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EXCAVATION OF CAVITIES BY CLASSES. 183
cavities, on account of the difficulty of access and the danger
of undermining the enamel.
With the 8-3-23 hoe, or, if the cavity is small, the 6-2-23,
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 hoe 6-2-23 near
the incisal angle and hoe 8-3-12 or 6-2-12 for the remainder.
This should be completed to, and into, the axio-linguo-gingival
angle. Undercutting at the axio-linguo-gingival angle for reten-
if
tion will depend upon the strength of the incisal anchorage ;
this be good, but slight retentive form — just sufficient to serve
in starting the filling — is all that is needed in the gingival posi-
tion. The axio-labio-gingival angle, which has been left suffi-
ciently definite by the bur, is now slightly grooved for a short
distance toward the incisal, completing the retentive form by
squaring out with the hoe 6-2-12 or hatchet 6-2-23.
Convenience form. Convenience points should be cut in
the labio-axio-gingival and linguo-axio-gingival angles, in the
same way and in the same form as described for bicuspid and
molar proximal cavities, using an inverted cone bur 6 or 8. Fig-
ures 170-173, inclusive, and in cross section. Figure 256.
Removal op remaining carious dentin. Any decay now
remaining in the deeper parts of the central portion of the cavity
is removed with spoons 10-6-12. If the cavity is large, spoons
15-8-12 may sometimes be better.
Finish of enamel wall. The enamel walls are planed
smooth in every part and any errors in inclination corrected.
If the operator has noted carefully the direction of the cleavage
of the enamel at all points while chipping it away, he will be at
no loss in determining the correct inclination of the enamel walls
at the different points, remembering that this shall follow closely
the cleavage lines. This is done with hoes 12-5-6 and 12-5-12,
or with the chisels, except some portions of the gingival enamel
wall and a short reach upon the lingual wall where it joins the
incisal angle. The movement of the instrument 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