My 26 year old BIL is currently having his teeth straightened but isn't using traditional braces. He has a clear plastic mouth guard that he wears all the time except for when eating. Every month or so he goes back to the orthodontist to get a new mouth guard that has a slightly different shape to move his teeth. You can't tell he has it in unless you're close up near his face. I think it's roughly $4-5000 which covers all the mouth guards and appointments.