My teeth are so yellowish which would have caused from drinking coffee ( i'm a coffee addict!) A friend of mine has been using hydrogen peroxide and he says it was quite effective. It has to be mixed with baking soda until it forms a paste. Then it is to be applied on the surface of the teeth avoiding the gum line. Keep it for few minutes, rinse with water and brush with a fluoride toothpaste. I'm also considering getting a dental treatment from a clinic in Toronto - Centenary dental. Most probably I will be going for the treatment as I may not get enough time trying the DIY tips. I have actually tried most of them but nothing could make much difference in the yellowish shade of my teeth.