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226 CLASSIFICATION OF DECAYED CAVITIES.

and difficulty of manipulation are increased the farther
back in the mouth the decay is situated. The modi-
fications of this class are the same as those of the
third class of cavities, and, except the second modifi-

cation are susceptible of the same methods of filling.
Special Cases.—The first case that we shall con-
sider here, consists in a complication of proximal
decay with decay on the buccal or palatal portion of
the tooth, thus undercutting one of the crown angles.
Sometimes these decays are on both sides, in the
form of transverse grooves, meeting at the corner of
the tooth. In such cases, if the pendent crown
angle of the tooth is firm and strong, the cavities
may be formed in the proper manner, and filled
without interfering with the masticating portion of

the tooth at all ; but, if the pendent portion is friable,
it should be cut away, and the corner built up with
gold. The method of forming the part to be filled
will depend on the extent of the decay. When this
is large, a greater number of retaining-points will be
required than when it is small ; and these should be
located at such parts as will make them most tena-
cious of the gold, and least subversive of the strength
of the tooth. The filling may be built up so as to
restore the original form of the tooth, thus presenting
three surfaces, the proximal, the buccal or palatal,

and the masticatory ; or, it may be made with a single