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CELLULOID AS A DENTAL BASE. 63
plexion of the healthy gum tissue as a good porcelain imita-
tion, yet the near approximations of celluloid to the desired
color makes the use of single plain teeth admissible for
permanent dentures, and this is unquestionably its crown-
ing merit, and makes it desirable as a so-called cheap base.
The indiscriminate and almost universal employment of
block or sectional gum teeth in connection with rubber has,
it may be safely affirmed, done more to degrade the pros-
thetic department of dental practice than all other causes
combined. The optional arrangement of each tooth to meet
the requirements of special cases in respect to expression,
articulation, and antagonism is one of the absolute and
indispensable requirements of a perfect artificial denture.
Composition.—Celluloid is composed of pyroxylin,* cam-
phor, oxid of zinc, and vermilion in proportions of about
100 parts of pyroxylin, 40 of camphor, 2 of oxid of zinc,
and .06 of vermilion.
Manner of Preparing Cast.—It is necessary to have a
harder and stronger cast than for rubber work. This is
due to the inferior plasticity of celluloid when exposed to
the heat, and the consequent greater amount of pressure
required to mold it. To secure these important qualities,
the very best hard-setting plaster should be used, or a small
quantity of marble-dust may be mixed with the plaster.
A metal cast, however, will give better results, especially in
case of deep undercuts. In this case block-tin or Babbitt
metal may be used, and can be poured directly into the
plaster impression. The cavity for the vacuum chamber
should, of course, be cut in the impression before the metal
is poured.
* Pyroxylin, commonly known as gun-cotton, is made by macerating
cotton wool—though linen, hemp, etc., are sometimes employed—in a
strong mixture of nitric and sulphuric acids for 15 hours, when it
should be washed thoroughly and dried. The proportions are : cotton-
wool, 1/2 oz. ; nitric acid, 3^ ozs. ; sulphuric acid, 4 ozs.