/ THf % O LieSARIES ^ ^ KJL? J \ mSS3 ^ ^'ry Of »»* HEALTl 3CI£» Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons http://www.archive.org/details/americantextbook1905kirk LIST OF CONTRIBUTORS. ANGLE. EDWARD H., M. D., D. D.S. ; BURCHARD, HENRY H., M. D., D. D. S. ; CASE. CALVIN S., M. D., D.D.S.; CLAPP. DWIGHT M.. D.M.D.; CRENSHAW, WILLIAM, D. D.S.; CRYER, M.H., M.D., D. D. S. ; DARBY, EDWIN T.. M. D., D.D.S.; GODDARD, C. L., D.D.S.; GUILFORD, S. H., A.M.. D.D.S.. Ph.D.; HEAD, JOSEPH B.. M.D., D. D. S. ; JACK, LOUIS. D.D.S. ; KIRK, EDWARD C. D. D. S. ; NOYES. FREDERICK B.. B. A., D.D.S. ; OTTOFY. LOUIS. D.D.S.; PEIRCE. C. N.. D.D.S.; THOMAS. J. D.. D. D. S. ; THOMPSON. ALTON HOWARD. D.D.S. TRUMAN, JAMES. D.D.S. THE AMERICAN TEXT-BOOK OF OPEPiATIVE DENTISTRY. m CONTRIBUTIONS BY EMINENT AUTHORITIES. EDITED BY EDWARD C. KIRK, D.D.S., Professor of Clinical Dentistry in the University of Pennsylvania, Philadelphia; Editor of "The Dental Cosmos;" Officier de l'Academie de France. THIRD EDITION, REVISED AND ENLARGED. ILLUSTRATED WITH 875 ENGRAVINGS. LEA BROTHERS & CO., PHILADELPHIA AND NEW YORK. 1905 Ksd Entered according to Act of Congress in the year 1905, by LEA BROTHERS & CO., in the Office of the Librarian of Congress, at Washington. All rights reserved. WESTCOTT & THOMSON. ELECTROTYPERS. PHIU*0*. WITH THE CONSENT OF THE CONTRIBUTORS THIS BOOK IS DEDICATED TO JAMES TRUMAN, D.D. S., THE CHARACTERISTIC OF WHOSE LONG PROFESSIONAL CAREER HAS BEEN THE INCULCATION OF THE PRINCIPLES UPON WHICH THE WORK IS BASED. PREFACE TO THE THIRD EDITION. The early exhaustion of the second edition of this work has afforded opportunity for its complete revision, the results of which are now pre- sented in a third edition. The excellent chapter on Dental Embryology, by Dr. R. R. Andrews, has been omitted because the growth of that subject and, indeed, of all that pertains to dental anatomy and histology has compelled the retention in this work of only those special anatomical features which are directly applicable to the elucidation of dental oper- ative procedures. The number of excellent treatises now exclusively devoted to dental embryology and histology makes it no longer neces- sary to include the general treatment of these topics in a work strictly devoted to Operative Dentistry. As new matter, there has been added to this edition a chapter upon the Use of the Matrix in Filling Operations, by Dr. Crenshaw, which, it is confidently expected, will prove to be an addition valuable and helpful to teachers as well as to students. The section on Orthodontia has been treated anew, from the stand- point of occlusion as the scientific basis from which this important departure should be studied. With the cordial consent of the late Dr. Clark L. Goddard, the treatment of the subject of orthodontia was committed to Dr. E. H. Angle, the chief exponent of the modern trend of thought upon ortho- dontia as a problem of occlusion. The text of each chapter has been carefully revised by its author, with the exception of those originally written by the late Dr. H. H, Burchard, whose work has been revised by the Editor. It is due to each of the contributors to state that the Editor is respon- sible for the terminology used throughout the work. In assuming this responsibility the terms upon which divergence of opinion was found to be greatest were "canine" and "cuspid," "bicuspid" and "premolar," " maxilla " and " upper," or " superior, jaw," " mandible " and " lower," or " inferior, jaw," " approximal " and " proximal." In each instance the 8 PREFACE TO THE TIIIRH EDITION. term which seemed to be most in harmony with the trend of good scien- tific usage was adopted, regardless of the preferences of individual writers, in order to avoid confusion and to secure that harmony of treat>- ment so necessary in a text-book for the use of undergraduate students. The Editor records his sense of deep personal loss in the death of Dr. Clark L. Goddard, whose rare attainments, both as a man and as a dental teacher, could ill be spared from the ranks of contributors to the literature of dentistry. The thanks of the Editor are heartily accorded to his associate, Dr. Julio Endelman, for his painstaking work in the preparation of the new and copious index for this edition ; to many colleagues for helpful suggestions ; to the contributors for their cordial co-operation in the revision of the work, and especially to the large body of dental teachers, whose practical use of the work in the instruction of their classes is the most satisfactory commendation of its usefulness as a text-book. The present edition is issued in the confident hope that the work will, in even greater degree, merit the approval which has been so gen- erously accorded to its predecessors. E. C. K. Philadelphia, 1905. LIST OF CONTRIBUTORS. EDWARD H. ANGLE, M. D., D. D. S., President of the Angle School of Orthodontia, St. Louis, Mo. HENRY H. BURCHARD, M. D., D. D. S., Late Special Lecturer on Dental Pathology and Therapeutics, Philadelphia Dental College, Philadelphia. CALVIN S. CASE, M. D., D. D. S., Professor of Orthodontia, Chicago College of Dental Surgery, Chicago, 111. DWIGHT M. CLAPP, D. M. D., Clinical Lecturer on Operative Dentistrj', Dental Department, Harvard University, Boston, Mass. WILLIAM CRENSHAW, D. D. S., Dean and Professor of Operative Dentistry and Dental Pathology, Atlanta Dental College, Atlanta. M. H. CRYER, M. D., D. D. S., Assistant Professor of Oral Surgery in the University of Pennsylvania, Philadelphia. EDWIN T. DARBY, M. D., D. D. S., Professor of Operative Dentistry and Dental Histology in the University of Penn- sylvania, Philadelphia. C. L. GODDARD, D. D. S., Professor of Orthodontia, University of California, College of Dentistry, San Francisco, Cal. S. H. GUILFORD, A. M., D. D. S., Ph. D., Professor of Operative and Prosthetic Dentistry and Dean of the Philadelphia Dental College, Philadelphia. JOSEPH B. HEAD, D. D. S., M. D., Philadelphia. 10 LfSr OF CONTRIBUTORS. Lolls JACK. I). I). S., Philailelphia. EDWARD C. KIRK, D. D. S., So. D., Professor of C'linioal Uciuistiy and Dean of the Department of Dentistry in tlie Univei-sity of Pennsylvania, Philadelphia ; Officier de lAcadeiuie de Fi-anee. FKKDEKICK B. NOYES, B. A., I). D. S., Professor of Dental Histology in the Northwestern University Dental School, Chicago, 111. LOUIS OTTOFY, D. D. S., Professor of Clinical Therapeutics, Chicago College of Dental Surgery, Chicago ; Attending Dental Surgeon St. Luke's Hospital, Manila, P. I. C. N. PEIRCE, D. D. S., Professor of Dental Physiology, Dental Pathology, and Operative Dentistry, and Dean of the Pennsylvania College of Dental Surgery, Philadelphia. J. D. THOMAS, D. D. S., Lecturer on Nitrous Oxid, Department of Dentistry, University of Pennsylvania, Philadelphia. ALTON HOWARD THOMPSON, D. D. S., Profes.sor of Dental .\natomy, Kansas City Dental College, Kansas City, Mo. JAMES TRUMAN, D. D. S., Professor of Dental Pathology, Therapeutics, and Materia Medica in the I'ni versity of Pennsylvania, Philadelphia. CONTENTS. CHAPTER I. PAGE MACROSCX)PIC ANATOMY OF HUMAN TEETH 17 By Al,ton Howard Thompson, D. D. S. CHAPTER II. DENTAL HISTOLOGY WITH REFEKENCE TO OPERATIVE DENTISTRY 53 By Fredrick B. Noy'es, B. A., D. D. S. CHAPTER HI. ANTISEPSIS IN DENTISTRY 117 By James Truman, D. D. S. CHAPTER IV. THE EXAMINATION OF TEETH PRELIMINARY TO OPERATION- METHODS, INSTRUMENTS, APPLIANCES— RECORDING RESULTS, ETC 133 By Louis Jack, D. D. S. CHAPTER V. PRELIMINARY PREPARATION OF THE TEETH— REMOVAL OF DE- POSITS AND CLEANING OF THE TEETH— WEDGING— OTHER METHODS OF SECURING SEPARATION— EXPOSURE OF CERVI- CAL MARGINS BY SLOW PRESSURE, ETC 141 By Louis Jack, D. D. S. CHAPTER VT. PRELIMINARY PREPARATION OF CAVITIES— TREATMENT OF HY^- PERSENSITIVE DENTINE BY SEDATIVES, OBTLTSDENTS, LOCAL AND GENERAL ANESTHETICS— STERILIZATION, WITH A BRIEF CONSIDERATION OF THE PHYSIOLOGICAL AND THERAPEUTICAL ACTION OF THE MEDICAMENTS USED 149 By Louis Jack, D. D. S. 11 12 CONTENTS. CHAPTER VII. PAGF. PREPARATION OF CAVITIES— ol' KM. \( i TIIK CAVITY— RKM()VIN(i THE DECAY— SIIAPI.XC THE ( A VITY CLASSIFICATK )N OF CAVITIKS 175 By S. 11. GuiLFOKD, A.M., D. I). S., Pii. U. CHAPTER VIII. EXCLCSION OF MOISTURE— EJECTION ()F THE i^ALIVA— APPEIC.V TION OF THE DAM IN SIMPLE CASES, AND IN SPECIAL CASES PRP:SENTING difficult complications— napkins and OTHER METHODS FOR SECURING DRYNESS 199 By Louis .I.vck, D. D. S. CHAPTER IX. THE SELECTION OF FILLING MATERIALS WITH REFERENCE TO CHARACTER OF TO( )TII-STRUCTrRE, VARIOUS ORAL CONDI- TIONS AND LOCATIONS, DEPTH OF CAVITY, AND PROXIMITY OF THE PULP— CAVITY LINING Wmi ITS PURPOSES 209 By Louis Jack, D. D. S. CHAPTER X. TREATMENT OF FILLINGS WITH RESPECT TO CONTOUR, AND THE RELATION OF CONTOUR TO PRESERVATION OF THE INTEG- RITY' OF APPROXIMAL SURFACES 221 By vS. H. Guilford, D. D. S., Ph. D. CHAPTER XI. THE OPERATION OF FILLING CAVITIES WITH METALLIC FOILS AND THEIR SEVERAL MODIFICATIONS 227 By Edwin T. Darby, D. I). S., M. D. CHAPTER XII. USE OF THE MATRIX IN FILLING OPERATIONS 261 By William Crenshaw, D. D. S. CHAPTER XIII. PLASTIC FILLING MATERIALS-THEIR PROPERTIFi^, USES, AND MANIPULATION 289 By Henry H. Burchard, M. D., D. D. S. CONTENTS. 13 CHAPTER XIV. PAGli COMBINATION FILLINGS 329 By Dwight M. Clapp, D. M. D. CHAPTER XV. EESTOEATION OF TEETH BY CEMENTED INLAYS 353 By Joseph Head, D. D. S. M. CHAPTER XVI. THE CONSEKVATIVE TREATMENT OF THE DENTAL PULP— DEVI- TALIZATION AND EXTIRPATION OF THE PULP 385 By Louis Jack, D. D. S. CHAPTER XVII. THE TREATMENT AND FILLING OF ROOT CANALS 413 By Henry H. Burchard, M. D., D. D. S. CHAPTER XVIII. DENTO-ALVEOLAR ABSCESS 467 By Henry H. Burchard, M. D., D. D. S. CHAPTER XIX. PYORRHEA ALVEOLARIS 493 By C. H. Peirce, D. D. S. CHAPTER XX. DISCOLORED TEETH AND THEIR TREATMENT 523 By Edward C. Kirk, D. D. S. CHAPTER XXI. EXTRACTION OF TEETH 549 By M. H. Cryer, M. D., D. D. S. CHAPTER XXI {Continued). EXTRACTION OF TEETH UNDER NITROUS OXIDE ANESTHESIA . . 621 By J. D. Thomas, D. D. S. 14 COyTKNT^. CHAPTER XXI (Concluded). PACK LOCAL ANESTHETIC?^ AND TooTH EXTRACTION 631 By Henry H. Burchard, M. 1>., I). D. S. chaptp:r xxn. PLANTATION OF TEETH 639 By Louis Ottokv, I). I). S. CHAPTER XXni. MANAOKMENT OF DECIDUOUS TEETH 657 By CI.A14K GoDDAKD, A. ^l., I). I). S. CHAPTER XXIV. oKTIIoDoNTlA 677 By Edwakp H. Angle, M. D., D. D. S. C^HAPTER XXV. THE DEVELOPMENT OF ESTHETIC FACIAL CONTOURS 849 By Calvin S. Ca.se, D. D. S., M. D. INTRODUCTORY. A STUDY of the advances which have of recent years taken place in the field of Operative Dentistry will reveal, besides the important addi- tions to our knowledge in the shape of novel methods and improved technique, a vastly more important advance manifested in a better and more general understanding of scientific principles, and the application of dental science to dental art, resulting in a more rational practice. Especially is this true in regard to the etiology of dental and oral pathological conditions, and the rationale of the modes of treatment indicated for the morbid states constantly confronting the dental practitioner. The modifications in surgical methods and the greatly improved results which are the outgrowth of modern scientific studies in bacterial pathology, while they have made a considerable impress upon dental operative methods, have not, however, received that universal practical acceptance among dental operators which their immense importance demands. There is no field of special surgery in which the import- ance of exact knowledge with respect to aseptic and antiseptic treat- ment is more marked than in the practice of dentistry. The dental operator is continually confronted with septic conditions, so that pre- cise knowledge of their origin, causes, phenomena, and treatment are essentials to the legitimate practice of the profession. The performance of any operation, and especially those which are classified as capital, with unclean hands or infected instruments would in the present stage of surgical art be regarded as criminal malpractice. It should be so considered in dentistry. The loss of a patient's life as the result of surgical septic infection is no longer permissible. Lack of antiseptic precautions in certain dental operations may directly lead to and , as a matter of fact has been the cause of fatal results. It has been shown conclusively ^ that a large variety of pathogenic micro- organisms are almost constant inhabitants of the oral cavity. In addi- tion to the numerous forms which bring about an acid reaction, there are many specific organisms which produce in inoculated animals pyemia and septicemia in their several clinical classes. But while the dental practitioner is not often called upon to face the issues of life 1 W. D. Miller, Dental Cosmos, November, 1891. 15 1 6 INTR OD UCTOR Y. and (It-atli in tlic course of his worU, liis rcsj)onsil)ilitios as related tx) the issues with which he does deal demand of him the same care and thoroughness in order to attain the character of result which the pos- sibilities of modern dentistry reijuire of him. In the following pages the importance of asepsis and antisepsis in dental operations is con- stantly impressed upon the mind of the student. By the term awp,si,s is specifically meant the condition under which are excluded those influences or causes whit'h induce infection by patho- genic micro-organisms ; when a tissue or surface has been rendered germ-free it is said to be in an (uscptic condition. By antisepsis is meant the means by which the septic state is combated or the aseptic state is attained. Under the aseptic condition repair of tissues takes place normally without interference, w^ounds and injuries heal with a minimum of dis- turbance, and the inflanunatory concomitant is of the sim])lc traumatic type, without suppuration or tendency to diffusion. The aseptic state, in many operations in the mouth, is not readily attainable and cannot be maintained for any length of time ; but in all operations which involve the pulp and pulp chamber, as well as the periapical region through the pulj) canals of teeth, strict aseptic con- ditions, as regards external infection, are perfectly attainable through exclusion of the oral secretions by means of rubber dam, the use of suitable disinfectants, and sterilized instruments. It is the class of operations here alluded to which are most prolific of disturbance from infective inflammations caused by ignorant or careless manipulation. The time is at hand, if indeed it has not already arrived, when puru- lent inflammations following dental treatment will be regarded with the same condemnation by the dentist as by the general surgeon. The operative section of this work is written in full recognition of the prin- ciples here indicated. OPERATIVE DENTISTRY. CHAPTEK I. MACROSCOPIC ANATOMY OF THE HUMAN TEETH. By Alton Howard Thompson, D. D.S. 1. Definition. — The teeth are properly defined as hard, calcareous bodies situated in that portion of the alimentary canal near the ante- rior or oral extremity. In man they are confined to the oral cavity and are supported by the maxillary bones only. In the lower verte- brates they may be scattered over all of the bones and cartilages sur- rounding the mouth. 2. Function. — The main function of the teeth is the mechanical sub- division of substances used for food, preparatory to their digestion ; these organs therefore belong to the alimentary system. The elements of their function are prehension, incising, crushing, mastication, and insali- vation. For the performance of these various offices, different forms of teeth are found in the denture of man. In lower animals food-habit induces the evolution of many various and extreme forms of the teeth. The secondary offices of the teeth in man are as adjuncts in vocal- ization and articulate speech ; they also bear an esthetic relation to the mouth and face. Fig. 1. a b c d e The formatiou of single teeth from the single cone and its repetition in complex teeth. 3. Mechanical Design. — All tooth forms are evolved by modification from a simple cone, which is the primitive, typal form. The teeth of fishes and reptiles are but simple cones, and those of higher mammals are modifications of the single cone or combinations of two or more cones 2 17 18 MACROSCOPIC ANATOMY OF Till-: III'MAN TEETH. fused together. Tluis in mkiii the incisors arc formed of a single cone, the base of whieli is compressed to form the wicK- cutting edge (Fig. 1, a). The canine or cuspid is a singk' cone, the base of which is com- pressed into a trihedral point, or jxtinted jnramid (6). The bicuspids are composed of two cones fused together, the forms of the cones being <|uite distinct the entire length of the tooth, as in the upper bicus])ids (c). The tvi)al upper molar is fornu'd by the addition of the third cone to the bicuspid form, as |)hiiMly noticed in the three roots and the primitive three cusps {d). The usual (juadricuspid form is made by the addition of a cingule. The lower molar consists of four cones, which may be j)lainly distinguished i)y an analysis of its elements (e). Each cone in the structure of a tooth is surmounted by a cusp or tubercle. Extra cusps above the number of primary cones are but cingules or undeveloped cusps. In the genesis of tooth forms, therefore, the complex teeth, as the bicuspids and molars, are formed by the repetition and addition of cones and their accompanying cusps, both laterally and longitudinally of the jaw. 4. The Dental Arch. — The teeth of man are arranged around the margins of the upper and lower jaws in close contact, and have no Fig. 2. Square. Rounded Square. Rounded. Rounded V. The main types of the dental arch. interspaces between them. The basal arch is a graceful parabolic curve, with some variations which lead from the round arch to the incomplete parallelogram or even to a well-defined V shape. These variations may be classified as follows : First: The square arch (Fig. 2, a). This is found usually in persons of strong osseous organization, of Scotch or Irish descent — /. e. of Gaelic extraction — and is probably derived in the first instance from a dolichocephalic people. The squareness is more or less dependent upon the prominence of the large canines, which stand out very markedly at the angles of the square. The incisors present a flat front and project slightly, with little or no curve of the incisive line. The bicuspids and molars fall backward from the canines with no per- ceptible curve. The two sides are quite parallel, but sometimes there mav be a slight divergence toAvard the cheek at the rear. This is the low form of arch which appears in the apes and some low races. THE OCCLUSION OF THE TEETH. 19 Second : The rounded square (Fig. 2, b). This is the medium arch and is the form usually met with in ordinary, well-developed ro- bust Americans. The canines seem to be only so prominent as to give character to the arch without a resemblance to the arches of the lower animals. The incisors are vertical and the line curves slightly from one canine to the other. The bicuspid-and-molar line curves slightly outward from the canine and converges at the rear. Third : The rounded arch (Fig. 2, c). This is the circular or "horse-shoe" arch. It is nearly semicircular, the ends curving in- ward at the rear, the outlines of the arch tracing a decided horse-shoe shape. The canines are reduced to the level of the arch, so that there is no prominence of these teeth. The bicuspids and molars follow the line of the curve. This arch is quite characteristic in some races, as the brachycephalic South Germans. Fourth : The rounded V (Fig. 2, d). In this form the round arch is constricted in front or narrowed so that the incisors mark a small curve whose apex is the centre. It is the arch of beauty and is that most admired in women of the Latin races. These are but the basal forms of the dental arch. Ordinarily, mod- ifications of these types occur in all degrees ; it is the variations, the composites, which are most met with in dental practice. 5. The Occlusion of the Teeth. — The upper teeth describe the seg- ment of a circle larger than that of the lower teeth ; so that the edges of the anterior teeth above close over those below, and the buccal cusps of the grinding teeth above close outside of the buccal cusps of the lower teeth (Fig. 3). By this arrangement the buccal cusps of the lower grinders are received into the de- pressions or sulci between the buccal and lingual rows of the cusps and tubercles of the upper molars and bicuspids, and the lingual cusps of the upper grinders are received into the sulci of the lower grinders. By this arrangement the whole of the morsal surfaces of these teeth are brought into contact in the several move- ments of mastication, .thereby rendering the performance of this function more effective. Then, again, the upper incisors usually close over the lower for one-third of their length. This allows of the shearing action by which the incisive func- tion is performed as the edges of these teeth are drawn past each other. The line of the horizon of occlusion (Fig. 4, A-B) presents a decided Incisors. Fig. 3. Bicuspids. Molars. The relative position of the upper and lower teeth in occlusion. 20 MACROSCOPIC ANATOMY OF THE IIVMAN TEETH. curve from front to rear, of (greater or less dogrcc in different forms of the arch. Thus it is hit^dj at the ineisors, curving downward at the bicus- pids, reaching its k)west ])()int at the first niokir ; it cuirves upwanl raj)- idly at the second molar, and is highest, again, at the third. In the rounded arcli the pUme is more flattened, and it exhibits the extreme Fig. 4. The horizon of the line of occlusidn and plane of occlusion. downward curve in the square arch. Between these extremes there is of course every variety of modification. The form of the plane of occlusion is shown in Fig. 4, C Fig. 5. The apposition of the upper and lower teeth. The tendency of the bolus of food is toward the lowest part of the curve at the region of the lower first molar, so that the extraction of this tooth always affects the performance of mastication. In the apposition of the teeth of the opposite jaws the mechanical THE OCCLUSION OF THE TEETH. 21 arrangement is such that the dynamics of mastication is subserved and the greatest effectiveness secured (Fig. 5). Thus the morsal sur- face of the upper central incisor is opposed to all of that of the cen- tral incisor below and to the mesial half of the lateral ; the upper lat- eral opposes the distal half of the lateral below and the mesial face of the canine ; the upper canine, the distal half of the face of the lower canine and the mesial half of the first bicuspid ; the upper first bicuspid opposes the distal half of the lower first bicuspid and the mesial half of the second ; the upper second bicuspid opposes the distal half of the lower second bicuspid and part of the lower first molar : the upper first molar opposes the distal part of the lower first molar and the me- sial half of the second ; the upper second molar opposes the distal half of the lower second and part of the third ; and the upper third covers the remainder of the lower third molar. By this method of apposition the teeth are so arranged that two teeth receive the impact of half of two of the opposite jaw, thus distributing the force of occlusion and ensuring the safety and strength of the teeth. This " break-joint " arrangement permits each tooth to bear two opposing ones, and also helps to preserve the alignment. Fig. 6. Incisors. Canines or Premolars or cuspids. Bicuspids. Molars. The classes of the teeth, comprising the left half of a full denture. Then again, if one tooth be lost, the opposing teeth still rest against two teeth, one at each side of the space. The normal condition of the articulation is rarely preserved, however, as mutilation usually dis- turbs it ; the teeth move on account of the force of occlusion, and effec- tive mastication is more or less destroyed. 22 MACROSCOPIC ANATOMY OF THE IIl'MAX TEETH. (). Number and Classes of the Teeth. — Man lias thirtv-two teeth, diviiU'd into four classes, viz. — (Ist) ixcisoks, (2(1) canines or crspiDS, (3d) I'KEMOLAPvy or bicuspids, and (4th) molars (Fig. G). This is expressed by the dental formula as follows : 2—2 1 — 1 ,. 2 - 2 .3—3 -, e. , Oi. , in. 2-2' 1 — 1' 2—2' 3—3 (1) The incisors are oigiit in number, iour above and four below, — two on each side of the median line. The two next to the median line are called the central incisors, the ones next to them distally, the lat- eral incisors. (2) The canines are four in number, two above and two below, — one on each side immediately approximating the lateral incisor on the distal side. (3) The bicuspids are eight in number, four above and four below, — two on each side ap])roximating the canines on the distal side. The first of these next the canine is called the Jird bicuspid, the one next to it on the distal side the second bicuspid. The same designa- tion applies to both upper and lower bicuspids. (4) The molars are twelve in number, three on each side of each jaw, approximating the second bicuspid on the distal side. The molar next to the second bicuspid, both above and below, is called the first molar; the next one distally is called the second molar ; the next one distally, and the last tooth in the jaw, is called the third molar or " wisdom tooth " {dens sapientice). Functionally, the incisors are formed for cutting, as their name im- plies ; the canines for prehension and tearing (for which purpose this tooth in lower animal forms is often excessively developed). It also serves in guiding the bite. The bicuspids are the crushing teeth, and the molars are formed for grinding, triturating and insalivating the food. The Incisors. 7. The Upper Central Incisor. — This is the first tooth in the den- tal series in man. It is situated in the front of the mouth, next to the centre of the arch, which is the mesial border of the intermaxillary bone. In adult man these bones fuse with the anterior borders of the right and left superior maxillary bones. Their junction with each other marks the centre of the dental arch. The general form is that of a truncateil cone with its base flattened out to form the cutting edge. Its function is to cut or incise food, hence its name from the Lat. incisus, "to cut into." THE INCISORS. 23 The mechanical structure of the croion is a matter of importance. It will be observed that it consists of several elements : first, a broad cut- ting blade (Fig. 7, a) supported by two strong lateral columns (6) on each side, and that these columns are upheld by two strong marginal Fig. 8. Fig. The mechanical design of the crown of the upper central incisor : a, the blade ; b, the two columns supporting the blade ; c, the marginal ridges acting as guys, brac- ing the columns ; d, the basal ridge as the base of attachment for the guys. d f Diagram of the labial face of the upper central incisor. ridges (c) leading up from the lower ridge (d). These ridges are but- tresses, which guy and uphold the columns which contain and carry the blade. Hence, when these ridges are destroyed by caries or in operating, the support of the column is lost and the blade readily breaks away. The form of the crown is spade-like, or a compressed-w^dge shape, the edge being quite thin and the thickness increasing rapidly to the base. It is slightly bent toward the lingual side, or much curled over in some cases. The labial face is imperfectly square or oblong, the cervical margin being rounded (Fig. 8, a). It is convex from side to side, but only slightly so from cervix to edge. Two shallow depressions or furrows extend the length of the face perpendicularly (6) dividing it into thirds, called lobes, — the mesial, (c), median (d) and distal lobes (e). These furrows and lobes are quite conspicuous when the tooth is erupted, but are abraded by age and the wear of use and denti- frices, until the face becomes smooth. The mesial margin is a little longer than the distal so that the cutting edge slopes upward toward the distal side(/). _ The lingual face is smaller than the labial, being on the inner and smaller curve of the crown, and is narrower from side to side (Fig. 9). It is triangular in outline, being wide at the edge and narrow and rounded at the base or cervix. The marginal ridges (a) are high and conspicuous, and extend from the basal ridge to the edge on the Diagram of the lingual face of the upper central in- cisor. 24 MACROSCOPIC ANATOMY OF Till: III' MAS TKKTU. mesial :iml distal inarThe thickness increases rapidly from the edge to the neck (Fig. 12, B). Fig. 12. ^^■^ B C D The upper lateral incisor. The labial face (Fig. 12, C) is more rounded than that of the cen- tral. It is half incisor and half canine (a), the mesial half toward the central incisor resembling that tooth (6), and the distal half toward the canine resembling it (c). The mesial angle of the edge is quite acute, while the distal angle is rounded and obtuse. The three lobes may be well developed, similar to those on the central incisor, but are usually indistinct, although the central ridge is prominent. The lingual face (Fig. 12, D) is much depressed, but less concave than that of the central incisor. The marginal (cZ) and basal ridges (e) are quite prominent. The basal ridge is often raised into a prominent cingule or talon, an exaggerated example of Avhich is shown in Fig. 13, which is a revival of the basal talon found in the lower quadrumana, — and the insectivora. This cingule oeenrs more frequently on the lateral 26 MACROSCOPrr AXATOMV OF Till: //r.l/.l.V TKKTH. incisor than on the neck of the tooth (Fig. 1-,/). Sometimes the entire surface is full and rounded without any concavity whatever. The mesial face (g) is of triangular form similar a to that of the central incisor. It is rounded toward the edge lahio-lingually, but flattened at the neck, ** with a depression at the enamel line which leads Showing unusual develop- *^ mi i i • i i • ment of the cinguie or Upward upon the root. 1 he labial angle is some- basal talon on an incisor, ^jj^^^.^ ^j^^. ^^,^^ ^^^- ^ depression (/(), wllich givCS the (From case reported by Dr. ^ . . , w. H. Mitchell, Dattai Cos- angle a hook shape. The depression varies in «,o.,voi.xxxiv.p.i036.) ^^.j^^jj^ ,^j^^j ^l^^^^^j^ .^j^^l j^^,j^. become the seat of caries. The point of contact with the central incisor is at the junction of the lower with the middle third of the length of the face. The dktal face is more convex in all directions and resembles the canine in form, being in harmony with the general form of the distal half of that tooth. From cervix to edge it is rounded and the contact eminence in the middle third is very full (/). From this point it rounds off rapidly to the edge. The upper third is depressed rapidly toward the cervix, with a considerable depression at the enamel line leading off to the distal groove on the root. The edge is divided into two portions by the prominent tubercle (_/) in the middle which terminates the prominent central ridge of the labial face. The mesial half is straight, like that of the central. When worn, these features disappear and the edge becomes almost straight. The pitch of the edge, like that of the central, is toward the median line. The neck is much flattened mesio-distally, and is of a compressed pear shape, or flattened oval on section. The enamel margin pursues the same course as on the central incisor, rounding upward toward the root on the labial and lingual sides and dipping downward on the distal and mesial. It does not terminate so abruptly as that of the central incisor, and presents less of a ridge at the gingival margin. The root is commonly longer than that of the central incisor, is narrower, flattened mesio-distally (Fig, 12, A, B). It tapers gradually, not rapidly like the root of the central incisor. It is a flattened oval on section (e). Sometimes there is a hook at the end, curved distally. Grooves sometimes occur on the mesial and distal sides. The pulp canal is flattened in conformity to the shape of the root, but is readily entered if the root be straight. THE INCISORS. 27 The lateral incisor is very irregular as to form, presenting various degrees of deformity or abnormality, and may sometimes be reduced to a mere peg. It is also erratic as to eruption, being sometimes sup- pressed, not appearing for several generations of a family. It follows the third molar in the frequency of its irregularities both as to form and frequency of non-eruption. The third incisor of the primitive typal mammal sometimes reap- pears in man, and is known as a supernumerary. It rarely assumes the proper incisor form and position in the arch, but usually erupts within the arch and is a mere pointed-peg-shaped tooth. 9. The Lo^wer Incisors. — These are most conveniently described as a group, as they are very similar in form, having but slight variations between the central and lateral incisors to be noted. They are located in the anterior portion of the lower jaw, upon each side of the median line, opposite the incisors above. Their function is the same as that of the upper incisors, the cutting of food, which they per- form by opposing the upper. The lower central opposes only the cen- tral above ; the lateral, both the upper central and lateral incisors. The lo-wer central incisor is the smallest tooth in the dental series. It is of spade-like form (Fig. 14), the crown being a double wedge shape (a, 6). The first wedge (a) is observed on viewing the crown from the front, the widest portion being at the morsal edge and the point at the cervix. The second wedge is observed from the side (6), the widest part being at the neck and the point at the morsal edge of the crown. The edge is thin, but the labio-lingual diameter increases rapidly to the cervix, which is the widest part. The crown is widest mesio-distally at the edge, but diminishes to the neck, which is scarcely more than half the width of the edge. The tooth cone is therefore compressed in one direction at the edge, and in another at the cervix. The mechanical elements are the same as those of the upper central, but with the parts less strongly marked. The labial face is a long wedge shape («), the widest part at the edge and narrowing to the cervix. It is usually straight, or nearly so, longitudinally, and straight across the edge, but round and con- vex at the neck and the cervical half. Sometimes vertical ridges are found on these teeth when they are first erupted, but these soon wear oif. The lingual face is depressed and concave from edge to cervix (c), but less so from side to side. The marginal ridges are often well The lower incisor. 28 MACL'OSCOI'IC A.XA'J'O.VY OF TUI'. IITMAX TKKTII. marked. In the lateral ineisoi- the fossa is often more markeci and the mariiiiial ridges more distinct. The iiusidl nnd didal sides are of wi-tlge-liki" i'orm, straight from edge to cervix and widening in the same direction. A depression runs across the neck just above the enamel line. 'i'he neck is much compressed disto-mesially, and the rf)ot partakes of this flattening through its entire length. The section presents a compressed oval {e). The enamel line dips downward on the labial and lingual sides, and curves upward on the mesial and distal, in a manner characteristic of" the incisors. The edge is perfectly straight from side to side, after the three tuber- cles, found when first eru])ted, are worn off. The root is flattened like the neck, and frequently a groove runs the entire length on the mesial and distal sides. Occasionally complete bifurcation residts, which recalls the form of this tooth found in lower animals. The pulp canal (e) is of similar form t(» the root, and is flattened and thin, so that it is often difficult to effect an entrance to it with instnnuents. The lateral is similar in form to the central incisor, but is wider at the edge and the distal corner of the edge is slightly rounded (d). In all other features it resembles the central incisor. The Canines or Cuspids. 10. The Upper Canine. — This is the third tooth from the median line and a|>i)roximates the lateral incisor on its distal side. It is the first tooth |)osterior to the intermaxillary suture and is imbedded in the maxilla })roper. It is commonly said to form the spring of the arch, and conveys the impression of great strength, as is indicated by its strong imphuitation. It is more strongly implanted, and by a longer and larger root, than any of the other teeth. Zoologically it is the largest tooth in the dental series, but in man is much reduced from its prototype, the larger carnassial canine of lower animals, especially the carnivora. It is the principal prehensile tooth, and is therefore first in order of function in the dental series. The canine in man preserves the typal form, for its mechanical structure is still that of a single cone, brought to a point (Fig. 15, a). This is the earliest form of teeth found in the lower verte- brates, the fishes and reptiles, which present only simple conical teeth in all parts of the jaw. It has an older history than any other tooth, and stiil bears the marks of the many changes through which it has passed in the course of its evolution. THE CANINES OR CUSPIDS. 29 The crown has a spear-head shape (6), hence the name, cuspid, by which this tooth is frequently designated, from the Lat. cuspis, " point, pointed end." It is constructed essentially for piercing and tearing. The central cusp or point is braced in all directions ; the edges leading up to it both mesially and distally (which serve for cutting as well), the Fig. 15. The upper canine. strong labial ridge coming downward from the cervix (c) to the median ridge leading up on the lingual surface (rf), all support it in the office of prehension and the laceration of flesh. The labial face (b) presents the outlines of the spear shape, more or less rounded in diiferent cases. Starting from the well-defined cusp just in front of the central axis of the tooth, it widens sharply for about one-third of its length, whence it narrows gradually to the gum line, which is fully rounded. In some cases the mesial and distal angles are rounded and the outlines are more of a leaf shape (e). The surface is slightly rounded mesio-distally, so that the sides slope roundly or flatly away from the central ridge. This ridge descends from the middle of the cervical margin, curving slightly forward and then backward to the point of the cusp (c). This curve recalls the curving shape of this tooth in the Felidse. It is usually a sharp, prominent ridge, but may be reduced and rounded so as to be scarcely perceptible. The three lobes of the surface are imperfectly marked, — the central ridge dominating and dwarfing the lateral ones. The lateral furrows on each side of the central ridge separating it from the lateral lobes are more or less marked, especially toward the edge. Wear reduces in time the prom- inence of the lobes and ridges and obliterates the furrows. The Ungual face is of similar spear shape (d), but is more flat. It is rarely concave. The thickness of the crown increases gradually to the lateral prominences, which gives a blade-like edge, then rapidly to the shoulder at the base. A strong vertical ridge extends from the cusp to the basal ridge (d), with a slight concave depression on each side. The basal ridge is well marked and sometimes develops into a cingule, more or less marked. The marginal ridges lead up on each 30 MACROSCOPIC AS ATOMY OF TIIK HI-MAX TKKTH. side only so far a> the lateral jn-otiilHTaiico. Tlicy arc not strongly marked as a rule. The fosste on each side of the vertical median ridge, between it and the marginal ridges, may he <|uite deep hut are usually shallow and ill defined. The mesial face in outline is not unlike the central ineisor, but its contour is very diU'erent, for it is more or less rounded in all direc- tions, and the lateral eminence in the lesser third makes this part espe- cially full (i). From this j)oint the surface is depressed roundly to the enamel line at the neck, where a depression of greater or less depth is lound. It is someNvhat flattened at the cervix. The point of contact is at the eminence, which touches the lateral incisor. The (Jisfdl face is of similar form to the mesial, exce])t that it is more full and the eminence more pronounced, which gives the increased width of the crown on that side. The surface descends rapidly toward the neck and is rounded labio-lingually. The point of contact with the first bi- cuspid is on the lateral protuberance. The morsal edge presents a prominent cusp which is almost central to the long axis of the tooth. The side facets slope away, but still retain their cutting edge (6). The distal side of the edge is longer than the mesial, by reason of the increased size of the distal protuberant angle. The sharp point is soon worn off to a rounded cusp, and, as wear increases with age, it may be reduced to a straight surface between the mesial and distal protuberances {>/■• TJI/-: ^[l'^fA^ TEETH. The mot is lontx, Hattciicd, and tajx-rin^ {per molar is, there- fore, composed of three tubercles, and a cingule which has not yet developed a root to sujiport it. The trituberculate molar is the primitive form of this tooth, the ((uadrituberculate appearing later, and is found in only a few living forms, as some of the lemurs and the insectivorous and carnivorous mammalia. In man there is sometimes a reversion of the up])er molar to the trituberculate form, which is a marked degeneracy in the form of this tooth. In an analysis of this tooth, therefore, the mesio-buccal tubercle (c) is the canine cusp ; the mesio-lingual, the bicus- pid cusp {d) ; the disto-buccal, the molar cusp (e), and the disto-lingual is but a supplemental cusp, — it is not a true cusp, as it has no root to support it. The architecture of the upper molar presents some interesting features. We observe that the crown is in a general way a geometrical form, a cube (/), when perfect and symmetrical. It is suggestive of symmetry, but wdien taken with the root form is not quite perfect, for it is sup- ported on three roots instead of four to correspond with the four tuber- cles at the four corners. So it lacks the " harmony of adequate sup- port," which is a cardinal principle in architecture. But the crown separately is a symmetrical form, a cube, although the angles are rounded off and the corners and points are toned down and not acute. We no- tice that there are four strong columns, one at each of the four corners (ff). They are connected on the four sides by the marginal ridges acting as strong connecting arches (h). These arches are related to the col- umns of the crown, and both are impressively proportioned. The cusps may be likened to the capitals of the columns, and the descending mar- ginal and triangular ridges to the cornice, gathered together to form the capitals. The triangular ridges may be considered girders (i), bind- ing the four together and also bracing the square obliquely. Or, the four triangular ridges running to the centre may be regarded as half- arches or buttresses, supporting the roof vault, — the grinding face. Other elements could be marked out in an architectural study of the crown of this tooth, showing its beautiful design and symmetry. THE MOLARS. 39 The upper first molar approximates the second bicuspid on its distal side. There is a marked and abrupt change in form, as the molar has double the number of cusps of the bicuspid, — being formed like two bicuspids fused together. The four tubercles mean an extension of sur- face and a further adaptation to functional requirements. The crown is large and cubical in form, and more or less rounded. Fig. 21. A e Architectural diagram. s q The upper molar. The buccal face (k) is wide and rounded. It is twice the width of the bicuspids. It is broadest at the morsal margin, narrowing upward to the cervix, where it is widely rounded or arched. A vertical depression, the buccal groove (I), extends from the cervical border to the morsal margin, dividing the face into two oblong rounded eminences, the mesial and distal buccal lobes {m m). The lingual face {n) is more rounded than the buccal, the cervical por- tion being the most convex (o), the mesial and distal sides being depressed toward the single lingual root. The morsal half is divided by the lingual groove (q), which descends over the lingual marginal ridge be- tween two lobes, the mesial (?■) and distal (p), which are usually much rounded. The morsal half of the face curves toward the grinding sur- face. The mesial lobe sometimes presents the lingual cingule (s), a sort of fifth tubercle of greater or less size. A groove branches from the lingual groove and extends over, between the cingule and crown. The mesial face {T) is flat longitudinally, descending from the marginal ridge to the cervix in a nearly straight line. Bucco-linguallv it is 40 MACROSCOPIC .l.V.17Y>.V}' OF THE HUMAN TEETH. convex, nearly flat at the marginal ridge, aii OPERATIVE DEyiTISTRY. tlir position of tlu: cavity inar<;iiis must he governed hy our knowledge ot' tlie structure of the enamel. In the execution of the work a niiiuite knowledge of the direction of enamel rods becomes the most important element in ra[)idity and success of operation. From the standpoint of comparative anatomy, the teeth are found to l)e not a part y>j^^^H^^H 1 ^ J ^^^V Shark's skull (Lainua cornubica), showing succession of teeth. small simple cone-shaped teeth. The mouth cavity is to be regarded, when viewed in the light of its development, as a part of the outside surface of the body which has been inclosed by the development of the neighboring parts, and the dermal scales or rudimentary teeth which were found in the skin covering the arches which form the jaws have undergone special development for the purposes of seizing and masti- cating the food. In the simplest forms there is only a development in size and shape of these scales, and they are supported only by the connective tissue which underlies the skin. These teeth are easily torn off in the attempt to hold a resisting prey, and, as in the shark, they are constantly being replaced by new ones (Fig. 31). In the more highly de- veloped forms there is a growth of the bone of the arch forming the jaw DENTAL TISSUES. ^^ upward around the bases of these scale-like teeth, to support them more firmly and render them more useful. If we compare the structure of the hair with that of the tooth, we find in the case of the hair a horny structure formed by epithelial cells resting upon a papilla of connective tissue; in the case of the tooth, a calcified structure formed by epithelial cells resting upon a papilla of connective tissue which is also partially calcified. The relation of the bones of the jaws to the teeth is entirely a secondary and transient one. The bone grows up around the roots of the teeth to Fig. 32. Changes in the mandible with age ; buccal and lingual view. support them, and is destroyed and removed with the loss of the teeth or the cessation of their function. In this way the development of the alveolar process takes place around the temporary teeth ; all of this bone surrounding their roots is absorbed and removed with the loss of the temporary dentition, and a new alveolar process grows up around the roots of the permanent teeth as they are formed. This development of bone around the roots of the teeth leads to the changes in the shape of the body of the lower jaw, increasing the thickness above the mental foramen and the inferior dental canal. When the teeth are finally lost this bone is again removed and the body of the jaw is reduced in thick- ness from above downward (Fig. 32). These phenomena are of im- portance in their bearing upon the causes and treatment of diseased con- 66 DENTAL HISTOLOGY AND OPERATIVE DENTISTRY. ditions of the teeth, particularly those which involve the supporting tissues. Dental Tissues. — The human teeth are made up of four tissues (Fi^^. 33) : 1 . The enamel covers the exposed portion of the tooth, or crown, and gives the detail of crown form. Its function is to protect the tooth against the wear of friction. 2. The dentin forms the mass of the tooth and determines its class form, the number <»f cusps and the innnber of roots being indicated by the dentin form. 3. Cementum covers the dentin beyond the border of the enamel, overlapping it slightly at the gingival line and forming the surface of the root. Its function is to furnish the attachment of the fibers of the peridental membrane, which fastens the tooth to the bone. 4. The pulp or soft tissue filling the central cavity in the dentin is the remains of the formative organ which has given rise to the dentin. Its functions are the formation of dentin and a sensory function. In describing the structure of the teeth and the arrangement of the structural elements of the tissues directions are described with reference to three planes : The mesio-disto-axial plane, a plane passing through the centre of the crown from mesial to distal and ])arallel with the long axis of the tooth. The bucco-linguo-axial plane, a plane passing through the centre of the crown from buccal to lingual and parallel with the long axis of the tooth. The horizontal plane, at right angles to the axial planes. The Supporting- Tissues. — The human teeth are supported on the maxillary bones, their alveolar processes growing up around the roots of the teeth, so that the roots fit into the holes in the bone. The calcified structures of the tooth and the bone are not, however, united, but the roots are surroiuided by a fibrous membrane, the pendenlal membra'ne^ or peincementinn, which fastens the tooth to the bone. Enamel. The enamel differs from all other calcified tissues in the nature of the structural elements of which this tissue is made up, in the degree of calcification, and in origin, being the only calcified tissue derived from the epiblast. The enamel is formed from an epithelial organ derived from the epithelium of the mouth cavity and indirectly from the epiblastic germ layer, while all other calcified tissues are products of the niesoblast. In the case of bone and dentin the formative tissue is persistent. It ENAMEL. Fi(i. 33. 57 Ground section of a canine : E, enamel ; Cm, cementum ; I), dentin ; Pc, pulp chamber ; De, dento- enamel junction ; £rf, enamel defect ; G', junction of enamel and cementum at the gingival line; 6t, granular layer of Tomes. (Reduced front photomicrograph made in three sections.) 58 DENTAL HISTOLOCY AMt tn'EllATIVK DENTISTRY. is possible ill the boiic at least, tlwretorc, to have (h'jreiierative and re- generative changes, or the removal of part of the ealciuni salts and their rephieeinent tlirougli tlie aireiiey of the formative tissue ; while in the enamel no sucii regenerative change is possible, as the formative tissue disappeared when the tissue was completed and before the eruption of the tooth. The enamel is the hardest of human tissues. Chemieallv it is com- posed of the phosphates and carbonates of calcium and magnesium and a very small amount of the fluorids, water, also a very small amount of organic matter if any.' The enamel in the natural condition, bathed in the fluids of the mouth, contains a considerable amount of water. If dried at a little above the boiling-point of water, it gives up part of it and shrinks considerably, so as to crack in fine cheeks. If heated almost to redness, it suddenly gives off' from ."3 to o per cent, (of the dry weight) of water with almost explosive violence. These facts were demonstrated some years ago by Charles Tomes," and account for nu)st of what was formerly recorded as organic matter in old analyses. If we observe under the microscope the action of acids upon thin sections of enamel, when the inorganic salts are entirely removed, the structure of the tissue vanishes, there being no trace of organic matrix left as in the case of bone or dentin. In the growth of bone and dentin the formative tissue produces first an organic matrix in the form of the tissue, and into this the inorganic salts are dej)osited, combining with the organic substances of the matrix. This union is comj)ara- tively weak, however, for by the action of acids the combination is broken up and the inorganic salts arc dissf>lved ; or by heat the organic matter is removed, and in either case the form of the tissue will be maintained. In the case of the enamel, the formative organ produces organic substances containing inorganic salts, and the substances are arranged in the form of the tissue after the manner of a matrix; but finally imder the action of the formative organ all of the organic matter is removed and substituted by inorganic salts, whatever organic matter is ' Von Bibra gives the following analysis of enamel : ( alcinm phosphate and fliiorid 89.82 Calcium carbonate 4.37 Magnesium phosphate 1.34 Other salts 88 Cartilage 3.39 Fat 20 Total organic 3.59 " inorganic 96.41 * Journal of Physiology, 1896. ^ ENAMEL. 59 found in the fully formed tissue being the result of imperfect execution of the plan. The enamel is composed of two structural elements, the enamel, rods, or prisms, sometimes called enamel fibers, and the interprismatic or CEMENTING SUBSTANCE, both of which are calcified. It is to the arrange- ment of these structural elements that the characteristics of the tissue with which we are most concerned in operative procedures are due. While both the prisms and interprismatic substance of the enamel are calcified, or, better, composed of inorganic salts, the two substances — that is, the substance of the rods and the substance between the rods — show markedly different properties both chemical and physical. If treated with acid, the interprismatic substance is acted upon more rapidly than the rods, so that the latter become more conspicuous. By this means sections of the enamel may be etched to render it easier to study the direction and arrangement of the rods. If the action of the acid is carried far enough, the rods will fall apart before they are them- FiG. 34. Enamel rods isolated by caries. (About 465 X.) selves entirely dissolved. Fig. 34 is from the debris in a carious cavity, and shows rods isolated by the action of the acids of caries. The interprismatic substance is not as strong as the rods, so that in splitting or breaking the enamel the tissue separates on the lines of the cementing substance, occasionally breaking across a few rods but fol- lowing their general direction, the lines running between rods, not at their centres. In cleaving the enamel the chisel does not enter the tissue sepa- rating rod from rod, but the edge engages with the surface, and the 60 liKSTAl. insTolJxiY AM) OPERATIVE DEyTlSTRY. force applied at an acute angle with the d throughout their length. They are from 8.4 to 4.5 microns' in diameter, some of them apparently reaching the entire distance from the surface of the dentin to the surface of the enaiuel ; but as the diameter of the rods is the same at their outer and inner ends, and as the crown surface is much greater than the surface of den- tin covered by enamel, there are many rods which do not extend through the entire thickness. These short rods end in tapering points between the converging rods which extend the entire distance. To express this in terms of development : as the formation of enamel begins at the surface of the dentin, the increasing area of crown sur- face requires more ameloblasts, and as new ameloblasts take their place in the layer the formation of new enamel rods begins between the rods which were jireviously forming. These short rods are most numerous over the marginal ridges and at the points of the cusps, and will be considered more fully in connection with those positions. In ground sections cut at right angles to the direction of the rods'' the tissue has the appearance of a mosaic floor, the outline of the rods being more distinct if they have been marked out by treating the section .slightly with acid (Fig. 35). In longitudinal sections (Fig. 36) the si(h's of the rods are not smooth and even like the sides of a lead pencil, but are alternately expanded and constricted. They are well illustrated by taking balls of soft clay and sticking them together one above another to form a rod, then ])utting a nimiber of rods together so that by mutual pressure they take hexagonal forms. This illustrates also the manner of growth of the tissue in formation. The expansions and constrictions can be seen in rods that have been scraped from a cleaved surface of enamel, but better by isolating rods by the slight action of dilute acid (Fig. 37). In the construction of the tissue the rods are so arranged that the ex- ' A micron is tlie unit of microscopic mensiiremont. and is ecpial to f.ne one-tlionsandtli of a millimeter. •^ In describing the direction of enamel rods tliey are always considered as extending from the dentin to tlie sinface, and the angle is formed at I he sni-face of the dentin with the locating plane, either horizontal or a.