OBJECTIVETo figure out the differences of the morphological characteristics of mandibular symphysis between Class II and Class III adult skeletal malocclusions with different abnormal vertical skeletal patterns.

METHODS109 Chinese female adults of skeletal Class II and Class III were chosen and divided into four groups according to vertical and sagittal skeletal pattern: Class II--vertical-growth-pattern group (n=30), Class III--vertical-growth-pattern group (n=25), Class II--horizontal-growth-pattern group (n=29), Class III--horizontal-growth-pattern (n=25). Lateral cephalograms were taken. The symphyseal widths and heights, along with lower incisor positions were evaluated. Observation and statistics analysis were done to clarify the morphological characteristics of the symphyseal region of different skeletal patterns.

RESULTSThere were morphological differences of symphyseal region between Class II and Class III skeletal malocclusions, but not significant in width and total height. With a vertical-growth-pattern, Class II malocclusions had higher alveolus than Class III, but smaller chin prominence and lower basal bone (P < 0.01). With a horizontal-growth-pattern, Class II malocclusions had higher alveolus (P < 0.05) and larger alveolar top width (P < 0.001). With a same sagittal skeletal pattern, vertical-growth-pattern group had thinner but higher symphyseal region and bigger chin prominence (P < 0.001 in Class II while P < 0.05 in Class III). Besides, a vertical-growth-pattern malocclusion was prone to have a cucurbit-morph chin, of which Id width was larger than basal width (P < 0.01).

CONCLUSIONThere are morphological differences in symphyseal region between Class II and Class III skeletal malocclusions with different abnormal vertical skeletal patterns. The influence of abnormal vertical skeletal pattern to symphyseal morphological characteristics is greater than that of abnormal sagittal skeletal pattern. There is a risk of orthodontic movement of low incisors in vertical-growth-pattern skeletal malocclusion.