Researchers 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.-Cornell University
“Chemical Gradients in Human Enamel Crystallites,” a study by the researchers, was published in Nature on July 1st. Lena Kourkoutis, an associate professor of applied and engineering physics at Cornell, spearheaded the university’s effort. The study was led by Derk Joester, a Northwestern University professor of materials science and engineering. Karen DeRocher, a PhD student at Northwestern, and Paul Smeets, a postdoctoral researcher, are the paper’s co-authors. Tooth enamel is a tough material that can resist eating, but too much acid in the mouth may eat away at it and cause decay. The structure and chemical makeup of enamel at the nanoscale have eluded scientists for a long time, despite prior peeks inside the crystallites that make up the material. Scan transmission electron microscopy, often known as STEM, involves shooting an electron beam across a sample. However, there are limitations to this method. When placed under an electron microscope, enamel is a mechanically highly robust material, yet it is very sensitive to an electron beam. “Enamel crystals, on the other hand, can only hold a fraction of the electrons found in electronic crystalline materials. To get to the atomic level, you usually have to put in additional electrons in the substance. However, if the material is damaged before the information can be extracted, everything is lost.”
Joester’s Northwestern team has used atom probe tomography to scan delicate biological materials in recent years. This technique removes atoms from a sample’s surface one at a time and reconstructs the material’s structure. A low-temperature electron microscopy technique developed by Cornell University researchers at PARADIM (Platform for the Accelerated Realization, Analysis and Discovery of Interface Materials), which is funded by the National Science Foundation, can now image the atomic structure of radiation-sensitive materials. By measuring how much energy is lost when electrons contact with atoms, the method may also be used to safely map a sample’s chemical makeup. Kourkoutis, the facility’s director for electron microscopy, says that while working at low temperatures, materials become more resistant to damage from an electron beam. In the area of cryogenics, we are currently working at the confluence of advances in the physical sciences, which have brought electron microscopy down to the atomic size.
An electron microscopy summer school run by PARADIM drew the two university groups together in 2017. One of the students, Smeet, had previously attended Joester’s summer school. At PARADIM, he discovered how cryogenic electron microscopy from PARADIM might help with the university’s human enamel research. Dr. Berit Goodge and Dr. Michael Zachman, Ph.D. ’18, co-authored the article with Smeets. Researchers used liquid nitrogen to freeze enamel samples to around 90 kelvins, or 298 degrees Fahrenheit. Cryogenic electron microscopy was used to examine the samples. The Cornell and Northwestern researchers were able to examine an enamel crystallite and its hydroxylapatite atomic lattice by combining their complimentary methods. However, the picture was not quite clear: Towards the crystal’s core, the lattice had dark distortions produced by two nanometric layers of magnesium and sodium impurities as well as fluoride and carbonate ions. It has been shown via further modelling that the crystallite’s imperfections are a source of stress. It’s possible that these imperfections and the enamel’s core-shell design work together to strengthen the enamel and increase its resiliency. New therapies for tooth enamel strengthening and cavity prevention may result from the results, according to the researchers.
Atom probe tomography and correlative electron microscopy, Joester added, “will have enormous effect on our knowledge of how enamel develops” and how disorders like molar incisor hypomineralization “disturb” this process. Cryogenic electron microscopy isn’t only useful for studying lips. As a result, Kourkoutis is investigating the chemistry of energy systems like batteries and fuel cells, which use a combination of soft electrolytes and hard electrode materials.
Cornell University. (2020, July 21). Smile: Atomic imaging finds root of tooth decay. ScienceDaily. Retrieved October 5, 2021 from http://www.sciencedaily.com/releases/2020/07/200721132848.htm