Page 65 - My FlipBook

DYSTROPHIES OP THE TEETH. 21
a more considerable part of the cusps is calcified, but I have
never seen the calcification so advanced at birth that the cusps
were united by calcified tissue, and evidently they are not so
united, until much later. On the other hand, it was only occa-
sionally that the least bit of calcification had occurred on the
central incisors. More often calcification does not begin on these
until about the end of the first year. Therefore, an illness that
brings about serious malnutrition during the first year of the
child's life is liable to wreck the occlusal surfaces of the first
molars, while all of the other teeth escape injury.
The injury to these teeth occurring so early is very charac-
teristic if seen soon after the eruption of the teeth and before
further injury has occurred by breaking away the sharp spiculae
representing the malformed cusps or by caries. But it is exceed-
ingly difficult to obtain specimens from which to make illustra-
tions. If the injury has occurred very early, or before the
enamel plates forming the lobes of the teeth have joined together,
the spiculae of cusps will stand much closer together than the
cusps of the normal tooth. The whole of the occlusal surface
of the tooth is dwarfed, often discolored and sunken into the
tooth crown. The pulp chamber will be nearer to the occlusal
surface than in the normally developed tooth in proportion to
the sinking of this part into the body of the crown. Figure 26.
All around this the enamel of second formation wells out in the
form of a broad collar to the normal size of the tooth crown at
or about the base of what would have been the normally devel-
oped cusps. The whole of the injured area is apt to be rough
and pitted, and the pits and grooves are very apt to be wide open.
This condition gives unusual opportunity for the beginning of
caries and the early exposure of the pulp. It is for this reason
particularly that they are so often destroyed very early. In
cases occurring a little later, but before the completion of the
occlusal surface, the conditions inviting the beginning of caries
are equally bad. The cusps will stand further apart, are
stronger, but the central part of the occlusal surface and the
outer slopes of the cusps are in very bad shape. At a still later
date, after the completion of the occlusal surface, the injury
appears as a groove around the crown of the tooth and is gen-
erally of less consequence.
In all of these cases the zone of injury in the dentin is one
of the very grave features, for the reason that caries reaching
this zone of interglobular spaces spreads through it quickly. It
has been exceedingly difficult to get material for the illustration
of this for the reason that very generally the occlusal surfaces
of these teeth are destroyed by caries before their removal,