I started dating my first girlfriend at the very end of her orthodontic treatment, about a month and a half or so before she got her braces off. I never told her I had a thing for braces, but I secretly wish I could've enjoyed them for a bit longer.
She got a retainer afterwards (that one with a single metal wire across the top teeth) which she had to wear for almost a year. I wasn't into it as much as I had been with proper fixed braces, but I suppose it was better than nothing. She hated it though, so I never mentioned that I thought she looked hotter with it on. Still, it was an interesting experience.