Arola, Dwayne DRenteria, Cameron2023-09-272023-09-272023Renteria_washington_0250E_26051.pdfhttp://hdl.handle.net/1773/50858Thesis (Ph.D.)--University of Washington, 2023Tooth enamel, a tissue recognized for its ability to survive a lifetime of cyclic contact and other functions, has attracted research attention across a variety of fields. In this dissertation, two fields of enamel research are advanced including: i) our understanding of the “woven-rod” microstructure (i.e., decussation) and rod geometry in the tooth enamel of various mammals, and ii) our understanding of the evolution in structure-property relationships for human enamel with aging. The overall objective was to identify correlations that are associated with the changes in structural integrity of enamel with aging and contributions of the microstructure to differences in its durability across mammals. This research pursues a unique paradigm in which enamel is treated as a universal material that undergoes “processing” by Nature to achieve its function-specific properties. The research adopted a variety of experimental modalities to characterize the chemical, structural, and mechanical properties of enamel from a wide range of mammals and applied unsupervised machine learning (ML) techniques to achieve further understanding. To advance knowledge regarding the structure and mechanical properties of enamel, spectroscopy, tomography, and indentation techniques were applied from the nano- to the micro-scale to characterize the hardness, reduced modulus, resistance to fracture and brittleness of enamel from a variety of species. Results showed that the structure-property relationships exhibited some similarities across species, but there were significant differences between groups when categorized by the bite force quotient (BFQ). These compositional and mechanical adaptations could be exploited to design enamel-like microstructures that are tailored for specific function. The enamel microstructure, including rod geometry, rod-interrod geometry and decussation pattern were investigated using micro-synchrotron computed tomography (SCT) and nano-SCT. Results showed that there were structural variations in the enamel rods (i.e., diameter and surface area), interrod thickness, diazone band width, and diazone rod pitch angle across the enamel thickness. The rod spacing, rod packing density, and overall mineral density changed as a function of distance from the DEJ to the OES and exhibited the maximum packing density in the outer enamel region. Implications of these structural parameters on the mechanical behavior of enamel were then interpreted with respect to bioinspired design . Human enamel is of particular interest due to its implications in oral healthcare and dental medicine. Using the detailed chemical and mechanical property data acquired by experimental measures, a multivariate analysis of properties across the enamel thickness was performed in combination with unsupervised machine learning in the form of SOMs and K-means clustering. A stratification of properties was pursued within three enamel regions (i.e., inner, middle, and outer enamel) and with respect to donor age. Results showed that the outer enamel of seniors was most prone to brittle fracture when compared to the young adult and primary enamel groups. Building on that knowledge, age-targeted topical gel treatment formulations were applied to the outer enamel surface of senior enamel to reduce the brittleness and propensity for brittle cracking. These investigations revealed a distinctive stratification of structure-property relationships with aging and the potential for mitigating the deleterious effects of aging by topical treatments focused on patient-centric dental medicine. Overall, the findings from this research will advance our understanding of the materials science of enamel and are expected to have broad applications within the fields of dentistry as well as to the advancement of enamel-like bioinspired materials.application/pdfen-USnoneAgingBioinspirationDurabilityEnamelMachine LearningSynchrotron X-rayMaterials ScienceEngineeringMaterials science and engineeringThesis