Page 197 - My FlipBook

CABIES AS A WHOLE. ITS CLINICAL FEATURES. 99
of the enamel which, so weakens it that it often breaks away
early in the progress of the decay. The decay in the mesial sur-
face, or right-hand side of the picture, has not been well shown
by the engraver, but in this, in the central area of the decay in
the enamel, the enamel rods are broken down and lie in a tangled
mass near the dento-enamel junction.
After the photograph of this tooth was made, the cut sur-
face was cemented to a cover-glass, and this in turn to a
grinding-disk, which was placed in the grinding machine, and
a section ground thin enough for microscopic examination by
transmitted light. From this, photomicrographs were made
which show the carious areas in greater detail. The sides to
which each belong have been preserved as they appear in the
small photograph.
If the decay on the left in the photomicrograph, Figure 115,
is studied, the amount of the solution of lime salts from the
dentin, as it is shown at y, is easily followed. The injury to the
dentin, however, extends from the point of the dentin cusp near
the occlusal, down past the decay of the enamel toward the gingi-
val. At z the outline of the backward decay of the enamel, seen
in the small photograph, is quite plainly shown, but by trans-
mitted light it is dark. A backward decay toward the gingival
is not so well shown, because of some little cracking of the enamel
in that region, which mars the picture. The occlusal portion of
this picture is upward, as it is in all of the photomicrographs.
The decay on the right of the small picture, Figure 114, is
represented in Figure 116. Although this decay has not caused
enough solution of calcium salts in the dentin to show shrinkage
in drying, the injury to the dentin seems to be considerable. The
enamel rods are broken down in the central area, which occurred,
I am persuaded, in the process of grinding, for my notes say
that the surface of the enamel showed no loss of enamel rods.
The grinding of the surface from which the small photograph
was made, was without any protection by cementing the enamel
rods together by solutions of balsam or shellac to prevent move-
ment, and some distortion of the enamel rods on the superficial
portion of the cut surface would easily be overlooked. It will be
seen in the photomicrograph that many of the partially dissolved
enamel rods lie in a tangled mass in the deeper parts of the
cavity. The very unusual extension of the carious process in the
enamel toward the occlusal at z will also be noticed here, sepa-
rated partially from the principal area of decay, a flamelike
tongue shoots inward from the surface and is making progress,