Effect of hydroxyapatite on bone formation around exposed heads of titanium implants in rabbits.

Dense hydroxyapatite (HA)--collagen was placed around the protruding heads of titanium and titanium alloy implants in the femurs of 38 rabbits. After 6 months, bone apposition was evaluated by gross examination and scanning electron microscopy. Although bone was observed in direct contact with the implant heads, the extremities of the implant heads were surrounded by connective tissue. Compared with the control animals, packing dense HA-collagen around the implant heads did not increase the area of osteogenesis. When the implants penetrated into bone through previously placed HA-collagen blocks, there was a decrease in the amount of bone attached to the body of the implants compared with the controls. The results of this study suggest that the use of dense HA does not increase the amount of bone tissue formed around titanium implants.