COLUMBIA LIBRARIES OFFSITE 
 
 HEALTH SCIENCES STANDARD 
 
 HX00044482 
 
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CoH^e of ^i^^saitian^ anb ^urgeonss 
 ICttiratp 
 
A MANUAL 
 
 OF 
 
 DENTAL MECHANICS 
 
A MANUAL 
 
 OF 
 
 DENTAL MECHANICS 
 
 BY 
 
 OAKLET COLES 
 
 LICENTIATE IS DENTAL SDBGBRT OP THE ROTAL C0LLK6K OF SORGEOSS; DENTAL 
 
 SDBGEON TO THE NATIONAL DENTAL HOSPITAL, AND TO THE HOSPITAL 
 
 FOR DISEASES OP THE THROAT 
 
 WITH ONE HUNDRED AND FORTY ILLUSTRATIONS 
 
 ^etonb ^bilioii; 
 
 L N D IN" 
 J. & A. CHUECHILL, IS^EAY B L ELINGTON STREET 
 

 1% 
 
TO 
 
 ROBERT HEPBURN, Esq. 
 
 THE FIEST LECTURER ON DENTAL MECHANICS AT THE LONDON SCHOOL OF 
 DENTAL SURGERY 
 
 THIS WORK IS DEDICATED 
 
 EXPRESSION OF SINCERE RESPECT AND REGARD 
 
 BY 
 
 THE AUTHOE 
 
PEEF ACE 
 
 TO THE 
 
 SECOND EDITION 
 
 In a little more than two years the First 
 Edition of the Manual of Dental Mechanics 
 was exhausted. Sufficient evidence was thus 
 afforded that such a book was needed, and ;t 
 is not unwarrantable to suppose that the want 
 in some measure was met by the earlier edition 
 of this work. It has been translated into 
 French, and has met with a favorable recep- 
 tion in the United States. 
 
 The Second Edition I have endeavoured to 
 make worthy of the consideration with which 
 
Ylll PREFACE TO SECOND EDITION 
 
 its predecessor was received. Availing myself 
 of tlie criticism of my Reviewers, I have en- 
 deavoured to so modify and revise this edition 
 as to bring it down to the present time, and 
 make it worthier than the first issue of the 
 recognition of the Dental profession. 
 
 5, Uppee Wimpole Steeet, Catewdish Sqitaee i 
 October, 1876. 
 
PREFACE 
 
 The present work makes no pretence to 
 originality, and is intended for the Student 
 rather than the Practitioner. 
 
 Within the bounds of a handbook I have 
 endeavoured to give information of a purely 
 practical nature upon all matters relating to 
 Dental Mechanics, excluding, as far as possible, 
 everything of doubtful value or merely theoreti- 
 cal interest. I may have carried my attempt at 
 brevity to an extreme extent, but noting the 
 present rage for " big books," this is a fault 
 that I trust will be forgiven in a work that is 
 entitled ' A Manual,' and should not, therefore, 
 extend beyond moderate limits. 
 
 To the questions of the greatest interest 
 
X PREFACE 
 
 I have devoted tlie most space, while many 
 details I have passed over with but brief notice, 
 since they can only be properly acquired in the 
 Dental Laboratory. 
 
 I have collected information from many dif- 
 ferent sources, and have given the knowledge 
 thus obtained, as far as possible, in the words 
 of the original author, so that proper credit 
 may be awarded where it is due. To my 
 American brethren I am under deep obligations 
 for valuable investigations and new facts in the 
 Science of Dentistry. 
 
 To Mr S. S. White, of Philadelphia, my 
 thanks are due for the great good nature with 
 which many woodcuts for illustrating the pre- 
 sent work have been supplied. 
 
 To Messrs Ash and Sons, and Mr Gr. W. 
 Rutterford, of this city, and Mr Fletcher, of 
 Warrington, I am also indebted for similar 
 courtesies. 
 
 I am especially obliged to Mr Gr. H. Makins 
 for the readiness with which he not only 
 supplied me with illustrations for the section on 
 ^' Assaying " but also sent notes of the additions 
 
PREFACE XI 
 
 to the letter-press that he proposed making to 
 the second edition of his work on ' Metallurgy.' 
 In conclusion, I may state that this volume 
 has been prepared during spare moments in 
 the course of heavy professional work, and on 
 this account I would ask that it may, in some 
 respects, be leniently judged by my "".ritics and 
 readers ; at the same time 1 trust it will be 
 found useful by those for whom it is espe- 
 cially intended. 
 
 0. C. 
 
 81, WiMPOXE Steeet, Cayendish Squabe 
 March 2bth, 1873. 
 
CONTENTS 
 
 PAGE 
 
 Dedication ...... v 
 
 Preface . . . . . . . vii 
 
 List of Illustrations ..... xxiii 
 
 SECTION I 
 
 PREPARATION OF THE MOUTH FOR ARTIFICIAL TEETH 
 
 Removal of Diseased Stumps and Teetli . . .1 
 
 Removal of Tartar, and Treatment of Caries . . 2 
 
 Length of Time after Extractions tliat should elapse be- 
 fore Inserting Artificial Denture . . . .3 
 
 SECTION II 
 
 ON TAKING IMPRESSIONS 
 
 Bees-wax ...... 
 
 Best means of Softening and Filling Impression Tray- 
 Introduction of Tray and Wax into the Mouth 
 Removal from the Mouth .... 
 Plaster of Paris ..... 
 Mode of Mixing and Introduction into the Mouth 
 
 8,9 
 
xiy 
 
 CONTENTS 
 
 PAGE 
 
 Hind's Composition . . . . .10 
 
 Cases in which, it is most useful . . .10 
 The best way of Softening and applying in the Mouth 11 
 
 Stent's Composition, Gutta Pekcha, Wax and 
 
 Paratpin, their special characteristics . 10, 11 
 
 Impression Cups and Trays . . . .12 
 
 For Plaster of Paris Impression . . . .12 
 
 For Plastic Material . . . ■ . . .12 
 
 For Lower Impressions in Plaster . . . .14 
 
 For Lower Impressions in other Materials . . .15 
 
 SECTION" III 
 
 THE VARIOUS MODES OF APPLYING HEAT EMPLOYED IN 
 THE DENTAL LABORATORY 
 
 The Common Blowpipe, description of . 
 Blowpipe, with Bulb attached, for Checking Flow 
 
 Moisture ..... 
 Bellows' Blowpipe .... 
 Burgess' Blowpipe .... 
 Owen's Blowpipe, with Gas Supply attached 
 Snow's Blowpipe, with Gas Supply attached 
 Fletcher's Blowpipe . 
 Fletcher's Hot-blast Blowpipe 
 Self-acting Blowpipe (English) 
 Self-acting Blowpipe (American) 
 Self-acting Blowpipe (French) 
 Gas Burner for Blowpipe Work 
 Oil Lamp for Blowj^ipe Work 
 Spirit Lamp for Blowpipe Work 
 Structure of Hand Furnace . 
 Fire- Clay Furnace for Melting Precious Metals 
 
 of 
 
 17 
 
 18 
 17 
 18 
 20 
 20 
 21 
 21 
 23 
 22 
 23 
 23 
 24 
 25 
 25 
 26 
 
CONTENTS 
 
 XV 
 
 PAGE 
 
 Fletcher's Gas Furaace for Melting Precious and other 
 Metals 27 
 
 FuiTiace for Continuous Gum Work, heated with Anthra- 
 cite Coal 29 
 
 SECTIO]S' ly 
 
 CASTING IN PLASTER OF PARIS AND METAL 
 
 Casting Model in Plaster from an Impression taken with 
 
 any Plastic Material . . . . .30 
 
 Preparation of the Impression, Strengthening of Teeth, 
 
 Use of Galvanised Iron Wire and Wooden Pegs , 30 
 
 Shape of Model for Metal Work . . . .31 
 
 „ „ Yulcanite Work . . .31 
 
 Removal of Impression from Model . . .32 
 
 By means of Hot Water or Dry Heat . . .32 
 
 Casting a Model from a Plaster Impression . . 32 
 
 Preparation of the Surface of the Plaster . . .32 
 
 Separation of the Impression from the Model . 32 — 34 
 
 Trimming-up of Plaster Models . . . .34 
 
 Preparation of Plaster Models for Gold Work . . 34 
 
 Casting in Metal . . . . . .35 
 
 Description of Casting Sand to be used . . .35 
 
 Mode of Moistening with Oil or Water . . .35 
 
 Coating Model with French Chalk . . . . 36 
 
 Use of Iron Casting Ring . . . . .36 
 
 Pouring of Molten Metal into Mould . . .36 
 
 Hawe's Casting Ring for Undercut Models . . 37 
 
 Use of Cores in Undercut Models . . . .38 
 
 Franklin's Mode of Casting Dies and Counter-dies . 39 
 
 Counter-die obtained from a Ladleful of Lead . . 42 
 
 „ „ Casting Ring and Sandbank 43 
 
XVI CONTENTS 
 
 PAGE 
 
 Counter-die obtained from an Impression of Plaster Model 
 
 dipped in Lead . • . . . .43 
 
 Casting Model from Lead Counter-die . . .44 
 
 Materials for Metallic Castings . . . .44 
 
 Composition of various Fusible Metals . , .44 
 
 Professor Austen's Table of Fusible Metals . . 45 
 
 Annealing Dies and Counter-dies . . . .45 
 
 SECTION y 
 
 PRECIOirS METALS ITSED I2T DENTISTRY 
 
 Gold, its Equivalent, Specific Gravity, Melting Point, and 
 
 General Properties . . . . .46 
 
 Alloys of Gold witb Copper . . . . .47 
 
 5, J, witb Silver and Copper . . .47 
 
 „ „ with Silver, Copper, and Platinum . . 47 
 
 On Assaying Gold Alloys .... 48 — 64 
 
 Melting Gold. . . . . . .64 
 
 Admixture of Flux . .. . . . .64 
 
 Pouring the Metal . . . . . .65 
 
 Treatment after Pouring into Ingot . . .66 
 
 Forging of Ingot . . . . . .67 
 
 Flatting of Ingot into Sheet . . . .67 
 
 Use of Gauge to test the thickness of Metal . . 67 
 
 ISTecessity of frequent Annealings . . . .67 
 
 Means to be Used for obtaining the best results in pre- 
 paring Gold Plate . . . . .68 
 
 To Melt a small quantity of Metal by means of Charcoal 
 
 Blocks . . . . . . .68 
 
 Wire Making, preparation of Gold for . , .69 
 
 Use of Forging . . . . . .69 
 
 „ Draw Plate . . '^'" . . . .70 
 
DENTAL MECHANICS 
 
 SECTION I 
 
 THE PEEPAEATION OF THE MOUTH FOR AETIFICIAL 
 
 TEETH 
 
 Preparation of the mouth. — This is a prac- 
 tical point on whicli depends very often the 
 success or faihire of any mechanical appliance 
 introduced into the mouth for the sake of appear- 
 ance or utility. 
 
 The most important thing to bear in mind is 
 this, that the mouth should be in a thoroughly 
 healthy and sound state. If the gums are 
 edentulous they should be firm and insensible 
 to slight irritation, and it is above all things 
 important that there should be a normal condi- 
 tion of the salivary and mucous secretions. 
 
 When there are teeth standing they should 
 be carefully examined, any tartar attached to 
 them thqroughly removed, and any carious 
 cavities properly filled. 
 
 1 
 
2 DENTAL MECHANICS 
 
 Any teetli that cannot be restored to a per- 
 fectly sound and healthy condition should be 
 extracted, including those that from absorption 
 of their roots, or death of the periosteum, 
 have become loose, although they may not be 
 carious. 
 
 Stumps that are quite firm, give no pain on 
 sharp percussion and have no indication of 
 inflammation connected with them around the 
 adjacent tissues, may be cut down level with 
 the gum, and allowed to remain. The pulp 
 cavities however had better be opened up and 
 plugged with gold, or such other material as 
 may be indicated. 
 
 If a stump on the other hand is loose, or 
 firm but necrosed or carious, it must be ex- 
 tracted, or, again, if the remains of a broken 
 down tooth are quite firm, give no pain on 
 touching, but slight pain on sharp percussion, 
 and there is a red or purplish tinted line around 
 the gum, then extraction is inevitable. Still, 
 further, if a tooth locally gives no reason for 
 supposing it to be unhealthy, but a gum-boil or 
 scar is discovered near, it will be necessary to 
 remove it. 
 
 On all these points no persuasion or assumed 
 direction on the part of the patient must be 
 allowed to influence your own conviction and 
 
DENTAL MECHANICS 6 
 
 opinion. Firmness of will is on all accounts 
 desirable under such circumstances. Submission 
 to the wishes of your patient only involves much 
 vexation as a direct result, whilst it defers chat 
 which they regard as a great trial until a future 
 time, when the results of the operative inter- 
 ference render the entire readjustment necessary 
 of any artificial appliance that may have been 
 fitted in when the stumps and teeth were 
 intact. 
 
 The question how soon after extraction arti- 
 ficial teeth may be inserted, is one of great 
 perplexity if the operator be unguided by prac- 
 tical experience. Theoretically one would con- 
 clude that a considerable time should be allowed 
 to elapse, from my own experience, practically 
 I consider twenty-four hours enough, that is, I 
 have many times taken out ten or more teeth one 
 day, and put in a full set of artificial teeth the 
 next day, and I have found the least absorption, 
 especially in comparatively young subjects, in 
 those cases where the shortest time has elapsed 
 between the operation and the insertion of a new 
 denture. 
 
 Beyond the advantage of ready treatment 
 which this plan offers, there is the still greater 
 benefit of preserving more completely the contour 
 of the face. Many practitioners consider that a 
 
4 DENTAL MECHANICS 
 
 temporary set of teeth may be fitted in at the 
 end of a fortnight or three weeks, and a perma- 
 nent set of teeth at the expiration of twelve or 
 eighteen months. I have found, however, that 
 those dentures that I have fitted in immediately 
 after operating have fulfilled every requirement 
 of a permanent set, so that no further change 
 has been necessary. 
 
 After removing tartar or extracting teeth, 
 the following preparation will be found very 
 useful. 
 
 ^ Tinct. Krameria, 5J ; 
 Aq. Cologne, 3J ; 
 Aq. Rosse, 3viij ; 
 As a wasli for tlie moutli ; or Potass. Chloratis substituted 
 for the Krameria, according to the condition of the 
 patient. 
 
 This may be used as a mouth-wash every two 
 hours the first day, and thrice daily for a week 
 afterwards. 
 
DENTAL MECHANICS 
 
 SECTION II 
 
 ON TAKING IMPRESSIONS 
 
 "Wax. — For tlie purpose of taking impressions 
 of tlie moutli the wax should be pure and well 
 seasoned, if inclined to be brittle and dry it may 
 have a few drops of pure oil added to it while in 
 a melted state and the two well mixed together, 
 this gives a smoother surface and tougher 
 texture than when wax is used alone. It should 
 not contain, however, any spermaceti (with 
 which it is frequently adulterated) or anything 
 likely to reduce its tenacity. For convenience, 
 it may be poured when in a melted state into 
 small earthenware plates, and in this form it 
 is usually sold at the depots, and can be most 
 readily used. 
 
 Softening is best accomplished by immersion 
 in warm but not very hot water ; it is better to 
 put the wax into water only luke-warm at first, 
 and then gradually increase the temperature by 
 adding hotter water until the wax is sufficiently 
 soft to be easily moulded in the hand. Each 
 
6 DENTAL MECHANICS 
 
 piece of wax that is intended for use should be 
 dried thoroughly on a cloth before massing all 
 the pieces together, this preserves the tough- 
 ness, and to some extent prevents sucking when 
 the impression is being removed from the mouth. 
 The trays for taking the impression, having 
 been previously fitted to the jaws, should be 
 kept in the hot water, and when the wax is 
 ready taken out and thoroughly dried, and even 
 held for a moment over the flame of a spirit 
 lamp or Biinsen's burner, this prevents the not 
 uncommon accident of the tray leaving the wax 
 in the mouth when its removal is attempted, 
 as the tray being warmed causes the wax to 
 adhere firmly to it. 
 
 The filling of the tray must depend to some 
 extent upon the formation of the mouth, but as 
 a general rule fill up to a level with the free 
 border of the tray. Keep the impression tray 
 filled with the wax in the hot water until the 
 moment you are ready to introduce it into the 
 mouth, immediately before doing which you 
 may request the patient to wash the mouth 
 with cold water. This increases your own 
 facilities and reduces the discomfort of the 
 patient. Put one corner of the tray in the 
 mouth at a time, and thus save painful dis- 
 tension of the lips, and if it is necessary use 
 
DENTAL MECHANICS 7 
 
 an ivory handled instrument to draw back the 
 angle of the month on putting the second 
 corner of the tray into position. When pro- 
 perly in place over the gum to be modelled 
 press the tray firmly and evenly up or down as 
 the case may be. When it is nearly home, 
 with one of the £ngers bring all the margins of 
 the wax into close contact with the gums or 
 palate, so that the whole surface of the wax may 
 give a true and not a false impress. In using 
 wax in the mouth I believe too much care cannot 
 be taken in this particular. 
 
 When you are satisfied with the position of 
 the tray in the mouth it must be carefully 
 released from the surrounding atmospheric 
 pressure by allowing air to enter under the 
 margins of the wax. This can be done by 
 drawing back the cheeks from along the edges 
 of the impression and also by pushing back the 
 tongue if it be an impression of the lower jaw. 
 The tray should then be elevated or depressed 
 in a line with the direction of the teeth or 
 outline of the e^ums so as to avoid drao-aino- 
 as much as possible. Cold water may after- 
 wards be poured over the back of the tray so as 
 to harden the wax and prevent the risk of 
 distortion. 
 
 Plaster of Paris. — Mistaken notions exist as 
 
8 DENTAL MECHANICS 
 
 to the difficulties attendant on tlie use of plaster 
 as a material for taking impressions. With a 
 little practice it is quite as easy to manipulate 
 as anything else, and infinitely more certain in 
 its results. 
 
 The best plaster only should be used, the 
 water should just have the chill off, and to this 
 must be added (before the plaster) a dram of salt 
 to a quarter of a pint of water. 
 
 The plaster must be shaken in so that it does 
 not fall into the water in masses, and when there 
 is enough of it to absorb the water it may be 
 well mixed with a flexible knife, such as a steel 
 palette knife, or better still, an india-rubber 
 paper knife. 
 
 The plaster will now be of the consistency of 
 cream, and in this state it may be put into the 
 tray and introduced into the mouth. Ordinary 
 trays of the form shown in Figs. 1 and 2 will 
 answer very well if the surfaces be well 
 roughened. 
 
 The great secret of saving your patient any 
 discomfort is to have exactly the right quantity 
 of plaster in the tray to suit the case, and then 
 with a steady hand place it well back in the 
 mouth before you let it touch the teeth. After 
 this bring the free border of the back of the tray 
 into contact with the posterior part of the palate, 
 
DENTAL MECHANICS 9 
 
 and tlieu press upwards from behind forwards 
 until tlie whole of the traj embraces the dental 
 arch. Adopting this plan secures two points, you 
 prevent the plaster running backwards and fall- 
 ing on the base of the tongue so as to produce 
 retching, and, with the patient's head bent for- 
 ward and the chin depressed, bring the overplus 
 to the front of the mouth where it is visible, 
 and, therefore, more manageable. Another 
 advantage to be gained by adopting this method 
 of taking the impression is this — that the 
 operator runs less risk of leaving air in the 
 space between the surface of the plaster and the 
 vault of the palate. Where sufficient care has 
 not been taken to obtain perfect contact between 
 the plaster and every part of the palate, the 
 impression will have a rough appearance, with 
 irregularly shaped concavities on its surface. 
 With a view to giving a means of escape to the 
 imprisoned air, Mr Turner has suggested 
 inserting a small peg of wood or ivory through 
 the tray and plaster in such a direction that it 
 would reach the vault of the palate, and just be- 
 fore carrying the impression tray quite ''home," 
 could be removed so as to allow air to be driven 
 out freely without distorting the surface of the 
 impression. When the plaster that remains in 
 the basin will break with a clean sharp fracture 
 
10 DENTAL MECHANICS 
 
 the impression must be removed from the moiitli. 
 Air having been let in at the sides by drawing 
 away the cheeks and hps, steady downward 
 pressure must be applied to detach the mould 
 from the teeth and gums. 
 
 At this point in the process there must be no 
 hesitation on the part of the operator as every 
 moment the hardness of the plaster is increased, 
 and the diflB.culty of safe removal becomes 
 greater. 
 
 A plaster impression must be left for an hour 
 before it is ready for casting. 
 
 Hind's composition. — In those cases in which 
 the upper gum is very hard and firm with some 
 teeth standing, and when in the lower jaw 
 there is much loose, flabby, mucous membrane, 
 then Hind's composition is very useful, and, in 
 the latter cases mentioned, it is a really valuable 
 material. 
 
 If the upper gums are thoroughly solid then 
 the required pressure does no harm, and a very 
 good impression can be obtained. When in the 
 lower we have those conditions which I have 
 mentioned, there is a great liability of the im- 
 pression sucking, that is, the composition re- 
 mains adherent to some portions of the gum, 
 and thus gives a false mould. 
 
 Hind's composition by becoming very hard in 
 
DENTAL MECHANICS 11 
 
 the mouth prevents the possibility of this occur- 
 ring, and enables the operator to obtain a reliable 
 model ; whereas in using wax he would, in all 
 probability, have a false one. 
 
 Hind's composition can be softened like wax 
 in boiling water, and the same treatment should 
 be adopted in manipulating it. Stent's prepa- 
 ration was brought out ear Her than Hind's, but 
 it requires softening by dry heat to use it to its 
 greatest advantage, the surface also needs coat- 
 ing with grease of some sort when in the tray to 
 get a clean impression, these are objections, 
 besides which, it is wanting in plasticity. 
 
 If there are many teeth standing, or a few 
 only in isolated positions, it will require some 
 care lest those materials that possess the pro- 
 perty of hardening in the mouth become as 
 troublesome to remove as plaster of Paris. 
 
 Gutta percha was largely used a few years 
 back being thought better than wax, and plaster 
 of Paris was not then used to any extent, it cannot 
 however be relied on as it is apt to shrink and 
 it is sticky and troublesome to prepare for use. 
 
 Amongst the combinations of the materials I 
 have mentioned, a mixture of wax and paraffin 
 is very good — it toughens the wax, but gives a 
 rather disagreeable smell. Wax and Castor oil 
 will however be found serviceable in some 
 
12 
 
 DENTAL MECHANICS 
 
 cases ; a dram of castor oil added to a pound of 
 wax will very much increase the toughness of 
 the wax without imparting an objectionable 
 flavour. 
 
 Impression cups and trays.— These vary in 
 form, and must be adopted in accordance with 
 the size and shape of the jaws and teeth of 
 which we desire to obtain a model. 
 
 To dispose immediately of one sort I may 
 say that, in using plaster of Paris in the upper 
 jaw, only the full-palate tray is reliable. Of 
 these the best forms are those shown below. 
 
 Fia. 1. 
 
 ¥ia. 2. 
 
 For wax, Hind's, Stent's, and gutta percha, 
 other forms are available, such as those shown 
 in the annexed engravings, by means of which 
 we take an impression of only a part of the 
 palate and dental arch for the purpose of fitting 
 
DENTAL MECHANICS 
 
 ]3 
 
 in a small number m teeth, or it may be an 
 entire upper set, retained not by means of a 
 suction palate plate, but with spiral springs 
 connected with a lower piece or set. 
 
 Fig. 3. 
 
 Fig. 4. 
 
 Fig. 
 
 Fig. 6. 
 
 When plaster is used in trays it is always 
 necessary to roughen them with a scorper or 
 
14 
 
 DENTAL MECHANICS 
 
 three-pointed file, and it is very useful to adopt 
 the same plan with the trajs used for any of 
 the plastic materials, as it prevents the liability 
 of their leaving the smooth metallic surface. 
 
 For the lower jaw it is sometimes requisite 
 to make a special tray, though this but seldom 
 happens ; the method of preparing these trays 
 will be described therefore under the head of 
 Special Cases. If plaster is used for the inferior 
 maxilla, then the best form of tray is that 
 shown in Fig. 7. A thin strip of wax is 
 
 Fig. 7. 
 
 Fig. 8. 
 
 attached to the lower border of the tray, and 
 this is pressed on the surface of the gums, the 
 wax will keep the saliva from flowing into the 
 plaster when it is introduced into the mouth. 
 In taking the impression, I prefer to fill the 
 
DENTAL MECHANICS 15 
 
 tray in the moutli when it is in position, pouring 
 the plaster through the opening at the top of 
 the tray, shown in the engraving Fig. 7. 
 
 In the lower jaw I have found this a very 
 useful expedient. For the other materials the 
 trays shown below will be most useful, varying 
 the size according to the age and development 
 of the patient's jaws. 
 
 Fiof. 8. — For cases in which there are teeth 
 remaining at different parts of the jaw. 
 
 Fig. 9. Fig. 10. 
 
 Fig. 9. — For those cases in which the jaw is 
 entirely clear of teeth. 
 
 Fio*. 10. — For those cases in which the lower 
 front teeth remain, but the bicuspids and molars 
 are lost, beyond this use, the form shown above 
 is advantageous, on account of leaving room 
 for prominent molars in the upper jaw, a condi- 
 tion very often associated with a loss of the 
 
16 DENTAL MECHANICS 
 
 lower molars. Wlien from tlie loss of their 
 antagonists the remaining teeth have become 
 elongated, it is occasionally very difficult to 
 withdraw the impression from the mouth, on 
 account of the small space left between the 
 lower jaw and the upper molars. 
 
DENTAL 3IECHANICS 17 
 
 SECTIOX III 
 
 THE VAEIOUS MODES OF APPLYING HEAT REQUIRED IN 
 THE DENTAL LABORATORY 
 
 The blowpipe.— This is the readiest and most 
 common appHance in use by the dentist for 
 heating a small sm^face, soldering, and melting 
 gold and its alloys, in quantities up to three or 
 four ounces. The ordinary blowpipe consists 
 of a brass tube about half an inch in diameter 
 at one end, and gradually tapering down to an 
 aperture into which a full- sized sewing-needle 
 can be passed. They vary in length from six 
 to ten inches, and are bent with a sharp curve 
 about one fourth of their length down, so that 
 the fine portion is at right angles to the stem. 
 
 If the blowpipe be used for a long time the 
 moisture from the lungs is apt to accumulate 
 and condense in the stem, and become ejected 
 on to the metal being soldered or melted. To 
 provide against this, it is well to have one of 
 the form shown in Fig. 1 1 with a bulb in the 
 
18 DENTAL MECHANICS 
 
 middle of the tube so that any accumulated 
 
 Fm. 11. 
 
 moisture may flow into it and allow of the free 
 passage of dry air. 
 
 The danger indicated only happens, however, 
 when the lungs are used for the supply of air. 
 Many prefer a blowpipe that can be used with a 
 bellows, so as to save the exertion and injury 
 that may follow the working with the mouth- 
 blowpipe, in those who are delicate or have 
 any pulmonary affection. 
 
 It is impossible to enumerate all the various 
 forms of blowpipe that have been introduced 
 for acting without the aid of the lungs. 
 
 The simplest is that shown in the annexed 
 woodcut, Fig. 12, by using which a continuous 
 blast is kept up with but slight pressure of the 
 foot upon the bellows. 
 
 The same principle can of course be applied 
 in many different forms. Thus, many prefer 
 to use the Burgess blowpipe, with the bellows 
 arranged underneath, as shown in Fig. 13. 
 
 A more important point is the increase of 
 heat and economising of the heating material, 
 
DENTAL MECHANICS 
 
 19 
 
 Fig. 12 
 
 Fig. 13 
 
20 
 
 DENTAL MECHANICS 
 
 whether it be gas or spirit. This, again, has 
 received great attention, and an infinite variety 
 of blowpipes have been invented in order to 
 obtain the best result. One of the simplest, 
 known as " Owen's Blowpipe," is shown in 
 Fig. 14. The gas and air are discharged by two 
 
 Fig. 14. 
 
 tubes running parallel with each other. Another, 
 invented by Mr. Snow, is seen in Fig. 15, and 
 possesses the advantage of keeping only a small 
 
 Fig. 15. 
 
 jet of gas alight when hung up by the ring in 
 the upper tube. 
 
 A simple form of blowpipe has also been 
 
DENTAL MECHANICS 
 
 21 
 
 introduced by Mr Fletclier, of Warrington, in 
 whicli the tube moves by a swivel in all direc- 
 tions. This can be worked either by bellows 
 or with the mouth. 
 
 Fig. 16. 
 
 The best blowpipe, however, and one produc- 
 ing the most powerful flame, is that known as 
 
 Fig. 17. 
 
 the " Hot Blast Blowpipe," also invented by 
 Mr Fletcher. 
 
 The heat produced by this instrument is so 
 great that steel wire burns in the flame, and 
 five or six strands of fine platina are instantly 
 
22 
 
 DENTAL MECHANICS 
 
 converted into a bead. The intense heat is 
 produced, as will be seen in Fig. 17, by the 
 introduction of Bunsen's burners into the appli- 
 ance. 
 
 Yet another class of blowpipes has to be 
 mentioned, '' The Self-acting." 
 
 These instruments produce a jet by the eva- 
 poration of alcohol, the lamp being so arranged 
 as to convey heat to an upper chamber con- 
 taining the spirit, which, becoming vaporised, 
 sends out a current with suflB.cient force to 
 take the place of a mouth or bellows blow- 
 pipe. 
 
 Threeforms of self-acting blowpipes are shown 
 in the accompanying engravings ; one, Fig. 18, 
 
 Fig. 18. 
 
DENTAL MECHANICS 
 
 23 
 
 an American invention ; and the other, Fig. 19, 
 of French origin ; while the third pattern is 
 Enghsh. In the last-named (Fig. 20) the heat 
 
 Fig. 19. 
 
 Fig. 20. 
 
 from the lamp below vaporises the spirit in the 
 upper chamber and then ignites it. 
 
 Gas is of course the most convenient ag:ent 
 for producing heat in the dental laboratory ; 
 and for using the mouth-blowpipe the best form 
 of burner is seen in Fig. 21. A large volume of 
 flame is obtained from the enlaro-ed end of the 
 pipe, which is packed with layers of iron gauze. 
 This burner is fitted also with a small supply 
 pipe running forward to the end, so that it may 
 constantly have a small jet ready to light the 
 larger burner. When it is impossible to obtain 
 gas, oil or spirit lamps are used. Oil is very 
 
24 
 
 DENTAL MECHANICS 
 
 objectionable on account of tlie smoke and the 
 disagreeable smell, and in the absence of gas. 
 
 Fig. 21. 
 
 spirit is much more useful. In order to avoid 
 the danger of explosion, however, a somewhat 
 different form of lamp is required to that which 
 is used for oil (Fig. 22). 
 
 Fig. 22. 
 
 Oil lamp. 
 
DENTAL MECHANICS 
 
 25 
 
 A spirit lamp for soldering is sliown in Fig. 
 23. The construction of this lamp prevents 
 the flame beino- communicated backwards from 
 the wick into the vessel containing the alcohol. 
 
 Fig. 23. 
 
 Spirit lamp. 
 
 A soldering pan or hand furnace is of great 
 use for the purpose, of warming up cases that 
 require soldering, and cooling them down very 
 gradually afterwards; 
 
 It consists of a case made of sheet iron, with 
 a grating to hold charcoal, and a cover to keep 
 in the heat ; a long shaft with a wooden handle 
 is attached by means of a pivot, which enables 
 the operator to turn it round at will. It is 
 
26 
 
 DENTAL MECHANICS 
 
 shown botli witli and witliout tlie cover in the 
 annexed woodcut. Fig. 24. 
 
 Fig. 24. 
 
 The piece may remain in the pan while it is 
 being soldered, and so reduce the amount of 
 heat required by the blowpipe. 
 
 Two other modes of applying heat remain to 
 be noticed, the melting furnace and the furnace 
 for continuous gum work. 
 
 In Fig. 25 is seen a furnace (Ash and Sons^) 
 composed of fire-clay, requiring to be supplied 
 
DENTAL MECHANICS 
 
 27 
 
 Fig. 25. 
 
 Ash and Sons' furnace for melting gold, 
 silver, &c. 
 
 ■with charcoal and coke ; and in Fig. 26 
 (Fletcher's) we have a construction of iron in 
 which the heat is produced by a cluster of 
 Bunsen's burners arranged within a circle ; 
 both are very powerful,- but Fletcher's being- 
 supplied by gas is the more readily worked. 
 
 The furnace for continuous gum work and 
 gum -blocks is quite different in structure, and 
 must be supphed with anthracite coal to avoid 
 
28 
 
 DENTAL MECHANICS 
 
 Fig. 26. 
 
 Double-jacket furnace for operating at a white 
 lieat (section). 
 
 Plan of burner. 
 
 any smoke. A sketcli of one is shown in Fig. 
 
 27. 
 
DENTAL MECHANICS 
 
 29 
 
 Fig. 27. 
 
 The otlier varieties of furnaces wliicli are 
 used for melting large quantities of metal are 
 not suitable for use in tlie dental laboratory. I 
 think therefore it wiser to omit them in a work 
 that is intended to be both practical and con- 
 cise. 
 
30 DENTAL MECHANICS 
 
 SECTION IV 
 
 CASTINGS IN PLASTEE AND METAL 
 
 To cast a model in plaster from an impression 
 taken in either wax, gutta-percha, Stent's or 
 Hinds' composition : — With, all these materials 
 it is wise before casting, to paint over the 
 impression with sweet oil (not thick in consist- 
 ence) with a camel-hair brush. A better surface 
 is thus obtained, and the impression more easily 
 separated from the plaster model when cast. 
 If the impression indicates any teeth standing 
 in the mouth in an isolated position they may 
 be strengthened on the plaster model by putting 
 stiff iron wire, pin-size, into the impressions 
 of the teeth, pressing them well into the 
 wax or Hind's as the case may be, to hold 
 them in position while the plaster is being 
 poured. To avoid the trouble that arises from 
 the oxidation of the wire it is an improvement 
 to use galvanised iron wire or even lead wire 
 such as is used for garden purposes ; or, again, 
 
DENTAL MECHANICS 
 
 31 
 
 pegs of wood may be inserted ; tliese answer 
 very well for this purpose, dipping tliem in 
 water before use to prevent the wood swelling 
 durinof casting^. 
 
 The shape and height of the model must 
 depend upon whether a gold or vulcanite piece 
 is to be made; if metal castings have to be 
 made then the model in plaster must be high 
 and solid, as seen in the annexed cut (Fig. 28). 
 
 Fig. 28. 
 
 Fig. 29. 
 
 ^<Tl^^^ 
 
 If for vulcanite, however, it may be made very 
 thin and for lower cases of the form indicated 
 in Fig. 29. 
 
 Whether the dentures are to be complete or 
 partial the models may be cast according to one 
 or other of these two plans. To prevent the 
 plaster running about and to maintain the 
 desired form a thin strip of sheet lead or zinc, 
 
32 DENTAL MECHANICS 
 
 or wax, or gutta perclia may be fixed round 
 tlie impression, the whole resting on a square 
 of paper, so that when the plaster sets the 
 model can be readily removed from the casting 
 bench. The plaster must first be poured into 
 the impression at different points so that it will, 
 with a slight tap of the tray, run down easily 
 into the deeper portions, and when the entire 
 surface is covered with a layer of plaster the 
 eighth of an inch thick, and of the consistence 
 of cream, the portion remaining in the bowl 
 may be thickened and the rest of the model 
 built up. As soon as the plaster is quite hard, 
 the wax can be softened by immersing the 
 impression and model together in a bowl of hot 
 water, allowing it to remain sufficiently long to 
 soften all the impression before attempting its 
 removal. Some prefer dry heat or the flame of 
 a spirit-lamp, from my own experience I think 
 the hot water is the best method, from the fact 
 that there is no liability of the material with 
 which the impression has to be taken melting 
 and sinking into the plaster model. 
 
 To cast a plaster model from a plaster im- 
 pression care must be taken that the plaster 
 impression is quite dry, any mucus hanging 
 about it must be removed by means of boiling 
 water poured over the impression, then with a 
 
DENTAL MECHANICS 33 
 
 camel's-liair brusli tlie surface must be painted 
 over with a solution of brown Windsor soap, 
 this prevents the adhesion of the two surfaces 
 of plaster when the model is cast. Dr 
 Eichardson ('Mechanical Dentistry,' p. 132) 
 recommends preparing the impression first with 
 varnish to harden it ; for this purpose he 
 suggests one or other of the two following 
 formulae ; the first consisting of an uncoloured, 
 and the second of a coloured, varnish ; 
 
 Transparent Varnish. 
 
 Gum sandarach . . . 5 oz. 
 Alcohol 1 quart. 
 
 Coloured Varnish. 
 
 Gum stellac . . . . 5 oz. 
 
 Alcohol 1 quart. ' 
 
 The surface of the plaster having been 
 varnished it is then necessary to coat over this 
 with a thin layer of oil. In my own experience 
 these two coatings reduce the sharpness and 
 fineness of the impression; I would, therefore, 
 recommend the use of a solution of soap. 
 Either plan being adopted the model is made 
 in the same way as if the impression had been 
 taken in wax or some other plastic material. 
 As soon as the model is hard it should be 
 placed in a basin of boiling water and allowed 
 
 3 
 
34 DENTAL MECHANICS 
 
 to remain for two or three minutes. The lieat 
 produces expansion of tlie plaster, and the one 
 portion (the impression) having been mixed 
 earher than the model this expansion is un- 
 equal and thus starts the division of the im- 
 pression from the model, a few taps on the 
 back of the tray will sometimes detach the one 
 part from the other, at any rate it will loosen 
 the tray, *« and the impression can then be 
 prised off at some point where the greatest 
 loosening appears. Any injury to the model 
 can afterwards be repaired by means of a little 
 plaster. The model is now ready for trimming 
 up — that is cutting the sides down evenly, so 
 that they slope slightly outwards, leaving all 
 the surface of the impression untouched within 
 the eighth of an inch of where the denture will 
 extend to. This point is shown and will be 
 best understood by reference to the two last 
 woodcuts. 
 
