Page 196 - My FlipBook

the teeth. And yet, as most of you have found, we cannot
ignore the vitahty of the teeth ; our patients cannot ignore
the vitality of the teeth. The teeth are sensitive, and under
the influence of caries they become hypersensitive. There
are no nerves in the dentin, and the question may come to
many of you, how is it that dentin can be sensitive, having
no nerves. I think there is a pretty widespread error pre-
vailing that sensation depends upon nerves. I think not.
I don't think there is any more sensation in nerve tissue
than in the other cellular elements of the body. Nerves
are the conveyors of sensation. Take the amoeba, a simple
cell having no nervous system ; pass an electric shock through
the water in which it is traveling about and it will immedi-
ately roll itself up into a ball ; there is sensation. Take va-
rious of these lower organisms that have no observable
nervous system and they display sensation ; they are sensitive.
Sensation belongs to the cellular elements of the body, and
certain cellular elements have more of it than others, or
dififerent orders of it. Nerves convey these sensations to
the central ganglia and we perceive them. If the nerves
are cut off there will be no sensation from the part, not
because the elementary tissues are not sensitive, but because
there is no means of communication. Then, in order to
have sensation conveyed to the central ganglia of the brain
we must have the cellular elements in physiological relation
with nerves. Some of the muscular fibers are very long,
and so far as we have been able to determine there is a single
nerve ending upon some particular portion of that mus-
cular fiber ; an impulse from the central ganglia to that nerve
ending will set the whole fiber into contraction ; further-
more, we may set that whole fiber into contraction without
a nerve plate by a mechanical irritation.
Now, a word of explanation regarding sensitiveness
of the dentin. I have here an outline of an incisor tooth
(referring to chart) ; here the pulp (indicating) ; here I have
drawn some of the fibrils of Tomes ; you will remember that
these are prolongations from the odontoblasts. The odon-
toblasts form a layer over the entire surface of the pulp
between the pulp tissue proper and the dentin. Now, these
fibrils are not simply fibrous tissue, but they are prolonga-
tions of the substance of the odontoblasts and form a part

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