 
 was the first of record to com])ound a substance which would 
 more nearly fulfill the reciuirements of duraliility, apyjearance 
 and ease of a])])lication, for prosthetic sulistitutes, than did 
 the organic materials in common use. 
 
 FIRST SUGGESTION OF PORCELAIN WORK 
 
 Fauchard, in 17l'S. sng.ucsted the use of porcelain for 
 teeth and dentures, but did not follow u]i and develop what 
 has since proven to be one of the most inqjortant as well as 
 esthetic i)hases of ])rostlietic science. It seems that he made 
 use of enamels for staining both teeth and gums to resemble 
 those of nature. Hourdet, in 175(3, stated that he "had used 
 the pink enamel of Fauchard." This enamel must have been in 
 the nature of a jiaint or varnish, and so applied since, if of 
 porcelain, the heat necessary to fuse the latter would have de- 
 stroyed lioth teeth ami base of bone or Ivory. 
 
 DUCHATEAU'S EFFORTS IN PORCELAIN WORK 
 
 In 1774, Dnchateau, a French chemist, near Paris, who 
 was wearing a tlenture made from hippo])ntanuis tusk, and 
 which had accjuired a disagreeable odor, conceived the idea 
 that a porcelain denture would l)e free from the ol),iection men- 
 tioned. He i)resented his idea to (luerhard, a i)orcelain manu- 
 facturer in Paris, and together they proceeded to ex])erinient. 
 The first denture, on account of the contraction of the ]iorce- 
 lain in baking, was too small. A number of others were con- 
 structed, noni' of which foi- \arious reasons proved sat- 
 isfactory. 
 
 THE WORK OF DUBOIS DE CHEMANT 
 
 Discouraged by the many failures encountei-ed, Dncha- 
 teau apjilied to Dubois de Chemant, a well-known dentist of 
 Paris, for ad\ice and assistance. I>y modifying the porce- 
 
1126 A BRIKF HISTOltY OP PROSTHETIC DENTISTRY 
 
 lain ui' Ducliatcau willi |ii|K' clay and coldriiij;- earth, its i'ns- 
 ing point was reduced, the color improved, and contraction 
 was lessened. Finally, after a number of efforts, a denture 
 was produced that Dnchateau was able to use. Although he 
 endeavored to ccmstruct dentures for others, Duchateau's ef- 
 forts resulted only in failure, his general knowledge of ])ros- 
 thesis being insufficient to accom])lish the required results. 
 
 He received a vote of thanks and an honorable mention 
 from the Royal Academy of Surgeons of Paris in 177(i, be- 
 fore whom his process was laid. The failures mentioned dis- 
 couraged Dnchateau from further efforts in this field, nor 
 does it appear that he again renewed them. 
 
 De Chemant, to whom the success of Duchateau's et¥orts 
 were largely due, continued his experiments, and, after a 
 number of years, suc<'eeded in compounding a porcelain, the 
 contraction of which could be determined to a fairly accurate 
 degree, of modifying the shade to a considerable extent as 
 desired, and of iminoviiig the sjirings and other means of 
 attachment. 
 
 Desirabode, writing in 18-18, says in reference to the in- 
 troduction of porcelain: "Fauehard seems to be the inventor 
 of porcelain teeth, then Dnchateau improves the manufacture ; 
 De Chemant, by accident, gets hold of the secret, which he 
 further improves and gives as his own in 1788 when he imb- 
 lished the first edition of his work. De Chemant carried the 
 art to England, where he obtained the exclusive right to work 
 the invention for twelve years. ' ' 
 
 In tlie work alluded to De Chemant shows by means of 
 engravings the various types of prosthetic substitutes he 
 could produce in porcelain. Among these were included a 
 crown, a bridge, full dentures and an obturator. 
 
 With few exceptions, Fauehard being a notable exainiile 
 to the contrary, the writer on dentistry in those days pub- 
 lished a book, not so much to enlighten his professional breth- 
 ren, as to impress the public with his superior attainments. 
 De Chemant was one of the latter class. His work was largely 
 made up of eulogistic effusions of himself and the new process 
 of which he claimed to ))e the sole inventor, thus denying to 
 Dnchateau auy credit whatever, in either the conce]ition or 
 development of the porcelain idea. 
 
 Furthermore, he studiously avoided giving to the i)rofes- 
 sion so much as a hint of the com]iosition or manner of work- 
 ing the paste for the making of "indestructible teeth," which, 
 as appears, still lacked many desirable qualities. Indirectly 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1127 
 
 his selfish, commercial attitude resulted in l)enefit to the pro- 
 fession liy instigating others to enter the field in au elTort to 
 find something as good or better tlian that which he had dis- 
 covered. 
 
 Dubois Foucou, dentist to the King, was one of the jury 
 appointed by the French Academy of Surgeons to examine into 
 the merits of De Chemant's discovery. He was at first op- 
 posed to the idea, but later mi began experimenting and suc- 
 ceeded in improving both the ([uality and color of the porce- 
 lain over that used by De Chomant. While this was indeed 
 laudable, the greatest benefit resulting from Foucou 's re- 
 searches consisted in publishing to the profession all of the 
 formulas and methods he had discovered. His dentures were 
 jiroduced in three shades, bluish white, grayish white and yel- 
 lowisli white, in varyins,' gradations. 
 
 INTRODUCTION OF SINGLE TEETH AND BLOCKS OF 
 PORCELAIN 
 
 Fonzi, au Italian, practicing in Paris, in 1808, introduced 
 for the first time single teeth and blocks of teeth, having baked 
 within and projecting from them small pins or hooks of 
 ])latimim, by means of which Ihey could be attached to bases of 
 various kinds. This was a decided and valuable improvement 
 in itself, for it encouraged the production of bases of more 
 permanent character, such as gold, silver, and platinum, and 
 the consequent development of teehnic in metallurgical lines. 
 The porcelain of which these teeth were composed was some- 
 what translucent and much more nearly resembled the nat- 
 nral teeth than did that of either De Chemant or Foucou. 
 vStill further credit should be given Fonzi from the fact that 
 these teeth were, to a limited extent, manufactured and ren- 
 dered available to other members of the profession, and, 
 further, were capable of comparative ease of application. 
 
 Til us when the facts are known Fonzi stands out as a 
 indiniiient character in the advancement of jtrosthetic sci- 
 ence, for it is apparent that from his time on progress in the 
 porcelain field shows gradual but marked improvement. 
 
 The jiroduction of dentures carved from bone, ivory and 
 similar substances continued for many years after Fonzi 's 
 time, largely becau'Se of imperfect technical methods, and the 
 difficulties encountered of fusing porcelain in the cumbersome 
 furnaces in use in those days, some of this material reciuiring 
 a temperature of 3,000 degrees F. to vitrify. 
 
naS A HKIIOK IIISTDKY Oh' I'liOS'l'l I lO'l'lC HKNTIS'I'HV 
 
 FIRST INTRODUCTION OF PORCELAIN IN THE UNITED 
 STATES 
 
 111 1S17, I'laiitoii 111' Paris (■aiiic to I'hiladcliiliia. liriii,i;iii,u' 
 witli liiiii a stock v\' iioirdain Iccth made in l''raiirc. 'riicsc 
 liavc been descrilicd as Kciiiii inrcridr in Imlli (|iiality and 
 color, somewhat reseiiihliiii'- a split bean, liaviiii;- a liall'-round 
 STOOve in the back, in tlie sides of which were inserted small 
 
 OI!()(l\ FJI I'DKCKI.An 
 
 i:ii r.iiTH Kill! 
 
 \NI1 IIENTI ItK WORK 
 
 stri))s of ])latinniii for bciidiiifj,' over and sohlcTinn- to a j^old 
 wire post attached to the deiitnre base. 
 
 The arrival of Plantoii ]iroved an incenti\'c to incinliers of 
 the profession in this country to enter tlie porcelain field in 
 an endeavor to improve the iiiiality and forms of the teeth 
 then available. 
 
 THE FIRST MANUFACTURE OF PORCELAIN TEETH IN 
 AMERICA 
 
 In 1822 Chas. W. Peale began the manufactnre of ]iorce- 
 lain teeth, in the backs of which platinmn ]nns were inserted 
 and baked for attachment purpose. 
 
 In 1825 S. W. Stockton began the manufactnre of jiorce- 
 lain teeth with such success that in a few years liis business 
 had grown to ipiite extensive pro])ortions. In reality he was 
 the first in this country to engage extensi\-ely in the produc- 
 tion of porcelain teeth for the jirofession. 
 
 It was customary, about this time and for many years 
 later, with a number of men in the profession to manufacture 
 teeth, both single and in blocks or sections, to meet the re(|iiire- 
 ments of individual cases in practice. 
 
 These teeth and blocks were attached to bases of various 
 kinds, being mounted on i^'ory or hi])po])otamus tusk l»y means 
 of screws or rivets. ]iassiiig tliniiigli hoh's driih'd through Imtli 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1129 
 
 ba.si' and ixn'celaiii, wliilc to metal liases they were attaclicd 
 in the same manner and l)y soUh'rini;- a liackinii' to pins baked 
 in the poreehiin. 
 
 Ambler states that "among tliose who made teeth for 
 their own nse were Doetors Mellhennv (182(i), Ambkn- and 
 Spooner (1828), Fhigg (1830), S. Spooner (1831), Harwood 
 and Tucker (1833), Aleock and AUen (1835), and Wildman, 
 who began liis experiments in 1837. The latter made pains- 
 taking investigations and achieved iiotabU' results. 'Mis work 
 was so imjiortaiit and far-reaching that he has been aecordei] 
 
 I.AHIAL AND LINliUAL VIFAVS OF DENTUHK I'OX- 
 
 STKICTED BY DR. MclUlENXV IN ISJI.'i. TOOTH 
 
 ISIX)(KS WERE (■AR\En BY HAXI) 
 
 till' honor of baxiiig been iirst to ]ilace tlie manufacture of 
 teeth on a scientitic basis.' " 
 
 In 1844, kSamuel S. White of Philadelphia began tlie manu- 
 facture of teeth, in a small way at first, but liis products w^ero 
 of such excellent quality that the business soon grew to large 
 l)roportions. r])on the foundation which he laid was estab- 
 lished tlie S. S. ^Vhite Dental Manufacturing Company, which 
 to-day is one of the most extensive, il' not the hirgest, concern 
 of its kind i?i Ihe worlil. 
 
 \'\)\- uiany^vea'rs the i|ualit\- of porcelain teetli, both for- 
 eign and domestic, has been reasonablx- satisfactory in color 
 and texture, Imt few, if any, have fullilled anatomic require- 
 ments. The bicuspids and molars are usually too small and 
 
1130 A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 ai'c rchitixcly (lispropdrtioiifd to each otliiM" a8 well. Laliial 
 and biUH-al surfaces, wliile i'alling short of ])erfectioii in 
 t'onii, presented a nnieli better appearance than did tlic in 
 cisal edges of tlie anterior or the oeclusal surfaces of bicusiiiils 
 and molars, particularly the latter, the planes and surface 
 markings of wliicli oftentimes in no way resembled in form the 
 surfaces they were supposed to represent. 
 
 Within recent years, since mandibular movements are 
 better understood, the demands of the profession for better 
 
 TYPE OF (OKI HIKNUE I OM 
 
 M0NI1 I sti) [^ iHE ^iRI^ 
 Bws roR I [ si\f moi k tlftii 
 
 \X1) IO\ri\LIOt'f (,l M DIN 
 TUBl/S 
 
 forms of artificial teeth iiave been and are being met by the 
 manufacturers with commendable and in many instances ex- 
 tremely gratifying results. 
 
 INTRODUCTION OF GOLD FOR DENTURE BASES 
 
 As previously stated, Bourdet, in 1757, mentions the use 
 of gold for denture bases. It was not introduced into the 
 United States until 1780, when Dr. James Gardette of Phila- 
 delphia described and used it for this purpose. 
 
 Silver and platinum were also employed for baseplates, 
 but the use of all of these metals was limited, because of tlie 
 difficulty met with in secnrimi' ada|)tation to the oral tissues. 
 
 DIES FOR SWAGING METAL BASES 
 
 Dies were frequently made of brass, the model being sent 
 to a brass foundry for casting, no laboratory being equipped 
 with furnaces suitable for fusing this alloy. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1131 
 
 Ijutor Oil zinc was ciniiloyod for dies heeanse of its com- 
 liaiativoly low fusibility and hardnoss. Still later, about 1860, 
 Babbitt's metal was made use of for the same purpose, it 
 Ix'ina,' almost as hard as zine, fused lower and contracted less 
 
 EXfir.ISH XriiE TEKTH MOUNTED ON SWAGED 
 
 GOLD BASE. CONSTRUCTED ABOUT 1S44 
 
 (LOANED BY C. R. SYKES. OF C. 
 
 ASH & SONS) 
 
 than the latter metal. Dr. L. P. Haskell is largely responsi- 
 ble for the introduction of and improvement in Balibitt metal, 
 which, without doubt, is the best alloy available for die pur- 
 poses. 
 
 As late as 1840, De Loude of London, in writing of his 
 methods of technic, says: "Tlie im]iression is ])(mred with 
 
 FULL UI'I'Ell AND LOWlvIl DENTURES. GOLD BASES. WITH SFIilNGS FROM FOX AND 
 HARRIS. ED. 1855) 
 
 plaster and the model sent to a brass founder to have a 
 similar one mgfde of brass ; after which a she-mold of lead is 
 made on the one of brass, then plates of gold, silver or ]ilatina 
 are swaged." (Ambler.) 
 
1132 A liini':K IIISTOIiY l)l'" I'KOSTIIKTIC DKNTISTKV 
 
 FIRST USE OK CAST BASES 
 
 Till liases made li>' rastiiii;' llic innllcn metal iiiln a matrix 
 (•(iiitaillilii;- llle teeth, and directly tn tllelli, was ilil rndllced liy 
 Dr. Edward Hudson oi' Pliiladelpliia in 1S-J(I. I''urtlier wurk 
 along similar lines was carried mi hy Dr. W. A. Koyce of 
 Newlmrgli, X. \.. in IS.'KI, and hy Dr. (icorge K. Ilawes of 
 Xew ^'ol■k in IS.IO, hut with mure or less indifft'i'ent success. 
 
 Di'. A. .\. I^)landy of Baltimore, in 1S5(), greatly imjiroved 
 the then existing nictliods of technic, and introduced an alloy 
 for denture bases wliicli cast more sharply than tin. The 
 process was termed "Cheoplasty, " and deiitui-es so con- 
 
 (iflM) HA.SK llE-NTUUK. SIN<;l,E CUM StX'TIOX TKHTH. 
 
 HACKKl) ,\XD SOLDERED. WITH PEHIPHEH.U, UIM. 
 
 CIINSTIU ITED BY DR. VV. X. MORRISON .iBOI'T I.<ili!l 
 
 stiucted were called chroplasfu- dctit iiU's. Harris' Edition, 
 187o, states that "the name chosen hy him (Blandy), signify- 
 ing the making of ])lates by pouring a metal, made plastic by 
 heat, is equally apjilicable to all alloys of tin noiv nsed. 
 Blandy 's alloy of chcoplastic metal was silver, with some 
 bismuth and a trace of antimony." Tin, combined with 
 bismuth or cadmium, was introduced shortly afterward, and 
 these alloys are used, more or less, for lower weighted den- 
 tures at the ]n-esent time. 
 
 Hard vulcanite, although discovei'ed in IH.')!. had not 
 come into genei'al use as a denture base, and the teeth used 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 11:1". 
 
 ill metal liasc ilciituii' consl i-nrtidii were not suitcil because 
 of their foriii and type oT iiiiis, for linn allaciinieiit in the cast 
 l)ases, therefore teeth of iimililieil fonus were designed and 
 used for tliis |mr[)ose. 
 
 SPECIAL FORMS OF TEETH FOR USE WITH CAST BASES 
 
 111 IS.")*). \V (i. ()liver and Thomas Harrison introduced 
 teeth witli uroii\es and holes for anchorage purposes, to ho 
 
 Ql^f 
 
 ,%>. 
 
 used in the casting process. These teetli were phmiied souk 
 what on the oi-der of tlie present diatoric teetli. 
 
 DENTAL VULCANITE LITIGATION 
 
 In 1852 John A. ('uinmiiigs of Boston filed a caveat, an 1 
 in 1855 ai)])lied for a iiateiit for the method and use of rnhiier 
 in denture constiin-tion in i)ractically tlie same manner as it 
 is used to-day. This i)a1ent was granted in 18(U, and there- 
 upon liegan a long and drastic siege of litigation, on the part 
 of Cmnmings and others, to enforce n])on the members of the 
 profession who were using vulcanite, the pavment of ojpcc 
 rif/hts, or roifiilfi/. -for the i)ri\'ilege of using rubber for tliis 
 purpose. 
 
 The hiial sunmiiiig up and outcome of this now famous 
 legal battle can be fiumd in the Dental Cosmns, .\i)ril, 1S7;;, 
 
ii:m a \uukv ]iis'1'()kv ok iMiosTiii'rnc I)iontisti{y 
 
 the entire issue dl' Ihiil llKilitil heilli; (le\'()1eii t(i llie court 
 ti'aiisacliojis in tii<' linal case. 
 
 The followin.n' pai'a.iiraph hrietlx explains the |uinei|ial 
 ])oiiits of history of the vulcanite litigation: 
 
 "Letters patent were granted to John A. ('uniinings on 
 June 7, 186-1, for an 'iiii])rovement in artificial gums and pal- 
 ates,' and on account of a defect were reissued January 10, 
 18()5. to the Dental \'ulcanite ('oin])any, and later on account 
 of a defect were again reissued March iM, ]S(ir>. to said com- 
 ])any. 
 
 "The Goodyear Company, by assignment, l)ecame the 
 legal owners and issued to densists, for various sums, 
 'licenses and agreements' to use its process only in their own 
 business, the license not to be assigned, sold, transferred or 
 otherwise disposed of, and the licensee not to encourage in- 
 fringements, and if he found any one infringing he was to re- 
 port it to the company and they were to bring suit against the 
 infringer. These licenses were generally given for one year, 
 and were signed by the licensee, the agent and Josiah Bacon, 
 treasurer, who, on account of his arbitraiy methods and mean- 
 ness in dealing with the dental profession, was shot and killed 
 in San Francisco. 
 
 "The contest as to the validity of the ])atent between the 
 Groodyear Company and the whole dental profession of the 
 United States was long and bitter. Finally S. S. White took 
 up the cause for the profession and spent much time and 
 money and in the end won the case and wiped out the abomina- 
 tion." (Dr. H. T. Aml)lei', in Mistory of Dental Surgery.) 
 
 COLLODION AND CELLULOID AS DENTURE BASES 
 
 The refusal of many to use rubber, on account of pending 
 claims of the patentee, led to the introduction of collodion as 
 a denture base in 1859, by John Mackintosh of England. 
 
 Dr. J. A. McClelland of Louisville, Ky., in 1860, improved 
 the collodion base and introduced it under the name of "Rose 
 Pearl," but this, as well as Mackintosh's product, proved lui- 
 satisfactory on account of contraction, warpage and lack of 
 ]H'rmanent quality. 
 
 Celluloid, having collodion as a base, was invented by 
 Isaiah S. and John W. Hyatt of Albany, N. Y., in 1870, and 
 for many years was used extensively, and is to a limited ex- 
 tent to-day employed in denture construction. 
 
 Although any of the existing forms of vulcanite teeth 
 can be used in conjunction with celluliod as a base, a special 
 form of tooth having a constricted cervix and of more natural 
 
A BRIEF HISTORY OP PROSTHETIC DENTISTRY tl35 
 
 form generally was designed for tiiis }>uri)ose. The counter- 
 suuk piu tooth followed closely on the introduction of im- 
 proved teeth for celluloid work. 
 
 Some of the most notable attempts to reproduce natural 
 tooth forms were made by Dr. E. T. Starr in 1869. A few of 
 the molds he jn'oduced are scai'cely eciualed l)y tlie liest efforts 
 of present-day tooth designers. 
 
 Ash & Sons of London liave long been noted for the pro- 
 duction of teeth which, in both form and color, closely resem- 
 ble the natural organs of mastication. Their tube teeth, which 
 were introduced al)out 1840, are capable of varied applica- 
 tion, both for dentures and single crowns. These teeth can 
 be reshaped by grinding and the glaze restored by polishing so 
 perfectly that the moditication cannot be detected. Because 
 of the materials employed and the mode of manufacturing, the 
 finished product is very dense and free from porosity. 
 
 Most of the manufacturers of teeth have, within recent 
 years, improved the quality of materials in their products, and 
 practically all of the present-day teeth can be modified and 
 re])olished as described. 
 
 VULCANIZING RUBBER BETWEEN METAL SURFACES 
 
 The })rocess of vulcanizing rubber between two polished 
 metal surfaces was introduced by Dr. Stuck in 1868. His 
 method consisted in forming a cast of the mouth in tin, de- 
 veloping the baseplate in wax or securing the recpiired thick- 
 ness and form of the model denture l)ase with several layers 
 of tinfoil, investing the case in the flask, and on opening re- 
 moving all but the outermost layer of tinfoil from the matrix 
 side. This resulted in the formation of a metal matrix in 
 which the rubber was packed and vulcanized. The product 
 was much denser than when vulcanized in a ])laster matrix, 
 and in addition recjuired no polishing except where the sur- 
 plus margins were trimmed away. A similar method is some- 
 times resorted to at present, except that instead of the tin 
 cast of the mouth a plaster cast as ordinarily constructed is 
 used, to which a thin sheet of tinfoil is carefully adapted, 
 cemented to the cast with a thin film of sandarac varnish or 
 Le Page's glue, which thus affords a metallic surface against 
 which the vulcanite is molded. 
 
 DENTURE BASES PRODUCED BY ELECTRO-DEPOSITION OF 
 GOLD AND SILVER 
 
 Denture bases fonncd li\- electro-deposition of gold, and 
 also of gold combined with silver, have at various times been 
 
113(; A imilOK HlSTOliY OK I'KOSTHI'rnC IJKNTlSTItV 
 
 tricil, lint Avitli iiKlilTcrciit success. Metal (le|insileil l)y this 
 pi'ocess lacks tli(> cohesiveness of either casi (ir idlleil plate, 
 and although beautiful results and gcxMl adaptation may he 
 secui'ed, unless the hase is formed \'ery hea\y, so thick, in 
 fact, as to he ohject ioiiahle. it will fractui-e rea<lil\' under 
 stress. 
 
 ARTICULATORS 
 
 The i)!'o,iiress of improN'cment in articidntors. or, more 
 correctly, occliidnig fruitn'ti, is extremely interesting. The 
 development of this appliance, which is practically indispensa- 
 ble in the correct occlusion of teeth, has been retarded because 
 of lack of accurate knowledge of mandibular movements, or, 
 more exactly, those movements of the mandil)le concerned in 
 the frictional contact of the lower against the upper teeth. 
 Without a fundamental and exact knowledge of these move- 
 ments, it is im])ossible to construct an a]ipliance whicli will 
 rejiroduee them. 
 
 Even with present estalilished ihita, there is no appliance 
 yet devised that will i-eproduce all of the varied essential 
 movements discerned in every individual with exactness, but 
 some approach very closely the desired re(iuirements. ()\\\y 
 a brief outline of those appliances most familiarly known can 
 be given here. 
 
 A metl'.od of building a distal extension to eacji cast, the 
 first ha\'ing notches oj- deiiressions into which the ))laster of 
 
 CASTS lO.X'I'UNDEU iHSTAl.l.V T(l FdKiM AltTUM! LATiXd SUIU'WCES 
 
 the opi)osite side was filled, to serve as guides, constituted the 
 first articulator. 
 
 J. B. Grariot is ci'edited with having invented the tirst den- 
 tal articulator in ISO.l. An extended search through dental 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTKY 1137 
 
 literature by the writer has faih'd to (lisrh)se more than a 
 mere mention of the fact as stated. 
 
 Ill 1840, Dr. Daniel T. Evans of Phihidelphia patented an 
 articulator in which an eH^'ort was made to i-eprodnce tlie hit- 
 eral movements of the mandilih'. 
 
 THE E\ANS AXATOMU'AI. ARTUTLATOIl 
 
 The distance between the condyle slots of the frame was 
 less than the average, while the center of rotation in lateral 
 movements was located in the center of the frame. 
 
 In 185.S. Dr. W. G. Bonwill introduced his "Anatomical 
 .Vrticulator. " and presented his theory of the equilateral tri- 
 angular relation of the mandibular condyles and the lower 
 central incisors. lie claimed that by such an arrangement it 
 was clearly Nature's plan to thus provide a more perfect bal- 
 ance for the masticatory app)aratus in lateral movements ; that 
 these movements were most effective in the reduction of food, 
 and that dentures should be so constructed that the mandibu- 
 lar muscles could perform their functions in the same manner 
 as when the natural teeth were present. 
 
 Ilis tlieories, although in the main correct, aroused con- 
 si(lei-al))e antagonism, because, in many cases, the results he 
 claimed couhl be dt>rived fi'oni the use of bis articnlator were 
 not realized. 
 
