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52 PATHOLOGY OF THE HARD TISSUES OF THE TEETH.

erosions that had occurred in the mouth in the ordinary way,
I should not have questioned their genuineness. Certainly Dr.
Miller has demonstrated the possibility and the probability that
teeth are often injured by vigorous brushing with gritty powders,
persisted in several times per day for many years together. I
am not j^et convinced, however, that all erosions are produced
in this way, even admitting that they may be assisted in part by
an acid that may be present in the fluids of the mouth.
One thing particularly Dr. Miller seems to have ignored,
and that is the extreme sensitiveness that is so often present in
cases of erosion. I know, however, that Dr. Miller had not fin-
ished his investigation of the subject at the time of his death,
and that the peculiar sensitiveness occurring in erosion would
have been considered by him later if he had had the opportunity.
This I have regarded as peculiar to erosion, admitting, however,
that cases occur in which there is no history of this symptom.
It is my belief, based on the examination of many cases, that
frequently sensitiveness is soon annulled by the rapid calcifi-
cation of the pulps of the teeth. This has the effect of cutting
off the connection of the dentinal fibrils of the crown of the tooth
with the remaining pulp tissue. Then sensitiveness is ended.
Therefore, many of the bad cases of erosion have not been sensi-
tive for several years. This calcification has been a result of
the condition of irritation communicated through the dentinal
fibrils.
During the time of this irritable condition there is generally
a history of the cessation of brushing, for the reason that the
friction of the brush can not be borne. In the case illustrated
in Figure 55, the young man said he had used a brush before
his teeth became so sensitive, but most of the loss of substance
had occurred afterward. This is but a repetition of the history
I have had from many persons.
The THIRD SUPPOSITION — that it is the action of an acid —
has been held by many persons, and in one form or other prob-
ably has more adherents to-day than any other. How it is that
an acid can so act to cut away the substance of the tooth, leaving
a hard, polished surface which is a constant characteristic of
erosion, while in all laboratory experiment and in caries as it
occurs in the mouth the effect is a gradual softening by the
solution of the calcium salts, is left unexplained, unless Dr.
^Miller's work noted above may be so regarded. As yet no acid
has been found tliat will remove the whole of the tissue, calcium
salts and basic substance, without previous softening.