350 B439o THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES On Herbst's Method of Gold-Filling by Rotating Burnishers. STOKER ,BENNETT, F.R.C.S. & L.D.a.Exu., L.R.C.P.LOXO. ~ Reprinted from Transactions of the Odontological Society of<> Britain, January, 18 s LONDON: HARRISON & SONS, ST MARTIN'S LANK. \V C. PEI^TEES IX ORDINARY TO HEE MAJESTY. 1885. On Herbst's Method of Gold-filling by Rotating Burnishers. BY STORER BENNETT/F.B.C.S. &L.D.S. BUG., L.B.C.P.LoND. MR. PRESIDENT AND GENTLEMEN, IN the April number of the Journal of the British Dental Association for last year appeared an article on a method of filling teeth with soft gold by means of burnishers rotating in the burring engine, introduced to the profession by Dr. Herbst of Bremen. But little notice was taken of the subject until towards the end of the summer, when Dr. Herbst's brother visited England, and gave a demonstration at the Dental Hospital of London. The occasion was inopportune, as most of us were already away, or just starting for the autumn vacation, so the subject again received but scant attention. Later in the year I made a series of experiments, which proved so far satisfactory that I considered it desirable the subject should be brought before this Society, that its merits might be discussed, and the various experiences of those who had tried it be obtained. Dr. Herbst claims for his method that by its use we can obtain a solid, hard gold-filling, with A 2 ON HERBSTS METHOD OF GOLD-FILLING more perfect adaptation of the gold to the walls of the cavity, with greater ease, and a far less expenditure of time than by any other method ; and as he has worked on this plan for six years it is to be presumed he feels satisfied as regards the test of time. During the process of filling it is necessary to have four walls to the cavity, and where these do not exist already they are temporarily supplied by means of a matrix. Large soft cylinders are employed, and packed into the cavity unannealed, becoming cohesive during the course of manipula- tion. And herein lies the greatest peculiarity of the process ; for by other methods we introduce into the cavity gold which is already cohesive, but here we introduce soft cylinders which when pressed together show no tendency whatever to cohere, yet, in the course of a few. revolutions of the burnisher, become coherent and welded into a solid mass, like a piece of cast metal. The instruments employed consist of various sized and shaped burnishers, worked by the burring engine, and of the following forms. They are numbered from 1 to 15. No. 1 is a large inverted cone ; 2, 3, and 4 are large pear- shaped points, all highly polished. No. 5 is ground to a blunt (" roof-form ") point, but this must not be polished, but simply finished on an Arkansas stone; as this instrument is much employed, two BY ROTATING BURNISHERS. or three sizes of it are desirable. The remaining instruments, from 6 to 14 inclusive, are polishers 1 1 r 12 8 9 10 11 12 13 14 15 used in finishing; fillings. No. 15 is a needle for O O a special purpose to be described hereafter. A cavity is prepared in the usual way, care being taken that its interior is larger than its entrance ; undercuts may be made if convenient, but are not essential, and no retaining points are re- quired ; the edges of the enamel, though smoothed and polished, should not be bevelled, but left quite square. In filling a cavity, take for instance the distal surface of a second upper bicuspid, with the masti- cating surface also involved. Such a cavity by the ordinary method would be filled cohesively from the beginning, and built up in order to re- produce the contour. By the addition of a matrix the distal wall is restored, and we have now to A 2 4 ON HERBST S METHOD OF GOLD-FILLING treat a simple crown cavity. This matrix (which is best formed of a piece of clock spring deeper than the cavity) is wedged between the bicuspid and first molar, if that is standing, and secured by two pins, jamming it as tightly as possible. It is essential that the matrix be perfectly firm and steady, or the filling will be unsound. The tooth being prepared, the rubber-dam applied, and the matrix in position, the cavity is loosely filled with the largest cylinders that can be conveniently introduced, and the largest burnisher selected that the mouth of the cavity will admit. By slow rotation of this instrument in the engine, and the exercise of moderately firm and steady pressure, the gold is squeezed towards the floor and sides of the cavity, acquiring as it is compressed a brightly polished non-cohesive surface. If it is found that the gold rolls beneath the burnisher, it is because too few cylinders have been introduced, and more must be added, or because too small a burnisher is being employed. If sufficient gold is placed in the cavity, and a large burnisher used, the gold will not roll, and it is of course essential that this, the base on to which all the subsequent filling is built, should be abso- lutely steady and immovable. The burnisher is now changed, and a No. 5 point, not too small in size, and which it will be remem- bered is left unpolished, is substituted. This is BY ROTATING BURNISHERS. 