 Tins was largely due to ignoring the variation in pitcli 
 of condyle jniths of different iiulividuals, and in an inaccurate 
 metlioil of mounting casts on the articulator. 
 
1138 A BRIKF HISTORY OK I'KOSTHI'ITU: DENTISTRY 
 
 J)i-. I)Oii\vill \v;is ii iijitni'al horn ])r()slliotist iiiid in tlio 
 analomie Held overcame, by intuition, the obstaeies resnltin,n' 
 fidni his imperfect appliance, fn liis euthusiasm he failed 
 
 I. AiniriI.AT(JK 
 
 to recognize the limitations of the articulator, or to realize 
 that it was his intuitive skill and not the appliance that was 
 resi)onsible for much of his success. 
 
 His persistent effort in tliis field for more than forty 
 years finally aroused the interest of various investigators. 
 
 PLAIN LINE OR COMMON ]IIN(!E AltTUT l.ATdl! USEIi I'dl! MANY YEARS 
 
 with the result that to-day the problem of anatomic occlusion 
 has almost reached solution. The anatomic method of den- 
 ture construction is a reality, established on a practical work- 
 
A BRIEF HISTORY OP PROSTHETIC DENTISTRY 1139 
 
 iiig basis, and its great iiujiortaiicc and value are gradually 
 becoming recognized by the profession iu general. 
 
 In 1868, Dr. E. T. Starr devised an articulator, having a 
 latei'al movement, with horizontal condyle initlis. 
 
 THE SiTAKU ARTIClI.ATnlt 
 
 In 1889, Dr. Richmond 8. Hayes introdnced an articula- 
 tor having a lateral movement and with inclined condyle paths. 
 From the Patent Office drawings of this appliance it appears 
 that the condyle ]iaths inclined too steeply and were not ca- 
 pable of adjustment. 
 
 THE HAYES .iETICULATOK 
 
 As a matter of fact, a practical method of registering the 
 human condyle paths had not yet been discovered, nor had the 
 importance of such registration been recognized, so that ad- 
 justable conilyle paths were not even considered. Dr. Hayes 
 
1140 A BKIKK HISTORY OK I'l{OSTHETI(' IJKNTISTIiY 
 
 also (l('\'is(Ml a cniilc scirt oT I'acc how For cslaMisliini; I lie cor 
 reel disfancc of casls rroiii I lie rraiiH' hinges. 
 
 FIRST SUGGESTION OF THE FACE BOW 
 
 l'i-('\'i()iis to this tiinr. Dr. 'I'. L. (Jilmci-, in a paper |)r(' 
 sented before tiie Illinois .State Dental Society, in 1882, sus'- 
 gested measurement of the distance from condyles to tlie 
 middle of the npper jaw so lliat casts miuht lie mounted a cor- 
 responding distance fi-om (he articulator hinges, thus a\oid 
 in:;- disturbance of occlusion in fracture cases. 'I'his in reality 
 was (Mpiivalent to the use of a face how. 
 
 STUDY OF CONDYLAR IVIOVEMENTS 
 
 In 188!», J)rs. liowditch and Luce of Ihirvard, Conn., con- 
 ducted a series of exjieriments to determine detinitel.v tlie 
 condylar movements of the mandible. The results of these 
 experiments were ])ul)lisheil in the Boston Medical and Sui'- 
 gical Journal of tiiat year, hut imt heiny re])rinted in any of 
 the dental .iournals, were not hrouuiit ])romiuently to the at- 
 tention of the profession. 
 
 WALKER'S RESEARCH WORK 
 
 In 1895. Dr. W. K. Walker, without knowin,": of the work 
 of Bowditch and Jjuce, carried out a similar line of investiga- 
 tion, and arrived at i)ractically the same results. Just what 
 he strove to and did accomplish can best be stated l)y (|Uot- 
 ing from one of his ))apers, published the following year: 
 
 "Up to that time T had not been able to find menti(m of 
 the facts which I had observed that, in the movements of mas- 
 tication, the mandibular condyle moves 'not only forward, 
 but downwai'd also, causing the ramus to drop in the anterior 
 and lateral excursions of the mandible, ' and that the condyl<> 
 on the side toward which the jaw is advancing, in the lateral 
 excursions, does not merely 'rotate on its axis,' otherwise 're- 
 maining stationary,' as we are taught, ))ut that it also moves 
 l)oth upward and backward, very slightly, it is ti'ue, in many 
 subjects, and not at all in some, but iiuite c()nsideral)ly in 
 others." 
 
 The discovery of this fact led to another liitherto unreco.g- 
 nized fact, viz., that the lateral rotation centers of the man- 
 dibl(> mav or mav not be located in the condvie centers. 
 
A BRIEF HISTORY OF PROSTHKTIC DKXTISTKY 
 
 1141 
 
 WALKER'S ANATOMICAL ARTICULATOR 
 
 \\'alkcr (li's'n;iic(l ail atiafoinical articiilalor. Iia\iii,i;' Ixitli 
 adjustable condyle patlis and varialilc rotation (■enters wliieli 
 could 1)0 set in aeeordanee witli records olitained in each in- 
 dividual ease. 
 
 'i'liese records were secured iiy means of another api)li- 
 ance he devised and called a "facial clinometer." In 
 the light of our present knowledge, a prosthetist familiar with 
 the ])resen1 day ap])liances, if given the AValker articulator 
 
 
 1 1*^ 
 
 1 
 
 ■ 
 
 
 
 A, 
 
 1^1 
 
 l^^^l 
 
 
 ■■^si^^^ 
 
 — 
 
 ^ ^ J^l^s^^l 
 
 
 
 ^n 
 
 
 1 ^ 
 
 ' 
 
 ^^^ '' m 
 
 1 
 
 1^ 
 
 
 iM 
 
 
 L' 
 
 JHI 
 
 \i, .uiTini.ATdi; 
 
 and clinometer and a Snow face how, could construct anatomic 
 dentures e<jual to those constructed by any other system. 
 
 Practically the only essential ])oint which Walker over- 
 looked was the importance of and necessity for setting the 
 casts on the occluding frame so that their alveolar planes 
 sustained a similar relation to the frame hinges that the 
 natui'al alveolar i)lanes did to the condyles. Although he does 
 not exi)lain how he mounted the casts on the frame, it is more 
 than likely that he followed Bonwill's method of cali])ering — 
 setting them so that the calii)ers registered four inches from 
 each rotation center, to the i)osition to be occupied by the 
 
1142 A BRIEF HISTORY OP PROSTHETIC DENTISTRY 
 
 iiH'sio-iiicisnl angles of I lie Uiwcf ccnli-al incisors, wiicii 
 occluded. This inctliod, alUioui^ii decidedly liellei' tliaii tlie 
 usual plan of qiiessirig the proper position oi" tiie casts, pro- 
 vided for neitluM' iMM'pcudicular nor horizontal ))laiie relation 
 ship and tlievefore led lo errors. 
 
 WAUCEB'S FACIAL CLINOMETER 
 
 Walker's efforts were more far-reaohing and valuable 
 than he himself or the profession realized at the time, but on 
 the foundation which Bonwill laid, and he strengthened and 
 added to, the present system of anatomic occlusion of artifi- 
 cial dentures rests. Three valuable papers by Walker on 
 mandibular movements and methods of registering them ap- 
 peared in the Dental Cosmos, in 1896-7. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 In 189-1: Dr. C. E. Bixby desigiied an attai-hincnt for 
 moiuitiiig casts on a plain line artieixlator. 
 
 This device regulated the correct antero-posterior posi- 
 tion. I)ut j^rovided no means for establishing the horizontal 
 
 THE BIXISY ATTACIIMlCN'l' 
 
 ])lane relationship. It, however, was a forerunner of the face 
 bow. 
 
 GRITMANS ARTICULATOR 
 
 In 1899, Dr. A. D. Gritman introduced an improved form 
 of ai-ticnlator, having the same general proportions as the 
 Bonwill, but more rigid, and with condyle slots set at an angle 
 
 THE liniTMAX AltTKIT.ATdR 
 
 of al)ont 15 degi'ees slant. In this, as in all articulators hav- 
 ing fixed condyle paths, the pitch of the path of the frame was 
 often increased or decreased in moimting the casts on the 
 frame, depending on the thickness of the cast and the care used 
 in mouutini'- them. 
 
144 A BKIKK lllSTOIiV OK l'K( )STH KTIC DKNTISTHY 
 
 SNOWS FACE BOW 
 
 In llic saiiic \c;ii-, Di-. (icoriAc 15. Snow (if llic I'liiNcrsitv' 
 if I'lilValo inli'odiircil llic fdci' linif. a calii)!'!- likr i|c\icc used 
 
 T 
 
 
 ^'IT^'*'^' 
 
 
 c f^ '6. 'd i,^^^^. " 'J, c_ A 
 
 H- 
 
 \ 
 
 '■ c. 
 
 ill inouiitiug casts on the occliidino- frame. This device is one 
 of the most valualiU^ ac(|uisitions in the anatomic field. By 
 means of this api)liance, correct antero-posterior, as well as 
 
 THE KERI! ANATdMlCAr. ARTK Tr.ATdR 
 
 ix'rpeiidicuhtr ami liorizoiital i)hiii(', rehitioiislii]! of casts to 
 frame hinges can be estahlisiied. As a result, when teeth are 
 arranged on occlusion models, clearance paths for the cusps 
 
A RKIKF HISTORY OF PROSTHETIC DKNTISTKY 114.') 
 
 (if the liiwcr lncusi)i(ls and ludlai-s hctwccn tliosc of the upper 
 teeth can be develoix'd, so tliat in latcnil cxiairsidns there is 
 no marked interference. 
 
 THE KERR ANATOMICAL ARTICULATOR 
 
 In IMOl' th<' Ken- lirothei-s of Detroit inti-odneed an an- 
 atomical ai'tienhitor haxint;' adjustahh' condyle paths and a 
 latftral movement. The first frame was arranged witli hinges 
 about on the same plane as the occlusal plane of iii)])er cast 
 when mounted, the idea lieing to copy the c(Miter of rotation 
 of the mandible in wide open movements. 
 
 p'or oltvious reasons this was found incorrect, and the 
 design of the frame changed to the form shown on page 1144. 
 
 CHRISTENSEN'S WORK 
 
 111 lilOi'. Dr. Carl Christeiisen of ( 'ojienhagen, Denmark, 
 disco\-ered a simjile method of recording the condyle i)alhs in 
 
 THK rllTlI.STF.XSEX AXATCIM ll-.M. A It'l UTI.ATOR 
 
 the living subject, and devised an articulator having adjust- 
 able condyle paths which could be set according to such regis- 
 tration. (See i)age 337.) 
 
 SNOW'S ANATOMICAL ARTICULATOR 
 
 In 1906. Dr. Snow imtiroved the (iritman articulator by 
 converting the fixed into adjustalile condyle jiatlis, and api)ly- 
 ing a tension si)ring which ])erniitted a greater range of niov(»- 
 ment without impairing the stabilitv of the frame. 
 
 riiristensen's method of registering the cotkIvIc jiatlis in 
 
1146 A HRIIOK HISTORY OK I'KOSTIl KTIC DKNTISTKY 
 
 coiijiiiicl idii witli llic use (iT the Siiow "Xcw Cciitm-y Arlicu 
 hitor, " and llic J'acc 1mi\v, sni>i)ly the means I'or cunsl rnctin.i;' 
 dentures anatomical iy and is to a great exicnl Hie system 
 mosl n'eiierallv iti'aclii'fd and 1aiif>iit in this rniiii1i-\-. 
 
 (TT SUOWIXU COllPEXSATINIi ITTtVE (criJilSTIiNSKX) 
 
 Dentures constructed by tliis method, when introduced in 
 the mouth, will perform essentially the same functions as the 
 natural teeth, and are capable of I'educing food witli less effort 
 tlian are those in which hinge action alone is i)ossiljle. 
 Furthermore, they are much less liable to displacement when 
 
 THE NEW CENTURY AIITII 'ULATOR (SNOW) 
 
 in use, as haluncing contact is one of the essential features that 
 in jiractically all cases can be attained. 
 
 The Snow Articulator, like the Ohristensen, Walker and 
 Bonwill appliances, has its rotation centers placed four inches 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1147 
 
 apart, which, arcordiiiy to rxjuwill's measurements, corre- 
 sponds witli tlie average distance from center to center of the 
 human condyles. 
 
 Wahver ch^arly proved that the lateral rotation centers of 
 the mandible, in some individuals at least, were located, not in, 
 but between the condyles at varying distances in different 
 cases. Others have since proven the truth of Walker's find- 
 ings, and in addition have shown that the rotation centers may 
 lay outside of the condyle centers as well. 
 
 Excepting the efforts of Ohristensen as noted, this de- 
 scription has been confined to what has been accomplished by 
 men in this country. It will now be in order to mention some of 
 the contributions to this subject by the members of the profes- 
 sion in Europe, whose interest was aroused by Bonwill's work. 
 
 In 1890, Graf von Spee, a German anatomist, called at- 
 tention to the curved arrangement of the occlusal planes of 
 the natural teeth and of corresponding curves in the con- 
 dyle paths. (See i)age -302.) 
 
 SCHWARZE'S ARTICULATOR 
 
 In 1900, Dr. Paul Schwarze of Leipsic constructed an 
 articulator somewhat on the order of the Bonwill appliance. 
 
 TIIK SCHWARZE ANATIIMICAI. AUTU'UI.ATOR 
 
 but having both a 'forward and downward movement to the 
 condyles. 
 
 In 1901, Tomes and Dolamore made a series of records 
 of condyle paths as disclosed by the hinge action, or opening 
 
1148 A HIUKF IIISTUKY OK I'ROSTUKTIC DIONTISTUY 
 
 and closing niiiiidilnilar inoxcnicnts. 'I'liose were of no special 
 value in a ])ractii>ai way, I'lirther tliaii to verify the research 
 work of Walker and others in reference to the downward pitch 
 as well as variations in the condyle ])aths. (See pajije 275.) 
 
 Parfitt, Constant, Cainpioii, Warnekros, Peckert and oth- 
 ers have contrihuted in various ways and at different times 
 to this most interesting suhject. 
 
 Recently Bennett has shown that there is an actual l)odily 
 side movement to the mandihle, which, although caused by 
 the muscles that induce lateral rotation, cannot l)e classed 
 as rotary. This is a most important recent discovery in 
 mandibular movements, and one which, in some cases, miglit, 
 with profit, be reckoned with in denture construction. 
 
 GYSrs WORK 
 
 In 1910, there appeared in the Dental Cosmos a series 
 of articles bv Dr. Alfred Gvsi of Zurich, Switzerland, de- 
 
 <IIVI.K ItlOCiSTKIt 
 
 scribing in detail various registering devices for recording 
 mandibular movements, together with many records, secured 
 by means of them. 
 
 The principal a])pliances shown are an (irticulator, a coii- 
 (l/flc path rpfj'istef. and an iiicism ixtth ref/isfer. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 114'J 
 
 The articulator has adjustahlc (•(hkInIc paths, and also 
 adjustable rotation centers, the niaxinunu distance between 
 which is tive and one-fourth inches, while the minimum dis- 
 tance is about two and three-fourths inches. 
 
 The condyle register as its name indicates, records the 
 inclination and curvature, if any exists, of the condyle |)aths, 
 on cardl)iiai(l, in such manner tliat the anyular inclination 
 
 I'ATH RKcaSTKIt 
 
 may be read and the condyle paths of the articulator set ac- 
 cordingly. 
 
 The condyle register also fulfills the saiiK purpose as a 
 face bow in mounting casts on the occluding frame. 
 
 The incisor ])ath register consists of a metal plate, at- 
 tached to the occlusal surface of the lower occlusion model, the 
 upper surface ol which is covered with a thin film of carbon- 
 ized wax. A small steel point, l)acked by a fine spring within 
 a socket, and attached to a small plate, is fixed to the labial 
 
A BRIKF HISTOllY OF PROSTHETIC DENTISTRY 
 
 surface of the upper occlusion model in such manner that 
 when tlio mouth is closed the point rests upon the waxed sur- 
 face of the incisor path register, which extends somewhat for- 
 ward of the labial surface of the baseplate. In lateral and pro- 
 trusive movements of the maiidil)le the point marks upon the 
 waxed surface the lines of travel of the mandible in the in- 
 cisal region. Later on, when the occlusion models are returned 
 to the casts on the articulator, the rotation centers of the 
 frame are moved to such position that the marker on the ujjper 
 occlusion model will follow the same lines it marked on the 
 waxed register during mandibular movements. By this 
 means the lateral rotation centers of the mandible are de- 
 termined and the centers of the articulator set accordingly. 
 
 Since 1910, Dr. Grysi has devised a lateral covdyle path 
 register, which records the bodily side movement of the man- 
 dible. The articulator condyle j)aths are so arranged that 
 they may be set to reproduce this movement to a fairly accia- 
 rate degree. (See page 465.) 
 
 The Gysi Adaptable Articulator, with accessory appli- 
 ances enable the careful prosthetist to register more of the 
 essential mandibular movements than can be accomplished 
 by any other available means. 
 
 Consequently, with such registration i)0ssible, and with 
 the generally improved methods in denture construction that 
 have recently been and are being developed, prosthetic den- 
 tistry is rapidly advancing into the field of an exact scientific 
 specialty. 
 
 LOWER SEOTIOX OF T.IK'K A Ullri I.A 1 OK. .SIHIUIM. 1K\CIN'0 
 KNOBS" IN I'OSITION ON LOWER OCCLUSION MODEL 
 
 Dr. C. E. Luce has designed an articulator in which cer- 
 tain anatomic movements may be reproduced as follows : 
 
 Round liead tacks, or ' ' tracing knobs, ' ' are pressed into 
 the lower occlusion model, the wax rim of the upper model 
 
A BRIEF HISTORY OP PROSTHETIC DENTISTRY 1151 
 
 softeiu'il, and introduced in tlic nionlli and the mandililc snl)- 
 jected to lateral movements. The round heads of the pniject- 
 iug tacks mark lateral paths iu the upper wax rim. 
 
 To use this appliance successfully, tlie casts should be 
 mounted on it by means of a face bow. 
 
 When so mounted, the hinge pin of the articulator is 
 removed, the eu]i situated immediately in front and between 
 
 the hinges lilled with softened modeling compound, the upper 
 bow of tile frauie carrying the cast and occlusion model is set 
 in position and subjected to lateral movements, the round- 
 head tacks guiding tlie direction of movement. During this 
 
1152 A liUIIOK HISTORY OK I'UOS'lM I KTlC DIONTISTliV 
 
 lateral inoA'ciiiciit, prnjcclions on the nndcrsidi' nf llic ii|ip('i' 
 1)()W, inini('(liat('l\' (i\('i- the liiiiiic cup, rm-iii pnllis in llic niod- 
 cliiiii' coniiioiuiil. 
 
 '^riiosc i)atlis in tlic cup rcjircscnt shorter ares of circles 
 than those in tlie ocelusion rims. They inwe, liowever, coiii- 
 moii centers. \iz., the centers of rotation of the niandilile. 
 
 ( »ii I'emovinn' tin' tacks from the ocolnsion rini the i)ins of 
 the franu'. restinn' ami nio\inn' in tln^ n'rooves in the compound. 
 
 UKTAIL.S UK .\RTIcrLATINi: ITl' 
 
 within the liinge enp gnide and control the lateral movements 
 of the k)wer a^'ainst the njiper ooclnsion moth'! on nuich tlie 
 same ])rinciple as a ])anta,i>'raph works. 
 
 CROWN WORK 
 
 The ])lacin!i' of ai'tilicial crowns on the roots of natural 
 teetli lias been practiced for hundreds of years, yet it is only 
 witliin the last half century that much advancement has been 
 made o\'er the lu■imiti^■e methods of Fauchard's time. 
 
 PIVOT TEETH OF DE CHEMANT 
 
 Pivot teeth of ])orcelain were mentioned hy de Chemant 
 in ^^()^2. althoniJ.h for manv vears after his time, teeth c;ir\-ed 
 
 from hone, ivory and various substances were used in single 
 crown replacements. Frequently, sound natural tooth crowns 
 were also used for this inirjiose. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1153 
 
 THE GROOVED FLAT-BACK FACING 
 
 In the early part of tlie last century, a porcelain facing, 
 grooved on the back, and with small strips of platinum baked 
 
 in the porcelain along the sides of the groove for attachment 
 to the wire pivot, was used both in Europe and this country 
 in crown work. 
 
 THE ASH TUBE TOOTH 
 
 The Ash Tube tooth, introduced about 1840, was used in 
 both denture construction and, to a limited extent, in crown 
 replacements. (See page 529.) 
 
 The recent articles, within the last two years, by Dr. 
 Girdwood, have shown the modern application of this type of 
 tooth to prosthetic restorations. (Dental Cosmos, 1914-1915.) 
 
 THE WOOD PIVOT TOOTH 
 
 A full contoured porcelain crown, with a circular open- 
 ing in the base for the reception of a wood pivot, was intro- 
 duced, probably between 1850 and 1860. This crown was at- 
 tached to the root by means of a wood pivot which fitted 
 tightly into both crown base and root canal. The pivot was 
 
 r R E P A R ATION (IF 
 ROOT FOR RECEPTIOX 
 OF r^ROWN AJfD DOW- 
 EI-. LABIAI, VIEW 
 
 forced to place while dry, and on absorbing moisture swelled 
 and firmly held the crown in position. The writer a number 
 of years ago removed two central incisors which had been 
 set in this manner eighteen years i:)revionsly, neither of which, 
 in that time, had required resetting. 
 
 THE SMITH CROWN 
 
 In 1844, Dr. J. Smith Dodge devised a crown which was 
 of similar form to the one just described, but in which a wood 
 
A BRIIOF HISTORY OF PROSTHKTIC DIONTISTRY 
 
 ^rOOO PLUG 
 
 DI!. J. DODGE SMITira CRf)\VN 
 
 pivot containing a metallic tube for a core to strengthen it 
 was used. 
 
 THE CLARK CROWN 
 
 In 1849, Dr. F. H. Clark devised a removable crown, which 
 was attached to the root by means of a metal dowel, split to 
 
 form a spring, for bearing against a metal tube firmly fixed in 
 the root canal. It was so formed as to afford drainage for pus 
 or vent for gas which might accumulate in the pulp chamber. 
 
 THE LAWRENCE-FOSTER CROWN 
 
 In 1849, Dr. Henry Lawrence invented a porcelain crown 
 having an opening extending through from base to lingual 
 
 DR. HENRY I-AWTtKNTES 
 
 CROWN. AFTERWARD 
 
 CALLED THE •■l.'dSTER" 
 
 CROWN 
 
 surface. It was held in place by means of a screw anchored 
 within the root canal. 
 
 This crown was afterward known as the "Foster" Crown. 
 
A BRIEF HISTORY OP PROSTHETIC DENTISTRY 1155 
 
 THE DWINELLE CROWN 
 
 In 1855, the American Jonrnal of Dental Science con- 
 tained a description by Ur. W. H. Dwindle of a gold baud 
 \\\t\i floor, iitted to a tooth with vital pulp, and held in place 
 
 THE D WINELT-E 
 CROWN FOB VITAl, 
 TEETH AND NON- 
 VITAL TEETH 
 
 by means of two screws passing through the floor and into the 
 dentin. The "tubbing." or gold-bound cavity, was filled with 
 crystal gold, while to the labial or buccal surface of the band 
 a porcelain facing was affixed. 
 
 This same principle was also applied in the crowning of 
 pulpless teeth, the crown being held in position by means of 
 
 THE DWINELLE CEOWN FOB VITAL TEETH 
 
 a screw anchored within the pulp chamber. The five cuts show 
 the Dwindle method of attaching a porcelain-faced ferrule 
 crown to the stub of a vital tooth with crystal gold. 
 
 This work of Dr. Dwinelle is about the first reference 
 found of combining gold and porcelain in the restoration of 
 lost natural crowns. 
 
 THE WOOD CROWNS 
 
 In 1862, Dr. B. Wood describes the restoration of de- 
 fective teeth by the application of enamel caps. These were 
 
 B. WOOD'S -ENAMELED CAP" CROWNS 
 
 formed by fusing to platinum caps, previously fitted to the 
 teeth, some form of enamel, probably such as jewelers used. 
 
A BRIEF HISTOltY OP PROSTHETIC DENTISTRY 
 
 Willi 
 
 •lili>ri( 
 
 These caps were cemented in \>\i\i 
 or attached with gutta ix'iclia. 
 
 Dr. Wood also constructed tliin gold crowns with interior 
 staples by means of wliieh anchorage to the teeth was secured 
 
 f*?" 
 
 THIN GOLD CM' t'llOWNS DESCItlP.ED ItY DH. li, WOOD 
 
 with cement. These crowns, because of their thin walls, were 
 more or less unstable. 
 
 THE MORRISON CROWN 
 
 In 1869, Dr. W. N. Morrison described in the May number 
 of Missouri Dental Journal a gold shell, two-piece crown. This 
 
 GOLD SHELL CliOWX CONSIIHlllD \M> 
 DESCniBED P.V DR. W. \ MOUniSO% 
 
 IN ISGO 
 
 crown was substantially the same as is constructed to-day 
 and is quite generally known as the "Morrison Crown." 
 