 If the models are to be used for making a 
 vulcanite piece they are now ready; if, how- 
 ever, a gold plate is to be fitted up they had 
 better have the surface hardened by boiling 
 them in a strong solution of alum, borax, melted 
 paraffin, stearine, or a mixture of resin 2 parts, 
 wax 1 part, melted together in a pipkin. 
 Before putting a model into any of these pre- 
 
DENTAL MECHANICS 35 
 
 parations it should be tliorougUy dried and 
 then made warm, in this state the plaster 
 absorbs a considerable quantity of any substance 
 in which it may be placed. By one or other of 
 these plans being adopted the plaster is made 
 harder and stronger, and is less likely to suffer 
 from wearing away by the frequent fitting on of 
 a gold plate and bands or collars around the 
 teeth ; it also preserves the prominent markings 
 of the palate and alveolar ridge. 
 
 After remaining in the vessel containing the 
 preparation in which it has been dipped for a 
 few minutes, the model must be removed and 
 any superfluous hquid allowed to drain off, and 
 when cold it is ready for use. 
 
 Casting in metal. — Casting sand, such as that 
 which is used by brassfounders, should be 
 obtained in a fine state of division and free from 
 dirt or grit. It should be kept in a closed box 
 in order to keep it clear of the dust of the work- 
 room, and made cohesive by adding water four 
 hours before it is used ; a little practice will 
 indicate the amount of water required. When 
 ready for use it should form a compact mass 
 if pressed in the hand, and break with a 
 clean fracture. Some recommend usinsf oil 
 instead of water, in that case the proportions 
 are one quart of oil to a peck of sand ; others, 
 
36 DENTAL MECHANICS 
 
 again, advise the mixture of glycerine with 
 water to prevent rapid drying, using glycerine 
 one part, water two parts. 
 
 The model to be cast must be placed in the 
 centre of an iron ring about four or five inches 
 deep and six or seven inches in diameter ; it is 
 well to dust over the surface of the plaster with 
 a little French chalk (soap stone) : an ordinary 
 powder puff is the best thing to apply it with. 
 Sand may now be packed all over and around 
 the model and pressed carefully down with the 
 fingers, and filled up to the level of the top of 
 the ring. Now turn it over, run a sharp point 
 round the line of union of the plaster and sand 
 so as to prevent any overhanging portion of the 
 latter remaining, and whilst holding it over the 
 sand box with the model downwards, give two 
 or three taps with a mallet or hammer so as to 
 detach the model and allow it to fall (vertically) 
 into the box ; if it is held to one side there is a 
 chance of dragging, as occurs in removing 
 an impression from the mouth in a one-sided 
 fashion. 
 
 The mould being ready, the melted metal 
 must be poured in, beginning at the highest and 
 most prominent parts and filling up steadily but 
 not too slowly. Do not have the metal too hot 
 or it will burn the sand and give a rough 
 
DENTAL MECHANICS 
 
 37 
 
 casting, nor yet too near tlie setting point or it 
 will give an unsound model. For cases where 
 there are deep undercuts and depressions it 
 will be well to use Dr Hawes' casting ring 
 (Figs. 30 and 31). 
 
 The lower portion, Fig. 30, is divided into 
 three compartments held together with pins, 
 and the upper ring fitted with holes for attach- 
 ment to the lower part. 
 
 Fig. 31. 
 
 The model to be cast is put into the centre 
 of the lower part of the ring, so that the highest 
 points of the undercuts are on a level with the 
 top of the ring ; it is then surrounded with sand 
 
38 
 
 DENTAL MECHANICS 
 
 up to the level of tlie ring, as seen in Fig. 32, 
 leaving the palate exposed. The upper por- 
 
 FiG. 32. 
 
 tion of the flask is now adjusted (first dusting 
 over the surface of the sand with French chalk 
 to prevent union) and the whole filled in with 
 sand to the top of the ring. When this is done 
 the upper complete ring may be taken off, and 
 removing one of the pins from the lower ring 
 the sections can be opened and the model 
 removed afterwards ; the whole being closed up 
 again is turned over the reverse way and metal 
 poured in as with an ordinary mould. With 
 lower models, when undercut at the angles of 
 the jaw and at the back of the overhanging 
 front teeth, it is best to fill in first with wax 
 and then trim away with a scorper after casting 
 and while the metal is still soft. 
 
 If, however, the undercut is so great that 
 "trimming" up is likely to give an imperfect 
 model, it will be better to adopt the plan that 
 
DENTAL MECHANICS 39 
 
 is in use at tlie large metal foundries. This 
 consists of making a mixture of asbestos, 
 sand, and plaster, and filling in the undercuts 
 in such a way that the model will *' draw." The 
 model should be dried and dipped before the 
 " core," as it is called, is cast, and after it has 
 remained in place sufficiently long to become 
 quite hard it must be removed and made per- 
 fectly dry. It will be readily understood that 
 cores may be so cast that they will enable the 
 model to '' draw " easily out of the sand in one 
 direction, whilst from the nature of the under- 
 cut, the core itself can only be removed in 
 some other direction, so it is that we are enabled 
 to fit the cores in place on the model, obtain a 
 mould in sand, removing the model and cores 
 together, and then taking the cores from the 
 undercuts replace them in the sand, in such a 
 way that the mould thus completed represents 
 the whole of the plaster model in reverse. 
 
 Still another method of casting dies and 
 counter dies is proposed by Dr Franklin in Dr 
 Richardson's ' Mechanical Dentistry,' consisting 
 of the following process : 
 
 " I take all impressions, full and partial, in 
 plaster. A small hole, less than yg- inch, is 
 drilled through the highest point of the palatal 
 surface of the impression, through cup and all ; 
 
40 DENTAL MECHANICS 
 
 into this place two or three broom splints 
 cutting tliem off even with the surface of the 
 plaster, to allow any vapours to pass off. I 
 sometimes smoke the surface of the impression. 
 Around the impression place sufficient putty to 
 form a ring the size and height required for the 
 die. Into this pour, at as low heat as consistent 
 with the mobility required for sharp castings, 
 the bismuth alloy known as Sir Isaac Newton 
 metal, or, which is better in some respects, 8 
 parts bismuth and 4 parts each of tin and lead 
 — the latter composition being a little harder. 
 If a little judgment is exercised in pouring 
 either of the above alloys, a perfect die will be 
 secured from moist plaster impressions without 
 any drying. As the bismuth is expansive, and 
 the alloy is hard and somewhat brittle, I run 
 only a thin casting, not more than half an inch 
 in thickness, over the highest portion of the 
 impression. I have cast iron or brass heads 
 made three inches and a quarter in length, three 
 inches in diameter at large end, and two inches 
 at the other ; the large end is flat and well 
 coated with common tinman's solder. This 
 head is heated until the solder begins to soften ; 
 it is then placed in a pan or other convenient 
 vessel, and the die, face side up, is placed upon 
 the tinned surface. When the die begins to 
 
DENTAL MECHANICS 41 
 
 melt, and perfect union is secured, cold water 
 is dashed upon the die and head ; and thus we 
 have a sharp die, with an iron head, to sustain 
 the force of the blow in stamping the plate, and 
 by this means preventing any spreading of the 
 face of the die or liability of breaking in the 
 process of swaging. 
 
 " I now take sheet lead of the thickness of 
 about 'No. 24 standard gauge, and adapt it to 
 the face of the die by means of a wooden mallet 
 or burnisher, or other convenient means. Trim 
 the lead plate to the size required for the plate 
 to be stamped; when the lead plate is nicely 
 fitted, remove it carefully from the die, and 
 place it in a ring or narrow moulding flask, the 
 palatal side up ; now gently stamp moulding sand 
 into the plate and flask up level with the edges 
 of the flask ; then reverse the flask and cut the 
 sand away clean for half an inch or more down 
 to the edge of the lead plate all around. Around 
 the plate place a common moulding ring suf- 
 ficiently large to form the counter, which is 
 made by pouring melted tin or lead (or an}^ 
 alloys of these metals) on to the lead plate, 
 being careful not to run the metal so hot as to 
 melt the lead plate. When the counter is cool 
 enough to handle, the adhering sand is brushed 
 or washed away ; the die is then placed into the 
 
42 DENTAL MECHANICS 
 
 bed or counter, and, with a moderate-sized 
 hammer, give one or two sharp blows to bring 
 the die and counter together. In swaging gold 
 plates, two or three or more dies may be re- 
 quired ; these may be made either by running the 
 die-metal into the impression (if not broken), or 
 by running into lead plates, gotten up as before 
 described, reserving, of course, the first die and 
 counter for the final swaging of the plate. I 
 have gotten up a die and counter from the im- 
 pression, with the aid of an assistant, in the 
 foregoing manner in twelve minutes. I usually 
 get out my die immediately after taking the im- 
 pression ; adapt a wax or gutta-percha plate to 
 the die, and get the articulation before the 
 patient leaves the office." 
 
 We have now the metallic die. The next 
 step is the counter die. This may be obtained 
 in three ways. 
 
 The simplest plan and that most commonly 
 practised is to melt a ladleful of lead, and 
 when the metal is beginning to set dip the 
 model into it, letting it go down a depth suffi- 
 cient to cover all those parts that the plate 
 is to be fitted to. On cooHng, the model 
 can be easily detached by a few blows of the" 
 hammer. 
 
 Another plan is to place the model on the 
 
DENTAL MECHANICS 
 
 43 
 
 casting board, bank it round with moist casting 
 sand, and then put an iron ring on the sand to 
 prevent the lead, when poured over the sur- 
 face, .from running about (Fig. 33j. 
 
 Fig. 33. 
 
 This admits of the greatest pressure falling on 
 the parts where it is most required, and for par- 
 tial cases is very useful. Or, again, a third mode 
 is to dip from the plaster model. First having 
 provided a shallow iron tray, three or four 
 inches deep and five inches square, pour lead 
 into it, and just as it is beginning to set dip 
 the plaster model in the same way that you 
 would the metallic one; remove the model 
 when the lead is set, and wash away all particles 
 of plaster. For this plan several models must 
 be on hand, as one or two will be destroyed. 
 
44 DENTAL MECHANICS 
 
 and before using tliem be careful that they are 
 thoroughly dry. We may, if we desire, cast 
 the model from this di'p by putting an iron ring 
 round, driven slightly into the lead, and then, 
 pouring zinc into the ring. This last plan, 
 however, is not so good as the ordinary method 
 of casting the zinc model in sand first of all, 
 from the plaster one. 
 
 The materials for metallic castings are zinc 
 for the models or dies, and lead for the counter 
 dies. With Fletcher's gas furnace they can 
 both be very readily melted, and answer better 
 than any other metals that can be prepared in 
 an ordinary workroom ; there are, however, 
 sometimes occasions on which a more fusible 
 metal than either of these is of great service. 
 
 Of these the following are the most useful :* 
 
 Type-metal. — Lead 5 parts, antimony 1 part; 
 fuses at 500°. 
 
 Zinc 4 parts, tin 1 part; melts at a lower 
 temperature than zinc ; contracts less, but is 
 not so hard as zinc. 
 
 Tin 5 parts, antimony 1 part; melts at a 
 lower temperature than either of the previosly 
 mentioned alloys, but is easily oxidized; it 
 must therefore be poured quickly. 
 
 The following table of alloys, fusing at a still 
 
 * E-ichardson's ' Mechanical Dentistry.' 
 
DENTAL MECHANICS 
 
 45 
 
 lower temperature, is given by Professor Austen 
 in the ' American Journal of Dental Science' 
 (vol. vi). 
 
 
 :Melting 
 point. 
 
 Contrac- Hard- 
 tility. ness. 
 
 Brittle- 
 ness. 
 
 1. Zinc 
 
 2. Lead 2, tin 1 
 
 3. Lead 1, tin 2 
 
 4. Lead 2, tin 3, antimony 1 . 
 
 5. Lead 5, tin 6, antimony 1 . 
 
 6. Lead 5, tin 6, antimony 1, 
 bismuth 3 . . . . 
 
 7. Lead 1, tin 1, bismuth 1 
 
 8. Lead 5, tin 3, bismuth 8 
 
 9. Lead 2, tin 1, bismuth 3 
 
 770° 
 440° 
 340° 
 420° 
 320° 
 
 300° 
 250° 
 200° 
 200° 
 
 •01366 
 •00633 
 •00500 
 •00433 
 •00566 
 
 •00266 
 •00066 
 •00200 
 •00133 
 
 •018 
 ■050 
 •040 
 •026 
 •035 
 
 •030 
 •042 
 •045 
 
 •048 
 
 5 
 3 
 3 
 
 7 
 6 
 
 9 
 
 7 
 8 
 
 7 
 
 The zinc die and lead counter die will 
 become very hard in striking up the plates ; 
 they must, therefore, to make them wear well, 
 be annealed occasionally ; this can be done best 
 by putting them together and placing in a ladle 
 with a little water over them ; when the water 
 has boiled away allow them to remain for a 
 minute or two longer according to the state of 
 the fire and then cool them down, when they 
 will again work well. 
 
46 DENTAL MECHANICS 
 
 SECTION Y 
 
 PEECIOUS METALS USED IN DENTISTET 
 
 Gold. (Au.) — Equivalent 196'6; specific 
 gravity 19*34; fusing point 2016°. 
 
 Properties. — Extreme malleability, ductility, 
 and tenacity; non-liability to oxidation, and 
 resistance to the action of the simple acids. It 
 is, however, soluble in nitro-muriatic {Aqua 
 regia) and nitro-fluoric acids. 
 
 Grold, alloyed with other metals, is used in 
 mechanical dentistry in the form of plate, wire, 
 and foil. All of these may be obtained ready 
 for use, of the required thickness and sizes, at 
 our dental depots; and many dentists with a 
 view of saving the trouble and expense of 
 melting and flatting for themselves, always 
 purchase their precious metals in this way. 
 
 Some, however, may not be able to do this 
 on account of location in the provinces or 
 colonies ; it will be well, therefore, to give 
 some of the characteristics of gold and par- 
 
DENTAL MECHANICS 47 
 
 ticulars of the method of working it into the 
 forms required by dental surgeons. 
 
 Gold in the pure state is too soft for use, 
 readily losing its form on comparatively slight 
 pressure ; it must therefore be combined with 
 certain other metals to give it the requisite 
 amount of hardness. 
 
 Alloys of Gold. — With copper a reddish alloy 
 is formed, very much harder than either metal 
 separately. The copper must be quite free 
 however, from antimony, arsenic, and lead, or 
 a brittle alloy will be the result. The greatest 
 degree of hardness is obtained by combining 
 seven parts of gold with one of copper. 
 
 The best alloy for hard wear however (such 
 as coinage), is equal parts of copper and silver, 
 regulated according to the quantity of gold 
 plate or wire required. American gold coins 
 are chiefly prepared with copper only, hence 
 their extreme hardness and red tint. 
 
 One other alloy is of interest in this depart- 
 ment, that is, a combination of gold, silver, 
 copper, and platinum. This alloy is extremely 
 useful for clasps, bauds, pin wire, and other 
 purposes where great toughness and strength 
 are required. The exact proportion of the 
 various alloys useful to the practitioner will be 
 found under a separate heading. Before passing 
 
48 DENTAL MECHANICS 
 
 on to the purely practical part of the pre- 
 paration of gold for use in the workroom, it 
 may be convenient to describe a process which, 
 although of too complex and scientific a nature 
 to be very well carried out in the dental 
 laboratory in the midst of the ordinary work of 
 every day practice, is nevertheless of great 
 importance ; I shall therefore introduce a sec- 
 tion on assaying from the valuable Manual of 
 ' Metallurgy,' by Mr Makins. 
 
 Assay of Gold Alloys. — " In earlier days of 
 these operations, when, for commercial pur- 
 poses, they were not carried to the nicety of 
 the present time, it was common to make a 
 kind of rough assay by means of the touch- 
 stone, and, in experienced hands, with pretty 
 good results. The requisites for the process 
 were a few needle-shaped pieces of gold, of 
 various known qualities, a piece of a roughish 
 black stone, and a little nitric acid, of about 
 1*20 specific gravity. The sample to be 
 examined had some angular part of it drawn 
 across the surface of the stone; but, as in 
 articles of jewellery, the surface is often what 
 is termed " coloured," and consequently richer, 
 a few rubs were given of the part to be examined 
 upon some rough surface, previous to making 
 this testing line upon the touchstone. The 
 
DENTAL MECHANICS 49 
 
 assajer tlien took one or two needles wliicli 
 lie supposed to be near in quality to the one 
 sought. These are drawn across the stone, and 
 then the streaks are moistened with the nitric 
 acid. If the qualities are nearly the same, the 
 action of the acid will be nearly similar ; if not, 
 the streak made by the coarser of the two will 
 be most acted upon, and his experience would 
 then point out, by peculiarities in the test streak, 
 which needle he should have to choose for final 
 comparison, if it had not already been employed 
 where more than one was first used. The 
 practice is, however, a very rude one, and at 
 best depends too much upon judgment. 
 
 " The outline of the operation for the actual 
 assay of gold is as follows: — An assay pound of 
 the alloy is first very accurately weighed ; next, 
 pure silver, to the amount of from two to three 
 times the supposed weight of gold is added ; 
 then this is cupelled with a proper proportion 
 of pure lead. The button so obtained is now 
 flattened somewhat by the hammer, and then 
 rolled into a ribbon. This ribbon is annealed 
 and coiled, and is then ready for the parting 
 operation, which consists in boiling it twice in 
 nitric acid, and, between and after the boihngs, 
 washing in water. Lastly, annealing the gold, 
 and weighing. Gold (in assaying operations) is 
 
 4 
 
50 DllJNTAL MECHANICS 
 
 best weiglied decimally. Thus, in a pound, or 
 1000 parts of English standard gold, we should 
 find 916*66 of fine. The decimal weights may- 
 be conyerted into trade bj calculation. 
 
 " But the system of trade weights for gold arc 
 not the pound divided into ounces and penny- 
 weights, as for silver, but the pound is said to 
 contain 24 carats, each carat 4 carat grains, and 
 these latter are divided into halves, quarters, 
 and eighths ; the eighth, or 768th part, being 
 the lowest amount reported. The actual weight 
 of the pound varies much, thus some assayers 
 (those who follow the French directions) use 
 only 7*5 grains, while, on the other hand, 
 English assayers will use from 10 up to 16 
 grains . The capability of using a tolerably large 
 weight of course assists in the greater delicacy 
 of the small weighings. By a trade report, as 
 it is termed, standard gold, which contains 11 
 of gold to 1 of alloy, would be said to be 22 
 carat gold, any specimen containing more would 
 be called ''better," and less than that amount 
 '' worse." As this method of weighing is still 
 used by many assayers, an illustration or two 
 may be given. Having at first " weighed in " 
 an assay pound of metal, and carried it through 
 the various stages of the operation, the fine 
 piece of gold resulting is placed in the balance ; 
 
DENTAL MECHANICS 51 
 
 in the other pan is put the 22 carat, or standard 
 weight. Suppose the gold does not counterpoise 
 this, sufficient weights are added upon the gold 
 pan, and thus, supposing a carat grain, a half, 
 and an eighth, were found necessary, the gold 
 would be reported, W, carat, ] |- gr. If, on 
 the other hand, it was heavier than standard, 
 and weights (say) of 1 carat, 2J gr. were re- 
 quired to be added to the weight pan, the report 
 would then be, B, 1 carat, 2|- gr. Thus gold 
 of 18 carats fine would be written, W, 4 carats. 
 
 '' The rough weights of metal for the gold 
 assays being prepared by an assistant, are 
 weighed in for the furnace by the assayer him- 
 self, who, judging quality from external ap- 
 pearances, &c., adds to them at the same time 
 the requisite amount of pure (or ' water ') 
 silver, and then wraps silver and gold together 
 in a piece of sheet lead, weighing half the 
 amount of the lead required. 
 
 '' The quantity of lead to be employed will be 
 about 6 times the weight for gold down to about 
 920. Below that and down to 750, 8 times 
 will suffice. And for qualities below the latter, 
 10 will often be required, although these pro- 
 portions are often modified by the presumed 
 nature of the alloy. 
 
 " The furnace being prepared and heated just 
 
52 DENTAL MECHANICS 
 
 as described for silver, the assays are charged 
 in when the heat is judged to be sufficient, and 
 the cupel operation is then carried on, as with 
 silver. But the care requisite here is very 
 much less than in the latter class of assays, the 
 object being as much the alloying of gold and 
 silver as the complete separation of oxidisable 
 metals ; because any small amount of the latter 
 left in the assay will be removed by the acid in 
 the parting operation, which retained alloy in a 
 silver assay, where there is no after- assisting 
 operation, would be just so much of error. A 
 certain amount of care is, however, to be 
 exercised for several other reasons ; thus, for 
 example, if assays, and especially gold ones, be 
 charged into cupels insufficiently ' seasoned ' 
 in the furnace, ' spirting ' is sure to result : 
 this is the throwing up from the bath of fused 
 metal of a number of small beads of the assay ; 
 these will be projected even to the crown of the 
 muffle, and falling all around, spoil the assays 
 in the surrounding cupels. 
 
 '' Again, loss may accrue from vegetation or 
 springing if the assays have been carelessly 
 cooled down ; and, lastly, a muffle not properly 
 cleared, or having a fragment of coal shut up in 
 it, will, by containing an atmosphere of carbonic 
 acid, cause reduction of the oxide of lead at the 
 
DENTAL MECHANICS 53 
 
 external parts of the cupel, whicli reduced lead, 
 being taken by the yet fluid button, will render 
 it so brittle as to fly to pieces under the 
 hammer. 
 
 " The flattening hammer requires some 
 dexterity in its use. The buttons being taken 
 from the furnace are one by one placed upon an 
 anvil and struck three blows; the first, a down- 
 right one, gives the piece the diameter equal to 
 the width required of the ribbon. The next blow 
 is a kind of drawing one upon the edge, whereby 
 a kind of tongue is drawn out sufficiently thin 
 to cause it to be readily seized and drawn in 
 between the rollers of the flatting-mill. The 
 other end of the assay is then turned round, and 
 a similar blow and conformation given to it. 
 
 " The board containing the flattened buttons 
 is now taken to the rolling-mill, and all are 
 passed through, with the rollers set just at such 
 distance apart as will equalise the assays. They 
 are next adjusted down to the distance, which 
 shall elongate the assay into a ribbon of metal 
 required ; and now if the flattening operation 
 with the hammer has been well performed, they 
 should all be of equal breadth, and for an assay 
 pound of 10 grains, measuring about "4 of an 
 inch wide, the rolling operation, bringing them 
 to 2*2 inches long. 
 
54 DENTAL MECHANICS 
 
 " This treatment of the metal will, however, 
 have rendered it very hard and dense, therefore 
 annealing is required before the parting opera- 
 tion, for which purpose the assays are placed in 
 a solidly made iron tray, each one in a separate 
 division. The tray is put into the muffle and 
 heated to dull redness, after which it is taken 
 out and the ribbons of metal coiled up into small 
 cylindrical rolls, called ' cornets.' 
 
 u rpj^g requisite number of assay glasses are 
 then charged with from 2 to 3 ounces of nitric 
 acid of a specific gravity of from 1'16 to 1*25; 
 and these are arranged upon a gas parting 
 apparatus. This consists of a tube, A, connected 
 with the gas supply, from the upper part of this 
 rises a number of cocks ; and on the outer 
 screw of each of these a cup -shaped burner, B, 
 is screwed, the jets of the burner, passing out 
 horizontally from its circumference, cause the 
 flame from each to wrap itself round the end of 
 the glass. For a small set of from six to twelve 
 burners the arrangement shown in the drawing 
 may be adopted where the whole are fixed in a 
 mahogany stand. This latter is furnished with 
 a set of long tubes, D, one for each glass, C ; 
 and when the evolution of acid vapours com- 
 mences, they may be inserted in the necks of 
 the glasses, thus condensation of the acid takes 
 
DENTAL MECHANICS 
 
 Fig. 34. 
 
 ff ff ff f? ff fl 
 
 55 
 
 place in tliem, and tlie condensed product runs 
 back into the glass, while the escape of noxious 
 
56 DEXTAL MECHANICS 
 
 yapour is to some extent moderated. In an 
 active laboratory, where fifty or more are worked 
 at a time, it is necessary to arrange tlie whole 
 in some convenient chamber, provided with a 
 flue for carrying the acid vapours away. The 
 tubes D are then dispensed with, and the burners 
 are better to be placed upon two or even three 
 gas tubes, so as to be more under the eye. 
 
 " After the assay glasses have cleared of red 
 fumes, from three to five minutes' brisk boiHng 
 is kept up, they are then removed from the 
 burners, and the solution of nitrate of silver 
 poured off*, the cornets washed with a little hot 
 distilled water, and a fresh dose of acid put 
 into each glass (of a specific gravity of 1'3). 
 They are then boiled again for fifteen or twenty 
 minutes, after which the acid is poured off" and 
 the glasses quite filled with warm distilled 
 water. 
 
 '* It will be found that acid of the above 
 density is apt to boil unsteadily, and its vapours, 
 by adhesion to the sides of the glass, will be 
 given ofi" irregularly and with such violence as 
 even to project nearly the whole of the acid from 
 the glass. Hence it is found necessary to put 
 some body in with the assay, which, by aff'ording 
 points for the evolution of the vapours, shall 
 facilitate its steady delivery from the fluid. For 
 
DENTAL MECHANICS 57 
 
 this purpose tlie practice by many is to use a 
 piece of charcoal, but this is apt to induce the 
 evolution of nitrous acid, which by absorption 
 in the acid will even dissolve portions of the 
 metal. This has been proved by the author, 
 and put forward in a paper lately published 
 by him (' Quarterly Journal of the Chemical 
 Society,' 1860). Moreover the acid becomes 
 much discoloured by charcoal, hence Mr Field, 
 the Queen's Assay Master, has proposed 
 the use of small balls of porous earthen- 
 ware, and these answer the purpose most 
 admirably. 
 
 '' The assays are next turned into small 
 porous earthenware crucibles for annealing, but 
 the cornets, with the silver now removed, occupy 
 the same bulk as before parting ; hence from 
 their spongy, and consequent friable nature, 
 much care is required in effecting this, or they 
 are sure to breakup. The pot is therefore first 
 filled with water, and the neck of the glass 
 stopped by the forefinger, then being dex- 
 terously inverted under the water of the pot, 
 the finger is removed, and the assay allowed to 
 fall steadily into the pot, time also being given 
 for any pieces (if any should by chance have 
 become detached) to fall on to the assay. In 
 this operation, if the piece even touch the finger 
 
68 DENTAL MECHANICS 
 
 in its transfer portions are very likely to be 
 detaclied. 
 
 " The pots are now arranged in tlie fur- 
 nace, and heated up to an annealing heat, 
 thus the former bulky cornet is condensed 
 and shrunk considerably, while its surface, 
 by incipient fusion, becomes perfectly metallic, 
 changed from the brown lustreless appearance 
 it had when washed off to a pure golden 
 surface. 
 
 " It now only remains to weigh the assay, but 
 compensation must be made for a certain reten- 
 tion of silver; this not only varies with different 
 operators, ranging from one to ten grains in the 
 troy pound, but is subject to slight difference 
 with the same assayer, dependent upon the 
 furnace heat, atmospheric influence upon the 
 boiling of the acids, and other disturbing actions. 
 Beyond this there will be, on the other hand, 
 an allowance to be given from the precious de- 
 duction for loss of gold during the operation, 
 which is subject to like variation with the silver 
 retention. This averages about one to six 
 grains in the pound troy. Hence the operation 
 can only be carried on to perfection by those 
 who are continually practising it ; and in such 
 hands it needs daily tests to be passed with 
 the working assays, as proofs or standards, 
 
DENTAL MECHANICS 59 
 
 whereupon to base the necessary corrections to 
 be applied. 
 
 " In addition to the operation of assaying for 
 the amount of silver or gold as already detailed, 
 there are cases where it is required to estimate 
 silver contained in gold, and also gold in silver, 
 such are called ' parting assays.' The latter, 
 viz. that of silver contained in gold, is effected 
 by simply dissolving the metal in dilute nitric 
 acid, and collecting the gold powder left ; this is 
 then to be washed with boiling distilled water, 
 and annealed to brightness, when it will be in a 
 state for weighing. 
 
 " The valuing^ of silver in o-old is somewhat 
 more complex. A double gold assay is made 
 in the usual way, and at the same time an assay 
 pound of the metal is cupelled with no silver 
 added. Thus the copper and oxidisable metals 
 are removed, and the button left will be 
 composed of the gold and silver of the specimen 
 only. The difference of weight of this above 
 the parted assay will of course be due to silver. 
 But in this operation, not only are comparative 
 assays necessary, but much judgment and 
 experience upon the part of the assayer, or the 
 results will be quite unworthy of confidence. 
 
 " In the dental laboratory, where it is pro- 
 bably of advantage to be able to obtain assays 
 
60 DENTAL MECHANICS 
 
 upon very small quantities of metal, very good 
 approximate ones may be obtained by means of 
 tlie blowpipe, witli the additional advantage of 
 rapidity of execution dependent upon their 
 smallness. Thus a common candle urged by 
 the blast of the ordinary mouth blowpipe will 
 afford the requisite heat in the hands of a prac- 
 tised blowpipe manipulator ; but where the gas 
 blowpipe, joined with the double bellows already 
 described can be obtained, the operation becomes 
 very easy and certain. 
 
 " A grain of gold will be sufficient for the 
 assay pound ; and if to this we add the two to 
 three grains of silver requisite, and seven grains 
 of lead, the whole mass of metal will at first only 
 weigh ten grains, or a little more, according to 
 the amount of silver used, a quantity managed 
 with ease. 
 
 " For this a small cupel of about a quarter of 
 an inch each way may be employed. This may 
 be rested in a small cavity cut in a piece of sound 
 charcoal. The tip of the flame is first to be 
 directed on this so as to heat it up somewhat ; 
 after which the assay, prepared as in ordinary 
 assays, is to be put in, and when fused by the 
 flame directed upon it, the cupel is to be kept 
 just in that position in the oxidating flame as 
 will carry oxidation on, and at the same time 
 
DENTAL MECHANICS 61 
 
 maintain the heat of the cupel so that the lead 
 oxide may be absorbed ; although much in this 
 operation passes off in vapour. These actions 
 are to be steadily maintained until the assay 
 brightens. It is then removed from the cupel, 
 flatted and rolled. The ribbon may then be 
 annealed by a spirit-lamp, after which it is rolled 
 up, and parted with two acids. These last 
 operations may even be effected in a test tube 
 over a spirit-lamp. The little cornet is, lastly, 
 to be washed into a small porcelain or platinum 
 basin, and annealed over the lamp, when it will 
 be in a state for weighing. And if this opera- 
 tion be well and carefully carried out, very close 
 approximations may be obtained. 
 
 " As a most delicate balance would be required 
 for these minute weighings, and such an one is 
 not always at hand, I may state that the little 
 instrum^ent described by Mr Faraday in his 
 ' Chemical Manipulation,' as Dr Black's sub- 
 stitute for a delicate balance, will answer very 
 well for these weighings. 
 
 Fig. 35. 
 
 ' ^ /// 
 
 •* It consists of a thin slip of pine about twelve 
 
62 DENTAL MECHANICS 
 
 inches long and *3 of an incli broad in the 
 centre, but slightly tapering both in breadth 
 and thickness to each end; in the middle of this 
 a very fine needle is fixed at right angles upon 
 its flat and upper side. Upon each side of this 
 needle or fulcrum, ten divisions are marked at 
 exactly equal distances from each other, starting 
 on each side from the needle. The bearing upon 
 which the beam is to play is a small piece of 
 sheet brass turned up to equal heights, so that 
 a very narrow plane is thus formed on each side 
 of the beam for the needle fulcrum to rest upon; 
 and as this rises only a quarter of an inch from 
 the little slip of mahogany upon which it is 
 screwed, the play of the beam is very small. 
 The beam of course after thus being shaped is 
 to be adjusted so as to equipose upon this 
 bearing. 
 
 " The weights requisite for decimal weighing 
 will be three only, viz. one grain (as an assay 
 pound) '1 of a grain, and '01 of a grain; and 
 these are best formed in platina wire of fit 
 degrees of fineness, as shown in the drawing, 
 where they are represented as lying upon the 
 mahogany base. 
 
 " An example may be given to illustrate the 
 method of using this little apparatus. 
 
 " Placing the grain or assay pound weight 
 
DENTAL MECHANICS 63 
 
 upon the lOtli or principal division on one end, 
 a slip of llie metal to be assayed is cut off, and 
 if of somewhat the shape of the pound, it Avill 
 be better for accuracy of weighing, as it will lie 
 better upon the beam division, care also having 
 been taken that it should be rather plus, it is to 
 be reduced to the correct weight. Then after 
 cupelling, and parting this as above, the cornet 
 obtained is to be placed upon the 10th as before, 
 and now being diminished in weight by the loss 
 of its alloy, the pound must be passed back 
 upon the beam divisions, but even at one back, 
 or division 9, the weight being found too light 
 for the cornet, it is allowed to remain at 9, and 
 the 2nd or "1 weight is placed on 8, and being 
 found too heavy is passed back, trying a division 
 at a time, until, arriving at division 1, it is 
 found too little. Hence, leaving the 2nd also, 
 upon division 1, the 3rd or '01 weight is used 
 in the same manner, and passing it back by 
 divisions its real position would be found to be 
 between divisions 6 and 7. Hence, the weight 
 ascertained is thus reckoned. First, the 1000 
 or pound weight being upon 9 gives the first 
 figure of the report, viz. 9. Secondly, the tenth 
 of the thousand on the first division gives 1 as 
 the second figure. Thirdly, the hundredth of 
 the pound, requiring to be placed at a point 
 
64 DENTAL MECHANICS 
 
 between 6 and 7 may be called 6*5. Therefore 
 the weight will actually be 9 IG'o, indicating the 
 specimen to have been one of standard gold. 
 
 " It will readily be seen that if necessary this 
 simple instrument might be equally easily 
 applied to trade weighings, by dividing the beam 
 into 8, as the |-th of a carat grain is the smallest 
 denomination, instead of 10 divisions, and then 
 using the 1 grain pound as 24 carats with pro- 
 portional weights of 22 carats, 2 carats, 1 carat 
 and 1 carat grain. But the decimal method 
 is very simple and its weights are easily con- 
 vertible." 
 
 Melting. — The quality of the gold plate or 
 wire having been decided upon, and the proper 
 relative proportions weighed out carefully, they 
 are to be put into a crucible, varying in size 
 according to the quantity to be melted, always 
 having the crucible a good size in comparison 
 with the " melt," and the metal covered with 
 borax, some of which is also mixed in with it. 
 The pot must be placed in the furnace, with 
 small pieces of charcoal put into the crucible 
 above the borax, and the whole well surrounded 
 with fuel. 
 
 The form of crucible best suited for small 
 quantities of metal is shown in Fig. 36. 
 
 When the gold is melted and thoroughly in- 
 
DENTAL MECHANICS 
 
 65 
 
 Fia. 36. 
 
 corpcrated Tvitli its alloys, it must be poured 
 into an ingot mould held in a frame (shown in 
 Fig. 37). Previous to pouring, however, the 
 
 Fig. 37. 
 
 two portions, of which the mould is formed, 
 must be warmed with a lamp or over the fire, and 
 then wiped with an oily cloth such as is always 
 found in use in connection with the flattinsf mills 
 and other machinery. This causes the metal to 
 flow better. 
 
 Everything being ready the gold is poured 
 
 5 
 
(56 
 
 DENTAL MECHANICS 
 
 into the ingot mould, and after a moment or 
 two being allowed for setting, it is taken out 
 and dipped in weak acid and water to cool it 
 and cleanse tlie surface. Any sharp edges of 
 metal that are likely to break off had better be 
 removed at once with the file ; it may then be 
 
 Fig. 38. 
 
 Flatting Mill on iron stand to fasten to the floor, 
 witli hardened rollers 4 inclies long and 2i inches 
 diameter, with a double set of cog-wheels for mnlti- 
 plying the power, and two handles (Fig. 38) . 
 
DENTAL MECHANICS 67 
 
 annealed by placing on the ashes in the furnace 
 or forge. Some proceed now to flatten the 
 ingot at once in the mills; it is, however, better 
 to forge first, and reduce the thickness some- 
 what on the anvil with a smooth-faced hammer, 
 taking care to have the edges of equal thickness, 
 and preserving the even surface of the plate as 
 much as possible, constantly annealing so as to 
 avoid brittleness. Having been reduced one 
 fourth of its original substance by forging, it 
 may be taken to the flatting mills and rolled 
 out till it is thin enough for ordinary plate 
 work. 
 
 Flatting.— The best form of flatting mill is 
 that shown in Fig. 38. During the process 
 of flatting frequent reference must be made to 
 the gauge (Fig. 39) to see that the plate is of 
 
 Fig. 39. 
 
 equal thickness all round, the screws holdino- 
 the two rollers together being regulated ac- 
 cordingly. 
 
