It’s a comforting thought, isn’t it? You’ve invested time and money into getting a dental crown, and now that tooth is surely encased in an impenetrable fortress, safe from the relentless assault of decay. Many people understandably believe that once a tooth is capped, it’s essentially invincible. After all, the crown itself is made of robust materials like porcelain or metal, which bacteria can’t eat through. So, problem solved, right? Unfortunately, this is a common misconception, and believing it can sometimes lead to unwelcome surprises down the road.
Understanding the Role of a Dental Crown
Before we dive into why a crowned tooth can still get a cavity, let’s quickly recap what a crown is and why it’s used. A dental crown, often called a cap, is a tooth-shaped covering placed over a damaged or weakened tooth. Its primary jobs are to restore the tooth’s original shape, size, strength, and improve its appearance. Dentists recommend crowns for various reasons: to protect a weak tooth from breaking, to restore an already broken or severely worn tooth, to cover and support a tooth with a large filling when there isn’t much tooth left, to hold a dental bridge in place, or to cover a dental implant.
The crown essentially becomes the tooth’s new outer surface. It’s custom-made to fit snugly and is cemented into place, covering the visible part of the tooth above the gum line. So, yes, the part of the tooth covered by the crown is indeed well-protected from direct attack by acids and bacteria.
The Vulnerable Points: Where Decay Can Strike
So, if the crown itself is invulnerable, how can decay still occur? The problem isn’t with the crown material itself, but with the natural tooth structure that remains underneath and around the crown. Here are the primary ways decay can still set in:
Decay at the Crown Margin
This is the most common culprit. The “margin” is the line where the edge of the crown meets the natural tooth surface, usually at or just below the gum line. No matter how perfectly a crown is fitted, there’s always a microscopic seam or junction. If plaque – that sticky film of bacteria – is allowed to accumulate around this margin, the bacteria can produce acids that attack the exposed tooth structure right at the edge of the crown. This is often called “recurrent decay” or “secondary caries.”
Think of it like a perfectly tiled roof. The tiles themselves are waterproof, but if the sealant around the edges or where tiles meet a wall fails, water can seep underneath. Similarly, if oral hygiene isn’t meticulous, bacteria can creep in at the crown’s edge, leading to a cavity forming on the tooth right where the crown ends.
Gum Recession Exposing the Root
Over time, gums can recede for various reasons, including gum disease, aggressive brushing, or simply aging. When gums recede, they pull away from the tooth, exposing the root surface. The root surface is not covered by hard enamel like the crown of the tooth; it’s covered by a softer material called cementum. Cementum is much more vulnerable to decay than enamel. If gum recession occurs around a crowned tooth, a portion of the root that was previously covered by gums (and not by the crown) becomes exposed. This newly exposed root area is a prime target for decay, and the crown offers no protection to this specific part.
Leakage or Washout of Dental Cement
The crown is held in place by dental cement. While modern cements are very durable, they can, over a long period, degrade or wash out, especially if the crown doesn’t fit perfectly or if there are strong biting forces. If the cement washes out, it can create a tiny gap between the crown and the tooth. This gap becomes a haven for bacteria to enter and begin the decay process on the tooth structure hidden beneath the crown. You might not even notice this until the decay is quite advanced, as the crown can hide the initial signs.
A New Cavity on a Different Part of the Tooth
This is less common if the crown covers most of the visible tooth, but it’s theoretically possible, especially with partial crowns or if a very small area of the natural tooth wasn’t covered and is susceptible. The main concern, however, remains the margin and the root.
Important Reminder: A dental crown is an excellent restorative solution, but it doesn’t make your tooth invincible. The junction where the crown meets your natural tooth, and any exposed root surfaces, remain vulnerable to decay. Diligent oral hygiene and regular dental check-ups are absolutely essential to protect your investment and your underlying tooth. Failure to do so can lead to further dental problems that might compromise the tooth.
Signs That Decay Might Be Lurking Under Your Crown
Detecting decay under a crown can be tricky because the crown itself can mask visual cues. However, there are some signs and symptoms that might indicate a problem:
- Sensitivity or Pain: You might experience sensitivity to hot, cold, or sweet foods and drinks. Pain when biting down can also be a sign. However, if the tooth has had a root canal, it won’t have nerve sensitivity, making decay harder to detect based on feeling alone.
- Bad Breath or a Bad Taste: Persistent bad breath (halitosis) or an unpleasant taste coming from the area of the crowned tooth could indicate bacteria accumulating and causing decay.
- Looseness of the Crown: If the crown feels loose or wiggles, it could be a sign that the underlying cement has failed or that decay has eaten away at the tooth structure supporting it.