\ial. ENAMEL. 61 pansions of one rod come opposite to the expansions in the adjoining rods, and do not interlock with their constrictions. This arrangement Fig. 35. Transverse seetiun of enamel rods. (About so .) leaves alternately a greater and a less amount of cementing substance between them. Fly. 36. Enamel rods in thin etched section. (About 800 X.) When observed under the microscope, the enamel rods show a char- acteristic appearance of light and dark lines running across them. These markings are similar to the striations of voluntary muscle fibers, <>2 DENTAL HISTOLOGY AND OPERATIVE DENTISTRY. and are described as the striation of the fiuuncl. It is seen not only in isolated rods (Fig. 34), but also in sections ground in their direction (Fig. Fi... :{7. Enamel rods isolated by scraping. (About SUO a .) 38). This appearanw of" striation in the enamel is caused by the alter- nate expansions and constrictions of the rods refracting the light like a Fu;. .'is. Enamel showing striation. (About IfniO v.) lens. In sections the expansions in adjoining rods are opposite to each other, the difference in the refracting power of the prismatic and inter- prismatic substances producing the same effect. ENAMEL. 63 The appearance of striation is the record in the fully formed tissue of the manner of growth, each dark stripe, or expansion, in a rod representing a globule of partially calcified material. The ameloblasts build up the rods by the addition of globule after globule, surrounding them with a cementing substance and completing the calcification of both. In this sense the striation of the enamel may be said to record the growth of the individual rods. While the enamel is a very hard substance when its structure isi complete and perfect, its most striking physical characteristic is a ten- dency to split or crack in the direction of its structural elements when a break has been made in the tissue. While it is difficult to cut across the rods or make an opening on a perfect surface, if a break has been Fig. 39. Sli , • ,t- rm^^^^t >i ..-ja^.y|HJ M 1' ■ 1. 1 \. i ' "^^H m \\ J ^^H^ .■''i?.'f '^ t, j lliltlllllMillll 'll'l'li*ll l^^^gg J Enamel showing direction of cleavage. (About 70 X.) established it is comparatively easy to split off the tissue from the sides of the opening when the rods lie parallel with each other. Fig. 39 shows a field of enamel illustrating the way in which the tissue splits or cleaves in the direction of the rods. Upon the axial surfaces the enamel rods are usually straight and parallel with each other, except where there has been some flaw or disturbance in development ; but upon the occlusal surface, although sometimes straight, they are very often much twisted and wound round each other, especially at their inner ends. This difference in the arrangement of the rods causes the greatest difference in the feeling of the tissue under cutting instruments. Such a specimen of enamel as shown in Fig. 40 can be cut away easily, the tissue breaking through to the dentin and splitting off in chunks ; while a specimen like Figs. 41 and 42 will not cleave if supported upon sound dentin. If the outer 64 DENTAL HISTOLOGY AXP OPERATIVE DENTISTRY. I'ui. 40. Strai;;lil eiiaiiu-1 rods, i Alxnit 8fi:-;.) Fu;. 41. Gnarled enamel. (About .'OX.) ENAMEL. 65 ends of the rods are straight, they will split part way to the dentin (Fig. 42) ; but where they begin to twist round each other they will break across the rods. If the dentin is removed from under such enamel, it will break in an irregular way through the gnarled portion. From a study of the arrangement of the enamel rods in the forma- tion of the crown it is apparent that the plan is such as to give the Fig. 42. Gnarled enamel. (About 50 X.) greatest strength to the perfect structure, and may be likened to an arch. At the gingival border the rods are short and are inclined apieally 6 to 10 centigrades ^ (20° to 35°) from the horizontal plane. These short rods ^ In the Centigrade division the circle is divided into one hundred parts, each called a centigrade. One centigrade is equal to 3.6 degrees of the astronon)ical circle, 25 centigrades to 90 degrees, 12^ centigrades to 45 degrees. The cut gives a comparison of the two systems of meas- uring angles. 270 180 Centigrade division. 66 DENTAL HISTOLOGY AM) OPERATIVE DENTISTRY' arc overlapped for a short distance l)y the ceiiicntiim. This inclination grows less and less, and at some |)laet' in the uinuival halt" of the middle third of the snrface they are in the horizontal i)lane. At this jioint they are also nsnally perpendicular to the surface ot' the dentin. Passing from this j»oint they become inclined more and more occlnsallv from the horizontal plane, at the Junction of the occlusal and middle thirds about 8 to 12 centigrades (28° to 40°) in bicuspids and molars, and 8 to 18 centigrades (28° to 65°) in incisors and canines. In the occlusal third the inclination increases raj)idly, and often the outer ends of the rods Fig. 43. Iiin. 44-4G. At the time the rod at .1 ( Fiir. 4")) was completely i'onned the rod at B was just beginning to form at its dentinal end. From this it Mould li(.. 15. Incisor tip showing stratiliratinu cr incremental lines. Rods at .1 were fully forined at the time the rods at B were beginning to form. (.Vbout 50 X.) seem that any structural defect due to imperfect development would not follow the direction of the enamel rods from the surface to the dentin, but would follow the stratification lines ; and if these structural defects influenced the penetration of caries, we should expect to have the direc- tion of penetration modified. Fig. 44 shows a structural defect in the enamel over a cusp following the stratification band, and it will be noticed also that there is a structural defect in the dentin at a corre- sponding position. HISTOLOGICAL REQUIREMENTS IN ENAMEL WALLS. 69 HISTOLOGICAL REQUIREMENTS FOR STRENGTH IN ENAMEL WALLS. 1. The enamel must be supported upon sound dentin. 2. The rods which form the cavo-surface angle must run uninter- ruptedly to the dentin and be supported by short rods, with their inner ends resting on the dentin and their outer ends abutting upon the cavity wall, where they will be covered in by the filling material. 3. That the cavo-surface angle be cut in such a way as not to expose the ends of the rods to fracture in condensing the filling material against them. The first step, then, in the preparation of an enamel wall is to deter- mine the direction of the enamel rods by cleavage with a chisel or hatchet. Fia. 4B. Enamel show triation and stratification, i Aii^ut sO,-'.) In Figs. 47 and 48, No. 1 shows an enamel wall after cleaving the enamel with a hatchet. It will be noticed that the split has not followed the direction of the rods exactly, but has broken across them, slivering the rods as wood slivers in splitting. This would cause in the cut surface a whitish, opaque appearance. The plane of the enamel wall should be extended so as to form a small angle with the plane of the dentin wall, by shaving the surface with a very sharp hand instrument. No. 2 shows the same wall after it has been extended somewhat ; but it will be seen that it has not been extended enough, for the rods forming the sur- face at A do not reach the dentin, but run out at B on the cavity '/all, and that piece would chip out in packing against it or if force came upon the surface afterward. The angle should be extended so as to produce 70 DENTAL HISTOLOGY AM) OPERATIVE DENTISTRY o — C tr. c V «5Q HISTOLOGICAL BEQUIBEMENTS IN ENAMEL WALLS. 71 Preparatioa of enamel wall in gnarled enamel: 1. Enamel wall as cleaved, showing breaking across rods and slivering at a. 2. Wall as smoothed but not extended to remove short rods whose inner ends are cut off at b. 6. Wall extended and trimmed to a position of strength. D, dentin ; De, dento-enamel junction ; c, cavosurface angle ; b, point where inner ends of rods are cut off; a, slivering of the tissue. (About -SO K-) 72 DF.\r.\L IIISTOLOOY AND OPERATIVE DENTISTRY. the plaiu' shown in NO. "?> ; then the eavo-surlaee angle may or may not 1)1' Ix'velled as the position demands. In some positions, as on the axial snrfaces, it is not possible to ex- tend the phme of the entire enamel wall as described ; all that can be doni' is to shave the cut surface, leaving the wall in the direction of the enanicl rods, and then the margin is strengthened by bevelling the eavo- Fio. 49. Occlusal fissuri ill an iij.).! ; !.,( ,i>(iid, showing direction of rods. (About 80 X.) surface angle, so that the rods forming the margin are supported by at least a few rods which are covered by filling material. In cutting out the fissures on the occlusal surfaces of molars and Ijicuspids, the rods are inclined centrally from the axial |)lane, as seen in Fig. 49. In opening a fissure the lines of cleavage will not be in the axial plane, but sloj^ing inward toward the body of the cusp, in the HISTOLOGICAL REQUIREMENTS IN ENAMEL WALLS. 73 direction indicated by the direction of the cracks in Fig. 49. The outer ends of the enamel rods must be shaved away, to bring the plane of the enamel wall parallel with the dentin wall or into the axial plane. When this has been done a strong margin has been formed, for the Fig. 50. Preparation of enamel walls in occlusal fissure cavities (the same as Fig, 49). rods which form the point of the cavo-surface angle are supported by the piece A, B, C(Fig. 50), made up of rods resting upon sound dentin and covered by the filling material. Often the angle will be too sharp, however, and the cavo-surface angle should usually be bevelled to pro- tect the margin from accident. This illustration may be taken as typ- ical of occlusal cavities. 74 DEyTAL HISTULOGY ASD OPERATIVE DENTISTRY. Fi(i. 51. Prepantlioii of enamel walls m i:i\it_v in a iiiular: '.', gingival wall; O, occlusal wall (About 70 X.J HISTOLOGICAL REQUIREMENTS IN ENAMEL WALLS. 75 Fig. 51 shows a cavity prepared in the buccal surface of an upper molar. The occlusal margin is placed in the occlusal half of the middle third, and the gingival margin in the gingival half of the gingival third Fig. 52. 2. Wall as trimmed. Preparation of occlusal wall of Fig. 51. (About 70 X.) of the surface. In the occlusal wall the rods are inclined occlusally about 8 centigrades (28°) from the horizontal plane. After cleaving, the broken and slivered rods should be shaved away, but the angle can- 76 DENTAL HISTOLOGY ASD OPERATIVE DENTISTRY. iH)t be increased witlumt iiiakiii<; tlit- margin of lilliiig luiitcrial too thin; the rods forming tlie margin should therefore be protected by bevel- ling the cavo-surfaco angle. At the gingival wall the rods are inclined a})ioally from the horizontal plane abont 6 centigrades (20°). The wall should be shaved in that plane, increasing the angle a little, and the cavo-surface angle should be bevelled. Fig. 52 shows the occlusal enamel wall alone, after cleaving and trimming into form. Such enamel walls may be taken as typical of axial surface cavities, the Fig. 53. structure of enamel about a fissure : /?, huccal side ; L, liiiRii: angle of the enamel with the dentin wall being determined by the direction of the enamel rods in the position where the margin is laid. Grooves, fissures, and pits are always positions of weakness, and when a cavity ap})roaehes a groove or pit a good margin, histologically, cannot be prepared without cutting beyond it. Fig. 53 shows an occlusal fissure in a bicuspid, which illustrates the conditions of struct- ure characteristic of these positions. The rods are inclined toward the fissure, and between the bottom of the fissure and the dentin are verv irregular. If a cavity wall were made to approach this fissure from the lingual side, so as to come to the dotted line, the wall would have to be inclined 6 to 8 centigrades (20° to 28°) from the axial plane toward HISTOLOGICAL REQUIREMENTS IN ENAMEL WALLS. 77 the fissure, and then the cavo-surface angle bevelled, when the condi- tions would be similar to those in the wall of an axial surface cavity, and not as strong as the location requires. Not only is this true, but it also leaves a vulnerable point next to the margin of the filling — a point of liability. Cutting just beyond the fissure, the wall may be left in the axial plane and have an ideally strong margin, and the point of liability is removed. To state the conditions in general Fig. 54. B A Bucco-lingual section of upper bicuspid. Enamel is broken from grinding . Aio B, area of weak- ness for enamel margins. (About 20 X.) terms, a strong margin is more easily obtained where enamel rods are inclined toward the cavity than where they are inclined away from the cavity. The points of cusps and the crests of marginal ridges are positions of strength in the perfect tissue ; but when a cavity margin approaches them they become points of weakness, because it is impossible to sup- port properly the rods which form the margin. Over the marginal 78 DESTAL HISTOLOGY AND OPERATIVE DENTISTRY. ridges are many short rods Avliidi do not icacli the dentin, and these are usually very much twisted about each otiier, so as to form the strongest possible keystone in the jieii'eet strnctnre. In preparing a Fi.;. o5. Enamel over tip of dentin cusp : D, dentin cusp, f About 80 X.) margin in such a position it is impossil)le to have the rods which form the margin reach the dentin with their inner ends, and these short rods are sure either to break in completing the operation or to HISTOLOGICAL REQUIREMENTS IN ENAMEL WALLS. 79 break out later. The arrangement of enamel rods in such positions is to be borne in mind, especially when extending approximal cavities in incisors toward the lingual side and in large pit cavities in incisors. A similar condition is found over the points of the cusps. Fig. 54 shows a bucco-lingual section of an upper bicuspid. It will be noticed that the rods forming the point of the cusp are not in the axial plane, and Fig. 56. Tip (jf an incisor. (About 50 X.) do not reach the tip of the dentin cusp, but reach the dentin a little way down on the outer slope. The enamel covering the tip of the dentin contains many short rods, and they are very much twisted about each other, so that the area from A and B to the point of the cusp is an area of weakness for the cavity margins. If the margin reaches this area, the cusp must be cut away and the enamel wall carried out in the horizontal plane. Fig. 55 shows this area more highly magnified, and 80 DKNTAL HISTOLOGY AND OPERATIVE DESTISTHY. illustrates the structuro. It will bo noticed that, in grinding, some of the short twisted rods have broken out of the section. Fig. 56 shows the tip of an incisor in labio-lingual section, and is of interest in relation to the formation of margins in step cavities in in- cisors. The tip of this tooth has been worn off in use. The illustration shows that the great inclination of the rods toward the axial plane in the occlusal third of the incisors is such as to bring tiie wear almost at right angles to the direction of the rods. Dentin. The structure of dentin is of eom|»aratively little interest in the present consideration, as its histological forms do not diicetly iuHueuee Fig. 57. Dentin at dento-enamel junction, showing tubuk-s cut longitudinally: /y^ dentinftl ttibuli's : D, dentin matrix. (About 760 X.) the cutting of the tissue in the excavation of cavities. Its histological forms have, however, much to do with the penetration of caries and with other considerations which are of importance to the intelligent practice of operative dentistry. DENTIN. 81 Dentin belongs to the connective-tissue group, and is made up of a solid organic matrix impregnated with about 72 per cent, of inorganic salts ^ and pierced by minute canals or tubules, which radiate from a central cavity which contains the remains of the formative organ, or pulp. The minute canals, or dentinal tubules, are occupied in life by protoplasmic processes from the odontoblastic cells which form the outer layer of the pulp. Dentin contains two kinds of organic matter, the contents of the tubules and the organic basis of the matrix. The dentin matrix, after the removal of the calcium salts by acids, yields gelatin on boiling and resembles the matrix of bone, reacting in a similar, though not identical, way with staining agents. The portion of the matrix immediately surrounding the tubules shows different chemical Fig. 58. Dentin showing tubules in cross-section: Z)<, dentinal tubules: J), dentin matrix; S, shadow of sheaths of Neumann. (About 1150 X-) characteristics from the rest of the matrix, resembling elastin, and re- sisting the action of strong acids and alkalies after the rest of the tissue has been destroyed. This portion of the matrix surrounding the tubules and lying next to the fibrils is known as the sheaths of Neumann. The dentinal tubules are from 1.1 to 2.5 microns in diameter, and are separated from each other by a thickness of about 10 microns of * Von Bibra gives the following analysis of dentin : Organic matter 27.61 Fat 40 Calcium phosphate and fluorid 66.72 Calcium carbonate . . . 3.36 Magnesium phosphate 1.08 Other salts 83 6 DENTAL HISTOLOGY AND OPERATIVE DENTISTRY. dentin matrix. This is fairly uiiifonn thnniiilioiit the (U-ntin. The character of the tubules is different in tiie crown and root portions. In the crown tlie tubules branch but little throuijh most of their course ; but in the outer part, close to the enamel, they branch and anastomose with each other (piite freely. Fig. 57 shows a held of dentin just beneath the enamel, as seen with a high power, and shows the diameter of the tubules, their branching, and the amount of matrix between one tubule and the next. The relation of one tubule to each other is shown also in sections cut at right angles to their direction (Fig. 58). In the crown portion the tubules pass from the pulp chamber Fk;. r)9. Crown of a molar, mesio-distal section, showing peiuiruti in t tin; B, line of abrasion : P. i>ulp cliainlnT. iliug den- Atioul JO ■ .) to the dento-enamel junction in sweeping curves, so as to enter the pulp chamber at right angles to the surface, and end next to the enamel at right angles to that surface. This produces S- or F-shaped \ or curves, which are known as the primary curves of the tubules. Through- out their course the tubules are not straight, but show a great many wavy curves, known as the secondary curves. These appear as waves when seen in longitudinal sections, but are really the effect of an open spiral direction, as is seen by changing the focus of the microscope in studying sections cut at right angles to the direction of the tubules. Dentin from the root, showing tubules cut longitudinally. (About 700 X.) Fro. 61. Dento-enamel junction. (About 70 X-) 84 DESTAL HISTOLOGY AND OPERATIVE DENTISTRY. The l)r:inclu's tlirontjjlKMit llicir Iciiiitli ai'c fi'W and small, ami are jiivcii ofl' at an acute aii«ile to tlie direetioii ni" tlie tiihtile ; l)Ut just Ix'fore the eiiaiiK'l i.s ri'aehed tlie tubules I'ork and branch, pr()ducin<2; an a|)])earance similar to the delta of a river. These brunehe.s are j^iven of!" Irom the tubules for some little distance back from the enamel, and thev anasto- mose with other tubules very freely. The branching of the tubules in their outer portion causes the spreading of caries just beneath the enamel, the micro-organisms growing through the branches from tube Fi f » J ♦ rf> . ^':' V -o -Bl -N v>» A pulp bloodvessel, showing- the thin wall : C, blood corpuscles in the vessel ; Bl, bloodvessel wall showing nuclei of endothelial cells; N, nuclei of connective-tissue cells in the body of the pulp ; /, intercellular substance, showing a few fibers. (About 2fX) X.) representing the media, while the walls of even the large veins are made up of only the single layer of endothelial cells forming the intima, and PULP. 91 are in structure like large capillaries (Fig. 68). This peculiarity of the bloodvessel walls is of great importance, as it renders the tissue specially liable to such pathologic conditions as hyperemia and inflammation. NEEVE OF THE PULP. Several comparatively large bundles of medullated nerve fibers, coi^.- taining from six or eight to fifteen or twenty fibers, enter the pulp in company with the bloodvessels and pass occlusally through the central portion of the tissue. These bundles branch and anastomose with each other very freely. Most of the fibers lose their medullary sheath before reaching the layer of Weil, in which position they form a plexus of non-medullated fibers ; from these fibers free endings are given off, which penetrate between the odontoblasts. In some cases these have been followed over on to the dentinal ends of the odontoblasts, but in no instance have they been followed into the dentinal tubules. THE FUNCTIOlSrS OF THE PULP. The pulp performs two functions, a vital and a sensory. The vital function is the formation of dentin, and is performed by the layer of odontoblasts. This is the principal function of the pulp, and it is first manifested in the development of the tooth before the dentinal papilla is converted into the dental pulp by being inclosed in the formed dentin. After the tooth is fully formed the vital func- tion is not manifested unless the pulp is stimulated by some excitation affecting trophic centres and which causes the formation of secondary dentin. There are some exceptions where the formation is entirely local. The Sensory Function. — In regard to sensation, the pulp resembles an internal organ. It has no sense of touch or localization, and re- sponds to stimuli only by sensations of pain. The pain is usually locahzed correctly with reference to the median line, but, aside from that, is localized only as it is referred to some known lesion. If several pulps on the same side of the mouth and in teeth of both the upper and lower arches were exposed so that they could be irritated without impressions reaching the peridental membrane, and the patient were blindfolded, it would be impossible for him to tell which of the pulps was touched. The pain originating from a tooth pulp may be referred to the wrong tooth or to almost any point on the same side supplied by the fifth cranial nerve. The pulp is especially sensitive to changes of temperature, but is incapable of differentiating between heat and cold ; this fact is often made use of in differential diagnoses (see Chapter XVI.). The pulp is 92 DENTAL HISTOLOGY AND OPERATIVE DENTISTRY. also very sensitive to trauinatie ami elieniical irritations, even when these are conveyed to it throno;!! the auciicy of the dentinal til)rils. Dr. Huber has suggested ' that this transmission may he aceomplished hv the traumatic or chemical action upon the lihrils setting up metabolic changes in the odontoblastic cells, which act as stimuli to the sensory nerves ending between the cells of that layer, Cementum. The cementum covers the surface of the dentin ajucally from the border of the enamel, lapping slightly over the enamel at the gingival margin (Fig. 69). It forms a layer, thickest in the apical region and Fig. 69. Gingival border of enamel, sho\\ 1 riapping it: /?, enamel ; C, cementum ; D, viMiut 10 X.) between the roots of bicuspids and molars, and becoming thinner as the gingival line is approached. The cementum resembles subperiosteal bone in structure, but differs from it in the character and arrangement of the lacunae and in the absence of Haversian systems ; the layers, or lamellae, of the cementimi also are less uniform in character than those of bone. The function of the cementum is to furnish attachment for the fibers of the peridental membrane which holds the tooth in its position. The surrounding tissues are never in physiologic connection with the outer surface of the dentin, except to form cementum over it or to remove its substance by absorption ; and when absorption of the dentin ' Dental Cosmo.% October, 1S9S. CEMENTUM. 93 has occurred on the surface of a root it is never repaired except by the formation of cementum to fill up the cavity and reattach the membrane. The cementum is intermittently formed during the functioning of the tooth, being added layer after layer over the entire surface of the root, the difference in thickness of the tissue in the gingival and apical portions being chiefly, though not entirely, due to the difference in thickness of each layer in the two positions (Figs. 69, 70), The cementum on the roots of newly erupted teeth is thin, and on the roots of teeth of old persons is thick. This continued formation of cementum Fig. 70. Cementum near the apex of the root : Gt. granular layer uf Tomes ; L, lacunae , h, point at which fibers were cut off and reattached. (About &iX.) is due to the necessity for change and reattachment of the fibers of the membrane. In the gingival portions, where the cementum is thin, the tissue is clear and apparently structureless, and usually contains no lacunae ; while in the apical half and between the roots the lacunae are numerous. In general, wherever the lamellae are thin, the lacunae are absent ; but where the lamellae are thick they are found. The canaliculi which radiate from the lacunae are not as regular as in the case of the lacunae of bone. Sometimes they are numerous, sometimes few ; they may extend from a lacuna in all directions, or they may be confined to one side, usually the side toward the surface of the cementum (Fig. 71). 94 DENTAL HISTOLOGY AND OPERATIVE DENTISTRY Fi.i. 71. Thick lamella- of cementum with many lacuiicf. uiiiiii; mi iiMMUptiou in dentin: L, lacunae: Jl, Howship's lacunae filled ; D, dentin. (About JoOx.) Fig. 72. Two fields of cementum showing penetrating libers: (jrl. granular layer of Tomes; C, cementum not showing fibers ; /", penetrating fibers. (About 54 X.) PERIDENTAL MEMBRANE. 95 The cementum is penetrated through all its layers by fibers of the peridental membrane which have been imbedded in the matrix of the tissue and calcified along with it. The first layer, — that is, the one next to the dentin, — is usually structureless and shows no fibers in it, at least in its inner half. In ground sections the imbedded fibers often appear in a number of layers, while they are not apparent in the rest of the thickness. This is because just before and just after the forma- tion of the layers in which they appear the fibers were cut off and reattached, changing their direction, so that in the other layers the fibers are cut transversely or obliquely. This is illustrated in Fig, 72. These imbedded fibers are very numerous in some places. If properly stained, the tissue seems almost a solid mass of fibers. In ground sec- tions these have sometimes been mistaken for minute canals from the fact that they are not always as fully calcified as the cementum matrix, and shrinkage causes the appearance of little open canals. Hypertrophies of the cementum (formerly often called exostoses, or excementoses) are very common. The increased thickness may be of one lamella or of several lamellae in the region of the hypertrophy, or all of the layers from first to last may take part in it. Small local thickenings of a single lamella are seen in connection with the peri- dental membrane wherever a specially strong bundle of fibers is to be attached to the root to support the tooth against some special strain. Peridental Membrane. The peridental membrane may be defined as the tissue which fills the space between the root of the tooth and the bony wall of its alveolus, surrounds the root occlusally from the border of the alveolus, and supports the gingivus. It has been referred to under many names, as pericementum, dental periosteum, alveolo-dental periosteum, etc. While this tissue performs the functions of a periosteum for the bone of the alveolus, it differs in structure from the periosteum in any position, so that any name including the word periosteum or implying a double membrane should be avoided. The peridental membrane belongs to the class of fibrous membranes, and is made up of the following structural elements : 1. Fibers. 2. Fibroblasts. 3. Cementoblasts. 4. Osteoblasts. 5. Osteoclasts. 6. Epithelial structures which have been called the glands of the peridental membrane. 7. Bloodvessels. 8. Nerves. The peridental membrane performs three functions : a physical function, maintaining the tooth in relation to the adjacent hard and soft tissues; a vital function, the formation of bone on the alveolar wall and of cementum on the surface of the root; and a sensory 06 DENTAL HISTOLOGY AND OPERATIVE DENTISTRY. function, the sense of touch for the tooth being exclusively in this membrane. The fibrous tissue of the membrane is of the Avhite variety, and may be divided into two classes, the principal fibers and the indifferent or Fig. 73. -4;). -1 Diagram of the fibers of the peridental membrane : 6, gingival portion : Al, alveolar portion ; Ap, apical portion. (From a photograph of a section from incisor of sheep.) interfibrous tissue. The principal fibers may be defined as those which spring from the cementum and are attached at their other end to the PERIDENTAL MEMBRANE. 97 bone of the alveolar wall, to the outer layer of the periosteum covering the surface of the alveolar process, to the cementum of the approximating Fig. 74. Longitudinal section of peridental membrane from young sheep, showing iibers penetrating cementum: D, dentin; C, cementum, showing imbedded fibers; F, fibers running to outer layer of periosteum covering the alveolar process ; F', fibers running to the bone at the border of the process ; B, bone. (About 80 X.) tooth, or become blended with the fibrous mat of the gum supporting the epithelium. They were so called by Dr. Black, not only because 7 98 DEMAL HISTOLOGY AND OPERATIVE DENTISTRY. they form the j)riiK'ipal bulk of the tissue, but tliey also perform the principal function of the membrane, the support of the tooth and sur- rounding tissues. The interfibrous tissue, also of the white variety but made uj) of smaller and more delicate fibers, is ft)und tilling spaces between the principal fibers and surrounding and accompanying the bloodvessels and nerves. For convenience of description and study, the peridental membrane is divided into three portions : {\\q , ci.itli X'liK'ntuin ; 7^, doiitin. ( About '.lOK ,■;.) structures; surface of the root, where they are crowded between the fibers. The eementoblasts often have processes projecting into the cementum like those from the osteoblast, but processes projecting into the membrane have never been demonstrated. In the formation of the cementum occasionally a cementoblast be- comes inclosed in the formed tissue filling one of the lacunae, in which position it becomes a cement corpuscle. ^ Periosteum niul Perile in this operation there is no longer any excuse for injuries resulting from infection, and a suit for malpractice could he well sustained against an individual who had failed to observe the well-understood methods of antisepsis, while no intelligent practitioner could conscientiously appear on behalf of the defendant. External Infection. The danger to the operator from external infection from instruments is a constant menace ; the constant use of these with general freedom from serious results, however, leads to a degree of carelessness not war- ranted by the ever-present danger from wounds. There is more real danger to the operator from this source than to the patient. All the excavators, drills, and broaches are hourly in contact with infectious matter, and it requires but a slight wound to produce any of the possi- bilities of blood-poisoning. The operator should be on constant guard in this respect, upon the slightest abrasion immediately taking measures to destroy all possibility of infection from germs that may have been introduced into the wound. This should at once be carefully washed and an escharotie employed, burning the parts. For this purpose zinc chlorid or carbolic acid is ])robably the best agent to use, followed by an antiseptic. The latter should be frequently renewed. Experience has demonstrated the value of turpentine in the various mechanical shops where this agent has been for many years in common use for wounds from rusted iron, the possibility of trismus resulting from such injuries being well understood. The writer has used this agent, after burning the wound, almost to the exclusion of other antiseptics. An illustration of the ever-present danger from wounds occurred to a friend of the writer's, one of the many young women who have graduated in dentistry in this country. She accidentally wounded her hand by a drill, and regarded it as of no moment. The result was severe blood-poisoning that for two years kept her hovering between life and death. After suffering from severe metastatic abscesses, she was finally restored to partial health, but with her constitution shattered and her practice ruined for the time being. Implantation and Transplantation. Previous to the recognition of the importance of antisepsis, the dentists of that period had a very natural objection to reimplanting teeth ; the practice of transplantation was then practically an unknown operation. The danger of the operation was appreciated, but the reason AGENTS USED FOR STERILIZATION. 125 was not then comprehended. When the study of bacteriology had ad- vanced to a science through the labors of Pasteur, Koch, and a host of investigators, the reasons for this fear were explained, and the condi- tions necessary to avoid unpleasant results being understood, the danger from infection was changed to absolute security. It is, moreover, to be ever borne in mind that but for this knowledge implantation and trans- plantation could to-day not be practised without the probability of serious results. A case illustrating this point occurred prior to the knowledge of anti- sepsis in the hands of a well-known dentist. He had removed three teeth and successfully reimplanted them for the cure of a violent case of neuralgia presumably due to calcific depositions in the pulp and about the external portions of the roots. Relief was so immediate that upon return of the pain another tooth was attempted. Trismus followed, resulting in the death of the patient. It is safe to assume that this unfortunate result could not have happened under the antiseptic care usual at the present time, even imperfect as it frequently is. To accomplish antisepsis in this operation the greatest care is neces- sary. In transplantation, teeth being procured from other mouths, the danger is necessarily much increased. The method, adopted by some, of immersing these teeth in various antiseptic fluids cannot be commended. Miller says of this : ' "It is generally accepted that the operator takes every possible precaution when he allows the tooth to lie for one-half to one hour in a 1 per cent, solution of carbolic acid, or in a 1 :1000 solution of bichloride of mercury. ... In order to reach bacteria that may have penetrated into the lacunae or chance vas- cular canals a much longer action of the antiseptic is necessary, and to be perfectly certain that we have accomplished our object we should have recourse to boiling water." Agents used for Sterilization. The possibility of injuring instruments has deterred dentists from using many of the agents recommended for the purpose of sterilization. Miller^ made tests of various agents with indifferent results, with the exception of carbolic acid, trichlorphenol, and mercury bichlorid. The list tested included the following : Carbolic acid in 5 per cent aqueous solution and in pure form. Lysol in 5 per cent, aqueous solution. Trichlorphenol in 5 per cent, aqueous solution. Sublimate in 5 per cent, aqueous solution ; also in the strength of 1 : 1000 of water. Benzoic acid in the strength of 1 : 300 of water. ^ Dental Cosmos, July, 1891. ^ Ibid-, page 520. 126 ANTISEPSIS IN DENTISTRY. Potassium pornianly five — minutes. Instead of corrosive sublimate solution, ordinary mustard flour mixed in the hands into a thin paste with sterilized water, used with gentle friction for two or three minutes and then removed with sterilized water, will prove a most successful germicide." While the foregoing may serve as a basis for comparison, it would ' Loc. cil. AGENTS USED FOR STERILIZATION. 131 be wholly impracticable in dental practice. It remains, however, that the hands of the dental operator should be the subject of constant care. Nails should be kept short and scrupulously clean. It seems to the writer that the use of a good potash soap and nail-brush, with bathing the hands in alcohol, will be amply sufficient unless working on a syphilitic patient, when more effective methods must be resorted to, and there can be nothing better than the mode described by Dr. Nancrede. The conclusions to which the writer has arrived from experience and study of the subject may be summed up briefly as follows : 1. Dipping instruments in an antiseptic fluid previous to operating, while beneficial, is not sterilization. 2. That boiling with soda is for the dentist the most convenient means of sterilizing instruments without injury, w^hile the more recently introduced method of formaldehyd antisepsis is a dry process that does not rust or injure steel instruments and is also promptly effective. 3. That the ordinary methods used to effect sterilization in surgical practice are not possible in dentistry, but that every dentist is legally and morally bound to live as near to the rules of antisepsis as is possi- ble with the demands of a daily practice. CHAPTER lY. THE EXAMINATION OF TEETH PRELIMINARY TO OPERA- TION—METHODS, INSTRUMENTS, APPLIANCES— RECORD- ING RESULTS, ETC. By Louis Jack, D. D. S. The Operator. The attitude of the body of the dental operator has considerable influence upon the ease with which the various positions required in operating may be assumed, and also has some bearing upon the free- dom of his hands. The erect position should be maintained as far as possible and the preponderance of the weight should be sustained upon the balls of the feet. This secures equilibrium and enables movements to be made with little embarrassment. The shoulders should be held well back in order that the arms may not be cramped, and to permit the respira- tion to be carried on deeply and with quietness. For obvious reasons the breathing should be deep, slow, and always through the nose. The precise use of the fingers requires that in each application of the instrument a 7-est, as a fulcrum or base of action, should be used, and when force is to be applied a guard in addition is necessary to give security to the movement of the hand. The positions of the rest and the nature of the guard required in operating are various, depend- ing upon the situation of the territory of operation and somewhat upon the natural tact of the individual, so that a definition of them is scarcely required. Upon a careful application of the rests and guards depends the graceful and comfortable use of the instru- ments, and by means of them the hand passes by quick and easy grada- tion from the most delicate touch to the safe exhibition of considerable force. Each student should study and practice the use of the various rests and guards until by repetition their employment becomes invol- untary and appropriate to the situation.^ The contact with the patient should be at as few points as possible and should be generally made with the fingers. Examination of the teeth and mouth in all their particulars is a ^ To aid in this study see American System of Dentistry, vol. ii. p. 44 et seq. 133 134 EXAMINATION OF TEETH. necessary preliiuinarv to the treatiuent of any diseased or distnrbed condi- tion which may appear. The importance of this procedure cannot be overestimated, as on it depends the formation of a correct diagnosis of departures from the normal state and it becomes a basis for the formulation of plans for the treatment re(piired to restore the teeth and the related structures to a state of health, as well as to define the order in which the several ojicrations shall l>e taken up, since an orderly prr- vedeiur in the treatment of individual teeth is frequently necessary. It is essential that the examination be most thorough, to prevent any failure to notice the least defect; since an unoliserved slight lesion may become a deeper injury in a few months, and the consequences of an oversight may prove serious. Appliances used in Examination. The appliances required to effect thorough observation of every portion of each tooth to ascertain the extent of any lesion are of several kinds, viz. mirrors, magnifying glasses, explorers, floss silk, and wedges. The mirrors should be both plane and concave. The j)lane mirror is important as a means to assist by the reflected image in determining the position of defects ; the concave as an adjunct to effect illumination, as it concentrates the rays of light and also may be used to produce an enlarged image. The enlarged image, however, is less sharp in defini- tion than the image of the plane mirror. Working to flic Iinar/c. — The plane mirror is an important adjunct in all operative procedures connected with the teeth. Many situations in the mouth do not permit the direct reflection of the rays of light to the eye without assuming positions of the bo(l\ and of the head of the operator which arc awkward and embarrassing to iVec movement of the hand, as well as necessitating inconvenient and tiresome positions of the head of the patient. In addition, it frequently is impossible to secure correct observation of the progress of various procedures by direct vision. These difficulties may be overcome by the movements of the hand being directed by the image of the field of the pro- cedure on the mirror. This method of working to the image is at first difficult to the novice, since the images are reversed ; but by continued effort it becomes as easy to make correct a|)plication of movements by this method as l)y the direct rays of light. Further continued ])ractice in this way renders the movements so completely under reflex control that the operator passes from a direct movement to a reverse one, and the contrary, without an apparent effort of the brain. This is equally true in all the various movements, even of those where the employment of considerable force is required. APPLIANCES USED IN EXAMINATION. 135 Fig. 99. The Quality of the Uirror. — These appliances should constantly be in good condition to insure clear definition in the image. The best kind of glasses are those in which the surface is covered by a deposit of pure silver. This furnishes a better reflect- ing surface and is more durable than is the so-called " silvering " with tin and Fig. 101. mercury. Magn;[fying lenses of about V^ four diameters are useful to de- tect minute defects either in the teeth or in the condition of pre- vious operations upon the teeth. They are used either directly to magnify the parts, or else to mag- nify the image shown on the face of the plane mirror when direct rays of light cannot be caught. The latter method gives a clearer definition than the magnified image of the concave mirror. The magnifying glass may be the ordinary watchmaker's glass held before the eye by the muscles of the brow and cheek ^ ,^^ Fig. 100. or the lens mounted -, as shown in Fig. 144. / Such glasses are indis- pensable to the careful practitioner, since with their aid defects of the teeth and of operations may be detected which would escape obser- vation by other means. Explorers are, es- sentially, prolongations of the fingers ; they convey impressions by their vibrations to the Explorer. tactile nerves, and are principally intended to be applied to parts where direct rays of light cannot reach. The forms required are simple and few. Their points should be delicate, to enable the smaller apertures and spaces to be entered, and are best when made Magnifying lens. Self-contained socket. 136 EXAMINATION OF TEETH. of j>ian(»-\vir(', Xo. IS B. & S. gatitre, filed to acuteness ami bent to a shape similar to that shown in Fig. 100. This form may be apj)lie(l to all surfaces of the teeth, and but slight modifications are needed to explore posi- tions difficult of direct approach. At part a the size of the finer ones should be No. 25, and near the ultimate point, h, No. 30. The temper of this kind of steel gives sufficient stiffness ayd also permits slight bending to make modifications of the form to meet all requirements. The ultimate jioint may be sharpened and renewed at pleasure. The handles in which these instruments are inserted may be of wood, with metal sockets which should be of sufficient length to come into contact with the finger ; or they may be fixed in metal holders, in Avhich case the latter should be tapered to avoid weight and to give balance. Either form of handle should be round, to permit fractional rotary change of direction. Fig. 145 shows an explorer, which consists of a socket, into which the wire point is secured by means of powd(>rcd shellac or powdered sidfur. The points may be displaced and renewed when required. This socket fits into the usual cone-socket handles. Fig. 101 is a self-contained socket for the same purpose. These points may also be connected with broach holders that have a clutch actuated by a screw nut. Explorers of this kind may be re-formed by straighten- ing and then re-dressing between two emery-cloth disks in the dental engine, when the ])oints can be shaped at will. Floss rilk is used to pass between the approximal surfaces of the teeth at the places which are in too close contact to permit the ingress of fine explorers. In these positions floss silk may detect the presence of superficial softening of the enamel by the character of the friction or by the fraying of its fibers. It also is of use in determining the con- dition of fillings on approximal faces or the presence of a deposit of sali- vary calculus at similar jwrts. The Dow electric lamp for nii/iuli illnniinjitiiiii w it'.: nllcctdis. Reflector .4 is jointer! to vary the angle of retiection. Reflector B is for illuniin;itiiin (ft lie fauces. Reflector C'is for lateral illumination. THE EXAMINATION. 137 silk should be slightly waxed in order to bind the fibers. Entire reliance cannot be placed upon the use of silk, since it may in some cases pass slightly carious spots without the fibers being displaced, but it frequently furnishes indications for further procedures by which to establish certainty as to the state of approximal surfaces. Wedges are used when neither explorers nor silk give positive indi- cations of carious action but have raised doubts of the integrity of any part. They may be of wood where the teeth are not firmly fixed, when the space may be immediately made ; otherwise, where the fixation is firm, thin india-rubber or linen tape may be forced in. Transillumination of the teeth by the electric mouth lamp (Fig. 102) is extremely useful in cases where a question has arisen as to the condi- tion of an approximal surface. ■ Superficial changes of the enamel may frequently be detected by this means, and it is particularly useful in deter- mining the condition of approximal surfaces at the margin of the gums. It is also of service in testing the vitality of the pulp. The Examination. The parts of the teeth most liable to carious action are those which most easily retain deposits of sedimentary matter composed of food debris, thickened mucus, and bacterial growths. These are the labial and buccal surfaces, where, the mechanical relations of the lips and cheeks tend to retain sediment ; the sulci, which by the direct force of mastication have food driven into them ; and the opj^rox- imal surfaces. The latter are the most important to consider. The interproximal space is a serious predisposing cause of caries, be- cause the counteraction of the tongue and cheek in adapting the food between the occlusal surfaces of the teeth forces the finer particles of the food into the interproximal spaces, where it is retained by capillary attraction, assisted by the viscidity of these deposits, and by the apposi- tion of the cheeks with the buccal surfaces of the teeth. This space is usually triangular, the gum forming the base of the triangle. The point where caries usually begins is at the apex of this triangle, where there is the least movement and interchange of the. contents of the space, as here the capillary force is the greatest, so that the fermentative processes of food decomposition are least interfered with. The technique of examination is as follows : After a cursory in- spection of the denture with the mirror, the explorer is applied to the previously indicated surfaces, particular care being used in determining the condition of approxirtial surfaces, by introducing the instrument into the triangular space, the point being directed toward the acute angle. It should be drawn back and forth with a slight rotary move- ment so as to impinge the point successively upon the whole approxi- 188 EXAMINATION OF TEETH. nial surface of each tooth. This movement should be made from the inner as well as from the outer aspect. In this manner the instrument will he hrou«»;ht into eontaet with everv accessible jiortion of the inter- proximal surfaces. Then the .sw/Av' are explored and the hnnnil and livf/nal fiiirfaces examined. The inspection is thus conducted from tooth to tootii. Next the lines of apparent contact are critically tested with the mirror for evidence of slow ehanu^es of structure as shown by discoloration or rapid alterations shown by a milk-like appearance of the tooth surface. Finally, all approximal surfaces which could not be explored are si/kfcl. To do this the Hoss is wrapped upon the index linger of the left hand, and with the right is drawn between the contact surfaces with a sliding lateral movement. Care should be exercised that no injury be done to the gingival margin of the interproximal space by suddenly and forcibly driving the floss into contact with it. This acci- dent may be effectually avoided by projierly guarding and supporting the fingers by contact with the adjacent teeth. Practice gives facility in determining by means of thci silk the state* of the parts in contact with it. In the inspection of ])revi()us fillings, all margins, particularly those about the cervix and beneath the gum, should be critically inspected. Lastly, doubtful situations should be noted for subsequent examina- tion, to be made after separation. (The tests for pulp exposures are considered in Chapters VI. and VII.) The order of examination is best conducted bv bei;inninf st'curiuiT a so))arati()n of the front teeth to determine their condition and to ])cniiit polishinjt"^ strips to be inserted for the removal of super- ficial discolorations and for the treatment of superficial softening. Here the procedure is to insert a wooden wedge between the incist)rs near the incisive edge, when it is forced by pressure or by percussion until a suf- ficient opening is effected, the space then being secured by another wedge of hard close-grained wood forced between the teeth at the cervix. This process in some instances is repeated by forcing farther the first wedge and again increasing the security by driving the cervical wedge. This plan is not a])]ilicable when the interspace at the neck is quite angular, since the fixing wedge cannot be made secure, as it then is disposed to advance against the gum. In this case one of the subsequent methods should be jiursucd. If the fixation of the teeth be not firm they yield by a slight enlarge- ment of the arch and by closing the neighboring slight spaces. Immediate separations may be effected by mechanical separators, notably the William A. Woodward (see Fig. 105), for the front teeth and Fig. lOo. Fkj. 106. Woodward's separator. Perry's separator in conjoint use with matri.x. the Perry (see Fig. 106) for the bicuspids and molars. It should be stated that each of these is preferably to be used when some previous space has been made by other means, following Avhicli a considerable increase of space may be secured by these appliances. Separation by the Swelling- of Fibrous Materials. — These act by the capillary force of water upon the fibrous structure of the material, whether pledgets of cotton or tape. This means is also more applica- ble when the fixation of the teeth is not firm, and has the advantage of being painless and more readily tolerated by children and by persons who are impatient of pain or of any form of dental distress. Pledgets of cotton are more applicable where a ])artial preliminary opening of a carious cavity has been made, and are more ai)propriate for the posterior teeth. Here, when there is no danger of pulp exposure, the pledgets may be packed with considerable firmness. In some instances it is advantageous to saturate the pledget with thin sandarac SEPARATION OF THE TEETH. 147 varnish, which attaches the fibers, but the time required is much in- creased, as the cotton yields to capillary attraction only as it loses the resin. Tape is more useful for the incisors ; it should be of linen and may or may not be waxed. Its entrance is facilitated by an immediate pre- liminary application of a wooden wedge. Caoutchouc^India-rubber. — When a strip of india-rubber is drawn into a close interspace the middle portion is constricted to great tenuity. The action is by the resilience determining the two exposed ends toward the middle, with the result that at length the space attains the size of the thickness of the strip. It will be perceived that the physical force is that of two opposed wedges acting with constant power. The effect is such that it overcomes the greatest resistance to separation of the parts and therefore is the most eflFective means which we have. Caution is required in the use of this material both as to the thick- ness of the rubber and as to its purity. The pronounced resilience of pure rubber is generally painful, and in most instances greatly so. The resilience can be reduced by employing adulterated specimens of the material. The white-rubber tubing of the shops cut longi- tudinally into various widths effects the object with less rapidity but surely, and generally without pain. The strip is drawn into position by a sliding motion, care being taken not to force the piece into contact with the gum. To prevent the rubber being conveyed to the gum as the space enlarges, a small portion should extend slightly beyond the occlusal surface. As this kind of rubber is more difficult to introduce when the contact is close and firm, a previous partial opening should be made with a piece of rubber dam. This method has the value of pain- lessness, and also does not usually necessitate a period of rest after the separation has been effected. Red Base-plate Gutta-percha. — When it is desirable to gradually effect considerable spacing between teeth, where the carious cavities are deep with well-defined boundaries but not involving the pulp, the method of Dr. Bonwill, of packing the cavities and the existing space with a sufficient mass of this form of gutta-percha, produces expansion by the continued force of mastication driving the material upward. This method also has value in some instances where it is desired to force the gum beyond the cervical margins, and may be an acceptable sub- stitute for aseptic cotton for this purpose. Securement of the Space. — Should soreness of the teeth have been caused by the separation, a period of rest should be given the parts until the distress has passed over. It is, however, important that large spaces should not be long retained, since in some instances alveolar resorption 118 PRELIMINARY PREPARATION OF THE TEETH. mav be induced by the contiiuuitioii <»f the changed ])ositi()n. An inter- val of two days usually suffices for the pericementum to recover from the disturbance, when the restorative ])rocedures may be conducted. The retention of the space may be etiected with f/uttd-pcrrlia or with the pladic cemeiits, — the first being suitable when an open cavity appears; zine plwuphatc when from tiie smallness of the cavity gutta- percha may not be readily retained. 