Skip to Content

Can a tooth rot under a crown?

Getting a dental crown is a common procedure done to restore a damaged or decayed tooth. A crown covers the entire visible portion of the tooth, protecting it and holding it together. While crowns can last many years, they do not make teeth invincible to future decay. It is possible for a tooth to develop new decay under a crown, requiring additional dental work.

What is a dental crown?

A dental crown, also known as a cap, is a restoration that covers or “caps” a tooth to restore its shape, size, and strength. Crowns can be made of various materials like:

  • Porcelain fused to metal
  • All-ceramic
  • Gold alloys
  • Base metal alloys

The crown covers the entire visible part of the natural tooth above the gum line. A crown is usually needed when a tooth is extensively damaged due to decay, cracking, root canal treatment, or large fillings. The crown holds the tooth together, strengthening it and restoring its appearance and function.

Why do teeth need crowns?

There are several reasons a dentist may recommend a crown for a tooth:

  • Extensive decay: Large areas of decay can weaken a tooth extensively. A crown covers the entire tooth to prevent further decay.
  • Root canal treatment: After a root canal, a tooth is more brittle and prone to cracking or breaking. A crown protects the tooth.
  • Large fillings: If a tooth has had substantial reconstructive work with large fillings, a crown can protect what remains of the natural tooth.
  • Fractures or cracks: Crowns can hold together cracked or broken teeth to prevent loss of the tooth.
  • Worn enamel: Teeth can wear down due to grinding habits or acid erosion. Crowns rebuild the worn tooth.
  • Cosmetic improvement: Discolored, misshapen or misaligned teeth can be restored with crowns.

Can decay occur under a crown?

Yes, it is possible for decay to occur under an existing dental crown. While the crown covers and protects the visible portion of the tooth above the gum line, bacteria can still get below the crown margin and cause decay at the neck of the tooth. Reasons decay may occur under a crown include:

  • Poor oral hygiene allowing plaque buildup near the gumline
  • Using sugary drinks, acidic foods, or dry mouth conditions that increase decay risk
  • Cracks or gaps in the crown margin allowing bacteria inside
  • An imperfect crown fit leaving space for bacteria
  • Recurrent decay in a tooth with a history of decay issues

Decay under a crown can also start if the tooth already had untreated decay when the crown was placed. Even if the crown covers the decay, it is still active under the crown.

Signs of decay under a crown

Some signs that a tooth may have decay under a crown include:

  • Tooth pain or sensitivity, particularly to cold foods/drinks
  • A bad taste or odor from the tooth
  • Visible discoloration, staining, or darkening near the crown edge
  • A loose crown that doesn’t fit like it used to
  • Swelling, tenderness, or infection in the gums around the tooth
  • Pus draining from around the tooth

However, decay under a crown does not always cause obvious symptoms until it is advanced. Even without pain or visible signs, decay may be silently progressing under the crown. Regular dental exams are essential to detect decay early.

Risk factors for decay under a crown

Factors that can increase the risk of decay under a crown include:

  • Poor oral hygiene and plaque buildup
  • A history of tooth decay or cavities
  • Dry mouth from medications, health conditions, or habits like smoking
  • Diet high in sugary and acidic foods and beverages
  • Grinding or clenching habits that can crack the crown
  • Gum recession exposing more tooth area underneath the crown
  • An improper crown fit allowing space for bacteria
  • Cracks or gaps in the crown material
  • Missing dental work allowing decay to spread to the crowned tooth

Can a crown be fixed or replaced?

If decay is detected under a crown, the decayed portion of the tooth can often be repaired with a filling. The crown may be temporarily removed, decay removed, and a new filling placed to restore the tooth. If the decay is extensive, a new crown may be needed.

Factors to consider regarding crown repair or replacement include:

  • Extent and location of the decay
  • Strength of remaining tooth structure
  • Quality of the current crown fit
  • Age and condition of the current crown
  • Cost of crown repair vs. replacement

A crown with an imperfect fit or margin, underlying decay, or other defects may be better replaced with a new crown for optimal results. Porcelain or ceramic crowns can often be replaced while keeping the underlying metal base if present. An all-metal crown usually requires full replacement.

Can crown decay be prevented?

Proper ongoing care of a crowned tooth can help prevent decay from developing underneath the restoration. Recommendations include:

  • Maintain excellent oral hygiene with brushing twice a day and daily flossing to control plaque
  • See your dentist regularly for exams and professional cleanings
  • Get cracks or loose crowns repaired immediately to prevent bacteria entry
  • Avoid frequent snacking and acidic or sugary drinks
  • Use fluoride toothpaste and dental products to strengthen enamel
  • Have any gum disease treated to prevent the gumline from receding
  • Wear a nightguard if you grind your teeth to prevent crown damage

With proper home care and professional treatment, a crown can protect your tooth for many years. But ongoing maintenance is essential even with a protected tooth. Regular dental visits and checkups will help find any potential problems early when they are easiest to correct.

Key Points

  • Decay is possible under crowns due to plaque buildup, crown flaws, or other factors
  • Symptoms of decay under a crown include pain, discoloration, swelling, or a loose crown
  • Repairing or replacing the crown can fix the problem if decay is caught early
  • Prevention with oral hygiene, dental visits, and limiting sugary foods helps avoid decay under crowns


While a dental crown covers and protects a tooth, the tooth is still vulnerable to new decay at the gumline or under the crown margin. Ongoing dental care and checkups can detect and treat any signs of decay early. With proper hygiene and monitoring, crowns can last for many years before needing repair or replacement. Being proactive preserves both your restoration and your tooth.

Decay Rate Statistics

Here are some statistics on how common it is for decay to occur under dental crowns:

Time After Crown Placement Decay Rate Under Crown
1 year 1-3% affected
5 years 8-12% affected
10+ years 15-20% affected

As shown, the longer a crown has been in place, the more likely decay is to occur underneath the restoration. Getting crowns checked regularly can find issues early before they progress.