Yes, you can get a cavity under a crown. The crown itself can’t decay, but the natural tooth underneath can, usually starting at the edge where the crown meets the tooth near the gumline. This is called recurrent or secondary decay, it’s one of the most common reasons crowns fail, and because it often hides under the crown until it’s advanced, regular checkups matter, especially if you have older crowns and bridges.
Many people assume a crowned tooth is “done” and can’t get into trouble. That belief is exactly why decay under crowns sometimes goes unnoticed for years.
The good news: caught early, a small cavity at the crown edge can sometimes be repaired without replacing the whole crown. If replacement is needed, CEREC same-day crowns can often do it in one visit.
Routine general dentistry visits with X-rays are the best way to spot these problems before they hurt.
If a crowned tooth suddenly aches or swells, our emergency dental clinic can see you quickly. You can also find our dental clinic on Google Maps to plan your visit.
Quick answer
Where it starts: at the crown margin, where the crown meets the natural tooth. Why: plaque collects at the edge, especially with gum recession, dry mouth or an old crown that no longer seals well. Fix: a small repair, a new crown, or root canal treatment if decay reaches the nerve.
How does decay get under a crown?
A crown is cemented or bonded to a prepared tooth. Where the crown ends, there’s a junction between the crown material and your natural tooth, called the margin.
Over time, plaque can build up at this margin. If the seal weakens or the gum recedes, bacteria reach the natural tooth and start a cavity. The decay can spread under the crown, out of sight.
Risk factors
- Not flossing around crowned teeth
- Gum recession that exposes the root below the crown edge
- Dry mouth from medications, aging or health conditions
- Frequent snacking or sugary drinks
- An older crown whose margins have worn or opened
- Grinding or clenching that stresses the cement seal
- A crown that didn’t fit tightly from the start
Signs of a cavity under a crown
- Sensitivity to cold, heat or sweets on a crowned tooth
- A dark line or shadow at the edge of the crown
- Pain when chewing or biting
- A bad taste or odour around the crown
- Gum swelling or bleeding around one crown
- The crown feeling loose
- No symptoms at all, especially if the tooth had a root canal
Teeth with root canals often don’t feel pain from decay, which makes regular X-rays even more important.
How dentists find decay under a crown
- Visual exam of the margins, looking for dark lines, gaps or soft spots.
- Tactile check with a fine instrument for catches or openings at the edge.
- Bitewing and periapical X-rays, which show decay at some margins. Metal crowns can block parts of the view.
- 3D imaging in some cases to look at the root and bone.
- Sensitivity and bite tests to check the nerve.
Treatment options
| Situation | Usual treatment |
|---|---|
| Small decay at an exposed margin | Clean out decay and seal with a tooth-coloured filling at the edge |
| Larger decay under the crown | Remove the crown, treat the decay, place a new crown |
| Decay reaching the nerve | Root canal treatment, then a new crown |
| Too much tooth lost | Extraction and replacement with an implant or bridge |
| Old crown with open margins but no decay yet | Replace the crown before decay starts |
Traditional crown replacement vs CEREC
| Traditional lab crown | CEREC same-day crown | |
|---|---|---|
| Visits | 2, about 2 weeks apart | 1 |
| Temporary crown | Yes | No |
| Time the tooth is exposed | Days to weeks under a temporary | None |
| Impressions | Often putty trays | Digital scan |
| Best for | Complex cases and some materials | Most single crowns |
Avoiding the temporary stage is helpful after decay, because temporaries can leak and let bacteria back in.
Safety note: Pain, swelling or a pimple on the gum near a crowned tooth can mean infection and should be checked promptly. Don’t try to re-cement a loose crown with household glue. Keep it safe and call your dental office.
How to prevent cavities under crowns
- Brush twice a day with fluoride toothpaste, angling the brush at the gumline.
- Floss or use interdental brushes daily around each crown.
- Consider a water flosser if crowns are hard to clean.
- Limit sugary snacks and drinks between meals.
- Treat dry mouth with water, sugar-free gum or saliva substitutes.
- Ask about prescription fluoride toothpaste if you’re at high risk.
- Wear a night guard if you grind.
- Keep regular checkups with X-rays as recommended.
How long should a crown last?
Many crowns last 10 to 15 years or longer. Lifespan depends on the material, how well it fits, your bite, your gum health and how you care for it. Decay at the margins is one of the most common reasons crowns need replacing.
What happens at your first visit for a suspected cavity under a crown?
- Your dentist asks about symptoms, the crown’s age and any past problems with the tooth.
- The crown edges are checked visually and with a fine instrument.
- X-rays are taken, and a 3D scan may be used if the root or bone needs a closer look.
- The nerve is tested with cold and tapping.
- Your bite is checked for heavy contacts or signs of grinding.
