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42 PATHOLOGY OF THE HAED TISSUES OF THE TEETH.

patients witliin five or six weeks. He gave me a set of casts
from a young man of twenty, his father, his grandfather and
his great-grandfather, all taken the same week, each showing
erosion. This practitioner is fully convinced by his observations
among these people that erosion is hereditary. They are prac-
tically all descendants of a few Jewish families who settled in
this country many years ago, who have been very much devoted
to the maintenance of their especial set. From the descriptions
first given of erosion among these people, it was expected that
much of it would be of one character as to form, but the examina-
tion of the casts revealed a wide variety of form, so much so
that one could not say that any one particular form prevailed
to the exclusion of others. There were among them two cases
of marked erosion of proximal surfaces, cutting holes between
the bicuspids.
I have also supposed from my reading of the literature,
and especially from examination of illustrations, and from
inquiry in certain localities in this country and abroad, that cer-
tain forms prevailed in certain localities.

FORMS OF EROSION.
ILLUSTRATIONS: FIGURES 48-62.
DisH-sHAPED AREAS. One of the very common forms of
erosion we may describe as a dish-shaped excavation, in which
the center of the eroded area is deepest, and from this it rounds
up to the surface of the enamel in every direction. This may
attack a central incisor first and spread to the teeth at either
side of the tooth first attacked, hardly ever exactly bilateral,
but usually more extended on one side of the mouth than the
other, destroying the labial surfaces. Its place of beginning
varies from the middle of the gingival third to the mid-length
of the crown. Mesio-distally it is usually about the center, but
if there are irregularities in the positions of the teeth it is most
likely to begin on the most prominent part.
It first forms a little facet upon the enamel, then destroys
more and more, and finally passes through to the dentin, cutting
without any distinction whatever between the dentin and enamel,
and increasing the size of these facets until the whole labial
surface has been removed, not touching the proximal surface,
and not touching the inclsal except as it is approached from the
labial. This form is represented in Figure 48. There is fre-
quently an offshoot from the true dish shape toward the incisal.