Professional teeth whitening at dentist - is it any good?

Have you had it done? how long do you teeth stay white for... My dentist does it for £300. I dont know if its worth it or not.
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There are free methods. You are easily found in google a lot. Try searching for "natural teeth whitening". http://www.yournaturalteethwhitening.com There is a lot of remedies an natural teeth whitening.
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