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216 THE TECHNICAL PKOCEDUEES IN FILLING TEETH.

much to do with the form of the worn surfaces. Usually in the
beginning, whether the amount of the abrasion is eventually to be
great or small, the cusps (or some certain cusps) are worn flat,
and the developmental grooves, which were prominent features
before, gradually disappear and the occlusal surface generally
becomes flattened, as is seen in the molar tooth in Figure 298.
"When the abrasion has gone further, the dentin, under the promi-
nence of some or all of the cusps, becomes exposed, as shown in
Figures 299, 300. The dentin, being softer, wears more rapidly
than the enamel, and cups out into rounded cavities of more or
less considerable depth. The dentin becomes yellowish in cases
that are rapidly wearing away. If the wear is slower, it becomes
darker, and, in many cases, almost black. In the meantime, the
remaining enamel retains its white color. If a section is made
through one of these darkened areas, and this is photographed
by reflected light, a cloud will appear stretching to the pulp
chamber following the direction of the dentinal tubules. The
pulp chamber is already undergoing changes. The horns of the
pulp chamber have shortened and many of the cases show that
secondary dentin is being deposited on all sides of the pulp
chamber. With the greater abrasion shown in Figure 301, all
of these changes will be markedly increased. Up to this time
the patient is apt to have periods of sensitiveness of some of the
abraded surfaces and more especially when a certain cusp first
shows an exposure of the dentin. This sensitiveness comes and
goes for a time and then is likely to disaj^pear entirely and per-
t)
manently. With the continuance of the abrasion, we will finally
find the condition shown in Figure 302, in which the entire
occlusal surface proper has disappeared. The enamel remains
higher than the dentin. The dentin is cui3ped out in its center,
sometimes very deeply, and in its center the form of the pulp
chamber shows as a lighter area. The bulb of the i>ulp has
become completely calcified. A section of this calcified area will
show that true dentin was formed for a time after the pulp
chamber began to diminish in size. After this had continued
for a space, more or less of the dentinal tubules disappear, and
in a little space farther all have disappeared, and the rest of
the mass is a clear calcification showing none of the histological
forms of dentin. In some cases the calcification will be incom-
plete; one side, angle or other part not having closed. This lat-
ter is more often seen in the incisors.
Figure 303 shows a badly worn lateral incisor, split mesio-
distally, and photographed by reflected light. It will be seen