i want to have my dentist whiten my teeth?

I was curious what the procedure is. Does it hurt? How long does it take? Approximately how much does it cost?
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I had mine done: the dentist made a cast of my teeth and gave me a gel, I then had to wear the cast and the gel for about 40 mins a day over a few weeks. The results were good, cost about £250 I think, and lasted about a year. I've heard laser whitening makes your teeth very sensitive and can be painful, and I think it's more expensive.
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