A home tooth-whitening kit contains carbamide peroxide, a bleach that can remove both deep and surface stains and actually changes your natural tooth color. If you have coffee-stained teeth, a tooth-bleaching kit can help. With some kits, you apply a peroxide-based gel (with a small brush) to the surface of your teeth. In other kits, the gel is in a tray that molds to the teeth. The tray must be worn daily (for 30 to 45 minutes) for a week or more.