A dental crown is a full-coverage, tooth-shaped cap placed over a damaged or weakened tooth to restore its shape, size, and strength. The crown encases the entire visible portion of the tooth, serving as a new outer surface. Dentists recommend crowns to protect a tooth after a root canal, restore a fractured tooth, or cover a severely discolored or misshapen tooth. Crowns also improve the tooth’s appearance and help anchor dental bridges.
Crowns Based on Metal Content
Crowns based on metal are known for their exceptional durability and longevity, particularly in the back of the mouth where biting forces are highest. Full metal crowns are cast entirely from metallic alloys, such as gold, palladium, nickel, or chromium. Gold alloys are often preferred for their high biocompatibility and ability to wear down at a rate similar to natural tooth enamel. These restorations require the least amount of natural tooth structure to be removed during preparation because the metal can be cast thinly while maintaining strength. Full metal crowns rarely chip or fracture, making them reliable for molars. Their metallic appearance limits their use to less visible areas of the mouth.
Porcelain-fused-to-metal (PFM) crowns offer a compromise between the strength of metal and the look of natural teeth. They feature a metal alloy coping underneath for structural integrity, overlaid with tooth-colored porcelain for aesthetics. This combination makes them suitable for both front and back teeth, as the metal substructure prevents the porcelain from fracturing under heavy force. A common aesthetic limitation is the potential for the underlying metal to create a dark line visible at the gum margin, especially if the gums recede. The porcelain overlay is also less translucent than all-ceramic options, resulting in a less lifelike appearance.
All-Ceramic and Porcelain Crowns
Crowns made entirely of ceramic or porcelain are favored for their superior ability to mimic the light-reflecting properties and translucency of natural tooth enamel. Traditional all-porcelain crowns are highly aesthetic, providing an excellent match to surrounding teeth. These materials are a good option for patients with metal sensitivities, and lacking a metal core eliminates the risk of a dark line appearing at the gum line.
Lithium disilicate is a glass-ceramic material prized for its exceptional aesthetics and light-transmitting qualities. This material offers a flexural strength of around 400 Megapascals (MPa), making it significantly stronger than older all-porcelain crowns. Due to its superior optical properties, lithium disilicate is typically the material of choice for highly visible front teeth where blending with the natural smile is important.
Zirconia crowns are a modern ceramic option that combines the strength of metal with a tooth-colored appearance. Monolithic or solid zirconia crowns can have a flexural strength up to 1200 MPa, making them exceptionally resistant to fracture and suitable for posterior teeth. Newer high-translucent zirconia options offer improved aesthetics while still maintaining a strength range between 590 and 720 MPa. Zirconia’s high strength and biocompatibility make it a versatile material used for single crowns, bridges, and in patients who exhibit heavy biting forces. Because it is a solid block of crystalline material, zirconia resists chipping better than layered porcelain restorations.
Alternative Materials and Specialized Uses
Composite resin crowns are a budget-friendly alternative that uses a tooth-colored material similar to that used in dental fillings. They are the least durable of the permanent crown materials, with a lifespan generally ranging from five to ten years before replacement is needed. Resin is prone to staining and wear, making it less ideal for teeth that experience heavy chewing forces. These crowns are sometimes used as long-term temporary restorations or in situations where cost is the primary concern, such as in areas of the mouth that do not receive high biting pressure. Composite resin requires less tooth reduction than PFM crowns and provides a quick, aesthetic solution.
Stainless steel crowns (SSCs) are pre-formed metal caps used almost exclusively in pediatric dentistry to restore primary (baby) teeth. They are a cost-effective and quick solution for damaged or heavily decayed teeth that are too compromised for a filling. SSCs are the standard for restoring large cavities in primary molars because they protect the tooth until it naturally falls out. They are also occasionally used in adult dentistry as an interim or emergency crown while a permanent restoration is being fabricated. SSCs are durable, have a low fracture rate, and can be placed in a single appointment, preserving the space needed for the eventual eruption of the permanent tooth.
Factors Influencing Material Choice
The selection of the appropriate crown material is guided by functional requirements, aesthetic preferences, and individual patient factors. The location of the tooth is a primary consideration. Back teeth, such as molars, require materials with high fracture resistance to withstand significant chewing forces, making full metal alloys or monolithic zirconia often recommended. Conversely, teeth in the aesthetic zone, such as incisors and canines, benefit from materials that best replicate the natural translucency of enamel, like lithium disilicate or high-translucent ceramics.
A patient’s habits, particularly the presence of bruxism (teeth grinding or clenching), heavily influence the choice of material. Bruxism can cause pure porcelain to chip or fracture, leading dentists to recommend tougher options like monolithic zirconia or metal alloys, which resist destructive forces. Budget and insurance coverage also factor into the decision, as the cost of materials varies significantly. The amount of existing healthy tooth structure remaining is another physical constraint; metal crowns require less tooth reduction than some porcelain types, which helps preserve the natural tooth. Finally, a patient’s overall oral health and any known metal allergies must be addressed, as all-ceramic and zirconia crowns are excellent choices for individuals with sensitivities to base metals.