<<The major tissues known to incorporate fluoride are bones and tooth
enamel. Fluorine appears to increase deposition of calcium,  thereby
strengthening
teeth and bones.>>

<Sounds like out of a brochure from the American Dental Association. ;-)>

Long-term exposure to levels of fluorides in excess of 200 micrograms per
kilogram of body weight per day — levels that are much higher than those to
which the average Canadian is exposed on a daily basis, including exposure
from fluoridated drinking water — may be associated with skeletal fluorosis.
This is a progressive but not life-threatening condition in which the bones
increase in density and gradually become more brittle. In mild cases,
symptoms of skeletal fluorosis may include pain and stiffness of the joints.
In more severe cases, symptoms may include reduced mobility, skeletal
deformities, and an increased risk of bone fractures. It is likely that
individuals must consume considerably higher amounts before crippling
symptoms will develop.
source: www.hc-sc.gc.ca/ehp/ehd/catalogue/general/iyh/fluoride.htm

Rob