question: The last cap my dentist put on over a year ago, is gold.  I started noticing sensitivity to cold & hot to it.  It is completely black around the crown & down in my gum.  I went back to my dentist & he poked around the top of the cap & I felt no pain.  He said it was a black tattoo & laughed.  Then my sister who was a dental assistant for years said she thought the tooth was dead.  It has been over a month since I went to the dentist & now on the left side of my mouth another cap looks like a blister along the gum line.  What do you think?  Thank You