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THE PORCELAIN INLAY. 393

porcelain inlay. If gum-water be used for mixing the paste, it will be
found necessary to remove these overhanging particles with great care,
as the tendency naturally is for the gum-water to cause the particles of
powdered porcelain to stick to the gold or platinum margin of the ma-
trix. In building up the inlay for restoring lost corners of teeth and for
general contours the work will be much facilitated if, after the first
baking has been carried through as above described, to secure perfect
union with the walls of the matrix, a small piece of solid porcelain be
placed at the point representing the highest point of the contour of the
inlav. These pieces of porcelain may be made by crushing old porce-
lain teeth in an iron mortar. Care should be taken to use a piece small
enough so that the outer edge will not show through when the inlay is
completed. Corners like the one shown in Fig. 376 may be produced
in this manner without much difficulty."
Dr. Williams's method of separating the gold matrix from the porce-
lain, and grooving the inlay and cementing it into the cavity, need not
be dwelt upon, the subject having already been fully discussed.
In summing up the advantages and disadvantages of the high-fusing
and low-fusing bodies it will be seen that the advocates of the low-fusing
materials claim the sole point that gold is more easily adapted as a
matrix than platinum ; while the others claim that porcelains of high-
fusing bodies are known to be permanent, to keep their color under
firing, to contour without spheroidal tendency, to dispense with the
use and consequent restrictions of an investment, and to furnish a
process so simple and reliable that fillings may be constructed with
greater certainty of good results and with more rapidity.
Furnaces suitable for fusing the porcelains used in inlays are of
two classes — gas and electric. The gas furnace is usually noisy, odor-
ous, and dirty ; but it seldom, if ever, gets out of order. On the other
hand, the electric furnace is clean, silent, and beautiful ; but it has only
a limited life. Even in experienced hands its wires will burn out
and need mending once or twice a year, and with the inexperienced it
may easily be rendered useless in a few seconds. Nevertheless, in
spite of these drawbacks, the electric furnace is to be preferred to the
gas, as with a little practice it can be easily mended, while the gas furnace
is suitable only for the laboratory. The only feasible gas furnaces for
high-fusing bodies are those which have a platinum muffle, in which the
fusing porcelain can be thoroughly protected from the gas, for no fusing
porcelain can keep its color if subjected to the products of combustion
of carbon. The two most practicable gas furnaces are the Downie
(Fig. 377) and the Midget Land. Either of these properly manipu-
lated will fuse continuous-gum body within three minutes. They
w^ork on the blowpipe principle, and necessitate either a pressure-