Low Levels of Sexual Dimorphism and High Levels of Correlation Within the Human Deciduous Molars From the Ratón Pérez Collection.

OBJECTIVES: The study of deciduous teeth provides insights into early dental development, morphological variation and underlying biological processes, with relevance to oral biology, pediatric dentistry and anthropological research. Here, we analyze the linear dimensions of the largest known sample of associated deciduous molars to investigate patterns of sexual dimorphism, covariation, and developmental integration. MATERIALS AND METHODS: The sample comes from the Ratón Pérez Collection, a modern human sample curated at the National Research Center on Human Evolution (Burgos, Spain). Standard odontometric measurements were collected from 428 upper and lower deciduous molars from 211 children, including mesiodistal (MD) and buccolingual (BL) diameters, crown index (CI) and crown area (CA). The sample included isolated and associated individuals, enabling within-individual comparisons across teeth and jaws. Statistical analyses evaluated sexual dimorphism and correlation between molars within and across dental arcades. RESULTS: Sexual dimorphism is generally low, with significant differences restricted to a small number of comparisons, mainly involving mandibular second deciduous molars. Within individuals, crown size-related variables (MD, BL, and CA) show strong and consistent metameric covariation (dm1-dm2) and between dental arcades (upper-lower), indicating developmental integration. Crown proportions (CI) display weaker and less consistent associations. DISCUSSION: These findings indicate that crown size during early odontogenesis is shaped by shared developmental influences operating across the deciduous molar field. In contrast, crown proportions reflect localized aspects of crown morphology. The weak expression of sexual dimorphism supports the use of pooled samples, while the strong integration of size-related variables helps explain the effectiveness of odontometric approaches.