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EXCAVATION OF CAVITIES BY CLASSES. i t

the tooth has been injured and because of the increased difficulty
of making the filling. The injury to the attachment of the
gums is necessarily permanent, and yet, if the operation is well
and smoothly made, a fair degree of health of the gum margin
is generally maintained. In these cases it is best to remove the
attached membrane from the cementum sufficiently to allow
room for the clamp and provide additional room to readily see
the cavity margin after the filling is in place, in order that the
filling may be, finished definitely and smoothly to the tooth sur-
face. It is better to destroy the attachment a little further and
secure a smooth perfect finish, than to risk imperfect work at so
important a point.
Class 3.— Cavities in the proximate surfaces of the
incisors and cuspids, which do not involve the removal
and restoration of the mesial or distal angle.— In the
excavation of this class of cavities a much greater range of forms
of cutting instruments may be used effectively than in other
classes, and a greater variation of method of instrumentation is
consistent with rapid and thorough operating. In the work the
ordinaries are used almost exclusively, the bur being employed
only to accomplish a few special purposes. The cavities are all
smooth-surface cavities and the rules of extension for prevention
are applied in their preparation.
Case I.— The left upper central incisor has a decay in its
mesial surface, just to the gingival of its contact point. Appa-
rently it is small, but a curved exploring instrument introduced
from the labial or from the lingual enters through the enamel.
Procedure.— The first procedure is to free all of the incisor
teeth of debris or micro-organisms and gummy material, par-
ticularly about their gingival portion, and apply the rubber dam.
Dry the teeth and apply the- Perry separator and get sufficient
separation to pass a thin polishing tape between the teeth.
Then, with the 8-3-6 hoe used as a chisel, begin near the labial
margin of the cavity to break down the overhanging enamel,
chipping from the surface into the cavity. This should generally
be done by hand pressure, being careful to place the edge of the
cutting instrument very near the margin in each instance and
split off the enamel in little flakes. In this cutting the third
finger should be very securely rested upon the adjacent teeth
and the motions of the instrument so closely controlled that its