5 very rapidly rotated with moderate pressure, and the gold prodded by it, if I may be permitted the expression, as it exactly conveys my meaning. The whole of the filling must be gone over in this manner, especial care being taken that the gold is thoroughly driven down to the cervical edge towards the matrix, for here if anywhere will be the weak place when the filling is complete. The rapid rotation causes the gold to be still more condensed than it was at first, to lose its polish, and become converted into a hard and solid mass of cohesive gold. This may be readily proved, for on a soft unannealed cylinder being lightly pressed on to its surface, and then an attempt made to lift it away with the foil-pliers, the cylinder will be found to tear in half, rather than leave the surface to which it has become closely coherent. The cavity must again be loosely filled with cylinders, and these treated in a similar manner to the former ones, first the large burnisher being used, and then the No. 5, and so on with more and more cylinders until the cavity is quite full, when the matrix may be removed, and the filling smoothed and polished in the usual manner, where necessary. But little finishing, however, will be required if the matrix has been adapted closely to the cervical A 3 6 ON HERBSTS METHOD OF GOLD-FILLING and lateral margins of the cavity, and in this way much time and trouble are saved. During the process of filling it will be noticed that the burnishers become coated with gold, which may be cleaned off by rotating on a piece of emery paper, the large ones on very fine, and the No. 5 on somewhat coarse paper ; or, better still, they may be cleaned by being pressed while rotating on a block of pure tin. A little of the tin is apt to be conveyed to the filling, but it does not appear to affect either its working quality or its colour. Care must be taken that the instruments be not kept too long in contact with the gold, or the filling w r ill soon become very hot and painful to the patient. Occasionally, if the pressure be retained too long, the gold acquires a highly polished surface, which cannot be made cohesive in the ordinary way ; this may be overcome by rapidly rotating on it a fine cut burr such as is used for dressing down fillings ; this tears up the polished surface, and leaves a perfectly cohesive one in its place ; the filling may then be proceeded with in the ordinary manner. It is in all cases desirable that the matrix should extend well beyond the margins of the cavity, both towards the cervical edge and the grinding surface. Unless it extends beyond the BY ROTATING BURXISHERS. 7 cervical edge it is apt to catch in this part of the tooth, and a ledge of uncovered dentine will here be left when the filling is finished. If it does not extend beyond the grinding surface it will be found a very slow and difficult process to epply the last layers of gold, but not so if the matrix is made sufficiently deep. This is a matter of the greatest importance, and Dr. Bodecker, in an admirable article in the " Independent Practi- tioner/' which was reproduced in the November number of the Journal of the British Dental Association, and which I cordially commend to your notice, says : " The adjustment of the last layers of gold requires almost as much time as when made by the mallet." In my earlier experi- ments I was inclined to agree with Dr. Bodecker in this view, but subsequently I increased the depth of my matrices ; from that time the diffi- culty disappeared, and I now find it almost as easy to put on and finish the last pieces of gold as the first ones. When a corner of a tooth, as for instance an upper incisor, is to be restored, a somewhat different method must be adopted for applying a matrix. Here, however, the same general prin- ciples for filling will be observed, viz., the cavity must be smaller at its entrance than its interior, and four walls must be provided, since they do not exist already. A 5 8 ON HEEBSTS METHOD OF GOLD-FILLING These artificial and temporary walls may be formed by imbedding the tooth and two or three adjoining it in softened shellac, brought well over the cutting edges of the teeth and between them, so as to afford as much support as possible. Should any shellac have oozed into the cavity it may be removed when cold by the aid of an excavator. When it is possible, however, it is eminently desirable that the walls should be formed of metal, such as clock spring or platinum foil, which can be moulded to the shape of the tooth in the form of a collar, and soldered or not, as may best suit the case, being subsequently imbedded in the shellac. The metal gives an increased support, and prevents the heat which is apt to be generated in working softening the shellac and causing the gold to sink into it and become spongy and porous. Should this happen, it will be found that a portion of the gold comes away from the filling and attached to the shellac when the matrix is removed. When two interstitial cavities in front teeth are to be filled, they are separated sufficiently to allow a thin dividing file to pass between them, on more room being necessary; they are excavated and as good a hold obtained in each as required, then a few cylinders are packed in one cavity and condensed, &c., as previously described, the process being repeated in the other tooth, more gold is BY ROTATING BURNISHERS. 