Purchased a groupon a while back and had my teeth whitened a few months ago. While the employee whitening my teeth was extremely informative of the entire process, while applying the gel on my teeth some got on my gums that she didn't wipe off that pretty much burned through the process. After my treatment my gums looked really irritated and felt like it, and she said it was normal-- although it obviously wasn't. Although my teeth did look whiter post treatment, after following the "white diet" and over less than a week after, I feel like I was right where I started, which is disappointing. Lesson learned, I will stick to crest 3D white strips because my gums felt killer and it's not worth it for me, plus I like long lasting results!