Cortical bone distribution in the human mandibular symphysis: Ontogenic and morphometric approaches in archeological context

The human mandibular symphysis concentrates multiaxial loads during function and remodels throughout growth, but the precise mechanisms underlying cortical bone shape during growth remain relatively unexplored. Approaches based solely on thickness or external cortical contours provide only partial insights and do not capture the functional, genetic, and allometric interactions driving morphogenesis. In this study, we analyzed symphyseal cross-sections from 63 subadult mandibles from two French archeological assemblages using elliptic Fourier analysis. Micro-computed tomography volumes were reconstructed, and external and internal cortical outlines digitized and quantified with Fourier descriptors. Principal component analysis summarized shape variation, and linear models tested the effects of size, age, total cortical area, and geographic origin on each outline. A similar workflow was applied to the size variable expressed as the logarithm of centroid size to test the following predictors: age, total cortical area and archeological site of origin. Across cortical outlines, symphyseal shape was governed primarily by allometry, with a smaller additional contribution of total cortical area. Age significantly affected the inner cortical outline but not the outer one, and geographic origin had no detectable influence. Individuals examined before and after eruption of the first permanent molar occupied largely overlapping morphospaces, indicating a continuous developmental trajectory rather than a shift at eruption. Collectively, the results support bone-tissue remodeling that progresses throughout growth and is dominated early by size-related change, with the hypothesis that inter-individual divergence emerges later. The approach provides a reproducible, resolved framework for quantifying bone remodeling across ontogeny and for testing form-function relationships.