General dentist and past president of the Pennsylvania Dental Association (PDA) on what fluoride does:
In developing teeth, the fluoride becomes part of the enamel and actually causes it to become denser and stronger so it is more resistant to the acids that are produced by the bacteria that cause decay. Once the teeth are fully formed and present in the mouth, fluoride can be taken in by exposed root surfaces, strengthening them, making them more resistant to decay and can even reverse decay that is forming.
Via the Hartford Courant:
A far as making teeth more resistant to cavities, fluoride works [though maybe not for all], according to research published in JADA]. Exactly how, we don’t know, says a new study.
Media release from the American Chemical Society:
In a study that the authors describe as lending credence to the idiom, “by the skin of your teeth,” scientists are reporting that the protective shield fluoride forms on teeth is up to 100 times thinner than previously believed. It raises questions about how this renowned cavity-fighter really works and could lead to better ways of protecting teeth from decay, the scientists suggest. Their study appears in ACS’s journal Langmuir. [Full text of study available here.]
* * *
Some thought that fluoride simply changed the main mineral in enamel, hydroxyapatite, into a more-decay resistant material called fluorapatite.
The new research found that the fluorapatite layer formed in this way is only 6 nanometers thick. It would take almost 10,000 such layers to span the width of a human hair. That’s at least 10 times thinner than previous studies indicated. The scientists question whether a layer so thin, which is quickly worn away by ordinary chewing, really can shield teeth from decay, or whether fluoride has some other unrecognized effect on tooth enamel. They are launching a new study in search of an answer.
But even if you believe fluoride has benefits that outweigh its risks, it still doesn’t follow that fluoridation is the answer. Whatever its specific mechanism, the consensus is that fluoride’s greatest effect comes when it’s applied to the teeth, not when swallowed.
“Fluoride is most effective when used topically, after the teeth have erupted.”
SOURCE: Cheng KK, et al. (2007). Adding fluoride to water supplies. British Medical Journal 335(7622):699-702.
“…it is now accepted that systemic fluoride plays a limited role in caries prevention.”
SOURCE: Pizzo G, Piscopo MR, Pizzo I, Giuliana G. (2007). Community water fluoridation and caries prevention: a critical review. Clinical Oral Investigations 11(3):189-93.
“…the major anticaries benefit of fluoride is topical and not systemic.”
SOURCE: National Research Council. (2006). Fluoride in Drinking Water: A Scientific Review of EPA’s Standards. National Academies Press, Washington D.C. p 13.