Was ZOOMED yesterday and went through 4 sessions and it was NOT painful as I was so afraid it would be. If it would have been (as I did have one "zing") they stopped right away and put something on my tooth to cool it off and it felt better and then they reapplied the gel and we went under again and it was just fine. They didn't think my teeth would show a BIG difference due to a grayish color but they turned out so good I'm thrilled. I didn't listen though about taking ibuprofen and was thinking, "wow this is great, no pain even later" and then about 9PM the pain came and I was wishing I would have listened. The pain hurt alot all night so I kept taking the drugs. Today they still hurt but not as bad as last night. Would I do it all over again??? In a heartbeat! I am looking forward to the trays arriving so I can keep up on it as I am a coffee drinker and have hopes of them turning even whiter.