Anne Tucker, age 10, of Biloxi, Miss., for her question:

WHAT IS IN TOOTHPASTE?

Toothpaste and toothpowder are both substances that are used with a toothbrush to clean the teeth. Both products contain a mildly abrasive substance, such as finely powdered calcium carbonate, or chalk, together with a soaplike material called a detergent.

Some toothpastes contain a sweetening agent other than sugar, along with various flavoring oils that are used to make the toothpaste taste good.

Glycerin or a similar material is added to the basic ingredients of toothpaste.

Some toothpastes contain stannous fluoride, a chemical that some scientists believe helps prevent decay.

Most dentists urge this simple rule: Brush your teeth well after every meal.