A Component Type Of Bilateral Mandibular Distracter And Animal Experiment

Objective: Bilateral mandibular hypoplasia result from kinds of congenital or acquired deformity was common in clinic, which may lead to physiognomic malformation and dysfunction. Conventinal surgery by using bone trasplantation had been adopted to cure this disease, but it had many shortcomings. While distraction osteogenesis had been used to avoid the problems of conventinal surgery, it could lengthen the mandibule and surrounding soft tissues simultaneously. The development of distraction osteogenesis was connected with the kind of distracter closely. At present, the distracters had many merits and shortcomings. This experiment was to study and develop a component type of bilateral mandibular distracter, which had the virtues of external and internal distracter. The hybrid type bilateral mandibular distracter had the characters of intraoral incison, extraoral distractin, with low infection incidence, and without skin scars. The distracter was used in animal experiment to investigate the structure character of new bones of osteogenesis during different period of distraction, and to observe the effect of bilateral mandibular distraction osteogenesis on temporomandibular joint. Methods: 1 Distracter design: A component type of bilateral mandibular distracter custom-made was consisted of center threaded rod, oriented rods, horizontal joint arms and fixed arms. The center-threaded rod had a bidirectional screw thread, each turn of which resulted in 1mm of expansion. The largest liner expansion was 19mm. 2 Animal experiments: Twelve healthy goats randomly divided into 4 groups of 3 goats for each group, were fixed on the bilateral mandibulars for 1,2,3,4, weeks, respectively. The mandibles were held in a neutral position for 7 days, and then lengthened at a rate of 0.5mm per 12 hours for 10 days. After the distraction, the goats were sacrificed on days 7,14,21,28, respectively, and the radiographic examinations were made. On the 6th and 12th days before sacrificed, tetracycline (0.5mg/kg) was administered. The specimens were consisted of new bone and normal bone bilaterally. The soft tissues and redundant bone were eliminated. The lengths of the new bones were measured. Half of the specimens were fixed with 10% formaldehyhe for 7 days and 8% formic acid were used to dissolve the bone calcium for 20 days. After rinsed 24 hours with water, the specimens were stained with HE for histological examination. Another specimens were fixed with 70% alcohol for 3 days and dissolve the bone calcium gradually. Fluoroscopical study was performed to observe the quality and speed of new bone's formation during different period of distraction. The bilateral condyle specimens of group 4 were harvested to observe the change of superficial ultrustructure.Results: 1 Gross observation: (1) After surgery all the experimental animals were alive. The operative procedure was well tolerated by the animals. Mandible was lengthened. During the experiment period, well healing was found between the distracter and surrounding tissues except two distracters were removed for infection. (2) The new bone regenerated from the edge of the distraction gap toward the center. At the 4th weeks of the fixed period, the new bone was full of the distraction gap. The color and luster of new bone were dimmer than original bone, and the surface was rougher. (3) The condyles had an oval form and covered by a smooth, white fibrocartilage layer. There was no abnormal bone follicle and defect on them. 2 The radiographic examination: On the first day of fixation, X-ray examination demonstrated that the mandibles were prolongated, and the line of osteotomy could be seen clearly. No new bone formation in the interspaces of the distraction gap immediately after the distraction. From the 2nd weeks of the distraction, new bone began to regenerate, and the gap was filled by new bone gradually. Four weeks later the gap was replaced completely by the low-density bone. 3 In all the animals, the means of lengthened mandible was 8.90±0.52mm. 4 The results of light microscopy were as follows: group1: Fibrous tissue and hemorrhage was seen in the center region. On bilateral bone ends, longitudinal new bone trabeculae were seen. Group 2: The distraction gap was filled with fibers arrayed from the distraction direction; early bone...