CONTROLLED MULTIPLANAR DISTRACTION OF THE MANDIBLE, PART II - LABORATORY STUDIES OF SAGITTAL (ANTEROPOSTERIOR) AND VERTICAL (SUPEROINFERIOR) MOVEMENTS

The application of distraction osteogenesis in craniofacial surgery ha s significantly altered the treatment of congenital mandibular deficie ncies. However, evaluation of results in both animal studies and clini cal cases has revealed deficiencies, particularly in two areas. First, distraction using a uniplanar device in an anteroposterior direction can result in a persistent anterior open bite. Second, the lateralizat ion of the distracted hemimandible was often limited, with insufficien t incremental gain in the bigonial distance. To overcome these shortco mings, a multiplanar distraction device was developed and tested in th e canine model. This report details canine studies addressing the firs t problem: combined anteroposterior or sagittal (z-axis) and superoinf erior or vertical (y-axis) movements. Six dogs underwent bilateral man dibular distraction with an external (extraoral), multiplanar device a nd completed sagittal plus vertical distraction. Evaluation included c linical examination (facial form, jaw position, and occlusion), photog raphy, cephalograms (posteroanterior, basilar, and lateral), three-dim ensional computed tomography reconstructions, and examination of dry s kulls. The dogs averaged 18.5 mm (range, 15-20 mm) of sagittal distrac tion and 41.0 degrees (range, 21-50 degrees) of vertical distraction. Marked anterior open bites were produced after vertical distraction se condary to premature contact of the maxillary and mandibular molars. D istraction in the vertical direction also had the additive effect of i ncreasing the sagittal gains by approximately 5% to 10%. In conclusion , a multiplanar distraction device (with the potential for distraction in three planes) was effective in increasing mandibular anteroposteri or thrust (sagittal distraction) and also in creating an anterior open bite (vertical or superoinferior distraction). Vertical distraction p robably requires bilateral osteotomies to obtain optimal results. The preliminary gains in sagittal length are modified (reduced or increase d) after distraction in a second plane (vertical and horizontal). Spec ifically, vertical distraction in the inferior direction (creating an open bite) also leads to isolated increases in the anteroposterior pla ne. Conversely, vertical distraction in the superior direction (closin g an open bite), as seen in a human malocclusion, may lead to isolated decreases in the anteroposterior plane, but this question remains to be investigated in the laboratory.