An infected crown looks normal, because the visible signs appear in the gum around it: swelling, redness, a pimple-like bump, or a dark gumline. The tooth underneath and the gum around it are living tissue that can become infected. At Mary Qian Dental Group, we find these problems on crowned teeth where the porcelain still looks perfect.
Highlights
- A crown cannot get infected, but the tooth and gum underneath it can.
- The visible signs are gum signs: swelling, redness, a bump on the gum, or a dark gumline.
- Some infected crowned teeth show nothing at all and cause no pain, especially after a root canal.
- Facial swelling with a fever needs same-day care rather than a wait-and-see week.
| What you can see | What it points to | How fast to act |
|---|---|---|
| Red, puffy gum around the crown | Inflammation or plaque trapped at the crown margin | Book a visit |
| A pimple-like bump on the gum near the root | An abscess draining through the gum | Same day |
| A dark line where the crown meets the gum | An exposed metal margin, or decay at that margin | Book a visit |
| Gum pulled back so more of the crown shows | Recession exposing the margin | Book a visit |
| Nothing visible at all | An infection at the root can stay hidden | Book a visit |
| Face or jaw swelling with a fever | The infection is spreading | Get it checked if anything feels off |
What an Infected Crown Looks Like
The crown looks the same as the day it was cemented, and the gum around it does not.
Porcelain and metal do not change colour, shape, or texture when bacteria are at work underneath them. Your gum does. Every visible sign of a crown infection is a change in the soft tissue at the gumline or in the tooth structure at the margin, which is the seam where the crown meets the tooth.
Swollen or red gum around the crown
Gum tissue that has turned red, puffy, or tender around one crowned tooth points to inflammation at the margin. Healthy gum sits flat and pale pink against the crown. Bacteria collecting in a gap at the margin will inflame the tissue in that one spot, which is why a single swollen area next to a crown reads differently from general gum soreness across the whole mouth.
A pimple-like bump on the gum
A small raised bump on the gum above or below a crowned tooth is a sinus tract, often called a gum boil. Pus from an infection at the root has found a path out through the gum. The bump may drain, shrink, and come back, and the pain often eases when it drains, which is the reason people talk themselves out of calling. Draining is not healing. The infection is still there and still has a source.
A dark line at the gumline
A grey or dark band where the crown meets the gum has two common explanations. On a porcelain-fused-to-metal crown, the metal substructure can show through as the gum recedes, and that band is cosmetic rather than infectious. Decay forming at the margin also darkens the same area. Only an exam and an X-ray separate the two, since both look nearly identical from the outside.
Gum that has pulled back from the crown
Recession leaves more of the crown visible and exposes the margin to plaque, food, and acid. Root surface below the margin has no enamel, so decay starts there faster than it would on the biting surface. If you have noticed receding gums around a crowned tooth, the margin is now doing a job it was not shaped for.
A bad taste or smell that brushing does not fix
A persistent foul taste near one tooth suggests bacteria in a space your toothbrush cannot reach. Pus and decay both produce it. A bad taste tied to a single crown is a different problem from general bad breath, which usually comes from the tongue or from gum disease across several teeth.
Pain, swelling, redness in the gums, a bad taste in the mouth, and a fever are the symptoms the American Dental Association lists for an abscessed tooth. None of that list describes the crown itself.
Why the Crown Itself Cannot Get Infected
A crown is not living tissue, so there is nothing in it for bacteria to infect.
Think of the crown as a helmet rather than a head. A cracked helmet is a problem you can see and a problem you can replace. An infection is under the helmet, in the part that is alive, and the helmet looks fine while it happens.
What sits under a dental crown is a prepared natural tooth, its pulp or a root canal filling where the pulp used to be, the root, and the bone and gum holding all of it in place. Those tissues get infected. The porcelain, ceramic, or porcelain-fused-to-metal shell over the top does not.
Bacteria reach the living part through the margin. A crown that fits well seals that seam, and a crown that has loosened, cracked, or lost cement opens it.
When an Infected Crown Looks Like Nothing at All
Plenty of infected crowned teeth show nothing on the outside and cause no pain.
An infection at the tip of the root sits in bone, below everything you can see in a mirror. It can develop slowly and stay quiet for months. According to the American Association of Endodontists, an infection in or around the root of a tooth may or may not be painful.
The silent version is most common on teeth that have had root canal treatment. Once the pulp is removed, the nerve that would have sent a pain signal is gone. A crowned, root-canal-treated tooth can carry an active infection at the root and feel like every other tooth in your mouth. That is also why patients are often surprised at a checkup.
Two things find these infections. A digital X-ray shows the dark area at the root tip where bone has been lost. A periodontal probe measures the pocket depth around the tooth and picks up gum-level infection the X-ray misses. Both take a few minutes at a routine exam, which is the strongest practical argument for keeping checkups on schedule.
Recommended Reading: Do You Need a Dental Crown After a Root Canal?
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When It Is Not an Infection
Several things that look and feel alarming around a crown turn out to be something else.
Soreness in the first few days after placement is normal healing. Gum tissue was retracted during the appointment and needs time to settle. A crown that feels tall when you bite is a bite adjustment, and the ache it causes lands in the jaw muscle rather than the tooth. Food packing between the crown and the neighbouring tooth irritates the gum in a way that mimics infection, and it resolves once the contact is corrected.
