[Comparison of mandibular and chin morphology in adults with skeletal Class III malocclusion in different vertical facial types].

PURPOSE: The purpose of this study was to compare the difference of mandibular and chin morphology in adults with skeletal Class III malocclusion in different vertical skeletal types, and to find the relationship among them. METHODS: The pretreatment lateral cephalographs of 60 adults (30 males, 30 females, with an average age of 21±3.020 years) with skeletal Class III malocclusion[ANB<0° average (-3.927±2.7637)°] were selected randomly. They were divided into three groups according to mandibular plane angle: high angle group(20 cases,FH/MP<32°, average angle group(20 cases, 22°<FH/MP≥32° and low angle group(20 cases, FH/MP≤22°. Then the vertical and horizontal craniofacial pattern, mandibular and chin dimensions (angular, linear and proportional measurements) were measured and analyzed statistically using SPSS 16.0 software package. RESULTS: Compared with the low and average angle groups, high angle subjects exhibited increased mandibular angle, chin height and curvature, and decreased chin minimal depth, chin minimal depth /depth ratio, depth/height ratio, chin angle(P<0.05). Further comparision of every two groups showed that there was significant difference in mandibular angle, chin minimal depth, chin minimal depth /depth ratio, chin height between low and high angle group, and between average and high angle group(P<0.05); There was significant difference in chin curvature between low and high angle group(P<0.05). Positive correlation was found between mandibular plane angle and mandibular angle, chin height and curvature, while negative correlation between mandibular plane angle and chin minimal depth, chin minimal depth /height ratio, depth/height ratio, chin angle. CONCLUSIONS: Mandibular and chin morphology are different in adults with skeletal Class III malocclusion in different vertical skeletal types, and there is relationship between mandibular plane angle and mandibular and chin morphology, which deserve to be taken into consideration in orthodontic treatment plan.