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EXCAVATION OF CAVITIES BY CLASSES. 85

care being taken not to expose the pulp. But in these cases it
is ahvays better to expose and remo\e the pulp, than to fill with
an anchorage that is manifestly insufficient. The groove is the
principal dependence for the incisal anchorage. This should be
squared out with a fissure bur and its walls made parallel. No
undercuts or pits are needed. A little broadening and rounding
away where it joins the proximate cavity will make this connec-
tion stronger. In the incisal enamel walls formed in making
this incisal step, both labial and lingual, the enamel rods incline
toward the incisal, and these walls should take that form rather
than be cut at right angles with the long axis of the tooth, and
then the cavo-surface angle must be slightly beveled ip order to
give it greater strength.
Teeth with thin, cutting edges are very difficult of manage-
ment in making incisal steps for the restoration of a lost or weak
angle, because the gold built on them is too thin to have suffi-
cient strength. In many of these cases, the incisal edge of all
of the incisors, or only the centrals, may be ground away in
imitation of normal wear, and the incisal edge thickened without
injury to the appearance. In doing this it is well to remember
that in very thin teeth the horn of the incisal pulp is likely to be
long and slender, and the danger of exposing them in cutting
the step is increased.
In cases where there has been such wear of the incisal edges
of the teeth that the dentin is exposed, the step should include
all of the exposed dentin. In this case very little cutting from
the lingual enamel plate will be needed, and generally none from
the labial. In the management of this class of cases it should
be remembered that in such large cavities the bulk of gold in
close proximity to the pulp is liable, through its conductivity of
thermal changes, to set up irritation that will destroy its vitality.
In cases in which there seems to be imminent danger of this, it
is better to remove the pulp at once. It is also better to remove
the pulp at once than to run serious risk of losing the filling
from insufficient anchorage in the effort to save the pulp alive.
Class 5.— Preparation of cavities in the proximate
surfaces of bicuspids and molars.— The preparation of
proximate cavities in the bicuspids and molars, if estimated by
the comparative number of failures in filling teeth, must be
regarded as the most difficult of filling operations. Therefore,