Objectives: This research focuses on the effects of radiotherapy on the osseointegration and the cortical bone apposition rate around dental implants in mandible of 11 male beagles. Methods: 3 dogs were implanted without radiotherapy (Control group), 4 dogs were irradiated 4 weeks after implantation (IrA group) and 4 dogs were irradiated 8 weeks before implantation (IrB group). Eight implants were placed by dog. Each dog received 10 daily fractions of 4,3 Gy (total dose = 43 Gy) cobalt-60 radiation. Fluorescent markers of osteogenesis were given respectively at the time of implantation and of irradiation. The dogs were killed after 6 months of osseointegration, i.e. 5 months after radiotherapy for the IrA group and 8 months after radiotherapy for the IrB group. Each hemi-mandible was dissected, stained with basic fuchsin, embedded in methylmethacrylate and cut into undecalcified sections performed along the main axis of the implants. Results: At microscopic examination of the sections under ordinary and ultraviolet light, new bone formation was visible around 85 of the 88 implants. Bone remodeling appeared more active in the irradiated mandibles than in the nonirradiated ones. Quantitative evaluation of the bone apposition rate was performed with ultraviolet light microscopy by measuring the surfaces of bone apposited in osteons between the successive fluorescent labellings. No difference was observed between the control and IrA groups whereas in group IrB the apposition rate was significantly reduced. Conclusions: The quantitative data of bone remodeling dynamics strengthen previous observations which suggest that osseointegration is more effective when irradiation takes place after than before implantation.

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