What Is an Infection Under a Dental Crown?
An infection under a dental crown means bacteria have invaded the tooth structure, pulp (the nerve and blood supply inside the tooth), or surrounding bone beneath the crown restoration.
A dental crown is a cap that covers a damaged or weakened tooth. It protects the tooth from further damage and restores its shape. However, the crown itself does not eliminate the risk of future infection. The natural tooth underneath remains vulnerable to bacteria if they find a way past the crown's margins or through cracks in the tooth. [2]
This type of infection can develop months or even years after a crown is placed. In many cases, the infection starts silently. You may not notice symptoms until the bacterial invasion is well established. That is why understanding the warning signs matters.
The clinical term for an infection at the root tip is a periapical abscess. An infection along the gum line near the crown margin is called a periodontal abscess. Both types require treatment. Left alone, either one can damage bone, spread to adjacent teeth, or cause systemic health problems. [1]
What Causes an Infection Under a Crown?
Infections under crowns typically result from bacteria reaching the living tooth tissue or root through decay, cracks, or a failing seal at the crown margin.
Decay Beneath the Crown
A crown covers the visible part of a tooth, but the junction where the crown meets the natural tooth, called the crown margin, is a potential weak point. Over time, plaque and bacteria can accumulate along this margin. If the seal breaks down, bacteria seep underneath and cause decay in the remaining tooth structure. [2]
This process is sometimes called recurrent decay or secondary caries. It can be difficult to detect because the crown hides the damage from plain sight. Recurrent decay may progress slowly for months before symptoms appear. Once the decay reaches the pulp chamber inside the tooth, infection develops.
Cracked Tooth Root
A crown is often placed on a tooth that was already weakened by a large filling, fracture, or previous dental work. In some cases, the root of the tooth develops a crack after the crown is placed. A cracked root creates a direct path for bacteria to enter the deeper structures of the tooth and the surrounding bone.
Cracks can result from heavy biting forces, teeth grinding (bruxism), or simply from long-term stress on an already compromised tooth. A vertical root fracture, which runs along the length of the root, is particularly problematic because it is difficult to repair. [1]
Failing or Incomplete Previous Root Canal
Many crowned teeth have had root canal therapy. During a root canal, the infected pulp tissue is removed and the canal system is cleaned and sealed. However, teeth have complex canal anatomy. Some canals are curved, branched, or extremely narrow. Occasionally, bacteria remain in a missed canal or in microscopic branches that were not fully cleaned.
Over time, these residual bacteria can multiply and cause a new infection at the root tip. The seal at the top of the root canal filling can also break down, allowing bacteria from the mouth to reenter the canal system. According to the American Association of Endodontists, retreatment of a previously treated tooth is a common and predictable procedure when this occurs. [1]
Leaking or Poorly Fitting Crown
If a crown does not fit precisely, a small gap can exist between the crown and the tooth. Saliva, food particles, and bacteria work their way into that gap over time. Cement washout, where the adhesive holding the crown dissolves gradually, can also create space for bacterial invasion.
A crown that felt fine for years can begin to leak as the cement ages or as the gum tissue recedes and exposes new areas of the tooth root. This is one reason regular dental checkups matter: your dentist can detect early signs of a failing crown margin before a full infection develops. [2]
When to See a Dentist
Contact your dentist promptly if you have persistent pain, swelling, or a pimple on the gum near a crowned tooth.
Some situations are more urgent than others. A mild, short-lived sensitivity to cold when eating ice cream, for example, is less concerning than a constant throbbing ache that wakes you at night. Below are red flags that suggest infection and warrant a prompt appointment.
- Constant or worsening pain around a crowned tooth, especially pain that lingers after biting or exposure to heat.
- Facial or gum swelling near the crowned tooth. Swelling that spreads to the cheek, under the jaw, or near the eye requires same-day or emergency care.
- A gum boil or fistula, which looks like a small pimple on the gum tissue near the tooth. It may drain pus and temporarily relieve pressure.
- A persistent bad taste or foul odor coming from the area around the crown, which can indicate active drainage of infection.
- Fever, difficulty swallowing, or difficulty breathing in combination with dental pain. These are signs of a spreading infection and require immediate medical attention.
- A loose crown combined with pain or a bad taste, which may indicate the cement seal has failed and bacteria have entered.
How an Infection Under a Crown Is Diagnosed
Diagnosis typically involves a clinical exam, X-rays, and specific tests to locate the source of infection and determine which treatment is appropriate.
Your dentist or endodontist will start by asking about your symptoms: when the pain started, what makes it better or worse, and whether you have noticed swelling or a bad taste. This history helps narrow down the possible causes.
Clinical Exam and Pulp Tests
The dentist will visually inspect the crown and surrounding gum tissue for swelling, redness, or a draining fistula. They will gently tap on the crown (percussion test) and press on the gum tissue around the root tip (palpation test). Pain with percussion often suggests inflammation at the root tip. [1]
If the tooth has not had a previous root canal, the dentist may perform a pulp vitality test. This involves placing a cold stimulus or a small electrical current on the tooth to check whether the nerve inside is alive, damaged, or dead. A tooth that does not respond to any stimulus is likely necrotic, meaning the pulp tissue has died, which is a strong indicator of infection.
