Study on Radiation Hazard : Influence of the Teeth on Mandibular Hazard

Progressive necrosis of the mandible is often seen as an undesirable condition after a radiation therapy of malignant lesions in or near the oral cavity. It has been believed that the possibility of this complication is decreased by the preliminary extraction of the teeth that are located in the irradiation area. This opinion, however, is not universal and some radiotherapists have advocated to keep the teeth in the irradiation area. Recently, many inverstigators believe that an extraction of the teeth before a radiation therapy reduces the radiation hazard. Both opinions on the radiation hazard for mandible mainly consist of clinical impressions. There are few experimental studies on the radiation hazard which were performed to evaluate the difference between the dentulous mandible and the edentulous mandible. A series of experiments were designed to know the influence of the teeth on the radiation hazard for mandible in this study. The right mandible of adult dogs were irradiated by means of an X-radiation generator. The physical factors used were : 200kVp, 19mA, filters 0.5mm. Cu+1mm. Al, half value layer 1.5mm. Cu, target skin distance 40cm. The irradiation was given in 1000R/time/3 days, and total dose was 3000R and 6000R. The results obtained are as follows : 1) Radiation hazards for the soft tissue revealed a significant difference between the dentulous and edentulous mandibles, macroscopically. The gingiva of irradiated dentulous mandible showed an ulceration after the irradiation. Necrosis of the alveolar mucosa, buccal mucosa and skin followed an ulceration, and eventually exposure of the alveolar bone of mandible occurred. The pathologic condition progressed rapidly and a loosening and an exfoliation of the teeth or a pathologic fracture of the mandible occurred eventually. 2) In the edentulous mandible (6000R irradiated group only) an ulceration of the skin developed as the first disturbance. The tissue necrosis progressed from the skin to the buccal mucosa and gingiva. Eventually an exposure of the alveolar bone occurred but no pathologic fracture was seen in the edentulous mandible. No specific pathologic findings were seen in the 3000R irradiated edentulous mandible. 3) The early roentgenological findings in the irradiated dentulous mandible were resorption of the alveolar crest and widening of the periodontal membrane space. Another changes of bone were osteoporosis and cortical bone destruction. 4) In the edentulous mandible (6000R irradia