Years ago (2002, to be precise), while I still had railway tracks, I bumped into a girl in a biker bar in Seattle (Alki Point, to be precise) who shared a tin-grin.
She was pretty, and we had something in common, so I made conversation: "So, how long you in for?"
Her response: "Oh, I'm done."
Me: "Well, not to be obtuse, but I see your braces right there..."
Her: "Oh, I asked for them back. I felt naked without them, and I went back. Told them I paid for them, their mine, and got them back."
Told me that they were willing to put the backets back on as long as she wasn't being stupid about it. A girl after my own heart!
Two reasons I did not ask her out that night. 1) she had a voice like Fran Drescher on helium, and 2) she was there with her fiancé.
So basically, it seems if you are just honest, they will keep 'em on for you.