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132 THE TECHNICAl. PKOCEDXJEES IN PILLING TEETH.

and driven under it with a circular motion, following as closely
as possible the hard dentin beneath, the endeavor being to turn
out the whole of the softened mass at a single sweep. Often this
may be done, but frequently it will hang at one side or the other
and require a second, more rarely a third, stroke to completely
remove it. In the case under consideration, the pulp is not
exposed in this process. Any remaining softened material is
now carefully removed by a scraping motion with the same
instrument, and its fellow, and all parts of the cavity cleaned.
Completion of outline fokm. The cavity is now in the
form shown in Figure 133, which, in a young person, must be
regarded as a deep ca\dty. At this point anj^ deep grooves that
would interfere with the perfect finish of the filling should be
cut out to obtain a finishing point, thus completing the outline
form. The grooves in a cavity of this depth need to be cut no
deeper than just a little into the dentin. But no endeavor will
be made to show them in the present cavity.
Eesistance foem and eetention fokm. If it is the judgment
of the operator that the pulp of the tooth will be in no danger
from the proceeding, the pulpal wall should now be squared out
and made flat, as shown in Figure 134, completing the resistance
form and the retention form. An examination of the figure,
however, shows plainly that such a procedure would, under the
conditions, be extremely hazardous. On the lingual, the reces-
sional line of the lingual horn of the pulp as shown, is danger-
ously approached or actually cut, and on the buccal it is also
closely approached, though as this tooth is cut from buccal to
lingual only the extended crest of the pulp is shown on the buccal
side, the horns proper under the point of the cusp being much
longer. For these reasons great care should be taken in squaring
out deep cavities in the teeth of young people, that unnecessary
pulp exposure may be avoided. Therefore, for the completion
of the retention and the resistance form, a ledge should be cut
around the border of the deeper part of the cavity, as shown in
Figure 135. In this procedure the recessional line of the horn
of the pulj) is approached less closely and the point of approach
is farther from the pulp. In doing this, the better plan is to use
the enamel hatchets or the binangle chisels, placing the blade as
shown in Figure 136, using a scraping motion, or, in some cases,
the fissure bur may be used as shown in Figure 137.
Neither is it necessary in a cavity of this depth that even
this ledge be cut all the way around the cavity. Certainly it is
. better to leave parts sloped or rounded away for the protection