Quantification of mandibular sexual dimorphism during adolescence

The present study investigates how sexual dimorphism in the human mandible develops in three-dimensionally during adolescence. A cross-sectional sample of mandibular meshes of 268 males and 386 females, aged between 8.5 and 19.5 years of age, were derived from cone beam computed tomography and were analysed using geometric morphometric methods. Growth trajectories of the mandible in males and females were modelled separately using a recently developed non-linear kernel regression framework. Growth rate and direction at a dense array of points all over the mandibular surface were visualized within each group and compared between groups. We found that mandibular sexual dimorphism already exists at 9 years of age, but this is mostly in size not in shape. The differential growth rate and duration between the sexes during pubertal growth largely explained by adult sexual dimorphism: the growth direction in both males and females is similar but the male mandible changed more quickly and over a longer period than the female mandible, where the growth rate peaked and declined earlier. This results in increasing dimorphism in form, which is evident in both size and shape. The development of dimorphic features, concentrated in the chin and ramus, were further visualized. The dense morphometric approach provides detailed three-dimensional quantitative assessment of the development of sexual dimorphism of the mandible.