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331
G UTTA-PERCHA .
admit of permanent gutta-percha fillings. Of course due attention
Fig. 301. Fig. 302. Fig. 308. Fig. 304. Fig. 305.

rervicD-labiiil iiiul liure.-il cavities.

must be given to the retention of the fillings by enlarging the interior
walls of the cavities when they have not already such expansions.
After suitably preparing the cavity, it should be made as dry as possible
and so kept. The problem of conveniently and properly softening
pellets of gutta-percha has been solved by the production of the ther-
moscopic heater shown in Fig. 306, which approximates the exact size

Fig. 30tj.

Thermoscopic heater for gutta-percha.

of the device. The heater is in this instance made of steatite, because
of its heat-retaining property and the desirable physical qualities of its
surface. The handle is of wood, at the opposite end from which, in
the centre of the circular recess, is a small disk (.4) of metal, fusible at
about 212'^ F. On the heater near the metal a suitable number of
gutta-percha pellets, as 1, 1, are placed, and the heater held over the
flame of the annealing lamp or burner (as in the illustration) until the
fusible metal melts, M'heii the heater is placed on a piece of cardboard
(or an empty foil-book), and the gutta-percha will be found to be })rop-
erly softened. The steatite plaque retains the heat long enough for an
ordinary operation, but if the metal meantime loses its fluidity and so