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 METALLIC INLAY. 
 
 BY 
 
 ZAHNARZT H. W. C. BODECKER, B.8.,D.D.S.,M.D. 
 
 WITH 158 ILLUSTRATIONS 
 AND 14 PLATES. 
 
 BERLIN: 
 HERMANN MEUSSER. 
 
 STEGLITZERSTR. 58. 
 
 1911. 
 
Copyright 1911 by Hermann Meusser, Berlin. 
 
 Druck der Spamerschen Buchdruckerei in Leipzig. 
 
To My Father, 
 
 C. F. W. Bodecker, d.d.s., m d.s , 
 
 This Book Is 
 Affectionately Dedicated. 
 
Digitized by tine Internet Archive 
 
 in 2010 with funding from 
 
 Open Knowledge Commons 
 
 http://www.archive.org/details/metallicinlayOObd 
 
Introduction. 
 
 The metallic inlay, and with it the general application of 
 casting, is undoubtedly one of the most valuable acquisitions 
 made by dentistry in the last few years. As a result of its 
 success in practice, the gold inlay has become a recognized 
 means of filling teeth. The fact that metallic inlays are 
 indicated only in the posterior teeth, does not detract from 
 their value, as in this position, the inlay is superior to all 
 other classes of fillings. 
 
 The value of the inlay process was recognized many years 
 ago; the material and the method of constructing the inlay 
 itself, offered difficulties however. To the ingenuity of Tag- 
 gart, in America, and of Solbrig, in Europe the dental pro- 
 fession is indebted for a metallic inlay which fulfills all just 
 requirements. 
 
 The object of this book is to explain in a concise manner, 
 the mechanical principles upon which the retention of metalhc 
 inlays depends; to apply these principles to the preparation 
 of cavities, and to formulate a method of procedure in 
 making and setting inlays. Though intended primarily as 
 a practical guide, theoretical considerations could not be 
 disregarded, as it is never wise to make a single step in any 
 practical operation without knowing the theoretical reason. 
 
 In writing this book the arrangement of the German 
 edition has been followed. It has been revised in some points, 
 and a chapter on inlay abutments has been added. 
 
 The technique suggested, can by no means be considered 
 complete. It is offered, so that others may improve upon it. 
 If this little book in any way, directly or indirectly, should 
 help in furthering the progress of the metallic inlay, the 
 work of the writer will not have been in vain. 
 
Contents. 
 
 Introduction. 
 
 Index of Plates. page 
 
 Chapter I. The Evolution of the Metallic Inlay 1 
 
 Chapter II. The Advantages and Disadvantages of the Metallic Inlaj' 5 
 
 Chapter III. Retention of Metallic Inlays 16 
 
 Cement-Retention 17 
 
 Self-Retention 26 
 
 Chapter IV. Retention and Cavity Form 35 
 
 Chapter V. Caries and Cavity Form 53 
 
 Chapter VI. The Enamel Margin 62 
 
 Chapter VII. Instruments for Cavity Preparation 68 
 
 Chapter VIIJ. Cavity Preparation 74 
 
 Chapter IX. The Impression 90 
 
 The Indirect Impression 90 
 
 The Direct Impression 92 
 
 The Hollow Wax Model 102 
 
 Chapter X. The Construction of the Inlay 104 
 
 By Older Methods 104 
 
 By Casting 107 
 
 The Investment 107 
 
 The Casting Metal 112 
 
 The Casting Macliines 118 
 
 Combination Inlays 127 
 
 Chapter XI. Setting the Inlay 131 
 
 Fitting the Inlay 131 
 
 The Cement 139 
 
 Drying the Cavity 142 
 
 Setting the Inlay 144 
 
 Finishing and Polishing 145 
 
 Chapter XII. The Inlay as a Bridge Abutment 148 
 
 Index 165 
 
Index of Plates. 
 
 Plate I. Lower Molar with Mesio-Occlusal Cavity 76 
 
 Plate II. Lower Molar with Disto-Proximal Cavity. Adjoining Tooth 
 
 Missing 77 
 
 Plate III. Lower Molar mth Lingual Wall Missing 78 
 
 Plate IV. Lower Molar with Abraded Occlusal Surface . 79 
 
 Plate V. Lower Bicuspid in a Crowded Arch, with Mesio-Occlusal Cavity 80 
 Plate VI. Upper Bicuspid ^^ith Large Mesial and distal Cavities (Tooth 
 
 Pulpless) 81 
 
 Plate VII. Upper Bicuspid Aiith Lingual Wall Missing . 82 
 
 Plate VIII. Upper Bicuspid with Buccal Wall Missing 82 
 
 Plate IX. Upper Bicuspid with Erosion 84 
 
 Upper Bicuspid mth Simple Cervical Cavity 84 
 
 Plate X. Cuspid with Small Distal Cavity 85 
 
 Plate XL Cuspid with Large Distal Cavity 86 
 
 Plate XII. Abraded Cuspid, A-^ith Inlay Anchored on the Lingual Surface 87 
 
 Incisor with Small Proximal Cavity 87 
 
 Plate XIII. Incisor with Mesial and Distal Cavities 88 
 
 Plate XIV. Abraded Incisor \\ith Mesial and Distal Cavities 89 
 
Chapter I. 
 The Evolution of the Metallic Inlay. 
 
 Never will it be known to whom the honor belongs of 
 having placed the first gold inlay in a tooth. Those who long 
 ago practiced this method, kept their discovery a dark secret. 
 Even the patient was not informed that the "gold filling" 
 inserted, differed in any way from one made in the usual 
 manner. Now, however, that the gold inlay has become a 
 recognized means of filling teeth, the long guarded secret of 
 the first gold inlays transpires. In all cases, the "method" 
 was about the same. A large, imperfectly prepared cavity 
 was laboriously filled with gold, the matrix removed and the 
 filling polished. Before the finishing was completed, however, 
 the whole filling had loosened. After some hesitation, the 
 operator determined to reset the filling with cement, and at 
 a subsequent sitting to polish the filling, — if possible, or, if 
 necessary, — confess. If success attended the experiment, the 
 filling was finished and booked in the journal with a question- 
 mark. In how many cases this mark was justified will never 
 be ascertained. There are, however, cases on record where such 
 fillings have performed effective service for five, ten, and even 
 fifteen years, as proven by patients presented at dental con- 
 ventions. 
 
 I mention these cases only, to call attention to the fact 
 that we have to-day examples which prove that the gold 
 inlay can favorably compare in durability with the foil filling. 
 But not only upon the inlays produced as the result of an 
 accident, is our experience based, but also upon intentio- 
 nally constructed inlays that were inserted many years 
 ago. Since that time, a great number of methods for inlay 
 construction have been proposed, but, especially in the be- 
 ginning, a lack of interest prevented the profession at large 
 
 Bodecker, Metallic Inlay. 1 
 
from adopting the inlay process. Tlie introduction of por- 
 celain as a filling material, however, resulted in the recognition 
 of the advantages of the inlay. This material, extensively 
 used for several years in all classes of cavities, is now limited 
 to visible cavities in the anterior part of the month. During 
 the porcelain era a certain number of men did not loose 
 faith in the gold inlay. They experimented and perfected their 
 methods, until the profession in general, dissappointed at the 
 failure of porcelain in the posterior teeth, was willing to give 
 the gold inlay a fair trial. The rapidity with which this method 
 of filling has won new adherents in the last few years, is due 
 less to the failure of porcelain, than to the increased simplicity 
 in the production of the metallic inlay. 
 
 One of the oldest methods, in imitation of the inlays 
 accidentally made, as described above, consisted in lightly 
 filling the cavity with sponge-gold, carefully removing the 
 whole, saturating with solder and resetting with cement. 
 Numerous other methods soon followed, in which a matrix, 
 as used for glass and porcelain inlays, played the most im- 
 portant part. The difference in these methods lay in the use 
 of various kinds of foil, viz., gold, gold and platinum, and 
 pure platinum; in the method of removing the matrix from 
 the cavity; and in the use of gold of different karats for filling 
 the matrix and for the production of contours and cusps. 
 
 The success attending the use of gold inlays in large cavities 
 justified the attempt to use them for still larger restorations. 
 The difficulty of building up such large contours and cusps 
 with sponge-gold and solder, soon brought forth new methods. 
 A matrix was made of thin 24 kar. plate. A cap, suitable 
 for the case, was swedged on the die plate of a crown outfit 
 and the requisite part soldered upon the matrix. In this 
 manner the first hollow inlay originated. This procedure was 
 soon improved upon in so many ways, that the hollow gold 
 inlay can claim more methods for its construction than any 
 other inlay filling, be it of gold or porcelain. In spite of these 
 numerous methods, the construction of hollow inlays, instead 
 of becoming simpler, became more and more complicated. 
 
 In the meantime the solid gold inlay had made progress. 
 
The matrix, upon a model of the cavity, was filled with wax, 
 tried in the mouth, replaced on the model, and the essential 
 surfaces, that is, grinding surface and contactpoint, were 
 smoothly covered with foil. The whole was then invested, 
 leaving only the uncovered wax exposed. The latter was 
 burned out and the resultant chamber filled with molten gold 
 or solder. The next step was to neglect the foil covering, and 
 to completely embed the matrix with its wax form. To pro- 
 duce a channel to the surface, a pin around which a cone of 
 wax had been formed was stuck into the wax model. A vent 
 was produced by a straw running from the model to the 
 surface. The investment was then heated until the wax 
 burned out. In a small depression beside the opening of the 
 channel, the gold was melted with a blow-pipe. At the proper 
 moment the mold was tipped, so that the gold flowed into 
 the channel and into the mold. In this manner, as suggested 
 by Solbrig (Paris), the first cast gold inlay, made by the wax 
 dispersion method, was produced. To simplify the process, 
 an electric furnace was constructed. It consisted of tw^o parts; 
 a lower, which could be heated to 600 — 700 °F, for the 
 reception of the mold, and an upper part in which the gold 
 was fused. By removing a plug, the gold flowed down into 
 the mold. 
 
 The finer details of the wax model could not, however, 
 be reproduced without pressure. In the methods of casting 
 employed in the arts, this is obtained by using a large amount 
 of excess metal. As this is not practicable in casting gold, 
 it was necessary to devise other means of obtaining sufficient 
 pressure. 
 
 Dr. W. IT. Taggart solved the difficulty, and in doing so 
 inaugurated a new era in dentistry. Not alone was the con- 
 struction of perfect inlays made possible, but also in crown 
 and bridge-work, as well as in plate-work, has the value of 
 casting become evident. The writer fully agrees with the 
 words spoken by Solbrig at the Dental Congress held in 
 Lille, 1909*. "In these various methods the construction of 
 
 *) Ash's Quartely Circular, Jan. 1910. 
 
a matrix in gold or platinum was still indispensable, and it 
 was Taggart, of Chicago, who first did away with it, by the 
 application of pneumatic pressure in combination with the 
 wax dispersion method. His merit lies not only in the in- 
 genious invention of his apparatus, but also, and above all, 
 in the influence which he exercised upon many colleagues with 
 inventive minds, who were led by his enthusiasm and his 
 success to make research in the same direction. Before his 
 apparatus could be procured several other systems were pressed 
 upon the notice of the profession, but not withstanding this 
 Dr. Taggart must without doubt be considered the pioneer 
 of the present period, as regards the casting of metals." 
 
Chapter II. 
 
 The Advantages and Disadvantages of the Metallic 
 
 Inlay Filling. 
 
 The interest which the dental profession has shown for the 
 gold inlay during the past few years, proves that this method 
 of filling teeth has steadily been gaining general recognition. 
 The enthusiasts, however, go decidedly too far in claiming the 
 method to be everywhere applicable. They recall the porcelain 
 fanatic, who in answer to the question "Where is porcelain 
 indicated ?" replied, "On the hundred and sixty surfaces of 
 the thirty two human teeth." Experience, sad to say, has 
 taught us something different. Those who to-day predict that 
 in the near future mallet, plugger, and gold foil will become 
 relics of the past, may wait a long time for the fulfillment of 
 their prophecy. 
 
 The truth of Franklin's motto : "A place for everything, and 
 everything in its place," has been amply demonstrated by the 
 filling materials introduced into dentistry in the past. I need 
 only recall the fact that cement, amalgam and later porcelain, 
 each at first indiscriminately used, are to-day confined to 
 certain definite spheres of usefulness. That the metallic inlay 
 will prove an exception to this rule, may be doubted, in spite 
 of the many good qualities that this form of filling possesses. 
 
 The disadvantages of the above filling- materials are well 
 known. Cement is more or less rapidly dissolved under the 
 mechanical and chemical influences in the mouth. Amalgan 
 often presents an unesthetic appearance, is liable to change 
 its form, and under certain circumstances discolors the tooth. 
 Porcelain, on account of the nature of the material, cannot 
 be burnished against the margins of the cavity, and a seam, 
 equal in width to the thickness of the foil used for the matrix, 
 must therefore always remain. This seam constitutes the chief 
 
disadvantage of the porcelain inlay. When in time the cement 
 is dissolved at this point, the edges of the inlay being un- 
 supported, chip off; they then become rough and often dis- 
 colored. The ideal result, a restoration true to nature, is not 
 attained under such circumstances. 
 
 The gold inlay is free from the imperfections mentioned 
 in connection with the above filling- materials, but its con- 
 struction requires a high degree of accuracy in order to pro- 
 duce a perfect filling. This fact has, by some, been considered 
 a deficiency of the metallic inlay system. The success or 
 failure of an inlay is determined by its adaptation to the 
 cavity margin. The durability of an inlay is absolutely assured, 
 if the space between the edge of the inlay and the enamel 
 margin, is limited to the theoretical thickness of thinly- mixed 
 cement. The possibility of producing such inlays has been 
 demonstrated, but it is not probable that even the majority 
 of gold inlays show such perfection at all their margins. Every 
 operator should however remember, that in placing an im- 
 perfectly adapted gold inlay into a tooth, he is not only doing 
 himself and his patient an injustice, but that he is also in- 
 juring the repute of a valuable filling-method, to-day on trial 
 before the dental profession. 
 
 Before discussing the question of advantages, disadvantages, 
 and general indications for the use of the metallic inlay, atten- 
 tion must be called to the functions of the cement. These are : 
 
 1. to intimately unite the inlay with the tooth; 
 
 2. to fill out all space between the inlay and the cavity wall. 
 The contention that in the same manner as the impression 
 
 was removed from the cavity, the inlay itself may drop out 
 if the cement does not happen to be sufficiently adherent, 
 rests upon a misinterpretation of facts. Without here entering 
 into a discussion of this subject (see Chap. Ill) it must be 
 mentioned, that a truly adherent cement is not necessary. 
 With almost any cement on the market, a metallic inlay can 
 be firmly set in the cavity. Adhesion plays no essential part, 
 as the attachment depends upon entirely different mechanical 
 principles. The quality most desirable in a cement for this 
 purpose is resistance to compression strain, i. e. crushing 
 
strength. In order to utilize this property, the undercuts in 
 the inlay and in the tooth must be in such relative position, 
 that the inlay cannot be removed from the cavity without 
 crushing the layer of cement. The shape of a properly formed 
 inlay, materially aids the cement in preventing a displace- 
 ment of the inlay. The topic of self-retention will be dis- 
 cussed in Chapter III. 
 
 The second function of the cement, the filling out of all 
 spaces between the inlay and the cavity wall, has always been 
 the point of attack of those opposed to all systems of inlays. 
 To simplify the discussion of this question, it has been divided 
 into two parts. 
 
 1. The office of the cement in the depth of the cavity, 
 i. e., between dentine and inlay, and 
 
 2. The office of the cement at the margin of the cavity, 
 i. e., between enamel and inlay. 
 
 The cement layer in the depth of the cavity should be as 
 thick as possible. Especially is this necessary in large cavities 
 in teeth with living pulps, in order to interpose a layer of 
 thermally non-conducting material between the large mass of 
 metal and the pulp. Besides this, a thick layer of cement is 
 more advantageous in holding the inlay in the cavity. 
 
 It has been claimed by the opponents of inlay fillings, 
 that thinly mixed cement cannot be considered a reliable 
 filling material. As proof, they cite the disintegrated and 
 evil-smelling cement sometimes found upon the removal of 
 shell crowns that have been worn a long time. As proof to 
 the contrary, mention may be made of the cement layer found 
 upon the walls of those cavities out of which porcelain inlays 
 have fallen. The hardness and density of the cement in such 
 places leaves nothing to be desired. If putrefaction occurs, 
 it denotes the presence of organic matter in the cement. This 
 is possible only under two conditions. Either the cement is 
 so porous that it can easily be permeated by the organic 
 constituents of the saliva, or an admixture of saliva has taken 
 place at the time when the crown was being set into place. 
 The latter is by far the more reasonable assumption. 
 
 Besides mechanically filling out all spaces, the cement has 
 
been proven to have a physiological action on the dentine. 
 No other filling-material is capable of producing such marked 
 changes through which the dentine becomes considerably more 
 resistant to caries. The investigations of C. F. W. Bodecker 
 upon the reaction of the dentine under various filling-materials, 
 have amply proven this fact.*) Under oxyphosphate of zinc 
 "the reaction is almost constantly present, and consists of 
 a solidification of the dentine and an obliteration of a number 
 of dentinal canaliculi. The dentinal canaliculi which are 
 obliterated under oxyphosphate fillings first become faint, 
 scarcely traceable and ultimately disappear, in consequence 
 of which disappearance the fields of basis-substance between 
 the dentinal canaliculi are considerably broadened . . . The 
 consolidation is densest along the border of the cavity, where 
 dentinal canaliculi are quite scanty; but the consolidated 
 dentine extends to a considerable depth before it blends with 
 normal dentine" (Fig. 1). 
 
 Upon the reaction of the dentine under gold fillings, the 
 same author expresses himself as follows : "In some instances no 
 reaction was noticeable in the dentine, only a zone of green co- 
 lour, attributable to causes just mentioned under gutta-percha." 
 (Due to coagulants applied before the introduction of the 
 filling.) "In other instances there was a distinct reaction along 
 the border ... In still other instances the goldfilling has 
 led to a partial obliteration of dentinal canaliculi similar to 
 that induced by oxyphosphate of zinc, though never as com- 
 plete as that which follows the introduction of the last-named 
 filling-material." Under amalgam and under tin the reaction 
 of the dentine is similar to that under gold. From these observa- 
 tions the great value of cement as a filling- material becomes 
 apparent. It changes normal dentine, which is easily destroyed 
 by caries, into a tissue which has the appearance and the re- 
 sistance of so-called senile dentine. This is probably the reason 
 why secondary decay hardly ever appears at the margin of 
 a cavity filled with an inlay. 
 
 Opponents of the gold inlay have recently asserted, that 
 as these observations were made in cases of teeth filled with 
 
 *) C. F. W. Bodecker, Anatomy and Pathology of the Teeth, page 323. 
 
porcelain, the assumption that metallic inlays will show the 
 same immunity to secondary caries is not justifiable. They 
 believe in the possibility of an electric circuit being set up 
 between the gold and the zinc of the cement, with the result, 
 that conditions favorable for the beginning of caries would 
 
 ^ hi'!/! 
 
 // 
 
 ' 
 
 V / 
 
 lii ////- 
 
 / 
 
 / / / 
 
 -■ / ' 
 
 ///^ 
 
 Fig. 1. 
 
 be produced. There is, however, no evidence in support of 
 this theory, and it may be safely assumed that owing to the 
 reaction of the dentine under the cement, secondary caries 
 will be observed as rarely under a metallic inlay as it has 
 been under porcelain. 
 
 In setting an inlay, more or less pressure is always exerted 
 upon the thin cement. Whether this is sufficient to force the 
 cement into the dentinal canaliculi and interglobular spaces. 
 
10 
 
 and whether the reaction of the dentine is more marked than 
 under an ordinary cement fiUing, are questions that cannot 
 at present be answered, as the experiments conducted by the 
 writer are not as yet complete. 
 
 The subject most important in all inlay methods will now 
 be considered, i. e. the cement seam between the inlay and the 
 margin of the cavity. Theoretically the width of the narrowest 
 possible seam is equal to a single layer cement grains. The 
 production of such a seam is possible only in certain places 
 and under the most favorable circumstances. In discussing 
 this question it will be assumed that the width of the seam 
 is such as occurs with a well-fitting inlay, constructed accord- 
 ing to the methods now in vogue. As in every other class of 
 filling, the durability of an inlay depends upon the accuracy 
 of its adaptation to the cavity margin. If therefore, an inlay, 
 imperfect in this respect, is set into a tooth, its permanency 
 is doubtful from the beginning. For the failure of such a 
 filling, the inlay-process cannot be held accountable. 
 
 The durability of the cement is dependent upon the 
 position of the seam on the surface of the tooth. Either it 
 lies on, or near, the grinding-surface, where it is exposed to the 
 pumping action of mastication, as it is named by C. J. Grieves*), 
 or it lies toward the neck of the tooth, unaffected by this 
 action. The conditions in the latter position will be dis- 
 cussed first. 
 
 In spite of claims to the contrary, cement, in time, dissolves 
 more or less in almost every month. Exceptions to this rule 
 are so rare that they may completely disregarded. This fact 
 would apparently justify the assumption that the cement 
 within the seam would in time be completely dissolved out. 
 An examination of a large number of seams in positions un- 
 affected by the pumping action of mastication has, however, 
 proven, that the cement is only dissolved out to a depth equal 
 to the width of the seam,. This rule, it must be mentioned, does 
 not hold good for seams exposed to the action of mastication. 
 
 The explanation of this fact, so important for the durability 
 
 *) Dental Summary. Vol. 27, p. 93. 
 
n 
 
 of the inlay, rests, according to C. J. Grieves and others, upon 
 the protective action of the mucus present in the secretions 
 of the mouth. All surfaces in the mouth, with the exception 
 of those cleansed by mastication, are normally covered by 
 a layer of mucus. W. D. Miller described mucin as a clear, vis- 
 cous fluid, of alkaline reaction. It is albuminous, and there- 
 fore forms a nutrient medium for bacteria. It mixes with water, 
 in the form of threads, without being soluble. It is insoluble 
 in alcohol, ether, chloroform, and dilute acids ; soluble in dilute 
 alkalies and in concentrated acids. The layer of mucus on 
 the teeth, containing albuminous bodies, offers the putrifac- 
 tive bacteria of the mouth a suitable medium. As the reaction 
 during putrifaction, at least in the first stages, is alway alka- 
 line, the decomposition of mucus cannot act as a factor in 
 the causation of caries. 
 
 The protective action of the mucus on the cement is 
 explained by the fact, that mucin is insoluble in water and 
 in dilute acids. As soon as the cement is dissolved out of a 
 seam so far, that the mucus layer is no longer destroyed by 
 the circulation of fluids during mastication, or in cleansing 
 the teeth, the solution of the cement ceases. This, as has 
 been already mentioned, occurs when the solution has pro- 
 ceeded to a depth equal to the width of the seam. 
 
 Some interesting investigations have been made upon this 
 subject by J. Head*). He found that a seam filled with 
 Harvard Cement, and placed in a one percent, watery solution 
 of lactic acid, dissolved out in two to three days. The same 
 material under the same circumstances, placed in a one percent 
 solution of lactic acid in saliva, showed no evidence of being 
 attacked. Head, also, believes this to be due to the presence 
 of the mucin in the saliva. 
 
 If the seam lies on the occlusal surface, the above men- 
 tioned rule does not apply, because the pumping action of 
 mastication, as well as the mechanical contact of the food, 
 prevents the formation of a sufficiently thick layer of mucus. 
 This evil, the most dangerous of all, for the inlay process, 
 
 *) Dental Cosmos Vol. XLVII, p. 789. 
 
12 
 
 has been the subject of much thought, and many experiments. 
 It is evident that in this position the width of the seam must 
 be confined to its theoretical minimum. The narrower the 
 seam, the less disturbance can be caused by the pumping- 
 action, and the stronger is the action of the capillary attraction 
 holding the mucus layer in place. 
 
 To make such seams less vulnerable, bevelling the cavity 
 margin has been suggested. The success of this measure alone 
 may be doubted, as the seam remains exposed to the pumping 
 action. The author beleives that the only possible protection 
 against the solution of the cement in this place, is an almost 
 theoretically perfect adaptation of the inlay to the cavity 
 margin. 
 
 For this reason the author adheres to the use of 24 kar. 
 gold in the construction of inlays. With this material it is 
 easy, especially on the occlusal surface, to force the gold 
 against the margin of the cavity with a tomato-burnisher. 
 The disadvantages of 24 kar. gold are : that high cusps cannot 
 be built up in case of a sharp bite; that it does not take as 
 smooth a polish as 22 kar. ; and that considerably higher heat 
 is necessary in casting. The objection, that an inlay of 24 kar. 
 gold is much softer than a hammered foil filling, does not affect 
 its usefulness. If a pure gold inlay, which is a trifle too high, 
 is examined in the mouth, it will show that the area con- 
 stantly struck by the antagonist, is harder than any foil filling. 
 
 The time necessary for the construction of an inlay has, 
 by some, been considered as an objection to inlay methods. 
 If, however, the inlay is used only where large surfaces, con- 
 tours, or cusps are to be restored, this process offers a decided 
 saving of time. 
 
 Another apparently more justifiable objection is, that all 
 inlays require an extensive sacrifice of healthy tooth- structure. 
 If by this is meant a thorough cutting out of the fissures, 
 then it can only be of advantage in protecting the tooth from 
 redecay. If it refers to the ruthless destruction of tissue, 
 simply to make the removal of the impression easy, or to 
 produce a typical box-shaped cavity with steps and squared 
 angles, then the objection is more than justified. An inlay 
 
r.', 
 
 cannot be made in quite such narrow limits as an amalgam, 
 (jr an ordinary gold filling. But if we compare the cavity- 
 preparation of a conservative inlay operator, with a cavity 
 prepared according to the teachings of Black, but little diffe- 
 rence in the extent of the cavities will be found. In some 
 cases it will even be in favor of the inlay (see Chap. V). 
 
 The advantages the tooth derives from the use of the inlay 
 are briefly as follows: 
 
 1. The cement causes a reaction in the dentine, making 
 it more resistant to decay. 
 
 2. The cement forms an insulating layer, which protects 
 to pulp from rapid changes of temperature. 
 
 3. The cement, intimately uniting the inlay with the tooth, 
 gives support to weakened vzalls. 
 
 4. The cement adheres to dry dentine, so that in the case 
 of self-retentive inlays, under cuts, if properly placed, 
 need not be very deep at excessively sensitive places. 
 
 5. Very weak walls which are liable to fail later may be 
 removed, as the work of constructing an inlay does not 
 depend upon its size. 
 
 6. Prolonged malleting, which often causes a hyperaemia 
 of the pulp or a slight pericementitis, is avoided. 
 
 7. The danger of fracturing a wall, due to the expansion 
 of the filling under the mallet, as well as, 
 
 8. The danger of injuring the enamel margin with a plugger, 
 cannot occur with an inlay. 
 
 9. Contours and contact-points of inlays are more easily 
 built up, and preserved while finishing, than those of 
 fillings made in the mouth. 
 
 10. Cusps with proper articulation can be readily produced 
 on an inlay. 
 
 11. The filling is of a uniform density. Hollow spaces are 
 not present, and the surface is smooth. An exfoliation, 
 as is often the case with foil fillings, does not take place ; 
 food particles, etc. can therefore not adhere. 
 
 12. Over porcelain, the metallic inlay has the advantage, 
 that the seam is not increased in width by the removal 
 of the matrix. 
 
14 
 
 13. The use of the metallic inlay enables us to fill cavities 
 with gold, which on account of their unfavorable position, 
 cannot be filled with a foil filling. For example, cervical 
 cavities extending deeply under the gum, where the use 
 of the dam is not possible. 
 
 14. Many extensively decayed teeth, upon which shell- 
 crowns are usually set, may do good service for years, 
 if restored by means of a metallic inlay. 
 
 For the patient also, the inlay process offers conveniences 
 which he soon learns to appreciate. 
 
 1. The time consumed by the work in the mouth is con- 
 siderably shortened. 
 
 2. The use of the mallet, the rubberdam and its accompany- 
 ing evils, the ligature and the clamp, are avoided. 
 
 3. Separators are applied less often. 
 
 4. Setting an inlay takes no longer than introducing an 
 ordinary cement filling. 
 
 5. The operation of filling a tooth with an inlay, may be 
 discontinued at more stages than with other fillings. 
 
 Besides being more agreeable to the patient, the inlay pro- 
 cess offers certain advantages to the operator. In case of large 
 fillings, a saving of time is effected. But the chief value is, 
 that the operator, knowing to a certainty whether the filling 
 he has placed into a tooth is perfect or not, can foretell its 
 durability more positively than if he had used any other filling 
 material. 
 
 The indications for the use of metallic inlays are briefly 
 the following: 
 
 1. In all larger cavities where a sufficiently direct and free 
 access for the introduction of a foil filling cannot be 
 obtained. Such are the cavities on the distal surfaces 
 of the bicuspids and molars. In cases of extensive decay, 
 the inlay may also be used on the mesial surface of 
 these teeth. 
 
 2. Large defects of the grinding surface, requiring a restora- 
 tion of the cusps. 
 
 3. In all cervical cavities extending beneath the gum in 
 the molars, and, exceptionally, in the bicuspids. 
 
15 
 
 4. To make large restorations on the teeth of children and 
 nervous patients. 
 
 5. In cases of so called soft teeth, where secondary caries 
 usually appears at the margin of the most carefully 
 introduced metallic fillings. 
 
 6. In building up abraded cutting edges of the incisors 
 and cuspids. 
 
 7. In teeth loosened from any cause. 
 
 8. Teeth loosened by pyorrhea may be supported by solder- 
 ing together a series of proximal inlays at their con- 
 tact points. 
 
 9. Interproximal spaces into which the food easily packs, 
 may be restored to normal conditions, by inserting 
 inlays with exaggerated contours. 
 
 10. As bridge abuttments, various inlays have been sug- 
 gested and some successfully used. 
 
 11. In orthodontia, inlays alone or in connection with an 
 apparatus may occasionally be used to retain the teeth. 
 
 12. In making shell crowns, the true bite may be obtained, 
 by modelling wax onto the band in the mouth, invest- 
 ing, and casting the occlusal surface directly onto the 
 band. 
 
 In spite of the number of indications mentioned above, 
 it is to be doubted whether the result would be a success in 
 every case. The chief disadvantage of the inlay process, the 
 difficulty of producing perfect adaptation at the cavity margin, 
 would justify the assumption that it is almost impossible to 
 solder a number of inlays together without endangering their 
 perfect adaptation to the margin of the cavity. As a filling 
 method, however, the metallic inlay process deserves full 
 recognition, if its application be limited to filling larger cavities 
 of the bicuspids and molars. 
 
