The Effect of X-Ray Irradiation on the Development of the Mandibular Joint of the Mouse

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Abstract
38 Swiss and C57 black mice 2-7 days of age were irradiated in the area of the mandibular condyle using a contact type X-ray machine. The diams. of the irradiated field varied from 5 to 7 mm. and dosages of 1500, 3000 and 5000 were used. Following irradiation exptl. animals and littermate controls were sacrificed at time intervals of 5-62 days. The heads were fixed, decalcified, embedded in paraffin, and sectioned. The characteristic radiation changes in the condyle are marked reduction or cessation of osteoblastic activity, marrow aplasia and subsequent fibrosis of the marrow. The greatest radiosensitivity is exhibited by the cells of the proliferative and hypertrophic zones. Ten days following irradiation osteoblastic activity is slowly restored and an immature fibrous type bone is formed adjacent to the damaged cartilage cells. Irregular trabeculae are formed and in some cases this fibrous bone appears to seal off the entire cartilage cap. The late postirradiation changes consist of an increase in activity of the cells of the undifferentiated and intermediate zone. However, hyperplasia of these zones is occasionally seen in normal animals.
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