Mechanism of fluoride uptake by hydroxyapatite from acidic fluoride solutions. I. Theoretical considerations.

It is well established that fluoride plays an important role in the prevention of dental caries. Fluoridation of drinking water has been a successful public health measure in reducing the prevalence of tooth decay.' Beneficial results have also ensued from incorporation of stannous fluoride into a dentifrice.2 Wellock and Brudevold3 and others4,5 have reported a reduction in carious surfaces, as compared with controls, after one or more topical applications of an acidic fluoride and phosphate solution to teeth. The tooth mineral hydroxyapatite decomposes and calcium fluoride adheres to the apatite and can serve as a source of fluoride for subsequent conversion of hydroxyapatite to fluorapatite.6 Recently there has been interest in the application of physical chemistry principles to hydroxyapatite, the primary mineral of teeth. Gray7 has studied dissolution behavior of enamel and applied kinetics to charac-