Enamel: The body part that lasts a lifetime and doesn’t wear out
Friday, October 18, 2019
Tooth enamel is forever. That’s not quite as catchy as “Diamonds are forever,” but it turns out it’s just as true. Tooth enamel is the hardest substance in the human body. But, until recently, no one knew how it managed to last an entire lifetime.
The authors of a recent study concluded that enamel's secret lies in the imperfect alignment of crystals.
Consider this. If you cut your skin or break a bone, the injured tissues will repair themselves. Our bodies are really good at recovering from injury.
Tooth enamel, however, cannot regenerate. And the oral cavity is a hostile environment. Every time you sit down to the dinner table, your tooth enamel is put under incredible stress. It also must endure extreme changes in both pH and temperature. It’s a lot to ask.
But despite all these challenges, the tooth enamel that we developed as a child stays with us for our entire lives. How?
The Secret Life of Tooth Enamel
With help from researchers at the Massachusetts Institute of Technology (MIT) and the University of Pittsburgh, the research team, led by Dr. Pupa Gilbert, took a close and detailed look at the structure of tooth enamel.
The team of scientists published the results of their study in the journal Nature Communications. Here’s the gist of what they found:
Enamel is made up of tiny enamel rods, which consist of hydroxyapatite crystals. These long, thin enamel rods are microscopic. By using advanced imaging technology, the team could see how individual crystals in tooth enamel are aligned.
The technique, which Dr. Gilbert developed, is called polarization-dependent imaging contrast (PIC) mapping. Before PIC mapping, it was impossible to study enamel with this level of detail.
Why Does it Matter Which Way the Crystals are Oriented?
To test whether variations in crystal alignment influences the way tooth enamel responds to stress, the team recruited help from the engineering department at MIT. Using a computer model, they simulated the forces that the crystals would experience when a person chews.
Inside the model, they placed two blocks of crystals next to each other so that they touched along one edge. The crystals within each of the two blocks were aligned, but where they came in contact with the other block, they met at an angle.
Over the course of several tests, the scientists changed the angle at which the two blocks of crystals met. If the researchers perfectly aligned the two blocks at the interface where they met, a crack would appear when they applied pressure.
However, when the crystals were just slightly misaligned, the interface deflected the crack and prevented it from spreading.
“Now we know that cracks are deflected at the nanoscale and, thus, can't propagate very far,” said Dr. Gilbert. “That's the reason our teeth can last a lifetime without being replaced."
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