Deformation behavior of normal human enamel: A study by nanoindentation. (August 2020)

• Record Type: Journal Article
• Authors: Shen, Lu; Barbosa de Sousa, Frederico; Tay, NamBeng; Lang, Teo Siew; Kaixin, Vivian Lin; Han, Jongyoon; Kilpatrick-Liverman, LaTonya; Wang, Wei; Lavender, Stacey; Pilch, Shira; Gan, Hiong Yap
• Is Part Of: Journal of the mechanical behavior of biomedical materials. Volume 108(2020)
• Publication Date: 2020-08
• Subjects: Dental enamel -- Deformation mechanisms -- Nanoindentation -- Intra-tooth variation; Biomedical materials -- Periodicals; Biomedical materials -- Mechanical properties -- Periodicals; Biomedical materials; Biomedical materials -- Mechanical properties; Periodicals; Electronic journals; 610.28
• DOI: 10.1016/j.jmbbm.2020.103799
• Languages: English
• ISSNs: 1751-6161

Abstract

Abstract: Tooth enamel has an important mechanical function for human dental health, yet characterizing its mechanical properties is not trivial due to its complex nanoporous structures. We examined the distribution of hardness and modulus across the lingual-buccal enamel cross-section by nanoindentation. At the occlusal surface, the hardness and modulus of enamel were found to be 5.00 ± 0.22 GPa and 97.12 ± 2.95 GPa, respectively. At the area close to the enamel-dentine-junction (EDJ), the hardness and modulus were 3.72 ± 0.35 GPa and 76.83 ± 5.71 GPa, respectively. At the middle region in between the EDJ and the outer enamel layer, the hardness and modulus were found to be 4.23 ± 0.18 GPa and 87.62 ± 2.50 GPa, respectively. The surface and area underneath the nanoindent were analyzed using the following microscopy tools: Scanning Electron Microscopy, Focused Ion Beam imaging, and Transmission Electron Microscopy. The deformation mechanisms of enamel were found to be location dependent and influenced by changes in the chemical composition within enamel. The EDJ forms the interface between enamel and dentin. The deformation behavior differed at the EDJ, due to the increased organic phase at the interface. Within the intermediate enamel region, intra-rod cracks were formed at the center of enamel rods and propagated into the neighboring inter-rod region at deviated directions along the orientation of the local crystallites. At the outer enamel layer, crack propagation was constrained by the rigid structure surrounding the indented site. Most of the cracks were formed close to the surface. A significant amount of material was also pushed upwards and delaminated from the enamel surface of the indentation area. Graphical abstract: Micrograph taken underneath an indented surface at the intermediate enamel layer. Cracks and slip-bands were formed within the enamel rod and propagated towards the boundary of the prisms. Some cracks propagated into the neighboring inter-rod region and deviated along the orientation of the enamel crystallites. Image 1 Highlights: Deformation behavior of the inner enamel layer is regulated by the organic phase closed to the EDJ. Cracks initiated at the center propagate perpendicular to the indentation direction within the same enamel rod at intermediate enamel region. Cracks become less intense as they propagate towards regions with different crystallite orientation. Outer enamel layer has shallowindentation depth with excess volume of material being pushed upwards causing significant damage to the surface.