Fluoride inhibition of bone mineralization may depend on physical/chemical properties

The properties of fluoride (F) incorporation into bone powder in vitro were studied in an attempt to clarify possible mechanism for F inhibition of bone mineralization and soft tissue mineral deposition in vivo. Rat bone powder was prepared with minimal physical and chemical stress, and exposed to F (less than 1 mmol) in aqueous solutions buffered to pH 7.4. Initial experiments confirmed reported data that the rates of F incorporation into bone mineral in vitro resemble F clearance from blood in vivo. The rate of F incorporation was inversely proportional to the amount of F added to supernatants and decreased exponentially with time. Following F incorporation, the bone mineral became less soluble, with solubility inversely proportional to bone F concentration. However, a fraction (about 20%) of F freshly incorporated in bone powder dissolved readily in pH 7.4 buffer and appears to be adsorbed F. The fraction of incorporated F that was readily dissolved decreased with time over the initial 24 h after incorporation, was proportional to the amount of F freshly incorporated, and was associated with an inhibition of further F incorporation.