A practical treatise on mechanical dentistry . distribute a few gentle taps over the surface of the the cast cannot then be withdrawn, continue the process and atthe same time distribute a few gentle blows over the edge of themolding-ring, when it will usually be found that the cast can be 158 MECHANICAL DENTISTRY. readily lifted out. All these manipulations must be very gentleor the cast may be tilted or rocked in the sand, and thus make afalse impression. Another method of removing the cast from the sand, usuallygiven in the text-books, is to reinvert the ring and contents, holdit ab
A practical treatise on mechanical dentistry . distribute a few gentle taps over the surface of the the cast cannot then be withdrawn, continue the process and atthe same time distribute a few gentle blows over the edge of themolding-ring, when it will usually be found that the cast can be 158 MECHANICAL DENTISTRY. readily lifted out. All these manipulations must be very gentleor the cast may be tilted or rocked in the sand, and thus make afalse impression. Another method of removing the cast from the sand, usuallygiven in the text-books, is to reinvert the ring and contents, holdit above the table, and dislodge the cast by tapping it gently un-derneath. The writer would, however, in nearly all cases reject amold from which the cast had fallen out by its own weight. Manner of Molding where Undercuts are Present.—Where wehave an overhanging alveolar ridge producing a slight undercut,the front of the cast may be raised by first building an inclinedbed of the molding material, and resting the cast upon its highest Fig. point with the heel upon the molding-tray or table, as is shown inFig. 61. It can then, in ordinary cases, be readily withdrawn. Molding with Cores.—Where the undercuts are too great to beovercome by the method just described, what is known as core-molding is employed. First set the cast on some smooth surface;oil at the site of the undercut; mix plaster and asbestos, or plasterand marble-dust, equal parts. When dry, apply the mixture ofproper consistency to the front of the model, from the bottom upto the edge of the alveolar line, spreading it on both sides so as en-tirely to fill up the depression, making the lower edge ^2 of an inchthick, and sloping off toward the alveolar ridge (Fig. 62). Whenthis has hardened, separate it from the model, and draw the top of METALLIC DIES AND COUNTER-DIES. 159 it over sand-paper to obtain a flat edge, and let it dry. Readjustthis front piece to the model; procure a mold in sand or othermaterial, in
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectdentist, bookyear1903