 Throughout the time of flatting, after every 
 five or six turns through the mill, the plate 
 must be annealed by heating to a dull red 
 colour, as previously mentioned. If a small 
 
68 DENTAL MECHANICS 
 
 piece only, this may be done with a blowpipe, 
 but if large it can be more perfectly accomplished 
 with the furnace or forge. For the furnace it 
 must, according to the description in use, be 
 protected from the liability of " sweating," 
 that is, the thin edges and surface becoming 
 partially melted. 
 
 Briefly, then, the best results are obtained by 
 compact and careful forging, frequent annealing, 
 and a very gradual and accurate adjustment of 
 the screws of the mill, whereby the rollers are 
 slowly, and at both ends, more nearly approxi- 
 mated, till the plate is finished. 
 
 Avoid, especially, straining both gold and 
 mill by jerking and violent rotation of the 
 rollers. 
 
 A small quantity of metal may be melted on 
 a block of charcoal and then run into a space 
 formed by another block attached, and having 
 a rim of flattened iron wire interposed, so that 
 
 Fig. 40. 
 
DENTAL MECHANICS 69 
 
 a miniature ingot mould is formed. The cliar- 
 coal blocks may be embedded in plaster to pre- 
 vent tlie hands being liable to injury from the 
 breakage of the charcoal. This plan will be 
 easily understood from the accompanying wood- 
 cut (Fig. 40). 
 
 The two pieces of charcoal must be tied to- 
 gether with binding wire before melting either 
 with the gas, spirit-lamp, or blow-pipe, is 
 begun. 
 
 Making wire requires the gold to be left a 
 good thickness according to the size you require 
 your wire. Then cut off strips with the shears, 
 (Fig. 41), so that they may be square when so 
 
 Fig. 41. 
 
 cut off; these must be annealed, then their 
 edges forged with hammer and anvil to take off 
 the sharp borders, and thus reduce the rod to 
 something like a round surface, the metal 
 being constantly annealed throughout; a draw- 
 plate, shown in Fig. 42, must be fixed in a strong 
 standard vice and the wire drawn through one 
 hole after another with strong '' wire pullers " 
 till it is of the size required for use ; it must be 
 
70 
 
 DENTAL MECHANICS 
 
 constantly annealed and tlien cooled by passing 
 through a piece of wax ; this assists its passage 
 through the holes in the plate. For large 
 
 
 
 Fig. 
 
 42. 
 
 
 
 
 1 o 
 
 © 
 
 o o 
 
 o 
 
 o 
 
 s^ 
 
 
 
 HJL^-^--- 
 
 o 
 
 o © 
 
 o 
 
 1 
 
 
 O 
 
 
 quantities of wire a draw bench is used, by 
 which means a greater amount of force can be 
 applied, but with a small quantity, a little care 
 and steady pulling with the arms will produce 
 very satisfactory results. 
 
 Spiral springs.— No one in the present day 
 would think of making their own spiral springs, 
 as they may be obtained of a much better cha- 
 racter than home-made ones, at all the depots, 
 and beyond this a large number of practitioners 
 have dispensed altogether with their application 
 to sets of teeth. 
 
 As the appearance of a spring would indicate. 
 
DENTAL MECHANICS 
 
 71 
 
 the wire is drawn down thin and then being 
 held firmly at one end the other is attached to 
 a mandrel and gradually spun up till the spiral 
 spring is produced. An instrument in use by 
 dentists some years back, (when they made 
 their own springs,) is shown in Fig. 43, copied 
 from ' Robinson on the Teeth.' 
 
 Fig. 43. 
 
 Silver (Ag.) . — Equivalent 108 ; specific 
 gravity from 10*43° to 10*63°; fusing point 
 107*3°. 
 
 Projoerties. — Exceedingly ductile and malle- 
 able, surpassing gold in tenacity, but inferior in 
 this respect to platinum. 
 
 Soluble in nitric and sulphuric acids. 
 
 Alloys. — Silver is scarcely ever used in the 
 workroom in the pure state on account of its 
 
72 DENTAL MECHANICS 
 
 softness ; alloyed with platinum it may be used 
 for wire for certain purposes, but should not be 
 employed as a base for artificial teeth, from the 
 rapidity with which it is acted upon by sulphu- 
 retted hydrogen. Silver combines with platinum 
 in varying proportions to form a metal known 
 as Dental alloy ; this is very tough and of a 
 grayish colour. With copper an alloy is formed 
 similar to that of our silver coinage, possessing 
 much greater hardness than pure silver, while 
 it retains its purity of colour. A good propor- 
 tion is — silver nine parts, copper one part; this 
 is the composition of the silver coinage of the 
 United States, and wears very well. This alloy 
 of silver and copper, however, is of but small 
 interest to the dentist, the more important 
 alloy being with platinum, and this latter 
 having only a very limited apphcation. 
 
 Platinum (Pt.). — Equivalent 98*56°; specific 
 gravity 21*5° ; fusing point, blue heat. 
 
 Properties. — In colour it is grayish white, 
 resembling polished steel; it is harder than 
 silver and has a greater density than any other 
 metal at present known. It can only be melted 
 by the oxy -hydrogen blowpipe and electricity ; 
 no amount of forge or furnace heat will act 
 upon it so that it can be run into an ingot. 
 This metal is exceedingly ductile and malleable 
 
DENTAL MECHANICS 73 
 
 when properly tempered and annealed. None 
 of the simple acids have any effect upon it ; 
 nitro -muriatic acid, however, dissolves it. 
 
 Alloys. — With gold it forms a straw-coloured 
 alloy varying in depth of colour with the quan- 
 tity of gold used, increasing both the hardness 
 and elasticity of the gold if the latter be in 
 excess ; hence the use of platinum in gold 
 intended for spring ware, clasps, &c. 
 
 Platinum is best used in the pure state — if at 
 all — for plates for artificial teeth, as it then 
 keeps a good colour and retains its polish very 
 well. Pure gold must be used as a solder if the 
 platinum be pure. 
 
'4 DENTAL MECHANTCS 
 
 SECTION yi 
 
 MAKING GOLD PLATES EOR PARTIAL AND FULL 
 DENTUEES 
 
 The models having been prepared in accord- 
 ance with the directions already given, a pattern 
 must be cut out in thin sheet lead, so that on 
 being applied to the model it perfectly covers 
 every part that is to be fitted with a plate ; 
 this being removed, is flattened out carefully 
 and placed upon a sheet of gold of the requisite 
 thickness, and the outline traced with a sharp- 
 pointed instrument or pencil. The size of the 
 plate will vary according to the position of the 
 tooth or teeth to be replaced, and according as 
 to whether it is to be retained by clasps or 
 bands around the other teeth or by suction. I 
 shall first treat of cases held in the mouth by 
 clasps and bands. If there is an opening 
 between the bicuspid and molar on either side, 
 the plate should be carried back so that a 
 support may be fitted around the latter, taking 
 
DENTAL MECHANICS 75 
 
 it for granted that an artificial tooth is required 
 at the anterior part of the mouth. For such 
 an arrangement the plate may be made of the 
 form shown in Fig. 44, or if the covering of 
 
 Fig. 44. 
 
 the palate produces discomfort it may be 
 narrowed in front and a bridge of metal carried 
 across from molar to molar, as shown in Fig. 
 45 ; this leaves all that part of the mouth 
 quite clear against which the tongue principally 
 presses in speech and deglutition. It is very 
 important in single tooth cases, especially, that 
 they should fit with great firmness and depend 
 for their support upon bands attached to very 
 sound teeth. If from any cause bands cannot 
 be adjusted to the first molars, the second 
 bicuspids may be used, but in some patients' 
 
76 DENTAL MECHANICS 
 
 Fig. 45. 
 
 mouths there is a liability of the clasp showing 
 when the teeth are displayed, as in laughter. 
 
 These remarks as to the clasps apply to all 
 cases where any of the eight anterior teeth are 
 required. The plan suggested of cutting out 
 the central portion of the plate, thus leaving 
 the palate exposed, may also be adopted for 
 these cases. 
 
 The plate having been cut out according to 
 pattern by means of the shears and nippers 
 shown in Figs. 46 and 47 and the situation of 
 the clasps decided on, the next step is "striking 
 up ;" this is accomplished by placing the plate 
 between the die and counter die and giving it 
 one or two steady blows with a flat-faced 
 hammer weighing about six or seven pounds, 
 the weight of the hammer varying according to 
 
DENTAL MECHANICS 
 
 11 
 
 the strength of the workman. The gold must 
 have been struck and bent somewhat into shape. 
 
 Fig. 46. 
 
 Fig. 47. 
 
 Fig. 48. 
 
 first, on the zinc model with the aid of a mallet 
 of wood or horn and the pliers for this purpose 
 (Fig. 48). If the teeth in the mouth are very 
 
78 DENTAL MECHANICS 
 
 long they may be cut down (after the model is 
 dipped in lead) to within one eighth of an inch 
 from the gum ; this will facilitate the process 
 of striking up, and the teeth having been cut 
 down after the counter die is taken admits 
 of more pressure being brought directly 
 upon the plate instead of upon the crown of 
 the teeth. During the process of fitting the 
 plate it will become necessary to frequently 
 anneal it, in order that it may not become 
 cracked and brittle from the hardening ; 
 previously to annealing it is very important to 
 bear in mind that it should always be placed 
 for five or ten minutes in dilute hydrochloric 
 acid or boiled in dilute acid, and afterwards well 
 brushed with pumice powder and water, so as 
 to remove all particles of lead or zinc that may 
 have adhered to the surface; these, if not 
 removed before annealing, injure the quality of 
 the plate. 
 
 By the aid of the blowpipe or furnace it 
 should then be brought to a dull red heat. 
 
 One model and counter die will scarcely suffice 
 to make a plate fit the plaster model and mouth 
 perfectly, there should always be a second set 
 ready for use; and in the event of the markings 
 on the palate being very prominent, or the 
 plate having to fit over stumps, it is even well 
 
DENTAL MECHANICS 
 
 79 
 
 to use a third zinc model and lead. The fit of 
 the plate round the necks of the remaining teeth 
 should be very accurate, to attain this end 
 many use chasing punches of the form shown 
 in Fig. 49. Others again prefer only to trust 
 
 Fig. 49. 
 
 to the fit obtained by the striking up. Before 
 the final swaging the plate must be reduced to 
 the size it is to assume in the finished state. 
 This can be done with the file, the palatine 
 border of the plate being finished off with a 
 bevelled or scissor edge, and the other portions 
 so as to present no rough edges to the tongue. 
 If teeth are to be mounted on the gum, then the 
 plate must be cut away in a scalloped fqrm, 
 corresponding with the outlines of the face of 
 the teeth, the teeth must, however, slightly 
 overlap the border so that none of the plate 
 
80 DENTAL MECHANICS 
 
 may be seen wben in the moutli. It is scarcely 
 necessary to point out tliat during the process 
 of making the plate any fractures that may 
 have taken place in it must be repaired with 
 solder, and, if necessary, a small strip of gold 
 put across the breakage to act as a brace; 
 any parts, also, that from their position will be 
 subjected in the mouth to great strain, must be 
 strengthened either by doubling the plate at 
 this point, or by soldering on a strip of half 
 round wire, striking it up with the plate before 
 fixing, so as to obtain perfect apposition of the 
 two. When the narrow strip of plate is 
 carried across the arch of the palate, it should 
 be increased in substance carefully, so as to 
 withstand the pressure that may be applied in 
 putting it into and removing it from the mouth. 
 When in situ there is but slight strain upon it, 
 resting as it does between two fixed points 
 on a solid base. It is particularly important to 
 well sustain those parts of the plate that run 
 forward to carry only a single tooth, as these 
 are peculiarly liable to breakage, and have to 
 resist great force when the teeth are closed in 
 the natural bite during mastication. 
 
 Bands and clasps.— The plate completed, is 
 ready for trying in the mouth ; any altera- 
 tions that are necessary must now be made 
 
DENTAL MECHAXICS 
 
 81 
 
 before fitting the bands. If its adaptation to 
 the mouth is perfect we may at once pro- 
 ceed to make the clasps. Here we enter 
 upon a much debated topic, for there are many 
 very diverse opinions as to the proper way 
 of making and arranging them. The plan 
 most generally adopted is to take a strip of 
 gold (alloyed with platinum is best), of a suit- 
 able width, and with the hand pliers (Fig. 50) 
 adjust it to the tooth, so that the surfaces of the 
 two are in perfect apposition ; the band is then 
 fitted carefully to the plate, and united as I 
 shall presently describe. 
 
 Fig. 50. 
 
 Dr Spalding, of the United States, has in- 
 vented a form of band called the " Standard " 
 clasp, that allows the neck of the tooth to be 
 exposed, thus enabling the tongue and saliva to 
 clear away any particles of food that might 
 accumulate. The band is fitted as just de- 
 scribed, but it is not allowed to rest upon the 
 gum, it is supported midway between the neck 
 
 6 
 
82 
 
 DENTAL MECHANICS 
 
 of the tooth and the grinding surface by means 
 of standards, which, running up from the plate 
 (itself cut clear of the tooth), supports the band. 
 This plan will be more readily understood by 
 reference to the accompanying sketch (Fig. 51). 
 
 Fig. 51. 
 
 The standards and bands should both be of the 
 same width, and made of platinized gold. This 
 plan is, however, open to the objection that the 
 gum will yery probably become hypertrophied, 
 and grow through the spaces left in the plate, 
 and thus produce a more mischievous condition 
 than if ordinary clasps had been used. 
 
 Still a third, and in my own opinion in many 
 respects the best way of applying bands to 
 molar teeth, is to take a strip of platinum very 
 thin and soft, and applying this to the tooth, 
 press it carefully with a burnishing instrument 
 into all the inequalities, so that it perfectly em- 
 braces the tooth from the neck to the crown; 
 
DENTAL MECHANICS 88 
 
 remove this very carefull}", and place in the 
 open centre of it a mixture of plaster and sand 
 or plaster and asbestos (2 parts plaster, 1 part 
 sand or asbestos). As soon as it is thoroughly 
 dry, brush over the exposed surface with borax 
 and water, and put on some small pieces of 
 plate gold, and then applying a good solid 
 flame with the blowpipe, fuse the gold evenly 
 over the surface of the platina, repeat this till 
 you have the substance of the band rather 
 thicker than an ordinary clasp ; it may, after 
 this, be filed down to a suitable form like a 
 common band, we thus get the most perfect 
 adaptation, with great strength and elasticity. 
 It is generally a matter of difficulty to retain 
 the clasps in their right position when removing 
 them from the model or mouth after they have 
 been fitted to each other. If the plate and 
 bands attached can be removed easily on 
 account of the sides of the teeth being perpen- 
 dicular, then it is only necessary to see that 
 you have the clasps attached to the plate 
 securely before attempting removal ; this may 
 be done in several ways : first, and most com- 
 monly, by means of resin and wax applied 
 round the neck of the band where it joins the 
 plate ; secondly, by using sealing wax instead 
 of the former substance, which possesses the ad- 
 
84 DENTAL MECHANICS 
 
 vantage of greater hardness, and breaks with a 
 clean fracture instead of bending like resin and 
 wax ; thirdly, by coating over with a solution of 
 soap the surface of the model near the plate, and 
 then pouring on plaster and sand, and when it is 
 set hard removing, if possible, with the plate 
 and bands attached ; if not, adjusting them to it 
 afterwards and then resting the under surface 
 of the plate and the clasps in a mass of the 
 plaster compound, and when hardened removing 
 the upper and first cast that was made to give 
 their relative positions ; this is a little trouble- 
 some, but a very certain mode of procedure. The 
 same may be done in the mouth ; fit them into 
 their places and then take an impression ex- 
 tending well beyond the plate, in either wax or 
 plaster of Paris. They will be tolerably certain 
 to come away with the tray ; if they do not 
 they can easily be removed and put into their 
 proper place in the cast. The impression can 
 now be cast, not, however, with plaster only, 
 but with a mixture of plaster and asbestos ; we 
 then obtain a model with the plate and 
 clasps in position, so that we may warm up in 
 the oven and proceed to solder at once with 
 the most perfect assurance that they cannot 
 have shifted. 
 
 When by one or other of the preceding 
 
DENTAL MECHANICS 85 
 
 methods the bands and plates are safely im- 
 bedded ready for soldering, the surface must be 
 carefully cleaned of wax if it has been used or 
 any particles of plaster ; the joints coated with 
 borax and water, and small pieces of solder put 
 on. As soon as the furnace has brought the 
 case up to a good red heat it may be soldered 
 by the blowpipe. After cooling down (not too 
 rapidly) and " pickling," trim up with a file and 
 scorper, and the plate is ready for mounting 
 the teeth on. It is, however, a wise precaution 
 to again try it in the mouth to see that the 
 bands are correct. 
 
 For lower plates the proceeding is nearly the 
 same as for the upper, with the obvious differ- 
 ence that they do not require support to be 
 given them, but steadiness ; this may be done 
 by a couple of clasps round the bicuspids when- 
 ever it is possible, or clips passing between 
 them. These teeth being the most favorable 
 for applying bands, this rule applies with 
 equal force whether the teeth have to be re- 
 placed at either the anterior or posterior part 
 of the mouth. 
 
 The piece must always be strengthened with 
 a double thickness of gold at the most central 
 part, as from the formation of the lower jaw 
 there is no mechanical advantage to be gained, 
 
86 DENTAL MECHANICS 
 
 such as we have in the flat palate of the upper 
 maxilla, where a comparatively thin plate will 
 suffice. Three cliflerent forms of lower plates 
 are shown in Figs. 52, 53, and 54. 
 
 For lower cases, where there is much loose 
 mucous membrane, it is well to build up the 
 model a little, so that the edge of the plate may 
 present a rounded border ; this is done by adding 
 some thin plaster or resin and wax to the model 
 before casting in metal. 
 
 Instead of this plan being adopted, thin wire 
 may be soldered on the upper edge of the 
 plate, and the lower edge filed up to it so as to 
 give the same result. 
 
 Suction plates. — A plan that is frequently 
 adopted for retaining upper dentures in their 
 place is that of atmospheric pressure or suction ; 
 by this method all fastenings to the natural 
 teeth are avoided ; the plate is extended over 
 a considerable surface of the hard palate, and 
 the pressure of the air against its lower surface 
 is sufficient if it be accurately fitted to retain 
 the plate firmly in its proper position ; for this 
 mode of attachment the impression should 
 always be taken in plaster of Paris, and great 
 care be taken to obtain a perfect adaptation of 
 the plate to the mouth. 
 
 Air chambers are formed occasionally in 
 
DENTAL MECHANICS 
 
 8: 
 
 Fig. 52. 
 
 Fig. 53. 
 
 Fig. 54. 
 
88 
 
 DENTAL MECHANICS 
 
 the plates for the purpose of increasing the 
 suction, but from my own experience pieces as 
 a rule hold up quite as well if not better 
 without them. 
 
 To make a suction chamber, either cut out a 
 depression, oval or shield-shaped, in the plaster 
 impression before casting the model, or form 
 with plaster or wax an elevation of the required 
 form on the palatine surface of the plaster model 
 before making a metal cast ; the plate is struck 
 up to this, and the sharp angles obtained by 
 chasing round with a suitably shaped punch. 
 In the preceding cuts are shown air chambers of 
 the various forms in most common use, Figs. 
 55, 56, and 57. They admit, of course, of great 
 variety in form, according to the nature of the 
 case under treatment. 
 
 Fig. 55. 
 
DENTAL MECHANICS 89 
 
 Fig. 56. Fig. 57. 
 
 Making plates for complete upper dentures.— 
 
 Cut out tlie pattern in tliin slieet lead as for 
 a partial plate; if it is to be retained in tlie 
 moutli by suction, let it not only invest en- 
 tirely the alveolar ridge, but also cover com- 
 pletely tlie hard palate ; if, on the other hand, 
 it is to be supported by spiral springs, the plate 
 need not extend so far over the palate, but may 
 assume the form of a horseshoe for its palatine 
 outline. Having been well annealed, it may be 
 bent with the pliers and beaten into shape with 
 the mallet till it will rest upon the model with 
 something approaching the finished form. 
 Though this part of the process takes but few 
 words to describe, it requires some time and 
 skill to accomplish, the principal difficulty 
 arising from the "buckling" of the plate bending 
 it over upon itself in the most awkward places, 
 and tending to a displacementfrom the position 
 you desire it to occupy. It is especially apt to 
 
90 
 
 DENTAL MECHANICS 
 
 slip backwards or forwards on the zinc model. 
 A very useful and simple contrivance to avoid 
 this lias been devised by Dr Kurras, of New- 
 York. The form is shown in Fig. 58. The 
 
 Fm. 58. 
 
 metal die with the plate on it is placed near 
 the edge of the work board; the clamp is 
 applied to the central portion of the palate 
 (protecting the plate by some linen, or two or 
 three folds of brown packing paper) and the 
 screw being tightened underneath the bench, 
 the plate is held firmly in position, while 
 with the mallet the overlaps are brought 
 into contact with the alveolar ridge. If 
 this descends perpendicularly, or is undercut at 
 
DENTAL MECHANICS 91 
 
 all, tlie plate will double upon itself. V-shaped 
 portions must be cut out, allowing only suffi- 
 cient for the one cut edge to overlap the 
 other; they may afterwards be bevelled off 
 on the reverse sides of the edges, so as to leave 
 a smoother surface when they are soldered up. 
 The plate being now roughly bent into shape, 
 is ready for striking up ; this is done as with 
 partial cases by placing it between the die 
 and counter die, and giving it a succession of 
 steady blows with a heavy hammer. 
 
 Another plan is to apply the blow by an 
 arrangement somewhat like a guillotine, in 
 which a heavy weight retained between two 
 upright bars is allowed to fall directly upon the 
 die ; and ensure an evenly distributed blow ; it 
 is open to the objection, however, of not being 
 so easilv reo^ulated as when a hammer is used 
 with the hand. 
 
 If an air chamber is introduced into the plate 
 it may be made in the same way as for a partial 
 denture ; there is, however, another variety of 
 chamber that is only well suited to complete 
 dentures ; this is known as Cleveland's, and 
 its construction is thus described by Dr 
 Richardson ; an ordinary plate with chamber 
 struck up, is first made, and the chamber cut 
 out. 
 
92 DENTAL MECHANICS 
 
 A tbin sheet of wax, or a laj^er of plaster, 
 is then placed upon the lingual side of the plate, 
 extending from two to three or four lines from 
 the edges of the orifice in the main edge ; a 
 thin, retreating edge is given to the wax or 
 plaster at the outer borders, making it con- 
 tinuous with the surface of the plate. The 
 plate with the wax attached may now either be 
 tacked to the model with softened wax along 
 its outer borders, and shaped in such a way as 
 to permit the model and plate to be withdrawn 
 from the sand, and a mould of the parts taken 
 in the ordinary way, and from this a die and 
 counter ; or an impression in wax or plaster 
 may be taken of the lingual face of the plate 
 and wax, and afterwards a model, die, and 
 counter. With the latter, a second plate, 
 covering nearly or quite all of the palatal con- 
 cavity is swaged, and when this is applied to 
 the main plate over the cut chamber, and united 
 by soldering, a space, equal to the thickness of 
 the wax, or plaster placed on the primary plate, 
 will be found to exist between the two lamina. 
 Fig. 59 exhibits a transverse section of the two 
 plates, disclosing the space between them, and 
 also the opening through the gum jolate into 
 the cavity. Before soldering on the dupHcate 
 plate, a half-round wire should be soldered 
 
DEXTAL MECHANICS 93 
 
 around tbe opening in the palatal plate on its 
 lingual side, to protect the soft tissues of the 
 mouth from injury when drawn in as the air is 
 exhausted from the chamber ; or, what is pre- 
 ferable, this form of cavity may be converted, 
 practically, into what is known as " Gilbert's 
 chamber" (which is the central swaged cham- 
 ber before described), by filling in the space 
 between the two plates with some impervious 
 substance, as Hill's filling, or an amalgam of 
 gold, the excess of mercury being driven ofi* by 
 
 Fig. 59. 
 
 heat. In the construction of continuous gum 
 work, the interspace may be filled in with gum 
 body. The advantages of these double plates 
 are, a greatly increased strength imparted to 
 the base, a diminished liability of warping in the 
 process of soldering, a smoother surface pre- 
 sented to the tongue, and a more decidedly 
 anofular form of the chamber. 
 
 It is occasionally useful to solder a thin wire 
 on the palatal surface of the plate following the 
 
94 DENTAL MECHANICS 
 
 inner border of tlie alveolar ridge, and crossing 
 tlie palate about one eigbtb of an inch from the 
 free border of the plate. A plate prepared in 
 this way will generally have remarkably good 
 suction, and hold up very firmly, and as the 
 wire ridge makes for itself a depression in the 
 soft tissues of the hard palate, the amount of 
 lateral movement (of which most plates are 
 capable) will be very much reduced. 
 
 It is desirable occasionally to solder a rim of 
 wire or plate round the alveolar border of a 
 full upper denture to present a rounded surface 
 in the mouth, and thus avoid cutting into the 
 mucous membrane ; this is done by bending the 
 wire or strip of plate to the proper form and 
 then fixing with binding wire to hold it in 
 position while soldering. 
 
 Making a plate for complete lower denture. 
 — This process is for the most part the same 
 as for an upper plate. 
 
 It is very necessary, however, that the metal 
 should be thicker and more elastic ; it must 
 also be strengthened by a rim of plate covering 
 the alveolar ridge, and thin wire should be 
 soldered all round if possible, but in any case 
 on its lingual border. Some prefer using a thin 
 plate first and then adding a second thick layer 
 of metal to its external surface, thus avoiding 
 
DENTAL MECHANICS 95 
 
 the use of the wire border and producing a very 
 strong serviceable base for the denture. 
 
 Whether the wire and strengthener together 
 or separately are used, the piece must be well 
 swaged afterwards to counteract the warping 
 that generally takes place from the contraction 
 during soldering. One other plan yet remains 
 to be mentioned, that is, to use a single thick 
 plate and turn up the edges and fill in the 
 depression with good solder, and thus obtain a 
 rounded border. The wire I consider, how- 
 ever, the best mode to adopt. The general 
 form of plate for a full lower denture is shown 
 in Fig. 60. 
 
 Fig. 60. 
 
 Obtaining the bite for a partial denture.— 
 
 This may be done in three different ways. The 
 first plan is to have a model of both the upper 
 and lower jaws. 
 
 When the plate is made cover those spaces 
 that are to be filled up with artificial teeth, with 
 strips of tough wax (one formula recommended 
 
96 DENTAL MECHANICS 
 
 consists of two ounces of gum mastic to a 
 pound of wax, and one ounce of Spanish 
 whiting ; this has to be melted, and the 
 other ingredients added in a fine state of 
 division). 
 
 The wax is made to adhere firmly by slightly 
 warming the plate over the spirit lamp. As 
 soon as the wax is trimmed up neatly it may be 
 placed in the mouth and the patient directed to 
 close the jaws in the usual way. Great care 
 must be taken to see that this is done ; as a 
 rule patients will shut the jaws in any possible 
 manner rather than that which is normal ; it is 
 therefore wise to repeat the process several 
 times to see that each " bite " corresponds. If 
 the rim of wax has been left full above the 
 level of the surrounding teeth in the model, 
 we shall find when the plate is removed from 
 the mouth that the points of antagonism are 
 accurately marked on the wax. Being replaced 
 on the model, the opposing jaw in the plaster 
 cast can be adjusted to the impression of the 
 natural teeth in the wax, and held in this 
 relation, a permanent articulation can be made. 
 The back surfaces of the models must be coated 
 with soap and then mixing some plaster very 
 stiff, place the models in it, the plaster resting 
 on a smooth surface, such as marble or glass, 
 
DENTAL MECHANICS 97 
 
 with a sheet of thin paper interposed to prevent 
 adhesion; the result that will be obtained is 
 shown in Fig. 61. 
 
 Fig. 61. 
 
 The second form o£ articulation is known as 
 a hawksbill bite : to obtain this jou act in 
 precisely the same way as for the last, only 
 instead of having a model of the opposing jaw, 
 you use the impression left on the wax instead, 
 and by filling in with plaster, obtain a model 
 from it, of those teeth only that come into 
 contact with the artificial denture. The form 
 thus obtained is shown in Fig. 62. Before 
 pouring the plaster over the wax the operator 
 must be careful to fill in the centre of the model 
 with paper, to avoid an excess of plaster here, 
 and at the same time make either crucial 
 grooves or depressions on the back of the 
 
 7 
 
98 
 
 DENTAL MECHANICS 
 
 Fig. 62 
 
 model as an indication for tlie after-adjustment 
 of tlie two parts of the bite. 
 
 A modification of the last form of bite is made 
 by extending the back of the model thus, Fig. 63 ; 
 
 Fig. 63. 
 
 and putting on the wax bite, proceeding as in 
 the last case, only making the upper and poste- 
 rior surfaces flat, so that the articulated models 
 
DENTAL MECHANICS 
 
 99 
 
 will stand either way, as seen in Figs. 64 
 and 65. 
 
 Fig. 64. 
 
 Fig. 65. 
 
 By binding them together with a broad 
 elastic band, we obtain a very convenient work- 
 ing bite. 
 
 If the front teeth of the upper jaw have to be 
 replaced, then the central and horizontal lines of 
 
100 DENTAL MECHANICS 
 
 the moutli must be obtained wlien taking tlie 
 bite. This can easily be done by marking the 
 wax crucially with a sharp instrument, and 
 afterwards marking the models to correspond 
 before displacing the wax. 
 
 Obtaining the bite for an entire upper and 
 lower denture.— This is very difficult to do 
 with certainty, unless the patient has an old 
 artificial case by which you may be assisted. It 
 is scarcely possible to get the bite right the first 
 time, so that it is wiser to carefully watch the 
 relative position of the jaws when the patient 
 is not conscious of your observation; then 
 taking a bite as nearly accurate as you can, 
 mount up artificial blocks of wax strengthened 
 with wire and without any teeth attached, and 
 by their use get a more certain closure of the 
 jaws. It is sometimes advisable also to watch 
 for the position of the jaws during the act of 
 swallowing, taking care to divert the attention 
 of the patient at the time. Of two "bites" 
 taken together, but differing in the position of 
 the lower jaw, it will always be safer to choose 
 that in which the inferior maxilla is most re- 
 tracted, since as the backward movement of the 
 jaw is very limited, you have under these cir- 
 cumstances the least liability to derangement of 
 the normal position of the jaws. It is a very 
 
DENTAL MECHANICS 101 
 
 good plan to load tlie lower in the centre of the 
 wax with strips of lead so that it may not move 
 about in the mouth ; this, of course, must not 
 be done with the upper. 
 
 Spiral springs may occasionally be used with 
 advantage in taking a " bite," as they keep the 
 upper and lower trial plates in good position, 
 and by offering some slight opposition to the 
 closure of the jaws probably induce a more 
 natural movement of the inferior maxilla than 
 if they were not used. 
 
 I believe, from my own experience, it is only 
 possible to get a good bite after you have all the 
 teeth mounted on the plates with cement ; you 
 can then fairly judge of the effect produced by 
 any malposition, which you cannot do with a 
 block of wax alone. The depth of the bite 
 should be such that with the mouth in a state 
 of repose, the margins of the lips touch without 
 any muscular action whatever ; this, I think, 
 will be found in all normal cases, a sound 
 guide. 
 
 The two models may be arranged in either 
 of the forms of bite already described, or they 
 may be fitted up in an adjustable articulator, as 
 shown in Fig. 66. 
 
 This articulator is recommended as having all 
 the necessary movements for obtaining a cor- 
 
102 
 
 DENTAL MECHANICS 
 
 Fig. 66, 
 
 rect articulation of artificial dentures. Tlie 
 lower plate is moulded from the lower jaw, and 
 moves on cone-shaped pivots in Y-shaped 
 grooves (without hinges), being retained in 
 position by elastic- rubber bands or rings. A 
 backward, forward, and lateral motion is pro- 
 vided for, corresponding with the movements 
 of the natural jaw, by which the arrangement 
 of the denture can be practically tested without 
 disturbing the articulation. The upper plate 
 has a backward and forward movement of two 
 inches, and may be retained at any point by 
 the set screw. The upper plate has a double 
 bend, so that when reversed from the position 
 
DENTAL MECHANICS 
 
 103 
 
 shown in the cut an increase of one inch in 
 the space is obtained between the plates, allow- 
 ing for both upper and lower dentures. 
 
 Another form, simpler in structure, is shown 
 in Fig. 67. This is made of brass, having a 
 
 Fig. 67. 
 
 screw and hinge, whereby it can be adjusted 
 at any desired angle ; the top plate can be 
 thrown right back and the set screw allows 
 the plate to slide either backwards or forwards. 
 
104 DENTAL MECHANICS 
 
 SECTION YII 
 
 ON THE VARIOUS FOEMS OE POECELAIN USED IN 
 MECHANICAL DENTISTEY 
 
 ScAECELY any dental surgeon in the present 
 day would think of making his own mineral 
 teeth and blocks ; at the same time it is desir- 
 able that some account of the process by which 
 they are prepared by our large dental manu- 
 facturers should be given; I must, however, 
 warn the reader that it is not to be taken as an 
 accurate description of the actual work carried 
 on by them ; as in this country at any rate they 
 Sfuard the secrets of their tooth factories with a 
 most religious jealousy. We know, however, 
 sufficient to form a tolerably clear idea of the 
 methods by which our present make of mineral 
 teeth are prepared. We shall speak first of 
 single teeth ; then of sectional blocks with 
 mineral gum attached; and, lastly, as an asso- 
 ciate process, of continuous gum work. 
 
 Composition. — Some makers' teeth are of the 
 same composition throughout; others, how- 
 
DENTAL MECHANICS 105 
 
 ever, have a less dense but stronger material 
 for the body of the tooth, and a transparent but 
 somewhat brittle preparation as an enamel or 
 outer covering. 
 
 The materials used are kaohn (white clay), 
 silex, and felspar ; none of these minerals are 
 fusible at a low temperature, nor, when fused, 
 are they acted upon by acids, hence their 
 extreme utility for artificial teeth. The various 
 colours and shades are imparted by means of 
 metallic oxides in a fine state of division, of 
 which I shall presently give an account. 
 
 The materials having been prepared very care- 
 fully so as to reduce them to a complete 
 powder, are weighed ofi" in their relative propor- 
 tions and then made into a paste by the 
 addition of distilled or rain water. Brass or 
 copper moulds are used for forming the teeth 
 in, consisting of two portions, one in which 
 is the impress of the tooth and the other which 
 represents the back of the tooth, and is pierced 
 with two fine holes, opposite each impression 
 through which the platina pins are passed. 
 The paste for the body is pressed into these 
 moulds, and the pins put in through the 
 openings on the upper plate. A few taps of 
 the hammer will dislodge them from the mould 
 when dry, and they are then taken out and 
 
106 DENTAL MECHANICS 
 
 placed on a fire-clay slide and heated to a bright 
 red ; as soon as they are sufficiently cool they 
 are trimmed up carefully and all roughness or 
 inequality removed, and placed again on the 
 slide with the face upwards (the pins resting in 
 a grove and the slide being sprinkled with 
 silex). 
 
 The enamel is now very carefully and evenly 
 applied with a brush, the various tints being 
 arranged on the face of the tooth in accordance 
 with the result desired. They are again dried 
 and then introduced into the furnace. 
 
 The great perfection to which this branch of 
 manufacture has attained during the last few 
 years is very surprising, but it can be easily 
 understood when we consider the enormous sale 
 that has been created with the supply, and the 
 very potent stimulus that has thus been given 
 to enterprise, and invention, so as to produce the 
 most perfect results. 
 
 It is owing to the numberless inventions and 
 varieties of procedure, in connexion with this 
 department, that such jealousy is induced on the 
 part of the makers in guarding the secrets of 
 their laboratories. 
 
 American authors publish a large number of 
 recipes for the enamel and body of teeth, but 
 whether they are identical with those in use by 
 
DENTAL MECHANICS 
 
 107 
 
 American tootli-makers we have no means of 
 ascertaining ; from tlie fact, however, that many 
 American dental surgeons prepare their own 
 sectional blocks, they are sufficient for our pre- 
 sent purpose. 
 
 According to Harris, a good compound for 
 single teeth consists in the following : 
 
 Body. 
 
 Spar 
 
 . 
 
 10 oz. 
 
 Silex 
 
 . 
 
 1 ,. 
 
 Kaolin . 
 
 • 
 
 2dwts 
 
 Titanium 
 
 Enamel. 
 
 1 „ 
 
 Spar 
 
 
 1 oz. 
 
 Silex 
 
 . 
 
 3grs. 
 
 Flint glass 
 
 . 
 
 2 „ 
 
 Titanium 
 
 , 
 
 1 „ 
 
 Platina sponge 
 
 3 „ 
 
 These will produce ordinary tints for the 
 teeth ; they are, however, capable of infinite 
 variety by the use of one or other of the 
 following metals or metallic oxides, alone or in 
 combination, as the case may require. 
 
 Metals and their oxides* 
 
 Gold in a state of minute division 
 Oxide of gold .... 
 
 Platina sponge and filings . 
 
 Colours produced. 
 
 Rose red. 
 Bright rose red. 
 Grayish blue. 
 
 * Richardson's ' Mechanical Dentistry.' 
 
108 
 
 DENTAL MECHANICS 
 
 Metals and their oxi6l,es, 
 
 Oxide of titanium . 
 Pui'ple of cassias . 
 Oxide of uranium 
 Oxide of manganese 
 Oxide of cobalt 
 Oxide of silver 
 Oxide of zinc 
 
 V: »«s, 
 
 Colours produced. 
 
 Bright yellow. 
 Rose purple. 
 Greenish y ello w. 
 Purple. 
 Bright blue. 
 Lemon yellow. 
 Lemon yellow. 
 
