Fluoride uptake by partially-decalcified enamel: a study of possible involvement of acid phosphate ions.

Ionic fluoride and HPO(2-)4 concentrations were determined in partially-decalcified enamels before and after exposure to NaF or MFP toothpastes, to determine whether fluoride uptake could be attributed to reactions with HPO(2-)4. Acid phosphate concentrations did not alter upon exposure to fluoride, even though large uptake of fluoride did occur. Infra-red spectroscopy showed HPO(2-)4 in artificially decalcified enamel to be adsorbed rather than present as a discrete secondary orthophosphate.