The narwhal’s long, white, spiralled tusk is not magical – but it is nevertheless somewhat mysterious. For example, scientists are still not certain what the narwhal uses it for.

However, a research team has now used advanced 3D X-ray techniques to determine how the tusk obtains its characteristic structure.

It turns out that the tooth does not contain just one spiral, but two.

On the outside, the structure twists to the left, while the interior structure twists in the opposite direction, forming a kind of biological counterbalance, where two opposing forces meet at the interface between interior and exterior parts.

Researchers have long known that the left-handed shape must reflect a particular organisation of the mineralised collagen fibrils – the microscopic building blocks that give the tooth its strength – but exactly how this organisation works has been impossible to map in three dimensions.

Until now.

To see how the building blocks are oriented inside the tooth, the researchers combined several X-ray imaging techniques, particularly a special 3D X-ray technique called tensor tomography. The technique works by sending powerful X-rays through the tooth and analysing how they scatter from the nanoscale mineralised collagen fibrils.

The narwhal’s tusk is in fact the left canine tooth, which grows through the jaw and lip and can reach more than two meters in length. Unlike human teeth, it has no enamel but consists of dentin on the inside and cementum on the outside.

Because the narwhal tusk is both large and structurally extremely complex, the researchers had to deploy the biggest technological tools available. They combined the capabilities of the ESRF, MAX IV in Sweden, and Swiss Light Source − to obtain enough resolution and power to map the entire interior of the tooth in three dimensions at the atomic, nano and micro scale.

The analyses revealed a fascinating pattern: while the building blocks are primarily oriented along the tooth’s longitudinal axis, they systematically deviate at small angles, creating a twisted structure. In the outer cementum, the fibrils form a left-handed spiral, while in the inner dentin they form a right-handed spiral.

More complex than previously believed

The two opposing structures meet at the transition between dentin and cementum – a complex biological boundary that now appears to be even more intricate than previously believed.

This double-spiral structure gives the tusk favourable mechanical properties. The structure is far more stable against bending and twisting than either a single spiral or a straight rod would be. It is an architecture also found in other biological materials that must withstand large forces.

“No one has previously carried out such an advanced experiment of this type. We have only been able to do it by collaborating across several disciplines – namely chemistry, physics, materials science and biology. Without collaboration with the biologists at the Greenland Institute of Natural Resources, we would not have been able to interpret the results,” says Adrian Rodriguez-Palomo, the study’s lead author and scientist at the ESRF (previously a postdoctoral researcher at Aarhus University).

To enable this interdisciplinary endeavour, the project reunited groups from Aarhus University, Chalmers University of Technology, and the Greenland Institute of Natural Resources in collaboration with the synchrotron facilities.

Growth Layers Reveal Stability

Remarkably, the study shows that the double-spiral structure is preserved across the tooth’s annual growth layers – like tree rings, but with a constant twist. This suggests that the left-handed growth pattern is genetically programmed and remains stable throughout the animal’s life, which can extend to around 80 years.

The discovery provides new insight into how nature constructs advanced materials with extreme mechanical properties – knowledge that could eventually inspire the design of new composite materials for fields such as construction and medicine.

And the research team’s investigations do not stop there:

“Since whales can live for up to 80 years, their teeth form a kind of historical record of changing environmental conditions throughout the animal’s lifetime. And because the North Atlantic is currently undergoing very rapid changes, it is obvious to investigate whether we can trace these changes in the hard tissue of the narwhal tusk. That is what we are now working on,” says the leader of the research project, Henrik Birkedal, professor at Aarhus University.

Reference:

Rodriguez-Palomo, A., The narwhal tusk assembles its macroscopic helix from building blocks with opposing twists, Nature Communications (2026). DOI: 10.1038/s41467-026-75689-z. www.nature.com/articles/s41467-026-75689-z

Top image: Narwahls in Greenland. Credits: Carsten Eqevanq.