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EXCAVATION OF CAVITIES BY CLASSES. 189

injured. Wlien this cut is made before the removal of the pulp
from the canal, the pulp prevents the clogging of the smaller
parts with cuttings from the bur. This cutting is made to
straighten the path for the broach in the removal of the deeper
parts of the pulp from the canal and facilitates the filling of the
canal. The canal should be filled with gutta-percha only to the
beginning of the widened canal. When tlie tooth is ready for a
gold filling, the whole of this internal portion may be solidly
filled with cohesive gold. This will give an anchorage that may
be depended upon to support the overhanging incisal angle and
give it strength.
In case the incisal angle should be regarded as too weak to
stand, it may be cut away. A strong irido-platinum post may
be set in against the mesial wall of the cut made in widening
the pulp chamber, cut to the right length and made tight by driv-
ing gold in about it. The first of this gold should be non-cohesive.
But when the post has been made fast with this, cohesive gold
should be used. In this way an angle may be built that will be
sufficiently strong without a step in the incisal portion of the
tooth.
General observations on the preparation of proximal cav-
ities IN the incisors and cuspids. In all cases the enamel mar-
gins should be cut sufficiently around the curves of the surface
toward the labial and lingual, that the margin will be well away
from the contact of the two teeth when the filling has been
finished. This does not mean that the cavity wall must be cut
over onto the labial surface so as to be especially conspicuous.
But it should be cut out into the embrasure where the surface at
the angle of the tooth begins to round away from close proximity
to the surface of the proximating tooth, so that the margin of
the filling may be kept clean. This should be carried fully to,
or under, the free border of the gum and then curved sharply to
form the gingival wall. The gingival wall must be placed far
enough to the gingival to make this possible and should be con-
vex in the incisal direction or arched from labial to lingual, if
necessary, as shown in Figure 257. At the gingival, the mar-
gin should be well covered by the gum septum when this is in its
normal position. The gum septum should be carefully preserved
from injury in all parts of the operation, for upon the health
of this tissue depends largely the health and good appearance
of the tooth. The habit of tying ligatures on the incisor teeth
and forcing them strongly to the gingival, can not be too strongly
condemned. In doing so, the soft tissues are cut away from their