How Fluoride Works on Teeth

Preventing Tooth Decay, and the Fluoridation Debate

Dec 4, 2007

Fluoride protects teeth from developing cavities when it comes in direct contact with tooth enamel. Swallowing fluoride has little or no benefit and may be harmful.

Fluoride is a compound that contains the element fluorine. We’ve known for a long time that fluoride protects teeth from decay, but current evidence suggests that we’ve been approaching the issue in the wrong way. In order to protect teeth, fluoride has to come in direct contact with them—ingesting it in water is not beneficial and may even be harmful to health.

The Mechanism of Fluoride

Fluoride prevents cavities from forming by promoting stronger tooth enamel and helping to rebuild it when it breaks down. This is how scientists believe it works:

Our teeth are covered with a layer of enamel composed largely of calcium and phosphate. Enamel is a very hard and resistant substance but it can be demineralized—that is, the calcium and phosphate can be dissolved out.
When we ingest sugar (both refined sugar and carbohydrates) the sugar promotes the growth of oral bacteria, including those on the surface of the teeth (plaque) which, in turn, produce acids.
Our saliva eventually neutralizes the acids; however, while acid is present, it can demineralize enamel, weakening natural tooth protection.
Once the acid has been neutralized, enamel is remineralized. As long as enamel is rebuilt as fast as it is broken down, the softer inner parts of the teeth are protected from dental caries. If, however, more minerals are lost from enamel than are replaced, cavities form.
Having some fluoride present in the mouth appears to not only encourage the remineralization of enamel, but also to create stronger enamel that is more resistant to future demineralization.
Evidence suggests that fluoride may also inhibit the production of acid by oral bacteria.

Myths About Fluoride

In the past, people have believed that increasing intake of fluoride will prevent dental caries, and many Western countries have routinely added fluorine to municipal drinking water supplies to be sure that everyone gets enough. Today, much of this former wisdom is crumbling in the face of new evidence that fluoridation of drinking water has little or no effect on dental health and may even be harmful:

A decrease in tooth decay formerly attributed to fluoridation of drinking water is now thought by some to be due to other factors, such as a higher standard of living, and increased consumption of certain foods.
Ingested fluorine, once thought to be particularly important during the formation of teeth below the gums has been shown to have little or no positive effect.
High fluorine intake, once reported to be completely safe, is now associated with destruction of tooth enamel, a form of bone cancer, brittle bones, and other disease.
Dental fluorosis, mottling of the teeth caused by too much ingested fluoride, was once thought to be purely cosmetic. Evidence now points to associated dental decay and possible effects on the rest of the bones.

Fluoridation of drinking water is now the subject of a growing controversy, with even the experts speaking up, and it seems likely that this practice will be discontinued. If use of fluoride for teeth is recommended in the future, toothpaste containing fluoride and fluoride treatments at the dentist are likely to suffice.