Character of distracted bone in irradiated canine mandibles and electrophysiological changes in the inferior alveolar nerve

Our aim was to explore the character of distracted bone in irradiated canine mandibles and the electrophysiological changes in the irradiated inferior alveolar nerve (IAN). Twelve Chinese dogs were studied, 10 of which were given unilateral irradiation of ⁶⁰Co in the mandible with a total dose of 22.8 Gy in four 5.7 Gy fractions (biologically equivalent to 50 Gy/25 fractions) (experimental group). The other two dogs were not irradiated and served as controls. All had a bilateral corticotomy 3 months after irradiation. After a 1-week latency period distraction of the mandible was activated at a rate of 0.5 mm twice daily for 10 days, followed by a consolidation phase of 8 weeks. New bone was assessed by radiographic, histological, and single-photon electron computed tomographic (SPECT) analysis. The IAN was analysed electrophysiologically. One dog in the experimental group was excluded from the study with anaesthetic problems. After 8 weeks of consolidation there was no difference between the percentage area of new bone in the two groups. New bone was more mature and organised in the control group than in the experimental group. SPECT analysis showed that there was active osteogenic activity in dogs in the experimental group. The action potential of the IAN showed corresponding changes during the irradiation and distraction processes.