Pearl Drops. But only brush with it three times a week or less, the dentist told me that it can remove tooth enamel because it is that abrasive on getting rid of stubborn stains. That is the original whitening toothpaste though which started all the other brands brining out whitening versions.
Alternatively, write a letter to Serena Williams. I don't know what the hell she uses on her teeth but I want some when I get my brace off next week.