I have two weird brown spots at the bottom of my teeth?

A couple of days ago, I noticed these two little brown spots at the bottom of my front teeth. I have tried to brush them away and pick at them, but it hurts really bad, and no matter what I do they won't go away. At first I thought it was something stuck on my tooth, but now I'm thinking that it might be decay or something like that. I'm going to the dentist today, but I was just wondering if anyone could tell me what the spots were and how they might be fixed.