Is it bad form to say, "you are my #1 program"?

its bad form if you tell multiple programs that "you are my number 1". the ortho community is small, and people talk. If you get caught playing that game, it could mean trouble.

its not bad form if you are speaking the truth.

As long as your honest, I think it can only help you to tell your top program that they are your top program. The only thing I would consider is that your top program may change as you interview at different places. It will definitely come back to haunt you if you tell multiple programs that they're your top choice. It's always safe to say you're "one of my top," but it's also probably not very helpful. Imagine the difference between being told "we've ranked you to match" and "we've thought very highly of your application."