RESORPTION OF HYDROXYAPATITE AND FLUORAPATITE COATINGS IN MAN - AN EXPERIMENTAL-STUDY IN TRABECULAR BONE

The clinical use of hydroxyapatite (HA) coating is controversial espec ially in regard to the long-term performance of the coating and the ef fects of resorption. In each of 15 consenting patients we inserted two implants, coated with either HA or fluorapatite (FA) into the iliac c rest, They were harvested at a mean of 13.6 +/- 0.6 months after surge ry. Histological examination showed that bone ongrowth on the HA-coate d implants was significantly greater (29%) than that on the FA-coated implants, When bone was present on the coating surface the HA coating was significantly thicker than the FA coating, when bone marrow was pr esent, the HA coating was significantly thinner than the FA coating, T he reduction in coating thickness when covered by bone or bone marrow was 23.1 +/- 9.7 mu m for HA and 5.1 +/- 1.7 mu m for FA (p < 0.01) su ggesting that FA is more stable than HA against resorption by bone mar row. The findings suggest that in man the osteoconductive properties o f HA coating are superior to those of FA. Resorption rates for both co atings were approximately 20% of the coating thickness per year, Bone ongrowth appears to protect against resorption whereas bone marrow see ms to accelerate resorption, No adverse reaction was seen in the surro unding bone.