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THE PORCELAIN INLA Y. 375

ities and finally to be cemented in place (Fig. 348). Some, however,
instead of being ground to fit the cavity, reqnire the cavity to be
ground to fit them. Dr. George H. Weagant has devised a set of
instruments suitable for this purpose (Fig. 349), consisting of five tre-
phines of consecutive sizes made of copper charged with diamond
dust. These instruments are intended to cut pieces of porcelain out of
an artificial tooth that matches the color of the natural tooth, and the
cavity in the natural tooth is prepared with one of Dr. How's inlay

Fig. 349. Fig. 350.

Dr. Weagant's diamond trephines. Dr. How's inlay burs.

burs (Fig. 350) corresponding in size to the trephine. This method has
several serious objections, one of the principal being that in order to
give the cavity a circular shape much sound tooth structure is usually
sacrificed. Take for example the decayed spot shown in Fig. 351, «.
This would have to be enlarged as in Fig. 351, 6,
Fig. 351.
—a very serious objection.
As early as 1882 Dr. Herbst advocated glass
fillings. These were made by taking impressions
of the cavity in wax and making two moulds in
some such material as plaster or asbestos. The
ground glass was then flowed into the first mould,
in which most of the shrinkage occurred. The
partly formed filling w^as then removed and placed in the second
mould, when more glass was added until the filling was complete.
Even with this crude method the results were fairly satisfactory, although
the margins were far from perfect and the glass was permeable to such
an extent as to blacken ; nevertheless, fillings M^ere made that preserved
the teeth for years.
In 1887 Dr. C. H. Land made mechanically perfect edges possible
by devising the metal matrix. He used both gold and platinum, but
found the latter preferable, as platinum could be adapted with a facility
equal to gold, and allowed the use of a high-fusing tooth body much
stronger and less likely to deteriorate than bodies capable of being fused