Geometric morphometrics and topographic analyses of dental wear in modern human populations

[eng] Dental wear is a natural, complex, physiological process of gradual enamel tissue loss that occurs during an individual’s life span and provides information about dietary habits, food processing techniques and cultural practices. Many studies have characterised dental wear in human populations by using observer-dependent, qualitative methods. In contrast, more objective, quantitative approaches have been scarcely used. This thesis aims to assess differences in molar morphology among modern human populations and the effect of dental wear on shape by using novel quantitative methods, such as the percentage of dentine exposure (PDE), 3D geometric morphometrics (GM) and dental topography. The PDE of mandibular permanent first molars recorded in a known-age Baka Pygmy forager population showed an close relationship between wear and age, no sexual dimorphism in wear patterns and reduced PDE values of ≈4% for a foraging population relying on Underground Storage Organs (USO) consumption, likely due to culture-specific dietary proclivities that influenced dental wear rates. Three-dimensional (3D) dental crown analyses (GM and dental topography) carried out in maxillary and mandibular permanent first and second molars of the Coimbra International Exchange known age-at-death skull collection showed significant regressions between the morphometric variables and age-at-death, with a significant portion of the overall shape variation attributed to anatomical traits (e.g. cusp and groove patterns) independently of wear, while another significant portion attributed to the loss of dental crown height with age. The 3D-GM PCA procedure applied to the repeated measurement test showed an intra-observer methodological error <5%. Dental topographic analysis of the Portuguese sample showed negative correlations with age in all analysed teeth, with surface curvature (DNE), complexity (OPCR) and crown relief (RFI) scores decreasing with age. Dental topography procedures applied to maxillary permanent molars of Central African populations with distinct dietary habits (Pygmy foragers and Bantu-speaking agriculturalists) and distinct degrees of dental wear patterns showed DNE and occlusal relief (OR) scores that also decreased with wear, while ambient occlusion (PCV) and OPCR increased with wear. The Pygmy foragers showed higher OPCR and DNE values than the Bantu-speaking agriculturalists. These variables also proved to effectively distinguish between foragers and agriculturalists in the PC analysis. This research has also shown that it is important to pay attention to the different cropping methods used in the quantification of RFI and OR since the different methodological perspectives may cause distinct methodological errors.[spa] El desgaste dental es un proceso fisiológico, natural y complejo de pérdida gradual del esmalte que se produce durante la vida de un individuo y que proporciona información sobre los hábitos alimentarios, las técnicas de procesamiento de alimentos y las prácticas culturales. Muchos estudios caracterizaron el desgaste en poblaciones humanas mediante métodos cualitativos dependientes del observador. En cambio, pocos estudios utilizaron métodos objetivos y cuantitativos. Esta tesis pretende evaluar las diferencias morfológicas de los molares en poblaciones humanas modernas, así como el efecto del desgaste en la forma del diente mediante métodos cuantitativos novedosos, como el porcentaje de exposición de dentina (PDE), la morfometría geométrica (MG) en 3D y la topografía dental. El PDE de los primeros molares inferiores de una población de cazadores recolectores de pigmeos Baka de edad conocida mostró una relación significativa entre desgaste y edad, sin dimorfismo sexual en los patrones de desgaste y valores reducidos de PDE del ~ 4% para una población cazadora recolectora dependiente del consumo de Underground Storage Organs (USO), probablemente debido a las particularidades culturales relacionadas con la dieta que influyeron en el desgaste. Los análisis 3D (MG y topografía dental) en primeros y segundos molares superiores e inferiores de la colección de Trocas Internacionais de cráneos de Coímbra, con edad de la muerte conocida, mostraron regresiones significativas entre las variables morfométricas y la edad de la muerte, con una parte de la variación de la forma del diente atribuida a su anatomía (p. ej. patrones de cúspides y surcos) e independiente del desgaste, y otra, a la pérdida de altura de la corona con la edad. El ACP de la MG en 3D aplicada a la prueba de medición repetida mostró un error metodológico intraobservador del