9 added, until finally the two cavities are united, one filling stretching across and occupying both teeth. When the cavities are quite full, the point of instrument No. 15, which is a clean smooth sewing needle set in a socket, is placed on the gold in the interval between the two teeth, and by slow rotation and steady pressure passed right through the gold, first near the gum, then near the cutting edge, then between the two ; more holes are now drilled if necessary, and finally they are joined by means of a saw or fine file. The two fillings are now finished in the usual manner. In using the needle, care must be taken that it is passed backwards exactly in the right direction, or it is apt to be driven into one of the cavities instead of between them. These needles are readily renewed when broken, as they are merely fastened into the socket of the holder by shellac or soft solder. It will be noticed by this method of filling that soft, unannealed, non-cohesive cylinders are intro- duced into the cavity, and by subsequent working are converted into a mass of cohesive gold. This effects an immense saving of time, as we are thereby enabled to use large cylinders and several at once ; for being soft they are readily adapted to the walls and floor of the cavity, whereas by our ordinary method we can only use small pieces of 10 ON HERBST'S METHOD OF GOLD-FILLING gold, and one piece at a time ; if we attempt to pack a large cylinder which has been annealed we find it becomes hard on the exterior and spongy within. The difference being that one is heated before any attempt is made to adapt it to the walls of the cavity, and the other becomes cohesive only subsequently to the adaptation having been produced. This adaptation of the gold to the walls of a cavity is very perfect, as will be noticed when a tooth is split open, for every little hollow and depression will be found perfectly reproduced ; the centrifugal force of the rotating burnisher having driven the gold before it into every hollow and crevice presented to it. On splitting open a tooth and removing the filling, the gold will be found quite solid and incapable of breaking up by pressure between the fingers, and may be beaten on an anvil into a thin sheet without splitting, showing that the com- ponent cylinders are not mechanically pressed together, but actually welded into a homogeneous mass. I have used this means of filling in the case of several patients who have previously had teeth stopped by the aid of the mallet, and they all express a preference for the new method, as it saves the jarring which is so painful where teeth have been separated. BY ROTATING BURNISHERS. 11 Dr. Herbst invariably employs cylinders pre- pared by a German manufacturer, Carl Wolrab, of Bremen, which seem admirably adapted to this kind of work, and I believe much of our success will depend on their employment ; no other gold I have met with appears to possess such a softness and adaptability as this, though the soft cylinders sold by some of our makers also work extremely well. Should a filling become damp before it is com- pleted, it may be dried as far as possible by the ordinary means, and if a burnisher to which some gold is allowed still to cling is rapidly rotated over its surface for a short time, sufficient heat is generated to perfectly dry it and enable one to proceed with the filling to its completion. There is an undoubted w^aste of time in changing the points so frequently, and I think it very desirable that some means be introduced to overcome this difficulty, such as the employment of two engines or two arms working on one engine, or better still, an electric motor for working the No. 5 point, which requires rapid rotation with but little pressure. It would also save the fatigue which is experienced from a prolonged use of the burring engine. Tin-foil may be worked in a similar manner to gold ; from its natural softness it easily adapts itself to the walls of the cavity, and readily 12 ON H BREST'S METHOD OF GOLD-FILLING coheres when a burnisher is rotated against it; when beaten on an anvil, like gold, it may be flattened without splitting, showing how intimate is the union between its component portions. From the ease with which it packs, it is more rapidly worked than gold. Gold is readily built on to tin ; a filling may thus be partly built up with tin and completed with gold in such parts as are subject to the greatest amount of wear. I have been unable