. Operative and dental anatomy technics; a class-room and laboratory manual for freshmen dental students . indicated. 12. Tertiary Polish.—Polish again to remove the oxidesformed on the surface, so that the colors may again be seento appear in case of subsequent tempering. 13. Spring Temper for Shank.—Cover with soap andplace the blade of the instrument in contact with a hammer orsome other large piece of metal, so that it will conduct awaythe heat and prevent drawing the temper already given theblade. Place that portion of the shank back of where thetemper is required in the flame, heat and w
. Operative and dental anatomy technics; a class-room and laboratory manual for freshmen dental students . indicated. 12. Tertiary Polish.—Polish again to remove the oxidesformed on the surface, so that the colors may again be seento appear in case of subsequent tempering. 13. Spring Temper for Shank.—Cover with soap andplace the blade of the instrument in contact with a hammer orsome other large piece of metal, so that it will conduct awaythe heat and prevent drawing the temper already given theblade. Place that portion of the shank back of where thetemper is required in the flame, heat and watch closely forthe blue color, on the appearance of which, plunge immediatelyas before. 14. Sharpening and Final Polish.—Again polish, andsharpen the blade for use. Technic Work in Brass.—If the instruments are made inbrass, practically the same procedures are followed, exceptthat no hardening or tempering is required and the polish-ing is done only on completion of the work. The brassshould be first annealed, when it is ready for the variousmanipulations (Fig. 124). TECHNIC WORK IN BRASS 89. Fig. 124.—Set of instruments made from brass wire as used at NorthwesternUniversity Dental School. Courtesy of Dr. Fred. W Gethro. CHAPTER IIIPREPARATION OF CAVITIES Causes of Decay.—Cavities occur in teeth as a result ofdecay beginning on their surface. Decay is the result of thefermentation of food debris. Fermentation is a decomposi-tion of carbohydrates (starches, sugars, etc.). Food debrisaccumulates because of neglect in the application of theordinary rules of cleanliness to the care of the teeth. Fer-mentation of food debris is due to the constant presenceof germs in the mouth. The action of certain of these germson the fermentable material produces lactic acid. Lacticacid dissolves out the lime salts, of which the major part ofthe tooth is composed. Other germs, constantly present,liquefy the organic material, which constitutes the remainderof the tooth. The result is
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