Yes, You Can Get a Cavity Under a Crown - Signs, Treatment, and Prevention

Clinical Content Reviewed by Dr. Jay Khorsandi, DDS
Last Modified:

Table of Contents

  1. What Is a Crown?
  2. Causes of Cavities in Teeth with Crowns
  3. Did My Dentist Do Something Wrong?
  4. Signs & Symptoms
  5. Treatment
  6. Prevention

Contrary to popular belief, a cavity can develop beneath a crown. Tooth decay can form at the margins of a crown or even underneath its surface. But because crowns cover so much of a tooth's surface, it can be difficult to spot these cavities without careful examination.

However, if your dentist confirms that that you do have a cavity on the same tooth on which you have a crown, it is important to get treatment as soon as possible.

You can help prevent these cavities by practicing the same good oral hygiene that keeps all tooth decay at bay.

What Is a Crown?

A dental crown is a tooth-shaped cap that your dentist places over your tooth as protection. Your dentist might recommend a crown if you have a tooth that has been badly damaged by injury or decay. The crown replaces the damaged tooth structure with a sturdy synthetic surface that helps keep the tooth from breaking when you use it to chew or bite.

  • Crowns are made from many materials, including:

  • Porcelain

  • Metals such as gold, palladium and stainless steel

  • Porcelain-fused-to-metal

  • Resin composite

Dentists routinely perform a root canal procedure to ensure the tooth is ready to receive a crown, but a root canal is not always necessary. If you do have one before having your tooth it crowned, the nerve inside the tooth will be dead and will not transmit any pain. Otherwise, you will still be able to feel the tooth as usual.

Causes: How Do Cavities Develop in a Tooth with a Crown?

Two types of cavities can occur in a crowned tooth: marginal decay and residual decay.

Marginal decay is the more common of the types. Crowns cover the top and sides of a tooth, but they still have margins around their edges. Margins are often difficult to keep clean and can even leak bacteria into the space under the crown, making them vulnerable to decay.

Cavities from residual decay are not new cavities at all: they are actually larger versions of the cavity that caused the tooth to need a crown in the first place. This happens when a dentist misses some decay when cleaning out the tooth during the root canal or crown preparation process.

Did My Dentist Do Something Wrong?

In most cases, cavities that develop under crowns have nothing to do with anything your dentist did. However, there are some exceptions.

A tooth with a crown that was not seated properly will develop leakage along the margins, causing marginal decay. It takes skill to make sure the seal along the margin of a dental crown is tight enough to keep plaque out. However, it’s difficult to say for sure whether any one case of marginal decay took place because of a dentist’s error or if it was because the patient’s oral hygiene was not ideal.

The cause of residual decay is much more clear-cut: dentist’s error. This type of cavity always happens because your dentist missed some of the decay that was present when your crown was placed. As long as the bacteria under the crown have something to feed on, they will multiply and eat away at your tooth. Because the crown hides the full extent of the damage, cavities that develop this way typically grow large before they are noticed.

If either type of decay is going to develop under a crown as a result of poor dentistry, it will usually happen fast. This is why some dentists (including any practicing through the NHS) will redo a crown or other restoration for free if decay develops underneath it within a certain period of time. For NHS dentists, this guarantee is valid for the first full year after your treatment.

Signs and Symptoms

It can be hard to spot a cavity under a crown, but there are a few tell-tale signs that indicate something might be wrong. These include:

  • Pain or sensitivity in your crowned tooth, especially in response to hot or cold temperatures or sweet food and drink

  • Discolored tooth surfaces around the margins of the crown

  • Foul smells in the area around your crowned tooth

  • Bleeding gums in the area around your crowned tooth

In addition to these symptoms, you should also be on the lookout for signs that your crown is beginning to fail. In this case, you might notice:

  • Small holes worn in the top of your crown, especially on the tips

  • Unusual looseness in your crown, which you might feel as a slight shift when chewing or biting

What to Do

If you think you might have a cavity under a crown, here are steps to take:

1. See your dentist. You may suspect you have a cavity under your crown, but you can’t diagnose it yourself. You’ll need to see a professional.

2. Have a visual exam. Your dentist will start by examining the tooth in question. They may be able to see evidence of the cavity just from this visual exam.

3. Get an x-ray. Even if they suspect its presence from the exam, the dentist will take an x-ray to confirm the cavity is there. They will be able to clearly point it out to you on the x-ray.

4. Discuss treatment options. Your dentist will recommend a treatment that makes the most sense given the location and severity of the cavity. In some cases, they may be able to fill the cavity without removing the crown, but in others, they’ll need to remove the crown to properly clean and fill the cavity. Part of this discussion will involve details on cost as well as insurance coverage.


When a crowned tooth has a cavity, here are three possible solutions: a filling, a new crown or an extraction.


Because a crown covers most of the tooth, it is only possible to fill a cavity in a crowned tooth without removing the crown if the cavity is on the crown’s margins. There is a risk that your dentist will fail to drill out some of the decay that is covered by your crown, making it likely that the decay will continue to get worse. Most dentists will only consider placing a filling under a crown if the decay is minor.

Replacing the Crown

More often, your dentist will recommend removing your crown to drill out the new decay and then placing a new crown on top of your tooth. This should stabilize the condition of your tooth and keep the decay from spreading.


In some cases, the decay beneath a crown is so advanced that there is nothing a dentist can do to save the tooth. When this happens, extraction is the only viable option. This is why it’s important to act quickly when you suspect that you might have a cavity under your crown.


You can take several steps to prevent decay under a crown. Be sure to:

  • Brush your teeth at least twice a day, paying special attention to any crowned teeth

  • Floss carefully around your crown at least once a day

  • Avoid consuming too many sweet foods and drinks, restricting them as much as your willpower allows

  • Get treatment for any nighttime teeth grinding habits you might have. (These behaviors put extra stress on your crown and may cause it to develop loose margins or holes more quickly than expected.)

  • Visit your dentist for regular checkups so that the dentist can inspect the margins of your crown for any decay

  • See your dentist as soon as possible if you notice any signs that there might be a cavity under your crown

Disclaimer: This article is intended to promote understanding of and knowledge about general oral health topics. It is not intended to serve as dental or other professional health advice and is not intended to be used for diagnosis or treatment of any condition or symptom. You should consult a dentist or other qualified healthcare provider with any questions you may have regarding a medical condition or treatment.