It works but it was VERY pain full afterwords. I felt some pain to wards the last part of the last 20 minute session. As soon as I was done the pain started. It was a throbbing and sharp pain through out my teeth. They tell you to take Advil or Tylenol and to treat it like a headache. I took 4 Advils in the 4 hours time frame and it didn't help at all. In the end I started drinking Whiskey heavily and I felt much better.
I will warn anyone with sensitive teeth to think hard and prepare with some serious pain killers before going to the treatment. Also it's not a good ideal to have your teeth cleaned by a dentist before the treatment because your teeth will become even more sensitive to the bleaching.
I will not go through the treatment again even if it was free. I'm glad I woke up the next day with out any pain. I'm very scared to brush my teeth now. I'm afraid the pain will come back. I will just have to take very good care of my teeth going forward and hopefully they will remain as white as they are now.