Correct statements about fluoride include all of the following, EXCEPT:
a) Fluoride is effective for the prophylaxis of dental caries
b) Fluoride is accumulated by bone and teeth, where it may stabilize the hydroxyapatite crystal
c) Subjects living in areas with naturally fluoridated water (1-2 ppm) had more dental caries and fewer vertebral compression fractures than subjects living in nonfluoridated water areas
d) Chronic exposure to very high level of fluoride dust in the inspired air results in crippling fluorosis, characterized by thickening of the cortex of long bones and bony exostoses.
