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52 PATHOLOGY OF THE HARD TISSUES OF THE TEETH.
illustrate these forms only. This has led me to suspect that in
some regions, particular forms are more frequently met than
others. It seems certain that in the central part of the United
States one would not observe many cases of the wedge-shaped
areas without finding varieties of form that would be very difficult
to explain as resulting from abrasion by the tooth brush. "When
Charles Tomes edited another edition of his father's work, he
had seen cases that he believed could not have been made with
the tooth brush, and he rewrote the chapter entire. Dr. C. R. E.
Koch (Dental Cosmos, Volume 15, 1873, page 463) tried by every
device he could think of to produce the conditions seen in erosion
by the use of brushes and brush wheels, aided by acids in some
cases and by alkalies in others. His conclusion was that it could
not be done in any of these ways. He did not have the modern
electric motor to run his brushes, however.
Dr. W. D. Miller, of Berlin. Germany, recently published
(Dental Cosmos of January and February, 1907) the results of
two years' work on the etiology of erosion. He announced his
belief that it is caused by weak acids or gritty tooth powders, or
by both, assisted by the tooth brush. He seemed to be convinced
that the tooth brush is the main factor, and that what we have
designated as erosion is nothing more nor less than abrasion
brought about by these agencies.
During several weeks that the author was in Berlin during
the summer of 1906, he was frequently in Dr. Miller's laboratory
while he was engaged in these studies. Through his kindness
much was seen of his plans of work in the effort to produce
erosion by artificial means. Having placed a number of teeth
in wax, gutta percha. or similar substance, somewhat in the form
they would be in the mouth, he saturated a cloth with a weak
acid solution (different solutions being used in various experi-
ments) and laid it lightly over the teeth so that it would touch
only on the most prominent part of their crowns. After this
had remained in a moist chamber intended to prevent too much
evaporation, for a predetermined length of time, the cloth was
removed and the preparation placed on a machine run by an
electric motor, and the teeth were vigorously brushed for a
given number of minutes or hours, as determined for the par-
ticular case. The cloth was then resaturated with the acid solu-
tion, placed again upon the teeth, and the preparation returned
to the moist chamber for the predetermined number of hours
for that experiment. This was kept up day after day for weeks
or for months, the experiments being much varied as to acid
solutions, time, and brushing; also, certain experiments were