An experimental study of radiation hazard to mandible at deciduous dental stage

In order to make a radiological and histopathological investigation of radiation injury to jaw bones at growth stage, the region of left mandibular third deciduous tooth of young dogs were irradiated for 3,000 R with 200 kVp X-ray. In the periodontal tissue of deciduous teeth, inflammatory cell infiltration was observed in the periodontal membrane on 12th day after irradiation. Thereafter, with progress in bone resorption, proliferation of cementum and alveolar bone was seen at 4th month. At 8th month, prolifered alveolar bone filled the periodontal membrane space and infiltrated into the region where root dentin was resorbed. As injury to the cortical bone, resorption in moth-eaten pattern and vacuolation or enlargement of bone lacunae were observed at 2nd month. At 4th month, however, resorption and vacuolated bone lacunae decreased and new Haversian system was also seen at 8th month. As injury to the alveolar bone, radiological finding of irregular trabeculae was seen on 9th day and spotty bone resorption was seen at 2nd month. Formation of fatty marrow began on 12th day after irradiation of bone marrow. About at 2nd month, fibrous marrow was observed and inflammatory cell infiltration was seen there. Resorption of bone trabeculae was due to appearance of osteoclasts and the appearance of osteoclasts was closely related with inflammatory cell infiltration. As changes in the inferior alveolar artery, extension of elastic fibers and looseness of circular tunica media were seen between 1st and 4th month. At 8th month findings were nearly normal. As injury to tooth germ of permanent teeth, hyper-calcification image resulting from early completion of calcification of dentin at the crown portion was observed. Root formation stopped at 2nd month. The root region was obstructed by osteodentin and root formation was no longer observed thereafter. (J.P.N.)