Looking for a better way to understand tooth decay and possibly detect it earlier, researchers are turning to nature and an animal well known to possess a champion set of choppers -- the beaver.

Although they don't drink fluoridated water and certainly don't brush their teeth, the beaver's outsized incisors are protected from decay by something in the chemical structure of their tree-chewing teeth -- and its iron, scientists at Northwestern University have found.

The pigmented enamel of beaver teeth -- stained a rusty red from the iron -- is harder and much more resistant to acid and decay than regular enamel, including enamel treated with fluoride, the researchers determined. The findings may help them better understand the mechanics of tooth decay and improve current fluoride-based treatments.

"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," says study leader Derk Joester, a professor of materials science and engineering.

Enamel is a very complex structure, making study of it challenging, the researchers note.

Layers of hydroxylapatite "nanowires" create the core structure of enamel, but its acid resistance and mechanical properties come from material surrounding these nanowires--material containing small amounts of amorphous minerals rich in iron and magnesium.

The Northwestern study is the first to reveal the exact structure and composition of this "amorphous" or unstructured material.

"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."

In a series of experiments of rabbit, mouse, rat and beaver enamel, Joester and his colleagues imaged the never-seen-before amorphous structure atom by atom.

"A beaver's teeth are chemically different from our teeth, not structurally different," Joester says. "Biology has shown us a way to improve on our enamel."

Tooth decay is one of the most common chronic diseases and represents a major public health problem, despite strides made with fluoride treatments, causing Americans to spend $111 billion annually on dental services, according to the American Dental Association.