The hidden structure of human enamel

• Published in: Nature communications Vol. 10; no. 1; pp. 4383 - 13
• Main Authors: Beniash, Elia, Stifler, Cayla A., Sun, Chang-Yu, Jung, Gang Seob, Qin, Zhao, Buehler, Markus J., Gilbert, Pupa U. P. A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 26.09.2019; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/1023; 639/301/54; 692/698/3008/3012; Amelogenesis; Axes (reference lines); BASIC BIOLOGICAL SCIENCES; Crystal structure; Crystallization; Crystals; Dental Enamel - metabolism; Dental Enamel - ultrastructure; Enamel; Humanities and Social Sciences; Humans; Microscopy, Electron, Scanning; Microscopy, Electron, Transmission; Molar, Third - metabolism; Molar, Third - ultrastructure; Molecular dynamics; Molecular Dynamics Simulation; multidisciplinary; Nanocrystals; Organic chemistry; Rods; Science; Science & Technology - Other Topics; Science (multidisciplinary); Thickness; Young Adult
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-12185-7

Enamel is the hardest and most resilient tissue in the human body. Enamel includes morphologically aligned, parallel, ∼50 nm wide, microns-long nanocrystals, bundled either into 5-μm-wide rods or their space-filling interrod. The orientation of enamel crystals, however, is poorly understood. Here we show that the crystalline c -axes are homogenously oriented in interrod crystals across most of the enamel layer thickness. Within each rod crystals are not co-oriented with one another or with the long axis of the rod, as previously assumed: the c -axes of adjacent nanocrystals are most frequently mis-oriented by 1°–30°, and this orientation within each rod gradually changes, with an overall angle spread that is never zero, but varies between 30°–90° within one rod. Molecular dynamics simulations demonstrate that the observed mis-orientations of adjacent crystals induce crack deflection. This toughening mechanism contributes to the unique resilience of enamel, which lasts a lifetime under extreme physical and chemical challenges. Enamel is the hardest tissue in the body and has been widely studied, yet aspects of its structure remain unclear. Here, the authors report on a study of the orientation and alignment of enamel crystals and challenge previous assumptions.