A dental crown is a custom-made, tooth-shaped cap placed over a damaged or weakened tooth, completely encasing the visible portion. This restoration acts as a protective shield, restoring the tooth’s structure and improving its appearance. The decision to place a crown involves weighing the restorative benefits against the inherent risks and long-term maintenance requirements. Suitability depends entirely on the condition of the underlying tooth structure and the material chosen for the restoration.
Indications for Dental Crowns
Crowns are necessary when a tooth has lost too much natural structure to be repaired with a standard filling. Teeth with extensive decay or large restorations are structurally compromised and susceptible to fracture under normal chewing forces. A crown holds the remaining weakened tooth together, distributing mechanical stress across the surface. This is crucial for back teeth, which handle significant biting forces.
A crown is also commonly indicated following a root canal procedure, especially on a posterior tooth. The root canal process and previous decay cause a significant loss of internal tooth material. This structural reduction leaves the tooth brittle and vulnerable to vertical fracture. Full coverage with a crown substantially increases the tooth’s resistance to fracture, preserving long-term function.
The procedure is necessary when the remaining tooth material is insufficient to withstand chewing forces. Without the crown’s encasement, severely compromised teeth would eventually crack, often requiring extraction. A full-coverage restoration ensures structural integrity and restores the tooth’s ability to function normally.
Types of Crown Materials
The material selected impacts the crown’s longevity, strength, and aesthetic outcome. Full metal crowns, typically made from gold or base-metal alloys, possess exceptional strength and resist fracture and wear. These are generally limited to molars due to poor aesthetics but require the least tooth removal during preparation.
Porcelain-Fused-to-Metal (PFM) crowns offer a compromise, using a metal substructure for strength overlaid with tooth-colored porcelain. While successful, the metal layer can sometimes show through at the gumline as a dark line. The porcelain layer is also susceptible to chipping or fracturing away from the metal framework.
All-ceramic crowns, such as lithium disilicate or zirconia, are the modern standard for aesthetics. Lithium disilicate is favored for its high translucency, mimicking natural enamel, making it suitable for front teeth. It offers a flexural strength of approximately 400 Megapascals (MPa).
Zirconia is favored for its superior strength, often exceeding 1,000 MPa, making it ideal for posterior teeth and patients with heavy biting forces. Traditional zirconia is more opaque than lithium disilicate. Modern all-ceramic crowns demonstrate survival rates comparable to PFM crowns.
Potential Risks and Drawbacks
The placement of a crown is an irreversible procedure that carries specific risks. The preparation process requires removing a significant amount of healthy tooth structure to create space for the crown material. This reduction can irritate the tooth’s nerve, leading to post-cementation sensitivity to hot or cold temperatures. This sensitivity typically resolves within a few weeks as the pulp tissue calms down.
Sensitivity can also be caused by the drilling process exposing microscopic dentinal tubules, allowing fluid movement that stimulates the nerve. In rare cases, persistent sensitivity may indicate irreversible pulp damage, necessitating a subsequent root canal treatment. Another common complication is marginal leakage, which occurs when a microscopic gap exists between the crown margin and the prepared tooth edge.
This microleakage allows oral fluids and bacteria to seep underneath the restoration, leading to recurrent decay on the underlying tooth structure. This issue is often difficult to detect until it is advanced. Furthermore, the crown itself can fail mechanically, such as the porcelain chipping off the substructure or the entire crown loosening. Loosening occurs due to the washout of the luting cement, accelerated by poor marginal fit or excessive shear forces.
Care and Expected Lifespan
The longevity of a dental crown depends heavily on proper home care and avoiding damaging habits. Crowns have an average lifespan ranging from 5 to 15 years, which diligent maintenance can extend significantly. Effective plaque removal is crucial, as the crown margin where the restoration meets the natural tooth is the most vulnerable area for recurrent decay.
Patients should use a soft-bristled toothbrush and pay special attention to the gumline around the crown. Flossing requires careful technique, using a “C” shape around the tooth and sliding the floss out sideways rather than snapping it upward. This prevents the floss from catching the crown margin and potentially dislodging the restoration.
Dietary modifications are necessary to prevent mechanical failure. Patients should avoid chewing hard objects such as ice or popcorn kernels, which can cause chipping, especially in all-ceramic restorations. Sticky foods like caramel should also be avoided, as they can place undue tensile stress on the cement and pull the crown off the tooth. If an individual grinds or clenches their teeth, a custom-fitted nightguard is recommended to shield the crown from excessive, non-functional forces.