A dental crown, commonly referred to as a teeth cap, is a prosthetic covering designed to restore a damaged tooth. This restoration fully encases the entire visible portion of a tooth. It is necessary when a tooth has suffered decay, fracture, or wear too extensive for a traditional dental filling. The crown’s primary function is to restore the tooth’s original shape, size, and strength while improving its appearance.
Metal and Porcelain Fused to Metal Crowns
Metal alloy crowns are distinguished by their exceptional durability and long-term wear resistance, making them a traditional choice for teeth that endure heavy biting forces. These crowns require minimal removal of the natural tooth structure because of the inherent strength of the metal. Dental alloys are categorized based on their noble metal content, including high-noble alloys, which contain at least 60% noble metals like gold and palladium.
High-noble alloys are favored for their biocompatibility and corrosion resistance, while base-metal alloys, containing less than 25% noble metals like nickel or chromium, offer a more budget-friendly and harder option. Due to their metallic color, these full-metal restorations are typically reserved for posterior teeth, such as molars, where aesthetics are less of a concern. Their ability to withstand the forces exerted during chewing ensures a longer lifespan.
A compromise between the strength of metal and the appearance of ceramic created Porcelain Fused to Metal (PFM) crowns. This hybrid design features a strong, thin metal alloy substructure, which is then covered entirely by layers of tooth-colored porcelain. The metal core provides the structural integrity to resist high masticatory forces, allowing PFM crowns to be used successfully in both the anterior and posterior regions of the mouth.
The limitation of the PFM crown is aesthetic, stemming from the opaque nature of the underlying metal. Over time, as gum tissue naturally recedes, the metal margin can become visible at the gumline, creating a dark or gray line. Furthermore, the porcelain layer, while cosmetic, can sometimes chip or fracture, exposing the metal beneath and compromising the restoration’s appearance.
All-Ceramic and Zirconia Crowns
All-ceramic crowns contain no metal substructure and mimic the natural translucency of tooth enamel. Early forms of porcelain and ceramic crowns offered superior aesthetics, but historically lacked the structural integrity for use in high-stress areas. These materials are highly valued for patients with metal sensitivities or those who demand the most natural-looking restoration for their visible front teeth.
Modern all-ceramic options include Lithium Disilicate, which is a glass-ceramic material known for its favorable combination of strength and aesthetics. This material features a flexural strength of approximately 400 Megapascals (MPa), making it more fracture-resistant than traditional layered porcelains. Lithium Disilicate crowns can be fabricated as a single, solid piece, offering excellent durability for both single crowns and smaller bridges.
Zirconia, a polycrystalline ceramic composed of Zirconium Dioxide, is often referred to as “ceramic steel” due to its exceptional strength. Monolithic or solid zirconia crowns boast a flexural strength that can exceed 1,200 MPa, making them highly suitable for the back teeth and for patients with grinding habits. This extreme toughness allows for a very thin yet strong restoration, conserving more of the natural tooth structure.
For front teeth, high-translucent zirconia is utilized, which balances a lower but still high strength (around 590 to 720 MPa) with light-transmitting properties. The increased translucency makes this material aesthetically comparable to natural tooth enamel, eliminating the graying effect. Zirconia can be used as a full-contour crown or as a substructure layered with traditional ceramic for maximum cosmetic effect.
Choosing the Right Material Based on Tooth Location
The choice of crown material is primarily dictated by the tooth’s location and the forces it must withstand. Teeth in the anterior region, such as incisors and canines, require materials with the highest aesthetic quality and light-handling characteristics. For these visible teeth, all-ceramic options like Lithium Disilicate and high-translucent zirconia are often preferred due to their ability to mimic natural tooth color and translucency.
Posterior teeth, including premolars and molars, must endure force during mastication. Materials like monolithic zirconia and full-metal alloys are the strongest choices for these areas, where durability is prioritized over aesthetics. PFM crowns also remain a viable option for back teeth, offering a balance of strength and a masked aesthetic at a generally lower cost than advanced all-ceramic options.
Patient-specific factors also influence the material selection process. Individuals who exhibit bruxism, or teeth grinding, often require the maximum strength offered by full-metal or monolithic zirconia crowns. Additionally, patients with a known sensitivity or allergy to base metals like nickel must opt for all-ceramic or zirconia restorations to avoid adverse reactions.
Cost is another variable, as the materials vary significantly in price, with base-metal alloys being the least expensive and high-tech ceramics like zirconia and lithium disilicate being at the higher end. The material must satisfy the functional requirements of the tooth location, the patient’s aesthetic goals, and their individual oral health needs.