Chapter III. 
 Retention of Metallic Inlays. 
 
 The durabihty of an inlay is largely dependent upon its 
 mode of attachment to the tooth. In porcelain inlays the 
 chief reliance was placed upon the adhesive qualities of the 
 cement. In the case of the metallic inlay, however, the cavity 
 may be so prepared that the inlay receives support in every 
 direction except in that, opposite to the one in which it was 
 inserted into the cavity. If this direction is parallel to that 
 of the pressure of mastication, the inlay cannot be bitten out 
 of the cavity as long as the tooth remains intact. The possi- 
 bility of giving the cavities such a favorable form is due to 
 the fact that metal, in contradistinction to porcelain, is suffi- 
 ciently resistant to the force of mastication, to permit the 
 construction of comparatively thin anchorage-extensions, fit- 
 ting snugly into the fissures and grooves of the tooth. 
 
 The retention of the finished inlay should be considered 
 in the early stages of cavity-preparation. Before beginning 
 with the excavation of the dentine, the direction and amount 
 of the force of mastication must be studied, and the position 
 determined, where sufficient anchorage may be obtained on 
 the tooth. Which form of anchorage should be chosen in a 
 given case, depends upon the position and the depth of the 
 cavity, upon the structure of the tooth itself, and upon the 
 distribution of the healthy tissue about the cavity. 
 
 The writer has divided the retention of inlays into two 
 classes : 
 
 1. Retention depending upon an intermediary body. 
 (Cement-retention.) 
 
 2. Retention depending upon the form of the inlay itself. 
 (Self -retention.) 
 
17 
 Cement-Retention. 
 
 Retention Depending upon an Intermediary Body. 
 
 The material used for the attachment of metallic inlays 
 is oxyphosphate of zinc cement. Sufficient data has been 
 gathered during its use in connection with porcelain inlays, to 
 prove that this material possesses the necessary qualities for 
 setting metallic inlays. The fact that thinly mixed cement 
 adheres to dentine is generally recognized, but the explanations 
 regarding it differ. It has been claimed, that a chemical union 
 takes place. A more probable explanation is that the acid, 
 corroding the dentine, produces a rough surface on which 
 the cement obtains a purely mechanical hold. However this 
 may be, the cement is sufficiently adherent to the dentine 
 for the purpose of retaining the inlay in a cavity. The hold 
 which the cement finds on the surface of the inlay is purely 
 mechanical, and should be the subject of special attention. 
 This hold may be produced in two ways, either by deeply 
 undercutting with a saw or knife-edged stone, or by roughening 
 with a pointed instrument. Which of these two methods is 
 to be used in a given case, depends on the following circum- 
 stances. If the free surface of the inlay is comparatively 
 larger than that within the cavity; or if the inlay is exposed 
 to the force of mastication without itself having sufficient 
 self-retention ; or if the cement layer between inlay and cavity- 
 wall is very thin, deep undercuts are to be used. A general 
 roughening of the surface, being easier to produce than the 
 undercuts, is indicated where the latter are deemed unneces- 
 sary. 
 
 The Undercut. 
 
 If deep undercuts are to be made use of, they should be 
 so placed that those in the inlay lie exactly opposite to those 
 in the walls of the cavity (Fig. 2). The retention of the inlay 
 is dependent in this case, upon a ring of cement whose strength 
 is proportional to the compression-strength of the cement, and 
 to the thickness of the ring. If the undercuts in the inlay 
 and in the tooth are exactly opposite each other, the force 
 necessary to dislodge the inlay is equal to that which could 
 
 Bii decker, Metallic Inlay. 2 
 
18 
 
 crush a layer of the thickness a—h (Fig. 3 A) of the cement 
 used to set the inlay. If the undercuts are not quite opposite 
 one another, the effective thickness of the ring is reduced 
 
 Fig. 2. 
 
 to G — d (Fig. 3 B). In case no parts of the undercuts face 
 each other, they become practically useless. The cement lying 
 in the undercut in the tooth (II, Fig. 3 C) finds little or no hold 
 
 A 
 
 Fig. 3. 
 
 on the inlay. This undercut is therefore superfluous. Owing 
 to the fact that thinly-mixed cement adheres to dentine, the 
 cement in the undercut in the inlay (I, Fig. 3 C), finds some 
 hold on the cavity wall. The retention so obtained is, however. 
 
19 
 
 not comparable to that of a ring of cement, or that produced 
 by a general roughening of the surface of the inlay. 
 
 As experience has shown the difficulty of bringing the 
 undercuts in exact apposition, a more certain method of trans- 
 
 Fitr. 4. 
 
 mitting the pressure from the inlay to the tooth is required. 
 By thickening the layer of cement between the inlay and 
 the cavity walls at certain points, a more uniform distribution 
 of pressure is obtained. This is accomplished by a further 
 
 Fis. 5. 
 
 excavation of the walls of the cavity; this in most cases 
 obviates the necessity of making undercuts in the tooth (Fig. 4). 
 In a cavity such as Fig. 5, a deep undercut at a, would 
 appreciably weaken the edge b. A slight excavation, as 
 shown, would be equally effective in anchoring the inlay. It 
 may be stated here as a general rule, that undercuts with 
 
20 
 
 square angles (Fig. 9 B and C) alway weaken a structure more 
 than if these angles were rounded (Fig. 10). 
 
 All undercuts made into an inlay must be of proper form 
 and in their theoretically correct position. To understand this 
 correct form and position, the part played by the cement in 
 the retention of an inlay must be studied. Its chief function 
 will be made clear by the following: Two metal parts with 
 holes drilled at a and h, are suspended as shown in Fig. 6. 
 
 Fig. 6. 
 
 If a and h were filled with exactly fitting metallic rods it would 
 be almost impossible to separate the parts. If the holes were 
 filled with cement, plaster, sealing-wax, or rosin, the weight 
 necessary to separate the parts would vary with each sub- 
 stance. 
 
 The moment that the separation of the parts begins, 
 a change of form of the holes a and b takes place (Fig. 7). 
 If the holes are filled, the filling must bear the weight of the 
 whole mass placed on the scale-tray below. The diameter of 
 the hole, a — h (Fig. 8 a), tends to diminish, and pressure is 
 therefore exerted upon the filling material in the direction a — b. 
 At the same time the diameter c — d elongates, so that the 
 
21 
 
 filling material looses its support in this direction. As long 
 as the filling-material possesses sufficient resistance to com- 
 pression, i. e. crushing strength, to prevent a change of form 
 of its mass, no movement of the parts can take place. The 
 value of a material for this purpose is therefore dependent 
 upon its crushing strength. 
 
 The pressure which a material can bear is dependent upon 
 the area subjected to pressure, as well as upon the thickness 
 of the material itself. These facts must be taken into con- 
 sideration in determining the form and position of an undercut. 
 
 Fig. 7. 
 
 Fig. 8 a. 
 
 In selecting the position, leverage by which the inlay might 
 be pried out of the cavity during mastication, must be taken 
 into account. As the margin of the cavity acts as a fulcrum, 
 it is evident that the farther the undercut (hold) is away 
 from the margin of the cavity, the greater will be the force 
 necessary to dislodge the inlay. For this reason, undercuts 
 are to be placed near the floor in simple cavities. 
 
 The difficulty of bringing the undercuts in the tooth and 
 in the inlay in apposition has already been mentioned. By 
 changing the form of the undercuts and widening the cavity 
 in certain places, a more favorable distribution of pressure in 
 the cement layer can be brought about. Fig. 9 — 12 are en- 
 largements of the shaded portion of Fig. 8 b. Fig. 9 shoves the 
 
22 
 
 wall of a cavity slightly enlarged at A, and having an under- 
 cut made with a wheel at B. The inlay is undercut with 
 a saw at C. If an attempt is made to remove the inlay in the 
 direction of the arrow, pressure will be set up in the cement 
 layer. The main pressure between inlay and tooth will be 
 born by a cone of cement, of the form, ahcd. 
 
 The resistance which the cement offers, depends mainly 
 upon the direction of the pressure cone a — d in relation to 
 the direction in which the inlay may be removed from the 
 cavity. The more nearly these two directions correspond, the 
 more does the cement depend upon its crushing strength for 
 the retention of the inlay. Another factor determining the 
 
 Fig. 8 b. 
 
 effective resistance of the cement, is the area of the cross- 
 section of the pressure cone. Other things being equal, the 
 larger the area, the stronger the retention. 
 
 A consideration of Fig. 9, will show, that the undercuts C 
 and B could have been made less deep, without thereby de- 
 creasing the sectional area of the pressure cone; that is, the 
 inlay would have been equally resistant, if the undercuts were 
 of the form a, h, c and e, d, c. It also becomes apparent, that 
 if the corner e were removed, the pressure cone would gain 
 in cross-sectional area, and at the same time lie in a con- 
 siderably more favorable direction. The cement in the depths 
 of the undercuts C and B takes little or no part in the retention 
 of the inlay. Fig. 10 shows the undercuts, correct in form and 
 position; the points discussed in Fig. 9 having been practi- 
 cally applied. The corner e (Fig. 9) has been removed, and 
 the pressure cone, now filling out the entire space, has thereby 
 been widened and brought into a more favorable direction. 
 
21} 
 
 The undercuts are less deep, and have no sharp angles. The 
 latter is, however, of less importance with metaUic than with 
 porcelain inlays. The form of undercut in the tooth. Fig. 10, 
 weakens the wall far less than one made with a wheel. The 
 lower part of the undercut in the inlay, has been cut obliquely 
 so that the pressure cone rests at right-angles upon the sur- 
 face of the inlay. 
 
 A further advantage of this form of undercut is the follow- 
 ing. It is a known fact that most cements expand while 
 
 ///////////////y/,-y//^'.' '^///.'///^//y// '/^//X 
 
 Fig. 9. 
 
 Fig. 10. 
 
 setting.*) This causes the inlays, set with such cements, to 
 rise out of the cavity to a greater or lesser extent. If, however, 
 undercuts, correct in form and in relative position be used 
 (Fig. 10), an expansion of the cement does not force the 
 inlay out, but on the contrary, presses it more firmly into the 
 cavity. In such cases attention should be paid to the fact, 
 that the mass of the cement mu.t be contained in the under- 
 cuts, the cement at all other points being limited to the 
 thinnest possible layer. 
 
 *) See Poundstone"s table p. 140. 
 
24 
 
 Where the undercut in the inlay lies above that in the 
 tooth (Fig. 11), the pressure-cone finds but little hold upon 
 the almost vertical wall of the cavity. The retention of the^ 
 inlay in this case does not depend upon the crushing strength, 
 but almost v/hoUy on the tensile strength of the cement. 
 Tension, like compression, spreads through a mass in the form 
 of a cone. Therefore, in the cement layer of Fig. 11a tension- 
 cone will extend from the undercut a — h in the direction c. 
 
 ' "'itlll III! "Illll III III' 
 
 Ym. 11. 
 
 Fig. 12. 
 
 The cross-sectional area at a is too small to give sufficient 
 retention to the inlay. As the tensile strength of cement is 
 far lower than its compression, or crushing strength, the 
 sectional area of the tension-cone must be far greater than 
 that of the pressure-cone to give the same retention. Besides 
 this, it is necessary to make regular undercuts in the tooth 
 as well as the inlay, as the adhesive qualities alone can not 
 be depended upon (Fig. 12). 
 
 Roughening the Surface. 
 
 The second method of producing a hold for the cement 
 is by roughening the under surface of the inlay with a sharp 
 instrument. Hersey*) recommends the Bonwill mallet. Any 
 
 G. S. Hersey, Dental Cosmos, Nov. 1906, p. 1167. 
 
mechanical mallet with a sufficiently strong blow can be used. 
 The writer has had the best and quickest results by using 
 a sharp instrument in the mechanical engraving instrument, 
 shown in Fig. 113. 
 
 If the cement layer is thin, the blows must fall at right- 
 angles to the surface, so that the roughening consists of in- 
 numerable depressions placed close to one another. An en- 
 largement of one of these depressions is shown in Fig. 13. 
 Where the cavity has been widened, the point of the instrument 
 is applied obliquely to to surface, and small step-like pro- 
 jections are thrown up (Fig. 14). The projections should be 
 
 
 Fig. 13. Fig. 14 
 
 miniature reproductions of the undercut shown in Fig. 10. 
 The step should always face the direction in which the inlay 
 can be removed from the cavity, so that the retention may 
 depend upon the crushing strength of the cement. A slight 
 widening of the cavity, below the margin, is the only treat- 
 ment the tooth requires before setting the roughened inlay. 
 Regular undercuts into the dentine are unnecessary. 
 
 The retention of a roughened inlay depends upon the 
 number and size of the pressure-cones produced by the pro- 
 jections. These in turn are dependent upon the area of the 
 surface of the inlay within the cavity. A roughening is there- 
 fore indicated in proximal, cervical, and labial inlays, as they 
 are not exposed to mastication and their free surface is always 
 less than that within the cavity. Proximal inlays in molars 
 and bicuspids may be roughened if they are sufficiently an- 
 
26 
 
 chored by means of self-retention. Regular undercuts are, 
 however, to be used in the restoration of incisive edges, corners, 
 and cusps. 
 
 Upon what might be called accidental retention, rests the 
 explanation of the durability of so many inlays, gold as well 
 as porcelain, that have been set in improperly prepared cavi- 
 ties. Upon the dentine the cement always finds sufficient 
 hold. On the inlay there are usually present, in smaller or 
 greater numbers, projections accidentally formed. If some of 
 these are favorably placed, the cement finds a support to 
 resist compression. The strength of such retention is very 
 small, and being a matter of chance, should be totally dis- 
 regarded. 
 
 Ketention by means of cement may always be depended 
 upon if employed only in cases where it is indicated. The 
 preparation of the cavity must be correct, and there should 
 be a mechanical reason for the position of each undercut. 
 The practice of indiscriminately under-cutting both tooth and 
 inlay is unscientific, and is probably the cause of .many 
 failures. 
 
 Self-Retention. 
 
 Retention Depending upon the Form of the Inlay Itself. 
 
 Inlays of this description are confined almost exclusively 
 to the molars and bicuspids. The hold, or anchorage of a 
 self-retentive inlay must be so located, that, without depend- 
 ing upon the retentive power of the cement, it can easily 
 resist the forces which tend to dislodge the inlay during 
 mastication. The extent of the hold, which the inlay finds 
 upon the tooth, is of less importance than its location. A slight 
 hold at the proper place, is more valuable than a stronger an- 
 chorage at a point where it can not counteract the forces 
 which tend to dislodge the inlay. Though all so-called self- 
 retentive inlays do not strictly fulfill the above requirements, 
 they nevertheless are anchored in more directions than inlays 
 depending entirely upon cement-retention. 
 
 The strength and the direction of the force acting upon 
 an inlay, are dependent upon the size and form of the occlusal 
 
surface. The direction of the force is of prime importance. 
 If the antagonist strikes the obHque occlusal surface of the 
 inlay (Fig. 15), force will be exerted in two directions; toward 
 the middle, and toward the neck of the tooth. The more 
 oblique the surface, the greater will be the pressure forcing 
 
 Fig. 15. 
 
 the inlay into the cavity. This fact is of practical significance 
 if two adjoining proximal cavities are to be filled with inlays. 
 As in this case the position of the contact points is not pre- 
 determined, they may be placed slightly nearer the cervical 
 margin than normally, thereby giving the inlay a decidedly 
 more oblique occlusal surface (Fig. 16). Such a procedure 
 
 Fig. 16. 
 
 is valuable in filling bicuspids extensively destroyed by caries, 
 as it obviates the necessity of cutting deeply into the weakened 
 walls in order to obtain complete anchorage by this means 
 alone. 
 
 If the occlusal surface is horizontal, as in the case of the 
 molars, simply closing the jaws will force the inlay against 
 the cervical margin, while the masticatory movements will 
 tend to tip the inlay out of the cavity. To prevent such 
 dislocations, the inlay must be formed so that it finds a hold 
 
upon the tooth. In order to determine the exact location of 
 this hold or anchorage, the different phases during the dis- 
 location of an inlay must be understood. The inlay may be 
 dislodged in two ways, depending upon the shape of the cavity. 
 If the wall at the cervical margin is narrow (Fig. 17), the 
 inlay is insufficiently supported against vertical pressure. It 
 
 Fig. 17. 
 
 Fig. U 
 
 may then be forced out of the cavity, as on an inclined plane, 
 and the margin a at the same time fractured. In the second 
 case, where the wall is wide enough to give support against 
 the vertical pressure, forces acting obliquely produce a leverage 
 which tends to tip the inlay out of the cavity (Fig. 18). The 
 
 Fig. 19. 
 
 Fio-. 20. 
 
 cervical margin always acts as the fulcrum. To successfully 
 oppose this leverage, is the function of a self-retentive inlay. 
 To a limited extent, porcelain inlays of this description 
 have been made. In Stockholm, in 1902, N. S. Jenkins showed 
 such a porcelain inlay made by Ottolengui (New York). The 
 inlay (Fig. 19) was compact, without thin processes or ex- 
 tensions. On account of the brittleness of porcelain this was 
 the only form possible for a self-retentive inlay made of this 
 material. Though this cavity form (Fig. 20) was very ingenious, 
 it was not applicable to larger cavities, as in such cases suffi- 
 
2U 
 
 cient tooth-substance was lacking. The difficulty of preparing 
 such cavities has caused this form to be discarded. For metal 
 inlays other forms, more satisfactory and easily made, have 
 been adopted. 
 
 Metal, in contradistinction to porcelain, not being brittle, 
 permits the construction of thin processes and extensions 
 which firmly anchor the inlay into the tooth. 
 
 Groove Anchorage. 
 
 In considering the action of the leverage shown in Fig. 18, 
 it becomes apparent, that the dislocation is greatest at a, 
 and gradually decreases toward the point b. If this fact is 
 
 Fig. 21. 
 
 Fig. 2-2. 
 
 practically applied, an inlay of the form shown in Fig. 21 
 will result. The extension is strongest at a. This, the point 
 of greatest movement during dislocation, is farthest away from 
 the fulcrum, and is also most easily accessible in cutting the 
 groove into the cavity wall. The extension need not be carried 
 to the point h as sufficient anchorage can be obtained at a, 
 to firmly lock the inlay in the cavity (Fig. 22). 
 
 Fissure Anchorage. 
 
 If the lateral walls of a proximal cavity are weak or entirely 
 absent, or if the fissures in the occlusal surface require filling, 
 
 Fig. 23. 
 
30 
 
 the anchorage mentioned above should not be used. In such 
 cases the fissure-anchorage is indicated. The fissure is excavated 
 until a fissure running in a bucco-lingual direction is reached 
 (Fig. 23). This is excavated in one or both directions. If a 
 fissure of this description is not present an artificial one 
 running in this direction must be made. 
 
 Hook-Anchorage. 
 
 This form of anchorage is indicated in cases where the 
 occlusal surface has been almost entirely destroyed (Fig. 24), 
 
 Fig. 24. 
 
 and where at the same time the lingual or buccal wall is 
 lacking. With a thin disk-wheel a groove is cut into the 
 occlusal surface of the remaining wall. At its outer end the 
 groove is extended vertically for a short distance [a, Fig. 25). 
 
 Fiff. 25. 
 
 Fig. 26. 
 
 The resultant inlay then has a hooklike process, which pre- 
 vents any dislocation through the forces of mastication. If two 
 opposing walls are standing, the double hook-retention not 
 alone anchors the inlay, but it also gives support to weakened 
 walls (Fig. 26). This form of anchorage is of value in pulpless 
 molars, where the proximal surfaces have been extensively 
 destroyed by caries, and the weakened buccal and labial walls 
 still remain standing. 
 
31 
 
 Dove-tail Anchorage. 
 
 This is a modification of the form just described. Strength 
 is the first requisite of the wall into which such an anchorage 
 is placed. The dove-tail cavity should have walls {a and b. 
 Fig. 27) parallel to the direction in which the inlay may be 
 
 Fig. 27. 
 
 removed from the cavity. The floor of the cavity (a, Fig. 28) 
 should incline, from within outward, toward the neck of the 
 tooth. The segment c (Fig. 27) of the inlay should be suffi- 
 ciently strong to prevent stretching of the metal at this point, 
 under the force of mastication. If the body of the inlay is 
 firmly seated (Fig. 28), thereby resisting all vertical pressure. 
 
 Fig-. 28. 
 
 the segment c need not be excessively strong. If, however, 
 the floor of the main cavity is narrow or sloping, the segment 
 must resist the vertical as well as the oblique forces of masti- 
 cation, and must therefore be accordingly strong. The pre- 
 paration for the dove-tail anchorage is made with a knife- 
 edged stone, and the resultant inequalities in the floor finished 
 with a thin wheel. For larger inlays, this is the most easily 
 and quickly made form of anchorage ; a strong wall is, however, 
 always necessary. 
 
32 
 
 Anchorage through Combination of two Cavities. 
 
 Inlays having this form of anchorage are used in filling 
 molars, and more often bicuspids, v/ith cavities on both 
 
 Fig. 29. 
 
 mesial and distal surfaces (Fig. 29). The same applies to 
 inlays extending over the cutting edges, of the incisors and 
 cuspids. 
 
 Reciprocal Anchorage of two Inlays. 
 
 If one or both of the proximal cavities in a molar or bicus- 
 pid extend to the neck of the tooth, it is preferable to obtain 
 retention by means of reciprocal anchorage of two inlays. This 
 method has several advantages. As two impressions are taken. 
 
 Fig. 30. 
 
 each may be removed in the direction most convenient. If a 
 single impression of both cavities were to be taken, much 
 healthy tooth structure would, in most cases, have to be 
 sacrificed in order to allow the impression to draw. Another 
 point is the difficulty of making a perfect inlay which in- 
 volves three surfaces of a tooth. 
 
 The procedure of combining two inlays is as follows (Fig. 30). 
 
33 
 
 An impression is taken of the more difficult cavity. The 
 inlay I, should not extend to the occlusal surface. At b, a 
 depression should be made, and the surface sloped in the 
 direction a. This is done upon the wax-model. The inlay is 
 then completed and set into the cavity and an impression 
 of the remaining part of the cavity taken. The second inlay II, 
 Fig. 30, is made and set in the usual manner. By means of 
 the projection c, and the inclined surface a, the second inlay 
 anchors the first in the tooth. The second inlay is itself an- 
 chored by the projection and the inclined plane as well as 
 by the hold it finds on the walls of the fissures and in the 
 second cavity. 
 
 Pin -Anchorage. 
 
 Another form of retention which may be used in double 
 as well as single inlays, is the pin-anchorage. At the proper 
 
 Fig. 31. 
 
 point, a canal is drilled through the inlay into the one lying 
 beneath, and into this a pin of suitable size is set with cement. 
 
 Fig. 32. 
 
 For double inlays the projection described above is preferable, 
 as it is easer to construct and does the same service. This 
 form of anchorage may, however, be used where other methods 
 
 Bodecker, Metallic Inlay. 
 
34 
 
 are not easily applicable, as in restoring the corners of in- 
 cisors (Fig, 31). In certain forms of inlay bridge -abutments 
 this method of anchorage has been employed. The principal 
 use of the pin-anchorange is in restoring the abraded sur- 
 faces of molars and bicuspids. The pins are let into the tooth, 
 and removed with the impression. The inlay is then cast 
 onto the pins (Fig. 32). In the experience of the writer, 
 German-silver has proved to be the best material for such 
 pins. In casting, the gold forms a perfect union with this 
 metal. 
 
Chapter IV. 
 Retention and Cavity-Form. 
 
 The practical apphcation of the different forms of an- 
 chorage will be discussed in a later chapter. The fundamental 
 principles of retention, which must be considered in the pre- 
 paration of every cavity, should be perfectly well understood 
 by those doing inlay work. 
 
 The cavity for an inlay should be so prepared, that the 
 wax model or the impression may be removed without dis- 
 tortion, and that the inlay may find sufficient hold on the 
 tooth to resist the force of mastication. This hold should, 
 whenever possible, depend upon the shape of the inlay, and 
 
 Fig. 33. 
 
 not upon an intermediary binding-material, such as cement. 
 In complex cavities this requirement is easily fulfilled. In 
 simple cavities the conditions are, however, somewhat different. 
 When porcelain inlays were first introduced, many opera- 
 tors, gave the cavities a saucer-shaped form, assuming that 
 the adhesion of the cement would keep the inlay in position. 
 Numerous failures occured; but these were ascribed to in- 
 equalities in the adhesiveness of the cement. A consideration 
 of Fig. 33 will show that the position of the undercuts in a 
 saucer-shaped cavity are most unfavorable for cement-reten- 
 tion. The walls of the cavity, and therefore also the sides 
 of the inlay, lie obliquely to the direction in which the inlay 
 
36 
 
 may be removed from the cavity. (Fig. 34. An enlargement 
 of an undercut in Fig. 33.) The undercuts in the inlay are 
 placed above those in the tooth; a condition which has been 
 described in discussing Fig. 11 and 12. The retention of the 
 inlay is therefore entirely dependent upon the tensile strength 
 of the cement. This is probably a truer explanation of the 
 failures than the assumption of differences in the adhesive 
 qualities of the cement. 
 
 To avoid these failures, it was then suggested to prepare 
 the cavity in the shape of a box, and to confine the thickness 
 
 Fia-. 34. 
 
 of the cement layer to a minimum. This procedure undoubtedly 
 gave the inlay a sort of self-retention. The box-shape was 
 then adapted to other cavities. By far the greater majority 
 of the authors writing upon the subject of cavity preparation 
 for gold inlays, have recommended the box-shape, strictly 
 carried out, for complex cavities in molars and bicuspids. 
 This necessitates extensive cutting into healthy tooth structure 
 and has, as a result, caused many operators to disapprove of 
 the metallic inlay as a means of filling teeth. 
 
 Before entering into the question of the proper thickness 
 of the cement layer, the influence of the box-shape on retention 
 will be discussed. As the conditions for cement-retention in 
 saucer-shaped cavities are unfavorable, and the inlay itself 
 has no anchorage in the tooth, direct pressure on its surface 
 
37 
 
 will force the inlay it out of the cavity (Fig. 35). If the cavity 
 is box-shaped, the inlay cannot be dislodged in this way 
 (Fig. 36). Not alone does the inlay here find a hold in the 
 cavity, but the conditions for cement-retention are as perfect 
 
 Fig. 35. 
 
 Fig. 36. 
 
 as possible. The theoretically correct undercuts (Fig. 10) may 
 be employed, with the certainty that the cement-retention 
 will not fail. The success of this form of cavity is based upon 
 the fact, that the walls of the cavity lie farallel to the direction 
 in which the inlay can he removed from the cavity. This funda- 
 mental rule should be observed in the manner described later, 
 in preparing all inlay cavities. 
 
 "Box-shaped" does not suggest the same form to every 
 operator. A cavity such as Fig. 37, has been so designated. 
 
 Fig. 37. 
 
 But in spite of the straight walls and vertical floor, such a 
 cavity possesses most of the physical characters of the ordinary 
 saucer-shaped cavity. According to the opinion of the writer, 
 the characteristic feature of the box-shaped cavity, is the 
 presence of walls, parallel to the direction of removal of the 
 inlay (Fig. 38). The general form of the cavity is immaterial. 
 The floor need not be horizontal, nor need the angles at this 
 point be sharp, as usually shown in illustrations. 
 
38 
 
 There are some places where it is impossible to prepare 
 a cavity box-shaped, in the strictest sense of the word. §uch 
 a cavity with four parallel walls cannot be cut into the neck 
 
 Fig. 38. 
 
 of a bicuspid (Fig. 39). The upper and lov/er walls of the 
 cavity {a and b) may be made parallel, but the lateral walls 
 (c and d) must converge in order to be at right-angles to the 
 surface of the tooth. These walls are therefore not suitable 
 
 Fig. 39. 
 
 for cement-retention. The walls a and h, lying opposite each 
 other, have the proper direction and are of considerable length. 
 If these are correctly undercut, sufficient anchorage for 
 cement-retention will be obtained. If the pulpal wall of the 
 cavity c — d (Fig. 39) is convex or even straight, and it is not 
 deemed advisable to further weaken the neck of the tooth 
 
by extending the cavity (Fig. 40, a), another method of pre- 
 venting lateral dislocation may be used. At a and b, Fig. 41, 
 broad notches are cut into the inlay. These should lie at 
 right-angles to the direction in which the inlay can be dis- 
 lodged. If the pulp is sufficiently distant, grooves (e and /, 
 Fig. 42) may also be cut into the tooth. The latter should 
 
 Fig. 40. 
 
 Fis. 41. 
 
 Fig. 42. 
 
 Fig. 43. 
 
 be wider than those in the inlay, to allow for the difficulty 
 in bringing these undercuts into exact apposition. The cement 
 filling out the grooves acts as an inclined plane, changing 
 the direction of pressure applied laterally, so that the inlay 
 seeks to escape in the direction c, (Fig. 41). The cement- 
 anchorage on the upper and lower walls {a and h, Fig. 39), 
 is sufficiently strong, however, to prevent the inlay from being 
 forced out in this direction. 
 
 Instead of the anchorage illustrated in Fig. 40, that 
 
40 
 
 shown in Fig. 43 may be used, if the pulp is sufficiently 
 distant. Of these forms (Figs. 40 — 43), several may be em- 
 ployed in the retention of a single inlay. The presence of the 
 anchorage Fig. 40 or 43 on one end is desirable; it acts as 
 a guide in setting the inlay into the cavity. 
 
 From the above explanation, it becomes evident, that a 
 complete box -shaped cavity is not always possibile, nor 
 is it necessary for the retention of even a simple inlay. In 
 certain places, however, where the inlay is exposed to the 
 force of mastication, the complete form, with four walls, 
 should be used. This refers especially to inlays on abraded 
 surfaces. In preparing such cavities the following fact should 
 always be remembered. Two walls, opposite each other, and 
 lying parallel to the direction of removal of the inlay, are of 
 far greater value than four walls lying obliquely to this direction. 
 
 The application of the box-shape to complex cavities of 
 molars and bicuspids has occasioned much adverse criticism. 
 For this exaggerated type of cavity, there are neither practical 
 nor mechanical reasons, and its acceptance as the correct 
 cavity-form for metal-inlays, has caused many operators to 
 question the value of this method of filling teeth. In simple 
 cavities the box-shape is employed to give the inlay a certain 
 amount of mechanical anchorage in the tooth. In complex 
 cavities, however, there are so many other forms of anchorage 
 to select from, that, in the opinion of the writer, an exact 
 box-shaped preparation becomes quite unnecessary. 
 