 THE BLACK CROWN 
 
 In the June nuuilicr of the same journal. Dr. G. V. Black 
 described and illustrated the construction of a porcelain-faced 
 
 crown for an anterior tooth, held in place by means of 
 screw passing into a gold-lined root canal. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1157 
 
 The similarity between tliis and the erown Dr. Richraoiid 
 patented years afterward is obvions. 
 
 THE BEAN CROWN 
 
 In the duly nuniher, IS*)!), of the American donnial of 
 Dental Science, Dr. J. B. Bean described a porcelain-faced re- 
 
 CROViT^' rONSTRU('TED 
 AKD DESCKIBED BY 
 
 DR. J. B. BEAN IN 
 18G9 
 
 mo\able crown tlie dowel of which was split and received 
 within a permanently fixed tube in the root canal. 
 
 THE MACK CROWN 
 
 In 1S72, Dr. (Hias. If. Mack designed a pivot tooth liaving 
 a dovetailed depression in the base of the crown. 
 
 THE MAIK c'li<>\V> 
 
 Metal i)in"s, roughened, were first fixed in the root 
 of the tooth and the crown attached with cement or amal- 
 gam. 
 
1158 A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 THE BEERS CROWN 
 
 In 1873, Dr. J, B. Beei-s of Oalifoniia patented a gold cap 
 crown practically the same as described some four years pre- 
 viously bv Dr. Morrison. 
 
 Till! BEERS CKOWN 
 
 THE GATES CROWN 
 
 In 1875, Dr. W. H. Gates devised a "vertically open con- 
 tour crown," composed of metal and porcelain, designed to 
 be held in place with cement. In this, as in the Mack crown, 
 
 THE GATES CHOWN' 
 
 the dowel was first permanently set in the root canal and 
 the crown adjusted and attached later. Manufacturing diffi- 
 culties, however, prevented its introduction and use. 
 
 THE RICHMOND CROWN 
 
 In 1880, Dr. C. M. Bichmond designed a porcelain-faced 
 crown backed with metal and held in place on the root by 
 means of a screw similar to the crown designed by Dr. Black. 
 
 An internally and externally threaded tube was fixed in 
 the root canal, the crown formed with a groove in its lingual 
 surface for the passage of a screw which entered the tube 
 within the root, and by means of which it was lield in place. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY lloO 
 
 THE mcllMOND CROWN 
 
 THE IMI'HOVEI) RICHMOND CROWN 
 
 A cap diaphragm rested upon the root end and over this 
 the crown hase, also of ca]i form, telescoped. 
 
 THE GATES-BONWILL CROWN 
 
 In 1881, Dr. W. CI. A. Boiiwill desiiined a crown wholly 
 of porcelain having a central opening- slightly enlarged at 
 either end fonr the reception of metal dowel. 
 
 /\mm 
 
 THE OATES-BONWILIi CROWN 
 
 These crowns were set with an amalgam specially pre- 
 pared by Dr. Bonwill. Both three-sided and triangular metal 
 dowels were iised. 
 
 The specifications of the Mack patents, issued six years 
 previously, were so broad that they covered the principle of 
 this crown. Therefore, when placed upon the market it was 
 given the name of the "Gates-Bonwill Crown." 
 
1160 A BRUOP" HISTORY OF PROSTHETIC DENTISTRY 
 
 THE BUTTNER CROWN 
 
 Til 1SS1, "Or. W. II. r.iiltiici- pntcnlcd a scf of appliances 
 i'oi- rcdiiciinj;- the mmiI iH'ii|ilici'\ (if a Idtith \u a iiniroi'in cylin- 
 
 
 ||1 111 
 
 I ji 
 
 TUB BUTTNKIl SYSTEM OF CROWN CONSTRUCTION 
 
 dor. fitting a doep-sided doTvel cap to same and root canal and 
 attaching a porcelain facing to tlie base so formed. 
 
 THE HOW CROWN 
 
 In 1S83, Dr. W. S. How designed what was called the 
 "fonr-pin crown." These pins were set within a depression 
 on the lingual surface of the facing, were folded aronnd a 
 
 § 
 
 '"'i? 
 
 tmi 
 
 THE HOW FOUll-I'lN CROWN 
 
 threaded dowel fixed in the root canal and tlie lingual con- 
 tour of the tootVi developed in amalgam. 
 
 Dr. How also designed the Dovetail Crown in 1889. 
 
 THE WESTON CROWN 
 
 Tn 1883, Dr. Henry Weston designed a "porcelain pivot 
 crown" having two pins located in a depression on its lin- 
 gual surface for the reception of a cross-head dowel. The 
 dowel and facing were attached with solder and the crown 
 attached to the root by gold, cement or amalgam. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1161 
 
 Another form of ci'own devised by Dr. Weston consisted 
 in a more fnllv contoured iiorcelaiii faciiii;', in wliicli the (hiwel 
 
 WESTOXS ntdSS lIKAli DOWLI I'BOWN 
 
 WESTON'S FIXED IIOWEI, IROWN 
 
 was baked. This crown was secured to the root in the same 
 manner as was the preceding crown. 
 
 THE LOGAN CROWN 
 
 In 1885, Dr. ]\I. Ij. I^ogan devised a full contoured porce- 
 lain crown having a ]ilatinum dowel permanently fixed within 
 its base. 
 
 THE LOiiAX I'liOWN" 
 
 This crown has, almost from its introduction, been ex- 
 tensively employed and has proven most serviceable as a sub- 
 stitute of the fixed dowel type. 
 
 THE BROWN CROWN 
 
 In 18!M), Dr. E. Painily T.rown designed a crown very 
 similar to tlie "Logan," iiut with a convex instead of a con- 
 cave base. 
 
 THE E. PARMf.V P.I'.nWX CIIOWX 
 
 AVithin recent years many forms of detached dowel 
 crowns have l>een introduced, which, because of comparative 
 ease of adaptation, are fast coming into favor, both as crown 
 
1162 A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 rfiplaceinents and lor use in liriilgx' and di-nture work as 
 well. 
 
 Among these may be mentioned the Davis, S. S. White, 
 Justi, Brewster Twentieth Century, illustrations of which are 
 found elsewhere. 
 
 An analysis of the various means I)y which crowns, Itotli 
 ancient and modern, are fixed to natural teeth and roots shows 
 but two general principles of attachment, viz., with dowels, 
 the telescoping principle, or a comlnnation of tlie two methods. 
 
 Much of the material contained in the foregoing history of 
 crowns has been obtained from a monograph published by 
 the S. S. White Dental Manufacturing Company, entitled 
 "Origin and Development of Porcelain Teeth," and from vari- 
 ous articles which have apjieared from time to time in the 
 Dental Cosmos. 
 
 BRIDGEWORK 
 
 Modern bridgework, of a practical character, is of very 
 recent origin as compared with dental procedures in general. 
 
 Dental literature of modern times contains scarcely any 
 reference to bridgework previous to 1869. 
 
 In addition to the three greatly improved crowns pre- 
 sented by Drs. Morrison, Black and Bean in that year, Dr. 
 Bennett described, in the Dental Cosmos of October, 1869, 
 a method of bridging in the space of a single missing tooth as 
 suggested by Dr. B. J. Bing of Paris. 
 
 THE BING BRIDGE 
 
 This method consisted in preparing cavities in the teeth 
 proximating the space, fitting a square bar across the space, 
 its ends resting within the cavities, and by suitable steps 
 
 adapting and soldering a facing to the bar. The appliance 
 was fixed by packing gold foil into the cavities and around 
 the bar ends. 
 
A BRIEF HISTORY OF PROSTHRTIC DENTISTRY 11C2 
 
 DR. WEBB'S WORK 
 
 In 1873, Dr. Marshall II. Webb suggested a modification 
 of the Bing method, consisting of a flattened "two stop back- 
 ing and saddle," and in 1879 a "stop post," consisting of a 
 
 MODIFICATION OF THE BING BRIDGE (WEBB) 
 
 facing attached to a rigid wire staple, the ends of which were 
 anchored within the root canals of the proximating teeth. 
 
 In both cases the stops were surrounded by and anchored 
 within gold foil filling in the cavities of the adjoining teeth. 
 
 DR. LITCH'S WORK 
 
 In 1880, Dr. Wilbur V. Litcli suggested two modifications 
 of the Bing bridge. The first was called a "wing plate," in 
 which the backing was extended beyond the dummy so as to 
 rest upon the lingual surfaces of the proximating teeth. Per- 
 forations were then made in the wings and corresponding 
 
 DK. LITCU'S FIRST MODIFICATION OF THE BING BRIDGE 
 
 holes in the teeth, through the enamel, and as deeply in the 
 dentine as practicable, without endangering the pulp. 
 
 Headed platinum pins were passed through the plate 
 into the holes, the relation between backing and pins secured, 
 the case invested' and the pins soldered to the wings. The 
 substitute was set with cement. 
 
 The second modification consisted in devitalizing either 
 one or both teeth and extending dowels through the wings into 
 
11fi4 A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 tlic n.ot canals. Ij will he imrM-cd llial holli Di's. \Vel)!> and 
 l;ilcli increased ilic anclioran'cs of ilic diiiiiniics li\' root dow- 
 
 0''''h\^ 
 
 DR I.ITCirS SECOXI) JIUIUKUATll LN (IF THK lilXG ISl'.IDGE 
 
 els, being impelled to do so l)eeanse of failures iu their first 
 attempts. 
 
 DR. WILLIAMS' WORK 
 
 In 1884, Dr. J. Leon Williams, in the Dental Cosmos, 
 called attention to the neeessitv for more sta1)le anchorage for 
 
 MODIFIED KICHAEDSOX CROWN (WILLIAMS 
 
 bridges and suggested the use of a modified, so-called, Eich- 
 mond crown, wliich, in a general way, represents a common 
 type of porcelain-faced crown of to-day. 
 
 FOUR-TOOTH ANTERIOR BRIDGE (\VIMiI.\MS) 
 
 ""'"^ \s.^X^*^-^ 
 
 This article was followed, the next year, with illustra- 
 tions and descriptions of two very practical bridges by the 
 same writer. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1165 
 
 Dr. Williams remarks, in Jamiarv Cosmos, 1884: "As 
 the single crown is the beginning and the end of all bridge- 
 work, a description of that particular form, which is of the 
 greatest practical value, will be necessary. This is known as 
 the Richmond crown, though not the crown he claims as his 
 invention. It consists essentially of three parts — a pin 
 [post .n which enters the root canal; a root cap of gold; and 
 a porcelain face, which is the ordinary plate tooth." 
 
 It is evident that our modern system of bridgework could 
 not have been possible without the evolution of suitable crowns 
 for supporting the same. 
 
 DR. STARR'S WORK 
 
 In the Dental Cosmos, 188(i, Dr. R. Walter Starr de- 
 scribed a difficult case of restoration in which two removable 
 l)ridges were successfully applied. The telescoping crown 
 ])rinci]ile is here mentioned for the first time. 
 
 EEMOVABLE BRIDGES BY DB. STARB. ISSi; 
 
 In 1887, Dr. Starr suggested a modification of the Bing 
 bridge tooth, consisting of a porcelain tooth with two parallel 
 bars extending through it by means of which the projecting 
 ends of the substitute were anchored within fillings placed in 
 the proximal ing teeth. 
 
 The names of Drs. Cryer, Starr, Ilodgkin, E. Parmly 
 Brown, EoUo Knapp, Stowell, and Rhein are associated with 
 
1166 A BRIEF HISTORY 0I<" PROSTHETIC DENTISTRY 
 
 the early history of recent bridge methods, nearly all of 
 whom presented modilications of the Bing bridge. 
 
 Drs. Williams, Eichmond and Knapp seem to have been 
 among the first to reeognize the necessity for the use of 
 
 STARR'S MODIFICATION OF THE 
 BING BRIDGE. 1887 
 
 stronger and more hygienic abutments in bridge appliance, 
 although no doubt many others were coming to recognize the 
 same fact. 
 
 In 1888 Dr. Sidney S. Stowell described an extension 
 stop-supported bridge, similar to those frequently constructed 
 
 TWO-TOOXn STOP AND SADDLE BRIDGE 
 
 to-day, except that with present methods the stop rests in a 
 depression within an inlay instead of being enclosed within a 
 filling, as described by Dr. Stowell. 
 
 BASIS OF OUR PRESENT SYSTEM OF BRIDGEWORK 
 
 The crowns of "Wood and Dwinelle in the "50's" formed 
 the basis. The great improvements by Morrison, Black and 
 
A BRIEF HISTORY OP PROSTHETIC DENTISTRY 1167 
 
 Bean, in crowns, and the appearance of the Biug bridge tooth, 
 all of which were presented in 1869, although crude, furnished 
 the necessary elements which had previously been lacking. 
 
 Further improvements in crowns, the development of 
 various forms of dummies, together with simplitied' technical 
 procedure, gradually followed, but only after many failures 
 and a considerable lapse of time. 
 
 It is singular to note that practically all of the pioneers 
 in bridgework failed to recognize the heavy stress in mas- 
 ticatory effort delivered against bridge replacements. Neither 
 were the limitations in regard to resistance of stress of the 
 materials employed well understood. 
 
 This lack of knowledge of the strength of materials used, 
 together with an indefinite or exaggerated idea of the ca])acity 
 of natural teeth or roots for performing their own work and 
 carrying the additional burden imposed by the replaced teeth 
 were some of the discouraging features. 
 
 Peridental troubles, the splitting of roots and recurrent 
 decay of the abutment and pier teeth and roots were of fre- 
 quent occurrence. 
 
 A recognition of these facts, which could only be gained 
 by experience, led to further improvements in crowns of 
 greater strength and of more hygienic form and in more judi- 
 cious selection of cases for substitutes of this type. 
 
 PORCELAIN BRIDGE 
 
 Baked porcelain crown and bridge work went through a 
 similar jn'ocess of trial, failure and development before the 
 limitations in this field were finally determined. The principal 
 
 PLATINUM FRAMEWORK FOR PORCELAIN 
 BRIDGE (SCHWARTZ. 1902) 
 
 failures were due to insufficient strength to the metal sub- 
 structure and deficient bulk of porcelain. One of the pioneers 
 in this field was Dr. G. W. Schwartz of Chicago, who was en- 
 gaged in the production of porcelain crowns, bridges and in- 
 lays as early as 1893. 
 
1168 A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 While to-day, tlie application of fixed bridgework is not 
 as extensive, the results of such application at the ])resent 
 time are generally far more satisfactory than in the past. 
 
 REMOVABLE BRIDGES 
 
 Bridges of the remo\'able type, and partial dentures sup- 
 ported by saddles resting upon the alveolar process, retained 
 in position by some of the various forms of fractional appli- 
 ances, are now introduced in many cases where formerly 
 bridges of the fixed type were a])pli('d. 
 
 INLAYS 
 
 An inlay, in its dental meaning, refers to a filling com- 
 posed of some dense material, constructed outside the tooth 
 cavity, and which is held in position in the cavity by some 
 adhesive medium. 
 
 FIRST RECORDED ATTEMPTS IN FILLING TEETH 
 
 The first attemi)ts at filling teeth must naturally have 
 been extremely crude, and the results of the ])ioneer efforts 
 in this field have ])roved but temporary in character. Be- 
 cause of the difficulty in adapting dense materials, the first 
 fillings were undoubtedly of the ])asty, plastic or pitchy class. 
 
 Mastic and alum, a substance of this class, was recom- 
 mended for filling carious cavities, by Rhazes, a Persian phys- 
 ician, about 850 A. D. (Guerini). Frequently medicinal agents 
 were incorporated with the mastic base for the purpose of 
 arresting the progress of decay, myrrh, sulphur and tur- 
 pentine being mentioned in this connection. The comfort 
 derived from the use of such stoppings, although only of tem- 
 porary nature, gradually led to the general practice of filling, 
 and the use of more permanent materials. 
 
 Mesu, an Arab surgeon, in the latter part of the eighth 
 century recommended the use of gold foil for filling teeth, 
 while from the thirteenth century on various writers mention 
 the use of both gold and lead for this purpose. 
 
 FIRST MENTION OF INLAYS IN DENTAL LITERATURE 
 
 In 1()90, Pierre Dionis, a surgeon of Paris, in discussing 
 the filling of teeth, says: "For this purpose, gold or silver 
 leaf is made use of; but this method of stopping is not dur- 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1169 
 
 able, liecaiise gold or silver leaf is apt to become loosened 
 and fall out. It is tberefore preferable to make a stopping 
 with a piece of gold or silver corresponding in size and shape 
 to the cavity. Many prefer lead on account of its softness, 
 while others simply use wax." (Guerini.) This is the first 
 definite reference to the inlay method of filling teeth, so far 
 as the writer knows, in any of the old-time treaties on dental 
 procedures. 
 
 In 1718, Lorenz Heister, a German surgeon recommended 
 the filling of teeth with various substances. In reference to 
 crown cavities in molar teeth he recommends gold or lead leaf, 
 or a piece of the latter fitting into the cavity. (Guerini.) 
 
 Unfortunately, few specimens of ancient inlay work are 
 in existence, and the genuineness of such as are preserved is 
 questionable. 
 
 PREHISTORIC INLAY WORK 
 
 In the Peabody Museum of. Harvard University is a pre- 
 historic skull, in the central incisors of which are inlays of 
 green stone. This specimen was found a few years ago 
 among the Aztec or Toltec ruins, near Copan, Honduras, by 
 Professor Owen. Whether these inlays were placed in the 
 teeth to correct the ravages of decay or merely for ornamental 
 purposes cannot, of course, be determined. 
 
 THE BEGINNING OF MODERN INLAY METHODS 
 
 Authentic records of inlay work in modern times date 
 back only about one hundred years. At the beginning of this 
 period, tin, lead and gold, in the form of foil, were the only 
 metallic fillings in use. Amalgam had not yet been introduced. 
 It came into vogue as a filling material, under the name of 
 "silver paste," about 1825, but for years was looked upon 
 with disfavor and used to a very limited extent. Cohesive 
 gold was not introduced until 1855, and therefore, since none 
 of the foils were cohesive, extensive contour restorations 
 were impossible. Added to these difficulties, the general dis- 
 like on the part of patients to the display of metals in the 
 mouth, rendered the filling of teeth a discouraging and often- 
 times unsatisfactory, jirocedure. 
 
 It is not surprising, therefore, that efforts were early 
 made to find a material for filling operations less obiection- 
 able in appearance, and easier to manipulate than the metals. 
 The records of these attempts are scattering and difficult to 
 
1170 A BRIF^P" HISTORY OF PROSTHETIC DENTISTRY 
 
 find. Many efforts in inlay work, and probably some reason- 
 ably successful results, were without doubt never disclosed, 
 because, as a rule, the pioneer practitioner kept his methods 
 a secret. 
 
 Such early records as are available are usually found in 
 little handbooks, published in the early days by the prac- 
 titioner, and intended for circulation among prospective pa- 
 tients. Later on, the dental journals from time to time con- 
 tained descriptions of inlay methods, as they developed. 
 
 BRIEF SUMMARY OF INLAY WORK, BEGINNING WITH 1820 
 
 In 1902, Dr. Walter W. Bruck of Breslau, Germany, in 
 the Items of Interest, presented an outline of the history of 
 inlay work, gathered from common and obscure sources. A 
 portion of the following brief description of the progress of 
 this work is based upon tlio article mentioned. 
 
 In 1820, C. J. Linderer filled teeth by the "fournieren'' 
 (inlaying) method and the "plattieren" (veneering) method. 
 The first procedure consisted in i)reparing a cavity in circu- 
 lar form, and from the tooth of some animal shaping a cylin- 
 drical rod to fit. This was driven into the cavity, the project- 
 ing portion cut off and polished even with the tooth surface. 
 The expansion of the inlay, due to absorption of the oral 
 fluids, caused it to swell and thereby furnish retention. Some- 
 times both inlay rod and cavity walls were threaded to fur- 
 nish positive mechanical retention. 
 
 The plattieren method was adapted to shallow cavities 
 and consisted in shaping small, flat pieces of rhinoceros teeth 
 to fit the prepared cavity. These veneers were usually held in 
 place with dowels of the same material. Difficulty in 
 matching the shades of the natural teeth, discoloration from 
 use and general lack of permanency, were the principal objec- 
 tions to the Linderer inlays. 
 
 In 1837, Dr. Murphy of London conformed a platinum 
 matrix to the prepared cavity, and in this matrix a glass in- 
 lay was fused, which was held in place with amalgam. 
 
 In 1857, Dr. A. J. Volck recommended the use of porce- 
 lain for filling cavities in the front teeth. The inlays so 
 formed were held in place by packing ropes of gold foil around 
 their peripheries. 
 
 In 1862, Dr. B. Wood shaped porcelain blocks to tooth 
 cavities by grinding to form. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1171 
 
 In 1870, Dr. Hickman formed inlays from sections of 
 porcelain teeth, shaping the pieces to fit the cavities by 
 grinding. 
 
 In 1870, Dr. Starr designed "cavity stoppers," small 
 pieces of porcelain of various shapes and sizes, which were 
 fitted to cavities by grinding. The pieces were provided with 
 platinum pins for retention purposes. 
 
 DR. C. H. LAND'S METHOD OF PORCELAIN INLAY WORK 
 
 In 1870, Dr. C. H. Laud constructed inlays by "fusing 
 pieces of artificial teeth in a platinum impression of the outer 
 borders of the cavity." This method, as he later on modified 
 it by pulverizing the teeth before fusing, represents the basic 
 principle of our porcelain inlay system of to-day. 
 
 In 1876, Dr. Bogue described a method suggested liy Dr. 
 Fisk of veneering a carious tooth with small gold caps, which 
 he likened to "little gold toadstools, set with gutta percha, 
 somewhat resembling an umbrella." 
 
 DR. BING'S METALLIC 
 FACING 
 
 DR. BING'S METALLIC FACING 
 
 In 1877, Dr. B. J. Bing recommended the use of "metallic 
 facings" for protecting fillings of cement or gutta-percha. 
 These facings were usually made of pure gold or platinum. 
 
1172 A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 and when set very much resembled in ;i}»i>eariiuce tlic metallic 
 inlays of the present time. 
 
 Dr. Wilber F. Liteli describes llicsc J'ac^ings quite fully in 
 the American System of Dentistr}-, p. IMU. Of their practica- 
 bility, he says: "In large crown cavities they have an in- 
 definite durability, and in the writer's practice large numbers 
 of proximal facings have been in use for three and four years 
 and still give no sign of failure." This system, although 
 crude, proved an incentive to many to attempt the restoration 
 of badly decayed bicuspids and molars by these or similar 
 means. The writer constructed and placed a number of fac- 
 ings of this type for patients in the clinic of Washington 
 University Dental School in 1891. (Mo. Dental College.) 
 
 ROLLINS' METHOD OF INLAY WORK 
 
 In 1885; Dr. W. Rollins, in the Archives of Dentistry, de- 
 scribed as follows a method of inlay work employed by him- 
 self for a number of years previous to the date mentioned. 
 An impression of the tooth with cavity prepared is taken in 
 a material composed of two parts mastic, one part paraffin, 
 and one part graphite. The tooth and cavity surfaces should 
 be previously oiled with vaseline. When secured, the im- 
 jaression should be i^laced in a bath of copper sulphate, and 
 a film of copper deposited by electrolysis, the process usually 
 requiring from two to three days to develop a sheet about 
 11/2 m.m. thick, or sufficiently rigid to obviate distortion in 
 handling. The impression was then removed, and a hole bored 
 in the bottom of the cavity in the copper reproduction of the 
 tooth, to facilitate the removal of the matrix. Into the cavity 
 a piece of No. .30 gold foil was adapted with pellets of cot- 
 ton. The matrix thus formed was filled with enamel powder 
 and fused in a gas muffle furnace. Before the mass hardened 
 it was pressed into the copper mold with a platinum instru- 
 ment. After cooling, the enamel was removed from the mold 
 by pressure through the opening in the base of the copper 
 pattern, and the gold matrix peeled off. It was set with a 
 mixture of zinc oxide and gutta-percha, the excess being re- 
 moved with chloroform. 
 
 DR. DUNN'S METHOD OF INLAY WORK 
 
 In 1885, Dr. C. W. Dunn, in the British Journal of Den- 
 tal Science, described a method practiced by himself since 
 1868, of taking a wax impression of the tooth, and cavity, 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1173 
 
 from whicli a modrl iii plaster was secured. This was painted 
 with a mixture of wax and rosin, to prevent friability of the 
 cavity margins. Into the cavity a filling was tittecl by re- 
 peated grinding and trial, until satisfactory adaptation had 
 been secured, after which it was set with cement Various sub- 
 stances were used by him for inlays, such as mineral and 
 natural teeth, as well as the teeth of cattle and lambs. 
 
 DR. STOKES' METHOD 
 
 In 1887, Dr. J. L. Stokes, in the Southern Dental Journal, 
 described a method of first making the inlay, and shaping 
 the cavity to receive it. After setting, he removed the hard- 
 ened cement, from the joint to a slight depth, and tilled be- 
 tween the cavity walls and inlay with gold. A similar method 
 of retention had been previously introduced by Dr. Essig of 
 Philadelphia some time in the seventies. 
 
