Collaborative Research: Normal and pathological covariation in the anthropoid masticatory apparatus

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The investigators will study skull and jaw anatomy in primates, to better understand how the anatomical components of the chewing system (teeth, jaws, and related joints) work together and how these components are affected by aging and pathological changes. Although the components of the masticatory (chewing) system are known to work together as a unit, previous analyses of this system have typically examined specific components in isolation from the rest of the anatomy, providing an incomplete picture of anatomical interrelationships. This project will address how the different anatomical components are correlated with each other across the entire masticatory system, in the context of changes that may occur during the lifetime of an individual, such as normal and pathological dental wear, and normal and abnormal (e.g. arthritis) changes in temporomandibular joint (TMJ) shape. Quantifying anatomical correlations using three-dimensional modeling in the dentition and TMJ will allow for new interpretations of the skeletal masticatory system and an improved understanding of the evolutionary pressures associated with different feeding behaviors and diets across primates. Determining whether TMJ pathology covaries with dental wear and pathology in multiple non-human species will provide an evolutionary context for dental and TMJ disorders that are very common in humans. The broader impacts of this research include encouraging gender and ethnic diversity in science by providing research opportunities for undergraduate students at universities that primarily educate first generation college and minority students; supporting the research of three early career female scientists; training a postdoctoral researcher in advanced techniques for capturing and analyzing shape variation; building a large database of 3D data that will be available to both anthropological and biomedical researchers and that may inform clinical studies of dental problems in humans; and conducting community outreach that will further disseminate the results of this investigation and help generate public interest in STEM research. Because changes in diet and subsistence patterns often lie at the root of major evolutionary shifts, documenting and understanding the adaptive significance of the masticatory system during human evolution, as well as across living primates, has been a major goal of functional morphological studies in biological anthropology. The masticatory system acts as a single functional unit, such that perturbations in one portion of this system may affect other regions of anatomy; thus, age-related changes and pathological conditions of the masticatory apparatus are likely to be multifactorial and affect the entire system. Through a detailed assessment of dental and TMJ morphology and covariance between the dentition and the TMJ, this study examines both normal and pathological dental wear and TMJ remodeling in 16 anthropoid primate taxa, including humans. The specific aims include testing for covariation between the maxillary and mandibular teeth, the cranial and mandibular components of the TMJ, the teeth and TMJ, and dental and TMJ pathologies. Shape variation in the dentition and TMJ will be quantified using advanced morphometric techniques, including 3D landmark and surface data. Specimens will be assessed for pathology using published criteria for antemortem tooth loss, tooth wear, pulp cavity exposure, and TMJ osteoarthritis. By determining whether TMJ pathology covaries with dental wear and pathology in humans and non-human primates, this research will provide an evolutionary context for the evolution of primate feeding behaviors and of TMJ disorders in humans. The research has public health relevance, given the high prevalence of antemortem tooth loss and TMJ disorders in modern human populations. The resulting data and analyses will be relevant to a variety of fields including public health, dentistry, biomechanics/kinematics, feeding ecology, functional morphology, and mammalian evolution.