Purpose: The tissue reaction around hydroxyapatite (HA) implants irradiated at 3 different time points after placement was histologically and histomorphometrically analyzed to further determine the relation between irradiation and tissue reaction.
Materials and methods: Cylindrical high-density HA implants were placed in the mandibles of 48 Japanese white rabbits. The mandible was then irradiated with a single 15-Gy dose 5, 14, or 28 days after implantation. The rabbits were sacrificed on days 7, 14, 28, or 90 after irradiation. Nonirradiated rabbits with implants were used as controls. Nondecalcified specimens stained with toluidine blue were used for histologic analysis and histomorphometric measurements.
Results: In the rabbits irradiated 5 days after implantation, the HA-bone contact occurred later than in the controls. The bone-implant contact surface ratio was lower than in the controls at each time of sacrifice because of necrosis of the newly formed bone just after irradiation. The HA-bone contact in rabbits irradiated 14 and 28 days after implantation was similar to that of the controls. Bone remodeling was suppressed in the rabbits in each group sacrificed 90 days after irradiation.
Conclusions: Therapeutic irradiation shortly after implantation inhibits direct contact between the HA implant and the surrounding bone. Bone contact occurring before irradiation was minimally affected. Regardless of the interval between implantation and irradiation, postimplantation irradiation inevitably delays bone remodeling.