0.rychlorid of zinc should be used wiien the cavities are shallow but sensitive, — the reason for which will appear later. It is generally advisable to introduce a thin wedge of wood at the cervix and in contact with the gum to ])revent the re- taining material from impinging upon this tissue and to give a base to support the introducing force. Exposure of Cervical Margins. — AVhen cavities extend beneath the gum, which frccpicntly is the case when caries has recurred above the cervical margins of fillings, it becomes necessary to force the gum somewhat above the carious border. This shoidd be done (piickly rather than slowly, otherwise in adult subjects the continued pressure may arouse diffused inflammatory disturbance of the contiguous tissues. Generally it is preferable first to cut away the gum between the teeth with a straight, narrow bistoury, and gently force red gutta-percha against the gum, gradually moulding it to the form of the depression. Cotton pellets for this purpose are not admissible unless they are anti- septically charged, for which purpose an admixture of aristol with the cotton is the most suitable, since not being soluble in water it better maintains the asepsis. Cotton may be conveniently charged with aris- tol by saturating it with a solution of aristol in chloroform and allow- ing the greater portion of the solvent to evaporate before introducing the pledget. The solution of aristol in oil of gaultheria may also be used for the same purpose. When hypersensitiveness of the gum tissues exists it is admissil)le to paralyze the sensation wnth a suitable solution of cocain ])revi()us to introducing the pellet of either gutta-percha or cotton fiber. A four per cent, solution of cocain hydrochlorid applied upon cotton to the sensitive tissues will speedily relieve the condition. Adrenalin chlorid, 1 : 1000, combined with a weak solution of cocain, may be substituted for the above. CHAPTER YI. PRELIMINARY PREPARATION OF CAVITIES— TREATMENT OF HYPERSENSITIVE DENTIN BY SEDATIVES, OBTUND- ENTS, LOCAL AND GENERAL ANESTHETICS— STERILIZA- TION, WITH A BRIEF CONSIDERATION OF THE PHYSIO- LOGICAL AND THERAPEUTIC ACTION OF THE MEDICA- MENTS USED. By Louis Jack, D. D. S. Hypersensitive Dentin. Dentinal hypersensitiveness frequently presents the most serious impediment to the procedures connected with the treatment of dental caries. This condition must be considered an exaltation of the normal sensitiveness of the dentin, and presents a wide range from slight pain on contact being made to so high a degree of sensitiveness as to be un- endurable. In the latter instance persons of the greatest capacity for tolerating pain will shrink from the most careful instrumentation. Im- mediately upon the opening of a carious cavity there usually are indica- tions of excitement of the vital elements of the dentin. This con- dition may be so slight as to present no obstacle to further procedures, or it may on the other hand be so excessive as to forbid all instru- mentation until a reduction of the sensitiveness has been effected. This altered state of the dentin has been considered by some as one of inflammation of the dentin. As the opportunity does not exist for the usual concomitants of inflammation as pathologically defined and which are induced by the alterations of the circulation of the blood, viz. heat, redness and swelling, with exaltation of nervous function caused by the additional supply of arterial blood, the term inflamma- tion is a questionable one to apply to a hyperesthetic condition of dentin. This manifestation is more logically explainable as a disturb- ance caused by changed relations of a tissue which is naturally pro- tected by the enamel from irritating influences. The relation of the enamel and the dentin is analogous to that of the epidermal coat of the skin and the rete mucosum. Pain caused by abrasion of the epidermis is immediate and acute, and occurs before the increased supply of blood increases the intensity of it. It is hence induced by 149 150 PRELIMINARY PREPARATION OF CAVITIES, ETC. the altered relation (»!' the inucosiun. Tlu' analogy is fnrther borne out by the faet that in each instance a protective covering affords salu- tary relief. The normal sensitivity art of the pnlp are paralyzed, the organic elements of the tissue become denuded to a greater extent, and therefore sensitivity is increased to a j)ropor- tionate degree. As these fibrillar elements arc the means of extending the irritation to the pnlp of which they are the peripheral prolongations, it is evident how important a factor the active advance of caries is, and also to what extent the rapidity of the process increases the morbid concomitants of dental caries. It has been pointed out that the area of hypersensi- tiveness generally pertains to a narrow line at the outer limit of the dentin, but in rapid caries this line is a broader one. The anatomical element of the dentin concerned with its sensi- tivity is contaiiKMJ witliiii the tubuli. ^^'hil(' the exact nature of the matter in these tubules has not yet been certainly determined, it has been shown to have sufficient consistence to permit of extension, as in separating sections under the microscope what appear to be fibers have been seen. Also the same appearance has been presented in fresh specimens when the pulj) has been drawn away from the dentin. It is not difficult in reviewing these facts in connection with the various conditions and phases of dentinal sensitivity to conclude that the exalta- tion is inseparably connected with an irritated state of the tubular con- tents. The variation in the degree of sensitivity of different teeth of the same mouth — of those which are side by side and in a similar degree of progress of carious action ; the profound fact, heretofore stated, that the dentin at a short distance beneath the decay is much less sen- sitive ; that in some instances sedatives modify the degree of pain, and that coagulants produce a marked impression upon the capacity of the tubular contents to convey sensation, force by inference the conclusion that in diseased conditions this anatomical element is largely concerned in conveying im])ressions to the central organ of the tooth. It is also undoubted that unusually high sensitivity of dentin is an inherent constitutional condition with some persons, and that it pertains to some families apparently as an inheritance, but may be explained in these instances as the transmission of acute nervous impressionability. In connection with this subject should be considered the further observation that the temperature sense of the teeth is various ; that with some the application of ice makes no impression upon the teeth when in normal condition, while with others in the same condition the least cold induces pain. It would further appear that the degree of sensitivity TREATMENT OF DENTINAL HYPERSENSITIVITY. 153 when caries occurs bears some relation to the relative tolerance of the teeth to reduction of temperature. On these premises it is not difficult to account for the manifestation of acute sensitivity, and to build thereon an hypothesis governing the various conditions presented by dentin when it is subjected to the irri- tation of the carious process. These views have steadily gained sup- port with the advance of microscopic study of the tissues, and have supplanted the older view that the sensitivity of dentin is a result of mechanical vibrations extending to the dental pulp. Treatment op Hypersensitivity op the Dentin. Having considered the general principles governing hypersensitivity of dentin, we are prepared to enter upon a study of the treatment. This is to be considered under the following general lines : namely, the therapeutic, the chemical, the anesthetic, and the mechanical. Treatment of Slight Hypersensitivity. — The first requisites to be observed here are a calm manner and earnest sympathy, accompanied with the assurance that if severity of pain occurs, mitigating means will be resorted to. It is an important and laudable object to remove dread and secure confidence, which is attained among other means by select- ing at first the simpler and less painful operations. When confidence is secured, slight pain arouses the courage of the patient. The effect of the opposite course of indifference and harsh cutting alarms the patient, arouses apprehension, and greatly increases the nervous exaltation. In the simpler cases sharp instruments used with quick, light, and rapid movements are called for. It should in this connection be noted that cutting in this manner stimulates somewhat the nervous force of the patient, and if the movements are in very quick succession they appear to paralyze the part ; the pain is thus lessened in comparison with deliberate and slow instrumentation. The movements of the ex- cavators should be in a direction away from the pulp rather than toward it, and the cuts should be by drawing the points instead of pushing them ; this is for the reason that the pressure in the latter case is greater than in the former. When the sensitiveness is so great as to interdict immediate excava- tion and formation of the cavity, some method of treatment of the sur- face is required to overcome or to confine it within a tolerable degree. The Therapeutic Treatment. — Under this head the available reme- dies are moi'phin, veratrin, and cocain, — each of them being applied with glycerin as a menstruum. It should be stated that neither have much immediate effect, and therefore they should be sealed in the cavity after the opening in the enamel has been prepared, and the softer caries has been lifted and peeled off". The closure should be effected by 13 154 PRELlMr.WMiY PREPARATION OF CAVITIES, ETC. means of gutta-jnnvha, or with what is ])rohahly better, a thin paste of phosphate of zinc laid over the dressing. After some days tlie pain will be fonnd diminished in many instances. The therapensis is effected by the absorption of these sedatives by the partially disorfranized tissnes. Another method of applying cocain is to secnre the cavity from the entrance of moisture, and after desiccating the surface a saturated pledget of vapocain, a solution of cocain in sulfuric ether, is introduced. As evaporation of the ether takes place cocain is forced by osmosis into the tissue. In cases of subacute sensitivity this means frequently is efficacious, but is of little value in hypersensitive conditions. It is advantngeous as preparatory to this line of treatment first to neutralize the (iciiJitii of the cavity with an alkaline solution, which may be either ammonia, sodium carbonate, or sodium dioxid, afterward removing the excess of alkali by thorough washing with warm water. Treatment of Hypersensitivity of Dentin by Electrical Osmosis. Within a recent period a means of treatment of this condition has become prevalent which has been designated by the terms cata- PHORESIS, ELECTRICAL DIFFUSION, and ELECTRICAL OSMOSIS. It has been demonstrated that the action of electrical currents conveys fluids, with the substances held in solution, from the positive elec- trode toward the negative electrode. Further, that an electrical current ]>assing through a membrane accelerates the natural process of osmotic diffusion if the positive pole is a])plied on the side of a membrane or tissue from which the osmotic diffusion is taking place; in case the situation of the poles be reversed, the osmosis is retarded or prevented from occurrence or is reversed. This action bears some analogy to that which takes place in electro-metallurgy when a metal in solution is conveyed from the anode (positive pole), and is deposited upon the cathode (negative pole). If the current be reversed the deposited metal is again taken up by the solution and is conveyed back again to the other pole. This is a law connected with the passage of electrical currents through fluids which are capable of con- duction. The following will illustrate the action which takes place : " If two compartments separated by a membrane are filled with a fluid and in each an electrode is placed, there is a streaming of the fluid through the septum from the positive to the negative pole, so that in time there is an increase in the negative side. This osmotic action, as is well known, occurs naturally between two fluids of unequal density from the lighter to the denser liquid, but if the anode is placed in the denser liquid DENTINAL ANESTHESIA BY ELECTRICAL OSMOSIS. 155 and the cathode in the lighter the natural osmotic current is not only- overcome but is reversed." If a substance containing water, as a ball of wet clay or a piece of muscular tissue, have an anode connected with a current of sufficiently high potential attached to one side, with a cathode attached to the oppo- site side, the watery contents of the substance are conveyed to and appear in excess on the cathodal side ; at the same time the anodal side be- comes less damp ; also, if a capillary tube be filled with water and an anode and a cathode be similarly arranged, the water flows toward the cathode. As a membrane or tissue may be considered to be a series of tubes in close contiguity, it is apparent that the movement of fluids must take place through them in the direction the current is passing. These examples are an expression of electrical force. The applica- tion of this law of the passage of fluids from a higher to a lower elec- trical potential is the fundamental process which is employed in electrical diffusion of medicaments. The depth to which medicaments may be conveyed depends upon the conductivity of the tissue and that of the medicament which is being applied. " The cataphoric action of electricity has often been made use of experimentally to introduce drugs into the system through the skin. In man quinin and potassium iodid have been thus introduced and subsequently been detected in the urine." As early as 1859 Dr. B. W. Richardson used this process to pro- duce local anesthesia, and completely demonstrated its power in this direction. It has also been clearly proven that when a solution of cocain is applied to the skin, its characteristic action upon the mucous membrane will not here take place. But when the anode is wet with the solution and a galvanic current is passed through the epidermis to the cathode, placed upon an indifferent surface, anesthesia is effected over the surface covered by the anode and to an indefinite distance inward. This effect is not produced by the current alone, which has been abundantly proved by conclusive experiments, these having been fol- lowed by demonstrations confirming the above statement. When the medicaments so applied have anesthetic or analgesic properties their characteristic effects are produced. When this principle is applied to the transfer of medicaments it is found that they pass for an indefinite distance into the contiguous tissue along with the current from the anode toward the cathode, but with some degree of diffusion ; the diffusion depending upon the resistance of the tissue and upon the extent of the surface of the cathodal (nega- tive) electrode. 15() PRELIMINARY PREPARATION OF CAVITIES, ETC. GENERAL PRINCIPLES INVOLVED IN THE METHOD. The application of electricity requires the consideration of the general principles or laws governing its transmission. The source of this force is to be found in chemical transformation, lender the laws of the correlation of force it is capable of being con- verted into heat, light, magnetism, and mechanical power, and may be used to disorganize substances, when its action is called electrolysis. Its movements are constant in their direction, viz. from bodies of high to those of low potentiality. In perfectly conducting substances electricity moves with entire free- dom under any electro-motive force however small. In perfectly non-conducting substances electricity will not move under any electro-motive force however great. In imperfectly conducting substances electricity moves only on the exhibition of intense electro-motive force, the force varying according as the substance is a more or less indifferent conductor. Electricity has two elemental properties. These are defined as cur- rent strength, designated by the term amperage; and electro-motive force, which is termed its voltage. The active energy of electricity depends upon the first property, its distribution upon the latter. Since it must be assumed that few bodies are perfect conductors, this force or pressure is of that degree wdiich may be required in any given case to move the active energy, the amjierage, against the resistance it meets with. The unit of strength is the AMPi:RE. The unit of pressure is the VOLT. The unit of resistance is the OHM. The unit of jioiver is the avatt. A VOLT represents the electro-motive force (E. M. F.) required to impel one ampere of current through one ohm of resistance. ' An AMPfiRE of current is so much as will deposit 0.00118 gram of silver per second when passing through a standard solution of nitrate of silver — or which will decomjiose 0.0932(3 milligram of water in one second. Hence the ampere is the measure of rate of flow of an electri- cal current, and in connection with the voltage measures the energy of the current. The unit of resistance (ohm) is that degree of resistance which will permit the passage of one ampere of current at one volt of pressure. The WATT is the power exerted by one ampere of current at one volt of pressure. In the economic application of electricity its transmission is effected DENTINAL ANESTHESIA BY ELECTRICAL OSMOSIS. 157 through metallic conductors. The resistance of these is varied by the character of the metal, the cross section, and the distance. For certain purposes other substances are employed to effect greater resistance than the metals. The current strength flowing in a circuit is equal to the pressure divided by the resistance. The resistance equals the pressure divided by the strength. The pressure equals the strength multiplied by the resistance. In elementary terms : Amperes = volts -^ ohms. Ohms = volts -^ amperes. Volts = amperes X ohms. Watts = volts X amperes. It follows from the formula that the' amount of power and the cost of producing it is the same whether the current is of large amperage at low voltage or of small amperage at high voltage. Thus an incandes- cent lamp may be supplied by 100 volts at |- ampere or by 50 volts at 1 ampere — the result in each case being 50 watts. Comparative Illustration. — Given a current of 100 volts at fifteen amperes, and we wish to use only ^ ampere, the resistance t6 be put in the circuit is found thus : 100 v ^ 2^ a = 4:0 o. In case we have 2^ amperes under 7 ohms resistance, it requires 17^ volts to move this degree of amperage through the given resistance, thus : 2|- « X 77" = 17^ v. If one has a current of 110 volts, and de- sires to use a ^-horse-power motor, the least amperage required is ly^o"? which is found by dividing 186 watts by 110. These examples make plain the means of determining the character of current required for any given purpose. Electrical force may be produced from its source in galvanic cells by arranging them in series or in multiple. If in series the voltage is the sum of the volts of the cells so arranged, and the amperage is that of each of the cells. If joined in multiple, the strength in amperes is the sum of the amperes of the cells, and the voltage is that of one cell. Fig. 107 ^ represents the arranging of cells in series, the positive of one with the negative of the next. In case each cell has a voltage of 2 and an amperage of 1 the electro-motive force of 5 cells will be 10 volts at 1 ampere. Fig. 108 ^ represents the joining of cells in multiple. Here all the ^See Denial Cosmos, December 1896, p. 998. ^ Ibid. 158 PRELIMINARY PREPARATION OF CAVITIES, ETC. positive cloniciits are joined tos;eth( r ami similarly all the negative to eaeh other. The voltage now is 2 and the amperage 5. Vui. 107. 4-' S. The former method of assembling the cells is designated as "high tension," the latter method as 'Mow tension." AVhcn the source is the Fig. 108. dynamo, high and low tension are produced by the strength or weakness of the magnetic field. For electrical osmosis the source should be from batteries in series, for the reason that in multiple the amperage would be too great when the voltage is of sufficient force to overcome the resistance. The degree of electrical energy tolerated by living dentin is exceed- ingly small, on account of the peculiar and intense pain excited by the transmission of electrical currents through the teeth. This is shown by the low initial voltage of the batteries used for the purpose, varying from less than 5 to rarely more than 20. But the initial passage of a current of as high electro-motive force as these would not be tolerable, and must therefore be reduced by suitable methods of eifecting re- sistance. The apparatus used for this purpose is the controller, the purpose of which is through its resistance to diminish the energy of the current to sufficient weakness to meet the requirements of any given case. All forms are constructed on the principle of the use of materials which are highly resistant of the passage of electric currents. These substances DENTINAL ANESTHESIA BY ELECTRICAL OSMOSIS. 159 are water, carbon, graphite, and coils of wire of known high resistance, the most effective being of German silver. In the case of the latter the degree of resistance is regulated by the length and fineness of the wire, the cross section being reduced to the size which will conduct the cur- rent without excessive heating, and to that end it is graded with refer- ence to the initial amperage of the current. In comparison with silver as a unit German silver has a resistance of 13.92. The carbon and graphite controllers usually are constructed in the form of a broken ring — one pole of the battery being connected at one end of the ring, the other pole being attached to an index which travels over this annular disk. This method of construction gives a fine grada- tion of current with high resistance. It may be used in connection with a German-silver wire rheostat, where currents of great strength are used for reasons which will appear later. In the use of high-voltage cur- rents, such as the 110- volt circuit, it may be switched through the coils to a nearly definite low voltage by means of a rlieostat, when the adaptation to the case may be effected through the graphite con- troller. In the arrangement of the apparatus to effect electrical osmosis the battery, the controller, the instruments of observation, and the patient are in series. In the analysis of the course of the current it appears that the patient is another element of resistance, and that dentin is more highly resistant than the other tissues. In other words, there are two resistances in the circuit — the controller and the tissues of the patient. The result of the resistance of the dentin, unless the initial voltage is small and is reduced by the controller to an infinitesimal degree, is the occurrence of pain, which takes place with different persons at various degrees of amperage. The approach to intolerance of the current is designated the " pain limit." This condition has been assumed by some observers to be caused by the evolution of heat in the dentin con- sequent upon the resistance of this tissue. This view is not now con- sidered to be conclusive, as the calculated elevation of temperature at jIq milliampere is not sufficient to account for the degree of irritation which occurs on increasing the rate of flow. This determination leaves two other hypotheses to account for the irritation : a, the ten- dency of the current to disorganize some of the anatomical elements of the canaliculi ; and h, the osmotic pressure of the migration of the medicaments. Here the student is not confused with consideration of the complicated forces which are in action connected with the electroly- sis of the cocain solution.^ The pain limit is variable with different persons, and in different ^ See "The Foundation Principles of Dental Cataphoresis," Items of Interest, vol. xx. p. 345 et seq. 160 PRELIMINAUY PliKPARATIOy OF CAVITIES, ETC. teeth of the same person. Witli some it is rcnclicd -with tlie first influx of the current at low voltage witli a record of ^\, inillianipere, this low record indicating higli resistance of dentin and ])erniitting but slow increase of the force until after cocain lias diminished the sensitiv- ity of the irritated surface. With others the j)ain limit may not be reached with a voltage of 20 and a recorded amperage of -j3j to y*^ milli- ampere. Yn respect of electrical irritation there must be taken into account also the high nervous sensitivity of some persons, as with these there usually appears greater susceptibility to electrical irritation. The following table of calctdated resistances shows the resistance in ohms, and the liability to the generation of heat in the dental tissues in view of their density, or the tendency to disorganization as previously stated, and it suggests that care be used in the application of electrical force for the purpose under consideration. With 15 volts iuitial pressure at x% milliampere in circuit the ohms are 37,500. " 15 " " ijs " '• " 150,000. " 10 " " -^ " " " 25,000. " 10 " " iJjj " " " 100,000. " 5 " " T*Tr " " " 12,500. " 5 " " jV " " " 50,000. As the resistance of the body including the dental tissues varies from 10,000 to almost 70,000 ohms, it would appear necessary that the con- troller should have at the highest ])oint a resistance of not less than 400,000 ohms. This degree of resistance is required to obviate the effect of impulse which may occur in closing the circuit. Occasionally slight shock is felt at 500,000 ohms. The varying resistance of the current through the tissues depends upon the density of the dentin, the distance traversed, the condition of the surface of the skin, and the thickness of the adipose tissues. The average resistance of the ])atient as recorded by Dr. W. A. Price is about 25,000 ohms from cavity to hand, and the difference of resistance from tooth to hand and cheek to hand is from 3000 to 5000 ohms. He reports one ease where the resistance from cavity to hand with a 40 per cent, solution of cocain was 28,500 ohms, which on placing the i)ad on the cheek was reduced to 23,000 ohms. Dr. Price further places the average resistance from hand to tongue at 9000 ohms, and from cheek to tongue at from 3000 to 7000. This would make the resistance of the dentin nearly 20,000 ohms. An exact determination of the resistance of the skin in any given case would enable a very close approximation for the dentin to be calculated. The condition of the cavity as to relative moisture and the degree of saturation of the pledget of cotton containing the anesthetizing agent DENTINAL ANESTHESIA BY ELECTRICAL OSMOSIS. 161 as well as the percentage of the medicament exert a considerable quali- fying control of the resistance, as appears from the experiments of Dr. Price. When a section of dentin partially dry on the surface had a resistance of 30,000 ohms, after being dried and saturated with a 40 per cent, solution of cocain the resistance was reduced to 4500 ohms. The principles here stated and the facts presented apparently demon- strate the importance of careful selection of the degree of voltage at the battery; of the use of a relatively low amperage to the voltage; of the necessity of controlling the current within the boundary of the pain limit ; of the importance of avoiding impulses of current by rapid advancement or by movements of or displacements of the anode ; and of attention to the maintenance of a constantly moist state of the anodal and cathodal contacts. These principles and facts have led to the application of galvanic currents for the production of a state of anesthesia of hypersensitive dentin ; and the results of experimentation in this direction have proven that the same effects have followed here as have occurred in the softer tissues. The extreme sensitiveness of the teeth to electrical currents and their resistance to the passage of electrical force were obstacles to the earlier application of this method of treatment in dentistry. The absence of means to control the current strength (the amperage) and to reduce the pressure (the voltage) to the capacity of the teeth prevented experi- mentation in this direction until within a comparatively recent period. It follows from the above statements that the current strength that is tolerable at the commencement of the application is so small as to be scarcely measurable in many instances. To produce this small current, either the battery voltage must be low or the resistance in the controller exceedingly high. Any form of battery which is constant when the amperage of the individual cell is from one-fourth to one-half of an ampere will have sufficient current strength. The E. M. F. may be from one to two volts per cell. The voltage required to produce the necessary electro-motive force in an application to the teeth to produce dentinal anesthesia varies from five to thirty. For children and where the teeth are apparently not dense, ten cells sometimes are sufficient, but generally fifteen to twenty are needed. The cells should be arranged in series and connected in a manner which enables the selection of any number to produce the re- quired E. M. F. for any given case and to permit an increase of cells during the administration. The most important condition of the electrical force for the purpose is that the amperage shall he inconsiderable, since high amperage is intol- erable to the teeth. As the most efficient results are produced when the U 1(;2 PRELIMINARY PREPARATION OF CAVITIES, ETC. recorded amperai^cMs not over tliree-tcntlis of a iiiilliani|u"Tc, the use of a current ot" liiuh anijuTaLTc is unneces!*arv, and it i- attcndccl with distress. Jlitrli voltage is ecjually painful, as tlie endeavor to force tlic current against the resistance of the dentin results in eleetrleal irritation, as already described. The chlorid of silver cell is probably the one best suited for the jnirpose, as its electro-motive force remains practically constant under various conditions. The E. M. F. of each cell is about one volt ; the internal resistance eight ohms; the strength one-fifth of an amp5re. This battery on account of its constancy and durability is largely used in electro-medical apparatus. It is now furnished dry, and is more acceptable as being less troublesome on this account. The dry Leclanch^ battery is also one of the best forms, as it is an open-eireuit battery. As long as the circuit is open there is no action in the cell and consequently there is no loss. At present these two forms of galvanic battery cell appear to be the kinds best adapted for the purpose of inducing electrical osmosis. The life of a chlorid of silver dry cell battery is stated to be 700 hours of eataj)horic \\'ork under a high resistance of tissue, but it must be remembered that the continuance of energy of all forms of battery is varied by the resistance and the conversion of electrical energy into heat by the controll(>r which regulates the amperage and the voltage. This principle applies to all sources of electrical force. The controller which at present appears best adapted to be interposed between the battery and the anode is the Willms controller, which, as before stated, should be constructed with a resistance at the highest point of at least 400,000 ohms. The gradations of resistance decrease from this through 112 contact points. These permit a very gradual reduction of the resistan(;e as the switch is conveyed from point to point in the circle. This controller also has the advantage of being moderate in cost and easily procurable. An important adjunct of any apparatus is a reliable laiUkimpPremeter. This should have a scale to record divisions of fortieths of a milliampere, from the fact that the amperage of the current through the dentin is fre- quently efficient at less than two-tenths of a milliampere. The milli- amperemeter also aids in detecting leakage of current, as where the indicated amperage exceeds four-tenths milliampere there is reason to suspect imperfection of the insulation of the tooth. In this case a longer period than usual will be required to effect the anesthetization, and the degree of this effect may be less. The use of the direct current generated by the dynamo is of ques- tionable utility as compared with the current from a battery. The DENTINAL ANESTHESIA BY ELECTRICAL OSMOSIS. 163 current from the dynamo is subject to changes of voltage and the amperage is liable to fluctuations consequent upon alterations of the load in the general circuit. This instability causes a series of pulsat- ing shocks upon sensitive dentin and the pulp, which react with the expression of pain. The possibility of the transmission of severe shock through accidental grounding or defective apparatus where such excessive voltage is used is another and sufficient reason why the steady and low-voltage current of a battery is preferable for this class of operations. TECHNIQUE OF THE ADJIINISTRATION. At the present period cocain has been found to be the most effective anesthetic for obtunding dentinal sensitivity by electrical osmosis. It is used in strength varying from 12 to 24 per cent., and by some as high as 40 per cent, has been used ; 11- grain of one of the salts of cocain added to 5 minims of water procures a solution of 24 per cent. ; to 7^ minims, 18 per cent. ; to 10 minims, 12 per cent. The salts of cocain which have been used are the hydrochlorid and the citrate. Each is efficient in the strength stated. The resistance of cocain citrate is for 12 percent, solution 234 ohms; for 24 percent. 153 ohms. The resistance of cocain hydrochlorid is for 12 per cent, solution 80.85; for 24 per cent. 61.25. These provings indicate that the hydrochlorid is the better salt of cocain for the purpose.^ The tooth to be operated upon is isolated by means of a rubber dam and is ligated at the cervix to prevent leakage of current. If there are metallic fillings in the tooth, these should be covered Avith a coat of varnish carefully laid on and dried. This precaution does not always possess the value claimed for it, as the dentin beneath a metal filling, because of its density or lack of porosity, will not convey the current as well as the carious matter and the softer dentin of the fresh cavity. In some cavities where caries has occurred at the cervix above gold fillings, and which do not permit of complete isolation of the fillings, the cataphoric influence is not interfered with. The carious matter should not be completely removed and need only be partially dried. The cavity is loosely filled with a small pledget of lint saturated with the solution of cocain. The anode, the point of which is of platinum, is covered with a thin stratum of lint which is dipped in the solution and inserted in the cavity in contact with the pledget previously introduced. The cathode, which should be at least one and a half inches in diameter, is placed at a convenient place on ^The writer is indebted for the determination of these resistances of cocain solutions, etc., to Mr. A. W. Schramm, of the University of Pennsylvania. 164 PRELIM IS Mi Y PREPARATION OF CAVITIES, ETC. the face or neck. Tlu' desiivd number of colls arc placed in cinuit with the controller at zero. All bcinji: ready, the switch is ])laccd on the first contact point. At this moment, however great the resistance of the controller, a slight sensation is sometimes exjierienccd, hut at once the switch may be passed slowly over the contacts until som(> sign from the j)atient indi- cates that the current is being felt. Here it is retained until subsidence of the sensation occurs, when the resistance of tiie controller should be very gradually lessened. This process is continued, keeping con- stantly within the limit of pain ; at length the switch may be more rapidly advanced to the last pin. When this can be done without thrill, the indication is that anesthesia is complete. The switch is then rnrried back to the zero point, when the excavation may be conducted. AVhere it is necessary to remove the rubber (as the solution of cocain is strong) the preparation should be previously washed away to prevent any of it from being swallowed. The period of admiuisfrafion varies from eight to fifteen minutes in ordinary cases where the indicated amperage is from -^^ to -f^ milli- ampere. Wlien, however, the dentin is dense, as where denudation has taken place by attrition, a longer time is required to effect penetration by the cocain. Also where from any condition the indicated amperage at first is 2^0 niilliampere or less, time and patience arc demanded. The loss of time is more apparent than real, since there usually is a direct relation between the pain limit at very low amp&rage and high sensitivity ; what is apparently lost in the time of the application is gained in the after facility of instrumentation. The sphere of the action extends throughout the cavity, but to a somewhat less degree at the extreme lateral margins, and more particu- larly at the occlusal margin. Here usually no more than a normal degree of sensitivity is found, which appears to be due to the fact that in making the retentive undercutting this procedure may extend beyond the sphere of the complete influence of the cocain. The effect is most pronounced when the application is made directly to the carious matter. In this case the diffusion is greater than Avhen the caries is freely re- moved, for the reason that in the latter case the current seeks the line of least resistance toward the pulp. It follows from this that when all parts of the cavity are equidistant from the pulp, the action should be more effective throughout upon the surface of the dentin. This is proven to be the case from the profound effect in cavities upon buccal and labial surfaces and in shallow cavities of occlusal surfaces. Besides the less diff'usion of the cocain when the carious matter is removed, a decree of electrical force which in the former case is easilv toieratcfl DENTINAL ANESTHESIA BY ELECTRICAL OSMOSIS. 165 becomes painful. These facts make conclusive the importance of retain- ing some of the carious contents of the cavity. An explanation of the influence of the current is found in the prin- ciples and examples given on page 154. As the anode is put in con- nection with the lint saturated with the cocain solution the fluids of the tooth advance toivard the pulp through the canaliculi, their place being taken by the solution of cocain. At the same time it is observed that loss of fluid from the lint occurs, necessitating additions to maintain the proper M^etness, some loss of water taking place by evaporation. Conditions Influencing Tolerance of the Current. — As already stated, when the electrical force is brought into connection with the carious matter the irritation caused by the current is of trifling degree and soon subsides, indicating that the anesthetic effect has been produced ; but when the cavity is denuded of caries the above-stated degree of current force is not so tolerable, the irritation continues longer and does not subside in the same manner, but the effect upon the tissue is nearly if not quite as marked. The nearer the bottom of the cavity is to the pulp, the greater the irritation. Hence in this condition it becomes necessary to begin with a low degree of voltage. While in the one case fifteen cells may be selected, in the other ten cells are more satisfactory. To avoid the removal of caries the condition of the dentin as regards sensitivity should be tested at the line of its connection with the enamel. Some stress has been laid upon the necessity for rendering the solu- tion of cocain more highly conductive. This claim is probably more theoretical than practical in its character, since experience with the solutions given indicates that the conductivity is sufficient, and that the resistance is more to be looked for in the dentin than in the solution, and that when the tooth has become tolerant of the current at a com- paratively low voltage an increase of pressure of the current is suf- ficient to complete the anesthesia. The form of the platinum anode should be such as to permit its easy entrance into the cavity when its point is covered with a layer of absorbent lint. For all cavities in the approximal surfaces and in most occlusal positions an excellent form of anode is made by curling the end of a fine platinum wire (No. 25) into a flat knot, or forming it in a loop. On the loop a properly sized piece of lint may be gathered. This may be packed into the cavity and secured with additional lint when required. This method is a self-sustaining one. The connection between the free end of the anode and conducting cord is made with a spring clip, as shown in Fig. 110. 166 PRELIM IS ARY PREPARATIOX OF CAVITIES, ETC. For labial and hiiccal surl'art's two or more small points to sorew into a ootimioii liaiulU' are sufiiciont (see Fig. 109). These have to be Fi.i. MX.). Dental anodes for cataphoresis. held hi situ. A iorm and arrangement to make these self-sustaining offers an important field for inventive skill. Fig. 110. Snap and wire electrode. A convenient cathode electhode is shown in Fig. 111. Tn this the surface is recessed to receive a disk of amadou (spunk) or cottonoid, Fig. 111. Cathode for cataphoresis. one and a half to two inches in diameter, which retains an abundance of a solution of sodium chlorid to maintain contact. The surface is platinized to prevent corrosion. The reverse side has the usual socket to receive the conducting cord, which is placed in a projection intended to pass through an opening in the band which supports the rubber dam. It is indifferent where this electrode is placed ; the objects to be attained are to lessen the resistance as much as possible and to secure constant apposition with the surface with which it is connected. If the person be comparatively lean, the face before the ear is to be preferred. When there is much adipose tissue on the face, the usual negative hand electrode, covered with a small wet napkin to maintain close contact, may be iietter than the application to the face ; but in general the nearer DENTINAL ANESTHESIA BY CHEMICAL AGENTS. 167 the cathode is phiced to the angle of the jaw, the quicker and surer is the result of the administration. The action of cocain administered in this manner is profound. The effect is primarily upon the contents of the canaliculi, as is shown in the cataphoric treatment of shallow cavities. After superficial anes- thesia has been established much lateral cutting will later elicit a degree of pain; in deep cavities nearing the pulp, the effect extends to that organ. The recurrence of sensitivity takes place within a few hours. No injury appears to follow. This method of treatment is little required where the degree of hypersensitiveness is such as to yield to desiccation of the dentin or the application of carbolic acid combined with caustic potassa (" Robin- son's Remedy "). But when the pain attending excavation requires active treatment, such as the employment of zinc chlorid or general anesthesia, the cataphoric method is far preferable to either, and is nearly certain to give relief. The condition where cataphoresis is most required is when the impatience of the dentine to mechanical irri- tation is extreme. Usually in this case the condition extends deeply. The results of successful cataphoresis are marvellous, and it may be truly stated that no advance of recent years in the therapeutic treat- ment of the teeth is comparable to this.^ Cautious excavation is required after cataphoric treatment, as in the absence of sensitivity indiscriminate cutting may needlessly encroach upon the pulp. In case exposure really exists the action of cocain does not prejudice conservative treatment of the pulp. When devitalization is determined upon, the anesthesia facilitates this procedure. As stated in Chapter XVI. cocainization may be then continued either cata- phorically or by instillation. Should arsenous acid be selected as the devitalizing agent, cocainization may be used as a preparatory measure to lessen arsenical irritation. The Chemical Treatment. Under this head are included the application of warmed air, the use of coagulants, notably carbolic acid or zinc chlorid, and, in combination with these, one of the essential oils, preferably oil of cloves, for reasons stated below. Warmed Air. — This method is of great value in subacute cases. It is especially serviceable for the cavities of incisors and biscuspids and others of easy access. The effect here produced is due to the depriva- ^ For further study of this subject, see " International System of Electro-Thera- peutics," Section C, p. 1 et seq., Peterson; also, "Foundation Principles of Dental Cataphoresis," by Dr. Price, Itevis of Intrrest, vol. xx. p. 345. 168 PRELrMIXARV I'liKPAHATION OF CAVITIES, ETC. turn of the tissue, to a (greater or l('.th. The cessation of the pain prodnced by it indicates the time for its removal, when nsnally the dentin will be fonnd to be insensitive. There arc instances, how- ever, when no a[)parent effect is prodnced, which can oidy be satisfac- torily explained on the ground that the vital resistance of tlie tissue is sufficient to overcome the coagulative power of the zinc salt. In general, zinc chlorid must be regarded as an entirely safe agent if used with discretion. It is more aj)plicable to shallow cavities which are so situated, or are of such form, as to rccpiirc much formative cutting at the margins of the cavities, as in buccal and labial surfaces and in the very superficial cavities of incisors and bicuspids. A warning, however, should be presented that as the pulp c(n"nua of incisors frequently pro- ject near the surface, j)articularly in the young subject, considerable care is here recpiired in any but shallow cavities of decay. If it were used in excess and its action extended there would always be danger, as its energies would not cease tnitil the affinities of the whole amoinit were satisfied. In deep cavities the effi^ct, particularly in soft teeth, would eventuate in the ultimate devitalization of the pulp. It fol- lows, therefore, that it would be improper to seal up any quantity of this substance in a cavity. The action of zinc chlorid is terminated when the excess is removed and the cavity irrigated with water. The affinity it has for water quickly removes the excess and soon deprives the tissue of the remain- ing portion. When cavities are deep and it is found necessary to resort to this agent the surface of the deeper parts should be protected by an insoluble coating, after which the margins, where the sensitivity is acute, may be acted upon without detriment. Here it is requisite to remove the deep caries, desiccate the surface and make a coating with a varnish. For this purpose red gutta-percha rubbed in chloroform is applicable, since it may be deftly applied to any given part and when the chloroform has escaped is protective. To properly apply zinc chlorid it is highly important to isolate the tooth by means of rubber dam to protect the gum and to prevent the entrance of moisture. Its affinities for water are so great that even the vapor of the mouth dilutes it so much as to lessen its power. The DENTINAL ANESTHESIA BY CHEMICAL AGENTS 171 form in which it is best to employ it is the saturated deliquesced salt, which is taken from a bottle containing the salt in excess. The fluid is introduced on a pledget of cotton and is permitted to remain until the pain occasioned by it has ceased. It will be found that there are two periods of pain : the first from its irritation of the fibrils in the bottom layer of the caries, and then again when it has reached the zone of exalted dentin a little beneath this ultimate layer of decay. It follows, if the caries has all been previously removed and the sensitive tissue interdicts further cutting, that but one period of pain is encountered. The cutting should therefore be deferred until after the second period of pain has passed. The disregard of this considera- tion has sometimes cast discredit upon the efficiency of this sovereign remedy. It is requisite that the chlorid be chemically pure, and the fused form is preferable to the crystals of the shops. The PAix attending the application is sometimes extreme for a mo- ment. This can be moderated by air-drying the cavity and dressing it with carbolic acid, which does not seem to prevent the action of the chlorid. To avoid the loss of time which may be occasioned by the slow action it is advisable, after securing the dam at the neck of the tooth by a ligature, to very tightly tie the free portion of the rubber a short distance from the tooth with a strong ligature, and after cutting away the excess of rubber some other service may be rendered. AVhen the pain has ceased the case may be proceeded with, or the excess of chlorid may be thoroughly washed out and the cavity temporarily closed until a subsequent time. Another method of securing the action of zinc chlorid is to make a paste of zinc oxychlorid and fill the cavity with it. Even after crys- tallization of the paste takes place it contains a slight excess of the chlorid, which slowly acts upon the hypersensitive tissue. This method, however, is not adapted to deep cavities, and care must be exercised con- cerning its use in teeth of inferior grade. Zinc chlorid is an extremely valuable remedy when the previously described agents prove insufficient or are not indicated. Conditions lohich render Zinc Chlorid inadmissible. — It has been stated that the chief danger of its use consists in the liability of the coagulant and escharotic action reaching the pulp in deep cavities. This danger is further enhanced when the teeth are soft, as in this con- dition the penetration is liable to be greater than would be the case with dense dentin. The same caution must be observed when the structure is incomplete, as it is in the teeth of young subjects. Even here, as extreme sensitiveness is always found at the peripheral limits of the 172 PRELIMINARY PRFPARATfOy OF CAVITIKS, ETC. tubule?:, it is not difticull to limit the action to this |)art hy tlio means abov(> j)oini*'(l out if care he taken in the rc(|nin(l ]iroc(Mhn'('s. The Acids. — Chromic and nitric acids are ot' service in extremely shallow cavities of very high sensitivity. The former acts by coagula- tion of the organic elements of the dentin and the latter l)y decomposi- tion and solution. To apply these the adjacent tissues require to be protected. Each should be carried in small quantity upon a gold probe. Silver nitrate is applicable for reducing the sensitivity of dentin after the removal of superfit;ial caries or when by abrasion or by erosion the exposed tissue is intolerably sensitive. It is, however, only to be used in the back of the month, on account of the discoloration "which it produces. Antimony chlorid is applicable only to cases of exposed cemeu- tum, where it is claimed that it is equally as efficient as silver nitrate, and has not the objection of discoloring the tissue. General Anesthesia. AVhile some reluctance should exist as to the propriety of inducing general anesthesia, it sometimes becomes necessary to resort to this means of alleviation. Necessity for this election arises where the sen- sitivity is extreme, when the previous remedies have been inefficient, and when from the nature of the case zinc chlorid is inadmissible. The subjects should generally be adult persons of intelligence, who possess moral force and, having confidence in their adviser, are capable of giving the requisite indications of the j)rogress of the anesthetic influences. Sulfuric ether is the most suitable anesthetic to be employed, and the operative procedures should be performed in the first stage, that of peripheral anesthesia. At this period, which is before the stage of excitement commences, dentin may be cut without the slightest pain being felt. This is an important consideration, since if the ad- ministration is continued into the period of excitement nothing can be done, and if it is conducted to a full degree the patient is not manage- able. Also the subsequent depression is to be avoided. AVhile general anesthesia in the first stages is available for the relief of dentinal sensi- tivity, it is found, on the contrary, w'hen resorted to for the removal of the pulp, as may occasionally be required in the most severe cases of congestion, that nothing short of profound anesthesia will suffice. When the first strif/e is reached, the patient being conscious and able to reply to questions, the cutting is commenced ; as the pain returns a few more inhalations are given, when another part of the cutting may be proceeded with. This may be repeated until the cavity is formed. GENERAL ANESTHESIA. 173 Fig. 114. The cutting- should be quickly and deftly conducted. The amount of ether administered is far less than is required to induce full anesthesia, and the patient suffers far less depression than if the operation were performed without this means. There is also no danger of shock, since the patient is, or should be, intelligently concerned in the progress of the case. If the condition were carried into the second stage, when excite- ment exists and alarm is aroused in addition to the operative interfer- ence, there is liability to shock, which, being due to a profound impres- sion on the nervous system, is not liable to occur when the patient concurs in all the steps of the procedure. The time required to bring about a sufficient degree of dentinal anesthesia frequently is less than two minutes. The ether should be pure and should be given with a free supply of air mixed with the vapor. The ordinary custom of using the towel to envelop the face is questionable, since this method does not permit enough air to accompany the ether vapor. An invaluable inhaler for this purpose is the one invented by Dr. Allis (Fig. 114). This consists of an oval frame composed of a series of wires through which passes back and forth a continuous band of muslin. The layers of muslin are near each other, and still so far apart as to permit the free passage of the at- mosphere. The correct manner is to continuously drop the ether in small quantity upon the muslin to maintain it at an even degree of partial saturation. This appliance is one of value to the dental operator, as by it the anesthetic state can be more quietly brought about with less of the characteristic disturb- ances Avhich attend the usual modes of applying sulfuric ether. The use of chloroform for the purpose under discussion is wholly inadmissible. The mechanical means consist in the use of temporary fillings, which may be either metallic or non-metallic. The metallic act by inducing, in consequence of the slight irritation of thermal conductivity, a consolidation of the subjacent dentin, which in time obliterates the tubules. The non-metallic act simply as a protective covering to the denuded dentin. Their action hence is more tardy than that which follows the use of the former. The metallic stoppings for this purpose may be composed of either tin foil or amalgam. Each of these requires cavities of reasonably good The Allis inhaler. 