It's more complicated than this. I've tried many brands of toothpastes, and used many brands of toothbrushes. I'm 13. I've always had yellow teeth. No matter what I do, their the same to be exact. I don't chew, only rarely and occasionally. I don't eat hard foods. I don't eat chips or crackers.

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Additional Details
I have a Arm&Hammer Whitening Booster. I don't drink soda. I stopped at age 8. At 7, I wondered why many drank coffee, so I tried a sip, and I spit it out and threw it away. Even though I never liked it, I hated it as much as before.