 Sectional blocks are made by striking up a 
 gold plate first with a rim round the alveolar 
 ridge, then modelling up with the body, of which 
 the various compounds are given further on. 
 Being set up in solid blocks they are allowed to 
 dry and then trimmed up and carved with a 
 steel instrument or penknife into the shape the 
 teeth are to assume, great care being taken to 
 avoid crumbling when in this dry state ; the 
 platina pins are then introduced, the blocks 
 being placed on the furnace slides resting on 
 their lower border so as only to let the part that 
 fits the plate come into contact with the pulver- 
 ized silex with which the slide is covered. 
 These blocks are made usually in three sections, 
 if for an entire denture ; one for the four in- 
 cisors and canines, and two for the bicuspids 
 and molars, consisting of two bicuspids and two 
 molars to each section. 
 
DEXTAL MECHANICS 
 
 109 
 
 Composition for 
 
 1. Delaware spar 
 Silex 
 Kaolin . 
 Titanium 
 
 2. Delaware spar 
 Silex 
 Kaolin . 
 Titanium 
 
 3. Delaware spar 
 Silex 
 Kaolin . 
 Titanium 
 
 4. Delaware spar 
 Silex . 
 Kaolin . 
 Titanium 
 
 5. Delaware spar 
 Silex . 
 Kaolin . 
 Titanium 
 
 body of block 
 
 teeth. 
 
 . 12 oz. 
 
 . 2 oz. 8 dwts 
 
 . 7i dwts. 
 
 . 18 to 36 grs. 
 
 . 16 oz. 
 
 . Sh„ 
 
 i 
 
 2 J> 
 
 . 20 to 60 grs. 
 
 . 12 oz. 
 
 . 2 oz. 8 dwts 
 
 . 12 dwts. 
 
 . 24 grs. 
 
 . 8oz. 
 
 . 1^,, 
 
 4 dwts. 
 
 . 22 grs. 
 
 2 oz. 
 
 . 8 dwts. 
 
 . 2 „ 
 
 4 grs. 
 
 Gi-ayish-blue enamel for porcelain blocJc teeth. 
 
 1. Spar 
 Platina sponge 
 
 ^ Oxide of gold 
 
 2. Spar 
 Platina sponge 
 Oxide of gold 
 
 3. Spar 
 Platina sponge 
 Oxide of gold 
 
 2oz. 
 igr. 
 
 2 5J 
 
 2oz. 
 i gr. 
 h „ 
 
 2oz. 
 f gr. 
 
 X 
 
 2 ,"> 
 
no 
 
 DENTAL MECHANICS 
 
 4. 
 
 Spar . . . . , . 2 oz. 
 
 
 Flux 24 grs. 
 
 
 Platina sponge . . . . ^ gr. 
 
 
 Yellow enamel for porcelain hlocTc teeth. 
 
 1. 
 
 Spar 2 oz. 
 
 
 Titanium 10 grs. 
 
 
 Platina sponge . . . . i gr 
 
 
 Oxide of gold . . . . i „ 
 
 2. 
 
 Spar 2 oz. 
 
 
 Titanium 14 grs 
 
 
 Platina sponge . . . . | gr 
 
 
 Oxide of gold . . . . i „ 
 
 3. 
 
 Spar 2 oz. 
 
 
 Titanium 16 grs. 
 
 
 Platina sponge . . . . | gr 
 
 
 Oxide of gold . . . . i „ 
 
 4. 
 
 Spar 2 oz. 
 
 
 Plux 20 grs. 
 
 
 Titanium 10 „ 
 
 Grayish-hlue enamel for porcelain hloch teeth. 
 1. Spar 1 oz. 
 
 Blue frit 
 
 2. Spar 
 
 Yellow frit 
 Gold mixture 
 
 5 grs. 
 
 1 oz. 
 
 4 grs. 
 10 .. 
 
 Composition and preparation of gum enamels. 
 1. Gum frit, No. 1 . 
 
 Spar 
 
 2 Gum frit, No. 2 
 Spar 
 
 3 dwts. 
 
 9 to 12 dwts. 
 
 3 dwts. 
 
 3 to 18 dwts. 
 
DENTAL MECHANICS 111 
 
 Boston spar is preferred on account of its 
 greater fusibility. Flux is composed of — 
 
 Silex . . . . 4 oz. 
 Borax . . . . 1 ,, 
 Sal tartar . . . 1 „ 
 
 These are ground to an impalpable powder 
 and packed in tlie bottom of a clean, light- 
 coloured crucible. A piece of fire-clay slab is 
 then fitted into the top of the crucible and luted 
 with kaolin clay. 
 
 It is then exposed to the heat of a furnace 
 until completely fused, when it is removed, and 
 as soon as it is cold the crucible is broken, 
 all foreign particles or discoloured portions 
 thoroughly removed, and the remainder well 
 pulverized. Blue frit is composed of — 
 
 Spar . . . . I oz. 
 Platina sponge . . 4 dwts. 
 
 Powder very finely, make up into a ball with 
 water, and fuse very slightly upon a slide in a 
 furnace. It must then be plunged into water 
 while hot, and when dry, finely pulverized. 
 
 Yellow frit is made by mixing intimately ^ oz. 
 of spar with two dwts. of titanium and heating 
 as above. 
 
 Grold mixture is made by dissolving 8 grains 
 of pure gold in aqua regia, then stirring in 12 J 
 dwts. of very finely pulverized spar. "When 
 
112 DENTAL MECHANICS 
 
 nearly dry it is formed into a ball, and fused 
 upon a slide, and then coarsely pulverized. 
 
 Continuous gum work, tliougli very useful 
 and beautiful, requires great care, special con- 
 veniences, and considerable experience to pro- 
 duce in a satisfactory state, and wlien finished 
 to the delight of the dental surgeon, is not 
 appreciated by the patient for whom it has 
 been prepared, chiefly on account of its extreme 
 weight. These remarks apply especially to this 
 country, where the knowledge of the patient is 
 far behind the resources and capabilities of the 
 dental practitioner ; hence dentures of con- 
 tinuous gum work are comparatively rarely 
 made here. In the United States, however, it 
 is much more in fashion, in part owing, pro- 
 bably, to its having been invented there, partly, 
 also, from the greater willingness of American 
 patients to put up with personal inconvenience, 
 and even discomfort for a time, in order to 
 obtain a perfect result. 
 
 To Dr Allen is given the credit of this inven- 
 tion. I shall, therefore, give a description of 
 the process in the Doctor's own words as it 
 appears in Dr Eichardson's work. 
 
 Dr Allen^s Modes of Practice. — The following 
 descriptions, contributed by Dr Allen, embrace 
 a clear and concise account of the manipula- 
 
DENTAL MECHANICS IIS 
 
 tions at present practised by him in the con- 
 struction of artificial dentures, with continuous 
 gums. 
 
 " The plate or base is formed of platinum, 
 or platinum and iridium. The plate being 
 properly fitted to the mouth, and wax placed 
 upon it for the bite, as in ordinary plate work, 
 the teeth are arranged thereon, with special 
 reference to the requirements of the case. 
 They are then covered with a thin coating of 
 plaster mixed with water to the consistence 
 of cream. After this has become firmly set, 
 another mixture of plaster and asbestos with 
 water, somewhat thicker or more plastic than 
 the first, is placed round on the outside of the 
 previous covering and the plate. A convenient 
 way of applying the second covering is to turn 
 the mixture out of the vessel upon a piece of 
 tin, say four or five inches square, thus forming 
 a cone upon which the plate with the teeth 
 upward, is pressed gently down until within an 
 inch or less from the tin. Then with a spatula 
 the mixture is brought up over the teeth, 
 forming an investient that will not crack in 
 the process of soldering. Sand may be used 
 with the plaster for this purpose, but I think 
 asbestos preferable. 
 
 " When the covering has become sufficiently 
 
 8 
 
114 DENTAL MECHANICS 
 
 hard the wax is removed, and a rim of platinum 
 is then fitted to the lingual side of the teeth, 
 below the pins, and to the base plate. The 
 pins in the teeth are then bent down upon the 
 rim, and soldered with pure gold, or a mixture 
 of gold and platinum, at the same time the rim 
 is soldered to the plate. This rim, which forms 
 the lining for the teeth, is usually about the 
 thickness of the plate upon which they are set, 
 say 28 to 30 ; * but should the case require 
 more than ordinary strength, a double or triple 
 thickness of rim should be used. This may 
 become necessary in cases where the natural 
 molar teeth are standing firmly in the opposite 
 jaw, and antagonise with the artificial piece, or 
 where from any cause, an undue strain is brought 
 to bear upon the artificial teeth. To attain suc- 
 cessful results, the dentist must take into con- 
 sideration all the circumstances or conditions 
 of each particular case, and then exercise his 
 best judgment in executing the work. 
 
 " In soldering platinum with pure gold, flat 
 surfaces of this metal should be brought in 
 positive contact, in order to become firmly 
 united. Therefore, in mounting teeth upon 
 a plate of this kind, the backing or inside 
 rim should be a little wider than the distance 
 
 * American gauge. 
 
DENTAL MECHANICS 115 
 
 between the pins in the teeth and the plate, say 
 from an eighth to a fourth of an inch. This extra 
 width of rim should be bent at right angles along 
 the base of the teeth so as to admit of being 
 pressed down upon the plate after the rim is 
 adjusted to the teeth, and the pins bent down 
 firmly upon it. In this way flat surfaces of the 
 rim and plate are brought together and soldered. 
 The pins in the teeth are also soldered to the 
 rim at the same time. When the parts are 
 thus united, they will remain so during the sub- 
 sequent bakings; but if the edge of the rim 
 only is fitted to the plate and soldered like gold 
 or silver work, the subsequent heatings for 
 baking the body and gum will cause the gold to 
 become absorbed in the platinum, and leave the 
 joints not united. It may be asked why not 
 use common gold solder for this style of work ? 
 Answer, because the alloy in the solder will 
 greatly injure the colour of the gum enamel in 
 baking. Copper alloy will turn it to a greenish 
 shade, and silver will give it a yellow tinge. 
 Although pure gold requires more intense heat 
 to melt it (being about two thousand degrees), 
 than ordinary gold solder, yet when melted it 
 flows much more freely than the latter. The 
 best way to solder the teeth upon platinum 
 plate is, to place small pieces of gold upon the 
 
116 DENTAL MECHANICS 
 
 joints or parts to be soldered, with wet ground 
 borax, and then slowly introduce the piece with 
 the investient into a heated muffle, and bring the 
 whole mass up to a red heat ; then withdraw it 
 from the furnace, and bring it quickly under 
 the blow-pipe to flow the gold. In this way 
 the teeth do not become etched, as they are 
 liable to be if the soldering is done in the 
 furnace. 
 
 " The piece being soldered and cooled, the 
 covering is removed from the teeth, taking care 
 to preserve the base unbroken for the plate to 
 sit upon during the subsequent bakings of the 
 body and gum enamel. 
 
 '' All particles of plaster or other foreign 
 matter should be removed from the teeth and 
 plate by thoroughly washing and brushing them. 
 It is well to immerse the piece for a short time 
 in sulphuric acid, after which rinse and brush it 
 well with water. This done, a colourless 
 mineral compound, called the body, is applied 
 in a plastic state (with spatulas or small in- 
 instruments for the purpose) to the teeth and 
 plate. It is then carved to represent the gum, 
 roof and ruga of the mouth, taking care to keep 
 the crowns of the teeth well defined. The 
 piece is then placed on the base upon which it 
 was soldered and set upon a slide on the apron 
 
DENTAL MECHANICS 117 
 
 in front of one of the upper muffles of the 
 heated furnace, — and every eight or ten minutes 
 it should be moved forward into the muffle, say 
 two or four inches each time, until the piece 
 shall have passed the centre of the same, which 
 should be at a red heat. It is then withdrawn 
 and passed into a lower muffle where the heat 
 is greater, in which the body soon becomes 
 semi-vitrified, which is sufficient for the first 
 bake. It is then taken out and (together with 
 the slide on which it was baked) placed in a 
 cooling muffle, the mouth of which should be 
 closed to prevent the change of temperature 
 from being too rapid, and causing the teeth to 
 become brittle. When the piece is sufficiently 
 cool to handle, a second application of body is 
 made for the purpose of repairing any defects 
 that may have occurred in the baking; this 
 done, the piece is again introduced as before 
 into the upper muffle, then in the lower, 
 allowing the second bake to become a little 
 harder than the first, but not so much as to 
 appear glossy. It is then withdrawn, and 
 cooled as described above. 
 
 " A flesh-coloured compound is then applied, 
 which is called the gum enamel. This is also 
 made plastic with water, and a thin coating is 
 put over the body, and closely packed and 
 
118 DENTAL MECHANICS 
 
 carved around tlie teetli with small instruments 
 made for the purpose, — still taking care to keep 
 the crowns of the teeth clean and well defined. 
 Small camel's-hair brushes are used wet with 
 water, to cause the gum enamel and also the 
 body to settle more closely around the necks of 
 the teeth ; other brushes are also used dry to 
 remove all , particles of body, gum, or other 
 substances from the crowns of the teeth. 
 
 " After the application of the gum enamel 
 the piece is again subjected to the heat of the 
 furnace as described for baking the body, with 
 this difierence : — the heat should be a little 
 greater than for either of the preceding bakes. 
 It should be a strong, sharp heat, in order to 
 produce a smooth glossy appearance which is 
 required for the enamel. These different de- 
 grees of heat for the first, second and third 
 bakings should be carefully observed for the 
 purpose of getting an even temper in the piece, 
 and thereby preventing it from crazing or 
 cracking in cooling. 
 
 '' The enamel being thoroughly fused, the 
 piece is withdrawn from the heated muffle, and 
 passed into another, outside of the furnace. 
 This muffle should be made quite hot before the 
 denture is placed in it, in order to prolong the 
 cooling process ; for if the piece is cooled too 
 
DENTAL MECHANrCS 119 
 
 rapidly, it is rendered more fragile. It is well 
 to let the case remain in tlie cooling^ muffle, 
 with the mouth of it closed, several hours before 
 exposing it to the air. By baking just at night, 
 the piece will be in proper condition to finish 
 up the next morning. 
 
 " The finishing process consists simply in 
 smoothing and polishing the plate, and bur- 
 nishing the rim. It is then ready to be ad- 
 justed to the mouth. In baking, great care is 
 necessary to prevent the piece from becoming 
 gassed. This can be avoided by allowing the 
 gas to escape entirely from the burning coal or 
 coke in the furnace before the piece is intro- 
 duced into the muffle. The presence of gas is 
 indicated by the blue flame escaping from the 
 coal. When the fire becomes clear, it is then 
 safe to introduce the case to be baked (as before 
 described) into the muffle. Pure anthracite coal 
 is the best for this purpose, as it maintains a 
 lons^er and strono^er heat than coke. Bitu- 
 minous coal is not good for this kind of work 
 unless first converted into coke. 
 
 ** It often occurs that the natural gums will 
 change more or less after the teeth are inserted. 
 In such cases a new impression should be taken 
 from the mouth and a fusible die formed. The 
 denture is then placed upon the die, and it will 
 
120 DENTAL MECHANICS 
 
 be seen at once where the change has taken 
 place, then with the piece resting upon the die 
 the artificial gum may be chipped off with a 
 small hammer and chisel. The platinum plate, 
 being soft, can be refitted to the die very accu- 
 rately with a burnisher, hammer, and small 
 driver made for the purpose. A new coat of 
 body is then applied where the plate has been 
 refitted, and then baked, cooled, enameled, and 
 baked again — still observing the same direc- 
 tions as detailed in the management of new 
 pieces. 
 
 " If a tooth gets broken (a mishap which 
 seldom occurs by use in the mouth), it can be 
 replaced with another, by grinding out the re- 
 maining portion of the broken tooth, and the 
 gum which covers the fang, and then fitting a 
 new one in the place. This tooth need not be 
 soldered to the inside rim; it is sufficient to 
 grind a small notch or groove in the enamel 
 which covers the lingual side of the rim for the 
 pin of the tooth to fit into. The pin resting in 
 the groove is covered with the body, at the 
 same time it is applied around the base of the 
 tooth, and when this body is baked the tooth 
 will become firmly fastened in place of the 
 broken one. Any number of teeth that may be 
 required can be replaced in this way. If it is 
 
DENTAL MECHANICS 121 
 
 desired to change the position of one or more 
 teeth, or to make them longer, this can also be 
 done as described above, with this additional 
 precaution, which is simply to press softened 
 wax upon the inside of the teeth and palatal 
 arch of the denture before the others are re- 
 moved, — this wax will serve as a guide or index 
 as to the relative change to be made, and also 
 to sustain the teeth in place while they are 
 beinof fitted as desired to the denture. The wax 
 soon becomes hard and is readily removed as 
 each successive tooth is ground and adjusted in 
 its proper place. 
 
 " When the teeth are thus fitted with each 
 pin accurately pressed into the groove prepared 
 for it, and the wax being placed upon the inside 
 to support the teeth in proper position, — body 
 is filled in around the base of the new ones 
 which are carved, trimmed and brushed, so as 
 to have the crowns of the teeth clean and 
 properly defined. The w^ax is then carefully 
 removed from the piece, and more body is filled 
 in around the teeth upon the inside, — filling up 
 the grooves over the pins, and then carving, 
 trimming, &c., as before, to give it the desired 
 form. This done, if the teeth are set a little 
 apart, and it is desired to keep them in that 
 position, take a small piece of asbestos and 
 
122 DENTAL MECHANICS 
 
 gently press it in between the teeth at the 
 cutting edges ; this will prevent them from 
 being drawn together when the body is being 
 baked. The piece is now ready for the furnace, 
 but it should not be baked hard enough to gloss 
 the newly applied body; it should have more 
 the appearance of Parian marble. 
 
 " This being done, it is then withdrawn from 
 the furnace and transferred to a cooling muffle 
 as before described. When sufficiently cool 
 the gum enamel is applied and baked with a 
 sharp heat until it becomes smooth and glossy. 
 To prevent the old gum from bleaching or be- 
 coming lighter coloured in consequence of re- 
 peated bakings, a very thin coating of fresh 
 gum enamel should be lightly brushed over the 
 entire enameled surface of the piece. The 
 enamel thus applied should be mixed with 
 water, quite thin, so as to flow evenly over 
 the surface, when applied with a camel' s-hair 
 brush. This should be done before the last 
 baking, that the whole may be fused at the 
 same time. Experience and judgment are 
 essential requisites in order to produce good 
 practical results. For example, if the carving 
 of the body is not properly done, the form 
 and shading of the gum and roof will not 
 appear natural when the work is finished ; if 
 
DENTAL MECHANICS 123 
 
 the gum enamel is put on too thick it will 
 produce a dark red colour ; if not thick enough 
 it will be too light ; if fused too hard it will be 
 liable to craze or crack ; if not hard enough it 
 will be rough and granular ; if the piece becomes 
 gassed in baking it will be porous and of a bluish 
 colour. Again, the teeth of different persons 
 vary as much as any features of the face, and 
 present as great a variety of expressions. 
 Therefore, in the construction of artificial den- 
 tures, the dentist should select and arrange the 
 teeth with special reference to each individual 
 case. The length, size, form, shade, and posi- 
 tion of the teeth should be varied to meet all 
 the different physiognomical requirements that 
 occur in dental practice. 
 
 " This system also combines with great ad- 
 vantage the restoration of the face in cases 
 where the muscles have become sunken or fallen 
 in from the loss of the teeth and consequent 
 absorption of the alveolar processes. Here, 
 again, the artistic skill of the dentist is brought 
 into requisition. He should study the face of 
 his patient as an artist studies his picture, for 
 he displays his genius not upon canvas, but 
 upon the living features of the face; and of 
 how much more importance is the living pic- 
 ture, that reflects even the emotions of the 
 
124 DENTziL MEOHANICS 
 
 heart, than the lifeless form upon canvas. He 
 should know the origin and insertion of ever j 
 muscle of which the face is formed, and what 
 ones he is to raise, otherwise he will be liable to 
 produce distortion instead of restoration. This 
 improvement consists of prominences made 
 upon the denture of such form and size as to 
 bring out each muscle or sunken portion of the 
 face to its original fulness ; and when these 
 are rightly formed they are not detected by the 
 closest observer. There are four points of the 
 face (of many persons) which the mere insertion 
 of the teeth does not restore, viz., one upon 
 each side beneath the malar or cheek bone, and 
 also a point upon each side of the base of the 
 nose, in a line toward the front portion of the 
 malar bone. 
 
 " The extent of this falling-in varies in dif- 
 ferent persons, according to their temperaments. 
 If the lymphatic temperament predominates, the 
 change will be slight. If nervous or sanguine, 
 it may be very great. The muscles situated 
 upon the side of the face, and which rest upon 
 the molar or back teeth, are the zygomaticus 
 major, masseter, and buccinator. The loss of 
 the above teeth causes these muscles to fall in. 
 The principal muscles which form the front 
 portion of the face and lips are the zygomaticus 
 
DEXTAL MECHANICS 125 
 
 minorj levator labii superioris alaeque nasi, and 
 orbicularis oris. 
 
 " These rest upon the front, eye, and bicuspid 
 teeth, which, when lost, allow the muscles to 
 sink in, thereby changing the form and expres- 
 sion of the mouth. 
 
 '' The insertion of the front teeth will in a 
 great measure bring out the lips, but there are 
 two muscles in the front portion of the face 
 which cannot, in many cases, be thus restored 
 to their original position ; one is the zygoma- 
 ticus minor, which arises from the front part of 
 the malar bone, and is inserted into the upper 
 lip above the angle of the mouth ; the other is 
 the levator muscle, which arises from the nasal 
 process and from the edge of the orbit above 
 the infra orbitar foramen. It is inserted into 
 the ala nasi or wing of the nose and upper lip. 
 
 *' The prominences before mentioned applied 
 to these four points of the face, beneath the 
 muscles just described, bring out that narrow- 
 ness and sunken expression about the upper lip 
 and cheeks to the same breadth and fulness 
 which they formerly displayed. If skill and 
 judgment have presided over all parts of the 
 operation, the result will be highly pleasing, 
 and of practical utility.'^ 
 
126 DENTAL MECHANICS 
 
 SECTION YIII 
 
 PIVOT TEETH 
 
 The simplest arrangement for fixing a single 
 tooth in the mouth, is bj means of a pivot 
 attached to the artificial tooth, and entering the 
 canal of the pulp cavity of the natural tooth 
 which has been already enlarged to receive it. 
 
 The cases most suitable for pivoting, are 
 those in which the central incisors or canines o£ 
 the upper jaw, have been fractured by accident, 
 and have not decayed gradually away, leaving 
 a soft broken down root in the gum. If the 
 latter condition prevail, then the stump must be 
 extracted, and not have an artificial crown 
 pivoted on. Care and discretion must also be 
 used not to treat patients who are of an inflam- 
 matory tendency, for they seldom do well, and 
 on several occasions serious results have fol- 
 lowed the apparently trifling operation of pivot- 
 ing. 
 
 In the case also of the crown of the natural 
 tooth having been lost from fracture, time must 
 
DENTAL MECHANICS 127 
 
 be allowed for the periostal inflammation to sub- 
 side, before attempting to affix a new crown. 
 
 It seems hardly necessary to point out that 
 if there be any evidence of alveolar abscess 
 in the neighbourhood of the fang, there again 
 this operation is inadmissible ; in fact, to put 
 the matter in the most concise yet clear form, 
 the stump must be perfectly healthy in every 
 respect. If the stump is not fractured even 
 with the line of the gum, or the decay of the 
 crown has not entirely destroyed the tooth sub- 
 stance up to the neck, it will be necessary to 
 remove by means of the tooth saw, and excising 
 forceps, the portions projecting beyond the gum 
 line. If but a small portion is remaining use 
 the forceps alone, as the sensation of the saw is 
 almost unendurable to many patients. When it 
 is used, however, a cut must be commenced at 
 the neck of the tooth on either the mesial or 
 distal surface, and carried on towards the pulp 
 cavity, following as nearly as possible the cur- 
 vilinear margin of the gum. Before the pulp 
 cavity is reached on the one side the saw must 
 be removed and applied in the same manner to 
 the opposite side ; we then have the crown 
 supported by a ridge of bony tissue in the centre, 
 running from before backwards. This can 
 be now readily divided with the excising forceps. 
 
128 
 
 DENTAL MEOHAXICS 
 
 Care must be taken not to saw into tlie pulp on 
 account of the pain, but it is well to get nearly 
 into the pulp -cavity, as it renders excision much 
 easier. The form of saw and forceps used for 
 this operation are shown in the annexed en- 
 graving. 
 
 Fig. 68. 
 
 Excising forceps, curved and straight. 
 Fig. 69. 
 
 Dividing saw. 
 
 Under ordinary circumstances, the nerve will 
 now be exposed to view; if possible pass a 
 nerve extractor, Fig 70, into the cavity, and 
 
DENTAL MECHANICS 
 
 129 
 
 witMraw tlie pulp, or use an ordinary ^i<^ 
 untempered brooch, passing this up and 
 then twisting sharply round so as to 
 destroy the connection of the nerve 
 filament. It may then be removed easily 
 with the barbed nerve extractor, if it 
 should not come out on the brooch. It 
 is never wise, and seldom safe, to use 
 arsenic for the destruction of the nerve 
 where pivoting is to be performed. It 
 is much better if there is likely to be 
 much trouble on account of the nervous- 
 ness of the patient, to destroy the nerve, 
 before cutting down the stump, by re- 
 peated applications of Pepsina porci and 
 dilute hydrochloric acid, as recommended 
 in my notes on ' Dental Pathology.' 
 
 The pulp- cavity being now clear must 
 be enlarged for the reception of the pivot. 
 This can be done with one or other of 
 the instruments shown in Fig. 71, gradu- 
 ally increasing the size until the requisite 
 diameter has been obtained. In young 
 subjects, care must be taken not to drill 
 through the pulp cavity in the apex of 
 the toothj lest you pass into the investing 
 membrane of the fang. It is well at this 
 stage to file down the rough edges of the 
 
 9 
 
 70. 
 
 m 
 
130 
 
 DENTAL MECHANICS 
 
 stump, SO as to present a perfectly smootli sur- 
 face, convex from back to front and concave 
 from side to side, on wliicli tlie crown of the 
 pivot tootli may be fitted. The most convenient 
 way of fitting the crown to the fang is to make 
 a temporary wooden or wire pivot, that will 
 
 Fig. 71. 
 
 1 
 
 pass easily in and out of the fang, with half an 
 inch of the point projecting into the mouth. A 
 wax impression may now be taken of the stump 
 and adjacent teeth. When this is removed 
 from the mouth the wooden pivot will be seen 
 standing in the wax. On the model being cast 
 from this the temporary pivot will occupy the 
 same relative position as when in the mouth, 
 and by removing it we have the fang cavity 
 reproduced also, which will act as a guide for 
 the direction of the pivot. 
 
DENTAL MECHANICS 131 
 
 The choice of the tooth is a most important 
 tiling, of greater moment for pivot cases than 
 for any other, since tliey generally are isolated, 
 and if not matched perfectly for shape and 
 colour produce a most unsatisfactory result by 
 the side of the natural teeth. One of three 
 varieties may be used. Either a pivot tooth 
 proper. Fig. 72, a tube tooth fitted with a pivot, 
 Fig. 73 ; or a flat tooth with a gold back and a 
 gold or platina pivot soldered on, Fig. 74. 
 
 Fig. 72. Eig. 73. Fig. 74 
 
 Section. Section. 
 
 The advantage of the tooth made expressly 
 for pivoting, is the perfect resemblance to the 
 natural crown, and from the fact that the tube 
 does not pass right through, enabling the 
 operator to use compressed hickory wood as a 
 pivot pin. 
 
 The advantage of a tube tooth is its greater 
 strength, being used with a metal pin, and 
 having a platina tube down the centre, which 
 
132 DENTAL MECHANICS 
 
 the first description of tooth has not, whilst its 
 great disadvantage is that the pinhole is rarely 
 in precisely the right place, being generally too 
 near the face of the tooth. 
 
 The benefit of using a flat tooth is especially 
 seen in a close bite, where there is little room 
 for either a pivot or tube tooth, or when, from 
 the abnormal position of the pulp-cavity, an 
 ordinary tooth is not available. In these cases 
 the pin can be arranged in almost any position 
 that can possibly be required, since there is 
 ample room for adjustment by reason of the 
 thinness of the tooth. The only objection to 
 its use is the rough surface presented in the 
 mouth, and its relative fragility. 
 
 The model when obtained had better be 
 dipped or varnished, or a little resin and wax 
 run over it before fitting the tooth, in order 
 to prevent wearing away of the surface of the 
 stump as shown in the plaster. 
 
 The tooth must be ground at the lathe with 
 a corundum wheel. Fig. 75, and then finely 
 fitted by colouring the model over the stump 
 with vermilion and oil, and noting the points 
 of contact when the tooth is put on the stump ; 
 these will be indicated by the colour adhering, 
 and must be ground away till all the surface of 
 the tooth is in perfect contact with the stump. 
 
DENTAL MECHANICS 
 
 133 
 
 Care must be taken to adjust the tooth and 
 pivot together in fitting, so that they may not 
 occupy a malposition when fixed in the mouth. 
 
 Fig. 75. 
 
 Some dental surgeons prefer fitting the tooth 
 to the stump direct in the patient's mouth, 
 colouring the stump for fine fitting. 
 
134 DENTAL MECHANICS 
 
 This process is, however, tedious to both 
 patient and operator, as well as being somewhat 
 disagreeable to the former. The tooth being 
 fitted, the pivot, if of wood, must be made so as 
 to pass firmly but not tightly into the pulp -canal, 
 and somewhat tightly into the tube of the pivot 
 tooth ; it will not do, however to apply too 
 much force in introducing either, lest you should 
 crack the tooth or give pain in the stump 
 when the wood has begun to swell from the 
 moisture. Previous to finally fixing the pivot, 
 syringe the pulp-cavity with a weak solution of 
 carbolic acid and water, then plug the extremity 
 of the nerve canal either with gold or cotton 
 wool soaked in creasote, or osteo-plastic care- 
 fully applied, so as to seal up the extreme 
 opening of the canal. 
 
 The wooden pivot may be wrapped round 
 with one or two layers of gold foil, thus pro- 
 tecting both the pivot and the walls of the 
 fang from the action of the secretions of the 
 mouth. 
 
 No greater pressure than can be applied with 
 the thumb and finger should be required for 
 adjusting a wood pivot, as the swelling that 
 takes place will quickly render it quite firm. 
 
 Wooden pivots may be strengthened if de- 
 sired by drilling carefully down the centre after 
 
DENTAL MECHANICS 135 
 
 fitting, and passing a gold or platina wire 
 througli. 
 
 If a metal pivot is used tlien it must be fast- 
 ened into the artificial crown witli powdered 
 sulphur placed over the opening of the tube in 
 the tooth, and melted carefully over a spirit 
 lamp. The pin at this part having been pre- 
 viously roughened will be held quite secure by 
 this method. For adjustment to the dental 
 canal, the extremity of the pin may be rough- 
 ened or slightly barbed, and then fitted in with 
 floss silk wound round, and coated with mastic, 
 or the cavity may be filled with osteo-plastic, 
 and the pivot introduced while the stopping is 
 in a soft state. The attachment of the pin to 
 a flat tooth I shall treat of further on. 
 
 It is impossible to enumerate in a work of 
 the present nature all the ingenious con- 
 trivances that have been introduced for the 
 fixing of pivot teeth. Each plan has some 
 special merit of its own, but the methods that 
 I have described are those most widely in use, 
 and are open to the fewest practical objec- 
 tions. 
 
136 DENTAL MECHANICS 
 
 SECTION IX 
 
 CHOOSING AND ADJ[JSTING MINEEAL TEETH 
 
 Above all other departments of tlie Dental 
 Surgeon's work, the choosing and adjusting of 
 mineral teeth gives the fullest opportunity for 
 the display of sound judgment and artistic 
 feeling. 
 
 In all reproductions nature must be imitated, 
 but not servilely copied. Utility must be borne 
 in mind, but not at the sacrifice of appearance 
 and beauty, still less must we forget the special 
 services which the teeth perform in the human 
 economy. Every condition requisite may be 
 fulfilled, by the exercise of those faculties to 
 which I have already alluded. 
 
 For partial cases it is essential, above all 
 things, that the shape and texture of the teeth, 
 should be reproduced in the artificial substi- 
 tutes, as well as the mere colour and shade. 
 The first are the marks of individuality, the 
 last merely a matter of complexion, and are in 
 the natural organ subject to variation. 
 
DEKTAL MECHANICS 137 
 
 Beware how you reproduce in tlie moutli 
 deformities, that have resulted from the mal- 
 formation, or arrangement of the teeth. 
 Though your work be true to nature, you will 
 but rarely find a patient suflBciently educated 
 up to your stand-point, to appreciate your 
 skill in this respect. If irregularities of the 
 natural organs are imitated in the artificial 
 teeth, it must be done with great care and 
 discretion, as the same amount of displacement 
 — say of the laterals — will not be tolerated in 
 the reproduction, that was present in the 
 original arrangement. 
 
 In choosing teeth for partial cases there is, 
 of course, the guidance given as to shape and 
 shade by the remaining teeth, but where the 
 gums are edentulous, and you have not had the 
 opportunity of seeiog any of the patient's 
 natural teeth, you must be guided in your 
 choice, by the size and shape of the gums, and 
 then by the complexion and characteristics of 
 your patient. As a broad rule, it may be laid 
 down that it is wiser to use artificial teeth, of a 
 somewhat smaller size than the natural ones. 
 When an entire set is fitted in, the result is 
 more pleasing by following this plan than if 
 large teeth were used, however natural they 
 may be in actual dimensions. 
 
138 DENTAL MECHANICS 
 
 Leaving these general observations, we will 
 now pass on to tlie more special consideration 
 of— 
 
 Adjusting and fixing teeth to partial cases. 
 
 — However carefully the teeth maj have been 
 chosen, they will scarcely fit into their respec- 
 tive places, without some amount of grinding 
 with the corundum wheel at the lathe. If the 
 stumps are remaining, or there be but slight 
 absorption, then the tooth must be fitted on 
 the gum at its anterior and lateral borders, 
 but the remaining portion may rest on the 
 plate. If an artificial tooth has to be fitted on 
 a stump care must be taken to have the stump 
 filed down level with the gum. On the plaster 
 model, this portion should be covered with 
 resin and wax in solution, (if the model has not 
 been dipped) so that it may not be worn away, 
 with the fitting of the tooth to its surface. 
 Should the model become at all injured on 
 the surface, the artificial tooth will ride on the 
 stump in the mouth, and if it does not do this, 
 the mineral tooth will soon be broken, from the 
 extra pressure that is brought to bear upon it. 
 When, however, the teeth are to rest upon 
 the gum only, the stumps having been removed, 
 it is advisable to scrape the plaster model away 
 slightly, so that the contact may be perfect 
 
DENTAL MECHANICS 139 
 
 between the artificial teeth and the gums, when 
 the plate is fitted into the mouth. 
 
 As to the adjustment of teeth to awkward 
 bites or articulations, it is difficult to give 
 directions that will be of much service in 
 practice. It will be necessary to sacrifice 
 utility for appearance in the arrangement 
 of the teeth for partial cases, situated in the 
 anterior portion of the mouth ; but with cases 
 for the masticatory region, I should unreservedly 
 reverse this order, and sacrifice appearance for 
 usefulness. On both points, it is well to 
 make up your own mind firmly, and then abide 
 by it ; once submit to the dictates or sugges- 
 tions of your patient, and your peace of mind 
 and conscience are gone ; it is better to lose a 
 patient than to submit to the discomfort that 
 will inevitably ensue if you follow their instruc- 
 tions or fulfil their desires (contrary to your 
 own judgment). 
 
 It is sometimes desirable to raise the bite 
 slightly (that is, not allow the patient to close 
 the mouth so much as formerly) ; this must be 
 done very carefully and to a very slight extent, 
 or great discomfort will be caused, and by 
 destroying the perfect articulation injury will 
 be done to any teeth still standing in the 
 mouth. When, however, the teeth posterior to 
 
140 DENTAL MECHANICS 
 
 the incisors of tlie upper and lower jaws are 
 absent, and the front teeth are being worn 
 away, and the upper incisors protruded by 
 the pressure brought to bear upon them, great 
 benefit will follow raising the bite to such an 
 extent at the back of the mouth with the 
 artificial denture, as to relieve the undue 
 pressure that has been exercised in front. 
 
 After the teeth £,re fitted to the model and 
 attached to the plate by means of resin and 
 wax, they must be tried in the mouth, and any 
 alteration that is necessary, made at once, as 
 after they are soldered on it will be difficult to 
 readjust them. 
 
 Investing in plaster and sand or asbestos,— 
 presuming that the teeth are for plate — some 
 use both the latter substances, adding only 
 sufficient plaster, to produce cohesion of the 
 other materials — they must be mixed to a 
 tolerably stiff paste, and placed on a smooth 
 surface, with a square of paper underneath so 
 as to allow of easy removal ; the plate with the 
 teeth attached is then pressed gently down, so 
 that all the lower surface is well supported, 
 and the teeth surrounded on their labial sur- 
 face, with the plaster and sand, so that when 
 trimmed up, a thickness of nearly half an inch 
 is left around them. 
 
DENTAL MECHANICS 141 
 
 As soon as the plaster and sand is suffi- 
 ciently bard to bear handling, the resin and 
 wax must be cleansed away thoroughly, and 
 the backs fitted to the teeth and plate. A 
 plan practised in America is to remove the 
 teeth from the investing material carefully, and 
 fit the backs on. The more general practice 
 in Enofland is to fit the backino:s of the teeth 
 after fitting them on to the plate, but before 
 investing in plaster, and the latter is, I think, 
 a better method ; the backing in either case 
 must be somewhat thinner than the metal used 
 for the plate, and should be stiffened, by the 
 addition of platinum as an alloy. 
 
