The hidden structure of human enamel
E Beniash and CA Stifler and CY Sun and GS Jung and Z Qin and MJ Buehler and PUPA Gilbert, NATURE COMMUNICATIONS, 10, 4383 (2019).
Enamel is the hardest and most resilient tissue in the human body. Enamel includes morphologically aligned, parallel, similar to 50 nm wide, microns-long nanocrystals, bundled either into 5-mu m-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 degrees-30 degrees, and this orientation within each rod gradually changes, with an overall angle spread that is never zero, but varies between 30 degrees-90 degrees 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.
Return to Publications page