A new study has uncovered a rare behavior in the material of the teeth of the Atlantic wolffish. This material is osteodentin, the tissue at the tooth’s core, which appears to shrink in every direction when it’s squeezed along its length, a response that is exceptionally rare in natural materials, particularly mineral-rich materials. The finding helps explain how the wolffish’s teeth endure repeated punishing biting forces and could point researchers toward new designs for tougher, more resilient synthetic materials.
The Atlantic wolffish is known for its powerful bite, capable of crushing hard-shelled prey with ease. Now, researchers have discovered that the fish’s teeth don’t just withstand these extreme forces, they respond in a way that almost no natural hard tissue does.
In a new study led by Prof. Ron Shahar of the Koret School of Veterinary Medicine at Hebrew University, the team found that the teeth contain a rare internal material, osteodentin, that actually shrinks in every direction when compressed. This unusual behavior, known as auxeticity, has never before been documented in vertebrate mineralized tissues. Auxetic materials, very rare in natural materials, have become an objective of man-designed artificial materials, so-called meta-materials. The research was published in Acta Biomaterialia.
Most materials expand sideways when compressed along theie length. Osteodentin does the opposite. When the researchers applied force along the tooth axis, similar to the wolffish’s natural biting forces, the material consistently contracted laterally as well as longitudinally, a phenomenon corresponding to materials with “negative Poisson’s ratio.” Across all eight teeth examined, the team recorded effective values mostly between -1 and -2, a range rarely seen even in engineered materials.
To document this behavior and reveal its mechanism, the researchers used advanced phase-contrast X-ray tomography combined with digital volume correlation, allowing them to create detailed 3D maps of how intact teeth deform under load. The results showed that osteodentin contracts uniformly along all three axes during compression, a surprising and highly unusual response.
The secret appears to lie in osteodentin’s microscopic structure: a very dense network of vertically oriented canals of 10-20 microns in diameter, that runs from the base of the tooth to its top, and curve outward near the tooth surface. The team suggests that this architecture causes the mineralized columns between canals to bend inward under pressure, creating a natural mechanism that increases toughness and helps prevent cracking.
“We were astonished to find that osteodentin behaves in a way that almost no other natural mineralized tissue does,” said Prof. Shahar. “Its internal architecture allows the tooth to absorb heavy loads safely and efficiently. Nature has essentially engineered a structure that protects the animal from the extreme mechanical demands of its diet, and this may inspire future synthetic materials with similar resilience.”
While nano-indentation tests showed that the mineralized components of osteodentin have stiffness values similar to bone, its unique internal architecture appears to be what gives it its remarkable performance. Similar auxetic behavior in mineralized tissues has previously been observed only in two invertebrate species, limpet teeth and nacre.
The researchers believe this phenomenon may extend beyond the Atlantic wolffish, suggesting that auxeticity could be a broader feature of osteodentin in other fish species. Beyond expanding scientific understanding of how teeth evolve to survive extreme mechanical stress, the discovery also offers a rare blueprint for designing synthetic materials that combine strength, damage resistance, and energy absorption, properties highly sought after in engineering and biomedical applications.