Microstructure, elemental composition and mechanical properties of enamel and dentine in the polar bear Ursus maritimus

• Published in: Archives of oral biology Vol. 134; p. 105318
• Main Authors: Loch, Carolina, Hemm, Louisa, Taylor, Bertie, Visser, Ingrid N., Wiig, Øystein
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-02-2022
• Subjects: Animals; Dental Enamel; Dentin; Elastic modulus; Hardness; Hunter-Schreger bands; Incisor; Male; Teeth; Ursidae; Elastic modulus; HSB; Teeth; EDX; CEJ; EDJ; SEM; Ursidae; OES; SiC; Hardness; Hunter-Schreger bands
• ISSN: 0003-9969; 1879-1506
• DOI: 10.1016/j.archoralbio.2021.105318

To investigate the microstructure, elemental composition and mechanical properties of polar bear teeth.
Incisors, canines and fourth premolar teeth of two subadult male museum specimens were analysed. Teeth were measured, photographed, embedded in Epoxy resin, sectioned, polished and etched for scanning electron microscope (SEM) imaging, elemental composition and nanomechanical testing analyses.
The thickness of enamel ranged from 350-430 µm in canines, 220–330 µm in incisors and 320–510 µm in premolars. SEM images showed distinct transversely-oriented undulating Hunter Schreger bands from the enamel-dentine junction (EDJ) to the outer enamel surface. Enamel prisms had a hexagonal shape, with open prism sheaths. Prisms measured 6–8 µm in diameter. The EDJ was straight with no evidence of scalloping. Larger tubules adjacent to the EDJ were observed in the mantle dentine zone. Enamel Hardness and Elastic modulus values were higher in premolars (6.9 GPa and 269 GPa), followed by canines (6.5 GPa and 230 GPa) and incisors (4.9 GPa and 187 GPa). Dentine Hardness and Elastic modulus values were higher in canines. CaO and P2O5 were the components with higher oxide weight percentage in both enamel and dentine.
Understanding the microstructure, elemental composition and mechanical properties of polar bear teeth can help elucidate the biology and functional morphology of this globally threatened species and could be used as a proxy for studies with fossil ursids.
•This study concerned teeth in the polar bear Ursus maritimus•Enamel thickness greater in canines (350–430 µm) followed by incisors and premolars•Enamel is composed of transversely-oriented undulating Hunter-Schreger bands•Higher Hardness and Elastic modulus in premolars, followed by canines and incisors•Tooth microstructure and properties linked to biology and functional morphology