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220 CLASSIFICATION OF DECAYED CAVITIES.

the force applied in the process of consolidation, as
gutta percha or plaster of Paris. If the former is
employed, it should be softened by warming, moulded
upon the tooth, and then permitted to harden. The
hardening may be facilitated by throwing cold water
on it from a syringe. It is then to be trimmed even

with the border of the cavity, so as to admit the fill-
ing. If plaster of Paris is used, it should be the best
article. Yet gutta percha is to be preferred. But a
better protection than either may be made of cheo-
plastic metal, taking an impression of the tooth, and
from that moulding the shield ; and this material is
always to be recommended in extreme cases. In
these fillings, when the enamel is clear and translucent,
the gold will be visible through it. To obviate this

difficulty, some appropriate substance may be placed
between the outer wall and the gold—some substance
that will restore the natural color of the tooth. Quill,
horn, paper, and asbestos have each been employed
for this purpose. Horn is, perhaps, the best material,
as it can generally be selected of a suitable color. A
thin lamina of this may be obtained by pounding a
piece of the horn for a few moments, till a layer is
detached; which may then be dressed down to the
proper size, softened in warm water, and placed in
the cavity next to the outer wall, yet so as not to
extend quite to the border. The presence of this