title: Ultrastructural organization and micromechanical properties of shark tooth enameloid.
abstract: The outer part of shark teeth is formed by the hard and mineral-rich enameloid that has excellent mechanical properties, which makes it a very interesting model system for the development of new bio-inspired dental materials. We characterized the microstructure, chemical composition and resulting local mechanical properties of the enameloid from teeth of Isurus oxyrinchus (shortfin mako shark) by performing an in-depth analysis using various high-resolution analytical techniques, including scanning electron microscopy, qualitative energy-dispersive X-ray spectroscopy and nanoindentation. Shark tooth enameloid reveals an intricate hierarchical arrangement of thin (50-80nm) and long (>1μm) crystallites of fluoroapatite with a high degree of structural anisotropy, which leads to exceptional mechanical properties. Both stiffness and hardness are surprisingly homogeneous in the shiny layer as well as in the enameloid: although both tooth phases differ in structure and composition, they show almost no orientation dependence with respect to the loading direction of the enameloid crystallites. The results were used to determine the structural hierarchy of shark teeth, which can be used as a base for establishing design criteria for synthetic bio-inspired and biomimetic dental composites.
authors.affiliation: Institute of Inorganic Chemistry and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen, Universitaetsstr. 5-7, 45117 Essen, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Enax
authors.affiliation: Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, 40237 Düsseldorf, Germany.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Janus
authors.affiliation: Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, 40237 Düsseldorf, Germany.
authors.forename: Dierk
authors.initials: D
authors.lastname: Raabe
authors.affiliation: Institute of Inorganic Chemistry and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen, Universitaetsstr. 5-7, 45117 Essen, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Epple
authors.affiliation: Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, 40237 Düsseldorf, Germany. Electronic address: h.fabritius@mpie.de.
authors.forename: Helge-Otto
authors.initials: HO
authors.lastname: Fabritius
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D003460:Crystallization; D003743:Dental Enamel / Q000502:physiology* / Q000648:ultrastructure*; D055119:Elastic Modulus; D006244:Hardness; D008903:Minerals / Q000737:chemistry; D012754:Sharks; D013052:Spectrometry, X-Ray Emission; D014070:Tooth / Q000502:physiology* / Q000648:ultrastructure*
chemical_list: D008903:Minerals
keywords: Biomineralization; Calcium phosphate; Nanoindentation; Shark tooth enameloid; Structural hierarchy