I'm on tray 4 of 27 and just recently had the buttons put on some of the teeth. Since then I've had horrible gum sensitivity to both cold as well as warm foods/drinks. If I breathe through my mouth the air (room temp) hurts my gums. The glue for the buttons ended up all over the teeth that had them; I'm guessing some went under the gumline and that's what accounts for the sensitivity. I'm not sure how they are going to get this stuff off later (have seen other reviews where they have to grind it off) but I'm having doubts that it will relieve the gum sensitivity and not sure it will ever come out from under my gumline. Actually, I suspect my gums will have receded by then.
Also, you're supposed to wear them 22 hours a day. Which means you have to brush and floss your teeth immediately after every meal, and can't drink or eat anything in between. Plus wear them at night.
Wish I hadn't gotton them. Bottom line: don't get Invisalign.