Julian Chavez, age 12, of Gamerco, N.M., for his question:

WHAT ARE TEETH MADE OF?

The importance of our teeth cannot be overestimated, and proper diet and good care are essential if we are going to keep them healthy. Actually, each tooth has two parts, the crown, which grows above the gums, and the root, which grows in a socket in the jawbone. Each tooth is made up of four different kinds of tissue.

What we see is the outer portion, or enamel, which is the hardest substance in the human body, consisting mainly of calcium phosphate. Next is the dentin, a hard, yet elastic, tissue containing organic matter in addition to calcium phosphate. The dentin surrounds the pulp cavity, or dental pulp, which contains tissues, nerves and blood vessels. The fourth tissue, cementum, covers and protects the root of each tooth.

These four tissues work together to help keep each tooth in good shape. Our second set of teeth is permanent and does not replace itself, so it is our job to make sure these teeth get proper care every day of our lives.