Page 153 - My FlipBook

FORMING CAVITIES. 149

a sharp angle, and hence the necessity of obliterating
such when they occur. This may be done either

with a small delicate cutting instrument, or with a
small bur drill. It is an operation requiring great
care and delicate manipulation, at least so far as the
anterior teeth are concerned. When a sharp angle
occurs in the proximal cavities of the front teeth,
it is usually near the cutting edge of the tooth,
just at the union of the labial and palatal plates of
enamel. A small chisel-shaped instrument is very

good for cutting out such angles : indeed, in fissures
of crown cavities of molars, where the decay extends
backward, the straight, chisel-shaped instrument is
just adapted to this purpose ; but when there is an
anterior extension, the instrument should be curved
to almost a right angle, and forced down by pressure
of the thumb of the left hand. Some good operators
recommend a slight reaming at the orifice of all cavi-
ties, where it can be accomplished. The object of
this is twofold : to remove the sharp angle at the ori-

fice of the cavity, as it is liable to be roughened in
putting in the filling ; and to give a better margin to
the filling. In making this bevel, the bur, if one is
used, should be but little larger than the orifice of the
cavity. The cutting should be but slight — just suf-
ficient to remove the sharp corners ; much cutting here

would give too thin and yielding an edge to the filling.