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tXTRACTIOX OF TEMPORARY TEETH 271

The lower figures represent the order of eruption of the temporary
set. The upper figures represent the order of the replacement by
the permanent set including this first permanent molar. Nature has
wise reasons for this change in the order.
The Inferior Teeth Generally Precede the Superior in the an-
terior part of the mouth by a few weeks and in the posterior part
by a few months with the exception of the third molars. The inferior
third molars sometimes precede the superiors by years. It must also
be borne in mind that the variance in length of time and age of erup-
tion is shorter in the case of females than of males.
Difference in Time as to Sex. Some females erupt their third
molars as young as the sixteenth year, some males do not erupt them
as late as the tAventy-seventh year. They may be in part or entirely
wanting in either male or female, during life. They are sometimes

Fig. 143.—Irregularity resulting from premature extraction of the first deciduous molar.

so far retarded that they do not erupt until after the extraction of
the first and second molars late in life. This sometimes gives rise to
an idea in the patient's mind that he has at least part of a third set
of teeth.
Compare Orders of Eruption. A careful consideration of the
two tables will show that in the temporary set the cuspid teeth erupt
before the temporary molars, while these are replaced by the per-
manent teeth in a different order. The first temporary molar is re-
placed by the first bicuspid. Then the second temporary molar is
replaced by the second bicuspid and next we have the cuspid tooth
coming into place, forming the keystone of the arch.
The Reason for Nature's Change of This Order. At five years
we find the full coinplemcnt of temporary teeth in place, only twenty
in number. Then nature puts in this dividing line by putting into
place one permanent tooth, the first permanent molar, before she