Page 160 - My FlipBook

is a basis substance in dentin that is sufficient in amount and ; ;
sufficient in consistency to maintain its physical and its his-
tological forms after the lime salts have been dissolved from
it; consequently the solution of the lime salts of dentin by an
acid does not form a cavity. Now, any of you may try this
by placing a freshly-extracted tooth in a two or three per cent
soultion of nitric acid (a pint of water should be used) and al-
low it to remain two or three days. At the end of this time
you will find that the enamel has disappeared completely. The
dentin has become softened, so that you may cut it with a
knife, or you may put it in the microtome and cut sections for
the microscope. The lime salts have disappeared, and yet its
form remains complete. You can take it in your fingers and
bend it, but when you have cut sections you will find the tu-
bules and the histological forms remaining complete. There-
fore the solution of lime salts by an acid does not form a cavity
other processes must come in before a cavity can be formed.
Micro-organisms are first attached to the outer surface of
the enamel ; then, as the enamel is dissolved, they finally come
in contact with the dentin. Now, the dentin ' has radiating
through it from the pulp to the enamel, in the crown of the
tooth, the dentinal tubules which I have tried to illustrate here
(referring to the chart), which have, just at the dento-enamel
junction, abundant branches, by which the tubules are united
the one with the other at that point. There are more or less
intercommunicating small branches elsewhere, but in this re-
gion the intercommunications are pretty large, almost as large
as the tubules themselves. As soon as the enamel is destroyed
the entrance into the tubules by micro-organisms is unopposed
they can grow into them. They do not enter the tubules by
any movement or motion of their own. There are some micro-
organisms that have motion that seem as though they might
produce dental caries, and yet I have never found them in the
deeper portions of the tubules, and we do not suppose that they
enter by any motion of their own, but they simply grow into
the openings, as a grapevine would grow through a lattice-
work, until they are completely filled. When they have broken
through the enamel they immediately begin to spread laterally
along the dento-enamel junction through the anastomosis of
these tubules, and as they reach new tubules they also begin
to grow along them directly toward the pulp. There are these
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