well....i thought i may as comment on this being as i'm a qualified dental nurse with about 20 years....lol
anyway about 4 years ago i had the teeth whiting done cost £500 for treatment....yeah i know ur thinking i would get a discount, but i didn't go were i used to work cos they didn't do it..lol anyway, they took a polaroid before and after and u could really see the difference, espically as i'm quite a heavy smoker and coffee drinkier...(yeah yeah i know..lol) anyway, they prop ur mouth and lips open/apart with a prop to keep them free from saliva. then paste the gel on then put the blue light (lazer) on it, give u some glasses, ask ur choice of dvd u want to watch from what they have ..or u can take ur own... come back in half an hour, paste some more on then come back again in half an hour, turn everything off, take out the prop, ask u to rinse then take another pic....wollahhh all done......but about 5 hours later thats when the sensitivity kicks in....if u have it done have the last appointment as late as possible of the day...my mouth was going like i was eating a load of strong pickled onions, when it really starts to kick in the best thing to do is go to bed, but when u wake up in the morning it's all gone....u don't suffer from the sensitivity again after that, it's just that evening and the same thing happened to me mate aswell, so it wasn't just me... since then i have heard of this home kit u can buy from them which is about £250 so i don't know if u have ur prices round the wrong way.....