How Long Will the Pain Last from Tooth Whitening?

It is very common for patients to develop post operative sensitivity for 8-10 hours following any laser whitening procedure.  We typically give the patient  400-600mg of Advil prior to the procedure to keep the pain to a minimum.  Not everyone has sensitivity , but a good portion of patients do.  As far a your the person you read about being sensitive for a year, I doubt that this was from the whitening.  I have never had a patient have sensitivity even for 48 hours, much less a year.  

Some patients will have pain after Zoom.  It will last the first 24 hours and then will be back to normal.  We have been giving patients pain medicine in the office before the treatment to make the experience so much nicer.  This does not help you now!.  Try to take some Alleve and call the Dentist office and ask for a something for pain.  Try to keep air off of your teeth as this makes the teeth sensitive.  

Most whitening sensitivity is from dehydration of the teeth, and they will rehydrate within 24 hours. Ibuprofen or Acetominophen usually is enough to get through.
If it hurts for a year, something ELSE is wrong.
When done right, with the right products, teeth can get very white. Some methods out there are only moderately (to NOT) effective, but still dehydrated. Pain does NOT necessarily mean "working".