I'm 40 years old and in excellent health. I brush regularly and floss 2-3 times per week. I've never had a cavity and always receive comments (from dentists) such as "Great looking teeth" and "You've taken great care of your teeth".
I am coffee drinker (2 cups a day), I rarely drink soda and use to smoke (pack a day for 13 years), but quit 11 years ago. My teeth were A2-3...not too bad, but obviously not white anymore. I wanted a brighter smile... I was the perfect candidate, or so I thought.
After the 2nd session, and after they added the next layer of peroxcide, it felt as if they were sawing through my teeth. It was the most pain I have ever felt and considered rating it the worst. I started to sweat and my hands started to shake - we had to stop. It was awful.
I left the dentist 90 minutes ago and have experienced 5 "zingers", one only seconds ago. It feels like pins are trying to push their way through my teeth (gums are ok).
Anyway, I gained one shade...my teeth loook better, but if I had to do over again, I wouldn't. Just sharing my story...good luck.