There is a thread somewhere in Beauty&Style where a LOT of people complained about burnt gums with the Zoom system... and the dentists didn't want to know anything, and the company didn't care.

I'd be very very careful. Try GoSmile - they're at home ampules that you pop and apply. Very easy, super convenient. A little pricey. I obsess about how white my teeth are so they weren't very dark to start with (according to everyone that knows me, except me) but I liked them. Crest Whitestrips worked well but gave me excruciating sensitivity when I did two strips per day on top and bottom as instructed.

I'm thinking of trying the Aquafresh trays next.