Why is my crown dark near the gum?
Crowns can be dark near the gum for reasons as follows:
1. METAL COLLAR: Many crowns made of porcelain and metal have a thin metal collar along the gum line edge of the porcelain (indicated by the black arrows). This often makes the porcelain a little stronger. Generally when a metal collar is used on a crown, it is positioned sufficiently below the gum line as not to be seen. However, as patients age, it is common for the gum line to recede. Frequently this leads to exposure of the metal collar leading to a less than desirable cosmetic situation. The solution for this problem is to have the offending crown remade with the metal collar below the gum line again, or preferably to have the crown made without the metal collar at all (indicated by the white arrow). Crowns without metal collars are generally the preferred choice for cosmetic areas today.
2. DISCOLORED TOOTH ROOT: Even if your crown was made with porcelain all the way down to the root (no metal collar), the area may still be discolored. This typically happens when the crown margin stops before it gets under the gum line. There will then be tooth root exposed between the crown margin and the gum line (indicated by the yellow arrow). The porcelain on a crown almost never matches the root color; therefore, the exposed root surface may look dark compared to the crown. Your crown may have been made like this, or the crown margin may have been under the gum originally and subsequent gum recession has led to part of the root being exposed. If this presents a cosmetic problem, the only good solution is to replace the existing crown with a new one.
3. DEFECTIVE MARGIN: If your crown does not fit well, the gap between the edge of the crown and the tooth may appear dark. If your well fitting crown develops decay (dental caries), the area will appear dark. Both of these situations constitute a defective margin. Occasionally a defective margin can be repaired with tooth colored filling material, but in most cases the best solution for this problem is replacement of the crown. Replacement of the crown is the only way to be sure that all of the decay has been removed.