Fluoride (F) is a normal constituent of the human body, involved in the mineralisation of both teeth and bones. The fluoride concentration in bones and teeth is about 10,000 times that in body fluids and soft tissues. Nearly 99% of the body's fluoride is bound strongly to calcified tissues. Fluoride in bone appears to exist in both rapidly- and slowly-exchangeable pools. Fluoride is required for normal development of teeth enamel and prevents decay. Excessive amounts of fluoride ingested during development of the enamel and bone results in a crippling disease with bony deformities called fluorosis.