Page 84 - My FlipBook

80 THE TECHNICAL PROCEDURES IN FILLING TEETH.
dentin close against the dento-enamel junction and afterward
removing the enamel. In excavating and extending cavities in
the proximate 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 at 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 surface de-
cayed. The gingival wall should be perfectly flat mesio-dis-
tally with the axio -gingival line angle sharp. Labio-Iingually it
should be either straight and parallel with the horizontal plane
of the tooth, or curved with its convexity to the incisal.
The incisal angle should next receive attention. It often
happens that decay has extended along the dento-enamel junc-
tion considerably in this direction. The enamel should be
chipped away with hoe 12-5- 12 or 8-3-12 until sound dentin has
been fully reached, and in doing this, very careful attention
should be given to the direction of cleavage with reference to
the final inclination of the finished enamel wall. When the out-
line form has been attained, the incisal angle should be undercut
for retention. Usually this should be done before looking
specially to the retention in other parts of the cavity, for the
strength required of these will depend much upon the strength
of the incisal retention. The incisal retention is made by under-
cutting to the incisal in the form of a groove. The incisal angle
is first well rounded and the dentin cut away to some depth
from the dento-enamel junction directly at right angles to the
axial surface of the tooth, with hoes 8-3-12 and 8-3-23, or
equivalent hatchets, using angle 23 mostly close against the
labial wall. Then hatchet 5-3-28, or if that blade is too long,
hatchet 3-2-28 is used for cutting a groove in the incisal angle,
and extending it along the labio-axial line angle. The instru-
ment is introduced from the labial, its edge directed to the
incisal, and, beginning at the labio-axial line angle a little
removed from the incisal angle, carry its edge toward the incisal
and lingual around the angle, in part by a twist of the instru-
ment. Then it is placed well to the lingual and swept in the
opposite direction, or toward the labial, all the time cutting close
against or slightly into the axial wall. These motions are
repeated until the groove is of sufficient depth. Now, with the