EFFECTS OF ALUMINUM(III) AND FLUORIDE ON THE DEMINERALIZATION OF BOVINE ENAMEL POWDER AND HYDROXYAPATITE - IN-VITRO KINETIC-STUDIES SHOWINGSYNERGISTIC INHIBITION

The effect of Al(III) and fluoride on the rate of dissolution of powde red enamel in 0.1 M lactate solution has been studied at pH 4.5 and 5. 0. The dissolution rate of synthetic hydroxyapatite (HAP) microcrystal s in similar solutions is reported for pH 5.0. A combination of Al(III ) and fluoride has a stronger inhibitory effect on dissolution of enam el and HAP at pH 5.0 than that of these substances separately, even th ough the concentration of free fluoride ions decreases in the presence of Al(III). The effects on dissolution of enamel at pH 4.5 are simila r, but less pronounced. It is suggested that Al(III) and its major com plexes is slightly acidic solution, being positively charged, are adso rbed at different sites on the mineral surface from fluoride, thereby producing a synergistic effect. When the dissolution process takes pla ce far from equilibrium, inhibitor concentrations greater than about 1 00muM (approximately 3 ppm for Al(III) and approximately 2 ppm for F-) show significant inhibition under the conditions studied. In such sol utions the real concentration of Al3+ is of the order 1muM. Close to e quilibrium, the total inhibitor concentration need only be of the orde r 1muM (i.e. 0.03 ppm for Al(III), 0.02 ppm for F-) for a strong effec t. In such solutions, the real concentration of Al3+ is in the nanomol ar range.