I could be wrong on the intent here, but in English we would say 'There's something in your teeth.' We use this when a piece of food is caught in between teeth (like a piece of lettuce or broccoli or something). I think this what the Indonesian sentence saying, but I could be wrong. Best example I can think of is in the cartoon The Emperor's New Groove and yzma has a piece of broccoli in her teeth. Kuzco could have told yzma 'there's something in your teeth'. Saying it as 'on' just sounds weird.