Surface properties of hydroxyapatite: I. The effect of various inorganic ions on the electrophoretic behavior.

The zeta potential of hydroxyapatite (HA) at a constant pH depends on the type of acid used. Fluoride ions increase the charge density and make the surface less prone to attack by acid or alkali. Sn2+ and Th4+ ionic complexes with fluoride ions and increase the uptake of fluoride by HA.