. A manual of mechanical dentistry and metallurgy . e mixed with the metal cast, however, will give better results, especially incase of deep undercuts. In this case block-tin or Babbittmetal may be used, and can be poured directly into theplaster impression. The cavity for the vacuum chambershould, of course, be cut in the impression before the metalis poured. * Pyroxylin, commonly known as gun-cotton, is made by maceratingcotton wool—though linen, hemp, etc., are sometimes employed—in astrong mixture of nitric and sulphuric acids for 15 hours, when itshould be washed thoroughly and
. A manual of mechanical dentistry and metallurgy . e mixed with the metal cast, however, will give better results, especially incase of deep undercuts. In this case block-tin or Babbittmetal may be used, and can be poured directly into theplaster impression. The cavity for the vacuum chambershould, of course, be cut in the impression before the metalis poured. * Pyroxylin, commonly known as gun-cotton, is made by maceratingcotton wool—though linen, hemp, etc., are sometimes employed—in astrong mixture of nitric and sulphuric acids for 15 hours, when itshould be washed thoroughly and dried. The proportions are: cotton-wool, 1/2 oz.; nitric acid, 3^ ozs.; sulphuric acid, 4 ozs. 64 MECHANICAL DENTISTRY AND METALLURGY. When metal is employed, a shell is more advantageousthan a solid cast; and a plate, where there are any consider-able undercuts, can be more readily detached from theformer. But before the cast is run, whether it be frommetal or plaster, the vacuum chamber, if used, should be carved in the impression. Fig. To Make a Hollow Metal Cast.—Prepare the impressionas instructed for running cast, or else secure mold in sandfrom plaster cast, then fuse pure block-tin and pour in theusual manner. The metal cools first at the surface; bytaking advantage of this fact and, after waiting a fewseconds, inverting the mold and quickly pouring out thecentral fluid, a thin metal shell can be secured. Whenobtained it can be filled with plaster, which will form, infact, a metal-faced plaster cast. When the case is finishedand the plaster removed, the edges of the shell may be CELLULOID AS A DENTAL BASE. 65 drawn in with a pair of pliers, which will allow it to bereadily removed from the undercut spaces. The manner of taking the bite and articulating the case,as well as the arrangement of the teeth, is precisely thesame as has been directed for rubber work; more pains istaken, however, in carving and modeling. Carving.—Dr. \\\ ^V. Evans, in the American
Size: 1117px × 2237px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookidman, booksubjectmetallurgy
