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MANAGEMENT OF CAVITIES BY CLASSES. 219
cleaning and the mild stimulation of the interproximal gum
tissue to induce a regrowth that will fill the space. This will
often be successful, but often it will fail.
Thermal sensitiveness is met with more frequently in the
management of cavities 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 conditions make the use of oxyphosphate of zinc
or other non-conducting material under these fillings more diffi-
cult than in other teeth. The cavities, even when deep for the
locality, 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 as a non-conductor, 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 protec-
tion. Instruction in the use of the quill as a non-conductor will
be found in technical procedures in filling teeth.
In bicuspids and molars, the form of the occlusal surface,
in its relation to the interproximal 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 embrasures, buccal and
lingual, of the lower teeth. The cusps of the lower teeth are in
position to perform the same service for the upper; that is,
a portion of the occlusal surface of the teeth of the one jaw over-
hangs 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, as has
been related in the text in relation to Figures 101, 102, 103.
Irregularities of the teeth often prevent this form of cleaning
being effeetiyely done. Also the forms of teeth may be such
in particular instances that it is not well done. In many cases
where a more effective cleaning of an interproximal space by the
process of mastication seems desirable, the form of the part of
the occlusal surface formed by the filling may be so modified
that, in the crushing of food, a greater amount of it will be
directed into the embrasure and effect a more thorough cleaning
of the marginal lines of a filling. This may usually be done by