to obtain any cohesion with platinum leaf when worked in a similar manner. Burnishers made of agate answer admirably for compressing the gold, and possess the advantage of not becoming coated with the metal ; they are, however, difficult to obtain, and readily break, so that I have been reluctantly compelled almost to abandon their use. To summarize my remarks, I would say that by this method we possess a very rapid, and I hope reliable, method of filling those long and somewhat difficult cavities in teeth where, one or more of the walls being absent, we are compelled to resort to cohesive filling for restoration of the missing portion. The method is easy when one is accustomed to it, the most troublesome part being the accurate adap- tation of a satisfactory matrix, though this and other difficulties rapidly disappear after a little practice. BY ROTATING BURNISHERS. 13 Too much attention cannot be paid to the matrix extending well beyond the margins of the cavity. Great care is necessary that the gold be well compressed towards the cervical edge where it and the matrix join, for this is the most critical part of the whole filling. Should the gold rock, it is due to too few cylinders being in the cavity, or too small a burnisher being used to start with ; probably the former is the fault. Though the cylinders are soft and non-cohesive, they must not be annealed. When possible, a layer of metal should always intervene between the gold and shellac matrix. Should the gold remain polished and refuse to become cohesive, a fine cut burr rapidly rotated over it will immediately convert the surface into a cohesive one. To those who may be interested in the subject I strongly commend the perusal of the articles by Dr. Herbst and by Dr. Bodecker. In conclusion, I beg in support of my remarks to submit for your inspection a few specimens of the fillings which have formed the subject of my experiments, merely observing that any imper- fections noticed in them are due rather to my want of familiarity with the method than to any inherent fault in the system. 14 ON HERBST'S METHOD OF GOLD-FILLING The following specimens were exhibited during and after the reading of the paper : 1. Dr. Herbst's set of 15 rotation burnishers for the engine. 2. Wolrab's and Jamieson's soft gold cylinders. 3. Molar with large cavity occupying masticating and distal surfaces filled by rotation with Jamieson's gold. The tooth and filling are sawn through vertically. The matrix not having been carried low enough had caught at the cervical edge, leaving a ledge of uncovered dentine at this spot. 4. Shellac matrix used in filling the right upper central and lateral teeth of a patient exhibited after the meeting. The shellac became softened at one point during use, and yielding, allowed the gold to sink into it, and become spongy, a portion of it (shown) coming away attached to the shellac. This accident suggested the use of a thin layer of metallic matrix between the shellac and gold. 5. A large cavity in a molar had been prepared with numerous pits and grooves, and filled with gold by rotation; the tooth was split up and the filling exhibited, in order that the close adaptation of the gold to the inequalities might be noticed. 6. Two specimens of Wolrab's gold which had filled a tooth ; the fillings were removed and beaten out ou an anvil to show their malleability, and how inti- mately welded the mass had become. 7. A similar specimen of Jamieson's gold removed and beaten out. 8. Large cavity in masticating and distal surface of molar filled with Wolrab's gold ; the introduction of the gold occupied 40 minutes. 9. Outer fourth of upper central incisor built up with Wolrab's gold, restoring the labial, palatine, and distal surfaces, and the cutting edge. 10. Cavity in masticating and distal surfaces of bicuspid BY ROTATING BURNISHERS. 15 filled with Jamieson's gold. Tooth and filling cut through vertically. 11. Large cavity on masticating and distal surface of molar filled with tin cylinders and sawn through vertically ; the cervical wall of filling was left untouched after the removal of the matrix, in order that the character of surface left by it might be seen. Time of introducing the tin, 21 minutes. 12. Large tin filling, restoring masticating and distal surface of molar; tooth and filling sawn through vertically. 13. Half of No. 12 removed and beaten out. 14. Tin filling in lower molar masticating and distal surface. Tooth and filling sawn through vertically. Time in introducing the tin, 25 minutes. 15. Combination filling. of tin and gold. Large cavity in masticating and distal surface of upper molar, three parts filled with tin occupying 10 minutes, and finished with Wolrab's gold occupying 12 minutes. Together 22 minutes. 16. Shellac and platinum matrix adapted to three upper front teeth, for restoration of distal corner of left upper central. Arranged so that the filling can be made from ihe front. 