Retrospective analysis of hydroxyapatite development for oral implant applications.

Ceramic forms of calcium phosphate, particularly HA, have been investigated extensively and used for hard-tissue implant applications for the past 20 years. HA ceramics still remain the most biocompatible bone implant material known and possess the added feature of becoming strongly bonded to living bone through natural-appearing bonding mechanisms. A variety of new or improved bone and tooth implant products have been developed using HA ceramics and thus this system has lead to overall improvements in dental hard-tissue repair and replacement. Because of HA's weak mechanical profile and relatively high chemical reactivity, however, bone implant devices composed in whole or in part of HA ceramics will fall short of being ideal permanent implant devices. Nevertheless, the development of a more fundamental and complete understanding of HA's bone-bonding mechanism could pave the way for a generation of surgical metals with permanent bone-bonding sites incorporated on their surfaces.