Assessment of symphysis morphology as a predictor of the direction of mandibular growth.

The purpose of this study was to determine whether symphysis morphology could be used as a predictor of the direction of mandibular growth and to assess growth changes of the symphysis. Cross-sectional data included lateral cephalometric radiographs of 115 adults (58 women, 57 men) with the longitudinal sample a subset of 62 subjects (30 females, 32 males) at four age groups. The direction of mandibular growth was evaluated with seven cephalometric measurements that included Y-axis, SN to mandibular plane, palatal plane to mandibular plane, gonial angle, sum of saddle, articulare and gonial angles, percentage lower facial height, and posterior/anterior face height. The mandibular symphyseal dimensions studied were height, depth, ratio (height/depth), and angle. Symphysis morphology was found to be associated with the direction of mandibular growth, especially in male subjects with symphysis ratio having the strongest relationship. A mandible with an anterior growth direction was associated with a small height, large depth, small ratio, and large angle of the symphysis. Conversely, a posterior growth direction was associated with a large height, small depth, large ratio, and small angle of the symphysis. Symphysis dimensions continued to change until adulthood with male subjects having a greater and later occurring change compared with female subjects.