Page 153 - My FlipBook

BICUSPIDS.
139
where the cavity is enlarged. Early in my career it was my pride to
make these thread-like fillings in bicuspids, and in molars as well,
all the of the sulci. But
following windings it is an error, for it
leaves the sulcus practically existent, and in it food will lodge, so that
caries will probably recur, the gold dropping out. Fig. 153 shows
an enlargement of the cavity, the filling now extending up and filling
the sulcus, so that we have left the cusps sufficiently well marked for
masticatory uses, whilst we have obliterated the dangerous lodging-
place for food and other material. In order to be sure to have suffi-
cient gold in this sulcus, it is well to overbuild, so that after doing so
the gold must be cut away to permit normal occlusion. By this means
we have as much gold as will be tolerated, and the tooth is safer for
it. This rule holds with all crown cavities. The of the
preparation
cavity to make it retentive is simple. With a reversed-cone bur dip
into the cavity at one end, and cut until it emerges at the other.
This will form a slight undercut, which may be deepened by following

FIG. 154. FIG. 155. FIG. 156.

the same course with a wheel bur. Before a fine hatchet
filling,
excavator should be introduced at each end to make sure that all
caries is removed. The which will often be reached before this
depth
is done will astonish those whose habit has been to neglect bicuspids
till the cavities become visible to the eye. For these cavities gold is
the only proper material, and it can be placed so rapidly and readily
that there is no excuse for the use of amalgam.
no to-
Leaving Fig. 153, special directions are needed relating
simple crown cavities till we come to such as is shown in Fig. 154, a
sectional view of which is given in Fig. 155. The entrance to this is
along the full extent of the sulcus. If prepared with engine- burs
alone, it would be more than probable that much caries would be left
unremoved. Generally speaking, it should be remembered that the
dentine, as a whole, assumes about the same form as the entire tooth.
From this it follows that as the enamel over the cusps forms cones,
tooth we would find cones of
underlying this enamel in a healthy
dentine. Caries finds its way through the weakest part of the
enamel, which is along the sulcus, but once it reaches the dentine,
further loss of the enamel is rather by a destruction of the dentine,