I brush and floss my teeth twice a day and rinse with mouthwash before going to bed at night. I never had any extraction done and had only one tooth with a filling. It was the second molar on the upper left side. Yesterday, while I was brushing my teeth, I noticed slight sensitivity on the filled tooth. When I looked at it in the mirror, there was a slight patch of dark gray at the bottom part of the tooth. It hurt when I put pressure on it. It was yellowish on top. The rest of my teeth seem okay. Any ideas what the discoloration is and what is causing the pain? Is this related to the filling I have in that tooth? Please help. Thanks a lot.