It is well known fact that the mechanical or physical potentialities can influence the biological tissue behavior .In this current study this biological tissue response was investigated through gradual distraction of the mandibular bone. This study was performed on 20 dogs divided to two groups. The first group (group I) included 10 animals subjected to corticotomy at the angle of the mandible then distracted on either side of the corticotomy line by external distractor for 10 mm length using

more »

... o different rates of distraction. Half of this group (5 dogs) underwent distraction rate of 1.0 mm / day for 10 days, while for the rest of the group the distraction rate was 2.0 mm / day for 5 days. The second group (group II) included the other10 animals subjected to the same procedures undertaken to the animals of the first group but the distraction was performed for 20 mm distance. In each subgroup of the two main groups one animal was subjected to bilateral corticotomy but distracted only at one side. The non-distracted side was taken as a control. Dogs were left for consolidation period of 6 weeks before they were sacrified.The results indicated that the biomechanical distraction has induced lengthened skeletal repair simulated in the interstitial bone growth at the corticotomy site. In the mean time, the osteogenic activity was denser with the distraction rate of 1.0 mm per day than that with 2.0 mm per day. The Histological examination of distracted part of mandibular bone revealed an area of fibrosseous tissue containing collagen fibers interspersed with fibroblasts and small blood vessels. Many newly formed bone trabeculae composed mainly of immature woven bone were also showed, as well as small foci of bone resorption. Inferior alveolar nerve changes, comprising signs of severe degeneration, marked separation of the perineural sheath, decrease in number of axons and intervening areas of edema were seen in animals subjected for increased length with higher rate of distraction. In conclusion, the results revealed the capability of osteodistraction technique to stimulate osteogenesis, bone remodeling and also the deleterious effect on the inferior alveolar nerve following gradual mandibular osteodistraction in the dog.