Why is my gum line dark, even though I have a zirconium crown?

It is possible that the temporary crown covered more of the tooth than the permanent crown, going beyond the margin created in the tooth preparation.There are some tricks to hide a dark tooth that shows through a crown.  One is to prepare more of the tooth, going deeper and further under the gums.  Another is go drill away the dark tooth that is showing through and place a filling over that area to hide it, and the have the crown go over that (this is oftentimes called "the Dickerson ditch).Your dentist, who actually has seen the underlying tooth and the results would be better able to diagnose the problem than any of the dentists on RealSelf who have not seen it.

I can think of two reasons that dark gum line shows even though you have a zirconium crown:1.  Poor margin, meaning the crown does not fit properly2. Slight gum recession after placement of the crown Since your tooth has a root canal and is dark under the crown, any slight gum recession will show the darkness no matter what type of crown you use.  However, Emax crown would be best to control darkness around the margins initially..Best,Dr. Maddahi

Zirconia crowns are no more translucent than other porcelain fused to metal crowns.  All these types of crowns stop any light from getting into your tooth and showing down the root.  Since the tooth was already dark, this just makes it look darker.  It is possible to help make the root of a dark tooth look lighter and place an all porcelain crown like E-max.  It is not real easy, but is possible.Good Luck