 DR. AMES' METHOD OF GOLD INLAY WORK 
 
 In 1888, Dr. W. V. B. Ames of Chicago constructed gold 
 inlays by adapting a foil matrix of platinum to the tooth 
 cavity, and fusing in it gold plate or solder to the recpiired 
 contour. The inlay was then cemented in position. Shortly 
 after this he demonstrated the method at a meeting of the 
 Illinois State Dental Society, a description of which is found 
 in the Proceedings of 1890. 
 
 So far as the writer is able to learn, this was the begin- 
 ning of the gold inlay methods by the matrix system. It 
 demonstrated the practicability of fillings of this type. 
 
 VARIOUS METHODS OF INLAY PRODUCTION IN RECENT 
 YEARS 
 
 In 1889, Dr. W. Storer-llow, in the Dental Cosmos, de- 
 scribed in detail the method of constructing inlays by gi'ind- 
 ing sections of ]iorcelain teeth of suitable shade, to the de- 
 sired form 
 
 In 1889, Dr. ITerbst descrilied a metiiod of making glass 
 inlays. An impression of the tooth with cavity prepared was 
 secured in Stent's Compound, from which a plaster model 
 was formed. To make the base of the inlay rough, for re- 
 tention purposes, grains of sand were jjlaced in the bottom of 
 the cavity of the plaster tooth, and the latter, while moist, 
 was filled about two-thirds full of powdered glass. Tlie 
 moisture was then absorbed and the glass fused. This was 
 then repeated until the inlay was of the desired contoui-. 
 
1174 A BRIEF HISTORY OF PROSTHRTIC DKNTISTRY 
 
 111 1890, Prof. Sachs reeouiiiiciKlcd making a matrix of 
 Williams' gold foil No. 60, or of platinum foil, and fusing the 
 glass direeth' into tiiis reproduction of tlie cavity. Sachs also 
 described an excellent method of making inlays from porce- 
 lain teeth of suitable shade. From a porcelain tooth a piece 
 nearly cylindrical in form and slightly larger than the cavity 
 was cut. This cylindrical section was mounted with melted 
 sliellac on the end of an engine mandrel. The mandrel was 
 revolved in the engine and the porcelain held against the face 
 of a lathe stone revolving in the opposite direction. The 
 mandrel was held at a slight angle to the face of the lathe 
 wheel, so as to form the mounted block into a slightly tapering 
 cone. The cavity was prepared in circular form by means of 
 suitable wheel burs. The inlay, still mounted on the mandrel, 
 was introduced into the cavity with emery powder or pumice 
 stone, and revolved rapidly to secure close adaptation at the 
 margins. When closely adapted a groove was cut near the 
 peripheral base of the inlay for retention purposes. After 
 setting, the surplus, or projecting end, was reduced to a level 
 with the tooth surface with stones and discs. Copper 
 trephines charged with diamond dust were also used for cut- 
 ting the section from the porcelain tooth, while cylindrical 
 burs corresponding in size to the section cut by the trephine 
 were used for forming the cavity. 
 
 In recent years the supply houses have introduced rods 
 of porcelain for inlay work, of varying sizes and tints, with 
 trephines of corresponding sizes, for cavity preparation. This 
 system obviates grinding the periphery of the inlay. A sec- 
 tion of rod, slightly longer than the depth of the cavity, is cut 
 and cemented to place, and the surplus reduced with stones 
 and discs. 
 
 DR. ALEXANDER'S INLAY METHODS 
 
 In 1896, Dr. C. L. Alexander described a method of in- 
 lay construction, the substance of which is as follows: Pre- 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1175 
 
 pare cavity with definite margius. I\Iake lioles for retaining 
 pits in dentin. Adapt platiunm foil to tootli surface. In- 
 sert retaining iiosts through matrix. Take impression of 
 
 PIN INl-AY FOR JIOI.AR TOOTH 
 
 posts and foil; rciuo\e, invest and unite with \mve gold. Re- 
 turn to tooth for iiual adaptation and trimming. 
 
 YAKIOUS VIEWS OF INCISOR AND MOLAR INLAYS 
 
 When fitted, a wax or modeling compound bite is taken, 
 occlusion casts are formed, the bite removed, and the desired 
 restoration developed in wax. 
 
 RESTORATIONS FOR THE ANTERIOR TEETH 
 
 Over this -restoration in wax, gold or platinum foil is 
 burnished. 
 
 Invest, leaving one side open for removal of wax with hot 
 water and into the metal-lined matrix thus formed gold is 
 
n76 A HHIIOF HISTORY OF PROSTHKTIC DKNTISTRY 
 
 fused. Tli(> various ilhistratimis here shown ai'e IVoiii tli 
 Dental Cosmos. 
 
 Ul'PER BlilDGE SL I'l'OUTED UY THREE I'lN INLAYS 
 
 lu 18!)7, Dr. M. S. Fiiiley deseribed a similar method of 
 restorinn' the occlusal surfaces of hicnsiiid and molar teeth 
 
 Heavy gold, however, instead of foil, was iised for adaptation 
 to tooth surfaces. When swaged on a die and adapted to the 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1177 
 
 tooth, tlic cus]! foi-nis were (Icveloiu'd on this rigid fouuda- 
 tion. 
 
 Gohl inlays were made liy iircparinn' tlie cavity without 
 iiudereiits, and into this Watts' crystal gold was moderately 
 condensed, the filling being built to general contour by this 
 means. It was then removed and the cavity surfaces of the 
 inlay were painted witli rouge and alcohol to prevent the 
 solder, which was afterward flowed into the interstices, from 
 spreading and modifying tlie form of the inlay The origina- 
 tor of this method is not known to the writer. Dr. W. M 
 Griswold of Hamburg, Germany, described it a number of 
 years ago, and stated that he had been using it since 1898. 
 
 SLOW PROGRESS OF INLAY WORK 
 
 Inlay work advanced slowly because of the prejudice ex- 
 isting in regard to the use of cement as a retention medium for 
 fillings of this class. The objections urged against inlays in 
 general, both porcelain and metallic, were, first, the liability of 
 the cement to solution liy the oral fluids, and second, the 
 tendency of such fillings to become displaced under sti'ess. 
 
 Three factors contributed largely to the production of 
 botli classes of inlays under consideration: First, the intro- 
 duction of the Custer electric furnace in 1894, and of im- 
 proved porcelain bodies, revolutionized and simplified the 
 making of jDorcelain inlays; second, the methods of cavity 
 preparation in general, suggested by Dr. Black, of opening 
 up cavities in order to gain access to all parts, and of de- 
 veloping flat seats and parallel walls so as to furnish resist- 
 ance form, largely overcame the liability to displacement, of 
 inlays of both gold and porcelain, when set and subjected to 
 stress; third, observation of cases where properly adapted 
 and correctly set inlays had been subjected to stress and the 
 action of the oral fluids for a considerable length of time, dis- 
 closed the fact that cement, although not ideal, was a reason- 
 ably good retaining medium, not lial)le to solution as rapidly 
 as was at first deemed probal)lo, and that under favorable con- 
 ditions there was no recurrence of decay. 
 
 The improvements mentioned in porcelain bodies, and 
 means of fusing the same, together with the beautiful results 
 accomplished by experts in this field, developed a widespread 
 wave of enthusiasm in ceramic dental art. Like all new 
 things which promise reasonably good results ]iorcelain be- 
 came a fad and was grossly misapplied, not only in the con- 
 struction of inlays, but in crown and bridge work as well. 
 
1178 A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 In limited bulk, porcelain is inherently weak, friable and ex- 
 tremely liable to fracture luidor stress. These facts were 
 overlooked, or not recognized by many, with the result that 
 many discouraging failui'es occurred. Warpage of the 
 matrix, resulting in imperfect adaptation of inlays to cavities, 
 dithculty in matching the tints of natural teeth, with frac- 
 ture and displacement of the fillings imder stress, were some 
 of the discouraging features of porcelain inlay work. 
 
 From flood to ebb tide, the wave of enthusiasm in ceramic 
 work lasted about ten years, beginning about 1895, just fol- 
 lowing the advent of the Custer electric furnace. It reached 
 its highest level in 1903-4. Since the latter date mentioned, 
 as time and service disclosed the limitations of porcelain as 
 a filling material, its use has gradually declined. Its value in 
 favorable locations is unquestioned. 
 
 PROGRESS OF GOLD INLAY METHODS 
 
 Meanwhile, although less desirable from an esthetic stand- 
 point than porcelain, the production of gold inlays rapidly 
 increased, because of their great inherent strength and wide 
 range of application. During the period from 1900 to 1907, 
 the method of gold inlay production by means of a matrix 
 gained in favor, technical steps improved, and the value and 
 permanence of this system of filling teeth was practically 
 established. 
 
 One of the greatest difficulties met with in the making of 
 gold inlays by the methods then in vogue was in warj^age of 
 the matrix while fusing the gold in it to the desired contour. 
 In 1905, Dr. Barnes of Cleveland, Ohio, demonstrated that 
 by substituting 1-500 platinum foil for the 1-1000 gold or 
 platinum foil then in use, warpage could be practically 
 eliminated. 
 
 While the matrix method of inlay production had ap- 
 proached a stage bordering on perfection, the technical steps 
 involved were at times tedious and sometimes compli- 
 cated, depending on the form and location of the cavity to 
 be filled. The production of the matrix itself, although much 
 less trying on both patient and operator than tedious filling 
 operations, required time and skill to secure the desired re- 
 sults. Some easier method, therefore, was sought. 
 
 INCEPTION OF THE WAX MODEL METHOD 
 
 The idea presented of making a model of the filling by 
 pressing wax into the tooth cavity, or a reproduction of it. 
 
A BRIEF HISTORY OP PROSTHETIC DENTISTRY 1179 
 
 This model, wlieu properly carved and contoured, was in- 
 vested and cast in metal. Where or when this idea originated, 
 or to wliom credit for it helongs, cannot now, and probably 
 never will, be determined. 
 
 AN ANALYSIS OF THE CASTING PROCESS 
 
 By analysis, the casting process, as applied to dental 
 operations, may be set forth as follows -. 
 
 First, forming in a plastic material as wax, or in wax and 
 metal, a model or pattern of the ol),iect it is desired to repro- 
 duce by casting. 
 
 Attaching to the model, before investment, a wax or metal 
 sprue former to form a pouring gaine, or sprue, for the injec- 
 tion of the metal into the mold. 
 
 Enclosing the pattern with sprue former attached, in a 
 single mass, or a sectional mass of refractory material, capa- 
 ble of setting in a short time and of withstanding heat with- 
 out material change. 
 
 Eliminating the wax from the investment by some form of 
 applied heat, thus freeing the mold for the introduction of the 
 metal. 
 
 Fusing the metal in a crucible-like depression in the in- 
 vestment, which is connected with the mold, through the 
 sprue; or melting the metal in a crucible and pouring it di- 
 rectly into the enlarged outer extremity of the sprue, through 
 which it is conducted into the mold. 
 
 Applying pressure to the molten metal to force it into all 
 parts of the mold, to insure the production of a sharp cast- 
 ing. 
 
 Some of these various processes will now be considered 
 in detail, after which their application in the production of 
 prosthetic restoraticms of different kinds will be presented 
 somewhat in chronological order. 
 
 FORMING MODELS IN WAX OF THE CASTING TO BE 
 PRODUCED 
 
 The construction of a plastic model, usually wax, of the 
 object it is desired to reproduce in metal. 
 
 This princi]ile'is centuries old among artizans, and even 
 among uncivilized peo])le, with some of whom it was customary 
 to form in wax, a model of an implement and enclose it in a 
 clav investment. On heating the clay, the latter was hardened 
 
1180 A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 and the wax dissipalcd, tliiis lca\ iiii;- a matrix oi- mold into 
 wliicli the molten metal, usually copper, was cast. 
 
 METHODS OF FORMING A SPRUE OR POURING GATE 
 
 A siirue is delined as follows: "In castin.i;- metal, one of 
 tile passages leading from tlie 'skinmiing gale' to the mold; 
 also, the metal wliicli (ills tlie sprne oi- sprue gate after solidi- 
 lieation, same as dead-iiead." (('entnry Dictiiuiary.) "A 
 piece of metal or wood used hy a molder in making the ingate 
 through the sand." {K. IT. Knight.) 
 
 For many years, in ))rostlietic jiroeednres it was custom- 
 ary, and is, even at the present time, in two-piece molds, to cut 
 the sprue after investment of the model. More often, how- 
 ever, a piece of wax is attached to the patteru leading exter- 
 nally to the outside of the investment flask, so as to form a 
 groove in both parts of the investment. When the matrix 
 is separated and the wax removed, tlie groove thus formed 
 may be enlarged if necessary for the injection of the metal. 
 In single investments, a piece of wax, metal or wood, of suit- 
 able size for the sprue, is attached to the model before invest- 
 ing, and removed after the investment has hardened. When 
 wax is used, its removal is effected liy heat. 
 
 In Harris, Ed. 1873, the first suggestion of "small cylin- 
 drical wax gates" are mentioned in connecticm with the Bean 
 process of casting. These wei-e enclosed in a single invest- 
 ment to serve as sprue formers through whicli the nu'tal was 
 cast in attaching the teeth to the aluminum base. 
 
 In Richardson, Ed. 1880, mention is made of a tapering- 
 sprue former of wax, in connection with Reese's cast base den- 
 tures. The name pouring-gaine is there api)lied to it. In the 
 final investment of a pattern, the wax S2:»rue form<M' was en- 
 tirely enclosed, and subse(|ueidly dissipated in heating the 
 case. 
 
 ENCLOSING THE WAX MODEL IN A SINGLE INVESTMENT 
 
 The object in enclosing a wax model in a single invest- 
 ment rather than in a sectional matrix is to prevent fracture 
 of the margins of the mold, which nearly always occurs in 
 opening a matrix formed in two or more pieces. 
 
 Rough margins of the mold result in rough castings, while 
 oftentimes, even though the margins may not be fractured, 
 slight contraction in the investment material, or failure of the 
 
A BRIEF HISTORY OP PROSTHETIC DENTISTRY 1181 
 
 several sections of the matrix to register correctly, will permit 
 the fused metal to escape into the joint areas. 
 
 This fact has been recogiiized by many and for the past 
 twent}^ years or more the single investment has been gradu- 
 ally coming into favor. 
 
 ELIMINATING THE PATTERN BY HEAT 
 
 This is a logical ontcome of the use of wax for a pattern 
 and of its enclosure in a single investment. 
 
 FUSING THE METAL IN CLOSE PROXIMITY TO THE MOLD 
 
 The principal cause of failure in casting operations is due 
 to the metal when fused of becoming chilled and more or less 
 sluggish in injecting it into the mold. This difficulty is spe- 
 cially noticeable when the metal is melted in a separate re- 
 ceptacle from which it is poured into the mold. 
 
 To cast sharply, a metal or an alloy must be superheated 
 sufficiently so that after injection into the mold it will be in a 
 liquid, conformable condition, in order to become adapted to 
 irregular surfaces. 
 
 APPLYING PRESSURE TO THE FUSED METAL TO INDUCE 
 SHARPNESS OF DETAIL IN THE CASTING 
 
 Tlie necessity for applying pressure in some manner to 
 the fused metal to insure sliarpness of detail in castings was 
 recognized by Blandy in 1855, and many others, since his time. 
 
 The manner of api^lying pressure to eliminate the air in 
 the mold and permi■^t•he-metaltafillit perfectly varies greatly, 
 as will subsequently be seen. 
 
 Briefly summed up. some of these methods are as follows : 
 Gravity, vibration, mechanical pressure, compressed air or 
 gas, partial vacuum, centrifugal force and steam. 
 
 PIONEERS IN THE PRODUCTION OF CAST WORK 
 
 The casting of denture bases of tin, as stated on page 
 1132, was first attempted by Dr. Edward Hudson of Phila- 
 delphia in 1820, liy Dr. W. A. Royce of Newbnrgh, N. Y., in 
 1836, and by Dr. George E. Hawes of New York in 1850. 
 
 Tin does not cast sharply by the ordinary or crude 
 methods employed in those days and therefore the production 
 of dentures by this method was not very satisfactory. 
 
 The introduction by Dr. A. A. Blandy of an improved tin 
 alloy gave a decided impetus to casting methods since his time. 
 
1182 A BRIEF HISTORY OP PROSTHETIC DKNTISTRY 
 
 THE ^LANDY CAST BASE DENTURE 
 
 The Blandy Process of casting metal base dentures, which 
 was presented in 1856, was described in Harris, Ed. 1873, in 
 substance as follows : 
 
 A wax model of the required denture was formed in which 
 the teeth were arranged, mueli as for vulcanite cases, a special 
 tooth being used for this purpose. 
 
 The waxed case was enclosed in a two-piece investment 
 composed of plaster and feldspar. On separating, the larger 
 
 n r^? 
 
 rrr" i ' I'l 
 
 TEETH DESIGNED FOR DSE WITH THE BLA^•DY PROCESS. 1S55 
 
 portion of wax was removed, but the smaller portions between 
 the teeth were allowed to remain, being subsequently dissi- 
 pated in the heating process. 
 
 A channel was cut in the back of the case, at least two 
 inches long, to serve as a sprue, and on either side vents for 
 the escape of the air were formed. A deep sprue was sug- 
 gested so that when filled, the weight of the metal therein con- 
 tained would insure density in the casting. In addition to this 
 means, it was suggested that jarring the flask as soon as the 
 metal was poured would aid in tlie production of a sharp 
 casting. 
 
 BEAN'S METHOD OF CASTING ALUMINUM 
 
 In 1867, Dr. J. B. Bean of Baltimore formed denture bases 
 in wax, arranged gum section teeth in occlusion and alignment 
 and carved the denture to required form. The gum sections 
 were then removed and a recess of dovetailed form was 
 carved in the wax baseplate to the lingual of the pins to af- 
 ford anchorage for the ,gum sections in final attachment. 
 
 The wax model, minus the teeth, was then enclosed in a 
 special flask, in an investment composed of plaster and 
 pumice stone previously boiled, so treated to form a denser 
 mass than would result from an ordinary mix. 
 
 When the investment was hardened, the flask was opened, 
 the wax removed, the flask again closed and thoroughly heated 
 to evaporate the moisture. 
 
 The flask was su])plied with three openings, one centrally 
 located to serve as a sprue for the introduction of the fused 
 metal, and a smaller one on either side for the admission and 
 exit of hvdrogen gas at the moment of casting. At the time of 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 clearing- tlio matrix of wax, grooves were cut from these open- 
 ings to the interior of the mold. 
 
 The terminal end of tlie the sprue on the flask was cone- 
 shaped, to receive an extension sprue, some six inches long, 
 which was heated and set in position just before pouring the 
 metal. 
 
 HI V.LW Al'i'LIANC'lO FOR CASTING 
 ALUMINUM (REPRODUCED FROM 
 HARRIS ED. ISrS) 
 
 When the aluminum was fused, hydrogen gas was inti'o- 
 dueed in the mold through one of the lateral openings in the 
 flask, to expel the air and thus prevent oxidation of the heated 
 metal, the extension' sprue set in position and the metal cast 
 into the hydrogen filled mold. 
 
 As the metal filled the mold, the hydrogen escaped through 
 the other lateral opening. Both lateral openings were par- 
 tially olistruf'tod by fine wire wliich, although permitting the 
 
1184 A mUEF HISTORY OF PROSTHETIC DENTISTRY 
 
 introduction of gas in one and I he escape of gas and air 
 tlirougli the otlier, i)ievented tlie escap(! ol' tlie metal under 
 pix'ssure of tliat contained within the hjng sprne. 
 
 When cast, the baseplate was finished, the porcelain 
 bloclcs adjusted in i)osition and attaclied by a second casting 
 process in wiiich a more fusible alloy was injected into the 
 dovetailed groove previously mentioned, and iiround the jjins 
 of the teeth. 
 
 In this second step the use of "small cylindrical wax 
 gates" were mentioned. These served the purpose of sprue 
 formers, were enclosed witli the baseplate and teeth in a sin- 
 gle investment, subsequently dissipated by heat, and through 
 them the low fusing alloy was cast under gravity pressure 
 into the groove and around the pins of the teeth. 
 
 In these two operations described by Dr. Bean are pre- 
 sented several of the fundamental processes of casting, viz., 
 in the first steps are mentioned a wax pattern ; its investment 
 in a sectional matrix of refractory material; injection of the 
 molten metal into the mold under gravity jiressure; in the 
 second steps are mentioned "cylindrical wax gates," or sprue 
 formers, a single investment, or one piece matrix, and dis- 
 sipation of the wax by heat. 
 
 SAUER'S METHOD OF CASTING ALUMINUM 
 
 On page 630 of the Dental Cosmos, 1873, is illustrated 
 an apparatus designed by C. Saner of Berlin, for casting alum- 
 inum denture bases. This appliance resembles in manj' re- 
 spects the Bean apparatus which had been introduced a few 
 years previously. 
 
 The points of interest in this article are the use of an 
 alloy of aluminum, recoimiiended because it cast more sharply 
 than the pure metal, the application of a deep si^rue to the 
 flask to increase the pressure on the metal within the mold, 
 and the casting of the fused metal directly against the teeth. 
 
 REESE'S METHOD OF CASTING TIN ALLOYS 
 
 In 1879, Dr. Gr. F. Reese introduced a new alloy of greater 
 hardness than that previously in use, which was designed for 
 upper denture bases. A special flask of his own design was 
 recommended for the investment of the case. 
 
 HAYFORD'S METHODS AND APPLIANCES 
 
 In 1884, Dr. J. W. Hayford of Xenia, 0., patented an 
 appliance for casting Watt's, Weston's and other fusible al- 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1185 
 
 loys then in use. This ajipliance consisted of a press and a 
 flask having an opening in its upper side through which tiie 
 fused metal was poured into the sprue and mold. 
 
 DK. HAIKIKI) 
 
 By means of a lever a plunger was pressed downward 
 into the flask and against the fused metal and in this manner 
 it was forced into all parts of the mold by mechanical pressure. 
 
 THE WATT'S FLASK 
 
 In the latter part of the 80 's, Dr. Geo. E. Watt designed 
 a flask having two extensions in which the sprues were formed. 
 When the cast metal was injected into the mold the weight of 
 that contained within the sprues condensed that within the 
 mold by gravity ])ressnre. (See page 224.) 
 
 DR. MARTIN'S METHOD OF CASTING 
 
 Beginning about 1889, and for a num))er of years follow- 
 ing. Dr. G. M. Martin of Indiana demonstrated and taught tlie 
 method of casting inlays, crowns and bridges in the Indiana 
 Dental College, and in post-graduate work in Indianapolis. 
 
 The method was substantially as follows : 
 
 Formation of the pattern in wax, investment in refrac- 
 tory material within a cuplike receptacle, eliminating the 
 wax with heat, melting the metal in a crucible-like depression, 
 which was connected with the mold by a sprue, and casting the 
 fused metal by mechanical and later by centrifugal force. No 
 matrix was used in forming the jiattern in wax for an inlay. 
 
 The crucible and sprue were formed by attaching a piece 
 of wire in case of inlays, or a strip of metal plate in bridge- 
 work, to the curved side of a section of cork, mounting the 
 
Il8t; A BRIEF HISTORY OF I'ROSTHKTIC DENTISTRY 
 
 pattern at the outer ('xti-ciiiit\ of the siii'uc t'oniu'i- and ai)l>ly- 
 ing the investment ai-dund lhe |iatteni and over tiie curvf'd 
 cork base. 
 
 THE CARROLL METHOD OF CASTING ALUMINUM 
 
 In 1888, ])r. ( ". ('. Carroll patented an apparatus i'or 
 casting alnniinnni deiilure liases, bridges and crowns. The 
 principal inipi-oveiiient <>\' tlie method ovei- those in-eceding 
 
 it was in the use of a sealing cai) for closing the crucible, and 
 casting the metal by ine^ns of compressed air. 
 
 Dr. Carroll demonstrated his appliances and method of 
 casting aluminum at the World's Columbian Dental Congress 
 in Chicago, in ]89;>, as well as at ]irevious times. 
 
 THE ZELLER CASTING APPLIANCES 
 
 In 1891, the Zeller aiipliances were introduced. These 
 consisted of a tlask for investment of the case, burners for 
 heating the flask and fusing the aluminum, and a suction tube 
 by means of which a partial vacuum could be created in the 
 
A BRIEF HISTORY OF PROSTHFTIC DENTISTRY 1187 
 
 mold. When tlie ease was licated and the iiit'tal fused, it wan 
 drawn into the mohl li>' inoutli suction (W a suction bulb. 
 
 THE FENNER CASTING APPLIANCES 
 
 In 1893, the Fenuer appliances were introduced. These 
 consisted of a flask with attached crucible for investment of 
 the case and holding the metal while fusing, of a stove and 
 jacket for heating the case, a sealing cap fitted with a packing 
 by means of which the metal could be forced into the mold by 
 compressed air. The writer used and demonstrated both wax 
 and metal s])rue formers with this aiipliance as early as 1895. 
 
