what is the best way of whitening your teeth,i brush them twice a day,?

i would like my teeth to be abit whiter,i have even bought some whitening stuff from boots but it was expensive rubbish i have 2 crowns at the front of my mouth that make the ones at the side of my mouth look darker,so i look like i only brush my 2 front teeth
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try the smokers toothpowder, it work wonders ad makes them nice and fresh and white
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