 Many authors have advocated making the cement layer 
 between inlay and tooth in the depth of the cavity, as thin 
 as possible, believing that under such conditions cement would 
 be less liable to fail as a retentive agent. The fact however 
 remains, that any force exerted upon the inlay is transmitted 
 to the tooth through the cement layer, and that the force 
 which a self-retentive inlay can resist is dependent upon the 
 crushing-strength of the cement. Not the thickness of the layer, 
 but the quality of the cement, is the determining factor, as 
 can be seen from the following test. 
 
 Into the rough -walled chamber of the metal block B 
 (Fig. 44), a roughened metal plug Z is set with cement, and 
 
41 
 
 the parts suspended as shown in the diagram. By gradually 
 increasing the weight on the scale-pan, the exact tension 
 necessary to cause a failure of the cement layer is determined. 
 If in a subsequent test, the block is made of cement instead 
 of metal, the plug occupying the exact relative position as 
 in the previous test, the weight supported will be the same 
 or even greater. If instead of tension, pressure is applied to 
 the plug, the tests with the metal and the cement block will 
 
 Fig. 44. 
 
 give the same result. The force necessary will however be 
 much greater, as the crushing strength of cement is about 
 ten times that of its tensile strength. The conclusions to be 
 drawn from these experiments are, that a thin cement layer 
 offers no advantage, and that the box-shape of a cavity, 
 except at the margin, may be produced by cement. Practi- 
 cally this is of importance in cavity-preparation, as it often 
 prevents the sacrifice of healthy tooth substance. The above 
 tests emphasize a point to which attention has been called 
 in Chap. Ill, that is, in using cement as a retentive agent 
 the undercuts should be so placed and of such shape, that 
 the crushing strength and not the tensile strength of the 
 cement is relied upon. 
 
 As a result of making the cavities box-shaped and the 
 cement layer as thin as possible, the inlay itself became box- 
 shaped. 
 
42 
 
 A careful consideration of Fig. 45 will show that the 
 direction of the walls in the defth of the cavity, has no in- 
 fluence upon the retention of a box-shaped inlay, as soon as 
 the intervening space is filled with cement. Far different, 
 however, will be the result, if in a box-shaped cavity the 
 direction of the lateral walls of the inlay are altered (Fig. 46). 
 
 Fig. 45. 
 
 Fig. 46. 
 
 The greater the inclination of these surfaces, the more un- 
 favorable will be the conditions for retention by means of 
 cement (see Figs. 33 — 35). The good results which the box- 
 shaped cavity preparation has shown, depend, in the opinion 
 of the writer, less upon the form of the cavity, than upon 
 the box-shape of the inlay. 
 
 Equally applicable, is this principle to the complex cavities 
 of the molars and bicuspids. In the case of simple cavities 
 it has been shown, that the superiority of the box-shaped 
 
43 
 
 inlay depends upon the presence of at least two surfaces lying 
 on opposite sides of the inlay, and being parallel to the direction 
 in which the inlay may he removed from the cavity. By applying 
 this simple rule to the most complex cavities of the molars and 
 bicuspids, perfect retention can be readily obtained, and the 
 unnecessary removal of healthy tooth-structure avoided. In 
 describing the application of this principle to such cavitives, 
 a lower molar with an occluso-proximal cavity has been 
 chosen as an example. The retention is to be obtained by 
 means of fissure-anchorage. Fig. 48 shows a section through 
 tooth and inlay, Fig. 49 shows the form of the inlay on the 
 occusal surface. For convenience of explanation the longitu- 
 dinal fissure has not been completely filled. In practice this 
 should never be omitted. 
 
 Mention has been made of the fact, that a proximal inlay 
 extending to the occlusal surface, must be able to resist 
 pressure in two directions, vertically and obliquely. The first 
 is produced by the closure of the jaws and tends to force 
 the inlay out of the cavity in the direction of the neck of 
 the tooth; the second, produced by masticatory movements, 
 tends to pry out the inlay in the direction of the interproximal 
 space. 
 
 To give an inlay resistance to vertical pressure, the authors 
 in whose opinion the box-shaped cavity preparation should 
 be strictly carried out, advocate making as many surfaces 
 as possible at right angles to the direction of pressure (Figs. 47 
 and 66). This in itself is perfectly correct. It gives the inlay 
 a secure base; and in transmitting the force from the inlay 
 to the tooth it puts the cement layer under compression, 
 and not, as in the molar of Fig. 57, under tension. But it is 
 questionable whether the practive of giving an inlay such 
 an unnecessarily great power of resistance to vertical pressure 
 is justifiable, if this is done by the removing large quantities 
 of healthy tooth structure. 
 
 Fig. 17 shows how vertical pressure may dislodge an inlay 
 resting upon a narrov/ cavity floor. In Fig. 18, to avoid this 
 danger, the floor of the cavity has been broadened, i. e., a larger 
 surface lying at right angles to the direction of pressure has 
 
44 
 
 been produced. It is, however, not necessary, nor in larger 
 cavities advisable, to place the whole of this bearing surface 
 upon the gingival wall of a proximal cavity. A more favorable 
 distribution of these surfaces will be discussed later. Strict 
 box-shaped cavity preparation demands, that the floor of a 
 proximal cavity be prepared in the form of steps. This be- 
 sides being difficult and tedious, requires the unnecessary 
 destruction of tooth substance. 
 
 Fig. 47. (From a dental journal.) 
 
 Inclined grooves (Fig. 21) increase the bearing surface of 
 the inlay. As in this case the inlay, under pressure, acts as 
 a wedge, the lateral walls of the cavity must be very strong. 
 To some extent this pressure may be relieved by giving the 
 inlay a broad bearing surface upon the gingival wall of the 
 cavity. It is however advisable to confine the use of this 
 method of giving inlays the power of resisting vertical pressure, 
 to the smaller proximal cavi titles. 
 
 There remains another method by which the bearing sur- 
 face of an inlay may be increased, and that is the fissure 
 anchorage. This method has several advantages. 
 
45 
 
 1. By cutting out the fissure, the surface effective in 
 resisting vertical pressure is increased. 
 
 2. As this is done upon the grinding surface, the pre- 
 paration is easier, quicker, and less painful than cutting 
 steps or broadening the wall of the cavity at the neck 
 of the tooth. 
 
 Fig. 48. 
 
 3. By filling the fissures, caries will be prevented. 
 
 4. By means of a specially prepared pit in the fissure 
 {a, Fig. 48) or by an extension in the transverse fissure 
 (e, e, Fig. 49), the inlay gains additional resistance to 
 
 Fie-. 49. 
 
 vertical pressure. Only by fracturing the tooth in the 
 direction a — h (Fig. 48) or e — f (Fig. 49), can vertical 
 pressure dislodge the inlay. The amount of pressure which 
 an inlay of this form can resist, is dependent upon the 
 depth of the pit a; the length of the extension e — e; 
 the strength of the connection d, lying in the longitu- 
 dinal fissure ; and upon the strength of the tooth-struc- 
 
46 
 
 ture between the points a and h, or e and /. The area 
 of the floor of the proximal cavity is of but little con- 
 sequence in this method of retention. As a result, the 
 wall h — a (Fig. 48) need not be vertical, as in true box- 
 shaped cavity preparation, thereby preserving a thicker 
 layer of dentine over the horns of the pulp without 
 decreasing the resistance of the inlay to vertical pressure. 
 Special attention must be called to the fact that in 
 this method of cavity preparation, the depth of the 
 pit a, or the length of the extention e — e, and the strength 
 of the connection d, should stand in direct ratio to the 
 length and inclination of the wall h c. 
 5. Beside the above mentioned advantages, this form of 
 inlay offers the most secure anchorage against the 
 oblique pressure caused by the movements of masti- 
 cation. 
 In the previous chapter the different forms of anchorage, 
 designed to resist oblique pressure, v/ere described. It is, how- 
 ever, necessary to explain the application of the principle — 
 walls farallel to the direction of removal of the inlay, — to this 
 class of retention. Fig. 18 shows the manner in which an inlay 
 is tipped out of the cavity by oblique pressure. It has been 
 mentioned that this may be prevented by the fissure-anchorage. 
 If the cavity has been prepared in the manner shown in Fig. 50, 
 the inlay will be able to successfully resist the vertical pressure. 
 If oblique pressure be brought to bear on the point a. Fig. 51, 
 the inlay will be tipped out of the cavity. Pressure exerted 
 upon the proximal surface (Fig. 52), by hard particles of food 
 wedging against the neighbouring tooth, or by forcing a tooth- 
 pick into the interproximal space, may cause a dislocation of 
 the inlay. In this form, the fissure-anchorage does not meet 
 the requirements of the case. 
 
 The inlay must be so constructed that it can be removed 
 from the cavity in hut one direction. Preferably this direction 
 is to be so chosen, that it is opposed to that of the ver- 
 tical pressure. In order that an inlay may be guided in but 
 one direction during its removal from the cavity, it must possess 
 two surfaces which are opposite each other and parallel to the 
 
47 
 
 direction of removal of the inlay. Fig. 53 shows that these 
 parallel surfaces may be situated at a and h, h and c, or on the 
 same inlay at a, h, and c. An inlay of this form can be dislodged 
 
 Fis;. 50. 
 
 Fig. 51. 
 
 Fig. 52. 
 
 neither by vertical nor by oblique pressure, as the parallel 
 walls form a guide which allows the inlay to be removed 
 only in the direction of the arrow. The presence of these 
 
 guide-surfaces is essential in every case, their size, however, 
 in order to oppose the oblique pressure need not be large. 
 This question will again be referred to in discussing the cement 
 attachment of this class of inlays. 
 
48 
 
 The office of the cement as a retentive agent for inlays 
 in proximal cavities has not as yet been touched upon. Many 
 inlays doing service for a long period of time in carefully 
 prepared, but mechanically incorrectly shaped cavities, owe 
 their retention entirely to the cement (Fig. 57). The same is 
 true of some inlays in cavities prepared strictly according to 
 the box-shaped principle (Fig. 66). 
 
 In certain proximal cavities of the posterior teeth, it is 
 justifiable to disregard the mechanical anchorage, and to 
 depend entirely upon the cement for retention. Such cavities, 
 facing the space caused by an extraction, have their greatest 
 diameter at the neck of the tooth, and involve but little of 
 the occlusal surface (Fig. 54). To prepare the cavity so, that 
 
 Fig. 54. 
 
 the impression could be removed only in the direction con- 
 trary to that of the vertical pressure, would be useless labor 
 and an unnecessary destruction of tooth-substance. The prac- 
 tice of extension for prevention would not be indicated in 
 this case, as there is no contact with an adjoining tooth. 
 
 If the impression is removed from the cavity in the direction 
 of the space, the construction of a self-retentive inlay becomes 
 impossible. It is therefore upon the cement that complete 
 reliance must be placed. With a properly shaped inlay, this 
 mode of retention may, however, be relied upon. The fact 
 that the inlay possesses a small occlusal surface (Fig. 54), 
 may be disregarded, and the cavity considered as a simple 
 one, lying on the proximal surface of the tooth. It has been 
 shown that sufficient retention can be given an inlay, by 
 constructing two of its surfaces parallel to the direction of 
 
49 
 
 removal. In the present case this direction would be toward 
 the space, as the oblique pressure would tend to tip the inlay 
 out of the cavity. In discussing mechanical anchorage it 
 was shown, that to prevent dislocation, the hold should be 
 applied as high as possible, that is, as far away from the 
 fulcrum of the leverage as circumstances will permit (Fig. 21). 
 The preparation of the parallel walls a and h (Fig. 54) is begun 
 at the occlusal surface and continued as far as possible in the 
 direction of the neck of the tooth, constantly keeping in mind 
 that they are to be made parallel to the direction in which 
 the inlay could be tipped out of the cavity. It is not necessary 
 to make the walls parallel to the points c, as the chief hold 
 lies at a and h. The gingival wall of the cavity should, however, 
 be broad and horizontal, in order to oppose the vertical 
 pressure. 
 
 Whether the inlay should be regularly undercut or simply 
 roughened, must be decided from case to case. If the parallel 
 surfaces a and h are small, or ii the occlusal surface of the inlay 
 is large, regular undercuts should be employed. If the con- 
 trary is the case, simple roughening will give ample security. 
 As a rule, it is best to make short undercuts at a and h, lying 
 at right angles to the direction in which the inlay can tip, 
 and to employ the step-like roughening (Fig. 14) upon the 
 remaining surfaces. Bevelling the occlusal surface toward the 
 space, is to be recommended (Fig. 16); instead of being tipped 
 out, the inlay is then pressed into the cavity more firmly 
 by the vertical pressure. 
 
 The principles just described are applicable not only to 
 the posterior teeth, but to proximal cavities of other teeth 
 as well. Inlays constructed in this manner do very good 
 service, but as a rule the anchorage of all larger inlays in the 
 bicuspids and molars should depend upon self-retention. 
 
 Th3 office of the cement, in retaining a correctly con- 
 structed, self-retentive inlay in the cavity, is confined to a 
 filling out of all spaces between the inlay and the tooth, and 
 to the prevention of dislodgement in the direction of removal. 
 In discussing Fig. 53, it was stated that the parallel surfaces 
 a and h need not be large in order to resist the obUque pressure. 
 
 Tiddecker, Metallic Inlay. 4 
 
50 
 
 For a reliable cement attachment, these surfaces alone are, 
 however, too small. Only such surfaces which lie on sides 
 opposite each other, and which are parallel to the direction of 
 removal, are suitable for cement-retention. If no other sur- 
 faces of this description are present upon the inlay, the trans- 
 verse fissure must be deepened considerably to increase the 
 area of the surfaces a and h (Fig. 53). 
 
 In a cavity whose buccal and lingual walls are lacking 
 (Fig. 49) and whose axial wall is inclined (c, h, Fig. 48), the 
 parallel surfaces may be made upon the connecting segment 
 of the inlay lying in the longitudinal fissure at d (Fig. 48 
 
 Fig. 55. 
 
 and 49). The depth of excavation necessary in the transverse 
 fissure {a. Fig. 48 or e — e. Fig. 49) depends upon the area of 
 the surfaces g and Ji (Fig. 49), and the inclination of the axial 
 wall c — h (Fig. 48). If the parallel surfaces are small, regular 
 undercuts are necessary at these points for reliable cement- 
 retention (Fig. 10). As a rule however, roughening the sur- 
 face of the inlay as shown in Fig. 14 is sufficient. 
 
 In case the lingual and buccal walls of the cavity have 
 been preserved, the parallel surfaces on the inlay should be 
 situated there. By virtue of the fact, that the inlay can be 
 removed in but one direction, the proximal part may be con- 
 sidered as a simple cavity opening upon the occlusal surface. 
 If then, the walls a and h (Fig. 55) are, for a short distance, 
 made parallel to the direction of removal, ideal conditions 
 for cement-retention will have been produced. If the axial 
 wall is inclined, the surfaces a and h should be increased in 
 
51 
 
 area. If the axial wall is vertical, and the walls a and h cor- 
 rectly prepared, deep excavation will become unnecessary in 
 transverse fissure (e — e, Fig. 49), 
 
 Regular undercuts are not necessary in this class of inlays. 
 That part of the inlay, lying in the fissure, is roughened by 
 blows at right-angles to the surface (Fig. 13). The surface 
 of the inlay, lying within the proximal cavity, is roughened 
 
 Fig. 56. 
 
 by an obliquely applied instrument (Fig. 14). As this throws 
 up small projections, thereby slightly increasing the size of 
 the inlay, a thin layer of dentine should be removed from 
 
 Fig. 57. (From a dental journal.) 
 
 the walls of the cavity at the points opposite to the surfaces 
 so roughened. 
 
 In discussing the fundamental principles of retention, only 
 certain cavities of the molars and bicuspids have been cited 
 as examples, as these are the ones most commonly filled with 
 metallic inlays. The application of the principles to other 
 cavities is perfectly simple if the reader has understood the 
 writer's ideas upon the subject of cement-retention and self- 
 retentive inlays. 
 
52 
 
 Before leaving this subject, a few examples of inlays with 
 insufficient retention will be given. Fig. 56 shows a form of 
 anchorage which has been repeatedly recommended. Without 
 going into details, it is only necessary to call attention to the 
 fact, that an inlay of this form cannot resist oblique pressure, 
 as the hold it has on the tooth (the extension) is situated very 
 close by to the fulcrum of the leaverage. Among the hollow 
 inlays many examples of insufficient retention may be found 
 (Fig. 57). In filling out the space, the cement gains a firm 
 hold on the inlay ; the hold upon the tooth, however, is entirely 
 dependent upon the adhesive power of the cement. Granting 
 the latter to be sufficiently strong, the retention of the inlay 
 then depends upon the tensile strength of the cement, and 
 this, as has been previously mentioned, is not very great. 
 
Chapter V. 
 Caries and Cavity-Form. 
 
 Though this subject has been thoroughly discussed in text- 
 books on operative dentistry, it is deemed advisable to empha- 
 size certain points which should be considered in preparing 
 cavities for metallic inlays. Experience has shown, that it is 
 not necessary to remove any more, and sometimes even less, 
 tooth-substance in preparing a cavity in which a metallic 
 inlay is indicated, than in preparing the same cavity for a 
 perfect gold foil filling. For comparison, the cavity preparation 
 for foil fillings as advocated by G. V. Black*), has been chosen. 
 
 In preparing a cavity, the fact should never be overlooked, 
 that the office of a perfect filling is not alone to restore the 
 destroyed parts, but that it should also protect the tooth at 
 that point from recurrent caries. For this reason, it has 
 become a recognised practice in filling the fissures on the 
 occlusal surfaces of the posterior teeth, to excavate the affected 
 fissure throughout its whole length. To what extent this 
 principle should be applied to the proximal cavities is a mooted 
 question. Theoretically the practice is justifiable, practically, 
 however, experience has proven that it is not always necessary. 
 
 The point of origin of dental caries is either a fissure, or a 
 smooth surface protected from the cleansing action of masti- 
 cation. The course of the carious process is dependent upon 
 its point of origin. Caries in enamel, as well as in dentine, 
 progresses in the form of a wedge. In caries of the fissures, 
 the points of the wedges lie in opposite directions {a, Fig. 58). 
 In the enamel the process is somewhat limited, while in the 
 dentine, owing to the less resistant dentine-enamel margin, 
 the spread of caries is far more rapid. The effected area of 
 
 *) G. V. Black, Operative Dentistry, Vol. II. 
 
54 
 
 the dentine is therefore considerably larger than that of the 
 enamel. - 
 
 In caries beginning upon smooth surfaces, the points of 
 the affected wedge-shaped areas lie in the same direction 
 
 Fig. 58 (after Black). 
 
 i 
 
 Fig. 59 (after Black). 
 
 [h. Fig. 58, a and h, Fig. 59). In contradistinction to caries 
 of the fissures, the area of the enamel involved is larger than 
 that of the dentine. This is explained by the fact, that the 
 agents producing caries can more easily attack the surface 
 of the enamel at more protected points than upon the self- 
 cleansing occlusal surface of the teeth. 
 
 An examination of Fig. 58 proves, that a broad excavation 
 
55 
 
 of the fissures is perfectly justified on account of the spread 
 of the caries along the dentine -enamel margin. This is of 
 advantage to the inlay, as thereby the extensions lying in 
 the fissures are greatly strengthened, thus giving the inlay 
 a firmer anchorage in the tooth. 
 
 The writer considers the box-shaped cavity, as usually 
 recommended, not at all necessary for an inlay. It requires 
 extra labor and a useless destruction of tooth substance, some- 
 times to such an extent as to endanger the horns of the pulp. 
 A cavity prepared in the tooth Fig. 58, would fulfill all require- 
 ments, if it had the form shown in Fig. 60. The course of the 
 enamel prisms is such that the cavity margin need not be 
 bevelled. This gives the inlay two parallel surfaces lying 
 
 Fig. 60 (Black). 
 
 Fig. 61 (Black). 
 
 Fig. 62 (Black). 
 
 opposite eachother, which is amply sufficient for cement- 
 retention. The impression can be more easily removed from 
 this form, than from a box-shaped cavity. 
 
 If the cavity (Fig. 60) is to be filled with gold, the floor 
 must be made flat. If this is done at right-angles to the 
 deepest point, the form shown in Fig. 61 will result. This 
 would probably endanger the horns of the pulp. To avoid 
 this danger. Black advocates cutting a ledge a little above 
 the deepest part of the cavity (Fig. 62). For an inlay this 
 form of cavity offers no advantage over that of Fig. 60. 
 Besides being a loss of time, cutting the ledge increases the 
 danger of making undercuts in the walls of the cavity. It is 
 just in the fissure cavities, where the amount of the material 
 is small, that the slightest undercut may produce distortion 
 during the removal of the impression. 
 
 The preparation of box-shaped cavities upon the smooth 
 
56 
 
 surfaces, necessitates a still greater destruction of tooth-sub- 
 stance than is the case in fissure cavities. This becomes 
 evident in examining cervical caries on the buccal surface of 
 a lower molar. Caries at this point spreads in a horizontal 
 direction (h, Fig. 59), while vertically it remains limited 
 
 Fig. 63. 
 
 Fig. 64. 
 
 Fig. 65. 
 
 (£, Fig. 58). Instead of box-shaped (Fig. 63), such a cavity 
 may, without endangering the retention, be prepared almost 
 saucer-shaped in the horizontal direction (Fig. 64) as long as 
 the vertical section shows two parallel walls, lying opposite 
 each other (Fig. 65). 
 
 Proximal cavities prepared along similar lines, also show 
 the same advantage. A box-shaped cavity cut into the tooth 
 at a (Fig. 59), would require the removal of a considerable 
 quantity of healthy dentine. By preparing such a cavity in 
 
57 
 
 the maimer described (Plate I), this needless destruction is 
 obviated. A vertical section through the proximal cavity 
 shows that it is necessary to remove less tooth-substance in 
 preparing a cavity for a metallic inlay than in preparing the 
 same cavity for a foil filling. The inlay has the following 
 advantages: The gingival wall of the cavity need' neither be 
 large nor perfectly horizontal (Fig. 48); the cavity walls need 
 not meet at sharp angles; and the axial wall need not be 
 
 Fig. 66. (From a dental journal. 
 
 vertical. These requirements not only denote a saving of tooth- 
 substance, but they also make cavity preparation considerably 
 less difficult. 
 
 To what extremes the advocates of strictly box-shaped 
 cavity preparation have gone, is shown in Fig. 66. In the 
 preparation of this cavity, intended for a bridge-abuttment, 
 the vertical pressure to which the inlay is subjected, has 
 almost exclusively been taken into account. The oblique 
 pressure, caused by the movements of mastication, has received 
 but little attention. Neither the grooves a, a (Fig. 66), nor 
 
58 
 
 undercuts can give sufficient anchorage to prevent the leverage, 
 which is especially great in a bridge-abuttment, from, dis- 
 locating the inlay. 
 
 So far only those points, in which the cavity preparation for 
 an inlay differs from that of a foil filling, have been mentioned. 
 In other respects, the principles underlying the preparation of 
 cavities for foil fillings and for metallic inlays are identical. 
 
 These principles will only be briefly mentioned in order 
 to emphasize the fact, that a more extensive excavation is 
 not necessary for an inlay than for a gold filling. Proximal 
 cavities to be filled with inlays must be extended laterally, 
 to allow the impression to be drawn. This procedure has been 
 condemned as a useless sacrifice of healthy tooth-substance. 
 If, however, the long experience of operators who have given 
 this subject their special attention, counts for anything, then 
 the extended cavity, inevitable to a certain extent in an 
 inlay, represents the most perfect form for a foil-filling. This 
 method of cavity preparation, the so-called "extension for 
 prevention*)" of Black, is a prophylactic measure, pure and 
 simple, and never should be regarded as anything else. The 
 marked difference in opinion as to the value of this method, 
 has bred extremists in each direction. It is, however, just as 
 unreasonable to disregard it entirely, as to practice it in every 
 case. Being a prophylactic measure, it should be practiced 
 only when indicated. 
 
 The theory of extension for prevention**) is based upon the 
 fact that caries but very rarely attacks surfaces cleansed by 
 the food during the act of mastication. In normally placed 
 teeth, the surfaces especially immune to caries are situated 
 in the region of the mesio-lingual, the mesio-buccal, the disto- 
 lingual and the disto-buccal angles, and extend from the neck 
 to occlusal surfaces of the teeth (Fig. 67 and 68). For this 
 reason, it is often advisable, as a prophylactic measure, to 
 place the margin of the cavity in the region exposed to the 
 cleansing action of the food. 
 
 *) This term is here used in the most Umited sense, and does not include 
 the idea of contour or contact-point. 
 
 **) G. V. Black, Operative Dentisby. 
 
59 
 
 The cleansing action of mastication is dependent upon the 
 width and depth of the embrasures formed by the surfaces 
 of adjoining teeth. If the embrasures are narrow, (Fig. 69), 
 
 Fig. 67 (Black). 
 
 Shaded portions represent areas most liable to caries. The continuous black line 
 
 represents the free margin of the gum, while the dotled lines show its attachment 
 
 to the necks of the teeth. The double line shows the course of the saw in making 
 
 the cross-section Fig. 68. 
 
 the food ghdes only over the lingual and the buccal surfaces 
 of the teeth, if on the other hand, they are wide (Fig. 70) 
 
 Fig. 68 (Black). 
 
 a greater part of the proximal surfaces are also cleansed. As 
 the form of the embrasure is dependent upon the contour 
 
 Fig. 69 (Black). 
 
 Fig. 70 (Black). 
 
 of the tooth, it is necessary, in order to obtain a wide embrasure, 
 to build out the filling or inlay, as far and as rounded as 
 possible. Even though the natural tooth does not possess this 
 rounded contour (Fig. 69), it should be present on the finished 
 filling. As a rule there is not sufficient space for a contour filHng, 
 
60 
 
 and seperation must be resorted to. Guttapercha as a slower, 
 and cotton with varnish as a more rapid method, give good 
 results. For immediate seperation, the seperator must be used. 
 To forcibly produce a wide space at any point in the arch, 
 in cases where the teeth stand very closely, is a procedure 
 which the writer believes to be injurious to the other teeth. 
 Secondary caries will probably be prevented at the place filled, 
 but the increased pressure will make the proximal surfaces 
 of the other teeth more liable to attack. To produce an inlay 
 with a good contour in such an arch without taking up more 
 space than the tooth originally occupied, the proximal sur- 
 face should be ground flat with a diamond-disk (Plate V). 
 
 Fig. 71 (Black). 
 
 The margins of the cavity then lie in the region immune to 
 caries, and there is sufficient space to give the inlay a good 
 contour without still more crowding the arch. The best results 
 are obtained by this procedure v/hen tv/o proximal cavities, 
 lying opposite one another, are to be filled at the same time. 
 With inlays, the form of the interproximal space and that 
 of the cervical margin should be the same as with gold fillings. 
 The cervical margin should lie well toward the margin of the 
 gum; should be horizontal; and not too short in the linguo- 
 buccal direction. It is not, however, necessary to make the 
 lingual and the buccal angles as sharp as is recommended 
 for gold fillings (Compare Plate I and Fig. 71). To obtain 
 sharp angles, burs or chisels must be used, and these are 
 very liable to produce undercuts. With stones of proper shape 
 and size, the proper cavity-form is produced almost automati- 
 cally. 
 
61 
 
 The shape of the interproximal space is determined by 
 the distance between the teeth and the position of the con- 
 tact point. The latter should form a decided eminence (Fig. 72), 
 and not be gently rounded as in Fig. 73. The contact point 
 should lie just above the junction of the upper and middle 
 thirds of the crown of the tooth (Fig. 72). The inlay should 
 
 Fig. 72. 
 
 Fig. 73. 
 
 Fig. 74. 
 
 be as flat as possible below the contact point, as in Fig. 72, 
 not as in Fig. 73 or 74, so that the "pumplike action" of 
 mastication can readily keep the interproximal space clear. 
 A careful consideration of the facts discussed in this 
 chapter, will disprove the assertion, that the inlay requires 
 an unnecessary sacrifice of tooth-structure, if the theory of 
 extension for prevention is accepted and exaggerated box- 
 shaped cavities are avoided. 
 
Chapter VI. 
 The Enamel Margin. 
 
 Of prime importance for the durabihty of an inlay, is the 
 correct preparation of the enamel margin of the cavity. This 
 margin should be so prepared, that it possesses the greatest 
 possible resistance to injury under the following circumstances: 
 
 1. During the time that the cavity is temporarily filled, 
 that is, between the time of taking the impression and 
 of setting the inlay. 
 
 2. During the process of fitting and burnishing the inlay. 
 
 3. When the cement has been slightly dissolved out of 
 the seam. 
 
 4. In reclosing the seam by burnishing the gold against 
 the enamel margin. 
 
 Simply bevelling the edge does not, in all cases, insure 
 against failure. It is the structure of the enamel, that is, the 
 course of the prisms, that must be taken into account. As 
 has been mentioned, the surface of the cement is dissolved 
 to a depth equal to the width of the seam. The right-angled 
 enamel edge, no longer supported by the cement, is very 
 liable to fracture. To prevent this, bevelhng the edge 30 to 45 ° 
 has been advocated. If the enamel were a body equally 
 resistant in all directions, this precaution would suffice. The 
 fact, however, is that enamel is easily cleavable parallel to 
 the course of the prisms. If in preparing the margin, the 
 direction of the prisms is not accurately noted, a failure will 
 result in certain places on the teeth in spite of the fact that 
 the enamel edge was carefully bevelled. Fig. 75 shows a section 
 through the margin of a cavity filled with an inlay. The 
 enamel has been bevelled as advocated. The prisms, however, 
 lie, as they do in various places on the teeth, very obliquely 
 to the surface. As long as the cement within the seam remains 
 
63 
 
 inta(;t, tli(! onamcl cannot fracture, when in time the cement 
 is (lisH()]v(!(l, the oblique prisms loose their support, and are 
 soon broken away. The seam is thereby widened, allowing 
 a further solution of the cement to take place. When the 
 dissolution of the cement has reached the point a (Fig. 75), 
 a part of the cnarncl, of the form h — a, will gradually crumble 
 away. If the course of the prisms is at right angles to the 
 surface and the enamel edge slightly beveHed (P'ig. 76), the 
 danger of fracture is reduced to a minimum. It is therefore 
 
 Fig. 11 
 
 Fij,'. 70. 
 
 f'vident that thf; most favorjiljlc position for tlif; cavity wall 
 in the enamel region, is paralle] to the direction of the prisms. 
 This may, or may not result in a cavity wall lying at ri^^jt- 
 angles to the surface of the tooth. 
 
