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36 PATHOLOGY OF THE HARD TISSUES OF THE TEETH.
HISTOLOGICAL CHARACTERISTICS.
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The mottled teeth which I received were split labio-lingually
through their centers longitudinally when they came to me.
Many of the crowns were incomplete in that they had been cut
from the roots some little distance from the gingival line. I
ground the broken surfaces flat, polished them, and photo-
graphed them mounted in the pairs from each tooth. These
were photographed by reflected light with enlargements of from
six to eight diameters. (See Figures 44a, 44b, 44c, 44d.) The
material did not give very brilliant pictures, but they showed
the outlines of the imperfectly developed enamel.
Sections were then ground for microscopic study. They
presented a very considerable variety of injuries. The teeth
were all from young persons, and were practically unworn
except a few on the incisal edge. The enamel was normal in
its outline form and normal in thickness in all of the specimens,
but not normal in color. The group presented, as I found later
by personal examination of many children, a series of bad cases
of mottling. Some portions of the enamel were perfectly nor-
mal, both in color and histological development, in the majority
of the specimens. A number of them were of a very dark brown
color over a considerable portion of the labial surfaces, shad-
ing from the brown areas through varying shades of yellow,
to opaque paper-white, and from this into the normal enamel
color. All of the abnormal areas showed the same lack of devel-
opment of the cementing substance which usually binds the
enamel rods together. The degree of this injury varied in the
different teeth and in the different parts of the crowns of indi-
vidual teeth. Later, in examining the children, I saw many teeth
that were much darker in color than those I had for cutting.
This, however, was only a matter of degree of injury without
difference in kind.
In all of the specimens the enamel rods were well formed
throughout; in the imperfect areas the enamel rods seemed as
regular and perfect in form as in the areas in which the cement-
ing substance between them was normal. In areas in which the
difficulty was simply a lack of the cementing substance which
should be between the enamel rods, the spaces were empty, or
filled with air. Such areas were opaque paper-white because of
the presence of air between the enamel rods.
In the dark-colored areas the brownin was found to be in
the spaces between the enamel rods. The enamel rods them-
selves were as perfect and presented the same cross markings
as in normal teeth, but they often made very dark photomicro-