How long to whiten teeth?

So ive read the baking soda solution works to whiten teeth, but i would like to know about how many brushes or how long does it take to see results?
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Buy a Crest Pro Spinbrush. I bought one a week ago for $7.99 [plus tax] and my teeth are about 3 shades whiter by just using the brush and regular toothpaste. The brush has a round brush that spins on top, and a square brush that moves up and down on the bottom. Your teeth will be squeaky clean after you use it, and the stains I had on my teeth are almost gone, and like I said my teeth are about 3 shades whiter in only a week.
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