X-Rays and Advanced Imaging
A periapical X-ray, a small film focused on the specific tooth, is the most common first step in imaging. It can reveal a dark area at the root tip (periapical radiolucency), which indicates bone loss from infection. It can also show decay under the crown, a short or inadequate root canal filling, or a visible fracture line. [2]
In more complex cases, a cone-beam computed tomography (CBCT) scan may be recommended. CBCT is a three-dimensional X-ray that provides detailed views of the tooth roots, surrounding bone, and nearby structures. It is especially useful for detecting vertical root fractures, missed canals, and the full extent of bone damage. Endodontists frequently use CBCT for treatment planning. [1]
Periodontal Probing
The dentist will use a thin instrument to measure the depth of the gum pocket around the crown. A deep, narrow pocket on one side of the tooth can indicate a root fracture. Generalized deep pockets may indicate gum disease rather than a tooth-level infection. This distinction is important because the treatment for each condition is different.
Taken together, these tests help your provider build a clear picture of what is happening beneath the crown and which treatment approach is most likely to succeed.
Treatment Options for an Infected Crowned Tooth
Treatment depends on the underlying cause and may range from root canal therapy to extraction, with the goal of eliminating infection and preserving the tooth when possible.
Root Canal Therapy Through the Crown
If the pulp inside the tooth is infected or dead, root canal therapy is typically the first-line treatment. An endodontist can often perform the root canal directly through the existing crown by drilling a small access hole through the top. The infected pulp tissue is removed, the canal system is cleaned and shaped, and the canals are sealed with a biocompatible filling material. The access hole is then sealed with a permanent filling. [1]
This approach allows you to keep your existing crown in many cases. However, if the crown is poorly fitting or if significant decay is found underneath, the crown may need to be removed and replaced after the root canal is completed.
Root Canal Retreatment
If the tooth has already had a root canal that has failed, retreatment is often possible. The endodontist removes the previous root canal filling material, re-cleans the canals, and looks for missed canals or areas that were not adequately treated the first time. Modern tools like operating microscopes and CBCT imaging have improved the success of retreatment procedures. [1]
According to the American Association of Endodontists, retreatment is a common procedure with favorable outcomes in many cases. The tooth is then resealed, and a new crown is typically placed to restore the seal.
Apicoectomy (Root-End Surgery)
When retreatment through the crown is not practical, such as when a post is cemented deep inside the canal or when a persistent infection remains at the root tip despite previous treatment, an apicoectomy may be recommended. This is a minor surgical procedure performed by an endodontist. [1]
During an apicoectomy, the endodontist makes a small incision in the gum tissue, removes the infected tissue and the very tip of the root, and places a small filling to seal the end of the root. Healing is typically monitored with follow-up X-rays over several months.
Crown Replacement
If the infection was caused by a leaking or poorly fitting crown, removing the old crown and placing a new one may be part of the treatment plan. The dentist will remove all decay, rebuild the tooth structure if needed, and fabricate a new crown with a precise fit. A well-fitting crown with a good marginal seal is critical to long-term success. [2]
In some cases, crown replacement alone resolves the issue, particularly if the pulp was not yet involved and the problem was limited to decay at the crown margin.
Extraction
Extraction becomes necessary when the tooth cannot be saved. Common reasons include a vertical root fracture that extends below the bone level, extensive decay that leaves insufficient tooth structure to support a new restoration, or repeated failure of root canal treatment. [1]
If extraction is needed, your dentist will discuss replacement options such as a dental implant or bridge. Losing a tooth is not ideal, but removing a severely infected tooth protects your surrounding teeth, bone, and overall health.
The Role of Antibiotics
Antibiotics may be prescribed to help control an active infection, especially if there is significant swelling or systemic symptoms like fever. However, antibiotics are a support tool, not a standalone cure. The source of the infection must still be treated with a dental procedure. Once the bacteria's entry point is sealed or the tooth is removed, the body can heal the remaining infection. [2]
Your dentist will determine if antibiotics are appropriate for your specific situation. Overuse of antibiotics contributes to antibiotic resistance, so they are prescribed selectively.
Cost Factors for Treating an Infected Crown
Treatment costs depend on the procedure needed, the tooth's location, and your geographic area. Costs vary by location, provider, and case complexity.
A root canal on a back tooth (molar) performed by an endodontist typically ranges from $1,000 to $1,800. Root canal retreatment tends to cost slightly more, often in the range of $1,200 to $2,000, because it involves additional time and complexity. An apicoectomy may range from $900 to $1,500 per root. These figures do not include the cost of a new crown if one is needed, which typically adds $1,000 to $2,500 depending on the material and lab fees. [1] [2]
Diagnostic costs also add up. A periapical X-ray is relatively inexpensive, but a CBCT scan may cost $150 to $500 depending on the practice. An initial consultation with an endodontist, including the exam and basic X-rays, typically ranges from $100 to $350.
Dental insurance often covers a portion of root canal therapy and related procedures, but coverage limits, annual maximums, and waiting periods vary widely. Ask your dental office for a pre-treatment estimate and check with your insurance provider before scheduling.
Find an Endodontist Near You
An endodontist is a dentist who has completed additional years of specialized training in diagnosing and treating infections inside teeth. If you have pain, swelling, or other symptoms around a crowned tooth, an endodontist can pinpoint the problem and recommend the most effective treatment. Visit the endodontics page on My Specialty Dentist to learn more about what endodontists do and to search for a qualified specialist in your area.
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