Atomic Insights On Shark Teeth

Considering that neither brushing nor flossing is part of a shark’s daily dental regimen, the animals get remarkably few cavities. To get an idea of what makes shark teeth so resistant to decay, researchers in Japan aimed a transmission electron microscope at the enamel on the creature’s chompers. Normally the microscope’s electron beam can damage biomineralized material. But by using low-dose imaging techniques, Yuichi Ikuhara and Zhongchang Wang of Tohoku University and colleagues were able to minimize such damage and directly image every individual atom in the enamel (Angew. Chem. Int. Ed. 2014, DOI:10.1002/anie.201307689). The enamel is made of fluorapatite, Ca₅(PO₄)₃F, which appears to the researchers as hexagons of calcium, phosphorus, and oxygen atoms with fluorine atoms at their centers. Making calculations based on these images, they determined that fluorine is partially covalently bound to calcium in the enamel. This suggests that fluorine is critical to stabilizing the hexagonal frames. Loss of fluorine atoms would leave atom-sized holes and weaken the teeth.