It is one of the most active elements of the halogen group. It is never found free in nature. Traces of fluorine are present in bones, teeth, thyroid gland and skin. It protects teeth from decay. There is no evidence that it is indispensable in other tissues.
A proper intake of fluorine is necessary to prevent dental caries. It is required for normal mineralisation of bones.
The main source of it is drinking water. It occurs in traces in many foods but some foods such as seafish, cheese and China tea are rich in it.
Deficiency and Excess of Fluorine
Fluorine is often known as a two-edged sword. Fluorides are deposited on the developing teeth of children. There is no deposition of fluoride on adult teeth. Deposition of the fluoride discourages the solubility of minerals and growth of acid forming bacteria. If there is a deficiency of fluorine during the growing period, it will result in dental caries and tooth decay.
When taken in excess it causes damage to teeth and bones. The enamel on the teeth loses its luster, becomes patchy, chalky-white and pits appear on its surface. This condition is known as dental fluorosis. In human beings dental florists is not usually associated with skeletal fluorosis. Fluoride poisoning may occur among workers in the aluminum smelting industry where cryolite is used. It is characterised by loss of appetite, sclerosis of the spine, pelvis and limbs (enclosing spondylitis). Some parts of North India have as much as 14 ppm of fluorine in the drinking water. In these areas fluorosis poses a public health problem.
Fluoride is required in small amounts only. A small amount, 1 ppm, is considered enough for normal healthy teeth. When the fluorine content is high, fluorosis ensues. Soft water has little or no fluoride, while in hard water the fluoride content may be as high as 10 ppm. The average adult man may ingest about one milligram of fluorine daily from drinking water that contains one part per million (1 ppm). In addition the average diet may provide 0.25-0.35 mg of fluorine.