 DR. HARPER'S CAST CROWNS AND BRIDGES 
 
 In 1894, Dr. W. E. Harper of Chicago constructed cast 
 aluminum bridges by the following method, one special type of 
 abutment of which will be outlined : 
 
 A molar tooth having a }n'oxiiuo-occlusal cavity was pre- 
 pared by reducing its occlusal and axial surfaces in the usual 
 manner recjuired for the receipt ion of a shell crown. 
 
 The cavity in the tooth was prepared as for the reception 
 of a tilling, but without undercuts, the axial walls flaring out- 
 ward slightly. 
 
 An axial liand of alnminuiu was then fitted to the tooth, be- 
 ing carried slightly under the gingiva, the occlusal end being 
 left open. 
 
 Wax was i)ressed into the open end of the band, directly 
 into the cavity against its various walls, and over the reduced 
 occlusal areas of the tooth, without the interposition of a 
 matrix. 
 
 The patient was instructed to bite into the wax to de- 
 velop occlusion, after which the cnsps were carved to re- 
 quired form. 
 
 This wax-nu'tal abutment was then united to the dummies, 
 which were of wax, or, in some cases, of wax aud porcelain 
 combined, a wax sjjj-ue former attached, the whole piece in- 
 vested in a Zellcr flask, and heat<'il to dissi])ate the moisture 
 and wax. 
 
 The alumiiuim was then fused in the attached crucible 
 and drawn through the sprue into the mold by partial vacuum 
 force. 
 
 In sjtecimens shown the writer in 18i)6 and subsequently, 
 there api>eared to be perfect union between the cast metal an 1 
 the band. 
 
1188 A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 This abutment might appropriately be termed a crown 
 inlay, since it constituted not only a crown, Imt an accurately 
 iitting inlay as well. 
 
 Dr. Harper frequently demonstrated and described this 
 method of crown-inlay construction at various clinics and to 
 different individuals as well. He stated to the writer as early 
 as 1896 that he had been successfully following this plan of 
 bridge construction in liis practice. 
 
 By analysis this metliod embodies the pressing of wax 
 directly into the tooth cavity, and against various tooth sur- 
 faces, in the formation of the crown-inlay pattern, without the 
 interposition of a matrix, the use of a sprue former of wax, 
 investment of the pattern in refractory material, dissi])ating 
 the wax by heat, casting tlie fused metal into tlie matrix by 
 vacuum force. 
 
 THE ALEXANDER METHOD OF CASTING INLAYS 
 
 Reference has previously been made to Dr. C. L. Alex- 
 ander's method of forming inlays. His first paper on "Cast 
 ing Fillings and Abutments for Bridges" was reported at a 
 meeting of the Southern Dental Association, held at Asheville, 
 N. C, in July, 1896. The discussion which followed clearly 
 brought out the fact that the durability of the cement by which 
 inlays were held in place was still a point not yet determined 
 by experience, and many in the profession opposed the ap- 
 plication of inlays on this ground. 
 
 The "casting of fillings," however, was "in the air," and 
 the possibilities in this field were beginning to be recognized. 
 
 THE HOLLINGSWORTH METHOD OF CASTING 
 
 In the American Text Book of Prosthetic Dentistry, pages 
 669-70, Ed. 1896, is described the Hollingsworth method of 
 casting bridge dummies, the patterns of which were composed 
 of wax, wax and paraffin, or wax and gutta percha. 
 
 The pattern after being carved to correct occlusion and 
 form between the two abutments, was removed. To one end 
 was attached a cylindrical piece of wax about one-eighth of an 
 inch in diameter, to serve as a gate or sprue former. 
 
 A shallow, oblong, sheet iron pan, to which a handle was 
 attached, was used as a table on which to invest the case. 
 
 The investment, composed of a mixture of plaster and 
 marble dust, was mixed to medium thin consistency, the pan 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1189 
 
 filled with it and the wax pattern with sprue former attached, 
 laid on it near one end, and covered over to the depth of about 
 one-half inch. 
 
 The investment in the other end of the pan was not con- 
 toured hut left flat, and when hardened a depression or shal- 
 low crucible was formed in this surface and connected by a 
 groove with the exposed end of the sprue former, tlie invest- 
 ment around which was removed to form a funnel-shaped 
 opening for the ready entrance of the gold into the mold. 
 
 All surfaces were cleared of debris and the case heated to 
 dissipate the moisture and wax. 
 
 In the crucible depression, gold scrap or plate was placed 
 and with a blowpipe, brought to a thoroughly li(|uid condition, 
 
 THE KIKST HOLLINGSWORTH ArPLIANCK FOR lASTI.NU GOLD DIJIMIES 
 
 when, by tipping the pan in an upright position, the gold was 
 cast into the mold by gravity. 
 
 In 1902, Patent No. 708^811 was issued to Dr. M. W. Hol- 
 lingsworth for a machine for forcibly casting dental bridges. 
 The fundamental principle of this machine resembled some- 
 what his first crude appliance, previously described. 
 
 This appliance consisted of a base provided with a hinged 
 table, on which the investment rested. Through the bottom of 
 the table projected a sprue former of brass, having a reduced 
 upper extremity to which the wax model was attached. A 
 metal hood for supporting the sides and outer end of the in- 
 vestment was adjusted to the table, and which, being adjust- 
 able, permitted the investment to be closely applied to the 
 
A BRIEF HISTORY OF PROSTHP^TIC DENTISTRY 
 
 pjittcrii and thus exclude the air, at'tei' wiiirh, wliihr" tlu; invest- 
 ment, was still soft, the IukxI was adjusted and filled. 
 
 When hardened, the sprue former was removed and a 
 stick of carbon of corresi)onding size was inserted into the 
 opening. 
 
 In investing a ease in tliis ajipliance, tlie crucible for melt- 
 ing the gold was formed in one end of the table, being con- 
 nected with the sprue by a lateral groove and opening. 
 
 When the investment was thoroughly dry and heated, and 
 the wax dissi])ated, gold was placed in the crucible, where it 
 was fused. 
 
 THE Hor.l.INXiSWOUTII I'll] 
 
 By means of a lever device the hinged tal)le was raised to 
 an upright position. This movement cast the gold into the 
 si)rue and mold liy gravity. 
 
 When the table was in nearly an upright position the outer 
 end of the carbon was brought in contact with a cam surface 
 of the base, thus pressing it forward into the sprue and forcing 
 the gold into the mold by mechanical pressure. 
 
 These processes involve a wax model, enclosed in a sin- 
 gle investment of refractory material, a removable metal 
 sprue, formation of a crucible depression in the investment, 
 dissipation of the wax model by lieat, fusing and casting the 
 gold under both gravity and mechanical iiressure. 
 
A BRIEF HISTORY OF PROSTHP^TIC DKNTISTRY 1191 
 
 FLASK DESIGNED BY THE WRITER 
 
 In litOO, the writer designed a flask for casting aluiniiuun 
 in wliicli a metal sprne former was used in conjunction witli a 
 wax model enclosed in a single investment. 
 
 Tlie metal was melted in an attached crucil)le and forced 
 into the mold with a metallic piston which fitted the interior 
 of the crucible. Because of difficulty at times resulting from 
 tiie piston becoming locked within tlie crucible chamber, a 
 sealing cap, with tube attached, was substituted and l>y tliis 
 means the fused metal was injected into the mold with com- 
 pressed air, and also steam pressure. These flasks were used 
 for some time in the teclinic laboratories of the Northwestern 
 I'niversity Dental Scliool l^y Dr. Wahlhcrg, Dr. Mctlivcn and 
 the writer. 
 
 DR. PHILBROOK'S METHOD OF CASTING INLAYS 
 
 Between 189(5 and liH)."), Dr. H. F. IMiilhi-ook of Hennison. 
 la., developed a system of casting inhiys whicli in substance 
 was as follows: 
 
 In his first efforts, l)etween the jieriod from 1896 to about 
 18.9S, he formed a model of the desired filling by pressing wax 
 into the cavity of a tooth, reprcnluced in the usual way, in 
 plaster. This is known as the indirect method. From 1898 
 and thereafter he formed the filling by pressing the wax di- 
 rectly into tlie natural tooth cavity, without the interjiosition 
 of a matrix, and carved it to the required form. 
 
 To each extremity of the inlay a cylindrical piece of wax 
 was attached, one to serve as a sprue former, the other to 
 form a channel thi'ongh which to clear out the wax. 
 
 'I'lie pattern and extensions were then invested in refrac- 
 tory material in a ring in such manner as to exclude the air, 
 the sprue former occupying a central position, the other ex- 
 tension situated near one side. 
 
 When the investment had set, it was trimmed out aroniul 
 the sjirue former to form a crucible-like depression in which 
 to melt the metal. 
 
 With a bulb syringe, hot water was forced iuto the sprue 
 aiid mold, and out the side channel, thus freeing the mold and 
 openings leading to it of the greater bulk of wax. 
 
 The invested case was heated to ex])el the moisture and 
 any remaining wa-x present, the metal placed in the crucible, 
 fused with a blowpipe, and forced into the mold as follows: 
 
 A sealing cap consisting of a metallic disc of larger diam- 
 eter than the investment ring, having attached an asbestos 
 
1192 A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 packing for sealing against the escape ui' air, was pressed 
 firmly and evenly down upon the upper end of the ring. 
 
 Through a tube of metal which was attached to the upper 
 central side of the disc, air was forced by moutli pressure into 
 the crucible containing the fused metal, thus injecting it 
 through the sprue into the mold. 
 
 By 1904, several important modifications in tlic al)i)v<' 
 methods were made b.y Dr. Philbrook, viz., tiie use of a metallic 
 sprue former, the designing and use of a metallic crucible 
 former, dissipation of the wax by dry heat or fiame, a sealing 
 cap containing moist asbestos, the steam from which, wlien 
 heated and confined, injected the fused metal into the mold. 
 
 The methods and ap]iliances employed l)y Dr. Philbrook. 
 from 1896 to 1905, inclusive, may he briefly summed up as 
 follows : 
 
 A model formed without a metal matrix ; both liy the in- 
 direct method of pressing wax into a plaster model of the pre- 
 pared tooth and cavity, and by the direct method, by pressing 
 the wax directly into the natural tooth cavity ; the use of both 
 wax and metal sprue formers; a metallic investment ring; 
 metal as well as wax sprue formers for supporting the pattern 
 and forming the sprue; investment of the wax ]iattern in a 
 single mass of refractory material ; dissipation of the wax by 
 hot water in some cases, dry heat or flame in others ; fusing 
 the metal in the crucible depression of the investment in the 
 upper end of the ring; injecting it into the mold Ity com- 
 pressed air or by steam pressure. 
 
 DR. SCHLOTTER'S CLINIC 
 
 In 1904, Dr. Jacob Schottler at Manitowoc, Wis., gave a 
 clinic before the Wisconsin State Dental Society on cast gold 
 inlays, in which successful castings were shown, made by grav- 
 ity pressure. This clinic demonstrated the method he em- 
 ployed in his practice. 
 
 THE LENTZ CASTING PROCESS 
 In August, 1905, Dr. John A. Lentz of Pluenix, Ariz., 
 applied for a patent for a "process for forming dental struc- 
 tures," which patent was granted in October, 1906. Briefly 
 described, his processes are outlined as follows: "My inven- 
 tion relates to such dental work as making inlays, onlays, 
 crowns, bridges, artificial dentures and other dental structure, 
 or certain parts of the foregoing." 
 
 He iTientions specifically his method of preparing a molar 
 
A BRIKF HISTORY OF PROSTHETIC DENTISTRY 
 
 1193 
 
 tooth for a crown in tlie usual manner, to which was fitted 
 a properly contoured band. A iilastic impression material 
 was then placed on the occlusal end of the band, forced between 
 its inner walls and the axial surfaces of the tooth and against 
 its occlusal surface as well, without the interposition of a 
 metal matrix. By closing the jaws in various positions, clear- 
 ance paths for the opposing cusps were developed, after 
 which the cusps were carved to desired form. 
 
 The crown was then removed and inclosed in a suitable 
 investing material in a two-])iece i-iiig. On wanning and sep- 
 
 THE I.ENTZ l-ASTIXG APPUANTE 
 
 arating the latter, the plastic material which lined the in- 
 terior of the band and of which the cusps were formed was 
 removed. In one portion of the ring the root sides and end, 
 reproduced in investment material, were thus exposed within 
 the enclosed gold band, while in the other part of the ring the 
 investment presented the reverse of the carved cusp surfaces. 
 The casting was accomplished by drying and heating the 
 investment in the two halves of the ring, placing an excess 
 amount of gold in the cusp depressions, where it was fused, 
 while i)ressure, sufficient to force it into all parts of the mold, 
 
ll'.M A BRIEF HISTORY OK I'R(JSTHETIC DENTISTRY 
 
 wjis (lc\('l()j)('(l by dropiniiii' the Icxcf ol' the iiioldiiii^ nuu'hino 
 down until the two liaKcs of the riii^ touched and registered. 
 By this process the fused gold was adapted to all the in- 
 e(|nalities of the root surfaces, as rejiresented in the investment 
 material within the ring-, and when properly linished, lilted tiie 
 root closely. Modelini;' comiiouml or wax was used as the im- 
 pression material. 
 
 THE OLLENDORF CASTING PROCESS 
 
 In 1906, or previously, Dr. OUendorf of Breslau, Ger 
 many, presented appliances and described a system for cast- 
 ing crowns, bridges and dentures under pressure. He used the 
 disa])pearing wax model, enclosing it in an investment of silex 
 and i)laster. Gravity force for producing jiressure on the gold 
 in casting was employed, as in some of the ])receding methods 
 mentioned. This method was described by Dr. Sachs in a 
 pai)er read before the American Dental Society of Kurope, 
 August, 1906. (Dental Review, March, 1907.) " 
 
 SUMMARY OF PROGRESS IN CASTING OPERATIONS 
 
 Thus it a])pears that the live fundamental principles in- 
 volved in the casting i)rocess as practiced to-day were widely 
 known and utilized prior to 1907 in crown, bridge and denture 
 construction, and the casting of inlays was practiced by a con- 
 siderable number of individuals with greater or less success. 
 
 That experiments had been and were being conducted 
 along these lines by a considerable number of individuals is 
 uni|uestioned. The results of these efforts were frequently 
 gratifying, but sometimes disappointing, due largely to a lack 
 of exact knowledge of the physical properties of materials 
 employed. 
 
 CAUSES OF FAILURE IN CASTING OPERATIONS 
 
 In the light of present knowledge, the causes of failure 
 in some of the pioneer efforts with cast inlays were due to 
 dimensional changes in the wax model during and after form- 
 ing it, this material being very susceptible to temperature 
 variations, to impurities present in the wax which remained 
 as a residue in the matrix, and failed to volatilize on heating; 
 to changes in the investment under heat ; but principally in 
 failure to render the gold suliliciently plastic to cast sharply. 
 
 Although it is possible to superheat gold to a sufficient 
 degree to cast sharply, by means of the ordinary ))lowpipe, 
 still, under some conditions, it is a difficult task. 
 
A i,RlEF HISTORY OF PROSTHETIC DENTISTRY liy^ 
 
 THE OM.ENDORF CASTIXC APIMJAXCES 
 
1190 A BKIP^F HISTORY OF I'KOSTHETIC DENTISTRY 
 
 Had the pioneers, in llic castin.iz,' of ]irostlietic substitutes 
 in gold, recognized the great value and effieieucy of the Knapp 
 nitrous oxide and gas blowpipe which was introduced about 
 
 l.l.dUI II L 
 
 1890, work in these lines would have progressed rapidly, and 
 the problem of casting inlays and various prosthetic appli- 
 ances would have been practically solved. 
 
 DR. TAGGART'S METHOD OF CASTING INLAYS 
 
 In 1907, Dr. AV. H. Taggart of Chicago made application 
 for patents on various processes and "Apparatus for making 
 models for the casting of dental inlays and the like," "Method 
 for making models for dental inlays and the like," "Method 
 for making dental inlay fillings and the like," "Apparatus for 
 making castings." The first two patents were granted in 
 1907, the last two mentioned in 1911. 
 
 Briefly, the steps of producing an inlay by the Taggart 
 method are as follows: 
 
 A pattern of the desired filling is made by pressing wax 
 directly into the prepared tooth cavity, without the interposi- 
 tion of a matrix, and carved to required form. 
 
 The pattern is mounted on a metallic sprue former, which 
 rests in and is supported by a metallic, dome-shaped crucible 
 former. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1197 
 
 A mix of refractory investment material is made and 
 carefully ai)plied around tlie wax model in such manner as to 
 eliminate the air. 
 
 The investment ring or flask is then set on the crucible 
 former and its interior filled with investment material, thus 
 surrounding tlie previously coated model. 
 
 17 - 15 
 
 THE TAGGART CASTING .yPI.IAXCKS 
 
 Wlien the investment lias hardened, the crucible former 
 and sprue former are removed. 
 
 The invested case is then heated to expel the moisture and 
 dissipate the wax. 
 
 The flask or investment ring is then set in the depressed 
 base of the casting macliine. the metal placed in the crucible 
 depression of the investment and fused with the flame from 
 an attached blowpipe of the nitrous oxide and gas type. 
 
 When fused, the i^lunger which carries a sealiug cap ou 
 its lower end is brought forcibly down upon the upper end of 
 the flask, thus preventing escape of the nitrous oxide gas. 
 
lUlS A liRlKK HISTORY OK I'UOSTHIOTK; DIONTISTRY 
 
 wliicli is autoiiiiiticjillx- ;i(linittc(l at llic time (if scaling' tlic 
 enu'ible space. 
 
 TTnder coinprcssioii of the ,i;as, the fiiseil metal is forced 
 through the sjirue into the mold. 
 
 The essential principles iii\dl\cd in this i)i-ocess iriay l)e 
 Itriefly summed uj) as follows: 
 
 A wax model formed with or without a metallic matrix, 
 an investment ring, a metallic sprue former, a metallic 
 crucible former, a sealing cajj for confining the compressed 
 gas, a single investment matrix, dissipation of the wax i)attern 
 by heat, injecting the fused metal into the mold by com 
 ])ressed gas. 
 
 The discovery by Dr. Taggart that in order to cast 
 shar])ly gold must be superheated, constitutes the most valu- 
 able contribution to the casting i)rocess introduced within re- 
 cent years. 
 
 This he accomplished and demonstrated by means of his 
 casting appliances to which a blowpipe of the Knapp pattern 
 was adapted. With the Taggart appliance or the Knapp blow- 
 pipe, gold in small quantity can be readily heated several hun- 
 dred degrees above its melting point. 
 
 In using either of these appliances, care must be observed 
 not to overheat the gold or hum it. When excessively over- 
 heated, even pure gold is slowly but gradually dissipated, 
 while if composed of an alloy some of the lower fusing con- 
 stituents will be oxidized or volatilized, thus impairing the 
 quality of the metal for specitic j^urposes. 
 
 Again, in superheating the gold excessively, the invest- 
 ment deteriorates, resulting in rough surfaces in the mold, 
 change in form of the latter, and in some cases intimate union 
 of the investment with the casting. 
 
 By means of an ordinary gas blowpipe, with a free inlet 
 for both gas and air, and means for controlling the same, to- 
 gether with a strong pressure of air such as can be developed 
 with a large foot bellows or power pumjj, equally good results 
 may be accomplished without danger of dissipating the gold 
 or impairing the investment. (See page 1050.) 
 
 RECENT APPLIANCES 
 
 Within recent years many devices in which some of the 
 older methods of pressure mentioned were employed have 
 been introduced, two of which will be described. 
 
A BRIEF HISTORY OF PROSTHETIC DENTISTRY 1199 
 
 THE SOLBRIG CASTING PLIERS 
 
 'I'his devic'i^ consists of |ilit'i- liainllcs; to the shorter (MkI 
 of one is attaolied a pad coiitainiiiu,' moidiiu' or moist asbes- 
 tos. 'Pile ojii)osite beak coiitains a depression in whioli rests 
 the investment ring'. When t'liseil, the metal is foreed into tlie 
 
 LURKi CASTING AI'PLIANCE 
 
 mold by closing the plier handles, thus Ijringing the pad at- 
 tached to the opposite beak in contact with the ring margins 
 and sealing the crucil)le chamber. (Ash's Quarterly, 1910.) 
 
 THE BIBER CASTING APPLIANCE 
 
 This consists of a base for snjjporting tiie investment 
 ring, and a cup device containing moldine or clay. 
 
 THK IJIBEU CASTI.NG APPLIANCE (ASH'S 
 (lUARTERLT. 1910. SLIGHTLY MODIFIED) 
 
 When the gold is fused, the caj) is applied to the ring and 
 the metal forced into the mold liv hand pressure. 
 
 From this brief outline of casting operations in the past, 
 the names of a number of men who engaged in this work, to- 
 
l:iOO A BRIEF HISTORY OF PROSTHETIC DENTISTRY 
 
 gether with a description of their methods and appliances, 
 have been omitted for laclc of time and space. 
 
 The writer has attein])ted to present in a concise and dis- 
 passionate manner those facts which lie has been able to care- 
 fulh^ gather from reliable sources, pertaining to the inception 
 and growth \\\) to present development of the five funda- 
 mental principles of the casting jorocess. 
 
 That the science of precision casting is yet imperfect is 
 evident since the control of dimensional changes in tlie ma- 
 terials used lias not yet been accomplished. 
 
 By simplest means and with crudest appliances some arc 
 able to secure results equal to the best. Others, ecpiipped with 
 the most convenient and improved apparatus meet with fre- 
 quent failures. Personal equation in this as in many other 
 fields largely determines the (piality of results attained. 
 
 From this outline it will also be seen that the development 
 of the five fundamental principles of casting as practiced to- 
 day is the result of the composite effort of many men, extend 
 ing over a period of many years. Practically all of the proc- 
 esses had become, and most of them were long ago recognized, 
 as heritages of the profession, since time and use had rendered 
 them more or less common methods of ]>rocedure. 
 
INDEX 
 
 Absorption of alveolar borders. .. .18-22 
 
 irregular 191 
 
 under stress 497 
 
 unequal 320 
 
 Abutments, in engineering bridge 
 
 construction 783 
 
 in dental bridgework 781) 
 
 preparation of roots and 
 
 teeth for 795 
 
 selection of suitable roots 
 
 and teeth for 790 
 
 Acid for pickling 169 
 
 Adaptation, denture, comparative 
 
 results with different bases 126 
 
 Adhesion, physics of 24 
 
 useful in denture retention 24 
 
 Adjusting the face boiv to occlu- 
 sion models and face 330 
 
 to occluding frame 332 
 
 Affinity of metals for each other... 1000 
 
 Alabaster 43 
 
 Alexander, Dr. A. C, denture re- 
 pair 573 
 
 Alexander, Dr. A. C, method of re- 
 pairing vulcanite 673 
 
 Alexander, Dr. C. L., inlays. .1174-1176 
 Allen, Dr. John, continuous gum... 
 
