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204 PATHOLOGY OF THE HABD TISSUES OF THE TEETH.
iug to the intensity of the susceptibility and favorable or unfavor-
able local conditions. If the first molar is found with occlusal
decay at eight years, two years after it takes its place, the second
molar is apt to be decayed in the occlusal surface at fourteen, or
two years after it presents in the arch. The same rule follows
in pit cavities in other teeth. If, however, the first molar is not
decayed until twelve, other pit cavities will also be late occur-
ring, and not so many will occur. Pit cavities do not occur if
there are no pits, but they do not necessarily occur if there are
pits. The number and the time of their occurrence will be con-
trolled mostly by tbe susceptibility to caries in the individual.
Cavities of the other classes occur at a later date as the rule.
Therefore, when cases are closely followed with respect to indi-
vidual teeth, we have to deal with one class first, then another
and then a third, as our patient grows older. In following the
history of one hundred persons, we find beginning decays in the
first molars in five distinct localities which, in a considerable
majority, appear in the following order as to time: (1) In the
pits of the occlusal surface; (2) pits of the buccal surface (less
frequent) ; (3) in the mesial surface; (4) in the distal surface;
(5) in the gingival third of the buccal surface.
Cases occur frequently, however, in persons twenty-five to
thirty years old or more, in which caries progresses so slowly
that when the patient presents for treatment the several classes
of cavities may be present at the same time. These must be
sharply distinguished from cases in which the different classes of
cavities begin very nearly together in persons of fifteen to eight-
een years old. In the first, the intensity of susceptibility has
been sufficient to start many areas of decay, but the early ten-
dency toward immunity has checked the progress, and the case
is readily manageable, while in the treatment of the second we
have to deal with the full intensity of the susceptibility. Special
conditions, which are due to early childhood, will be presented
under the heading, "Management of Children's Teeth."
Cavities of the First Class.
Cavities of the first class, in the large majority of persons
met with in practice, are first to appear. These include pit and
fissure cavities in the molars, bicuspids, upper lateral incisors,
and more rarely in the upper central incisors also. In a large
proportion of persons, the first of these are in the molar teeth,
and in many persons these are the only cavities of this class, the
incisors being free from pits and fissures, and decay not occur-