- Gum Inflammation or Swelling: Red, swollen, or bleeding gums around the crowned tooth can indicate plaque buildup and potential decay at the margin, or even gum disease.
- Discoloration: You might notice a dark line or discoloration at the edge of the crown where it meets the tooth.
- Visible Evidence on an X-ray: Often, decay under a crown is first detected by your dentist during a routine dental x-ray. X-rays can show cavities forming beneath the crown that are not visible to the naked eye.
Prevention: Keeping Your Crowned Tooth Healthy
The good news is that with proper care, you can significantly reduce the risk of decay developing around or under your crown. The strategies are largely the same as preventing cavities in any other tooth:
Meticulous Oral Hygiene
This is non-negotiable.
- Brushing: Brush your teeth thoroughly at least twice a day for two minutes each time, using fluoride toothpaste. Pay special attention to the gum line where the crown meets the tooth. Angling your toothbrush bristles towards the gum line can help clean this critical area.
- Flossing: Floss daily! This is crucial for cleaning between teeth and around the margin of the crown where your toothbrush can’t reach effectively. Gently slide the floss down and up, curving it around the tooth and the crown. Some people find floss threaders or interdental brushes helpful for cleaning around crowns.
Regular Dental Check-ups and Cleanings
Visit your dentist regularly (typically every six months, or as recommended) for check-ups and professional cleanings. Your dentist can:
- Examine the crown and the surrounding tissues.
- Take x-rays to detect any hidden decay.
- Professionally clean plaque and tartar from around the crown margin.
- Identify any potential issues with the crown’s fit or cement early on.
Dietary Considerations
A diet high in sugar and acidic foods and drinks increases your risk of decay on all teeth, including those with crowns. The bacteria in your mouth feed on sugars, producing acids that attack tooth structure.
- Limit sugary snacks and beverages.
- Be mindful of acidic foods and drinks (like citrus fruits, sodas, sports drinks) as they can erode enamel and cementum over time.
- If you do consume sugary or acidic items, try to do so with meals rather than snacking on them throughout the day, and rinse your mouth with water afterward.
Consider an Antibacterial Mouthwash
Using an antibacterial or fluoride mouthwash can provide an extra layer of protection by helping to reduce bacteria levels in your mouth and strengthen tooth surfaces against acid attacks. Ask your dentist for a recommendation.
Address Teeth Grinding (Bruxism)
If you grind or clench your teeth, especially at night, this can put excessive stress on your crowns (and natural teeth). This stress can potentially lead to cracks in the crown, dislodgement, or wear at the margins. If you suspect you grind your teeth, discuss it with your dentist. They may recommend a custom-fitted nightguard to protect your teeth and dental work.
What If Decay Does Occur Under a Crown?
If your dentist finds decay under an existing crown, the treatment will depend on the extent and location of the decay. In many cases, the crown will need to be removed. This can sometimes be done carefully to try and save the crown for re-cementation, but often a new crown is required, especially if the old one is damaged during removal or no longer fits properly after the decay is treated.
Once the crown is off, the dentist will remove all the decayed tooth structure.
- If the decay is relatively small, the tooth can be cleaned, and a filling might be placed to build up the tooth structure before a new crown is made and fitted.
- If the decay is extensive and has reached the pulp (the inner nerve tissue of the tooth), root canal therapy may be necessary before a new crown can be placed.
- In very severe cases, where the decay has destroyed too much of the tooth structure, the tooth might not be salvageable and could require extraction.
The Lifespan of a Crown
While not directly about decay, it’s worth noting that crowns don’t last forever, even without decay. The average lifespan of a crown is typically cited as 5 to 15 years, but many can last much longer with excellent care. Factors like oral hygiene, diet, biting forces, and the material of the crown all play a role. Regular dental check-ups help monitor the condition of your crown and the underlying tooth.
The Takeaway Message
A dental crown is a fantastic way to restore a tooth’s function and appearance, offering significant protection to the part of the tooth it covers. However, it is not a magical shield against all future dental problems. The critical areas remain the junction between the crown and your natural tooth, and any exposed root surfaces. These areas are just as susceptible to decay as any other part of your natural teeth if not cared for properly.
So, while you can feel confident in the strength and purpose of your crown, don’t let it lull you into a false sense of security. Maintain your diligent brushing and flossing routine, keep up with your regular dental visits, and be mindful of your diet. By doing so, you give your crowned tooth the best possible chance of staying healthy and serving you well for many years to come. Your dentist is your partner in this, so don’t hesitate to ask questions about how to best care for your specific dental work.