 590, 901, 902, 905 
 
 Alloys 999 
 
 affinity of metals for each other.lOOO 
 
 binary 1014 
 
 copper amalgam 1O02 
 
 dental amalgam 1001 
 
 eutectic 1001 
 
 for crown, bridge and plate 
 
 work 1026 
 
 for inlay casting 1030 
 
 for prosthetic casting 1028-1029 
 
 for tempering 1067 
 
 Matthiessen's theory of 9i)9 
 
 specific gravity of 1002 
 
 triple 135 
 
 Alloying metals, object in 1000 
 
 Alpha rays of radium 963 
 
 Alumino-thermy 992 
 
 Aluminum 1079 
 
 denture bases 120 
 
 cast 191 
 
 swaged 212 
 
 physical properties of 1080 
 
 Alveolar borders IS 
 
 absortion of 18-22 
 
 adapting base plates to 313-320 
 
 reduction of flabby 19-20 
 
 selecting and fitting trays to.... 64 
 
 Amalgam 1001 
 
 dental, history of 1169 
 
 dies, In crown work 664 
 
 restoi-ation of badly decayed 
 
 teeth with 736 
 
 Ambler. Dr. H. L 1111 
 
 Ames, Dr. W. V. B., inlays 1173 
 
 Ansesthetics. local 630 
 
 Analysis of the casting process 1179 
 
 Anatomic and esthetic forms of 
 
 teeth 631-633 
 
 Anatomic method of denture con- 
 struction , 304-463 
 
 masticatory mechanism 269 
 
 Anchorage, of te^th to various 
 
 bases 525 
 
 of plastic substances to metal 
 
 bases 174 
 
 In restorations for crowns 736 
 
 for Inlays 934 
 
 Ancient, prosthesis history of 1101 
 
 records of 1110 
 
 prosthetic appliances 1105 
 
 Anderson, Dr. C. L., bridge 796-840 
 
 Angle, Dr. E. H., impression trays 73 
 
 Annealing metals 168-984 
 
 An outline of metallurgy 960 
 
 Anterior, teeth, bridges for 792-807 
 
 cla.ssiflcation of 807 
 
 crowns for 640 
 
 palatine foramina 11 
 
 typal forms of 362 
 
 ."Antimony 1090 
 
 Antiquity of Ebers' papyrus 1102 
 
 Aphrodite facial outlines 371 
 
 Appliances, in die and counterdie 
 
 construction 128 
 
 anatomical, Gysi 465-1148-1149 
 
 Snow 308-1144-1145 
 
 Application, of bridge restorations 786 
 
 of crown replacements 625 
 
 of full dentures 304 
 
 of heat in soldering 995 
 
 of occlusion rims to base plates 314 
 
 of porcelain 609-SSS-S96-922 
 
 of face bow 330 
 
 Aqueous solutions, separating medi- 
 ums 94 
 
 borax and shellac 94 
 
 soap 95 
 
 Arch, alveolar 291 
 
 bar, palatal 522 
 
 in engineering 783 
 
 palatal 10 
 
 Argol 1058 
 
 Arranging and occluding the teeth 
 
 in full dentures 382 
 
 Arrhenius, Prof. Svante, nebular 
 
 temiperatures 976-994 
 
 Articulation, tempero-mandibular. . . 274 
 
 of sound 401 
 
 Articulators 
 
 Bonwill 1138 
 
 Christensen 1145 
 
 Evans 1137 
 
 Gariot 1136 
 
 Gritman 1143 
 
 Gvsi 465 
 
 Hayes 1139 
 
 Kerr 1144 
 
 Luce 1150-1151 
 
 Plain line 1138 
 
 Plaster 1136 
 
 Schwarz 1147 
 
 Snow 1146 
 
 Starr 1139 
 
 Walker 1141 
 
 Artificial, dentures, physical and 
 mechanical problems involved in 
 
 their construction 23-304 
 
 stone 110-495 
 
 Artistic judgment necessary in de- 
 veloping wax model dentures.... 396 
 
 Asbestos, for investment 689 
 
 Ash's tube teeth 529 
 
 Assembling bridge, structural parts 
 
 of a 829 
 
 crown 687 
 
 .atmosphere 24 
 
 aid in denture retention 1'i 
 
 pressure exerted bv 25 
 
 Atomic weight .' 980 
 
 unit of 980 
 
 Atomic relation of elements to each 
 
 other 971 
 
 Atoms 969 
 
 vibration of 969 
 
 1201 
 
Attaching, bite fork to occlusion 
 
 model ;i26 
 
 ancliorage loops to metal base 
 
 dentures 177 
 
 casts to occluding frame 333 
 
 clasps to baseplate 188-268 
 
 facings to crowns and bridges, 
 
 in repairs 863 
 
 peripheral shoulder wires to 
 
 metal bases 175-4S9 
 
 teeth to baseplate, by soldering 188 
 Attachments, for retention of partial 
 
 dentures 233 
 
 clasps 236-500 
 
 specialized frictional appli- 
 ances 305-525 
 
 for bridges S32 to 858 
 
 Carmichael 832 
 
 modified 836 
 
 Corcoran 835 
 
 Goslee, inlav clasp 851 
 
 Heddy 840 
 
 split dowel crown 845 
 
 St John inlay 936 
 
 telescoping crown . . . : 844 
 
 Autogenous soldering, (sweating) . . 995 
 Automatic, blowpipes, Knapp, Tag- 
 
 gart 958 
 
 flask closing devices 446-454 
 
 gas regulators 452 
 
 safety valve 453 
 
 Babbitt metal 134-1087 
 
 Backing, porcelain facings, in crown 
 
 and bridge work 682 
 
 Bailey flask 129-156 
 
 Bak iiig, of porcelain 
 
 615-878-885-888-897-926 
 
 Balancing contact 
 
 299-307-317-334-391-404 
 
 Banded, crowns 
 
 . . . 640-721-733-735-S44-S48-S73-S81-8S3 
 
 Bar, forms of lingual bars 491 
 
 contact 506 
 
 lingual, combined with gold sad- 
 dles 496 
 
 palatal arch 622 
 
 Barium 968 
 
 Barns. Dr., inlay.s 1178 
 
 Bartlett. Dr. Walter M 38-622 
 
 Base metals 980 
 
 Baseplates 118 
 
 celluloid 123 
 
 ideal 126-230 
 
 metal 119-126-166-1S0-208-222-588 
 
 requirements of 313 
 
 Bases for artiflcial dentures lis 
 
 alu!ninum 120 
 
 alloys of tin 120 
 
 celluloid 125 
 
 comparative results in adapta- 
 tion 126-127 
 
 gold lis 
 
 platinum 119 
 
 vulcanite 121-127 
 
 Basic ingredients of porcelain 904 
 
 constituents of rubber 436.439 
 
 Bean, Dr. .1. B 218-1157, 1182 
 
 Beautv. science of 360 
 
 Beeswax 59-946 
 
 Bennett, Dr. N. G 299-1148 
 
 Benson. Dr. C. W 750 
 
 Bequerel Radium 963 
 
 Berdmore 1123 
 
 Beryllium 967 
 
 Bessemer steel 1066 
 
 Beta rays 903 
 
 Bevan, Dr., experiments in vu)can- 
 
 izlng 43S 
 
 Beveling 681 
 
 Biber 1199 
 
 Bilious 356 
 
 Binary 1014-1026 
 
 Bing ' 1162-1167-1171 
 
 Birkland, Dr. J. W 769 
 
 Birmingham wire gauge 1094 
 
 Bismuth 1089 
 
 Bite fork 326 
 
 modified 675 
 
 Bite, meaning of term 327 
 
 difficulty in taking 327 
 
 practical method for securing. . 329 
 
 various methods of such 327-330 
 
 Black, Dr. O. V 
 
 IS, 125, 278, 305, 306, 931, 1156 
 
 Blanch Barkley, nugget 1005 
 
 Hlandy, Dr. A. A 227-1182 
 
 Blocks, porcelain. 532-620-621-622-1127 
 
 Blowpipe 
 
 flame, structure of 996-1198 
 
 Knapp's nitrous oxide 958 
 
 Stiver's gas 692 
 
 Bodily functions 7 
 
 impairment of 8-397 
 
 Bogue, Dr. E. A 1171 
 
 Bonwill, Dr. W. G. A : 
 
 . . 238-273-308-1137-1138-1141-1142-1159 
 
 Borax 1057 
 
 Boron 967 
 
 Boser's rule 1010 
 
 Bowditch 283 
 
 Brantt 436 
 
 Brass 1078 
 
 Bridgeford, Dr., rubber paste for 
 
 repairs 586 
 
 Bridges (Engineering) 783 to 7S6 
 
 arch 783 
 
 cantilever 785 
 
 girder 784 
 
 Howe truss 784 
 
 pontoon 785 
 
 suspension 785 
 
 Bridges (Dental) 786 to 856 
 
 fixed 786 
 
 classification of 786-798 
 
 extension 789, 1166 
 
 saddle 787 
 
 .sanitary 789 
 
 removable 841 
 
 repair of 856 
 
 Bridgework (dental) 786 to 856 
 
 fixed 786 to 841 
 
 abutments and piers 790 
 
 preparation of teeth and 
 
 roots for 795 
 
 selection 791 
 
 constructive technic 823 
 
 factors to be considered in 
 
 planning 790 
 
 history of 1162 
 
 means of attachment other 
 than crowns 
 
 Oarmichael 832 
 
 modified 835 
 
 Corcoran 835 
 
 Heddy 840 
 
 inlays 797, 939 
 
 St. John 936 
 
 removable 841 to 856 
 
 attachments 842 
 
 inlay 851 
 
 lingual half crown 852 
 
 split dowel 845 
 
 telescope crown 844 
 
 modifications of .... 855 
 
 repair of 856 to 872 
 
 Brief outline of recent discoveries.. 962 
 
 Britannia 35-1090 
 
 Bromine 967 
 
 Bronze 1079 
 
 Brophv, Dr. R. C 220 
 
 Brown, Dr. E. P 1161 
 
 Brown and Sharp 1094 
 
 Briick, Dr. W. W 1170 
 
 Bryant repair system 861 
 
 Buckingham. Dr 54 
 
 Bunsen burner 997 
 
 Burchard. Dr. H. H 19 
 
 Bush, Dr. A. .T.. classification of 
 bridgework 798 
 
 Cadmium 1084 
 
 Caesium 967 
 
 Cajaput 954 
 
Calcar 129 
 
 Calcium 968 
 
 Calipers 460-654 
 
 Calorie, the unit of heat energy 121 
 
 Candle, flame 996 
 
 Cantilever bridge 7S5-7S9 
 
 Caoutchouc, tlie basis of rubber.... 436 
 
 Cap, in crown work 651 
 
 construction of 651-662 
 
 direct method 651 
 
 indirect method 662 
 
 Carat, use of term 1010 
 
 Carbon 967 
 
 Carmichael attachment 832 
 
 modified 835 
 
 Carroll, Dr. C. C, casting alumi- 
 num 219-1186 
 
 Case, Dr. C. S., enamel cleavers.. 644 
 
 Cassius, purple of 900 
 
 Cast, definition 33 
 
 crowns 770 
 
 cusp of 769 
 
 denture bases 120-190 
 
 aluminum 120-190-1182 
 
 Watts metal 120, 222 
 
 trays. Impression 38 
 
 iron 1065 
 
 Casting Counterdies 159-759-760-761 
 
 clasps 264-851-852 
 
 crowns 770 
 
 dies 153-256 
 
 inlays 957 
 
 materials used in inlay work.. 
 
 944 to 953-1047 
 
 plaster , 33 
 
 rings for molding 129 
 
 root restorations 737 
 
 Casts, production of 90 
 
 change of form under stress.... 100 
 
 construction of 100 
 
 distinction of term, from model. 33 
 
 forms for 96-98 
 
 materials used for 101 
 
 necessity for use of resistant 
 
 materials 101 
 
 partial cases 104 
 
 removal of iinpn-s.-^inns from.... 
 
 106, 107, 109 
 
 strengthening isolated teeth on. 105 
 treating surfaces of, for vulcan- 
 ite 432 
 
 treatment of impressions for 105 
 
 warpage 106 
 
 Cavitv preparation for inlays 912 
 
 gold 931 
 
 porcelain 912 
 
 Celluloid 551 
 
 dentures 550 
 
 casts for 97, 560 
 
 technic of construction.... 
 
 555-559 
 
 Cement, as an Impression material 57 
 as a medium for setting crowns 
 
 and inlays 694-910-913-930-959 
 
 general composition of 117 
 
 shadow problem in inlay resto- 
 ration 92S 
 
 Cementation process 1066 
 
 Cementum 625 
 
 Cerium 968 
 
 Change of volume in rubber during 
 
 vulcanization 447 
 
 color, in porcelain due to metal 
 
 backing 6S2 
 
 dimensional in material em- 
 ployed in casting 944 
 
 Chase's molding sand 129 
 
 Chaser 183, 763 
 
 Character of emanations from 
 
 radio-active substances 963 
 
 Chemical constituents of rubber. . . . 440 
 changes in ru'bber due to vul- 
 canization 441 
 
 formulae of wax and paraffin... 
 
 946-917 
 
 of plaster of Paris 43 
 
 Chemistry of vulcanization 441 
 
 photograpliy 1075 
 
 Chlorination process 1008 
 
 Chlorine 956 
 
 Christensen, Dr. Carl.. 275, 308, 337, 1145 
 
 Chromium 968 
 
 Cicero, facial outlines 369 
 
 Cinnabar 1087 
 
 Clamps, soldering 185, 186 
 
 Clapp, Dr. G. W., color analysis.. 379 
 
 Clark, Dr. F. H., crown 1154 
 
 Clark, F. W., unequal distribution of 
 
 elements 970 
 
 Clasp metal 10.S3 
 
 formuUe for (Weinstein) 1034 
 
 gauges commonly used 241 
 
 Clasps 236 
 
 advantages and objections 236 
 
 application of 246-249 
 
 indications and contra-indica- 
 
 tions governing 246 
 
 requisites of T.'," 
 
 technic of construction 250-264 
 
 t.N'pes most commonly used .... 
 
 "242-249-500-505 
 
 Classification, bridgework (Bush).. 798 
 
 natural teeth (Williams) 362 
 
 temperaments 356-357 
 
 Clay 902 
 
 Clearing, matrix of wax in vulcan- 
 ite work 414 
 
 mold of wax in cast base den- 
 tures 204 
 
 in inlay work 956 
 
 Cleavers 644-645 
 
 Cocaine 630 
 
 Coefficient of expansion 989 
 
 Coin gold 1010-1018-1060-1061 
 
 Coke furnace, for baking porcelain. 1130 
 
 Collodion 93-1134 
 
 Colloids 4::6-437-969 
 
 Color problems in tooth .selfction 373 
 
 compleinentary 377 
 
 principles, syhop.sis of 374 
 
 primary, secondary, iiitrnx 
 
 ' chart' of .'. .... . . !■ i..niisi,i,-ce 
 
 Columbium 96S 
 
 Compensating curve, meaning of the 
 
 tert 
 
 300 
 
 development of, on occlusion 
 
 models 343 
 
 fundamental principles of.. 344 
 
 omitting 353 
 
 practical steps in 348 
 
 Ulsaver's method 352 
 
 Wilson's method 354 
 
 modification of 302 
 
 Composition, alloys of gold plate.... 
 
 1011-1026-1027-1038 
 
 artificial stone HO 
 
 Babbitt's metal (Haskell's) .134-1087 
 
 beeswax 946 
 
 celluloid 551 
 
 clasp metal 1012-1034 
 
 dental rubber 439 
 
 Hux, oxidizing 1059 
 
 reducing 1058 
 
 soldering 1056-1060 
 
 gold, for casting 1029-1030-1032 
 
 investment materials. .1044-1046-1047 
 
 Melotte's metal 135-136-1089-1090 
 
 modeling compound 58 
 
 plaster 43 
 
 porcelain continuous gum body 904 
 
 gum enamel 906 
 
 solders gold 1011-1036-1038 
 
 platinum 1012 
 
 silver 1075 
 
 tinner's 1086 
 
 Compressibility of plaster 56-428 
 
 Condit, Dr., attachment 512 
 
 Conductivity, denture base material 121 
 
 electricitv S87 
 
 heat ..." 986 
 
Condyles, articular surfaces of man- 
 dible 274 
 
 form of -72 
 
 location of 272 
 
 patiis of 274 
 
 lateral 297-472 
 
 methods of registering. . .336-466 
 
 protusive 296-466 
 
 variation In pitch of 275 
 
 Conic forms of natural bicuspids 
 
 and molars 633 
 
 method of band construction. 635-745 
 
 Constitution, Kinetic, of matter 968 
 
 Construction of, dentures 304 
 
 aluminum 190-208 
 
 celluloid 551 
 
 contiiluous gum 588 
 
 wax model 405 
 
 weighted 221 
 
 vulcanite 304-463-476 
 
 bridges 783-849-891-900 
 
 casts 96-97-100 
 
 counterdies" '.'.'139-159-165-759-760-761 
 crowns.. 625-7S2-S44 to 856-873 to 893 
 
 dies 139-153-165-256 
 
 inlays 901-959 
 
 occlusion models 314 
 
 Continuous gum, body and enamel 
 
 608-904-906 
 
 dentures 583 
 
 advantages 588 
 
 disadvantages 588 
 
 sequent step in construction 
 5SS-619 
 
 Contouring, shell crown band 749 
 
 cast crowns 770 
 
 continuous gum dentures 588 
 
 occlusion models 322 
 
 patterns for seamless crowns.. 773 
 
 pliers 25S-750-751-900 
 
 wax model dentures 395 
 
 Contour models in anatomic worlc.. 313 
 construction of 314 
 
 Copper 1077 
 
 alloys of 1078 
 
 amalgam 1002 
 
 as a hardening agent in gold 
 alloys 1026 
 
 Corcoran attachment in bridgework 
 787-835-838 
 
 Cores 99-142-147 
 
 Coronium 976 
 
 Counterdies 159 
 
 construction of, by casting 159 
 
 dipping 161 
 
 metals and alloys 136 
 
 fusing points of 136 
 
 for partial denture bases 164 
 
 partial 162 
 
 requirements of 136 
 
 Countersunk, pin teeth 528 
 
 retention holes, aluminum bases 
 
 210-218 
 
 root cap 669 
 
 Cradle in placer mining 1006 
 
 Crowns, artificial, various forms. 625-7S2 
 
 banded, baked porcelain 874 
 
 Bean 1157 
 
 Beers 1158 
 
 Black 1156 
 
 Bonwill 1159 
 
 Brown 1161 
 
 Buttner 1160 
 
 cast 770 
 
 Clark, F. H 1154 
 
 Davis, plain 725 
 
 banded 733 
 
 cast base 731 
 
 DeChemant 1152 
 
 Dwlnelle 1155 
 
 Foster 1154 
 
 Fouchard 1116 
 
 Gates 1158 
 
 How 1160 
 
 Johnson & Lund 716 
 
 Justl 730 
 
 Crowns — Continued. 
 
 Logan, plain 717-1161 
 
 banded 721 
 
 Land, jacket 885 
 
 lingual half 852 
 
 Mack 1157 
 
 Morrison 735-1156 
 
 porcelain faced 640 
 
 jacket 880 
 
 Richmond 1159-1164-1165 
 
 shell, two piece 735 
 
 seamless 772 
 
 shoulder 771 
 
 Smith 1153 
 
 split dowel 845-849-1154 
 
 telescope 844 
 
 tube. Ash's 529-1135 
 
 Twentieth Century 716 
 
 Weston 1160 
 
 White, S. S 1162 
 
 Wood 1155-1156 
 
 wood pivot 1153 
 
 replaceable porcelain teeth and 
 
 facings for 696 to 725 
 
 diatoric 715 
 
 Dimelow 857 
 
 Evslin 702-703-704 
 
 flat back, Ash's 529-531 
 
 grooved 1153 
 
 Gardiner 712-713-714 
 
 Goslee 707 
 
 long pin 700 
 
 Merker 714 
 
 Steele 697-698-858 
 
 technic of construction 697 
 
 cap and dowel 641-662-663 
 
 cast base 731 
 
 plain base '726 
 
 shell 739 
 
 various repair methods for 856 
 
 crown slitter 870 
 
 post puller, Skinner 868 
 
 White, S. S 869 
 
 systems. Bryant 862 
 
 Steele's 858 
 
 Crucible, in steel production 1066 
 
 chamber 1199 
 
 former 201 
 
 space in investment 1198-1199 
 
 Crystallization, of plaster 47 
 
 effect of cohesiveness on metals 
 
 983-984-985 
 
 Crystals of plaster, size of 48 
 
 Cupellation 1074 
 
 Curie, Madame 963 
 
 Curve, compensating 300 
 
 Spec, Graf von 302 
 
 Cushing. Dr. George H., clasp.... 241 
 Cusps, development of in crown 
 
 work 755-772 
 
 adapting to axial band 763-766 
 
 developing in plaster 754 
 
 metalline compound 761 
 
 wax 755-764 
 
 reproducing in gold, casting 769 
 
 swaging 759 
 
 Custer. Dr. L. E., furnace 926-1177 
 
 Cutting, bands in crown work. .. .651-744 
 
 conic method 635-746 
 
 compensating curve on occlusion 
 
 models 343 
 
 Cyanide process .1008 
 
 David (facial forms) 371 
 
 Davis crown 725 
 
 Debasement of elements 964 
 
 DeChemant, early porcelain work.. 1125 
 Decomposition, oxides of aluminum 993 
 
 radium compounds 963 
 
 Deglutition, the tongue as an aid in 14 
 
 Dental amalgam alloy 1001 
 
 alloys 1072 
 
 arch 291 
 
 bridgework 786-872 
 
 organs 288 
 
 Dentimeter for root measurement... 649 
 Dentin 625 
 
Dentures, anatomic method. .304 to 475 
 
 full cases 304 
 
 Gysi system 465 
 
 technlc 465-475 
 
 Snow-Christensen method.. 304 
 
 technlc of 304-465 
 
 partial 475 
 
 technlc of 475 to 525 
 
 repairing 561-5S7 
 
 Developing, balancing contact 391 
 
 cusps In gold 759 
 
 metalline compound 761 
 
 plaster 754 
 
 wax 764-765 
 
 Devitalization, in crown work 641 
 
 Diatomaceous earth 1044 
 
 Dies, definition 33 
 
 for clasp construction 256 
 
 for denture construction 153 
 
 metals used for 132-134-136 
 
 purpose of 126 
 
 Differential limit 299 
 
 Digestion 7-8 
 
 Dimelow facing 529-530-531-857 
 
 Direct method of casting denture 
 
 bases 200 
 
 counterdie construction 759-761 
 
 inlay, matrix and wax model 
 
 formation 920-942-953 
 
 root cap construction 659-661 
 
 Discoloration of pink vulcanite in 
 
 repair 567-571 
 
 Discoveries, recent, in chemistry 
 and metallurgy-.. 962, 969, 976, 992-993 
 
 Dispersion of light 374 
 
 Displacement 
 
 Distal margins of upper denture, 
 
 outline form of 30-312 
 
 Distribution of elements, unequal.. 970 
 
 Dobereiner, triads of 372 
 
 Donham flask spring 433-434 
 
 Dovetailing, preliminary in vulcanite 
 
 repair work 576 
 
 Drawing split dowels i<47 
 
 Draw plate 847 
 
 Du Chateau, first efforts in por- 
 celain 1125 
 
 ITuctility 9S3 
 
 Duff. Prof, A. Wilmer, Kinetic con- 
 stitution of matter 970 
 
 Dummies, various forms of 
 
 825-826-827-828 
 
 Dunn. Dr. C. W., inlays 1172 
 
 Dwindle, Dr. W. H., crown 1155 
 
 Early efforts in porcelain 1125 
 
 records of dental prothesis. . . .1110 
 specimens of denture replace- 
 ments 1105 to 1110 
 
 Edge tools, table for tempering. .. .1067 
 Effect of X-ray on various sub- 
 stances 965 
 
 Eka-alumlnum 976 
 
 Eka-boron 976 
 
 Eka-silicon 976 
 
 Elasticltv in metals 986 
 
 modulus of 986 
 
 rubber 439 
 
 Electricity, conductivity of metals.. 987 
 
 exceptions 988 
 
 Electrons 969-970-976 
 
 Electro-welding 991 
 
 Elemental gases 962 
 
 eleotricitv 
 
 Elements 961 
 
 outline of recent discoveries.... 962 
 table of, in order of discovery.. 966 
 
 atomic weight . .•. 967 
 
 periodic table of 975 
 
 their atomic reli-tion to each 
 
 other 971 
 
 Elgin casting machine 959 
 
 Eliminating wax patterns in casting 
 
 204-225-956-1179-1181 
 
 Emery lathe bands 457 
 
 Eminentia articularis 274 
 
 Enamel, removal of from roots 
 
 644-739-741 
 
 Enameling, metal caps in crown re- 
 placements 1155 
 
 Engineering, principles of bridge. 783 
 
 Enlarged raphe 11 
 
 Equalizing denture bearing 105 
 
 Equilateral triangle of Bonwill 273 
 
 Esthetics of denture construction.. 2 
 
 tooth selection 355 
 
 Etching porcelain inlays' 930 
 
 E'thereal solution 93 
 
 Etruscans 1105 
 
 dental art of 1106 
 
 Eucaine 630 
 
 Eutectics 1001 
 
 Evans, Dr. Daniel T 1137 
 
 EVslin tooth in crown and bridge 
 
 construction 702-703-704 
 
 Expansion, coefficient of 989 
 
 compensating for 29-133 
 
 control of 53 
 
 of investment materials 
 
 949-1040-1047-1048-1053 
 
 of plaster 51-52-1043 
 
 silex 1044 
 
 wax 945-1053 
 
 Expression, muscles of 279 
 
 Extension, bridge ((see cantilever) 
 
 785-789-1166 
 
 Extraction of gold 1007 
 
 metals 960 
 
 Eye, color functions of 377 
 
 Face bow 309-1140-1144 
 
 adjusting to occlusion models.. 330 
 
 occluding frame 332 
 
 bite fork of 326 
 
 application to occlusion 
 
 models 326 
 
 object accomplished by its use 309 
 
 Facer, root, Ottolengui 659 
 
 Roach 660 
 
 Facial outlines 360 
 
 proflle 322 
 
 Facing gum porcelain. 532-534-608-617-906 
 
 granular 440 
 
 protesyn 537 
 
 vulcanite, pink 439 
 
 in repairs 567 
 
 Facings, teeth, Dimelow. 529-530-531-857 
 
 Evslin 702-703-704 
 
 flat back. Ash's 531 
 
 grooved 1153 
 
 long pin 680, 715-863 
 
 Steele 697-698-858 
 
 Enactors to be considered in crown- 
 work 625 
 
 bridgework 790 
 
 denture construction 23 
 
 Fact.-!, hypotheses, theories and 
 
 speculations 961 
 
 Farragut, Admiral 367 
 
 Fauchard, bridgework 1116 
 
 crown work 1115 
 
 dentures 1117 
 
 summary 1119 
 
 Feldspar 903 
 
 Fenner 1187 
 
 Ferrite 999 
 
 Fine, Dr. W. M 459 
 
 Finishing, bridges 830 
 
 crowns 693, 725, 767, 781 
 
 dentures 456-461 
 
 Inlays 959 
 
 Finley, Dr. M. S 1176 
 
 First reference to prosthesis 1110 
 
 Fixed dowel crowns 640-716-721 
 
 Flame, structure of 995-998 
 
 Flare of axial surfaces of bicuspids 
 
 and molars 633 
 
 average 634 
 
 greatest 634 
 
 least 634 
 
F.asks, casting 11 
 
 Bean's 1183 
 
 Carroll's 1186 
 
 Fennel's 1187 
 
 Havford's .' 118r> 
 
 Watts 224 
 
 molding 129 
 
 Wood's 203 
 
 Zeller 11S6 
 
 Bailey 129-156 
 
 Hawes' 129-156 
 
 Lewis' 129-157 
 
 rings, nest of 129 
 
 vulcanite 4ns 
 
 Flasking, aluminum, wax models 
 
 for 196-201 
 
 celluloid 556 
 
 vulcanite, full cases 410 
 
 partial cases 481 
 
 Flexure, elasticity of 239 
 
 Flow of metals under stress 986 
 
 Fluorine 968 
 
 Flux, oxidizing 1059 
 
 reducing 1058 
 
 soldering 1056 
 
 Fogg's interstitial gum facings. .480-620 
 
 Fonzi, teeth 1127 
 
 Force of mastication 271-306-806 
 
 Forms of matter 979 
 
 F'ormuUe for casting gold "A," 
 
