they said that to me also and i continued to never ever put them in again for the rest of my life as soon as braces were off. i will have crooked teeth before i wake up every day to a mouthful of dead mouth skin cells and dried saliva pressed up against the roof of my mouth and tongue. its bad enough without the layer of plastic sealing it in. so far so good but i bet some people probably have it worse than me and would need surgery otherwise. i'm not a doctor so don't take this as medical advice.