Page 124 - My FlipBook

120 THE TECHNICAL PROCEDURES IN FILLING TEETH.

are broken, ' ' just in biting a piece of soft bread crust. ' ' In these
several ways very powerful stress is brought upon fillings, and
cavities must be cut with the view of giving great strength to
the fillings and of maintaining the strength of the teeth.
It is for this reason that cavities are prepared in certain ways.
In occlusal cavities, as they are formed by decay, the pulpal wall
will usually be rounded— will be circular. This would be the
form of the cavity after the removal of the decay. Now, this
gives an opportunity for the rolling of fillings ; the filling is not
as easily placed ; it is more difficult to make a good filling in such
a cavity and the filling is more easily moved by the force of mas-
tication. It might stand for a considerable time in chewing
beefsteak, if it had no bones in it, no bits of gravel, or in chew-
ing game, if there were no shot that would come upon a partic-
ular portion of a filling and cause it to roll. But if the seat is
cut flat, then the filling is supported in such a way that it is not
disposed to roll. Again, a still more important point— when in
a mesio-occluso-distal cavity in a molar or a bicuspid, with the
pulp removed so that the tooth is open through from mesial to
distal, the breadth of the pulp chamber is considerable ; and
perhaps there has also been decay that has further weakened the
dentinal walls. If the filling is finished in the normal form of the
occlusal surface, leaving the inclines of the cusps toward the
central area of the tooth standing, the food catches between
these inclines of the cusps upon the buccal and upon the lingual.
In this case the patient crushes down upon a bread crust ; it
packs between these inclines of the cusps and great force is
brought upon them, and the lingual wall or the buccal wall is
broken away, "just biting a piece of bread crust." For this
reason it is necessary to take great care in the preparation of all
such cavities. Never leave the central incline of a cusp under
such conditions. No matter how good it may be, no matter
how perfect the enamel may be, no matter if it is supported by
dentin immediately beneath, never leave it. It may be strong
toward the occlusal, but more toward the gingival it is weak, and
it is that weak portion that we need to protect. In all of those
cases cut to the crest of the cusp, at least so that when food
is packed between the cusps the stress will come entirely upon
the filling ; let the filling material take this strain instead of the
cusp of the tooth. This will also remove the possibility of