 The holes for the pins of the teeth, may be 
 either drilled, punched out, or perforated with 
 a pair of pliers of the form shown in the accom- 
 panying cut, Fig. 7Q. 
 
 Fig. 76. 
 
 These nippers are so arranged that the 
 cutting-pins can be renewed as often as neces- 
 sary. This is accomplished by unscrewing the 
 
142 DENTAL MECHANICS 
 
 movable socket A, and dropping in the pin from 
 tlie back. The pins are flattened at the 
 opposite end, to prevent them turning round or 
 falling through, and when the socket A is 
 screwed home in the head of the nippers the 
 pin is secure. 
 
 The plate being fitted to the back of the tooth, 
 the rivets are then split with a scorper and 
 spread outwards ; as soon as all the backings 
 are fitted satisfactorily, the joints must be 
 strengthened by means of fine gold wire cut off 
 to the width of the tooth, and bent so as to fit 
 accurately at the base of the backing, thus 
 increasing the strength and giving stiffness and 
 solidity to the piece. Where the bite requires 
 it metal boxes may be made and attached to 
 the backs, but for such a case it will be better 
 as a rule to use a tooth that of itself gives a 
 masticating surface. When these things are 
 done, the pins being thoroughly cleansed, must 
 be coated with borax and water, wherever it is 
 necessary for the solder to flow. The borax 
 can be prepared by rubbing on a piece of slate 
 or porcelain with water, till the fluid is of a 
 creamy consistence. 
 
 The solder must be carefully placed in every 
 position where it will be required, so as to avoid 
 having to use more after the piece is made hot ; 
 
DENTAL MECHANICS 143 
 
 everything being arranged in a satisfactory 
 manner the piece is placed in the hand furnace 
 and gradually warmed up, then the top of the 
 furnace may be removed, and the heat applied 
 with the blowpipe till the mass is of a bright 
 red colour ; the well-directed flame of the 
 blowpipe will by this time cause the solder to 
 flow in every direction required ; or instead of 
 this plan the piece invested in the plaster may 
 be taken out of the furnace when sufificiently 
 hot, and placed on a slab of charcoal (sur- 
 rounded with plaster of Paris), and the heat 
 then raised by the aid of the blowpipe. 
 
 The first plan is, however, the best, unless it 
 be a very small case that requires soldering. 
 
 For full sets of teeth, the same rules and 
 modes of procedure apply as for a partial set ; 
 it is necessary, however, to adopt some plan to 
 prevent the plaster and sand breaking, when 
 the denture is being warmed up in the furnace, 
 or during the time of soldering. 
 
 Some pass two or three pieces of iron or 
 copper binding wire round the teeth, before 
 investing in plaster and sand, others use a strip 
 of copper, somewhat in the shape of the outline 
 of the gum, thus affording a support to the 
 outer surface of the plaster. A plan that I 
 deem better still, however, is to obtain a shallow 
 
144 DENTAL MECHANICS 
 
 saucer, with perpendicular sides, made of fire- 
 clay or plumbago, and after filling this with 
 plaster and asbestos or sand, sink the denture 
 in it and thus use the saucer at once as a 
 support, and a means of retaining the heat, after 
 it is taken from the furnace for soldering. 
 
 As soon as the soldering is completed, remove 
 the piece from the furnace, and place it on cold 
 charcoal or pumice stone to cool down. 
 
 Some recommend cooling down at once, by 
 pouring boiling water, over the plaster and 
 sand, no risk being run of cracking the teeth ; 
 but it is better to wait a little longer, and let 
 the plaster cool of itself. 
 
 After removing the plaster and sand, or 
 asbestos, as the case may be, the plate should 
 be thoroughly washed in water, and then boiled 
 in a solution of sulphuric acid (one part acid, 
 two parts water) so as to destroy the borax, 
 that has become fused and attached to the 
 gold. Scorpers of the form shown for finishing 
 up vulcanite work, can now be used to remove 
 any projecting portions of solder or wire 
 strengthening that has been applied, or these 
 may be cut down at the lathe with a fine 
 corundum wheel and plenty of water. The 
 entire surface must be then rendered smooth 
 by means of Ayrstone and water and a stick 
 
DExVTAL MECHANICS 145 
 
 and pumice powder, then polislied at the lathe, 
 first with pumice powder and a hard brush, 
 then with whiting and a softer brush, and, 
 finally, with rouge and a softer brush still, 
 commencing this last stage with the brush wet, 
 and working at it till the brush becomes dry. 
 For those spaces where a brush cannot be 
 applied, two or three threads, fixed at one end 
 to the work bench, may be passed through or 
 between the space to be polished, and the plates 
 passed up and down these threads (which 
 should be loaded with a little of the polishing 
 material) until a smooth and polished surface is 
 obtained. Strips of tape and cord may also be 
 used for the same purpose, using a different 
 size according to necessity. After this the 
 plate must be thoroughly cleaned with hot soda 
 and water, and dried in a bag filled with box- 
 wood dust. The case is now ready for fitting 
 in the mouth. 
 
 Fitting tube teeth to a full set.— These 
 should first be roughly fitted down to the plate, 
 and the gum as well, if they are to overlap the 
 edge of the plate, each tooth as it is fitted in 
 this way being attached to the plate by means 
 of cement, such as I have recommended for flat 
 teeth, and in this way the entire denture must 
 be mounted up so as to assume the form re- 
 
 10 
 
146 DENTAL MECHANICS 
 
 quired in the finished set, allowing just suffi- 
 cient excess of tooth surface for fine fitting. 
 As soon as they are all suitably arranged, a 
 finely pointed broach must be passed down each 
 tube very carefully and rotated, so as to leave 
 a mark over the plate, or, instead of this, a 
 piece of straight steel wire with a flat extremity 
 may be dipped in a mixture of vermilion and 
 oil, and then Hghtly dropped down the tube of 
 the tooth, thus marking with the point the 
 position for the pin. Or still another plan may 
 be adopted ; imbed the front of the teeth and 
 model in plaster up to the level of the tops of 
 the teeth (after soaping their surfaces) ; then 
 fill in the palatine surface also with plaster ; 
 this will keep the teeth in position, and as soon 
 as it is set, the holes in the plate may be made 
 by means of an Archimedean drill passing down 
 the tubes of the teeth ; in this way the direction 
 of the tube is continued into the perforation of 
 the plate, and the pin can be applied and sol- 
 dered in, so as to avoid the necessity of bending 
 afterwards. Before the pins canbe fitted to 
 the plate the plaster overcastings must of 
 course be removed with the teeth. When the 
 pins are all in good position the teeth may be 
 fine fitted, by means of the vermilion and oil 
 and a small-grained corundum wheel. 
 
DENTAL MECHANICS 147 
 
 Tube teetli are attached to tlie pins and 
 plate, by means of sulphur ground to a coarse 
 powder. The plate with teeth on, is made hot 
 over a spirit lamp and the sulphur then applied; 
 as it melts with the heat it runs down the tubes 
 of the teeth, and on hardening retains them 
 quite firmly in position. After this the ends of 
 the pins which project may be ground down at 
 the lathe, so as to be flush with the surface of 
 the teeth. 
 
148 DENTAL MECHANICS 
 
 SECTION X 
 
 THE YULCANITE BASE 
 
 In a work that is intended to be thoroughly 
 practical in its nature, it is neither wise nor 
 necessary, to go into the history of the invention 
 of every substance treated of. On this account 
 I shall make no reference to the successive 
 patents, trials, disputes, and works that have 
 been published upon the vulcanite base, but 
 shall confine myself to its composition, pro- 
 perties, and uses. 
 
 The toughest and strongest rubber in every 
 way is that which is sold as uncoloured or brown 
 rubber. It contains the largest proportion of 
 the natural gum, mixed with one of the various 
 forms of sulphur, and is not deteriorated by the 
 introduction of any colouring matter. From 
 this rubber all the other varieties may be said 
 to be built up. 
 
 The manufacture of the different rubbers 
 
DENTAL MECHANICS 149 
 
 used, is a secret kept very securely by tlie 
 makers. From the experiments , however, of 
 Professor Wildman (of Philadelphia) contained 
 in his ' Instructions in Vulcanite,' we are able 
 to form a very fair judgment as to the compo- 
 sition and mode of treating this valuable 
 natural j^roduct. 
 
 " Caoutchouc may be mixed with sulphur, 
 and the colouring matter, by being passed re- 
 peatedly between steam-heated rollers ; or the 
 caoutchouc may be first reduced to a pulpy or 
 gelatinous state by some one of its solvents, 
 and the sulphur and colouring matter then 
 mixed with it ; in either case the sulphur and 
 colouring should be ground extremely fine, and 
 then the whole ingredients thoroughly incor- 
 porated together to ensure a satisfactory result. 
 
 " For experimental purposes the latter 
 method of mixing can be readily practised by 
 any one. Of the solvents, ether deprived of 
 its alcohol, chloroform and bisulphide of carbon 
 are objectionable on account of their expense, 
 and also the operator being compelled to inhale 
 their vapour during the manipulation. Coal 
 naphtha, or benzine, are preferable on this 
 account ; they readily reduce the caoutchouc 
 to the proper consistency; but after having 
 been mixed, and the solvent evaporated, the 
 
150 DENTAL MECHANICS 
 
 rubber is non-adliesive, and does not pack well. 
 Oil of turpentine leaves the rubber somewbat 
 adhesive, and in a good condition to pack. 
 Therefore I have found it a better plan to 
 soften the caoutchouc in oil of turpentine, or 
 in equal parts of cold naptha, or benzine, and 
 oil of turpentine. 
 
 " In reducing caoutchouc to a gelatinous 
 condition, it requires a large quantity of the 
 solvent in proportion to the gum. This is 
 remedied bj introducing into the solvent from 
 five to fifty per cent, of alcohol ; in this case 
 the caoutchouc becomes gelatinous, but does 
 diffuse itself through the solvent, thereby 
 leaving much of it after the softened caoutchouc 
 is removed, for future use. 
 
 " I generally levigate the colouring matter 
 and sulphur in spirits of turpentine, first 
 reducing the colouring matter very fine, then 
 adding the sulphur, and also reducing it very 
 fine, then add a little of the pulpy caoutchouc, 
 mix thoroughly, and proceed in this manner 
 until the whole is incorporated into a perfectly 
 homogeneous mass. When the colouring matter 
 is ground in linseed oil, the caoutchouc may be 
 softened in naphtha, or benzine, and it will pack 
 well, as the oil renders it adhesive ; but I am 
 inclined to believe that oil, even in a small 
 
DENTAL MECHANICS 151 
 
 quantity, injures the hardness and polisli of the 
 rubber. 
 
 " After the materials are well mixed the mass 
 should be spread on a glass plate with a 
 spatula, and allowed to remain until the sol- 
 vent has been evaporated. 
 
 " The apparatus used in making the following 
 mixtures were a muller and glass plate to grind 
 the colours and sulphur, a spatula, broad-mouth 
 bottles, in which to gelatinize the caoutchouc, 
 and window glass, upon which to spread it 
 when mixed. The caoutchouc was the best 
 Para, and the time and temperature in vul- 
 canizing was the same as that for the American 
 Hard Rubber Company's red rubber. 
 
 " To test the Combination of Caoutchouc and 
 Sulphur alone : 
 
 1. Caoutchouc .... 48 
 Sulphur 24; 
 
 This gave a dark brown rubber, varying shade 
 in different mixtures ; it was strong, compact, 
 and tough, and received a fine polish. This 
 colour may be toned down to a dark oak by 
 bleaching in alcohol. 
 
 " 2. This experiment was performed with 
 caoutchouc which had not been smoked ; this 
 gum was translucent and nearly colourless. 
 
152 DENTAL MECHANICS 
 
 having merely a light straw tint. The propor- 
 tions were the same as for 1. 
 
 " Result. — Colour and properties the same as 
 the above, showing that the natural colour of 
 hard rubber composed of simply caoutchouc 
 and sulphur is a dark brown. 
 
 " To test the Colouring Properties of Bed 
 Oxide of Iron. — The following formula gave the 
 
 best results of the many tried : 
 
 3. Caoutcliouc .... 48 
 
 Sulpliur 24 
 
 Red oxide of iron (rouge) . . 36 
 
 " Besult. — Texture good ; colour in different 
 mixtures varied from almost black to black red ; 
 the colour was more on the red when the rouge 
 was ground in oil than when in spirits of tur- 
 pentine ; after exposure in alcohol to the rays 
 of the sun, the red was better developed, but 
 even then it was much darker than the Com- 
 pany's red rubber. The sulphur decomposed 
 the oxide of iron, forming a dark sulphide, 
 thereby destroying its colouring effect. 
 
 <c Yermilion for producing a Bed. — JSTume- 
 rous experiments were tried to ascertain the 
 quantity of vermilion necessary to overcome 
 the natural brown and produce a red colour ; 
 the following mixture may be set down as the 
 lowest : 
 
DENTAL MECHANICS 153 
 
 4. Caoutcliouc .... 48 
 
 Sulphur 24 
 
 Yermilion .... 36 
 
 " Some mixtures made according to tliis 
 formula were darker and some lighter, owing 
 to the different varieties of vermilion used. 
 The shade was made much lighter by bleaching 
 in alcohol. To bring it to a bright red when 
 vulcanized would require much more vermilion, 
 perhaps equal proportions of caoutchouc and 
 vermilion. This formula produced a good, 
 strong, compact rubber. If not identical in 
 composition with the Company's red, it so 
 closely resembles it in texture, strength, and 
 appearance, and in every particular it must very 
 nearly approximate thereto. 
 
 " To joroduce a Yelloiu. — The colouring effect 
 of chrome yellow was tested ; it gave a slate 
 colour, the chromate of lead being decomposed, 
 setting free the chromic acid, and forming a 
 sulphide of lead, stone ochi^e, and Naples yellow 
 and the common orpiment of commerce, were 
 tried with no better results. Pure orpiment or 
 king's yellow gave, when bleached, a lemon 
 yellow, when mixed as follows : 
 
 5. Caoutcliouc .... 48 
 
 Sulphur 24 
 
 King's yellow .... 36 
 
154 DENTAL MECHANICS 
 
 '' Althougli the colour produced by this sub- 
 stance was mucli more satisfactory than any of 
 the preceding, its use is objectionable, because 
 the texture of the rubber was not good, and the 
 king's yellow being sulphide of arsenic is very 
 poisonous. 
 
 " The following formula gives a good reliable 
 yellow, viz. : 
 
 6. Caoutcliouc . . . . 48 
 
 Sulphur 24 
 
 Sulphide of cadmium . . 36 
 
 " This requires bleaching to develope the 
 colour fully ; it is then much better than that 
 produced by orpiment, is more on the orange, 
 the texture of the rubber is good, and its use is 
 not objectionable. 
 
 " For a Lighter Yellow — 
 
 7. Caoutcliouc .... 48 
 
 Sulphur 36 
 
 Sulph. ed 36 
 
 White ox. zinc .... 12 
 
 " The white oxide of zinc toned down the 
 deep yellow to more of a lemon colour, similar 
 to that produced by the orpiment, at the same 
 time the rubber was of good texture. 
 
 " Experiments to produce a pink and a flesh- 
 colour so far have not been successful in pro- 
 
DENTAL MECHANICS 
 
 155 
 
 ducing the desired results, yet some of them 
 are worthy of note. 
 
 8. Caoutcliouc .... 48 
 
 Sulphur 24 
 
 White ox. zinc 
 Yermilion 
 
 30 
 10 
 
 " When bleached, gave a dark pink, the colour 
 not so good as the English ; texture close ; not 
 so strong as the brown or red. 
 
 " Variation of the above. 
 
 9. Caoutchouc .... 48 
 
 Sulphur 24 
 
 White ox. zinc .... 36 
 
 Yermilion . .• . . 10 
 
 " Vulcanized brown, after bleaching ; it was a 
 shade lighter than the preceding. 
 " The mixture of 
 10. 
 
 Caoutchouc 
 
 48 
 
 Sulphur .... 
 
 24 
 
 White ox. zinc . . . . 
 
 48 
 
 E. vermilion 
 
 10 
 
 Sulphide of cadmium 
 
 6 
 
 after bleaching, produced a buff. 
 " Variation of above. 
 
 11. 
 
 Caoutchouc 
 
 48 
 
 Sulphur .... 
 
 24 
 
 White ox. zinc . 
 
 96 
 
 Vermilion 
 
 5 
 
 Sulphide of cadmium 
 
 3 
 
 This produced a lighter shade — a Ught buff. 
 
156 DENTAL MECHANICS 
 
 " To ascertain the effect of wliite oxide of 
 zinc upon the natural brown of vulcanized 
 rubber, numerous mixtures were made. The 
 best Lehigh white oxide was used. 
 
 12. Caontcliouc .... 48 
 
 Sulphur 24 
 
 White ox. zinc .... 36 
 
 " This produced a drab after bleaching — tex- 
 ture good. 
 
 13. Caoutchouc .... 48 
 Sulphur , . . . . 24 
 "White oxide of zinc ... 48 
 
 " When bleached gave a light drab of good 
 texture, and in appearance approximates verj 
 near to that of the American Hard Rubber Com- 
 pany's white. 
 
 14. Caoutchouc .... 48 
 
 Sulphur 24 
 
 White oxide of zinc ... 96 
 
 " This after bleaching gave a grayish white. 
 These three preceding mixtures were repeated 
 by varying the proportion of sulphur, substi- 
 tuting thirty-six for twenty-four ; the object of 
 this was to give the rubber additional hardness ; 
 this change of proportions had the desired 
 effect, but at the same time the colour was 
 impaired. All of these mixtures vulcanize a 
 
DENTAL MECHANICS 157 
 
 brownish colour, and require to be bleached by 
 the rays of the sun in alcohol for their deve- 
 lopment. 
 
 " To produce a Black Rubber. 
 
 15. Caoutchouc .... 48 
 
 Sulphur 24 
 
 Ivory black, or drop black . 24 
 
 " This mixture gave a good black. 
 
 16. Caoutchouc .... 48 
 
 Sulphur 24 
 
 Ivory, or drop black . . 48 
 
 " This produced an excellent jet black, the 
 rubber was hard and of good texture. 
 
 " The drop black which is in lumps contain- 
 ing gum I have uniformly found to produce a 
 porous rubber, whilst the article under the 
 same name found in commerce, free from gum, 
 gave good results. 
 
 " By taking several of these different mix- 
 tures (such as the taste of the operator may 
 dictate), and cutting them into shreds, then 
 incorporating them together, and again cut- 
 ting the mass into small pieces suitable for 
 packing, a very pretty mottled rubber may be 
 made suitable for hurdles, &c. 
 
 " After being vulcanized and polished, it 
 must be bleached in alcohol to fully develope 
 
158 DENTAL MECHANICS 
 
 the colours, although some of the mixtures 
 present a pleasing appearance without the 
 bleaching process. 
 
 " In finishing mottled rubber, owing to the 
 several coloured mixtures having a different 
 degree of hardness, after the file, prepare for 
 the polishing process by obliterating the file 
 marks with a flat piece of Scotch stone. 
 
 " The introduction of shellac was tried in one 
 experiment, viz. : 
 
 Caoutcliouc . . . . 48 . 
 
 Sulphur 24 
 
 Yermilion .... 40 
 
 Shellac 12 
 
 " The addition of shellac did appear to im- 
 prove the compound in appearance or texture. 
 
 " I have now presented the most interesting 
 of the successful results of my experiments in 
 compounding mixtures for making hard rubber, 
 and would now call the attention of those who 
 desire to pursue this subject experimentally, 
 that to colour rubber three points are essen- 
 tial : First, the colour must remain unchanged 
 at the heat required for vulcanization. Second, 
 it must withstand the action of sulphur at this 
 temperature ; and third, sufficient quantity 
 must be added to the mixture to overpower the 
 natural brown of vulcanized rubber, before its 
 
DENTAL MECHANICS 159 
 
 shade can be developed. This fact shows us 
 that all highly coloured rubbers, or where the 
 brown is widely departed from, must be weak- 
 ened by their being loaded with so much colour 
 or foreign matter ; in proof of this I have 
 found no other mixture possessing strength and 
 toughness equal to that made of simply caou- 
 tchouc and sulphur. 
 
 " The following table gives, very nearly, the 
 percentage of caoutchouc contained in several 
 of the preceding formula. Also that of Ash and 
 Sons' Pink JSTo. 1, their S. P., their white, and 
 the white made by the American Hard Eubber 
 Company. The percentage given by these 
 latter is based upon calculation. 
 
 " From the results of the preceding experi- 
 ments it is evident we may substitute Ash and 
 Sons' black and the American Hard Rubber 
 Company's brown for the 1 brown in the table. 
 Also the English deep red and the American 
 Hard Rubber Company^s red for 4, the red in 
 the table. 
 
 
 
 Caoutchouc. Sulphur. 
 
 Vermilion. 
 
 
 Parts in 
 
 1. 
 
 Brown 
 
 . 66^ . SS\ 
 
 , 
 
 
 .100 
 
 4. 
 
 Red . 
 
 . 44 . 22' 
 
 . 33 . 
 
 
 . 99 
 
 6. 
 
 Yellow . 
 
 .44 .22 
 
 • 
 
 
 Sulph. Cad. 
 
 . 33 . 99 
 
 Ox. Zn. 
 
 8. 
 
 Pink . 
 
 . 43| . 21^ 
 
 . 9 . 
 
 
 . 27 . 100 
 
 11. 
 
 Buff . 
 
 . 35-4. 17-2 X 
 
 Sulph. 
 
 . 7-3 . 4 4 
 
 Cad. 
 
 . 35-4 . 100 
 
160 DENTAL MECHANICS 
 
 Caoutcliouc. 
 
 Sulphur. 
 
 Vermilion. 
 
 Ox. Zn. Parts in 
 
 14. Drab . 
 
 44 . 
 
 22 
 
 . 
 
 .33 .99 
 
 15, Lighter Drab . 
 
 40 
 
 20 
 
 . 
 
 . 40 . 
 
 16. Grayish White . 
 
 28-5. 
 
 14-3 
 
 • 
 
 . 57-1+ 100 
 
 Black. 
 
 17. Black. . , . 
 
 50 
 
 . 25 
 
 . . 
 
 . 25 . 100 
 
 18. Jet . . . 
 
 40 
 
 . 20 
 
 • 
 
 . 40 . 100 
 
 White earthy 
 matter. 
 
 Ash & Sons' Pink, ^o. 1 
 
 24 
 
 . 12 
 
 . 18 . 
 
 . 48 . 102 
 
 Ox. Zn, 
 
 „ „ S. P. 
 
 35-6 
 
 17-8 
 
 .26-6. 
 
 . 20 . 100 
 
 „ „ White 
 
 32f 
 
 . 16i 
 
 , 
 
 . 51 . 100 
 
 Am. H. R. Co.'s White 32| 
 
 . 16i 
 
 . 
 
 . 51 . 100 
 
 " The calculation for the component parts of 
 Ash and Sons' Pink E-nbber is based npon the 
 method given in the patent for making pink 
 rubber for dental uses, the quantity of fixed 
 matter it is found to contain, and taking for- 
 mula 4 as the composition of red rubber. It 
 will be found, upon examination of this data,' 
 that, if there is any error in the quantity of 
 caoutchouc given to the pink, it is in its favour. 
 A glance at the table will at once show its and 
 other light rubbers' inferiority to either brown 
 or red for dental purposes. 
 
 " The calculation of the percentage of Ash 
 and Sons' S. P. is based upon the quantity of 
 fixed matter found in it, and that fixed matter 
 having been mixed a red rubber compound 
 as in formula 4. This is evidently superior to 
 
DENTAL MECHANICS 
 
 161 
 
 the pink, but inferior either to the red or 
 brown. 
 
 " Caoutchouc being the cement which binds 
 the whole together, if any compound should 
 contain but a small proportion of it, and if any 
 substance prejudicial to the system should 
 enter into its composition (and in the patent 
 referred to for making pink rubber, such sub- 
 stances are recommended), its weakness of tex- 
 ture from the want of sufficient adhesion of its 
 particles would render it liable to produce in- 
 jurious effects by its susceptibility to abrasion 
 in the mouth." 
 
 Some very interesting experiments were also 
 made by Prof. Wildman to ascertain, by the 
 apphcation of heat, the amount of fixed matter 
 contained in various specimens of rubber com- 
 pounds. A condensed statement of the results 
 obtained is exhibited in the following table : 
 
 1. Specimens of Deep Pink 
 
 2. English Pink .... 
 
 3. Ash & Sons' Pale Pink, No. 1 
 
 4. „ „ Deep Pink, No. 1, X 
 
 5. ,, „ S. P. . 
 
 6. ,, ,, Black 
 
 7. „ „ White 
 
 8. English Bed . 
 
 9. Dieffenbach's Red 
 
 Per ceut. of 
 fixed matter. 
 
 . 60 
 
 . 48 White Clay. 
 . 48 „ 
 
 . 47 Oxide of Zinc. 
 20 
 
 4 Dark Ash. 
 . 51 White Ox. Zic 
 
 6 Dark Ash. 
 • 16 „ 
 
 11 
 
162 DENTAL MECHANICS 
 
 Per cent, of 
 fixed matter. 
 
 10. Am. H. R. Co.'s Red .... Dark Asli. 
 
 11. „ White ... 51 White Ox. Zic. 
 
 12. „ Brown, near . . 4 Dark Ash. 
 
 13. My own Brown (0 2, S 1) near . . 3 „ 
 
 14. „ Red (C 48, S. 24, Y. 36) . 2 „ 
 
 The author observes : " These experiments 
 show us that pink and light rubbers for dental 
 purposes are heavily loaded with such foreign 
 matter as white clay and oxide of zinc, and 
 some to the extent of fifty-one per cent, of their 
 weight. Ash and Sons' S. P. is decidedly the 
 best of his light rubbers, containing only 
 twenty per cent, of fixed matter. 
 
 " Again, Ash and Sons' black (brown), the 
 American Hard Rubber Company^s brown, and 
 my own brown, give results, respectively four, 
 near four, and near three per cent, of fixed 
 matter. My own, I know, was made of pure 
 caoutchouc and of sulphur; hence from the 
 residues of the two former so nearly approxi- 
 mating thereto, and also from their similarity 
 of texture and appearance after being vul- 
 canized, we must arrive at the conclusion they 
 are of the same composition, and are therefore 
 good and reliable brown rubbers. 
 
 " When we examine the results of the experi- 
 ments upon the English deep red, that made by 
 
DENTAL MECHANICS 163 
 
 the American Hard Rubber Company, and 
 my own red, we find the fij^ed matter to be 
 six, five, and two per cent, respectively. 
 My own red was made of pure Para caout- 
 chouc, vermihon, and sulphur. The small dis- 
 parity of fixed matter found in these rubbers 
 may have arisen from the different state of 
 purity of the caoutchouc used in compounding 
 them. 
 
 " It is evident that the specimens of English 
 Red and of the American Hard Rubber Com- 
 pany's red were not loaded with earthy matter 
 or oxides of zinc or lead, for if they were, the 
 clay would have given us a greater percentage 
 of fixed matter. Oxide of zinc is fixed in the 
 fire at a white heat, and if present would have 
 produced a similar result. Oxide of lead would 
 have shown itself by its reduction, and the 
 greater weight of residue. 
 
 " The conclusion we would naturally arrive 
 at from the results of these experiments is, that 
 the American Hard Rubber Company's red, 
 and the English deep red, are the best red 
 rubbers offered for dental purposes." 
 
 The properties of vulcanite are extreme hard- 
 ness and toughness when subjected to the 
 action of super-heated steam for a variable time 
 (according to composition) ; extreme softness 
 
164 DENTAL MECHANICS 
 
 and elasticity when composed witli a special 
 view to that result or when vulcanised in a pecu- 
 liar manner which I shall hereafter refer to, 
 extreme lightness, the power of resisting most 
 chemical agents, whilst it is not acted upon by 
 any ordinary degree of heat, such, for instance, 
 as the temperature of the mouth. Its chief 
 advantage, however, is the facility with which 
 it can be adapted to any form and receive a 
 perfect and sharp impression fi^om any hard 
 counterpart into which it may be pressed. 
 
 With regard to the uses of vulcanite in 
 dental surgery and mechanics, they are innu- 
 merable ; in almost all cases where gold was 
 formerly used exclusively, vulcanite can now 
 be apphed instead ; whilst in place of bone 
 work, vulcanite may be always employed with 
 equal advantage, and very often with greater 
 comfort to the patient. 
 
 This material has, however, been used more 
 extensively for regulating plates (superseding 
 gold and bone work) than for any other pur- 
 pose in dental mechanics, since, from its 
 peculiar properties and market value, greater 
 facilities are offered to the operator for the 
 frequent renewal of mechanical contrivances 
 for regulating the teeth. 
 
 Under their several departments the various 
 
DENTAL MECHANICS 165 
 
 forms and manners in whicli vulcanite is used 
 will be treated of. 
 
 When vulcanite was first introduced nume- 
 rous cases were reported of salivation being 
 produced, owing to the presence of sulphuret of 
 mercury as a colouring agent. Some of these 
 were, doubtless, well and clearly marked ; but 
 it is not improbable that others were due to 
 the prejudice with which the new base was re- 
 ceived by a large number of those practising 
 dentistry. There is no question that some of 
 the earher and carelessly prepared specimens of 
 vulcanite did contain mischievous agents, but 
 in the present day, rubber pm'chased of makers 
 of good repute need give no occasion for alarm 
 to the most scrupulous of practitioners. 
 
 In another part of the work will be found the 
 time and temperatm^e advised for cooking the 
 various descriptions of rubber which are used ; 
 there are, however, certain general conditions 
 that may be best discussed in the present 
 section. Whenever practicable the flask should 
 occupy a central position in the vulcanizer, and 
 should not rest on metal, but pumice stone, so 
 that heat may not be communicated by conduc- 
 tion to one part more than another. For all 
 varieties of rubber the longer the time, and 
 the more slowly the temperature is raised the 
 
166 DENTAL MECHANICS 
 
 better ; thus, a piece will come out tougher 
 and stronger in every way, by being vulcanized 
 four hours at a low temperature, rather than 
 an horn" and a quarter at 315^, and with elastic 
 rubber especially six or even eight hours are a 
 great advantage. 
 
 The most obvious evil resulting from rapid 
 vulcanizing is porosity of the rubber, and this 
 is undoubtedly caused, as Professor Wildman 
 points out, by the rapid evolution of sulphur- 
 etted-hydrogen gas, and its confinement to the 
 central portion of the block of rubber by the 
 superficial hardening of the external layer 
 only of the denture. This evolution of gas 
 during vulcanizing is, in fact, proved to demon- 
 stration by the following experiment of the 
 Professor : 
 
 "To ascertain if sulphm^etted-hydrogen is 
 given off during vulcanization, a bulb was blown 
 at the end of a glass tube ; this was filled with 
 red rubber, the tube was then drawn out very 
 small from immediately above the bulb, and 
 curved so that the small part when the bulb 
 was in the paraffin bath could be inserted into 
 a vessel beside it. 
 
 " The bulb was then placed in a paraffin bath 
 and the curved end of the tube inserted in a 
 vessel containing a solution of acetate of lead. 
 
DENTAL MECHANICS 167 
 
 The heat was raised to 320° F., and retained at 
 that point for one hour and a quarter. 
 
 " The mean results of several experiments 
 conducted in this manner were, that durino- the 
 first thirty or forty minutes after the heat had 
 attained to 320°, bubbles of sulphuretted- 
 hydrogen came over at short intervals, and at 
 the expnation of this time it was evolved in a 
 continuous stream which continued for a few 
 minutes, causing a copious precipitate of sul- 
 phide of lead. After this, until the expiration of 
 the hour and a quarter, the gas was only given 
 off sparingly at intervals. This experiment 
 gives us ocular demonstration that this gas is 
 evolved during vulcanization, and in large 
 quantities, and conclusively shows that in thick 
 pieces, especially, the heat should be slowly 
 raised, and the rubber should be under strong 
 pressure to ensure a successful result." 
 
 To construct a full upper set of teeth in the 
 vulcanite base. — The impression of the mouth 
 should always be taken in plaster of Paris, and 
 the model cast so that its thinnest part may 
 not be more than half an inch thick ; this will 
 prevent the trouble of cutting it down after the 
 teeth are mounted ready for flasking, and 
 admits of its being placed in the articulating 
 frame up to the last moment, to make sure that 
 
168 DENTAL MECHANICS 
 
 no displacement has taken place. I must, for 
 the moment, suppose that the model has been 
 fitted up to an articulation in a bite frame, so 
 that we may proceed to the mounting of the 
 teeth. A plate of wax rolled out to the thick- 
 ness of a sixteenth of an inch may be softened 
 by the spirit lamp, or in warm water, and 
 pressed carefully all oyer the upper surface of 
 the model, that is, the palate and alveolar ridge ; 
 or thin gutta percha may be used, which is 
 better when it has to be tried in the mouth 
 (especially in hot weather). Another plan that 
 I have adopted, and like very much, is to take 
 some good white or pink blotting-paper, not too 
 thick, warm it before the fire, or on a hot plate, 
 then immerse in melted wax, letting the super- 
 fluous wax drip off, and allowing the wax to 
 harden, then cut out patterns from this ac- 
 cording to size and shape, and having softened 
 the pattern before the fire, apply it in the 
 same way as the wax plate or thin gutta 
 percha. There are several advantages con- 
 nected with this mode of action : you obtain 
 a more equal thickness (by applying a number 
 of layers as you require them) ; you do not by 
 extra pressure reduce the substance where there 
 are prominent ridges in the gums, as you may 
 do with wax, or even gutta percha, and at the 
 
DENTAL MECHANICS 
 
 169 
 
 same time you have a touglier base to rely upon 
 when trying the set in the patient's mouth. 
 
 Still another plan, more troublesome, but 
 infinitely better in its results, is that known as 
 " Stent's process ;" it consists of mounting up 
 the plate in a soft metal in thin sheets (about No. 
 6 gauge) ; they must be struck up with a zinc 
 or tin model in lead, and may be composed of 
 one or more layers of metal, but when finished 
 they are very strong and neat, and the teeth 
 may be fitted on to them with wax in the same 
 way as when wax, gutta percha, or paper are 
 used. 
 
 The plate, whatever the material used, being- 
 fitted to the model perfectly, must be trimmed 
 up to the required size, as shown in accom- 
 panying di^awing (Fig. "17). As a rule, it may 
 
 Fig. 77. 
 
170 DENTAL MECHANICS 
 
 extend all round to tlie extent of tlie impres- 
 sion, except posteriorly, that is, if the patient 
 has been allowed to nearly close the mouth 
 when taking the impression; plaster of Paris 
 gives the most accurate representations of all 
 the delicate folds of membrane, that are usually 
 absent if wax is used instead. The plate being 
 completed, a narrow strip of wax, half an inch 
 wide, must be warmed and bent round to the 
 shape of the dental arch, its thickness varying 
 according to the depth of the bite, that is, the 
 distance between the upper gum and the tops 
 of the lower teeth. On this rim of wax the 
 teeth may be mounted, simply warming them 
 and pressing their fang portion in ; when they 
 are all adjusted, (1), with a view to their per- 
 fect articulation with their fellows of the lower 
 jaw ; (2) with regard to their restoration of the 
 outline of the jaw that has been lost by absorp- 
 tion ; and (3) with some display of artistic 
 feeling as to their general appearance and dis- 
 position ; the spaces smTOunding them may 
 be filled in with wax, on the labial surface, 
 being made continuous with the remains of the 
 gums, and on the lingual surface continuous 
 with the palate. On the outer surface avoid a 
 smoothness and continuity that is never found 
 in the natural state, and which, if present, shows 
 
DENTAL MECHANICS 171 
 
 a want of taste in tlie finished piece ; and on 
 the lingual sm^face avoid depressions and sharp 
 ridges or boundaries that will allow of the 
 lodgment of food, and induce irritation in the 
 tongue. Bear in mind that what the wax is, 
 such will the perfected piece be in these 
 respects, and that as a matter of economy in 
 time and materials what you desire the finished 
 piece to be, that also the wax model should be. 
 Convenient instruments for modelling up the 
 wax around the teeth are shown in the woodcut 
 below (Fig. 78). 
 
 Fig. 78. 
 
 Flasking is the next step. Opinions difi*er 
 as to the best form of flask to use, but for an 
 upper set of teeth there is little doubt that 
 shown in the annexed cut is the most service- 
 able (Fig. 79). 
 
 Fig. 79. 
 
 ^ c 
 
172 
 
 DENTAL MECHANICS 
 
 This flask is made after a pattern designed 
 by Messrs Bell and Turner, in tkree sections 
 (Nos 1, 2, 3), and is constructed for the purpose 
 of avoiding the evils complained of in the old 
 kinds, viz. that of leaving a stratum of vulca- 
 nite between the two halves of the mould, and 
 thus altering the articulation of the piece ; and 
 not only this, but causing often a derangement 
 of the arch or position of the teeth, through 
 the difficulty of getting the two halves of the 
 mould to shut down in their proper position. 
 
 By the use of the intervening plate B (the 
 invention of Mr Bennett) an exact fac-simile of 
 the palate of the patient can be produced upon 
 the external surface of the vulcanite piece. 
 
 If any of the accompanying descriptions of 
 
 Fig. 80. 
 