174 PRELIMINAPxY PREPARATION OF CAVPriES, ETC. ivti-ntivoness, tlu'ivforc they are not applicable tu .shallow cavities Oi unsuitable form. The non-mctallir may he either j^utta-percha, zinc ph()s])hate, or zinc oxyehlorid. The two hitter arc tlic most desirable, as they adhere to anv well-dried cavity, and having- some irritating influence on the tissues tend to induce structural consolidation in addition to their ])roteetive action. They have, however, the disadvantatre of sut!'crin active means needed to reduce dentinal sensitivity. For these cases gutta-percha stoppings when carefully introduced are a great boon, since they ])rotect the tissues during the period of completion and consolidation of the dentin. CHAPTER VII. PREPARATION OF CAVITIES— OPENING THE CAVITY— RE- MOVING THE DECAY— SHAPING THE CAVITY— CLASSI- FICATION OF CAVITIES. By S. H. Guilford, A. M., D. D. S., Ph. D. General Considerations. — The importance of the proper preparation of a cavity for the insertion of a filling can scarcely be overestimated. Upon its being well done the success of the completed operation largely depends. As many fillings fail from lack of thoroughness in the pre- paration of the cavity as from any other cause. The operator should not be actuated by haste, but should be deliber- ate, careful, and painstaking. Each stage of the operation should be thoroughly performed in order that when completed the cavity may be in the best possible condition for the reception and retention of the filling. The operation is naturally divided into five stages : 1. Opening the Cavity. 2. Establishing the Cavity Outlines. 3. Removing the Decay. 4. Shaping the Cavity. 5. Perfecting the Enamel Margins. 1. Opening the Cavity. Every cavity to be excavated must first be opened, so that it may be approached and operated upon at all points. The particular manner of doing this will have to be determined by the extent of the decay and its position, but in all cases the opening must be as full and free as the conditions will permit. The accessibility of the cavity will depend upon its location. Upon the three exposed surfaces of a tooth crown (occlusal, lingual, and labial or buccal) access to a cavity is usually easy, but upon the unexposed surfaces (approximal) access can only be had after the teeth have been pressed apart. For methods of securing temporary separation of the teeth see Chapter V. A cavity upon an exposed surface, if small, can usually best be opened by the use of some form of engine bur. A few sizes each of the forms known as "fissure," "inverted-cone," and "round" (or 175 17(> PREPARATION OF CAVITIES. "rose-head") arc shown in Figs. 115-117. A spear-pointed drill is sometimes used, Ixit is less serviceable on account of its tendency to be eanght or broken in the irregnhirities of the cavity orifice. A modified form of fissure bur has found nuu-h favor in the opening of small cavities on exposed surfaces. It is made from an ordinary bur Fu;. 115. Fi(i. 116. Fk;. 117. Fissurt" burs. luvLTtfil-cuiie t'ur- from which the head has been broken, by cutting spiral blades on the tapering neck of the shank. Being pointed, round, and tapering it easily effects an entrance into the cavity and enlarges the orifice grad- ually and symmetrically. It is shown in Fig. 119. In cavities of larger size, where decay lias made more progress, the overhanging walls of enamel can best be broken down by chisels of suitable size and form. AVhere a straight cliisel can be employed it will be found most efficient, but in positions difficult of access one having a slight curve or angle may need to be employed. Figs. 120 and 121 represent both forms as well as the sizes usually preferred. The Fig. 118. Fig. 119. Fig. 120. Fig. 121. ^ J Li Li L Cross-cut burs. Modified fissure bur wiUi taperiug point. itraiglit chisels. Curved chisels. width of the blade may vary from one-sixteenth to one-cightli of an inch, but wider ones than these will seldom be required. A chisel may be used with either hand ])ressure or mallet force. If the former, great care must be exercised to prevent its slipping and causijig pain or possible injury. The best safeguard in its use is to place the thumb of the right hand on the tooth being operated upon or some adjoining one and use it as a fulcrum or pivot upon which the. REMOVING THE DECAY. 177 Fig. 122. instrument may move in a curve. By this means the motion of the chisel is regulated and controlled and all danger of slipping avoided. It will sometimes be of advantage to roughly pack the interior of the cavity with cotton or spunk to receive the impact of the instrument should the chisel accidentally be forced to the bottom of the cavity. The better plan, however, in most cases, is to employ mallet force for the cleavage of enamel unsupported by dentin. By holding the chisel between the thumb and three fingers of the left hand and resting the little finger of the -same hand on an adjacent tooth for steadiness, a smart but light blow of a mallet in the right hand upon the end of the chisel will easily and painlessly cleave oif portions of the enamel. In opening cavities of small extent or limited depth upon approxi- mal surfaces a round or inverted-cone bur will best serve the purpose, but where caries is more exten- sive and the surrounding enamel is unsupported by dentin the orifice of the cavity can be more advan- tageously enlarged by means of a delicate chisel (shown in Fig. 122) the blade of which is bent at a slight angle to the shank and all three of the edges of which are bevelled to convert them into cutting edges. This instrument will be found especially useful in opening cavities of medium or larger size on the approximal surfaces of the incisors, the point doing the cleaving and the side edges being used to smooth the enamel margins. After the orifice of the cavity has been sufficiently enlarged to aiford a full view of its interior the next stage of the operation is entered upon — 2. Establishing the Cavity Outlines. In all cases, and especially for those on approximal surfaces, it is necessary to extend the boundaries of cavities not only to include all decayed or injured tooth structure, but also all such healthy tooth tissue as may be required in order to bring the outlines of the cavity to such points as will establish relative immunity from future decay. To this end, in cavities upon the approximal surfaces of biscuspids and molars, if of considerable size, the buccal wall should be extended to the approximo-buccal angle of the tooth ; the lingual wall to the approximo-lingual angle, and the cervical or gingival wall to a point beneath the free margin of the gum. Thus extended, the buccal and lingual walls will be in such position as to be kept clean and free from food deposits, and consequently from decay. The gingival wall, extended beneath the gum margin, is protected and immunized by the overlapping gum tissue. 12 Delicate three-sided chisel, useful for opening cavities on approximal sur- faces. 178 PUKPAUATIOX OF CAVITIKR. Cavities on tlio appr(>xim:il surfaces of tlie incisors and canines sliould in like manner l>e extended to include the entire area of possible future decay, l)nt tiiey do not need to he extended so far lahially as to make the p)ld conspicuous. 'i'he liiiLiual niartrinsof these cavities may he freely extended linjjually, both to in-ure necessary streiii^th and to atfitrd room for ajtproaeh in the act <»f HlliiiLT. In stndvintr the size and form necessary for each cavity to jiossess, a mental ])icture should he drawn and the cavity shapecl in accordance •ith it. 3. Removing the Decay. The character or consistence of the carious structure has much to do witli the method and means employed for its removal. If it be of the i^cmi-clastic or leathery variety so often found in the teeth of y(»un(r persons, it can be most easily removed by means of npoon-xliaped or round-bkided EXCAVATORS, which being; oval or circular in ed^v out- line and free from marginal angles, will lift and separate the layers without danger of injuring the underlying healthy dentin and with the infliction of a minimum amount of pain. Fig. 1G7 illustrates this kind of instrument in some of its forms, selected from the Darby-Perry set. In the cJarJ:, hard variety of caries, as also in the white, chcdky variety, the different forms of burs and excavators will" be found best suited for the purpose. In the removal of caries care should be exercised to inflict as little pain upon the patient as possible. To this end, in cavities of con- siderable extent, it is best, after the orifice has been sufficiently enlarged, to make a sweeping cut with an excavator around the cavity just below P>;. T23. " u i f 11 ii n n r w 1 Excas-ators. the enamel line, thus freeing the decayed portion at that point. Follow- ing this the remaining portion of carious dentin should be removed by placing the blade of the excavator near the bottom of the cavity and REMOVING THE DECAY. 179 making draw-cuts toward the orifice. To cut in the reverse direction would produce uncorafortable pressure upon the most tender portion of the cavity, and possibly, by inadvertence, expose and wound the pulp. When burs are employed for the removal of caries it is safest to use only those more or less rounded on their circumference, such as the round ■ or oval forms, for they more nearly conform to the natural outline of the cavity, leave no angular grooves in the dentin, and are not so likely to injure the subjacent healthy dentin. The varieties of bur known as the inverted-cone and wheel, while very useful for opening cavities, should not be used for the removal of caries in deep cavities, because of the irregularities of surface which their peripheral angles produce. Rapidly revolving burs in an engine handpiece are very apt to cause pain by the development of frictional heat. This may largely be pre- vented by lifting the bur at short intervals and allowing it to run free for a moment, which will prevent overheating the tooth and thus avoid unnecessary pain. Thorough excavation of the cavity and the removal of all carious dentin is absolutely essential to success. To allow any portion of it to remain and trust to the employment of germicides for its sterilization is running the risk of failure, for we can never be entirely sure of disinfection. Besides this, there is no good reason for allowing it to remain . By carious dentin is meant the remains or debris of the action of caries, — a product resulting from this disintegrating action upon both the organic and inorganic constituents of dentin. In nearly all cavi- ties we find tivo varieties of altered tissue. That nearest the surface is a mass of thoroughly disorganized and usually decomposed matter filled with micro-organisms. Beneath this and lying next to the healthy den- tin there is a zone or layer from which the calcium salts have been re- moved by the acid solvent, but which still retains its original form and vitality. This layer of decalcified dentin may be allowed to remain, especially in the bottom of a cavity, as it serves to protect the subjacent tissue from thermal shock, but as a precautionary measure it should be treated to an alkaline application or some germicide such as carbolic acid, mercury bichlorid, formalin (10 per cent, aqueous solution), or oil of cinnamon, before the insertion of the filling. Occasionally caries will be found to be self -limited . In such cases, through some unexplained change of conditions, the progress of caries has been checked and the layer of decalcified dentin re- stored to its previous normal condition. AVhere this has taken place the restored tissue is usually of a darker color than ordinary dentin, and on this account may be mistaken for carious dentin and removed. 180 PREPARATION OF CAVITIES. It is, however, easily distinguished irom ciiries hy its hanhiess, and shouhl in no case be removed exeept from the sides of a eavity, and then only when its dark color sho\vin<; throu;;h the walls would prevent the cavity, after being filled, from having that clear and clean appear- ance which it should possess. "With some practitioners it is the custom to prej)are a cavity f //•//, because in this way the operation is more rapid and usually less ])aiuful. In such case the rubber dam is applied first of all and the operations of opening, cleansing, and shaping the cavity are all performed without the presence of moisture. He])eated applications of warm air from a syringe, at intervals (hiring the operation, desiccate the dentin and di- minish its j)o\ver of sensation. Others, in order to avoid the unpleasant- ness to the patient of having the dam in position for so long a time, prepare the cavity roughly in the presence of moisture, then apply the dam, dry the tooth thoroughly, and finish the operation. Whichever plan is adopted it is absolutely necessary, in all cases, to finish the preparation with the dam on and the tooth dry, for it is only after a tooth has been deprived of its moisture that we are able to decide whether all the niceties of })reparation have been successfully carried out. Certain marginal and structural defects that are not noticeable w^hile the tooth is moist are plainly revealed after it has been dried. 4. Shaping the Cavity. This is one of the most important of all operations associated with the stopping of a cavity, for according as it is properly or improperly performed success or failure will result. Too much stress cannot be laid upon its importance, nor too great care be exercised in its accom- plishment. Inasmuch as a filling is retained in place inecJuinicaUij it follows that the cavitv must be of such shape as to secure retention. To this end it should be larger within (at least at certain points) than at the orifice. An exception to this rule lies in cavities where the depth is greater than the diameter. In cavities of this character parallel walls will suffice, because lateral-surface contact is so great in proportion to the mass to be held in place that displacement could not occur. In larger cavities of moderate depth, however, the reverse is the case, and they will require the assistance of internal enlargement for the retention of the filling. To govern each of the conditions two rules may be formulated : 1. When the depth of the cavity is greater tlian the diameter of the orifice, parallel lateral walls will prove retentive. 2. When the diameter of the orifice is greater than the depth of the cavitv, the latter will have to be somewhat enlarged internally to retain the filling. SHAPING THE CAVITY. 181 Examples of the first class are found in the narrow but rather deep cavities which occur on the lingual surfaces of the upper incisors near the cervix ; in the pit cavities on the buccal surfaces of molars ; and in the small cavities found on either side of the enamel ridge on the occlusal surfaces of the lower first bicuspids. Examples of the second class are found in numberless places on any of the crown surfaces. In some cases cavities will be found of such form that when caries has been removed they will have a naturally retentive shape, but in the great majority of cases more or less sound tissue will have to be removed in order to give them the required form. To give a cavity a retentive form it is not necessary that its interior be enlarged throughout its whole extent, but it must be larger at two or more points, and these points must be opposite one another. Frequently it will be easier to enlarge the cavity at all points, and to this no objection can be urged provided too much sound tissue be not removed or the pulp be not too nearly approached. Too great enlargement tends to weaken the cavity walls and therefore should be guarded against. In shaping the cavity internally instruments should be employed that will leave the surface free from angles. Excavators for this pur- pose should have curved edges, and burs should be of a round or oval form. If grooves are required they should be made neither deep nor too near to the enamel, to avoid weakening the walls. At the cervical margins of cavities grooves and starting pits should be avoided when- ever possible, for they weaken the portion of the cavity which is sub- jected to the greatest strain in the introduction of the filling, both mechanically and by cutting off the nutrient supply to the cervical margin, which tends to alter the resistive character of that portion of the tooth structure by devitalizing it. For the same reasons deep grooves or undercuts should not be made near the incisal or occlusal surfaces, for the strain of mastication will be liable to result in fracture of the wall if it is thus unduly weakened. In the process of shaping the cavity internally the enamel margins will naturally be assuming their proper form, but the final part of the preparation should consist in giving these frail portals of the cavity very careful and minute attention. The permanency of a filling will depend largely upon the strength of the enamel walls and their proper preparation. The enamel cap of a tooth when intact is exceedingly strong and capable of resisting great strain, but when its continuity has been broken by caries and it is left unsup- ported by dentin it is very weak and brittle. This is readily understood when we remember that enamel is composed of an aggregation of enamel 182 PREPARATION OF CAVITIES. rods or prisms in close juxta}K>sition, slightly joined together by a cementing substance, with their greater diameters perpendicular to the plane of the surface of dentin upon which they rest. AVhcn continuous, these rods mutually support one another and are thus capable of resisting great strain ; l)ut Avhen a lesion has occurred they lose support on the adjoining side and hence are easily separated in the direction of their lentrth. Fig. 124 (after Black') shows this condition perfectly. A de- tached section of enamel prisms is represented at a, and at b is shown a portion about being separated by a chisel. Fig. 124. Showing enamel stmcture. This will explain why enamel unsupported by dentin should not be allowed to form the margin of a cavity, for it will probably either be fractured while the filling is being introduced or afterward in mastication. On all convex surfaces of a tooth the enamel rods radiate outwardly, and by forming the margins of a cavity on these lines it will have a slightly flaring or trumpet-shaped orifice, which will not only afford the greatest strength but will admit of a better finish being given to the edges of the filling. In many cases it will be necessary to give the margins of a cavity more of an outward bevel than would be obtained by simply following the cleavage lines of the enamel rods. This can be secured by cutting away the (juter ends of the enamel rods in an oblique direc- tion as shown at c in Fig. 124. ]Vo weakening of the border will result in such cases, inasmuch as the shorter rods will still rest upon the dentin. If, however, the rods were cut so as to leave only their outer ends in place, as shown at (/, they would have no substantial support, and would be liable to be crushed during filling or afterward. All cavity margins should have the outward bevel to a greater or less extent in order to secure the best and most permanent results. In cavities upon depressed or concave surfaces of teeth it would not ' Dental C'omnos, vol. xxxiii., ji. 441. PERFECTING THE ENAMEL MARGINS. 183 Fig. 125. B B Cross-sectiou of a bi- cuspid showing- treat- ment of enamel in the sulcus. do to have the enamel margins formed on the lines of enamel cleavage for this would make the margin of the orifice the most contracted por- tion and result in frail marginal edges. Fig. 125, representing a cross-section of a bicuspid tooth with a cavity in the sulcus, will illustrate this point : a shows the cavity orifice prepared on the lines of enamel cleavage, and b the dressing across the outer edges of enamel required to give the necessary strength. It may therefore be laid down as a rule that to secure the best results the line of the enamel wall from within outward should form tcith the surface of the tooth at this- point an obtuse angle. 5. Perfecting the Enamel Margins. Beside the proper shaping of a cavity margin it should be made as smooth as possible. In accessible cavities upon exposed surfaces of teeth the final marginal smoothing or finish can best be eifected bv the use of a bur shaped somewhat like a fissure bur, but having a rounded end and being simply file-cut upon its surface instead of being bladed. Such a one is shown in Fig. 126. Its sides being parallel, no rounding of the cavity margins can occur when it is used with the end inside of the cavity. Any other form of bur with a short head would unavoidably give to the cavity margin either a concave or a convex surface, both of which would be incorrect. The buccal, lingual, and cervical enamel margins of a compound approximal cavity should never be finished with a round bur, even of the plug-finishing variety, but should be smoothed with suitable chisels, broad-faced excavators, or approximal trimmers, the latter being shown in Fig. 127. Fig. 126. Fig. 127. File-cut enamel finishing bur. Approximal trimmer. The practice of finishing enamel margins with sand-paper disks is very objectionable, as they are almost certain to give to the margins a 184 PREPARATION OF CAVITIES. rounded edge wliich cannot be filled and finisiied without leaving a feather edge of the filling overlying the enamel, \vhieh will eventually be broken off or flared up, leaving an imperfect margin. The Gem cavity trimmers, recently introduced, are probably the best instruments yet "devised for giving to enamel margins the perfection of finish required for gold filling. They produce a smooth but unpolished surface, to which the gold is readily adapted and along which it cannot slip or slide. Classification of Cavities.' I. Simple Cavities on Exposed Surfaces. Bicuspids and Molars. Incisors and Canines. A. Occlusal. D. Labial. B. Buccal. E. Lingual. C. Lingual. F. Incisal. 11. Simple Approximal Cavities. Incisors and Canines. Bicuspids and Molars. G. Mesial and distal. H. Mesial and distal. III. Compound Cavities. Incisors and Canines. Bicuspids and Molars. I. Mesio-labial. P. Mesio-occlusal. J. Disto-labial. Q. Disto-occlusal. K. Mesio-lingual. R. Occluso-buccal. L. Disto-lingual. aS'. Occluso-lingual. 31. Mesio-incisal. T. Mesio-disto-occlusal. N. Disto-incisal. O. ]Mesio-disto-incisal. In the foregoing classification the cavities have been arranged pro- gressively from the simplest (^1) to the most complicated (T). I. Simple Cavities on Exposed Surfaces. BICUSPIDS AND MOLARS. Class A. — Cavities upon the occlusal surface are very accessible and in full view, enabling the operator to see every part of the cavity and affording him plenty of room in which to operate. Naturally those nearest the front, as in the bicuspids, present the advantage of greater ^ Following the suggestion of Dr. Black, in the above list the word Untjmd is u.sed for the same surfaces in both the upper and lower teeth, doing away with the word palatal. In the forming of compound terms, where the mesial or (li.-siin' (•avit\-, l)iit when hirjjer they may be opened by means of" a chisel ibllowed by a suitable bur. In these, as in all cavities in sulci, the fissures must be followed and opened up to their extreme.st limits in order to ensure success, while the maririns and maruinal edges must be so formed as to be strong, smooth, and bevelled. The general form of these cavities when prepared is shown in Fig. 131. It will frequently be found that these two occlusal cavities Fir;. 130. Fig. 131. Fig. 132. Fu;. 13.3. Upper molar fi.ssure cavities. I'pper molar fissure cavities prepared for filling. are joined underneath, wdiile near the surface they are separated by a ridge of enamel and dentin. In such cases the ridge should be cut away and the tw^o cavities converted into a single larger one as illus- trated in Fig. 132. If the ridge were allowed to remain it would almost certainly be fractured either in the operation of filling or subsequently by the force of mastication. The upper third molar differs from those anterior to it in having but three cusps and consequently but one central ])it with radiating fissures. A cavity occurring here when properly pre])areit at its termination on the lingual surface is affected. Another ])oint on the lingual surface liable to decav is on or near the mesio-lingual angle of the upper first molar, about midway between the cervical and occlusal margins. At this place is often found a supple- mental cusp, diminutive in size, and where it joins the main surface of the tooth a small fissure exists which invites decay. This additional cusp, when it does exist, is found only upon the first molar. It is shown at A in Fig. 138. (See Chap. I., p. 39.) Neither of these cavities presents any difficulties in prepara- tion except such as occur from their slight inaccessibility. Occasionally, though very rarely, the lingual surface of any of the molars may present a cavity of decay close to the gin- gival line and partly beneath it. Such cavities are doubtless caused by the retention of food debris beneath the free margin of the gum, and owing to their position they are difficult to treat. Thev should be opened and packed over-full with cotton and sandarac varnish or gutta- percha for a day or two, to press the gum away, after which they may be prepared and filled in the usual manner. INCISORS AND CANINES. Class D. — Cavities upon the labial surfaces of incisors and canines are usually found along the gingival margin, and are the result of the direct action of acids probably formed at this point. In the beginning, and when small, they are entirely exposed, but when of greater extent they frequently extend l)eneath the fr(H> margin of the gum. They are nearly always elliptical in outline and may consist of simple decalcified enamel still retaining the usual surface form, or they may possess the common characteristics of cavities in general. The opening and preparation of this class of cavities arc not attended with any marked difficulties except that when they extend beneath the gum care will have to be exercised not to wound this tissue, as the consequent bleeding would obstruct the view and interfere with the progress of the work. This may be prevented by pressing and holding the gum away with a suitable instrument held in the left hand while the cavity is being prepared. Particular attention should be paid to the care- ful preparation of the cervical margin of the cavity and to its terminal points. The former should l)c made smooth and even, and the latter should be extended far enough to include any enamel that shows the least sign of acid alteration. Slight grooves or enlargements at the SIMPLE CAVITIES ON EXPOSED SURFACES. 189 base of the cavity along its upper and lower margins will give it a suf- ficiently retentive form. A second locality on the labial surface where decay is frequently found is anywhere between the central portion and the incisal edge, in pits and depressions that indicate imperfect development of the enamel. These pits or grooves extend in a nearly straight line parallel to the incisal edge, and are frequently the seat of decay. When quite shallow they may be obliterated by grinding the surface with a small corundum wheel and polishing, converting the surface at this point into a distinct concavity. When the pits are deeper and isolated they may be filled separately, the result being a lesser degree of conspicuousness ; but when they are connected by a groove, as they usually are, they will have to be converted into a single cavity and pitted incisor. filled. A common type of this defect is shown in Fig. 139. When these pits occur upon the incisal edge or in close proximity to it the choice lies between an unsightly gold filling, sections of porce- lain rods inserted into the pits, or their removal by grinding and the resultant shortening of the crown. Class E. — There is usually but one point upon the lingual surface of incisors and canines that is liable to decay. It is in the pit at the junction of the basilar ridge or cingulum with the adjacent tooth surface. The incipiency of caries at this point presents only as a mi- nute cavity, the opening and shaping of which is readily accomplished with a round bur. Although the orifices of these cavities may be small, the dark spot that marks their direction is often continued quite a distance toward the pulp chamber. This black point should in all cases be followed to its termination and obliterated. As the depth of these cavities is greater than the diameter of their orifices, no special retentive shape need be given them. The orifice should always be bevelled and enlarged, if necessary, to include any neighboring fissures. When these cavities are of greater extent they are prepared and filled like others of similar size and form. Class F. — Cavities upon and confined to the incisal edge of incisors and canines are easily pre})ared on account of their accessibility. This particular surface should, and generally does, remain free from decay on account of the attrition to which it is constantly subjected ; but when defects in the enamel exist, caries sometimes occurs in connection with it. This surface often needs covering with gold to check abrasion in cases where, after middle life, the crowns (especially those of the upper teeth) have been shortened by excessive wear. Under these conditions 190 PREPARATION OF CAVITIES. the surface iiuist he so prepared and sliaped as to retain the lipoid that is to eover and protect it just as thoui^h caries had originally injured the part. lu ibnning the cavity in tlie exposed dentin Fig. 140. j^ j^ oidy necessary to cut dee])ly enough to aHord a lodg- ment for the filling, hut the orifice must he so enlarged and excessively hevelled as to reach to the marginal edge of enamel all around. This is done to protect the enamel from chipping or fracture in mastication. To aflord the greatest .security U) the filling the cavity should be under- cut throughout its whole extent. AVhen thus prepared, c^avitv or"in- the cavity in cross-section will resemble a double dove-tail cieal surface. aS shown iu Fig. 140. II. Siraple Appro ximal Cavities. INCISORS AND CANINES. Class G. — Cavities upon the mesial and (Ji.sfal surfaces of the anterior teeth present only the difficulty arising from inaccessibility. To reach and operate upon these cavities, the teeth, if in normal contact, will usually have to be pressed apart either by gradual wedging or by immediate separation with a "separator." Even after this has been accomplished the cavity cannot be operated upon in a direct way as are cavities upon exposed surfaces, but will have to be approached from either the labial or lingual aspect of the crown. To do this, if the cavity be small, will generally necessitate an additional enlargement of the cavity toward the surface from which it is to be approached. As the lesser of two evils the enlargement is usually made toward the lingual surface, for in this way there will be no exposure of gold when the filling is completed. When the cavity is of larger size and the enamel wall on the labial surface has been weakened by caries it will have to be removed, and access will thus necessarily be afforded from that side. Whenever possible, however, undue enlargement of the cavity and consequent exposure of gold should be avoided. In ordinary cavities upon the approximal surface the frail walls bordering the orifice should be broken away with a small chisel, and after the decay has been removed by means of burs or excavators and the proper form given to the cavity, the margins should be carefully smoothed and bevelled from within outward with small plug-fini.shing burs or with the side-cutting edge of the small chisel shown in Fig. 122 and here reproduced (Fig. 141). Anchorage is obtained in these cavities by flattening the cervical wall so as to form distinctly rounded angles with the labial and lingual walls respectively. Slight depressions should also be made at the labio- SIMPLE APPBOXIMAL VAVITIES. 191 cervico-axial and the linguo-cervico-axial angles for starting and securing the first portions of the filling. A shallow undercut in the dentin near the incisal border will also be necessary to serve as an opposite anchorage. Retaining grooves should never be made in the labial or lingual walls of the y|! cavities, as they would seriously weaken them. In approximal cavities of large size, where they extend from near the incisal edge to or beyond the free mar- gins of the gum, the difficulties of producing a perfectly formed cavity are greatly increased. While affording greater ease of approach on account of their size, the cervical border of this class of cavities is apt to be less perfectly prepared owing to its obscure location. When the cervical border extends beneath the free margin of Delicate three-sided Mie gum the latter should be pressed and held away chisel, useful for ,. . , •in 1 opening cavities on durmg excavating, so that the cervical wail may be approximal sur- plainly seen and operated upon throughout its extent. ^^^'^^• Cutting of the wall should be sufficiently extended rootward as well labially and lingually to include any defects or checks in the enamel bordering it, and should be made entirely smooth and free from angles, for it is the most vulnerable border of the cavity after the filling has been completed. Should the cavity extend near to the enamel termination at the cervix, it will be best to still further extend it so as to pass beyond this margin ; for if a small portion of enamel be left t^ere it will be liable to be broken away in the process of filling and thus render difficult the proper finishing of this portion of the approxiuial surface. So, also, if the cavity on account of its size should approach very near to the incisal edge, it is best to remove this frail corner and con- vert the cavity into a compound one. Where such a weak corner is allowed to remain it is very frequently broken away in subsequent mas- tication. Such a result is shown in Fig. 142. An accident like this is more likely to occur in thin, fiat teeth where the plates of enamel meet- ing at the incisal edge have little or no dentin between them. Where doubt exists as to whether the corner should be p, ^^^ removed or allowed to remain, it is well, after the cavity has been prepared, to test the strength of the corner by strong pres- sure upon it in the direction of the long axis of the tooth with a piece of orange-wood. If it resists this strain it will prob- ably resist the force of mastication, and if it break away under the test it will demonstrate that it would have been unwise to allow it to remain. If the corner be left as a border and support for the filling it should not be weakened by a deep retaining groove. Such groove or anchorage 192 PREPARATION OF CAVITIES. should 1)0 sluillow, and as far removed IVoiii the ineisal border as tlie conditions will j)erniit. In nianv oases whore the incisal wall would he seriously weakened by any attempt to use it as an anohora<;o or su))port for the filling, and where it seems undesirable to roiuovo it. an ox- oellont anohoraco for the lower border of the filliui:; may be obtained by outtinjj^ an extension upon the lingual surfaoe in the form of an arm, as shown in Fig. 14.'3.' Such extension, if made but little deeper than the enamel, will not materially weaken the tooth and will seeuro the filling perfectly. Its position should bo near the incisal edge, but not so close to it as to weaken the part. In the anterior teeth the relative difficulties betw^een mesial and distal cavities are insignificant. BICUSPIDS AND MOLARS, Class H. — The preparation of small cavities on the mesial and distal surfaces of the bicuspids and molars, though simple in character, is usually most difficult of thorough performance. This is duo entirely to their inaccessibility when the teeth are closely approximated. How to approach these cavities is often a matter of no small concern to the student or young practitioner, and the preparation and filling of them is generally more difficult than that of larger and more complicated cavities in exposed situations. To lessen the difficulty of approach it is important, whenever practicable, to create by wedging beforehand as great a separation as possible between the teeth. The greater the space gained the less the difficulty of approach. When conditions warrant cutting down to them from the occlusal surface, and thus converting them into compound cavities, it is the better plan to pursue, for, although this method involves the loss of more tooth tissue, it greatly facilitates the operation of filling by affording additional space and accessibility, AVhen, however, the cavities are small and situated at the centre or toward the gingival margin of the approximal surface, they should be dealt with as are similar cavities in the anterior teeth, depending upon previous spacing for room in w'hich to work. These cavities can usually be best opened and maiidy prepared with a round bur. After the caries has been removed and the walls defined and prepared, the cavity may be made retentive in form by slight under- cutting throughout its entire circumference, or it may be enlarged at two opposite points only. The cervical wall can be shaped with an obtuse- ' Dental Cosmos, vol. xxxvi., p. 198^ and Dental Review, vol. ix., pp. 812 and 819. COMPOUND CAVITIES. 193 angle hatchet excavator as illustrated in Fig. 144, and the lower or occlusal wall be slightly undercut by an acute-angle excavator like Fig. 145. Fig. 144. Fig. 145. Obtuse-ansrle hatchets. Acute-angle hatchets. The sharp angles on the cutting edges of these excavators should be rounded before being used, so as to avoid the formation of angles in the cavity. As the enamel rods on this surface radiate outwardly at such an angle as to give the proper bevel to the orifice of the cavity, a careful following of their lines in the preparation of the cavity margins will be all that is necessary to give them the desired form and strength. Where simple cavities upon the approximal surface are large they may extend so near to the occlusal surface as to weaken it. When this is the case the enamel wall should be cut away and the cavity converted into a compound one of the approximo-occlusal type. III. Compound Cavities. INCISORS AND CANINES. Fig. 146. Classes I and /. — Mesio-labial and disto-lahial cavities occur from the near approach or union of simple cavities upon their respective surfaces. Cavities of considerable length up- on the approximal and labial surfaces are very apt to join one another by extension of caries. When they do not join they are usually separated by a narrow terri- tory of more or less impaired tooth tissue, and in such cases must be united to obtain a satisfactory result. Each cavity should be as nearly prepared as possible separately, after which the intervening tissue should be cut away and the margins of the channel connecting the two be made as strong and smooth as possible. This channel will usually be of less width than either of the cavities, but not more difficult to fill on this account such a compound cavity. 13 Mesio-labial cav- ity prepared. Fig. 146 shows a front view of 194 PREPARATION OF CAVITIES. Whether tlie cavitv 1h' a iiiosi(»-lal>i:il or a (Jistu-lahial one will not materially atleot the inaiincr or difficulty of o|)t'ratino;. Classes 7v' and L. — Mcs-io-fiiif/iui/ and (lisfo-Ziuf/nal cavities are formed in the same manner as those of classes / and ./, except that in ^ ,,_ these cases tlie linuual surface is involved instead of the labial. Fio. 14/. ^ -^ Kxtensive caries in the region of the basilar pit or of the iissures connected with it often approaches so nearly to an aj)))roxinial cavitv in the same tootli as to demand the union of the two (see Fiy. 147). The method of ])reparinir and unitins: the two is substantially the same as that followed in classes / and J, just described, A mesio-lintjual cavity is perhaps more easily prepared and filled than a mesio-labial one, for in its preparation the free cutting away of the intervening wall is permissible, which affords increased room for operating. Fortunately, a lingual cavity rarely extends so far as to connect with both a mesial and a distal cavity. When it does, the joining of the three cavities very seriously weakens the crown at the point where the greatest strain occurs. Classes M and N. — These classes include cavities upon either the mesial or distal surfaces connecting with a cavity upon the incisal edge. They usually occur in consequence of the wearing away of the latter surface throun:illy boj^ins at this margin. When, however, the cavity wall extends licncath the gum margin, althouoh the difficulties of operatintr are inereax'd, recurrence of decay is seldom met with, because the conditions favorable to decay are not present there. In the ]ire])aration of these cavities the teeth should have been pre- viously separated in order to afford light and room for excavating, as well as for the subsequent introduction and finishing of the filling. If the cavity extend beneath the margin of the gum the latter should be pressed away by packing the cavity over-full with gutta-percha for a day or two previously. After opening and roughly preparing the cavity the rubber dam should be adjusted and the cavity thoroughly dried, after which the prep- aration can be completed more satisfactorily, as the dryness of the tooth will enable the oj)erator to readily distinguish between sound and un- sound tissue. Whether the cavity be of large or moderate size, simple or difficult in character, the niceties of preparation must receive due consideration. The cervical portion of the cavity should be cut away until a strong sound wall is obtained having no distinct angles, no decalcified tooth structure bordering it, and no checks in the enamel. Should either of the latter be found, further cutting of the wall will be necessary until these defects are entirely obliterated. If the cavity should extend rootward to near the termination of the enamel, it will be necessary to deejien the cavity so as to include this portion, otherwise injury will be liable to result from the fracture of this frail section of enamel during filling. The outline of the cervical wall should be distinctly flattened, as shown „ ,.. „ ,., in FiiT. ISO, A, on accountof the assistance it renders Fig. 150. Fig. lol. . . in filling. The buccal and lingual walls must be dressed to a smooth outline and bevelled, and , .,, , ^ ^— „ should be extended so far toward the buccal and ^ ^ •= lingual surfaces as to free them from the danger of future decay. In Fig. 151 the dark portion represents the buccal aspect of the completed filling somewhat exaggerated. None of these walls should be deeply undercut to assist in either the introduction or retention of the filling, for such undercutting is a source of weakness, but shallow grooves are not objectionable when needed. Starting pits or grooves should not be made in the cervical wall except in rare cases, slight depressions at the axio-gingivft-buccal and the axio- gingivo-lingual angles being sufficient to furnish all the retentive form needed in this portion of the cavity. That portion of the cavity in the sulcus on the occlusal surface should be made flat and also retentive by widening it at its termination, as shown COMPOUND CAVITIES. 197 at A, Fig. 152. Where the occlusal and approximal portions of the cavity meet, the angles should be removed and the cavity well opened so as to afford access and give strength to the filling (b, Fig. 152). Fig. 152. Fig. 153. Fig. 154. Prepared cavity and anchorages. Prepared cavity and anchorages. Fig. 153 represents a compound cavity of this class incorrectly formed. In it moderately sharp angles are seen at the points where the occlusal and approximal portions of the cavity join. In Fig. 154 the black portion represents the floor of the cavity ; a and B indicate the points to which the buccal and lingual walls should be cut ; c and d show the curved form of cavity after the occluso-approxi- mal angles have been removed, while the curved line outside of the cavity indicates the approximal contour of filling, with contact point at H. Fig. 155 represents a compound cavity (mesio-occlusal) in a lower second molar. These cavities differ from similar ones in bicuspids principally in having the occlusal portion of the cavity extend in different directions along the sulci. All of the terminations should be well rounded and in no portion of the cavity should distinct angles be allowed Mesio-occiusai cav- , . ity in lower sec- to remain. Fig. 155. ond molar, pared. Pre- FiG. 156. Class Q. — Disto-ocdusal cavities in either the bicus- pids or molars are not essentially different from mesio-occlusal cavities in the same teeth. Owing to their position they are more difficult of approach, but their manner of preparation and their form are vir- tually the same. Class R. — Occluso-buccal cavities are more frequently met with in the lower than in the upper molars. This is due to the general presence of a pit upon the buccal surface of the lower molars, in which decay by extension reaches so near to the occlusal surface that the occluso-buccal wall is weakened and has to be removed. Coincident with this there is usually a cavity of some size upon the occlusal surface, and the union of the two cavities becomes necessary to insure a satisfactory result in filling them. A common type of such cavity is shown in Fig. 156. The channel connecting the two cavities is usually narrower than either of the latter and also more shallow, thus conserving the strength of the tooth. As, however, the strain upon the walls bordering this channel is very great in mastication they Occluso-buccal cav- ity in lower molar. Prepared. 198 PRKPARATIOS OF CAVITIES. Fig. 157. should he triiniiicd until solidity is olitaincfl, :iud mIso he considerably bevelled f<>i- purposes of" stfeuiitli. Cr.Ass N. — ()rc/iis<>-/lit(/ii(i/ cavities in the l)icusj)ids and molars are of rare occurrence except in the upper first and second molars, where they follow the line of the sulcus extending between the mesio-lingual and disto-lingual lobes. Sometimes the cavity is nearly confined to the occlusal surtiice, running over on to the lingual surface but slightly. In such cases the cavity is easily prepared by simply cutting the occlusal cavity through to the lingual surface, thus giving it a relatively uniform depth at all points. At other times the fissure on the lingual surface will extend farther toward the cervical margin, and the cavity when prepared will have the form of an L, the longer arm, A, represent- ing the occlusal, and the shorter one, B, the lingual por- tion of the cavity (see Fig. 157). Where the extent of decay does not demand it, it would be a mistake to make the floor level of the two portions of the cavity uniform, as the extensive removal of sound dentin would greatly weaken the disto-occluso-lingual cusp. Where extensive decay has already weakened this cusp it is better to amputate it below the level of the occlusal plane and extend the filling over it. Class T. — With the exception of those iniusual cavities which involve the greater portion of the crown of a tooth, the mcsio-disto- ocdusal cavities in bicuspids and molars are the largest in extent of any met with. Being well exposed there is no lack of either light or room in which to operate, and the only difficulty associated with their preparation and filling lies in their size and extent. Their prej)aration is accomj)lished in the same man- ner as those of classes P and Q, except that no special retentive form need be given to the occlusal portion, for with the filling once in place its general form will eecnrc it in position. Fig. 158 represents a typical cavity of this class in a bicuspid tooth. Fig. 158. CHAPTER VIII. EXCLUSION OF MOISTURE— EJECTION OF THE SALIVA- APPLICATION OF THE DAM IN SIMPLE CASES, AND IN SPECIAL CASES PRESENTING DIFFICULT COMPLI- CATIONS—NAPKINS AND OTHER METHODS FOR SECUR- ING DRYNESS. By Louis Jack, D. D. S. The interference of the secretions of the mouth offers a considerable obstacle to the treatment of the teeth. In some in- Fig. 160. stances the flow is naturally excessive, and in all cases it is stimulated by the operative procedures. An excessive flow of saliva is uncomfortable to the patient ; its accumulation also impedes the operation, and interferes with the view of parts by refracting the rays of light. During the preparation of accessible cavities, par- ticularly those of the upper front teeth and the occlusal surfaces, the accumulation may be carried off by the use of a SALIVA EJECTOR, a simple form of which is shown in Fig. 159, which form, or some modification of it, is used where a connection can be made with the water supply, and ordinarily it is used in association with the fountain cuspidors. An- other form, which is connected with a small reservoir of water, is shown in Fig. 160. Either of these forms has a further use for drawing off the saliva in con- nection with the employment of the rubber dam to lessen the dis- comfort of the patient. Fig. 159. Use op Rubber Dam. During the preparation of cavi- ties on the approximal surfaces of the bicuspids and molars where it is essential to have unrestricted 199 200 EXCLUSIOX OF MOISTURE. vicir ami the r.rchislon of blood, the jircsence of which is insej)arah]e from thorougli pivparatiuii of the ciTvioal margins, it is necessary to make use of the KUBiJi:n dam. Wlien used for this j)urpose the material generally becomes imj)airecl hy the action of the instruments in their free use at the cervix ; but the economy of time and the essen- tials of thorough performance of this class of operations warrant the application in many cases during this portion of the treatment. ^^'hen the case is ready for the filling process a new piece of the dam should be prepared, and adjusted with great care to prevent the ingress of the least moisture. "Without this appliance the greatest skill is pow- erless to secure soinid results in large, difficult, or complicated cases. The introduction of this invention has made it possible to execute with gold, operations which previously were impossible ; not the least advantage resulting from its use is that the operator has free use of the left hand to assist the right. Quality of the Rubber. — The quality of the rubber greatly modi- fies the facility of its application. It should be of medium thickness and of light color, as it then absorbs less light. It should be freely extensible and so elastic that when the thumb is forcibly pressed into it it returns to its normal form on the removal of the force. If it re- sponds to this test it will not tear if fairly applied. The size and form of the piece should be such as to avoid encum- bering the face of the patient and to permit the lateral extension to be folded out of the way in such manner as to prevent obstruction of the view. The f«u'm generally best suited is a triangle, Mhich form also permits of its most economical use. For the front teeth the piece should be moderately small ; for the bicuspids and molars the size should be ample and is best adapted when cut from strips about seven and a half inches in width. The selected piece should have holes cut in it of such size as to correspond with the dimensions of the teeth over which it is to pass. AVhen more than one hole is required the holes should be at such dis- tances apart as Mill present a sufficient amount of material to allow for the take-up in the application, so that the strait which passes between the teeth shall be sufficient to allow the edge to be carried upward to form a valve at the cervices of both teeth and not be under such strain as to interfere with the valvular action of the edges of the rubber. At the same time there should be no excess to hamper the view or inter- fere with the placement of the filling material. Attention to the valvular arrangement of the dam at the cervix will avoid subsequent difficulty and will prevent in many instances the infliction of pain in using ligatures except upon the tooth under treat- ment and the adjacent one. The diagrammatic appearance of this valve is sh!>wu by Fig. 161, and in perspective by Fig. 162, a,b,v,d. USE OF RUBBER DAM. 201 Fig. 161. Fig. 163. Fig. 162. h c d Diagrammatic drawing : form of valve. The holes in the rubber may be formed with a punch of suit- able size, which should be forced upon the end of a close-grained piece of hard wood. They may be made with a little practice by drawing the rubber over a round-ended instrument with some force and pricking the rubber at a suitable point with a sharp knife, Avhen a round section escapes. The difference in size of the holes is deter- mined by the distance from the end of the instrument at which the puncture is made. The deter- mination, however, of size and distance is not easily made in this manner. The best appliance for the purpose is the Ainsworth punch (see Fig. 163), with which complete control of size and distance may be easily effected. The Ainsworth punch. 202 EXCLUSION OF MiHSTVRE. The arrangement of the holes in the tii:m^iil:ir piece should dilVcr for each section <»f" the inoiitli. Fig. 1()4 shows a piece for tluMv/fZ/vr/ ineisnts. The figures represent inches. Fig. 1G5 shows the arrangement of holes for the upper bicuspkls and molars. It will be observed the line of holes is not parallel with the upper edge. Fig. 164. Fio. 165. Fiu. 166. 11" y^ A For central incisors. For ui»i»er bicuspids and molars. For lower bicuspids and molars. Fig. 167. For lower front teeth. Fig. 166 shows the arrangement for the l(yu:!er bicuspids and molars. Here, too, the line of holes is not parallel with the edge, to allow for the difference in distance from the commissure of the lips to the ante- rior and posterior holes. Fig. 167 shows the arrangement when the lower incisors and canines are included. Here the line of the apertures is curved. Rv conforming to these arrangements of tlu> openings in the rubber, and by extend- ing the line in conformity with it, as well as l)y increasing the size of the piece, any num- ber of holes may be made, to include any portion or all of the teeth of one cpiarter of the denture when that may be re(inired. The number of a])ertures in the rubl)er should l)e such as to give easy access to the o])eratiou and to permit the free entrance of light. For the anterior teeth five to si.\ holes are necessary, and for the pos- terior teeth from four to si.x as may be needed to secure the al)Ove-stated objects. In general, at least tw^j teeth anterior to the one operated upon, and when admissible the one posterior, should be included. The Placement of the Dam. — When the teeth are not in firm con- tact or when their attachments are flexible the adjustment of the dam is simple. But when the teeth are rigid certain preliminary conditions should be secured. It has been pointed out in speaking of the prepara- tion of the teeth for a series of op(>rations that they should be well cleaned of any deposits which may be upon them and be poli.'