. The principles and practice of dental surgery. nished which are to havemelted metal brought in contact with them. In sand-moulding we may use a deep model or a very shallowone. The process with the latter will be hereafter using the former, modifications of shape are sometimes calledfor to overcome difficulties arising from undercutting on theoutside of the upper ridge and on the inside of the lower. Thesemay be overcome: 1, by filling up the undercut with wax orplaster in all places where it is unnecessary or impracticable tocarry the metallic plate; 2, by using a peculiarly-co
. The principles and practice of dental surgery. nished which are to havemelted metal brought in contact with them. In sand-moulding we may use a deep model or a very shallowone. The process with the latter will be hereafter using the former, modifications of shape are sometimes calledfor to overcome difficulties arising from undercutting on theoutside of the upper ridge and on the inside of the lower. Thesemay be overcome: 1, by filling up the undercut with wax orplaster in all places where it is unnecessary or impracticable tocarry the metallic plate; 2, by using a peculiarly-constructedflask for moulding, such as the one invented by Dr. G. E. Ilawes(Figs. 201, 202); 3, by making a sectional model (Figs. 197,198). (This method was first introduced, we believe, by Dr. , and is best made by filling the central third of thewax impression with the plaster, keeping it from the lateralthirds by a temporary use of clay or putty. This is then re-moved and trimmed, leavins: the lower surface Avider than the Fig. upper (Fig. 197). This done, it is replaced in the impression,and filled up on each side with plaster; the model is then re- 654 PLASTER MODELS. moved, properly trimmed, and varnished, when it presents theappearance represented in Fig. 198); 4, by filling the undercut Fig. 198.
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