It has been known that widening of the periodontal space is one of the initial radiographic signs of radiation bone injury. For the analysis of this sign, histologic changes of tooth supporting tissues followed by Co-60 irradiation were investigated in this study. Mandibular first molar regions of 12 rats were irradiated at level of 40 Gy with Co-60 γ-ray. The histologic changes of periodontal tissues were observed at 6 hours, 1, 3, 7 and 14 days after irradiation. Predominant changes were dilatation and engorgement of vessels, decreased number of cell components and pyknotic change of nuclei of fibroblasts, osteoblasts and osteocytes. At 14th day after irradiation, pyknotic change of nuclei of osteoblasts and decrease of osteoid were observed obviously.
Osteoclasts, however, seemed to be as quantitatively and qualitatively identical as in control group at 14th day.
From these findings, it was suggested that widening of the periodontal space might be a result of the relative increase of bone resorption after irradiation.