^hed on their approximal surfaces. This makes easier the insertion and the application (tf the rubber. USE OF RUBBER DAM. 203 Generally where the case under treatment is an approximal surface the necessary preparatory separation makes easy the immediate open- ing of any interstices near the operation. In cases of extreme fixa- tion of the teeth a piece of rubber dam placed for a day or so in a couple of the neighboring spaces makes it easy to enter the margin of the interstices. The passage of a silver tape with a little benne oil or cosmolin on it often answers as an equivalent means. In the front teeth a thin wedge inserted just above a tight point permits an easy entrance. The preliminary silking of the adjoining spaces, particularly if the silk be coated with cosmolin or its equivalent, also facilitates the passage of the rubber, and for this purpose soaping the under surface of the rubber adjacent to the holes is recommended. At first the novice finds difficulty in making application of the dam, but practice cultivates facility. In general it is better to commence with the anterior hole and proceed posteriorly until all the intended teeth are included. Thus for the left lower teeth the rubber is taken with the index fingers applied to the upper surface, the other fingers to the under surface, and is grasped near the hole for the front bicuspid ; the hole is extended ; the edge of the rubber is inserted in the mesial inter- stice and is carried down to the gum. It is then drawn over the tooth and passed into the next interstice in the same manner. This method is pursued with each tooth until all are included. The passage of the rubber is facilitated by helping it downward by the insertion of floss silk, which is held taut, and with a firm and gently sliding movement the rubber is conveyed toward the cervix. When the most distant tooth is the lower third molar, it is generally best when the cavity is on either side of the last interstice to pass the jaws of a dam clamp through the posterior hole ; the clamp is then made to grasp the tooth, the dam is conveyed to the gum by silking, and the adjustment is then carried forward from tooth to tooth. The same pro- cedure is sometimes applicable with short third molars in the upper denture, or in case any of the posterior teeth are so shaped as not to retain the rubber. When the rubber is adjusted over the teeth the purpose of the dam is effected by directing the edge of the dam under the free margin of the gum. This is done by passing a silk thread around the tooth, and crossing the ends, when by a drawing movement of the thread it travels down the inclined surface of the cervix, carrying the dam with it, thus making a more secure formation of the valve. This method avoids the needless paining of the patient caused by pushing the threads against the gum with instruments. Whenever necessary for securement the ligature should be tied. This should be 204 EXCLUSION OF MOISTURE. done to the teeth on both sides of an iipproxinud cavity. Jt is neces- sary here to place the cervical margin of the cavity in full view and to make certain the exclusion of moisture, which otherwise might pass the valve by capillary attraction. The ligature should usually be passed but once around the tooth and then be tied with a surgeon's knot, the place of the knot being on the outside. \Mion there is much strain the thread may be passed twice around the tooth, but this shoidd be avoided as being more painful and as increasing the bulk of the ligature. To prevent the rubber from displacement by the movement of the cheeks on the posterior teeth when they are long, if after drying the surface a little sandarac or damar varnish is applied at the last inter- stice, the rubber becomes fixed. In cavities extending above the cervix where a ligature cannot be placed above the cervical border of the cavity, other means have to be adopted to obstruct the entrance of fluids. Here the strait of rubber between the holes should be much wider than usual ; the abundant fold may then be forced beyond this margin with a matrix, when, by drying the parts and by the deft introduction of alcohol varnish and suitable wedges, dryness of the parts is attained. In the most extreme cases of this nature the part beneath the normal gum line may be filled with a permanent plastic substance, as described in the section on Lining Cavities (see Chapter IX., p. 218). The Securement of the Dam from Displacement. — When the teeth are short from incomplete development or when their form is tapering from the gum toward the occlusal aspect there is always ten- dency of the rubber to escape, and the contraction of the commissure of the lips tends to the displacement of the dam at the posterior teeth, the latter movement often being sufficient to overcome the friction of the ligatures. When these difficulties arise a clamp is required. The Clamp. — This is an instrument of much value not only as a means of securement of the rubber, but as an adjunct to prevent the Fig. 168. Fig. 169. Dr. Southwick's clamps. Dr. Uuey's clamps. rubber from obstructing the view. Clamps are more especially needed to detain the rubber on the molars and are rarely required for the bicus- pids or the anterior teeth, since, if the foregoing directions are followed, the necessity for their use will l)ut seldom be presented. USE OF RUBBER BAM. 205 Forms of Clamps. — For the molars various sizes and shapes of the " Southwick " and of the " Huey wisdom-tooth clamp " are sufficient for general use. In addition to these " Palmer's set of eight," after the sharp points of the jaws are rounded, will furnish the requisite variety. Fig. 170. Dr. Delos Palmer's set of eight clamps. The Application of the Clamp. — The selected clamp is extended by the clamp forceps to enable it to pass over the molar. It is con- veyed to the middle portion of the tooth, when the inner beak should be brought against the tooth at the gum margin ; then with this point as a fulcrum the outer beak is carried to the cervix on the buccal sm-face. Much pain may be avoided in the employment of this appliance by deft and careful placement. Injury of the gum and needless pain has frequently been inflicted by careless use of force in the application of this appliance. Much of this may be avoided by the previous ligation of the tooth, which will prevent the tendency of the clamp to descend beneath the gum when the necks of the teeth are much inclined inward. When it is necessary to force the clamp against the soft tissues the previous application of a solution of cocain will obtund the tissue and render the application tolerable. The Arrangement of the Dam on the Pace. — This concerns the convenience of the operator and the comfort of the patient. To give easy access and permit the entrance of light, the rubber is drawn aside at each upper corner by dam-holders. The simpler forms of these are sufficient and are more convenient than the more complicated ones when triangular pieces of rubber are employed. In addition a supporter, shown at Fig. 172, passes over the head and engages at each end with the holder. The comfort of the patient is secured by including a nap- kin along with the rubber in the clasps of the holder. The excess of the rubber at each side should be taken up in a fold and secured to the 206 EXCLUSIOX OF MOISTURE. napkin hv (Irossini: pins. Tlu^ suspended part of the nihlxT is kept taut by ])on(l('nt weights. Tlie a])])lieati()n and arrangement of the dam becomes Kkj. 172. bv practice a very sim]ih^ matter, and slioiild not be the occasion of discomfort or pain to the patient. Fig. 171. Design of Dr. Cogswell. A s\iii))()rter. The Use of Napkins. — There are many instances of simple cases in accessible jjositions not of approximal surfaces, when the general flow of saliva can be kept under control by the saliva ejector, where it is not necessary to use a rubber dam. Also for children, when the teeth are too short to ])ermit the correct a])plication of the dam, it is necessary to find other means to control the moisture. Here the reliance is upon napkins, and \\ ith them much skill may be ar('nt sc])ai'atinii uf" tlic lill- iiiij from the borders of tin- cavity. Tlic causes ^vllicIl jtrodiicc this condition are slowly ])roj>;rossivo and arc continuous. This kind of erosion is most marked when contraction takes place, from ineorreet preparation or improper ratio of the metals entering into the formula, or careless manipulation, when capillary defects are liable to oeenr at the mar(2:ins. The most probable hyjK)thesis to account for these observed changes is that the presence of moisture having acitl reaction, by inducing elec- trolvtic action between the imperfectly combined metals, brings about the erosion of the material immediately within the margins. In these eases the exposed surfaces generally suffer little waste, for the reason that they are subject to the continued movement of the oral fluids, but it is often observed that entire fillings undergo a similar gradual loss and disappear. This result is common where there is an excess of gold or mercury. In some instances the above descril)ed action takes place to a limited degree upon the whole surface in proximity with the dentin, when a residue is found upon the filling as well as on the surface of the dentin. The conclusion from these observed facts is that the secin*ement of edge strength depends upon an approximation to the chemical ratio of the elements of the alloy. This would apjiear to be most nearly secured when the material is subject neither to shriidvage nor expansion. Ex])an- sion under some circumstances might ])roduee marginal space and there- fore lead to the same result ; for instance, if in apj)roxinial or buccal cavities the depth were greater at one division than another the expan- sion of the thicker ])art of the filling wo^uld tend to raise the edge sur- rounding the shallow part of the cavity, and would then subject the edge of the filling to electrolytic changes. A related condition sometimes appears when an amalgam filling, quite hard at completion, after some years becomes comparatively soft, which apparently is due to molecular changes. The close conformity of the alloy to the proportions recently estab- lished by Black, and anticipated by the much earlier experimentation of Flagg, furnishes a result that is directly conducive to fixity of form and edge strength when the margins of the cavity are overlapped. This formula is a]i])roximately — silver, 68 ; tin, 26 ; copper, 5 ; zinc, 1. The maintenance of size, form, and strength depends largely, if not entirely, u])on the influence of silver. When the proportion of this element becomes less than 60 ])er cent, of the formula, the tendency to shrinkage appears and holds a nearly direct relation with the diminu- tion. When the ratio of silver "advances above 70 per cent, the expan- sion becomes marked, and at 80 i)er cent, is excessive. THE MINERAL CEMENTS. 215 Lightness of Color. — The means by which this property may be secured have not as yet been well determined and should be the sub- ject of extended experimentation. Some of the so-called white alloys approximate stability in this respect, but the ratios of the modifying metal have not been accurately determined. Amalgam as a filling material is adapted to large cavities in the pos- terior teeth when the margins are too frail to permit gold to be con- densed ; for positions where mechanical force cannot be exerted with efficiency, notably the cavities of the third molar ; distal cavities of the second molar when of large size ; and the lingual cavities of the lower molars. When the teeth are of deficient resistance and when the con- dition of the oral secretions favors the rapid progress of caries these limitations may be extended to cavities where otherwise gold would appear to be a more suitable material. As a material for the filling of the deciduous teeth amalgam possesses superiority over any other substance, for the reasons that it can be intro- duced with less effort than tin and has greater durability than either the mineral cements or gutta-percha preparations ; the exception to its use here being when the conditions prevent retentive formation of the cavity. Concerning the /orm of the caviti/ adapted to amalgam, it is necessary that the retentive formation be equally exact as for gold, since many of the formulas in use undergo slight movement for some time after their introduction, during which there is liability of marginal displace- ment which may lead to the defects treated of under the section con- cerning " edge strength." Amalgam, while presenting in its appear- ance an unfavorable comparison with gold, is capable of rendering important service when every consideration is given to the require- ments governing its successful employment. To attain the best results in the use of the amalgams requires extreme exactness as to the ratios of the ingredients and great care in all the procedures connected with the formation of the cavity, the form of the filling, and the subsequent finishing process. The disqualifications of amalgam are its unsatisfactory color and the unknown character of the composition of the formulas as furnished by the depots of supply. THE MINERAL CEMENTS. Oxychlorid of Zinc. — This material, because of its lacking the quality of indestructibility, is contraiudicated in all exposed situa- tions. It possesses, however, a considerable degree of antiseptic power, and for this reason renders valuable service in deep cavities not nearly approaching the pulp, or even here when the pulp wall of the cavity 216 FILLING MATERIALS. has been })revi(tusly protected by u layer oi" gutta-pereha or a disk of asbestos })aper. In such cases, particularly on occlusal aspects, the cavity may be nearly tilled, leaving a remainder the thickness of enamel to be comjileted Avith o:(»l jiurpose. "When the cavity is deep the layer of cement should be brought to the inner line of the retentive grooves. As soon as hardening takes place the metallic covering may be given. When the shallowness of the cavity will not ])erniit a considerable laver of the cement, a metal ca]) covering the ])ulp wall of the cavity tilled with the cement may be laid in place, the metal of the cap thus sustaining the force. These forms of cavity lining are of great utility, and should be regarded as of importance. Marginal Cavity Lining. — \\'hen cavities are situated on approxi- mal surfaces of the teeth and extend high up on the cervical aspect so as to place them beyond the probability of efficient service with metal foils, and when the lateral walls of cavities are weak either by their thinness or by instability from defects of structure, some form of "lining" is necessary. In the one case, to ensure certainty of per- formance at the cervix ; in the other, to prevent injury. For the cervical i)art the choice is between (1) tin, (2) a combination of tin and r/o/d, and (o) (iinalgam. Tin has the objection when superimposed above gold tiiat it suffers waste, in most instances by electrolysis, to which the mixture of tin and gold is not liable. This latter combination — made by folding a layer of the tin within the gold foil — appears to give the tin protection. This combination is more plastic and more yielding than gold alone, and permits adaptation and consolidation in places difficult of approach. CAVITY LINING IN RESPECT TO PROXIMITY OF THE PULP. 219 When used in connection with a matrix thorough consolidation may be effected without injury to tlie cervical margin Avhen the tissues are not dense. When the color of a lining at the cervix Avill not be objectionable, a quick-setting amalgam answers extremely well, and may at the same sitting be followed by the completion of the operation with gold. In this situation, whatever the lining material, close conformity w^ith the lines of the cervical form of the tooth must be assured. In many instances the lining and the completion of this portion of the filling should be effected before the rubber dam is placed, when the lining portion is for the time being considered in its relations as a part of the tooth. When it is necessary to use the mineral cements on approximal sur- faces of the posterior teeth for temporary purposes, the cervical border should be covered with a line of gutta-percha stopping, to protect this ^ vulnerable part of such fillings from the exposure of this border by the solution to which they are there liable. Lining- Lateral "Walls. — For this purpose choice should be made of zinc phosphate, since it has the required strength and enters into the necessary adhesive union with the margins to give the required secur- ity. The layer should be kept within the extreme outer border of the cavity, to permit the metal filling to overlay the margin of the enamel. When the cavity is deep the retaining groove may be formed in the cement. A general summary of cavity lining is, that this procedure is required in proportion to the difficulty of effective approach, and for the safe treatment of teeth below the average of structural quality. CHAPTER X. TREATMENT OF FILLINGS WITH RESPECT TO CONTOUR, AND THE RELATION OF CONTOUR TO PRESERVATION OF THE INTEGRITY OF APPROXIMAL SURFACES. By S. H. Guilford, D. D. S., Ph. D. The treatment of a cavity of decay by filling must have a tAVofold object in order to subserve its best purposes : first, the . restoration of the affected part to a healthy condition ; and second, the prevention as far as possible of a recurrence of the lesion. The first is accomplished by the removal of all disintegrated tissue and the perfect filling of the cavity with a suitable and durable material. The second demands for its success a proper understanding of the cha- racter of the surfaces operated upon and their mechanical, physio- logical, and pathological relations. While the simple filling of a cavity, if properly done, will generally prevent the extension of decay on ex- posed surfaces, the same operation on surfaces less favorably situated may utterly fail to subserve the desired end. The contiguity of the approximal surfaces of teeth greatly favors the retention of food and the harboring of micro-organisms, while at the same time it prevents the free cleansing movement of saliva be- tween them. For these reasons such surfaces, though originally per- fect in their continuity, are attacked by caries more frequently than any others, except the occlusal surfaces where continuity is broken by fis- sures and pits. When once affected by caries, their restoration by fill- ing is difficult owing to their inaccessibility, and while the operations on this account often lack the perfection that would otherwise be secured and the fillings consequently fail, the recurrence of decay is due to the persistence of the same influences that brought about the initial lesion. This being the case it is obvious that the original conditions must be changed if immunity from future decay is to be expected. This principle was early recognized, and the first attempt to alter the conditions was by filing or cutting the approximal surfaces so as to free them from con- tact, on the principle of " no contact, no decay." Where all of the teeth were thus separated decay was temporarily checked, although at the cost of great loss of masticating surface, much disfigurement, and subsequent serious injury to the gum and pericementum. 221 222 THE SELF-CLEANSL\G SPACE. WhvYv only :m occasional ^pacc of this character was niado, the o})eration proved a failure because in a short time, through the pressure of adjoinint;- teeth and altered occlusion, the mutilated teeth would a^in l)e hrouoht into contact and the opportunity for decay be increased a hundredfold. With the recurrence of decay, cutting or filing would again have to be resorted to until but little of the teeth remained, and they M'ere eventually lost. On account of its unfortunate results the method was for a time abandoned, but in 1870 it was revived in a modified form through the teachings and writings of Dr. Robert Arthur. His method consisted in altering the form of the approximal surfaces of teeth by filing or grinding so as to change the point of ap- proximal contact from near the occlusal surface to near the cervical margin. This not only changed the normally convex a])proximal sur- face into a fiat or plane one, but was also supposed to free it from further liability to decay by preventing the retention of food d6bris and render- ing the surfaces and spaces " self-cleansing." The method was measur- ably adopted by numbers of conscientious practitioners as a means of obviating: a difficultv hitherto unsuccessfullv combated. In a short time, however, it was discovered that its promise of success was not being realized, and it was also gradually abandoned. Its failure was due to its being wrong in principle, for, while it seemed to offer tem- porary relief, its after results were most disastrous. Bv leaving a shoulder near the cervical margin the point of contact was simply transferred from one point to another with the result that the latter point was far more liable to caries than the former one, owing to its position. ^Fcn-e than this, the exposed dentin on the cut surfaces, lacking the natural j)roteetion of the enamel covering, was apt to be sensitive, and the food crowding into the space and pressing upon the gum rendered it hyj)ersensitive and eventually caused its recession. The discomfort following this operation, together with the increased lia- bility to decay resulting from it, were sufficient to condemn the method and cause its abandonment. These failures to secure freedom from decay by an unnatural altera- tion of the natural forms of approximal surfaces led to a more carefnl investigation of the causes responsible for its recurrence on these surfaces, and the gradual adoption of more rational and scientific methods for its prevention. It was apparent to even the most casual student of compara- tive dental anatomy that the number and kinds of teeth found in the jaws of man, their arrangement in the arches, and their general form, were all such as to best subserve the wants and needs of the individual, but the more minute points of their external anatomy, their interdepend- ence and relation to one another, and the conditions productive of caries had not previously been carefully inquired into. Under the old belief NORMAL CONTOUR IN RELATION TO CARIES. 223 that contact caused decay it was thought that decay upon approximal surfaces always began at the point of contact and that this was due to fermentation occurring in food debris retained there. Investigation proved, however, that the points of contact between teeth were not only free from decay, but more or less polished from slight motion of the teeth in their sockets, and that approximal decay always began jugt above the contact point, that is, slightly nearer the gum margin. It was further noted that the normal contact of teeth on their approximal surfaces, which was formerly supposed to be essential only for mutual support, was equally necessary for the protection of the tender gum tissue from injurious pressure of food in mastication. Finally it was observed that those portions of the crown of a tooth that were beneath the gum margin or those above it that were constantly covered by saliv^a (as on the approximal surfaces near the gum) were always free from the beginnings of decay, and that the approximal and buccal or lingual surfaces, when faultless in structure, were first attacked by caries on a line corresponding with the point to which the fluids of the mouth usually rose. An explanation of this peculiarity was found in the fact that the saliva is usually alkaline and consequently protective of the parts covered by it, but at its surface, in a state of rest (as in sleep), this condition of alkalinity is changed to one of acidity — the calcium salts are dissolved and decay is begun. Furthermore, the micro-organisms which bring about fermentative changes in the debris of carbohydrate food in the mouth produce lactic acid, which is a solvent of the inorganic constituents of tooth substance. This action takes place more readily on surfaces not normally covered by saliva, and in the protected locations not subject to the mechanically cleansing action of the tongue and buccal walls. As a result of the foregoing observations and investigations it became apparent to the mass of intelligent workers in the field of operative dentistry : 1st. That the natural form or outline of each tooth was the best for its particular function, and that to materially alter it was to lessen its usefulness and hasten its loss. 2d. That contact of ad- joining teeth was essential both to the comfort of the individual and the durability of the organs. 3d. That inasmuch as the teeth originally decay in spite of their natural form and contact, some plan would have to be devised by which, in their repair after decay, liability to a recur- rence of caries would be greatly lessened if not entirely prevented. To fulfill these requirements there was but one course left to pursue, namely, to fill approximal cavities in such a way as to restore the original contour of the surface, and, in all cases where the extent of decay was sufficient to warrant it, to extend the cavities so far over upon the buccal and lingual surfaces as to bring the enamel margins within the range of protective influences. 224 CAPILLARITY OF APPROXIMAL SURFACES. The rationale of original antl recurring deeay upon approxiraal surfaces is readily made apparent by considering certain facts and prin- ciples of physics. When a tube is inserted in a liquid capable of wetting its surface the liquid will rise to a higher level within the tube than the surface level of the surrounding liquid. The force which produces this result is known as capillary attraction, and is explained upon the principle of " surface tension of liquids." If, instead of a tube, two rounded or flat plates are immersed in the liquid, the same rising of the fluid between them will be noticed. The smaller the tube, or the nearer the two plates are together, the higher will the liquid rise. Applying the principles governing these facts to the teeth and con- sidering them as bodies immersed in a liquid, it will readily be seen that if the approximal surfaces of the teeth were parallel and close together the fluids of the mouth would rise to a higher level between them and cover more tooth surface than if they stood farther apart, and being retained in this narrow space with little opportunity for motion they would assume an acid character and destruction of the tooth tissue begin. This is what takes place upon approximal surfaces made flat by filing, and will occur whether fillings have been placed in such surfaces or not. Normally, however, the crowns of the human teeth are more or less convex upon their approximal surfaces and touch each other only at the point of their greatest transverse diameters, which is near to and just above the occlusal surface. From this point their diameters gradually become less until they reach the cervical border, where they are smallest. This leaves a triangular interdental space Avith the base of the tri- angle at the gum, as shown in Fig. 176, in which the saliva will rise but a short distance owing to the se])arati()n near the gum and the consequent lessening of the capil- lary attraction. For this reason teeth preserving their normal forms are less liable to approximal decay than they could possibly be under any Showing normal contact of otllCr COuditioUS. teeth The earliest treatment of approximal sur- faces with a view to the prevention of caries consists in gaining access to them by wedging, and if found to be superficially aifected by caries the removal of the injured structure and the perfect polishing of the surfaces. When cavities of moderate size are discovered they should be care- fully prepared and filled, preserving the original contour as far as possible. Decay may recur, but it is less likely to do so with advan- cing age, increased density of tissue, and proper prophylactic treatment. CONTOURING AS A PROTECTIVE MEASURE. 225 Where the decay is of larger extent, however, we have it in our power to make such physical change in the parts aifected as to render future immunity from decay reasonably certain. First, it is necessary to separate the teeth well by wedging, to so enlarge the cavities as to bring their lateral margins well out upon the lingual and buccal surfaces, and to extend the cervical margins of the cavities down to or beneath the free margin of the gum. Next, the fillings must be carefully inserted, built out to fully restore the original contour, and most perfectly finished. When this has been done and the teeth have returned to their former positions the approximal surfaces will be in a better condition to resist the influ- ences of decay than they originally were, and while the cervical border of the filling is protected by being constantly covered by saliva the lateral borders are so far out upon their respective surfaces as to be sub- ject to the cleansing influences of the lips and tongue. In addition to this, and scarcely less important, the restoration of contact on the approximal surfaces aflbrds normal protection to the tender gingivae by preventing the lodgment and pressure of food upon them. The contour method of filling, based as it is upon physiological, anatomical, and mechanical principles, has become the accepted method of operating. Experience has proved it to be the only rational method of treatment of approximal surfaces, for by it we secure all the desir- able conditions of preservation of the natural outline of the teeth, necessary contact, immunity from future decay, and protection of the gum margins. Its practice involves some sacrifice of healthy tooth structure along the buccal and lingual aspects, as well as greater ex- penditure of time in filling and finishing, but the results compensate for both of these. To properly perform the operation of filling and restoration of approximal contour requires not only manipulative skill of a high order, but also an artistically trained eye in order that the restoration may in all respects correspond both in extent and form to the original outline of the tooth ; both of these requisites will be acquired through frequent repetition. In certain cases, as where the teeth originally were not quite in contact, the contour may often be advantageously exaggerated, sometimes considerably, in order to close the space, but it should never be less than normal or the result will not be satisfactory. In the filling of an approximal surface next to a space, as where a tooth has been lost, the necessity for full restoration of contour does not exist and is not absolutely demanded, although a more artistic result will be secured by its performance in all cases. 15 CHAPTER XI. THE OPERATION OF FILLING CAVITIES WITH METALLIC FOILS AND THEIR SEVERAL MODIFICATIONS. By Edwin T. Darby, D. D. S., M. D. In the selection of a filling material the operator should consider the character of the secretions of the oral cavity, the position of the tooth to be filled, the extent of the diseased area, the physical structure of the tooth, and the strength of the cavity walls. A filling material must possess certain inherent qualifications, the most important of which are adaptability, indestructibility, non-conductivity, hardness, absence of shrinkage, harmony of color, and ease of manipulation. All of these are not to be realized in any one material, and yet some of the more important are to be found in a single metal or in a combination of metals. Lead possesses the quality of softness and is easy of adaptation but is readily oxidized when exposed to the air or the secretions of the mouth. Likewise tin possesses characteristics, such for instance as duc- tility and softness, low conducting power, and the ease with which it may be manipulated, which place it in the front rank as a preservative of carious teeth, but it is inharmonious in color, and its very softness, which is so desirable in manipulation, is an obstacle to its use upon surfaces where there is much attrition. The zino phosphates, which are composed of zinc oxid and phosphoric acid in solution, form a com- bination which at first attracted the favorable attention of the dental surgeon as possible substitutes for metallic foil fillings. They possess, owing to their plasticity, ease of manipulation, harmony of color, com- parative non-conductivity, and absence of shrinkage, many desirable qualities, but are lacking in one essential qualification, namely, inde- structibility. Gold. Gold, which has been used for about a century, has fulfilled in a more marked degree than any other material or combination of materials the requirements sought for in a filling for carious teeth. It has one or two objectionable features, such as high conductivity of heat and inhar- monious color. 227 228 Tin: uPEiiATios or I'UJ.iSd ca\ith:s. Too imu'li stress cannot he laid ujxtn the uncstioii of" its pnrity it' tli(> best results arc to he ohtaincd from its nsc. NN'liilc it is claimed hy manufacturers ot" d-'iita! Ljiild i'oil that tiieir products ai'c ahsohitelv free from alloy, it is nevt'rtheli-ss true thai hut few specimens of dental foil show a fineness ahove !H)!>. W this standard wci'c always attained the operator would have little cause for complaint. So small a |)ercentage of alloy as 1 in lOOO would not materially affect the workinji; (pialitics of the product, but when this is increased to 4 or (j parts ])er lOOU it manifesto itself by harshness and intractability under the instrument. Great care should be exercised in the })reparation of the foil, since so much depends upon its purity and cleanliness. For a detailed description of the process of manufacture, from the injjot to the beaten and annealed foil, the reader is referred to an article by a practical foil- maker.' In former times the dental surgeon was restricted to one form of gold for filling. This was foil ranging in thickness from 4 to 10 grains to the leaf, but as the requirements of the operator broadened the art of manufacture increased, and new pre[)arations were oficred, until to-day the most fastidious can find such as will please ids fancy : foils ranging in weight from 4 to 120 grains to the leaf; cylinders of various sizes and composed of non-cohesive and semi-cohesive foil ; cohe- sive blocks prepared for use ; rolled gold, varying in thickness from No. 30 to 120, and crystal gold possessing great cohesive properties. These are the more important forms in which gold is offered the operator at the present time. Before entering upon a description of the classes of cases where each of these seems best adapted, it may be well to describe somewhat in detail the peculiar qualities which each form of gold presents when subjected to clinical use. Soft or Non-cohesive Foil. — Prior to 1854, when l>r. Robert Arthur discovered and promulgated the desirability of cohesive foil in certain cases, the operator used gold which possessed very low cohesive properties. Used as it then was, in the form of large rope, tape, or as cylinders, the property of cohesion would have been a serious objection, since there would be constant danger of the mass clogging and bridging in the cavity, and the cause of many unfilled places along the cavity walls. The terms soft and Jtdrd, when used to designate the kind of gold, are misleading, since all gold foil prepared from pure gold or gold that is nearly pure possesses great softness under the instrument. The distin- guishing characteristics between the two kinds of gold are the inability to make a certain kind of foil cohesive when exposed to a reasonable ' American System of Dentistry, vol. iii. p. 839. GOLD. 229 degree of heat, and the ability to render another make of equal purity- cohesive by the application of a similar degree of heat. It has been claimed by some manufacturers of dental gold foils that they are able to procure from the same ingot samples of non-cohesive, semi-cohesive, and extra-cohesive gold, attaining these physical properties of the mate- rial without alloying with other metals. This has led to the belief that, since absolutely pure gold possesses inherent cohesive properties, some metallic salt or other foreign substance has been deposited upon the surface of the leaf of non-cohesive foil which has the power of pre- venting the union of the surfaces of the foil when contact is sought. It has been surmised that a thin film of iron has been deposited upon the surfaces of the leaf of non-cohesive foil, for the reason that if a leaf of such foil be melted into a globule, it presents a reddish brown appearance, which is not true of the leaf of cohesive foil when melted as above. Much of the so-called non-cohesive foil offered for sale is not, strictly speaking, of this variety, as the application of moderate heat will render it quite cohesive. It possesses the softness peculiar to pure gold foil, but it should not be classed with the variety which does not weld with other particles of the same metal except when subjected to great heat. It has been claimed by some that non-cohesive foil has no place in dental practice — that any tooth which can be filled with gold may be filled with cohesive foil. This statement may be true in the main, but it is also true that many teeth having strong cavity walls can be just as well filled where a large portion of the filling is made with non-cohe- sive foil, and with a great saving of time. Adaptation, not hardness, constitutes the saving quality in cavity filling. As most non-cohesive foil is prepared in the form of sheets and is placed in books containing one-eighth of an ounce, the operator is compelled to prepare it in some form suitable for introduction to the cavity. The size and shape of the cavity will be some guide as to the best method of preparing the gold. The narrow tape, the mat, the tightly rolled cylinder, and the roll or rope are the forms best adapted for the use of non-cohesive gold foil. The tape is best made by taking one-half or one-third of a leaf of No. 4 or No. 5 foil, laying it upon a table napkin of medium size folded square as it comes from the laundry ; the napkin is then taken in the palm of the left hand, and the foil spatula is placed in the middle of the piece of foil ; the hand is then closed tightly, thus folding the nap- kin, likewise the foil, upon the sides of the spatula. This process is repeated until the tape is one-eighth or one-sixteenth inch in width (Fig. 177). ^30 THE OPERATION OF FILLING CAVITIES. If iiiatx arc rcHiuired, the foil may he iokled twice or three times aud then fohled h'lijrthwise upon itself until mats of any thickness are pro- duced, as shown in Fig. 178. * AVhen non-cohesive cyHnderii are desired, it is better for the operator to make them rather than depend upon the ready-made ones as prepared by the mamifacturer, since these are usually loosely rolled and more or less cohesive. The tape is quickly made into the cylinder by rolling it Fig. 177. Fig. 178. Tai.o> til' j^'olcj loil. gs Mats of gold foil. upon a five-sided broach to the desired size. The depth of the cavity is a guide to the widtli •>!' tlic tape, and the width of the tape determines the length of the cylinder. These should be somewhat longer than the depth of the cavity. The manner of introducing and condensing will be described later when special cases are under consideration. The roll, or " ro})e " as it was formerly called, is made in the ft>llowing ■wav : A leaf or half leaf or a third of a leaf of Ibil is rolled between the goM foil. thumb and finger until a roll of UKjderate density is obtained. As foil is contaminated by contact with the moisture and surface impurities of the hands, it is better to avoid such contact as much as possible. This can be completely attained by rolling it upon the little device shown in Fig. 179. Any operator can make one of these by taking two pieces of thin board, such for instance as the lid of a cigar box, and fastening to the two pieces with glue a piece of white kid about eight inches in GOLD. 231 length, and in width equal to the sheet of foil. Two little drawer- knobs of ebony should be inserted into the centre of each of the pieces of board. These act the part of handles for holding the appliance. The gold is then placed upon the kid strip between the two pieces of board, and by bringing the two surfaces of the kid in contact the foil is rolled between them. The undressed surface of the kid should be the one upon which the gold is rolled. Ropes thus made may be cut in lengths to suit the size of the cavity to be filled, and, as gold thus pre- pared has great softness and ease of adaptation, it may be inserted in quite large pieces if plenty of condensing force be applied to it. Cohesive Gold Foil. — All gold which has been refined by any of the ordinary methods and is in a pure state may be said to be cohesive. Nor is absolute freedom from alloy an absolute necessity. It has been shown that softness is dependent upon purity, but a foil may contain quite a percentage of silver, copper, palladium, or zinc, and yet its cohesion may not be impaired. It may also be alloyed or combined with platinum and not lose its cohesive properties. It is, however, desirable that cohesive gold be pure, since the smallest percentage of alloy destroys its softness. When two sheets or laminae of freshly annealed foil are brought into contact and slight pressure is applied, they form a permanent union and are practically inseparable. It is this property in gold to which the term cohesive has been applied. But this property is soon lost by the occlusion of gases or impurities of any kind which may be deposited upon the surface of the gold.^ Experiments have demonstrated the fact that if the gold be sub- jected to the fumes of ammonia, hydrogen, hydrogen carbid, hydrogen phosphid, or sulfurous acid gas its cohesive property is quickly de- stroyed, but this property may be restored by heat except in the case of sulfur or phosphorus fumes. Hence the importance of excluding the gold as much as possible from the atmosphere, especially during the winter months when gases arising from the combustion of coal are most liable to be present in the operating room. Dr. Black has shown that animoniacal gas has the power to prevent the deleterious influence of other gases, and recommends that the foil be subjected to the influence of carbonate of ammonia by keeping it in a drawer with a bottle of that salt. The advantages of cohesive foil cannot be overestimated. With its introduction in 1855 began a new era in the possibilities of saving cari- ous teeth. Operations which were deemed impossible by the use of non-cohesive foil were made comparatively easy by the intelligent use of cohesive foil. The restoration of broken-down or badly decayed ^ G. V. Black, Dental Cosmos, vol. xvii. p. 138. '>:V2 Tin: ol'KJlATloX or FUJJXa ('AVITIKS. teeth became the common practice in the hands of the skilfnl, and niod- ern methods of practice coupU'd with intelligent use of this form of vTiAiX have made it possible for the operator of iiKxh in times to do that which the earlier practitioner deemed impossible. The beginner, iiowever, must not lose sight of the fact that cohesive foil cannot be worked after the same methods as non-cohesive foil. To use cohesive foil in the form of mats or cylinders or in tightly rolled ropes would mean inevitable failure in adaj)tation. The very property which renders it valuable in the restoration of broken-down teeth and in surfacinir is the one which would condemn it if used carelesslv in the interior of inaccessible cavities. Non-cohesive gold may be introduced into a well-shaped cavity in large masses, and because of its softness and ease of adaptation may be made to touch all points of the cavity walls if persistent pressure be applied. On the contrary, cohesive foil should be introduced in small pieces, the first of which should be well anchored in a retaining pit oY groove and each subsequent piece welded thereto. There arc several modes of preparing the beaten cohesive gold foil for the cavity, and good results are obtained by either of the following methods. A loosely rolled rope made of a quarter sheet of No. 4 or 5 foil may be cut into lengths varying from one-eighth to one-quarter of Fig. ISO. e Ribbons and .-trips. cl an inch, and after annealing carried to the cavity upon the point «^f the plugging instrument. Or a leaf may be folded with a spatida four GOLD. 233 times, making a broad ribbon, which may be cut either lengthwise or crosswise of the ribbon in pieces one-sixteenth or one-eighth of an inch in width (see Fig. 180). This is a very convenient manner of working cohesive gold. Or the heavier foil up to No. 20 or No. 30 in thickness may be cut in strips of a single thickness and of the widths above indi- cated, and after annealing may be packed into the cavity — the essential idea being ever in mind, that but a small quantity of the gold shall be under the instrument at a given time. Cohesive gold which has been rolled instead of beaten to the desired thickness is much prized by some. It has been asserted that greater softness is obtained when gold has been thus prepared. Such gold should not be more than No. 20 or No. 30 in thickness to insure the best results. ' It should be cut into narrow strips and after annealing be folded back and forth as rapidly only as each previous fold has been well condensed. Good results are only attainable if each lamina be thoroughly welded. The loosely rolled cylinders and blocks which are prepared by some dealers and offered as cohesive gold are usually but slightly cohesive, and if used in this form, without re-annealing, may be packed in the interior of cavities without danger of clogging, but if freshly annealed they are contraindicated, since there is more or less danger of imper- fect union of all particles of the gold. It is questionable whether the larger sizes are admissible when the filling extends beyond the cavity walls and great solidity is an essential factor. Crystal Gold. — This form of gold was introduced by Mr. A. J. Watts in 1853, and as prepared at the present time is one of the best preparations of cohesive gold. When first brought out the method of manufacture was faulty, since it was difficult or impossible to rid the spongy mass of nitric acid which was used in its preparation, but since Mr, Watts adopted electrolysis instead of chemical precipitation the objectionable features no longer exist. Gold thus prepared manifests great cohesive properties, and when used with care as beautiful opera- tions can be made with this gold as with any form of cohesive foil. The operator should not lose sight of the fact that the gold is to be intro- duced into the cavity in small quantities. Should failure attend its use, it would doubtless be from the attempt to introduce it too rapidly. Gold of this variety comes in bricks containing one-eighth of an ounce each, and is either torn apart in irregular-shaped pieces or cut by means of a razor into small cubes. This gold should be excluded as much as possible from the atmosphere and when used should be well annealed, although when recently made it is quite cohesive. There is no prepara- tion of gold better adapted for starting fillings in shallow or irregular cavities, or for surfacing fillings. Many operators make use of it always for starting and for finishing fillings. 234 THE OPEJiATloS OF FILLING CAVrVIES. Crystal Mat Gold. — Tliis is nnolhcr form of crystal gold, and differs from that ])i-cviously dcscrihcd in that it presents a more compact form, the crystals appearing smaHcr and matted together. It breaks and crundjles under tlie instrument to a greater degree than the other, and possesses no desirable ([ualities which the othleted. It will be shown later on, when considering the various types of cavities to l)e filled, that in small cav- ities of simple shape the gold ])rcpared in the form of tape is best suited, whereas in compound cavities or those of greater size the gold may be introduced in the form of comjxict cylinders or blocks. When it is desirable to use a combination of non-cohesive and cohe- sive gold, the former is generally introduced first and the cohesive is in- corporated with it by driving or forcing layers of cohesive into the non- cohesive. This is best effected by using single layers of heavy foil or rolled gold of a thickness equal to 20, 30, or 40 grains to the leaf. If the filling is to be made of but one kind of gold and that the cohesive varictv, both hand pressure and percussion l)y means of the mallet may advantageously be employed. The operator who has learned to combine the two forms of gold and is not restricted to eitiun" method of packing is best qualified for the requirements which are presented in general practice. Perfect adaptation to the walls may be effected by either method, but gn^ater celerity and the attainment of eqnal excel- lence mav be reached by combining the two. Plugging Instruments. — In the selection of instrnments fir pack- ing gold the operator should have a sufficient number to meet his every need. Thev should be of such a variety of patterns that every part of every cavity, however remote, can be reached with ease. It is a mis- taken notion that a large number of instruments (if well selected) is confusing. Tlie operator should study his instrnments and know their uses as thoroughly as he knows the letters of the alphabet, and if this be done and they be arranged in an orderly manner in his case, the con- fusion will be manifest in their ai)sence, not in the possessit)n of them. For ])acking non-cohesive foil none are better adapted than the set shown in Fig. 182, made from patterns furnished by Dr. B. J. Bing. INTRODUCTION OF THE GOLD. Fig. 182. 237 14 15 16 17 Dr. Bing's set of pluggers. 1 his set should be supplemented by a small and a medium ized foot-shaped condenser (Fig. 183j, for packing -p^^ jgg rliuders, mats, or blocks against the cervical wall. The handles of instruments used for packing T on-cohesive foil should be of such size that they can be grasped firmly in the hand. When made of wood they are light in weight and agreeable to touch. Plugging instruments should have as few curves and angles as is consistent with the ability fto reach all points in the cavity. As these are multiplied, direct force is sacrificed. The point of the instrument should be as nearly as possible in a line with the shaft. Deviations from this rule are sometimes necessary in order to reach all points in the cavity. Most plugging instruments have serrated points and are used for all forms of gold. As a rule these serrations should be shallow, and when cohesive gold is to be employed they should be only sufficient to prevent slipping, as gold that is quite cohesive packs as readily with smooth points as with rough ones. It is not definitely known when packing gold by percussion was first suggested, but the idea is quite generally accorded to Dr. E. Merrit of Pittsburg, who as early as 1838 used the hand mallet for condensing 238 THE OPERATfON OF FILLING CAVITIES. Vu:. 185. Fig. ISO. Fig. 184 Snow and Lewis auto- matic mallet. The Abbott mallet. S. S. White electric mallet " Xo. 2.' Founded on the " Bonwill." INTRODUCTION OF THE GOLD. 239 the surface of fillings which had been introduced by hand pressure. The first mallets used were of light weight and were made of wood or ivory. As the method became more general, heavier mallets were em- ployed, and those made of lead, tin, various alloys, and steel found much favor. Before the introduction of rubber dam for excluding moisture one hand of the operator was employed in holding the napkin, and it became necessary to have an assistant at hand to do the malleting. This led ingenious minds to discover some means of percussion besides the hand mallet, and several spring instruments known as automatic pluggers were introduced. The Snow and Lewis, the Foote, and the Salmon found greatest favor, and all of them were good of their kind. The accompanying cut (Fig. 184) shows the Snow and Lewis Automatic Mallet as made at the present time. When pressure is applied to the point of the instrument a spring is liberated which throws a plunger forward with great force, which is expended upon the gold beneath the point. The impacting quality of this blow is not excelled by any of the mechanical devices in use. It is so constructed that a light or a heavy blow can be given at will. The operator will do well to adjust the instrument for light blows when using it in close proximity to frail or delicate walls, as there is more or less danger of fracturing them. Instruments of this class are not well adapted to packing gold in the posterior teeth of the lower jaw, as the blow is delivered at a more or less acute angle, and unless care be exercised when the operation is nearing completion the plugger point will slip from the surface of the filling and wound the soft tissues. Another instrument of this type devised by Dr. Frank Abbott (see Fig. 185) has a socket at either end of the hand-piece, the one giving a pushing and the other a pulling blow. The latter is serviceable for condensing gold upon distal surfaces. The ELECTRIC MALLET is ouc of the most ingenious devices em- ployed in dentistry. The first practical application of electro-magnetic force for dental malleting was made by the late Dr. W. G. A. Bon will. Its latest development is shown in Fig. 186. This instrument has found great favor among dentists for packing cohesive gold . Its blows are delivered with great rapidity and with such force that great solidity is attainable. A pair of electro-magnets transforms the electric cur- rent into electro-magnetic force, which is transmitted to the hammer. The electric current is furnished by a Bunsen or Partz battery, or the controlled current from a dynamo or storage battery can be used as the motive power. The direct dynamo current of 110 volts can be so modified by the use of a rheostat that its use may be employed, and the trouble incident to keeping a battery charged avoided. In the hands of a skilful operator there could be nothing 240 THE OPERATION OF FILLING CAVITIES. better tor jnicking cohesive gold. The best results are obtuiiietl bv its use wlien tlie gold is prepared iu thin lani- inte or where a single thiek- ness of heavy foil or rolled gold is employed. Considerable experience is necessary to enable the operator to use this instrument with satisfaction to himself" and his patient. If the plngger point be pressed hard against the filling, the blows, which are delivered with great rapidity and force, become painful and dis- tressing and there is also danger of chipping the cavity walls. The better plan is to hold the point slightly away from the surface of the filling and allow the momentum which is given the instru- ment by the falling armature to complete the union of the various pieces of gold. The ENGINE MALLET (scc Fig. 187) is intended for use upon the dental engine. It is made with a slip joint and can be applied in place of the hand-piece to nearly all of the dental engines in use, although it is best adapted to one of the " cord " engines because of the greater freedom of action. The instrument siiown in the illus- tration embodies many improvements in con- struction which have been suggested by various operators since the " Bonwill mechanical mallet," on which it is based, was introduced, and a point of relative perfection has been reached where are combined great efficiency with compactness and lightness in handling. It will be seen by the illustration that the essential feature of this in- strument is a revolving wheel having inserted in its periphery a hollow cylindrical steel roller. This constitutes the hammer. It gives a " spring," not a " dead " blow, as it is held to its position by a stiff steel spring. The roller revolves slightly in its socket at each contact with the plunger. When the engine is run at ordinary speed the small wheel revolves with great velocity, deliver- ing upon the head of the plunger as many as fif- INTRODUCTION OF THE GOLD. 241 teen blows per second. The force of the blow can be modified at will by an extremely simple contrivance, as follows : The interdigitations seen around the upper end of the sleeve are held together by means of a spring attached to the sleeve. Pulling the sleeve away from the head against the spring, and revolving it to the right or left, raises or lowers the head of the plunger. Upon releasing the sleeve the spring at once throws it back to engage with the head, and the blow is heavier or lighter, according to the direction in which the sleeve has been revolved. The impacting power of the blow from this is great, and in the hands of an experienced operator a large quantity of gold can be con- GSS Fig. 188. £m^!2 fciiiMB Cuiuis EuimS E":"::::ki! * Webb's set. ijilffflj" Chappell's set. densed in a short space of time. AVhen cohesive gold foil is employed smooth oval points may be used with most satisfactory results. The point should not be pressed hard against the filling, but a skimming or smoothing motion given to the instrument. The surface of the filling when thus packed has a polished or planished appearance as if done with a hand burnisher. Such fillings are usually of great density. There are other mechanical mallets intended for use on the engine which have what is known as a " cam " movement. They are not, 16 242 TlIK OVKRATIOX OF I'lLlJyu CAVITIKS. strictly spoakin. It is usually necessary to pack the gold in these cases almo.st entirely by hand pres- sure because of the inaccessible situation of the cavity. Incisors and Canincx. Class D. — Cavities upon the labial surfw-cs of the incisors and ca)dnes situated at or near the gingival border of the gum were formerly the source of much annoyance to the dentist when gold was the material selected for filling. The principal difficulty was occasioned by mois- SIMPLE CAVITIES ON EXPOSED SVPFACES. 