Indiana University School of Dentistry - Prognosis Yearbook (Indianapolis, IN)

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l 'V i7LlJe1911ng11n5i5 zginniana Dental Ql:DlIBQB1l904. Qmwal follows: F or those bordering on nervous prostration and tho-se high strung nervous temperaments for whom it is a physical impossibility to prepare a cavity even for a cement filling, to say nothing of gold, you can 'do permanent work with porcelain. After the cement has completely crystallized a thin porcelain filling in the occlusal surface of molars will have the full strength -of the whole tooth to resist the masticating stress and is in no danger of frac- ture. A dentist has been brought up all his life on one law of self-retentive form of cavity and interlocking form of filling and it is hard for him or inlay workers to break away from that law. There are inlay workers to-day who are working upon self-retentive form of cavity formation, and grooving their inlays or baking into- them platinum pins or loops to make them as near interlocking as possi- ble. I believe inlays depend upon the law of clo-se adapta- tion and the medium of completing the clo-se adaptation crystallizing under pressure. If such statements were true there wo-uld be no- need of other filling materials. But such as these have misled many skillful dentists, and after a few failures they have decided that porcelain as a filling material is not practicable. Cavities for inlays should be prepared with the same carefulness- that should be used for other fillings. The op-, posite walls of simple proximal cavities should be parallel and form right angles with the pulpal wall. In cavities where steps are used they should involve enough of the tooth structure to resist the force of mastication. It is bet- ter to cut the 'step through the middle third of the crowns to prevent the porcelain- and cement from showing through the enamel on those incisors that are thin labio-lingually through the incisal third. Where pins are inserted to as- sist in retaining inlays in teeth with vital pulps they should extend far enough into the dentin to give necessary resist- ance, but not far enough to encroach upon their pulps. All frail enamel should be remo-ved and the margins of all cavities should be smooth and in definite curves or straight lines. The margins should be so fo-rmed that there will be no short bevels -to give frail edges of porcelain. The best instruments for the preparation of cavities for

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y be zient, r the most gold F the most ecia- picu- lveo- erial 1 an with will . GE e rn masts nmana ental Qtnlle e 1 O4 II 1 IJ 19 Q 131 ' ag z 9 annual The classification of cavities where porcelain is indi- cated may be as follows: T I. All cavities in the labial and buccal surface of teeth. 2. Some simple proximal cavities- on incisors and cuspids. - 3. Proximo-incisal cavities, if the cavities can be so prepared that the retentiveresistance will be greate-rthan the stress. A . 4. Cavities involving all or a portion of the incisal edge. 5. Deep cavities on the occlusal surfaces o-f molars. 6. -Proximo-occlusal cavities of b-icuspids and molars, provided a large enough mass of porcelain can be used to withstand the force of mastication. T i 7. Cavities. involving the entire occlusal surface o-f molars. v The contra-indications for porcelain inlays are: 1. In those cavities where the stress will dislodge the filling or cause it to fracture., 'o 2. In all cavities where it is impossible to construct a good matrix because of the inaccessibility of the cavity. i 3. On incisors which are thin labio-lingually through the incisal third. The construction of porcelain inlays involves four sets of manipulative principles: T I. The preparation o-f the cavity. A 2.. The construction of the matrix. 3. The fusing of the porcelain. 4. The setting and finishing of the inlay. Each step presents a number of -mechanical principles which, if not properly observed, will cause an imperfect filling. The failure of many inlays may be attributed to faulty manipulatio-n, and too many beginners attempt the construction of inlays for the mouth before they have mas- tered the technic. That many dentists fail to comprehend the principles by which inlays are retained is' shown by their cavity prep- aration, and when- asked how they expect the inlay to be retained, their answer is, by the cement. .This lack of comprehension may be largely due to the radical statements of some of the porcelain enthusiasts, some of which are as

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I - . 'QUE-19EDQIID5f5 1. ggnniana Dental QEDIIBQB 1-1904 annual inlays are Hat-face fissure and inlay burs, small Arkansas stones and excavators with short blades and their edgesso formed that they will make all angleseither right or obtuse and well defined. A q There are three' general methods o-f constructing matrices for cavities: . I. Swaging the foil over a negative or an impression of the cavities. A 2. Swaging into a positive o-f the cavity. 3. Burnishing directly into the cavity. In cavities involving only the labial or buccal or lingual surfaces or in simple proximal cavities, a matrix can be swaged over an impression and an' inlay constructed which accurately Hts into the cavity. The method of swaging into a' positive die of the cavity has some followers, but it hardly seems possible that a positive die can be obtained that will reproduce the margins of the cavity with that degree of accuracy that is required in inlay work. The method of burnishing the foil directly into the cavity has more advo- cates than either ofthe other methods, and many who have tried the swaging processhave returned to this method. A combination of 'theiswaging and burnishing methods can be used successfully. The technic of constructing a matrix is as follows: Take an impression of the cavity in dental lac or cement and then construct a'positive die of the cavity by mixing a mass of cement and imbedding the impression in it. Allo-w the cement to harden, then separate and invest the die' in the ring of a swaging device. Coat the die with soapstone, thennplace a piece of foil over it and swage with a water bag or unvulcanized rubber., Remo-ve the matrix and co-ver and burnish the metal to the margins. The heat required to fuse the po-rcelain thor- oughly, anneals the metal. This method is especially good in large cavities, and has the advantage of conforming the foil to the cavity by the use of the die so that the final bur- nishing is made quite easy. THE FUSING OF PORCELAINS Porcelain is divided into- high and low fusing bodies. There is a difference o-f opinion regarding the relative mer-