Materials Science

Broken Teeth

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Science  11 Mar 2005:
Vol. 307, Issue 5715, pp. 1535
DOI: 10.1126/science.307.5715.1535c

Teeth are made up of two calcified tissues that have very different properties: enamel and dentin. The outer coating of enamel is harder but more brittle than the dentin it surrounds. The interface zone between these two structures has been thought to prevent cracks in the enamel from traversing into the dentin, which would cause the fracture and complete failure of a tooth. Using interfacial fracture mechanics, Imbeni et al. show that the thin interface layer is not responsible for crack arrest. By creating a series of Vickers microhardness indents in polished sections of healthy extracted teeth, they were able to observe the angle and depth penetration of the cracks that formed. In a majority of the cases, the crack penetrated into the dentin, where it was stopped by the bridging links that form between its mineral and biological components. Although the interface itself is not that strong, the dentin near the interface has collagen fibers that are preferentially oriented perpendicular to the interface and also has a lower mineral content relative to the bulk material, and it is this combination of factors that stops the cracks in their tracks. — MSL

Nature Mat. 4, 229 (2005).

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