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Dental Tribune U.S. Edition | February 2012XX XXXXX Dental Tribune U.S. Edition | March 2015A2 Beavers reveal way to toughen enamel Fig 1: Northwestern University research reveals that the pigmented enamel of beavers’ teeth, which contains iron, is both harder and more resistant to acid than ‘regular’ tooth enamel, including that treated with fluoride. Photo/Michael Graydon, Toronto Figs 3, 4: Left, Polished mouse enamel. Right, after an acid bath, the grain boundar- ies dissolve quickly, leaving behind crystals that make up the nanowires. Fig 2: Scanning electron microscope image of inner enamel from rat incisor. Photos/Provided by Northwestern University NEWS diversity — that really make the difference in protection. In regular enamel, it’s magne- sium, and in the pigmented enamel of beaver and other rodents, it’s iron.” The unprecedented imaging study of tooth enamel at the nanoscale was published Feb. 13 by the journal Science. Dental caries is the breakdown of teeth due to bacteria. (“Caries” is Latin for “rottenness.”) It is one of the most common chronic diseas- es and a major public health problem, despite strides made with fluoride treatments. According to the American Dental Associa- tion, $111 billion a year is spent on dental ser- vices in the United States, a significant part of that on cavities and other tooth decay issues. A staggering 60 to 90 percent of children and nearly 100 percent of adults worldwide have or have had cavities, according to the World Health Organization. Experiments on rabbit, mouse, rat and beaver enamel In a series of experiments with 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 expo- sure. They found the periphery of the nanow- ires 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 resis- tance 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 enam- el in resisting acid. (The presence of iron gives the teeth a reddish-brown color.) “A beaver’s teeth are chemically different from our teeth, not structurally different,” Jo- ester said. “Biology has shown us a way to im- prove on our enamel. The strategy of what we call ‘grain boundary engineering’ — focusing on the area surrounding the nanowires — lights the way in which we could improve our current treatment with fluoride.” The full title of the paper is “Amorphous In- tergranular Phases Control the Properties of Rodent Tooth Enamel.” (Sources: Northwestern University and the journal Science) Researchers find protection against caries in chemical structure of beavers’ teeth Beavers don’t brush their teeth, and they don’t drink fluoridated water, but a new Northwestern University study reports bea- vers do have protection against tooth decay built into the chemical structure of their teeth: iron. This pigmented enamel, the researchers found, is both harder and more resistant to acid than “regular” enamel, including that treated with fluoride. This discovery is among others that could lead to a better understand- ing of human tooth decay, earlier detection of the disease and improving on current fluo- ride treatments. Material surrounding the nanowires Layers of well-ordered hydroxylapatite “nanowires” are the core structure of enamel, but Derk Joester and his team discovered it is the material surrounding the nanowires, where small amounts of amorphous minerals rich in iron and magne- sium are located, that controls enamel’s acid resistance and mechan- ical properties. Enamel is a complex structure, which makes studying it challeng- ing. Joester’s team is the first to show un- ambiguously that this “amorphous” (or un- structured) phase ex- ists in enamel, and they are the first to show its exact composition and structure. “We have made a re- ally big step forward in understanding the composition and struc- ture of enamel — the tooth’s protective outer layer — at the smallest length scales,” said Jo- ester, lead author of the study and an associate professor of materials science and engineer- ing 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