A permanent dental crown is a tooth-shaped cap placed over a damaged or decayed tooth to restore its original shape, size, and strength. This restoration completely encases the visible portion of the tooth. The material chosen determines its longevity, functional performance, and aesthetic outcome. This choice is based on the tooth’s location, the forces it must withstand, and a patient’s aesthetic priorities.
All-Metal and Gold Alloy Crowns
Crowns made entirely of metal, often called full-cast restorations, offer superior strength and are highly resistant to fracture. The metal is an alloy categorized as high-noble, noble, or base-metal. High-noble gold alloys, which must contain at least 60% noble metal and 40% gold, are highly biocompatible and resistant to corrosion.
These metal crowns require the least amount of tooth structure removal during preparation compared to other materials. Base-metal alloys, such as those containing nickel, chromium, and cobalt, are less expensive and exceptionally hard, making them suitable for molars that experience the heaviest chewing forces. The primary drawback is their distinct metallic color, meaning they are typically reserved for teeth in the back of the mouth where they are not visible.
Porcelain Fused to Metal Crowns
Porcelain Fused to Metal (PFM) crowns combine the strength of a metal core with the appearance of natural porcelain. Construction involves a thin, cast metal shell acting as a strong substructure. Layers of dental porcelain are chemically bonded and fused over this shell, providing a restoration that withstands significant biting forces.
The layered structure necessitates aggressive removal of the natural tooth structure to accommodate both materials. A common aesthetic concern is the potential for the underlying metal to create a dark line at the gum line if gums recede. PFM crowns are also susceptible to the porcelain chipping away from the metal, which compromises the restoration’s integrity.
All-Ceramic and Zirconia Crowns
All-ceramic crowns offer the highest aesthetic similarity to natural tooth enamel through their inherent translucency. Traditional feldspathic porcelain materials mimic the light-reflecting properties of a tooth but were historically less resistant to fracture. The development of modern ceramic materials has significantly broadened their application across the mouth.
Advanced materials include lithium disilicate, often branded as Emax, which offers excellent strength and natural appearance. Zirconia, or zirconium dioxide, is a ceramic material that provides exceptional durability. Monolithic zirconia crowns, made from a single block, offer strength that rivals or exceeds metal, making them highly suitable for back teeth.
The strength and aesthetic properties of zirconia make it a popular choice for both front and back teeth. Layered zirconia provides an extra coat of translucent porcelain for enhanced visual appeal. All-ceramic options are also highly biocompatible, making them suitable for patients with metal sensitivities or allergies.