Yeah, I was just reading a thing in a beauty mag about this. They said a lot of those kits don't have the right buffers or something, so the bleach just goes wild on your enamel. I've seen friends end up with these weird orange streaks and really sensitive teeth for weeks. It's crazy how a cheap box can lead to a huge dentist bill to even try and fix it. Some people's gums look so sore from the trays.
Ugh, it's so true. I read this article online where a dentist was saying some strips have way too strong a peroxide mix for home use. They told a story about a woman who used a kit two days in a row and burned her gums so bad she could barely eat soup. Her front teeth got these white blotchy spots from where the enamel just gave up. Makes you wonder why they even sell that stuff.