DENTAL MECHANICS 173 
 
 flasks are used (Fig. 80), tlien the model 
 must be wliat is called " sunk " in the lower 
 portion thus, (Fig. 81), so that the plaster rises 
 
 Fig. si. 
 
 to the level of the wax around the model, not 
 higher. The plaster must be mixed thin, and 
 the model pressed firmly down, in order that it 
 may rest upon the floor of the flask ; when it is 
 hard, paint it over with soap and water, by 
 means of a camel' s-hair brush, teeth, plaster, 
 and wax altogether, or dust it on the sm^face, 
 when dry and hard, with soap stone (French 
 chalk) : this is to prevent adhesion of the plaster 
 when the upper part of the flask is filled in. 
 This upper part must now be fitted on, the top 
 being taken ofl*, so that plaster may be poured 
 in from above, and well shaken down, to avoid 
 any air bubbles getting between, what will 
 presently be, the mould and counterpart ; when 
 
I 
 
 174 DENTAL MECHANICS \ 
 
 1 
 
 the space is ttorouglily filled up, tlie top piece | 
 
 ma J be put on, and the whole, while the plaster ' 
 
 is soft, put into " the wrench " shown below, so ' 
 
 as to ensure all the parts of the flask being in i 
 
 i 
 
 Fig. 82. - ! 
 
 accurate and complete contact, any superfluous 
 plaster being wiped away from the outside of 
 the flask in order to see that this is accom- 
 phshed. Or the method of flashing the piece 
 as directed at p. 197 may be adopted which in 
 many cases has advantages over that just 
 described. 
 
 Opening the flask must be delayed until the 
 plaster is quite hard ; it can then be removed 
 from the wrench, and placed in a basin of 
 boiling water, the joints prised apart with the 
 edge of a knife or scorper, and the separation 
 made between the upper and lower parts ; care 
 
DENTAL MECHANICS 175 
 
 must be taken to open the flask evenly all 
 round, or there is a liability of breaking away 
 some portion of the plaster. 
 
 To clear away the wax. — Pour boiling water 
 over the upper portion of the flask — in which 
 the teeth will be found imbedded — until every 
 particle, and even the appearance of gloss, is 
 gone from the surface of the mould. 
 
 Packing may now be proceeded with. The 
 rubber cut up into sizes suitable for the case 
 should be warmed on a hot water-plate (Fig. 
 83). Packing is not a matter of so much 
 
 Fig. 83. 
 
 importance as having the rubber thoroughly 
 softened and very clean, so that it may be 
 packed closely together and have no dirt or 
 sulphur on the surface to prevent perfect cohe- 
 sion of the whole mass. The same description 
 of instrument may be used for packing as for 
 modellino'. If more than one sort of rubber is 
 used, care must be taken to keep the line of 
 union as true as possible, so as to prevent a 
 
176 DENTAL MECHANICS 
 
 patcliy appearance in the finished case. Pack- 
 ing should always be commenced in that part 
 which will tend to keep the teeth most firmly 
 in position. This in most instances will be 
 close down by the pins of the teeth, as shown 
 in Fig. 84. When there appears to be sufficient 
 
 Fig. 84. 
 
 rubber to fill up the mould thoroughly, place it 
 in the wrench fitted to a celluloid base tank 
 (Fig. 85), and having boiHng water in the tank, 
 keep up the temperature with the spirit lamp 
 or gas, and gradually close the flask as far as it 
 will go without gi'eat pressure, then remove it, 
 immerse for a minute in cold water, and open, 
 if there is not sufficient rubber put in more, if 
 
DEXTAL MECHANICS 
 
 177 
 
 there is excess, as there should be, then cut 
 gutters round, as shown in Fig. 84 ; this will 
 allow the superfluous rubber to flow out when 
 it is again put in the wrench, and enable you to 
 close the flask completely. 
 
 Fig. 85. 
 
 The great advantage in using the celluloid 
 tank is, that it enables you to warm the rubber 
 and flask, and apply the wi^ench simultaneously. 
 
 The benefit derived from the plan of screwing 
 up, before cutting the gutters, is that you press 
 the rubber well home into all the deeper 
 portions of the mould, and also well around the 
 teeth. 
 
 To facilitate the opening of the flask for 
 
 12 
 
178 DENTAL MECHANICS 
 
 examining tlie quantity of rubber, a piece of 
 unsized cloth, such as that usually placed 
 between the layers of rubber when sold, only 
 with the size washed out of it, may be interposed 
 between the surface of the rubber and the 
 plaster counter-part. This prevents adhesion 
 of those surfaces, and does not interfere with 
 the perfect union of the pieces of rubber. Care 
 must be taken to remove the cloth before finally 
 screwing up. 
 
 Some authors advise coating the plaster with 
 French chalk, liquid silex, collodion, or tinfoil, 
 to prevent adhesion to the rubber ; for my own 
 part I prefer leaving the plaster untouched, as 
 anything that is applied will give to the surface 
 of the rubber when hardened, a smooth surface, 
 that is very objectionable if you want to obtain 
 suction ; and the plaster adhering to the exposed 
 portion of the plate — that must be finished with 
 file and scraper — is of no consequence. 
 
 When the piece is packed and ready for 
 vulcanizing, it must be fitted into its proper 
 clamp, or ring, to secure it, or if it has screws 
 attached, they must be brought home to prevent 
 any chance of gaping, when the rubber begins to 
 swell in the vulcanizer. 
 
 Vulcanizers are so numerous that it is 
 somewhat difficult to make a choice ; the 
 
DENTAL MECHANICS 
 
 179 
 
 most carefully made and perfectly finished 
 are those manufactm^ed by Messrs Ash; the 
 least expensive and most ingenious are those 
 supplied by Messrs White, of Philadelphia; 
 the simplest is that made by G. W. Eutterford, 
 of this city, and known as the " Single-screiv 
 vulcanizery There are many other makers, but 
 these three indicate the chief characteristics 
 belonging to their several manufactures. We 
 will speak of Ash's first (Fig. SQ). 
 
 Fig. 86. 
 
 Dimensions : height 15 in., diameter 5? in. 
 
 The vulcanizing chamber is made of ivrought 
 copper, nearly a quarter of an inch thick, and 
 the malleable iron cover is held down by means 
 
180 
 
 DENTAL MECHANICS 
 
 of a strong iDrougM-iron screw collar with set 
 screws. 
 
 The thermometer registers 350° Fahrenheit, 
 and the small fusible metal plug inserted in the 
 cover will only blow out when that degree of 
 heat is exceeded. 
 
 The vulcanizers are tested, before leaving 
 their factory, to a pressure of upwards of 600 lbs. 
 to the square inch, or nearly seven times the 
 degree of pressure usually required in the 
 process of vulcanization. An iron ring with 
 handle is with each vulcanizer, to hold the 
 boiler while screwing on the wrought-iron screw 
 collar. It is useful also for turning out the 
 flask when the vulcanizing is complete. The 
 india-rubber packing requires renewing occa- 
 sionally to keep the chamber steam-tight. 
 
 Fig 87. 
 
DENTAL MECHAXICS 
 
 181 
 
 Of the American vulcanizers, Whitney's are, 
 all things considered, the best for ordinary use, 
 and the accompanying woodcut (Fig. 87) shows 
 the most convenient size for general purposes. 
 
 The heater is composed entirely of copper and 
 brass, is of two pieces only, a copper pot, and 
 brass head that screws on to the pot, dispensing 
 with all bolts and nuts. They are uniformly 
 3-|- inches diameter inside ; for two flasks 5 
 inches, and for three flasks 7 inches deep. The 
 whole thing complete for use only weighs from 
 4 to 5|- pounds, according to the size, whether 
 for two or three flasks. Special directions for 
 using accompany each machine. 
 
 A small Yulcanizer (Fig. 89), known as Hayes' 
 
 Fig. 
 
 Fig. 89. 
 
 iron-clad, is very useful in travelling or when 
 there is not gas conveniently near ; it is made for 
 either one or two flasks, but for real con- 
 
182 
 
 DENTAL MECHANICS 
 
 yenience tlie single flask oven is tlie best; 
 with tins tlie antomatic lamp is very good, 
 as it will shut off the spirit when the steam is 
 getting np too high (Fig. 88). 
 
 This automatic lamp may be used for gas or 
 
 Fig. 90. 
 
 Yulcanizer. 
 
 alcohol, and with or without the automatic ar- 
 rangement. When properly adjusted the flow of 
 gas or alcohol is controlled by a spring cut-off. 
 
DENTAL MECHANICS 
 
 183 
 
 that is held open by a fusible alloy that 
 breaks loose and extino^uislies the flames when 
 the heat reaches a point slightly above that 
 required to finish the process, and before the 
 work or the vessel can receive injury. The 
 wick, being protected from combustion, does 
 not require renewal. 
 
 A very complicated, but perfect, apparatus, 
 
 Fig. 91. 
 
 Register. 
 
 whereby the thermometer is dispensed with 
 entii^ely, is shown in the accompanying drawings 
 (Figs. 90, 91), and is known as Hoffstadt's 
 
 self-reoulatino' vulcanizer. 
 
184 DENTAL MECHANICS 
 
 Many attempts have been made to regulate 
 the flame used for heating vulcanizing machines, 
 and in this vulcanizer the flame is not only 
 regulated as desired, but the degree of heat 
 indicated without a thermometer, and the at- 
 tention of the operator drawn by the tap of a 
 bell when the heat has reached any given point. 
 The boiler is very strong indeed. A brass ring 
 is well brazed on the outside of the boiler ; the 
 lid, which is made of bell-metal, is fastened to 
 the boiler with three hook-shaped screws made 
 of steel. There is a ring cast sohd with the 
 outside of the lid, which encloses the inner ring 
 or regulator, that will expand or contract by 
 changes of heat, and work the lever which 
 extends on the platform. The lever comes in 
 contact with the hand on the dial registering 
 the degree of heat, and when the heat has 
 reached any determined point — say 320° — it 
 disconnects the lever which is attached to a 
 spring stop-cock, and turns down the flame as 
 far as the set-screw allows, which may be set to 
 any desired point. 
 
 Eutterford's single- screw vulcanizer has a 
 wrought-copper boiler, dome-shaped lid held 
 down by one screw in the centre ; the case sup- 
 porting the boiler is of sheet iron, with cast-iron 
 stand and screw holes to fix it to the work-bench. 
 
DENTAL MECHANICS 
 
 185 
 
 The steam is let off at a separate escape- 
 screw, thus leaving the safety-valve undisturbed; 
 there is also a steam-gauge as well as ther- 
 mometer attached ; it can be used, as seen in 
 woodcut (Fig. 92), for either gas or spirit lamp. 
 
 Fig. 92. 
 
 The engraving shows clearly the manner in 
 which it is closed by means of the double ended 
 lever. 
 
 The choice of a vulcanizer havino- been settled, 
 the flask should be placed as near the centre as 
 
186 DENTAL MECHANICS 
 
 possible, resting, if there be room, on some 
 pieces of pumice-stone. The amount of water 
 must vary according to the size of the boiler, 
 but with Eutterford's medium-sized vulcanizer I 
 put in half a pint of warm water. When the 
 vulcanizer is closed the heat must be gradually 
 raised — the slower the better — and kept at the 
 temperature required for the necessary time ; 
 for most rubbers the best heat is 310° for an 
 hour and a half; if you lengthen the time, you 
 may reduce the heat to 305°; if you raise the 
 heat you may shorten the time proportionately. 
 This latter plan should only be adopted, how- 
 ever, under some great emergency, such as 
 for a hurried repair. 
 
 When the time of vulcanization is completed, 
 if possible let the boiler cool down before let- 
 ting off the steam and opening, as this gradual 
 reduction of temperature tempers the piece 
 better than if you take it out suddenly and cool 
 down with water. 
 
 If on opening the vulcanizer, the flask is not 
 quite cold, it may be placed under a tap, and a 
 stream of water allowed to run over it ; the 
 screws can then be loosened, or the clamp or 
 ring released, and a thin- edged knife intro- 
 duced between the joints of the flask, and the 
 parts gradually separated all round, or the top 
 
Fig. 93. 
 
DENTAL MECHANICS 189 
 
 piece may be taken off first of all, and water 
 allowed to soak througli so as to soften the 
 plaster. In opening either way, however, the 
 only thing required is care and attentionj with 
 the recollection of the position the teeth occupy 
 in the flask. After taking out the piece, cleanse 
 it thoroughly with cold water and a good stiff 
 tooth or nail brush so as to free it from plaster. 
 As it is now ready for filing up, with straight 
 and curved rough files remove the superfluous 
 rubber, and reduce all the surface (except the 
 interior, which is to fit the gums and palate) to 
 their proper thickness and size and shape. 
 The files best suited for this purpose are shown 
 in Fig. 93. 
 
 A quicker, but somewhat dangerous plan, is 
 to thin down the piece with a burr or steel wheel 
 (file-cut) on the lathe. There is, however, an 
 obvious risk of cutting through the palatine 
 portion of the plate unless great care is used. 
 The cut. Fig. 94, shows the burrs made by Messrs 
 Ash to fit on the lathe heads manufactured by 
 them. 
 
 An even surface having been obtained by one 
 or other of these means, the vulcanite must be 
 cleared away from around the teeth, so as to 
 give the outline of the artificial gum as natural 
 an appearance as possible. This is best done 
 
190 
 
 DENTAL MECHANICS 
 Fig. 94. 
 
 by means of scorpers, or sculptors as thej are 
 also called, the drawing sliows them in plane 
 and in section, the various forms being used 
 according to the position of the rubber to be 
 removed by them. 
 
 The plate having been filed up is ready for 
 '' finishing," that is, reduced to a smooth surface 
 by means of scrapers, fine files, glass cloth, 
 pumice powder, and lathe. Some very useful 
 forms of scrapers are shown in woodcut, Eig. 
 95. They are capable, however, of very many 
 modifications, according to the skill and fancy 
 
DENTAL MECHANICS 
 
 191 
 
 Fig. 95. 
 
 ^:^==^ 
 
 o 
 
 D 
 
 of the operator. Tliese various shapes it will 
 be seen are made with a view to fit into the dif- 
 ferent parts of an artificial denture. Many will 
 finish up with the scraper and glass cloth alone, 
 and then lathe with pumice, while others prefer 
 to use Ayrstone, after the glass clothing, using 
 a fine file also with the scraper to improve the 
 surface. Some, again, like to go over the 
 entire surface with a stick, and water and 
 pumice powder, to take out all the scratches. 
 All these diff'erent plans are matters of indi- 
 vidual taste. The only thing to be remembered 
 is this, that you must have all the scratches 
 
192 
 
 DENTAL MECHANICS 
 
 Fig. 96. 
 
DENTAL MECHANICS 
 
 193 
 
 out by one means or other before you begin 
 polishing at the lathe wheel. The best arranged 
 polishing lathe is shown in Fig. 97. The 
 
 Fig. 97. 
 
 splashings are prevented from scattering about, 
 and there is plenty of room for the hands to 
 move the plate of rubber in all directions. 
 When using the pumice powder and hard brush 
 for polishing be careful to have plenty of water ; 
 
 13 
 
194 DENTAL MECHANICS 
 
 this gives a better finisli in shorter time. 
 When a smooth continuous surface has been 
 obtained, change the hard brush for a soft one, 
 or an American buff wheel or cone, and proceed 
 with whiting and water to put on the finishing 
 polish. To do this use plenty of water at first, 
 and then complete the process by working the 
 brush till it is dry ; by these means I have 
 always obtained the best results. Some use 
 after this, crocus and oil as a final surface 
 polish. I prefer, however, using only the 
 whiting. Last of all, cleanse the piece carefully 
 with warm water and soap, using a soft brush, 
 and it is ready for fitting in the mouth. 
 
 A full lower set can of course be made in 
 precisely similar fashion to an upper set. I 
 shall, therefore, now go on to treat of — 
 
 Partial cases (for the upper jaw) . The upper 
 and lower models with their articulations, we 
 shall take for granted are complete. The teeth 
 must then be in most cases fitted to the gum 
 very carefully, so that there may be no rubber 
 likely to show underneath, when the piece is 
 finished. If the bite is very close it may be 
 necessary to use plate teeth ; then unless the 
 pins are very long and strong, it will be wiser 
 to strengthen them by means of a strip of gold 
 soldered to them, varying the shape of the gold 
 
DENTAL MECHANICS 195 
 
 accordino^ to circumstances. For most cases the 
 forms sliown in Fis^s. 98 and 99 will answer best. 
 This gives plenty of room for rubber all round, 
 and holds very firmly. Another way is to 
 form a loop thus, Fig. 100, or as in Fig. 101, the 
 
 Fig. 98. Fig. 99. Fig. 100. Fig. 101. 
 
 ends being clubbed. It will be seen at once 
 how much they may be varied to suit the pecu- 
 liarities of the case. The teeth being fitted 
 into their places on the model, they may be 
 attached to the temporary plate made up ac- 
 cording to the instructions already given, but 
 altered in size according to the number of teeth 
 it is to carry, and whether it is to be kept up 
 by suction or by bands. If it is necessary to 
 use bands round some of the teeth to support 
 the case, gold clasps are the neatest, but I 
 consider vulcanite the least injurious. 
 
 In every artificial denture there is invariably 
 a certain amount of friction produced by the 
 movement of the plate in mastication, if gold 
 is used, the metal, being harder than the tooth, 
 wears it away ; if, on the other hand, vulcanite 
 
196 
 
 DENTAL MECHANICS 
 
 is used, that substance, being softer tlian the 
 tooth, is itself worn away instead ; and for 
 these reasons I should advise the use of vul- 
 canite bands, if possible, instead of gold clasps. 
 If vulcanite bands are necessary they will of 
 course be formed of wax on the model previous 
 to flashing ; if clasps of gold are thought desir- 
 able they had better be adjusted after fitting the 
 teeth, and may be formed thus : — A strip 
 (varying in width according to the length of 
 the tooth) of clasp gold, about No. 7 gauge, 
 
 Fig. 102. 
 
 Fig. 103. 
 
 A strip of plate 
 
 perforated and 
 
 soldered on. 
 
 For a canine tooth, three 
 
 strips soldered together at 
 
 one point, and then 
 
 diverged. 
 
 Fig. 104. 
 
 Fig. 105. 
 
 Fig. 106. 
 
 Clubbed strips 
 
 soldered on and 
 
 bent up at 
 
 ends. 
 
 Club-headed 
 pieces sol- 
 dered on. 
 
 Band drilled and 
 countersunk, the 
 lower edge rough- 
 ened and bent 
 outwards. 
 
DENTAL MECHANICS 197 
 
 must be bent up to fit tlie tooth well, after the 
 manner described in the section on gold work; 
 it must then be fitted up so as to have a firm 
 hold in the vulcanite. The annexed cuts show 
 various ways of doing this, according to the 
 space and thickness of rubber you have to sur- 
 round the clasp. 
 
 The teeth and bands having been properly 
 adjusted to the model, and to each other, the 
 case is ready for flashing ; one other thing 
 remains to be done, however, that is, to cut 
 down to half their length, the plaster teeth on 
 the model ; the object of this will be seen pre- 
 sently. The model and case are now sunk in 
 the lower portion of the flask (into which 
 plaster mixed to the consistence of cream has 
 already been poured). Instead of leaving the 
 teeth exposed, the plaster is carried over so that 
 only the inner surface of the teeth show (Fig. 
 107). This plan may also be adopted for a full 
 set of teeth, as seen in the drawing given. 
 
 By this method displacement of the teeth is 
 almost impossible, at the same time that any 
 accession of rubber in the wrong place (that is, 
 under the teeth) is also prevented. The rest 
 of the process is the same as that already de- 
 scribed for a full upper set. Only one caution 
 must be given, and that is, to well bevel the sides 
 
198 
 
 DENTAL MECHANICS 
 Fig. 107. 
 
 of the overlap of the teeth, so that the central 
 portion, especially the plug, may draw away 
 easily and without the risk of breaking. Partial 
 cases must be made of varying thickness 
 according to the nature of the piece, and may 
 sometimes be strengthened with strips of gold 
 wire flattened, running across any narrow or 
 weak part. 
 
 The strengthening of a vulcanite plate may 
 be advisable sometimes in either the upper or 
 under jaw. For the upper it generally occurs 
 when, from the thinness you desire to have the 
 plate or the conformation of the arch, there 
 occurs greater liability to fracture than usual, 
 from the increased strain on weak points. 
 
DENTAL MECHANICS 
 
 199 
 
 A strengtliener must be made by bending up a 
 strip of gold, one sixteenth of an inch wide, to 
 fit fairly well to the palate from side to side, 
 about opposite the second molars. This must 
 be pierced with holes along its borders. Now 
 take this strip and place it edgeways upon 
 another piece of plate, and trace the outline of 
 its concave surface. Draw another line one six- 
 teenth of an inch beyond this again, and cut up 
 the pattern indicated by the lines ; you will then 
 have two pieces of the annexed form (Fig. 108). 
 It is evident now that the convex edge of a will 
 
 Fig. 108. 
 
 Fig. 109. 
 
 fit on to the concave surface of b, and being 
 placed in the centre of b the two may be soldered 
 together. Now, if we look at them in section 
 
200 DENTAL MECHANICS 
 
 we have this view (Fig. 109), combining at once 
 the greatest strength with the greatest hghtness 
 and but small expenditure of material, while at 
 the same time we have only the thin edge of A 
 presented on the palate, supposing the work- 
 man should be so unfortunate as to file awaj 
 the rubber to such an extent as to expose it. 
 The size of the two plates of gold can of course 
 vary according to circumstances, but the prin- 
 ciple is the same. An identical plan can be 
 adopted for the lower jaw (letting the one plate 
 rest against the natural front teeth, if they are 
 present). By this method we can give to a vul- 
 canite case very great strength and stiffness, 
 without making it much heavier for the mouth. 
 When spiral springs are to be fitted to the set 
 you may even cut all the central portion of the 
 palate away, simply leaving a band of rubber 
 running across the back of the mouth, and 
 strengthened in this way. Lower pieces also 
 may be much reduced in bulk. If this plan is 
 adopted it will at once be seen how much 
 stronger it is than a piece of round wire flat- 
 tened, or even an ordinary gold plate strength- 
 ener. It is also applicable as a means of 
 increasing the strength of teeth, running out 
 alone, on a narrow strip of rubber between large 
 natural teeth. 
 
DENTAL MECHANICS 201 
 
 Repairing vulcanite plates is not very 
 satisfactory, as the second vulcanizing neces- 
 sarily renders tbe piece brittle and darker in 
 colour than it naturally should be. The plan 
 adopted in all cases is essentially the same, so 
 that o^eneral instructions will be sufficient. In 
 the event of either a fracture of the plate or a 
 tooth being broken off, cut out with a fine saw 
 all the impaired portion of rubber, having of 
 course first secured a model of the mouth. 
 Then cut dovetails into the rubber where union 
 is desired. If it be a lower piece and there is 
 plenty of substance, drill into the surface of the 
 dovetails to give the rubber firmer hold. Xow, 
 instead of filling in the gap around the tooth or 
 fracture with wax, use modelling clay, and you 
 will have an equally smooth surface, and when 
 it is vulcanized you will find the joining is 
 scarcely perceptible — a thing that is above all 
 others to be desired by those who take a proper 
 interest in the appearance of their work when 
 finished. AYhen sinking a repair in the flask 
 cover everything but the portion that will 
 require packing, and instead of flasking in the 
 lower portion, use the upper section, first 
 because it is deeper and prevents the risk of 
 the rubber being near the iron and so becoming 
 blackened ; and, secondly, because the top 
 
202 DENTAL MECHANICS 
 
 taking off it allows of easier removal of tlie plate 
 after vulcanization is completed. 
 
 If there be any discoloration after repairing 
 a piece, it may be removed to some extent, ac- 
 cording to Dr Richardson (' Mechanical Den- 
 tistry,' p. 42), by " moistening the surface with 
 dilute nitric acid for a short time, after which 
 the piece is thoroughly washed and then placed 
 for a few minutes in an alkaline solution, to 
 remove any remaining traces of acid," or 
 *' expose the piece to the rays of the sun in 
 alcohol for five or six hours." 
 
 To reset a vulcanite piece.— Make a false 
 model first, by soaping the rubber on the palatine 
 side, pouring in plaster and building up as for an 
 ordinary model ; then round the outside of the 
 plaster cast cut out four grooves horizontally 
 or make two depressions in front of a conical 
 form with a sculpter or knife ; soap or oil all 
 this surface, and the fronts of the teeth as well, 
 and pour over plaster tolerably stiff in substance, 
 so as not to run aboat easily ; bring this out 
 beyond the model, half an inch in thickness, 
 and let it extend upwards to a level with the 
 cutting edge of the teeth ; we then obtain 
 results shown in Fig. 110. These two portions 
 having been carefully separated may be again put 
 into place, the palate of the piece soaped, as well 
 
DENTAL MECHANICS 
 Fig. 110. 
 
 203 
 
 as tlie top edge of tlie outer casting, and plaster 
 poured over like a liooded bite. 
 
 Wlien these are divided and tlie piece to be 
 reset taken off the model, it will be seen that 
 we have all the dimensions of the old plate in 
 such a form as to be able to reproduce them 
 with the same teeth but fresh rubber, or if it is 
 for a duplicate case, with another set of teeth, 
 fitting into the same moulds. 
 
 Supposing, however, that the piece is simply to 
 be reset, by this plan we avoid the risk of break- 
 ing the teeth by taking them out of the old setting 
 of rubber when sunk in the flask, and if an 
 accident should by any chance occur, it is more 
 easily remedied. The castings being completed, 
 the teeth taken off the old plate and cleaned 
 
204 DENTAL MECHANICS 
 
 carefully, and tlie pins readjusted, they are 
 placed in their moulds in the outer casting, con- 
 nected together with wax, and the rest of the 
 plate filled in according to the space in the 
 moulds ; by this mode of procedure any altera- 
 tion may be made in a piece whilst at the same 
 time we retain exact models of the original 
 form. 
 
 From the various ways in which vulcanite can 
 be used it will at once suggest itself as a con- 
 venient material to reset ill-fitting gold plates, 
 when from a large amount of absorption of the 
 alveoli the denture can no lono^er be worn with 
 comfort. Several plans may be adopted in order 
 to ascertain the amount of fresh material that 
 it is required to add to the plate. For either 
 method first perforate the plate, to be refitted, 
 with a number of small holes (tooth pin size is 
 best), choosing for their situation, as far as 
 possible, the borders of the plate ; but in addi- 
 tion any spot that indicates a capability of 
 giving good retaining power to the rubber when 
 vulcanized; the most simple and at the same 
 time certain thing to do after this is to fill the 
 hollow portion of the gold plate with plaster of 
 Paris rather thicker than for an ordinary im- 
 pression, then introduce it into the mouth and 
 tell the patient to close the jaws, and see that 
 
DENTAL MECHANICS 205 
 
 the articulation is correct. When the plaster is 
 quite hard remove it, soap the surface and cast 
 in the lower part of a flask, as if it were an 
 ordinary impression, then trim ofi* the burrs of 
 plaster that have worked through the perfo- 
 rations, coat over any irregularities with wax, if 
 necessary, soap the whole and fill in the upper 
 part of the flask as for an ordinary case ; when 
 hard separate carefully; the gold plate and 
 teeth will now be found in all probability in the 
 upper part of the flask, separated from the 
 plaster impression; this latter must be prised 
 ofi', the holes in the plate cleaned of wax or 
 plaster with boiling water, and packing may then 
 be proceeded with in the usual manner. If 
 there are tube teeth on the case they must be 
 taken ofi* previously to the sinking of the plate, 
 and fixed on as^ain afterwards with floss silk and 
 mastic ; if only backed teeth are on the case it 
 need give no extra trouble of this sort. 
 
 Another plan consists of taking a model and 
 articulation, then lining the plate with wax or 
 gutta percha and pressing on the model instead 
 of in the mouth to obtain indications of the 
 parts to be refitted ; it will at once be seen, 
 however, that the first-mentioned method is 
 infinitely better if carefully carried out. 
 
 The impression having been obtained in the 
 
206 DENTAL MECHANICS 
 
 plastic material, the remaining portion of the 
 process is of course identical with the one first 
 described. 
 
 A third plan is to place the plate upon the 
 model and seal the edges where they are not 
 close to the model, to prevent the ingress of 
 plaster. The model with the piece upon it is 
 now sunk in the flask, keeping the gold case quite 
 clear of plaster, so that it will readily leave the 
 model and be included in the other half of the 
 flask. Into the non-fitting parts of the plate 
 rubber is placed and vulcanized, having pre- 
 viously prepared the plate to hold it, either by 
 soldering small pieces thereto, or by roughening 
 the plate with a pointed instrument. By this 
 mode there is no trouble required in modelling 
 up the plate with wax, &c. ; but where the whole 
 surface of a plate has to be covered with vul- 
 canite, and the articulation of the piece conse- 
 quently altered, either of the methods previously 
 described will be found more applicable. 
 
 When the rubber is vulcanized to gold and 
 it is necessary to bevel off" the plate at any part 
 to make it continuous with the rubber, do not 
 file the plate, but grind at the lathe with a very 
 fine wheel. In this way you will avoid the 
 danger of turning up the thin edge of gold 
 that your grinding has produced. With the 
 
DENTAL MECHANICS 207 
 
 file great trouble sometimes occurs in getting 
 a smooth surface wliere the gold and rubber 
 join. 
 
 For lower and partial cases the same rules 
 will of course apply as for an upper set. 
 
 To improve the colour of vulcanized rubber 
 it maybe placed in a glass covered vessel con- 
 taining alcohol, and set in the sun for six or 
 eight hours ; the longer the time (in reason) the 
 better the colour will be. 
 
208 DENTAL MECHANICS 
 
 SECTION XI 
 
 THE CELLULOID BASE 
 
 The Albany Dental Plate Company in 1871 
 took out patents and sent over specimens of a 
 new base for artificial teetli. The composition 
 is said to consist of solid collodion, prepared in 
 a peculiar manner. It is really gun-cotton and 
 camphor, and from the specification we learn 
 that " in the manufacture of collodion for these 
 dental plates the inventors prefer to use at 
 least fifty parts by weight of gum camphor to 
 one hundred parts of soluble cotton (a greater 
 proportion of camphor may be used), whereby 
 the product is rendered more plastic than when 
 a less quantity is employed. The collodion 
 thus produced is made into plates of suitable 
 thickness, which are preferably formed into 
 shapes approximating to those of finished 
 dental plates by pressure in heated moulds. 
 The plates thus formed are now thoroughly dried 
 by placing them in a drying-room heated to a 
 temperature which should not exceed 180° Fah., 
 
DENTAL MECHANICS 209 
 
 150° to 180° being the temperature found best 
 adapted for expelling the camphor solvent. A 
 temperature much higher than 200° will expand 
 the material, and render it porous and brittle. 
 The plates when properly dried, although freed 
 from liability of shrinkage, still retain the 
 quality which enables them to become plastic 
 under a proper degree of heat, and may be 
 readily moulded into any desired shape with- 
 out subsequently shrinking to any injurious 
 extent." 
 
 There are two varieties, — the coloured, which 
 is of a gum-like pink; and the uncoloured, 
 which is semi-transparent, and of an amber- 
 yellow. 
 
 We will first take the properties of the two, 
 and then their application to dental purposes. 
 
 Both are in their uncorked state stronger 
 and lighter than any dental rubber. The un- 
 coloured celluloid is, however, stronger and 
 lighter than the pink, but the amber-coloured 
 base is more liable to warp than the pink. 
 
 In opposition to the statement contained in 
 the circular sent out, I must say that in my ex- 
 perience both kinds are affected by the acids of 
 the mouth : the uncoloured, instead of remain- 
 ing semi-transparent, assumes an opaque 
 appearance, becomes much harder, and is dis- 
 
 14 
 
210 DENTAL MECHANICS 
 
 coloured by blood ; wliile the pink, after a few 
 weeks' wear, lias a white granulated look over 
 the surface. These changes, however, do not 
 affect the durability of the piece. 
 
 It has a strong smell, and a slight taste of 
 camphor, which remains for five or six days ; it 
 is not, however, as a rule, objected to by 
 patients, and to many is not even unpleasant. 
 
 To remove the smell of the camphor, if it 
 should be found objectionable, the piece maybe 
 placed for four or five hours in a solution con- 
 sisting of sulphuric acid one part, and water 
 two parts, a larger proportion of acid affecting 
 the piece injuriously. This suggestion I give 
 on the authority of the inventors. 
 
 With CMorMherine it is converted into a soft 
 gelatinous mass, but is not dissolved ; and as 
 the chlorgetherine evaporates, it again becomes 
 hard. With Sulphuric ether the surf aces of two 
 pieces may be softened, and, being kept in con- 
 tact for three or four hours, will become as 
 one. c. Pieces cannot be softened so as to unite 
 together by dry heat. 
 
 The older the plates are when received from 
 the depots the stronger they appear, and the 
 less liable to shrink ; this, I think, is owing to 
 the evaporation of a portion of the camphor 
 which they contain. All parts brought into 
 
DENTAL MECHANICS 211 
 
 contact with metal of any kind become white 
 and opaque more quickly than the rest of the 
 piece. 
 
 Pieces may be softened and allowed to 
 harden any reasonable number of times with- 
 out apparent deterioration of texture. The 
 temperature of the mouth does not affect it 
 injuriously, but the heat of boiling water will 
 soften it. Boiled for ten hours in water it 
 becomes deprived of a large portion of its 
 camphor, and remains a white friable mass. 
 
 As to the mode of using it, I do not think 
 we have arrived at anything like perfection, 
 nor even do we yet know the simplest way of 
 applying it. 
 
 The plan I at present adopt is, after sinking 
 the pieces made up on wax in the flask, as if 
 for vulcanite, to choose the base of an approxi- 
 mate size, cutting away any portions that may 
 appear in excess, and then softening the cellu- 
 loid sufficiently in boiling fluid to enable it to 
 be pressed into shape in the flask with the 
 fingers ; the two parts of the flask can be 
 brought more closely together at the begin- 
 ning, and there is less risk of injuring the 
 plaster castings. When the flask is nearly 
 closed I open it, and cut out gutters for the 
 excess that may be present. This plan insures 
 
212 
 
 DENTAL MECHANICS 
 
 plenty of the base being pressed well round the 
 teeth, and into any overlaps that the piece may 
 have. 
 
 Grutters having been freely cut, the flask may 
 be completely closed, after the heat has been 
 increased sufficiently, and then the whole taken 
 out of the tank and placed in cold water, where 
 it should remain for twenty minutes, or it may 
 remain in the tank for ten minutes, thus 
 cooking it more completely. 
 
 The best flask, clamp, and tank for the pur- 
 pose are those recommended and sold at the 
 depots, as being made by White, of Philadelphia 
 (Fig. Ill) ; the principal feature and advantage 
 
 Tig. 111. 
 
DENTAL MECHANICS 213 
 
 being that the flask can be gradually closed 
 while it is in the boiling fluid, which cannot be 
 done in the ordinary way. 
 
 As to the fluid in which the piece should be 
 softened, I think oil the best ; it is not so in- 
 jurious to the celluloid as I consider water to 
 be, and it toughens the plates. Dry heat I 
 believe to be unsatisfactory. The plaster for 
 the flasks, if mixed tolerably stifl", is quite strong 
 enough without the addition of any substance, 
 such as gum-arabic ; in fact, in using water alone 
 the plaster becomes so hard as to be difficult of re- 
 moval from the flask. To prevent the base ad- 
 hering, the castings may be painted over with oil, 
 or dusted over with French chalk. The piece can 
 be finished up in the ordinary way with scraper, 
 file, and glass-paper, or, better than glass-paper, 
 at the lathe with a wet hard brush, plenty of 
 water, and coarse pumice, afterwards whiting 
 and oil, and finally a dry felt cone with dry 
 whiting, or, according to White's circular, the 
 dry cone alone. It may be repaired in the same 
 way as vulcanite, by dovetailing ; but I do not 
 think the pieces, as a rule, become thoroughly 
 welded ; this, I believe, can only be perfectly 
 done by means of a solvent. By immersion in 
 boiling fluid any part of it can be altered in 
 form, in the same manner as vulcanite, and 
 
214 DENTAL MECHANICS 
 
 sliould afterwards be put into cold water to 
 thorouglily re-harden. 
 
 At present I liave no great faith in its use 
 for repairing vulcanite — there is simply me- 
 chanical union ; and, as the two substances are 
 of such very different density, they do not 
 hold very firmly even when thoroughly dove- 
 tailed. 
 
 After a series of experiments, carefully con- 
 ducted, with the celluloid base, I have obtained 
 the following results : — 
 
 Taking first the essential oils : — Two grains 
 of the base reduced by filing to a fine state of 
 division, were placed in a test-tube containing 
 Oil of Oassia, and the result was a transparent 
 gelatinous mass, insoluble with heat. With Oil 
 of Cloves we found the same action ; with Oil 
 of Rosemary a slightly gelatinous condition was 
 seen to be present, but it was not soluble ; 
 and with Oil of Origanum it was not acted upon 
 at all. 
 
 In Benzole, rectified spirits of ivine,pure Ether, 
 and Potassium Naphtha, it was quite insoluble. 
 It is but very slightly soluble in Chloroform, 
 and it is not acted upon at all by Thymol in any 
 of its forms. 
 
 By the action of Creosote, when heated, it 
 shows a mass in a gelatinous form suspended in 
 
DENTAL MECHANICS 215 
 
 tlie liquid ; and in Carbolic acid we have the same 
 conditions, only more strongly marked. 
 
