I'm surprised at the comments of people who said that they saw little or no improvement. I was beyond amazed with the results as was my wife - she couldn't believe the improvement. I didn't even bother to ask how many shades my teeth improved because the difference was blindingly obvious - even without looking at the before picture. I just got it done one day ago, 07/23/2009 between 8:15 and 10 AM, so I can't speak to how long it will last but I will post another comment - maybe in one year - once I can speak to that. I had three 20 minute sessions. I had it done at my regular dentist's office - which I would highly recommend - don't get it done in a mall. They took great care to make sure that my gums and lips were protected so I didn't get any of the burning or scarring that other people reported. NOTE: It takes 1.75 - 2 hours, not 1 hour. The actual whitening takes 1 hour, 3 - 20 minute sessions, but there is a fair amount of prep work and the hygenist took time in between each "whitening session" to suction, clean, etc... She also reapplied gel as needed. The CONS: The pain during the procedure wasn't that as bad as other users have posted. A few stabbing pains that came and went quickly on my right lower teeth during the last few minutes of round one. Given the postings I had read, I figured it was normal and didn't mention it to the dental hygenist. The pain is intense when it comes but it didn't last long. The pain during the second round was much more frequent. At the end of round two, I mentioned this to the hygenist. She examined my teeth and realized that my saliva had disolved more of the gel on my right lower side so she applied extra gel there before round three. I wish I had asked for additional gel before they started round 2 but I didn't know to ask. Needless to say, round three came and went much faster, because there was significantly less pain. Next she applied a gel to help reduce sensitivity and then she had me rinse with water and then with fluroide. Less than one hour after leaving, I started to get the same shooting pain in all of my teeth. Each time the pain came and went very quickly but this time it was happening virtually non-stop. One tooth, then another, then another and so on. I popped three ibuprofen, followed by two more a few hours later but with very little help. By the end of the evening, the shooting pains had subsided into a general dull ache. I got a good night's sleep - without any additional ibuprofen - and while my teeth are still a little sensitive to hot and cold today, there is no pain. I rated my pain as "uncomfortable" below because I think severe is a little extreme. I would say my pain was in between uncomfortable and severe. If you had asked me yesterday "Would you do it again?", the answer would have been an emphatic NO - I'm a bit of a wimp - especially when it comes to pain in my teeth. But today, I'm not so sure. I guess it depends on how long the benefits will last. If they only last a few weeks or months, then the answer will still be no, but if the benefits last a few years, then I would say it was worth it. I didn't use any Sensodyne toothpaste and I brushed my teeth twice yesterday - albeit very gently. Hope this helps. Danny