A. Built for crunching and chewing, teeth mostly consist of hard, inorganic minerals such as calcium. But they also contain nerves, blood vessels and specialized cells that manufacture the different parts of the tooth, said Bill Gengler, a veterinary dentist and oral surgeon with the UW-Madison School of Veterinary Medicine.

The tooth's outermost layer -- the part we brush -- is enamel. Deposited by cells called ameloblasts, enamel is 95 percent inorganic, says Gengler, making it the hardest material in the body. In contrast, only about 50 percent of our bone is mineral.

Enamel is thin, though -- in dogs and cats, for example, it's just a fraction of a millimeter in thickness -- so most of a tooth's substance comes from the dentin underneath. Made by cells called odontoblasts, dentin is about 70 percent inorganic and tubular in structure, like a network of "little conduits with liquid inside," Gengler said.

Inside the tooth, below the dentin, is the pulp chamber. The pulp includes blood vessels that nourish the tooth by delivering oxygen and nutrients, and fast- and slow-conducting nerve fibers that warn us of problems.

The fast-conducting fibers produce a quick, "ouch" response, says Gengler. "They tell us, Don't bite down on that popcorn -- it 's not popped.'" Slow fibers, meanwhile, transmit the constant, dull pain of a toothache.

Covering the root of the tooth is cementum, a slightly softer substance produced by -- surprise! -- cementoblasts. Cementum serves mainly as an attachment site for the periodontal ligament, which holds the tooth in its socket.

-- Produced in cooperation with University Communications

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