The erotic implications of dentistry are obvious. Assuming your dentist/hygienist is reasonably attractive, they are leaning over you, sticking their fingers in your mouth, asking you to "open wider," and telling you when to spit. And if you happen to be a masochist, all the scary implements are enough to make one giddy.
Speaking of (more common) fetishes, I was writing a campy spanking story set in a fantasy milieu for "publication" on a website that catered to that sort of thing. It was going great. But I stopped visiting that website for personal reasons. Now my drive to continue that story has dried up.
So, I'm back to writing my Magnum Opus. I don't consider it to be erotica, but it has erotic undertones, and it will have a sex scene or two. But never, it seems, the scene I'm currently working on....