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 (> 1X10-5 and < 1X10-4 M) and stimulate mineralization in addition to inhibiting demineralization at its concentration > 1X10-4 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.

Fluoride and Biological Calcification I: Effect of Fluoride on Collagen-Induced In Vitro Mineralization and Demineralization Reactions.

An in vitro system employing collagen isolated from the sheep tendons to induce mineralization and demineralization reactions was used not only to study the effect of various concentrations of fluoride on the collagen-induced mineralization and demineralization reactions but also to compare their action with the inhibitors of mineralization and/or demineralization. Studies demonstrated that under physiological conditions, at lower concentrations (5 × 10-6 to 5 × 10-5 M) fluoride inhibited while at higher concentrations (> 10-4 M), it stimulated the collagen-induced in vitro mineralization. At higher concentrations, fluoride was also found to inhibit the demineralization of the collagen bound preformed mineral phase. At low concentrations, fluoride acted like Mg2+ to inhibit mineralization while at higher concentration, it acted like crystal poisons (e.g., pyrophosphate phosphonates, citrate) to inhibit demineralization. However, unlike magnesium and pyrophosphate, fluoride at its higher concentrations was found to stimulate rather than inhibit the process of mineralization.