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METHODS OF FILLING TEETH.
io8
of the last, and there are
Fig. 114 is the direct opposite yet points
which some do not note. The approximal cavity here
of similarity
encroaches upon the palatal surface. Where the loss of the labial
of the
surface simplifies the operation, the absence of a part palatal
There is a curious fact to be observed
surface greatly complicates it.
here. Whereas many look upon the cavity shown in Fig. 1 13 as one
some are much disturbed by the cavity
which easily retains a filling,
is safe, because a will not
in Fig. 114. The first, apparently, filling
toward the labial aspect, whilst, per contra, gravitation may
jump up
down and out at the
have a tendency to cause a filling to drop palatal
opening. Those who argue thus are deceived into this error of judg-
ment by the fact that when the cavity is seen the patient is in the recum-
which makes the labial side of a tooth and the
bent position, ^lp,
side down. It should be remembered that when the patient is
palatal
erect there is neither up nor down to this condition, and
standing
will retain a in a
therefore whatever arrangement filling labio-approx-
FIG. 113. FIG. 114. FIG. 115.

imal cavity will serve equally well in a palato-approximal one. Conse-
quently the formation of the two classes of cavity are similar, though
not identical. We have the same extensions at a and 6, the same
groove at c, the same concavity at d, and the same absence of under-
cutting at e. But we find that c and e have changed places in the two
illustrations. In the previous one c represented the palatal part,
whereas now it becomes the labial. A similar change occurs in placing
the gold. The first pellet is to be placed in the labio-gingival exten-
sion, and, after the palato-gingival retainer has been connected with
it, we then follow along the groove, which here is at the labial instead
of the palatal border, so that we practically reverse the order of pro-
cedure. Yet really we do not, for now we are using a mirror, and in
the reflection this labial groove, though actually nearer to us, appears
to be farthest from us, and in this instance we must fill by appearances.
If the operator is not skilled enough to use the mirror, he then tips
the chair back and lowers his head, so that in that position the labial
groove becomes really the farthest point from his vision.
In Fig. 115 we see a cavity which is practically a combination of the
last two. We have an
presented approximal cavity in a central incisor