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Mystery of Tooth Strength Cracked

Fracture of teeth indented along a vertical axis with the flat end of a WC rod, human molar. (Image credit: National Academy Of Sciences, PNAS)

Our teeth are put to the test every day, withstanding all the crunching and munching of meals and snacks. This remarkable resilience appears to be due to the microscopic "basket-weave" structure of human tooth enamel, a new study finds.

Tooth enamel, which forms the outer coating of teeth, is a strong but brittle substance.

Given the brittleness of teeth, which is comparable to that of glass, it's a wonder that for the most part, they can last a lifetime without cracking to pieces.

"It's a bit of a mystery as to why they don't just fall apart," said co-author of the new study Brian Lawn of the National Institute of Standards and Technology.

Lawn and his colleagues took teeth extracted from humans, sea otters and a few other animals, and subjected them to loading from a metal rod, sort of a worst-case scenario bite.

The researchers, whose work was funded by the George Washington University Research Endowment Fund, wanted to "see how much force [the teeth] could withstand before they break," Lawn explained.

Basket-weave structure

The team found that the basket-weave-like microstructure of the enamel kept any cracks that did form from propagating through the enamel and breaking apart the tooth.

This finding, detailed in the April 13 issue of the journal Proceedings of the National Academy of Sciences, explains why dentists can examine the teeth of older people and find that "the teeth are full of cracks, and yet the teeth remain intact," Lawn told LiveScience.

Enamel thickness and the size of teeth can also affect how resilient they are to a lifetime of chomping. For example, gorillas have bigger teeth than humans and so their teeth can handle tougher meals. Orangutans have similarly sized teeth as chimpanzees, but their enamel is thicker so they can eat nuts and crunchier foods than chimps, whose "diet is much more lightweight," Lawn said.

Anthropologists can use all of this information about enamel to piece together dental evolution in primates and animals in general — they can even use it to posit what early humans might have chowed down on.

Materials engineers like Lawn can also use the structure of enamel to develop similarly resilient substances, including better replacement teeth.

Currently, the crowns used to replace bad teeth "look nothing like the microstructure of an actual tooth," Lawn said, and so are more likely to fail. If engineers can grow materials that simulate the actual structure of teeth, that could make for happier patients at the dentist's office.

Andrea Thompson
Andrea graduated from Georgia Tech with a B.S. in Earth and Atmospheric Sciences in 2004 and a Master's in the same subject in 2006. She attended the Science, Health and Environmental Reporting Program at New York University and graduated with a Master of Arts in 2006.