17. Similar matrix adapted to distal corner of right upper canine, so the filling can be performed at the back. 18. Clock spring matrix wedged between second upper bicuspid and first molar, for restoration of the distal and masticating surface of the bicuspid. 19. Clock spring collar surrounding molar, adapted to a case where there is no contiguous tooth against which a matrix can be wedged. 20. Patient exhibited. W . R., set. 22. Frail teeth. Proxi- mal sides of right upper central and lateral incisors restored. The enamel was very thin and chalky. The palatine, proximal, and labial walls were built up. Shellac matrix used which became soft, allowing the gold to become spongy at one part, 16 ON HEEBST'S METHOD or GOLD-FILLING. and needing extra gold to be added at the last. This matrix is described as No. 4 in this list. Time for the two fillings, 45 minutes. 21. Mesial surface of right upper central. The teeth were very close together, and were just wedged sufficiently at the time of operation to admit a thin dividing file. Time, 8 minutes. 22. Two shallow cavities in proximal surfaces of left upper central and lateral. No wedging. Time, 16 minutes the two. 23. Anterior surface of first left upper bicuspid, the cavity also involving the masticating surface. Clock spring matrix used. Time, 18 minutes. 24. Proximal surfaces of first and second left upper bicuspids. Clock spring matrix. The first bicuspid occupied 8 minutes, and the second 10 minutes. Wolrab's gold was used for all the fillings in this patient. NOTE. Wherever the time is mentioned it applies only to that of introducing the filling, as that is the special part to be noted ; the preparation of a cavity and finishing a filling being carried out in the ordinary manner are therefore not noted. (17) DISCUSSION. MR. VASEY asked if Mr. Bennett conld explain how the non- cohesive foil became cohesive during this process ? Was it due to the heat evolved by the friction of the burnisher ? MR. OAKLET COLES said that about six or seven years ago he tried some experiments in packing cohesive gold by means of the engine ; but his idea had been to consolidate the gold by means of a revolving instrument giving a rapid succession of blows. For this purpose he had used a burnisher with rounded interrupted facets, somewhat resembling a tomato, and with this he was able, out of the mouth, to get very good solid fillings. There could, how- ever, be no doubt that the cohesive quality of gold could be very quickly evolved by the heat generated by the rapid rotation of a perfectly smooth instrument, though he had not thought of this when he made his experiments. He con- sidered that the profession was greatly indebted to Dr. Herbst for calling attention to this fact, and that the Society was much indebted to Mr. Bennett for bringing Dr. Herbst's discovery so clearly before it. The cohesive property of gold under certain conditions was, of course, no recent discovery ; it had been known for thousands of years. But this mode of evolving it, and of securing condensation at the same time, was a novel application of known principles for which Dr. Herbst deserved all the credit. MR. HUTCHIXSON thought Mr. Bennett's paper very clear and practical, but a still clearer idea of the process would be obtained if at the close of the meeting he would have an engine brought in and give a short demonsti'ation of the principal points. Thus he had said that when the cylinders were first introduced, the engine was to be worked " slowly." How slowly ? And afterwards that the point of the instrument was to be alternately applied to the gold and then removed, 1 8 DISCUSSION. and that it must not be kept in contact too long. All these points could be shown in one minute by practical demonstra- tion, whilst the mere verbal description of them did not convey a sufficiently definite idea. Mr. Bennett had said that the most troublesome part of the process was the application of the matrix. He (Mr. Hutchinson) had been using a very simple matrix, which he believed to be a very decided improvement on the clock- spring, which had to be kept in place by wedges. It was made by breaking a small pen-knife blade with a thick back a very common one would do into short lengths. This formed a very perfect matrix, and its wedge-like shape made it very easy to fix in position, as it adapted itself well to the cervical edge ; it could be easily bent if heated. It occurred to him, also, that a very simple and ingenious contrivance shown by Mr. Brunton at the meeting of the British Dental Association at Plymouth two years ago would be an improvement on the shellac matrix described by Mr. Bennett. Mr. Brnnton's arrangement consisted of a short piece of clock-spring, with the temper taken out of the ends, which were sharply bent on themselves ; to these a rubber-dam clamp was attached, and a very efficient and readily applied matrix was thus made when a molar had to be built up. MR. WALTER COFFIN remarked that the great interest which this process had aroused in the United States might be taken as evidence of its practical value. Dr. Herhst's discovery that soft gold might be rendered cohesive bv means of a rotating burnisher was a remarkable one. The value of lining a cavity with soft gold had long been appreciated by the best operators, and the difficulty hitherto experienced in attaching cohesive gold, in order to finish with hard contour work, would appear to be greatly lessened by this very important observation. He doubted, however, whether the first layers of soft gold, if applied with the i-otating burnisher, would not be rendered less plastic and adaptable to the walls in proportion as it be- DISCUSSION. 