Page 394 - My FlipBook

392 RESTORATION OF TEETH BY CEMENTED INLAYS.

care, the finished inlay will always be found to fit perfectly. To facili-
tate the quick removal of the form, care should be taken to prevent
the wax overlapping the gold much at any point outside the margin of
the cavitv. To prevent this and also to assist in securing proper imbed-
ding of the gold matrix it is well to let the margin of the gold project
as much as possible beyond the edges of the cavity.
" The matrix may now be imbedded without the slightest fear that
its shape Avill be changed. For imbedding material I use plaster and
marble-dust. When the investment is sufficiently hard the wax is thor-
oughly melted out with a stream of boiling water. The investment is
then dried and brought to a full red heat wdth the blowpipe. It
is then allowed to cool, and is ready for packing. Xow. the first step
in the packing of the porcelain paste is the all-important one to prevent
the porcelain shrinking away from the walls of the matrix. This may
always be accomplished easily with porcelain of any make if the follow-
ing instructions are carefully observed : Mix the porcelain paste to the
consistence of soft putty, and with the upper point shown in Xo. 6, Fig.
372, place a ring of this putty around the entire circumference of the cavity,
Fig. 375. Fig. 376,

Showing bicuspid with cavity involving approxi- Canine tooth showing at a, large cavity, and
mal and grinding surfaces: o, tooth with at 6 and c, large porcelain inlay restor-
cavity prepared b, porcelain inlay c, inlay ing contour of tooth,
; ;
cemented in place.
leaving the centre quite free or empty. In melting a porcelain paste it
naturally shrinks toward the largest mass of its own body, or toward
the centre of the mass. If, then, this centre be removed we should
naturally expect the mass to shrink toivard the circumference, and this is
precisely w'hat happens wdien manipulated as directed. The matrix
always comes out from the first baking with the porcelain everywhere
firmly melted to the walls of the matrix. Xor will it start from this
position at any subsequent leaking unless it is very much overheated.
"After each packing of the porcelain paste, a small camel's-hair brush
with a fine point should be moistened (this is best done by drawing it
between the lips after the manner of water-color artist.s) and di*awn
around the margin of the matrix to remove all overhanging particles of
the paste. If this be not done, the margins of the inlay will often be
found ragged, and a perfect margin is the most essential feature of a