I just finished about 2 months worth of whitening. I scored a great deal ( free) by having a relative who's a dentist make me some trays. I used 15% and saw absolutely no change after many, many weeks of application. To be fair, my teeth are already white. He ( the dentist) even told me that the gel wouldn't whiten them any more than they already were. I just wanted to try and see if I could lighten the color of the tooth down near the gum line where they are a bit less white. I used the little tooth whitening guide, and saw absolutely no change in color. All I have to show for it is slightly more sensitive teeth, that feel a bit colder, but that's it. I have heard there is higher strength bleaching gel out there, but not sure if I want to bother. I've heard friends tell me that simply breathing thru their mouths hurt their teeth when they used gel this strong. Everyone has different porosity in their enamel, and will achieve different results, though.