 "B." "C," "D" 1029-1032 
 
 clasp gold 1012-1034 
 
 dental alloy 1072 
 
 amalgam alloy 1001 
 
 gold solder 1011-1038 
 
 gold plate No. 1-2 1026-1027 
 
 investment compounds (cast- 
 ing) 1052 
 
 investment compounds (solder- 
 ing) 1046 
 
 oxidizing flux 1059 
 
 platinum solder 1012 
 
 reducing flux 1058 
 
 silver solder 1075 
 
 soldering flux 1056 
 
 specific gravity 981 
 
 Foster crown 1154 
 
 Fracture of enamel 645 
 
 Fractured bridge S71 
 
 vulcanite dentures 561 
 
 Freezing of metals 981-1031 
 
 French's impression plaster 52-101 
 
 Friability of porcelain 909 
 
 F'rictional or working surfaces of 
 
 the teeth 288 
 
 Full dentures (see dentures) 
 
 Furlong's plastic rubber 586 
 
 Furnaces, porcelain 613-614-897-898 
 
 Fusible metals (Hall's formulas) . .1090 
 Fusing point of metals 981 
 
 Gadolinium 967 
 
 Gallium 967 
 
 Gardiner, replaceable facings 712 
 
 Gariot, Dr. .T. B 1136 
 
 Garretson bite guide 328 
 
 Gas and nitrous oxide blowpipe. . . . 958 
 
 regulator 451-452 
 
 Gasoline furnace 898 
 
 Gates crown 1158 
 
 Bonwill crown 1159 
 
 Gates, for surplus rubber 417 
 
 (gauges, steam 450 
 
 Gauging amount of rubber 427 
 
 General classification of bridgework 786 
 Genese. Dr.. developing lingual 
 
 forms of teeth in vulcanite 459 
 
 German silver trays 39 
 
 Germanium 968 
 
 Gilmer, Dr. T. L., suggestion for 
 
 correct mounting of casts 1140 
 
 Gllmore, Dr. Steele, frictional at- 
 tachment 514 
 
 Gingival, termination of cementum 626 
 
 Girder, in bridge engineering 784 
 
 Glaesenapp, Prof. M., plaster 45 
 
 Glands, salivary, function of l.'i 
 
 Glass inlays 1070-1073 
 
 Glazing porcelain 618-928 
 
 Glenoid fossa 274 
 
 Gold 1004 to 1063 
 
 alloys of, see index 
 
 carat, meaning of term lOlO 
 
 extraction 1007-1008 
 
 formula, see index 
 
 raining 1005 
 
 preparation of pure 1009 
 
 reduction of I Hosci'.s rule) 1010 
 
 .Sdlrt.TS. .S.'C toiiiiulie 1011 
 
 treatment i)f .■fi-iap 1009 
 
 Goldschmidt, I'rof 993 
 
 Goslee, Dr. H. J 193,851,954 
 
 tooth 707 
 
 technic of application 70S 
 
 Graphite 949-1053 
 
 Gravity, specific, formula for esti- 
 mating 981 
 
 casting 
 
 222-1182-1184-1185-1188-1194 
 
 Greene, Dr. J. W 27, 87 
 
 Grinding porcelain crowns 717, 728 
 
 facings 680-693-887 
 
 Grinding to correct occlusion 388 
 
 Griswold attachment 524 
 
 Grlswold, Dr. W. M 1177 
 
 Gritman, Dr. A. D 1143 
 
 Groove, rectangular 288-290 
 
 Ground gypsum 44 
 
 Guerini, Di". Vincenzo 1101 
 
 history of dentistry 1103 
 
 Gum, sandarac 93 
 
 Gutta percha 62 
 
 Gysi, Di-. Alfred 308. 460-465. 1148 
 
 Half band crown 845 
 
 crown 852 
 
 round wire clasps 243 
 
 for split dowels S46 
 
 Hammond furnace 614 
 
 Hancock. Thomas, vulcanite 438 
 
 Hard, bite wax 60 
 
 solder 995 
 
 Hardening steel 1066 
 
 Harmony defined 358-374 
 
 laws of, applied in tooth selec- 
 tion 360 
 
 Harper, Dr. W. E 741-1187 
 
 Haskell, Dr. L. P 134-135-1087 
 
 Hawes, Dr. G. E 129-148-1184 
 
 Hayes, Dr. R. S 1139 
 
 Hayf ord. Dr. J. W 1184 
 
 Head, Dr. Joseph 306 
 
 Heat 986-988-98! 
 
 Heating, flask in vulcanite work 4U 
 
 investment for soldering 1054 
 
 for casting inlays 956 
 
 Hebrews, dentistry among the 
 
 ancient 1111 
 
 Heddy, Dr 840 
 
 Helium 967 
 
 Heinrichsen appliance 504 
 
 Herbst, Dr 1173 
 
 Herder, reference to mouth 3 
 
 Herodotus, reference to ancient 
 
 dentists 5 
 
 Hickman, Dr., inlays 1171 
 
 High and low fusing porcelains.... 907 
 
 lip line 324 
 
 temperatures 993 
 
 Hindu prosthetic specimens 1109 
 
 Hinge tray 677 
 
 Hippopotamus, dentures of 1110-1114 
 
 Histology 626 
 
 History of dentistry (Guerini's) 1103 
 
 Holder, cotton roll 76S 
 
 crown 767 
 
 Hollingsworth, Dr. M. W 1188 
 
 Horn, mallet 171 
 
 pene hammer 262 
 
 Hot and cold molds 
 
 957-1049-1050-1054-1087 
 
 How. Dr. W. S., crown .....1160 
 
 Hutchinson, Dr., on temperaments. 356 
 
Hj'dro-carboii, rubber 140 
 
 Hydrogen, debasement of other ele- 
 ments into 964 
 
 Hygienic requirements of crowns.. 63!) 
 Hyperaemla, due to mechanical irri- 
 tation 124 
 
 Hypotheses in reference to ele- 
 ments 961 
 
 Impression 3:i 
 
 materials 42 
 
 beeswax 59 
 
 beeswax and paraffin 59 
 
 cements 57 
 
 classification of 42 
 
 gutta percha 61 
 
 modeling compound 5S 
 
 plaster 43 
 
 of clasp, teeth and baseplate.. 267 
 
 of root in crown work 663 
 
 of teeth to be clasped 252 
 
 rebuilding 254 
 
 relieving 27-31 
 
 technic of taking. .63-68-69-71-72-74 
 
 difficult cases 79 
 
 modeling compound Sl-86 
 
 partial cases 73-495 
 
 plaster 63 
 
 tray 34 
 
 fitting 36-3S-64 
 
 hinge 677 
 
 nomenclature 35 
 
 special 3S-39-40 
 
 treating and tilling of 90-105 
 
 Incisor teeth 28S 
 
 path 295 
 
 registering 469 
 
 India rubber (.see caoutchouc) 436 
 
 Indirect method of constructing.... 
 
 cast aluminum 193 
 
 counterdie 760 
 
 inlay matrix and wax model. 942. 943 
 
 root cap 662-S36-SS0 
 
 Indium 967 
 
 Individual saddles 78S-S26 
 
 Infection, the mouth as a focus of.. S 
 Inflammatory mucous tissue under 
 
 vulcanite 122 
 
 Inlays 901-959 
 
 gold, cast 944 
 
 cavity preparation 931 
 
 matrix method of produc- 
 tion 942 
 
 direct 942 
 
 indirect 943 
 
 technic of construction 953 
 
 physical properties of 
 
 materials employed . . 944 
 
 porcelain 901-908 
 
 basic ingredients 902 
 
 properties 904 
 
 cavity preparation 913 
 
 technic of construction. .919-931 
 
 Insoluljle constituents of rubber 440 
 
 Inter-articular fibro-cartilage 274 
 
 Interchangeable teeth 706 
 
 diatoric 715 
 
 Evslin, (posterior) ....:.. 702 
 
 Gardiner 712 
 
 technic of application 712 
 
 Go.slee 707 
 
 technic of application 708 
 
 Merker 714 
 
 Steele, posterior 697 
 
 tooth facings 697 
 
 Ash 531 
 
 nimelow 530, 857 
 
 Evslin 702 
 
 long pin 700 
 
 Steele's 697 
 
 application 697 
 
 Internal lateral ligament 286 
 
 Investing, aluminum, wax pattern 
 
 for 196. 203 
 
 banded, I>ogan 724 
 
 bridge, for soldering 830 
 
 Investing — Continued. 
 
 cap and dowel 672 
 
 celluloid 556 
 
 continuous gun, for soldering... 600 
 
 Richmond crown 890 
 
 vulcanite, wax model denture 
 
 for 410 
 
 wax model inlay for casting.. 955 
 wax model foi" weighted lower. . 223 
 
 Investment, compounding of 1052 
 
 compounds for casting 1047 
 
 soldering 1040-1044 
 
 directions for use 1053 
 
 for aluminum rases 203 
 
 heating of 1054 
 
 Iodine 631 
 
 Iridio-platinum 1023 
 
 Iridium 1023-1072 
 
 Iron ores 1062 
 
 hama?tite 1063-1064 
 
 magnetic 1063 
 
 occurrence 1063 
 
 pyrites 1064 
 
 reduction of 1064 
 
 spathic 1064 
 
 forms of 1063 
 
 cast 1065 
 
 steel 1065 
 
 wrought 1065 
 
 Ivoiy appliances 1110-1114 
 
 Ivory. Dr. J. W 644.768-843 
 
 Jacket crowns, porcelain 880 
 
 Land 885 
 
 Jenkins' porcelain 907 
 
 Jewelers' gauge 1095 
 
 gold plate 1011 
 
 Johnson and Lund crowns 716 
 
 Joint, tempero mandibular 274 
 
 bevel in vulcanite repairs. .. .564-565 
 
 Juno, facial outlines 371 
 
 Justi crown 730 
 
 impression trays 65-74-87 
 
 porcelain body 90'7 
 
 teeth, gum sections 621 
 
 plain 526 
 
 Justi. H. D.. teeth 526-621 
 
 K plier for inlav %vork 924 
 
 Kaolin 902 
 
 Kelly attachment 523 
 
 Kennedy, Dr. E.. modified Uarmi- 
 
 chael 835 
 
 Kerr articulator 1144 
 
 impression trays 82-85-88 
 
 metal forms for casts 96 
 
 soldering tweezers 766 
 
 Kieselguhr 1044 
 
 Kinetic, constitution of matter 968 
 
 Kingsley alloy 227 
 
 scrapers 29-458 
 
 Knapp. Dr. J. Rollo. blowpipe. .958, 1196 
 
 bridgework 1166 
 
 Knight. E. H., definition of a sprue. 1180 
 Koch. Dr. C. R. E., history of den- 
 tistry nil 
 
 Krypton, discovery of 961-962 
 
 Labial. contouring of occlusion 
 
 models 316 
 
 Ladles, melting 131-256 
 
 Land. Dr. C. H.. porcelain inlays.. 1171 
 
 jacket crown 885 
 
 Lane, Dr. J. G.. silica 1048 
 
 Lanthanum 967 
 
 Lathe, polishing 456. 457-461 
 
 Lavater. discourse on the mouth.... 3 
 
 Lawrence-Foster crown 1154 
 
 Lead method in silver reduction. . .1074 
 
 physical properties of 1085 
 
 Le Gro. Dr. A. L.. cavity prepara- 
 tion 941 
 
 Lever, the mandible as a 271 
 
 Leverage on denture bases 25 
 
 Lewis fla.sk for molding 129-:157 
 
Ligaments, the mandibular 284 
 
 capsular 285 
 
 lateral 286 
 
 external 286 
 
 Internal 286 
 
 spiieno-mandil)Uiar 2S6 
 
 stylo-mandil3ular 2S6 
 
 Lime bloclj, in fusing platinum .... 1071 
 
 Lingual muscle.s 14 
 
 marginal ridges ;!S8 
 
 Lips as a feature of the face 9 
 
 as a guide in establishing plane 
 
 of occlusion 320 
 
 Liquation 1000 
 
 Liquid silex in vulcanite work.. 417. 432 
 
 Lithium 967 
 
 a product of debasement of cop- 
 per 964 
 
 Litigation, dental vulcanite 1133 
 
 Lixiviation, in recovery of gold.... 1008 
 Locating high and low lip lines. 318-324 
 
 median line 318-324 
 
 outer ends of condyles 318-325 
 
 Logan. Dr. M. L.. crown 1161 
 
 Loop clasps 500-501-503-504-505 
 
 Loose pin anchorage for inlay abut- 
 ments 941 
 
 Lower jaw (mandible) 270 
 
 Luce. Dr. C. E.. condyle move- 
 ments, and articulator 283-1150 
 
 Lymphatic temperament 356 
 
 Magnesium 966 
 
 chloride 113 
 
 in alumino-thermy 992 
 
 Magnetic iron 1063 
 
 Malleability 983 
 
 Mallet, horn 171 
 
 horn pene 262 
 
 Mallett, Dr.. experiments in vulcan- 
 izing 438 
 
 Mandible 270 
 
 analysis of iatei'al movements. 297 
 articulation with temporal bone. 274 
 
 auxiliary functions 271 
 
 centers of notation 297 
 
 governing factors in movements 
 
 of 295 
 
 muscles whicli control 282-284 
 
 Mandibular ligaments 284-286 
 
 governing factors in movements 295 
 
 Manganese 968 
 
 Manufacture of celluloid 552 
 
 dental rubbers 436-441 
 
 gutta percha 61 
 
 plaster 44 
 
 porcelain 902-907 
 
 steel 1066 
 
 wrought iron 1 065 
 
 Marble dust 129-1043-118S 
 
 Martin. Dr. G. M.. castins: 11S5 
 
 Mash bite lSS-478-576-.i79-673 
 
 Mason spacing calipers 683 
 
 Mastication, muscles of 284 
 
 restoration of function of 1-304 
 
 Masticatory apparatus 269 
 
 mechanism 269 
 
 movements 273 
 
 muscles of 277-284 
 
 Matrix, counterdies 163 
 
 contour. in continuous gum 
 
 cases 598 
 
 direct method of production ... . 942 
 Indirect method of production.. 943 
 packing in vulcanite denture 
 
 construction 418-426 
 
 production of platinum, in por- 
 celain inlav work 911-929 
 
 sand 139 
 
 seamless crown method 773 
 
 Matter, forms 979 
 
 mutability of 961 
 
 Matthiessen's theory of alloys 999 
 
 McClelland. Dr.. rose pearl 551 
 
 McLeod, Dr. W. Bowman, expan- 
 sion of plaster 54 
 
 Measurement, angular divergence of 
 axial walls of bicuspids and 
 
 molars 634 
 
 compressibility of plaster 56 
 
 cutting band according to.. 651-745 
 
 expansion of plaster 52 
 
 plate and wire 1092 
 
 root, in crown work 649-743 
 
 width of band 744 
 
 Mechanical and physical problems 
 involved in denture constiuction. . 23 
 
 Medieval bridgework 1116 
 
 Mediums, separating 92-95 
 
 Melotte's 135-1090 
 
 Melting point, explanation of 981 
 
 Mendeleeff Dimitri. periodic sys- 
 tem of 974-976 
 
 Mercury 1087 
 
 Merker. Dr. M. E.. tooth 714 
 
 Metabolism 7 
 
 Metals, alloys of 999 
 
 a new series of 1' 25 to 1040 
 
 binary 1014 to 1025 
 
 alloying 999 to 1002 
 
 base 980 
 
 native 980 
 
 noble 980 
 
 physical properties of.... 980 to 998 
 
 Metallography 960 
 
 Metalloid 979 
 
 Metallurgy 960 
 
 Methven. Dr. H. F 838 
 
 Meyer. Lothar 974 
 
 Michaels, Dr. W.. translation of 
 
 Glaesenapp's work 45 
 
 Micro-structure of metals 999 
 
 Micrometer caliper 1097 
 
 Micron 969 
 
 Miller. Dr. H. C. celluloid Hask 556 
 
 Millimeter 970 
 
 Mineral, first reference of. for teeth. 1113 
 Minerals, occurrence of. in nature.. 9*9 
 
 Mixing cement 694 
 
 investment 955 
 
 plaster 66 
 
 porcelain 923 
 
 Model, use of term 33 
 
 wax contour and occlusion 313 
 
 denture 313 
 
 for inlay 953 
 
 nf looth for seamless crowns 
 
 773-777 
 
 Modeling compound 58 
 
 composition 58 
 
 manipulation 81 
 
 Molar tooth forms 288-293 
 
 typical forms of 756-757 
 
 Mold, eliminating wax from. .. .956-1181 
 
 variation in method of 956 
 
 expansion of 951 
 
 formation of single 1180 
 
 Molding sand 129 
 
 Molecular tension 169 
 
 disturbance 211 
 
 theory of matter 968 
 
 Molecule 968 
 
 Molydenum 966 
 
 Morgan attachment 509-510-511-512 
 
 Morrison. Dr. W. N.. crown. .. .735-1156 
 
 Mouth, a focus of infection 8 
 
 examination of 18 
 
 Mucous membrane of the palate.... 12 
 
 plaques 124 
 
 Muscle marking impressions 
 
 37, 67-71-85 
 
 Muscles of mastication 277 to 284 
 
 action, summary of 284 
 
 Native metals 980 
 
 Natural denture 288-289-290 
 
 Necessity for use of face bow.. 309. 330 
 
 Neodymlum 967 
 
 Neon 967 
 
 Nero, facial outlines 372 
 
 Nervous temperament 356 
 
 New elements 962-976 
 
 Newlands. octaves of 974 
 
Newtonium 976 
 
 Nickel 10S9 
 
 Nltrog'en 967 
 
 Nitrous oxide blowpipe, Knapp's.. 
 
 958, 1196 
 
 Noble metals 980 
 
 Nomenclature tray 35 
 
 Nonconductivitv of vulcanite 122 
 
 Noyes, Dr. Frederick B., histology.10-626 
 
 Occlude, definition of the term 288 
 
 Occluding frame 307-308 
 
 adjusting condyle paths of 342 
 
 applying face bow with occlu- 
 sion models attached to 332 
 
 arranging teeth to occlusion 
 
 models on 382 to 390 
 
 Gysi and appliances 465-1148 
 
 mounting casts on 332 
 
 removing casts from 406 
 
 Snow, and appliances 
 
 308-332 to 353. 3S2 to 393, 1146 
 
 various types of the 1136-1152 
 
 Occlusal plane, meaning of the term 293 
 
 curvature of 293 
 
 determining correct 319 
 
 Occlusion, anatomical, of natural 
 
 dentures 289-290-294-301 
 
 models 313 
 
 adjusting bite fork and face 
 
 bow to 
 
 330 
 
 arranging the teeth on 382 
 
 construction of 314 
 
 developing compensating 
 
 curve on 343 
 
 restoring disturbed facial 
 
 contour by means of 322 
 
 rims, approximate depth of 31."i 
 bucco-lingual relation of. 
 
 to borders 315 
 
 establishing height of 
 
 individual 319-320 
 
 i-eiiuirements of 314 
 
 trial of, in the mouth 318 
 
 points determined b,\' . . 
 
 318 to 327 
 
 retainer 412 
 
 Occurrence of metals in nature. . . . 979 
 
 Octaves of Newland 974 
 
 Offset crowns 632 
 
 dowels 727 
 
 Ollendorf casting appliances 1194 
 
 Onlays 1192 
 
 Opaque porcelain 929 
 
 quality of cement 928 
 
 vulcanite gum facing 440 
 
 Oral cavity 9 
 
 boundaries of 9 
 
 contents of 9-14 
 
 teeth 9-2S8 
 
 tongue 13-14 
 
 mucous membrane of 10 
 
 epithelium of 10 
 
 palatine vault 10 
 
 bony structure of 10 
 
 foramina of 11 
 
 rugse of 13 
 
 vestibule of 9 
 
 cul de .sacs of 9 
 
 Ores 980 
 
 Osmium 968-1024 
 
 Ottolengui, Dr. R., root-facers 659 
 
 Outline, an, of metallurgy 960 
 
 Overbite 301-535 
 
 Owen, Prof., prehistoric inlays. .. .1169 
 
 Oxides, reduction of, with flux. 99.'i- 1055 
 
 (See noble and base metals).. 980 
 
 Oxyacetylene blowpipe 994 
 
 Oxvchorid of magnesium 110 
 
 zinc 20-117 
 
 Oxygen : 967 
 
 Oxyhydrogen flame 994 
 
 Oxyphosphate of zinc 20 
 
 Packing rubber in vulcanite cases.. 
 
 418 to 42S 
 
 Palatine vault 10 
 
 epithelium of 10 
 
 Palladium. .968. 1021-1026-1027-1029-1034 
 
 Papyrus, Ebers' 1101 
 
 antiquity of 1102 
 
 Parabolic arrangement of the teeth 
 
 in the dental arches 292 
 
 Paraffin 59-946-947 
 
 Parker shot swager 163-164 
 
 Partial dentures 476 
 
 baseplates for 476 
 
 gold, technic of . .180-189-488-490 
 
 lingual bar 496 
 
 vulcanite 477-484 
 
 lingual bar 490-491 
 
 flasking of 481 
 
 planning of 476 
 
 protrusive bite for 478 
 
 retention of 187-233-236-476 
 
 settling of. from use 497 
 
 specialized frictional appliances 
 
 for 500 to 524 
 
 Pathological conditions, oral 628 
 
 treatment of 629 
 
 Peeso, Dr. F. A., removable bridge 
 
 methods ,';42-1013-1047-1056-1061 
 
 removable crown and bridge 
 
 work 1013 
 
 Pepperling, Dr. T. L 955 
 
 Peridental membrane 625 
 
 Periodic table of the elements (Men- 
 
 deleeft) 974 
 
 law 978 
 
 Peripheral outlines of dentures 
 
 Perlite in micro-structure of steel. . 999 
 Permanent dentures, when to intro- 
 duce 21 
 
 Philbrook, Dr. B. F., inlays. . .1191-1192 
 
 Phoenician dentistry 1104-1105 
 
 Phosphor bronze 107i) 
 
 Phosphorus 968 
 
 Photography, chemistry of 1075 
 
 Physiological relations of teeth and 
 sun-ounding tissues. . .627-801-805-806 
 
 Pickling, acid bath for 169-170 
 
 Pier, definition of 783 
 
 Piers and abutments 790 
 
 preparation of teeth and roots 
 
 for 795 
 
 selection of 790 
 
 Pig iron 1065 
 
 Pigments 375 
 
 Pink gum facing, porcelain 608-906 
 
 protesyn 537 
 
 granular 440 
 
 vulcanite 439 
 
 Pivot crowns. De Chemant 1152 
 
 Fauchard 1116 
 
 wood 1153 
 
 Placer mining 1005 
 
 Plain line articulator 1138 
 
 Plaster models to arrest expansion 
 
 of 133 
 
 Plaster of Paris, accelerators for.. 101 
 advantages of, for impressions.. 56 
 as a binder in investments. . .97-1043 
 
 chemical composition of 43 
 
 compressibility of 56 
 
 contraction of 52 
 
 deleterious properties of 101 
 
 deterioration when heated 101 
 
 expansion of 51 
 
 control of 51 
 
 warpage as result of 5:i 
 
 indications for use in impres- 
 
 sit)rrs 63 
 
 influence of mixing on quality.. 51 
 
 manufacture of 44 
 
 setting, time required for 45 
 
 size of crystals 48 
 
 use in cast production 103 
 
 Plate and wire gauge.- 1099 
 
 gold for denture bases 167 
 
 annealing 168 
 
 carat of used 167 
 
 for crown, bridge and plate 
 
 work 1026 
 
 gauges used 168 
 
I'latinum 1067 
 
 alloys of 1019-1072 
 
 fusing of, Custer's method 1070 
 
 in clasp metal 1033 
 
 physical properties of 106!i 
 
 uses 1071 
 
 I'liers used in crown, bridge, den- 
 ture construction 258-750-751-900 
 
 Plumpers for facial contour restor- 
 ation 317, 323 
 
 Polisliingr vulcanite dentures 456 
 
 Polyprene-india rubber 441 
 
 sulphides, formation of, in vul- 
 canization 442 
 
 Ponton bridge (engineering) 785 
 
 Porosity in porcelain 619-928 
 
 in vulcanite 441 to 445 
 
 Portland cement 101 
 
 I'dssilil.' sU'llar temperatures 994 
 
 I 'Mta,~,--iniri sulphate as an aocelei-- 
 
 ;iiu, 101 
 
 PuuTiiij; ;;;iine 1180 
 
 Melotte's metal 256 
 
 metal dies 154 
 
 counterdies 160 
 
 Watts 225 
 
 Powder, glass 1170, 1173 
 
 silex 1044 
 
 talcum 352 
 
 Praseodymium 967 
 
 Prehension 296 
 
 Preliminary considerations in crown 
 
 Pulp devitalization in crown woik. 
 
