Hydroxyapatite and Carbonated Apatite as Models for the Dissolution Behavior of Human Dental Enamel

¹ Chemistry Department, State University of New York at Buffalo, Buffalo, New York 14214

It is now well-established that kinetic aspects as well as considerations based solely on solubilities and thermodynamic driving forces should be taken into account while one is attempting to understand the mechanism of dental caries. In the present study, kinetic comparisons of the dissolution of hydroxyapatite, carbonated apatite, and ground human dental enamel have been made in order that the appropriateness of these synthetic phases as enamel dissolution models can be assessed. Specific additives used to form intactsurface layers in vitro have also been investigated. An interesting phenomenon related to surface-controlled dissolution has been revealed. During Constant Composition experiments, the dissolution rates for all thesystems decrease markedly as the reaction proceeds. Further tests with fresh crystals suggest that microimpurities, in addition to microstructural changes of the dissolving surfaces, may play a role in the case of hydroxyapatite but do not influence the dissolution of carbonated apatite. Kinetic results for ground human enamel indicate the release of dissolution poisons. Nevertheless, the results confirm expectations that carbonated apatite may be a better model for enamel than near-stoichiometric synthetic hydroxyapatite.