3D geometric morphometric analysis of morphological covariation in the modern human postcanine dentition

Analysis of 3D shape covariation patterns between different tooth types is rarely investigated but is important for human evolution, dental anthropology, and medicine. We explored shape covariation of the postcanine dentition (excluding third molars) within and between dental arches using geometric morphometrics. Based on micro-CT scans of 526 teeth from 136 individuals, we analyzed dentine crowns, considering enamel-dentine junction (EDJ) occlusal surface and cervical outlines. High pairwise correlations occurred within dental arches (lower P3-P4, r₁ = 0.89; upper P3-P4, r₁ = 0.81; upper M1-M2, r₁ = 0.86). Between antagonists, correlations varied from the highest in upper-lower M1 (r = 0.90) to the lowest in upper P4-lower M1 (r = 0.58). Unexpectedly high covariation appeared between some non-occluding teeth (lower P3-upper M2, r₁ = 0.88). Relatively high covariation also occurred between different tooth classes serving similar masticatory functions: lower P4-upper M1 (r₁ = 0.79) and upper P4-lower M1 (r₁ = 0.77). Crown height and relative proportions emerged as the main factors driving covariation within the postcanine dentition, independently from allometric effects. Overall, morphological integration is stronger within the same dental arch than between antagonistic teeth. These results provide baseline data for developmental, phylogenetic, and functional studies of the human postcanine dentition, including potential phenotype-genotype associations.