Evolution: teeth designed to last a lifetime (Introduction)

by David Turell , Friday, September 27, 2019, 16:07 (1883 days ago) @ David Turell

Tooth enamel is built from off line crystals to stop cracking:

https://phys.org/news/2019-09-picture-reveals-tooth-enamel-strong.html

"Break any bone in the human body, and the body can repair the tissue and fix the damage. Yet tooth enamel—the strongest tissue in the human body—cannot repair itself. Still, our teeth last a lifetime.

"'We apply huge pressure on tooth enamel every time we chew, hundreds of times a day," says Pupa Gilbert, professor of physics at the University of Wisconsin–Madison. "Tooth enamel is unique in that it has to last our entire lifetime. How does it prevent catastrophic failure?"

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"...used advanced imaging techniques to see a clearer picture of the organization of individual enamel crystals in human teeth. They found that these crystals are not perfectly aligned, as had been previously thought, and that this misorientation likely deflects cracks, leading to enamel's lifelong strength.

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"Tooth enamel is organized in micron-length rods made up of long, skinny crystals of hydroxyapatite. Gilbert and her group at UW–Madison applied PIC mapping to several human tooth samples and measured the orientation of each crystal in tooth cross sections.

"'By and large, we saw that there was not a single orientation in each rod, but a gradual change in crystal orientations between adjacent nanocrystals," Gilbert says.

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"Cayla Stifler, a physics graduate student in Gilbert's group and co-author of the study, went back to the PIC mapping data and measured the angular distance between every two adjacent pixels, generating millions of data points. She found that 1 degree was the most common misorientation angle, and that the angular distance never surpassed 30 degrees, consistent with the modeling result that a small misorientation angle is better than a larger one at deflecting cracks.

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"'Now we know that cracks are deflected at the nanoscale and thus can't propagate very far," says Gilbert. "That's the reason our teeth can last a lifetime without being replaced.'"

Comment: More evidence for design.