A new, first-of-its-kind look at the nanostructure of tooth enamel helps to explain why the most solid substance in the human body is so incredibly elastic.
The tooth enamel looks like bone but is not really living tissue. This outer layer of the tooth that encloses and protects other tissue inside the tooth is formed when we are young, and once the teeth are developed, it does not have the natural ability to self-manage or grow.
Fortunately, the process of mineralization that produces tooth enamel creates an incredibly tough substance that is harder than steel, and new research reveals a never-before-seen mechanism that helps make its extreme stability possible.
"We put enormous pressure on tooth enamel every time we chew, hundreds of times a day," says Biophysicist Pupa Gilbert of the University of Wisconsin-Madison.
"Tooth enamel is unique in that it has to lasted our whole lives. How to prevent catastrophic failure? "
The answer lies in what researchers call the 'hidden structure' of tooth enamel: the limitless structural arrangement of nanocrystals that make up our outer layer of teeth.
These extremely small crystals are made of a kind of calcium. apatite called hydroxyapatite, the same mineral found in the teeth of other creatures and crystals are really small, measuring less than a thousandth of a human hair.
They are so small that it is difficult to obtain
"Before that your study we just didn't have the methods to look at the structure of the enamel, "says Gilbert.
" But with the technique I had previously invented, I called mapping polarization-dependent image contrast (PIC), you could measure and visualize color orientation on single nanocrystals and see many millions of them at once. "
This method of electron microscopy, says Gilbert, renders the architecture of complex biominerals" immediately visible to the naked eye "and thus revealed something that scientists have never seen before.
When using the PIC mapping technique on human teeth, researchers note that hydroxyapatite nanocrystals are not oriented the way crystals bind in enamel in formations called rods and interrodes, but the team finds a gradual change in the crystal orientations between adjacent nanocrystals.
As to why such a discrepancy exists, Gilbert and colleagues think they have an answer.
"We suggest that the wrong one orientation of adjacent enamel nanocrystals provides a reinforcing mechanism, "write the authors
" If all crystals are co-oriented, the transverse crack can propagate through the crystal interfaces, whereas if the crystals are incorrectly oriented, the crack propagates mainly through the crystal
Of course, it would be difficult or impossible to test this hypothesis in human teeth in real life, but the molecular dynamics simulations performed by the team support the idea.
In a computer model (see video above) designed to simulate how cracking can propagate through the crystalline structure of an enamel by pressure, the cracking propagates more rapidly through crystalline nets that do not resemble misalignments of human teeth. (1
Therefore, researchers suggest that this range of nanocrystalline misorientation may represent a sweet spot when a deflection is deflected, and what may be the "long evolutionary history of enamel" may be chosen,
be crystals of the sweet spot at a distance of 30-30 ° which can maximize the release and quenching of energy ", explains the document."
"Crack deflection is a well-established reinforcement [mechanism] so we conclude that in enamel emb Human misalignments play a key mechanical role: they increase the strength of the nanoscale enamel, which is essential to withstand powerful gestural forces, approaching 1000 Newtons, repeated thousands of times a day. "
The findings were reported in Natural Communications .