245 ture, either iii the form of blood or serum from the wounded gum or mucus from the follicles situated along the mucous surface. Since the introduction of the rubber dam this difficulty has been greatly modified. But when the cavity extends somewhat above the nor- mal gum line there is more or less difficulty in keeping the rubber above the gingival border of the cavity. This is best done by taking a straight instrument the point of which has been made very sharp by rubbing it upon an Arkansas hone. The dam is then raised well above the cavity border and the point pressed firmly into the cementum and held with the left hand throughout tlic . Till Woodward clamp. operation oi nlhng the cavity. A very neat and valuable device in the form of a clamp has been introduced by Dr. W. A. Wood- ward for this purpose. It is shown in Fig. 196. The dam should include not only the tooth to be filled, but several on each side of it. With the left hand it is stretched above the margin of the cavity, while with the right hand the two little points on the bow of the clamp are pressed firmly into the cementum above the cavity. The clamp is then made secure by turning the set-screw. This clamp when well seated rarely moves, and the operator feels that this difficult operation has become a simple one. There are cases, however, where the decay has followed the receding gum or extended beneath it to such an extent that the clamp cannot be used. To overcome this difficulty the gum should be slit and a " Mack " screw inserted to the depth of two or three threads into the dentin. The rubber dam is then drawn above this and held securely above the cavity. When the operation is completed the screw should be cut off with the wedge-cutters and nicely smoothed. When the slit in the gum has healed, the portion of the screw remaining will be concealed. Most cavities upon the labial surfaces are shallow and are best filled with cohesive foil or Watts' crystal gold. It is well to fix the first piece securely in a small retaining pit and build each piece Fig. 19 1. upon a sure foundation. As fillings upon the labial Mj^J surfaces of teeth are usually conspicuous (Fig. 197), F>Ti it is often desirable to fill such cavities with plat- t ]| II inous gold, because the tint of the two metals in Labial fillings. combination is more nearly the shade of the tooth. Especially is this true in teeth of yellowish hue. Class E. — As cavities upon the lingual surface of the incisors are usually confined to the laterals and most frequently are the result of imperfect development of the enamel in relation to the cingulum (see Chapter I., p. 25) ; they are small in size and easily filled. A tape of 24(3 THE OPEllATloy OF I'll. LING CAVITIES. non-fohc'sive foil, or a small mat o<" tlic same material, may be inserted into the cavity first, ami the filling completed with cohesive gold as in other cavities surrounded by strong walls. Class F. — As caries rarely attacks the iiicisal ecUjc of the anterior tirf/i the operation of filling with gold is usually confined to artificially made cavities, with the view of arresting waste (»f tooth substance caused by attrition, or where for any reason it is deemed best to " oj)en the bite." Great strain is often brought to bear upon fillings in this position, and too great care cannot be exercised in the shaping of the cavity and the sul)se(juent packing of the gold. Cohesive gold is best suited to cavities of this (jcscrijition, and each piece shoidd be freshly annealed, that thei-e may be no doubt about the perfect union of each piece. It is well to start the first piece in a small retaining or stai'ting pit and then fill all dof the undercut before attempting to build the gold above the walls. As fillings in this position are subjected to great wear, the greatest hardness of surface attainable Edge restora- gj^Q^jj ]jq sought for, Otherwise there will be battering of the edges and possibly fiaking of the gold. Platinous gold is well adapted for this kind of fillings. Narrow strips of Xo. 20 or No. 30, well annealed and condensed with mallet force, will auswx^r a better purpose than lighter foil (Fig. 198). II. Simple Approximal Cavities. Incisors and Canines. Class G. — In selecting the kind of gold and the form iu which it should be prepared for fillings upon the approximal surfaces of the incisors and canines, the operator must consider the size of the cavity to be filled and the retaining hold wdiich he is able to secure without sacrificing too much of the tooth structure. If the cavity be a small one, situated midway between the labial and lingual walls, and the surrounding borders be strong, a rapid and easy way of filling such cavities is to ])rcpare the non-cohesive foil in the form of narrow taj)e. A leaf of foil cut into ibur j)ieces and folded with a s])atula U[)on a napkin to the width of one-sixteenth of an inch, and then cut into lengths of three-(|uarters or one inch, is a good way of preparing it. An excavator of an angle of fijrty-five degrees, with the extreme point broken off, makes a very good instrument for packing such fillings. Space should previously be obtained, either l)y the slow pro- cess of wedging with rubber or linen tape or by means of the Perry separator. COMPOUND CAVITIES. 247 When the cavity is two-thirds filled it is well to use a few pieces of No. 20 cohesive foil, so that a dense surface may be given to the filling. Such cavities may be classed among the simple ones, and p^^ jgg^ present no difficulties except their inaccessibility (Fig. 199). The operator should ever strive to conceal as much as pos- sible the gold in the anterior part of the mouth, and when it is possible he should preserve the labial wall intact. This can often be done by cutting away a portion of the lingual wall and by packing the filling almost entirely from the under side of the tooth. Where a large portion of the approximal surface is involved, the retaining hold for the filling must be had at the cervical border and at the incisal edge. The first pieces of gold should be anchored in a groove or retaining pit near the cervix and the cervical border made secure before any other portion of the cavity is filled. The beginner will ordinarily do better to start such fillings with cohesive foil or Watts' crystal gold. If the latter, he may then complete his filling with cohesive foil. Non-cohesive gold is rarely indicated in cav- ities of this description. The electro-magnetic mallet or the Bonwill mechanical mallet is well adapted for packing such fillings. Bicuspids and Molars. Class H. — Cavities of medium size situated upon the mesial or dis- tal surfaces of the bicuspids and molars and not involving the occlusal Fig. 200. surface may be filled after the same manner as small cav- ities in the incisors or canines. Operators who are not in the habit of using non-cohesive foil prefer starting such fill- ings in a small undercut or retaining pit and filling through- out with cohesive p-old prepared either in narrow ribbons Approximal ° '^ ^ bicuspid or loosely rolled cylmders (Fig. 200). ^^^^°^' Such fillings, because of their position, must be packed largely by hand pressure, although the mallet may be used as the filling approaches completion. III. Compound Cavities. Incisors and Canines. Classes I and ./. — Mesio-lahial and disto-labial cavities in the incisors and canines are usually best filled throughout with cohesive gold. Each cavity independent of the others should have retentive shape, so that in the event of one filling being displaced the other will remain intact. As a rule it is better to fill the cavity on the labial surface first, because the first pieces of gold are more easily anchored in an accessible ^ 248 riJE oi'FlLWlny OF IlLLTNG CUT7777X cavity, :uul hccaiisc also ot" tlic thiiiiicr ol' (li.-j»la*'iiin- the ^okl in tlie appniximal cavity wiicii lillint;- the cliaiiiicl connecting the two fillings. Evcrv i)(»ssil)lc cai'c siiould he exorcised in i)ackiii'r the trold in cavities of this description. The >jold shonld he made / \ thorontjhly c(»hesive hy recent annealing, and i)e used in pieces ^-I!2^j snfHciently small to prevent clogging. iSnch operations are . fl more or less ex})()sed to view, and the greatest degree of ^•^ artistic skill shonld be bestowed npon them to render them .Mcsio-laliiai _ _ r ^ ' • fiHiiiK. as pleasing as possible to the eye. The original outline of the tooth shonld be restored with the gold, because it pre- sents a better appearance than a space between it and the adjoining tooth (Fig. 201). Classes ii' and Jj. — Cavities upon the nuK'to-liiKjaal or ilLsfo-lingual swfaces of the teeth are filled in precisely the same way as those described under classes / and J. It" the cavity be of con- siderable depth, non-eohesive gold may be used as part of ''i'' '-02. the tilling, but in any event the bulk of the filling slioidd be made of cohesive foil (Fig. 202). Classes M and X. — Mesio-incisal ; Dlsto-uwisal. — Cav- ities situated upon the ai)proximal surfiiccs of the incisors , . A ^ / _ _ ^ Ml'sio - lin- and becoming confluent with one on the incisal edge require guaiiiUiiiK. great care in the luatter of packing gold. It is often an advantage to have the cavity on the approxiraal surface unite with a natural or an artificially made one upon the incisal edge, because much better anchorage can be obtained in such cavities. Cohesive gold prepared in the form of ribbon or in pellets or cohesive cylin- ders, if loosely rolled, may be used. The better method is to fill the undercut at the cervical border of the cavity first, and tlien bring the gold toward the incisal edge as squarely as possible, keeping the mass on a line with the labial and lingual walls. The operator feels a sense of security when he is able to an- chor such fillings in an undercut or retaining pit on the incisal edge. In teeth with broad incisal edges there is ample opportunity to make a strong retaining hold, but where the edge is narrow a lateral cut into the palatal wall one-third back from the incisal edge affords a strong and secure hold for that portion of the filling. Operations of this class require great thoroughness in the packing of the gold. It shoidd be very cohesive and when possible condensed with some form of mallet (Fig. 203). .* . . . Class 0. — Mcsio-cUsto-incisdI. — AVhere both approximal surfaces and the incisal edge arc united in one cavity^ the better plan is to begin the filling at the undercut near the cervical border of the distal cavity, COMPOUND CAYITIIES. ' 249 and build the gold squarely down as in classes M and N until the in- pisal edge is reached, thence across the incisal edge, then fill the mesial cavity after the same manner, uniting the three fillings at the mesio- incisal corner. It is better to insert such fillings with an electric or a mechanical mallet, as there is always dan- ger, when packing across the incisal edge by hand pres- sure, of pushing one or the other of the fillings out of the approximal surfaces. If no accident occurs in the packing of the gold a Mesio-disto-incisai . . . fllliriKS. filling thus made is very secure, for its form is like a staple and each portion helps to bind the others securely in the triple cavity. Non-cohesive gold should form no part of such fillings (Fig. 204).' Bicuspids and Molai's. Class P. — 3fesio-occlusal. — The filling of this class of cavities offers no serious difficulties provided sufficient space has previously been ob- tained. As it is desirable to restore with gold the original outline of the tooth, sufficient space to do this in is a necessity, and the operator will soon learn that he can only accomplish good results in proportion as he recognizes the importance of this preliminary. The cervical border is the vulnerable point for recurrence of decay, and imperfection here in the matter of packing the gold means speedy failure of the filling, hence the importance of a perfect joint between gold and tooth. This may be obtained by using a roll or rope of non- cohesive foil. One end of the roll should be carried with a suitable plugger into the gingivo-linguo-axial angle of the cavity, and ex- tended across the gingival border into the gingivo-bucco-axial angle. Gieat care should be exercised at this point in reference to the gin- gival border. The gold should be first thoroughly matted down with a broad-faced plugger and then a few blows from an auto- matic or hand mallet should be directed upon it to insure perfect adaptation to this wall of the cavity. Subsequent rolls of non- cohesive foil may be introduced in the same manner until one-third or even one-half of the approximal cavity has been filled, after which cohesive gold should be substituted for the non-cohesive, and its use continued throughout the balance of the filling. Freshly annealed gold should be used upon the surface, that a compact filling may be the result. It is always better to insert too much rather than too little gold, as the operator can shape the contour according to his fancy or to the necessities of the case. The occlusal portion of the filling should be thoroughly condensed^ 2.jO THS opera TIoX OF FILLISi; CAVITIES. as iiiiK'li (-lepc'iuls ujxtn tliis tor holding llic lilliiig in jtlacc (treat hard- ness is also essential to prevent hattcring in the Yii.. '_>or,. .j^.j ^^^. ,„.,^ti^^..,tion (Fig. 205). ^^"\ ^^^\ C'r.Ass (^. — 7>/Wo-o<'r/(/.s'a/ eavities may 1)(' tilled flA^; W^J '•> precisely the same manner as those situated ^*^i— ^ ^-^ upon the mesio-oeelusal surt'aee. The ditfieulties Approximo-occiusai ^y^, slightlv greater Ijecause these eavities are not cavities. m i /- • • /• i • i • • so accessible. Cavities of this description can be greatly simplified by the use of the matrix. This little device converts compound cavities into .simple ones, and when used with care and judg- ment facilitates the operation of filling to a wonderful degree. Experience has demonstrated that the only .-satisfactory method of filling cavities upon the approximal surfaces of the bicus])ids and molars is to restore, by means of filling material, the original outline of the tooth. This is termed "restoration of contour." To do this success- fully requires artistic sense and mechanical skill of a high order, and an accurate knowledge of the topographical anatomy of the teeth. To the man who has these the operation is easy, but otherwise persistent effort alone will enable him to acquire the ability. The inexperienced operator will often do better if he confine himself" in the beginning to but one kind of gold, and that of the cohesive variety. If this be done he should start the filling in a well-defined groove at the cervical border of the cavity, and then add, piece by piece, well-annealed foil until the filling is completed. Such a procedure is of necessity slow, but excel- lent operations can be made by this method. The beautiful and lasting o]ierations of Yarney and AVebb and others were made in this way. The matrix is best suited to disto-occlusal cavities. It is sometimes employed upon me.sio-oeclusal cavities, but, as a rule, obstructs the light and adds little to the convenience of the operator. The subject of filling with the aid of the matrix is treated in detail in Chapter XII. Fig. 206. Fig. 207. Fig. 208. Occliiso-biKcal filling. Occluso-lingual filling. Mc.^io-octluso-distal filling. Class R. — Occluso-buceal cavities are usually confined to the lower molars. If they be shallow it is better to fill throughout with cohe- sive gold. If, on the other hand, the cavity upon the occlu.sal surface be deep, non-cohesive gold may be used in })art and then cohesive gold FILLING WITH TIN. 251 used to fill the channel connecting the two cavities. Such fillings are subjected to great wear and should be solid (Fig. 206). Class *S^. — Occluso-Ungual. — These cavities are nearly always con- fined to the first and second upper molars, and, as a rule, are best filled, with cohesive gold. The channel running into the lingual aspect of the tooth is not often deep, and non-cohesive gold is contra-indicated (Fig. 207). Class T. — Cavities upon the mesial and distal surfaces of the bicuspids often become confluent with those upon the occlusal sur- face, and it becomes necessary to fill them as one cavity. Such ope- rations are simplified by the use of a matrix upon the distal surface. A band matrix could be employed, but it obstructs the light somewhat and the operator will more frequently confine himself to a matrix upon but one side of the tooth. The filling should be commenced at the disto-cervical border, and after inserting a few mats or cylinders of non-cohesive foil proceed as in cavities described under class Q (Fig. 205). If these cavities be of considerable size the buccal and lingual walls are weakened and there is danger of their being broken away in the act of mastication. It is often well to truncate the cusps somewhat and build the gold well across the occlusal surface, allowing the strain to come directly upon the gold instead of upon the tooth structure. Pilling with Tin. It is not definitely known when tin was first employed for filling carious teeth, but it has been used for at least a century and has found great favor with many. Prior to the improvement in the formulas of dental amalgams, tin was used more generally than at the present time. Tin possesses certain inherent characteristics which make it valuable as a filling material. Among these are great malleability, non-conduc- tivity, and it is thought by many to possess antiseptic properties. But while it has desirable qualities it has also some undesirable ones, such as softness, and when exposed to the secretions of the mouth it discolors, — which facts render it unfit for surfaces exposed to great wear in the act of mastication and upon surfaces exposed to view. The discolora- tion, however, is confined to the surface, and teeth filled with tin are not discolored in consequence of its presence. There are various inethods of preparing tin for dental purposes. That which has found greatest favor in the past is in the form of foil. The tin used should be chemically pure. An ingot of the metal is rolled into ribbon and then beaten, after the same manner a? gold foil, into sheets of the desired thickness. As a rule it is not beaten as thin as the former. The foil best suited for most fillinp's is ISTo. 10. '2-i'2 TUK ()I'FIi.\Tl<)\ OF FlLLISa C.W'ITIFS. I'lirc till, like |>iirt' i:13. o Felt jKilisliing wheels. Fig. 214. Iliiidostan poiIlt^. Fillinirs upon labial and buccal surfaces .-hould be dressed down with fine corundum points or the Hindostan stones shown in Fig. 212 until the outline of the cavity has been reached. Any overlap- ping of the gold upon th(\se surfaces gives a ragged a])pearance to the filling and detracts much from its beauty. Care should also be exercised in giving the filling the same degree of convexity that the tooth formerly had ; in other words, the filling should accurately re- store the lost anatomical contour of the tooth. When sufficient gold has been removed the surface should be nicely smoothed with re- volving wood points charged w^ith pumice powder and water, or a paste made of pumice and glycerin, after which the final finish may be made with flour of pumice, chalk, or ox id of tin, used l)v means of a revolving disk or wheel of felt or soft rubber (Fig. 2l3j. The soft rubber polishing cup of Dr. John 15. Wood is a valuable aid in ])olisliing the con- vex surfaces of approximal fillings or those upon the cervical portion of labial cavities. It is shown in Fig. 214. As fillings upon the labial surface are more or less conspicuous at best, it is better not to give them a burnished surface. The dead or satin-like finish which is left by the flour of pumice is usually preferred. Dr. Wood's polishing cup. FINISHING FILLINGS. 255 Fillings upon approximal surfaces are more difficult to finish, and too great care cannot be bestowed upon them. An operator is often judged by the finish which he gives his approximal fillings, and justly so, as no class of fillings requires a higher degree of skill in the finishing. There is of necessity more or less overlapping of the gold in the insertion of a filling, and the removal of all excess is as important as any other part of the operation. For this purpose a great variety of instruments is supplied. Files and gold trimmers, as shown in Figs. Fig. 215. :\ 1 Plug finishing files. 215 and 216, are best adapted. The cervical border is one which should receive most careful attention. The gold should be filed and dressed down until the finest excavator or probe will not catch when drawn from the cervix toward the cutting edge. In addition to the Fig. 216. Curved finishing files. file and gold trimmer, strips of emery tape or sandpaper should be used until all margins are well defined. The oj)erator should have at hand a great variety of these strips, some of extreme thinness and of various grits, of emery, of silex, and of buckhorn. When the filling has assumed the desired shape and all overlapping gold has been removed, the final finish should be given with linen or '2r>{] THE OPERATION OF FILLING CAVITIES. cotton tajH' c'luir^od with punuce of excoocling fineness. It" thoro arc places where the tape cannot be made to reach, a soft-rubber wheel in Via. 217. Approxiiiial triiuiiiors. the handpiece of the engine and charged with the same powder may be used (Fig. 218). Fillings in the bicuspids and molars because of their inaccessible position are often most difficult to finish, and for this reason should receive unusual care. If a matrix has been used at the cervical border, and has been made to fit the tooth perfectly at or near the gum, it will be found that the finishing process has been simplified in a great measure, because there is less overlapping of the gold at this point. Frc. 218. >(iliruljln.'r di^k^ The pointed files, right and left, as shown in Fig. 216, are admirably adapted to dressing away any overlapping of gold at the cervical border. Fir;. 219. With these and the trimmers shown in Fig. 217 the general outline of the filling may be oljtaincd. after which the emery and corundum tape may be used and the tilling polished after the same manner as FINISHING FILLINGS. 257 described above. Disks of sandpaper and emery cloth and finer ones chiarged with cuttlefish powder (Fig. 219) are exceedingly useful in shaping and polishing the filling. Fig. 220 shows two forms of disk mandrels which may be satisfactorily used in carrying disks. Fig. 220. Morgan-Maxfleld disk mandrel. Many approximal fillings in the bicuspids and molars extend to the occlusal surface. When this is the case the operator should pay special heed to the occlusion of the opposing teeth. If left too full the con- stant touching of an opposing cusp may batter the filling, or, if not securely anchored, dislodge it. A filling is not well finished until a delicate instrument can be passed from enamel surface to filling with- out catching. When this can be done, and dental floss is not frayed at the cervical margin, the inference is justified that no gold has been left overlapping. Repairing Fillings. Fillings somewhat defective are often susceptible of repair. The defect may sometimes be apparent in the finishing ; at other times it is the result of subsequent caries, and at still other times the result of a fracture of the tooth enamel along the border of the filling. The nature of the defect and the condition of the remaining filling must be taken into consideration before an effort to repair is undertaken. When the defect is due to insufficient gold at any point in the filling more gold may be added. It is well to first cut out a portion of the filling, making a distinct cavity of retentive shape. Cohesive gold is usually best suited to the purpose ; crystal gold often serves well in the repair of such defects. If the filling has been thoroughly condensed and the mass is solid there is little difficulty in adding more gold to it, provided the sur- face be clean. If it has been wet with saliva, the surface of the gold must be made not only dry but clean. It is well to wipe it with a pellet of cotton or paper saturated with alcohol or ether, after which the filling should be scraped with a suitable instrument. If the fill- ing be of considerable size and well anchored, shallow retaining pits 17 258 THE OPERATION OF FILLING CAVITIES. may bo drilled into it, which will make an additional hold for the ^old which is to be added. Defects which arise from snbse(|uent caries are perhaps more frequent in approxiniai surfaces at or near the cervical maririn. These borders are vulneral)le points for the recurrence of caries, and imperfect adai)tatiou is not infrequently the determining cause of the beginning of such decay. To effect a successful repair in such localities am})le space should be obtained, especially so if the repair is to be made with gold. If the decay has not extended beneath the filling, and sufficient space has been obtained, there is no greater difficulty in making a suc- cessful repair than in filling a simple cavity similarly located. If the operator is skilled in the use of non-cohesive gold, he will do well to prepare his foil in the form of narrow tape, and work it into the cavity fold after fold, allowing the loops to extend somewhat above the walls of the cavity. When the cavity has been completely filled the protru- ding folds may be well condensed and the filling finished in the usual way ; or the. repair may be made with cohesive gold, the first piece having been made fast in a groove or r(>taiuing pit. Such repairs are often required in the bicuspids and molars, and large fillings otherwise good are saved by a successful repair at the cervix. The plastics are sometimes indicated in this class of cases, provided they be not so near the anterior part of the mouth as to be unsightly. Gutta-percha often serves a good purpose here, but in some mouths undergoes decomposition and is less reliable than gold. The oxyphosphates are contraiudicated because of their liability to wash away after a few months. Amalgams are more frequently used, and nearly always serve well when thus employed ; but unfortunately the contact with gold produces discoloration, and an unsightly filling is the result. Whenever gold and amalgam are brought in contact in the same tooth, if the surface of each is exposed to the fluids of the mouth, the amalgam is almost sure to turn quite black. The discoloration of the surface of the alloy does not lessen its value as a j)reserver of the tooth, but its unsightliness is often too great to be tolerated ; nevertheless, utility enters so largely into the equation that the operator feels justified in using the alloy, because with it he feels sure of making a better repair. After the alloy has hardened it should be nicely dressed down and all overlapping of the material at the gum margin removed, when it should be smoothed and polished with the same care that other fillings receive. Fracture of one or more of the cavity walls is a common accident, and one which may be repaired if the filling has been securely anchored in portions of the tooth not involved in the fracture. Such accidents sometimes befall bicuspids and molars, especially the bicuspids, where fillings have b^'cn inserted in each aj)pr()ximal surface, the two meeting REPAIRING FILLINGS. 259 in the fissure upon the occlusal surface. The buccal wall is sometimes the one broken away, sometimes the lingual. In either case the ability to successfully repair depends upon the stability of the approximal fillings and the anchorage which can be obtained at the cervical w^all and in the exposed fillings. To restore with gold a buccal cusp or the entire buccal surface of a bicuspid might necessitate a show of gold which would be objectionable ; and a better plan would be to engraft a porcelain facing or an entire porcelain crown ; whereas such a restora- tion on the lingual surface would not be open to the same objections. Cohesive gold alone is indicated for repairs of this kind. Watts' crystal gold when used in cases of this description has been most satisfactory. If the fracture extends above the margin of the gum the operation is much more difficult because of the danger from a flow of blood, and the additional difficulty of getting the rubber dam above the border of the fractured surface. This may be accomplished by filling for a few weeks with gutta-percha, when there will be recession of the gum caused by the pressure of the gutta-percha upon it. When a similar fracture occurs in a molar, if the fractured surface does not encroach upon the pulp, and will admit of drilling retaining pits without danger to the pulp, there is no difficulty in restoring the broken portion with cohesive gold. Mack's screws are sometimes indicated in cases of this kind, since strong anchorage can be secured in this way without much loss of tooth substance. Fracture of the incisal edge of the anterior teeth is often a serious accident, because of the difficulty of repair and the unsightly display of gold when it has been accomplished. Large fillings situated upon the approximal surfaces of the incisors but not extending to the cutting edge, yet near enough to weaken the enamel overhanging, are especially liable to need repairs. The corner of the tooth breaks away, leaving the surface of the gold exposed, and the only hold the filling has is at the cervical border. In order to secure retaining hold for additional gold the operator must be careful not to displace the original filling, A wooden wedge should be inserted between the teeth and pressed home with sufficient force to hold the filling securely in place during the operation of repair. Sometimes a retaining pit can be made laterally into the sound dentin, or, by cutting a little channel through to the lingual surface and then deepening the channel at its ex- tremity with a round bur, a secure anchorage may be had for the fresh gold. Great care should be exercised in packing the gold, lest by inadver- tence the instrument should slip and push the original filling from its position. Fractured surfaces should receive prompt attention, for if left for a period of time disintegration of the dentin will set in and the 260 THE oPERArius of fiijjxg cavities. caries niav extend l)eneath the filling and thus jeopardize or riiiii the most thorough work. Eroded Areas. There is a ehis.s of cavities wiiii-h has not been specitieally treated in the foregoing chapter, partly because the lesions under consideration cannot, strictly speaking, be classed under the head of carious cavities, and thev are of such a peculiar formation that no definite rule can be laid down as to the best mode of treatment. It' the eroded area be narrow and confined to the cervical border of the labial surface, and in a mouth in which the teeth are not conspicuous, a filling of gold may be employed ; but not infrequently the eroded area extends over a considerable portion of the labial surface, and in such cases a filling of gold would be so inharmonious that it should be avoided if possible. Hitherto the operator has had little choice of filling materials, and has often been compelled, against his better judgment, to employ gold in these cases. The zinc phosphates have been almost as inharmonious in color as the gold, and their dural)ility has been so variable that they could not be regarded as permanent in character. The same may be said of gutta- percha. Happily, the progress which is being made in porcelain inlay icork promises something both artistic and durable. It is quite possible, with the great variety of shades of porcelain now being furnished, to match the tint of the natural tooth, and if care be exercised in the selection of shades and the contour given to the inlay these eroded areas may be covered and the tooth made to assume almost as natural an appearance as before the disease had attacked the surface. (For a detailed descrip- tion of porcelain inlays the reader is referred to Chapter XV.) CHAPTER XII. USE OF THE MATRIX IN FILLING OPERATIONS. By William Crenshaw, D. D. S. The matrix, as originally suggested and employed, was used exclu- sively between the molars and bicuspids, and consisted of curved pieces of thin metal of various kinds, which were braced with wooden wedges from one tooth to the other ; but now the matrix has been adapted to other teeth and other forms of cavities, as will appear in the further develop- ment of this subject. All forms of cavities occurring on molars, bicus- pids, and incisors, standing alone or together, excepting those cavities located in the occlusal surfaces of the first-mentioned class, and in the cutting edges and corners of the latter, are now subject to the use of the matrix as an aid in filling them. The large and difficult filling operations encountered between the molars and bicuspids, which in past decades so taxed the skill and vitality of the dentist, have been by various forms of device rendered easier of execution and more permanent and perfect in character. Matrices have been used more or less in one form or another for the past fifty years and some crude forms even longer. Dr. Louis Jack gave the profession thirty years ago the first practical idea and demonstration of the matrix and its possibilities, and his effort, more than all that had gone before, gave shape and impetus to the development of this important device. General Considerations. The limitations, no less than the possibilities, of the matrix are im- portant to understand, because, used indiscreetly, in locations which the judgment should forbid or in locations where it would be perfectly in place but for the unsuitable nature of the material employed, more harm than good may result from its use. To be able, therefore, to discern the proper class and location of cavities for the reception of the fillings, together with a knowledge of adapting the filling materials to the case in hand, are some of the requirements and demands on the operator who essays to use matrices. The matrix should possess as fully as possible the qualities of adapt- ability and fixedness to the teeth, at the same time provide for contouring and for leaving the teeth in proper position, and preserving the proper 261 262 USE OF THE MATRIX IX FILLIXG OPERATIOXS. intcr])i\)xiiual !^j)aro. Further (It'siclcrata arc that the matrix sliall be resistant cnougli t(» ., and \vc pass Iroiii the worst possible work doiu' witli ii:old, and made even worse hy tlic employment of the matrix, to that which has proveplied to the several walls of the cavity, should be limited, and apply to particular points, and particular points only. For instance, the depth of a cavity should mean from the point of decay toward the pulp, whether })enetrating from the occulusal, mesial, distal, buccal, or lingual aspect of the tooth. The width should mean from side to side of the cavity, whether on the occlusal, mesial, distal, buccal, or lingual surface of the tooth. The length, the longest dimension, should mean the greatest length, in whatever direction it extends. The bottom of a cavity should be called the floor, as seen at A and D, Fig. 221. By reference to Figs. 221 and 222 the tooth shown represents a left lower Fig. 221. Fig. 222. Fig. 223. E 'N Cavity preparation of a molar Cavity preparation, showing Section of molar, showing the for the matrix. siiuare corners. introduction of the cushion. molar, the decay of which penetrates frt»m the mesial surface in the direction of the line leading from F, and we would say that the depth of the cavitv seen at A and c was in that direction ; and that its width was bucco-lingual, from E to E, or from c on the buccal side to a point opposite on the lingual. This cavity, being a compound one, must have added together for its length, the floor of the step i), the axial wall F, and the floor A. The depth of the lingual and buccal walls is seen at C, and the depth of the floor at A. The axial wall and height of it is seen at F, and the floor of the step at D. In Fig. 221 is represented the cavity preparation, with which, in connection with the matrix and soft and cohesive gold, the operator is enabled to bring gold work in cavities of this class to a degree of per- fection rarely approximated without its aid. At the cervical margin of Figs. 221 and 222 it will be observed that CAVITY PREPARATION OF MAJOR CLASS FOR MATRIX WORK. 267 the floor of this aspect of the cavity, A, and the external wall of the tooth, B, form practically right angles, which is the angle, all things considered, with which to secure the best margins and best results. Beginning well up on the side wall at C, Fig. 221, passing down and along the base of the cement step and up the opposite wall, is a groove c, better shown in the sectional cut. Fig. 223, made with a No. 3 or 4 round bur, or Darby-Perry excavator, Nos. 11 and 12, designed as an anchorage for the base of the cervico-occlusal column, marked non- cohesive gold, Fig. 225. In this groove, which should be shallow and upon the floor surface. A, is condensed the gold. The groove extending up the side wall is not a necessity, though it may be incorporated in the cavity formation when the w^alls are strong, but that portion of it along the floor should be employed. In the instances where the lateral walls are weak and the groove cannot be formed, the occlusal anchorage shown at d, Figs. 221 and 222, should be employed. In the formation of the side-wall edges, e e. Fig. 222, care must be taken to leave them strong enough to prevent fracture under the pressure of the matrix band. These walls should be beveled on the lines e e, Fig. 222, terminating in an obtuse angle with the external surface of the tooth, if practicable. Less than a right angle should not be depended on, if it can be avoided, as there is danger of fracture. In the formation of the cavity in Fig. 221, with the rounded corner Fig. 224. A— -^ Fig. 225. COHESIVE GOLD. CEMENT. NIOKI COHESIVE GOLD. Fig. 226. Cavity preparation, showing subdivisions of filling. Section showing the plan of a Section showing the condensa- matrix filling. tion of cushion k of Fig. 223. C, is seen the preparation suitable for amalgam or other plastic materials in connection with the matrix ; and for cushions and cylinders of foil if the cavity approximates the form seen in this and Fig. 222, and at F and H of Fig. 226. But these corners should be modified as nearly as possi- ble into the form seen at N N, Fig. 222, if the cavity is shallower from A to D, Fig. 222, than from F to h. Fig. 226. The square corners aid in better locking and binding the foundation subdivisions in the process of building in the filling — see Fig. 224. But when the cavity assumes the proportions seen at F to H, Fig. 226, the matter of square corners is not necessary, because when the distance 2HH USK OF Tin-: .VATRIX /.V hll.LISd < il'KllATK >SS. f'ntni tlic tn|) nt' the f^tcp, Fij;. 2li<), In the Moor is nrrcatcr tlmii from i' (in the axial \\:ill lo H ou the matrix Itand, \\v have a form of cavity in wliicli the ousliioii.-? ante|)> whenever the dis- tance from the axial wall to the njatrix hand is jrreater tiian from the top of the step lo the fl(»or of tlie cavity, and hring the form of the cavitv as nearly as possible into that shown in Figs. 22.'i, 22U'ss molar t)e- fore placing in the cement step. RF. Section showing the recon- struction of pulples.s molar with cement step. In the introduction of the filling into the corners of Fig. 222, the method suggested is to carry in the cushion of .soft gold or tin, as the case may be, and place in the corner at a with pluggers, Nos. 257, 258, or 259, Fig. 265, whatever size of these forms shall best suit the case, and partially condense it. In the opposite corner place in the subdivi- sion B, and then the subdivision c. Only this last introduction is carried straight down in the direction of the long axis of the tooth, while the other subdivisions, as seen in Fig. 224, are placed in diagonally and compressed in ])lace. At this juncture hold down with a suitably shaped instrument, Xo. 174 or 175, F^ig. 265, on one side and condense the other with the automatic mallet carrying a .suitalily shaped plugger. No. 18, Fig, 265, until adequately condensed. After this, change in.struments about, and treat the opposite side in a similar manner. If the cushions are proportioned properly to the size of the cavity, two sets of each of these put into the subdivisions A, B, and r, Fig. 224, will bring the wall to the top of the step, or nearly so. Fig. 221 represents the preparation of decay cavities, whether appear- ing on bicuspids or molars, the outer outline of which appears in Fig. 230 and comes imder the head of the major class. All such decay.= CAVITY PREPARATIOX OF MAJOR CLASS FOR MATRIX WORK. 269 should as nearly as practicable be prepared after the suggestions of Fig, 221. In the formation of the cavity in Fig. 221, when the tooth is normal and its functions comfortably performed, care must be exercised to avoid too near approach to the pulp, particularly when the cavity is located in bicuspids, in which case we have a shallower zone in which to work than is found in the corresponding parts of molars. In the deeper cavities of bicuspids and molars, zinc phosphate should be used to bring the cavity into simple form, as seen in Figs. 225, 228, and 229. When these cavities are prepared after the suggestions and illustra- tions of the figures referred to and embraced by the matrix, not onlv is less material needed to bring up the cervico-occlusal wall to the top of the step, but additional advantages are gained in that the cavity is simpli- fied, the filling rendered easy of execution, and the character of the work improved. Oxyphosphate of copper cement, being more adhesive and less a thermal conductor, and possessing more of antiseptic property than the other forms of zinc cements, should be employed wherever practicable for step making. Its inky blackness perhaps is against its use in the anterior teeth, and farther forward than the molars. But it is also less irritant and is harder and stronger than any of the zinc phosphates. So that, in the insta:nces where the cavity penetrates to or beyond the pulp, and compels the formation of a cavity as deep from the matrix band to the axial wall, as is shown in the pulpless tooth, Fig. 228, or as already cited, when the depth of the cavity from f to h, Fig. 226, is greater than the height of the step, the cement should be placed in posi- tion to bring: the axial M'all close enough to the matrix band to form the cavity into the proportions shown in Figs. 223, 226, and 227 when em- braced by the matrix. This class of cavities, when filled with guld, should be filled with soft gold cushions or cylinders to the top of the step D, Figs. 221 and 222, when, after forming the groove shown at G, Figs. 225 and 227, shuuld be completed with cohesive gold and built seeurelv in place. The anchorage. Figs. 221, 222, and 224 at d, indicate, what this should be. The procedure in the intnjduction of the soft-gold part, or of tin when that is used, in the major class, is seen at k, Fig. 223, and when con- densed, at L, Fig. 226. The introduction is in the direction of the long axis of the tooth and not diagonal, as shown in Fig. 224. though the diagonal introduction may be employed in special cases favoring it. The cushions thtis introduced, rarely less in size and bulk than a size 3 cylinder, and generally much larger, do not fill up squarely out to their ends or to the lateral walls ; and the operator must look to these points, and level them up with small cylinders or their equivalent in cushions. 270 USE OF THE MATRIX IN FILLING OPERATIONS. The final condensing of this column as seen at i, Fig. 227, and before the cohesive ]xirt is begun, shouhl l)e done by lioUling down the gold at one side of the cavity, while the automatic mallet condenses at the opposite, as suggested in the tilling of the cavity of Fig. 222. Tiie student nuist appreciate the importance of condensing first the soft and afterward the cohesive gold into the angles formed at k and .\, l^'ig. 222, when that figure is embraced by the matrix. Pluggers Nos. 7 or 8, Fig. 265, of small treading surface are suitable for doing this part of the work. The cohesive gold should be used in narrow strips when the angle into which it must go is close and sharp. It is the purpose in engineering construction to secure the greatest possible strength from the arrangement of material entering into such construction. In the formation, theref()re, of tiie anchorage for the fill- ings of the major class of the cervico-occlusal cavities, due regard nuist be given to the proportion of gold and enamel in making the anchorage head in the occlusal surface of fillings of this class. Just as it is possible to weaken a carriage wheel by having the tenons of the spokes so large as to weaken the hub, it is also possible to have the tenons so small and the hub so strong as from this cause to weaken the wheel. So also with tiie anchorage of this class of fillings ; the neck of gold going into the head of the anchorage may i)e so small, narrow, and shallow that the stress of chewing will cause it to break at this point. And yet the neck may be widened and deepened so much that the gold becomes stronger than is necessary, and the enamel on either side becomes correspond inglv weak, and gives way under stress of mastication. The problem then is to proportion the neck of gold and the enamel so as to secure the greatest strength. Assuming the depth of the gold neck to be about its width, the rule of one-third gold in width and two-thirds enamel, one-third each side of the gold, answers the requirement. The Minor Class. While the principles inculcated by Drs. Webb, Black, and others in extension for prevention— extending the cavity margins well away from the contact point of the teeth — hold good in the larger proportion of cases, there are those individual instances presenting when the operator will not be justified in employing extension for prevention. Take, for instance, the highly developed teeth, with perfectly fused enamel through the sulci dividing the cones, lobes, and cus]is of the molars and bicuspids, which from the excellence of their quality and the cleanliness of the patient almost entirely prevent caries ; it would be unwise and untieces- sarv under these conditions to extend in preparation the borders of these cavities to the limits taught and endorsed in extension for prevention, and THE MINOR CLASS. 271 yet so necessary in many of the larger decays denominated the major class. The preparation of the minor class of decays, represented in the inner outline of Fig. 230, should be formed after the suggestions of Figs. 231 232, and 233. The student should comprehend the formation of both the major and minor class, as each must be prepared according to the suggestions made. The preparation, therefore, for the minor class may be enlarged to the Fig. 230. Fig. 231. Fig. 232. Bicuspid, showing the major and minor class cavity out- line. Side view, showing the out- line of the major and minor preparation. Transaxial section, showing anchorage of the minor class at line a of Fig. 231. proportions shown in the inner outline of Fig. 231, while the outer out- line of Figs. 231 and 233 would show the formation of the major class on the same tooth. Fig. 234 is a sectional cut showing the completed major class of the cervico-occlusal fillings, as adapted to and completed in the bicuspid. Fig. 232 is a transaxial section at the line A on Fig. 231 ; and at this point the anchorage for the minor class is seen in Fig. 232. The anchor- age can and should be made strong here under the buccal lobes of bicus- pids and molars, and similarly at the lingual sides. Above the anchorage, toward the occlusal surface, the cavity should be so modified as to come out on the occlusal surface, as shown in Fig, 233. Fig. 233. Fig. 234. Fig. 235. End view, showing outline of major and minor cavity preparation. Section showing the completed major class filling on bicus- pid. M, 2-grain cube of gold, show- ing relative size to the cav- ity in which it rests. The pluggers, Nos. 115 and 116 or 117 and 118, Fig. 265 — pairs in two sizes — are invaluable for tacking the cohesive gold into the condensed soft gold. Much of this part of the work must be done by hand pressure ; and it is important, in view of this fact, to prepare the gold in narrow strips, which should be annealed with electric heat to insure the strongest cohesion. 272 UiiK or THE matrix in fillisc operatioss. In the filliiii; »il" this i-hiss of cavities the matrix .sliouhl bi- applied, aiul soft goUl hroiight up to the anchorage shown in Fig. 232. At this point cohesive gohl shouUl be throughly condensed into the anchorages, and brought out, finishing the contour of the tooth. Care should be taken to bevel somewhat the occlusal surface of this filling to prevent the too positive iiH[)inging of the occluding tooth in the opposite jaw. The beginning of the cohesive on the condensed soft gold and the fastening of it there, in whatever class of cavities, dejK'nds on careful attention to several details: First, the operator must so conduct his operation as to control the saliva perfectly, keeping his work dry. Second, the matrix must be fixed and rigid in its application. Third, the pluggers should be kept freshly serrated, and of such forms as give direct entrance to and application of them at the ])oint on the work. Fourth, the ser- rations should be clean and deep. Fifth, the gold should be clean and freshly annealed. Any t)f the forms of cohesive gold may be used, if the portions carried each time to their destination are small clean, and annealed. Small cohesive gold cylinders, Nos, } and ^, are easily used for this work, and the smaller ones should not only be employed to begin with, when this form is used, but as far as practicable throughout. The strips or ril)l)ons, however, of cohesive gold when freshly annealed, and witii all other conditions above enumerated complied with, give best results. The ribl)on is taeked or pricked into the .soft gold by interdigita- tion, and the union made with this or any preparation of cohesive gold, while not strong, is enough so, to enable the operator to reach his anchor- age points, where he may thoroughly secure the work. In making matrix fillings, if the matrix employed is of the band or loop variety and has no separating feature, in order to secure contour, and to have the fillings finish in the original form of the tooth, the teeth, if two are together, should have the c-avities previously packed with cotton, long enough to produce mobility of the teeth so that they may more easily yield apart. This then gives opportunity to push the teeth apart still further, especially with those matrices provided ^vith the separating feature, and so to gain room in which to shaj)e the matrix band and to reproduce the contour of the tooth. Preparation of Gold for Matrix Work. In the soft-gold part of matrix work the form of the gold to be em- ployed is im|X)rtant to be understood. Large cylinders and cushions in comparison with those ordinarily used in cavities of given size are not only more safely and perfectly adapted, but more quickly done. This results from doubling and partly compressing the cushions, which, being further susceptible of compression, are still large enough to squeeze in place and bind as they are compressed. PREPARATION OF GOLD FOR MATRIX WORK. 273 In placing cushions into the bottom of large cervico-occlusal cavities of molars and bicuspids embraced by the matrix, it is important to start with those of sufficient size and density to bind as they are condensed, but it is not to be understood that the first such piece introduced must be fully condensed before other similar pieces are added. If this practice were followed, notwithstanding the fact that the first piece introduced binds as it is condensed, this is so only to a certain point of the conden- sation. Beyond this if we continue it, especially to that density which may be obtained against the resistance the tooth aifords, it loosens, will tilt and rock, and is worthless. But if after placing in one cushion which the operator learns to proportion to the size of the cavity, and partially condensing it, he introduces another and carries the condensation to the point of the first, and still another, he may then mallet until the mass will yield no more; and the wall thus built will be steady, well adapted, moisture proof, and, therefore, impervious to leaking by capillary force. This comes of the fact that when three or more cushions or cylinders are carried down as described, the bearing up and down of the axial and matrix walls is sufficient to insure binding and steadiness. In the illustration. Fig. 223, will be observed at K a gold cushion entering the cavity between the axial wall f and the matrix band h. Fig. 236. Leaf of No. -4 gold foil, twisted, ready for formation into cushions. The cushion is made of one-half of the gold twist shown at Fig. 236, and contains two grains of gold by weight. This cushion, when con- densed to its ultimate density, as by melting and hammering, is repre- sented in cube form and exact size at m, Fig. 235. A No. 4 gold cylinder, one-fourth of an inch long, contains one grain of gold bv weio;ht, and when this is condensed into cubic form it is one- half the bulk of the cube shown at M, Fig. 235. It transpires then that the large loosely-made cylinders of one grain weight are more difficult of satisfactory adaptation than those which contain the two or more grains, because the large loose ones lack the bulk and substance which is necessary to cause them to bind and lock in condensing. It will be seen further, by comparison of the 2-grain cube M, Fig. 235, with the proportions of the cavity in which it rests, that it reaches hardly half across the cavity, bucco-lingually, and that if this cube were elongated so as to reach across the cavity, its bearing against the axial wall and the matrix band would be lowered at least one-half, and there would not be sufficient bearing up and down these walls to hold the gold fixedly in place. This then demonstrates the difficulty of adapting gold 18 274 USE OF THE MATRIX L\ FILL I SO OPERATIONS. or tin-loil at siii'li jxtints witli cylindrrs or ciisliioiis containiii*; less than enough material to liind and lock the ina>< in jdaic in the process of"con- densino;. And if this hi." true, as is illustrated in Fig. 2o"), it is seen that the size 4 cylinder, containing only one grain, would he still more difhcult to control, because it lacks in greater degree tiie hulk and suh.