You teeth are covered with a delicate layer of white enamel that's prone to staining, particularly when it's exposed to acidic liquids such as coffee. According to the book "My Favorite Yankee Miracles" a mixture of hydrogen peroxide and baking soda can remove coffee stains on teeth. The baking soda is gentle enough to slough off the stains without damaging your tooth enamel, and the hydrogen peroxide is a whitening agent that's found in many commercial tooth-bleaching kits. Make sure to check with your dentist before using this treatment, as it may damage veneers and crowns.
Measure out 1 tsp. of baking soda into a small dish. Add three to five drops of hydrogen peroxide, and stir the mixture to make a thick paste.
Scoop the mixture up onto your toothbrush and brush your teeth with the mixture for about two minutes, making sure to pay special attention to the coffee-stained areas. Do not press harder on your teeth than you normally would, as that may damage your enamel.
Rinse your mouth with cool water to remove any traces of the mixture. Do not swallow the stain-removal treatment.
Repeat the treatment once daily to remove any fresh stains. It may take a few applications to completely whiten your smile.