Geometric Morphometric Analysis (GMA) Of Mandibular Symphysis In Class Iii Skeletal Base Patients

Objective: To investigate the mandibular symphysis (MS) shape variation among adolescents, emerging adults, and adults with Class III skeletal base, using geometric morphometric analysis. Materials and Methods: Pre-treatment lateral cephalometric radiographs of 254 patients aged between 11-40 years old, with Class III skeletal base (ANB <1o ) and lower incisor angle (LIA <99o ) were included. The sample was divided in to adolescents, emerging adults, and adults based on gonial angle (>130o : high angle, 120o -130o : average angle and <120o : low angle). Nine landmarks with x and y coordinates were identified on MS. Shape and statistical analysis carried out using Morpho J version 1.06d (Klingenberg Lab, Manchester, UK). Results: In high gonial angle group, adults had significantly narrower alveolar and basal part of MS (p=0.003) while emerging adults had significantly narrower alveolar part of MS (p=0.01) compared to adolescents. In average gonial angle group, only adults had a significantly narrower alveolar and basal part of MS compared to emerging adults (p=0.007) and adolescents (p<0.0001). Low gonial angle group showed wider and shorter MS with no significant shape variation for all age groups. Multivariate regression showed significant shape variation of MS shape with increasing age (p<0.0001). Conclusion: The shape of the MS can be affected by age groups where significant MS shape variation observed between adolescents, emerging adults, and adults. Hence, understanding the shape variation of MS especially in adults with high gonial angle is important during orthodontic treatment planning to avoid unwanted complications