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920 DISEASES OF THE PERIDENTAL MEMBRANE.
sensibility of the peridental membrane is not appreciably impaired by
the destruction of the nerves in the apical space.
The peridental membrane is the organ of touch of the tooth; the
enamel has no sense of touch. And the pulp is so encased within the
hard structures of the tooth that it could not exercise the sense of touch
if it possessed it; which, as a matter of fact, it does not. The pulp of
a tooth conveys painful impressions only, and under normal conditions
these impressions are aroused only by thermal changes. By means of
the nerves of the peridental membrane, however, every touch upon the
tooth is reported to the sensorium. These nerves are the proper nerves
of touch for the tooth—as much so as are the nerves distributed to the
finger-ends for the fingers. No other nerves of the tooth are so situated
as to receive impressions made upon the tooth, and these must receive
the impressions in a secondary way (which, by the way, is the case with
all nerves of touch. In the fingers' ends these nerves are covered by
the epithelium). When a tooth is touched, as by the tongue, by articles
of food taken into the mouth, or by the finger, the peridental membrane
receives the pressure, and through its nerves a sensation of touch is con-
veyed to the brain. Such a touch cannot affect the pulp of the tooth,
because it cannot reach it ; therefore the peridental membrane is the only
organ of touch possessed by the tooth. This sense of touch is in normal
conditions rather feeble, yet sufficiently pronounced to respond readily
to very slight pressure on any tooth. That these nerves of touch are not
distributed principally by way of the apical space I have satisfied my-
self by examination of the sensibility of this membrane after removing
everything from the apical space. One of the most noteworthy observa-
tions I have made on this point was in the case of a young lady who had
lost the pulp of the first bicuspid at a time when the apical foramen was
still widely open, and through which another operator had inadvertently
passed quite a large pellet of cotton. I found it necessary to cut through
the alveolar wall in order to remove it, and I took particular care to
remove everything in the apical space. The space was much enlarged
by absorption, and was in a septic condition. In this case the pulp of
the tooth was gone ; the nerves entering the peridental membrane by
way of the apical space were gone ; and yet this tooth, at the earliest
date at which the sense of touch could be differentiated from the sense
of pain, was found to possess the sense of touch in a high degree. As
progress toward recovery was made the sense of touch in this tooth
became the same as in the others—or, in other words, it became nor-
mal. This and similar cases in which the same results were observed,
establish the fact that the nerves of touch of the tooth are to be found
in the peridental membrane, and that they are received—for the most
part, at least—by way of the nerv^es distributed to the gum through the
wall of the alveolus.
Therefore we find that the teeth are normally well supplied with
nerves and blood from at least two different sources, and that, though
one of these sources of supply may be cut off, they seem not to suffer
materially on that account—at least, this is the case with the peridental
membrane. Now, the cementum of the tooth is supplied with nutrient
material from the peridental membrane. It follows that the loss of