1 9 came hard and cohesive under its action. He would therefore like to ask Mr. Bennett whether he did not think that the first layers of gold would be best applied by hand in the usual way? MR. WEST remarked that, so far as he had heard, this method appeared to be only applicable to easily accessible cavities He should be glad to know if it could be applied in the case of a cavity requiring a right-angle attachment ; such for instance as a buccal cavity in a lower molar ? DR. CUNNINGHAM (Cambridge) said the subject they were discussing was a most interesting one. It appeared to him that Dr. Herbst's discovery was likely to exercise a most im- portant influence on future practice. There were, however, some points which he should be glad to see made clearer. In the first place it seemed curious that only the Bremen gold should give good results. Then he should like to hear a scientific explanation of the statement, that the non-cohesive gold was made cohesive by the action of the revolving bur- nisher. He could not help feeling some doubts as to whether the gold did become cohesive in the sense in which that term was generally understood. No doubt the added gold could be made to adhere to that which had been previously introduced, but there was a difference between adhesion and cohesion. What made him feel more doubtful on this point was the statement in the paper that in certain cases where adhesion could not be obtained, rough-cutting the surface with a bur would make the fresh gold stick. Very likely it did ; but this was not what was usually meant when people spoke of gold being made cohesive. Then it was said that Dr. Herbst had been at work on this system for six years, and he brought forward clock-spring as the best form of matrix which he could suggest. It appeared to him (Dr. Cunningham) that Dr. Herbst was rather behind the times. With regard, however, to Mr. Brunton's clamp, referred to by Mr. Hutchinson, it was unfortunately only applicable in certain cases. He (Dr. Cunningham) would suggest that a good matrix might be made by rolling platinum 20 DISCUSSION. foil round the tooth, and securing it with a rubber-dam clamp. Possibly also some of the modelling compositions, such as the Al impression material, might do instead of shellac. He thought that Mr. Bennett might have subjected his fillings to some better test than merely beating them out on an anvil. It would be interesting, for instance, to compare the specific gravity of one of Dr. Herbst's fillings with that of one made by other methods. Had Mr. Bennett tried the Bremen gold in the ordinary mode of working ? The PRESIDENT said he feared the most important points in the paper were being lost sight of ; the precise form of the matrix was not an essential part of Dr. Herbst's method. He hoped that, as the time which could be allotted to the discussion was short, members would confine themselves as much as possible to the subject of the paper, viz., the advantages or disadvantages of filling teeth with soft gold with the aid of rotating points. Mr. F. J. BENNETT said he quite agreed with what the President had just said ; the exact form and material of the matrix was quite a secondary matter. He thought a good deal of what had been said was not very much to the point. Dr. Cunningham had talked about the gold being made to adhere but not to cohere. He (Mr. Bennett) had always understood that the only distinction between adhesion and cohesion was that the latter meant the union of similar bodies, and the former the union of dissimilar ; therefore when gold was joined to gold that was cohesion. Mr. Storer Bennett had, he considered, put the subject before them in a very practical form, and the best thing members could do was to go home and try it for themselves. MB. HERN said he happened to be present when Dr. Herbst's brother gave the demonstration at the Dental Hospital referred to by Mr. Bennett, and he could not say that the results were altogether satisfactory. He noticed that the operator used unannealed cylinders for the deeper part of the cavity, but filled the last third with cohesive gold. DISCUSSION. 