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EROSION OF THE TEETH. 55
branes, and these parts of the membrane showed also the same
acidity when tested with litmus. After a careful and somewhat
protracted study of these phenomena, my conclusion is that the
little swellings on the mucous membranes are caused by the
erosion, rather than the erosion by a secretion which they emit.
In a considerable number of persons we will find prints of the
teeth — the upper incisors particularly, and sometimes the
bicuspids and molars also — in the lips or buccal membranes,
and these are formed in the same manner.
This explanation is strongly emphasized by the fact that
erosions occur in cases in which the mucous membranes never
touch the teeth, as in the somewhat rare cases of erosion of
proximal surfaces, and in one case coming under my observa-
tion in a girl sixteen years old, in which the bicuspids were deeply
eroded in dish-shaped forms, where the tissues of the cheek had
been destroyed before the teeth came through the gums, so that
no mucous membrane could have touched them.
The fifth supposition has certain points of similarity with
the fourth in that the same raised points of the mucous mem-
brane are described as fitting into the eroded areas. But instead
of the erosion being caused by an acid, the supposition is that
this tissue acts as an absorbing organ, and that the result is
really an absorption similar to that by which the roots of the
teeth are cut away. Several writers speak of having seen the
usual lacuna? of absorbed areas in roots of teeth and in areas
of bone undergoing absorption, in these eroded areas. This
supposition necessarily carries with it the idea that certain
actively functioning cells become fixed against the tooth tissue
and keep that position long enough or steadily enough to effect
this result. The same objection to this theory applies as to the
previous one, namely, that cases of erosion occur in positions
in which no mucous membrane, or other tissue, is in contact with
the areas being eroded.
The sixth supposition is that it is caused by an acid that
is developed in association with the gouty diathesis. This is a
more recent supposition. Perhaps the most notable article upon
this supposition is that by Dr. Darby, of Philadelphia (Dental
Cosmos, Volume 34, 1892, page 629) Dr. E. C. Kirk, of the same
.
city, has expressed somewhat similar views. This supposition
has rapidly attained pretty wide credence. On this point my
own observation is negative. Very little gout has come under
my observation, and the few well-marked cases that I have had
opportunity to study have shown no erosion. Yet we must now
expect that the cause of erosion will eventually be found to