Metal-Ceramic Crowns
Understanding porcelain-fused-to-metal crown construction and properties.
Metal-ceramic crowns, also known as porcelain-fused-to-metal (PFM) crowns, combine a cast metal substructure with a porcelain veneer layer. The metal coping provides strength and a precise fit, while the porcelain overlay delivers tooth-like aesthetics. This design has been the workhorse of fixed prosthodontics for decades. The metal framework is cast from alloys classified as high noble (gold-based), noble, or base metal (nickel-chromium, cobalt-chromium). The metal surface is oxidized to create a bonding layer, and porcelain is applied in layers — opaque to mask the metal color, then dentin and enamel layers for aesthetics. Each layer is fired in a porcelain furnace at specific temperatures. PFM crowns offer reliable strength suitable for both anterior and posterior teeth, with flexural strength dependent on the metal substructure. However, they have limitations including potential for a dark line at the gingival margin where the metal shows through, porcelain chipping, and less translucency compared to all-ceramic restorations. The trend toward metal-free dentistry has reduced PFM use, but they remain a viable option in specific clinical situations.