Young’s modulus and hardness of shark tooth biomaterials Lisa B. Whitenack a,b, *, Daniel C. Simkins Jr. c , Philip J. Motta a , Makoto Hirai d , Ashok Kumar d a Department of Integrative Biology, University of South Florida, 4202 E. Fowler Avenue, Tampa, FL, United States b Department of Biology, Allegheny College, 520 N. Main Street, Meadville, PA, United States c Department of Civil and Environmental Engineering, University of South Florida, 4202 E. Fowler Avenue, Tampa, FL, United States d Nanomaterials and Nanomanufacturing Research Center, Department of Mechanical Engineering, University of South Florida, 4202 E. Fowler Avenue, Tampa, FL, United States 1. Introduction Teeth are an integral part of the vertebrate feeding apparatus. They can divide prey into manageable pieces, grip prey for reorientation, and process prey to remove inedible compo- nents. Despite this, the majority of studies on the evolution and function of feeding in elasmobranchs (sharks, skates, and rays) have focused primarily on the movement of cranial components and muscle function, with little integration of tooth properties or function. 1–6 Biomechanical studies that have addressed elasmobranch tooth form and function have largely focused on the qualitative mechanics (e.g. cutting, puncturing). 2,6–8 In general, the biomechanics of the tooth itself and its materials have been ignored. As teeth are subjected to sometimes extreme loads during feeding, they undergo stress, strain, and potentially failure. In order to continue performing their biological role, elasmobranch teeth must resist breakage until they are shed. While performance archives of oral biology 55 (2010) 203–209 article info Article history: Accepted 6 January 2010 Keywords: Nanoindentation Osteodentine Orthodentine Enameloid Mechanical properties Chondrichthyes abstract To date, the majority of studies on feeding mechanics in sharks have focused on the movement of cranial components and muscle function, with little attention to tooth properties or function. Attributes related to mechanical properties, such as structural strength, may also be subjected to natural selection. Additionally it is necessary to charac- terize these properties in order to construct biomechanical models of tooth function. The goal of this study was to determine hardness and elastic modulus for the shark tooth materials enameloid, osteodentine, and orthodentine. Five teeth each from one carcharhi- niform species, the bonnethead Sphyrna tiburo, and one lamniform, the sand tiger shark Carcharias taurus, were utilized for nanoindentation testing. Each tooth was sectioned transversely, air-dried, and polished. Both enameloid and dentine were tested on each tooth via a Berkovich diamond tip, with nine 2 mm deep indentations per material. t-Tests were used to determine if there were differences in hardness and Young’s modulus between the tooth materials of the two species. There was no significant difference between the two species for the material properties of enameloid, however both hardness and Young’s modulus were higher for osteodentine than for orthodentine. This may be due to differences in microanatomy and chemical composition, however this needs to be studied in greater detail. # 2010 Elsevier Ltd. All rights reserved. * Corresponding author at: Department of Biology, Allegheny College, 520 N. Main Street, Meadville, PA, United States. Tel.: +1 814 332 2888; fax: +1 814 332 2789. E-mail address: lwhitena@allegheny.edu (L.B. Whitenack). available at www.sciencedirect.com journal homepage: http://www.elsevier.com/locate/aob 0003–9969/$ – see front matter # 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.archoralbio.2010.01.001