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Abstract
Distraction osteogenesis (DO) has been used regularly in oral and maxillofacial surgery since it was first reported by McCarthy et al (10) in 1992.1 The technique is based on the regenerative properties of bone. To elongate hypoplastic bone, the bone needs to be osteotomized, after which the bone segments are gradually pulled apart. The callus in the resulting gap between the bone segments is eventually replaced with calcifying tissue. The success of the treatment depends on several factors. These include distraction parameters such as the latency time, the rate of distraction, the rhythm of distraction, and the consolidation time. Optimizing these parameters would result in improved and accelerated osteogenesis, and consequently in shorter treatment time. This would considerably increase the quality of life for the patient, knowing that treatment time can usually take several months, during which the patient
The present study was conducted for evaluate the effect of different rates of mandibular distraction osteogenesis on the inferior alveolar nerve. Eight dogs older than one year and an average weight of 15 Kgs were included in this study.
The surgery was performed under strict aseptic conditions. The periostium was elevated carefully to preserve it intact. At the planned osteotomy site anterior to the first molar, bone cut was initiated using surgical bur. With a medial cortex still intact and the bone incompletely
separated, the pin holes were drilled with a suitable driller ,Chisels and mallet were used at the planned osteotomy site to complete the bony cut Every effort was made to avoid direct injury of the inferior alveolar neurovascular bundle during the surgical procedure the pins were screwed through the drilled holes till engage the medial cortex .chisel were used carefully to complete the bone segment separation from the medial side. the distractor was fitted back on the pins. Readymade uniaxial mandibular distraction device used at the mandibular body unilaterally for linear distraction. After 5 days latency period, the distraction device was activated 1.0 mm.per day for 10 days for group I and 2.0 mm.per day for 5days for group II (10.0 mm. distraction distances. After completion of activation, the distraction device was left in place for two weeks consolidation period.
Two weeks after distraction the dogs were painlessly killed and the distracted segment of IAN and contra lateral non distracted IAN segment were carefully dissected , removed ,processed and stained to examine under light microscope, the result showed that mild Wallerian degeneration in group I and sever Wallerian degeneration in group II, The Quantitative histomorphometric assessment ,showed a decrease in the number of axons after mandibular lengthening in both groups Statistical comparison revealed that the mean axonal counts in group II were significantly less than in group I (P >.05) and group B (P>.05). Although group I showed a trend toward a decrease in axonal density,
from the result of this study the following may be concluded:
1- The results of this study suggest that a rate of 1 mm per day appears to be relatively safe for the inferior alveolar nerve during mandibular distraction. However, a higher rate of distraction seems to result in greater damage to the nerve. Thus, rapid mandibular distraction may not be advisable.
2-The mandibular lengthening through the use of distraction device is a feasible procedure.
3- Dogs are good animal model to study distraction osteogenesis