What I do is take a capfull of peroxide and mix it with some mouth wash. The peroxide alone leaves a weird taste and feeling in your mouth, so you won't notice it as much with the mouthwash. Swish it in your mouth for about a minute or two, and rinse your mouth out after. I promise, even after a few days you will notice a difference.
And as a plus, it's cheap and won't leave your gum sensitive like practically every other teen whitener.

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