 Pumice 
 
 Punch, anchorage loop. 
 
 ■Vi i> 
 
 jrk 
 
 .625 
 
 736 
 
 dovetailing of denture base in 
 
 repairs 576 
 
 steps in flask closing 428 
 
 impression taking 64 
 
 packing the matrix 41S 
 
 securing anchorage of teeth 
 
 to metal bases 174 
 
 Preparation of cavit'es. special 936 
 
 continuous gum body 608 
 
 pure gold .' 1009 
 
 roots or teeth for abutments.. 
 
 642-739-771-79D-S91 
 
 Preparing impression for cast pro- 
 duction 74 
 
 ingredients for porcelain. .. .903-904 
 
 Pressure, atmospheric 25 
 
 applied in flask closing 428 
 
 metal casting 1181 
 
 Price, Dr. W. A 907-951-1091 
 
 Prime object of crown and bridge 
 
 application 799 
 
 Principle, object sought in denture 
 
 construction 1 to 6-304 
 
 Principles, a synopsis of color 374 
 
 Primary colors 375 
 
 Prismatic colors 374-375 
 
 Pritchett. Dr. T. W 1-290 
 
 Production of casts 90 
 
 aluminum bases by casting.... 2"0 
 
 swaging 212 
 
 Profile, facial 320-321 
 
 Proportionate parts of teeth 534 
 
 Proposed law In bridge work 804 
 
 Prosthetic dentistry, definition and 
 
 scope of ..■■ 1 
 
 Protesyn as a gum facing 537 
 
 method of application. .. .537 to 545 
 
 Prout's hypothesis 971 
 
 Providing for escape of surplus cel- 
 luloid 556 
 
 rubber 417 
 
 settlement of dentures under 
 
 stress 497-517 
 
 uniform bearing of dentures on 
 
 issues 27 to 30 
 
 Proximal cavities for inlays prepa- 
 ration of 914 to 919-932 to 941 
 
 contact restoration of 632-738 
 
 surfaces reduction of 479 
 
 views of bicuspids and molars 
 
 766 to 769 
 
 Pruyn, Dr. C. P 20 
 
 Pterygoid muscles 278-280-284 
 
 ry plate 
 
 pcrloj-ating 
 
 riveting 
 
 Young 
 
 Purpie of Cassius 
 
 secondary color 
 
 Pyrometer furnace 
 
 Pyroxylin, basis of celluloid. 
 
 460 
 217 
 684 
 866 
 217 
 865 
 684 
 906 
 375 
 
 Radio-active substances 963 
 
 Radium 963 
 
 Ramsey, Sir "SViHiam 
 
 961-962-964-965-970 
 
 Ransom and Randolph, vacuum 
 
 casting machine 959 
 
 Raphe 11-18 
 
 Rawlinson, Dr. John, dentures for. 458 
 
 Ra.vleigh, Lord 962 
 
 Ravs, alpha 963 
 
 beta 963 
 
 gamma 963 
 
 X 962-963 
 
 Reaming 667 
 
 Rebuilding an impression for die 
 
 casting 254 
 
 Recent discoveries, a brief outline 
 
 of 962 
 
 Recording tlie condyle paths 336 
 
 Red, color principles 375 
 
 rubber 439 
 
 Reducing flame 998 
 
 flux 1057 
 
 Reduction, alloys of mercury lOSS 
 
 aluminum 1080 
 
 copper 1078 
 
 gold 1010 
 
 rule for (Boser's) 1010 
 
 iron 1064 
 
 lead 1085 
 
 silver 1073 
 
 tin 1086 
 
 Reenforcing partial baseplates of 
 
 gold 180 
 
 detailed methods 180-181 
 
 platinum bases 591-594 
 
 Reese, Dr C. N.. pin shaver 687 
 
 Reese. Dr. G. N., casting 1184 
 
 Refining gold 1009 
 
 Reflection gold base against teeth 182 
 
 Refractory materials 1040 
 
 Registering condyle path 336 
 
 Regrinding of teeth 462 
 
 Reheating modeling compound im- 
 pressions 83-84-85 
 
 Relation, atomic, of elements 971 
 
 securing of, between clasps, 
 
 teeth and baseplates. 266-267-483 
 root cap and dowel in crown 
 
 work 671 
 
 Relief of dentures over hard pala- 
 tine areas 27 
 
 border crests of lowers 31 
 
 Removable bridgework 841 
 
 attachments 842 
 
 Removal of a banded dowel crown . . 866 
 
 dowels from root canals 868-869 
 
 natural crowns 642 
 
 shell crowns by leverage force 870 
 
 slittinsr 869 
 
 tempoi-arily set crowns 69r 
 
 Removing the enamel from teeth 
 
 and roots 644-739 
 
 wax from matrix in inlay work 9^)6 
 
 vulcanite cases 414 
 
 dowels from root canals 868 
 
 Repairing crowns and bridges 857 
 
 dentures of vulcanite 561 
 
 Repilacing crown and bridge facings 
 
 . 857 to 867 
 
 Replacable teeth and facings 696-734 
 
Reproducing cusp surfaces in gold 
 
 in crown work 759-769 
 
 gum surfaces in porcelain 617 
 
 protesyn 537 
 
 natural denture in porcelain 
 
 teeth and wax 545 
 
 Reproduction of natural tooth forms 
 
 in porcelain 364 
 
 of wax model dentures in perma- 
 nent materials 407 
 
 Requirements of an impression ma- 
 terial 42 
 
 of a partial denture 233 
 
 of a base plate , 313 
 
 of an occlusion rim 314 
 
 Requisites of die metal 131 
 
 counterdie metal 136 
 
 clasps 237 
 
 models 97 
 
 denture bases US 
 
 Residual ridges 18 
 
 Resiliency of clasps 23S 
 
 Resistance, to stress of casts, neces- 
 sity for 110-42S 
 
 dies 132 
 
 Restoration of facial contour 322 
 
 masticatory function 1-269, 463 
 
 Reswaging partial gold bases 1S6 
 
 platinum bases plates 595 
 
 Retainer occlusion 412 
 
 Retention of dentures, full 23 
 
 partial 233 
 
 Rhodium 96S-1024 
 
 Kichmond. Dr. C. M., crown. .1158-1159 
 
 Rideout, J. B 856 
 
 Ridge lap 535-536 
 
 Rigid baseplates necessity for.. 118-313 
 Rim occlusion, requirements of.... 314 
 
 Ringer's solution 630 
 
 Roach, Dr. P. E 235-265-500 
 
 attachment . .503-505-508-660-769-842 
 
 Roentgen, Prof. William 962 
 
 Rollins. Dr. W. H., inlays 1172 
 
 Rolling mill for gold 1093 
 
 Roman, lady, facial outlines 372 
 
 history of prosthesis 1110 
 
 prosthetic specimen 1110 
 
 Root preparation for dovyel. crowns 
 
 in to 1)50 
 
 shell 73B-743 
 
 porcelain jacket S80 
 
 Rouge and alcohol as an anti-flux. 1177 
 
 as a polishing agent 693 
 
 Rubber, composition of dental 439 
 
 derivation 436 
 
 vulcanization of 454 
 
 chemistry of 441 
 
 Rubidium 967 
 
 Ruthenium 967 
 
 Saddle bridges 787 
 
 individual for dummies 788 
 
 with ling;ual bar 496 
 
 Sali\-a, function of 15 
 
 Salivary glands 15 
 
 Salts of radium 963 
 
 Samarium 968 
 
 Sand, molding 129 
 
 Sandarac varnish 93 
 
 Sanford 378 
 
 Sanguine temperament 356 
 
 Saphira facial outlines 36S 
 
 Sauer. Dr. C., casting 1184 
 
 Scandium 967 
 
 Schimmelpennick, Mme., facial forms 
 
 360-361 
 
 Schottler, Dr. Jacob, inlay 1192 
 
 Schwartz, Dr. G. W 62^-1167 
 
 Scrapers, vulcanite 457-458 
 
 Screw estimating, force of. in flask 
 
 closing 428 
 
 presses '. 433-434 
 
 Seamless crowns, matrix method.... 772 
 
 die method 776 
 
 Sectional m.olds in vulcanite work.. 407 
 
 Watts' metal casting 223 
 
 seamless crown wor'.c 777 
 
 Second vulcanization effect on pink 
 
 vulcanite 567 
 
 Secondary contraction in gold in 
 
 casting operations 952 
 
 Selection of impression trays 36-64 
 
 teeth, esthetics of 355 
 
 suggestion in 380-537 
 
 Selenium 968 
 
 Sense of harmony 359 
 
 taste 11 
 
 Sepai-ating mediums 92 
 
 Separation of impressions from casts 
 
 106-107-108-109 
 
 die and counterdie 161 
 
 Setting crowns and bridges. 767-S31-S50 
 
 inlays 930, 959 
 
 Shade guide in tooth selection 536 
 
 Shadow problem in inlay work 9iS 
 
 tooth selection 379 
 
 Shears for crown and bridge teehnlc 658 
 
 Shot swager, Parker's 164-165 
 
 Shoulder crowns, cast gold 771 
 
 porcelain jacket 880 
 
 Shrinkage of metals in passing from 
 
 liquid to solid state 132 
 
 Shut (proportionate parts of teeth) 
 
 534-335-536 
 
 Sieve in molding 130 
 
 Silex, powdered as an ingredient in 
 
 investments 949-1044 
 
 Silica, fused utensils of 1044 
 
 Silicate cements, protesyn 537 
 
 Silicon 96S 
 
 Silver, alloys of 1074 
 
 conductivity of 987 
 
 ores of 1073 
 
 photographic uses of 107.5 
 
 solders 1075 
 
 reduction of 1073 
 
 Slag in iron smelting 1064 
 
 Slow, mutation of elements 971 
 
 Sluice in placer mining 1006 
 
 Smelting of copper ores 1078 
 
 Smith, Prof. Alexander 965-970 
 
 Smith, Dr. J. Dodge, crown 1153 
 
 Snow, Dr. Geo. B., anatomical appli- 
 ances 30S-309-:;:;S-:^.3:i-1 144-111;; 
 
 Soapstone in fusing porcelain 926 
 
 In smoothing models 130 
 
 Sodium 96S 
 
 Soft palate, extent to which denture 
 
 should rest upon 30 
 
 Solarizing pink vulcanite 440 
 
 Solbrig casting pliers 1 199 
 
 Solder, gold 
 
 silv 
 
 .1036 
 .107 
 
 soft -lOSB 
 
 Soldering ■ • • 994 
 
 conditions essential to successful 995 
 temperatures applied =n some 
 
 cases • ^^2 
 
 Soldering jack •■'"^"°i„ 
 
 Solutions, alcoholic varnishes 93 
 
 aqueous 94 
 
 ethereal ■ 93 
 
 Sonorousness- in bell metal i"m 
 
 Spar, fluor, in alumino-thermics 993 
 
 Spathic iron ore 1064 
 
 "Special" Ideal baseplate 230 
 
 Specialized frictional appliances 
 
 _ 235-500 to o2.T 
 
 Specific gravity 981 
 
 heat "89 
 
 f^^?f;:sr':^.::::::::;:::96i:963:9?U?? 
 
 Spence. Dr. Stewart J.. bla_«te^r. . . ._^^^ 
 
 Spiral springs for denture retention 
 
 1117-ll-l-ll"l 
 
 Sol'it ' dowel ". 845. 1061 
 
 Spillers resin 4q |i 
 
 Spongy borders ViSn 
 
 Sprue, definition of 118I' 
 
 Staining fluids ^91 
 
 Staining porcelain teeth il8 
 
 Starr. Dr. E. J.^ }]f--]\ll 
 
 Starr, Dr. R. W II60-II66 
 
1212 
 
 INDEX 
 
 steam pressure, table of 450 
 
 Steel, hardening and tempering of. 1066 
 
 Steele, teeth and facings 697 to 700 
 
 repair outfit 858 
 
 Stellar bodies, temperature of the 
 
 larger 994 
 
 Stiver, Dr. D. S., blowpipe 692 
 
 Stomatitis 17 
 
 Stokes, Dr. J. L, 1173 
 
 Stowell, Dr. Sidney S.. extension 
 
 bridge 1166 
 
 Strontium 968 
 
 Structure of flame 996 
 
 Stuck, Dr., vulcanizing rubber be- 
 tween metal surfaces 113.=; 
 
 Submaxillary glands 15 
 
 Sublingual glands 15 
 
 Substituting artificial for lost natural 
 
 teeth in repairs 578 
 
 Substitution of a baseplate in 
 
 repairs 579 
 
 Substructure of a bridge 783 
 
 application of stress to 783 
 
 Sulphur 968 
 
 Sulphuric acid pickle 169 
 
 Summary, brief, of recent discoveries 965 
 Superheating gold in casting opera- 
 tions 952, 1049-1050-1051-11S1-1198 
 
 Superstructure 783 
 
 Support for continuous gum case... 612 
 
 Suspension bridge 785 
 
 Swaged crowns, seamless 772-776 
 
 cusps for crowns 759 to765 
 
 Swager, Parker shot 164 
 
 Swaging denture bases 
 
 .166-178-180-208-590 
 
 Sweating 995-1028-1061 
 
 Sykes, C. A 458 
 
 Synovial sacs 274 
 
 Table of alloys, binary (Weinstein) .1014 
 casting gold, "A", "B", "C", 
 
 ••D" 1029-1032 
 
 clasp metal 1034 
 
 hardness and elasticity 
 
 of 1036 
 
 gold and silver 1017 
 
 copper 1019 
 
 palladium 1023 
 
 platinum 1020 
 
 plate No. 1 1026 
 
 No. 2 1027 
 
 solders 1038 
 
 melting points of "New 
 
 Series" 1060 
 
 triple (fusible metal) 136 
 
 color, analysis of individual face 379 
 conductivity of heat and electri- 
 city 987 
 
 constituents of dental rubber. . 439 
 gum body and enamel. .905-906 
 
 coeffiicient of expansion 990 
 
 divergence of bicuspid and mol- 
 ar crowns 634 
 
 elastic force of steam 451 
 
 elements in the order of dis- 
 covery 966 
 
 for estimating thickness of 
 
 doubled gold baseplate 182 
 
 high and low fusing porcelains. 907 
 
 mandibular muscles 284 
 
 masticatory action on food.... 306 
 oxides used in coloring porcelain 905 
 
 shrinkage of metals 132 
 
 specific heat 988 
 
 screw force in flask casting...! 428 
 
 steam pressure 450 
 
 temperature as displayed by 
 
 color 982 
 
 temperaments 356 
 
 tensile strength of metals....! 986 
 thermal conductivity of sub- 
 stances 122 
 
 unequal distribution of elements 970 
 welding under pressure 991 
 
 Table of the periodic law 975 
 
 thermal conductivity of sub- 
 stances 102 
 
 measured in calories ...!!!!!' 122 
 
 fusible alloys ! 136 
 
 the temperaments 355 
 
 screw force in flask cloilng... 428 
 unequal distribution of the ele- 
 ments 97Q 
 
 the triads of Dobereiner !!!!!!! 973 
 
 welding under pressure 991 
 
 Taggart, Dr. W. H., Inlays 
 
 . . . 9,-)0-954-957-958-1051-1196-n97-1198 
 
 Taking bites 327-329 
 
 impressions 63 to 79-495 
 
 Tantalum ggg 
 
 Taste sense 14 
 
 Technic of bridge construction. .823! 891 
 
 crown work 641 to 782 
 
 full denture construction. .308 to 475 
 partial denture construction. 476-524 
 
 celluloid 651 
 
 continuous gum ! 588 
 
 repairing dentures 561 
 
 crowns and bridge repairs. 856 to 872 
 
 Teeth, fonnula of human 288 
 
 natural form of 755 
 
 porcelain forms of 525 
 
 Telescope crowns 844-845 
 
 Tellurium 968 
 
 Temperaments, table of the 356 
 
 Temperatures common and extra- 
 ordinary 993 
 
 Temporary dentures 21 
 
 Tempero-mandibular articulation... 274 
 
 Tenacity 985 
 
 Tensile strength 985 
 
 Terbium 968 
 
 Testing balancing cnntac t 391 
 
 base plates and ocrUi.si.m models 318 
 
 impressions S5 
 
 occlusal surfaces of teeth for 
 
 working efficiency 387 
 
 root preparation in crown work 
 
 649, 743 
 
 parallel relation of crown and 
 
 bridge abutments 843 
 
 Thallium 968 
 
 Theoretical belief in regard to new 
 
 elements 976 
 
 Therapeutic methods of treatment.. 629 
 Thermal conductivity of various 
 
 denture bases 12I 
 
 Thompson, Prof. J. J., experiments 
 
 in the debasement of elements 965 
 
 Thorium 968 
 
 Three point contact, in denture 
 
 construction 393 
 
 Thulium ! ! ! 958 
 
 Time a factor in fusing porcelains!! 614 
 
 Tin _ _ .1086 
 
 Tint, definition !,.!!! 374 
 
 Titanium oxide ! !! !965-968 
 
 Tolstoi, statue of 398 
 
 Tone definition 374 
 
 Tongue. mu.scles of 14 
 
 Tongs, muffle 92."; 
 
 Tooth, natural forms reproduced in 
 
 porcelain 352 
 
 shade guide 535 
 
 Tray nomenclature 35 
 
 selection 36 
 
 Treatment of diseased conditions.. 629 
 after setting crowns and bridges 
 
 631-695 
 
 Triads of Dobereiner 972 
 
 Trial base plates 311 
 
 Truss in bridge engineering 784 
 
 continuous gum dentures 605 
 
 porcelain bridge work K93-1167 
 
 Tube teeth. Ash's 529-113.". 1153 
 
 Tungsten .1091 
 
 Turner gasoline furnace 898 
 
 Tweezers K, for inlav work 924 
 
 Types of True Bite Teeth 363-364 
 
 Tynal forms of natural teeth 
 (Williams) 362 
 
Ulsaver, Dr. E. S., method of 352 
 
 developing the compensating 
 
 curve 
 
 Ultra-microscope of Zsigmondy. . . . 969 
 Undercut areas, use of cores in... 99 
 
 swaging gold In 179 
 
 Unetiual distribution of the elements 970 
 Uniform bearing of dentures essen- 
 tial 26 
 
 Unilateral mandibular movements.. 297 
 
 Unit of thermal conductivity 122 
 
 Upper dentures, retention of 26-27 
 
 outline form of distal 30 
 
 margin of 30 
 
 Uranium oompojnds of 963 
 
 the initial element in 
 
 the debasement scale 965 
 
 Use of the face bow 330 
 
 Utility one of the three pri^me ob- 
 jects in denture construction.... 1 
 
 Vacuum caisting machine 959 
 
 chamber 28 
 
 Vanadium 968 
 
 Vanderpoel, Emilv. the relation of 
 
 color to light 373 
 
 Van Horn, Dr. C. S 1048 
 
 Van Woert, Dr. F. T S78-943 
 
 Variations in the pitch of condyle 
 
 paths 275 
 
 lateral paths of the condyles... 474 
 
 Various forms of teeth 525 
 
 Varnish for impressions 93 
 
 Vault, palatine 10 
 
 Vegetable bases 551 
 
 Vein gold :1007 
 
 Veneers for denture gums, granular 
 
 facing 4 440 
 
 pink vulcanite 439 
 
 porcelain 608 
 
 prote.'i\n 537 
 
 inlay, Linderer's 1170 
 
 Vestal virgin, facial outlines 370 
 
 Von Wardroff, Prof. R., thermal 
 
 conductivity 121 
 
 Voick, Dr. A. J., Inlays 1170 
 
 Vulcan facial outlines 368 
 
 Vulcanite, conductivity of thermal 
 
 chan^-es 121 
 
 denture bases 121 
 
 advantages and disadvan- 
 tages of 121 
 
 double vulcanization process 
 
 227 to 4S6 
 
 inflammatory conditions re- 
 sulting from use of 122 
 
 dentures, full upper and lower 
 sequent steps in construc- 
 tion of 310 to 475 
 
 partial 477 to 48S 
 
 repairs of 561 to 587 
 
 finishers (Wilson) 457 
 
 lathe burs 456 
 
 Vulcanization of rubber, chemistry 
 
 of 441 
 
 dimensional changes during. ... 447 
 
 contraction 447 
 
 expansion 447 
 
 in automatically closed flasks.. 454 
 
 closed and bolted flasks 454 
 
 time of 455 
 
 Vulcanizers. danger from Improper 
 
 handling 449 
 
 safety devices for 449 
 
 gas regulator 451 
 
 safety valve 452 
 
 steam gauge 450 
 
 thermometer 449 
 
 time regulators 451 
 
 Walker, Dr. W. E 
 
 Ward. Dr. M. A • 911-1041 
 
 Warming oven for flask separation 413 
 
 Warpage of casts and impressions. 53-55 
 Watts' flask and metal. 223-224-227-1185 
 
 Wax, bees 69 
 
 and parafflne 59-946-947 
 
 rosin 60-1173 
 
 composition of 946 
 
 hard bite 60 
 
 ijilay 946-947 
 
 eliminating from mold 956 
 
 temperature required to ren- 
 der plastic 954 
 
 Weaver cleavers 644 
 
 Webb, Dr. Marshall H., bridge 1163 
 
 Webber, Carl O., Ph. D 441-443 
 
 Wedge of vulcanite 484 
 
 Wedging to regain lost contact 738 
 
 Weighted lower dentures 221 
 
 of vulcanite 221 
 
 with metal core 221 
 
 cast metal bases 222 
 
 Weinstein, Dr. L. J., artificial stone 
 
 495-1047 
 
 refractory materials 951-1040 
 
 some recent work concerning 
 
 gold alloys 1013 to 1063 
 
 spring for absorbing shock 500 
 
 Welding of metals 990 
 
 copper to iron (new process) 992 
 
 alumino-thermy 892 
 
 temperatures, common and ex- 
 traordinary 993 
 
 Weston, Dr. Henry, crown 1160 
 
 metal for cast bases 227 
 
 Wet method for recovering silver. .1073 
 Whetting hone, aluminum as a... 1082 
 White, Dr. J. D., platinum frame for 
 
 crown 8 ' ° 
 
 White, Samuel S., vulcanite litiga- 
 
 tion 1134 
 
 tooth manufacture 1129 
 
 White, S. S.. AVhite Dental Mfg. Co. 
 monograph on origin and develop- 
 ment of porcelain teeth 1162 
 
 Wildman, Dr. E 439-905 
 
 AVilliams, Dr. E. Lloyd 58 
 
 Williams, Dr. J. Leon 
 
 362-364-365-396-795-1164-1165-1166 
 
 Wilson, Dr. George H 
 
 35-312-354-360-433-454-457 
 
 Wire and plate gauge table 1099 
 
 Wiring denture bases, full gold 17.5 
 
 partial 4S9 
 
 platinum S93 
 
 Wood. Dr. B., crowns 1155 
 
 inlays 1171 
 
 metal, fusible 1 090 
 
 Wood, pivot, teeth 1153 
 
 Wood, Dr. W. W., casting appli- 
 ances 200 
 
 Wrinkles, removing from metal 
 
 bases l^J 
 
 platinum matrix 920 
 
 Wrought iron 1065 
 
 X (Newtonium) 976 
 
 Xenon 962 
 
 X-ray (Roentgen) 962 
 
 Yellow (primary color) 375 
 
 Yittrium 968 
 
 Young plate perforator 6»4 
 
 Zeller casting appliances 1186 
 
 Zero. absolute, conductivity of 
 
 metals at 988 
 
 Zmc 1082 
 
 for dies 132 
 
 Zitrconium 968 
 
 Zslgmondy. ultra-microscope of 969 
 
 Zygomatic arch, muscular attach- 
 ment to 278 
 
 Zylonite 551 
 
f^ 
 
Date Due 
 
 1 ' 
 
 
 
 
 ■■,'. - . ., 
 
 
 
 
 
 
 
 
 ■1 
 
 «^ 
 
 
 
 
 
 
 
 
 
 
 
 OECl 
 
 91949 
 
 
 ' 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 (f) 
 
 
 
 
<ienti< 
 
 try 
 
 COLiJf;'Ki- 'iivtK^;:', LIBRARIES 
 
 RK651 P94 1916 C.I 
 
 Prosthet'i >,: - • ■,•!,, 
 
 2002376237 
 
 P94 
 
 1916