Infection Under a Dental Crown: Symptoms, Causes, and Treatment

Pain and Sensitivity

Pain is the most common sign that something is wrong under a crown. The pain may be constant or come and go. It often worsens when biting down or when the tooth is exposed to hot foods and drinks. Sensitivity to heat is a particularly important warning sign, as it can indicate that the pulp inside the tooth is inflamed or dying. Unlike sensitivity to cold (which is common and often harmless), sensitivity to heat in a crowned tooth should be evaluated promptly.

Swelling and Gum Changes

Swelling near a crowned tooth can appear in the gum tissue directly around the crown or in the area below the root tip. The gum may look red, puffy, or darker than the surrounding tissue. In some cases, a small bump that looks like a pimple appears on the gum near the tooth. This is called a fistula or gum boil, and it is a drainage point for pus from the infection. If you see this, the tooth is almost certainly infected and needs treatment.

Bad Taste or Odor

A persistent bad taste in the mouth, especially near the crowned tooth, can indicate an active infection draining pus. The taste is often described as metallic, sour, or foul. A bad odor from the area that does not improve with brushing and flossing is another sign. These symptoms indicate that bacteria are producing waste products as the infection progresses.

Other Warning Signs

• The crown feels loose or shifts slightly when you bite
• Darkening of the gum tissue around the crown
• A sensation of pressure or fullness in the tooth
• Pain that radiates to the ear, jaw, or temple on the same side
• Fever or swollen lymph nodes under the jaw (signs of a spreading infection that requires urgent care)

Decay Under the Crown

This is the most common cause. Over time, the cement that holds the crown in place can wash out or develop microscopic gaps, especially at the margin where the crown meets the natural tooth. Bacteria enter through these gaps and cause decay on the tooth surface underneath. Because the crown hides the decay, it can progress significantly before symptoms appear. By the time you feel pain, the decay may have reached the pulp.

A Previous Root Canal That Has Failed

Many crowned teeth have had root canal treatment. If the original root canal did not remove all infected tissue, if the seal at the top of the root canal breaks down, or if bacteria re-enter through a crack, the infection can return. This is called a persistent or recurrent endodontic infection. It may not produce symptoms for months or years after the original treatment.

A Cracked Tooth Root

A crack in the root of a crowned tooth provides a direct pathway for bacteria to enter the tooth and surrounding bone. Root fractures can result from heavy bite forces, grinding or clenching habits, or weakening of the tooth structure over time. Cracked roots are difficult to detect on standard X-rays and may require a CBCT scan or direct visualization under a microscope by an endodontist.

A Poorly Fitting Crown

If the crown does not fit precisely at the gum line, a gap or overhang can trap food and bacteria. This leads to chronic inflammation of the gum tissue and, eventually, decay or infection of the underlying tooth. A crown with open margins is more likely to develop problems over time than one with a precise, sealed fit.

Root Canal Through the Existing Crown

If the tooth has not had a root canal before and the crown is in good condition, an endodontist can often perform a root canal by drilling a small access hole through the top of the crown. After the infected pulp is removed and the canals are cleaned and sealed, the access hole is filled. This approach preserves the existing crown and avoids the cost of a replacement. In some cases, however, the crown may need to be replaced afterward if its structural integrity has been compromised.

Root Canal Retreatment

If the tooth had a previous root canal that has failed, an endodontist can perform retreatment. This involves removing the old root canal filling material, re-cleaning the canals, and resealing them. Retreatment may require removing the crown to gain proper access. The success rate for retreatment is somewhat lower than for initial root canal therapy, but it saves many teeth that would otherwise require extraction.

Apicoectomy (Root-End Surgery)

When a standard root canal or retreatment is not possible or has already been attempted, an endodontist may recommend an apicoectomy. This surgical procedure involves accessing the root tip through the gum and bone, removing the infected tip, and sealing the end of the root. It is typically performed under local anesthesia and has a high success rate when done by an endodontist using a surgical microscope.

New Crown

If the infection was caused by decay under a poorly fitting crown or a crown with degraded margins, removing the old crown, treating the decay, and placing a new crown is often the best approach. This addresses the root cause (the gap that allowed bacteria in) and restores the seal over the tooth.

Extraction

In cases where the tooth root is fractured vertically, the remaining tooth structure is too damaged to support a new restoration, or multiple treatments have failed, extraction may be the most appropriate option. After extraction, the tooth can be replaced with a dental implant, bridge, or partial denture. Your endodontist or prosthodontist can help you evaluate replacement options.

Call Today If You Have

• Severe, constant pain in a crowned tooth that is not controlled by over-the-counter pain relievers
• Visible swelling in the face, jaw, or neck near the crowned tooth
• Fever or chills along with dental pain (this suggests the infection may be spreading)
• A foul-tasting discharge from the gum near the crown
• Difficulty swallowing or opening your mouth

Schedule an Appointment Soon If You Have

• Mild to moderate pain in a crowned tooth that comes and goes
• New sensitivity to hot or cold on a crowned tooth
• A small gum boil or pimple near a crowned tooth, even if it is not painful
• A bad taste that seems to come from a specific tooth
• A crown that feels loose or different when you bite