I had a dental ct scan and the dr. showed me a black circle above one of my root canaled tooth. He said it's not an infection, but he doesn't know why is it there. This was actually the second opinion for my ( now ) 10 weeks of gum puffiness after the tooth extraction, and he said he doesn't see anything wrong with the extraction site and he wouldn't re open it. He said this black circle is maybe from a sinus connection if it was one, but this black circle ( he called it an air bubble ) is above the tooth #5, and the extraction was of the tooth #2 .