Morphological characteristics of mandibular symphysis in adult skeletal class II and class III malocclusions with abnormal vertical skeletal patterns

Objective To 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.Methods 109 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.Results There 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(P0.01).With a horizontal-growth-pattern,Class Ⅱ malocclusions had higher alveolus(P0.05) and larger alveolar top width(P0.001).With a same sagittal skeletal pattern,vertical-growth-pattern group had thinner but higher symphyseal region and bigger chin prominence(P0.001 in Class Ⅱ while P0.05 in Class Ⅲ).Besides,a vertical-growthpattern malocclusion was prone to have a cucurbit-morph chin,of which Id width was larger than basal width(P 0.01).Conclusion There 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.