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FORMING CAVITIES. 143

at any given point on the enamel, after the decay is
removed, it should remain for the preservation of the

enamel ; it should not he cut through either by pits
or by grooves, much less should any considerable por-
tion be removed.
There are cases occasionally in which the dentine

is wholly decayed, and its removal lays bare the
enamel ; when such a case occurs, the enamel should
be retained as perfect as possible, and no attempt
made to form pits or grooves in it. The reason for
this is found in the friability of the enamel.
It may be. regarded as an axiom, that where it is
necessary to cut the healthy dentine to give proper

form to a cavity, it should be done at that part of
the cavity, where the tooth will suffer least from the
loss. The precise point and amount of cutting will
be determined by the form and size of the cavity, and
the amount of solid dentine remaining after the decay
is removed.
In small cavities, where there is sufficient material
to work upon, the object is to give the cavity a

regular form, and make the retaining points where it
is most convenient.

In large cavities, where one side of the tooth is
weak, places must be selected for making the retain-
ing points, that will not affect the weak point. Fre-
quently, in proximal decays of the anterior teeth, the