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THE PORCELAIN INLAY. 389
platinum matrix. The No. 30 gold foil is placed over the cavity mar-
gins in a manner similar to that prescribed for the use of platinum ; and
then, instead of burnishing or spinning it in place, it is pressed into
all parts of the cavity by means of spunk or cotton. The metal is so
soft and ductile that this can be accomplished in a manner impossible
with platinum ; and it is this easy manipulation of the gold that makes
the sole advantage of the low-fusing over the high-fusing porcelain
bodies. The gold matrix is then teased out of the cavity. This must
be carefully done, as, being more easily adapted, it is also more easily
distorted than the platinum. The proper mixture of porcelain is placed
in it, and the baking is performed exactly as with the high-fusing
materials, the only marked difference in the working of the low-fusing
Fig. 370. Fig. 371.

Large cavity in molar tooth involving appniximal and Showing restoration of broken lateral
grinding surfaces. Restored by porcelain inlay. incisor by porcelain tip.
and the high-fusing materials being that low-fusing bodies tend to
spheroid and lose contour. This can be remedied by mixing with the
paste a small quantity of similarly colored high-fusing porcelain.
When such porcelains are used as require the gold matrix to be
invested, the following additional points should be carefully observed :
The matrix must not be torn on the bottom at all, as in such event the
porcelain will tend to run through into the investment instead of draw-
ing away from the crack, as it does from a platinum matrix where no
investment is used. The gold matrix must be dropped bottom side
down into a paste of asbestos and alcohol, which is allowed to evaporate.
Then the porcelain may be flowed into the matrix little by little, to
minimize warping.
The method described by Dr. J. Leon Williams^ is as follows
:
" The thinner the gold can be used, the more perfect the fit of the
finished inlay. A proper set of instruments for shaping the gold form
and for manipulating the porcelain paste is an important matter. I
have devised for these purposes the set of instruments shown in Fig.
372. They are all double-end instruments. Nos. 1, 2, 3, and 4 are
designed for fitting the gold form to the cavity, while Nos. 5 and 6 are
for manipulating the porcelain paste. The gold should be cut out to
represent roughly the shape of the orifice of the cavity, but consider-
^ Dental Cosmos, November 1899, vol. xli. p. 1087.