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76 THE TECHNICAL PROCEDURES IN FILLING TEETH.

The difficult point in the preparation of buccal cavities in the
second and third molars occurs when considerable extension of
the cavity to the distal is required. If the dentin is hard and
firm, and the enamel still strong, it is difficult to cut with hand
instruments. This work is effectively done by placing an
inverted cone bur, i\ millimeter in diameter, used in the right-
angle hand-piece, in the distal portion of the cavity, and entering
it in the dentin near the dento-enamel junction, and pushing it
to the distal, and at the same time drawing it to the surface. By
repeating this motion in cut after cut, the required extension may
be made. This slot is now extended by chipping the enamel,
and again undermining with the bur as described for other posi-
tions. This plan of operating is not always available, however.
Often the clamp must be used on the second molars, always on
third molars, and the bow of the clamp is in the way of the
right-angle hand-piece. In this case, if burs are used at all,
they must be used by a different method. An A millimeter
inverted cone bur used in the straight hand-piece, is placed with
its end against the distal wall of the cavity, and its square end
entered in the dentin at the dento-enamel junction. Now by
swaying the hand-piece back and forth, the bur is caused to
enter the dentin to about the depth of its head ; then, by pres-
sure toward the surface while withdrawing the bur, it is made to
cut the enamel from its inner surface. By repeating this motion,
the enamel may be cut through and a slot formed of any desired
extension. The enamel may now readily be pared from the
margins of this with straight chisels, the enamel further under-
mined to the occlusal or to the gingival by cutting out dentin
along the dento-enamel junction with the bur, and removing
more enamel with the chisel. In_ this use of instruments the
axio-gingival and axio-buccal line angles, as made with the bur,
are rounded and not in good condition to receive filling mate-
rial. This is remedied by cutting these to sharp and definite
angles with hoe 6-2-12 or 6-2-23, by a scraping motion!. When
the cavity is broad gingivo-occlusally, the size 8-3 of tlie hoes
may be used.
Buccal cavities often extend so far gingivally that the gingival
wall is beyond the gingival line and the cavo-surface angle is of
cementum instead of enamel. This must always be regarded as
unfortunate, for the reason that the attachment of the gum to