Whitening procedures entail removing the extrinsic stain of the teeth and revealing the natural color underneath.  Stain naturally occurs on teeth over time and can sometimes occur as a result of congenital defects.  To whiten your teeth you must first make sure all of your teeth are healthy and that the bone and gums supporting them are also in good health.  Whitening teeth that have current decay or are periodontally involved may worsen the prognosis of the tooth and will not achieve the results you desire.  This procedure is very cosmetic so it is typically the last portion of a treatment plan after all decayed/infected teeth are treated.

For more information follow the link below

https://www.mouthhealthy.org/all-topics-a-z/teeth-whitening