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FILLING BY CLASSES AND MODIFICATIONS. 201

nealed foil, it is better to begin at the bottom of the
cavity and build up to the orifice, first completing the
fissure, as we have already described, and afterward

the main cavity.
Id Mod.—Two cavities on the same crown in close
proximity. The thickness of the portion of tooth in-
tervening between two cavities on the grinding surface
of the same crown is determined by the extent of the
decay and by the form of the cavities; and these two
conditions will suggest the method of operation. If
this intervening portion is thin throughout, and devoid
of vitality, it should be cut away, and the two cavities

formed into one ; but if it is thick within, though it
may be thin at the surface, the cavities should be

filled separately. In some cases it is proper to leave
a part of it standing, as a sort of ridge between the
cavities, though not as a definite partition; in which
case the filling would be begun as in two cavities,
and finished as in one. In no case, however, when
the tooth is living, should this intervening portion re-
main, if its vitality is gone. The details of the pro-

cess of filling crown cavities have already been indi-
cated.
Second Class.—Buccal and palatal cavities of the
molars and bicuspids, and labial and palatal cavities
of the canines and incisors. In the molars, this class
of decay begins either at the margin of the gum, in