New evidence on how fluoride fights cavities.

• Position: Tooth Decay - Brief article

In an advance toward solving a 50-year-old mystery, scientists present new evidence in the journal Langumir on how the fluoride in drinking water, toothpastes, mouth rinses, and other oral-care products prevents tooth decay.

Karin Jacobs, professor of experimental physics at Germany's Saarland University, notes that, despite a half-century of research, controversy still exists over exactly how fluoride compounds reduce the risk of tooth decay. Research established long ago that fluoride helps to harden the enamel coating, which protects teeth from the acid produced by decay-causing bacteria.

Newer studies already found that fluoride penetrates into and hardens a much thinner layer of enamel than previously believed, lending...