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Sodium fluoride is a compound of the elements sodium and fluorine with the chemical formula NaF. In the past, NaF was used to fluoridate water, but it has been mostly superseded by other fluoridating compounds. Sodium fluoride is still commonly found in toothpaste and is also used as a chemical reagent in the production of fluorides.
NaF is one of three water additives used to fluoridate water systems. The other two are fluorosilicic acid and sodium fluorosilicate. NaF is a dry substance that is added to water systems that supply only small populations. The compound is a soluble salt, and when ingested, the fluoride part of the molecule splits off to form a fluoride ion. This ion is easily absorbed by the body.
NaF is mostly derived from fluorosilicic acid, which uses phosphorite rock as a source. When the fluorosilicic acid is mixed with caustic soda, sodium fluoride is produced. Sometimes NaF is produced from mixing caustic soda with hydrogen fluoride.
Sodium fluoride is widely used in toothpaste to prevent cavities. The compound is also available as an oral medication for the same reason. The fluoride ion, which splits off from NaF in the gastrointestinal tract, strengthens teeth and reduces the chance of decay. The standard for fluoridation in the United States, for example, is from 0.7 mg per liter to 1.2 mg per liter. The difference in the optimal level stems from the fact that people in warmer areas tend to drink more water than those in cooler areas.
Ingesting excessive fluoride can result in a condition known as dental fluorosis, where the teeth become mottled and discolored and the surface of the enamel becomes pitted. Ingesting more than 1 mg per liter of fluoride can result in dental fluorosis, and taking in more than 4 mg per liter can result in skeletal fluorosis, which may cause abnormal bones and pain in the joints. Although it has been suggested that water fluoridation increases the risk of cancer, the World Health Organization states that the evidence does not show that fluoridation causes cancer in humans.
Sodium fluoride is also a chemical reagent used as a source of fluoride ions to create other fluoride compounds. This is due to the strong ability of the fluoride ion to attach to other ions and to form stable compounds. NaF also has several other industrial uses. The compound can be used to make enamel, preserve wood, and make foam. It is also part of a paper coating process and can assist in producing opal glass.