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EXCAVATION OF CAVITIES BY CLASSES. 197

tooth, and there should be no undercutting of the incisal edge
as described above. Instead of this, the pulp chamber should be
widely opened toward the incisal fully to the point of its horns,
or, in most cases, extended farther to the incisal, and the cutting
finished so that the incisal wall is at right angles to the long axis
of the tooth, and the root canal opened for a space, as shown
in Figure 269. Indeed, this figure would give very nearly a cor-
rect impression of the preparation if the incisal angle retained
in that case was cut away. A little more extension of the cutting
of the pulp chamber toward the incisal would be better. Gener-
ally the dentin should be cut away well to the lingual so as to
give good access to this portion of the cavity for packing gold
into this angle, and this should be made the retention to sustain
the angle built on. The anchorage at the gingival should be cut
similarly to that described for the preparation with the pulp
alive, with the additional retention in the pulp chamber. This
gives a more secure anchorage than either the undercutting of
the incisal edge or the incisal step, and a better appearance than
the incisal step.
In these cases the more rapid wear of the tooth than of the
gold filling gives a similar liability to excessive stress on the
filling, tending to force it out, as described in eases of anchorage
by undercutting the incisal edge; and the occasional trimming
down of the filling should have similar attention.
Some cases will be found in which the extension of decay
in the dentin has been so great as to render even this anchorage
insecure, and yet, it may seem desirable to make a restoration
with gold. This may still be made secure by placing a strong
irido-platinum post in the root canal for additional strength
of anchorage. The preparation of the root canal should be simi-
lar to that illustrated in Figure 269, but the slope of the widened
portion of the wall toward the mesial (or distal) should be such
as will bring the end of the post that will project into the fin-
ished filling in the most favorable position. The cut into the
canal may also be deeper. The post should be cut and fitted
to this slope of the pulp canal as made in this preparation, seeing
to it carefully that there is sufficient room by the side of it for
the insertion of gold forcing the post solidly against the wall
prepared for it. It is well in preparing the wall, or bed, for the
post in the dentin, to use a fissure bur as near the exact size of
the post as possible. "When it has been fitted to its position,
choose a slender plugger that will easily pass to the end of the
post. While holding the post securely with a second instrument