-tance sufhcient to give the i)earing up and down the walls necessary to the binding and locking in the process of condensing. XeitluT will the cylinders or cushions containing two grains or more in very large cavi- ties hear complete condensing, bef(jre adding other pieces without loosen- ing, for the reasons already given. In exceptionally large cavities of the major class, a sheet of No. 4 foil may be formed into a single cushion, and introduced to advantage. Such a cushion containing four grains would not build higher than is necessary to bind, even if it were formed into a rectangular parallelopiped — two cubes side by side, and extending from one lateral wall to the other. Fig. 235. The successful making of fillings with either gold or tin is not so much a question of securing the ultimate density of these materials, as tiiat of securing adaptation of them to the walls of the cavity in such manner as shall prevent leakage beneath the filling. This result may be obtained with a compression or condensation of much less density than is shown in the melting of them, or as is obtainable against the resistance which the tooth offers. Formation of Cushions from Foil. The cushion of either gold or tin, rather than the cylinder, is a better pre])aration for matrix work, even when it is made from cylinders compressed or doubled upon themselves, because the cushion, made of fiiil, while soft enough to be adapted to the irregularities of the cavity, contains from twice to four times the amount of material which the loose cylinders do, and because of this fact, in connection with proper cavity formation, they are more easily secured in place. The student should appreciate the fact that until he succeeds in laying the foundation of .soft-gold work in a manner to j)revent its moving or shifting position in the process of condensing, he will have failed to secure the results within his reach. The employment of the cushion, therefore, rather than the cylinder, is nrged as the best means to this end. The formation of cushions fnmi the foil is as follows: Take a full leaf of No. 4 soft gold-foil, and with clean hands crimple and wrinkle it. Straighten this out, but leave the sheet nndulated, when it should be loosely folded three to four times upon itself and loosely twisted. The twist thus made should l)e cut into from three to five pieces, Fig. 236, dejiending on the size of the cavity to be filled. The large cavitie.s, FINISHING THE FILLING. 275 such as are seen in the approximal surfaces of molars, Figs. 221 and 222, will take a cushion made from the longer section of the twist shown in Fig. 236, which may represent one-half or more of the sheet of No. 4 foil ; while cavities of the proportions shown in Fig. 231 will take one-fourth or less. Smaller approximal cavities in the incisors will take from one-fifth to one-third of a half-sheet prepared after the manner of Fig. .236. The cushions prepared after these suggestions, when used for the large cavities of the molars and bicuspids, should somewhat resem- ble the illustration in Fig. 237. The preparation thus cushion formed from made is more desirable than the cylinders made of soft 236,^ or from par- foil, because it is more easily manipulated and with ti^Hy compressed better results, and because the student learning to do this secures to himself a resource which enables him to prepare his cushions for all sizes of cavities, and is never at a loss for what is wanted when foil is to be had. But when this class of work is to be done with tin-foil, the cylinders, compressed or doubled, will serve best, since it is difficult to obtain a foil of tin light enough and soft enough to make desirable cushions. Tin-foil in cushions, made by doubling the cylinders upon themselves for the foundation portion of cervico-occlusal fillings, in connection with the matrix, works even more kindly, and adapts more easily than cushions made from soft gold-foil ; and if its use here is not forbidden by electrolysis, it is to be given first place as a tooth preserver, especially at the cervical margins, and as a non-conductor of the thermal changes to the pulp. Tin-foil and soft gold-foil laid together, and the two formed into cushions after the suggestions already made, may be used with results quite as beneficial for preservation of the margins embraced by the matrix as when gold or tin alone is used, with the advantage of avoiding the danger of electrolysis of tin under gold. Finishing the Pilling. No part of the work of making gold fillings, such as are included in the major class particularly, is more laborious than the finishing of them. Yet when the matrix has been projDcrly adapted to the teeth, the finishing of the cohesive gold part may be lessened to the minimum. The more rapid and satisfactory finishing of the work following the use of the matrix is no small part of the advantage of this device, since the matrix gives not only the form of the wall which it embraces, but more than any other method yet devised saves filling material. This comes of the fact that when it is properly adjusted the cavity is converted into a mold so nearly the shape of the filling to be, that when it has been made very little work remains to be done in polishing. 27(> USE OF THE MATRIX I\ FILIjyG OPERATIONS. The first step toward polishiiij^ ufttT rcinoviiii,^ the nuitrix is to go around the borders of the soft-gold portion of the filliiii; witli ii bhide huriiishor, wliich slioiihl \w kept highly poli.slud and clean. In this c)pt'ration the object should be to eonij)ress as nuu-h as possible hv hand- pressure the soft-gold portion that may have bulged under the nialleting. After this the Rheiu trimmers, Xos. 31 and 32, should go ttver the borders, and should be held so that the blade shall rest ecpially on the filling and the adjacent external surface of the tootli. At this point, if the operation is between molars or bicuspids, the Perry or the Ivory separator is valuable, and should be placed so as to have the beaks impinge above the margin of the filling, and should be made to open the teeth only enough to pass in the thinnest strips and sandpaper disks. Care and skill are rcfpiired in the handling of disks to avoid grinding away the contour of the filling, but the disk can be so held as to prevent this. The author finds, in removing the overhanging corners of the cohe- sive portion of these fillings, that the use of a stili" five-eighth inch garnet disk, held only to the corners and not permitted to jiass in between the teeth, answers better than any form of corundum or carborundum wheels. After thus carefully shaping the caj) or slab of cohesive gold at the contact points, and rounding them as the case permits and requires, flint strips and the "regular" grit, followed with the "fine" cuttlefish disk, completes the polish. The occlusal surface of cohesive gold is easily shaped with corundum wheels and polished with the cuttlefish disk, when these can be made to apply, or with leather wheels carrying ])nmice. There is no essential difference in polishing the major and minor class of these fillings, except in the extent of the work. Forms of Matrices for Molars and Bicuspids. A presentation of all the devices known as matrices is not the purpose of this chapter, but only of those whose efficiency commends them. Fig. 238. ii The matrices of Dr. Lmiis Jack. Fig, 238 represents the set of matrices devised by Dr. Louis Jack. This set of matrices is provided with concave surfaces for contouring the FORMS OF MATRICES FOR MOLARS AND BICUSPIDS. 277 teeth, which indicates the high ideal of the originator of the device. They are made thicker and heavy at the base of the lateral edges, which aids in steadying them between the teeth, and they are provided with slotted edges, which engages a special pliers to insert and remove. Fig. 239. I^oop matrices Fig. 239 shows a set of loop matrices, which at times, and with teeth of slight constriction at the neck, answer well, but, like all of the loop variety, they require space at both sides of the tooth to admit of adjustment. Fig. 240. Brophy's band matrices. Fig. 240 exhibits a set of matrices devised by Dr. Truman W. Brophy, which, with the flexibility of the thin steel bands and under the action of the screw, may be made to aid the operator most acceptably. The band is not unlike the loop in the matter of passing between the teeth, and the teeth must yield apart to admit it. Still, with the thinness of the bands in this set, there is no difficuty in this particular. This form of matrix, however, is unsteady and difficult to fix rigidly on very short crowns, and particularly on those of decided conicality. Fig. 241 exhibits an improved loop matrix devised by Dr. S. H. Guilford, in which the lip feature is added for the purpose of having the band to catch below the cavity, without the necessity of forcing the band elsewhere around the tooth into the gum. This device, made in several 278 U;SE OF THE MATRIX L\ FILLISd OPERATIONS. IciuTtlis <»f bands, altlioiigh tedious to adjust from the fact tliat throe pieces must be handled, is otiierwise vahiabK' and serviceable. Fig. 241. Guilford's band matrices and clamps. Fig. 242 illustrates T)r. W, A. Woodward's screw matrices. This form of matrix has valuable features in that the thin metallic ribbon constituting the matrix wall may be made as thin as No. 36 to 88 gautr(>, and yet possesses ad(>qnate tensile strength. The device is also valuable Fig. 242. because in its use only one thickness of the ribbon need be carried be- tween the teeth. Again, it has the separating feature, which makes it additionally desirable, as this forces apart the teeth to start with, and the separation is continued as the operation proceeds, or as the exigency of the case demands. To Chapter XIV. in this volume, on Combination Fillings, by Dr. Dwight M. Clapj), the student is referred for the desc-ription of his matrix devices and their application. These matrices are quite as well employed for making gold and the plastic fillings as for the specific purpose of combination fillings. Fig. 243 shows illustrations of Dr. E. R. Lodge's matrix bands, ten- sion screws, and wrench. Those marked a are adapted to bicus})ids and FORMS OF MATRICES FOR MOLARS AND BICUSPIDS. 279 molars of usual form, while those marked b are adapted to the same class of teeth, but of constricted necks and more pronounced bell-shaped crowns, c and d of this illustration show two forms of tension screws, and F and e the wrench for operating the screw D, Fig. 244 shows the Lodge device adiusted to the teeth. Fig. 243. F (^ ^^^mmmmf^miims d Lodge's system of loop matrices. The bands of the Lodge matrix are made of German silver, and are provided with two eyelets in each, giving ample range of adjustment. Figs. 245 and 246 show a form of matrix suggested by Dr. A. C. Hewett, which, for simplicity and efl&ciency, meets a constantly occurring want. In the instances where the matrix is employed between the teeth Fig. 244. and it is braced by an adjacent tooth, and where no straining apart of the teeth is required, this device is admissible. But it should be braced with a wedge, ordinarily at the cervical edge. Fig. 247 is a form of matrix which has been used by the author in extensive cavities occurring on the buccal surfaces of lower molars. 280 vsE OF nil-: .v.iv7;/.v f.\ rnj.ixa (/pkratioKs. Tlio IkuuI wliicli must Ik- fitted to facli case is iiuule i'rom No. 35 to 36 ^auge Gernum silver, ami so cut that the projecting arms turned down on the occlusal surface of the tooth prevent it from carrying down with the wedge as the device is tightened. In the instances where the cavity extends beneath the gum the hand can be provided with a lip to catch below the buccal margin. The dam can rarely be employed in these opera- tions, but fortunately it is not necessary for the first jiart of this ojH-ration. Vn;. 1245. Fig. 240. Fjc;. 247. The Hewett matrix held in The Itewett iniitrix held in The band matrix nsed in position with the I'armly position witli the ordinary exlensive buccal surface Brown clamp. rubber-dam clami). cavities on lower molars. When the lingual and buccal sides of these teeth are provided Avith ab- sorbent-cotton rolls, and especially when the saliva ejector is employed, the cavity can easily be filled to the top of the band with soft gold or tin, as suggested elsewhere in this chapter, before moistu're shall interfere. If the capping for this filling shall be of amalgam, it can be finished within the time the alxsorbents protect. If the purjiose is to finish with gold, the dam should at this juncture be placed over the band and tooth after the soft-gold ])art is brought to the top of the band, and the remain- der of the Avork finished with cohesive srold. Fiu. 248. Fifi. 249. The Hodson contoiir slip matrices. The Hodson matrix in jjosition between the teeth. Fig. 248 represents the contour sli]) matrices devised by Dr. J. F. P. Hodson. The device is a most meritorious one, with which the contour of molars and bicusj^ids can be fully restored, but can only be used between the teeth. Fig. 248 gives two views of the matrix ready to be slipped in place. These matrices are made preferably of thin annealed steel plate, forged or swaged on a leaden slab with an oval-end punch, giving them what- ever of concavity the case mav require, they are then slipped in place. FORMS OF MATRICES FOR MOLARS AND BICUSPIDS. 281 which causes the teeth to yield apart. The gingival end of the device should be braced against the adjacent tooth with an orange-wood wedge until after the filling is inserted. The Hodson device is better adapted to amalgam work than gold, be- cause it does not possess the rigid fixedness in sufficient degree to remain securely in place for extensive gold operations. If the filling material used is a plastic the device is left in place over night or longer, allowing the filling to set under pressure, which may be done readily, as the device shown in Fig. 249 is in no wise uncomfortable or troublesome to the wearer. When the adjustment of the matrix is properly made, it is unneces- sary in most instances, particularly in the uper jaw, to use the dam. Fig. 250 represents the contour matrix as devised by the author of this chapter. This device, which is of duplex form, is only used between the teeth, and acts in the three-fold capacity of matrix, separator, and rubber-dam clamp. The device is shown in position between two Fig. 250. Fig. 251. The Crenshaw contour matrix in position The contour matrix with one band between molars. turned out for removal. molars, the cavities of which have been prepared after the suggestions of Figs. 221, 222, and 223, and the manner of introducing the cushion. With this form of matrix the teeth may be drawn apart as with the sep- arator, and the fillings given the contour the teeth originally possessed. Fig. 251 shows the method of removing the matrix, as may be done when amalgam is used without lifting or unseating the filling. To do this the pin is withdrawn and the band embracing the unfilled tooth is turned out on the tension screw as a pivot. After this the band embrac- ing the filled tooth is lifted away from it, when the matrix may be removed from between the teeth. In amalgam work with this device only one tooth should be filled at a sitting, and after this filling has crys- talized and become fixed in the tooth the second one should be made. Fig. 252 shows how the operator may protect his work without the dam in the lower jaw by placing absorbent-cotton r'olls on each side of the teeth, and how these are held in place by the matrix. The employ- 282 USE OF THE MATRIX IS FILIJSU OrEIiATIOyS. inent of tlu' cotton rolls (iMuon between canine Enlarged figure of the anterior teeth matrix and first bicuspid, with buw brace attached. a and B, arms; c, projection screw ; d, metal- lic ribbon. Fig. 254 shows the contour matrix in position between a canine and first bicuspid, in connection with the bow brace, which prevents the matrix slipping from between the teeth, as it is inclined to do on account of the bevel of the lingual side of the canine. Matrix for the Anterior Teeth. In the effort to improve gold work in the approximal cavities of the anterior teeth bv a method which practically does away with cohesive gold, the author offers the anterior teeth device. Fig. 255 shows the device enlarged, as it appears before being placed in position about the teeth, and with the lower part shown in section. MATRIX FOB THE ANTERIOR TEETH. 283 The arms A and b project through the loops formed on the ends of the metallic ribbon d, the thickness of which is ^c^ of an inch, and which may be passed between teeth of rigid contact. The parts A and b are separable, and when the tension screw c is turned in, the arm b is extended, which puts the ribbon D under tension. Fig. 256. Fig. 257. The metallic ribbon in position before crimp- ing. Fig. 258. The metallic ribbon adapted to tooth after crimping. Fig. 259. The holder applied for tensioning the ribbon. The holder applied for taking up slack in the ribbon. Fig. 260. Fig. 261. Application of the ribbon pressing the left cen- tral forward. Application of the metallic ribbon between the anterior lower teeth. Fig. 256 shows a lingual view of four incisors with the matrix ribbon in position before it has been adapted at the iucisal edge. Fig. 257 shows the ribbon crimped and soldered, which Fig. 263. adapts it closely to the tooth at the incisal edge, and to the surface of the tooth beneath the ribbon. Fig. 258 presents a labial view with the device in position, and shows how cavities Fig. 262. Application of the holder pressing the lower right central forward. E, cervical, f, incisal, o, lingual, h, labial subdivision of approximal incisor filling. which extend through and open on the liugual face of the tooth may be floored and brought into simple form. Fig. 259 shows a means of taking up slack in the ribbon, if this 284 USE OF THE MATRIX L\ EILLLSU OPERATloSS. should iK'Comeiioecs.sirv, hytjlippiiiir tlicslittcd arm astride of tlic rihhoii, as shown in this ii<;inv. Jiy this means, if at any time the tension serew shonld 1)1' i-iin in to its limit, additional tension can lie nhtained witiiont removini; the ribbon. Fig. 200 is a view showing the eutting edge of tlie teeth and the crimp of the metallic ribbon. Fig. 2(51 is an ajjplication of the ribbon to the lower incisors. It mnst ordinarily be placed between the teeth before applying the holder. Fig. 262 shows the holder iu position. Filling Approximal Cavities with Cohesive and Non-cohe- sive Gold with the Anterior Teeth Matrix. Fig. 26.3 shows an aj)proximal cavity in a central incisor three-fourths filled by the aid of the matrix, after which the matrix is removed. The subdivisions of the filling, lettered e, f, and G, are made of soft gold, leaving the space marked h to be filled with cohesive gold. The pro- cedure which best accomplishes this is as follows: If the cavity be a large one, take a No. 3 or 4 soft-gold cylinder and double it upon itself and again crosswise, making a firm cushion. Let this cushion be large enough to squeeze into place. Take a foot-shaped plugger with light serrations, Nos. 257, 2.")8, or 259, Fig. 26o — whatever size of this form best suits the case — and ])ress this first cushion into the undercuts of the cavity at K. After settling it by hand-pressure, take a suitable fijot- sliaped j)lugger, No. 257 or 258 answers well, in the automatic mallet, and, while holding down at the lingual side of the cushioji, mallet the other, after which change the instruments about, and mallet the labial side. After this is done, treat the opposite end of the cavity at f in the same way, only the cushion going into this subdivision may occasionally have to be drawn into place with the throat of the instrument. When the F subdivision is condensed, use a No. 2 cylinder folded (jnce upon itself, and introduce end-wise at G, which when condensed keys E and F in place. If the cavity be a large one it will require two (»f the No. 2 cylinders, and in some cases three, to bring this part of the filling to the centre of the cavity, which is necessary in order to securely brace e and F in place. The author cautions against using small soft cylinders with which to make the key-block, because when condensed they do not build up high enough to ol>tain the necessary lateral bearing against blocks E and F to hold firmly in place. Neither should cohesive gold in any form be used here. It will be observed from the lines of the cavity division in Fig. 263 that the cavity is to be tilled from the labial side, and that it extends THE HANDLES ADAPTED TO THE PLUGGERS. 285 through into the lingual face of the tooth, also that the matrix ribbon, which has been removed to show the plan of the filling, envelops and embraces the tooth in such manner as to floor the lingual portion of the cavity, as may be seen in Figs. 258, 259, 261, and 262. The action of the device not only moves the tooth forward to be filled as seen in Fig. 260, so that it may be got at easily, but transforms a dif- ficult cavity into one of easy, simple form. In the instances where the opening of the cavity is toward the lingual aspect with a labial wall to be preserved, the device operates with as much favor in filling from the lingual as from the labial — see Figs. 257 and 260. In these figures the action of the device will be seen to move forward the left central, and depress the right central and left lateral. When the filling is made from the lingual aspect, the lines of the sub- divisions of the filling, Fig. 263, would be reversed, and the key-block would be placed at h, with H occupying the position of g. Pluggers for Matrix Work. The point of a plugger is not all of its efficiency. The handle may materially enhance or handicap its performance, and the average student, unless guided in the selection of points and handles, is apt to get together in the selection of excavators and pluggers an incongruous combination, much of which will prove unsuited and unfitted for anything he is called on to do. Some of the forms of pluggers here suggested for matrix work may be found in the student's case. All included in the list of Fig. 265 are regarded as cohesive gold instruments, but several of these forms are ill adapted to that work and well adapted for soft gold. Many of the forms of instruments included in sets of soft-gold pluggers cannot be utilized in the execution of the soft-gold part of the matrix fillings set forth in this chapter ; and to assist the student in knowing which instruments shall be used to manipulate the cohesive, and which the soft, and the handles best suited to them, are pointed out and explanation of their uses made.^ The Handles Adapted to the Pluggers. Nos. 7, 8, 10, 18, 115, 116, 117, 118, 207, and 208 should be placed in cone-socket handles Nos. 4 or 5, Fig. 264, according as the shank of the plugger point is small or large. These handles can be used for hand- pressure, but are designed especially for the hand-mallet. Nos. 174, 175, 248, and 250 should be placed in the cone-socket ^ The handles, pluggers, and numbers of same, are taken from the revised lists of the S. S. White Dental Manufacturing Company. 286 USE OF THE MATRIX IN FILLING OPERATIONS. hamllcs Nos. 2 or .'>, Fig. 204, according as the shank of the plugger point is small or large. Fig. 204. 3 4 5 10 Handles for cone-socket points. Nos. 257, 258, and 259 should be placed in the rubber handles No. 10 or 10a, Fig. 264, according as the shank of the plugger point is small or large. THE USES OF THE SEVERAL PLUGOEBS. 287 The Uses of the Several Pluggees. Nos. 1, 8, 115, 116, 117,118, and 207, Fig 265, are for cohesive gold, and may be made to answer the needs of this work in conection with matrix fillings. No. 60 Parmly Brown plugger point, for cohesive gold, is of uni- versal application, and is best used in the electric or the engine mallet. Nos. 174 and 175, Fig. 265, are assistant pluggers, used to hold down Fig. 265. ills 18 115 116 117 lis 174 175 207 208 218 250 257 258 259 Condensed set of pluggers. when malleting ; and may be used for packing cushions in the cervico- occlusal column of molar and bicuspid matrix fillings. Nos. 248 and 250, Fig. 265, are for soft gold, and used for placing and compressing the cushions into the subdivisions E and r. Fig. 263, of the smaller class of approximal incisor cavities. Nos. 257, 258, and 259, Fig. 265, are for compressing the cushions into the subdivisions e and r. Fig. 263, of the larger class of approximal incisor cavities. The square corners at the toe of these forms should be rounded off. Nos. 10, 18, 208, 248, and 250, Fig. 265, are for settling and mal- leting soft-gold cushions in the cervico-occlusal column of molars and bicuspids, see Figs. 223, 226, and 227, and for carrying down and mal- leting the subdivision g. Fig. 263, and fillings of this class. A Matrix Auxiliary. [Dr. Alfred P. Lee, of Philadelphia, has devised a simple and practi- cal method of overcoming the difficulty often experienced in adapting the matrix to an approximo-occlusal cavity when the cervical portion of the missing wall presents a concave surface, due to the tendency of the roots to bifurcate. By the use of sheet copper, not more than j-^^-^ of an inch in thick- ness, in conjunction with the Ivory or similar matrix, an appliance is made which when removed after the filling has been inserted will be 288 USE OF THE MATRIX IX FIIJAXd OPERATIONS. found to Ikivc kept the lilling tlic desired shape, leaving no overluinging portions at the cervix to trim away. A pieee of th(»roiighly anneah'd eopper phite, hirgo enough to cover the ai)proxinial portion of the cavity and extend, say one-eighth of an inch beyond the buccal and lingual margins, is pressed with cotton or bibulous paper pellets to conform to the concave root ])eriphery at the cervix. The copper is then carefully removed and, if the cavity be for amalgam, the depression in the copper representing the cervjcal concavity is filled with hard wax until a convexity is obtained ; Transverse section of tooth at Both matrices in position on Shows copper plate with cervi- a point near cervical border of cavity. Outer line show- ing copper matrix in posi- tion. Dotted line represents degree of contour supplied with hard wax or solder. tooth crown. cal depression filled with soft solder and applied to cavity before adjustment of outer matrix. the copper plate is then placed in position, and around it a steel matrix is adjusted, and when fully tightened the free edge of the copper is burnished against the steel. When gold is to be inserted it is necessary to use something more stable than the hard wax, therefore the concave surface at the cervical margin of the copper plate is touched with zinc chlorid, and over the alcohol or Bunsen flame soft solder is flowed into the depression. Any surplus may be trimmed off with a disk. — Editor.] CHAPTER XIII. PLA.STIC FILLING MATERIALS— THEIR PROPERTIES, USES, AND MANIPULATION. By Heney H. Burchaed, M. D., D. D. S. The materials included in the heading of this chapter are — (1) Amalgam ; (2) Gutta-percha and its preparations ; (3) The basic zinc cements. History. — The introduction of the first member of the group was not prompted by any specific merit that it had been demonstrated to possess, but was due solely to its properties of easy introduction, com- paratively perfect sealing and prompt hardening, qualities which appar- ently recommended its wide and general use to those not possessing the requisite degree of skill for the successful manipulation of gold foil. Applied upon a basis of glaring empiricism, with an absence of technical skill, the material received the prompt and sustained con- demnation which its abuse had warranted. The steps and phases of this opposition of the trained and skilled against untrained and un- skilled operators may be read in the dental journals of from 1846 to 1878 and even after. It was commonly known as the " amalgam war." The first dental amalgam was that of Taveau, called " Silver Paste." It was made of filings of coin silver (silver 9, copper 1), combined with sufficient mercury to make a plastic mass. It was presumably this alloy which was introduced into America by two charlatans named Crawcour, under the glittering title of " Royal Mineral Succedaneum," The discovery of the nature of the paste followed soon after its intro- duction, which was clearly prompted by the motives above stated. Thereupon followed a persistent and virulent attack upon the material and all who used it. Upon less than the merest shreds of evidence alleged cases of salivation and mercurial necrosis were recorded as due to the use of amalgam. That amalgam was still employed by the practitioners of France is evidenced by the presentation in 1849 of a formula for an amalgam alloy of pure tin and cadmium by Dr. Thomas Evans, an American dentist practising in Paris. An amalgam made from this alloy was found to shrink, and also to stain the dentin of teeth into which it had been introduced, owing to the formation of cadmium sulfid. It is note- 19 289 200 PLASTIC I'll. Lisa MATERIALS. worthy tliMt Dr. Kvans liiinsc'll" was tlif first to discover and make puhlic tlic deficiencies of his amalgam. In America amalgam remained nnder a ban nntil T)r. EHsha Towns- end of Philadelphia, a practitioner of snch great skill as to he safe from any im[)ntation of lack of manipulative ability, introduced in 1855 an alloy of 44^ silver, 55^ tin. The amalgam of this alloy received an endorsement and application based more upon the eminence of its author than upon the results of actual clinical tests, and a reaction occurred which brought amalgam again under general coiidc nination. What was known as the " new-departure corps" had its birth shortly after this time. This was composed of a limited number of practi- tioners and metallurgists, who were impressed by the fact that gold as a filling material was not the panacea of dental caries, and that by inves- tigation alone could the proper place of amalgam l)e found in the dental armamentarium. It is due to this group of investigators to state that the history of the rational employment of plastics is the history of the " new-departure corps." It was undoubtedly due to it that plastics have come to be regarded as substances having definite physical and chemical properties which fit them for application as restorative and therapeutic agents for the relief of clearly defined physical and patho- logical states. As the properties of these agents become better under- stood, their employment more closely follows what is known as rational therapeutics. The use of any or of all of these several materials is founded so entirely upon their individual properties that a discussion of these properties must precede and govern that of their methods of manipula- tion. Nature and Properties of Amalgam. An amalgam is a combination of one or move metals with mereuri/ ; it. is therefore any alloy into which mercury enters as a constituent. The word amalgam (Fr. anudgame) is derived from Gr. aiia, together, yafxiw, I marry ; or from S.na and /m/.ayna, from iialdaaco, I soften — because of the softness and fusibility which mercury confers upon alloys. It is to be understood that amalgams are classified as alloys, and may be therefore members of any of Matthiessen's groups as follows : A chemi- cal compound in which the affinities are exactly satisfied ; one in which there is unstable chemical equilibrium ; a sub-chemical compound, or a mechanical mixture — although this latter is rare, as mercurv exhibits some degree of affinity for all metais. There are two possible ways in which mercury brings about the solutier amalgam is the only alloy test<'d by Dr. l^lack which nnder- went no change of form in hai'dening. " Flow " OF Amalcjam. — A projuTty attrihnted to certain amalgam-s, that of spheroiding, has been shown by Dr. Black to be without exist- ence. The bulging of amalgams from the orifices of cavities was held to be due to tlu' tendency of the mass to assume a spheroidal form, hence the term spheroiding. Tests showed the appearance to be delusive, the phenomenon being due to expansion and not to a s})heroidal tendency. In addition to the properties of contraction and expansion the same investigator has discovered the property, hitherto unsuspected in amal- gams, that of flow. The j)roperty of flow — /. e. change of mass form, from molecular motion under stress— had been observed in the majority of metals, but as found in amalgams it has a unique expression. Instead of being limited to a definite degree, proixM-tioned by the stress applied, it has been found that amalgams yield repeatedly to the same amount of stress when a])plie(l at intervals, as in mastication, or yield contimiously when the stress is constant. The process appears to be without limita- tions. It is at zero in copper amalgams ; next less in amount with alloys containing 55-60 per cent, of silver with 5 per cent, copper and the remainder tin. It will be readily seen that this property exercises a great influence upon the integrity and adaptation of an amalgam filling. The notes quoted from Dr. Black were compiled from studies made of amalgams whose exact chemical composition had not been actually tested by the investigator. Later experiments ' made with alloys pre- pared with the utmost care and exactitude by the investigator himself, gave widely different results (particularly as to the effect of adding a third or fourth metal to the basal alloy) in the direction of both flow and shrinkage. The first series of experiments which appeared to show an enormous increase of shrinkage and flow together with a lessening of edge strength, by the addition of a third or fourth metal (except copper, which the latest experiments still show to lessen flow and increase rigidity) were not confirmed when Dr. Black experimented w'ith alloys made by himself, and an additional and unsuspected factor was taken into consideration, viz. the influence of heat upon the alloy. It has been noted by Dr. J. Foster Flagg ^ that alloys which were freshly cut possessed working properties different from the same alloys when " old cut," or when aged. Dr. Black's observations appeared to confirm this, and his later experiments were directed toward deter- mining the cause underlying the change. Motion, which was said to ' Dental Cosmos, December, 1896. ■■* Pla^itics and Plastic Fillings. NATURE AND PROPEBTIES OF AMALGAM. 293 bring about the change, was found .to have no influence. After exhaus- tive and conclusive experiments it was ascertained that the change was due to a molecular alteration of the cut alloy, through a process of an- nealing or " tempering " — i. e. heat was the agent producing the change. The degrees of heat applied ranged from 130° to 212° F. It was found that the amount of time during which an alloy was subjected to the action of heat governed the extent of tempering ; for example, alloy subjected to a temperature of 130° for a given period, had the amount of amalgam expansion reduced a given amount ; if the heat were maintained for a longer period the expansion was corre- spondingly decreased. Each formula has its zero point beyond which tempering has no effect. In general terms, it was found that alloys in amalgams which expanded in hardening had the extent of expansion reduced by anneal- ing ; those which contracted had the contraction increased. Alloys which were without alteration of volume unannealed, shrank when annealed. The following tables will show the extent of change produced by annealing. It will be noted that the alloy of 72.5 silver, 27.5 tin, ex- hibits the minimum contraction after annealing. It will also be observed that less mercury is required to effect amalgamation in the annealed alloy .^ Amalgams made from annealed alloys have both their flow and crushing stress slightly increased. I. Exhibit of Unmodified Silver- Tin Alloys: FOBMnT.s".. How prepared. Per cent, of mercury. Shrinkage. Expansion. Flow. Crushing stress. Silver. Tin. 40 60 Fresh-cut. 45.78 6 7 40.15 178 40 60 Annealed. 34.14 9 3 44.60 186 45 55 Fresh-cut. 49.52 4 8 25.46 188 45 55 Annealed. 32.13 11 1 28.57 222 50 50 Fresh-cut. 51.18 2 2 22.16 232 60 50 Annealed. 37.58 17 1 21.03 245 55 45 Fresh-cut. 51.62 2 2 19.66 245 55 45 Annealed. 40.11 18 17.53 276 60 40 Fresh-cut. 52.00 1 9.06 239 60 40 Annealed. 39.80 17 14.10 297 65 35 Fresh-cut. 52.00 1 3.67 290 65 35 Annealed. 33.00 10 5.00 335 70 30 Fresh-cut. 55.00 14 3.45 316 70 30 Annealed. 40.00 7 4.67 375 72.5 27.5 Fresh-cut. 55.00 42 3.92 275 72.5 27.5 Annealed. 45.00 3 3.76 362 75 25 Fresh -cut. 55.00 60 5.64 258 75 25 Annealed. 50.00 6 5.40 300 ^For a full exhibit of this stupendous work of Dr. Black's, the reader is referred to his contributions in the Dental Cosmos for 1895 and 1896. 2 Black, Dental Cosmos, 1896, p. 982. 2D4 PLASTIC FILIJMi MATERIALS. II. lu-hihit of Modified SUrcr-Tin Alloys} Formula. ' ": How pre- pared. Tin. Per cent, ofmercury. Crushing stress. Modifjing meUl. Silver. Shrinkage. Expansion. Flow. 65 35 Fresh-cut. 52.33 1 3.67 290 65 35 Annealed. 33.00 10 5.00 335 66.75 33.25 Fresh-cut. 51.52 4 3.35 329 66.75 33.25 Annealed. 33.53 7 5.06 380 Gold 5. 61.75 33.25 Fresh -cut. 47.56 1 4.62 330 Gold 0. 61.75 33.25 Annealed. 30.35 7 6.07 395 Platinum ^^. 61.75 33.25 Fresh-cut. 51.87 9 9.68 273 Platinum o. 61.75 33.25 Annealed. 37.33 7 8.20 352 (opper 5. 61.75 33.25 Fresh-cut. 53.65 23 2.38 343 Copper 5. 61.75 33.25 Annealed. 35.60 5 3.50 416 Zinc 5. 61.75 33.25 Fresh -cut. 56.65 68 1.83 290 Zinc 5. 61.75 33.25 Annealed. 40.65 9 2.07 345 Bismuth 5. 61.75 33.25 Fresh-cut. 46.26 4.78 288 Bismuth "). 61.75 33.25 Annealed. 23.67 6 5.58 308 Cadmium 5. 61.75 33.25 Fresh-cut. 57.57 100 6.40 225 Cadmium 5. 61.75 33.25 .\nnealed. 47.25 5 3.54 290 Lead 5. 61.75 33.25 Fresh-cut. 44.17 1 4.88 290 Lead 5. 61.75 33.25 .\nnealed. 32.76 10 7.18 276 Aluminum 5. 61.75 33.25 Fresh-cut. 65.00 445 Aluminum 1. 64.5 34.5 Fresh-cut. 46.98 166 12.60 198 Aluminum 1. 64.5 34.5 Annealed. 38.26 48 17.90 213 Edge Strength. — What is termed the edge .strength of an amal- gam is the degree of resistance an edge or angle of an amalgam mass oflfers to force which tends to fracture it. Amalgam."^ have heretofore been regarded as rigid crystalline masses, utterly devoid of malleability. The discovery of the existence of flow at once modifies all previous conceptions and data regarding edge strength, for it is evident that a corner or angle might not fracture and yet might flow under the stress of the impact of mastication, whereupon edge strength might be said to be great, and in reality be but slight. In view of the existence of the property of flow, edge strength must be measured as rigidity, the antithesis of flow, and a high crushing stress. It has been shown that contraction or expansion, and flow, are the influences which would disturb the maintenance of size and forai of an amalgam filling ; therefore, a minimum of shrinkage and flow are the primary considerations in a .'satisfactory dental amalgam, CoiX)R. — One of the serious drawbacks to the wide enij)loyment of amalgam has been its objectionable color, both in its original state and furthermore when it has suffered discoloration through the formation of oxids or sulflds upon its surface. The silvery white of amalgam in its most acceptal)le condition is not so harmonious a color as the vellow of gold, wliich fact has led first to the restriction of the u.se of amalgams to such spaces as are not readily visible, where its original and subse- quently its altered color could not be a .strong objection ; and, next, ' Black, hentd. Cosmos, 1896, p. 987. NATURE AND PROPERTIES OF AMALGAM. 295 has prompted a modification of the silver-tin formulae with the object of maintaining their original color. The discolorations are not alone upon the external surfaces of fill- ings, but frequently (and most frequently in improperly prepared and filled cavities) the discoloration affects the dentinal walls bounding the cavity (see Fig. 167). Fig. 267. staining of tooth structure with amalgam (Bodecker) : e, enamel ; D, d, dentin ; B, border of cav- ity; s, solidified dentin along the border of the cavity; r, reticulum brought forth by the amalgam. (X 500.) As shown in the illustration the discoloration may be deep. This danger is increased by leakage, when putrefaction of the protoplasmic contents of the dentinal tubuli or decomposing albuminous substances generate H2S, and metallic sulfids are formed in marked quantities. 206 PLASTIC FILLING MATERIALS. This danger of dentinal discoloration is gnardod againirt by interposing a barrier between the cavity walls and the amalgam prior to the inser- tion of the latter. The inflncnoe of individual metals upon color will be discussed later. Thermal and Chemical Relations. — As a conductor of thermal in- fluence, amalgam is midway between gold and the basic zinc cements. As to the actual effects upon the vital tissues of dentin, it has never been demonstrated that amalgam exercises any specific influence, except that cadmium appears to cause, through the cadmium sulfid formed, a degenerative influence (Flagg), and copper has antiseptic properties (Miller, Fletcher). Chemically the dental amalgams arc, to all intents and purposes, insoluble in the fluids of the mouth, the common solvent found in the oral cavity, lactic acid, affecting them but little. Classification of Amalg-ams. — Amalgams are divided into binary, ternary, quaternary, and so on, according to the number of constituent metals. The only binary amalgams employed in dentistry are those of copper and of palladium. Binary Amalgams. — Copper amalgam is made by adding freshly precipitated and washed metallic copper to an excess of mercury ; when solution is complete the surplus mercury is expressed through chamois. The plastic residuum is then packed into moulds to make small tablets of the usual form in which it is dispensed. A better method, which yields a product of greater purity, is to pre- cipitate the copper directly into the mercury by electrolytic process. This may be done conveniently by pouring a tjuantity of mercury into a suitable glass vessel — a small battery jar, for example — and suspend- ing a thick plate of copper, by means of a wooden support, some dis- tance above the surface of the mercury. A saturated solution of cupric sulfate is then poured into the jar until the copper plate is com- pletely submerged. The cathode pole of a battery or other source of electrical current is then connected with the layer of mercury, and the anode with the copper plate. All that portion of the cathode electrode in contact with the cupric sulfate solution should be insulated with gutta- percha, and only the point which is in contact with the mercury left exposed. The passage of the current causes solution of the copper from the anode and deposits it in the mercury continuously as long as the foregoing conditions are maintained. The precipitation should be continued until the mercury is saturated, which will be evidenced by the appearance of the characteristic red color of the excess of copper at the cathode pole. When the saturation point has been fidly reached the mass should be washed, first in dilute hydrochloric acid and then in water, dried and compressed as is usual with this amalgam when pre- NATURE AND PROPERTIES OF AMALGAM. 297 pared by the ordinary processes. This method was suggested to the writer by Dr. E. C. Kirk. In its typical form and condition, copper amalgam, when made plastic by heat, may be packed into matrices, such as cavities in teeth, where it sets quickly, undergoes no change of volume or form, and is devoid of flow. Therefore a cavity which has been sealed by it remains sealed. Upon its outer surface a coating of black sulfid quickly forms, which remains but does not penetrate the tooth struc- ture. The dentinal walls are commonly stained green through the absorption of the metallic salts. In improperly prepared specimens there is not a perfect chemical union between the metallic mercury and the copper. The presence in a filling mass of oxids of either of these metals establishes local electrolytic conditions which prevent the formation of the black sulfid coating and bring about the gradual dissolution of the amalgam mass. To recapitu- late : Copper amalgam is physically unchangeable as a filling material ; it brings about very oiFensive discoloration both of the dentin and of its own surface ; it is antiseptic. The second binary amalgam is that of palladium. Palladium is precipitated from a solution of its chlorid by iron or zinc, washed in nitric acid, and dried. To the precipitated metal, mercury is added, the combination being attended by the evolution of much heat (i. e. is an active chemical union). If an excess of mercury has not been used the amalgam sets quickly, does not alter in form,^ and becomes black upon the surface,'^ but does not discolor the dentin. The addition of an excess of mercury retards the setting, and produces an inferior filling. Ternary Amalgams. — The base of all ternary amalgams is the alloy of silver and tin. The first of these was the alloy of Townsend, 44^ per cent, silver, 55^ per cent. tin. From this point the investi- gations and experiments radiated — it being found after many years of clinical testing that those alloys containing more than 50 per cent, of silver gave the best results. The formula given by Dr. J. Foster Flagg as affording the most stable alloy for amalgam — 60 silver, 35 tin, and 5 copper — was found by Dr. Black to be that giving the highest degrees of resistance to change of form, to flow, and to crushing. In view of Dr. Black's researches into the effects of annealing alloys it is evident that the ternary amalgam of the future will have a composition closely approxi- mating 72.5 per cent, silver, 27.5 per cent. tin. The binary alloys of tin and silver form the basis of all of the quaternary amalgams used in dentistry. ^ Tomes, Trans. Odontological Society of Great Britain, 1872. ^ Bogue, Dental Cosmos, 1884. 298 PLASTIC FILLING MATERIALS. Quaternary Amalgams. — The nu'tal aiKlitioiial t<» the l)asal alloy is added for the purpose of modifying the cohjr or iiu'reasin<>: the edge strength of the amalgam. The addition of eopper o jx-r cent, to an alloy containing over 60 per eent. silver increases the crushing stress and lessens both flow and contraction. The alloy is white when fresh, but in the presence of sulfur compounds discolors. The addition of gold (o ])er cent.), as clinical records testify, aids in maintaining the color of the tilling. It lessens shrinkage slightly (com- ])are this and following statements with tal)le No. II.), and appears to have little or no influence upon flow and crushing stress. The addition of platinum causes dark fillings and notably increases the flow; the setting is slowed. The addition of zinc increases rigidity ; the amalgams expand for long ]ieriods after apparent hardening ; the crushing stress is moderately high — a direct contradiction of statements of several previous ob- servers.' Additions of bismuth, cadmium, lead and aluminum were made to the basal alloy, but all of them exhibited properties which exclude them from introduction into dental amalgam. Dr. Black ^ states that " alloys containing 5 per cent, of aluminum have their setting attended by the evolution of nuich heat ; an enormous expansion of the mass occurs ; the instruments used in packing are oxi- dized, and a distinct crackling of gas-disengagement is heard." " The formation of aluminum amalgam is characterized by an exhibition of the affinity of aluminum for oxygen. Aluminuin oxid is doul)tless formed, which increases the volimie of the amalgam mass." "Washing of Amalgams. — Alloys which have been cut for some time, and mercury the purity of which is questionable, are found to be coated with oxids of the metals — in the case of mercury, with the oxids of contaminating metals. The advisability of washing the amalgam mass in some solvent which will remove the oxids is a mooted question. It has been stated that the washing of an amalgam mass increases its shrinkage (Flagg). On the other hand it has been observed that washed amalgams retain their color better. It is difficult to see how the washing could aifect the integrity of the set mass unless oxidizing substances were left in it ; and this is clearly contraindicated by the maintenance of color in washed amalgam. The writer prefers wash- ing the plastic mass in chloroform j)rior to expressing the surplus of mercury. ' It is to be recalled in this connection that Dr. Black's measurements are made with instruments of unequalled accuiacy, those of previous observers with comparatively crude instruments. * Private communication. USE OF AMALGAM. 299 Use op Amalgam. It is to be understood that amalgam is to be employed only in those conditions and situations which clearly indicate it as the proper mate- rial. As a general rule, it is excluded from the ten anterior teeth of each jaw, although this rule is open to exceptions. Its anterior limit of application is usually regarded as the distal surface of the first bicus- pid. Its more general employment has been greatly reduced in many places since the introduction of what are known as combination fillings (see Chapter XIV.), and by improvement in the forms and character of artificial crowns. The first class of cavities to which amalgam is applied are those which extend beneath the gum margin ; the second, buccal cavities ; the third, compound cavities ; the fourth, approximal cavities ; the fifth, cavities upon the masticating faces of the teeth. These are the classes in which gold is most difficult of introduction and of proper shaping and finishing, in the order named. Amalgam should rarely or never be packed against dentinal or enamel walls without the interposition of a layer which will prevent either the discoloration of the dentin or the bluish appearance noted when amalgam underlies enamel. The shaping of cavities for the reception of amalgam fillings (see Chapter VII.) should be done with such care as will give assurance of the permanent retention of the filling and the perfect sterilization of the dentin before and during its introduction. The separation of the teeth, removal of gum overhanging cavity margins, and breaking down of frail enamel walls by means of chisels, precede the filling. The rubber dam is to be adjusted where and when possible, with such care that an exclusion of the fluids of the mouth is assured durino- the shaping, sterilizing, and filling of the cavity. As Dr. Black has shown,^ much of the permanency of form of an amalgam mass depends upon the even distribution of the constituents ; it is evident that every aid to this end should be utilized, an important one being that the mass should be packed into a cavity having but one orifice, that for the introduction of the filling. With the data relative to dental amalgams which have been given, it is evident that a dental amalgam mass is by no means simple, but is a very complex body. If sufficient mercury has been used to eff'ect solution of the alloy particles the mass will consist, first, of a quantity of a chemical amalgam — /. e. one in which the metals are united in atomic ratios — this being surrounded by one or more other distinct ^ Dental Cosmo.% 1895, vol. xxxvii. p. 553. 300 PLASTIC FILLING MATERIALS. amalgams, each liaving its own time of scttino: and rate of contraction. If only enough nierenry has been used to make a creaky mass the sur- faces of each aUoy particle are covered hy an amalgam of indefinite composition which acts as a cement binding the jiarticles together. In this line the same experimenter has shown that mixing the alloy and mercury in a mortar by means of a pestle, wringing the surplus mer- curial solvent from the mass by means of heavy pliers, and ]>acking the filling with steel burnishers are all influences which lessen the strength of the completed filling. The conditions are now a prepared and sterilized cavity ; any miss- ing wall re(piired to give four sides has been replaced by a properly adjusted matrix (sec Fig. 242, Chapter XII.). Fkj. 208. Dr. Herbst's matrix. Matrices. — Matrices may be readily and quickly formed by cut- ting strips from a sheet of very thin steel which has been annealed Fig. 269. Fig. 270. Herbst pliers. and polished. By means of contouring jiliers the matrix is given the correct contour, then wedged or tied into place. They must USE OF AMALGAM. 301 be so adjusted that they are immovably held during the filling ope- ration. A rapid method of forming a matrix is that of Dr. Wilhelm Herbst : A strip of German silver No. 33, wide enough to extend from the cervical margin of a cavity to its mouth, and long enough to more than embrace the tooth, is passed around the tooth (see Fig. 268) ; the strip is caught near its extremities by a pair of Herbst pliers (Figs. 269, 270) and drawn taut ; the pliers pinch the metal into close adaptation to the tooth walls. Held by the pliers the matrix is withdrawn, the line of junction touched with zinc chlorid solution, and soldered over an alcohol or Bunsen flame with soft solder. The matrix is replaced upon the tooth, the rubber dam applied, and the matrix pressed against the cervical margin of the cavity by means of a wooden wedge. The matrices of Guilford and' those of Brophy (Figs. 240, 241, Chapter XII.) are operated upon a common principle ; the band which most nearly fits the periphery of the tooth is adapted, then drawn into close apposition with the tooth by means of the screw appli- ances. The matrix of Woodward is one of the most convenient. Its mode of application is shown in Fig. 242, Chapter XII. The Miller matrix (Fig. 271) is useful and adapted for the class of cavities shown in Fig. 272, as held in contact with cervical mar- FiG. 271 gins through the action of the duplex spring leaflets. Fig. 272. When necessary a wooden wedge is forced between the leaflets. (For other forms and applications of matrices see Chapter XII.) Mixing the Amalg-am. — It is usually recom- MiUer matrix adjusted. mended that the proportion of mercury and alloy be determined by weight. An amount of alloy is first weighed, then weighed additions of mercury are added to it sufficient to make a plastic mass, when the two are to be mixed together; the relative amounts of mercury and alloy are to be gauged and recorded for each formula of alloy. With the " submarine " alloy of Flagg— 60 silver, 35 tin, and 5 copper— the 302 PLASTIC FILLING MATERIALS. ratio is equal parts by wx-i^ht of tilings and nu r- cury. When a mortar is used for making tlic auud- uani, one of glass and having a glass pestle (see Fiirs. 273, 274) is to be preferred. Mixing in the palm of the hand is a dirty process, the hand and Hiigers becoming nuicii discolored by the metallic oxids. Fig. 273. Fi.;. 1271. Glass mortar. Glass pestle. A rubber mortar (Fig. 275) to be received in the palm of the hand has been devised by Dr. Genese. In view of deductions from Dr. Dr. Genese's rubber mortar. Black's experiments this latter method of mixing is regarded as usually the preferable one. The filings are placed in the receptacle, the mercury is added, and the mass is triturated — if in a mortar, by the pestle, if in the rubber basin, by the forefinger guarded by a rubber finger-stall. When the ZrSE OF AMALGAM. 303 amalgamation appears to be complete the mass is transferred to the hand and kneaded, then pressed into a ball. It is next enclosed in stout muslin, or China silk as recommended by Dr. C. E. Kells, Jr., and the surplus mercury expressed by wringing ; when no more mer- cury appears through the muslin, the button is removed : it should break with a clean, white fracture surface. Another method of mixing the filings and mercury is that of Fletcher. Filings and mercury are placed in a long glass tube which is shaken vio- lently until amalgamation is complete. The Packing- Operation. — Several devices have been invented for the purpose of carrying the amalgam to the tooth cavity, one of the Fig. 276. most simple being shown in Fig. 283, and another in Fig. 284. An- other excellent instrument is shown in Fig. 285, one end having ser- FiG. 277. rated points which engage the soft amalgam, the other a plugger head. Numerous methods have been advanced and advocated for the pack- ing operation. The one commonly followed is that of burnishing the amalgam. This has been shown by Dr. Black to weaken the mass. A small piece, rarely more than a cube of |^ in. side, is carried to the deep- est and most inaccessible recess of the cavity and pressed against its walls by tapping, burnishing, or uniform pressure. Dr. Flagg's method is by tapping. Each successive piece of amalgam is tapped upon by the packing instruments until it combines with its predecessor and is per- fectly adapted to the cavity walls. The set of instruments shown in Fig. 279 are those by which this process is accomplished — Nos. 30-34 being packing instruments, while the others are shapers. 