Does Fluoride Really Fight Cavities?

A new study claims that the protective shield formed on teeth by fluoride (F) is up to 100 times thinner than previously believed, raising questions about how it actually protects teeth from cavities.

Researchers at Saarland University (Saarbrücken, Germany) used X-ray photoelectron spectroscopy (XPS) to investigate the structural and chemical changes that arise from fluoridation of hydroxyapatite (HAP), which form the synthetic counterpart of tooth enamel. The researchers examined the elemental depth profiles (with a depth resolution on the nanometer scale) to determine the effect of fluoridation in both neutral (pH = 6.2) and acidic agents (pH = 4.2).

The researchers found that in both cases the fluoridation affects the surface on a nanometer scale, a finding that is in contrast to recent literature (with respect to XPS analysis) on dental fluoridation, where depth profiles of F extending to several micrometers were reported. The researchers also presented quantitative depth profiles of the compounds CaF2, Ca(OH)2, and fluorapatite (FAP) that corroborated a three-layer model concerning the fluoridation of HAP in an acidic agent. The analysis showed, however, that the model differs by nearly 2 orders of magnitude from previous predictions, and that the amount of the Ca(OH)2 and FAP layers is small compared to that of CaF2 layer. The study was published in the December 2010 issue of Langmuir.

"Since the fluoride ions have only a small penetration depth, fluoride ions have to be continuously administered--as by the regular use of a neutral fluoridated toothpaste or mouthrinse--since the protecting FAP layer is only as thick as the daily wear of enamel,” concluded lead author Frank Muller, PhD, of the department of experimental physics, and colleagues. "Therefore, it has to be asked whether such narrow Ca(OH)2 and FAP layers really can act as protective layers for the enamel.”

Fluoride-containing compounds are used in topical and systemic fluoride therapy for preventing tooth decay. They are used for water fluoridation and in many products associated with oral hygiene. The fluoridation of water is known to prevent tooth decay and is considered by the US Centers for Disease Control and Prevention (CDC; Atlanta, GA, USA) as one of 10 great public health achievements of the 20th century. In some countries where large, centralized water systems are uncommon, F is delivered to the populace by fluoridating table salt.

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