Introduction
A metal ceramic restoration, or porcelain fused to metal (PFM), combines the strength of a metal frame with the esthetics of feldspar porcelain. It is one of the most widely used constructions in modern prosthetics.
Structure
The metal frame is strong and tough. Low-fusing or very low-fusing porcelain goes over it in opaque, dentin, enamel and glaze layers, which create the shape and optical properties of the tooth.
Requirements for the alloy
Noble alloys used include gold-platinum, gold-palladium, palladium-silver and palladium. Base alloys include nickel-chromium, cobalt-chromium and titanium.
The bond between metal and porcelain
The chemical bond through the oxide layer holds a metal ceramic together. Too little oxide gives a poor bond, so the layer must be thin and tightly bound.
Making one
- Model the frame in wax, cast it in the alloy, and finish it.
- Prepare the surface, for example by sandblasting.
- Apply and fire the opaque, which hides the metal and bonds to it.
- Build up the dentin and enamel layers, then fire them.
- Shape, correct and refire if needed.
- Glaze the surface.