Dissolution of Calcium Hydroxylapatite and its Application to Biological Demineralization*

Several aspects of the study of the rate of dissolution of calcium hydroxylapatite in aqueous solution are discussed. From a chemical point of view, this system provides the possibility to study the chemical processes taking place at the crystal surface during the dissolution process, both in the pure system and in systems containing foreign substances. From a biological point of view, the study has led to a model for the formation of subsurface lesions in tooth enamel. An approach to a model for demineralization of bone tissue comes from the sfudy of the effect of biologically relevant molecules on the dissolution process in vitro. Citrate ions are found to inhibit the dissolution process at low concentration, but accelerate this process at higher concentrations, where considerable complexing with calcium ions occurs.