Electrophysiologic evaluation of inferior alveolar nerve regenerated by bifocal distraction osteogenesis in dogs

The Effect of Distraction Osteogenesis on Peripheral Nerve Regeneration in Rats: A Preliminary Study In Vivo

Distraction osteogenesis (DO) is a widely employed method for the treatment of limb discrepancies and deformity correction. This study aimed at observing the histomorphological and ultrastructural changes of peripheral nerves around the distraction area during DO and investigating the self-repair mechanism of peripheral nerves in a rat DO model. Sixty rats underwent right femoral DO surgery and were randomly separated into six groups: Control (latency, no distraction, n = 10), Group 0-week (after distraction, n = 10), Group 2-week (n = 10), Group 4-week (n = 10), Group 6-week (n = 10), and Group 8-week (n = 10) at consolidation phase. The right femur of rats in Group 0-week, Group 2-week, Group 4-week, Group 6-week, and Group 8-week was subjected to continuous osteogenesis distraction at a rate of 0.5 mm/day for 10 days. Motor nerve conduction velocity (MNCV) of the sciatic nerve, sciatic function index (SFI), histological analyses, and transmission electron microscopy were conducted to evaluate nerve function. The MNCV and SFI of Group 0-week, Group 2-week, Group 4-week, and Group 6-week were significantly lower than the Control (P < 0.05). No statistical differences were found between the Control and Group 8-week in terms of MNCV and SFI (P > 0.05). Injuries to nerve fibres and nodes of Ranvier were observed in the Group 0-week, whereas the nerve fibres returned to the normal arrangement in the Group 8-week and oedema of myelin disappeared, with the continuity of axons and lamellar structure of myelin being restored. Femoral DO in rats with a rate of 0.5 mm/day may cause sciatic neurapraxia, which can be self-repaired after 8 weeks of consolidation. The paraneurium around the sciatic nerve enables it to glide during the distraction phase to reduce the occurrence of injurious changes.

Evaluation of inferior alveolar nerve regeneration by bifocal distraction osteogenesis with retrograde transportation of horseradish peroxidase in dogs

Background

Bifocal distraction osteogenesis has been shown to be a reliable method for reconstructing segmental mandibular defects. However, there are few reports regarding the occurrence of inferior alveolar nerve regeneration during the process of distraction. Previously, we reported inferior alveolar nerve regeneration after distraction, and evaluated the regenerated nerve using histological and electrophysiological methods. In the present study, we investigated axons regenerated by bifocal distraction osteogenesis using retrograde transportation of horseradish peroxidase in the mandibles of dogs to determine their type and function.

Methods and Findings

Using a bifocal distraction osteogenesis method, we produced a 10-mm mandibular defect, including a nerve defect, in 11 dogs and distracted using a transport disk at a rate of 1 mm/day. The regenerated inferior alveolar nerve was evaluated by retrograde transportation of HRP in all dogs at 3 and 6 months after the first operation. At 3 and 6 months, HRP-labeled neurons were observed in the trigeminal ganglion. The number of HRP-labeled neurons in each section increased, while the cell body diameter of HRP-labeled neurons was reduced over time.

Conclusions

We found that the inferior alveolar nerve after bifocal distraction osteogenesis successfully recovered until peripheral tissue began to function. Although our research is still at the stage of animal experiments, it is considered that it will be possible to apply this method in the future to humans who have the mandibular defects.