I just came back from the dentist and had the zoom whitening procedure. 3 sessions all 20 minutes long. I had no complaints during the sessions however the last few minutes of the third session i felt about 3 tiny zingers. As soon as i was done i felt the ZANGERS yes i said ZANGERS. Calling them zingers doesn't begin to describe the pain im going through right now. It is so bad i had a friend give me some vicodin and the zangers are still painful. Im getting them about 20 zangers every hour. :( Although the outcome is amazing. I had yellow stained teeth all my life and now i have these pearly whites! I think id do it again.. but to everyone else out there beware!