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42 PATHOLOGY OF THE HAED TISSUES OF THE TEETH.

EROSION OF THE TEETH.
ILLUSTRATIONS: FIGURES 48-62.
EROSION is a term applied to a peculiar and very charac-
teristic loss of substance of the teeth, beginning in the
enamel, or upon its outer surface, and slowly working its way
inward and spreading, destroying and removing the substance
of the tooth as it goes. At first it presents no symptoms what-
ever except this loss of substance, and this looks like a facet
that would be left after grinding slightly with a very fine stone.
There is no softening whatever, but simply a wasting of the
substance, leaving a perfectly smooth, polished surface; a sur-
face so smooth and polished and hard that an explorer passed
over it will glide just as smoothly upon the eroded surface as
upon the enamel that is perfect. The facet first formed grad-
ually deepens and widens, progressing very slowly in most cases,
until the enamel has been cut through. Then the dentin wastes
away in a similar fashion, and so smoothly that there is no line
of demarkation between the enamel and the dentin. "When the
enamel has been penetrated and the dentin begins to be eroded,
the dentin becomes very sensitive. This sensitiveness is charac-
teristic of erosion if in living teeth. Teeth that have lost their
pulps may suffer from erosion in precisely the same way, except
that in these there will be no sensitiveness.
Erosion is usually slow in its progress. The facets may
appear upon the enamel and be seen for a considerable time
before the enamel is penetrated ; as a year, two years or more.
It proceeds directly and steadily, in a large proportion of cases,
until the teeth are destroyed, requiring from three to ten years,
or even more, to cut through and destroy a tooth. In other cases
the progress ceases spontaneously, or the progress may be inter-
mittent.
The position of erosion is most commonly the buccal or
labial surfaces of the teeth. It is yet uncertain whether it
appears oftenest upon the incisors or upon the bicuspids and
molars. Sometimes, however, it will begin upon the proximal
surfaces, and a few cases have been observed upon the lingual
surfaces. "When it has begun upon a surface of a tooth, the
general rule is that it does not spread to other surfaces, i. e., if
it has begun upon a labial surface there is rarely a disposition
to begin upon a proximal surface or a lingual surface, but it will
be confined to labial surfaces ; it will, however, spread to other