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EXCAVATION OF CAVITIES BY CLASSES. 181

be introduced as before, and drawn toward the lingual with pres-
sure against the gingival wall, cutting the dentin close against
the dento-enarael junction, and the undermined enamel chipped
away with the hoes or hatchets, working from the labial. In
many cases, particularly where the loss of the enamel plate has
been considerable toward the labial, all of this cutting with the
bur can be better done from the labial, keeping the shaft of the
instrimient as nearly as possible in line with the long axis of
the tooth. The linguo-gingival angle should be extended with
the same bur introduced from the labial and its end entered
into the dentin at the dento-enamel junction in the direction to
undermine the portion of enamel most subject to superficial
beginnings of decay. In this position the first cut should gen-
erally be made as near to the lingual enamel plate as is desirable
to cut the cavity, and the bur should be drawn back with pressure
toward the gingival, extending the undermining in that direc-
tion. It is also generally desirable to again introduce the bur,
and, while drawing it toward the labial, make pressure against
the undermined enamel so as to weaken it. It may then be broken
away with hoe 8-3-12 or 8-3-6, catching the edge of the instru-
ment on the surface and using a pulling motion, throwing the
chips into the cavity, or it may be cut away by using a scraping
motion from labial to lingual with hoe 12-5-12, or with hatchets
12-5-12 or 8-3-12. In many cases, the pair of enamel hatchets
10-6-12 will be found very convenient for trimming the gingival
wall and the labio-gingival and linguo-gingival angles, one of
these instruments being used from the lingual direction, the
other from the labial. If still more extension to the gingival is
required, it is readily done by passing the square end of the bur
along the gingival wall, cutting out the dentin close against the
dento-enamel junction and afterward removing the enamel. In
excavating and extending cavities in the proximal surfaces of
the incisors and cuspids, it should be noted particularly that
these surfaces are wedge-shaped or triangular, with the base
of the triangle forming the gingival margin, and that the finished
cavity should have that form, with its labio-gingival and linguo-
gingival angles widely extended toward the angles of the sur-
face decayed. In undermining the enamel with the bur in making
extensions, care should be taken to keep the bur head against
the inner surface of the enamel, and generally in the incisors
the size 8 of the inverted cone bur should be used. It is an object
to keep this cutting very shallow in the first instance and deepen
it later if that is required. The gingival wall should be perfectly