Update: I went to my dentist today because of pain in the gums underneath the root canal. I asked him about the black color at the gum. He said it was a metal plate underneath the crown. He offered not explanation for the pain and suggested a toothpaste for sensitivity. Ugh! He said the x-rays were fine and I had no infection. At this point I don't know what to think. I might try a biological dentist for a second opinion. Hopefully, I can get some help soon.