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CARIES AS A WHOLE. ITS CLINICAL FEATURES. Ill
The most essential condition for the occurrence of decay of
this class is a saliva favoring certain kinds of deposits upon the
teeth which will cover in attached colonies of microorganisms
in such a way as to protect the acids formed from free dissipa-
tion in the general oral secretions. This may be such a condition
as will enable microorganisms to protect themselves by the for-
mation of gelatinous plaques (zooglea aggregations), or possi-
bly by other kinds of deposits from the saliva that will form a
membrane-like covering that will afford a sufficient protection.
It is a notable fact that where any kind of deposits are found
upon the teeth, they are first to be seen on the buccal surfaces at
the points where gingival third decays begin. It is not any
and every kind of aggregation of filth on the surfaces of the teeth
that gives rise to decay. Indeed, some forms of filth seem to
prohibit decay instead of causing it. Some of the filthiest of
mouths have no caries, and in some cases where caries has been
in progress it seems to have been actually stopped by extreme
filthiness in the same way as decay not very infrequently is
stopped in certain cavities by the establishment of putrefactive
decomposition in their interior, as has been mentioned. Neither
will loose aggregations of saprophytic microorganisms, or of
leptothrix buccalis, or the leptothrix of Vignon, or other harm-
less varieties which may form thick masses over the teeth,
through which water will run as freely as through a sieve, have
any influence favoring the production of caries. The covering
must be of a kind that will protect from free washings by the
fluids of the mouth, and in and under which the caries fungi
will grow and produce acid fermentation. This may be so thin
and so transparent that the teeth may appear clean and yet
afford an effective protection against the too free dissipation
of the acid products of fermentation. It has become evident
enough from clinical observation that the conditions which favor
the formation of these plaques is one that is liable to be inter-
mittent. It comes and goes. Decays of the gingival third of
buccal and labial surfaces are especially liable to start, to stop,
and to start again. Their exposed situation renders them more
sensitive to fluctuations of conditions than decays situated in
protected localities. This is said of decays of the enamel in
which enamel rods have not fallen away exposing the dentin to
invasion by microorganisms. Once caries is implanted within
the dentin, it will most generally persist, even when there is
complete immunity to the beginnings of caries on the enamel.
Figure 135 shows a decay, situated centrally in the labial