 The operator can only j^rfparf cavities correctly, if he has 
 a thorough knowledge of the course of the prisms on the 
 surfaces of each individual tooth. A study of the Figs. 77 — 82 
 shows that as a rule the prisms lie at right-angles to the sur- 
 face. Exceptions are ff^iind on thf occlusal surfaces and adja- 
 cent thirds of the crowns of the molars and bicuspids. The 
 enamel prisms of the incisors, particularly on the lingual sur- 
 face (Fig. 77), lie Vfry f^hliqiifly. In preparing a cavity on 
 this surface, the wall toward the incisive edge, must be espe- 
 cially oblique in the region of the enamel. The mesial, and 
 more markedly the distal angles of the cutting edge of the 
 incisors, show an oblique position of the enamel prisms (Fig. 78), 
 especially in the upper lateral incisor. In a cross section Xhrow^h 
 
64 
 
 Fig. 77 (Black). 
 An axio-labio-lingual 
 section of an incisor. 
 
 Fig. 78 (after Black). 
 
 An axio-mesio-distal section 
 
 of a lateral incisor. 
 
 Fig. 79 (Black). 
 "A bicuspid tooth split 
 bucco - lingnally showing 
 the directions of the ena- 
 mel rods in the different 
 parts of the plane of the 
 cut. The recessional lines 
 of the horns of the pulp are 
 shown by the dotted lines." 
 
 Fig. 80 (Black). 
 "A mesio-distal section of a lower 
 molar tooth showing the more 
 usual directions of the enamel 
 rods in the different parts of 
 the plane of the section." 
 
 Fig. 81 (Black). 
 Perpendicvdar section through 
 the cusp of a molar thooth. 
 
 Fig. 82 (Black). 
 
 Section across a deep 
 
 fissure. 
 
65 
 
 the middle of an incisor, the course of the prisms is at right- 
 angles to the surface, except at the mesio-lingual and disto- 
 lingual angle. Again in the upper lateral incisor this con- 
 dition is most marked. In the cuspids, the course of the 
 prisms is at right-angles, except upon the hngual surface, 
 where they lie similar to those of the incisors at this point. 
 
 In the molars and bicuspids the prisms lie at right-angles 
 to the surface, expect in the regions about the cusps and the 
 fissures. From the diagrams taken from the latest work of 
 Black*), it appears, that in preparing a cavity on the occlusal 
 surface but little bevelling of the margin is necessary to prevent 
 cleavage of the enamel. The most favorable conditions are 
 found in the neighborhood of deep fissures (Fig. 82). In such 
 cases bevelling the edge becomes quite unnecessary. 
 
 These diagrams show the normal course of the prisms at 
 various points upon the teeth ; in practice abnormal conditions 
 are, however, often encountered. During the preparation of 
 the cavity, the direction of cleavage can easily be determined, 
 if necessary, by fracturing the edge of the enamel with a 
 sharp chisel and noting the direction of the break. 
 
 Not the surface of the tooth, but the course of the prisms 
 determines the angle of the cavity wall within the enamel 
 region. The cavity wall should be parallel to the prisms or 
 cross their outer ends. Never under any circumstances should 
 the inner or dentinal end of an enamel priiim be needlessly cut. 
 This, not alone for mechanical, but also for physiological 
 reasons. 
 
 Morphologically the enamel may be divided into two zones, 
 an outer, in which the prisms lie parallel to eachother and 
 generally at right-angles to the surface, and an inner in which 
 the course of the prisms is very irregular (Figs. 84 and 83). 
 Cleavage of the outer zone takes place easily, of the inner 
 zone only with great difficulty. Usually the inner zone is by 
 far the broader of the two. This is of interest in connection 
 with cavity preparation as it proves the danger of fracture 
 to be greater near the surface of the enamel. 
 
 *) G. V. Black, Operative Dentistry, Vol. II. 
 Bodecker, Metallic Inlay. 
 
66 
 
 Fig. 84 shows that it is not possible to cut a cavity wall, 
 parallel throughout to the course of an enamel prism. The 
 theoretically correct preparation of the cavity wall within the 
 
 
 \ * '-.V ,»Y< 
 
 >ivMi?t^mhK<:"- 
 
 Fio-. 83. 
 
 enamal region is the following: in the inner two-thirds of the 
 enamel the wall should lie parallel to the direction of cleavage, 
 
 Fig. 84. 
 
 while in the outer third, it should be bevelled slightly. In 
 practice, however, this rule can but rarely be observed, as 
 abutting joints should be avoided on account of the con- 
 traction of the gold. Upon the occlusal surface the diffi- 
 
67 
 
 ciilty may be overcome by carving deep fissures in the in- 
 lay (wax model). The edge of the inlay will then no louger 
 be right-angled, but be so thin that it may easily be bur- 
 mished against the margin of the enamel. Upon the other 
 surfaces of the teeth the enamel margins should be bevelled 
 about 45°, unless the inlay already possesses a thin edge. 
 
Chapter VII. 
 Instruments for Cavity Preparation. 
 
 A description of all the instruments required for the pre- 
 paration of cavities is not necessary. Only those which are 
 of special value in inlay technic will be considered. 
 
 In preparing a cavity for an inlay, the possibility of remov- 
 ing the impression must always be kept in mind. On account 
 of the danger of undercuts the use of small burs or of in- 
 struments of unsuitable form, should always be avoided. 
 Almost all cavities can be prepared completely by the aid 
 of stones. Carborundum stones cut rapidly, leave smooth 
 margins, and if kept moistened are more agreeable to the 
 patient than steel burs. The forms most commonly used are 
 the barrel-shaped, ground somewhat conical upon a file, the 
 spherical and the thin wheel. 
 
 In order to suit individual requirements, it is advisable 
 for each operator to mount his own barrel-shaped stones. 
 If the mandril possesses a thread, this should by ground off 
 at two points opposite another, in order to prevent the stone 
 from unscrewing when used with the engine reserved. The 
 stones are mounted with thinly mixed cement. A number 
 may be mounted at the same time as they must all be trued 
 later. After the cement has hardened the mandril is mounted 
 in a lathe, and the stone trued up with a file, and any desired 
 special form produced. If no lathe is handy, the stones may 
 be trued under moisture, on the engine. Care should be taken 
 that no water mixed with carborundum is drawn up into the 
 hand-piece. Before grinding, the mandril should be well covered 
 with vaseline. Dry grinding is equally dangerous, as the 
 carborundum dust rapidly wears out the hand-piece. Instead 
 of a file, the instrument shown in Fig. 84 a, may be used. The 
 stone is cut by an adjustable diamond point. 
 
69 
 
 Barrel shaped stones can be obtained in sevoral sizes. The 
 most practical is about ^^ inch long and of about the same 
 diameter (Fig. 85). With a file, the stone is formed as shown 
 in Fig. 86. Wear constantly decreases the diameter of the 
 
 Fig. 84 a. 
 
 stones, making the preparation of stones of different sizes 
 unnecessary. If the tip, in time becomes too pointed, it should 
 be squared with a carborundum wheel (Fig. 87). Small zylindri- 
 cal stones, in shape similar to large fissure burs, and sold 
 
 9)1 9 
 
 Fis. 85. Fig. 86. 
 
 Fig. 87. 
 
 Fig. 88. 
 
 under the name of Miller's points (Chicago), are often of 
 service. Small round stones, about an ^/g inch in diameter 
 are indispensible for finishing the cervical enamel margin. 
 Different sizes result through wear. The other forms of these 
 points (Fig. 88) may sometimes be required. The small car- 
 
70 
 
 borunduni disk (j^ig. 89), as well as the stone shown in Fig. 116, 
 is used to cut out the fissures on the occlusal surface, 
 and to prepare cavities for the dove-tail or the hook an- 
 chorage. 
 
 If the smallest diameter of a cavity is less than an ^'g inch, 
 stones cannot be used. The caA^ity must then be prepared 
 with burs, and the margins finished with plug finishing burs, 
 or in a manner to be described later. 
 
 As a substitute for small stones, instruments impregnated 
 with diamond dust have been put upon the market. Owing 
 to their high price and their rapid deterioration, they have 
 not come into general use. Instruments made of copper and 
 used with carborundum powder are more satisfactory. It will 
 be found, however, that aluminum cuts still better. Small 
 disks cut out of aluminum plate, are mounted on a man- 
 dril and trued on the engine. A cylindrical form is made 
 bv cementing a short piece of small, thick- walled aluminum 
 tubing upon an old bur, and trueing as described above. 
 As a cutting medium, coarse carborundum powder, mixed 
 to a stiff mass with low -melting paraffin, can be recom- 
 mended. In grinding it becomes less fluid than vaseline and 
 is therefore not thrown off of the disk as easily. A small 
 piece of the mass is placed in the cavity. The heat generated 
 in cutting sufficiently Hquifies the paraffin to insure a constant 
 supply of carborundum powder at the cutting edge. If the 
 mass is too hard, the instrument should first be dipped into 
 vasehne. During the operation, it is advisable to cool the 
 tooth with air. In cutting with abrasive powders, pressure 
 should never be applied to the instrument. 
 
 Cavities cut by this process have extremly smooth walls 
 and almost knife-edged margins. It will never be generally 
 adopted, however, unless diamond- dust, real or artificial, can 
 be produced so cheaply as to replace the carborundum powder. 
 In that case it would be a most rapid and painless method 
 of excavating cavities. The great disadvantage in its present 
 form is, that in comparison to the cutting speed of carborundum 
 stones and steel burs, it is very slow. In small cavities, pre- 
 pared with burs, a very smooth enamel margin can be obtained 
 
71 
 
 more rapidly with carborundum-powder and aluminum than 
 with arkansas -stones. 
 
 The right-angle hand-piece is indispensable in the pre- 
 paration of cavities for inlays. In other methods of filling, 
 
 '^^ 
 
 Fig. 90. 
 
 Fk. 01. 
 
 the cavities can be prepared with the straight hand-piece. 
 The inlay, however, requires a cavity perfectly free from under- 
 cuts, and this can be produced only by working in the direction 
 in which the impression is to be removed from the cavity. 
 The cutting instrument must therefore in each case occupy 
 
72, 
 
 Fig. 92. 
 
 a certain definite position. This can be accom- 
 plished, as a rule, only by the use of the right- 
 angle hand-piece. 
 
 The general prejudice against this instrument 
 is the result of the incorrect form of most right- 
 angle hand-pieces. Usually the head of the bur lies 
 far from the axis of the hand-piece, thus making 
 accurate work impossible. In the contra- angle 
 (Fig. 90) this deficiency has been remedied to a 
 great extent. The head of the bur lies about in 
 the axis of the hand -piece, thereby giving the 
 operator almost the same control over the cutting 
 instrument as in a straight hand-piece. Even in 
 the contra-angle the tips of the long cylindrical 
 stones do not lie quite in the axis. This is rarely 
 disturbing unless the stones are too long. 
 
 In selecting a right -angle for inlay cavity 
 preparation, it must be ascertained that the head 
 of the ordinary bur lies in the axis of the hand- 
 piece, and that the distance from the angle of the 
 shank to the head is sufficiently long. If this 
 distance is too short (Fig. 91, a) the angle in the 
 shank must be more acute in order to bring the 
 head of the bur into the axis of the hand-piece. 
 This places the axis of the bur in an unfavorable 
 position; considerably less than at a right-angle 
 to the axis of the hand-piece. As the cutting 
 instrument must always be applied at right-angles 
 to the surface of the tooth, a hand-piece of this 
 form is almost useless in preparing cavities for in- 
 lays in the posterior teeth. 
 
 The use of stones causes the hand-pieces to wear 
 out very quickly, owing to water mixed with 
 carborundum being drawn up along the mandril. 
 The right-angle suffers most in this respect. The 
 straight hand -piece can be protected from this 
 injury, which is especially marked in working upon 
 the upper teeth, by using Kief er's aseptic rubber 
 
73 
 
 sheaths (Fig. 92). The mandril should be coated with vaseline 
 before introduction into the hand-piece. Though making a mois- 
 ture-proof joint, the objection to the use of these sheaths is 
 the difficulty of stretching them over the hand-piece. As, for 
 reasons of asepsis, a fresh sheath should be used for each 
 patient, their use entails considerable trouble. If a small 
 rubber cap of this style could be made, to easily slip over 
 the head of the right-angle, it would greatly prolong the 
 usefulness of this hand-piece. The instruments necessary in 
 finishing and polishing the inlay, will be described in a later 
 chapter. 
 
Chapter VIII. 
 Cavity Preparation. 
 
 A description of each and every cavity which could be 
 filled with an inlay, would be of little use to any one not 
 acquainted with the fundamental principles of the cavity- 
 forms for inlays (Chap. Ill and IV). The operator who fully 
 understands these principles has no need to follow a descrip- 
 tion or an illustration in preparing a cavity. He is able to 
 decide in each case, what form of cavity, and which anchorage 
 is most suitable. The description of cavities will therefore 
 be limited to those generally filled with inlays, and the chief 
 points to be considered in the preparation, will be only briefly 
 mentioned. 
 
 As a rule the cavity must be opened with chisels or burs, 
 before stones can be used. When the opening is sufficiently 
 large a stone of suitable form is employed. Care should be 
 exercised in the selection of the stone, as with one of proper 
 shape the correct cavity- form is cut almost autoraatically. 
 Leathery dentine must first be removed with excavators, as 
 stones cut it but slowly. 
 
 The cavity is prepared until it presents a margin of healthy 
 dentine and enamel. Carious spots, not near the margin are 
 removed after the impression has been taken. It sometimes 
 occurs, that the general form and the margin are satisfactory 
 while there still are undercuts in the walls of the cavity. 
 In such cases the latter should be filled with Fletcher's Artificial 
 Dentine, and the cavity again ground out with stones of 
 suitable form. 
 
 Where there is danger of injuring the neighboring tooth, 
 stones of small diameter should be used. If contact is un- 
 avoidable, placing a piece of a thin seperating file in the 
 
75 
 
 interproximal space, is to be recommended. When worn 
 through a new piece is substituted. This precaution is, how- 
 ever, rarely necessary. 
 
 The following plates are reproductions of cavities cut into 
 enlarged plaster models of teeth. In the mouth where the 
 conditions, especially in regard to accessibility, are not so 
 favorable, it is not always possible to prepare the cavities 
 so exactly. This is true particularly of the enamel margin. 
 
76 
 
 Plate I. 
 Lower Molar with Mesio- Occlusal Cavity. 
 
 The proximal cavity should be broad, and be prepared 
 with care in the region of the pulpal horns. These points of 
 danger lie upon a line drawn from the tips of the cusps to 
 the pulp-chamber (Fig. 81). Between the pulpal horns, the 
 cavity has been deepened, to make the segment {d, Figs. 49 
 and 53) as strong as possible. The enamel margin is to be 
 bevelled as described. 
 
 On the occlusal surface, the fissures have been cut out with 
 a carborundum disk. The sharp angles produced at the cross- 
 ing of the fissures have been rounded. If the excavated 
 fissure extends to the edge of the occlusal surface, the margin 
 of the enamel should be ground away horizontally. (On 
 plate I, the left end of the transverse fissure.) At other points 
 of the occlusal cavity, bevelling the enamel margins is not 
 necessary if deep fissures are carved in the inlay. 
 
Plate I. 
 
Plate II. 
 
77 
 
 Plate II. 
 
 Lower Molar with Disto -Proximal Cavity. 
 Adjoining Tooth Missing. 
 
 The presence of a filling upon the occlusal surface is 
 assumed. The adjoining tooth being absent and the occlusal 
 surface but slightly involved, the inlay may be made without 
 self-retention. The greater part of the proximal surface being 
 carious, the cavity could not be prepared like Fig. 54. Suffi- 
 cient retention has been obtained by cutting all the walls, 
 at right- angles to the proximal surface. The enamel margins 
 have been bevelled. On the inlay, the small occlusal surface 
 should be sloped proximally (Fig. 16). 
 
78 
 
 Plate III. 
 Lower Molar with Lingual Wall Missing. 
 
 To seat the inlay more firmly, the gutta-percha filling 
 the pulp-chamber has been partially removed, and the remain- 
 ing portion of the lingual wall ground off horizontally. The 
 enamel margins have been bevelled, with the exception of 
 those of the dove-tail anchorage cavity. For the preparation 
 of the latter see Figs. 27 and 28. 
 
Plate III. 
 
Plate IV. 
 
79 
 
 Plate IV. 
 Lower Molar with Abraded Occlusal Surface. 
 
 The cavity should be made as broad and deep as possible; 
 the walls cut vertically and their upper edges rounded. To 
 give greater security against dislocation, the grooves instead 
 of being cut obliquely, may extend entirely through the walls 
 of the cavity. If necessary, the pin anchorage (Fig. 32) may 
 be used. The enamel margins are to be broadly bevelled. 
 
80 
 
 Plate V. 
 Lower Bicuspid in a Crowded Arch, with Mesio- Occlusal Cavity. 
 
 The mesial surface of the tooth has been flattened with 
 a diamond disk. The margin of the enamel in this case should 
 not be bevelled. Retention is obtained by means of a strong 
 fissure anchorage, or if preferred by cutting a dove-tail in 
 the distal part of the occlusal surface. (See page 60.) 
 
Plate V. 
 
Plate VI. 
 
81 
 
 Plate VI. 
 
 Upper Bicuspid with Large Mesial and Distal Cavities 
 (Tooth Pulpless). 
 
 The cavities are prepared in the usual manner, and the 
 margin of the enamel bevelled. To prevent a subsequent 
 fracture of the lingual or buccal wall, the inlay should com- 
 pletely cover the occlusal surface. The gold should have the 
 greatest possible thickness and at the same time be invisible 
 in the mouth. To accomplish this, the occlusal surface is 
 bevelled lingually and bucally from the tips of the cusps 
 toward the fissure with a diamond-disk. 
 
 Bo decker, Metallic Inlay. 
 
82 
 
 Plate VII. 
 Upper Bicuspid with Lingual Wall Missing. 
 
 As the form of this tooth offers no broad seat for the 
 inlay (as in plate III), a pin must usually be inserted. This 
 should be placed as far lingually as possible. Its length is 
 dependent upon the strength of the wall still standing. Proxi- 
 mally the enamel margin is bevelled slightly, while cervically 
 it is broadly bevelled, especially at the lingual margin. The 
 occlusal surface of the buccal wall is bevelled lingually. To 
 make the gold invisible in the mouth, the hook retention 
 should be cut into the distal margin, behind the cusp. If the 
 wall is weak, a second hook retention mesially is necessary. 
 In the preparation, special care should be exercised to make 
 the wall {a, Fig. 25) on the buccal surface vertical, and suffi- 
 ciently large. 
 
Plate VII. 
 
Plate VIII. 
 
83 
 
 Plate VIII. 
 
 Upper Bicuspid with Buccal Wall Missing. 
 
 The remaining buccal portion of the tooth is ground off 
 to the margin of the gum, and if possible, the edge bevelled 
 buccally. The lingual cusp is removed and the surface sloped 
 lingually. The margins of this surface are all broadly bevelled. 
 The post, which should be long and strong, is placed into the 
 canal, and an impression taken with a thin copper ring and 
 modelling compound. The model is poured in Spence-metal. 
 Upon this model, the porcelain facing selected is ground up. 
 To permit the removal of the facing during casting, the pins 
 are covered with moldine, and the facing well oiled. Upon 
 -the Spence model, the wax form, with post and facing in 
 position but without an occlusal surface, is carved. This is 
 then tried in the month, and after the position of the facing 
 has been corrected and the margins smoothed, the wax is 
 chilled. To prevent distortion at this stage, there should not 
 be sufficient wax on the occlusal surface to come in contact 
 with the antagonist. The form, having been thoroughly chilled, 
 is removed from the mouth, dried, soft wax added upon the 
 occlusal surface, and again placed in the tooth, and the patient 
 requested to close quickly. By alternately chilling the form 
 with cold water and softening the surface with hot air, a per- 
 fect articulation can be carved without disturbing the lower 
 parts of the wax form previously completed. To prevent 
 distortion of the wax, the post is firmly held in a pin-vise 
 and the facing removed by the aid of a rod of sticky wax. 
 The form is then cast, and the facing attached with cement. 
 If but little of the lingual wall remains and the bite is favo- 
 rable, regular porcelain teeth with occlusal surfaces can be used. 
 
84 
 
 Plate IX. 
 Upper Bicuspid with Erosion. 
 
 If the margins of the defect are sharply naarked, two semi- 
 circular steps are cut at right- angles to the surface of the 
 tooth with a large fissur bur. The curved surfaces of these 
 steps should lie opposite one another and be parallel to the 
 direction in which the inlay can be removed from the cavity. 
 At these points regular undercuts (Fig. 10) should be made 
 in the tooth and in the inlay. If the margins of the defect 
 are not sharply marked, they can easily be made so with a 
 diamond disk. 
 
 Upper Bis cuspid with Simple Cervical Cavity. 
 
 The upper and lower wall are to be made parallel and 
 the margins bevelled (Fig. 39). 
 
Plate IX. 
 
Plate X. 
 
85 
 
 Plate X. 
 Cuspid with Small Distal Cavity. 
 
 The cavity should be prepared almost at right-angles to 
 the lingual surface of the tooth. The margin is to be care- 
 fully bevelled. The labial groove is prepared vertically, the 
 lingual, as horizontally as possible. 
 
86 
 
 Plate XI. 
 Cuspid with Large Distal Cavity. 
 
 The distal angle of the tooth is removed with a disk. The 
 labial surface is so cut out, that the walls of this part of the 
 cavity lie parallel to the long axis of the tooth. (In the illus- 
 tration this part has been cut out more broadly than necessary.) 
 The labial groove should lie vertically and the lingual groove 
 horizontally. The margin of the enamel should be bevelled 
 only between the two grooves and in the region of the lingual 
 cusp. 
 
Plate XI. 
 
Plate XII. 
 
87 
 
 Plate XII. 
 Abraded Cuspid, with Inlay Anchored on the Lingual Surface. 
 
 This form of retention is used chiefly in cuspids and in- 
 cisors with marked lingual abrasion. The incisive edge is 
 ground off horizontally and the enamel margin bevelled. In 
 the lingual surface of the tooth, a shallow cavity is cut, extend- 
 ing almost to the margin of the gum. Care should be taken 
 to make the lingual wall vertical and as large as possible, 
 as the retention of the inlay depends chiefly upon this wall 
 of the cavity. On the lingual margin the enamel should be 
 carefully bevelled. 
 
 Incisor with Small Proximal Cavity. 
 
 A metal inlay would not be indicated in a cavity of this 
 kind. If, however, such a case should occur, the cavity could 
 be prepared in a form recommended for porcelain inlays. 
 
Plate XIII. 
 Incisor with Mesial and Distal Cavities. 
 
 In cases of this kind also, a metal inlay would hardly 
 ever be indicated. At most, a combination inlay could be 
 recommended, as the smaller cavity offers sufficient hold to 
 allow the larger one to be filled partially with porcelain. 
 (Figs. 102 — 104). The enamel margins should be but slightly 
 bevelled, so as not to interfere with the removal of the im- 
 pression. 
 
Plate XIII. 
 
Plate XIV. 
 
89 
 
 Plate XIV. 
 Abraded Incisor with Mesial and Distal Cavities. 
 
 Such cases are suitable for gold inlays, especially if the 
 bite is strong. The incisive edge is bevelled labially and the 
 proximal cavities so prepared that the impression can be 
 removed easily. The final form of such a double cavities is 
 dependent upon the extent of the caries upon the proximal 
 surfaces, and will therefore vary with each case. The margins 
 of the enamel should be carefully bevelled. 
 
 If the tooth is considerably abraded horizontally, and there 
 is no caries on the proximal surfaces, the cavity for the inlay 
 may be prepared in the box-shaped manner recommended for 
 cohesive gold fillings*), with or without the pin-anchorage, 
 as the case may require. 
 
 *) L. Warnekros, Das Fiillen cler Zahne bei intakter Pulpa (Ash & Sons 1888). 
 
Chapter IX. 
 The Impression. 
 
 The wax-model of an inlay may be made in two ways, 
 either an impression of the cavity is taken in modeling com- 
 pound and a cement model made upon which the wax form 
 is built up, or the wax model is made directly in the cavity 
 of the tooth. Strictly speaking, the wax-model, in each case, 
 represents an impression of the cavity. The form made in 
 the mouth may be called a direct impression, while that made 
 on a model may be referred to as an indirect impression. 
 
 The indirect impression. 
 
 Since the first gold inlays were made, this method of 
 taking impressions has been in use. Though the models at 
 first were not very perfect, improvements in the methods, 
 as well as of the impression compounds, have led to satis- 
 factory results. 
 
 The impression compound should be made up in the 
 form of cones and rods of different sizes. The impression of 
 a simple cavity is taken with a rod-shaped piece of com- 
 pound whose diameter is slightly greater than that of the 
 cavity. The piece should be only about an inch in length, 
 as otherwise it tips easily under pressure and gives a double 
 impression of the margin. Only the tip of the rod is softened 
 over an alcohol- flame, and the compound then pressed into the 
 cavity at right-angles to the surface of the tooth. If the 
 cavity is situated at the neck of the tooth, the harder material 
 presses away the gum, thereby giving a perfect impression of 
 the margins. 
 
 Cavities not possessing four walls, require some appliance 
 to prevent the escape of impression material. Of these the 
 most commonly used are thin copper rings. A supply of such 
 
91 
 
 rings of all required sizes, should alway be kept on hand. 
 In all larger cavities, unless the direction in which the im- 
 pression may be removed from the cavity prevents, the copper 
 ring is of the greatest service. If the form of the tooth or the 
 position of the cavity makes the use of the ring impracticable, 
 other means must be employed to prevent the escape of the 
 impression material. Without describing the numerous appli- 
 ances, it may be stated that they are all more or less modified 
 matrices, similar to those used in making gold or amalgam 
 fillings. Impression-trays or other appliances with long handles 
 cannot be recommended. The almost inevitable lateral move- 
 ment while pressing the material into the cavity and while 
 holding it in this position until it has set, makes a double, 
 or a distorted impression almost unavoidable. 
 
 The model may be made of one of the following materials: 
 hard plaster, cement, amalgam, Spence or Melotte's metal. 
 
 The plaster model is the easiest to make, but has the 
 disadvantage that if ordinary plaster is used, thin walls are 
 liable to break off. With but little care in carving the wax 
 form, a model made of the so-called alabaster plaster will do 
 good service. This material is considerably harder than 
 ordinary plaster, and sets, if salt has been added, in about 
 half an hour. The hardest of all varieties of plaster, the so- 
 called marble-plaster, has the disadvantage that it sets com- 
 pletely only in about twelve to sixteen hours. It then furnishes 
 a model, equally as good as one made of cement or amalgam. 
 
 If the model is to be made of cement or of amalgam, the 
 impression should be so imbedded in plaster, that it cannot 
 be fractured by the force exerted in introducing the material. 
 The cement need not possess great edge- strength, as it is not 
 subjected to the high pressure formerly used in swedging the 
 matrices for gold inlays. The cement for the model is mixed 
 so that it is just kneadable, without sticking to the fingers. 
 The mass is firmly pressed into the oiled impression, and the 
 surplus formed under pressure, between the thumbs and index 
 fingers, into a small pyramid. After the cement has set, in 
 fifteen to sixty minutes according to the preparation used, the 
 impression is removed and the model cleaned with chloroform. 
 
92 
 
 Copper amalgam is the variety m.ost commonly employed 
 for models, as it may, by simply heating, be repealedly used. 
 The preparation of the impression and the introduction of 
 the material are the same as have been described for cement. 
 The slowness in setting is the chief disadvantage of the amalgam 
 model. 
 
 In making the model of Spence or Melotte's metal, the 
 impression is embedded in Moldine surrounded with a ring, 
 and cast under the usual precautions. By this method, in but 
 a few minutes the finished model may be produced. With 
 a good Spence metal, for example the White Inlay Metal, to 
 which flowers of sulphur are occasionally added, the model 
 presents smooth surfaces and sharp margins. 
 
 Upon the previously oiled model of the cavity, the wax 
 form is carved. It is always advisable to try the wax form 
 in the mouth before casting, in order to control the correct- 
 ness of the bite, the contact point, and the margins. If the 
 form cannot be tried in the mouth, the following method must 
 be employed. After the impression of the cavity has been 
 taken, a piece of fairly hard modelling compound, about the 
 size of a hayel-nut is placed upon the cavity and the patient 
 requested to occlude. The result is an impression of the margins 
 of the cavity, the proximal surfaces of the adjoining teeth, and 
 the occlusal surface of the antagonist. The model of the cavity 
 is then placed in this impression so, that the margins of the 
 cavity on the model and those in the impression exactly 
 correspond. After attaching the cavity model to the im- 
 pression with wax, the model of the bite is poured in plaster, 
 in two parts. If the bite has been taken carefully, and the 
 model of the cavity placed exactly in the bite impression, 
 a true reproduction of the conditions in the mouth will be 
 obtained. In spite of the greatest care, this method does not 
 give as good results, as trying the wax form, previously carved 
 on a model, in the mouth. 
 
 The direct impression. 
 
 Until lately, this method of taking an impression has not 
 received the recognition of which it is worthy. It represents 
 
93 
 
 in the field of metallic inlay technic, an advance, equal almost 
 to the introduction of casting. It was necessary in the old 
 swedged and soldered inlays to construct the form in three 
 stages. First the impression in the mouth, then the cement 
 model, and lastly the swedged matrix. Each of these stages 
 represents a source of error for the perfect fit of the inlay. 
 The introduction of casting, obviated the necessity of making 
 a matrix, and it soon became evident by the better adaptation 
 of the inlays, that one source of error at least, had been 
 partially removed. Only partially, however, as the form must 
 still, as in the indirect impression, pass through three stages. 
 But the error with easily adaptable wax is far less than that 
 with the stiff platinum matrix. Experience in the arts has 
 shown, that in a series of models, each reproduced from the 
 previous one, the form of the original becomes more altered 
 with each subsequent model. Applied to the inlay process, 
 it becomes evident that if the intermediary stages could be 
 avoided, that is, the wax form made directly, without com- 
 pound impression or model, a decided advantage for the inlay 
 would be gained. In theory the method of making direct im- 
 pressions rest upon a logical basis. In practice, the difficulties 
 at first met with are due to inexperience and to the use of 
 unsuitable instruments. Carving a wax form in the mouth 
 requires the same care as making a cement or gutta-percha 
 filling. As most operators have had no experience in the use 
 of wax as a filling -material, its manipulation must first 
 be learned. With patience and practice this is readily accom- 
 plished. 
 
 Before describing the process of taking a direct impression, 
 a few words upon the qualities of the wax used for this pur- 
 pose are necessary. Pure bees-wax cannot be used, as it is 
 too soft and tough to carve well. Other substances must 
 therefore be added to make it harder and more workable, 
 as well as, to give it the other necessary qualities. 
 
