Effects of local and whole body irradiation on appearance of osteoclasts during wound healing of tooth extraction sockets in rats

We examined effects of local and whole body irradiation before tooth extraction on appearance and differentiation of osteoclasts in the alveolar bone of rat maxillary first molars. Wistar rats weighting 100 g were divided into three groups: non-irradiation group, local irradiation group, and whole body irradiation group. In the local irradiation group, a field made with lead blocks was placed over the maxillary left first molar tooth. In the whole body irradiation group, the animals were irradiated in cages. Both groups were irradiated at 8 Gy. The number of osteoclasts around the interradicular alveolar bone showed chronological changes common to non-irradiated and irradiated animals. Several osteoclasts appeared one day after tooth extraction, and the maximal peak was observed 3 days after extraction. Local irradiation had no difference from non-irradiated controls. In animals receiving whole body irradiation, tooth extraction one day after irradiation caused smaller number of osteoclasts than that 7 day after irradiation during the experimental period. Whole body-irradiated rats had small osteoclasts with only a few nuclei and narrow resorption lacunae, indicating deficiency of radioresistant osteoclast precursor cells. Injection of intact bone marrow cells to whole body-irradiated animals immediately after tooth extraction recovered to some content the number of osteoclasts. These findings suggest that bone resorption in the wound healing of alveolar socket requires radioresistant, postmitotic osteoclast precursor cells from hematopoietic organs, but not from local sources around the alveolar socket, at the initial phase of wound healing.