I use to play with my fish letting them nip at my finger but none of them had teeth. I time I did get a little nip on the back of my hand from a niger trigger fish while cleaning the tank. It didn't break the skin but it felt weird.
My biggest has nipped at me while I was using the gravel vac and once when I stuck my fingers in the tank after lights out to check the temp I saw his silhoutte zoom by a second too late to get me.