A team of German scientists has analyzed the structure of shark teeth and human teeth. The results of their research are surprising: although the surface of shark teeth contains 100 percent fluoride, they are not harder than human teeth.

“I had wanted to do this for a long time,” explained Prof Matthias Epple of the University of Duisburg-Essen, senior author of the study published in the Journal of Structural Biology.

“We have been investigating biomineralization at the University of Duisburg-Essen for several years. It is our main goal to determine the effect of inorganic minerals on biological systems, such as teeth, bones and seashells. It is well known that sharks have enamel, which consists of the very hard mineral fluoroapatite. So far, no scientist has investigated this with high-end chemical and physical methods.”

By using X-ray diffraction technique and scanning electron microscopy, the scientists analyzed the order, the size and the nature of the fluoroapatite crystals and determined the hardness of the teeth of the Shortfin mako shark, Isurus oxyrinchus, and the Tiger shark, Galeocerdo cuvier.

The team found that the chemical and crystallographic composition of teeth is similar in different shark species, although mako sharks ‘tear’ into the flesh of their prey while tiger sharks ‘cut’ it. The interior consists of the more elastic dentin; the outer part is the highly mineralized enamel.

“The human enamel consists of a little softer mineral, hydroxyapatite, which is incidentally also present in bones,” Prof Epple said. By carrying out a comparative study with a human tooth, the scientists discovered something surprisingly new: it is just as robust as a shark tooth.

“This is due to the special micro- and nanostructure of our teeth. The crystals in human teeth have a special arrangement and they are glued together by proteins, which stops cracks from running through the whole tooth”, said Prof Epple.

The scientists are now continuing their research on shark teeth. They are trying to imitate these structures to lay the foundations for novel dental prostheses. “It would be great if, sometime in the future, one could repair teeth with a material, which is more natural than today`s provisional solutions.”

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Bibliographic information: Enax et al. 2012. Structure, composition, and mechanical properties of shark teeth. Journal of Structural Biology, vol. 178, 3, pp. 290–299; doi: 10.1016/j.jsb.2012.03.012