Page 150 - My FlipBook

part we can only wait and watch our patients and stop the
progress where we see it beginning-.
Caries of Enamel.

This morning I want to go over again the subject some-
what as presented in my last lecture, but more particularly
taking up these processes and making the effort to describe
more minutely the method of progress of dental caries. When
caries first attacks a tooth we will discover a whitish spot
upon the enamel. It is not a dark spot in its first beginning,
but is white, ashy, gray in color; the surface of the enamel
loses its translucency and becomes opaque, more or less,

and in passing a sharp exploring instrument over it it doesn't
glide smoothly as it does upon the surface of the perfect
enamel, but is inclined to catch, and by using a little force
we will find that it is softened slightly upon its surface. .Now
we may copy that very exactly by taking a freshly extracted
tooth, cleaning its surface and placing upon it a drop of
nitric acid, or somewhat diluted nitric acid copies it the more
perfectly. Allow that to act for a few moments, or until a
few bubbles arise in the acid that has been placed upon the
tooth. Or if you use a very dilute acid, 2 or per cent, and
3
let the action continue for a number of hours, vou will get a
still more perfect copying of the appearances produced by
caries. Then when you dry that ofT you will see that the
surface has become opaque and gray, and, trying it with an
exploring instrument, a sharp one, you will find that the sur-
face is softened, is broken up more or less, and that you may
scrape away powdery particles from its surface ; then, taking
these powdery particles to the microscope, you will find that
they are composed of fragments of the enamel rods. The
elements of which the tooth is composed have been taken
apart, or separated by the acid. Now, this separation of the
enamel rods the one from the other occurs in this wise : It
is found that the cementing substance that unites the enamel
rods together has been dissolved more rapidly than the rods
themselves, showing that the rods and the cementing sub-
stance are composed differently, and that cementing substance
—which compares with the mortar between the bricks in a
wall—dissolves in the acid more readily than the rods them-
selves. As you have already learned, the enamel is composed
of a number of rods laid together and cemented together, and
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