I have been needing to do this for quite some time, so when i came across a groupon I made my appointment for an exam, xrays, cleaning and zoom whitening. I checking this site for reviews do that i would knew what to expect, and was unnecessarily made nervous. I'm sure it's different for everyone, but my experience was great. Made it five minutes into the third fifteen minute session before the "zingers" really started bothering me. None in the first round, four in the second, and ten zingers in the third round. None of it was unbearable though, the mouth guard was more uncomfortable in my opinion. Two hours later now, and very minimal pain. Do it! So worth it. Updated on 19 Sep 2013: