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16 PATHOLOGY OF THE HARD TISSUES OF THE TEETH.
tion formed later, we must conclude that the shortening is much
greater than that shown by the apparent telescoping of the parts.
In the dentin the same thing occurs, only that it is expressed dif-
ferently because of the different character of the tissue. The
line of interglobular spaces shows where the second growth was
telescoped into the first.
A study of Figure 14 shows exactly the same plan in the
arrangement of the tissue in the second zone of injury, including
the overlapping of the new enamel onto the old and the accom-
panying line of interglobular spaces in the dentin. The shorter
overlapping of the enamel at the point of injury is due to the
changed direction of the lines of growth. The actual shortening
of the tooth may have been much greater. When we study the
short and stumpy forms of many of the crowns of these mal-
formed teeth, we must conclude that the shortening is often very
much greater than this overlapping. It is this shortening and
telescoping together 'of the different parts that is responsible
for the greater part of the distortion of form so often observed
in these teeth. It appears certain that the tendency is to form
each of the parts on the lines that each would have had at the
specified time of growth if there had been no interruption of the
growth.
We may gain another view of this by studying the lines of
the labial dento-enamel junction. In the study of sections of
many human incisor and cuspid teeth, this line is found to form
a continuous curve from the incisal edge to the gingival line, as
seen in the diagram, Figure 10. The amount of curve may vary
indefinitely, but it is always a continuous curve in every normal
tooth. In sections of these malformed teeth, this curve is found
broken by a recurve at the zone of injury in every case, even
in the lighter forms in which the growth seems not to have
been completely arrested. This disturbance of the direction of
this line seems to be due to the effort to form the second part
on the lines that would have been laid down at that time if the
growth had been going on regularly, and the larger and smaller
are patched together. In the dentin the growth has been in abey-
ance and the growth begins on the lines on which it was left off.
But immediately the tendency is to enlarge to the greater out-
line of the tooth as it would have been at the time had the growth
not been interrupted. This causes a recurve in the line of the
dento-enamel junction. In the enamel, the telescoping seems to
be actual. That part of the enamel organ that had not arrived
at the period of enamel building is uninjured and is pushed for-
ward over the previously formed enamel and lays down its layers
of the second growth of enamel thus far over the old. No other