 If placed in a vessel containing any of the 
 fatty oils, and heated up to their boiling-point, 
 it is completely decomposed, leaving only a 
 residue of carbon ; the same thing happens if 
 heated alone in a test-tube, the camphor being 
 driven off, and leaving carbon behind. In 
 fact, the application of great heat (especially 
 dry heat) causes the camphor to be driven off, 
 and tends to the rapid disintegration of the 
 compound. ^ 
 
 I have brought forward the results of these 
 experiments, because I think that the celluloid 
 base may be prepared in such a way as to be 
 most useful for a temporary stopping ; it is 
 therefore important that we should have some 
 knowledge of the action of those preparations 
 with which it might be brought into contact in 
 a tooth, as, for instance, Carbolic acid, Thjmol, 
 and others. 
 
 From the comparative facility with which 
 the celluloid can be prepared, and the ease 
 with which it can be produced in any colour, 
 I have fair hope we may obtain some temporary 
 stoppings of great value for many cases. 
 This, however, is a matter for future considera- 
 tion. 
 
216 DENTAL MECHANICS 
 
 I consider the base a useful introduction, but 
 not one of great valae at present ; still, it is 
 so good that I believe it is capable and worthy 
 of improvement. 
 
 For artificial dentures it is comfortable and 
 light to wear, the pink is natural in appearance, 
 and it adapts itself well to the mouth ; how it 
 will last, time alone can show. At present it 
 is most available for pieces intended only for 
 temporary wear, from the fact, as an American 
 writer amusingly puts it, that the teeth have a 
 tendency to shed. 
 
DENTAL MECHANICS 21 
 
 SECTIOX XII 
 
 THE TPvEATMENT OF DEFOEMITIES OF THE MOUTH 
 
 The Dental Surgeon is occasionally called 
 upon to treat certain deformities of the mouth 
 quite distinct from those malformations that 
 may arise from irregularity of the teeth. These 
 I have fully entered into in my work on that 
 subject published by the Messrs Churchill. In 
 the following section I shall therefore condense 
 what I have already written upon the subject in 
 the volume referred to. 
 
 Deformities of the mouth arise from three 
 distinct causes, — congenital deficiency, as in cleft 
 palate ; perforation and lesion of the hard or 
 soft palate, and sometimes both, from phagge- 
 denic or syphilitic ulceration ; or in the third 
 place from mechanical injury, such as gunshot 
 wounds, or injury arising from any other form 
 of violence. 
 
 We will consider first the treatment of 
 Congenital Cleft Palate. 
 
 Taking the Impression.— The materials gene- 
 rally used for taking impressions of the mouth 
 
218 DENTAL MECHANICS 
 
 are by no means satisfactory, in taking impres- 
 sions of parts that are so easily displaced as tlie 
 soft palate, for none of tliem can be used, under 
 tlie most favorable circumstances, without 
 applying pressure sufficient to render the im- 
 pression and model incorrect. 
 
 It being, then, necessary to introduce some 
 preparation into the mouth in such a state that 
 it will not move the most delicate fold of 
 mucous membrane, while in a short time it shall 
 become so hard as to admit of removal without 
 any alteration of form, I recommend plaster of 
 Paris. 
 
 In most cases the soft palate will be found 
 too sensitive at first to admit of a full impres- 
 sion being taken at once, or even of the holding 
 of the impression plate in position sufficiently 
 long to admit of a model being taken. Two 
 courses are open to the operator to overcome 
 this difficulty : one is to take an impression 
 first of only the front of the mouth and cleft 
 and then on successive occasions gradually 
 extend it backwards, till at last you are 
 enabled to get a good impression of the whole 
 of the parts, extending outwards to the alveolar 
 ridge, upwards to the remains of the vomer, 
 and backwards to the posterior wall of the 
 pharynx and pillars of the fauces. Another 
 
DENTAL MECHANICS 
 
 219 
 
 method is to paint the parts with a solution of 
 bromide of ammonia or tannin and glycerine, 
 5i to 3iv applied with a camel' s-hair brush — of 
 the form shown in Figr. 112 * the brush actinof 
 almost as beneficially as the preparation used. 
 
 Fig. 112. 
 
 One or other of these two plans must be 
 adopted before any hope can be entertained of 
 getting a good impression. When the parts 
 are rendered sufficiently insensible to the pre- 
 sence of a foreign body, an impression-tray 
 must be carefully prepared, so as to fit in front 
 closely to the teeth, and at the back part leave 
 a space about the eighth of an inch in extent 
 from its surface to the corresponding sm^face of 
 the soft palate. This does away with the 
 necessity of an excess of plaster, and the 
 consequent risk of any portion falling into the 
 
 * Made by Meyer and Metzler, of Great Portland Street. 
 
220 DENTAL MECHANICS 
 
 throat or upon tlie base of the tongue, and 
 thus produce such irritation that the utmost 
 self-control on the part of the patient will 
 scarcely be able to overcome it. 
 
 I have found that a good plan is to use a 
 tray of the form of a common spoon, that I have 
 had made for me by the Messrs Ash and Sons, 
 of Broad Street. These being of pewter, can 
 be bent about to the desired form and then 
 covering with sheet gutta percha, which is 
 placed on the tray and put into the mouth 
 while warm. In this manner you get the out- 
 line of the teeth, which will act as a guide in 
 introducing the tray with the plaster on it. 
 
 For an ordinary impression of cleft palate, 
 where there is plenty of room to pass the 
 plaster in and out of the mouth, the plate being 
 prepared for use, the next step is the mixing of 
 the plaster; and here several considerations 
 must be taken into account — (1) the dryness 
 of the plaster, (2) its strength, and (3) the time 
 it takes to set, which will depend partly on its 
 freshness, and partly on the temperature of the 
 atmosphere, as well as the water with which it 
 is mixed. 
 
 The best plan is to have the water with just 
 the chill off, and then add salt in the proportion 
 of as much as will lie upon a sixpence to half a 
 
DENTAL MECHANICS 221 
 
 pint of water. If jou wisli tlie plaster to set 
 quicker than under these circumstances it would 
 do, add to it before mixing a small portion of 
 rouge. This will make it set so quickly, and so 
 strongly, that increased care and watchfulness 
 will be required with regard to the proper time 
 for removal from the mouth. Everything being 
 ready, the plaster is mixed in the ordinary 
 manner to the consistence of thick cream, care 
 of course being taken to break up all lumps in 
 it during mixing ; a sufficient quantity is then 
 placed in or upon the impression-plate, and the 
 whole steadily introduced into the mouth and 
 held firmly in its place, the precaution being 
 adopted at the moment of putting the plate in 
 position to incline the patient's head forward, 
 so as not only to get a good overlap above the 
 anterior margin of the cleft, but also to lessen 
 the liability of any plaster running down back- 
 wards and causing retching. 
 
 When the remains of the unused plaster in 
 the bowl will break asunder and leave a clean, 
 sharp fracture, then it is time to remove the 
 impression from the mouth. If at the first it 
 cannot l3e disengaged easily, then at once and 
 without any hesitation use sufficient force to 
 detach it, bearing in mind that at such a time 
 every second's delay increases the difficulty. 
 
222 DENTAL MECHANICS 
 
 Under ordinary circumstances it will break away 
 in the line of the cleft. This need occasion no 
 alarm : only desire your patient to sit perfectly 
 still and keep the mouth well open ; you can 
 then without any anxiety or hurry push the part 
 which remains above the margin of the palate 
 carefully backwards to the widest part of the 
 opening, and, firmly seizing it with a pair of long 
 tweezers (as shown in Fig 113), withdraw it. 
 
 EiG. 113. 
 
 The entire lengtli of these tweezers is eleven inches with 
 
 the handle.* 
 
 The fractured parts, when put carefully 
 together, will be found quite as efficient for use 
 as if no breakage had taken place, especially if, 
 instead of using resin and wax cement, they are 
 united with liquid silex, as recommended in the 
 ' British Journal of Dental Science ' for June, 
 1868, t by which means any increase of bulk is 
 avoided. 
 
 * Made by Messrs Ash and Sons, Broad Street, Golden 
 Square, 
 t "Liquid SHes." By Oakley Coles. 
 
DENTAL MECHANICS 
 
 223 
 
 The impression, being thus perfect, must be 
 carefully washed over with a solution of soap 
 (brown Windsor is the best for the pm^pose), 
 and the model made in three portions, as shown 
 in the accompanying engraving (Fig. 114). We 
 
 Fig. 114. 
 
 now return to the more commonplace operations 
 of the work-room, and further minute parti- 
 culars would only become tedious and unneces- 
 sary 
 
 See section on Modellino-. 
 
224 DENTAL MECHANICS 
 
 The model being ready for use, the artificial 
 velum must be set up in gutta percha, haying 
 the precise shape which it will possess in its 
 finished form. Here instruction is useless, as 
 the formation of the palate-piece will depend 
 entirely on the characteristics of the case and 
 the ingenuity of the operator. The gutta 
 percha should be of the best description, and 
 the model prepared with soapstone, to prevent 
 any adhesion to its surface. When this is 
 worked up to a satisfactory state, the casting of 
 the plaster moulds can be proceeded with. For 
 an ordinary case the best form is that shown in 
 the engraving (Fig. 115). These, however, 
 admit of very many modifications, according to 
 the shape of the velum, in preparation. The 
 plaster castings, when complete, must be du- 
 phcated in type metal, the best metal obtainable 
 and the finest casting-sand only being used. 
 Great care must be taken here, as an imperfec- 
 tion in the metallic moulds will be communi- 
 cated to the surface of the rubber during 
 vulcanizing, and can only be remedied by 
 clipping and paring, which gives a very un- 
 sightly appearance to the finished work. When 
 the castings are complete, and the surfaces well 
 polished with pumice powder and water by 
 means of a stick of dog-wood, they should fit 
 
Fig. 115. 
 
DENTAL MECHANICS 227 
 
 together accurately ; if they do not, there is no 
 alternative but to commence de novo till you 
 arrive at a satisfactory result. 
 
 The accompanying engraving (Fig. 115) shovrs 
 the castings separated, also the metallic pin 
 fixed in the base for producing the hole in the 
 velum by which it is attached to the hard rubber 
 front piece. Any error with this will be found 
 to upset the entire arrangement. The greatest 
 care must therefore be used in getting it into 
 a good position, according to the shape of the 
 cleft and mouth. The moulds havinsf been well 
 soaped to prevent adhesion, and made warm — 
 not hot — the next step is to pack them with 
 elastic rubber. This is very easily accom- 
 phshed : the two side-pieces, being adjusted to 
 the base, are kept firmly in position by an iron 
 clamp, and the rubber packed in from above. 
 When there appears sufficient, the top is put 
 on, and the whole screwed tightly together, 
 being put on a hot plate for a few minutes to 
 soften the rubber. The casts are then taken 
 apart, any excess removed, or any deficiency 
 filled up. They are again screwed up and 
 fitted in an iron framework, as shown in Fig. 116, 
 with wedges to secure them, and put into the 
 vulcanizer. In reference to the rubber to be 
 used, there can be no question that which is 
 
228 
 
 DENTAL MECHANICS 
 Fig. 116. 
 
 prepared bj Messrs AsIl and Sons is by far the 
 best, both as regards quality of materials and 
 wear. 
 
 The time for vulcanizing this description of 
 rubber is six hours ; that is to say — 
 
 2 hours at 240°. 
 2 hours at 250°. 
 2 hours at 260°. 
 
 An artificial velum will then be produced of the 
 greatest elasticity and power of resistance to 
 the acids of the mouth. It has occasionally 
 been a subject of inquiry as to the description 
 of vulcanizer I use ; I may therefore state that 
 I prefer Eutterford's Single-screw vulcanizer. 
 
 The adjustment of a front piece to keep the 
 velum in the cleft will depend on the state of 
 the teeth. If they are all perfect, a simple 
 
DENTAL MECHANICS 229 
 
 suction-plate is all tliat is necessary. If any 
 teeth should be wanting, artificial ones to 
 supply their place should be mounted on the 
 front piece, as in an ordinary set of teeth ; and 
 if there be any deformity of the hard palate, as 
 in most cases there is when associated with 
 harelip, it will have to be restored and made 
 as symmetrical as possible by additions to the 
 hard rubber. When, however, the anterior 
 jDortion of the mouth is perfect, the palate 
 should be made as thin as possible, and not 
 extend further back than the second bicuspids. 
 
 The pin for connecting it with the elastic 
 velum should be of soft platina mre, larger at 
 the top so as to prevent it coming out of the 
 hole in the artificial palate easily ; that portion 
 which goes into the hard rubber front piece 
 may be either notched and roughened by the 
 file or have a small piece of plate soldered to 
 it at a right angle, so as to hold it firmly in 
 place. 
 
 The following cases will give examples of the 
 various forms of instruments that may be used 
 to remedy a cleft palate according to its peculiar 
 conformation. 
 
 The object has been in every instance to 
 close, by means of an artificial palate, the 
 defect in the mouth, and at the same time to 
 
230 
 
 DENTAL MECHANICS 
 
 offer eyery possible chance to a natural effort 
 to reduce the size of the opening, and not 
 under any circumstances to enlarge the cleft. 
 
 John T — , get. 4. — Brought to me July, 
 1868, with fissure of the soft palate and partly 
 of the hard jDalate also. After some little 
 trouble an impression was obtained, and an 
 artificial palate fitted in as shown in the 
 accompanying woodcut, Fig. 117. 
 
 Fig. 117. 
 
 The object and result of fitting in an artificial 
 palate at this early age is to reduce the size of 
 
DENTAL MECHANICS 231 
 
 the cleft, and so ultimately render the voice 
 less indistinct than it would be if allowed to go 
 on untreated. 
 
 When the cleft is left open, every act of 
 swallowing, by the pressure exerted against the 
 margins of the divided palate, tends to more 
 widely separate them ; but if an elastic flap 
 covers the opening, the pressure tends to 
 flatten out the bundles of muscular fibres on 
 each side and push them towards each othei*. 
 The instrument in the present case has been in 
 use for nearly two years, and the results are 
 most satisfactory. If it be urged that surgical 
 treatment is ultimately a more satisfactory 
 proceeding, this preparation only gives the 
 surgeon a greater chance of success, and for 
 this reason alone would be wise and justifiable 
 to adopt. 
 
 E. A — , ^t. 9 — , was brought to me October, 
 1868, with cleft of soft and portion of hard 
 palate ; the speech was very bad, and the child 
 had a vacant unintelligent stare ; with slight 
 deafness in both ears. 
 
 The margins of the cleft were thick and 
 widely separated ; under no circumstances did 
 they touch the posterior wall of the pharynx. 
 I deemed this a most favorable opportunity 
 for trying the utmost that could be done in the 
 
232 DENTAL MECHANICS 
 
 way of approximating tlie free borders of tlie 
 cleft, and also spreading out the muscular 
 fibres towards the posterior part of the 
 pharynx. The front part of the arch of the 
 palate was very deep, the teeth good and 
 perfect. 
 
 October 28th I fitted in a hard rubber palate 
 plate, just reaching to the apex of the fissure. 
 Strange to say, and greatly to my astonishment, 
 the voice was immediately improved. This 
 was worn for six or seven months ; then I 
 extended the posterior border of the plate over 
 about one fourth of the cleft, but without 
 putting any overlap. The child had got such 
 power of suction in the front portion of it that 
 this was readily kept in place ; every two or 
 three months I increased this flap a little, until 
 at the present time the cleft is completely 
 closed by the artificial palate. The front piece 
 fits quite easily, and is the original plate made 
 nearly two years ago, simply having the elastic 
 rubber added to it from time to time. There is 
 no overlap to any portion of the cleft, and the 
 plate depends absolutely on suction for its 
 support, not even fitting tightly to the necks of 
 the teeth. When the velum is taken out it is 
 most interesting to watch the movements of 
 the sides of the cleft, the muscular fibres of 
 
DENTAL MECHANICS 
 
 233 
 
 wliich are flattened and spread out by the 
 pressure from below of the elastic rubber. 
 They can be approximated so as to come into 
 actual contact, and the apices of the bifid uvula 
 rest against the back of the pharynx as in a 
 mouth without any deformity. 
 
 Fig. 118 
 
 Fig. 118. — Shows the size of the cleft when at 
 rest. 
 
 Fig. 119. — Shows the relative position of the 
 parts when thej are thrown forward. 
 
 Fig. 120. — Shows the ''bulging out" and 
 approximation of them towards each other. It 
 is hardly necessary to add, that the speech has 
 considerably improved during the last year and 
 three quarters, so that the child can go to 
 school and mingle with other children without 
 any difficulty. 
 
234 
 
 DENTAL MECHANICS 
 
 W. S — J a3t. 17. — Brouglit to me Marcli, 
 1869, with cleft of both hard and soft palate, 
 complicated with fissure of the alveolus on the 
 left side. 
 
 The appearance of the mouth, when fitted 
 with an artificial velum, and the central and 
 lateral incisor teeth, that had not been developed. 
 
 is shown in Fig. 121. 
 
 Fig. 121. 
 
 By a mistake in drawing this upon the wood 
 the cleft in the alveolus shows on the right side, 
 
DENTAL MECHANICS 235 
 
 whereas it was really on the left, as most of 
 these are. 
 
 It will be seen that I have altered the manner 
 in which the hard and soft rubber portions are 
 united together, bj giving a continuous flush 
 surface to them, instead of allowing the hard 
 rubber to present a prominent ridge in the 
 centre of the palate. Up to the present time 
 this case has gone on exceedingly satisfactorily. 
 
 Miss F — , 8et. 17. — Seen by me June, 1868, 
 fair complexion, nervous temperament. There 
 was not much sensitiveness as regards the de- 
 formity, and unfortunately no ear for musical 
 sounds, though the young lady played several 
 instruments with ordinary accuracy and ability. 
 There was also slight deafness, probably arising 
 from inflammation of the mucous membrane 
 around the Eustachian tubes, the inflammation 
 having arisen from the great exposure of the 
 parts to every change of temperature in con- 
 sequence of the opening in the palate. The 
 mouth when presented for treatment had the 
 appearance shown in Fig. 122. 
 
 A velum was made which restored the uvula 
 in the lower flap, and in upper flap reproduced 
 the septum of the interior nares where it was 
 absent, also the posterior nares with its two 
 openings. 
 
236 
 
 Fig. 122. 
 
 DENTAL MECHANICS 
 
 Fig. 123. 
 
 The artificial velum and front piece attached by means of the 
 
 platina pin. 
 
DENTAL MECHANICS 
 
 237 
 
 By these means the mouth, nose, and upper 
 part of the pharynx were restored to their 
 natural condition, and much satisfaction was 
 afforded by the improvement in a very short 
 
 Fig. 124. 
 
 Tlie mouth, as artificially restored. 
 
 time, not only in the facihty with which the 
 patient could make herself understood, but also 
 
238 
 
 DENTAL MECHANICS 
 
 in the tone of the voice, wMcli was unques- 
 tionably owing to tlie alterations that had been 
 produced in the form of the superior part of the 
 pharynx. 
 
 D. W — 5 aet. 38. — Consulted me in June, 
 1869, in reference to a cleft in his mouth, ex- 
 tending through the hard and soft palate and 
 alveolar ridge ; there was an overlap on one 
 side of the cleft only, the opposite margin 
 articulating with the vomer. 
 
 An instrument was made of the form shown 
 in Figs. 125 and 126. The drawings illustrate 
 
 Fig. 125. 
 
 Fig. 126. 
 
DENTAL MECHANICS 239 
 
 the manner in whicli the two parts are united, 
 so as to present a smooth surface in the palate 
 — a point of very great importance, where, 
 under the most favorable circumstances, there 
 is great difficulty in articulating with clearness. 
 In this case it will be seen, as in the previous 
 ones, the artificial velum is held up by the over- 
 lap, and not by any attachments round the 
 teeth. 
 
 W. H— , ^t. 68.— Cleft of hard and soft 
 palate, the harelip having been treated early in 
 life ; both the upper and lower jaws were with- 
 out teeth. The appearance of the upper jaw, 
 with the cleft, is shown in Fig. 127. A lower 
 set of artificial teeth was beins^ worn at the 
 time ; and I was desired to close the cleft 
 without producing any irritation in the nasal 
 cavity. I therefore made an ordinary full upper 
 set of teeth, and continued backwards from its 
 posterior border an artificial velum of elastic 
 rubber, simply covering the cleft without any 
 overlap. The form was, however, so simple 
 that I think it unnecessary to give a drawing 
 of it. The upper piece was connected with the 
 lower by means of sph^al springs, and fulfilled 
 the special object it was made for in a most 
 satisfactory manner, the patient having re- 
 covered and remained well ever since. 
 
240 
 
 DENTAL MECHANICS 
 Fig. 127. 
 
 Miss W — 5 set 19. — Brought to me March, 
 1869, suffering from thickness of speech, and 
 inability to give the letters M, 'N, B, P, &c., 
 with clearness. The young lady had suffered 
 from enlarged tonsils, and had improved in 
 utterance and general health since they had 
 been removed, but her friends had still great 
 difficulty in understanding her when reading ; 
 
DENTAL MECHANICS 
 
 241 
 
 and wlien slie suffered from cold, even during 
 ordinary conversation, slie found a difficulty in 
 making herself understood. The roof of the 
 mouth was very high, and the dental arch much 
 contracted. It was not thought desirable that 
 anything should be done to remedy the contrac- 
 tion of the circle of the teeth, but an artificial 
 palate was made to reduce the roof of the mouth 
 to its normal depth. 
 
 Fig. 128 shows in section the peculiarity in 
 
 Fig. 128. 
 
 the shape of the palate (a, a), and at the same 
 time shows the manner in which it was restored 
 by means of a hard rubber plate (b). Within 
 three weeks the speech was much clearer, and 
 the voice more asrreeable in sound. At the 
 present time, while the palate is worn, both 
 voice and speech are almost perfect. 
 
 16 
 
242 DENTAL MECHANICS 
 
 The construction of an instrument for this 
 purpose is so simple that it is not necessary to 
 say more than that the impression haying been 
 taken in plaster of Paris, the palate was restored 
 with wax to the proper shape, and the model 
 put in the flask and packed with rubber in the 
 usual way. After vulcanizing, it was finished 
 off very carefully, so as to give a thin edge to 
 the borders, and not offer any obstruction to the 
 action of the tongue. The portion coming in 
 contact with the palate should be left unpolished, 
 and, in fact, untouched, beyond washing off the 
 plaster, in order that better suction may be ob- 
 tained when it is fitted in the mouth. 
 
 Miss M. R — , get. 12. — -Brought to me June, 
 1869, with elongated palate and projecting 
 incisor teeth. The history of the case showed 
 most unmistakeably that the deformity arose 
 from sucking the thumb during infancy and 
 childhood ; and the evidence of the mother — a 
 lady of great intelligence — confirmed this view. 
 She said, when she had severe pain herself, she 
 was in the habit of sucking her thumb as a 
 diversion from the suffering, and her three 
 female children had got into a similar custom, 
 without any occasion but that of imitation. The 
 deformity was not hereditary, as both father 
 and mother had well-formed dental arches, and 
 
DENTAL MECHANICS 243 
 
 rather flat ttiaii deep palates. I extracted the 
 first bicuspid on each side of the upper jaw, and 
 made a vulcanite plate capping the side teeth, 
 and having a broad band of elastic rubber, 
 vulcanized with it, and passing in front of the 
 incisors and canines, these teeth having been 
 first reduced in the front, in order that suflBcient 
 pressure might be brought to bear upon them. 
 In two months the teeth were brought into a 
 fair position, considering the severity of the 
 case. The projection of the lip was entirely 
 reduced, but the teeth had an appearance — that 
 is not uncommon in these cases — of being too 
 long. The child will probably, however, grow 
 out of this in a few years, as the whole of the 
 face increases in size. 
 
 Syphilitic perforations of the palate are 
 generally in the median line, though not 
 always, and are more frequently of an oval 
 than round shape, having their long diameter 
 from back to front. There is not simply a 
 loss of substance clearly defined, but the hole 
 is bevelled olSf at the expense of its palatine 
 surface, thus giving it a funnel-shaped ap- 
 pearance. This condition is usually found in 
 perforations of the anterior third of the hard 
 palate. I have never seen anything like it in 
 the more posterior positions, or in the soft 
 
244 DENTAL MECHANICS 
 
 palate. Where there is simply a hole through" 
 the soft palate, there is generally, and I have 
 as a rule found, considerable induration and 
 thickening of the parts. 
 
 When the ulceration has gone on to such an 
 extent as to produce cleft of the palate, there are 
 often also present strong cicatrices, drawing the 
 cleft widely apart, sometimes in a symmetrical 
 position, and occasionally to one side of the 
 pharynx. In some cases I have seen the uvula 
 adherent to the back of the pharynx, or drawn 
 down to one side, and almost touching the 
 pillars of the fauces ; while in others it has been 
 strained forwards and downwards and attached 
 by strong bands of flesh to the sides of the base 
 of the tongue. I have seen, but only rarely, cleft 
 of the palate with but small loss of substance, 
 so that the two halves hung down into the 
 pharynx, and occasionally caused great irri- 
 tation from coming into contact with the epi- 
 glottis, and occasionally entire loss of the soft 
 palate. In the condition of palate I am now 
 describing examination with the rhinoscope will 
 generally show considerable, if not entire de- 
 struction, of the opening of the posterior nares, 
 or, speaking more correctly, the partition of the 
 naso-pharyngeal cavities. The septum will 
 be found much reduced in depth, and the whole 
 
DENTAL MECHANICS 245 
 
 of tlie upper portion of the space furnishing 
 many points of resemblance to congenital cleft- 
 palate. 
 
 Above the margin of the cleft, and springing 
 out from the sides of the pharynx, there are 
 frequently seen large nodulated masses of flesh ; 
 having sometimes the appearance of polypi, and 
 not unlikely to be mistaken for them. They 
 are, however, simply syphilitic outgrowths, and, 
 once carefully examined, easily recognised again 
 by.their hardness to the touch and general con- 
 sistency. 
 
 Judging from the cases I have treated, per- 
 foration of the soft palate is more frequent than 
 that of the hard, while cleft of both hard and 
 soft is more frequent than either. 
 
 It is well to mention that, occasion alty, after 
 the palate has been restored to such a state as 
 to enable the patient to speak distinctly as to 
 articulation, still the voice has an exceedino-ly 
 disagreeable sound. On examining the throat 
 with the laryngoscope, it will probably be found 
 that this arises from some syphilitic afl'ection of 
 the larynx, such as ulceration of the epiglottis 
 or of one or both of the vocal cords, or adhesion 
 of the two vocal cords, to each other in a por- 
 tion of their free borders, thus impeding vo- 
 calization; or there may be, as Dr Morell- 
 
246 DENTAL MECHANICS 
 
 Mackenzie has pointed out, paralysis of some of 
 the muscles of the larynx, produced by pressure 
 of cicatrices or injury to a nerve-filament. This 
 I mention to account for want of complete suc- 
 cess in some of these cases. Another condition 
 that affects the voice is the deafness often 
 present in these cases, from ulceration or block- 
 ing up with growths of the opening of the 
 Eustachian tubes. Some of the instances show 
 that it is utterly impossible to reproduce the 
 conditions necessary for perfect voice and 
 speech, the difficulties being even greater than 
 in congenital cleft palate. 
 
 Taking the impression. — It occasionally hap- 
 pens that the opening of the mouth is very 
 much contracted, either from the effect of old 
 cicatrices or gunshot wounds. This contrac- 
 tion may render it impossible to get a complete 
 impression of the palate out of the mouth at one 
 time. 
 
 To overcome this difficulty I have had a tray 
 made of the form shown in Fig. 129, still in the 
 shape of a spoon, but in two pieces, the handle 
 of each overlapping the other ; so that when 
 the handles are brought into proper contact 
 you may be quite sure that the two halves 
 inside the mouth are in proper relative position 
 to each other also. 
 
DENTAL MECHANICS 
 
 247 
 
 Tlie use of this sort of impression plate 
 requires a little patience and skill to manage 
 nicely, but there is no more difficulty than 
 any one with ordinary tact will be able to 
 overcome. 
 
 It may be used either with or without gutta 
 percha on its surface. If gutta percha be used, 
 
 Fig. 129. 
 
 care must be taken to roughen it, in order to 
 give attachment to the plaster of Paris. If 
 this be neglected, the liability is incurred of 
 leaving the plaster in the mouth, and bringing 
 the tray away alone. 
 
 The one half of the tray is thus covered with 
 a sufficient quantity of plaster, according to the 
 case under treatment, and placed carefully on 
 one side of the mouth, in such a position as to 
 get a fair half of the impression, the right haK 
 of the spoon, of course, being used for the right 
 side of the mouth. When the plaster is well 
 set, it is carefully removed from the mouth, 
 and the side which, with its fellow, is to form 
 
248 DENTAL MECHANICS 
 
 the median line of contact, pared down quite 
 smoothj and flusli with the edge of the spoon. 
 The second half of the tray is then placed in 
 its proper position with its fellow, to see that 
 no overhanging portion of plaster is present 
 before putting them into the mouth. 
 
 All the surface of the half impression already 
 obtained is then soaped thoroughly with brown 
 "Windsor soap, by means of a camel's hair 
 brush moistened either with water or sweet oil. 
 When this is ready, fresh plaster is mixed in 
 the manner hereafter described, and the impres- 
 sion already obtained is then placed again in 
 the mouth in the exact position it first occu- 
 pied, and held firmly in place by an assistant, 
 or the patient, if he has sufficient intelligence 
 and nerve to be trusted. The second half is 
 now covered with a sufficient quantity of 
 plaster, and introduced into the mouth, so as to 
 obtain an impression of the parts left exposed, 
 after the first impression is in position. The 
 guide, as to the situation of the moist plaster in 
 the mouth, is given to the operator by means 
 of the perfect apposition of the two handles, 
 which should have all their edges flush with 
 each other. 
 
 At the time of placing the second impression 
 in the mouth, the head should be thrown for- 
 
DENTAL MECHANICS 249 
 
 wards, and to one side, that is, to the right, 
 supposing the impression has been obtained of 
 the right side first. This will have the effect 
 of bringing plenty of plaster into the central 
 portion of the palate, and so jDroduce a more 
 accurate impression than if the head is kept 
 perfectly straight. 
 
 When the plaster in the basin indicates that the 
 impression is sufficiently hard to bear removal, 
 the first half — not the last — must be detached 
 from its fellow in the mouth. A firm, quick 
 pressure downwards will do this ; a sufficient 
 amount of space will then be found to remain 
 inside the mouth to admit of its removal with- 
 out suffering injury from di^agging against the 
 teeth. 
 
 By the time the first half is fairly removed, 
 the second half will be sufficiently increased in 
 strength to bear taking away without any 
 chance of damage. We now have the two 
 halves of the impression out of the mouth ; and 
 if the directions I have just given have been 
 carefully carried out, there should be no diffi- 
 culty in articulating them with each other. 
 They will be best kept in contact by means of 
 binding wire tied round the handles, and the 
 two articulating surfaces being coated with 
 liquid silex. 
 
250 DENTAL MECHANICS 
 
 The perfect impression may then be cast in 
 the usual way, or modified according to the 
 nature of the case. 
 
 Treatment.— There is one rule that I think 
 should be strictly adhered to in all cases of per- 
 foration of the hard and soft palate, and in most 
 cases of cleft of the hard and soft palate when 
 it arises from ulceration, and that is, never to 
 introduce anything into the cavity of the per- 
 foration or cleft for permanent use. The ten- 
 dency of the parts is to grow together, and thus 
 gradually obliterate the opening. 
 
 Anything rising above the lower margin has 
 the effect of checking this, and ultimately in- 
 creasing rather than reducing the size of the 
 space. In all these cases it is most essential 
 that nothing shall be done to produce irritation 
 and set up ulceration again. 
 
 The surface of the rubber comino^ next to the 
 part of the palate where there is an opening 
 must be highly polished, so that no chafing may 
 take place. It should be flat rather than convex, 
 so as to offer every inducement to the parts to 
 come together. 
 
 The earher these cases are treated the better 
 they succeed, both as to the general health and 
 the object we have specially in view, of remedy- 
 ing the defect in the palate. The plate pre- 
 
DENTAL MECHANICS 251 
 
 serves tlie parts from tlie irritation of foreign 
 bodies, and tlie membranes are in sucli a con- 
 dition as to grow more rapidly tlian under 
 ordinary circumstances they would do. 
 
 I think it safest, and therefore best, to use 
 black rubber for the plates, in order to avoid 
 any possibility of injurious effects arising from 
 the colom^ing matter used in the manufacture of 
 the ordinary red dental rubber. For cleft and 
 perforations of the velum it is generally neces- 
 sary to use elastic rubber, but wherever it 
 is possible to use hard rubber it is more effi- 
 cient, if it be desh^ed to reduce the size of an 
 opening. 
 
 On this account, I sometimes use hard rubber 
 for the front of the palate ; then a hinge formed 
 of elastic rubber, and then hard rubber again 
 beyond. This involves a little trouble in 
 making, but the satisfactory results amply 
 repay for the extra labour. 
 
 All the cases are held in position by the per- 
 fect fit of the plates to the mouth and teeth. 
 I do not use bands or metallic collars round the 
 teeth, and I never depend for the support of the 
 pieces on any overlap to be obtained on the 
 upper borders of the palate ; in syphilis I think 
 this is too great a risk to run. When the per- 
 foration is in the hard palate, the plate may be 
 
252 
 
 DENTAL MECHANICS 
 
 made of such a shape as to cover it without 
 unnecessarily encroaching on the roof of the 
 mouth ; when the opening is in the soft palate, 
 the rubber should extend about ^ to Jin. beyond 
 the sides and back of the cavity. A case of this 
 nature is shown in Fig. 130. 
 
 Fig. 130. 
 
 When there is a cleft, with the remains of the 
 velum on each side attached to, and continuous 
 with, the pharynx, it is neither possible nor 
 
DENTAL MECHANICS 253 
 
 desirable to close the cleft. The object here 
 should be to stimulate the rio-id marg^ins and 
 cicatrices into muscular action, in order that 
 the naso-pharyngeal cavities may be separated 
 at will. The hard rubber — for that is generally 
 the best in the first instance, though elastic 
 rubber may be used subsequently — should be 
 fitted to within yg i^* I'ound the sides, and ^ to 
 J in. at the portion coming in front of the pos- 
 terior wall of the pharynx. The object of the 
 diflference in the dimensions of these spaces is 
 that we desire to utilise and increase the lateral 
 contractile power, while we leave the muscles 
 at the back of the pharynx in their normal con- 
 dition, simply letting them touch the border of 
 the obturator without impinging. 
 
 It must be borne in mind that it is most 
 essential for the health of the patient that the 
 mucus of the nose should not be allowed to 
 accumulate to an unnatural degree, by the 
 complete closure of the space between the pos- 
 terior nares and mouth ; added to which, it is 
 necessary to avoid the chance of the artificial 
 palate being thrown out of position by the 
 tilting up of the margin coming in contact with 
 the pharynx. 
 
 In two cases, where there were no teeth in 
 the upper jaw, the obturator was held in posi- 
 
254 
 
 DENTAL MECHANICS 
 
 tion by means of spiral springs attached to a \ 
 lower piece. 
 
 The models must be taken in plaster of Paris, 
 but as there are occasionally perforations too ! 
 large to be covered with gold-beater's skin (to 
 prevent the plaster entering), there is a risk of 
 some considerable portion of it remaining in the i 
 opening when the impression is removed. I 
 have, therefore, had constructed an instrument 
 fashioned like a lithotrite, which, by being i 
 introduced into the opening, enables the ope- 
 rator to crush the plaster, and then remove j 
 it with a pair of tweezers, and afterwards wash I 
 away the fragments with a syringe and warm i 
 water. i 
 
 This instrument is shown in Fig. 131.* j 
 
 Fig. 131. I 
 
 Making the Palate Plates. — For all practical 
 purposes, hard and elastic rubber may be vul- 
 canized together, providing the temperature is 
 sufficiently high to thoroughly cook the hard 
 rubber. 
 
 * Made by Meyer and Metzler, Great Portland Street. 
 
DENTAL MECHANICS 255 
 
 The elastic rubber does not sujffer from this 
 increased temperature in elasticity, but in 
 power of resisting the acids of the mouth. 
 Still, it is sometimes desirable to put up with 
 this disadvantage on account of the other 
 benefits to be derived from the practice. It is 
 necessary when this is done to vulcanize on 
 metallic moulds, either fitted in a flask or held 
 together by a clamp. 
 
 The model having been cast in plaster, is 
 moulded in sand and cast carefully in type- 
 metal. All that portion of the palate which 
 has been recently the seat of ulceration is well 
 polished, so as to bring it up to a high metallic 
 surface. 
 
 Then, instead of mounting up the form of 
 the plate in wax, as you would do on a plaster 
 model, use modelling clay tolerably dry, that is, 
 as dry as it can be worked conveniently. When 
 it is nicely finished up, and has the form the 
 artificial palate is to have in rubber, whether 
 hard or soft, it is placed by the fire and gradu- 
 ally dried and made warm on the type-metal 
 model ; it is afterwards placed in a casting- 
 ring, with sand round it — in the same way that 
 we proceed for making the lead counterpart for 
 plate work — and type-metal poured in. This 
 saves the time and trouble of making a plaster 
 
256 DENTAL MECHANICS 
 
 model first, and also insures a more accurate 
 fit of the two castings. 
 
 All tlie surface of tliis last casting is tlio- 
 roughly polished, so as to give a smooth surface 
 to the rubber. The rubber is afterwards packed 
 in according to the position that you desire the 
 hard and elastic portions of it to occupy. It is 
 then fixed in a clamp and vulcanized. 
 
 Cases.— Sophia S — , set. 32. — Applied at the 
 Hospital for Diseases of the Throat for treatment 
 of severe ulceration and loss of parts at the back 
 of the mouth. Nearly the whole of the velum 
 palati had disappeared, the anterior and poste- 
 rior pillars of the fauces were likewise destroyed, 
 so that the roof of the mouth presented the 
 appearance of continuance backwards to the 
 posterior wall of the pharynx, as shown in 
 Fig. 132. 
 
