The formation of dental plaque by bacteria is one of the main reasons for discoloration of teeth. Surface stains, come from the usual suspects like coffee, red wine, tobacco, and dark coloured foods.
Commonly found in water filters, activated charcoal is essentially a form of carbon that has been treated to make the surface of its particles porous.
I recommend you to therefore use activated charcoal. Sprinkle a small amount of activated charcoal powder on your toothbrush and brush. Pay special attention to areas that have stains or discoloration. I used it on my teeth, and the stains were removed slowly. For best results, you should brush your teeth with activated charcoal 2 to 3 times per week. There are some concerns, however, about the use of charcoal, which some say could damage enamel if used regularly.