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46 MECHANICAL DENTISTRY AND METALLURGY.

placed on the lower portion which contains the teeth. A
perfect joint should l>e secured between these two sections,
the plaster should be mixed as before, and poured into this
ring while in position, jolting the flask at the same time

Fig. 21.

to induce the plaster to run around the teeth perfectly and
to force the air out. After the flask is well filled, the top
piece should be placed in position and forced home, which
w^ill drive out any surplus plaster; this pressure should be
continued until the plaster has thoroughly set.
Fig. 22.

Where deep undercuts are present, one of two processes
may be adopted. They are well described in the late Dr.
Alonzo Beale's article in the " American System of Den-
tistry," where he says : " First, the plaster in the lower