304 PLASTIC FILLING MATERIALS. A convt'iiii'iit and utlcetive sot of instrumcuts lor accoiuplisliing the packing are shown in Figs. 280-282. Fig. '27!t. 30 31 32 33 34 3.") 3fi 37 38 39 Dr. J. Foster Flagg's amalgam and zinc filling iiistruini-nts. Dr. W. G. A. Bonwill has advised a method wliich accomplishes the removal of surplus mercury and the even distribution of the mass, Fig. 280. Woodson's double-end amalgam instruments. during the progress of the filling. Small squares of folded bibulous paper are caught in the jaws of pliers and laid ujion the amalgam, when the exertion of pressure by means of amalgam pluggers or pliers forces out the surplus solvent and it is wiped away with the paper. The same end is also accomplished by the use of bulbous points of soft rubber. When through either method the cavity is more than half full, the remainder of the amalgam mass is wrung out to express more mercury, and the packing is resumed imtil the cavity is more than full. At the later stages of the filling the process of wafering is usually USE OF AMALGAM. 305 followed. By means of chamois and heavy pliers (Figs. 283, 284) the amalgam mass remaining is compressed into a wafer, driving the surplus mercury through the pores of the chamois. The amalgam is put in a piece of chamois, and the chamois sack A is entered between the beaks b and c (the latter a roller) ; closing the handles of the instrument progressively squeezes out the mercury till any desired degree of dryness is attained. When the amalgam is squeezed to the requirements of the operator, the han- dles are released, and the spring opens the ap- pliance. The action is analogous to the finger and thumb movement in common use, but is much more powerful, and therefore more cer- tain and more uniform. Small sections of the wafer are laid upon the half-completed filling and tapped into a union with it. The cavity is more than filled, and at the completion of the packing the amalgam should cut as though nearly set. Another and excellent method where applicable is to shape small pieces of half-vulcanized rubber and cement them upon broken excava- FiG. 284. Mercury expresser. Flagg's wafering pliers. tors, and use them as pluggers during the later stages of the filling. The fluid cementing amalgam will have its surplus mercury expressed about the sides of the plugger. Still another method is to fill the cavity more than half full, then cut away the softened portion, and complete the filling with drier amal- gam. Fillings the initial portions of which have been introduced com- paratively dry are more homogeneous and are less likely to discolor and crevice than when more fluid amalgam has been used to begin the 20 306 PLASTIC FII.IJSi; MATERIALS. filliiijX. An oxamiiiMtioii ot" an anial<;ani tillini;- iinnicdiatcly al'tcr com- pletion will show the marginal jtortions to contain the softer amalgam, tlic hanlcr hcint^ in the more central jiarts. The too common practice of j)la<'inii- in the prepared cavitv sutlicient amalgam in one mass to nearly or uriried gutta-jx'rcha probably consists of a liy(b'ocarbon fj>nre gutta) having tlie formuhi Ci^H,,; ; ali)ane, C,yH,gO; fluavile, ('^oHrt^Oj ; and a variabk' comj)ound named guttane. Pure gutta possesses all the good qualities of gutta-percha in a much enhanced degree, becoming soft and plastic on heating and hard and tenacious on cooling without l)eing in the least brittle. Tlie resins appear to be simply accessory components -which have a decidedly detrimental effect when they pre- ponderate. AVater, Avood, fibers, bark, sand, etc., occur as mechanical impurities of gutta-percha." (Obach.) History. — Gutta-percha was introduced into dental practice as a fill- ing material about the year 1847. Soon after this a secret preparation was introduced by a Dr. Hill, which received his name. Numerous alleged analyses of Hill's stopping have been given, all of wliieh are untrustworthy. It was found to subserve so useful a ])urpose that it rcccivetl the tribute of wide imitation ; in fact, the white gutta-})ercha preparations of the present day had their foundation in this imitation. There is no entirely trustworthy evidence that the original was superior to the best of contemporary preparations. As at present employed as a filling material gutta-percha is in two forms, the first the w'ell-known pink gutta-percha ba.se plate, which is colored by the insoluble sulfid of mercury, the second the white prep- arations, made firmer in texture by additions of the soluble zinc oxid. The .specimens of crude gum differ as to the amount of heat re(piired to soften them to an (>qual degree. Dr. Flagg ' states that the speci- mens requiring the greatest degrees of heat for softening, prior to the addition of the zinc oxid, afford the best dental gutta-perchas. The method of making the gutta-])ercha of dentistry is by softening a mass of the brownish-vellow gum on a slab which has been heated over boil- ing water, and driving zinc oxid into the softened mass by a process of kneading, using a Avedge-shaped steel instrument as the kncader. It requires infinite patience and much time to distribute the powder evenly throughout the mass. Overheating the material at any stage of its manufacture or manipulation is ruinous to its texture. Classes. — Gutta-perehas are divided into three classes according to the temperature of softening : Low heat, softening below 200° F. 3Ie- dium heat, becomes plastic at 200° to 210° F. Jflf/h heat, 210° to 218° F. The low-heat specimens contain 1 })art by weight of gutta-percha to 4 ^ Plastics and Plastic Filling. GUTTA-PERCHA. 311 of zinc oxid ; in medium-heat the ratio is 1 to 6 or 7 ; and in the high- heat specimens the gutta-percha is almost saturated with zinc oxid. Physical Properties. — Gutta-percha is an almost perfect non-con- ductor both of heat and electricity. It is less hard and rigid than any other filling material. It contracts in hardening, i. e. cooling. Softened masses of it are coherent when dry, but not when wet. Its color may be made to resemble that of the teeth. To vital tissues it is the most bland, unirritating filling material known. After it has served as a filling for a greater or less period it is found to have increased in hardness and difficulty of softening, and its surface, and perhaps its substance, has become porous in variable degree. The increased hardness is observed in such situations as those in which putrefactive decomposition occurs ; that is, in places where there is an evolution of hydrogen sulfid ; the gutta-percha apparently undergoes a species of vulcanization. It becomes somewhat porous in those situa- tions where the formation of a solvent is active (lactic acid), which abstracts the soluble zinc oxid from the mass. The pink variety con- taining the insoluble mercury sulfid does not become porous, but wears with a comparatively smooth surface when subjected to attrition. Examining in detail these several physical properties it will be noted that gutta-percha has but one property in common with gold — its insol- ubility. Its rational employment is therefore in such situations and conditions as those in which the use of gold is contraindicated. Indications for its Employment. — First, in its several forms it is employed as a temporary filling material for both the temporary and permanent teeth. Owing to its non-conductivity it is employed near the pulp ; its insolubility recommends its use at the cervical margins of cavities, particularly in the buccal cavities of molars which do not extend to the masticating surface, where the non-resistance of the material would cause its rapid wasting. This is the most common of the situations in which gutta-percha is applied : very deep cavities upon the buccal surfaces of molars, extend- ing beneath the gum, and having ragged enamel margins, the orifice of the cavity being much smaller than its body. Owing to its non- irritating quality, the condition of the gum in contact with a gutta- percha filling remains normal. It is used in approximal cavities of the anterior teeth which have a similar form to those just described ; also in labial cavities, particularly when these teeth are in any degree loose. For example : in a cavity opening alone upon the distal wall of a canine tooth the carious process has almost invaded the pulp, the enamel walls unsupported by dentin still retain their form and have a good texture. Pink base plate is invaluable for the temporary filling of spaces after 312 PLASTIC FILLING MATERIALS. wedging and also the cavities to be subsequently lllkd with nutul. A mass of the material may he packed into such spaces and be permitted to remain for months if previously prepared and dry cavity until the tooth is sensibly warm, hold the heater again over the flame to melt the metal, and then with a suitable broad and cold instrument pick from the heater a pellet or group of pellets sufiicient to a little more than fill the cavity, and by a quick, firm, rock- Trimming margins of iug pressure force the mass into the cavity as if it gutta-percha filling. ^^^^^,^ ^^^^^-^^ ^^ ^^j,^ ^^ imprcssion of thc Same. Then dip the instrument into ice-water, wipe dry, and hold it firmly against the filling for one or more minutes, after which with a keen- edged thin blade pare off the surplus, cutting from the centre obliquely toward the margin, as in Fig. 300, taking great care that the filling // shall be flush with the cavity margin at every point, as at A, A', Figs. 301 and 302. " Access to approximal cavities, as C, C, Figs. 291 and 292, will seldom permit the instantaneous mass-method just described, but in many such cases a w^arm, broad, flat blade, as stiff as the space will admit, can by repeated quick pressures be made to squeeze the soft mass into the cavity of the warmed tooth, and be instantly followed by a very thin strip of metal held tightly in both hands and wrapped with hard pressure over the filling around that side of the tooth, to both condense GUTTA-PERCHA. 317 and contour the plastic and produce the closest adaptation of the material to all parts of the cavity walls. " There is good reason for the belief that the common mode of suc- cessively introducing small pieces of imperfectly softened gutta-percha into a comparatively cold cavity, and employing instrument points more or less heated for packing the cooled plastic against one side of the cavity after the other, must in the nature of the case result in a leaky filling, such as gutta-percha is commonly said to make, whereas the defect is due not to the material, but to its inconsiderate manipulator. " In order to definitely determine whether or not suitably softened gutta-percha inserted by the mass-method will make a moisture-tight filling, some procelain teeth of natural size and forms were made, hav- FiG. 301. Fig. 304. Fig. 305. Fig. 306. ing cut in them, prior to baking, cavities of the class shown in Figs. 291-298. These cavities have been filled with gutta-percha, leaving a surplus over the margins, as at a' a', Fig. 303, and when quite cool paring them flush as at A, A', Figs. 301, and 302, and after several days' immersion in dilute aniline ink, the fillings have been removed without a trace of color showing on the walls of either the fillings or the cavi- ties. The only exceptions have been where the margins were rounded, as at a, a', Fig. 303, and the fillings not cut below them as shown, but left feather-edged, as at d, d' , Fig. 305. In these few instances discolor- ations were found under the laps, but in no case extending farther than to A', A', Fig. 306. The tests prove that under conditions as nearly practically parallel as extra-oral tests can well be, gutta-percha fillings properly made will exclude external moisture. Obviously, it is better to pare the filling below the enamel-slopes, as in Figs. 304 and 306, than to leave it overlapping, as in Figs. 303 and 305. For a final finish use a rapidly revolved, lightly touching, cuttlefish-paper disk, followed by a wisp of bibulous paper or piece of tape wet with chloro-percha, applied for but an instant, to glaze the surface of the filling. " In the case of a very thin enamel front like that of Fig. 292, that part of the cavity C may be varnished with thin chloro-percha and dried with hot air just prior to filling it as before said. It might first be thinly coated with a tinted oxyphosphate or oxychlorid of zinc, which 318 PLASTIC FILLING MATERIALS. should be given ample time to liardcn before placing the giitta-porelia. Indeed, it is a fundamental feature of good gutta-percha Morlv that while one cann(»t operate too ra])idly when the plastic i.s at its proper temperature, the preparatory and completing processes should be given as much time, care, and close scrutiny as more elaborate and often less enduring gold operations. There is furthermore room for the exercise of the artistic faculty in having at hand chloro-percha, or cellulose varnish of varied colors, with which, by means of a small brush, a gutta-percha filling as B, Fig. 294, and one in the like cavity C, may be given an inconspicuous shade, and the painting be renewed from time to time, if that be necessary by reason of wear. Fig. 307 is a sectional view of fillings like B, C, Fig. 294." Finishing- Gutta-percha Fillings. — If a gutta-percha filling has been packed with the proper amount of care and skill, it should require but little trimming. It should be undisturbed until cold. Its harden- ino; mav be hastened and intensified bv holdiny- ice-water in contact with it for a few moments. The portions overlying the margins are to be trimmed with extremely sharp lancets or by warm blades. Every cut should remove a little of the surplus material, never a mass of it, and should be made toward the cavity margins, never away from them. The filling should have been made so that no fulness is present to require reducing. It is a general practice to give a smooth face to a gutta-percha filling by wiping it with a tape slightly moistened, not wet, with chloroform. The surflice produced by this means, although smooth, does not retain its integrity so well as when the surface is formed by cutting. The use of gutta-percha as a canal filling is discussed in Chap. XVII. Basic Zinc Cements. Zinc Oxychlorid. — The basic zinc cements employed in dentistry are the oxychlorid and the phosphate ; the oxysnlfate should also be included. The oxychlorid is formed ])y the combination of calcined and pul- verized zinc oxid with a solution of zinc chlorid : ZnO + ZnCl^ + H.,0 = 2ZnClHO. This compound was introduced as a dental filling material about 1850, its hardness, whiteness, and apparent insolubility recommending it for that purpose. It required no lengthy ])eriod of time to demonstrate that as a filling material per se it was unfit for use. It disintegrated rapidly and was not free from shrinkage. Propekties. — Freshly mixed, this material is irritating to vital tissues with which it is brought in contact ; applied close to or upon an exposed pulp it may be productive of a transient or a persistent irritation, BASIC ZINC CEMENTS. 319 or even inflammation. The extent of the irritation is largely governed by the fluidity of the cement paste, i. e. the amount of ziuc chlorid present. It sets in fifteen minutes sufficiently to permit the packing upon it of an amalgam, and in half an hour a gold filling. After setting it is whiter though less hard than the zinc phosphate ; it shrinks, particularly when used in large masses. It is a poor thermal conductor, and, like all bodies containing zinc oxid, is soluble in lactic acid — the usual sol- vent in the oral cavity. These several features are at present regarded as limiting the application of oxychlorid to — first, a lining material for carious cavities over which the insoluble filling proper is to be placed ; second, as a root-filling material (its use in this connection is discussed in Chapter XVII.). It is to be noted that the cement retains after setting an antiseptic power for a greater or less period. Use. — Zinc oxychlorid is usually employed as a lining material in teeth having what is known as poor structure — those in which caries proceeds to great depths without external evidence of the extent of invasion. After these cavities have been partially excavated it is found that further excavation and the removal of the deepest layers of the leathery dentin which appear to have retained sensitivity would prob- ably uncover the pulp ; it may be that the pulp has given subjective evidence of a mild attack of active hyperemia. In such cases the deepest layer of the partially disorganized dentin is permitted to remain and is subjected to the prolonged — fifteen minutes or longer — contact of hydrogen peroxid in the 25 per cent, ethereal solution (caustic pyrozone), 5 per cent, aqueous solution of formalin, or preferably a saturated solution of thymol in alcohol. The cavity walls are well dried with bibulous paper and the warm-air blast. Upon a mixing slab (see Fig. 308), a drop or two of the zinc chlorid is placed, and beside it a quantity of the zinc oxid powder. The powder is gradually incorporated with the fluid by means of a spatula until a creamy paste is made. A number of balls of bibulous paper are to be at hand. A portion of the paste is taken upon the end of an instrument and placed in the cavity, where it is quickly pressed into a layer against the cavity walls by means of the balls of bibulous paper. The walls are to be covered to a uniform depth of about one-sixteenth of an inch. The prompt application of the bibulous paper usually pre- vents any irritation due to the contact of the oxychlorid with the dentin overlying the pulp. Should the cavity be very deep it is advisable to protect the pulp by interposing a film of ethereal varnish between the oxychlorid and the dentin over the pulp. At the completion of the lining operation, the margins of the cavities are to be cleansed of the oxychlorid and the filling completed with the material indicated. 320 PLASTIC FILLING MATERIALS. Zinc oxyclilorid as an obtiuuling atjent in tlic trcatiiiont of liyjH'r- scnsitive dentin is of considerable valno, and its nse f»>i' that jjiirpose is described in Chapter VI. The nse of zinc oxychlorid as a canal tilling, and the mode of nsing it, are discussed in Chapter XVII. T\\t} poirdcr of this cement is made of zinc oxid cah-ined and ])o\v- dered, to wiiicli have been added substances (borax, silica, etc.) Nvhich aifect its properties but little if at all. T\w Jiuid is made by dissolving ])ure zinc or its oxid in hydrochloric acid to the point of saturation ; or, by making a solution of zinc chlorid 4 parts, water 3 parts, and filtering the solution. The use and eifects of zinc oxychlorid as a pulp capping are dis- cussed in Chapter XVI. Zinc Phosphate. — These cements are nominally a combination of calcined zinc oxid with a syrupy solution of orthophosphoric acid : 3ZnO + 2H3PO, = Zn3(PO,)2 + 3H.O, although their actual composition is more variable than that of any other tilling material. Both base and solvent commonly contain impurities — those of the base owing to lack of discrimination, or worse, in the source of the oxid. Many of the impurities of the ])h()sphoric acid are due primarily to the well-known inconstancy of the acid itself, and others to the mode of its manufacture. IMany of the specimens of powder are prepared from commercial metallic zinc, and therefore contain the impurities of that metal. Among the latter is arsenic, so that the presence of arsenic compounds in inferior cement powders is by no means impossible, which may pos- sibly explain in some cases the death of non-exposed pulps in teeth which have been filled with zinc phosphate ; but as recent chemical in- vestigation has shown that the arsenic when present in cement powders is in the form of an insoluble zinc arsenite, the danger of arsenical irrita- tion of the pulp from that source would seem to be a remote one. A common source of the glacial phosphoric (metaphosphoric) acid of commerce is from sodium phosphate, variable quantities of which are retained in the acid solution as acid sodium phosphate (dihydrogen sodium phosphate). This substance is soluble in water, and must there- fore greatly increase the solubility of any cement containing it. To properly make pure specimens of zinc oxid and phosjihoric acid is a comparatively expensive operation — which will serve to explain the seemingly high cost of fine specimens of cement, and incidentally serve as a warning against the indiscriminate use of cheap cements. Making the Powder. — A quantity of pure zinc oxid is luted in a BASTC ZINC CEMENTS. 321 sand crucible and kept at the highest forge-heat for hours. When cool the crucible is broken away and the vitreous mass of yellowish zinc oxid is reduced to a powder which will pass through a fine bolting cloth. This powder is placed in tightly stoppered bottles, for if exposed to the air it absorbs carbon dioxid and a portion of it is converted into the hydrated carbonate of zinc. This change may be noted in old powders by the efferve'scence due to the disengagement of carbonic oxid when phosphoric acid is added to them. Numerous substances have been added to the basal powder with the object of lessening the disintegra- tion, i. e. chemical solution, when used as a dental cement. Usually these additions are the oxids of other metals. The oxid of magnesium added to the powders causes the cement to set more rapidly ; the oxid of aluminum increases the rapidity of setting and makes a finer-grained cement, the central texture of which is, however, inferior. Cements of zinc oxid and phosphoric acid alone are apparently less soluble in lactic acid than when the oxids of aluminum and magnesium are added. Various other substances have been added which do not enter into chemical combination with the phosphoric acid, in the hope of confer- ring greater durability on the cement, but as yet but few of them have been shown to possess any value. The Fluid. — Phosphoric acid in its pure state is formed by hydrating phosphorus pentoxid : PA + 3H20 = 2H3PO,. Much of the phosphoric acid used for cements is made by hydrating the glacial (metaphosphoric) acid, HPO3. The acid dissolves readily in water, being deliquescent when pure. Difficulty of solution is therefore an indication of impurity of the glacial acid. It requires a definite degree of heat to bring about the chemical hydration of the acid. At a temperature of 210° F. the union occurs, which is attended by the evolution of heat, the glacial acid being transformed into ortho- phosphoric acid. These acids are all hygroscopic. They will even ab- stract water from sulfuric acid. Impurities. — The commercial glacial acid is commonly, or as a rule, impure, containing variable amounts of sodium and magnesium phos- phates. These salts, particularly the dihydrogen (acid) sodium phos- phate, are permanently soluble in the phosphoric acid, and therefore give no evidence of their presence by the formation of precipitates. They are also soluble in water, w^hich fact has a direct bearing upon the durability of cements made with the impure acid. It has been stated by writers that the acids of cement were occasion- ally the meta- and pyrophosphoric. A test of some of them said to be 21 n22 PLASTIC FfLLLWG MATERIALS. of these varieties sliowcd none of them to ^ive tlie reaction of the pvro- acid ; a few givinji^ traees of the nieta- acid. Preeij)itates whieh form in cement fluids are prohahly metallic ])hos- phates. The instability of cement fluids is notorious. AsiaR'iit cxfoss of that rciiuircd, is heaped at a distance from it, taken from the hottlo hy the scoop (Fig. .'ilO). A portion of the powder is drawn into the fluid l>y means of a stout spatula (Fig. .'^11), and stirred with a rotary movement until a thin jxiste is made; another portion of powder is then added and is sh)wly and thor- oughly incorporated; mon* jiowder is added until the nuiss is as thick as putty and ditficult to smear with the heavy spatula; the mass is scraped together, taken from the spatula, and rolled between the forefinger and thumb, wliieh liavo been well scrubbed. The mass is now kneaded, then rolled into an oblong pellet. If for an occlusal cavity a piece al)out one-fourth the size of the cavity is set in the deepest portion and ta})ped into perfect apposition with the cavity walls by means of a burnisher. Other pellets are added, and the process is repeated until the cavity is exactly full, the l)urnisher form- ing the* surface of the filling and outlining clearly every margin of the cavity. The filling should remain under rubber dam for at least fifteen minutes — longer when possible. A coating of ethereal varnish, a solu- tion of gutta-percha in chloroform, or melted paraffin as suggested by Dr. Bonwill, is applied to the snrfiice and the grinding of the filling deferred for a day or two. Should the cavity be upon an approximal side of a tooth, a matrix is to be employed ; the most satisfactory and quickly adapted instrument for this purpose is one of the composition silver strips used for carrying polishing j)owders (Fig. 312). A strip Fig. ;;12. I'' ! -liiirj ^1 ii|i as wide as the length of the tooth is to have one end rolled upon itself until it forms a cylinder more than one-sixteenth of an inch thick (Fig. 313, -.1). The strip is passed into the next interdental space and drawn Fig. 313. through until the cylinder {A) rests firmly upon the teeth; the free end is now passed through the space into which the cavity opens ; where it BASIC ZINC CEMENTS. 325 rests upon the lingual surface of the tooth it is burnished into contact with the edges of the cavity, forming walls to the latter (313, B). The cement is introduced as in the preceding case, and when the cavity is full the free end of tke strip is drawn upon, compressing and round- ing the filling. Should the cement be an adhesive specimen or mixed thinner than described, the surface of the flexible mat- Fig. 314. rix is to be faintly oiled by means of olive oil. At the completion of the operation the cement should be exactly flush with the margins except at the labial aspect, and the surface of the cement should have such smoothness that polishing is not necessary. Cement fillings are polished dry with the finest of cuttlefish disks. The process of filling the body of any cavity is the same, except when the enamel walls are thin and frail. In the latter case, where space permits, it is preferable to line the walls with the oxychlorid of zinc, over which the phosphate is placed. Before inserting a veneer fill- ing of gold or amalgam, each cavity margin must be scraped free from cement. When orthodontia appliances such as rings or caps, or prosthetic appliances, crowns and bridges, are to be set it is preferable to use a cement prepared for that purpose, although it is the general practice to use the cement to which the operator is accustomed, mixing it thinner than for filling purposes. Wherever possible, it is advisable to operate under rubber dam, even while setting orthodontia appliances. The tooth is cleansed with chloroform — as, for ex- ample, when a ring or cap is set — to remove fatty mat- ters, and a layer of shellac varnish applied, which is then dried by the air blast (chip blower). Cement paste is formed, of such consistence that it will flow readily and yet not be watery ; the inside of the band or cap is filled with cement by means of an appropriate spatula (Fig. 31 4) ; a layer of cement is placed on the tooth where it is to be embraced by the band, which is then pressed into position and is to remain without disturbance until it is hard. The application of bands or ligatures should be deferred until the following day. As soon as the cement is hard the surplus is cut away and the dam removed. Pointed spatula. 326 PLASTIC FILLING MATERIALS. Temporary Stopping. Preparations of tliis name are eonipouiuls of irutta-jirrdin witli various substances added to lessen the tenijierature of softenin*;. As procured from the manufacturer they are of two varieties, the adhesive and the non-adhesive — or, to be more precise, the h>ss adhesive. The former preparations, the adhesive, are usually made of gutta-percha (generally the pink base plate). Burgundy pitch, white wax, and chalk or zinc oxid. In the non-adhesive varieties the I5urgundy })itch is omitted. The latter varieties are usually made of a pink color, to furnish a safe- guard against mistaking a tilling of temporary sto]>ping for one of gutta- percha. As the name implies, they are designed for temixtrary use, retaining dressings in teeth, to maintain space between teeth which have been wedged apart, until the attendant pericementitis subsides ; to press away gum tissue overhanging the margins of a cavity ; to fill excavated cav- ities for a few days. Unlike gutta-percha, most of these preparations cannot be ])crmitted to remain for a prolonged period ; they usually become otfensive, par- ticularly so when the hygiene of the mouth dt)es not receive proper attention. To maintain s})ace and press away gum tissue they are used as gutta-percha ; their lower heat of softening permits tiieir application close to the pulp of a tooth without the painful response associated with placing hot gutta-percha in the same position. X prominent use of the material is the sealing of arsenical applications in teeth. As with any other material, it is necessary, in order to have the minimum of pain, to make the ap})lication and manipulate the stopj)ing so that no pressure shall be exerted upon the pulp. Temporary stop- ping is inferior to zinc phos])hate for this purj)oHe, as the latter may be flowed into a cavity and over an arsenical ai>i)lication without causing the slightest pressure. Should the cavity of decay extend to or beyond the gum, a small conical piece of the temporary st()])ping shoidd be softened and packed carefully against the cervical margin and gum, to act as a guard to the latter against contact with the virulent irritant arsenic trioxid. The arsenical paste on a minute pledget of cotton is laid upon the exposed pulp — if the latter be hypersensitive, beside it — and the remainder of the cavity and interdental space are filled with one very soft piece of temporary stop])ing. Temporary stopjiing, in cones, has been used as a canal filling (see Cliapter XVII.) and as a filling for the bulbous portion of pulp chambers. Another important use of the material is the sealing of the occlusal cavities of teeth which are under treatment for septic pericementitis. OXYSULFATE OF ZINC. 327 Plugs of softened temporary stopping have been used for the arrest of alveolar hemorrhage ; also for the temporary setting of artificial crowns. Lining Varnishes. These are solutions of various gums and resins in alcohol, chloro- form, and ether, which are employed to furnish a non-conducting and impermeable film to cover the dentinal walls of excavated cavities. The first, sandarac varnish, is a thin solution of sandarac in alcohol. The second, a solution of virgin rubber in chloroform. The third a solution of hard Canada balsam, copal, or daniar in ether. Another is the preparation known as Jcristaline, a solution of trinitro- cellulose in anhydrous amyl acetate. Before lining a cavity with zinc oxychlorid, a film of one of these varnishes, the quick-drying ones preferred, is applied, and when this is dry the cement may be inserted wdthout causing pain. Varnishes have been used to furnish an adhesive surface upon which to pack gutta- percha fillings. It is always advisable to varnish the walls of a cavity which is to receive a filling of zinc phosphate, to prevent the action of any free acid or acid salt upon the dentinal walls. Some of these varnishes are admirable non-conductors, and serve in that capacity under gold or amalgam fillings in a most satisfactory manner. They may be used to prevent the tooth discoloration due to the pres- ence of amalgam, particularly of copper amalgam. Zinc Oxysulfate. What is known as the zinc oxysulfate in dental parlance is merely a thin zinc oxychlorid containing zinc sulfate. A true zinc oxy- sulfate is made by mixing a saturated solution of zinc sulfate with uncalcined zinc oxid. It forms a white paste which sets quickly and attains about the hardness of an inferior plaster-of-Paris. It is bland and unirritating to exposed pulps ; is a non-conductor ; is faintly and persistently astringent.^ Its principal use is as a pulp capping or protective. A thin paste is made, in which a disk of paper is dipped, then quickly and accurately laid upon the area of exposure. When hard (in a few seconds) a drop of fresh thin paste is flowed over the capping. The cavity may then be lined with zinc phosphate. As a pulp protector from thermal shock it is applied in a thin layer, and over it a lining of zinc phosphate is packed. ' J. Foster Flagg:. CHAPTEH XIV. COMBINATION! FILLINGS. By Dwight M. Clapp, D. M. D. The use of more than one material for filling a single cavity was suggested by the observation of the condition of fillings composed of but one material and noting the effects of time and use thereon. If a large number of amalgam fillings in occlusal cavities are exam- ined, many will be found to have imperfect edges. One cause of this imperfection is, undoubtedly, the brittle character of amalgam, in con- sequence of which the edges have become broken. In other words, amalgam as a filling material lacks edge strength. Its dark, sometimes almost black, color also renders it very objectionable, especially if used in conspicuous positions. If the same number of gold fillings in occlusal cavities are examined, the edges will be found in better condition than was the case with the amalgam. One reason for this is, undoubtedly, because gold is not brittle, but possesses sufficient edge strength to withstand the force of mastication. Its color is also less unsightly than that of amalgam. For occlusal cavities, therefore, gold is regarded as the better filling material. If a series of occluso-approximal cavities filled with gold be studied, it will be found that the teeth are in much better condition on the oc- clusal surface than at the cervical borders of the fillings. Compare gold fillings with a series of amalgam fillings in this same class of cavities, and the condition of the teeth will be reversed : at least a much larger percentage of the teeth will be found in good condition around the ap- proximal portion of the fillings than was the case with the gold. Hence, the deduction is inevitable that, of these two materials, amalgam is the better to fill the cervical portion of approximal cavities. ! The term " combination ' ' is adopted for the various fillings here described, in which more than one material is used, because it seems to be the most comprehensive. The putting together of different materials in filling teeth makes in no sense a chemical combi- nation, in which "any part of the compound is the same as any other part of it." Strictly speaking, the fillings are more "mixtures" than " combinations." According to the best authorities, however, the meaning given to combination makes its use here quite admissible. 329 ^-^0 COMBINATION FILLINGS. Zinr phosphate ot'inout has many a(hiiirahh' (|iialiti('s aiul is one of tlie uu)st vahial)k' filling materials known. It is easily worked, its color is good, its adhesiveness serves to Mnd tooth and tilling together as the stonemason's cement unites the blocks of graniti' that he piles one on the other into one solid piece of masonry. As a tooth-saver it has no equal ; but its one great defect, its solubility in the fluids of the mouth, restricts, in a great degree, its usefulness when exposed to these fluids. From this it will be easily understood why it is often desirable to combine in one filling two or more different materials ; and it may be said w ith truth that the operator who selects his filling materials with the best judgment, and combines and uses them with the most skill, will save the greatest number of teeth. There would be just as much common sense and scientitic reason for an electrician to make a dynamo entirely of copper, or a watchmaker to use nothing but gold in making a watch, as for a dentist to fill many of the cavities that come to him with but one material. It is an error to think that combination fillings are resorted to because more easily made than fillings of but one material, or that it indicates a lack of skill on the part of the operator who makes and recommends them. On the contrary, it is often much more difficult to make a suitable combination filling than one of any single material ; and the student will find that combination work will give ample opportunity for the employment of all the skill and ingenuity he may possess. Every operation must be made with the greatest amount of care and attention to minute details, or the object sought will be uuattained, and the result be an inferior piece of work which will sooner or later cause grief to the patient and chagrin to the operator. It is impossible to describe all the combination fillings that have been found advantageous and useful, therefore only some of the most important will be considered in detail. The list is limited only by the perverse manner in which teeth decay, and by the ingenuity of the ope- rator to devise scientific and practical combinations to meet the cases presenting. It is to be understood in every instance in this chapter that the teeth are in proper condition to be filled without further treatment. If pulp- less, the roots are supposed to have been put in a healthy condition and filled. In cases of exposed, or nearly exposed, pulps, they are supposed to have been properly protected, and the teeth ready in every respect for the mechanical operation of inserting the fillings. Cement (Zinc Phosphate) and Amalgam. In Simple Cavities. — This combination is of the greatest service in saving badly decayed teeth that otherwise might have to be cut off and CEMENT AND AMALGAM. 001 00 1 Fig. 315. crowned, or perhaps lost altogether. The simplest cases where it may judiciously be employed are occlusal cavities. Many such cases are seen where there is little left but the enamel, which, however, is thick around the orifice of the cavity, and, if properly supported, will have sufficient strength to withstand the ordinary strain of mastication. Great care should be taken to remove the decay from every part of the cavity, being sure that none is left under the cusps or any part of the overhanging enamel. The edges of the cavity must be carefully trimmed, so that the filling can be finished flush with the external surface, in order not to leave any overhanging portion of amalgam to be broken off, as it certainly will be if so left, to the great injury of the filling. There are but few cases, even in occlusal cavities, where the rubber dam should not be used, at least for the final excava- tion and for putting in the filling ; for it is almost im- possible to be sure that all decay has been removed from a cavity unless it is dry, No filliug should be allowed to get wet before it is all in place if it can possibly be avoided. It is much better to err by using the rubber dam too often than not often enough. Fig. 315 shows a cavity such as described. The cavity being ready, sufficient amalgam to fill one-third of it is prepared. Before introducing the amalgam, however, the cavity is filled two-thirds or three-fourths with rather soft cement, into which pieces of the prepared amalgam are crowded, forcing the cement into every portion of the cavity. The cement which has oozed out around the edges is then removed with an excavator, and the operation will have the ap- pearance shown in Fig. 316. The filling is then com- pleted in the same manner as an ordinary filling of amalgam in an occlusal cavity. The advantages of this kind of filling are many : The bulk of it is of cement, which does not change its shape perceptibly and is the best of materials when not ex- posed to the fluids of the mouth. The cement firmly unites the tooth to the filling, thus making a support to the frail walls as well as a stopping to the cavity. The amount of metal is reduced to just enough for a cover- ing of sufficient strength to guard the cement, and the tooth will not be discolored by the amalgam, as is often the case in teeth of not very dense structure, and especially in the mouths of young patients, when not thus protected. The combination of cement and amalgam, as described above for Large occlusal cavity. Fig. 316. Section showing amalgam and cement. (Sur- plus cement must now be removed; then finish with 1.) 332 COMBINATION FILLINGS. occlusal cavities, may l>o used in the same manner in simple approxinial cavities in the molars and bicuspids, and even in tiie six front teeth, when the cavities are so situated that the amalg:am does not show. When used in the front teeth the cement should be allowed to remain very near to the edges of the cavity. The amalgam need not be more in amount at this point than the thickness of an ordinary Fig. .S17. Cement and amalgam filling in an incisor. The surplus cement has been removed and the fill- ing is now ready for the finishing portions of amalgam : a, enamel ; b, cement ; c, amalgam. visiting card (see Fig. 317). For the front teeth very light colored amalgam should be selected, as color is of more importance than strength. In the temporary molars this combination can be used, frequently, with the greatest satisfaction, especially in those shallow approximal cavities where but little undercut can be obtained without exposing the pulp. The cement should be used quite thin, and the amalgam worked into it with a burnisher, or rounded instrument, forcing the cement to a feather edge at the margins of the cavity. In cases of this kind resto- ration of contour should not be attempted, as the force of mastication might serve to fracture the cement and dislodge the filling. In this manner many troublesome and difficult cavities can be successfully treated, and teeth made to last their allotted time that would otherwise be prematurely lost. In Compound Cavities. — A more extended description will be necessary for the treatment of compound cavities in the bicuspids and molars, especially where it is desirable to restore contour. In these cases a matrix is often a necessity. There are niaiiy matrices that may be used successfully, but, as they are described in otiier parts of this work, only one need be mentioned here. This is selected on account of being almost universal in its application. It can be made from any metal not acted on by the mercury contained in amalgam, (jerman silver is inexpensive and seems to meet every requirement, and is, therefore, recommended. For ordinary use it should be from No. 35 to No. 38 gauge. If stiff it should be annealed, so as to be readily bent to the form of the tooth. It can l)e easily polished so as to reflect light CEMENT AND AMALGAM. 333 into the cavity, by drawing a narrow strip of it between two pieces of stationer's rubber (ink erasers). Place one piece of the rubber on a table, then the strip of metal held with pliers in one hand is placed on the cake of rubber, while with the other hand another piece of rubber is held firmly down on the metal, which is drawn between the two until sufficiently bright. For ordinary cases, a piece is cut from the German silver, as shown in Fig. 318, A, wide enough to extend from the top of the tooth to a little beyond the cervical wall of the cavity, and long enough to a little more than cover the cavity laterally when tied in place. Sometimes it is necessary to make the matrix with a lip to extend under the gum, as shown in Fig. 318, B, or in some other irregular form, so that it can be Fig. 318. A, Matrix and ligature ; B, lipped matrix. made to properly fit the cavity. Special cases may require a very wide or a very narrow one. The operator's ingenuity must devise the right shape. For tying the matrix to the tooth, coarse, well- waxed floss silk is the best. It is passed through the holes punched in the metal, as shown in Fig. 318, A and B. When these holes are made, the edges must be finished smooth, or the silk will be cut when drawn tightly around the tooth. The operator must use tact as to Fig. 319. how and where to make his knots in tying on the matrix. Usually, a good way is to place one end of the ligature, a, between the teeth, then to make a sur- geon's knot, as shown in Fig. 319. The other end of the ligature, h, is then forced between the teeth, and the knot tightened. This will bring the knot between the teeth and opposite the matrix and will hold the latter until it can be shaped and bent into place with a burnisher or other suitable instru- ment. The knot is again tightened, and the two ends of the ligature carried to the back of the matrix and a similar knot tied there. The second knot, when drawn tightly against the back of the matrix, forces it closely up to the cervical border of the cavity, and makes a firm resistance when the filling is being condensed. The silk is then wound Manner of ligating the matrix. 334 coMniNA Tioy II I. r ixns. round and nmnd tlic tooth and matrix until it nearly coviM's both, or at least sntticicntly to insure its remaininsj in j)lac(' diirini; the o]>eration. A knot may he tied each time the silk is wound around the tooth, or not, as aj)|)ears to he necessary. Sometimes, when the sides of the tooth are slo))inij, the lijj^ature has a tendency to sli]i off. This can usuallv he ovei'come hv turninii; hack, with tweezers, the two u|)]K'r corners, as shown in Fijj^. 324. To saturate the lisj^ature with saudarac or other sticky varnish will sometimes he sufficient to j)revent the same tendency. Fig. 320 illustrates a simple and ch-licate, hut very powerful, little Pjj. ;^oo i^l'P matrix which is of great efficiency ^ ^ ^ — ^ ^ — ^ ^ — v,,^ in the treatment of occluso-approximal -.p^ ^- ■ I, ^^^ cavities. They were conceived originally K^J ^ 1 ( ^ J y^^^J f^r tlic plastics, in which case they are left iu place over night (tiie plastics thus settins^ under pressure), slipping out easily the next day away from the then hardened and perfectly contoured surface of the filling. " Thev are most easily made, even for each case (though in practice this is not necessary, as they may he employed over and over again), as follows: Suitable-shaped pieces, of a size to a little more than over- lap the cavity margins, are cut from thin . . . steel, . . . all corners and burred edges smoothly finished ; a tiny hole is punched close to the middle of both the buccal and lingual edges, and it is then laid upon a piece of lead and swaged (not merely bent, be it remarked) into perfect concavity, greater or less as the individual case shall require, bv tapping with a hammer a convex rod of hardened steel laid upon it; mv own instrument being a round-headed picture nail, case-hardened, ])olishcd, and with twisted wire attached at right angles to a handle. Any amount or shape of concavity required for each case can thus be produced in a monient, cither newly from blanks kept ready or changes made in those used for other cases to fit the one in hand, about a dozen of different sizes and' degrees of convexity being sufficient to select from, with little or no changes for all ordinary cases. The tapping having re-stiffened the steel somewhat, taken in connection with the impingement of the convex face against the apj)roximal surface of the adjoining tooth, gives firmness and strength to these delicate little strips and a perfect hugging fit to the surfaces of the tooth being filled, especially at its cervical margin, that is most satisfactory." ' When the cavity involves a large portion of the crown, or the mesial and distal surfaces, the matrix should be long enough to almost encircle ' Denial Cosmos, .June 1898, vol. xl. Xo. 6, p. 452. CEMENT AND AMALGAM. 335 Fig. 321. Fig, .S22. Matrix with marginal slits. the too^h, the ends nearly joining against the sound remaining wall (see Fig. 321). In such cases it may be desirable to slit it one or more times, in order that it may be made to take the form of the tooth more easily (Fig. 322). After the tying is completed, a suitably shaped bur- nisher is used to form the matrix, by pressing it outward, to a proper contour. One of the desirable features of the matrix here de- scribed is the ease with which it is made to give just the right shape and contour to the filling. When used for gold fillings it yields enough so that with a little care in packing the gold can be forced beyond the margin of the cavity suf- ficiently to insure a flush filling when burnished, after removing the matrix. A matrix put on as described will have sufficient resistance for a gold filling ; for amalgam, cement, or gutta-percha it may not be necessary to tie it quite so securely. For compound fillings of cement and amalgam two methods, A and B, are here given. A. Those cavities which, although large and involving much of the tooth, may have but small or comparatively small openings, especially if a matrix be used — and there are but few cases where the matrix is not advisable. If, after putting on the matrix, in this class of cavities, cement is introduced, and pieces of amalgam thrust into it, the cement will most likely be carried to the margin of the cavity at the cervical wall, and it will be found, after removing the matrix and finishing the filling, that a part of the external portion is of cement, and not being protected by the amalgam, would be washed out. To avoid this, a portion of the filling is made before the matrix is put on. Cement is put in, followed immediately by the amalgam as described for " occlusal cavities " with the added complication of the missing approximal wall. After sufficient amalgam has been put into the cement the portion of the latter which may have oozed out must be carefully cut away, so as to expose the entire outer edge of the cavity, including the cervical wall (see Fig. 323). After this has been done, the matrix may be tied on and the filling completed as though it were but a simple cavity. Sometimes it is well to leave the matrix in place until the amalgam is fully set. If this be done, care must be taken that no sharp edge or corner of it be left to wound the tongue or cheek. Fig. 323. Cement lining and amalgam. 336 COMBINATION FILLINGS. Fu;. -.VIA. Fig. .'VJo. B. Cavities with Idnji- opcninc/s. Tlic nihbcr tliini ami matrix having been adjusted, enoup;h amalgam is paeked afjdind the mairix to iurm a shell of suttieient strength to make the ai)|)ro.\imal wall ot" the filling (see Fig. 324). This will leave a large portion of the cavity unfilled as shown in the figure ; in this space is placed cement, which is gently worked into the o, Matrix : h.amnifram packed soft amalgam, but with care not to carry it against the matrix; c, por- ,, i . ^i ^ • T> c i.\ ^ 1 tion of cavity to he nearly through to the matrix. Before the cement be- fiiied with cement and (in- oomcs hard more amalgam is put in, the sur- ished with amalgam. , . ii,i ^ ^ n • ^ ^ plus cement is removed, and the whole finished to look like an entire amalgam filling, while in reality it is only a shell of amalgam, perfectly fitting the outside of the cavity, cemented into place. If the walls of the tooth are frail, the cement will serve to greatly strengthen them. If, as some claim, large metal fillings alter sufficiently under changes of temperature to fracture frail walls, the danger is bv this method reduced to a minimum, as the amount of metal is only just sufficient to give requisite strength. There is another class of cavities which may be described in this connection, presenting great difficulties in themselves, yet, with this simple matrix, they are often easily filled. It is those cases where decay has reached the alveolar border approximally, and extended on either the buccal or lingual portion of the tooth, or both, in such a manner that the dam cannot be made to stay beyond the cervical border of the cavity. If a liga- ture is used, it will draw into the lateral grooves of decay and be of no use (Fig. 325). The mode of treatment is as already described, with the exception that the matrix is adjusted before the rubber is put on. After the matrix is in place, it is but the work of a moment to put a Palmer clamp on to the tooth, and slip the rubber dam over clamp, matrix, and tooth. If the matrix has been carefully fitted there will be no trouble in keeping the cavity dry long enough for any ordinary operation. There are certain buccal cavities, also, below which it is difficult to retain the rubber dam. A very narrow matrix, adjusted with ligature and MHtri.x and clamp ^lamp (Fig. 326), ovcr which the rubber is placed, adjusted, ready for ^yiH often greatly simplify the operation. Modifica- app^ica ion o e ^.^^^ ^^ ^^^.^ method may also be applied to the a, Alveolar line be- yond which the lijra- tnre cannot be made to stay. Via. 326. CEMENT AND GOLD. 337 bicuspids, and sometimes even to marginal cavities in the incisors and canines, with good results. Cement and Gold. This combination may be used, with but slight modification, in the same manner and in the same class of cases that have been mentioned for the use of amalgam and cement, cases under B excejated. The cement is placed in the cavity, and, while soft, pieces of some of the so-called " plastic " golds are put into it, in the same manner as has been described for cement and amalgam ; the surplus cement is carefully cut away, and, after waiting for that in the cavity to become so hard as not to break or crumble under pressure, the pieces of gold placed in the soft cement are thoroughly condensed. For this pur- pose, de Trey's " Solila " Gold, Steurer's Plastic Gold, White's Crystal Mat Gold, and Watts' Crystal Gold are recommended. The filling can then be completed with the same or any kind of cohesive gold. Care must be taken to place a sufficient amount of the plastic gold into the cement to make, when condensed, a solid foundation upon which to build the rest of the filling. If too little gold has been used, it will " chop up " and not make a secure union with the cement. In some large cavities it may be found more convenient, after having filled the approximal portion with the cement and gold, to make a second mix of cement for the rest of the cavity, into which the gold is put as before. In some special cases it may be well to use foil in this manner, but, as a rule, the j)lastic golds will be found preferable. Too much stress cannot be laid on the desirability of this method for frail teeth, remembering always that the cement is the strengthening and supporting medium. The mason would not build a bridge pier of granite alone, or a house of bricks without mortar. However nicely the blocks of granite or the bricks might fit each other, it is the cement and the mortar that hold them together as in one piece. Especial attention is called to this combination of gold and cement for the six front teeth. In the teeth of young patients and teeth of low-grade structure there are often found large cavities which, if filled with gold alone, will in a few years, sometimes months, show discoloration around the fillings. Filled as above described, every vestige of decay having first been removed, a combination results which is the ideal preservative filling as fiir as present knowledge and facilities go. Pulpless front teeth that are much decayed can be improved in appearance and greatly strengthened by this method. Fig. 327 shows 338 COMBINATION FILLINGS. Fici. 327. Yui. 328. a cavity in a central incisor that can he fiUcd to a