3D X-ray imaging unlocks the secrets of the narwhal's spiral tusk

Aug 20 : In the Middle Ages, narwhal tusks were sold as unicorn horns blessed with magical powers such as neutralizing poisons and curing diseases — prized possessions of monarchs and nobles worth more than their weight in gold. They provided no such powers, of course, but even today remain objects of mystery.Researchers have now deciphered the internal structure of these spiral-shaped tusks — actually a straight and elongated canine tooth that protrudes from a narwhal's mouth, sometimes reaching up to 10 feet (3 meters) long. Using advanced three-dimensional X-ray imaging, they found that while the exterior of the tusk, made of dental tissue called cementum, displays a left-handed spiral, its interior, made of dental tissue called dentine, exhibits a right-handed spiral."We propose that t