 In the position that would be occupied by 
 the uvula and central portion of the soft palate, 
 when elevated for dividing the mouth from the 
 nose, there was a large opening of an oval form, 
 about one and a quarter of an inch in extent 
 one way, and three quarters of an inch from 
 side to side. In swallowing, there was not the 
 slightest movement at the back of the mouth, 
 except in the tongue, which was the only 
 member that could contribute any assistance to 
 
DENTAL MECHANICS 
 
 257 
 
 Fig. 132. 
 
 Showing cicatrices and old syphilitic scars in front of fissure. 
 
 the process of conveying tlie food to the open- 
 ing into the oesophagus. The back of the 
 mouth was in this way kept in a very irritable 
 condition by the continual lodgment of food in 
 the cleft. From the state of the palate, speech 
 was scarcely inteUigible, and the life of the 
 
 17 
 
258 DENTAL MECHANICS 
 
 poor woman was in every way a matter of con- 
 siderable discomfort. Owing also to the great 
 induration of the parts on each side, where the 
 indications of the anterior pillars of the fauces 
 were apparent, I concluded that no power 
 could be obtained to work an elastic velum with 
 any service or comfort, while at the same time 
 there was the consideration to be borne in mind 
 that the disease was still going on, and it was 
 desirable rather to protect the parts from the 
 irritation resulting from food, &c., than to 
 increase the trouble by having an artificial 
 velum, that must necessarily produce some 
 chafing, the mucous membrane being so ex- 
 ceedingly sensitive. A simple hard rubber 
 obturator was therefore made, partially closing 
 the aperture, and having the inner surface 
 highly polished. This has been very satis- 
 factory in its results. 
 
 William T — , engineer, set. 37. — In this case 
 the upper maxillary bone was destroyed on the 
 left side from the central tooth to the second 
 molar tooth, following the line of the inter- 
 maxillary suture, and the connection of the 
 palate-bone with the upper maxilla. The sep- 
 tum of the nose was quite perfect, articulating 
 with the maxillary bone of the opposite side. 
 The turbinated bones of the left side, with the 
 
DENTAL MECHANICS 
 
 259 
 
 walls of tlie antrum, were entirely destroyed up 
 to the floor of the orbit, leaving a gap for 
 restoration by artificial means of considerable 
 extent. The voice was very imperfect, masti- 
 cation and swallowing very difficult. 
 
 Fig. 133. 
 
 The instrument that was constructed to 
 remedy these defects is shown complete, ready 
 for wear, in Fig. 134. 
 
 The means that were adopted were not only 
 satisfactory, but immediate in their result — 
 
260 
 
 DENTAL MECHANICS 
 
 Fig. 134. 
 
 The parts connected ready for wear. 
 
 Fig. ]35. 
 
 The mouth as artificially restored. 
 
DENTAL MECHzVNICS 261 
 
 speech was restored at once to its normal tone 
 and distinctness. Graro-lingf the throat and 
 mouth (before impossible) were now accom- 
 plished with ease, while by the restoration of 
 the teeth to their natural state the patient's 
 appearance was very much improved. The 
 appearance of the mouth after treatment is 
 shown in Fig. 135. 
 
 The deformities arising from phagedsenic 
 ulceration must be treated on precisely the 
 same principle as those arising from syphiUtic 
 ulceration ; it is not therefore necessary to 
 enter into these separately. 
 
 The deformities of the mouth arisinof from 
 mechanical injury assume the most various 
 conditions, consisting either of defect owing to 
 loss of substance, or malformation dependent 
 on the influence of cicatrices of wounds inflicted 
 in the soft tissues. In the former instance we 
 have simply to reproduce the lost parts as 
 nearly like nature as possible, but in the latter 
 it may be necessary to construct an apparatus 
 or appliance in such a way as to counteract and 
 at last overcome the disfisfurement arisinsf 
 from the steady contraction of the flesh. 
 
 Each case must be treated according to its 
 special features and peculiarities. No precise 
 instruction can be of any use. Certain general 
 
262 DENTAL MECHANICS 
 
 rules of action may, however, be of service. On 
 every occasion when these deformities come 
 under treatment, make it a first, and hold it the 
 most important step to obtain a perfect model, 
 and always with plaster of Paris. For taking 
 the impression, if ordinary trays are not avail- 
 able make especial ones ; if there is not room to 
 place the tray in position with the plaster in it, 
 then contrive an opening in an accessible portion 
 of the impression cup, and after it is in the mouth 
 in its proper position fill up the intervening 
 space between the plate and the part to be 
 modelled, with very thin plaster of Paris in- 
 jected by means of a large-mouthed syringe ; 
 in this way impressions very accurate in charac- 
 ter may be obtained of apparently the most 
 awkward and inaccessible parts of the mouth. 
 
 In reproducing the defective parts use soft 
 or elastic rubber to supply soft parts, and hard 
 rubber to fill up the gap or deficiency in hard 
 tissue ; this is a rule that nearly always holds 
 good. Where you have no diseased condition 
 present always obtain a given and, if possible, 
 perfect result by the most simple method you 
 can adopt. Let ingenuity be applied to sim- 
 plifying an apparatus rather than to making 
 it curious in character and complicated in con- 
 struction. Rest assured that your patient will be 
 
DENTAL MECHANICS 263 
 
 best pleased with tliat appliance which answers 
 most perfectly and gives the least trouble rather 
 than with one that shows contriving skill on the 
 part of the operator, but from its structure is 
 likely to get easily out of repair and always be 
 a source of anxiety for its safety. 
 
APPENDIX 
 
 EECEIPTS FOE MAKING GOLD PLATE OF THE VAEIOUS 
 QUALITIES MOST IN USE FOE THE MOUNTING OF 
 AETIFICIAL DENTUEES.* 
 
 GOLD PLATE EIGHTEEN CARATS FINE. 
 
 Formula, No. 1. 
 
 18 dwts. pure gold, 
 4 dwts. fine copper, 
 2 dwts. fine silver. 
 
 Formula, No. 2. 
 
 20 dwts. gold coin, 
 2 dwts. fine copper, 
 
 2 dwts. fine silver. 
 
 GOLD PLATE NINETEEN CARATS FINE. 
 
 Formula, No. 3. 
 
 19 dwts. pure gold, 
 
 3 dwts. copper, 
 2 dwts. silver. 
 
 Formula, No. 4. 
 
 20 dwts. gold coin, 
 25 grains of copper, 
 40 + grs. of silver. 
 
 * Richardson and Harris, op. cit. 
 
DENTAL MECHANICS 265 
 
 GOLD PLATE TWENTY CARATS FINE. 
 
 Formula, No. 5. 
 20 dwts. pure gold, 
 2 dwts. copper, 
 2 dwts. silver. 
 
 Formula, No. 6. 
 20 dwts. gold coin, 
 18 grs. copper, 
 20 + grs. silver. 
 
 GOLD PLATE TWENTY-ONE CARATS FINE. 
 
 Formula, No. 7. 
 20 dwts. pure gold, 
 2 dwts. copper, 
 1 dwt. silver. 
 
 Foriinula, No. 8. 
 20 dwts. gold coin, 
 13 + grs. silver. 
 
 Formula, No. 9. 
 20 dwts. gold coin, 
 6 grs. copper, 
 7f grs. platinum. 
 
 GOLD PLATES TWENTY-TWO CARATS FINE. 
 
 Formula, No. 10. 
 22 dwts. pure gold, 
 
 1 dwt. fine copper, 
 18 grs. silver, 
 
 6 grs. platinum. 
 
 SOLDERS FOR GOLD WORK. 
 
 The following formula may be used in con- 
 nection with eighteen or twenty carat gold 
 plate, and is sixteen carats fine. 
 
266 DENTAL MECHANICS 
 
 6 dwts. pure gold, 
 2 dwts. roset copper, 
 1 dwt. fine silver. 
 
 Formula No. 1 of tlie following recipes is 
 a fraction over fifteen carats fine ; and No. 2 
 furnishes a solder eighteen carats fine. 
 
 Formula No. 1. 
 6 dwts. gold coin, 
 30 grs. silver, 
 20 grs. copper, 
 10 grs. brass. 
 
 Formula No. 2. 
 Gold coin, 30 parts, 
 Silver 4 „ 
 
 Copper 1 „ 
 Brass 1 „ 
 
 SILVEE SOLDER. 
 
 Formula No. 1. 
 SUver 66 parts, 
 Copper 30 „ 
 Zinc 10 „ 
 
 Formula, No 2. 
 Silver 6 parts, 
 Copper 2 „ 
 Brass 1 „ 
 
 BRASS SOLDER. 
 
 Brass solder consists of two parts of brass 
 and one of zinc, to which a little tin is occa- 
 sionally added. 
 
DENTAL MECHANICS 267 
 
 SOFT SOLDER. 
 
 Soft solder is an alloy composed of lead and 
 tin in the proportion of two parts of the former 
 with one of the latter. 
 
 rose's fusible metal. 
 
 The alloy known as Eose's fusible metal is 
 composed of 2 parts of bismuth, 1 of lead, and 
 1 of tin, and melts at about 200°. A still more 
 fusible alloy is composed of lead 3 parts, tin 2 
 parts, and bismuth 5 parts, which fuses at 197°. 
 
 rabbitt's metal. 
 
 Melt 4 lbs. of copper; add by degrees 12 lbs. 
 of tin and 8 lbs. of antimony. Then add 12 lbs. 
 more tin, first by adding 4 lbs., bring the whole 
 to a red heat and then add the rest of the tin. 
 
 GERMAN SILVER. 
 
 Genuine German silver is composed of copper 
 40-4; nickel 31*6; zinc 25*4 ; iron 2*6; but 
 the proportions of the metals of this alloy differ 
 according to the various uses to which this 
 compound is applied. 
 
 TYPE METAL. 
 
 Lead, alloyed with antimony in the proper- 
 
268 DENTAL MECHANICS 
 
 tion of from J to -|- of tlie latter, with the addi- 
 tion sometimes of very small portions of copper, 
 tin, and bismuth, forms different grades of 
 tij])e metal, which is harder than lead, and very- 
 brittle, and is sometimes used for dies ; and 
 sometimes, though very rarely, for counter-dies. 
 When used as a counter to a zinc die, it is 
 improved for the purpose by adding to it an 
 equal quantity of lead ; it may also be used in 
 the form of a die in connection with a lead 
 counter after rough stamping with zinc. 
 
 METHOD OF EEDUCING GOLD TO A LOWER OR HIGHER 
 STANDARD OE FINENESS AND OE DETERMINING THE 
 CARAT OF ANY GIVEN ALLOY. 
 
 The following practical remarks on the 
 method are copied from an article on ''Alloying 
 Gold,"* by Professor G. Watt. 
 
 "1. To ascertain the carat of any given alloy. — 
 The proportion may be expressed as follows : 
 
 " As the weight of the alloyed mass is to the 
 weight of gold it contains, so is 24 to the standard 
 sought. Take for example, Harris' No. 3 gold 
 solder : 
 
 Pure gold 6 parts, 
 „ silver 2 „ 
 „ copper 1 „ 
 
 Total ... 9 
 * ' Dental Register of the West,' vol. x, p. 396. 
 
DENTAL MECHANICS 269 
 
 " The proportion would be expressed thus, — 
 9 : 6 :: 24 : 16. 
 
 " From this anj one can deduce the following 
 
 ''Rule. — Multiply 24 by the weight of gold 
 in the alloyed mass, and divide the product by 
 the weight of the mass ; the quotient is the 
 carat souo-ht. 
 
 " In the above example, 24 multiplied by 6, 
 the quantity of gold, gives 144, which, divided 
 by 9, the weight of the whole mass, gives 16. 
 Hence, an alloy prepared as above, is 16 carats 
 fine. 
 
 " As another example, under the same rule, 
 take Harris' jS'o. 1 solder. 
 
 22 carat gold, 48 parts, 
 silver, 16 „ 
 copper, 12 „ 
 
 Total ... 76 
 
 " Now, as the gold used is but 22 carats fine, 
 one twelfth of it is alloy. The one twelfth of 
 48 is 4, which subtracted from 48 leaves 44. 
 The statement then is : 
 
 76:44:: 241:3*9. 
 
 '' This solder, therefore, falls a fraction below 
 14 carats. 
 
 "2. To reduce gold to a required carat.-- The 
 proportion may be expressed as follows : 
 
270 DENTAL MECHANICS 
 
 "As tlie required carat is to 24, so is fhe 
 weight of the gold used to the weight of the 
 alloyed mass when reduced. *The weight of 
 gold subtracted from this, gives the quantity of 
 alloy to be added. 
 
 " For example, reduce 6 ounces of pure gold 
 to 16 carats. 
 
 " The statement is expressed thus : 
 16:24:: 6:9. 
 
 " Six subtracted from 9 leaves 3, which is 
 the quantity of alloy to be added. From this is 
 deducted the following 
 
 " Rule. — Multiply 24 by the weight of pure 
 gold used, and divide the product by the required 
 carat. The quotient is the weight of the mass 
 when reduced, from which subtract the weight 
 of the gold used, and the remainder is the weight 
 of alloy to be added. 
 
 "As another example under the same rule, 
 reduce 1 pennyweight of 22 carat gold to 18 
 carats. 
 
 "As the gold is only 22 carats fine, one 
 twelfth of it is already alloy. The one penny- 
 weight, therefore, contains but twenty-two 
 grains of pure gold. The statement is, there- 
 fore, thus expressed : 
 
 18 : 24 : : 22 : 29i 
 " Twenty- two subtracted from 29|- leaves 7-g-. 
 
DENTAL MECHANICS 271 
 
 Therefore, each pennyweight of 22 carat gold 
 requires 7 J grains of alloy to reduce it to 18 
 carats. 
 
 " 3. To reduce gold from a loiver to a TiigJier 
 carat. — This may be done by adding pure gold, 
 or a gold alloy finer than that required. The 
 principle of the rule may be set forth in the 
 following general expression : 
 
 *' As the alloy in the required carat is to the 
 alloy in the given carat, so is the weight of the 
 alloyed gold used to the weight of the reduced 
 alloy required. The principle may be practically 
 applied by the following 
 
 '' Rule. — Multiply the weight of the alloyed 
 gold used by the number representing the pro- 
 portion of alloy in the given carat, and divide 
 the product by that representing the proportion 
 of alloy in the required carat ; the quotient is 
 the weight of the mass when reduced to the 
 required carat by adding fine gold. 
 
 " To illustrate this, take the following ex- 
 ample : 
 
 "Reduce 1 pennyweight of 16 carat gold to 
 18 carats. 
 
 " The numbers representing the proportions 
 of alloy in this example are found by respec- 
 tively subtracting 18 and 16 from 24. The 
 statement is, therefore : 
 
272 DENTAL MECHANICS 
 
 6:8:: l:li, 
 from wliicli it follows tliat to reduce one penny- 
 weiglit of 16 carat gold to 18 carats, tlieremust 
 be one third of a pennyweight of pure gold 
 added to it. 
 
 '' But, suppose that, instead of pure gold, we 
 wash to effect the change by adding 22 carat 
 gold. The numbers, then, respectively repre- 
 senting the proportions of the alloy would be 
 found by subtracting, in the above example, 
 16 and 18 from 22, and the statement would 
 be 
 
 4:6:: 1 : 11 
 
 '' It follows, then, that to each pennyweight 
 of 16 carat gold, a half pennyweight of 22 carat 
 gold must be added to bring it to 18 carats. 
 
 " By the above rules we think the student 
 will be able, in all cases, to calculate the fineness 
 or quality of his gold, and to effect any reduc- 
 tion, whether ascending or descending, which he 
 may desire." 
 
 DR HUNTEe's method OE SUPPORTING PARTIAL DEN- 
 TURES IN THE MOUTH BY MEANS OE CYLINDERS OF 
 WOOD ATTACHED TO TUBED PLATES. 
 
 Dr Hunter remarks: — ''The advantages 
 in many cases must be apparent to the thinking 
 
DENTAL MECHANICS 273 
 
 dentist, but, perhaps, it miglit not be amiss to 
 enumerate a few. 
 
 '' The fixture is held in place with greater 
 firmness than by means of clasps. 
 
 " In some instances where I have used clasps, 
 I have also used the tube in combination, to 
 give stability for masticating purposes. 
 
 " The injury to the natural teeth must be 
 much less, owing to the smaller amount of 
 surface in contact. 
 
 '' If decay should take place, it would require 
 but an ordinary filling to restore the tooth. 
 
 " It prevents that peculiarly disagreeable 
 sensation experienced, particularly in fruit sea- 
 son, upon removing and replacing artificial 
 teeth. 
 
 " After having tested it for more than a year, 
 I am satisfied that it greatly lessens the chances 
 of decay in those cases where it can be applied, 
 and I have removed the clasps in some old cases 
 with great satisfaction to my patients." 
 
 18 
 
274 
 
 DENTAL MECHANICS 
 
 TABLE SHOWING THE NAMES, COLOUES, AND DEGEEES 
 
 OF HEAT EEQUIEED FOE VULCANIZING THE EUB- 
 
 BEES THAT AEE MOST USED AT THE PEE SENT 
 
 TIME 
 
 C. Ash and Sons' Riibhers. 
 
 
 
 
 
 Degrees 
 
 Degrees 
 
 Degrees 
 
 Karnes. 
 
 Colours. 
 
 Time. 
 
 Fahr. 
 
 Cent. 
 
 Reamur. 
 
 Ix 
 
 Deep pink . . . 
 
 h. 
 
 m. 
 
 
 
 
 Ix, soft 
 
 No. 1 
 
 Pale „ ... 
 
 ^ 
 
 15 
 
 310 
 
 154 
 
 124 
 
 No. 2 
 
 Light „ 
 
 J 
 
 
 
 
 
 G 
 
 Bright red ... 
 
 2 
 
 
 
 315 
 
 157 
 
 126 
 
 Ord. 12/- 
 
 Deep red 
 
 2 
 
 
 
 315 
 
 157 
 
 126 
 
 Ord, 10/- 
 
 Black 
 
 Brown 
 
 2 
 
 
 
 315 
 
 157 
 
 126 
 
 
 2 
 
 
 
 315 
 
 157 
 
 126 
 
 S.P 
 
 Strong pink... 
 
 1 
 
 45 
 
 315 
 
 157 
 
 126 
 
 Wliite 
 
 
 1 
 1 
 
 15 
 15 
 
 315 
 315 
 
 157 
 157 
 
 126 
 126 
 
 Red 
 
 Orange 
 
 
 1 
 
 15 
 
 315 
 
 157 
 
 126 
 
 Brown 
 
 
 1 
 
 15 
 
 315 
 
 157 
 
 126 
 
 Soft 
 
 W 
 
 Red 
 
 1 
 1 
 
 15 
 15 
 
 310 
 310 
 
 154 
 154 
 
 124 
 124 
 
 Dark brown... 
 
 "WTialebone . 
 
 Light brown 
 
 
 
 50 
 
 320 
 
 160 
 
 127 
 
 
 
 f 2 
 
 
 
 240 
 
 115 
 
 92 
 
 Yela 
 
 Brown 
 
 2 
 
 .0 
 
 260 
 
 126 
 
 101 
 
 
 
 I 2 
 
 
 
 270 
 
 132 
 
 106 
 
 A/E 
 
 Dark red 
 
 1 
 
 15 
 
 310 
 
 154 
 
 124 
 
 American 
 
 C Deep red . . . 
 
 
 
 
 
 
 Whalebone 
 
 
 
 55 
 
 320 
 
 160 
 
 127 
 
 Rubber 
 
 
 
 
 
 
 In the course of some experiments that T 
 carried out four years ago with yarious rubbers 
 I found that nearly all of them could be ren- 
 dered elastic, like the vela rubber, by raising 
 the heat gradually to the point of vulcanization 
 
DENTAL MECHANICS 275 
 
 and then at once cooling down. To those who 
 may at any time find it difficult to obtain the 
 elastic rubber required for an artificial velum 
 this fact may be of service. 
 
 TO OBTAIN SUCTION 
 
 After a perfect model has been taken and an 
 artificial piece accurately fitted, the operator is 
 often much perplexed to find that the plate will 
 not hold up. In many cases this arises from 
 nervousness on the part of the patient, causing 
 the secretion of mucus to be arrested, and thus 
 alterinof the condition of the surface of the 
 mouth sufficiently to prevent suction being 
 obtainable. The best remedy is to paint over 
 the palate and adjacent gums with a solution of 
 carbolic acid and glycerine (1 in 12) ; this will 
 stimulate the action of the mucous follicles, and 
 in a short time perfect adhesion of the plate to 
 the palate will take place. 
 
 REPAIRING VULCANITE 
 
 Vulcanite cases may sometimes be success- 
 fully repaired and have teeth added to them by 
 means of soft solder applied with a small 
 soldering iron. The dovetails are cut in the 
 usual way, and the soft solder run in, the piece 
 
276 DENTAL MECHANICS 
 
 being supported by a plaster mould made warm, 
 biit not hot enough to injure the rubber. 
 
 TO EESTOEE VULCANITE CASES TO THEIE PIEST EOEM 
 
 Vulcanite plates are sometimes made warm 
 by means of hot oil or the spirit lamp, so that 
 they may be altered in shape. Occasionally this 
 is done with very unsatisfactory results, and it 
 becomes desirable to restore the piece to its 
 first form. This may be done by immersing 
 the plate for a few minutes in boiling water. 
 
 SPIEAL SPEINGS 
 
 I have intentionally omitted any notice of the 
 application of spiral springs in the body of this 
 work, as I believe they no longer hold a promi- 
 nent place in modern dentistry, and only proper 
 care is required in the adjustment of full upper 
 dentures to enable the operator to do without 
 springs altogether. 
 
 There are, however, sometimes cases where 
 the prejudices of a patient will compel you to fix 
 spiral springs, or else see your work thrown 
 aside as useless. Until our patients are better 
 educated in regard to these matters, spiral 
 
DENTAL MECHANICS 277 
 
 springs will therefore occasionally be called into 
 use. They are attached to the upper and lower 
 set by means of swivels. 
 
 The swivel consists of a pin made of pla- 
 tinum or gold passing through the " eye ;" to 
 this latter is joined the shank, to which the 
 spring itself is attached ; the swivel in its com- 
 plete form may be connected to a vulcanite 
 base by the pin passing through the vulcanite 
 and being riveted on the lingual surface, or 
 for a gold case it may be mounted on a small 
 plate, and attached by soldering to the side of 
 the denture. 
 
 Supposing the jaws to be normally deve- 
 loped, the best position for the swivels is 
 between the second bicuspid and first molar in 
 either jaw; the swivels in the lower jaw will 
 then be somewhat in advance of the upper jaw 
 when the teeth are closed, but will fall in the 
 same perpendicular line when the lower jaw is 
 depressed. If when the mouth is closed the 
 swivels are opposite to each other, that is, fall 
 in the same line, when the mouth is opened the 
 upper swivels will occupy a position in advance 
 of the lower ones, and the springs, having thus 
 lost their proper balance, will occasionally pro- 
 ject the teeth out of the mouth, often partially 
 and sometimes altogether. 
 
278 
 
 DENTAL MECHANICS 
 
 The manufacture of spiral springs has been 
 already mentioned in the section on gold. The 
 various forms of swivels, and their adjustment 
 with the springs to a full set of teeth, are 
 shown in the accompanying woodcuts. 
 
 Fig. 136. 
 
 Fig. 137. 
 
 Fig, 138. 
 
 Fig. 139. 
 
 Fig. 140. 
 
DENTAL MECHANICS 279 
 
 TO PEEVENT ABRASION OF THE CHEEK FKOM SPIRAL 
 
 SPRINGS 
 
 When it is necessary to use spiral springs for 
 the first time, much discomfort is often endured 
 by the patient on account of the chafing pro- 
 duced by them. This may be, in a great 
 measure, prevented or reheved by one or other 
 of the following plans : — Either make a solution 
 in chloroform of pink rubber and paint over the 
 surface of the springs before putting them on 
 the set of teeth, or else obtain some of the very 
 fine and thin elastic rubber tubing which is now 
 made ; and, having first passed a brooch up the 
 centre of the spring to prevent crippling, draw 
 this tubing over, so that the whole of it is 
 covered except those portions that play against 
 the teeth. In this way these necessary evils 
 may be made tolerable to sensitive mouths by 
 protecting the mucous membrane from their 
 metallic feeling and irritation. 
 
INDEX 
 
 
 
 . 
 
 PAGE 
 
 AlE chamber, manner of forming 
 
 . 88 
 
 Air vent in plaster impressions 
 
 
 9 
 
 Alloys of copper for dental purposes . 
 
 
 47 
 
 gold 
 
 
 47 
 
 „ platinum 
 
 
 47 
 
 „ silver 
 
 
 47 
 
 Application of heat 
 
 
 17 
 
 Articulating models for full dentures 
 
 
 100 
 
 ,, „ partial dentures 
 
 95-97, 99 
 
 Artificial palates . 
 
 224, 230, 238 
 
 Asbestos, use of . 
 
 39, 113, 140 
 
 Assay pound 
 
 49, 50, 60 
 
 Atmospheric pressure plates 
 
 . 86 
 
 Attaching mineral teeth to metallic base 
 
 142—144 
 
 „ „ vulcanite base 
 
 167—186 
 
 Baking furnace . . . . 
 
 25, 29 
 
 „ porcelain teeth 
 
 . 106 
 
 Balance, Dr. Black's 
 
 . 61 
 
 Bite, to obtain the partial . 
 
 . 99 
 
 » „ full 
 
 . 100 
 
 Block teeth, composition of body 
 
 . 109 
 
 ,, „ crown enamel 
 
 109, 110 
 
 Blowpipe, bellows 
 
 . 18 
 
 „ Burgess' 
 
 , 
 
 18 
 
282 
 
 INDEX 
 
 Blowpipe, Fletcher's 
 
 „ moutli . 
 
 „ moutli, with, bulb 
 
 „ Owen's 
 
 „ hot-blast 
 
 „ self-acting (American) 
 (English) 
 (French) 
 
 „ Snow's . 
 Brass solder 
 
 PA&B 
 
 21 
 17 
 17 
 20 
 21 
 22 
 23 
 23 
 20 
 266 
 
 Cauious teeth, necessity for their removal 
 
 Carving block teeth 
 
 Charcoal, use of, for melting and soldering 
 
 Chasing punches . 
 
 Clasps, their use . 
 
 „ cases suitable for 
 
 „ various forms of 
 
 „ method of fitting 
 
 „ standard . 
 Cleveland's air chamber 
 Cloth, use of, in packing vulcanite 
 Coke, use of, in mechanical dentistry 
 Composition of body for block teeth 
 „ crown enamels 
 
 „ gum enamels 
 
 „ vulcanite 
 
 Continuous gum work. Dr. Allen's method 
 Congenital clefts in the palate 
 Colouring materials used in porcelain work 
 
 „ „ preparing vulcanite 
 
 Converting gold alloys into various forms 
 Cores, casting with 
 
 Counter-dies, various ways of preparing 
 Copper, alloys of . 
 Crucible 
 
 2 
 . 108 
 68, 143 
 . 79 
 . 80 
 . 81 
 81, 82 
 81, 82 
 . 81 
 . 91 
 . 177 
 . 27 
 . 109 
 
 109, 110 
 . 110 
 . 159 
 . 112 
 . 217 
 
 107, 108 
 . 152 
 
 269, 271 
 
 38, 39 
 
 41—44 
 
 47, 72 
 
 . 64 
 
INDEX 
 
 283 
 
 
 
 PAGE 
 
 Dentures 
 
 5 in celluloid 
 
 . 211 
 
 jj 
 
 partial, in gold . 
 
 74, 85 
 
 j> 
 
 „ in vulcanite 
 
 . 194 
 
 jj 
 
 entire upper, in gold 
 
 . 89 
 
 )} 
 
 „ lower, in gold 
 
 . 94 
 
 >> 
 
 ,, upper, in vulcanite 
 
 . 167 
 
 )> 
 
 „ lower, in vulcanite 
 
 . 194 
 
 35 
 
 supported by atmospheric pressure 
 
 ! 86, 91 
 
 Defects of the palatine region 
 
 243, 261 
 
 Dipping in 
 
 metal . 
 
 • 43 
 
 >} 
 
 resin and wax, stearin, &c. 
 
 34, 35 
 
 Dies, mode of preparing 
 
 35—45 
 
 Duplicate 
 
 cases in vulcanite 
 
 . 203 
 
 Felspar 
 
 
 . 105 
 
 Fitting mineral teeth 
 
 . 138 
 
 „ pi'w:)t teeth 
 
 126—135 
 
 Flasks, vulcanite . 
 
 . 171 
 
 Flasking 
 
 . 
 
 . 172 
 
 Flux 
 
 . 
 
 . Ill 
 
 Formulae for gold plate 
 
 . 264 
 
 j> 
 
 gold solders 
 
 . 265 
 
 j> 
 
 silver solder 
 
 . 266 
 
 J) 
 
 brass solder 
 
 . 266 
 
 )> 
 
 German silver 
 
 . 267 
 
 )f 
 
 soft solder 
 
 . 267 
 
 y> 
 
 fusible metals 
 
 . 267 
 
 >j 
 
 type metal 
 
 . 267 
 
 }) 
 
 vulcanite . . 
 
 149, 158 
 
 » 
 
 body, gum, and enamel for porcel 
 
 ain 107, 109— 
 111 
 
 Forging . 
 
 . 
 
 67, 69 
 
 Fuel 
 
 . . . • 
 
 . 27 
 
 Furnaces 
 
 . 
 
 25, 26, 28, 29 
 
 Fusible metals, table of . 
 
 45, 267 
 
284 
 
 INDEX 
 
 German silver 
 Godiva composition 
 Gold, properties of 
 
 alloys of 
 
 assaying 
 
 melting 
 
 admixture of flux 
 
 solders 
 Gold wire 
 
 „ plate, manner of preparing 
 Gutta percha 
 
 PAGE 
 
 267 
 
 10 
 
 46 
 
 47 
 
 48—64 
 
 64 
 
 64 
 
 265 
 
 69 
 
 64—69 
 
 . 11 
 
 Hand furnace 
 Harden x^laster models, to . 
 Hawes' moulding flask 
 Horizontal line, liow to obtain 
 
 25 
 34 
 37 
 
 99 
 
 Impressions, materials used for 
 
 „ trays 
 
 „ in wax for full upper dentures 
 
 „ in wax for full lower dentures 
 
 „ in wax for partial dentures 
 
 „ in plaster for full upper dentures 
 
 „ in plaster for full lower dentures 
 
 „ in plaster for partial dentures 
 
 „ in various other materials 
 
 India rubber, general properties of . 
 
 „ method of preparing . 
 
 „ dentures 
 
 „ analysis of 
 
 „ action of, on the mouth 
 
 7, 9—11 
 
 12 
 
 6, 7 
 
 15 
 
 12 
 
 8 
 
 14 
 
 11 
 
 15 
 
 163 
 
 149 
 
 167, 207 
 
 159, 161 
 
 . 165 
 
 Kaolin . 
 Kurra's clamp 
 
 105 
 90 
 
INDEX 
 
 285 
 
 Lamp, spirit, for soldering . 
 
 „ oil, for soldering 
 Lead for counter die 
 
 Making cores 
 Manufacture of porcelain 
 
 „ of rubber 
 
 Materials used in taking impressions 
 „ used as bases for dentures 
 Materials for metallic castings 
 Metal dies 
 „ strengthener for vulcanite 
 „ clasps for vulcanite 
 ,, models 
 Mending vulcanite cases 
 Melting gold 
 
 Models in plaster for gold work 
 „ „ vulcanite work 
 
 ,, in metal . 
 Moulding 
 
 Moulding flask, Hawes' 
 Mouth, preparation of, for inserting 
 Moutli blowpipe 
 
 wash. . . 
 
 an 
 
 PAGE 
 
 . 25 
 
 . 24 
 
 41—43 
 
 . 39 
 
 104—111 
 
 148—158 
 
 5, 7, 9—11 
 
 46, 71, 164, 208 
 
 44, 45, 267 
 
 35-45 
 
 . 198 
 
 . 196 
 
 35—45 
 
 . 200 
 
 . 64 
 
 31, 34 
 
 . 31 
 
 35, 45 
 
 35, 40 
 
 . 37 
 
 artificial denture 1 — 3 
 
 . 17 
 
 4 
 
 Oil lamp 
 
 Owen's blowpipe . 
 Obtaining tbe bite for partial dentures 
 „ „ entire dentures 
 
 Opening tbe flask, precaution as to . 
 Objections to coating surface of plaster 
 Obturators for congenital defects of palate 
 „ for syphilitic defects of palate 
 
 Palatal defects . 
 Palates, deep 
 
 . 24 
 
 . 20 
 
 . 95 
 
 . 100 
 
 174—177 
 
 . 178 
 
 217—239 
 
 243—261 
 
 217—261 
 . 240 
 
286 
 
 INDEX 
 
 Partial dentures in gold 
 „ „ in vulcanite 
 
 „ „ supported by clasps 
 
 „ „ „ wooden cylinder 
 
 Parting assays 
 
 Pivot tootli, cases most suitable for a 
 „ „ preparation of stump for 
 „ ,, taking impression for 
 „ „ varieties of teeth, used for a 
 „ „ fitting crown for 
 „ „ fitting and adjusting pivot for 
 Pivots of wood, metal, &c. . 
 
 „ affixing to crown and stump . 
 Platinum, properties of 
 
 „ alloys of . 
 
 „ solder for 
 
 Plaster of Paris, mode of mixing 
 „ „ impressions 
 
 „ 55 to harden . 
 
 „ „ to set quickly 
 
 „ casting in 
 Porcelain, teeth of 
 
 „ blocks, preparation of 
 
 „ composition of . . • 
 
 PAGE 
 
 . 74 
 
 . 194 
 
 80, 196 
 
 . 272 
 
 . 59 
 
 . 126 
 
 . 127 
 
 . 130 
 
 . 131 
 
 . 132 
 
 134, 135 
 
 134, 135 
 
 134, 135 
 
 . 72 
 
 . 73 
 
 73, 115 
 
 8 
 
 7—10 
 
 34,35 
 
 8 
 
 . 30 
 
 104—111 
 
 . 108 
 
 109, 110 
 
 Rabbit's fusible metal 
 Remodelling with vulcanite 
 Repairing vulcanite plates . 
 
 „ „ with celluloid 
 
 Reducing gold to various degrees of fineness 
 Refitting gold plates with vulcanite linings 
 Rims to gold plates 
 
 Roots of teeth, preparation of, for fitting to 
 Rose's fusible metal 
 Rolling or flatting plate 
 
 . 267 
 
 . 204 
 
 200, 275 
 
 . 214 
 
 . 269 
 
 204—206 
 
 86, 93, 94 
 
 . 138 
 
 . 267 
 
 . 67 
 
INDEX 
 
 287 
 
 
 PAGE 
 
 Sand for casting . 
 
 . 35 
 
 „ preparing with oil or water 
 
 . 35 
 
 Self-acting blowpipe 
 
 22, 23 
 
 Silver, properties of 
 
 . 71 
 
 „ alloys of . 
 
 71,72 
 
 Silex, liquid, use of 
 
 178, 222 
 
 Soft solder, composition of . 
 
 . 267 
 
 Spirit lamp 
 
 . 25 
 
 Spiral springs, their manufacture 
 
 . 70 
 
 „ „ their adjustment 
 
 . 276 
 
 „ „ to prevent abrasion from 
 
 . 279 
 
 Standard clasp .... 
 
 . 81 
 
 Stent's composition 
 
 . 11 
 
 Strengthening teeth of plaster model 
 
 . 30 
 
 Suction plates 
 
 86, 91, 3 
 
 „ how to obtain 
 
 . 275 
 
 Snow's blowpipe . 
 
 . 20 
 
 Teeth, the choice of . . ' 
 
 131, 136 
 
 „ their adjustment 
 
 138, 147 
 
 „ attachment of bands to 
 
 . 74 
 
 Temporary dentures 
 
 4 
 
 Tin . 
 
 44, 45 
 
 Time that need elapse before insertion of artificial denture 3 
 
 Touchstone, use of 
 
 . 49 
 
 Ti-ying in cases 
 
 81, 84 
 
 Type metal 
 
 . 267 
 
 Undercut models, to cast in metal 
 
 38, 39 
 
 Uniting plates and clasps 
 
 . 83 
 
 Varnish for models 
 
 . 33 
 
 Yulcanite (see India mbber) 
 
 163—166 
 
 „ flasks . 
 
 . 171 
 
 „ to remove discoloration from 
 
 . 202 
 
288 i^DEX 
 
 PAGE 
 
 Yulcanizers , . . . . 178 
 
 Yulcanizing . . ... . 185 
 
 Wax . . . . . . 5,6 
 
 „ witli oil . . . . . 5, 11 
 
 „ witli castor-oil . . . .11 
 
 ,, witli resin . . . . .34 
 
 „ with, paraffin . . .11 
 
 Wood pivots . . . . . 134 
 
 ., cylinders . . . , . 272 
 
 Zinc . . . . . 44, 45 
 
 PRINTED BY J. E. ADLAED, BAETHOLOMEW CLOSE, LONDON, E.C. 
 
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RK651 
 
 Coles 
 
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 C67 
 1876 
 
 ^^7 
 
 COLUMBIA UNIVERSITY LIBRARIES (hsi.stx) 
 
 RK 651 C67 1876 C.I 
 
 A manual of dental 'T^echamsms / 
 
 2002450003