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92 THE TECHNICAL PROCEDURES IN FILLING TEETH.

Management of Weak Cavity Walls in Molars and
Bicuspids.
In the lower molars, especially when the contacts are very
broad, the proximate cavities are likely to be deepest toward the
lingual, and to burrow extensively along the lingual dento-
enamel junction. In these cases the lingual wall will be weak at
the mesio- or disto-lingual angle of the tooth, and this not
infrequently extends to the central line of the lingual surface.
In all such cases the removal of the angle, including the lingual
cusp, mesial or distal, is imperative. This should usually be
done by catching the enamel near the margin of the cavity with
the sharp edge of binangle chisel, and with a pull toward the
cavity, split it off. This may be thrown off, chip after chip,
easily, until a point is found at which it is supported by sound
dentin, or strong enough for a filling to be built against it and
restore .the lost contour with safety.
In occlusal cavities in these teeth, the central pit in which
decay begins is much nearer the lingual than the buccal surface,
because of the rounding of the buccal surface toward the
occlusal. For this reason the lingual enamel plate is often
undermined and weakened in its central portion mesio-distally,
even in cavities that are not very much extended in other
directions. In these cases the lingual groove should be cut out
over the crest of the marginal ridge and the marginal ridge
itself removed well toward both the disto- and mesio-lingual
cusps. The gap formed in the lingual wall may be built over
and the form of the tooth restored. In both these cases the
enamel wall remaining should be smoothly cut at right angles to
the axial plane of the tooth.
In the upper molars the buccal wall is more often the
weak wall. This does not so often occur in case of occlusal
cavities, though it is not infrequent. But often in mesial
cavities the mesio-buccal angle is found badly undermined by
decay. If the decay has spread along the dento-enamel junction
or if the decay has reached the enamel and left it unsupported,
the cusp should be cut away at once and be restored with the
filling material. Often in mesial cavities decay will have
extended far to the buccal without undermining the cusp, in
which case an extension of the enamel margin will not meet the