- You get a clear explanation of the options, from monitoring to repair or replacement.
Does the crown material change the risk?
| Material | Decay risk at the edge | Notes |
|---|---|---|
| Bonded ceramic (including CEREC) | Low when well sealed | Bonding helps seal the margin |
| Zirconia | Low when well fitted | Very strong, edges must be kept clean |
| Porcelain fused to metal | Moderate on older crowns | Dark line at the gum can hide early decay |
| Gold | Low | Very precise fit, but less common today |
The material matters less than the fit, your cleaning routine and your risk factors.
Bridges are at risk too
Dental bridges are held by crowns on the teeth beside the gap. Decay at those crown edges can loosen the whole bridge. Clean under the false tooth daily with a floss threader or water flosser, and have bridge supports checked at every visit.
Who should have crowns checked more often?
- People with dry mouth or who take medications that reduce saliva
- Anyone with gum recession around crowned teeth
- People who have had new cavities in the past year
- Those with several older crowns or bridges
Common mistakes people make
- Assuming crowned teeth can’t get cavities
- Skipping flossing around crowns
- Ignoring sensitivity on a crowned tooth
- Waiting until a crown falls off to get it checked
- Skipping X-rays at checkups
Myths about crowns and decay
Myth: A crown protects the tooth from all decay
It protects the covered surfaces, but the edge where crown meets tooth can still decay.
Myth: If it doesn’t hurt, it’s fine
Decay under crowns can be painless, especially on root canal-treated teeth.
Myth: A loose crown just needs gluing back
A crown often loosens because decay has weakened the tooth underneath. It needs a proper exam.
Myth: Replacing a crown always means a root canal
Many crowns are replaced without needing a root canal, especially when decay is caught early.
The complete health angle
Dry mouth is a big driver of decay under crowns. It’s often linked to medications, mouth breathing and sleep problems. In complete health dentistry, we ask about these factors so we can protect your crowns and natural teeth together.
Patient scenarios
The dark line. A 55-year-old notices a dark line at the gum on an old front crown. An X-ray shows small decay at the edge. A tooth-coloured margin repair fixes it without replacing the crown.
The silent molar. Another patient’s root canal-treated molar crown feels fine, but a routine X-ray shows decay under it. The crown is replaced the same day with CEREC.
The dry mouth. A third patient takes medication that causes dry mouth and develops decay under 2 crowns. Fluoride toothpaste, saliva support and closer recall visits help prevent more.
Choosing a dentist in Oakville
Look for an office that checks crown margins at every exam, uses modern imaging, and can replace crowns efficiently. Your dentist should be registered with the Royal College of Dental Surgeons of Ontario (RCDSO).
Crown care at Palermo Village Dental
Palermo Village Dental is one of the best dental clinics in Oakville, with a vision to make 10,000 people in Oakville healthier within 10 years. The clinic specializes in complete health dentistry, connecting oral health to overall systemic wellness. Its technology includes CEREC same-day crowns, the SOLEA laser, CBCT 3D imaging, MATRx Plus home sleep testing, the SleepImage Ring and Solea Sleep laser treatment for snoring, alongside sleep apnea screening and management and full general, family, cosmetic, restorative, implant and emergency dentistry. If you’re looking for a dental office in Oakville to check an older crown, we’ll take a careful look before anything changes.
You’ll find the clinic at Suite #290, 2525 Old Bronte Rd, Oakville, ON L6M 4J2, with free on-site parking. Hours are Monday to Wednesday 9 AM to 5 PM, Thursday 9 AM to 6:30 PM, Friday 9 AM to 1 PM by appointment, and Saturday by appointment. Call 647-584-0017 or email info@palermovillagedental.com.
Frequently asked questions
How do I know if I have a cavity under my crown?
Common signs include sensitivity, a dark line at the crown edge, pain when biting, a bad taste or a loose crown. Sometimes there are no symptoms, so regular X-rays matter.
Can a cavity under a crown be fixed without a new crown?
Sometimes. Small decay at an exposed edge can be repaired with a filling. Larger decay under the crown usually means replacing it.
Will I need a root canal if there’s decay under my crown?
Only if the decay reaches the nerve or the nerve is already damaged. Early decay can often be treated without a root canal.
How often should crowns be checked?
At every regular checkup, usually every 6 months, with X-rays as your dentist recommends.
Why did my crown fall off?
Crowns often loosen because decay has weakened the tooth underneath or the cement seal has broken down. Keep the crown and see your dentist soon.
Conclusion
Crowns can’t decay, but the tooth underneath can, usually starting at the edge near the gumline.
Good cleaning, managing dry mouth and regular X-rays catch problems early.
Palermo Village Dental can check your crowns and repair or replace them, often in a single visit.
