Baking powder is not useful for whitening teeth. On the other hand, baking soda, often confused with baking powder, is a common ingredient in some toothpastes. Its purpose is to eliminate stains on the surface of the teeth.
Baking soda whitens because it is abrasive. Continual use of baking soda alone, rather than as a toothpaste component, sometimes damages the protective enamel coating on teeth. The use of plain baking soda also does not specifically address cavities. Toothpastes containing baking soda have another ingredient, fluoride, which enhances tooth enamel and works against plaque. It is possible for plaque to build up in the mouth and cause gum disease and tooth decay.