Secret of Stronger Tooth
Tooth enamel makes up the normally visible part of the tooth. It is made up of hydroxylapatite (a type of calcium apatite) rods or nanowires, stacked and woven together. The nanowires are surrounded by a mineral layer rich in iron and magnesium. This mineral layer makes the enamel not only the hardest tissue of the body but also offers its acid resistance and other mechanical properties.
The ionic makeup of this lamination is the key to why beaver teeth are so strong, researchers found. Beavers are known for their ability to topple massive tree trunks by chewing them. However they are quite immune to tooth decay because of the tiny iron-rich nanowires interwoven throughout the enamel.
In studying the composition of beavers’ front teeth and other types of enamel the Northwestern University researchers were able to reveal the chemical contribution of these amorphous internal wires, for the first time. They treated the teeth with acid and photographed before and after acid exposure. Acid treatment dissolved the peripheral mineral layers of the nanowires leaving the nanowires intact. They found that beavers’ teeth are structurally similar but chemically different from human teeth. In regular enamel, it’s magnesium, and in the pigmented enamel of beaver and other rodents, it’s iron. The minority ions, offering diversity, make the difference in hardness and resistance to acid decay.
In a succession of experiments with rabbit, mouse, rat and beaver enamel, the team imaged the amorphous mineral structure surrounding the nanowires, for the first time. They used powerful atom probe tomography and other sophisticated techniques to map enamel’s detailed atomic structure. The technique involved a microscope-like instrument capable of revealing the cross-sectional atomic structure of materials inside.
Dental caries, or tooth decay, is one of the most common chronic diseases and a major public health problem. 60 to 90% children and nearly 100% adults worldwide have or have had cavities, according to the World Health Organization.
This discovery could thus lead to a better understanding of human tooth decay, earlier detection of the disease and its management. Experts think that researchers can look for strategies to harden enamel against acid corrosion, perhaps using the tougher iron-rich rodent enamel as a blueprint.
Amorphous intergranular phases control the properties of rodent tooth enamel. L. M. Gordon, M. J. Cohen, K. W. MacRenaris, J. D. Pasteris, T. Seda, D. Joester. Science, 2015; 347 (6223): 746 DOI: 10.1126/science.1258950
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