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56 MECHANICAL DENTISTRY AND METALLURGY. —

flask tends also to keep the plate in shape until its form
becomes permanent; whereas a quickly cooled and imme-
diately finished denture may surprise the dentist by unac-
countably changing shape, or by showing cracks in the
gum section ; in fact, either of these serious defects may
result after the denture has been hastily finished and the
patient dismissed only to return in a few days with dissatis-
faction, because of the meantime occurrence of the defects.
It is worth while to fake time to save time.
The Finishing Process,—When the plate is removed from
the flask, all adhering plaster should be carefully detached
with a pointed knife, after which it is thoroughly cleansed
by the use of a stiff brush and water. The rubber should
then be reduced to the desired thickness and shape by the
use of scrapers, files, lathe-burrs, and chisels. Fig. 28
represents some of the standard forms of these tools.
After this is obtained and the surface of the rubber is
rendered somewhat smooth and uniform, fine sandpaper is
employed to remove the marks and scratches left by the
use of the tools. The final finish is then given by first
using finely pulverized pumice-stone, on felt or cork wheels
or cones, driven by a lathe; this will give a smooth surface.
The case should then be washed, when the polish is given
by prepared chalk or whitting, applied upon a cotton or
soft brush wheel. In using the polishing materials they
should be kept freely saturated with cold water throughout
the operation. The denture should then be thoroughly
washed, when it will be ready for insertion in the mouth.
Pink Rubber Gum.—In the construction of a denture,
where *' plain " teeth are used and where the artificial gum
is to be made of pink rubber, the best practice is as follows,
which we c[uote from the late Dr. Alonzo Beal's teaching :
After vulcanization, enough of the rubber surface repre-
senting the gum should be removed from around and be-