Fluoride and Biological Mineralization II: Mechanism of Action of Fluoride to Influence the Collagen-Induced In Vitro Mineralization and Demineralization Reactions.

Fluoride had been shown to inhibit collagen-induced in vitro mineralization without affecting demineralization at its lower concentrations (> 1X10 and < 1X10 M) and stimulate mineralization in addition to inhibiting demineralization at its concentration > 1X10 M. The present studies were designed to investigate the mechanism by which fluoride acts to produce these concentration-dependent effects. The inhibition of mineralization occurring at the lower concentrations of fluoride was found to be due to the inactivation of the specific calcium binding sites of collagen involved in initiating the process of mineralization. Stimulation of mineralization obtained at the higher concentrations of fluoride was found to be due to the activation of the specific phosphate-binding sites of the collagen and the formation of a relatively less soluble and highly stable fluorapatite instead of hydroxyapatite. At its higher concentrations, fluoride was also found to inhibit demineralization by binding to the mineral phase associated with collagen. A model has been presented to explain the mechanisms whereby fluoride may act to produce the above observed effects.