Introduction
A combined crown joins a cast metal substructure, for strength, with a tooth-coloured veneer, for appearance. The two main families are resin-veneered (metal-resin) and porcelain-fused-to-metal (metal-ceramic) crowns; a third uses ceromer on metal. All are made by conventional wax-up, investing and casting, with the veneer added in a separate step.
Resin-veneer crowns (metal-resin)
A cast metal crown or coping veneered with PMMA or a light-curing composite where it shows, usually on teeth in the smile line.
Resin doesn't bond chemically to metal well, so it is held by mechanical retention: small beads or loops on the metal, plus bonding systems. In the wax-up, wax is cut back where the resin will go after the contours and occlusion are finished.
Resin veneers are cheaper but wear, absorb fluids and discolour over the years.
Porcelain-fused-to-metal crowns (PFM)
A metal coping (about 0.3–0.5 mm) carries layers of porcelain fired onto it: an opaque layer that hides the metal, then dentin and enamel/incisal porcelains that rebuild colour and translucency.
Designs
- Porcelain on the buccal surface and the buccal half of the occlusal surface.
- Porcelain everywhere except metal occlusal contacts.
- Fully covered by porcelain.
How porcelain stays on metal
Rules for the metal framework
- Rigid enough not to flex, or the porcelain cracks.
- Even porcelain thickness (about 1–1.5 mm); support every cusp.
- Smooth, rounded surfaces with no sharp angles under the porcelain.
- Metal-porcelain junction away from occlusal contacts.