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FILLING BY CLASSES AND MODIFICATIONS. 205

peculiar difficulties are met with: the decay is fre-
quently found two-thirds covered by the gum;, the
muscles of the cheek, thick and rigid, lie close against
the side of the tooth; and, in most cases of this kind,
the view, at best, is but partial. In operating upon
these cavities, an instrument for holding out the cheek

is required.
Third Class.—Anterior proximal cavities of the
molars and bicuspids. This class of cavities in teeth
with short, broad crowns, takes place at their necks;
but in those with long crowns, and with a diameter
less at the neck than at the masticating surface, it
begins at some distance from the neck, toward the
crown surface, or at the first point of contact of the

crowns. In almost all cases of proximal fillings sepa-
ration of the teeth is required; the method and extent
of this will be determined by circumstances. If all
the neighboring teeth stand in contact, it cannot be
easily accomplished by pressure ; in this respect, how-
ever, there will be found a great variety; but, if a
tooth has been extracted in the vicinity, or there are
natural spaces between the others, it can be either in
whole or in part. When, however, the teeth stand
close together, they must in such case be separated

chiefly with the chisel and file. If but one is decayed,
the cutting should be exclusively from that. If two
are alike affected on their proximal surfaces, it should