Friday has arrived, and with it the weekly column "A Taste of Physics" — issue #34.
This time — on the connection between skyscrapers, Roman arches, and our teeth.
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Despite taking them for granted, our teeth have a remarkable engineering structure that allows them to survive with us for decades.
To understand it, we first need to explain how a material becomes resistant to stress.
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Materials whose molecules are arranged in an organized structure with strong bonds between them withstand compressive forces — which press the molecules together — very well.
At the same time, such materials tend to fracture under a sudden impact, because the bonds between the molecules don't allow for flexible movement.
Looser molecular bonds, on the other hand, allow a material to be flexible and not break easily, but they also cause the material to lose its shape under pressure.
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Skyscrapers and Roman arches rely on building materials that withstand compression well — steel beams or bricks, for example.
The greater the pressure on these materials, the stronger they become, because the stress distributes evenly through them and presses them together.
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Teeth have a far more sophisticated structure.
Enamel — the outer layer of the tooth — is made of a crystal called hydroxyapatite.
Its basic units are arranged in a hexagonal pattern, and these hexagons join together to form tiny rods.
These rods are oriented so that their upper ends face the tooth's surface and their lower ends face the tooth's interior.
In this way they act as support columns capable of withstanding compressive forces of hundreds of kilograms without breaking.
At the same time, to prevent fracture under a sudden impact, the rods are connected to one another by a flexible protein called amelogenin.
Amelogenin allows the rods a degree of freedom of movement upon impact, thereby preventing fracture.
Dentin — the inner layer of the tooth beneath the enamel — also acts as a shock absorber, taking in the energy of an impact through the rods and dampening it.
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In this way, the tooth achieves both high resistance under pressure and sufficient flexibility to avoid fracturing under a sudden impact.
Shabbat Shalom ☺️
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