 In making the form in the mouth, the hardness of the wax 
 is of great importance. This being dependent upon temperature 
 and the quantity of resins etc. added, a wax can be produced, 
 that at 100 ° F will change its form only under considerable 
 
94 
 
 pressure. For the hardening point of the wax, 100 ° F is about 
 the most favorable temperature, as this is several degrees above 
 that of the teeth when the mouth has been opened for a short 
 time. If the hardening-point is below this, the wax remains 
 soft in the mouth, and the form is very liable to be distorted 
 during removal from the cavity. For the same reason, the 
 form cannot be easily handled outside of the mouth, nor 
 can it be carved while being held between the fingers. If the 
 hardening-point is much above 100° F, the wax becomes brittle, 
 and weaker processes and extensions are liable to break off 
 even before the wax form can be removed from the cavity. 
 
 Intimately connected with the hardening of the wax, is 
 its power of recovery. If two varieties of wax, both hardening 
 at 80 ° F, are slowly heated until they begin to soften, and 
 are then placed in water of 80 ° F, a marked difference in the 
 time required for each variety to harden, and to regain its 
 other qualities will be found. The inlay technic requires a 
 wax with rapid recovery. 
 
 More or less related to the hardness of the wax, is the 
 ease with which it can be scraped. A soft wax cannot be 
 scraped, it can only be cut. This in an inlay-wax is not per- 
 missible, as in cutting the tough mass, the form would un- 
 doubtedly become distorted. Yet not every hard wax is 
 suitable, as many of these also are tough. To test the scraping 
 quality, the wax should be scraped at room temperature with 
 a sharp instrument. The surface should be clear and smooth, 
 and the scrapings be of a fine grain. Rubbed on the palm 
 of the hand, they should not ball, but remain as small par- 
 ticles. The wax should not rapidly clog the grit of a sand- 
 paper strip. 
 
 Another quality possessed by a good inlay wax, is cohesion 
 at comparatively low temperature. This permits the wax 
 being formed by hand, in each case so, that the bottom or 
 the cervical margin of the cavity may with certainty be 
 reached. Folds produced by the introduction of the wax into 
 the cavity will disappear under pressure, thus making the 
 model a perfectly homogeneous mass. Another advantage 
 that a wax with marked cohesion at low temperature offers, 
 
95 
 
 is that fresh wax may be added outside of the mouth, without 
 danger of distorting the form through heat. 
 
 Under no circumstances should the wax be adhesive. 
 Adhering to the instrument, it would make scraping im- 
 possible. It would also prevent the easy removal of the model 
 from the cavity. 
 
 The wax should be sufficiently dark in color to readily 
 show where it extends beyond the margin of the cavity. It 
 should however not be so dark, that it is impossible to re- 
 cognize the cavity margin through a thin layer. The coloring 
 matter must contain no metal, as this would be deposited on 
 the walls of the casting form when the wax is burned out, 
 and thereby affect the surface of the inlay. 
 
 Convinced of the great value of the direct impression 
 method, the writer performed a number of experiments, to 
 determine the possibility of producing a wax having all the 
 qualities described above. In how far he has suceeded, he 
 leaves the profession to decide for itself. 
 
 Equal in importance to a good wax, are proper instru- 
 ments. Even the most skilful operator is not able to pro- 
 duce a perfect wax model in the mouth without suitable 
 instruments. It is not the intention of the writer to describe 
 a complete set of instruments, sufficient for every case. Only 
 a few, found to be of service will be mentioned. In all these 
 instruments, the cutting edges should be as sharp as possible, 
 so that the wax may be scraped without the exertion of 
 pressure. 
 
 As a spatula the instrument shown in No. 1 (Fig. 93) may 
 be used. To remove the excess upon the occlusal surface 
 a spoon-shaped excavator, about a quarter of an inch in dia- 
 meter is of service (No. 2). A smaller spoon (No. 3) is ne- 
 cessary to deepen the impressions made by the cusps of the 
 antagonist. In carving the fissures, the instrument shown 
 in No. 4 is used. This is a Darby-Perry excavator No. 3, the 
 tip of which has been ground to a point. The angle made by 
 the two cutting edges represents about the form of a fissure 
 of a natural tooth. In modeUing the proximal surface, the 
 last three instruments are of service. For the coarser work. 
 
96 
 
 a curved cement spatula (No. 5), and the spatulate end of 
 a Woodson's amalgam instrument (No. 7). To model the less 
 accessible cervical margin, the writer uses, the instrument 
 No. 6. This is made by grinding a right-angled exploring 
 instrument so, that in cross section it appears as a triangle. 
 One side of the triangle should face the handle of the in- 
 strument. In scraping, the point is pressed against the neck 
 
 Fiff. 93. 
 
 of the tooth, and all material overlapping the cervical margin 
 thereby smoothly removed. In the same manner this instru- 
 ment may be used to trim the other margins on the proximal 
 surface. Beside the instruments mentioned, sand-paper or 
 cloth strips are employed in modelling the wax in the mouth. 
 Every operator, in time, develops his own method of 
 taking a direct impression. The following description is, there- 
 fore, intended only as a suggestion. Oiling the cavity is to 
 be avoided, as a good inlay- wax is not adhesive. Before intro- 
 ducing the wax, the cavity is rinsed out with water. In ex- 
 ceptional cases cotton rolls are used to keep the field of opera- 
 
97 
 
 tion dry. As this makes carving easier, it may be recommended 
 to those trying this method for the first time. 
 
 The stick of wax is warmed slowly over an alcohol flame 
 until it is so soft that a piece can be pinched off with the fingers, 
 and kneaded. In warming, the surface of the wax should not 
 be overheated, as this affects its power of recovery and its 
 scraping qualities. The same is true of a prolonged kneading 
 of the wax. 
 
 As an example, the disto-occlusal cavity of a lower molar 
 has been chosen. If the interproximal space is large or un- 
 favorable in form, as in the lower bicuspids, a matrix lightly 
 held in position with cotton, is of advantage. The softened 
 wax is formed into a cone, sufficiently slender to reach the 
 bottom of the cavity. The surface of the cone is again softened 
 in the flame and quickly introduced. With the index- finger 
 firm downward pressure is brought to bear on the wax, until 
 the proximal cavity is filled, then by drawing the finger for- 
 ward under pressure, the excess wax is forced into the cavity 
 on the occlusal surface. The patient is requested to occlude, 
 and to keep the teeth together tightly at least thirty seconds, 
 to allow the wax sufficient time to escape. In case the bite 
 is very sharp, a small piece of thick rubber-dam should be 
 laid over the wax before closure of the teeth. The danger 
 of making the inlay too high, is thereby partially avoided. 
 
 The excess wax, lingually and buccally, is left untouched. 
 Into the distal surface of the form, the right-angled exploring in- 
 strument is stuck as deeply as possible, and an attempt made to 
 remove the whole mass from the cavity. If this is not successful, 
 either undercuts are present, which must be filled out before 
 a further attempt is made, or the wax is lodged against the 
 neck of the adjoining tooth. In the latter case the wax in 
 the interproximal space must be trimmed with the curved 
 cement spatula (No. 5). The mass removed from the cavity 
 is chilled in cold water, and may then be safely picked up 
 in the fingers. The cavity surface of the form is examined 
 and any evidence of undercuts or projections which might 
 obstruct the removal of the impression, are scraped off with 
 a small sharp spoon (No. 3). If on the lower part of the proxi- 
 
 Bodecker, Metallic Inlay. 7 
 
08 
 
 mal surface a large surplus of wax is present, this may be 
 removed partially before replacing the form in the cavity. 
 The upper part of this surface, where the wax lies against 
 the contact point of the adjoining tooth, should not be dis- 
 turbed. 
 
 The wax is then replaced in the cavity. If much force 
 was necessary in removing the mass in the first instance, the 
 wax should be softened with warm water, and pressed snugly 
 into the cavity with the finger. On the cervical part of the 
 proximal surface pressure is exerted with the spatulate end 
 of a Woodson's amalgam instrument (No. 7). If the bite is 
 very sharp this should be done while the teeth are in occlusion. 
 The patient having occluded, the wax, if necessary, is chilled 
 and the occlusal surface carved. 
 
 A great excess of wax on this surface may, to save time, 
 be partially removed with a warm, sharp spatula (No. 1). 
 Usually it is best, however, to do all the scraping until the 
 margins of the cavity appear, with the large spoon (No. 2). 
 Depressions made by the cusps of the antagonist are then 
 deepened with the small spoon. If the bite is sharp, the 
 articulation may be controlled, by softening the surface of 
 the wax with hot air. This must be done with great care, as 
 only the very surface should be affected by the heat, to avoid 
 subsequent contraction. Never should a small body of wax, 
 or even the neighborhood of the margins of a larger body, 
 be so treated. Upon cooling, this leaves a mat surface on 
 which the impressions of the cusps of the antagonist can 
 easily be seen. Such spots should again be deepened. Grooves, 
 representing the fissures, are then scraped with the instrument 
 No. 4. Only after the occlusal surface is completely finished, 
 should work on the proximal surface be begun. 
 
 In order that the wax form may remain firmly fixed as 
 long as possible, the margins of the proximal cavity are 
 finished before modelling the proximal surface. For this pur- 
 pose, the author prefers the three-cornered probe (No. 6). 
 When the edges are smooth, the probe is again stuck firmly 
 into the wax, preferably in the hole previously made, and 
 the model lifted out of the cavity. An examination of the 
 
99 
 
 form, shows whether the margins have been properly pre- 
 pared, and whether there is still any wax overlapping the 
 margins. In this case the form is replaced in the cavity, and 
 the excess removed. If the point of the probe should slip 
 over the margin of the cavity, and remove to much wax, 
 more material must be added at this point. 
 
 The form is placed in a dish of cold water and all adherent 
 blood and saliva washed off with a forcible stream of a water- 
 syringe. The form, held between the fingers, is dried with the 
 cold blast of a chip blower. Wax, softened upon the spatula 
 until it just liquifies, is dripped upon the form as near the 
 edge as possible at the place to be restored. The form is then 
 quickly replaced in the cavity, and the soft wax pressed over 
 the margin with the spatulate instrument No. 7. This must 
 be done before the surface of the wax becomes moist, as 
 otherwise the wax would not unite where it is accidentally 
 folded in pressing the excess over the margin. 
 
 Modelling the contour, may be proceeded with when the 
 margins are entirely satisfactory. For this purpose cloth-strips 
 are of service. By carefully scraping the model, outside of the 
 mouth, just sufficient space to admit the strip between the 
 form and the adjoining tooth is made. In the neighborhood 
 of the cervical margin the strip should lie snugly about the 
 semi-circumference of the tooth, and be gently drawn to 
 and fro. The nearer the contact-point is approached, however, 
 the less should the strip, at the same time, encircle the whole 
 contour of the wax-form. In finishing the buccal part of the 
 proximal surface, the strip should enter the lingual side of 
 the space loosely, and be drawn through in close contact with 
 the buccal surface of the tooth. In finishing the lingual part 
 of this surface, the above proceeding is reserved. When the 
 wax is everywhere smooth, and the margins are perfect, the 
 form is definitely finished. Before laying this wax model aside, 
 the point, where the contact-point is to be placed, should be 
 marked. The best way to preserve the wax models is to place 
 them in a small dish, or glass containing cold water. 
 
 If regular undercuts are to be made in the inlay, this may 
 be accomplished most easily upon the wax model, with the 
 
100 
 
 instrument used in scraping the fissures (No. 4). In places 
 were the inlay is to be specially roughened, it is advisable 
 to scrape off a thin layer of wax, in order to increase the 
 space between inlay and tooth at this point. If during the 
 scraping, the model has been handled much, it should be 
 given a final trial in the cavity. 
 
 With slight modifications, the method of making wax 
 models described above, may be applied to all cavities. In 
 very large cavities it is sometimes of advantage to first model, 
 and finish that part of the form lying near the margins of 
 the cavity, and later to add sufficient wax to build up the 
 rest of the form. Where but little of the crown remains and 
 a sharp bite tends to drive the wax out of the cavity, copper 
 rings will be of service. 
 
 Special attention may be called to the advantage offered 
 by the direct impression, in making large contoured inlays 
 under the clasps of artificial dentures already present in the 
 mouth. In preparing cavities of this description, the pressure 
 exerted upon the inlay by the clasp in removing the denture, 
 must always be taken into consideration. The wax is intro- 
 duced into the cavity, preferably with the clasp in position. 
 If this is not possible, the wax should be approximately 
 modelled in the cavity and the denture, with clasp well warmed 
 and oiled, then pressed into place. If the first attempt is not 
 successful the procedure should be repeated. 
 
 The wax model to be placed upon the sprue wire, is re- 
 moved from the water and laid upon a piece of blotting paper. 
 The sprue which should not be of too small a diameter, is 
 then heated, and a small quantity of wax melted upon the 
 point. Into the wax model, held with the proximal surface 
 uppermost, the point of the sprue is gently introduced at the 
 place marked as the contact point. In mounting the form, 
 the sprue should never be forcibly pressed into the wax. As 
 soon as the wax has set, the form is replaced in cold water. 
 After casting, the added wax and the sprue-stump furnish 
 sufficient material for the construction of an ideal contact 
 point (Fig. 94). 
 
 Beside a good wax and proper instruments, care and prac- 
 
tice are necessary in making a direct impression. The ad- 
 vantages offered, however, are so numerous, that the writer 
 feels confident, that in time this method will gain full re- 
 cognition. Summed up briefly the advantages are the following: 
 
 1. The adaptation of the wax model at the margins can, 
 with absolute certainty, be controlled in the mouth. 
 
 2. By repeatedly trying the form in the cavity, and by 
 scraping away all possible obsctacles, the wax model 
 can finally be removed from the cavity without dis- 
 tortion. 
 
 Fig. 94. 
 
 3. This results in a perfect adaptation of the inlay, making 
 fitting unnecessary. 
 
 4. An ideal contact point can be made. 
 
 5. The occlusal surface is always adapted to the case. 
 
 6. Long and tedious grinding is thereby avoided while 
 setting the inlay. 
 
 The only disadvantage which the direct impression possesses 
 is, that if a failure in casting occurs, the time and labor ex- 
 pended upon the production of the wax model is lost. Under 
 such circumstances, the indirect impression method offers 
 the possibility of making a second wax form upon the model. 
 If the failures in regard to adaptation of the inlay be exa- 
 mined, they will be found to depend upon three causes: 1. an 
 inexact impression, 2. an imperfect model and 3. defective 
 casting. If the failures due to each of these causes are 
 numerically compared, it will be found that those due to 
 defective casting are by far less numerous than those due to 
 each of the other causes. 
 
102 
 
 Hollow wax models. 
 
 To partially obviate the greatest disadvantages of the solid 
 metallic inlays, that is, cost and conductivity, hollow casting 
 has been resorted to. Castings of this kind are made, either 
 by modelling the wax over a core, or by hollowing out the 
 finished wax model. The first method, as practised by the 
 writer, is as follows. Sodium bicarbonate is made up into 
 pellets of different sizes, and these when dry, are coated with 
 wax. For use, a pellet of suitable size is warmed, and lightly 
 pressed into the cavity, care being taken not be approach 
 the margins of the cavity too closely and to keep the surface 
 dry. Soft inlay wax is then introduced into the cavity, and 
 the form modelled in the usual manner. After mounting the 
 wax model upon the sprue, a wide opening is made into the 
 
 r) 
 
 Fis:. 95. 
 
 bicarbonate pellet with a hot, sharp instrument, and the form, 
 then held by the sprue, is dipped into dilute sulphuric acid. 
 The reaction is almost immediate. The opening into the 
 chamber must be sufficiently large to prevent the button of 
 investing material from breaking off during the process of 
 casting. 
 
 The second method, which is perhaps more satisfactory 
 than that described above, consist in drilling out a chamber, 
 or in removing the necessary wax by aspiration. For this 
 purpose F. E. Roach has constructed an instrument which 
 does good service. Roach's Suction Wax Carver (section. 
 Fig. 95) consists of a small, thick walled metal bulb, from 
 one end of which a smaller bent tube protrudes. The other 
 end is continued as a larger tube, covered with a non-con- 
 ducting material, and serves as the handle of the apparatus. 
 The end of this tube is connected with the saliva-pump, or 
 taken into the mouth. For use, a pledget of cotton is placed 
 
103 
 
 in the metal bulb, and the latter heated until smoke appears 
 upon aspiration. The wax form mounted upon the sprue is 
 then hollowed out. The wax being melted by the hot point 
 is sucked into the tube and arrested by the cotton in the bulb. 
 With this apparatus and a suitable wax, models with extremely 
 thin walls can be produced. 
 
 Though the hollow inlay does reduce the conductivity as 
 well as the cost of production, it does not give better reten- 
 tion, as has been so often stated. If in hollowing out the 
 inlay the parallel walls are destroyed, the retention is en- 
 dangered, and the work of having carefully prepared the 
 cavity according to certain mechanical principles, will have 
 been useless. The reason, that crowns of thin gold plate 
 preserve a tooth, does not justify the assumption that inlays 
 of the same thickness will be of equal service. 
 
Chapter X. 
 The Construction of the Inlay. 
 
 The methods according to which metal inlays may be made, 
 can be divided into two classes. In the first class the inlay 
 is constructed upon a metal impression of the cavity, the 
 m.atrix. In the second, gold is cast in a form exactly represent- 
 ing the part to be restored. The matrix-method has been 
 entirely superseded by the casting process. The description 
 of the methods of the first class will therefore be brief, and 
 include only the chief types. 
 
 Of these the simplest and one of the oldest is the method 
 suggested by ITerbst (Bremen). The impression was taken with 
 platinum-gold foil, in the manner later employed for porcelain 
 inlays. The overhanging edges were coated with chalk, and 
 the depression filled with low-fusing solder over an alcohol- 
 flame. To facilitate handling and undercutting, a piece of 
 gold wire was at the same time fused into the inlay. Held 
 by the wire in a pair of pliers, the undercuts were made with 
 a saw, and the surplus of the matrix trimmed off. The wire 
 was then nipped off and the inlay set and polished. 
 
 According to a second method, whose originator is un- 
 known to the writer, the inlay is made as follows. Gold or 
 preferably platinum-gold foil is adapted to the cavity, and 
 sponge-gold, under light pressure filled in, until the contours,etc 
 are restored. If the sponge-gold does not adhere, the matrix 
 may be coated with a sticky varnish. The matrix is carefully 
 removed from the cavity, and the overhanging edges (and if 
 the bottom is torn, the lower surface also) coated with chalk 
 or rouge. It is then heated upon charcoal, and a strip of 
 18 — 20 kar. solder held upon the surface of the sponge-gold 
 until it becomes saturated. Thereupon the inlay is trimmed 
 and set in the cavity. A more agreeable color may be pro- 
 duced by using a platinum matrix and 22 kar. gold. 
 
105 
 
 Sponge-gold inlays were also produced without the use of 
 a matrix. According to this method, still used by some 
 practitioners for certain cases, the sponge-gold is filled directly 
 into the cavity, under slight pressure. At the margins there 
 should be an excess and a slight overlap of the gold. This is 
 well burnished against the margin of the cavity. The filling 
 is removed with a probe, the cavity surface coated, and then 
 saturated with 16 — 18 kar. solder. The inlay is set and finished 
 in the usual manner. 
 
 In the methods just described, the matrix was made directly 
 in the cavity ; in the following methods a model is necessary for 
 swedging the matrix. 
 
 The inlay most extensively used before the introduction 
 of casting was, what might for the lack of a better name be 
 called the soldered inlay, as it was chiefly composed of this 
 material. The cement model of the cavity, made as described 
 under the indirect impression method, is embedded in im- 
 pression compound in the cup of a swedging press. Platinum 
 foil is adapted to the model, and the cavity well filled with 
 spunk. The cup is then placed in a strong cylinder with the 
 rubber cushion and plunger in position, and put under strong 
 pressure. The matrix is carefully removed from the model 
 and the walls of the cavity reinforced with pure gold. It is 
 then replaced on the model and again put under pressure. 
 To prevent distortion of the matrix, the cavity is filled with 
 sticky- wax before removal from the model. The wax is burned 
 out, and the overhanging margins and the whole lower sur- 
 face of the matrix is coated with chalk. The cavity is then 
 filled out with solder, the use of borax being avoided as much 
 as possible. Beginning with 22 kar., and only heating suffi- 
 ciently each time to fuse the solder added last, the cavity 
 is gradually filled with 22, 20, 18, and even if necessary with 
 16 kar. solder. The object should be from the start to place 
 sufficient solder in the cavity to complete the inlay in one 
 heating, without having to add a second or third time. Cusps 
 and contour are produced by building up with sponge-gold 
 and saturating with a low grade solder. The inlay is finished 
 and set as above. 
 
 I 
 
106 
 
 Larger parts of the tooth are restored, in the following 
 manner: after the matrix has been reinforced and swedged 
 for the second time, the missing contour is built up in hard 
 wax. A piece of pure gold plate rolled extremely thin, is 
 cut to shape, and burnished against the wax. The plate should 
 lie in close contact with the margins of the matrix. If an 
 occlusal surface is to be restored, a suitable cap is swedged 
 upon die-plate and waxed upon the matrix. A part of one 
 surface, proximal or occlusal, must always remain uncovered 
 for the introduction of the solder. With the exception of this 
 opening, the matrix with the wax and plate is embedded in 
 asbestos powder. After drying, the wax is burned out and 
 the chamber filled with solder. 
 
 The inlays described so far are all solid, a large number 
 of methods, however, have been suggested for making hollow 
 swedged inlays. The following method, devised in its essen- 
 tials by Hinman (Atlanta), is as follows. For swedging, the 
 small S. S. White press was used. The impression of the 
 cavity, taken in the usual manner, is embedded in moldine, 
 and well oiled. The cup of this press is inverted over the 
 impression and through the hole in the bottom of the cup 
 "inlay- metal", an improved Spence metal, is poured. The 
 model being cleaned, is ready for immediate use. 
 
 The matrix should be made of rolled gold No. 60. Platinum 
 gold of this thickness is, however, preferable. The foil is adapted 
 to the model and covered with a rubber disk. The cylinder 
 of the press is filled with moldine, placed over the cup and 
 the plunger introduced. The latter is given a few light blows 
 with a heavy hammer. The matrix is removed, reinforced, 
 a hole cut into the bottom, and then reswedged. The model 
 is then filled with wax, and the contour and occlusal surface 
 carved. If possible this wax model is tried in the mouth. 
 The wax is again placed upon the Spence model, the surfaces 
 smoothed, and an amount carved away from the margins of 
 the cavity equal to the thickness of the gold used for outer 
 part of the inlay. An impression of the wax form is then 
 taken and cast in "inlay metal". The cap swedged upon this 
 second model, is carefully soldered from the outside with 
 
107 
 
 20 kar. solder upon the matrix, while through to hole cut in. 
 the bottom, the inside is thoroughly reinforced with 14 — 16kar. 
 solder. In setting the inlay into the cavity, the chamber is 
 filled with cement. 
 
 For making this class of inlays (Fig. 57), preeminent before 
 the introduction of casting, a large number of methods have 
 been devised. To-day such inlays are never made. Their dis- 
 advantage is not alone the difficulty of construction, but also 
 the inadaptability of the margin, as a result of soldering 
 the two parts together. The hardness of the gold makes 
 burnishing the margins impossible. The only advantages 
 which at that time could be claimed for this class of inlays 
 were, that they saved valuable metal, and that being filled 
 with cement, they were not as good conductors of temperature 
 as solid metallic fillings. 
 
 The Casting Process. 
 
 The wax model, mounted as described on page 100, is washed 
 off with alcohol. The sprue is placed upon the sprue-holder, and 
 together with the model, coated with investment material of 
 creamy consistency. The cup or casting-ring is then filled with 
 the same material, the sprue-holder inverted, and allowed to 
 gently settle down until its edges are in contact with the 
 cup; or the ring may be placed in position and filled from 
 above. The investment material must be so soft, that pressure 
 is never necessary in embedding. As soon as the investment 
 has set, the sprue-holder is removed, and the form gently 
 heated until the sprue can be withdrawn. The heat is then 
 gradually increased. In about half an hour the wax has been 
 thoroughly burned out, and a smooth walled chamber remains. 
 The form is then ready to be cast by any one of the different 
 casting processes. 
 
 The investment material. 
 
 Before describing the different systems of casting inlays, 
 a few words on the subject of investment materials, and on 
 the casting of metals in general are deemed necessary. All 
 
108 
 
 of the innumerable materials recommended for the investment 
 of metallic inlays are by no means satisfactory in practice. 
 Which of these is the best, or if any one of them possesses 
 all the necessary qualities of a perfect investment material, 
 are questions that can be determined only by a long series 
 of experiments or comparative tests. 
 
 The qualities which an ideal material, used as an invest- 
 ment for the production of inlay casting-forms should possess, 
 are briefly summed up below. 
 
 1. The material mixed to a thick creamy consistency, should 
 set, without contracting, within a quarter of an hour. 
 
 2. In drying and heating the mold, the material should 
 neither crack, burn, fuse, soften or change its form in 
 any way. 
 
 3. After the wax has been burnt out, the walls of the 
 form should be perfectly smooth. 
 
 4. The material should be sufficiently porous, to permit 
 the escape of the air compressed in the form during 
 casting. 
 
 5. A quality which the material should possess in a high 
 degree, is non-conductivity of heat. The more marked 
 this quality in an investment, the less need the metal 
 to be cast, be heated above its fusing point. 
 
 6. The material must be hard enough, and possess suffi- 
 cient edge-strength, to withstand the pressure of casting. 
 
 7. The material should not be disintegrated by the heat 
 of the molten metal. An investment, unsatisfactory as 
 regards the last two points (6 and 7), cannot be used 
 to cast inlays of complex form. The angles, which on 
 the cavity surface of the wax model were well defined, 
 would in the inlay appear quite rounded. The inlay 
 would then not fit into the cavity. 
 
 8. The investing material should contain no substance, 
 which under the action of the heat of the molten metal, 
 becomes adherent to the surface of the inlay. 
 
 To prevent the formation of bubbles, the material must 
 be slowly and carefully mixed. Though some investments are 
 more liable than others to the formation of bubbles, correct 
 
lOIJ 
 
 mixing and embedding will usually obviate this difficulty. 
 Tapping the cup or ring after the wax model has been em- 
 bedded will inevitably lead to the formation of bubbles. The 
 cup is tapped on the supposition that all bubbles will thereby 
 rise to the surface. This is, however, not the case. Gas bubbles 
 are strongly attracted by any foreign body present in a liquid 
 or semi-liquid medium. The bubbles will therefore collect 
 upon the surface of the wax-model, and no amount of tapping 
 can then dislodge them. 
 
 A number of methods have been suggested for the pre- 
 vention of bubbles in the investment. The simplest is pro- 
 bably the use of recently boiled water. The writer found this 
 to be used in the arts, in making fine plaster casts*). Contrary 
 to expectations, this procedure has given very satisfactory 
 results. Another method, suggested by the writer, is to place 
 the water or even the ready mixed investment material under 
 the bell -jar of an exhaust pump. After exhauting the air, 
 the wax-model is carefully embedded in the usual manner. 
 The necessity of an expensive apparatus, is the objection to 
 this method. Price**), on the other hand, compresses the air 
 contained in the investment material. The top of the cup, 
 with the recently embedded model is covered with a layer of 
 wax and placed, until the investment has set, in a hydraulic 
 press capable of exerting a pressure of 70 — 80 atmospheres. 
 The plastic material is thereby forced into the finest details 
 of the wax form, and the bubbles, in obedience to the law 
 of the volume of gases under pressure, are decreased to ^/^o 
 or i/so of their normal volume. Price says: "This produces 
 a model of great density and smoothness of surfaces, and 
 when applied to an investment around a wax-model has a 
 most beautiful effect on the surface of the cast gold, and the 
 greatly increased density produces a harder investment, and 
 one with greater expansion." The latter is, according to Price, 
 a very valuable quality. He argues, that as cast gold even 
 under the most favorable circumstances shows a contraction 
 
 *) Ed. Uhlenhuth, Formen und GieBen (Leipzig). 
 **) Weston A. Price, The Laws Determining Casting or Fusing Results, etc. 
 Items of Interest No. 3, 5 u. 6, 1908. ' 
 
110 
 
 of 1.3 per cent, an investment material with an expansion of 
 exactly the same amount, would correct this error. Such an 
 ideal investment material, having all the other necessary quali- 
 ties, has as yet, not been produced. 
 
 The amount of material used for investing, and consequently 
 the size of the cup, should be in proportion to the size of the 
 wax-model. As all investments expand more or less upon 
 being heated, the walls of the mould should be of the same 
 thickness at all points. This insures a uniform expansion, 
 preserving the correct proportion in the inlay. If a wall is 
 thin, yet sufficiently strong to withstand the pressure of casting, 
 it will expand less, and consequently the inlay will be flattened 
 on that side. If the wall cannot withstand the pressure, 
 it will either be bulged out or cracked in casting. "The best 
 that any of the investments now available will do is to expand 
 8,5 thousanths*) as a maximum at 1000 degrees F." (Price), 
 and as the metal of a steel or brass cup has a coefficient of 
 expansion of about twice this amount, it becomes evident, 
 that the mould receives but little support from the cup or 
 ring when it is heated. This proves the necessity of making 
 the walls of the mold sufficiently thick. 
 
 Price calls attention to the fact that the investment must 
 be homogeneous. His experiments have proven, that different 
 investment materials do not expand equally, and that this 
 is true of even a thin and a thick mix of the same material. 
 If therefore the wax model is coated with a thin mix, and the 
 cup filled with a thicker mix of the same material or even 
 with another investment, failure becomes imminent, owing to 
 unequal expansion of the mould. Cracks and crevisses are 
 formed, or the inner layer of investment may in places break 
 away from the outer. 
 
 The mould should be dried slowly and uniformly. If the 
 investment contains much plaster, drying may be more rapid. 
 The water and wax boil out of the sprue gate without doing 
 the mould any harm. The disadvantage of such material is 
 that it checks easily in heating, and that it is disintegrated 
 
 *) Taggart's Investing Material. 
 
Hi 
 
 by tlie heat of the metal. After the mould is dry, it must 
 be further heated to burn out every trace of wax. Tests made 
 by the writer have shown that this takes place at a tempera- 
 ture of about 450 °C. (842 degrees F.) The wax passes off 
 as a blue vapor, and a deposit of carbon blackens the sprue- 
 gate. Continued heating causes the deposit to disappear 
 gradually until the gate has resumed its natural color, only 
 a dark ring remaining upon the surface of the mould. Every 
 trace of wax has then been burned out, and the temperature 
 in the chamber of the mould is about 850 — 900 degrees F. 
 
