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SEPARATING TEETH. 93

requirements without the removal of the cusp. In such cases
the enamel wall should be finished in the bucco-lingual plane.
In upper first molars, with large disto-lingual cusps, the
contact point is often toward the lingual, and caries of the distal
surface is therefore likely to begin in such position as to under-
mine the linguo-distal cusp and weaken the lingual wall of the
cavity. Also the disto-lingual groove is usually deep and
sharply sulcate in these teeth, and forms a very weak line in the
enamel. Therefore, unless the lingual enamel wall is found well
supported by dentin, the cusp should be removed and the
enamel cut away to the disto-lingual groove, and the cutting
continued toward the gingival until good strength is found.
In the upper bicuspids, the buccal angles are most likely
to be undermined first because of the contact point being well
toward the buccal, and the first beginning of decay occurring
just to the gingival of it. When the angle, either mesial or
distal, is so undermined that the enamel is unsupported by den-
tin, it should be cut away to the buccal groove. This groove,
though generally so well closed on the buccal surfaces of the
bicuspids as not to be very apparent, is still a weak line in the
enamel, at which it is more than usually liable to break.
In addition to these special points of liability to weak walls,
decay is liable to burrow in any direction, causing weak walls in
other, and occasionally in unusual, positions. Any such are to
be treated upon the general lines that have been indicated. It
should be a rule that when a wall requires cutting away be-
cause it has been weakened by decay, and, in the cutting, a
developmental groove is approached, it should be cut to, or past
the groo\'e.
In mesio-occluso-distal cavities in the upper bicuspids,
from which the pulp has been removed, the whole of the occlusal
enamel plates should be removed to, and slightly over, their
crests to the buccal and lingual, and be restored by filling
material. This will bring the work of mastication entirely
upon the filling material and prevent the weakened cusps from
being split off.
Separating Teeth.
In filling proximate cavities in which the proximate
tooth is present, provision must be made before the fill-
ing is begun for finishing the filling. If the teeth originally