Page 88 - My FlipBook

72 THE TREATMENT OF TEETH
which it will facilitate the carrying of the gold over
the margins without damaging them. The greater
the bevel, the more difiicult it is to finish to a fine
•clean edge, and the labial margins of front teeth and
the margins of labial cavities in general, admit of
very little bevelling if the finest blending of tooth-
structure and gold is necessary for appearance' sake.
The thickness of the gold over the bevelled margin
must also be considered, for it is quite possible to
bevel to such an extent that a thin layer of gold over
a much-bevelled margin becomes lifted up in time
through the stress of mastication, and an imperfect
joint results. The main thing to consider is to
produce a margin that will not be chipped or
broken by the force used in condensing the gold
over it, and which is sufficiently cleanly cut to admit
of a fine margin when the gold is finished. Having
removed decay and trimmed the margins, proceed
to shape the cavity for retainage. (The final finish-
ing or smoothing of the margins should be done just
before the insertion of the gold.)
Retainage.—The retainage of a filling depends on
the shaping of the interior of the cavity, and in this
connection there are several points that demand
careful consideration. The retainage should be
made in such a manner that the tooth is weakened
AS little as possible ; the pulp is not unduly ap-