What kind of signs do you think could indicate that someone might have a dental fetish? Some people like to talk about their dental experiences rather openly, but I don't know if that is really a sign in most cases. Maybe it's just a timely topic of discussion for them if they recently had an appointment. Different people have different ideas of personal privacy anyways.
A long time ago I had a female colleague who seemed to like me, as she often came to me for a casual chat. Once she told me about her trip to her home country to see a dentist. I was too shy to pick up from there, which I still regret. She had some amalgam fillings, and maybe she had noticed that I liked to see a flash of them, although I never said anything about it. But I will never know for sure.
A few years ago I had a friendly chat with a nice lady at an expat event. She had a missing upper premolar which I noticed, and maybe she noticed that I noticed, although I tried not to pay attention to it. Anyway, we just had a normal small talk for a while and then went on mingling with others. Later in the evening, I saw her around. She looked at me, smiled and turned her head slightly so that the tooth gap was very clearly visible. Maybe it wasn't intentional, but I had a strong feeling that she did it on purpose. Her boyfriend was also at the event, and they left soon after that. I never met her again, but still remember her smile.
I also remember a young woman who was a colleague of my friend. Once I went out with my friend and some of his colleagues. She was there wearing a tooth-shaped earring. I wanted to ask about its meaning, but I thought it would be awkward, so I'm still wondering.