What contributes to the orange-brown colour of rodent incisors?

Chattering squirrels, charming coypus, and tail-slapping beavers along with some other rodents have orange-brown front teeth. High-resolution images of rodent incisors published in ACS Nano provide an atomic-level view of the teeth’s ingenious enamel and its coating. The researchers discovered tiny pockets of iron-rich materials in the enamel that form a protective shield for the teeth but, importantly, don’t contribute to the orange-brown hue — new insights that could improve human dentistry. To investigate the structure, elemental composition and colour transmission of the enamel, thin slices were taken from different sections of the teeth and prepared for imaging with optical microscopy, 3D focused ion beam tomography and scanning transmission electron microscopy. The micro- and nano-scale resolution images revealed that the intense orange-brown colour of rodent incisors doesn’t come from the filled pockets in the enamel, as was previously thought, but from a thin surface layer composed of aromatic amino acids and inorganic minerals. The researchers suggest that adding small amounts of ferrihydrite-like or other colorless biocompatible iron minerals to dental care products could provide exceptional protection for human tooth enamel. In addition, incorporating small amounts of iron hydroxides into synthetic enamel could produce longer-lasting restorations for human teeth.