Effect of fluoride ions on apatite crystal formation in rat hard tissues

Fluoride is widely believed to be a useful chemical substance for preventing dental caries. However, the mechanism underlying crystal perforation in the tooth enamel and the effect of fluoride on hard tissues are unclear. To clarify the mechanism of the biological action of fluoride in the mineralization process, we examined the hard tissues of rats having received water containing a relatively low fluoride level. Electron microscopy revealed that fluoride ions could interrupt the crystal nucleation process, resulting in crystal perforation in the developing tooth enamel and the presence of amorphous minerals in bone crystals. Furthermore, the results of enzymatic analyses indicated that fluoride directly interfered with the synthesis of carbonic anhydrase by the enamel-forming cells, rather than being directly involved in the crystal formation. From the results, we would like to provide a possible mechanism of crystal perforation in the enamel induced by fluoride intake. Also, we would like to suggest that regardless of its amount, fluoride intake has harmful effects on both tooth and bone formation.