Gonial angle changes after bilateral unidirectional mandibular distraction in sheep.

It was the aim of this study to investigate radiologically the distraction site in the gonial angle area after three different protocols of unidirectional mandibular distraction in sheep. Bilateral mandibular distraction was performed in nine sheep, and one other sheep served as a sham-operated control. In the nine experimental sheep, three different distraction protocols were used. In three sheep, an oblique corticotomy line was applied and the distractors were positioned perpendicular to the corticotomy line. In three other sheep, a horizontal corticotomy line was applied and the distractors were also positioned perpendicular to this corticotomy line. In the remaining three sheep, again, a horizontal corticotomy was performed, but with an angular positioning of the distractors relative to this corticotomy line. Distraction of 20 mm was performed over 20 days at a rate of 1 mm per day. After 3 weeks of retention the sheep were sacrificed, the mandibles were dissected and hemisectioned, and standardized hemimandibular contact radiographs were made of the specimens. The distracted gaps were traced from the radiograph and the gonial angle was measured. The displacements of the distracted parts were measured, the gonial angles were determined, and the values were compared with four additional control non-distracted sheep mandibles. The results show that there was a very large variability in the distracted gaps as well as in the gonial angle changes after distraction, and it was not possible to recognize any of the three different distraction protocols radiographically after distraction. Although performed under standardized conditions it is difficult to reproduce intended mandibular corticotomy lines in sheep.