^<60>Co 大量局所照射の成熟家兎下顎におよぼす影響について

Abstract

This study was performed in order to observe the effect of ^<60>Co γ-ray irradiation on rabbits' mandible, for as long as possible, approximately 18 months. Materials used were 56 adult male rabbits, weighing approximately 2.5Kg. They were subdivided into four groups : Group 1 was irradiated 5, 000 R (9 cases), Group 2, 8, 000 R (12 cases) and group 3, 10, 000 R (12 cases) respectively. Group 4 was a control group and was given no irradiation (23 cases). Dosimetry was performed with a Victoreen R-meter, chamber 621 in air. Irradiation method was as follows : Prior to irradiation, the rabbits were anesthetized with subcutaneous injection of 25% Uretan solution. Radiation equipment used was ^<60>Co double rotation apparatus, RT 2000 made by Shimazu, Containing approximately 1300 curie of ^<60>Co, with Filter 0.5mm Cd., Field size 4×4 cm. Anesthetized rabbits were fixed, except the head, in a specially constructed metal box. Between the focus and the animals, a 10×10×15 cm Pb-schield block with a 15 mm perforation in the center was placed as close to the head as possible, and then, irradiation was performed through the hole towards the right side of the mandible as a single dose. Gross examination, radiographical and histopathological studies were done after irradiation. Results obtained can be summarized as follows : 1. Depilation was noticed on the irradiated field of the rabbits' skin in the three respective groups. The more dose of radiation given, the earlier the onset of depilation occured. 2. The upper anterior teeth of all experimental animals showed elongation, lateral flection and diasthema. 3. Gross examination and radiologic investigation of the lower anterior teeth showed shortening or disappearance of the crowns and resorption of the root apex in all experimental animals. These teeth were lost eventually. Molar teeth disclosed shortening of crowns and irregular and partial loss on the surface of the dentine. Pulp chambers were extremely narrowed. These changes were most conspicuous in the 10, 000 R irradiation group. 4. Mandibular fractures occured in 13 cases, which include 3 cases with 5, 000 R, 4 cases with 8, 000 R and 6 cases with 10, 000 R. 5. Histopathological examination revealed that the alveolar bones were resorped, as the result, and were replaced with mandibular bone trabeculae. Various types of ankylosis of root surface and mandibulars were seen. These changes were more frequently noted in the molar regions than the anterior regions and in the groups with higher doses and longer days after irradiation. 6. Bone trabeculae and cortex of the mandibles were resorped in the 3 irradiation groups in the early stage, but regeneration and thickening of the bones occured later. 7. The usual case was that the anterior bone marrow became more gelatinous and the molar marrow became more fibrous. Hyperemia and abscess formation were recognized in some cases. Although in the molar regions these pathological changes were conspicuous in proportion to the amount of dose, in the anterior regions, the same changes were more conspicuous in the 5, 000 R irradiation group than in the 8, 000 R group.