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TWENTY-SIXTH LECTURE.

The rianagement of Cavities by Classes.

In presenting this subject I shall repeat with a some-
what different bearing many things I have said in previous
lectures.
Caries of the teeth presents considerable differences
when occurring in different localities in the mouth upon dif-
ferent surfaces of the teeth, and at different ages of patients,
that call for differences in the management of cases. Occa-
sionally all classes of cavities will be found in the same mouth
and requiring treatment at the same time. But this is com-
paratively rare, and when it occurs in a young person the
case is a grave one. The rule is that in very susceptible per-
sons particular classes of cavities make their beginnings at
about a certain time in the several teeth after each has taken
its place in the arch. This certain time will be early or late
with different patients, according to the intensity of the sus-
ceptibility. 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 four-
teen, 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 occurring, and not so many will occur.
Cavities of the other classes occur at a later date, as the
rule. Therefore, when cases are closely followed with re-
spect to individual 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 the first molars of one hun-
dred patients we find four distinct areas of liability to caries '.
First, the central pit ; second, mesial surface ; third, distal
surface; fourth, the gingival third of buccal surface. In a
considerable number of cases there will also be decay in a
buccal pit. These decays, except the last, will occur one
after the other in this order as to time.
Cases occur frequently, however, in persons twenty years
old or more, in which caries progresses so slowly that when

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