 With some investments, it is not advisable to allow too 
 long a time to intervene between embedding the model and 
 burning out the wax. While standing the investment looses 
 moisture, so that when the mould is heated, the wax instead 
 of boiling out of the sprue-gate with the water, is absorbed 
 by the investment. This, in some cases, seems to have a dele- 
 terious effect, producing an inlay with very rough surfaces. 
 The same effect is produced by heating such investments 
 too slowly. 
 
 An investment material, perfect in every respect, is up 
 to date, unknown to the writer. Price's artifical stone, though 
 not an investment in the strictest sense, possess many of the 
 most desirable qualities. It is a body equally related to the 
 Portland and silicate cements. For mixing an orthophosphoric 
 acid of definite specific gravity is used. This material is hard, 
 dense, and very resistent to temperatures up to 2700 degrees F. 
 Its linear coefficient of contraction in setting is "in some cases 
 as low as two-thousandths per linear inch". The stone model 
 is made from an impression, the cavity in the model waxed 
 up, and the model with the wax in position embedded in 
 investing material in the usual manner. 
 
 An investment recommended by W. Sachs (Berlin), and 
 extensively used in the northern part of Germany, consists of 
 
 Quartz flour 2 parts 
 
 Plaster 1 part (by volume). 
 
 The quartz flour, an almost perfectly pure silica, is ob- 
 tained from the Koyal Prussian Porcelain Factory. The in- 
 gredients should be well mixed, preferably in a rotary flour 
 
112 
 
 sieve. Another investment, which has been recommended by 
 Arvine*), consists of 
 
 Enghsh porcelain clay . 1 part 
 
 Quartz flour 1 part 
 
 Plaster 1,5 parts (by weight). 
 
 M. L. Ward (Ann Arbor)*) after carefully studying the 
 subject of investing materials, believes that a material for 
 this purpose, to be strong, must have a composition ana- 
 logous to that of concrete. This is a mass composed of gravel 
 in which the spaces are filled out by sand, and the spaces 
 beween the grains of sand are in turn filled out by cement. 
 In the investment suggested, the gravel is represented by flint 
 powder, the sand by quartz flour, and the cement by plaster. 
 The proportions as given, 
 
 Fhnt 30 cc. 
 
 Quartz flour 36 cc. 
 
 Plaster of Paris 17 cc. 
 
 refer only to the materials used by Dr. Ward. The grit of 
 the silicates and the quality of the plaster are the factors 
 which determine the relative quantities of the formula. 
 
 The casting-metal. 
 
 Only the noble metals and their alloys are used in casting 
 inlays. They possess all the qualities, necessary for sucessful 
 casting. These metals may be fused with the flame of an 
 ordinary blow-pipe, and become sufficiently fluid to reproduce 
 the finest details of the mold. In common with all metals, 
 they possess the property of contracting after having been 
 cast. The contraction occurs in three different stages; 1. con- 
 traction of the overheated metal in its liquid state, 2. con- 
 traction at the moment of solidification, and 3. contraction 
 of the solid metal while cooling. An exception to this rule 
 is made by cast-iron, bismuth, and some alloys of copper 
 and tin. These expand more or less at the moment of solidifi- 
 cation. In the third stage they again act like other metals. 
 
 *) F. B. Arvine, Gold Cast Inlay Investment, Cosmos, No. 1, 1908. 
 **) Marcus L. Ward.' A Consideration of the Casting Process, with Special 
 Reference to Refractory Materials. Dental Cosiaos, Sept. 1909. 
 
113 
 
 ' Uhlenhuth gives the linear coefficient of contraction of 
 some of the baser metals as: 
 
 from to average 
 
 Zink V65 V57 V62 
 
 -L'SaCl /l04 /sG /92 
 
 liri /173 /i2(, /147 
 
 Statuary-bronze .... — — ^/i2o 
 
 -t>rass /79 749 /eg 
 
 Cast iron Ves V95 Vse 
 
 Gun-metal V139 V130 V135 
 
 (100 copper, 12 V2 tin) 
 
 Bell metal — — ^/es 
 
 (100 copper, 18 tin) 
 
 Steel — — i/e.5 
 
 "The cubical coefficient of contraction, is found by trebling 
 the above fractions while for the coefficient for a surface, the 
 fractions are doubled. A cube of cast-iron will therefore shrink 
 along each edge ^/gg, upon each surface '^1^^ and in cubical 
 contents ^/32." 
 
 In regard to the shrinkage of the noble metals as determined 
 by W. A. Price, the appended table, though incomplete, shows 
 some interesting points. The linear coefficient of contraction 
 is given in thousandths. The influence of pressure upon 
 shrinkage is also shown. 
 
 Pressure 
 
 Gold 
 24 kar. 
 
 Gold 
 18 kar. 
 
 Gold solder 
 
 Gold 18 \ 
 Silver 2 1 
 Copper 2 {^^^^^ 
 
 Silver (pure) 
 
 Gold and 
 
 10% 
 Platinum 
 
 
 
 
 Zink 2 ] 
 
 
 
 
 
 22.5(V45)*) 
 
 — ■ 
 
 
 
 . 
 
 
 
 V50 oz. 
 
 20.5 
 
 
 
 18 
 
 
 
 
 
 /lO 55 
 
 18 
 
 
 
 — 
 
 
 
 
 
 3 pounds 
 
 14 
 
 
 
 — 
 
 20 (V50) 
 
 
 
 5V2 55 
 
 13 (V77) 
 
 15.5 
 
 15 
 
 — 
 
 14 
 
 *) Converted into fractions as in the table of Uhlenhuth. 
 
 That the gold used in casting an inlay does shrink, is an 
 indisputable fact. The amount of shrinkage, as well as the 
 
 Bodecker, Metallic Inlay. 
 
114 
 
 best metliod of controlling it, are subjects upon which opin- 
 ions differ widely. Ward*) beleives the shrinkage in a pro- 
 perly cast inlay to be far below the percentage given by 
 Price. As the coefficient of contraction of cast-iron decreases 
 in direct proportion with the size of the casting, Dr. Lane 
 argues by analogy, that as Price determined the percentage 
 of shrinkage on gold bars, the percentage of a small inlay 
 would be proportionately less. Upon this theory, the actual 
 shrinkage of a pure gold inlay of V4 inch in diameter is stated 
 to be 0,0008 in. This leaves a space of 0,0004 in. on each 
 side between the walls of the cavity and the inlay. This 
 could be filled only with the finest grained cement. (See Head's 
 table p. 140.) The progressive variation in the coefficient of 
 contraction is accounted for by the more rapid chilling of 
 the smaller masses of metal immediately after being cast. 
 In order to cast inlays with such low shrinkage, the mold 
 should be cool, and the gold as fluid as possible without being 
 heated much above its fusing point. The casting machine 
 must, therefore, be quick and reliable in action. 
 
 Lane**) found by a series of experiments, that the amount 
 of pressure has no influence on shrinkage, as long as an ex- 
 ceedingly hot mold is used. Equally good results were 
 obtained by using 45 or 5 pounds pressure per square inch. 
 Castings made from a half-inch pattern, showed a shrinkage 
 of 0,0008 inch. 
 
 Van Horn***) recommends the use of a superheated mold. 
 He, however, does not believe that this measure alone will 
 prevent shrinkage. This is accomplished by determining the 
 coefficient of expansion of the wax used, and making the 
 mold with a correspondingly hot investing material. (115 to 
 120° F.) The wax expanding uniformly, produces a slightly 
 enlarged mold, which in turn neutralizes the contraction of 
 the gold. By this method, it is possible to produce castings 
 which are even larger than the patterns. 
 
 *) M. L. Ward. A Consideration of the Casting Process etc. Dental Cosmos, 
 Sept. 1909. 
 
 **) Dental Digest, July, 1909, p. 498. 
 ***) C. S. van Horn. Casting: A Review and Commentary, etc. Dental 
 Cosmos, August 1910. 
 
115 
 
 Price*), in regard to shrinkage, says "that gold does con- 
 tract a definite amount no matter when, how, or by whom 
 it is manipulated, and that this total contraction will take 
 place under all conditions, though its exact position may be 
 changed in part; that is, as the mass of gold making up the 
 inlay and sprue is cooling, the gold may be moved from the 
 sprue to take up some of the total of the contracted gold 
 in the inlay." In another article Price claims that "the 
 location of the shrinkage or contraction (not the total amount) 
 can be partially transferred to another part of the cooling 
 mass by pressure on the molten gold while it is in a semi- 
 molten state, and that the distance or range in temperature 
 below the melting or fluid point through which it can be 
 moved from one part of the mass to another to take the 
 place of contraction at that latter place, is dependent upon 
 the pressure used." Price therefore claims that high pressure 
 is the only reliable means of preventing, or at least con- 
 trolling, shrinkage. This, of course, necessitates the use of 
 high pressure machines in connection with the stone model, 
 as ordinary investments v/ould under such circumstances be 
 worth less. 
 
 From the opinions quoted, it becomes evident that this 
 question is far from being settled. Granting the accuracy of 
 the experimental data in each case, it remains for future in- 
 vestigations to prove the fallacy of some of the deductions. 
 
 Mention has been made of the fact, that the shrinkage of 
 metals occurs in three stages. 
 
 1. Shrinkage of the molten metal. 
 
 2. Shrinkage daring solidification. 
 
 3. Shrinkage of the solid metal upon cooling. 
 
 For gold, only the shrinkage during the third stage has been 
 investigated. It may be safely assumed that any measure 
 taken to influence the shrinkage in this stage will have but 
 very little effect. Price found that the melting point, and 
 therefore also the point of solidification, of gold, could, by high 
 
 *) Weston A. Price. Some Adv^antages of the Stone Model Method etc. 
 Dental Cosmos, Sept. 1910. 
 
 **) Items of Interest, Sept. 1910. 
 
 8* 
 
116. 
 
 pressure, be reduced as much as 200° F. The question arises 
 whether the pressure prolongs the process of crystaUization, 
 or whether the point is simply reduced 200°, while the pro- 
 cess itself goes on in the time and manner as under normal 
 conditions. Price believes that as gold shrinks 0,001 with 
 every 100° F. under the fusing point, by lowering the fusing 
 point 200°, the shrinkage is reduced by 0,002. A thorough 
 investigation of the phenomena in the second stage of shrink- 
 age (solidification) will probably explain why contrary methods 
 of casting seem to give the same results. That metals in this 
 stage obey some special laws, is proven by the fact that cast- 
 iron, in contradistinction to most other metals, expands to 
 such an extent during solidification, that it is liable to burst 
 all but the strongest molds. 
 
 Any metal heated above its fusing point, will, with in- 
 creasing temperature, constantly expand. After casting an 
 inlay, the pressure equalizes the resultant contraction up to 
 the moment of solidification, by forcing liquid metal into the 
 mould to counteract the shrinkage. If, however, the channel 
 is long and narrow, the material used for investment not 
 a poor conductor, and the metal overheated, then the metal 
 in the channel will solidify while the metal in the cavity 
 of the mould is still liquid. When the latter gradually cools, 
 no additional metal can then be forced into the mould to 
 replace the shrinkage. The dead-head, or excess metal in the 
 channel, usually parts from the casting at the point where 
 it enters the chamber of the mould. This condition, known 
 as blowing, is recognized on an inlay by the presence of more 
 or less irregular depressions about the dead-head. The latter 
 does not always tear away from the inlay and may be normal 
 in appearance, in spite of the presence of blow-holes. Foreign 
 matter in the casting metal may produce the same conditions, 
 by obstructing the free flow in the channel. To prevent the 
 formation of blow-holes, special attention should be paid to 
 the quality of the investment used, as well as to the cleanness 
 and the heating of the metal. The reason for using a short 
 sprue, which in diameter is proportionate to the size of the 
 inlay, is evident. Perfect fluidity of the metal is absolutely 
 
117 
 
 essential to successful casting. Foreign matter, traces of in- 
 vesting material, products of oxidation, and other metals are 
 contaminations which tend to reduce the fluidity of the metal, 
 and should, therefore, be carefully removed before casting. 
 Foreign matter need be considered only if the gold has been 
 accidentally spilled. Investing material can be removed by 
 dilute hydrofluoric acid. The products of oxidation and other 
 metallic contaminations are removed only by refining the gold. 
 For this purpose Ward*) recommends the dry process. "A 
 number of different methods of purifying gold might be 
 enumerated, but perhaps nothing will ever be of more service 
 than about equal parts of potassium nitrate and borax. Both 
 are clean white powders which can be mixed and kept in an 
 accessible place. If a casting is about to be made, and the 
 gold is found to be too sluggish, the operation need not be 
 delayed much over five minutes to purify the gold, while 
 ten or fifteen minutes v/ould raise the karat considerably. The 
 process involves the oxidation of the base metals, the oxygen 
 being furnished by the potassium nitrate, and these oxids being 
 separated from the gold beneath the flux of borax. The gold 
 should be melted and the mixture added a little at a time 
 with one hand, and a blowpipe flame kept directed on the 
 gold v/ith the other, the gold all the time being kept melted. 
 This should be continued in most cases for about five minutes, 
 though it is often necessary to continue the process much longer. 
 As soon as the last particles of nitrate and borax have been 
 put on the gold the flame should be removed, to avoid its 
 contaminating influence. Gold known to contain certain quan- 
 tities of tin, silver, or lead could perhaps best be refined by 
 the ammonium or mercuric chlorid process, but for iron, bis- 
 muth, antimony, zinc, etc., nothing excels potassium nitrate 
 and borax." 
 
 The metal almost exclusively used in casting inlays, is gold. 
 Opinions differ, however, in regard to the fineness. Most 
 operators prefer to use 22 kar. gold, while the writer, for 
 reasons described in chapter II and XI, generally makes his 
 inlays of 24 kar. In cases where the anchorage extension must 
 
 *) M. L. Ward, Dental Cosmos. Sept. 1909. 
 
118 
 
 bear considerable strain, or where abraded occlusal sur- 
 faces are to be restored, 22 kar. gold is undoubtedly pre- 
 ferable. 
 
 A number of inlays of pure silver have been made by the 
 writer. The only objection to this metal is that it often 
 turns black in the mouth. It casts well, and can without 
 difficulty be burnished against the margins of the cavity. 
 Being as servicable as gold and requiring the same cavity 
 preparation, yet costing much less, the silver inlay would be 
 of use in college infirmary practice. 
 
 Though platinum can be cast in special apparatus, its high 
 melting point makes its use in inlay work almost impossible. 
 The writer has cast inlays of this metal, using the Jameson 
 apparatus and a gas -oxygen flame, and melting the metal in 
 a specialy constructed crucible. The results were only occa- 
 sionally satisfactory. Platinum inlays would be useful, for com- 
 bination with high-fusing porcelain (Figs. 102 — 105). Dental 
 alloy, silver and platinum, does not always keep its color in 
 the mouth. 
 
 Gold, owing to its color and its contraction, cannot be 
 designated as an ideal material for making inlays. Such a 
 metal would have to be constant in form, and possess the 
 durability and malleability of gold, the cheapness of silver and 
 soft lustrous color of aluminum. 
 
 The casting apparatus. 
 
 A description, or even an enumeration of all the apparatus, 
 which have been suggested or put on the market would almost 
 be impossible, as their number at present exceeds one hundred. 
 Neither can special directions for use be given in describing 
 the principles of each class of apparatus, as the author's ex- 
 perience is limited to but a few, and all directions necessary 
 may be obtained from the manufacturer. 
 
 According to the manner in which the pressure is pro- 
 duced, all machines used for casting inlays may be divided 
 into five classes. The pressure is produced in the different 
 classes by, — 
 
119 
 
 1. (jas, 
 
 2. Steam, 
 
 3. Direct contact, 
 
 4. Centrifugal force, 
 
 5. Vacuum. 
 
 An example of each class will be described, and the action 
 of the pressure upon the molten metal and upon the mould, 
 briefly explained. 
 
 1. Gas Pressure (Pneumatic force). 
 
 This class includes all machines using compressed gases, 
 as nitrous oxid, carbon dioxid, or air. The eldest of this class, 
 and at the same time the first machine for the purpose of 
 casting inlays, was invented by Taggert (Fig. 96). In this 
 
 Fi</. 9G. 
 
120 
 
 apparatus the compressed gas, nitrous oxid is not only used 
 for the production of pressure in casting, but also as a flame 
 to melt the metal. From the cylinder the gas flows through 
 the reduction-valve {a) to the stop-cock (h), then through a 
 rubber tube to the burner (c). The flame strikes the sprue- 
 gate of the mold {d), where the metal to be fused is placed. 
 By regulating the reduction-valve and observing the gage, 
 the pressure deemed necessary in each case, is set before 
 casting. When the gold is sufficiently heated, the lever (/) 
 is quickly pressed down. The cam {i) pressing against the 
 arm (o), turns the burner aside and extinguishes the flame, 
 at the same time permitting the gas to pass from the valve {a), 
 at the pressure perviously determined, through the tube (e) 
 to the head (A). Five small holes in the middle of the under 
 surface of the head serve to admit the gas to the mold, while 
 a packing pressing on the edge of the casting-ring prevents 
 escape. 
 
 In all machines of this class, the action taking place in 
 the mold is the same. The gas in pressing upon the surface 
 of the molten metal drives it into the mould. The gold in turn 
 compresses the air contained in the cavity of the mold, thereby 
 forcing the latter into the porous investment. 
 
 In regard to the effective pressure in the mold, Price says: 
 "When the pressure is obtained from gas or air it is equal 
 to the cross section area of the inlay or mold, not the gate 
 or sprue, in fractions of a square inch divided into the pressure 
 per square inch of the gas. For example, if the cross section 
 area of the inlay is ^/g of an inch square, it will be ^/^^ of a 
 square inch, and the pressure 16 pounds per square inch, the 
 effective pressure will be ^/^^ of 16, or ^/^ of a pound, less the 
 back pressure of the gas retained in the investment behind 
 the gold, and the leakage of the pressure around the gold, 
 for if the pressure can get away through the investing material 
 easily from behind the gold, it can easily get past around it 
 in the same way; which means that there would be con- 
 siderably less pressure than ^/^ pound, depending largely on 
 the compactness of the investing material and the leakage 
 of the closing device over the molten gold. The writer believes 
 
121 
 
 the effective pressure under the above conditions to be less 
 
 than ^/s of a pound actual pressure." 
 
 It becomes evident from, the above observations, that the 
 
 action of the pressure in machines of this class must be rapid 
 
 and intense, to prevent the penetration of the gas into the 
 
 investment. Another fact to be borne in mind is, that the 
 
 pressure indicated by the gage does not correspond to the 
 
 pressure in the mold, as there is always more or less leakage 
 
 through the packing between the head and the ring of the 
 
 mold. 
 
 2. Steam Pressure. 
 
 "Solbrig's Pliers" are the eldest machine of this class. 
 Upon one of the beaks, the mold is placed, while the other 
 is constructed in the form of a shallow cup with an internal 
 diameter corresponding to that of the ring of the mould. The 
 cup is filled with sheets of asbestos (Section, Fig. 97), which 
 
 Fig. 97. 
 
 are moistened before casting. The gold is fused directly upon 
 the mold. When the metal is sufficiently heated the pliers 
 are closed, whereupon the steam generated by the heat in 
 the moist asbestos, drives the gold into the mold. The sim- 
 plicity of this principle makes the construction of an inexpen- 
 sive apparatus possible. In Europe this is the type of machine 
 most used. Numerous machines of this class are now on the 
 market. The action taking place in the mold is the same 
 as in the first class. The pressure can not however be deter- 
 mined, as it is dependent upon three variable factors, the 
 amount of moisture contained in the asbestos, the temperature 
 of the metal and lastly upon the adaptation of the asbestos 
 packing to the edge of the ring of the mold. 
 
122 
 
 The pressure however varies in direct proposition to the 
 size of the casting. "A pressure gauge and the regulation of 
 the pressure are quite superfluous, since the pressure is regu- 
 lated automatically by the change of the factors which enter 
 into the formation of steam. Thus, for a small inlay, owing 
 to the small amount of metal, and the restricted quantity of 
 moistened asbestos employed, we have less pressure than for 
 the casting of a large plate, for which we employ a compara- 
 tively large mass of fused metal, and large asbestos discs for 
 the production of a greater volume of steam. The pressure 
 thus obtained varies between two and three atmospheres."*) 
 
 3. Pressure by Direct Contact. 
 
 Though probably not the eldest, one of the simplest 
 machines of this class is that of Biber (Pforzheim). It con- 
 
 Fig. 98. 
 
 sists of a metal foot-plate supporting a mold of the usual 
 form (Section, Fig. 98) and a loosely fitting cover filled with 
 moldine. The metal is fused upon the mold and pressure 
 exerted on the wooden knob of the cover. The pressure in 
 
 *) 0. Solbrig, Ash's Quarterly Circular, Jan. 1910. 
 
123 
 
 the mold depends upon the force used, and upon the softness 
 of the moldine. In contradistinction to class I and II, the 
 pressure does not penetrate the investment. The force must 
 be applied quickly, as the metal coming into contact with 
 the cold moldine solidifies rapidly. Solbrig*) claims that "the 
 moisture contained in the substance employed (moldine) is 
 the chief source of the pressure, and for this reason this kind 
 of press must be put in the class of steam pressure apparatus." 
 
 4. Centrifugal Force. 
 
 But few machines of this class have appeared upon the 
 market, the first was the Jameson machine (Fig. 99). This 
 
 Fig. 99. 
 
 consists of a circular casing attached to a solid iron base. The 
 casing is divided by an asbestos-covered plate into a lower 
 closed compartment, containing a spiral spring and a flywheel, 
 and an open compartment above, containing the casting 
 appliance proper. A vertical axle, to which below are attached 
 the spring and the fly-wheel, carries at its upper end short arms, 
 
 *) 0. Solbrig, Cast Metals in Dental Art, Asch Quartly, Jan. 1910. 
 
124 
 
 with movable holders for the flat crucibles and for the molds. 
 In casting, but one mold is used, the other serving as a counter- 
 weight. Owing to the horizontal position of the mold, a flat 
 crucible lying opposite the sprue gate is used. A large Bunsen 
 burner, for heating the mold, projects through the asbestos 
 plate. The walls of the casing prevent the loss of gold, if 
 spilled during casting. The process of casting with this machine 
 is the following: By turning the arm 8 — 12 times, depending 
 upon the amount of gold used, the spring is wound up. The 
 brake a is then set as soon as the mould is over the opening 
 of the Bunsen burner. The proper angle which the arm and 
 holder should make to prevent spilling, is dependent upon 
 the tension of the spring and the amount of gold used. After 
 rotation has begun the holder again straightens out. When 
 the mold is sufficiently hot, the gold is melted and the brake 
 released. By centrifugal force the gold is thrown into the 
 sprue-gate and into the mold. 
 
 As the writer prefers in most cases to use pure gold for 
 inlays, and as the crucibles withstand a much higher heat 
 than the investment, he employs oxygen in connection with 
 illuminating gas to melt the gold more rapidly. The ordinary 
 blow-pipe is used, the tube for the air being connected with 
 the reducing valve of the oxygen cylinder (Fig. 100). This 
 method is cheap and efficient, and is of great service in solder- 
 ing platinum bases in porcelain work. 
 
 On the subject of pressure in the mold Price*) says: "With 
 a centrifugal machine the actual effective pressure is the weight 
 of the mass of molten gold, for our purpose irrespective of 
 its shape, multiplied by the square of the velocity of the gold 
 in feet per second, divided by the the radius in feet (not dia- 
 meter) of the circle it moves in, divided by 32 to change 
 poundal units to pounds pressure. 
 
 For example, if V2 ounce of gold, which is ^/24 pound troy, 
 is revolving at the rate of ten revolutions per second, which 
 is 600 per minute, in a circle of a diameter of ten inches, 
 the velocity in feet is 10 (diameter) x 3,14 X 10 (revolutions) 
 ~ 12 (inches) ^ 26,17 feet per second, and the pressure 
 
 *) Items of Interest May 1908. 
 
125 
 
 V24 pound multiplied by 26,17 squared (the velocity), divided 
 by ^/i2 (the radius in feet) divided by 32 = 2,14 pounds actual 
 pressure on the inlay," 
 
 Ix 684,86 xfx^2= 2'"- 
 
 "If the revolutions are twenty times per second, which is 
 1200 per minute, the actual effective pressure is 8,56 punds. 
 
 M Arbpifsmanomefer 
 
 J Inbalhmesspp 
 
 Absperrhahn 
 
 FlaschenvenH) 
 
 Schlauchstutzp 
 
 Flasche 
 
 SicherheifsvGnh 
 
 Fig. 100. 
 
 or if only five revolutions per second 0,53 or ^/a pound. 
 Remember the pressure increases as the square of the velo- 
 city. If this pressure is on an inlay ^/g inch square ( ^1^^ square 
 inch) it is equal 
 
 at 5 revolutions per second to 34^/4 pounds per square inch 
 
 at 10 
 at 20 
 
 137 
 
 548 
 
 and without decrease for back pressure or leakage as in the 
 case of a gas pressure. If an ounce of gold is used instead 
 of one-half ounce the pressure is double the above." 
 
126 
 
 5. Pressure Produced by Vacuum. 
 
 This method was first suggested by Frink*). But few 
 machines of this class have been constructed; of these the 
 "Elgin Vacuum Casting Appliance" is probably the most per- 
 fect (Fig. 101). This machine consists of an iron tank containing 
 an exhaust pump. Attached to the tank are a gauge and an 
 
 Fio-. 101. 
 
 arm with two stop-cocks and two brackets of different size. 
 Before casting, the tank is exhausted until the gauge shows 
 a pressure of 15 units. The ring of the mould must be in 
 absolute contact with the bracket. This is tested by opening 
 the stop-cock. The gage should fall gradually without any 
 hissing noise. When the gold, fused upon the mold, is suffi- 
 ciently heated, the cock is opened. The metal is forced into 
 the mould by atmospheric pressure. 
 
 *) Dental Cosmos Feb. 1908. 
 
127 
 
 The actual pressure upon the inlay at the moment of 
 casting may approximately be determined as follows. The 
 atmospheric pressure .at thirty inches is 14.7 pounds to 
 the square inch. The gauge of the machine shows a negative 
 pressure of fifteen inches, that is, one-half of the normal 
 pressure or 7.35 pounds to the square inch. Assuming the 
 cross sectional area of the inlay to be Vs of an inch square, 
 or Vea of a square inch, the effective pressure will then be 7.35 
 X V64 or 0.115 pound. No allowance is therein made for leakage 
 between mold and bracket, or for the pressure penetrating 
 the investment in advance of the gold. The actually effective 
 pressure upon the inlay is therefore less than 0.1 pound. 
 
 With proper manipulation, successful work can be done 
 with machines of all the classes described above, and yet, the 
 ideal machine has still to be constructed. Price has suggested 
 such an apparatus, in which the pressure can be accurately 
 controlled and the temperature of the fused metal easily 
 determined ; a centrifugal casting machine, driven by an electric 
 motor, heated by electricity, and having a pyrometer attach- 
 ment. The cost of a machine of this kind would however be 
 very great. For experimental work such an apparatus would 
 be of the greatest value. 
 
 After casting, the mold should be gradually cooled. Sudden 
 chilling in water, though advocated by many, is liable to cause 
 distortion through unequal contraction of the metal. When 
 the mold is cool, the inlay is removed from the investment 
 and cleansed with a small brush. The dead-head is nipped off 
 at about an eight inch from the inlay. 
 
 Combination Inlays. 
 
 A combination of gold and porcelain in making inlays has 
 been advocated by a number of writers. The use of such 
 inlays is confined to the labial surfaces of anterior teeth. The 
 results, in regard to adaptation are not as satisfactory as those 
 obtained with all-metal inlays. In solidifying and in cooling, 
 a cast inlay is constantly under pressure, if then the inlay 
 is annealed, as it is in fusing the porcelain, it will undoubtedly 
 change in form. Compared to a porcelain inlay, its esthetic 
 
128 
 
 qualities are less satisfactory. The combination of a gold 
 inlay and silicate cement appears still more unesthetic. 
 
 Combination inlays are made by cutting away a part of 
 the metallic inlay, and restoring the form with porcelain. To 
 avoid the difficulty of cutting the metal, the part to be restored 
 with porcelain is removed from the wax model. This may be 
 done with a bur, a sharp carving instrument, or with Roach's 
 
 Fig. 102. 
 
 suction-carver. The porcelain is either fused directly onto the 
 roughened inlay, or an impression is taken, and the porcelain 
 with the matrix, cemented onto the roughened inlay. In this 
 method a line of metal is alway present between the porcelain 
 and the margin of the cavity. 
 
 Fig. 103. 
 
 Fig. 104. 
 
 The few combination inlays that the writer has set, were 
 made so, that no gold showed between the porcelain and the 
 enamel margin. As an example a proximal cavity involving 
 the incisal angle has been chosen (Fig. 102). The general 
 cavity-preparation is similar to that shown in Plate XIII. 
 The wax-model is made in the mouth, and into the surface, 
 visible in the finished inlay a cavity is cut (section Fig. 103). 
 At the cutting edge, where the metal should protect the 
 porcelain, the wax is extended slighty beyond the normal 
 length (section Fig. 104). This obviates the difficulty of carv- 
 
129 
 
 ing a feather edge upon the wax-model. After the porcelain 
 has been fused onto the inlay, the excess {a, Fig. 104) is care- 
 fully removed with a disk, so that no metal may be visible 
 in the mouth. 
 
 The inlay is cast in 22 kar. gold and tried in the cavity. 
 It is then removed and the walls of the cavity which are to 
 lie in contact with the porcelain, are covered with a piece 
 of No. 40 gold-foil. The foil should lie perfectly flat, without 
 any folds, and should extend slightly under the inlay (/, Fig. 105 
 
 Fig. 105. 
 
 At other points upon the margin of the cavity, small pieces 
 of the same foil are laid. This raises the whole inlay out of 
 the cavity a distance equal to the thickness of the foil. Later, 
 when the matrix has been stripped from the porcelain, the 
 inlay again fits into place, and the porcelain lies in absolute 
 contact with the walls of the cavity. 
 
 After the foil has been properly placed, the inlay is in- 
 troduced into the cavity and firmly held in position. Inlay 
 wax is then pressed into the cavity of the inlay and against 
 the matrix (Fig. 105) which is thereby quickly and accurately 
 adapted to the margin of the cavity of the tooth. The diffi- 
 culties often encountered in removing the inlay with the matrix 
 from the cavity, can be overcome only by patient and careful 
 manipulation. In order to facilitate the removal, the sprue 
 on the inlay should be left sufficiently long, so that it may 
 be firmly grasped with a pair of tweezers. The inlay and 
 matrix are then invested, and the contour restored with 
 Jenkin's Porcelain Enamel. 
 