Cement washing out from under a crown makes the tooth sensitive and the crown feel loose, without any infection present yet. Left alone it becomes one, because the seal is gone.
Flossing technique causes more gum irritation around crowns than most people expect. Snapping floss down onto the gum next to a margin will leave that spot red and tender by evening.
Recommended Reading: Jaw Pain After a Permanent Crown and Why Your Tooth With a Crown Is Hurting?
Signs That Need Same-Day Care
Some signs around a crowned tooth should not wait for the next available appointment.
Red flags, call the office today:
- A bump on the gum that drains, whether or not it hurts
- Pain that wakes you up or does not respond to over-the-counter pain relievers
- A crown that has become loose or moves when you touch it
- Gum swelling around one tooth that has grown over a day or two
Red flags, go to an emergency room:
- Swelling that has spread into your face, jaw, or neck
- A fever alongside any of the above
- Trouble swallowing, trouble breathing, or trouble opening your mouth
A gum boil is not something to open, squeeze, or drain at home. The pus is the visible end of an infection with a source at the root or in the gum pocket, and releasing pressure does nothing to the source while pushing bacteria into tissue that was containing them. A loose crown should not be pulled, reseated, or glued with anything from a drugstore either. Bring it in and bring the crown with you if it has come off.
Saltwater rinses ease soreness for a few hours. Rinsing is comfort, not treatment, and using it to get through a week costs you the tooth you were trying to keep.
Swelling around a crowned tooth today? Dr. Mary Qian offers same-day appointments in Palo Alto, and a short visit settles whether the problem is at the gum, at the margin, or at the root.
What Causes an Infection Under a Crown
Infections under crowns start at the margin, at the root, or in the gum, and the crown is rarely the cause.
Decay at the crown margin. The seam between crown and tooth is the vulnerable point. Recurrent decay at that seam was the second most common complication in a study of 1,037 tooth-supported crowns followed for an average of 11 years at Malmö University, appearing in 8.6% of them.
A root canal that did not fully heal. Bacteria can survive in a canal that was narrow, curved, or missed, and the infection at the root tip persists under a crown that looks and feels fine.
Gum disease around the crowned tooth. Periodontal infection works from the gum pocket downward rather than from the tooth outward. The same Malmö data found crowns on root-canal-treated teeth failed at a higher rate than crowns on living teeth, with cumulative survival at 80.9% after 10 years across the whole group. Ongoing periodontal care matters more once a tooth is crowned, not less.
A crack or a loose crown. Cement failure, a fracture in the remaining tooth, or trauma all break the seal and give bacteria a route in.
How a Dentist Treats an Infection Under a Crown
Treatment depends on where the infection sits and how far it has travelled.
The American Dental Association describes four paths for an abscessed tooth: antibiotics to control the bacteria, drainage of the infection, cleaning the space between the tooth and the gum where gum disease is the cause, and root canal treatment where decay or a crack is the cause. Which one applies is a diagnostic question rather than a preference.
Our approach at Mary Qian Dental Group starts with digital X-rays and 3D imaging to locate the problem before anyone touches the crown. Gum-level infection is treated with scaling and root planing. Decay at the margin often means removing the crown, treating the tooth, and fitting a new one. Infection at the root means root canal treatment or retreatment, and the crown may or may not survive removal depending on how it was cemented.
Where a replacement crown is needed, our in-house dental 3D printing lets us make one on site, so many patients leave with a permanent restoration rather than a temporary. Dr. Mary Qian has spent her career in restorative dentistry and will walk you through what she sees on the X-ray and what each option involves.
Not sure what you are looking at? A single exam separates gum irritation from decay at the margin from an infection at the root, and the answer changes what happens next.
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Frequently Asked Questions About Infected Crowns
1. Can an infected crown heal on its own?
No. The infection has a source, either decay at the margin, a gum pocket, or bacteria at the root, and none of those resolve without treatment. Symptoms often fade for a while, especially after a gum boil drains, which makes the problem look solved when the source is untouched.
2. How can I tell if my crown is infected?
You can check the gum around the crown for swelling, redness, a bump, or a dark line at the gumline. What you cannot check is the root. A digital X-ray and a periodontal probe are the only ways to see infection at the root tip or measure a deep pocket, so a visit settles what a mirror cannot.
3. Can you get sepsis from crowns?
A dental infection that spreads beyond the tooth can become serious, which is why facial swelling, fever, or trouble swallowing calls for emergency care rather than a dental appointment. The crown itself carries no such risk. Treating an infection under a crown early keeps it local and straightforward.
4. How do you treat an infection under a crown?
Treatment follows the source. Gum-level infection is treated by cleaning the space between the tooth and gum. Decay at the margin usually means replacing the crown after the tooth is treated. Infection at the root means root canal treatment or retreatment. Antibiotics support these and do not replace them.
5. Will I need a new crown if the tooth underneath is infected?
Sometimes. A crown removed for access often cannot be reused, particularly if it was bonded with resin cement or has to be cut off. Where the infection is at gum level and the crown fits well, it usually stays. Your dentist can tell you which situation you are in after imaging.
6. Can a crown get infected years after it was placed?
Yes. Margins wear, gums recede, cement fails, and decay can start at any point in a crown’s life. In the Malmö study, roughly 1 in 5 crowns had failed by the 10-year mark. Age is not protection, which is why crowned teeth need the same checkups as the rest.