CHEMICAL-REACTIONS OF CALCIUM-PHOSPHATE IMPLANTS AFTER IMPLANTATION INVIVO

Sintered microporous cylinders of hydroxyapatite (OHA), tertiary calcium phosphate (beta-TCP and rhenanite (CaNaPO4) were implanted in the bone of the forehead of the domestic pig (Sus scrofa). Implants together with the surrounding bone were retrieved after 6 and 12 weeks. X-ray diffraction showed that OHA and beta-TCP maintain their crystal structure upon implantation. However, rhenanite is transformed completely into an apatite within 6 weeks. This apatite later incorporates sodium and carbonate. Both beta-TCP and rhenanite implants showed some resorption but were otherwise covered with new bone. Electron microprobe analysis showed that the mineral at the interface had a Ca/P ratio characteristic of new bone. At a certain distance from the interface lower Ca/P ratios were found, characteristic of precursor phases of bone mineral. This suggests that the deposition of new bone starts, at least partially, from the surface of the implant. Therefore, beta-TCP as well as rhenanite may be called an osteoconductive biomaterial.