I've been having a major pain and sensitivity to cold, hot, and sweets on one of my upper molars. I think it's the one in which I had a filling several months ago, but I've had so many fillings over the past couple years I can't be completely sure, as I've changed dentists quite a few times. It feels like there's a line in the middle of the tooth where I bite down at, stretching horizontally almost the entire length of the underneath of my tooth. I'm not sure if I fractured the tooth, or if the filling is leaking? When I put my tongue on the line, it hurts a little bit, but doesn't hurt at all if I chew something hard or soft at room temperature. I don't have dental insurance at the moment so I am very cautious about going to the dentist. I just want to know if this is something serious or not, or what you all think.