Hierarchical Structures in Mammalian Enamel from Synchrotron X-ray Computed Tomography.

Abstract

Many natural and biological materials exhibit intricate hierarchical architectures to effectively manage crack propagation and fracture. This enables them to overcome the critical trade-off between strength and toughness that plagues modern ceramics and ceramic composites. This study investigates the microstructure of enamel from five different mammalian species to inform the synthesis of strong, fracture-resistant bioinspired materials. Dental enamel, the hard, outer surface layer of teeth, is renowned for its exceptional damage tolerance and high strength. Enamel can withstand cracks and other forms of structural damage without leading to catastrophic failure, a property that conventional ceramics often lack. The primary factor contributing to enamel's crack resistance, often attributed to its complex hierarchical microstructure, is the decussation of enamel rods. In this study, synchrotron micro X-ray tomography was performed to elucidate the microstructural assembly of the rods and to characterize the decussation bands. This analysis was conducted across samples taken from different teeth (molar, premolar, canine), tooth regions (cervical, mid-cervical, cusp, intercuspal), and species (lion, wolf, wild African dog, snow leopard, and black bear). Microtomography images were reconstructed and analyzed using a particle image velocimetry technique to offer detailed insights into the decussation bands and the orientation of rods within these bands. Overall, the decussation patterns exhibit branching of the decussation bands reminiscent of Turing patterns, and these organizational motifs within enamel architecture provide a mechanistic perspective on hierarchical structure and its role in damage tolerance. STATEMENT OF SIGNIFICANCE: This study explores the intricate microstructure of dental enamel from various mammalian species using synchrotron X-ray nano- and microtomography. Through a detailed examination of the enamel rods and their distinct Turing patterns, this new insight offers the potential to unlock the secrets behind enamel's extraordinary strength and unparalleled fracture resistance. Our findings suggest that these patterns help distribute stress and prevent catastrophic failure, offering insights that could inspire the design of advanced, damage-resistant ceramics. This research bridges biology and materials science, potentially leading to the development of innovative materials with applications in extreme environments, such as aerospace and nuclear reactors.