 Another method of combining gold and porcelain in an 
 inlay, is to make the porcelain part first, and then to com- 
 
 Bo decker Metallic Inlay. ' 9 
 
130 
 
 plete the metallic part of the inlay. The writer considers this 
 method practicable only when large pieces of porcelain or 
 whole facings can be used (Plate VIII). 
 
 The surface of a metallic inlay, after being properly roughen- 
 ed, may be covered with a layer of porcelain. This, however, 
 is applicable only to surfaces not exposed to the force of 
 mastication. 
 
Chapter XI. 
 Setting the Inlay. 
 
 After the inlay has been cast, all adherent particles of 
 investment material are removed with a stiff tooth-brush and 
 water. A perfect inlay at this stage should be an exact repro- 
 duction of the wax model. It should have smooth surfaces 
 with sharp margins and well defined angles. Before the inlay 
 is finally set with cement, it must be fitted, burnished, and 
 undercut or roughened. 
 
 Fitting the Inlay. 
 
 The excess metal, or dead-head is cut off, leaving a stump 
 about an eight of an inch in length attached to the inlay. 
 In trying the latter in the cavity, this stump, when not situated 
 at the contact point, offers a convenient hold for the tweezers, 
 while in roughening and undercutting the inlay, it can be 
 firmly grasped with a pair of flat-nosed pliers. In cases where 
 the sprue has been placed at the contact point, the stump 
 is cut somewhat shorter. While repeatedly attempting to 
 seat the inlay in the cavity, the sprue-stump is gradually 
 ground down , until with some slight force the inlay is brought 
 into its proper position. The contact point then presses firmly 
 against the adjoining tooth. The inlay is thereupon removed 
 from the cavity and the proximal surface finished and polished 
 with cuttlefish disks. Care should be taken to touch the 
 contact point as little as possible. 
 
 An inlay, perfect in form, can be introduced into the cavity 
 without difficulty. If the inlay does not go into place easily, 
 the reason must be sought, and the cause removed. If neces- 
 sary another inlay should be made. The fact should always 
 be borne in mind, that an inlay requiring much fitting can 
 never be considered a perfect piece of work. If a faulty inlay 
 
132 
 
 is set, the operator, and not tlie inlay process, is responsible 
 for any subsequent failure. 
 
 An inlay may be faulty from several causes. The sources 
 of error are: an inaccurate impression, improper investment, 
 and imperfections in casting. The impression was distorted, 
 if an inlay which had been properly invested and perfectly 
 cast, as shown by its smooth surfaces and sharp margins, 
 cannot be introduced into the cavity. Either the wax model 
 had changed in form, or the thin anchorage extenstions had 
 been bent in removing the model from the cavity. If such 
 an inlay cannot be forced into the cavity, it is far better 
 to make another, than to attempt to remedy the difficulty 
 by grinding. When only the extensions are bent, the inlay 
 is firmly pressed into the cavity with a large burnisher and 
 the extensions driven into place by means of a smooth plugger 
 upon which an assistant taps with a mallet. 
 
 Small rounded projections, occurring in three distinct 
 forms upon the surface of the inlay, point to the presence 
 of bubbles in the investment. A bubble directly upon the 
 surface of the wax model results in a hemispherical projection 
 on the inlay. If, however, a very thin layer of investment 
 separates the bubble from the wax model, the pressure in 
 casting will break down this wall, and the projection will 
 appear as an almost perfect sphere upon the inlay. If a number 
 of such bubbles lie together, the pressure will destroy not only 
 the layer of investment separating the bubbles from the wax 
 model, but also the walls between the bubbles. This gives 
 the projection upon the inlay an irregular form. The spherical 
 form can easily be removed with a sharp instrument. The 
 other forms can be removed only by grinding. If present in 
 greater numbers, especially at or near the margin of the cavity, 
 they are apt to make the inlay worthless. 
 
 An imperfectly cast inlay may be faulty in three respects ; 
 it may shov/ either a granular surface, rounded margins, or 
 blow-holes. The granular surface results from the use of super- 
 heated metal in casting. If the mould made of investment 
 material had the same physical properties as one made of 
 metal, overheating the gold would have no influence upon 
 
133 
 
 the exact size of the inlay. Overheated metal (h, Fig. 106) 
 cast in a metallic mold (a), shows a smooth surface with slight 
 depressions. In number, the latter depend on the degree to 
 which the metal has been overheated, and upon the mass of 
 the metal itself. The size of the casting is in no way altered. 
 If, however, an investment material is used in making the mold. 
 
 /CI 
 
 Fis. 106. 
 
 Fig. 107. 
 
 the high heat of the metal {h, Fig. 107), destroys the smooth- 
 ness of the walls of the mold (a), thereby producing slight 
 elevations and depressions which give the surface of the metal 
 a granular appearance. The size of the casting is somewhat 
 increased. It is not necessary to call further attention to the 
 significance of this fact in casting inlays. 
 
 The damage done by the overheated metal is sometimes 
 confined to the wall lying opposite the sprue-gate. In such 
 cases, the metal though not greatly overheated, is sufficiently 
 hot to disintegrate the surface of the investment where it first 
 strikes the wall of the mold. The current of the molten metal 
 then erodes the surface at this point. It is preferable, there- 
 
134 
 
 fore, that the point opposite the sprue-gate should he upon 
 a smooth wall, and not near the margin of the inlay, or near 
 the angles of an anchorage extension. The sharp angle of the 
 occlusal step at the axial wall, is therefore an unnecessary 
 source of danger which should be avoided by sloping this part 
 of the cavity, as shown in Plate I. As the point of attachment 
 is determined by the contact point, the direction of the current 
 of metal may be varied, by altering the angle at which the 
 wax model is set upon the sprue. 
 
 Overheating the metal in casting, often makes the inlay 
 worthless. Especially is this true of inlays having complex 
 anchorage extensions; as for example, a proximal inlay with 
 transverse fissure anchorage in a lower molar (Plate I). At the 
 angles, where the longitudinal and transverse fissures cross 
 each other, the current of overheated metal distintegrates the 
 investment and carries away the loosened particles. Under 
 such circumstances, the finished inlay cannot possibly fit into 
 the cavity. 
 
 The only means of fitting an inlay, with a partially or 
 totally granular surface, is by careful grinding. A perfect 
 result is, however, rarely obtained. If the defect is confined 
 to a small area, the following method may be tried. The 
 inlay is placed in the cavity and rocked back and forth under 
 pressure. Upon examining the under surface of the inlay, 
 burnished spots will be found which mark the places where 
 the inlay rests upon the tooth. The amount of metal to be 
 removed must be determined beforehand, as a second attempt 
 to locate the point of difficulty by rocking the inlay will 
 usually be unsuccessful, the burnished spots not being recogniz- 
 able upon the ground surface of the metal. If further efforts 
 to fit the inlay are to be made, the walls of the cavity should 
 be coated with coloring matter. The inlay can then be re- 
 peatedly tried in the cavity, and the places marked, ground off. 
 This procedure cannot, however, be recommended by the writer, 
 as the result always is an imperfect piece of work. In the 
 time spent in attempting to fit a faulty inlay, another wax 
 model can be made. And the finished inlay will then be far 
 more satisfactory. 
 
135 
 
 Rounded margins (Fig. 108) are the result of an insuffi- 
 cient heating of the metal in casting. Whether the faulty 
 inlay can be used or not, depends upon the degree of the 
 defect and upon the position of the cavity to be filled. An 
 inlay with slightly rounded margins, in a simple, easily access- 
 ible cavity, can by burnishing, be perfectly adapted to the 
 margins. On the other hand, a proximal inlay with edges 
 equally rounded is worthless, as the cervical margin of the 
 cavity is not sufficiently accessible. A proximal inlay must 
 therefore always be perfect in this respect. 
 
 For the purpose of adapting the rounded edges of the 
 inlay to the margins of the cavity, the corrugated burnisher. 
 
 i 
 
 Fig. 108. 
 
 Fig. 109. 
 
 Fig. 110. 
 
 also called tomato-burnisher, is the most suitable instrument. 
 The burnisher, rotating in the direction of the margin {a. Fig. 109) 
 throws up a ridge at this point. The purer the gold, the more 
 easily can this be accomplished. If the extreme edge of the 
 enamel is at right-angles to the surface of the tooth, there 
 still remains a space at h (Fig. 109) after the burnishing has 
 been completed. Further burnishing will not obliterate this 
 space, but will only force the metal over the edge of the 
 enamel (Fig. 110). If the margin of the enamel is bevelled 
 (Fig, 111), the gold can be more easily adapted (Fig. 112). 
 Adapting the slightly rounded edges of a faulty inlay by 
 burnishing, is therefore permissable only in simple cavities 
 with bevelled enamel margins. Upon an occlusal surface, where 
 the walls of the cavity have been prepared at right- angles to 
 the surface, such a procedure cannot be recommended, as at 
 this point a perfect adaptation, extending well towards the 
 
136 
 
 floor of the cavity is absolutely essential. An inlay with 
 rounded margins should, never be set in an occlusal cavity 
 unless deep fissures have been carved into this surface. 
 
 Blow-holes can be repaired only by filling the defect with 
 gold foil. If the hole has resulted from the presence of foreign 
 matter, the inlay should be boiled in acid. The form of the 
 defect is usually such, that it offers ample retention for the 
 filling. Should this not be the case, undercuts must be made 
 in the inlay. 
 
 When the inlay fits into the cavity, the bite should be 
 controlled. If the inlay is too high, this may be corrected 
 
 Fig. HI. 
 
 Fig. 112. 
 
 by allowing the patient to bite upon tracing-paper, and grind- 
 ing away the places marked until the articulation is correct. 
 The edges of the inlay are then burnished against the margins 
 of the cavity, upon the occlusal surface with a corrugated 
 burnisher, and on the proximal surface with a flat hand- 
 burnisher. 
 
 In removing the inlay from the cavity, care must be taken 
 to avoid injuring the edges. Occluso-proximal inlays should 
 be removed by placing the point of an instrument below 
 the contact point and pressing in the direction of the occlusal 
 surface. In simple cavities it is often difficult to remove the 
 inlay without injuring the edge. This danger may be avoided 
 by leaving the stump of the sprue attached to the inlay until 
 after it has been burnished. As the sprue-stump interferes 
 at certain points, special attention should be paid to these 
 in reburnishing the inlay after it has been introduced into 
 the cavity, and before the cement has set. 
 
137 
 
 Undercutting and Roughening the Inlay. 
 
 The inlay, at this stage, is ready to be undercut or 
 roughened. Simple inlays, firmly held with flatnosed pliers 
 by the sprue -stump, may be easily undercut with a fine 
 hand -saw. If the sprue -stump has previously been cut off. 
 
 ■ 
 
 ■■ 
 
 ^^^^^^^B 
 
 ■j 
 
 H 
 
 B 
 
 Ml 
 
 o fl 
 
 B • 
 
 
 K 
 
 1^^ 
 
 B^ 
 
 
 ^^H 
 
 1 
 
 li; 
 
 f^ri 
 
 1 
 
 
 m '-^ 
 
 
 
 1 
 
 p 1 
 
 Fig. 113. 
 
 or if the inlay is of complex from, it must be held in the 
 fingers, and the undercuts made with a small knife-edged 
 stone, or a crown saw in the dental engine. The rotary saw, 
 though useful, cannot be recommended, it being liable to jump 
 over the edge of the inlay and injure the fingers. As cutting 
 the metal always leaves feather-edges, these must be ground 
 
138 
 
 3 
 
 Fio. 114. 
 
 off from the margins of the un- 
 dercuts, and the inlay again tried 
 in the cavity. If the size of the 
 inlay permits, it is always pre- 
 ferable to make the necessary un- 
 dercuts in the wax model. 
 
 The best instrument for rough- 
 ening inlays is, in the opinion of 
 the writer, the mechanical engrav- 
 ing apparatus shown in Fig. 113. 
 It is known in the German jewel- 
 lers' trade, as the dot-engraving ap- 
 paratus Matador ( Gravier-Punk- 
 tierapparat Matador). It consists 
 of a clockwork which drives a 
 hinged weight {a), and a counter- 
 weight (6). Only the former strikes 
 '^^Sillll the end of the engraving instru- 
 
 ment. As the weight is usually 
 not heavy enough, a small piece 
 of lead must be screwed onto the 
 upper surface. Owing to the fact 
 that the weight is hinged, the blow 
 given by this instrument is per- 
 fectly "dead". The Bonwill mal- 
 let*), depending for its action upon 
 an immovable cam, carried on a 
 wheel and stricking the end of the 
 instrument at each revolution, 
 gives a short, sharp blow. As the 
 gold, in this case, has not sufficient 
 time to escape, the surface is but 
 slightly roughened. With the 
 Bonwill mallet the point of the 
 instrument, should be small and 
 very sharp, while with the en- 
 
 *) G. S. Hersey, Dental Cosmos Nov. 
 1906, p. 1167. 
 
189 
 
 graving apparatus the point should be ground in the form 
 of a half-round chisel. 
 
 At points where nothing has been removed from either 
 wax model, inlay, or cavity wall, the inlay is roughened by 
 blows at right-angles to the surface (Fig. 13). But where the 
 space between inlay and cavity wall permits, the step-like 
 projections (Fig. 14), made be applying the roughening instru- 
 ment obliquely, are to be preferred. 
 
 In the tooth, the undercuts should be placed and shaped 
 as has been described under "Retention" (Chaps. Ill and IV). 
 The removal of the last traces of caries, or of the material 
 filling the natural undercuts, often makes further undercutting 
 unnecessary. 
 
 The Cement. 
 
 Before discussing the subject of setting the inlay, the 
 requisite qualities of a cement for this purpose will be men- 
 tioned. The material used as an inlay cement should, 
 
 1. be so fine grained, that it forms a very thin film under 
 pressure, 
 
 2. possess great compression strength, 
 
 3. neither expand nor contract during the process of setting, 
 
 4. be impenetrable to moisture, 
 
 5. possess hydraulic qualities, 
 
 6. set sufficiently rapidly, 
 
 7. be as insoluble as possible, and 
 
 8. possess adhesive qualities. 
 
 Of these qualities the first four are essential, while the 
 last four add to the value of the cement. 
 
 1. Experiments to determine the relative value of cements, 
 in regard to all the above mentioned qualities, have not yet 
 been made. Joseph Head (Philadelphia) published an article*) 
 upon thickness of the cement line, and as the result of his 
 experiments, tabulated below, comes to the following con- 
 clusions. The thickness of the cement layer depends upon 
 the size of the cement grains. Great, or prolonged pressure 
 changes the result but little. 
 
 ^) Tests on the Inlay Cement Problem. Dental Cosmos, July 1905. 
 
140 
 
 
 8 poundsl), 
 1 Min. 
 
 8 pounds 
 until 
 set. 
 
 25 pounds, 
 1 Min. 
 
 25 pounds 
 until 
 set. 
 
 50 pounds, 
 1 Min. 
 
 50 pounds 
 until . 
 set. 
 
 lOOpounds, 
 1 Min. 
 
 100 pounds 
 until 
 set. 
 
 Harvard (coarse) 
 
 .002433) 
 
 .00249 
 
 
 
 
 
 
 
 ,, Inlay 
 
 
 
 
 
 
 
 
 
 (Jenkins) 
 
 .00168 
 
 .00171 
 
 
 
 
 
 
 
 ,, Special 
 
 
 
 
 
 
 
 
 
 (Head) 
 
 .00156 
 
 .00152 
 
 .00143 
 
 .00125 
 
 .00106 
 
 001175 
 
 .00114 
 
 .00089 
 
 Ames Inlav . . . 
 
 .00109 
 
 .00096 
 
 .000886 
 
 .000882 
 
 .000725 
 
 .000702 
 
 .00079 
 
 .000604 
 
 Ash 
 
 .00229 
 
 
 
 
 
 
 
 
 Harvard Pulv. 2) 
 
 .00033) 
 
 .00027 
 
 
 
 
 
 
 
 1) Pressure on ^/4 square inch. 
 
 2) Harvard Pulv. is a Harvard cement "pulverized in an agate mortar 
 until the grit was imperceptible to the teeth". 
 
 3) Thickness of film, in fractions of an inch. (The tMckness of No. 30 
 gold foil is about .0003 in.) 
 
 2. Experiments to determine the compression strength of 
 the various oxyphosphate cements, have not been made. 
 
 3. und 4. The second table, compiled from the article of 
 G. C. Poundstone*) (Chicago), shows the structure, the expan- 
 sion, and the permeability of a number of cements. The names 
 of the preparations are, however, not mentioned. 
 
 5. A hydraulic cement is one which sets under water. 
 It has been claimed, that oxyphosphate cements are not 
 hydraulic, that they are only apparently so, owing to the 
 rapidity with which they set. Only by practical tests can this 
 question be decided. 
 
 6. The rapidity with which a cement should set, depends 
 upon personal preference and upon the difficulty of introducing 
 the inlay into the cavity. With every cement, the time of 
 setting can be regulated by varying the relative amounts of 
 the liquid and the powder, or by using powders containing 
 more or less coloring matter. Some manufacturers recommend 
 the use of a retarding "flux". 
 
 7. All cements are more or less soluble in the mouth. The 
 solubility of any of the standard preparations is, however, not so 
 great as to endanger the durability of a perfectly adapted inlay. 
 
 8. In the retention of an inlay, other factors are far more 
 important than mere adhesiveness of the cement. While 
 
 *) The Cement Problem in Inlay Work. Cosmos, July 1905. 
 
141 
 
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142 
 
 cement is still very soft, it undoubtedly is "sticky", but after 
 it has set, it does not possess any adhesive qualities. The fact 
 that old cement can often be removed only with difficulty 
 from the walls of the cavity, does not prove the adhesiveness 
 of cement, but proves that the cement was of such a character, 
 that it could adapt itself to the most minute inequalities upon 
 the surface of the dentine. The tests made to determine the 
 adhesiveness of cements are of little practical value, as they 
 do not reproduce the conditions existing in the cavity of the 
 tooth, while in the mouth. Poundstone tested the cements 
 A to J, by cementing together ivory blocks whose surfaces, 
 60 square millimeters in area, were roughened with a vul- 
 canite file. "They were kept dry for 24 hours, when they 
 were pulled apart." The average force required varied from 
 231/2 — 59 V4 pounds. From a practical stand point the follow- 
 ing tests are of interest. "Repeated tests were made by 
 cementing the blocks together and keeping them in saliva 
 in the incubator at 37 ° C, but in every instance the force 
 necessary to separate them was so slight that it was impossible 
 to measure it with any degree of accuracy. These were flat 
 surfaces, with force applied perpendicular to the surface. When 
 force was applied parallel with the surface, i. e. when an attempt 
 was made to slide the blocks apart, considerable resistance 
 was met with, the film of cement apparently interlocking into 
 the uneven surfaces of the blocks on either side." 
 
 The constant improvements made by the manufacturers, 
 make it impossible to state which cement most completely 
 fulfills the requirements mentioned above. Each operator 
 must be guided by his own experience, in selecting an inlay 
 cement. Only standard preparations should be considered. 
 
 Drying the Cavity. 
 
 The use of the rubber dam is not necessary in setting an 
 inlay. The process occupies but so short a time, that the field 
 of operation can usually be kept dry very easily. In two to 
 three minutes after the first drying of the cavity, the inlay 
 may safely be exposed to the saliva, if a hydraulic cement, 
 mixed by an assistant, has been used. 
 
143 
 
 To keep the tooth dry, the usual appUances are employed. 
 As these are well known they need not be described in detail. 
 Cotton rolls, or napkins in connection with ordinary or specially 
 constructed clamps, tongue-holders, or mouth - specula are 
 most commonly used. The saliva-pump, also is of great value. 
 
 The tooth is cleansed with a stream of water, and the 
 cotton rolls put in position. The cavity is then dried and 
 disinfected. For this purpose a variety of medicaments are 
 used. The method of the writer is the following. A pledget 
 of cotton saturated with a solution of equal parts of sodium 
 hypchloride (NaClO) and potassium hypobromide (KBrO) is 
 placed in the cavity. If the dentine is sensitive, the wet cotton 
 is warmed over the flame of an alcohol lamp. With a broach, 
 around which a few fibers of cotton have been wrapped, 
 dilute sulphuric acid is added until the reaction ceases. The 
 reaction which take place, consists in a liberation of chlorine, 
 bromine and oxygen. As these are present in their nascent 
 state, they have a powerful germicidal action, thus thoroughly 
 disinfecting the tooth. The cavity is then again flooded with 
 the above-mentioned alkaline solution, to neutralize every trace 
 of the acid, and is dried, without being again rinsed out with 
 water. Even the most sensitive dentine can be disinfected, 
 if the solutions are used in the order mentioned, and care- 
 fully warmed. Experience has shown, that as a result of this 
 procedure the cement forms a strong attachment, probably 
 owing to the the action of the acid in roughening the surface 
 of the dentine. 
 
 Regarding the much debated question of thoroughly drying 
 the cavity, the writer, from practical experience, believes a 
 dry surface to be not alone desirable but absolutely necessary 
 for a perfect union between cement and dentine. W. V. B. Ames"^), 
 however, states: "I believe that it is thoroughly impractical 
 and unscientific to expect to be able to flow a proper mix 
 of cement to this desiccated surface and have it give the 
 maximum of adhesion, because this cement will simply bridge 
 across the microscopical irregularities of this surface, and the 
 tubuli — if you please — without knitting into them, as the 
 
 *) Dental Summarv Vol. XXV, Xo. 1 p. 71. 
 
144 
 
 cement must to give maximum, adhesion. Granting that 
 thorough cleansing and superficial desiccation is desirable, 
 I will claim that we should then thoroughly moisten this 
 surface with the liquid of the cement we are about to use, 
 or possibly better, some plain syrupy phosphoric acid, and 
 after being satisfied that this has caused the displacement of 
 air in all inequalities of the surface, all visible surplus of this 
 should be removed by air blast or absorbents." Only by 
 making a series of comparative tests, can this question be 
 decided. The writer, however, believes, that the thinly mixed 
 cement, under the pressure of forcing the inlay into place, 
 can more readily fill out all minute depressions if these are 
 empty, than if they have previously been filled with another 
 fluid. 
 
 With absolute alcohol and hot air the cavity is dried. If the 
 dentine is sensitive, the pledget of cotton saturated with 
 alcohol is ignited and allowed to burn 5 — 10 seconds. After 
 being extinguished, it is immediately placed in the cavity, 
 and the alcohol partially evaporated with the hot air syringe. 
 Thereupon the cotton is removed, and the drying of the den- 
 tine continued until its surface becomes white. After about 
 a minute the whiteness disappears, proving that the dentine 
 had been dried out but superficially, and that it rapidly regains 
 its normal moisture. This is of advantage to the hydraulic 
 cement in setting. 
 
 Setting the Inlay. 
 
 General directions for mixing the inlay cement cannot 
 be given, as each preparation requires special handling, 
 and this can only be determined by practical tests. With 
 the cement mixed to the proper consistency the walls of 
 the cavity are carefully covered. The dentine should be cov- 
 ered at every point, to avoid the danger of imprisoning 
 air under the inlay. The air forms a cushion, which drives 
 the inlay out of the cavity before the cement has set, or 
 it may escape partially and leave a space between the in- 
 lay and the wall near, or at the margin of the cavity. The 
 thin cement, to cover the walls of the cavity, is taken up on 
 
145 
 
 the point of a spatula and dripped into the cavity if the tooth 
 is in the lower jaw. If it is in the upper, the spatula is held 
 before the opening of the cavity and the cement pushed in 
 with a large ball-burnisher. With a smaller instrument it is 
 then quickly spread over the surface of the dentine, and an 
 additional quantity of cement introduced into the cavity. 
 With a pair of tweezers, preferably those suggested by A. Gutt- 
 mann (Berlin) for porcelain inlays (Fig. 115) as they prevent 
 the inlay from escaping from between the points, the inlay 
 is placed in the cavity. By alternately pressing with two 
 
 Fig. 115. 
 
 burnishers, the inlay is forced into place with a rocking motion 
 (Taggart). This seats the inlay more quickly and dislodges 
 the larger granules of cement more easily than steady pressure 
 in one direction. 
 
 After the inlay is in position the margins are rapidly bur- 
 nished and steady pressure is exerted for about one minute. 
 With an explorer the margins are then examined. If at any 
 place the inlay protrudes slightly, though this should not 
 happen in a perfect piece of work, the cement, still somewhat 
 soft, is removed at that point with a fine instrument, so that 
 later the metal can be burnished against the margin of the 
 cavity. As moisture can now no longer affect the hydraulic 
 cement, the cotton rolls may be removed. The patient should 
 be cautioned not to occlude tightly, as the cement only sets 
 in 8 — 10 minutes. The surplus cement should remain in place 
 until it has hardened. 
 
 Finishing and Polishing the Inlay. 
 
 When the cement has set, the excess is chipped off with 
 a sharp instrument. This, by the way, would not be possible 
 
 Bo decker, Metallic Inlay. 10 
 
146 
 
 if the cement were truly adhesive. With tracing-paper the 
 bite is controlled. If it proves to be too high, — a serious 
 matter if the inlay was of the proper height when previously 
 tried in the cavity, — the place marked must be ground off 
 with a small stone (Fig. 116), or with a plug finishing bur. 
 Care should always be taken, when grinding near the edge of 
 the inlay, to let the instrument rotate so, that the gold is 
 forced against the margin of the cavity. For this reason, it 
 is necessary to have left-as well as right-cut finishing burs 
 on hand. The pear-shaped form is the most serviceable (Fig. 117). 
 These instruments being small, confine there action to a limited 
 
 Fiff. 116. 
 
 lig. 117. 
 
 Fig. 118. 
 
 Fig. 1L9. 
 
 area. They cut more rapidly than the gem-points, as long as 
 they are sharp. The double cone-shaped bur (Fig. 118) is used 
 to restore the form of the fissures that has been destroyed 
 in grinding the inlay. The margins of the occlusal surface 
 are flushed with fine stones. 
 
 After the bite has been corrected, the margins of the 
 proximal cavity should be examined. If the unpleasant dis- 
 covery is made, that the inlay protrudes from the cavity, 
 the edges must be ground down, preferably with spear-shaped 
 finishing burs (Fig. 119). At accessible places a somewhat 
 thicker form may be used, as this does not become dull so 
 rapidly. As the metal should always be cut in the direction 
 of the cervical margin, right- and left-cut finishing burs are 
 required. In most cases it will be necessary to use them in 
 the right- angle handpiece. Where there is no danger of in- 
 juring the contact point, sandpaper disks may be employed. 
 Great care should be exercised in finishing the proximal 
 margins, as there is always danger of dislodging the newly 
 
147 
 
 set inlay by pressure upon this surface. It is better therefore, 
 to postpone any extensive operation of this kind until a sub- 
 sequent sitting. 
 
 The writer is not able to appreciate the beauty of a high 
 polish, prefering a smooth but dull surface, which makes a 
 metallic filling less conspicuous. The inlay is quickly polished 
 by using rubber or moose-hide disks, and cloth strips with 
 a mixture of carborundum flour and vaseline. The action is 
 rapid and the effect very satisfactory. 
 
 10* 
 
Chapter XII. 
 The Metallic Inlay as a Bridge Abutment. 
 
 Owing to its massiveness and apparent strength, the metaUic 
 inlay has appealed to many as a means of anchoring bridges. 
 Various forms of inlay bridge abutments have been suggested, 
 but the majority of these fail when put to a practical test. 
 Many men, therefore condemn the use of the inlay abutment. 
 Nevertheless it remains a fact, that inlays have been used 
 successfully for this purpose, and that if properly constructed 
 in accordance with certain definite mechanical principles, they 
 may certainly be used with safety in some cases. 
 
 It is not the intention of the writer to suggest still another 
 form of inlay abutment, but only to describe the mechanical 
 principles that must be taken into account in the construction 
 of an inlay of this kind. 
 
 In explaining the stress and strain upon an inlay used as 
 a filling, only the force of mastication was considered, while 
 movement of the individual tooth was disregarded. This move- 
 ment, however, becomes of prime importance in determining 
 the form of the inlay abutment. To the mechanical factors 
 to be considered in constructing an ordinary inlay, must be 
 added that of movement of the tooth in three directions; 
 bucco-lingually, mesio-distally, and vertically. The effects of 
 these movements on inlay abutments situated in bicuspids 
 and molars will be described in detail. For the sake of clearness, 
 a bridge with but one inlay abutment has been chosen as an 
 example. The inlay is placed in the second molar, while the 
 other abutment consists of a shell-crown placed upon the 
 second bicuspid. A square bar connecting the two, represents 
 the bridge. 
 
 Bucco-lingual Movement of the Anchor Teeth. 
 
 Movement in the bucco-lingual direction will not endanger 
 the anchorage as long as both abutment teeth move an equal 
 
149 
 
 distance in the same direction. If, however, these teeth move 
 unequally, or in opposite directions, both abutments will be 
 strained to the same extent. If the molar is firm and the 
 bicuspid is loose, the greater strain will be exerted upon the 
 inlay in the firm tooth. 
 
 A loose tooth in moving, describes the arc of a circle whose 
 center lies at the apex of the root. The crown, therefore, 
 changes its angle and is displaced vertically and horizontally 
 (0, a, h, Fig. 120). 
 
 Whenever the loose tooth changes its angle bucco-lingually 
 in relation to the firm tooth, a torsional strain is exerted upon 
 
 Fis. 120. 
 
 Fig. 121. 
 
 Fig. 122. 
 
 the connecting bar. The torsional force exerted upon the 
 inlay is proportional to the angle of torsion (the movement 
 of the loose tooth). It is, however, independent of the length 
 of the bar. The effect of this force is to twist the inlay out 
 of the shallow cavity upon the occlusal surface of the tooth 
 (Fig. 121). The point a acts as a fulcrum. To counteract this 
 force, a proximal cavity should be excavated with walls parallel 
 to the long axis of the tooth {a and h, Fig. 122). This locks the 
 inlay so that it cannot be dislocated by torsional strain. 
 
 The vertical displacement is slight {a, Fig. 120), as the 
 tooth moves through but a small arc of a circle. The effect 
 of this movement upon the inlay abutment, will be more fully 
 described later. 
 
 The horizontal or lateral displacement [h, Fig. 120) of the 
 loose tooth exerts a strain upon the inlay abutment pro- 
 
150 
 
 portional to the length of the connecting bar, and to the 
 force apphed to the loose tooth. The lingual or buccal edge 
 of the inlay acts as the fulcrum {a, Fig. 123). If the inlay is 
 firmly anchored, there is a tendency to rotate the firm tooth. 
 The mechanical action represents a lever of the first class, 
 applied at right-angles to the long axis of the tooth. 
 
