Does bi-carb soda and toothpaste really whiten teeth?

I have yellow teeth and I've heard that bicarb soda and toothpaste will help whiten my teeth... Will this actually work and will they stay white for ever or only a short period of time? And how many times should you brush your teeth with it?
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You first need to get to understand as to what is it in the toothpaste that helps in whitening the teeth. Toothpastes mainly consists of 2 ingredients --- a whitening agent like carbamide peroxide or sodium tripolyphospate and an abrasive agent like silica (or calcium carbonate or dicalcium phosphate). Whitening agents do not actually have much effect on teeth whitening since the contact time with the teeth is very less. Abrasives is what actually that helps in removing the stains on the teeth and whitenign toothpastes have more of the abrasives as their content as compared to the ordinary toothpastes. But usage beyond limits can cause damage to the enamel since the silica like abrasies can actually keep peeling off the enamel even while removing the stains from the teeth. Long term usage of these toothpastes could weaken the enamel quite beyond acceptable limits which could lead to related complications.
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