Teeth are composite materials of metals and proteins, with a large volume of bony dentin that is highly porous. This structure allows the teeth to be both strong and sensitive. In addition to calcium and phosphates, teeth contain trace elements such as zinc. Using complementary microscopy imaging techniques, a team from Charité Berlin, TU Berlin and HZB has quantified the distribution of native zinc along and across teeth in 3 dimensions. The team found that as the porosity in the dentin increases towards the pulp, the concentration of zinc increases 5-10 times. These results help to understand the effect of widely used zinc-containing biomaterials (eg, sealants) and could inspire improvements in dentistry.
Teeth have a complex structure: The dental pulp with nerves is surrounded by dentin, a porous bony material, covered externally by enamel in the mouth and cementum in the roots. Although dentin is criss-crossed by countless micrometer-sized dentinal tubules, teeth can withstand decades of cyclic, repetitive forces. The density of the dentinal tubules increases toward the pulp, meaning that the dentin becomes increasingly porous toward the interior. The tubules of the dentin carry impulses to the nerves and allow the sensation of cold and heat, through connection with cells found in the pulp and root canals. Similar to bone, dentin contains mostly calcium and phosphate (in nanocrystals) as well as organic substances and a range of trace elements that are usually homogeneous. But the trace element zinc is almost non-existent in some areas, but quite widespread near the pulp. Until this study, it was not known what the concentration of natural zinc is and how it is distributed in healthy teeth.
Perfect teeth
The team, led by Prof. Dr. Paul Zaslansky, Charité Berlin, and Dr. Ioanna Madouvalou, HZB, set out to solve this question, only to realize that discarded human teeth are usually contaminated with zinc from treatment or toothpaste. Therefore, they used cattle teeth, which were widely discarded by slaughterhouses. These show e.g. through infrared studies performed with the IRIS team of BESSY II a high similarity to human teeth, being much younger and with no history of dental treatment or tooth brushing.
Where is the zinc?
“First, we made thin sections and examined them under a scanning electron microscope. These images revealed that the material between the individual tubules is almost completely homogeneous,” says HZB SyncLab manager Madouvalou. The team then examined the teeth using different dental and industrial 3D X-ray tomography systems to map their three-dimensional microstructure, particularly their density. As expected, tooth density decreases near the pulp, corresponding to an increase in tubules. These findings made it possible to correctly model the material and evaluate the experimental data from X-ray micro-fluorescence spectroscopy maps. “We recorded the signals from many elements, particularly calcium, phosphorus and zinc. While calcium and phosphorus, both of which come from the dentin nanocrystals, are evenly distributed, we observed and quantified a very sharp increase in zinc concentration from the outside to the inside, that is, to the pulp,” says Madouvalou.
Useful ideas
“These results are very useful for further improving dental care, for example whether the dentist should recommend low- or high-zinc materials during treatment,” explains Zaslansky. In healthy teeth, zinc is enclosed in dentin. However, contact with acids, either through caries or root canal treatment with zinc-containing pastes, could potentially activate chemical enzymes, with possible negative effects. “Studies on human teeth are needed to confirm our hypothesis based on bovine teeth.”
Zinc as an indicator
Another important point: The study suggests that zinc could serve as a good proxy for determining bone mineral density. “Bone density is a huge concern for many patients: everyone knows we need calcium and more minerals for strong bones. But actually, maybe what we want is a good balance of microporosity?’ suggests Zaslansky and concludes: “We unexpectedly find that zinc can probably be used as a very sensitive measure of gradients in the material’s density, which can change over a lifetime. Density is related to the mechanical ability of bone tissues and should be neither too high nor too low to serve the human body. With highly sensitive methods such as X-ray fluorescence, we may be able to sample and monitor density changes with ageing, for example due to the use of well-chosen dental fillings or mouthwashes.”
Reference: Mantouvalou I, Bauer LJ, Truong VB, et al. Quantitative micro-XRF combined with X-ray imaging reveals correlations between Zn concentration and dentin tubule porosity in intact teeth. GODDESS. 2026. doi: 10.1002/VIW.20250173
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