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Researchers investigate how chewing affects teeth on the nanoscale

Nanocrystallites that make up tooth enamel before and after pressure was applied. (Image: University of Arkansas)
Dental Tribune International

Dental Tribune International

Wed. 1. November 2017

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FAYETTEVILLE, Ark., U.S.: Food leaves permanent traces on teeth. Examining these marks—or microwear—a team of researchers has documented the effects of chewing on the nanosized structures that make up tooth enamel. Their findings have broad implications and could lead to better dental care, but also provide new tools for scientists studying fossil teeth, as well as bioengineers building the materials of the future.

Prof. Peter Ungar and Dr. Ryan Tian from the University of Arkansas worked with researchers at the Tribology Research Institute at Southwest Jiaotong University in Chengdu, China, to observe the effects of wear on the nanostructures of tooth enamel. Using tips made from different types of material, pressure was applied to the surface of human molars, which had been extracted for orthodontic purposes. The researchers scratched the teeth, moving the tip across the surface to simulate the action of teeth moving against each other during chewing. They also indented the tooth surface, pressing the tip against the enamel to simulate the pressure caused by crushing food.

Under high-powered microscopes, the researchers observed that, at every level of pressure, scratching led to more damage than indentation, but both types of stress resulted in three different kinds of damage. Plucking occurred when the crystallites were separated from each other. Applying more pressure to the enamel led to deformation, or the bending and squeezing of the crystallites. At even higher levels of pressure, fragmentation resulted when the chemical bonds holding the crystallites together broke.

“Hydroxapatite crystallites are the fundamental units of enamel, each less than 1/1000th the thickness of a human hair,” said Ungar. “Most research on tooth wear to date has focused on effects at much larger scales, but we have to study enamel at this finer level to truly understand the nature of how the hardest tissue in our bodies resists wear and tear.”

“The findings in the surface tribological chemistry can help us understand the nature of the interfacial chemical bonding between the nanoparticles that Mother Nature uses to make biominerals of all types on demand,” said Tian. According to the researchers, understanding the effects of chewing at this fundamental level has implications for a wide range of fields, including clinical dentistry, evolutionary biology and biomedicine.

The study, titled “Enamel crystallite strength and wear: Nanoscale responses of teeth to chewing loads,” was published online on Oct. 25 in the Journal of the Royal Society Interface.

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