Experimental study of surface and lattice effects on the solubility of hydroxyapatite.

Abstract

The of hydroxyapatite (OHAp), Ca5 (PO4) 3OH, has been the topic of many investigations. It has been a subject of sustained interest because the solution behavior of OHAp is fundamental to processes of physiologic adaptation in bone and teeth. However, experimental studies of the soltubility of OHAp often have yielded confusing results. The responsibility for much of this confusion lies with the use of variable and nonrigorous definitions of solubility in the framework of a particular study, and with failure to consider the effect of on the dissolution process. Other factors' that may have caused difficulties include the sensitivity of the apparent of OHAp to impurities, the difficulty involved in the preparation of pure OHAp, and the slow growth of OHAp crystals in solution, which often results in failure to achieve equilibrium with the lattice. Many of these difficulties can be avoided if an internally consistent, thermodynamic treatment for the of OHAp is formulated. This has been done by Brown. Moreno, and Gregory.' Their treatment reveals the importance of separating lattice and surface reactions in the study of the of sparingly soluble salts. Lattice reaction refers to the process where in a local region of a crystal, the stoichiom-