Page 366 - My FlipBook

164 THE TECHNICAL PROCEDURES IX FILLING TEETH.

shows the form — in section — of this portion of the filling. In
this case the extent of tlie softening of the dentin is unusually
well shown in Figure 197. The other two figures show that the
depth of cutting is only sufficient to completely remove the cari-
ous area.
The cavity should be squared up to that depth whenever
this can be done without endangering the pulp of the tooth, which
is clearly permissible in this case. It is also best to have some
portion, or, where the necessary extension is not too great, all
of the dentin walls parallel, as shown in Figures 198, 199. The
enamel walls, however, must be cut in the directions shown,
varying their inclination to suit the direction of the enamel rods
in each particular case. In examining these illustrations, it will
be easily seen that polishing the cavo-surface angle of the enamel
with disks, or in any other way in which the definite cavo-surface
angle shown would be rounded, would result in a poor margin
of the filling material by forming a thin edge. The form of the
surface of the filling, as shown in Figure 199, is so rounded as
to give a small contact with the proximating tooth and to hold
its buccal and lingual margins well away from near approach
to the surface of the proximating tooth in order that the excur-
sions of food may clean them.
In Figure 200, a bicuspid is shown in cross section with
injuries to both mesial and distal surfaces by decay which has
penetrated the dentin but very slightly; yet the injury is as
broad bucco-lingually as in the previous series. In the two fol-
lowing pictures, the position of the recessional lines of the horns
of the pulp are well seen, but with increasing age they have
become shorter and do not penetrate the section. In this the
cavity (Figui'e 201) has been cut as deep as in the previous case
in order to give stability to the filling. The pulp is not especially
endangei'ed by such a cavity, provided the step is not cut too
wide and deep in the teeth of young people. These cavities are
necessarily wide, as will be seen by the injury of the enamel.
Therefore, considerable cutting of soimd tissue in their forma-
tion is a necessity. This should be carefully examined in com-
paring Figure 200 with Figures 201 and 202. In Figures 201,
202, a greater lievel has been given the cavo-surface angle of the
cavity, showing rather an extreme tliiuniug of the filling material
at the buccal portion. In studying Figure 202 one may note
that this extreme thinning could have l)een avoided l)y cutting
just a little farther so as to pass the sharply rounded portion
of the surface. This would necessarily have been at the expense