tooth cavities

The sea urchins create their hiding places using advanced technologies. When they dig themselves burrows on the sea floor, the round-bodied urchins use their five regenerating teeth

Sea urchins living on the seabed do not seem to belong in the world of advanced technology. But scientists at the Weizmann Institute of Science recently discovered, to their surprise, that these spiny creatures create their hiding places using advanced technologies. When they dig themselves burrows in the seabed, the round-bodied urchins use their five teeth, which, like the teeth of rodents, are worn at the ends and continue to grow on the other side, from the root, throughout the life of the urchin.

Surprisingly, these teeth, which should be stronger than the limestone in which the hedgehogs dig their burrows, are mainly made of calcite, the same mineral that most limestone is made of. How then do these teeth manage to cut and dig in the seabed? In a series of studies carried out for more than a decade, Prof. Steve Weiner and Prof. Leah Eddy, from the Department of Structural Biology at the Weizmann Institute of Science, discovered that the secret of sea urchins lies in a combination of original and outstanding design technologies.

The last study in the series, carried out by postdoctoral researcher Yorong Ma and research student Yael Politi, in collaboration with Prof. Popa Gilbert and Dr. Rebecca Metzler from the University of Wisconsin, Dr. Barbara Eichmeier, Oscar Farris and Peter Pratzel from the Max Institute in Potsdam, Germany, and Dr. Andre Meibom from the National Museum of Natural History in Paris, was recently published in the Journal of the American National Science Association (PNAS). In the first step, the scientists found that the teeth of sea urchins contain magnesium calcite crystals that are smaller, denser and stronger than pure calcite. These crystals are concentrated at the molar end of the tooth and especially in the center, where most of the force is applied. What holds the crystals in the correct position is a pattern of calcite crystals which are larger and softer. While most materials of this type are constructed as a matrix of hard fibers containing the softer filling, hedgehog teeth appear to be constructed differently: a matrix of relatively soft calcite fibers holds magnesium calcite crystals which are harder. This fact allows these crystals to spread along the surface of the tooth tip. The presence of the magnesium calcite crystals creates a sandpaper effect that helps grind the rock. By using high-resolution electron microscopy of the X-PEEM type, the scientists discovered another fascinating aspect of the tooth design in sea urchins.

It turns out that all the crystalline materials that make up the tooth are arranged in two different layers, and these layers "lock" on top of each other like the fingers of two joined hands. The scientists believe that in this way the sea urchins make themselves a jagged tool that resembles a saw. The edge sharpens itself when the tooth is ground. At the same time, the crystalline layers always break in such a way that the edge remains jagged. A better understanding of the structure of sea urchin teeth may lead to the design of improved mechanical tools, such as efficient tools for grinding and cutting that do not dull, just like the self-sharpening teeth of sea urchins.