I have only ever told one person, and I had dual reasons for telling him.
1) he kept mentioning how much he hated his braces and how they made him so much less confident, were ugly, etc, and was worried they were unpleasant to kiss. So I kind of HAD to tell him that I liked him. I couldn't keep letting him think I saw them as a negative, esp when he was so self conscious about it
2) I had just recently figured out that this was actually a fetish, not just an intense interest (I was a late bloomer lol) Up until that point, I would just make up these little fantasies in my head where either I was the patient, or I was the orthodontist. I didn't see it as sexual, and then suddenly I realized that actually, it was VERY sexual and I could make it a sexual thing btw me and a partner. I felt really sick and wrong about this, and hoped that he would tell me "it's not that weird" or "I like that you like it" because I wasn't feeling too great about myself right then
I had to tell him a few times before it really sunk in. The first time he just looked at me like I was being patronizing or something, so the second time I made sure to be the one to bring it up, and he responded by taking my finger and putting it in his mouth, I guess thinking that if I just said braces turn me on, this would be a good way to get some (it was). The third time I told him I made a point of saying " I am so messed up, I'm sorry I'm so weird" and he just sort of shrugged it off and said "some girls like them."
Apparently there had been a girl before me who also said she liked his braces.
I was never 100% sure if this was true or if he just said that to make me feel better. But it definitely wasn't what I expected to hear.