Whitening agents actually change the color of your teeth, but only are effective on certain types of stains. For example, bleaching agents have a difficult time removing brownish or grayish stains. These products also are not as effective on pitted or badly discolored teeth, or on restorations such as crowns, bridges, bonding and tooth-colored fillings (porcelain veneers or dental bonding may be more appropriate in this case).
One type of stain—caused by traumatic injuries, medications and fluorosis—actually begins inside the tooth; brushing and flossing don’t help. Another type of stain—one that can be more easily attacked by brushing, flossing and rinsing—is caused by external factors such as foods.