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44 PATHOLOGY OF THE HARD TISSUES OF THE TEETH.

I had supposed that this form of erosion was the prevailing
form in Germany, for in taking up the German writers I have
found that generally they have illustrated this form only, and
generally speak of erosion as the "keilformige defecte" (wedge-
shaped defects). Upon inquiry, however, among German den-
tists, I find that other forms are also found, but they think this
one the most common. I have seen a number of cases of this
form in which the teeth were cut through so deeply that they
finally broke away, cutting through the calcified pulp without
any distinction whatever from other parts of the dentin. These
wedge-shaped areas occur both in the upper and lower jaws,
less frequently in the incisors in the upper jaw, but more fre-
quently in the bicuspids and molars. It is not very uncommon
to see this form in the bicuspids and molars, and some irregular
forms or dish-shaped areas in the incisors and cuspids.
In Figure 51 is shown what appears to be a modification of
the wedge-shaped areas of erosion, occurring in two bicuspids.
In the deeper parts the cuts are well rounded from the occlusal
toward the gingival margins, but are flat mesio-distally. The
form is that of a segment of a cylinder. We see this form most
in bicuspids and molars, but it may occur in the incisors as well.
In the incisors, however, it is not apt to cut very deeply, so far
as present observation shows. It is more likely to thin out and
spread broadly over the labial surface of the tooth, producing
a flat labial surface.
In Figure 52 is presented a specimen of this, occurring in
the incisors of a young lady about nineteen years old. Three
casts of this have been made about one year apart, watching its
progress. The picture presented here is from the first cast
taken, and the erosion at that time had been noticed only about
one year. It has not gone deeper since, but has spread consid-
erably more toward the incisal. At the last observation it seemed
to have become stationary, all sensitiveness had disappeared
and tlie teeth were perfectly comfortable. The cutting is so
shallow that the teeth are not deformed so much as to be noticed
in ordinary conversation. It required careful adjustment of
light to get sufficient light and shade to make a good picture.
Flattened areas. The tendency seems evidently toward the
flat form, which is prominently presented in Figure 53. This
case was from a man about sixty years old, a laborer. He had
apparently taken no care of his teeth, and claims that he never
used a brush in his life. In this it will be noted in the cuspid
on the left of the picture, that the cutting has begun and gone