Based on retention methods, they can be categorized as fixed porcelain-fused-to-metal crowns and removable porcelain-fused-to-metal crowns. Based on the completed prosthesis name, they can be classified as inlays, veneers, full crowns, post crowns, fixed bridges, and removable bridges.Based on material composition: alloy-fused porcelain, all-ceramic, crystal porcelain. Based on alloy melting point and porcelain firing temperature: low-melting high-temperature porcelain, medium-temperature porcelain, low-temperature porcelain; medium-melting/high-melting alloys paired with high-, medium-, or low-temperature porcelains.
Porcelain restorations are categorized as metal-based or metal-free porcelain.
Metal-based porcelain involves first fabricating a metal inner crown as the framework. A porcelain veneer, resembling natural tooth color, is then applied to restore the tooth's shape. This assembly is fired in a vacuum porcelain furnace, fusing the porcelain to the metal alloy to form the porcelain-fused-to-metal crown.
The metal crown in porcelain-fused-to-metal restorations offers high strength, serving as the framework. The porcelain layer provides the natural tooth's color and texture. Covering the metal surface with porcelain compensates for the metal's color limitations, fully replicating the natural tooth's shade and form. Additionally, porcelain exhibits good biocompatibility with the gums, preventing gingivitis.
Metal-based porcelain-fused-to-metal restorations utilize two techniques: precious metal and non-precious metal.
Precious metal porcelain crowns typically feature inner crowns containing precious metals like gold or palladium. They offer two major advantages:
First, color matching—particularly where the crown meets the gum line—is aesthetically pleasing, avoiding bluish or grayish discoloration;
Second, the bond between porcelain and metal is exceptionally strong, minimizing porcelain chipping. This technology is now predominantly used in Europe, America, and other developed regions.
Non-precious metal porcelain-fused-to-metal crowns are typically made with a nickel-chromium alloy base. Their primary advantage is lower cost. Currently, China primarily employs non-precious metal porcelain-fused-to-metal technology.
Metal-free porcelain refers to all-ceramic crowns without a metal inner crown. This technology emerged in the late 1980s. In 1996, the ultra-ceramic composite fiber bridge technique was successfully developed.
Due to limitations in porcelain strength, it is currently used primarily for single crowns or anterior veneers to enhance aesthetics. Examples include cosmetic restoration for discolored teeth like tetracycline-stained teeth or teeth with necrotic pulp. In the near future, all-ceramic restorations will gradually replace metal-ceramic crowns.