Effect of Radiation on Rabbit Mandible Distraction Osteogenesis during Consolidation

PURPOSE: The purpose of this study was to evaluate the effect of radiotherapy on new bone formation in rabbit mandibles distraction during consolidation time. MATERIALS AND METHODS: Twenty New Zealand white rabbits were randomly divided into 2 groups. Group 1 received corticectomy in both sides of mandible and then began distraction 5d after surgery. The distractor were stretched 0.5mm each time and two times each day in the distraction period of 10 days. The fixation period is 8 weeks. Group 2 were treated as Group1. And at 4ws after consolidation, Group 2 was irradiated by 60Co, 5.4Gy every time, one time every other day and five times totally.All animals were sacrificed 8 weeks after fixation, and the callus in distraction area was harvested and assessed by X-ray photograph, histological observation,scanning electron microscope,Ca/P ratio analysis as well as 3-point bending test. RESULTS: New bone fill can be obtained in all distracted mandibles. X-ray examination showed no significant difference of new bone foramtion between irradiated and non-irradiated group. Histological observation and SEM showed new woven bone lining up in order can be obtained in all groups while there were more cartilage islands in the irradiated group and less mature.The contents of Ca/P were found to be no different in the two groups. The result of 3-point bending test demonstrated the biomechanical strength of new formed bone of no-irradiated group was better CONCLUSIONS: It seems that radiotherapy is feasible in the period of consolidation during distraction osteogenesis, although the new bone contains more cartilage component and lower mechanical strength. The results of this study support that bone distraction could be used for the repairment of mandibular defects following surgery for oral tumours which require early postoperative radiotherapy.