DISSOLUTION OF SYNTHETIC HYDROXYAPATITE IN THE PRESENCE OF LANTHANUM IONS

Numerous cations exhibit strong interactions with dental or synthetic hydroxyapatite (HAP) and of these, there are indications that lanthanu m improves the acid resistance of these compounds. In the present stud y, the reaction of La3+ ions with synthetic HAP in a water suspension has been investigated. It has been demonstrated that these cations rea ct with phosphate ions in equilibrium with HAP to form insoluble LaPO4 . This reaction releases protons which induce HAP dissolution up to it s solubility equilibrium and to complete precipitation of La3+ ions. T he kinetics of HAP dissolution at pH 5 with samples equilibrated for 2 h in the presence of 10 or 50 ppm LaCl3 show no differences compared with pure HAP. This strongly suggests that La3+ ions added to HAP in w ater suspension have no effect on the surface condition of this compou nd.