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. 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. 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 . 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.