Materials scientists drill down on vulnerabilities associated with human caries

Researchers at Northwestern University have identified one of the secrets of tooth decay. In a new study of human enamel, material scientists first identified a few impurity atoms that might contribute to the strength of the enamel, but might make the material more soluble. It is also the first company to determine the spatial distribution of impurities with atomic-scale resolution.

Caries, also known as cavities, is the destruction of teeth by bacteria. (“Cavity” in Latin means “perishability”.) It is one of the most common chronic illnesses and a major public health problem, especially as life expectancy in humans increases.

Northwestern discoveries in enamel building blocks — down to the nanoscale — can deepen understanding of not only caries in humans, but also genetic conditions that affect enamel formation and damage to enamel. Or it could lead to a complete lack.

The protective outer layer of human teeth, the enamel, covers the entire crown. Its hardness comes from its high mineral content.

Enamel is made up of closely packed rectangular crystals that are about one thousandth of the width of human hair. (Source: Northwestern University)

“The enamel has evolved over the decades to be sufficiently hard and abrasion resistant to withstand the forces associated with chewing,” he said. Derk Joester, Led the research. “But enamel has a very limited chance of renewal. Our basic research helps us understand how enamel is formed and helps prevent and treat tooth decay. It should help develop new interventions and materials. This knowledge will also help prevent or ameliorate the suffering of patients with congenital enamel deficiency.”

The study was published by the journal Nature on 1st July.

Corresponding author Joester is an associate professor of materials science and engineering. McCormick School of Engineering.. Karen A. De Rocher and Paul JM Smeets, Ph.D. Students and postdocs at Joester’s lab are co-authors.

One of the major obstacles to the study of enamel is its complex structure, which is characterized by multiple length scales. The enamel, which reaches a few millimeters in thickness, is a three-dimensionally woven rod. Each rod, about 5 microns wide, is composed of thousands of very long and thin individual hydroxyapatite crystals. The width of crystallites is on the order of tens of nanometers. These nanoscale crystallites are the basic building blocks of enamel.

Probably unique to human enamel, the center of the crystallite seemed more soluble, and his team wanted to understand why. Researchers set out to test whether the composition of minor enamel constituents differed in single crystals.

Using state-of-the-art quantitative atomic-scale technology, the team discovered that human enamel crystallites have a core-shell structure. Each crystallite has a continuous crystal structure in which calcium, phosphate and hydroxyl ions are periodically arranged (shell). However, in the center of crystallite, many of these ions are replaced by magnesium, sodium, carbonate, and fluoride (core). Within the core, two magnesium-rich layers adjoin a mixture of sodium, fluoride, and carbonate ions.

“Surprisingly, magnesium ions form two layers on each side of the core, which is just one-six billionth of a meter, like the smallest sandwiches in the world,” De Rocher said.

Detection and visualization of sandwich structures required cryogenic scanning transmission electron microscopy (cryo-STEM) and atom probe tomography (APT). Cryo STEM analysis revealed a regular arrangement of atoms in the crystal. APT has allowed researchers to determine the chemistry and location of a few impurity atoms with sub-nanometer resolution.

The researchers provide strong evidence that the core-shell structure and the resulting residual stress influence the dissolution behavior of human enamel crystallites while providing a plausible route for enamel extrinsic enhancement. discovered.

“The ability to visualize chemical gradients down to the nanoscale could lead to a better understanding of how enamel is formed and lead to new ways to improve enamel health,” Smeets said. States.

This study Early works published in 2015Researchers have discovered that the crystals are attached by a very thin amorphous film that has a different composition than the crystals.

This study was supported by the National Institute of Health National Dental and Craniofacial Institute (NIH-NIDCR R03 DE025303-01 and R01 DE025702-01 grants) and the National Science Foundation (DMR-1508399 grant). It was

The title of the paper is “Chemical Gradients in Human Enamel Crystals”. In addition to Joester, DeRocher, and Smeets, other authors of this paper are Linus Stegbauer, Michael J. Cohen, Lyle M. Gordon, James M. Rondinelli of Northwestern. Berit H. Goodge, Michael J. Zachman, Lena F. Kourkoutis of Cornell University. Prasanna V. Balachandran of the University of Virginia.