I have 2 days left using the renewal whitestrips by crest....and I really notice the difference.....I did both top and bottom at the same time. Nobody else really noticed though...I don't know if I would say "it took 20 years off"...but they are whiter....and brighter. I have some leftover regular white strips and I might continue those after just to get rid of them.....they are expired but I can't see how they can be bad...they are totally sealed.