A fluoride ion is the ionic form of fluorine. As a halogen, fluorine forms a monovalent ion (-1 charge). Fluoride forms a binary compound with another element or radical. Examples of common fluoride compounds include hydrofluoric acid (HF), and sodium fluoride (NaF).

Uses

Fluoride compounds are used in a wide range of applications.

Where used in very low concentrations (on the order of parts per million), fluorides are used in human health applications; specifically, fluorides such as sodium fluoride (NaF), sodium fluorophosphate (SMFP), tin(II) fluoride (SnF₂), and amine fluoride are common ingredients in toothpaste. Many dentists also give their patients semiannual fluoride treatments.

Similarly, many North American municipalities also fluoridate their water supplies, citing effectiveness in reducing tooth decay, safety of fluoridation, and the low cost to do so. The American Dental Association (ADA), World Health Organization (WHO), and some other health organizations recommend fluoridation of municipal water supplies to a level between 0.7 and 1.2 ppm. On the other hand, UNICEF warns against water fluoridation as does the Sierra Club. Water fluoridation is a highly controversial practice and banned in most countries in Europe, China, India and Japan.

When used in very high concentrations (on the order of 10% by volume or higher), sodium fluoride may be found in rat poisons, insecticides, and wood preservatives.

Hydrofluoric acid is used in the etching of glass and other industrial applications, including integrated circuit manufacturing.

Fluorides and human health

Higher concentrations

In high concentrations fluoride compounds are toxic. 5 grams of sodium fluoride will kill most adult humans. A lethal dose is approximately 75mg per kilogram body mass. When ingested directly, fluoride compounds are readily absorbed by the intestines. Over time, the compound is excreted through the urine, and the half life for concentration of fluorine compounds is on an order of hours. Implied is that fluoride is taken out of circulation by the body and trace amounts bound in bone. Urine tests are a good indication of high exposure to fluoride compounds in the recent past. Skin or eye contact with many fluoride compounds (in high concentrations) is dangerous. In case of accidental swallowing, give milk, calcium carbonate, or milk of magnesia to slow absorption. Eye or skin contact should be treated by removing any contaminated clothing and flushing with water.

Low concentrations

Fluoride is best known for its use in small quantities to help reduce Dental caries (cavity) frequency in teeth. A debate continues about whether fluoride ions (F^-) are a trace element beneficial, or detrimental to humans for other reasons.

Fluoride compounds, usually calcium fluoride, are naturally found in low concentration in drinking water and some foods, like tea. Fluoride ions replace hydroxide ions in calcium hydroxyapatite , Ca₅[(PO₄)₃OH], in teeth, forming calcium fluoroapatite , Ca₅[(PO₄)₃F], which is more chemically stable and dissolves at a pH of 4.5, compared to 5.5 pH for calcium hydroxyapatite. This is generally believed to lead to fewer cavities, since stronger acids are needed to attack the tooth enamel. In 1951, Joseph C. Muhler and Harry G. Day of Indiana University Bloomington reported their research results on stannous fluoride as a tooth decay preventive and the university first sold the technology to Procter & Gamble to use in Crest toothpaste.

The widely accepted adverse effect of low concentration fluoridation at this time is fluorosis. It is a condition caused by 'excessive' intake of fluorine compounds over an extended period of time, and can cause yellowing of teeth, hypothyroidism, or brittling of bones and teeth. The definition of 'excessive' in the context of fluorosis falls on the order of parts per million and is generally accepted to mean significantly higher than the 0.7 to 1.2 ppm amounts recommended for fluoridated water. However, dosage is crucial to adverse effects, and therefore, what concentration is problematic will depend on the amount of fluoride ingested, how much is absorbed, and the weight of the person ingesting it. For this reason, many doctors have advised against using fluoridated water to make up formula for infants. People with kidney problems, or those on dialysis, are also advised not to ingest fluoridated water.

See also

• Water fluoridation – discusses mass fluoridation and the issues surrounding it.
• Fluoride poisoning
• Chloride
• Halide

Research sites

• Journal of the International Society for Fluoride Research
• A Bibliography of Scientific Literature on Fluoride