When decay and cavities overrun a tooth so much that a crown becomes necessary, it’s fair to believe that the issues within that tooth are resolved when the crown goes on. After all, by the time a crown is placed, the decay is fully removed and the tooth surface is repaired. And, a dentist cements the crown in place to protect the existing tooth (and its neighbors). Unfortunately, this is not always the case. Even before a crown reaches the end of its viable lifespan, a problem referred to as open margin on crown can cause even more problems than the cavities that led to the crown in the first place.

What is an open margin on crown?

An open margin on crown occurs as a result of improper tooth preparation or improper crown placement. A crown is a dental restoration that can:

  • Protect a cracked or weakened tooth
  • To replace a broken tooth
  • Cosmetically fix a misshapen or discolored tooth
  • Support a weakened tooth that has a large filling in it

In most cases, your dentist will prepare the surface of the natural tooth by filing down an even surface for an attachment. They’ll take an impression of your teeth, and place a temporary crown while customizing the permanent crown. When the permanent crown is ready, they’ll smooth the tooth surface, and fix the permanent crown in place with dental cement.

This works beautifully when the process goes according to plan, but in some cases a gap will appear between the crown and the natural tooth surface. This is what is referred to as an open margin on crown. The margin, or the area where the crown contacts the natural tooth, is not sealed, allowing food and bacteria to enter the space between the crown and the tooth.

What causes an open margin?

An open margin crown is different than a simple space between the crown and the gumline. The crown may stop short of the gumline and still be sealed and properly applied.

The open margin specifically refers to a gap between the natural tooth and crown. This can be due to:

  • A rough surface
  • Uneven application of dental cement
  • Other errors in application or crown manufacturing

In some cases, the crown itself is defective or ill-fitting and will never be able to be effectively sealed. This can be difficult to detect with the naked eye as well. A dentist who does not follow accepted protocols for checking fit or who rushes the process of making a mold of the teeth for the crown is more likely to miss any errors in fabrication, too.

What are symptoms of an open margin crown?

The symptoms of an open margin crown may not be immediately detected and are not necessarily visible to the eye. The symptoms become more apparent as the years progress and can include all of the symptoms of cavity.

  • Sensitive gums and teeth: Decay can cause sensitivity to hot and cold as well as sensitivity to sweet foods.
  • Bleeding gums when brushing and flossing: As with other types of decay, eventually you might experience gingivitis symptoms like bleeding when brushing or flossing teeth. This may or may not go away over time.
  • Pain: As the cement holding the crown in place begins to dissolve in the face of the bacteria that has made its way underneath the dental restoration, the roots of the tooth will begin to be affected. Pain may be mild at first, but as decay continues it can progress.
  • Bad breath: This is a telltale sign of all types of decay, including the decay that occurs as a result of an open margin on crown.

If none of these symptoms occur, an X-ray can also confirm if a crown is properly sealed or not. In some cases, an open margin may be visible to the naked eye, but this is not often the case.

How to fix an open margin crown

Crown margin repair is essential for continued dental health. An ill-fitting or unsealed crown can cause many different problems down the road and may le