. The science and practice of dental surgery. een thatthe fitting could be greatly simplified ifthe cavity were of such a kind that itcould be made exactly circular on cross-section. The advantages of circular shapeare twofold : first, both cavity and inlaycan be shaped with mathematical accuracy,and secondly, there is no trouble aboutthe orientation of the inlay in placing itin the cavity, as is the case with othershapes. Even this method took a greatdeal of time \^hen the dentist had to makehis own inlay, and it was only when theBalls inlays were introduced that it cameinto general use. The
. The science and practice of dental surgery. een thatthe fitting could be greatly simplified ifthe cavity were of such a kind that itcould be made exactly circular on cross-section. The advantages of circular shapeare twofold : first, both cavity and inlaycan be shaped with mathematical accuracy,and secondly, there is no trouble aboutthe orientation of the inlay in placing itin the cavity, as is the case with othershapes. Even this method took a greatdeal of time \^hen the dentist had to makehis own inlay, and it was only when theBalls inlays were introduced that it cameinto general use. The principle of the Dallmethod is that the inlays are suppliedready made in definite numbered sizes, each ofwhich fits the hole made by the similarlynumbered burr. The fitting of a Balls inlay is a very simplematter. The cavity being considered a suitableone, it is cleared of carious debris and reducedto an approximately circular form with ordinaryburrs. The final shaijing is accomplished withthe special burr ; this should be of a size just too. B (J Fig. 475. (A) Large and small Dalls inlays. (B) The corresponding special burrs. (C) Cavities prepared for Dalls inlays. {All natural size.) large to enter the cavity; while cuttmg, itsshaft must be held perfectly steady and alter-nately advanced and -wdthdrawn so that theburr finds its way without the exercise ofany great force. The burrs are so gauged thatif the one chosen does not complete the shape,the grinding can, without difficulty, be con-tinued with the next size larger. As soon asthe cavity becomes truly circular, the grindingnuist be stopped and the inlay tried in, the 409 number of the burr last used indicating whichone to take; it should fit the cavitj^ tightly :if this is not the case, the cavity must be groundfurther until it takes the next larger size of sides of the inlay should now be groovedand the cavity undercut to correspond ; a littlethin cement is now smeared over both, and theinlay carefully and firm
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectdentistry, bookyear19
