Effect of distraction rate on biomechanical, mineralization, and histologic properties of an ovine mandible model

Craniofacial microsomia is a common congenital malformation. Ilizarov's met hod of distraction osteogenesis applied to the mandible has yielded promisi ng results both experimentally and clinically. Because the technique is use d predominantly in a pediatric population, length of treatment and complian ce may be problematic. To date, the limits of distraction rate in the crani ofacial skeleton have not been defined. This study was designed to investigate the effects of distraction rate, in a large animal model, on the mineralization, biomechanical, and histologic properties of lengthened mandibles. Clinically faster distraction rates wou ld decrease the overall treatment time. Twenty-four animals were divided into four groups, with varying rates of di straction (1, 2, 3, and 4 mm/day). A uniaxial distracter at the angle of th e mandible was used. The mandibles were lengthened to 24 mm and fixed for a period of 5 weeks, when the animals were killed. The specimens were analyz ed with respect to mineralization using dual energy x-ray absorptiometry, b iomechanical strength, through a modified three-point bending test, and his tologic properties with hematoxylin and eosin stains. Biomechanical, mineralization, and histologic analyses of the samples indic ated that group 1 (1 mm/day) samples were significantly superior (p < 0.05) to those of group 4 (4 mm/day). Although bone formation was achieved in all groups, group I (1 mm/day) demo nstrated the strongest biomechanical and histologic properties. Bone minera l density obtained using dual energy x-ray absorptiometry may be clinically useful as a reliable, noninvasive, and relatively cheap predictor for remo val time of the fixator.