Tooth broken or decayed under a crown — signs, causes and options

Key facts

• Teeth can still decay or fracture under crowns
• Decay usually starts at the crown edge near the gum
• A gap at the gum may be recession or a leaking margin
• Saving the tooth depends on remaining healthy structure
• Swelling or a gum bump needs prompt assessment

Can a tooth break under a crown?

A crown protects a tooth, but it does not make it indestructible. The natural tooth core and root beneath the crown can still fracture, especially if the tooth has had root canal treatment, if very little natural tooth was left when the crown was made, or if you clench or grind. Sometimes decay weakens the core until the crown comes off with a piece of tooth inside it. A fracture can also run vertically down the root, which is more serious. Patients often notice the crown feeling loose, pain on biting, or swelling. An X-ray and careful examination are needed to see how much sound tooth remains.

Why decay starts at the crown margin

The weak point of any crown is the margin, the line where crown meets tooth, usually close to the gum. Plaque that is not cleaned away can cause decay along this edge, and once it starts it can spread under the crown where it is hidden from view. Risk is higher with dry mouth, frequent sugary snacks or drinks, gum recession that exposes the softer root surface, and crowns whose margins no longer fit closely. Because decay under a crown often causes no symptoms at first, routine check-ups with bitewing X-rays are important. Early decay at the edge can sometimes be repaired without removing the crown.

A gap between the gum and the crown

Many people search for a 'gap between gum and crown'. This usually means the gum has receded, exposing the edge of the crown or a strip of natural root, or that the crown margin no longer seals well. A small exposed margin on a healthy tooth may simply need monitoring and good cleaning. However, a gap that catches food or floss, a dark line, or sensitivity at the gum can point to leakage or decay. Gum recession can be caused by aggressive brushing, gum disease or a crown that was over-contoured. Treatment depends on the cause: gum care, repairing the margin or replacing the crown.

Can the tooth be saved?

Whether the tooth can be saved depends on how much healthy structure remains above the bone and whether the root is cracked. If decay is small, it may be cleaned and the crown margin repaired. If decay is larger, the old crown is removed, the decay cleared, a new core built and a new crown made, sometimes after root canal treatment if the nerve is affected. A short tooth may need the gum and bone reshaped, called crown lengthening, to expose enough tooth. A vertical root fracture or decay extending deep below the bone often means the tooth cannot be predictably restored, and replacement with an implant or bridge is discussed.

When to see a dentist, and red flags

Book an assessment if you notice a dark line or gap at the edge of a crown, persistent sensitivity, a bad taste or smell from one tooth, food trapping, or a crown that feels loose or moves. Seek prompt care for swelling of the gum or face, a pimple-like bump on the gum, fever, or severe pain on biting, as these may indicate infection or a cracked root. If the crown comes off, keep it and bring it with you. At Manhal Medical Center in Dubai, Dr. Manhal Helfawee uses X-rays, and CBCT 3D imaging where a root fracture is suspected, before recommending the most predictable option.

A crown covers and strengthens a damaged tooth; a bridge replaces a missing tooth by anchoring to the teeth on either side. Zirconia and porcelain options combine strength with a natural appearance.

Prepared by the Manhal Medical Center editorial team · Updated: 2026-10-18 · Treating specialist: Dr. Manhal Helfawee

This page is general information and does not replace a consultation. Suitability, risks and results vary between patients.