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6 METHODS OF FILLING TEETH.

tissue is being operated upon. If after the removal of decay the
cavity naturally assumes this shape, it is permissible to fill it without
further alteration ; but whenever possible, it should be formed as in
Fig. 3, which, while equally retentive, leaves a greater amount of
dentine between the gold and the pulp. This method should be
adopted in all so-called "saucer-shaped" cavities (Fig. 4), which may
be deepened by grooving at a, a, the point b being left untouched.
In Fig. 5 we observe a form, which, though correct in its relation to
the pulp, and formed upon mechanical principles, is nevertheless unskill-
made. It would be for one to make such deep under-
fully improper
and where have been caries the
cuts intentionally, they produced by
orifice must be enlarged by chipping away the weak enamel, as indi-
cated by the dotted lines a, a. have failed through the
Many fillings
well-meant but unwise efforts of the operator to give great retentive
strength to his cavity by deep undercuts. Undercutting to a slight
extent is imperative, but beyond that all deepening is a source of weak-
ness. In in a formed as in Fig. 5, the force used
placing gold cavity
FIG. 5. FIG. 6

I f e

to pack the gold into the deep undercuts, whether with hand-pressure
or the mallet, would tend to strain the wall outward, probably result-
ing in a crack, which, escaping the eye of the dentist, would yet ulti-
mately result in the loss of a piece of enamel along the edge of the
This would be more to occur the
cavity. likely along palatal border,
6, because the palatal undercut would be more accessible during
the filling-operation. Thus an imperfection would be produced at a
point out of sight, and the patient would be unconscious of the mis-
hap until caries had supervened. Then we should hear our dentist
say, "My filling is all right, but your tooth has decayed around it."
The deep undercut at the labial aspect c would probably be not fully
filled because of its inaccessibility, especially where the separation was
but 6 makes this plain. The gold does not reach
slight. Fig. quite
the wall at a. It has been well proved that the most expert dentist
cannot fill a tooth with gold so tightly that an aniline solution cannot
stain the walls of a cavity. Therefore it is readily seen that as soon
as the fluids of the mouth pass the slight barrier at b and reach such a
space as that shown at . we have a most favorable condition for the
recurrence of caries ; which explains the occurrence of the mysterious