One of my new replacement porcelain crownsin the back seems to not go up as far as it maybe should. There is sort of a dark line at the top. The dentist says it is gum recession, but I don't recall having that before this crown replacement. Has anyone else seen that, and what did they do? The dentist said maybe I should have the crown replaced, but they were very non commital. I am seeing someone else soon, by the way.