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EXCAVATION OP CAVITIES BY CLASSES. 127

develop considerable heat. Often much unnecessary pain is pro-
duced, and, occasionally, serious injury done to the pulp of the
tooth by the heat deveh)ped by rapidly rotating burs.
To those who have learned to handle cutting instruments
well and have developed good finger power, the squaring up of
the enamel wall is best done with chisels and enamel hatchets.
Also the flattening of the pulpal wall will be better and more
accurately done with hoe 12-5-6 or 12-5-12, used with a scraping
motion. Often the binangle chisels may be used to advantage in
this work, especially in cavities of considerable area.
Parallel walls and a flat pulpal wall as a seat give perfect
anchorage. It will happen in very broad cavities that decay will
approach the marginal ridges so closely at some points that
insufficient dentin will be left to give sufficient strength to some
parts of the walls. Then the dentin wall itself, if the condition
as to caries will allow, must be sloped in such a way as to give
greater strength, i. e., flared outward in that particular part so
that in the deeper part the dentin will be stronger. T^Hiile it is
desirable that all parts of the dentin walls be parallel, this must
not be regarded as a necessity that shall lead to cutting them too
thin. Any two walls parallel with each other will generally give
sufficient anchorage. No undercuts are required.
Convenience eokm. Generally such cavities need no con-
venience points for starting fillings, but when large and the
operator feels that slight convenience points will aid him, there
is no special objection to their use. They should be placed in
the walls in the distal portion of the cavity and not in the pulpal
wall.
Removal of eemaining carious dentin. The deeper portion
should be freed of any remaining softened material with the spoon
excavators. In no case should any decayed and softened mate-
rial be left. It is better to expose the pulp of the tooth than to
leave it covered only with softened dentin.
Finish of enamel wall. Wlien the walls of the cavity have
been squared up and the angles of the pulpal wall with the sur-
rounding walls made sharp and definite, and all carious material
removed, the enamel walls may he planed to form and made
smooth in every part. Unless the enamel walls approach very
close to the marginal ridges, they may be in the same plane with
the dentin walls, or parallel to the long axis of the tooth. But
if they do approach closely to the marginal ridges, the enamel
rods will be inclined toward the ridges, and the enamel wall must
be similarly inclined to be in correct form. This may always be