Hello,
I normally recommend whitening AFTER the braces have been removed. If you are planning to get fixed braces, the braces will cover parts of your teeth and therefore the whitening product will not be able to work on those areas.
Similarly, if you are undergoing Invisalign treatment, attachments (ie Bonding of 'bumps' to your teeth) will prevent the whitening agent from working around those areas.
I feel that whitening treatment will be more successful once the braces are removed. I hope this helps.
Good luck!
Best wishes; Dr Sylvia Tan