Fluoride

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Fluoride acts mainly on teeth: when acid dissolves a little tooth enamel, calcium and phosphate settle back in, and fluoride takes part in this repair, making the rebuilt enamel more resistant to acid.

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Making enamel resist acid

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Fluoride does most of its work on the surface of the teeth: it makes the outermost layer, the enamel, more resistant to acid, so decay has a harder time getting started. Normal enamel is hydroxyapatite, which begins to dissolve when the pH in the mouth drops below 5.5. Fluoride ions take the place of the hydroxide in the crystal and turn it into sturdier fluorapatite, which does not start to dissolve until the pH falls to about 4.5.

Every day the tooth surface is etched by acid and then repaired with calcium, phosphate and fluoride from saliva. With fluoride around, repair is faster, and what grows back is the more acid-resistant crystal. That is why steady, low-dose contact right on the tooth matters more than any single large dose.

With children, think one step further: while teeth are still forming, swallowing too much fluoride causes dental fluorosis. So young children use only a rice-grain to pea-sized amount of toothpaste, with an adult watching to make sure they do not swallow it.

Educational content, not medical advice — consult a clinician.

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