Rodents’ Orange-Brown Incisors Protected by Iron-Rich Enamel: Study Reveals

front teeth. Scientists have created detailed pictures of rodent incisors, giving a close-up look at the enamel and its coating at the atomic level. They found small pockets of iron-rich substances in the enamel that create a protective barrier for the teeth, but do not affect the orange-brown color – new discoveries that could benefit human dental care.

Chattering squirrels, charming coypus, and tail-slapping beavers — along with some other rodents — have orangeScientists have released detailed images of rodent incisors in ACS Nano, showing the enamel and its protective coating at an atomic level. The researchers found small pockets of iron-rich materials in the enamel that create a shield for the teeth without adding to their brown color. These findings could lead to advancements in human dentistry. Human and animal teeth are covered in a tough substance called enamel. This substance is even harder in rodents, whose constantly growing incisors have an additional layer of protection.The natural outer layer of enamel in rodent incisors is resistant to acid and rich in iron. It was previously thought that this iron-rich material was responsible for the orange to brown color of the incisors. However, the microscopic structure of this enamel had not been fully understood. Vesna Srot and her team set out to study the composition of rodent tooth enamel by capturing high-resolution images of incisor specimens from various species.

The researchers obtained incisors from rodents that inhabit different environments, including beavers, coypus, squirrels, marmots, rats, voles, and mice. To study the structure and elemental composition, they used advanced imaging techniques.To analyze the composition and color transmission of the enamel, we took thin slices from different parts of the teeth and prepared them for imaging with optical microscopy, 3D focused ion beam tomography, and scanning transmission electron microscopy. The high-resolution images at the micro- and nano-scales revealed the following:

• Cells that synthesize enamel components initially produce particles of iron-storage proteins (ferritins) that are 6- to 8-nanometers wide, which serve as the source material for iron ions in matured enamel.
• As the enamel matures and solidifies before the teeth erupt from the gums, iron-containing ferrihydrite-like material moves into the outer layer.
• Enamel is a protective layer that fills the spaces between calcium-containing hydroxyapatite crystals.
• The iron-rich enamel’s microstructure contains nanometer-sized pockets filled with small amounts of ferrihydrite-like material, contributing to its acid resistance even though the filled pockets account for less than 2% of the enamel’s volume.
• These findings suggest that different types of rodents develop the iron-rich outer enamel layer in a similar way, but the depth of the layer varies by species, with mice having the thinnest and coypus having the thickest layers.
• Ultimately, the research demonstrates the importance of the iron-rich outer enamel layer in protecting rodents’ teeth from acid erosion.The brown color of rodent teeth is not due to pockets in the enamel, as previously believed, but actually comes from a thin surface layer made up of aromatic amino acids and inorganic minerals.

The scientists propose that including small quantities of ferrihydrite-like or other colorless biocompatible iron minerals in dental products could offer excellent protection for human tooth enamel. Additionally, incorporating small amounts of iron hydroxides into synthetic enamel could lead to longer-lasting restorations for human teeth.

The authors acknowledge funding from the European Union’s Horizon 2020 research