First, I'm assuming you are referring to a line around your gum area, not at the edge of the tooth where you bite into things.Most likely you have a porcelain-fused-to-metal crown, the most common type of porcelain crowns done for the past thirty or more years. It has an inner thimble of metal, most likely a white gold. Then, on top of the metal the porcelain is fused onto it. The reason that the porcelain had to have metal under it was that the older porcelains were not very strong or fit that well without the underlying metal to support it. It is the edge of the metal thimble that you most likely see.However, today there are several types of tooth colored porcelain crowns that are strong, well fitting, and last a long time without needing the underlying thimble of metal. Today my favorite material is Emax porcelain!Back to the "dark line" you see. You ask, can it be hidden? There are two ways that it could be done. One is to have a gum graft that covers over the metal line. You would most likely have that done by a periodontist (a gum specialist). In only a few cases can that successfully be done, so you would need to consult with a peridontist to determine the prognosis of such a procedure.The other way is to drill away the metal and replace that area with a tooth colored filling. Now, what might be best to overcome the black line problem. Replacing it altogether with an all porcelain (with no underlying metal) crown would give you the best results.There are many advantages to having crowns made with the newer porcelains and techniques. First, they can be bonded onto the tooth. This is a much better technique that just cementing it as porcelain-fused-to-metal crowns are done. Another advantage is the esthetics of the all-ceramic crown are much more natural, mimic real teeth in a much more realistic way. The porcelain-fused-to-metal crowns oftentimes look opaque and unnatural, while all ceramic crowns have some partial translucency that resembles natural enamel. And a commonly looked advantage to all ceramic crowns to porcelain-fused-to-metal crowns is that some people are actually sensitive or allergic to the underlying metal, and that may result in an ongoing chronic gingival irritation (bleeding, swelling, darker, more redish colored gums). All porcelain crowns are very bio-compatible and accepted much better, oftentimes resulting in much healthier gums. For some examples of how the unsightly black line problem is solved, I refer you to the web link below.
