A dental cap, commonly known as a crown, is a custom-made covering that restores a damaged tooth to its original shape, size, strength, and appearance. These restorations are necessary when a tooth is heavily decayed, fractured, or has undergone a large procedure like a root canal. The choice of material directly impacts the restoration’s durability, biocompatibility, and aesthetic outcome. Selecting the correct material ensures the crown can withstand the daily forces of chewing and maintain a pleasing aesthetic over many years.
Metal Alloys and Porcelain Fused to Metal Crowns
Full metal crowns are constructed from various alloys chosen for their strength and resistance to fracture. These alloys are categorized as high-noble (containing precious metals like gold, palladium, and platinum) or base metal (using non-precious metals such as nickel, chromium, and cobalt). Gold-based alloys are prized for their biocompatibility and require minimal tooth removal, but their metallic color limits their use primarily to back molars.
Porcelain Fused to Metal (PFM) crowns combine the strength of a metal substructure with the tooth-like appearance of porcelain. The inner core is a metal coping, typically made from a high-noble or base alloy, covered by layers of dental porcelain. This composition balances durability with moderate aesthetics, making PFM crowns a versatile option for both front and back teeth. A common issue is the potential for a visible dark line at the gum line if the gums recede, revealing the underlying metal margin.
Traditional All-Ceramic Materials
All-ceramic crowns are favored when high aesthetic quality is required, particularly for visible front teeth. These materials contain no metal, relying on compounds like silica, glass matrices, and crystalline fillers for structure. Pure porcelain and modern glass ceramics such as lithium disilicate are the primary materials in this category.
Lithium disilicate glass-ceramic is popular due to its balance of strength and natural appearance. Its composition allows for high light transmission and translucency, closely mimicking natural tooth enamel. However, traditional ceramics like feldspathic porcelain are inherently brittle and may be susceptible to chipping under heavy chewing forces compared to metal or high-strength ceramic options.
Zirconia: The High-Strength Option
Zirconia crowns are made from Zirconium Dioxide (ZrO2), a white crystalline oxide often described as “ceramic steel” due to its mechanical properties. This ceramic material offers fracture resistance that rivals metal alloys, challenging their dominance in posterior applications. Its strength comes from transformation toughening, a process that blocks the spread of cracks.
Zirconia is used in two primary forms to meet different clinical needs. Monolithic zirconia is milled from a single, opaque block, providing maximum strength suitable for molars and patients who grind their teeth. High-translucency zirconia is available for anterior restorations, sacrificing a small amount of strength for improved aesthetics that better mimic the light-passing properties of natural teeth. This dual capability makes zirconia a versatile choice for durable, natural-looking restorations throughout the mouth.
Composite Resin and Temporary Solutions
Composite resin crowns are constructed from a blend of acrylic polymers reinforced with fine filler particles, such as glass or quartz. These crowns are the most affordable and offer decent aesthetics, as the resin can be shaded to match surrounding teeth. However, they are the least durable material for a permanent crown, exhibiting lower wear resistance and being more prone to fracture compared to metal or ceramic options.
Composite resin crowns are most commonly used as interim or temporary restorations. Temporary caps protect the prepared tooth while the final, permanent crown is custom-fabricated in a dental laboratory. These temporary solutions are often made from acrylic resins, such as polymethyl methacrylate (PMMA), which are easily shaped and quickly cured. They maintain the prepared tooth’s position, function, and aesthetics for the short period before the long-term restoration is placed.