US researchers have combined complementary imaging techniques to explore the atomic structure of human enamel, exposing tiny chemical flaws in the fundamental building blocks of our teeth. The findings could help scientists prevent or possibly reverse tooth decay.
The team— a collaboration between researchers from Cornell University, Northwestern University and University of Virginia—have published their findings in Nature.
Thanks to its high mineral count, tooth enamel is a sturdy substance that can withstand the rigors of chewing, although excessive acid in the mouth can make it vulnerable to decay. While scientists have previously peeked into the crystallites that compose enamel, nanoscale images of its structure and chemical composition have been harder to come by. In one method, scanning transmission electron microscopy, or STEM, a beam of electrons is shot through a sample. But that process has its limits.
In recent years, the Northwestern group has imaged sensitive biological materials with atom probe tomography, a process that essentially strips atoms off a sample’s surface one at a time and reconstructs the structure of the material.
At the same time, Cornell researchers have advanced a form of low-temperature electron microscopy that can image the atomic structure of radiation-sensitive samples. The technique can also safely map a sample’s chemical composition by measuring how much energy is lost when the electrons interact with the atoms.
By combining their complementary techniques, the Cornell and Northwestern researchers were able to image an enamel crystallite and its hydroxylapatite atomic lattice. But all was not crystal clear: the lattice contained dark distortions—caused by two nanometric layers with magnesium, as well as sodium, fluoride and carbonate ion impurities near the core of the crystal.
Additional modelling confirmed the irregularities are a source of strain in the crystallite. Paradoxically, these irregularities and the enamel’s core-shell architecture may also play a role in reinforcing the enamel, making it more resilient.
The researchers said the findings could lead to new treatments for strengthening enamel and combating cavities.