I purchased the professional Zoom treatment through a local dentist's Groupon. Although I had heard about sensitivity, the office I went to said they have a newer Zoom system that minimizes the sensitivity. I was under the impression the "old" Zoom system did cause problems. I do have sensitive teeth due to acid erosion and I had no problem. Be prepared for several rounds within a session. The technician paints the bleach onto your teeth and then a light interacts with the foam to remove stains. It seems I went through 4 cycles. I was shocked at how white my teeth were. I think I was 6 shades lighter when I left the office. As with any professional service, I think the technician plays a huge role in the success. Ask how often the office performs the procedure. The office I went to had an excellent reputation and I did indeed receive excellent service and results. It's a great way to see a noticeable difference in a short period of time.