MIDFACE MEMBRANOUS BONE LENGTHENING - A ONE-YEAR HISTOLOGICAL AND MORPHOLOGICAL FOLLOW-UP OF DISTRACTION OSTEOGENESIS

Midface bone lengthening was performed on three young, adult sheep usi ng distraction osteogenesis following osteotomy of the maxilla and mou nting of an extraoral fixation device. The midface was,gradually distr acted, 2 mm/day, for 21 days, up to approximately 40 mm. A marked midf ace advancement was noted. Following a further 6 weeks of retention, t he device was removed and the animals were followed for 1 year. Biopsi es specimens were taken from the distracted area at the end of the dis traction period, after the additional 6 weeks of retention, and finall y 1 year later. A nondistracted area of the maxillary bone served as c ontrol. The specimens were analyzed histologically, histochemically, a nd by scanning electron microscopy for the ultrastructural pattern, mi neralization, mineral content, and approximate Ca2+ concentration. Cli nically and radiographically, all sheep fully bridged the experimental gap. Histologically, at the completion of distraction, collagen bundl es and slender bone trabeculae oriented in the direction of the distra ction could be seen. At the end of the retention period, the trabecula e thickened noticeably and were partially replaced by mature lamellar bone. At the end of 1 year and after completion of the process of remo deling, the pattern of the distracted area resembled the control area. The mineralization, as reflected by quantitative calcium analysis, co mpared with the nondistracted area, demonstrated a low rate of mineral ization after 3 weeks of lengthening, increased 6 weeks later, and aft er 1 year became nearly the same as in the nondistracted area. In conc lusion, distraction osteogenesis provides satisfactory quantitative an d structural new bone.