I got 22% whitening gel from the dentist. They gave me 4 syringes. I've used 3 of them. The application was 30minutes at a time and if teeth become sensitive lay off for a day or so. So after going through 3 syringes I feel my teeth have reached a whitening plateau. They just don't seem to be getting any whiter. Also they really aren't that white. I'm pretty dissapointed with the results. In some light they look white but in most lights they don't. I was wondering if going with a 36% gel would make the difference. Any users out there? Genetically I was not gifted with white teeth and they stain very easily. Thanks for the comments.