Alan Nursall

Nature's Strongest Teeth Belong to Aquatic Snails

By: Alan Nursall Posted:

The world’s strongest known animal teeth belong to aquatic snails known as limpets -- marine mollusks famous for their conical, tiny shells that resemble umbrellas.

The limpet's teeth, described in a new study in the latest issue of the Journal of the Royal Society Interface, are so tough and sturdy that they are now considered the strongest known biological structures on the planet, overtaking the prior holder of that record: spider silk.

"Limpets evolved strong teeth as the teeth scrape over rock surfaces every day to feed," the study's lead author Asa Barber, of the University of Portsmouth and Queen Mary University of London, told Discovery News.

"If the teeth broke easily," Barber explained, "then the limpet would not be able to feed and would die -- hence evolution selecting the strongest teeth over many years."

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Strength is based on material composition as well as the shape of the structure. In addition to analyzing limpet teeth sets and individual teeth, Barber and colleagues Dun Lu and Nicola Pugno cut ultra-small samples out of the teeth. Even then, at miniscule sizes, the material proved to be incredibly resilient.

The limpet's teeth have been found to be the strongest biological structures on the planet.
Further analysis by the team found that limpet teeth are composites (meaning they consist of two or more constituent materials with significantly different physical or chemical properties) made from mineral fibers known as goethite. The fibers are bound together in a "glue" of chitin, a natural polymer.
"The strength of the tooth is due to the diameters of the fibers being below a particular size, which is about 60 nanometers, or over a thousand times thinner than a human hair,” Barber said.

Limpets have rows of teeth on a tongue-like appendage called a radula, Barber said. The limpet sits on a rock and rolls out its radula over the rock's surface.

"The teeth are under the radula to scrape over the rock surface," Barber said. "Algae on the rock surface is scraped toward the mouth of the limpet and this is how it feeds."

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Barber estimates that there are a hundred rows of teeth on the radula. But even these super-strong choppers can become damaged from time to time, so there are always replacement teeth available from the many rows underneath the radula.

Barber and his team note that engineers use composite materials to make many things, including aircraft parts, hulls of boats, and Formula 1 cars.

Scientists, therefore, are eagerly eying limpet teeth, in hopes of duplicating their structure to fabricate higher performance materials. Duplicating the limpet tooth's resistance to abrasion could, for example, be useful in designing mining or digging equipment.

Peter Fratzl, of the Department of Biomaterials at the Max Planck Institute of Colloids and Interfaces, agrees that the material comprising limpet teeth holds promise for creating new and improved engineering materials. He told Discovery News that the new study "is extremely interesting in at least two ways."

"First," Fratzl said, "it shows that an intricate microstructure makes limpet teeth incredibly strong for biogenic material, certainly stronger than silk or cellulose. Second, the experimental approach, using tiny tensile specimens just a few microns long, is really impressive."

And, of course, what about human teeth? Why are they so prone to cavities and other problems? It's due to what we eat, the researchers said.

"Human teeth haven't evolved for our current diet," Barber said. "Maybe [they’d be sturdier] if we kept to the Paleo diet from birth?"