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CAEIES OF ENAMEL. 75
idea, however, is no longer tenable. If caries of the enamel was
caused by acids dissolved in the general saliva, we would not
have that strict localization of decay that is found in the mouth.
This localization is very important and should be very carefully
considered.
The points of localization are: (1.) Pits or fissures in
the occlusal surfaces of the bicuspids and molars, in the buccal
surfaces of the molars, and sometimes in the lingual surfaces
also, and occasionally in the lingual surfaces of the upper incis-
ors; (2) In the proximal surfaces of all of the teeth; (3) In the
gingival third of the buccal or labial surfaces of all of the teeth,
and rarely in the lingual surfaces also. Ninety-eight per cent
of all of the decays that occur in the human teeth are located
at the points included in this mention. Those beginnings of
decay located elsewhere in the teeth are usually the result of
accidental conditions, proving the accuracy of the rule; (4) The
most prominent tendency to wide spreading of decay on the sur-
face of the enamel is a direction that, when complete, encircles
the tooth following close to the free margin of the gum. Hence
proximal decays and gingival third decays spread most in these
directions. The tendency in cases of unusual severity is for proxi-
mal and buccal, and even lingual decays, to unite across the
angles of the teeth, making a complete circle around the tooth
near the free border of the gum.
It may be laid down as a principle that for caries to begin
in the enamel of the teeth anywhere, the caries fungus, which
forms an acid, must be attached to the surface of the enamel in
some such ivay as to prevent the acid which it forms from being
readily washed aivay and dissipated in the general fluids of the
mouth. Under all the observations of the surroundings of the
occurrence of decay of the enamel, I fail to be able to form a
conception of its beginning without the existence of some such
conditions. But it is not insisted here that this must always
be by the formation of zooglea or gelatinoid plaques. This may
be produced in an artificial way by cementing a band on a tooth,
as is done in orthodontia operations, and omitting the cement
in a part of the area covered. If such a band remains long on
the tooth, caries of the enamel will occur, even when the patient
is otherwise immune to caries. This has been a matter of care-
ful experiment by the author. It has also been observed in many
orthodontia cases. Indeed, the amount of injury being done in
this way during the treatment of irregularities, is giving rise
to much complaint.