Page 85 - My FlipBook

EXCAVATION OF CAVITIES BY CLASSES. 81
8-3-23 hoe, or if the cavity is small the 6-2-23 hoe, introduced
from the labial and with its edge turned to the labial or the axial
wall, the axio-labial line angle is made sharp and definite along
the length of it well to the gingival, using a scraping motion
from the gingival toward the incisal. Often the 6-2-23 hatchet
will do this as well, using it with a back and forth scraping
motion, holding the shaft of the instrument at right angles to the
long axis of the tooth. The axio-lingual line angle is now made
definite throughout its length, using hoes 8-3-12 or 6-2-12 or
the 6-2-23 near the incisal angle. This should be completed to,
and into the axio-linguo-gingival angle. Undercutting at the
axio-linguo-gingival angle for retention will depend upon the
strength of the incisal anchorage ; if this be good, but slight
retentive form, just sufficient to serve in starting the filling, is
all that is needed in this position. The ' axio-labio-gingival
angle, which has been left sufficiently definite by the bur, is now
slightly grooved for a short distance toward the incisal, complet-
ing the retentive form by squaring out with hoe 6-2-12 or
hatchet 6-2-23. Any decay now remaining in the deeper parts
of the central portion of the cavity is removed with spoons
10-6-12. Or if the cavity is large, the spoons 15-8-12 may
sometimes be better. The cavity is now ready for the finish of
the enamel walls and the cavo-surface angles.
The enamel wall is planed smooth in every part and its
inclination corrected. If the operator has noted carefully the
direction of the cleavage of the enamel at all points while chip-
ping it away, he will be at no loss as to the correct inclination at
the different points, he remembering that this shall follow closely
the cleavage lines.
This is done in all parts with the chisels, except some por-
tions of the gingival enamel wall and a short reach upon the
lingual wall where it joins the incisal angle. The movement of
the chisel should be along the length of the enamel wall, cutting
very lightly. It must be very sharp to be effective. At the
labio-gingival and linguo-gingival angles the outline should form
short curves, no matter how sharp the angles of the dentin
walls; sometimes it is difficult to plane the whole length of the
gingival wall smoothly with the chisel, especially where it joins
the curve at the linguo-gingival angle. Here hatchet 12-5-6 or
1 2-5- 1 2 answers better; or occasionally one of the hoes. These
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