Why Do I Have A Black Line Under My Crown?

Black lines around the edge of older crowns are a common problem that I see. They are almost never a problem initially with a crown but can show up after several years. Black lines are almost always preceded by some slight amount of gum recession. Your gums usually recede slightly over the course of your life and tend to progress more quickly on teeth with crowns. When they do recede, the margin (area where the crown meets the tooth) of the crown and the enamel/root surface also becomes visible. On back teeth it usually isn’t noticeable but on front teeth it can become a significant cosmetic problem. Depending on the specific type of crown you have, there can be a couple of different reasons for this black line developing.

Common Reasons For A Black Line Around A Crown

• The first, and most common reason for the black line is a tooth that has a porcelain fused to metal (PFM) crown on it. These types of crowns are made up of two separate materials: metal inside and a porcelain covering. The black line occurs when the gums recede and the metal starts to reflect through the tooth surface. In some cases the metal can even stain the tooth where it touches it.
• The second reason for a black line is if a cavity has started on the tooth surface where it meets the crown. These areas will usually start as brown and progress to a dark black color. If it is a cavity, you should have it taken care of as soon as possible. Crowns that get under crowns can progress rapidly and easily lead to a root canal or tooth loss if not treated.
• The last reason for a black line is if the margin has become stained. Teeth can stain for a variety of reasons but we see it most often with people who drink coffee, teas, red wine, and dark colored sodas.

How Can You Fix The Black Line?

Unfortunately in almost every case a new crown is needed to fix the problem. If the area is small enough your dentist can sometimes place a filling over the stained area but you usually don’t get a great cosmetic result. The filling material usually allows some of the stain to show through and it doesn’t match terribly well with porcelain.

If you do decide to get the crown replaced, your dentist will remove the old crown, any stained areas, and move the margin right to the edge where the gums meet the tooth. Most crowns on front teeth today are made out of porcelain and don’t have the same problems with black lines that some of the older PFM crowns did. Ask your dentist what material they would recommend on the tooth to get you the best result. I personally like to use EMax (lithium disilicate) crowns in cases like these but there are several other crown options out there that can work equally well.