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press till' pdiwlain into the mold. The mold containuitj the porcelain
can thru he ])laeed in a suitahle ladle and melted, thus delivering the
porcelain .shade sample in a ])erfect condition. Another mold can be
made in a few minutes by flowing metal over the original metal form.
Another method of making individual shade
Pourins method.' samples may be described as follows A metal mold,
:
consisting of four parts, can be readily constructed
so that the mixed porcelain can be poured or dropped into it and the
mixing medium absorbed. Fig. 92 represents the front face of such a
mold ; Fig. 93, the pouring gate ; Fig. 94, the part which carries the pins
for making the holes in the finished shade samples ; Fig. 95. the back
face, which holds the absorbent plaster. To make sample pieces in a
mold of this description it is necessary to thoroughly oil all working
faces, hold the parts together with a clamp of some kind, and then
drop the thinly mixed porcelain, drop by drop, into the mold, being careful
not to clog up the opening. When the mold is filled, put it aside until
(he porcelain sets; then open the mold and gently remove the porcelain
castings (Fig. 96). When the plaster becomes saturated with the mixing
fluid, knock it out of the frame and pour a new back.
One phase of inlay work which will always be
perplexing is the difficulty in obtaining colors that
niatchina
l)uman Cctth with accurately match the natural teeth. The enamel is
Porcelain. a hard dense substance, presenting a glazed-like ap-
pearance, which causes it to be almost transparent.
The dentin, on the other hand, is a porous-like substance which prevents
the light from being transmitted freely and causes it to be but slightly
transluscent. When we consider that teeth are composed of both organic
and inorganic materials with a variation in their density, and that they
are colored with pigments peculiar to them, we can readily understand
how difficult it is to match tooth structure with a substance inorganic in
composition, differing in density, and colored with different pigments.
In discussing this point Dr. C. N. Thompson, in Dental Cosmos,
May, 1907, says: "A study of the normal tooth reveals the fact that its
exact reproduction is impossible, yet to restore tooth-structure in ap-
pearance with porcelain without due consideration for the details of the
make-up of the normal tooth is a mistake, for an examination of a cross
section of the natural tooth reveals the enamel nearly opaque. Compare
this with a cross section of a porcelain tooth, and it is not hard to dis-
cover the reasons for some of our difficulties, as well as to know that
there nnist be method in our efforts if we would secure results.
"Dentin is so nearly opaque that it transmits light but feebly. Its
opacity seems to be due, as much as to anything else, to the condition of

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