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News / December 17, 2010

New study questions ‘cavity-fighting’ fluoride

by Guy Hiscott

Scientists have discovered that the protective shield fluoride forms on teeth is up to 100 times thinner than previously believed.

The study now poses a question mark over how this cavity-fighter really works and experts say it could lead to better ways of protecting teeth from decay.

Frank Müller’s study – Elemental Depth Profiling of Fluoridated Hydroxyapatite: Saving Your Dentition by the Skin of Your Teeth? – is published in the journal, Langmuir.

Widely accepted that fluoride makes teeth more resistant to decay, some expewrte believe that it changed the main mineral in enamel, hydroxyapatite, into a more-decay resistant material called fluorapatite.

But this new research finds that the fluorapatite layer formed in this way is only six nanometers thick and this questions whether a layer so thin – which is quickly worn away by chewing –can shield teeth from decay, or whether fluoride has some other unrecognised effect on tooth enamel.

The team is now launching a new study in search of an answer.

In an abstract of the study, the team notes: ‘Structural and chemical changes that arise from fluoridation of hydroxyapatite (Ca5(PO4)3OH or “HAp”), as representing the synthetic counterpart of tooth enamel, are investigated by X-ray photoelectron spectroscopy (XPS). ‘Elemental depth profiles with a depth resolution on the nanometer scale were determined to reveal the effect of fluoridation in neutral (pH = 6.2) and acidic agents (pH = 4.2). With respect to the chemical composition and the crystal structure, XPS depth profiling reveals different effects of the two treatments. In both cases, however, the fluoridation affects the surface only on the nanometer scale, which 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.’

It adds: ‘In addition to the elemental depth profiles, as published in various other studies, we also present quantitative depth profiles of the compounds CaF2, Ca(OH)2, and fluorapatite (FAp) that were recently proposed by a three-layer model concerning the fluoridation of HAp in an acidic agent. The analysis of our experimental data exactly reproduces the structural order of this model, however, on a scale that differs by nearly two orders of magnitude from previous predictions. The results also reveal that the amount of Ca(OH)2 and FAp is small compared to that of CaF2. Therefore, it has to be asked whether such narrow Ca(OH)2 and FAp layers really can act as protective layers for the enamel.’

For more on the study, go to