Even though your teeth are largely composed of a mineral softer than that found in sharks, new tests reported in the Journal of Structural Biology suggest that they're just as tough. In sharks, the material coating the teeth is largely composed of fluoroapatite, a fluoridated phosphate mineral that in its pure form is harder than the hydroxyapatite found in the enamel of human teeth. But by pressing tiny metallic pyramids into the surfaces of teeth from a shortfin mako shark (Isurus oxyrinchus, shown) and a tiger shark (Galeocerdo cuvier), researchers found that the enameloid coating on shark teeth is no harder than that of the enamel on a human wisdom tooth. The teeth are, in fact, of comparable hardness because their surfaces aren't pure mineral but instead are made of mineral crystals bound together with proteins so that the material doesn't shatter under a sudden impact.
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