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84 THE TECHNICAL PROCEDURES IN FILLING TEETH.

angle, and its restoration.— In this class of cases the prox-
imate cavity is prepared, with the exception of its mesial angle,
in the same way and with the same instruments as have been
described, except that the anchorages in the labio-gingival and
linguo-gingival angles are made deeper and stronger. That is,
the axial wall is cut deeper into the dentin in the gingival portion
to the lingual and to the labial than in its central area, for the
purpose of sinking these anchorage points deeper into the
substance of the dentin.
The weak incisal angle is cut away to the labial groove, mesial
or distal, as the cavity is to the mesial or distal. This groove,
although not very apparent, is a weak line in the enamel at which
it most often breaks, and it should always be included when the
angle is so weak as to require removal. When this has been
done, cut away the incisal edge of the middle lobe of the
tooth, i. e. , to the next labial groove mesial or distal, with the
corundum stone in the engine or with a small flat jeweler's file,
cutting more from the lingual than the labial. The depth of this
cutting should depend upon the thickness of the cutting edge of
the tooth. If the cutting edge be thick and already somewhat
worn, very slight cutting is sufficient. If unworn and thin, the cut-
ting should be greater. A small inverted cone bur, not more than
I'ij millimeter in diameter, is now caused to enter the dentin in the
proximate cavity, close to the junction of the labial and lingual
enamel plates, and carried, by a series of cuts in which the bur
is drawn out at the incisal edge, along the length of the incisal
edge across the middle lobe, or as far as the incisal edge has been
previously cut. In this cutting with the bur, the labial enamel
plate should be left complete and the cutting done at the expense
of the lingual enamel plate. After the first cut is completed,
forming a groove, in which the bur should always reach fully
into the dentin between the labial and lingual plates, the lingual
plate should be cut away to very nearly or quite the depth of
the cut by the bur. Then the bur should again be passed along
the slight groove left, cutting it deeper, keeping close to the lin-
gual rather than the labial enamel plate, forming a groove in the
dentin between the enamel plates. In making this groove it is
an object to leave as much dentin as possible supporting the
labial enamel plate. The depth of the cutting toward the pulp
of the tooth must be guided by the judgment of the operator,