The present study evaluates histological characteristics of the soft tissue response to long-term implantation of Apaceram™ discs composed of dense hydroxyapatite in rats. Discs were implanted into the subcutaneous tissue of 76 rats for six to 20 months. Decalcified histological sections stained with haematoxylin and eosin (H & E) and Mallory's azan were examined. Different cell types surrounding implants were counted. The greatest proportion of macrophages was found at six months (13.5 per cent). This proportion gradually decreased to four per cent at 20 months. Small numbers of lymphocytes and foreign body giant cells were observed in every group, but neither neutrophils nor osteogenesis were observed in any specimens. Results of the present study and previous related studies indicate that despite reappearance of a small number of macrophages six months after implantation, Apaceram™ is useful for reconstructive surgery.

A study was carried out in order to obtain further information about the soft tissue response to thin Apaceram® discs of dense hydroxyapatite (HA) implanted in rats for various periods of time between one day and 10 months. The Apaceram® discs were implanted subcutaneously into the interscapular region of 33 rats. A sham operation was performed on eight rats used as controls. Decalcified histological sections stained with haematoxylin and eosin and Mallory's azan were examined and the different cell types found around the implants were counted. It was found that an acute inflammatory reaction occurred after one day and disappeared at about two weeks after implantation. In the test groups, macrophages and lymphocytes disappeared about one week later, and no inflammatory reaction was observed from one to three months. However, a tissue reaction occurred at six months with the appearance of macrophages and lymphocytes, and decreased gradually at 10 months. Meanwhile, a few foreign body giant cells at the Apaceram®-tissue interface and a thick layer of fibrous connective tissue around the Apaceram® disc were observed at 10 months. No osteogenesis was observed in any specimen. The results obtained so far suggest that Apaceram® is still a useful material for reconstructive surgery, despite the possible appearance of a slight macrophage reaction at six months.