Beavers have protection against tooth decay built into the chemical structure of their teeth, according to a new study that could lead to improved treatments for human tooth decay.
Northwestern University researchers found that the pigmented enamel of beavers, which contains iron, is both harder and more resistant to acid than regular enamel, including that treated with fluoride.
"We have made a really big step forward in understanding the composition and structure of enamel - the tooth's protective outer layer - at the smallest length scales," said Derk Joester, lead author of the study and an associate professor of materials science and engineering in the McCormick School of Engineering and Applied Science.
"The unstructured material, which makes up only a small fraction of enamel, likely plays a role in tooth decay," Joester said.
"We found it is the minority ions - the ones that provide diversity - that really make the difference in protection. In regular enamel, it's magnesium, and in the pigmented enamel of beaver and other rodents, it's iron," he said.
Layers of well-ordered hydroxylapatite "nanowires" are the core structure of enamel, but Joester and his team discovered it is the material surrounding the nanowires, where small amounts of amorphous minerals rich in iron and magnesium are located, that controls enamel's acid resistance and mechanical properties.
In a series of experiments of rabbit, mouse, rat and beaver enamel, Joester and his colleagues imaged the never-seen-before amorphous structure that surrounds the nanowires.
They used powerful atom-probe tomography and other techniques to map enamel's structure atom by atom. Rodent enamel is similar to human enamel.
The researchers subjected the teeth to acid and took images before and after acid exposure.
They found the periphery of the nanowires dissolved (the amorphous material), not the nanowires themselves.
The researchers next identified amorphous biominerals in the structure, such as iron and magnesium, and learned how they contribute to both the mechanical hardness and resistance of enamel to acid dissolution.
Of particular interest to Joester and his colleagues was the pigmented enamel of the beaver's incisors. Their studies showed it to be an improvement over fluoride-treated enamel in resisting acid.
