blackness on bottom side of crown

I have had a bottom molar crown for over ten years and have just noticed a black line on the bottom inner side of it.  Is this normal or is this something to be worried about?  It doesn't hurt but I'm wondering if its loose or if the blackness is infection.  

[scottma]

Seeing a dentist is advised.

[StratRebel]

Without a light its difficult to tell the difference in black vs gray.  If its truely black, than its either calculus or a cavity.  If its gray, thats likely just the metal surface of the crown (most porcelain crowns have metal substructures for support).  Either way, at 10 years it would be a good idea to go see a dentist to have it checked as the average life of crowns is 7-10 years.

[lynn117]

if you have been having regular dental care it shouldnt be anything serious, i have a crown thats turning 30 this year. after the first few years the tooth margin turned gray. later on the gum changed to gray also. the metal in the filling material caused the color changes. have it checked by the dentist but dont worry yet. it could be nothing.