I just had it done today. They did a series of 4 fifteen minute sessions (I see most people get 3, so I don't know why I got 4- they weren't THAT bad.) I had prepared for the procedure by having coated my teeth in MI paste (Recaldent) for 30 minutes beforehand, followed by Sensodyne toothpaste swishing in my mouth for 20 minutes beforehand.) I had no pain at all during the procedure. After it was completed, the technician painted some type of Vitamin E gel on my teeth and then we again coated my teeth in MI Paste and Sensodyne, basically swishing it around in my mouth for 20 minutes. I also took an Advil. So far I've only had two bad twinges and that was from cold air sucked in while talking (I've decided to avoid talking for a few hours.) It wasn't really worse than having sensitive teeth and eating ice cream and it went away immediately. I think the key to surviving this procedure without major pain is to properly prepare your mouth and have supplies on hand to block the tooth tubules up so that the nerves are soothed. Swish Sensodyne before and after, take Advil, and don't talk for several hours. My teeth are 6 shades whiter so it worked very well for me. They told me it would continue to whiten for the next 24 hours up to 2 shades more. One thing I've noticed no one is posting, is that you should avoid anything that stains your teeth for 48 hours. The whitening opens up the pores in the teeth and they are more vulnerable to stains until the pores are sealed again. No coffee, pop, red wine, mustard, curry, etc for 48 hours. I know a lot of people experience pain, but I think with advanced knowledge of what to expect and what to do to counteract the effects, it is still worth doing.