| In this study, we investigated the structural and functional alterations in inferior alveolar nerve, accessed the quality of regenerate bone after distraction osteogenesis at different rates and lengths in a rabbit model of mandible lengthening, and primarily determined the right distraction rates and safe distraction lengths that could not result in or increase inferior alveolar nerve injury but could gain well bone formation. This study also brought forward the method of distraction osteogenesis by varying the rate at large length distraction, and it was hoped that the method could enhance the efficiency of distraction osteogenesis. We want to offer a reference to the reasonable, high effective and safe use of clinical distraction osteogenesis.Part I Effects of rates and lengths of distractionosteogenesis on the inferior alveolar nerve Objective: To discuss right methods by which one could lengthen the mandible satisfactorily and avoid injury to the inferior alveolar nerve by investigating the effects of distraction osteogenesis on the inferior alveolar nerve at different rates and lengths.Methods: 16 New Zealand rabbits were randomly divided into 5 groups at different rates and lengths. X-ray, electrophysiological and histological observations were performed to evaluate the qualities of the regenerate bone and inferior alveolar nerve.Results: A distraction rate of 2.0mm/d resulted in fibrous non-union of the distraction gap. After mandibular lengthening to 15mm at 1.5mm/d,the regenerate bone well formed, but the inferior alveolar nerve showed irreversible injury. After mandibular lengthening to 15mm at 1.0mm/d, the structure and function of inferior alveolar nerve showed recovery trend. After mandibular lengthening to 9mm at 1.5mm/d or l.Omm/d, the structure and function of inferior alveolar nerve recovered on the whole. Conclusion: The right rates of mandibular distraction osteogenesis should be 0.5 ~ 1.5mm/d. When the length was small, properly increasing the rate would be fit. When at large length, one should decrease the rate to reduce the inferior alveolar nerve injury.Part II Experimental study to enhance the efficiency ofdistraction osteogensis by varying the rate Objective: To discuss ways to enhance the efficiency of distraction osteogenesis by accessing the quality of regenerate bone after mandibular lengthening to 15mm by varying the rate that was fast early and slow late. Methods: 5 New Zealand rabbits underwent unilateral mandibular osteotomy. After a 5-day latency, the distractor was activated at a rate of 0.75mm×2/d to 9mm, then at a rate of 0.5mm×2/d to the other 6mm, consolidated for 15 weeks at most. X-ray and histological observations were performed.Results: Regenerate bone gradually maturated after the distraction period. At 15 weeks of consolidation, the quality of the regenerate bone in the distraction gap was similar with the original bone. Conclusion: Distraction osteogenesis by varying the rate could gain well bone formation, which reduced the distraction time and enhanced the efficiency.Part III Preliminary study on the effect of distraction osteogenesis on the inferior alveolar nerve byvarying the rateObjective: To study the effect of mandibular lengthening to 15mm on the inferior alveolar nerve by varying the rate that was fast early and slow late.Methods: 5 New Zealand rabbits underwent unilateral mandibular osteotomy. After a 5-day latency, the distractor was activated at a rate of 0.75mmx2/d to 9mm, then at a rate of 0.5mmx2/d to the other 6mm, consolidated for 15 weeks at most. Electrophysiological and histological observations were performed.Results: The mandible was lengthened to 15mm and the inferior alveolar nerve was average 21.99% longer than its original length. At completion of distraction, serious nerve degeneration was observed. The amplitude of the sensory nerve action potential was only 9.70% of that before operation and the latency period showed certain prolongation. Then recovery trend was found. The amplitude was 33.85% of that before operation...
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