Wired：美科学家找到牙齿再生之法

own building materials for oral repair would be a boon to dentists, who have been fixing cavities with metal fillings since the 1840s. Enamel and dentin are remarkably strong and long-lasting, and they can repair themselves. But as scientists are continuing to find out, dentin in particular is a remarkably complex structure.

The outer covering of teeth is enamel. The body makes it by growing tiny mineral crystals in a highly regular crystal lattice. Underneath that ceramic-like covering, dentin is like hard clay reinforced by fibers of collagen, similar to the way adobe bricks contain clay reinforced by straw fibers.

"The tooth is a beautiful structure," said Van Thompson, dentistry professor and chairman of New York University's Department of Biomaterials and Biomimetics.

But teeth, because they are made from minerals, are susceptible to what is essentially erosion. Acids, like those produced by bacteria or Coca-Cola, demineralize the enamel of the teeth. Usually the body is constantly repairing small amounts of damage, Marshall said. But when the body's defenses become overwhelmed, bacteria break through into the dentin below, and you get tooth decay, commonly called a cavity.

The acid produced by the bacteria eats into the minerals in the dentin, turning it mushy and useless. Normal dentin is twice as stiff as pinewood, but damaged dentin is more like rubber, which makes it pretty hard to chew with.

Marshall's newest work, which has been accepted for publication in the Journal of Structural Biology, focuses on regrowing dentin in damaged teeth with the help of a calcium-containing solution of ions (electrically charged particles).

By putting a layer of the solution on individual test teeth, Marshall has already been able to remineralize some parts of the teeth. The challenge is to get the crystals to regrow throughout the dentin.

To heal properly, the crystals need to form from the bottom of the tooth up to the enamel. Marshall isn't sure whether that's happening yet, but she is confident that she'll find a way to restore dentin functionality over the next few years.

Stephen Bayne, professor of dentistry at the University of Michigan, noted that while many groups are working on regrowing teeth, Marshall has "incredible stature" in dentistry for her groundbreaking work helping dentists understand the structure of the tooth.

Still, even with the recent progress, the very complexity that Marshall and other researchers have discovered in the humble tooth is likely to keep her technique out of your local dentist's office for a few more years.

"We're still a ways from being able to grow back dentin and enamel," Bayne said.

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