PURPOSE This study examined the ingrowth of bone into coralline, porous hydroxyapatite (HA) block (Interpore 200) over long periods after orthognathic surgery and analyzed their microhardness as a measure of the structural integrity of the ingrown bone as well as of the HA. MATERIALS AND METHODS Twenty-five maxillary HA implants (4 to 138 months of implantation; mean, 32 months) were removed from 17 patients. These implants had been placed into the lateral maxillary wall, juxtapositioned to the maxillary sinus during orthognathic surgery, and were harvested for analysis after voluntary consent. RESULTS Microscopic examination showed normal bone morphology in all implants; no inflammatory response was observed. Histomorphometric measurements indicated that there was significant bone ingrowth in all implants, with an overall mean of 23+/-7% bone (range, 7% to 31%), 51%+/-7% HA matrix (range, 39% to 65%), and the remainder being soft tissue or void at 26%+/-9% (range, 10% to 40%). No significant difference in microhardness values between the bone in the implant and the bone surrounding the implant was noted, indicating that the structural integrity of the porous block HA/bone aggregate had been maintained. Bone ingrowth appeared to plateau around 20 months, reaching an equilibrium in which the relative amount of osseous tissue remained constant. CONCLUSION Based on the findings in this study, porous block HA is a viable material for long-term implantation in the maxilla during orthognathic surgery.