The interaction between solutions of commercial monofluorophosphate (FPO32––/sup>) and amorphous and apatitic calcium phosphates was investigated at pH’s 4, 5, and 7. The affinity between FPO32––/sup> and apatite is minimal at pH 7 but materially increases with decreasing pH. Coupled with this greater uptake, however, is an increasing propensity for hydrolytic breakdown to orthophosphate and F1––/sup>. The strong interactions of free F1––/sup> and condensed phosphate contaminants with apatite do not appear to modify the weak FPO32––/sup> attraction toward apatite at pH 7. Both the F1––/sup> impurity initially present and the F1––/sup> released by FPO32––/sup> hydrolysis promote the formation of more stable F-containing apatites. This latter reaction may be the responsible factor for the caries-inhibiting effec
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