I had first used Crest white strips many years ago, and while the effects were subtle, I enjoyed them. When Crest came out with the new 3d line I was excited to try them. However, they made my teeth so sensitive, I had to stop after only about 4 days, and I didn't see any results in that time. I've heard tips about using them less frequently or using a sensitive toothpaste to help, but it was a painful experience, and I wanted the convenience of an at home whitening strip so that I wouldn't have to put a lot of extra time into making them work for me. I might try their gentle routine in the future, but I wouldn't recommend these to anyone with sensitive teeth. Ouch!