Professional bleaching a common form of teeth whitening, The active ingredient is either hydrogen peroxide or carbamide peroxide.
They work by breaking down and allowing oxygen access into the enamel, this makes the tooth color more light. The treatment must be done in stages and generally takes 3 to 4 weeks to complete.
First a mouth guard is made, for this impressions of your teeth need to be made, once the treatment has been started, the rest of the treatment can be done at home. Generally this will mean putting the whitening product for 30-60 minutes per treatment.
There are also treatments which are available where the product could be applied for up to 8 hours, meaning that results could be seen within one week.