A dental crown is a custom-made cap designed to completely cover a damaged or weakened tooth, restoring its original shape, size, and function. This protective shell reinforces the tooth’s structure, allowing it to withstand the forces of chewing. While crowns are highly durable, they are not indestructible, and failure can occur under certain conditions.
Material Strength and Durability
The strength of a dental crown depends on the material chosen for its construction. Porcelain-Fused to Metal (PFM) crowns, a long-standing choice, use a metal alloy base for structural support, covered with porcelain for a tooth-like appearance. While the metal core resists fracture, the outer porcelain layer is susceptible to chipping under heavy pressure.
All-ceramic crowns, such as those made from lithium disilicate (Emax), offer superior aesthetics by mimicking the natural translucency of tooth enamel. Zirconia is widely regarded as the strongest material available, boasting extremely high resistance to fracture. This ceramic is often the preferred choice for back molars or for patients with a history of clenching, where bite forces are highest.
Primary Reasons Crowns Fail
A crown’s failure (chipping, fracture, or detachment) usually results from excessive mechanical stress or a compromise to the underlying tooth structure. Catastrophic breaks often occur from biting down on hard, non-food objects, such as ice, hard candy, or pen caps. A severe, sudden blow to the mouth can also overwhelm the material’s strength, leading to a full break.
A common cause for failure is decay developing at the crown’s margin, where it meets the gum line. The natural tooth beneath the crown remains vulnerable to bacteria and cavities, which weakens the foundation and can cause the crown to loosen. Excessive forces from habitual teeth clenching and grinding (bruxism) also cause significant damage. This continuous pressure can exceed the crown’s capacity, leading to wear, chips, or a complete fracture.
Crowns can also become loose and detach due to the breakdown of the dental cement. Poor initial preparation or an improper bite alignment (malocclusion) can create uneven pressure points, causing stress fractures or premature cement failure.
Protecting Your Crown and Maximizing Lifespan
Proactive habits and routine professional care ensure a crown reaches its expected lifespan, typically ranging from 5 to 15 years. Maintaining excellent oral hygiene is important because the margin where the crown meets the tooth is susceptible to bacterial accumulation. Brushing twice a day and flossing daily around the crown margin helps remove plaque and prevents decay.
If a patient experiences bruxism, wearing a custom-fitted nightguard is a preventative measure to absorb the intense forces generated during clenching and grinding. Modifying dietary habits also plays a role in longevity, meaning minimizing extremely hard foods and avoiding chewing on non-food items. Regular dental checkups allow a dentist to inspect the crown for early signs of wear, evaluate the margins for decay, and ensure the bite remains properly aligned.
What to Do If a Crown Breaks or Becomes Loose
If a dental crown breaks or feels loose, contact the dental office immediately to schedule an urgent appointment. The exposed underlying tooth can be sensitive.
If the crown has fallen off completely, take the following steps:
- Retrieve the crown and clean it gently with water.
- Store the crown safely for the dentist to examine.
- Temporarily re-cement the crown using an over-the-counter dental cement kit, if necessary, to protect the tooth.
- Avoid chewing on the affected side and stick to soft foods until the appointment.
The dentist will assess the crown and the underlying tooth to determine the best course of action. Small chips on a ceramic crown may be polished smooth or repaired with composite resin, but a complete break or significant underlying decay usually necessitates the fabrication and placement of a new crown.