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KBOSION OF THE TEETH. 51

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 abrasiom
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
being carried on without the acid solutions, and others by the
use of tooth powders in use by the people. In some of the experi-
ments the brushing was done by hand, as by this method more
variety of motion could be used.
In these ways he had certainly produced results that looked
very much like many cases of erosion as seen in the mouth,
especially those of the partially dish-shaped, the wedge-shaped,
and the flattened varieties. I saw none of his artificial produc-
tion, however, that had the sharp, clean-cut margins so often
present in the real thing as it occurs in the mouth. Yet I feel
certain that if these specimens had been presented to me as