How are some sea mollusks able to chew rocks without destroying their teeth?
That’s what two researchers from Northwestern University aimed to answer with a sophisticated tool that takes images on an atomic scale. The resulting 3D map breaks down all the atomic components of the tooth’s incredibly hard surface.
An Atomic Image of Your Teeth
They used atom-probe tomography (APT) to uncover the strange hybrid substance. The technique reconstructs a substance atom-by-atom at a sub-nanometer 3D resolution. There are fewer than 12 APT machines in the nation, and they’re typically not used to scan organic matter, so some people thought that scanning a substance composed of both organic and inorganic matter wouldn’t work.
The scientists took small samples from the surface of an Eastern beaded chiton mollusk’s tooth. These samples were sharpened into tips with an ion beam tool. Science Daily explains the following process this way:
The APT technique applies an extremely high electric field to the sample; atoms on the surface ionize, fly off and hit an imaging detector (similar to those found in night-vision equipment). The atoms are stripped off atom-by-atom and layer-by-layer, like peeling an onion. Computer methods then are used to calculate the original location of the atoms, producing a 3-D map or tomogram of millions of atoms within the sample.
This way, scientists can take a look at the exact substance that makes up the tooth and how it’s arranged on a deeper level.
Teeth that Can Chew Rocks
This tiny sea mollusk, called the Eastern beaded chiton, uses its incredibly tough teeth to scrape algae from rocks. Its teeth are covered in one of the hardest biominerals known to man, yet the structure is similar to human teeth: a relatively soft inner core surrounded by a tough shell (like our enamel). Instead of enamel, the chiton’s outer tooth layer is a hard iron oxide called magnetite (which also makes its teeth appear black).
The chiton eats algae on the rocks by chomping away at it with continually rotating rows of teeth. It grows a new row of teeth every day to replace the old, worn-out ones, which move down like a conveyor belt toward its mouth.
How Does a Mollusk Help Us?
Tracking the exact interfaces in the combination of organic and inorganic materials can help doctors and dentists track tooth decay and bone disease at levels that are as yet inaccessible. It can also help track the exact location and progression of dental fluorosis, which occurs when a person is exposed to excess amounts of fluoride over an extended period.
The researchers plan to use the APT on the teeth of vertebrates next, and also plan to move on to other bones to learn more about their structure on the atomic level.