How Allometry and Sexual Dimorphism Influence Cortical Bone Morphology at the Mandibular Symphysis in Modern Humans: A Comparative Study Using Elliptic Fourier Descriptors

OBJECTIVES: The modern human mandibular symphysis displays a mental prominence, a unique trait in the human lineage. Beyond this shared pattern, considerable variability in shape and metrics exists. This heterogeneity is thought to result from multiple mechanisms, including biomechanical compensation, allometric and dietary effects, population genetics, or sexual dimorphism. While the influence of these processes on overall mandibular shape is thoroughly documented, limited information exists on their effects on the distribution of mandibular cortical bone. Thus, this study assessed the impact of local and global allometry, sexual dimorphism, and cortical area on the shape and size of the symphyseal cortical bone contours. METHODS: We analyzed computed tomography images of 62 modern human mandibles using Elliptic Fourier Descriptors. The effects of the investigated variables on external and internal cortical bone shapes and sizes were tested using a nested multivariate approach and predicted shape reconstructions were used to visualize morphological variation. RESULTS: In this sample, sex, and local allometry had significant effects on mandibular symphyseal shape and sex was the main predictor of local allometry. Cortical area significantly affected the shape and size of the external cortical bone contour and body weight influenced the size of the internal cortical bone contour. CONCLUSION: Sexual dimorphism, allometric effects, and biomechanical compensation impact the shape and size of the mandibular symphysis. External and internal cortical bone contours respond differently to these effects. Future studies could investigate the influence of other relevant factors on symphyseal shape and size.