 Eiff. 123. 
 
 Fie. 124. 
 
 The mechanical principles upon which the anchorage of 
 inlay abutments depend can most clearly and easily be ex- 
 plained by representing the tooth as a nut, and the inlay 
 and connecting bar as the head and handle of a wrench. 
 
 If the wrench shown in Fig. 126 has sufficiently wide jaws, 
 it v/ill grasp a nut firmly when placed at right-angles to the 
 
 Fig. 125. 
 
 nut, as in Fig. 125. Applied to the abutment in question, 
 this means, that if the inlay were extended across the occlusal 
 surface and then at right-angles upon the distal surface of 
 the tooth, the leverage exerted by the bucco-lingual movement 
 of the loose tooth could not endanger the anchorage of the 
 abutment (Fig. 124). 
 
 The best shape of inlay abutment for resisting the torsional 
 strain and the force of the leverage produced by the lateral 
 
151 
 
 movement of the loose tooth is one, which in the form of 
 the wrench Fig. 126, extends over the mesial, occlusal, and 
 distal surfaces of the tooth. On one of the proximal surfaces 
 the margins a and h, Fig. 122, should be parallel. Special care 
 
 Fig. 126. Fio;. 127. 
 
 must be taken to make the surfaces a and h. Fig. 136, represent- 
 ing the jaws of the wrench, parallel to one another. 
 
 Without going into detail, the action of a few types of 
 
 Fig. 128. Fig. 129. 
 
 bridge abutments in resisting lateral displacement of the other 
 end of the bridge, may be mentioned. No special comment on 
 the action of the square post, is necessary in this connection. 
 
 Fig. 130. 
 
 The wrench Fig. 126 applied parallel to the nut, illustrates 
 the principle upon which the Carmichael abutment depends 
 in resisting lateral displacement of the other end of the bridge 
 (Fig. 127). The wrench Fig. 128 shows the principle involved 
 in the use of shell-crowns and banded pivot-teeth (Fig. 129). 
 Even the alligator wrench (Fig. 130) may represent the proto- 
 
152 
 
 type of a serviceable inlay abutment, if the latter is con- 
 structed with a strong post (Fig. 131), and provided with a 
 hook-anchorage (p. 30). 
 
 Mesio-distal Movement of the Anchor Teeth. 
 
 In this direction also, a tooth moves in an arc of a circle 
 whose center is situated at the apex of the root. The slight 
 variation occuring in the molars may be disregarded. The 
 diagram Fig. 132 shows two pointed blocks representing a 
 
 Fig. 132. Fig. 133. 
 
 bicuspid and a molar across which a bar has been laid. In 
 moving, the blocks describe circles about their pointed ends. 
 If the bar is moved distally, both teeth, tipping in this direction, 
 support the bar only on their mesial edges (Fig. 133). When 
 moved in the contrary direction, the bar bears only upon the 
 distal edges of the teeth (Fig. 134). If instead of a bar, a double- 
 
 Fig. 134. Fig. 135. 
 
 ended wrench with long jaws, is placed upon the blocks, no 
 tipping movement can take place, as the blocks are firmly held 
 at right-angles to the long axis of the wrench, or, as the blocks 
 are at right-angles to the wrench, they are held by bearing 
 surfaces parallel to their long axes (Fig. 135). 
 
 Applied to the inlay abutment, these facts prove, that 
 movement of the anchor teeth in a mesio-distal direction may 
 be prevented by constructing at least two broad bearing sur- 
 
153 
 
 faces at right angles to the direction of movement. These, 
 if the tooth stands in its normal position, will be parallel to 
 the long axis of the tooth, that is, parallel to the direction 
 in which the ordinary complicated inlay may be removed from 
 the cavity. As this subject has been fully discussed in Chap. IV, 
 it need not be repeated here. A very satisfactory way of in- 
 creasing the area of the bearing surfaces, is to flatten the 
 
 Fig. 136. 
 
 proximal surfaces of the tooth with a diamond disk (Plate V). 
 Though these two surfaces {a and b, Fig. 136) ought to be 
 parallel, it is not possible to make them so absolutely. They 
 must converge slightly in order to prevent distortion of the 
 impression during removal. A vertical section through a Car- 
 
 Fig. 138. 
 
 Fio;. 139. 
 
 michael inlay (Fig. 137) shows the application of the wrench 
 principle for the prevention of mesio-distal movement. 
 
 When only one anchor tooth is loose, the conditions are 
 somewhat different. If oblique pressure is exerted upon the 
 loose bicuspid, the tendency is to raise the inlay almost verti- 
 cally out of the cavity of the m.olar (Fig. 138). The strain 
 upon the inlay is proportional to the force exerted upon the 
 bicuspid and to the amplitude of its movement. To prevent 
 a dislocation of the distal end of the bridge, a very broad 
 bearing surface on the mesial surface of the molar is necessary 
 (Fig. 139). Such a surface offers more resistance than a post; 
 
154 
 
 though the latter may also be used to give additional strength. 
 If the bicuspid is firm and the molar loose, the bearing surface 
 should be situated on the distal surface of the bicuspid. In 
 other words, whenever one end of a bridge is in danger of 
 being raised by the movement of the other anchor tooth, 
 a broad bearing surface should be constructed apon that 
 proximal surface of the firm tooth which faces toward the 
 
 Fig. 140. 
 
 loose tooth. As a surface of this kind was. recommended to 
 counteract the effects of torsion (Figs. 121 and 122), it becomes 
 evident that the broad proximal bearing surface fulfills a 
 double purpose. Special attention should be paid to the effects 
 of the movement of the anchor tooth just described, in con- 
 structing the posterior abutment of a bridge involving the 
 
 Fig. 141. Fig. 142. 
 
 anterior teeth. Owing to the curve of the dental arch, a linguo- 
 labial movement of an incisor will produce a vertical move- 
 ment of an abutment situated in the cuspid or in a bicuspid 
 (see p. 161). 
 
 The effect of an inclined position of one or both anchor 
 teeth on the inlay abutment must also be taken into con- 
 sideration. This condition is most commomy met with in 
 lower second and third molars (Fig. 140). If vertical pressure 
 is exerted upon a bridge supported by a tooth of this kind 
 (Fig. 141), the latter is tipped still m^re. The bar rests on 
 the distal margin of the tooth, while the mesial margin 
 
155 
 
 draws away from the bar. The remedy in this case also, is 
 a broad bearing surface (Fig. 142) against which the incUned 
 tooth can find support. Such a surface is always preferable 
 to a post. The latter may, however, also be used, and in effect, 
 replace the second jaw of the wrench. Not only in this abut- 
 ment, but also in others, may one of the jaws of the wrench 
 be represented by a post (Fig. 131) or an extension into the 
 pulp-chamber. But whenever possible, two flat surfaces of 
 sufficient area should be used. In pulpless teeth with crowns 
 weakened by decay, this is not always practicable, posts must 
 therefore often be relied upon. 
 
 Vertical Movement of the Anchor Teeth. 
 
 Though even the normal tooth has a slight movement in 
 this direction, it is only in the advanced stages of alveolar ab- 
 sorption that the movement becomes very noticeable. If both 
 abutment teeth move the same distance, the anchorage of 
 the bridge is not endangered. When but one tooth is loose, 
 the strain upon the firm tooth becomes enormous. If the 
 abutment is strong enough to transmit the strain, the firm 
 
 Fio-. 143. 
 
 Fie. 144. 
 
 tooth will sooner or later loosen to such an extent that failure 
 of the whole bridge becomes inevitable. 
 
 The diagram (Fig. 143) shows, that when pressure is exerted 
 upon the bar over the loose tooth, spaces are form.ed between 
 the distal margins of both teeth and the bar. As, however, 
 a loose tooth is easily tipped, it will remain at right-angles 
 to the bar, and the effect of the action will be that of a powerful 
 lever of the first class, the mesial margin of the firm tooth 
 acting as the fulcrum (Fig. 144). Applying the wrench prin- 
 ciple to counteract this force, large bearing surfaces, mesially 
 
156 
 
 and distally, as well as a strong post, should be used ^Fig. 145). 
 If the crown of the firm tooth is extensively decayed, an inlay 
 abutment is contraindicated. A strong shell-crown should be 
 used in its place. 
 
 Fig. 145. 
 
 Whenever an anchor tooth is loose, the inlay abutment 
 must cover the whole occlusal surface. It has been shown 
 (Chap. IV and Fig. 53), that the anchorage of a self-retentive 
 inlay is weakest in the direction opposite to that in which 
 
 146. 
 
 the inlay was inserted into the cavity. If therefore, the inlay 
 is firmly held in position by the bridge, and the force of 
 mastication accidentally exerted only upon an exposed cusp 
 of the loose tooth, the latter will be pressed into its socket 
 
 Fig. 147. 
 
 and the inlay forced out of the cavity in the direction of its 
 least resistance. Such conditions, necessary for the vertical 
 dislocation of a properly constructed inlay abutment, are always 
 present when the bridge is supported by more than two anchor 
 teeth, unless, and this is rarely the case, all the teeth are of 
 exactly the same degree of firmness. Figs. 146 and 147 show 
 
157 
 
 how either the middle or an end abutment tooth may be 
 depressed. If the inlay is to be attached to the bar, it must 
 cover the whole occlusal surface, so that in mastication no 
 force can be exerted directly upon this surface of the loose 
 tooth. The cusps should be bevelled v/ith a diamond disk 
 as shown in Plate VI. 
 
 The Flexible Abutment. 
 
 As a rule, the writer, in cases as those just described, 
 prefers to use a loose or flexible abutment; that is, an inlay 
 of special form upon which the bar simply rests, the bridge 
 being otherwise supported by one or more rigid abutments. 
 
 Fig. 148. 
 
 If the bicuspid in Fig. 148 possesses vertical movement, 
 a cavity is excavated extending across the middle of the 
 occlusal surface and involving the proximal surfaces to below 
 the contact points. The finished abutments in the cuspid and 
 
 Fio-. 149. 
 
 in the molar are then connected with a square platinum- 
 iridium bar of sufficient strength, which extends through the 
 excavated occlusal cavity of the bicuspid (Fig. 149). With the 
 bar in position a wax impression is taken. The inlay is cast and 
 set into place. The bridge is then finished in the usual manner. 
 
158 
 
 by casting occlusal surfaces, with or without removable por- 
 celain facings, onto the bar. When the bridge has been set, 
 the bicuspid is free to move in a vertical direction. Mesio- 
 distal movement is prevented by the adjoining teeth of the 
 bridge (Fig. 150), while the flat surfaces of the bar prevent 
 bucco-lingual motion (Fig. 149). 
 
 Fig. 150. 
 
 When the conditions are similar to those shown in Fig. 147, 
 it is not advisable to let the bar rest merely on the occlusal 
 surface (Fig. 154). Especially is this true, when the tooth 
 adjoining that of the abutment is also loose. In this case, 
 the end of the bar must be bent, or a piece soldered on, at 
 right-angles, and be extended well toward the cervical margin. 
 
 Fie. 151. 
 
 The inlay is constructed as described above, and set before 
 the introduction of the bridge (Fig. 151). 
 
 The flexible abutment may also be used to advantage in 
 connection with firm teeth. Such bridges v/ith but one rigid 
 abutment, though not often met with in practice, are by no 
 means new.*) Owing to its many advantages, especially in 
 
 *) W. S. Davenport. Dental Bridge and Pier Construction. Trans. N. Y. 
 Institue of Stoma;tology, 1902. 
 
15!) 
 
 connection with inlay work, this type of bridge deserves full 
 recognition by the profession at large. 
 
 The most common form of flexible abutment is the lug 
 (Fig. 152). Its bearing surface is, however, too small, and there 
 
 3' 
 
 M 
 
 Fig. 152. 
 
 Fig. 153. 
 
 is the constant danger of the abutment tooth moving away 
 and leaving that end of the bridge entirely unsupported. 
 
 The abutment shown in Fig. 153, a variety of socket joint, 
 at one time used by the writer, is open to the same objection. 
 Beside this, strong distal movement (tipping) of the molar 
 invariably forced out the inlay in a vertical direction, after 
 a longer or shorter time. Only where the length of the bar 
 was equal to the width of one bicuspid, and both anchor 
 teeth were perfectly firm, has this form of abutment been 
 successful in practice. 
 
 If both, the tooth adjoining the abutment and the tooth 
 supporting the other end of the bridge, are firm, the flexible 
 
 Fig. 154. 
 
 abutment shown in Fig. 154 may safely be depended upon. 
 (Section same as Fig. 149.) The cavity is easier to prepare 
 than that of Fig. 151, as but one proximal surface is involved. 
 The construction of the inlay is also less difficult, especially 
 about the end of the bar, as this is here situated upon the 
 easily accessible occlusal surface. 
 
160 
 
 Though possessed by all flexible abutments more or less, 
 the advantages enumerated below refer particularly to the 
 forms shown in Figs. 150, 151 and 154. 
 
 The flexible abutment interferes but very slightly with the 
 physiological movement, while at the same time preventing 
 any abnormal motion of the anchor tooth. The lateral move- 
 ments of the tooth (Fig. 150) are in direct ratio to those of 
 the end abutment teeth. If these are firm, the loose tooth 
 cannot move beyond physiological limits. (Compare Fig. 148 
 and 149.) 
 
 When the flexible abutment is situated at the end of a 
 bridge with but two piers, lateral displacement is dependent 
 upon the firmness of the other anchor tooth and upon the 
 length of the bar. With a long bar a perfectly firm tooth, 
 owing to a slight rotary motion in its alveolus, will permit 
 the loose tooth to move laterally somewhat more than normal. 
 The same is true, however, of every bridge, even with rigid 
 abutments. 
 
 Mesio-distal movement can occur only within physiological 
 limits, and in a normal manner. The distance is determined 
 by the movement of the firm anchor teeth (Figs. 148 and 150), 
 or by the firm adjoining tooth (Fig. 154). The anchor tooth 
 carrying the flexible abutment, not being attached to the bar, 
 does not follow the movements of the bridge bodily, but moves 
 in the arc of a circle (Fig. 120). 
 
 Vertical movement is in no way interfered with. This is 
 one of the most important advantages of this type of bridge. 
 When there are but two abutments, each tooth moving in- 
 dependently, can assume a position in which all points of the 
 root bear equally against the walls of the alveolus when force 
 is exerted upon any point of the bridge. The peridental 
 membrane will remain healthy, and no inflammatory changes 
 in the bone, due to localized pressure, will take place. 
 
 Another advantage of the flexible abutment is, that in- 
 clined anchor teeth do not cause serious difficulties in the 
 construction of the bridge (Fig. 155). Each abutment being 
 made seperately, can readily be brought into place. If two 
 inlay abutments are used, each one while being set, can be 
 
Ifjl 
 
 adapted perfectly to the margins of the cavity; a feat difficult 
 to accomplish with rigid abutments in the form of inlays. 
 In determining the force exerted upon an inlay abutment, 
 another factor beside the movement of the teeth must be 
 considered, that is, the width of the masticating surface of 
 the bridge suspended between the abutments. If this surface 
 is too wide, pressure exerted at but one point near the edge 
 {a, Fig. 150) will set up a severe torsional strain in the bar, 
 which in turn transmits it to the inlay. Such surfaces should 
 therefore be niade slightly narrower than normal, especially 
 near the flexible abutment. Attention should also be paid, 
 that the bar or central line of occlusion divides this surface 
 equally, as pressure exerted on the entire masticating surface 
 
 Fig. 155. 
 
 of the bridge will then produce no torsional strain. With un- 
 equally divided surfaces, this is, however, not the case. 
 
 In discussing the effects of strain upon inlay abutments, 
 only those in the molars and bicuspids have been considered. 
 All that has been said, applies also to abutments in the anterior 
 teeth. Another factor, however, plays an important part. The 
 bicuspids and molars are situated in a straight line, while the 
 anterior teeth occupy a position on the arc of a circle. This 
 difference in alinement produces a difference in the distribu- 
 tion, magnitude, and direction of the strain exerted on the 
 abutments and on the bridge. To describe the difference of 
 effects in detail, would neccessitate the repetition of much that 
 has already been explained. By following the description of 
 the strain exerted upon the molars and bicuspids, anyone 
 who is sufficiently interested can for himself determine the 
 effects on the anterior teeth. The task becomes very simple 
 if a wire, the length of the bridge, is bent in conformity to 
 
 Bcidecker, Metallk; Inlay. 11 
 
162 
 
 that part of the dental arch in which the bridge is situated. 
 By moving one end or the middle of the wire, reproducing 
 the movements of the abutment teeth, the effects upon all 
 parts of the bridge can readily be determined. 
 
 To specify the exact conditions in which inlay abutments 
 are indicated, is not possible. A rigid inlay abutment may 
 safely be used when the space to be bridged does not exceed 
 the width of two bicuspids, and when the anchor tooth is 
 firm and possesses a strong crown. The use of the flexible 
 inlay abutment is not so limited, especially when there are 
 more than two anchor teeth. In some favorable cases of this 
 kind, one rigid and two flexible abutments may be used, as 
 in Fig. 148 when the bicuspid as well as the other anchor teeth 
 are firm. 
 
 It is not the intention of the writer to make a plea for the 
 extensive use of the inlay abutment. But there are cases where 
 it undoubtedly offers an ideal form of anchorage. When a 
 space between two healthy, reasonably firm teeth is to be 
 bridged, say a space due to the premature loss of the first 
 molar, an inlay bridge, constructed as follows, is to be pre- 
 ferred to any other form of bridge-work. In such cases the 
 writer would recommend a rigid inlay abutment in the second 
 molar, and a flexible abutment in the second bicuspid. The 
 pulps in both teeth being intact, they should in no way be 
 interfered with. Recurring to the principle of the wrench, 
 the construction of large bearing surfaces upon the mesial 
 and distal surfaces of the molar, parallel to the long axis of 
 the tooth, becomes necessary. The quickest and most pain- 
 less way of preparing these surfaces is to flatten the tooth 
 with a diamond disk (Fig. 136, or as shown in Plate V). One 
 or both proximal cavities should be deepened slightly (some- 
 what less than shown in Plate V) in order that the inlay may 
 resist torsional strain. The occlusal surface is cut out to a 
 sufficient depth with a knife -edged stone, so that the platinum- 
 iridium bar does not interfere with the bite, and lies well 
 within that part of the inlay which fills this cavity (Fig. 156). 
 
 The flexible abutment is constructed either as in Fig. 151 
 or in Fig. 154. If both the bicuspid and molar are firm, the 
 
163 
 
 latter method is used, if the bicuspid is somewhat loose the 
 former should be employed. The platinum-iridium bar, re- 
 presenting the frame-work of the bridge, should bear upon 
 each abutment so, that any force exerted upon it vertically, 
 is transmitted equally to the lingual and buccal halves of the 
 anchor teeth. The bar should be square and be about 2 mm. 
 (i/ie inch) in thickness. One end of the bar is bent so, that when 
 laid upon the occlusal surfaces of the abutment teeth, the 
 bent end extends into the distal cavity of the molar parallel 
 to the axial wall and almost to the cervical margin (Fig. 156). 
 Inlay wax is introduced into the cavity and roughly modelled. 
 The bar, previously roughened, is then warmed and forced 
 
 Fig. 156. 
 
 into place, the impression finished, and the inlay cast onto 
 the bar in the usual manner. In difficult cases an indirect 
 impression is taken or a stone model made, and the wax 
 model again tried in the mouth. In order that the alinement 
 of the other end of the bar may be correct while taking the 
 impression of the molar cavity, the writer excavates the 
 occlusal surface of the bicuspid only so deep, that the bar 
 rests in the position that it is to occupy later. After the rigid 
 abutment has been cast, the cavity of the bicuspid is com- 
 pletely excavated, an impression taken with the bar in place, 
 and the inlay cast. The margins of both inlays are there- 
 upon burnished, and the one in the bicuspid set into the 
 cavity. At this stage the bridge consists of two perfectly 
 fitting inlays, the one rigidly and the other loosely connected 
 with the bar. Upon the latter a tooth is modelled in wax, 
 and then cast. If desirable a removable porcelain facing can 
 be used. 
 
 11* 
 
164 
 
 In conclusion the writer wishes to emphasize, that the inlay- 
 abutment is not applicable to every case, but that whenever 
 it is used, it should be properly constructed with due regard 
 to the strain which will be put upon it. In determining the 
 proper form, it is always advisable to regard the inlay abut- 
 ment as a combination of two wrenches, the one acting parallel 
 to the long axis of the tooth to prevent tipping, the other 
 at right-angles to the first , to prevent rotation and lateral 
 movement. 
 
 It is a regrettable fact, that in the construction of dental 
 bridge-work but little thought is given to the distribution of 
 force within the structure. The dentist should follow the 
 example of the engineer, who calculates the stress and strain 
 of every part of a bridge before begining with its construction. 
 
Index. 
 
 AVjutment teeth 
 
 inclined 154. 
 
 movement 138, 152, 155. 
 Adaptation at margin 5, 10, 12, 135. 
 Adhesion of cement 17, 142. 
 Advantages of metallic inlays 13. 
 Amalgam model 92. 
 Ames W. V. B. 143. 
 Anchorage 
 
 by combining two cavities 32, 81, 
 88, 89. 
 
 dove-tail 31, 78, 80. 
 
 fissure 29, 46, 76. 
 
 groove 29, 44, 85. 
 
 hook 30, 82, 152. 
 
 pin 33. 
 
 reciprocal 32. 
 ApjDaratus for casting 
 
 Biber 122. 
 
 Elgin 126. 
 
 Jameson 123. 
 
 Solbrig 121. 
 
 Taggart 119. 
 Artificial stone 111. 
 ArvineF. B. 112. 
 
 B 
 
 Bearing surfaces 154, 154. 
 Bevelling 
 
 occlusal surface 27, 49, 77. 
 
 enamel margin 63, 66. 
 Bite 
 
 for models 92. 
 
 on inlay 136, 146. 
 
 on wax form 97, 98. 
 Black G. V. 53, 58, 65. 
 Blowholes 116, 136. 
 Bodecker C. F. W. 8. 
 Bonwill mallet 24, 138. 
 Box-shape 36, 55. 
 
 cavity, simple 37, 38. 
 
 cavity, complex 42, 56. 
 
 extreme 57. 
 
 inlay 42. 
 
 Bridge abutments 148. 
 
 bar 159, 162. 
 
 Carmichael 151, 153. 
 
 flexible 157. 
 
 indications 162. 
 
 lug 159. 
 
 socket 159. 
 
 wrench principle 150, 152, 164. 
 Bubbles 
 
 in investment 109. 
 
 on inlay 132. 
 Burs 68, 146. 
 
 C 
 
 Carborundum 
 
 floixr 147. 
 
 stones 68. 
 Caries 
 
 point of origin 53, 59. 
 
 progress 54. 
 Carmichael inlay abutment 151, 153. 
 Casting metals 112. 
 
 shrinkage 113, ll5. 
 Cavity preparation 74. 
 
 box-shaped 36, 38, 57. 
 
 saucer-shaped 35. 
 Cement 
 
 adhesion 17, 142. 
 
 anchoring the inlay 17. 
 
 compression strength 21, 41. 
 
 disintegration 7. 
 
 hollow inlays 52, 103. 
 
 hydraulic 140. 
 
 reaction of dentine 8. 
 
 solubility 140. 
 
 tables 140, 141. 
 
 tensile strength 24, 36, 52. 
 
 thickness of layer 40, 139, 140. 
 Coefficient of contraction 
 
 base metals 113. 
 
 noble metals 113. 
 Combination inlays 88, 127. 
 Compression strength 21, 41. 
 Contact point 
 form 61. 
 
166 
 
 on inlay 131. 
 
 on wax model 100. 
 
 in direct impression 99. 
 
 in indirect impression 92. 
 
 position 27, 61. 
 Contour 
 
 of tooth 59. 
 
 of filling 60. 
 
 of wax model 99. 
 Copper rings 90. 
 
 D 
 
 Davenport W. S. 158. 
 Defective inlays 132. 
 Dentin 
 
 drying 143. 
 
 reaction 8. 
 Diamond disk 60, 80, 81, 162. 
 Disadvantages of metallic inlays 6, 12. 
 Disinfection of cavity 143. 
 Direct impression 92. 
 
 instruments 95. 
 
 method 96. 
 
 wax for 93. 
 Dove-tail anchorage 31, 78, 80. 
 Drying the cavity 143. 
 
 E 
 
 Enamel margin 62. 
 
 bevelhng 63, 66. 
 Enamel prisms 62. 
 
 cleavage 62, 65. 
 
 course 64. 
 Engraving instrument 25, 137. 
 Extension for prevention 58. 
 
 F 
 
 Flexible inlay abutment 157. 
 
 Finishers 146. 
 
 Finishing 145. 
 
 Fissure caries 54. 
 
 Fissure anchorage 29, 46, 76. 
 
 advantages 45. 
 
 excavation for 54. 
 Frink C. H. 126. 
 
 a 
 
 Gas pressure 119. 
 Gold 24 kar. 12, 117. 
 22 kar. 12, 117. 
 coefficient of contraction 113. 
 Goldfillings 55, 58, 60. 
 Granular surface of inlay 133. 
 
 Grinding instruments 
 
 of aluminum 70. 
 
 of copper 70. 
 Groove anchorage 29, 44, 85. 
 Guttmann pincette 145. 
 
 II 
 
 Head J. 11, 139. 
 Herbst inlay 104. 
 Hersey G. S. 24. 
 Hinman inlay 106. 
 Hollow inlays 2, 52, 106. 
 Hollo"w wax models 102. 
 Hook anchorage 30, 82, 152. 
 
 Impression 
 
 direct 92. 
 
 indirect 90. 
 Impression material 90. 
 Indications for metallic inlays 14. 
 Indications for inlay abutments 162. 
 Inlay abutments 148. 
 Inlays 
 
 bite 136, 146. 
 
 blowholes 116, 136. 
 
 casting 107. 
 
 combination 127. 
 
 defective 132. 
 
 evolution 1. 
 
 finishing 145. 
 
 fitting 131. 
 
 gold 24 kar. 12, 117. 
 
 gold 22 kar. 12, 117. 
 
 granular surface 133. 
 
 Herbst 104. 
 
 Hinmann 106. 
 
 hollow 2, 52, 106. 
 
 polishing 147. 
 
 roughening 17, 24, 49, 51, 137. 
 
 rounded edges 135. 
 
 setting 144. 
 
 silver 118. 
 
 sponge gold 105. 
 
 swedged 105. 
 
 undercutting 18, 22, 39, 49, 51, 137. 
 Instrximents 
 
 for modelling wax model 95. 
 Interproximal space 61, 99. 
 Investing material 107. 
 
 artificial stone 111. 
 
 bubbles 109. 
 
 composition. 112. 
 
 expansion 110. 
 
 I 
 
167 
 
 Jameson machine 123. 
 
 Lane 114. 
 
 Leverage oni nlay abutment 150, 155. 
 
 M 
 
 Mastication, cleansing action of 58. 
 Metal for casting 112. 
 
 coefficient of contraction 113. 
 
 overheating 116, 132. 
 
 unclerheating 135. 
 Miller W. D. 11. 
 Model 
 
 amalgam 92. 
 
 bite for 92. 
 
 cement 91. 
 
 Melott's metal 92. 
 
 plaster 91. 
 
 Spence metal 92. 
 Mold 107, 110. 
 
 drying 110. 
 
 heating 111. 
 Movement of abutment teeth 
 
 biicco-lingual 148. 
 
 mesio-distal 152. 
 
 physiological 149. 
 
 vertical 155. 
 Mucin 11. 
 
 
 
 Oxygen apparatus 124. 
 
 Parallel walls 37, 40, 43, 46. 
 Parallel surfaces on inlay 42. 
 Pin anchorage 33. 
 Plaster model 91. 
 Polishing 147. 
 
 Porcelain 5, 7, 23, 28, 88, 127. 
 Poundstone G. C. 140. 
 Pressure in casting 3, 118. 
 
 centrifugal 123. 
 
 direct contact 122. 
 
 gas 119. 
 
 steam 121. 
 
 vacuum 126. 
 Pressure 
 
 contraction of metal under 113. 
 Pressure on inlay 28, 36, 46. 
 
 obhque 29, 46. 
 
 vertical 28, 36. 
 Price W. A. 109, 111, 113, 115, 
 120, 124. 
 
 Projections on inlay 132. 
 Protection for handpiece 72. 
 Pulp, danger of injxiring 55, 76. 
 
 R 
 
 Retention 16, 26, 35. 
 
 cement-retention 17. 
 
 self-retention 26. 
 Right-angle handpiece 71. 
 Roach's wax carver 102. 
 Roughening the inlay 17, 24, 49, 
 
 51, 137. 
 Rounded edges 135. 
 
 S 
 
 Sachs W. 112. 
 Saucer-shaped cavities 35. 
 Seam 10. 
 
 dissolution of cement 10, 11. 
 
 metallic inlays 6, 12. 
 
 porcelain inlays 5. 
 Secondary caries 9. 
 Self-retention 26. 
 Silver 118. 
 
 Solbrig O. 3, 122, 123. 
 Solbrig pliers 121. 
 Spence metal 92. 
 Sponge gold inlay 105. 
 Steplike cavity preparation 44, 55, 
 
 57, 84. 
 Stones 68. 
 
 mounting 68. 
 
 truing 69. 
 Suction wax carver 102. 
 Swedged inlays 105. 
 
 hollow 2, 106. 
 Swedging apparatus 106. 
 
 T 
 
 Tables 
 
 coefficient of contraction of 
 metals 113. 
 
 properties of cement 140, 141. 
 Taggart W. 4, 110, 119, 145. 
 Taggart machine 119. 
 Tweezers, Guttmarm. 145. 
 Torsion 149. 
 
 U 
 
 Uhlenhuth 109, 113. 
 Undercuts 
 
 in the inlay 18, 22, 39, 49, 51, 
 137. 
 
 in the wax model 99. 
 
 in the tooth 22, 49, 50, 51. 
 
168 
 
 Undercuts 
 form of 22, 
 mechanics of 21. 
 
 Vacunm casting machine 126. 
 Van Horn C. S. 114. 
 
 W 
 
 Ward M. L. 112, 114, 117. 
 
 Wax 
 
 cohesion 94. 
 
 color 95. 
 
 hardness 94. 
 
 instruments 95. 
 
 recovery 94. 
 
 scraping 94. 
 
 suction carver 102. 
 Wax model 
 ■ expanding the 114. 
 
 hollow 102. 
 
 modelling in the mouth 96. 
 
 mounting upon the sprue 100. 
 Wrench princij^le 150, 152, 164. 
 
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