21 He had since made a few experiments himself, and he found that there was no doubt about the fact that the gold did become thoroughly cohesive as the result of this process. But whatever might be the advantages of this method, its range of adaptability was limited, since it could only be applied to fairly accessible cavities. At all events there was very great difficulty in applying it to cavities which were out of sight, and in using right-angle attachments. It was most useful in cases where the walls of the cavity were frail ; it was a great advantage in such cases to avoid blows, and better adaptation of the gold to the walls could be obtained in this way with less pressure. The gain of time appeared to him to be less clear ; he thought he could fill a crown filling by hand quite as quickly as with the rotating burnishers. Had Mr. Bennett found that it made any difference which way the instrument was rotated i.e., from the enamel to the gold, or from the gold to the enamel ? MR. BETTS said that he had only a few days before received a letter from Mr. Chas. Tomes in which he referred to various matters of professional interest which he had met with during his visit to the States. With reference to the subject under discussion he wrote : "About the Herbst method I feel less sure. It easily makes water-tight plugs, and so far is very good, but whether it is better or more rapid than other methods I feel less certain." The PRESIDENT said it appeared to him that a good deal of the criticism he had heard during the discussion was founded on theory rather than practice. But it was evident that Mr. Bennett had done a large amount of work, and had investigated the matter practically. All new methods pre- sented difficulties, and no doubt the Herbst method was no exception. But Mr. Bennett had shown that these difficulties could be overcome, and he thought that so far as the dis- cussion had gone his verdict would be in favour of the practical success of which the specimens before him were evidence, and against the theoretical objections. He must now ask Mr. Bennett to reply. 22 DISCUSSION. MR. BENNETT said his object had been to learn the views of the members with regard to this new method, and in this he had been fairly successful. In reply to Mr. Vasey's question, his opinion was that the gold was rendered cohesive by the heat which was developed during the process of condensing it. The gold certainly did become hot, and if the operator was not careful the tooth might become so hot as to be unbearable and the instrument too hot to be touched. With reference to what had been said about the matrices, he admitted that this was the least developed part of the process ; still they answered their purpose sufficiently well, except the shellac matrix, which was certainly not satisfactory ; lining it with metal was a decided improvement. In reply to Mr. Coffin's suggestion, that it would be better to line the cavity with soft gold and condense this by hand, after the manner of the best operators, he could only reply that very perfect adaptation of the gold to the walls of the cavity was obtained by the Herbst method, as Mr. Coffin might satisfy himself by an examination of some of the specimens exhibited, and that this close adaptation was not destroyed by rendering the gold cohesive afterwards. Dr. Bodecker advised that the last layers should be made of cohesive gold condensed with the mallet, but Dr. Herbst was in the habit of using soft gold throughout, and all his (Mr. Bennett's) work had been done in this way. The answer to Mr. West's question was that right-angle attachments could be used. With regard to Mr. Cunning- ham's remarks, he (Mr. Bennett) had used English gold as well as German, and had found that Jamieson's answered very well, though it was not quite as good, for this purpose, as Wolrab's. As to the distinctions between adhesion and cohesion, he could only repeat that the gold did cohere after using the smooth-cut bur, though it would not do so before. The A 1 impression composition, suggested by Mr. Cunning- ham for forming matrices would, he thought, be too soft for use in this process. He did not intend to imply that beating the filling out on an anvil was a conclusive test, still it was of some value. He DISCUSSION. 23 might mention, as evidence of durability, that Dr. Herbst's brother had some large gold fillings in his mouth which had been inserted by this method two years before, and they showed no signs of wear. Dr. Bodecker had tested the specific gravity of fillings inserted by this method and with the mallet, and that of the malleted plugs was the higher. Wolrab's gold worked very well when used in the ordinary way. He thought Mr. Hern would find, when he had had more practice at this method of filling, that a decided saving of time was effected by it. He admitted that it might be better to use the ordinary method of filling for inaccessible cavities. He had not found that the direction in which the instrument was rotated made any difference. LONDON : HARBISON AND SONS, PBINTEES IN OBDINABY TO HEB MAJEST5T, ST. MABTIN'S LANE. UNIVERSITY OF CALIFORNIA LIBRARY Los Angeles This book is DUE on the last date stamped below. 19 Jl MAR 1 2 FEB13 BIOMEO UB. JAN 3 1 1986 REC'D APR 1 5 1986 REC'D Form L9-116m-8,'62(D1237s8)444 3 1158 00635 9870 A 000 394 865 o