S.T.
Yes they work - I am a dental hygienist - they do work, but you have to work at it. Don't think that you can just wear them one time and you will have super white teeth! I have yellowish teeth too, and it takes a long time to whiten my teeth. I actually use zoom whitening, which gives amazing results but you have to use it with trays. Use sensodyne for a few days before you start whitening to reduce sensitivity. Zoom gives me zingers! But it's worth it!