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THIRTIETH LECTURE.

Cavities of tlie Second Class.

Cavities of the second class include those occurring in
the buccal surfaces of the bicuspids and molars—not pit
cavities—those in the labial surfaces of the incisors and those
in smooth portions of lingual surfaces. They are, therefore,
all smooth surface cavities. They are infrequent in lingual
surfaces. In the order of occurrence these are usually later
in life than cavities of the other classes ; though in this the
greatest variety occurs. Occasionally they occur very early,
even appearing in the deciduous teeth, but this is rare. Oc-
casionally they occur late in life or in old age. In the molars
cavities of this class must be sharply distinguished from pit
cavities, for these are all smooth surface cavities and occur
in the smooth portion of the enamel to the gingival of the
pit, generally in the gingival third of the surface close to the
gum margin. They are somewhat rare,before the age of i6
or i8, and are oftener seen at from eighteen to twenty-four
or five. Where they begin very early they are difficult cavi-
ties to treat. They are not only difficult in themselves, but
are coincident with cavities of the other classes, marking very
intense susceptibility and complicating the whole case at an

age when the patient is difficult to control.
In the buccal surfaces of the bicuspids, and in the labial
surfaces of the incisors, there are no pits, and all the cavities
are of this class. In all of these teeth, including the molars,
these cavities begin close to the gum margin. The distance
from the gingival line will depend upon the length of the free
margin of the gum. When they occur early the margin of the
gum is long and the beginning is some distance away from the
gingival line, leaving a good margin of enamel, provided the
cavities have not become so large that it is undermined by
decay of the dentine. Of these, some in which the decay of
the enamel is slow will be placed in better position by the fur-
ther protrusion of the tooth, or the shortening of the free
gum margin, and decay will cease before penetration of the

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