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578 EXTRACTION OF TEETH.

vessels, etc. As this process belongs to the teeth, being developed with
them, and is for the jiurposc of iiolding tlieni in position, it disappears to
a greater or less extent when the teeth :ire lost. The resorj)ti()n of this
process does not take place alike in each Jaw. In tlie ni)j)er jaw the
external platt' disapj)ears more rapidly and to a greater extent than
the inner plate ; in the lower jaw the resorption of the two plates is
about equal in extent and rate. The inner plate of the upper jaw is
partially snj)ported by the external plate of the palatal process, in fact
one merges into the other. The outer alveolar plate of the upper jaw
being resorbed to a greater extent than the inner one is of advantage
to the dentist in fitting teeth to the gums ; consequently, in extrac-
tion that fact should be remembered and injury to the internal plate
avoided. At the same time it does no harm to remove a small por-
tion of the outer plate, though loss of the gum tissue should be
avoided if pt)ssible. In the lower jaw it is not so im})ortant to avoid
Fig. 509.

Alveoli of permanent teeth—upper jaw.
removing slight jiortions of the inner plate, as resorption takes place
about equally in the two plates.
These plates may be resorbed in such a manner that a slight ridge
is left between the places which they occupied. This resorption of
both plates of the alveolar process of the lower jaw makes it more diffi-
cult to fit single plain teeth in the lower than in the upper jaw.