An infected dental crown typically shows red, swollen gums around the base of the crown, often with visible pus or a small bump on the gum tissue nearby. The surrounding gum line may look puffy, darker in color than the rest of your gums, and may bleed easily when you brush or floss. In more advanced cases, you might notice the gum pulling away from the crown or a whitish, pimple-like bump forming near the root of the tooth.
Visible Changes Around the Crown
The most obvious sign is inflammation of the gum tissue immediately surrounding the crown. Healthy gums sit snugly against a crown and appear pink and firm. Infected gums look noticeably different: they turn red or dark pink, swell outward, and may feel tender or spongy to the touch. The contrast is usually easy to spot if you compare the gum tissue around the crown to the gums around your other teeth.
Bleeding is another visual clue. If you see blood on your toothbrush or floss specifically around the crowned tooth, and not elsewhere, that localized bleeding points to infection or at least significant irritation in that area.
As infection progresses, you may see pus forming near the crown. This can appear as a small, raised bump on the gum (sometimes called a gum boil) that looks white or yellowish. Pressing on it may release a foul-tasting fluid. The presence of pus or an abscess near a crown is a clear sign of active infection and needs prompt treatment.
Gum recession around the crown is a subtler but important visual change. If the gum line appears to be shrinking back from the edge of the crown, exposing a dark line or the root surface underneath, bacteria have likely been working their way into the gap between the crown and the tooth.
Signs You Can’t See but Can Feel
Not all signs of infection are visible in the mirror. Many people notice symptoms they can feel before they notice anything visually wrong. The most common is a constant, throbbing pain around the crowned tooth that worsens at night. This throbbing quality, rather than a sharp or fleeting sting, suggests the infection has reached the nerve or the tissue around the root.
Pain when biting down or releasing pressure on the tooth is another hallmark. You might notice it while chewing food or even just clenching your teeth lightly. Sensitivity to hot or cold foods and drinks, particularly if the sensitivity lingers for more than a few seconds after the trigger is removed, also points toward infection rather than simple irritation.
One of the more distinctive sensory signs is a persistent bad taste or foul smell coming from the crowned tooth. This happens when bacteria seep underneath a crown that has become loose or lost its seal. The bacteria produce waste products that create that unmistakable metallic or rotten taste, even after brushing. If you notice a lingering bad taste localized to one area of your mouth, that’s a strong signal something is happening beneath the crown.
How Infection Gets Under a Crown
A crown covers and protects a tooth, but it’s not a permanent, airtight seal. Over time, the cement holding the crown in place can fracture or dissolve, creating microscopic gaps at the margins where the crown meets the tooth. Bacteria colonize these gaps, and decay begins forming underneath the restoration where you can’t see it or clean it.
This type of decay at crown margins is actually the most common reason crowns eventually fail. Early decay under a crown can irritate the tooth’s nerve, while deeper decay can destroy significant tooth structure and lead to infection of the pulp (the living tissue inside the tooth). Because the decay is hidden beneath the crown, it often goes undetected until symptoms appear.
Previous dental work also plays a role. If the tooth under the crown already had a large filling, deep cavity, or trauma before the crown was placed, the nerve may have been compromised from the start. A weakened nerve is more susceptible to infection months or even years after the crown is placed.
What a Dentist Looks for on X-Rays
When you visit a dentist with a suspected crown infection, they’ll take X-rays to see what’s happening beneath the surface. The key finding is a dark area at the tip of the tooth’s root. This dark spot represents bone that has been destroyed by the infection, creating a pocket of inflamed tissue. On an X-ray, healthy bone appears white or light gray, so a dark circle or halo at the root tip stands out clearly.
Dentists also look for loss of the thin white line that normally surrounds each tooth root on an X-ray. When that line disappears, it indicates the bone immediately around the root is breaking down. In some cases, the X-ray may reveal that the root itself has started to erode. Together, these findings confirm whether the infection is localized to the gum tissue or has spread deeper into the bone.
When Infection Spreads Beyond the Tooth
Most crown infections stay localized and respond well to treatment, but an untreated infection can spread. Left alone for weeks or months, a tooth infection can develop into a full abscess. If that abscess isn’t addressed, bacteria can eventually migrate to the jaw, neck, or other areas.
Signs that an infection has moved beyond the tooth include fever, swelling that extends into the cheek or under the jaw, swollen lymph nodes in the neck, difficulty swallowing, and trouble opening your mouth fully. Facial swelling that’s warm to the touch and visibly distorts one side of your face is a serious warning sign. Difficulty breathing or swallowing due to swelling is a medical emergency.
What Infected Crowns Look Like at Each Stage
In the earliest stage, the only visible change may be slightly reddened gums right at the crown’s edge. You might not even notice it without looking carefully. At this point, symptoms are mild: occasional sensitivity, maybe slight tenderness when pressing on the gum.
As the infection develops, the redness becomes more pronounced, swelling appears, and bleeding starts occurring with normal brushing. You may notice the bad taste or smell. Pain becomes more consistent rather than occasional.
In an advanced infection, you’ll likely see a visible gum boil or pus near the crown, significant swelling of the surrounding tissue, and possibly gum recession exposing the margin of the crown. The pain at this stage is typically constant and throbbing, and over-the-counter pain relievers provide limited relief. The gum tissue may appear shiny and stretched due to swelling, and the area around the crown can look dramatically different from the healthy tissue elsewhere in your mouth.