That a necessity also exists at this age, that the weak and delicate
teeth of childhood should be exchanged for a set stronger and more
durable in their structure, more robust and more powerful, will be
sufficiently apparent, if we only recollect the great change which has
gradually been taking place in the nature of the food of the two epochs
of childhood and adult age.
The second set, or permanent teeth, then, lying under the milk-teeth
and hidden in the jaw, undergo in this situation their full
developement, before they appear above the gum. This occurrence
commences about seven years of age, at which period the first set
begin to fall out from their roots becoming absorbed, and no longer
retaining their hold of the jaw; to be entirely replaced in the course
of a few years by the permanent set, which thus succeeds them. The
first teeth of this set which make their appearance are the large
double teeth, which emerge from the gum immediately behind the last of
the temporary set. Next the two front teeth of the lower jaw fall out,
and are succeeded by two others of similar character and form, but of
larger size; then the two corresponding teeth of the upper row are cast
off, and their place supplied; shortly after the teeth immediately
adjoining these; then the double teeth of the first set are exchanged
for their smaller successors of the second.
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