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AN EXPERIMENTAL STUDY FOR THE EFFECTS OF COBALT-60 IRRADIATION ON THE HEALING OF MANDIBULAR FRACTURE OF RATS

The purpose of this study was to observe the effects of cobalt-60 irradiation on the healing processes of rat mandibular fracture. Complete fracture was produced on the left mandibular body area of 105 white rats. 105 white rats were used for this study, divided into control and experimental groups. Experimental group was divided into three groups. Nonirradiated animal after fracture were served as the control group, and 4M 60 irradiation therapy unit was used for the irradiation on experimental goup rats. The single irradiation dosage were 530 rads, 800 rads and 1500 rads on subgroup Ⅰ,Ⅱ,Ⅲ, respectively on head and neck region. The experimental animals were sacrificed at 3rd days,1st, 2nd, 3rd and 4th weeks after irradiation. Each specimen was fixed in 10% formalin solution, decalcified with 5% nitric acid and embeded in paraffin. The specimens were sectioned to 4-6μ in thickness and stained with hematoxylin-eosin for histopathological observation. The obtained results were as follows; 1. All experimental groups showed generalized pyknosis of osteogyte, decrease in number of osteocytes and fibroblasts, the hemorrhage, the chronic inflammatory cell infiltration, and fatty degeneration in bone marrow space. 2. All experimental groups showed the retardation of callus formation and new bone formation, resulted delayed healing of fracture in mandible. 3. The healing was delayed with the increase of radiation dosage. 4. Radiation injury on the healing process of fracture was severe on 3rd and 7th days after irradiation, and showed the tendency of recovery on the 4th week after irradiation.