To investigate the biocompatibility of a synthetic auditory ossicle to host bone, small thin Apaceram® disks composed of dense hydroxyapatite were implanted under the periosteum of the left auditory bulla in 32 rats for periods ranging from 1 day to 270days. A sham operation performed on 10 rats served as a control. Decalcified histological sections stained with hematoxylin and eosin were observed using light microscopy. The experiment showed:1) a time-dependent mature fibrous connective tissue surrounding the Apaceram® disk, 2) no evidence of inflammatory reaction caused by the implant from 90 days after implantation until the end of the experiment, 3) no evidence of osteolysis by osteoclasts caused by the implant, and 4) direct contact of bone to the implant on the bone-disk interface at 180 and 270 days after implantation. The findings suggest that Apaceram® has a high degree of implant biocompatibility, making it a satisfactory substitute biomaterial for otological reconstructive surgeries
