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238 PATHOLOGY OF THE HARD TISSUES OF THE TEETH.

standpoint, we should regard all persons under fourteen or fif-
teen years old as children ; for the development of the permanent
teeth, exclusive of the third molars, which we need not consider,
is not completed until about that time.
The deciduous teeth of one side of the upper jaw are repre-
sented in outline considerably enlarged in Figures 172, 173. In
the first of these, the growth of the crowns and the roots of the
teeth is represented by figures placed upon the individual teeth.
In the second, the absorption of the roots of the deciduous teeth
is represented in a similar way. The two, taken together, give a
brief synopsis of the changes which take place, together with the
average time in years occupied. The calcification of the decidu-
ous teeth, according to this chart, Figure 172, begins in the
central incisor at about the seventeenth week of uterine life.
Reading from left to right, the position of the on the various
teeth represents the average calcification at birth, the figure 1
represents the growth of the roots at one year, the figure 2 the
growth at two years, and the figure 3 at three years, when the
growth of all of the roots of this set of teeth are complete. It
must be understood that this is a representation of averages from
which there are wide variations. Also, that it has little to do
with the time of cutting, erupting or presentation of the teeth
through the gmns. The time of this is probably more variable
than the process of calcification. Yet, careful- study of cases
shows that there is a fair relation between the calcification and
the cutting of both the deciduous and permanent teeth that is of
much value in the management of cases when the history can be
obtained. While it does not invariably follow, it is so with suffi-
cient frequency that we may reasonably expect that if the teeth
of a child have been very late in erupting, the completion of the
calcification (the growth) of the roots will also be later than the
average time. This history is often of great value.
Premature eruptions of teeth. Occasionally cases of pre-
mature eruption of teeth have been noted, i. e., cases in which the
crowns have protruded through the gums before sufficient root
has formed to serve as support to the crown, and as a conse-
quence the crown has been displaced. Within the observation of
the author, this has occurred only with the incisors. In one the
central incisors were found erupted at birth. Other cases have
been noted in which the teeth were erupted before there was suf-
ficient growth of dentin to form sufficient root to maintain them
in position. These latter have in each case been a single central
incisor erupted soon after birth and much in advance of the other