German researchers have uncovered how the mineral nanostructure and surrounding collagen in tooth dentin allow our teeth to withstand the daily stresses and avoid cracking.
Normally, when bone gets damaged, it can heal itself by growing new tissue or remodeling. But while teeth are bone-like, they do not have this facility.
In the journal Nano Letters, researchers from the Charité Universitätsmedizin Berlin in Germany describe how they examined the mechanical properties of tiny nanoparticle and fiber structures inside dentin—the layer of softer, porous material that lies under the much harder enamel covering of teeth. Knowing that dentin contains tiny layered structures of mineral nanoparticles embedded in, and firmly attached to, collagen protein fibers, and thinking that it is these layers of mineral nanoparticles and collagen proteins that make teeth tough and damage resistant, the researchers set out to see how they stopped cracks from growing.
The new study reveals that the nanoparticles are “pre-compressed” and it is this that stops cracks from traveling.
“The compressed state helps to prevent cracks from developing, and we found that compression takes place in such a way that cracks cannot easily reach the tooth inner parts, which might damage the sensitive pulp,” said the study’s senior author, Dr Paul Zaslansky of the Julius Wolff Institute of the Charité.
The researchers examined the tiny structures of tooth dentin using micro- and nanofocused x-ray beams generated by advanced synchrotron-based diffraction equipment. They altered the humidity of dentin samples to change its mechanical properties and study how stress was generated in the material.
They found that when the collagen fibers shrank, this increased the compression in the attached mineral nanoparticles.
In further tests, they found that heat weakens the link between the nanoparticles and the fibers, making the dentin more brittle.
The study’s first author Jean-Baptiste Forien, a PhD student in the Julius Wolff Institute, says, “We therefore believe that the balance of stresses between the particles and the protein is important for the extended survival of teeth in the mouth.”
The team suggests their findings may explain why artificial tooth replacements are not as resilient as healthy, natural teeth. Perhaps ceramic materials are too “passive” and do not respond to stress in the same way as the natural, pre-compressed structures.
Zaslansky concludes that these results might lead to the development of tougher ceramic structures for tooth repair or replacement.