Principles and practice of operative dentistry . rial to it or in the stressincident to mastication. In the final preparation of cavity margins, the best results will beobtained by slightly bevelling these borders by cutting the enamel-rods inan oblique direction, as shown in Fig. 375, c, c. If the walls are cut per-pendicular with the wall of the cavity, as in d, d, certain of the enamel-rods would have no support of dentin, and consequently they would bemore liable to fracture from cleavage than if cut away as shown in c, c. In cavities occurring upon concave surfaces, as, for instance, in t
Principles and practice of operative dentistry . rial to it or in the stressincident to mastication. In the final preparation of cavity margins, the best results will beobtained by slightly bevelling these borders by cutting the enamel-rods inan oblique direction, as shown in Fig. 375, c, c. If the walls are cut per-pendicular with the wall of the cavity, as in d, d, certain of the enamel-rods would have no support of dentin, and consequently they would bemore liable to fracture from cleavage than if cut away as shown in c, c. In cavities occurring upon concave surfaces, as, for instance, in thefissures upon the morsal surfaces of bicuspids and molars, the lines ofenamel cleavage would have an inward direction, the reverse of that shownat d. The bevel, therefore, given to the enamel margins in this class of 5 PREPARATION OF CAVITIES. 249 cavities should—in order that no enamel-rods be left without proper sup-port of the dentin—be a little greater than that given to the margins ofcavities occurring upon convex surfaces. Fig. The instruments which are best suited to the purpose of preparing theenamel margins are chisels, broad-face hoe excavators, barrel-shaped file-cut burs, and Arkansas stones. The margins should be left as smooth aspossible, but in the use of the burs and stones care must be exercised notto round the edges of the margins, as this would leave a feather-edge tothe filling after it was finished, and would be liable to peel up or becomerough, thus spoiling the appearance of the marginal contact and openingthe way for the establishment of secondary caries. CHAPTER XVII. TREATMENT OF CARIES BY OBTURATION, OR FILLING. Definition.—Obturation (from the Latin obturare, to stop up), theact of stopping a hole or covering an opening. Obturation of the Teeth.—The filling of cavities in the teeth pro-duced by caries with a substance capable of resisting the destructiveaction of fluids or the force of mastication. The operation of removing disorganiz
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