crown issue

Six months to a year ago I had a root canal and a full crown set on what was left of a tooth. I have now noticed a a black line that is running around the bottom of the crown between the crown and the gum.  The bottom of the crown never went into the gum and it still doesn't.

What is this black line from? (there is not pain).

[Jerome Bogin, D.D.S.]

The black line is probably the metal collar that is left just short of where the porcelain meets the metal on a porcelain to metal crown. There is nothing wrong with that as long as there is no decay. The tooth is without a nerve so that you would not be able to sense any decay so I would have it checked out by your dentist.