A dental crown is a tooth-shaped cap placed over a damaged or weakened tooth, encasing the visible portion above the gum line to restore its shape, size, and function. While crowns are a robust and long-lasting form of dental restoration, they are not permanent. They are durable prosthetics that will eventually need replacement due to normal wear and tear or other complications. The longevity of a crown depends on multiple factors, including the material used and the patient’s oral care habits.
Expected Lifespan of a Dental Crown
The lifespan of a dental crown typically ranges from 5 to 15 years, though some can last 20 years or more with meticulous care. This duration is largely influenced by the material chosen. Metal alloy crowns, such as gold, are exceptionally durable and resistant to wear, often lasting over 20 years, making them ideal for back teeth that handle heavy chewing forces.
Porcelain and ceramic crowns offer superior aesthetic matching to natural teeth but generally have an average lifespan of 10 to 15 years. While visually appealing, these materials are more susceptible to chipping or fracturing under extreme pressure compared to metal. Zirconia crowns provide a balance, offering high strength and durability, often lasting 15 to 20 years, while maintaining a pleasing appearance.
The crown’s location also plays a significant role, as molars experience far greater forces than front teeth. Patient habits, such as regular brushing and flossing, are important for maximizing the crown’s lifespan by preventing decay at the margins. Consistent professional maintenance allows a dentist to monitor the crown’s fit and integrity.
Common Causes for Crown Failure
Crown failure occurs when the integrity of the restoration or the underlying tooth is compromised, necessitating replacement. The most frequent cause is recurrent dental decay, which develops in the natural tooth structure underneath the crown. This decay usually begins at the crown margin, where the crown meets the tooth near the gum line, if bacteria accumulate due to poor oral hygiene.
The crown material itself can fail through fracture or chipping, especially with porcelain or ceramic crowns subjected to high biting forces. Habits like teeth grinding (bruxism) place immense stress on the restoration, accelerating wear and increasing the risk of structural damage. Failure can also result from compromised marginal integrity, where the cement bond between the crown and tooth washes out over time.
When the cement seal is lost, a microscopic gap allows oral bacteria and food debris to seep underneath the crown and initiate decay. Over time, gum recession can expose the crown margin, which is an aesthetic concern and makes the root surface more vulnerable to decay.
Steps in Replacing a Worn or Damaged Crown
Replacing a failed crown begins with a clinical assessment, including X-rays, to evaluate the health of the underlying tooth and bone structure. The dentist first determines the specific cause of failure, checking for decay, fracture, or fit issues. The old crown is then carefully removed, often requiring sectioning or cutting the restoration with a specialized bur to break the cement seal without damaging the remaining tooth.
Once the old crown is off, the dentist addresses any issues with the tooth structure underneath, such as removing recurrent decay. If decay is extensive or a fracture is present, the tooth may need additional procedures, like a core build-up to restore sufficient foundation or root canal therapy. New impressions or digital scans are then taken of the prepared tooth to ensure the new crown is custom-fabricated with a precise fit and contour.
A temporary crown is placed to protect the tooth while the permanent replacement is manufactured by a dental laboratory, a process that typically takes a few weeks. At the final appointment, the temporary crown is removed, and the new custom crown is cemented onto the prepared tooth after confirming the fit, bite alignment, and aesthetic match.