Do you brush your teeth at least twice a day? If you do, and you brush hard, have you ever wondered why you don’t wear your teeth down? The fact is that our teeth are pretty tough—about as hard as rocks. Every tooth is made up of the same two parts: a root, or roots, to anchor it in the jaw bone, and a crown, the part that can be seen in the mouth.

Teeth are composed mostly of mineral salts, of which calcium and phosphorus are the most prominent. The enamel is hard and shiny, and covers the crown. The cementum is a bonelike material that covers the root. The dentine is an ivorylike material that forms the bulk or body of the tooth. And the dental pulp is in a hollow space called the pulp chamber inside the tooth. The dental pulp is made up of tissue that contains nerves, arteries, and veins. These enter the tooth through an opening at or near the root end.

As you’ve probably noticed when you look at your teeth in the mirror, they are different in size, and in shape. In a full set of teeth, there are four types, each having a special duty. The incisors, in the center of the mouth, cut or incise food. The cuspids, which tear food, are on either side of the incisors at the corners of the mouth. They have long, heavy roots and sharp, pointed crowns.

The bicuspids, just back of the cuspids, have two points, or cusps, and one or two roots. They tear and crush food. The molars, in the back of the mouth, have several cusps and two or three roots. They grind food.