Page 83 - My FlipBook

EXCAVATION OF CAVITIES BY CLASSES. 79

wall. The cavity must now be extended so that it will include
all of these superficial injuries. To do this, place a small inverted
cone bur (I'V or lu millimeter) in the labio-gingival angle, intro-
ducing it from the lingual in most cavities, and enter the dentin
close to the enamel junction, and swaying the hand-piece as much
as the position will allow, undermine the enamel in the direction
of the line of superficial injury, sinking it at first about the depth
of the bur head. Then very slowly withdraw the bur, pressing
it toward the labial and incisal, thus widening the cut in this
direction. Now, with the hoe 12-5-6 or 8-3-6, the undermined
enamel may be chipped away. These cuttings may be repeated
until the extension in this particular direction seems sufficient.
If now it is desirable to extend the cavity to the gingival, the
same bur may be introduced as before, and drawn toward the
lingual with pressure against the gingival wall, cutting the den-
tin close against the dento-enamel junction, and the undermined
enamel chipped away with the hoes or hatchets, working from
the labial. In many cases all of this cutting with the bur can
better be done from the labial, keeping the shaft of the instru-
ment as nearly as possible in line with the central axis of the
tooth. After some cutting in this way, the attention should be
turned to the linguo-gingival angle. To extend this the same
bur should be introduced from the labial and its end entered into
the dentin at the dento-enamel junction in the direction to under-
mine the line of injured enamel. In this position the first cut
should generally 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 direction. It is also generally desirable in this position to
again introduce the bur, and while drawing it toward the labial
make pressure against the undermined enamel, so as to weaken
it. Then it may be broken away with hoe 8-3-12, catching the
edge of the instrument 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 83-12 if the first is too broad to enter the cavity well. Also
this is well done with hatchets 12-5- 12, or 8-3-12, or enamel
hatchet 10-6- 12 working 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