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H2 METHODS OF FILLING TEETH.

test will be at the gingiva. Here it will be seen at once that but little
exists between the teeth. Whilst the restoration be made
space may
the of the
without separation, polishing approximal surface of the
must necessarily produce a permanent space. This can be
filling
avoided only by spreading the teeth, overbuilding the gold, and pol-
ishing so that when completed the original width and shape of the
tooth is restored.
118 we see a central incisor from which the corner has been
In Fig.
lost. Is any special direction needed for the proper preparation of
In of the cavities illustrated
the cavity? speaking by Figs. 113, 114,
116, and 117, I have said that the groove at the labial or at the palatal
border was less for retentive purpose than for facilitating the operation
In I advised that the
of filling. Fig. 115, however, upper retaining
extensions should terminate toward the incisive edge in grooves which
extend about half-way. This was in view of the possible future loss
of the corner. Thus it is seen that though I do not depend upon lateral
grooves in the presence of the natural corner, in its absence I do, more
or less. Thus in such a cavity as shown in Fig. 118, after arranging
the upper portion as described in Fig. 115, I should continue the
grooves toward the incisive region, lessening them in depth and extent
until they meet about at d. Some dentists make a deep dip inward,
that is to say toward the pulp, at this point, endeavoring to obtain a
The result is that because of the narrowness of
retaining-pit. usually
the tooth in this region, this undercutting leaves the labial plate of
enamel so thin that the gold is seen through it when the filling is com-
Worse than this, the enamel often
pleted. appears cracked, and I
have seen not a few cases where it has chipped out afterward. Let
us consider for a moment what is gained by an extension such as is
indicated by the dotted line e.
The object of any undercutting is of course to prevent the filling
from being forced out of the cavity. Supposing, then, that a strain
out that is to
tends to press the filling laterally, say toward the adja-
cent tooth, will this incisive undercut prevent this? If the sur-
rounding wall be quite strong it might have such a tendency, but the
real resistance would be found in the palatal and labial grooves, which,
extending the full length of the filling , thoroughly protect it. The fill-
be movable toward the gingival wall, for there we
ing will scarcely
have the greatest resistance and the best arrangement for retention.
move downward toward the incisive If so, this
Can the filling edge ?
undercut might serve. But there is nothing but gravitation to urge
such a movement, and that is so slight that the upper extensions are
a million times more than adequate. Consequently we find that no-
thing is gained by the procedure. Is anything lost ? All undercutting
to the retention of a is mischievous. In
which* is unnecessary filling