Effects of local irradiation on osseointegration of implants during healing stage in rats

Abstract

Purpose: Reconstruction using oral implants has been a valuable treatment option for head and neck cancer patients after ablative surgery and additional radiotherapy. Complications of radiotherapy have been investigated for a long time, but there are few reports about the effect of post-implant radiotherapy on bone healing or osseointegration around the implant. The purpose of this study is to evaluate the effect of local irradiation on osseointegration of implants during the healing stage in the maxilla of rats. Materials & Methods: Forty-eight Sprague-Dawley rats (body weight 130-140 g, 4 weeks old, male) were first divided into the radiation group and control group. The radiation group was again divided into 1-day and 4-week groups, which represents the interval between implant surgery and radiation. The maxillary first molars in each rat were extracted. At 4 weeks after extraction, custom-made implants were inserted bilaterally. Group 1, 2 and 3 received local radiation according to the experimental schedule with a single dose of 15.0 Gy to the maxilla. The rats were allowed to survive for 2, 4, and 8 weeks after implant placement. To observe of bone formation pattern, fluorescence expression agents (Oxy TC, Calcein, Alizarin red) were injected intraperitoneally on the day of implantation, at 2 weeks later, and 1 day before sacrifice, respectively. The specimens were prepared for histological and micro-computed tomographic analyses. Results: 1. Group 1 and 2, which were irradiated during the early healing stage, showed significantly lower bone mineral density (BMD) than non-irradiated groups. Group 3, which was irradiated during the late healing stage, showed similar BMD to the control group. 2. Irradiated groups showed a lower bone-to-implant contact (BIC) ratio but without significance. 3. Irradiated groups (group 2 and 3) showed significantly lower bone volume (BV/TV) and higher empty lacuna count (EL/BV) than control groups (group 5 and 6). Conclusion: Within the limitations of this study, local irradiation resulted in retarded bone healing and reduced bone mineral density during the early healing stage. Local irradiation had relatively minor influence, but also caused retarded bone healing during the late healing stage. In summary, the timing of local irradiation has a critical influence on the bone healing mechanism, which is related to osseointegration around implants.