The assessment of the dental tissue proportions in the human dentition with a focus in the analysis of differences between males and females has triggered a special interest within forensic sciences. At the same time, the evaluation of the enamel and dentin dimensions has become a routine in taxonomic studies in human evolution. In this PhD dissertation, we employed microtomographic image analysis techniques to assess the three-dimensional dental tissue proportions of the permanent canines belonging to the Pleistocene populations of the Sierra de Atapuerca (Spain), as well as the canines of a large sample of modern humans of known sex. The main objective of this study is to explore the variability present in the dimensions of the different dental tissues of the populations under study and its utility to assess sexual dimorphism. Our study reveals that the dentin-pulp complex of permanent canines in modern humans is absolutely and relatively larger in males, resulting in a relatively thicker enamel in females.. This histological pattern has allowed us to define several variables that were used in the development of a new methodology for sex estimation. The accuracy rates obtained using this methodology reach values of up to 92.3% in modern humans, a reliability comparable to that of other methods commonly applied to the skull or pelvis. On the other hand, the study of the dental tissue proportions of the permanent canines of the Early and Middle Pleistocene hominins from the Atapuerca sites has helped us to improve our understanding about the polarity of the thin enamel described as typical of H. neanderthalensis dentition, as well as to assess the evolution of this trait in the Pleistocene populations of Europe. In particular, the similarities observed in the dental tissue proportions of the the Sima de los Huesos (SH) and the Krapina canines indicate that the thinly enameled pattern cannot be considered as a feature only present in the classic Neandertals but a trait shared by all members of the Neandertal lineage. Fur-ABSTRACT 3 ESTRUCTURA DE LA TESIS DOCTORAL 9