I have been reading about an alarming trend that some people are using Mr. Clean Magic Erasers to whiten their teeth. The Erasers are made of non-toxic melamine which in its solid state is a delicate but strong abrasive which makes it great for household cleaning. But if used on your teeth, it will wear your enamel down. The enamel layer is what gives teeth their whiteness, but the underlying tooth core called dentin is generally darker. As you wear off your enamel, you will eventually start to see your teeth getting darker, not whiter!
Remember, once the enamel is gone, it will need to be restored with veneers or bonding as it will not grow back. You may even experience increased sensitivity and problems with cavities without enough enamel protection. I will say the Erasers are great for household cleaning, but not for teeth whitening.