Page 157 - My FlipBook

GIVING THE CAVITY FORM 1 25

2. In Large Cavities with Soft Decay.—Use spoon excava-

tors, first flaking up the decay around the margins and then
peeling it off in layers, avoiding pressure.
3. Hard, Dark-brown and Black Decay.—Use spoon excava-

tors. The round bur may also be utilized, but never in close
proximity to the pulp.
3. Give the Cavity Form. — (a) Convenience Form. By
convenience form is meant the shaping of the cavity in
such a manner that it may be most conveniently seen and
approached with instruments. If the cavity be of difficult
access, owing to its location, the slight extension of a margin

is frequently admissible for this purpose. The extension of
the labial margins of proximal cavities for convenience is not
admissible, as this would result in too great a display of filling

material. In every instance where it becomes necessary to
extend margins for convenience form, the extension is made
at the expense of the lingual margin, the filling being packed
in that case largely from the lingual side. The display of exten-
sive gold operations in the front teeth is an offence against the

esthetic sensibilities of all refined individuals, and a sure sign of
a depraved taste on the part of both patient and operator.
For convenience in starting gold, the point angles to be
described under '^retention form" are frequently deepened,

or made more acute, this procedure, then, being really a
convenience form (see Fig. i68).
(b) Resistance Form.—The §o shaping of the walls of
the cavity that they may be best enabled to withstand the
stress brought to bear on the filling during the act of mastica-

tion. In mechanics, the general form of a cavity which is
to receive an inlay is the box or simple mortise. This general
idea is applied in preparing cavities in teeth. In this form,
all of the walls of the mortise are on plain or straight lines,
joining each other at definite line and point angles.