The distribution of multinucleated giant cells (MGCs) and osteoclasts after intraosseous implantation of synthetic hydroxyapatite (HA) was studied using light microscope and histomorphometry. HA dried at 200℃(2 HA) and HA sintered at 1,250℃ (12HA )were used in this study. Light microscopically, MGCs in response to 2 HA showed a ruffled border-like structure at the interface between 2 HA and MGCs,but MGCs in response to 12 HA did not. The amount of new bone formation after intraosseous implantation of 2 HA was similar to that after intraosseous implantation of 12 HA. However, MGC count in response to 2 HA was higher than in respose to 12 HA, especially 2～ 6 weeks after intraosseous implantation of HA. Moreover, osteoclast count on new osseous tissue without HA implantation was apparently higher than after implantation of 2 HA or 12 HA. These results suggest that MGCs responding to HA do not effect new bone formation around the intraosseous implanted HA. New osseous tissue remodeling,after implantation of HA, is either on a low level or delayed when compared with tissue not HA implantated.
