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firmary and the cast was made by Dr. Parker ; the other is one
that was presented to me some fifteen or eighteen years ago
in the condition in which this cast was taken. (Passes casts to
class.) The dish-shaped form presented in these is, we may
say, one of the more common forms. The particular char-
acter of the dish-shape may be varied indefinitely. Here
is another, a case that occurred in the practice of Dr. E. D.
Swain of Chicago, who was for a long time dean of this
school. That presents a different character, in which the
cutting looks as if a square file had been used across the
teeth, leaving a square shoulder toward the occlusal, with
the gingival portion of the cut sloping down to the gingivae.
The cutting of erosion never extends below the gingivae,
but will often extend smoothly to the line of the free mar-
gin of the gum. That form of erosion is not very uncom-
mon. Here is another cast of a case that is similar, but not
so extensive, and here is a case of erosion in a retained de-
ciduous cuspid of a somewhat similar character. The
impression was taken before removing the tooth and the
tooth placed in the impression, and the cast made with the
tooth in position. I have also another case here of what I
would call the dish-shaped variety—a cast taken by Mr. Wald-
berg of a case that was presented here in the infirmary in
which the eroded surfaces are very flat. In it the erosion
has extended to the lower teeth in a similar manner, almost
precisely, as to the upper teeth. It is a very characteristic
specimen, and shows the conditions very well indeed. I have
here still another case. I have foimd it extremely difficult to
get specimens of teeth in erosion, and one of the best that I
have ever been able to^ get was three teeth, a first, second and
third molar, with erosion upon the proximate surfaces ; but,
unfortunately, the second molar has gotten away from me,
and I only have the first and third. This is an erosion upon the
proximate surfaces, a rarer form than that upon the labial sur-
faces. I have seen, however, during my forty years of prac-
tice, five or six cases of erosion upon the proximate surfaces.
Notice the character of the eroded surfaces—a cut across as
though we had used a very fine file or stone, and made a per-
fectly straight cut across the proximate surface of the tooth,
leaving it polished so that an explorer would glide along that
just as it will glide along on the enamel. And, remember, al-

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