Page 297 - My FlipBook

decay. We often see these with the margins much dark-
ened from leakage remaining for years in otherwise good
condition—filhngs that would not stand six months in teeth
of highly susceptible young persons. These facts, however,
do not give operators license to do careless manipulation
in these cases, for the fillings come to look badly and any
recurrence of susceptibility is liable to destroy them within
a short time.
Thermal sensitiveness is met with more frequently in
the upper incisors than any other teeth, apparently for the
reason that they are most exposed to cold air. Precautions
against this should be taken wherever possible. The con-
ditions make the use of oxyphosphate of zinc or other non-
conducting material under these fillings more difficult than
in other teeth. The cavities, even when deep for the lo-
cality, are still so broad compared with their depth, and
the requirements for anchorage are so imperative, that there
seems to be no room for the oxyphosphate of zinc. In
most cases when it is demanded the operator may contrive
to overcome the technical difficulties, or he may substitute
a bit of quill, which is just as effective and does not occupy
appreciable space. Careful instruction to patients regarding
the danger of thermal sensitiveness and the means at their
command of avoiding it is, after all, the most effective pro-
tection.
lit bicuspids and molars the form of the occlusal surface,
in its relation to the interproximate space and the embrasures,
is occasionally of great importance to the cleanliness of the
parts. In the normal occlusion the arrangement of the
teeth is such that the cusps of an upper molar or bicuspid
are in position to force the food into and through the em-
brasures, buccal and lingual, of the lower teeth. The cusps
of the lower teeth are in position to perform the same serv-
ice for the upper. That is, a portion of the occlusal surface
of the teeth of the one jaw overhangs the embrasures of
the other, and in every act of chewing the food is forced to
sweep through these embrasures.
This forms the natural method of cleaning them. Ir-
regularities of the teeth often prevent this form of cleaning
being effectively done. Also the form$ of teeth may be such
in particular instances that it is not well done. In many
285