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48 PATHOLOGY OF THE HARD TISSUES OF THE TEETH.

noted that erosion is in progress in other teeth in the neigh-
borhood.
In Figure 62 is presented an illustration of a ease of erosion
of proximal surfaces observed a number of years ago. The pic-
ture is reproduced from pencil sketches made during the progress
of the case. I had the privilege of observing the progress of this
over a period of about seven years, nothing being done or
attempted in the way of treatment. The picture represents the
case as I first observed it. It appeared as if holes had been
bored between the teeth, cutting about equally from either tooth.
These grew larger and larger and the interproximal gum tissue
receded slightly until the teeth were cut away so much that they
broke, leaving the roots in position. During all of this time, the
margins of the cut at their junction with the enamel surface
were sharp, presenting no observable rounding. I have observed
this in the molars and bicuspids in several cases, and usually
the teeth have been extremely sensitive. One gentleman had
all of his molars removed from the upper jaw bcause of the pain
they gave him in chewing food and in any effort to clean his teeth.
The selection of cases for illustration has been confined to
a few which seem to represent the more typical varieties of
form. Variations from these, however, are constantly coming
up, almost every new case presenting characters peculiar to
itself. Many of them, even when the teeth are badly cut and
deformed, are so clean and white that the deformity is scarcely
noticeable a few feet away. But occasionally we see cases that
give a very bad appearance. A larger list of illustrations would
present variations without giving essentially new forms. For
instance, the case from which the irregular cutting of the incisors
was taken for Figure 56 had wedge-shaped areas of erosion at
the gingival of the bicuspids and molars in which the point of
the wedge, and of course the flat side of the cut, sloped toward
the occlusal instead of toward the gingival, as shown in Figure
50, which is the more common, and therefore the more typical of
the wedge-shaped areas. Similar changes from anything that
may be regarded as typical are continually occurring. These
are curious, but further illustration would give no broader view
of the general subject.
Whether or not these forms of erosion have any significance
in connection with the causation, can at present be only a matter
of speculation. In studying them it would seem that if some
eases of erosion are caused by the brush carrying abrasive
powders, certain of the forms may be due to that, while certain