Nothing is wrong.
What you are seeing is simply the metal that your crown is
made out of showing out from underneath.
I know I know, you thought that your crown was white and that
there wasn't any metal in it.
Well, there is. You have what is referred to as a porcelain
fused to metal crown of (PFM).
The crown is made of a metal substructure to give it it's strength and
then porcelainis layered over the top to make it look like a tooth.
The PFM has been used for years and has had remarkable success.
The only draw back to these types of crowns is the metal line showing through
and the fact that the porcelain layers can begin to separate from each other
and cause the pieces of porcelain to fall off the crowns.
Today there are new advances in crown technology that have
eliminated both of these problems.
There is a new material, to the world of dentistry that is, called zirconium.
Zirconium crowns are milled from a solid block and are very very strong.
This milling process means that they are not put together piece by piece.
Therefore there are no pieces to come apart. The crown is one solid unit.
Zirconium is also white so the color is that of most teeth and will never show a
metallic line because there is no metal.