Black top to crowns

Hi I hope you can help.  A year ago I had the top teeth crowned and unfortunately went to an unreputable dentist and ended up having to have 7 root canals.  I have now had them all redone but keep on getting and blue black colour appearing at the top of the crown on some teeth.  The dentist assures me that they are all porcelain and doesn't know why this is happening.  After all I have been through I am at a loss as to what I can do.  Any suggestions.  Many thanks.

[Jerome Bogin, D.D.S.]

If the crowns are all porcelain which I have no doubt they are, it is possible the gum tissue has reacted to the margins of the crowns in an unfavorable way. It is possible that the margins of the crowns are exposed or the gum tissue is inflamed. Either way if it is a cosmetic problem I would think it has to be corrected.

[mike1105]

something is not right. I've never seen black porcelain. get a 2nd opinion on what that blackness is, and on the work that was done and may need to be done again. request a new set of films and a full treatment plan.