What about over-the-counter teeth whitening kits?

Whitening products available for purchase in shops and online are designed to be "one size fits all" which often translates to "one size fits none". The effectiveness of over the counter formulations can vary but you will not get the best whitening result as these formulations are a much lower strength than what is available in professional whitening kits.  It is also importance to realise that some areas of the mouth may appear dark due to decay/old fillings/crowns/past root canal therapies and these areas won't respond to bleaching so it is best to have your teeth examined professionally to determine if bleaching is the right treatment to whiten your smile. Formulations should also be compatible with tooth structure and not cause any undue damage to the teeth in the bleaching process.