Cavities are caused by bacteria and are more often referred to as tooth decay. “Caries” means “rottenness” in Latin. One of the most prevalent long-term illnesses and a significant public health issue, since people are living longer on average. To better understand human tooth decay and genetic factors that influence enamel development, Northwestern University researchers have discovered the building components of enamel down to the nanoscale. This finding may lead to enamel that is severely damaged or entirely missing. Throughout the crown is enamel, the tooth’s protective outer covering. It’s high mineral content gives it its toughness.

Researchers say enamel has developed to be strong and wear-resistant enough to endure the pressures involved with chewing for decades. “Enamel, on the other hand, is very restricted in its ability to regenerate. Since we now know how enamel forms as a result of our basic study, we can use that knowledge to create novel treatments and materials to help prevent and cure dental caries. Patients with congenital enamel abnormalities may benefit from the information since it may help avoid or alleviate their symptoms.” Joester is a materials science and engineering associate professor at the McCormick School of Engineering. Co-first authors in Joester’s group are Ph.D. student Karen A. DeRocher and postdoctoral researcher Paul J.M. Smeets. An important roadblock in enamel study is the fact that it has a multi-scale structure. Enamel is a three-dimensional weaving of rods that may be several millimeters in thickness. There are hundreds of hydroxylapatite crystallites, each about 5 microns long and thin, in each rod. A crystallite’s width is measured in nanometers. Enamel is composed mostly of these tiny crystallites. Joester’s team sought to know why the crystallite’s core seemed to be more soluble in human enamel than in other animals. Minor enamel components were studied in single crystallites to see whether their composition changed over time.

They found that human enamel crystallites had a core-shell structure using cutting-edge quantitative atomic-scale methods. The ions calcium, phosphate, and hydroxyl are organized in periodic fashion in each crystallite’s continuous crystal structure (the shell). Magnesium, sodium, carbonate, and fluoride replace these ions in greater abundance in the crystallite’s center (the core). Magnesium-rich layers surround a sodium, fluoride, and carbonate ion mix in the center. Magnesium ions create two layers on each side of the center, similar to a 6 billionth of a millimeter-wide sandwich, according to the study’s lead author, DeRocher. The sandwich structure has to be detected and seen using cryo-STEM and atom probe tomography, two advanced imaging techniques (APT). The regular arrangement of atoms in the crystals was discovered via cryo-STEM analysis. APT enabled the scientists to identify the chemical composition and location of a tiny number of impurity atoms with a precision of sub-nanometer. Core-shell architecture and resultant residual stresses have a significant effect on the dissolving behavior of human enamel crystallites, according to the study’s authors, while also offering a plausible mechanism for enamel extrinsic toughening. Chemical gradients down to the nanoscale can be seen, which improves our knowledge of how enamel is formed and may lead to new ways for improving the health of enamel, according to Smeets.

Paraphrased and reposted : Northwestern University. (2020, July 1). Materials scientists drill down to vulnerabilities involved in human tooth decay: Enamel formation study could lead to new interventions to prevent and treat disease and defects. ScienceDaily. Retrieved October 5, 2021 from http://www.sciencedaily.com/releases/2020/07/200701125436.htm