Margin design for porcelain fused to metal restorations which extend onto the root.

A 90 degree shoulder is probably the most commonly used margin design for porcelain fused to metal (PFM) restorations. However, this design requires the removal of a significant amount of tooth tissue to provide a predictable restoration. This increases the risk of irreversible damage to the pulp, particularly if little tooth tissue is present, for example on exposed roots. In these situations more conservative designs, such as the 135 degree shoulder or deep chamfer, should be considered. Ideally these designs should be used with an all-metal margin since this is associated with the most predictable marginal seal. Where an all metal margin is aesthetically unacceptable a porcelain butt or subgingival margin can be considered. Newer techniques, such as resin bonded crowns, which minimise tooth destruction and provide acceptable aesthetics may be a viable alternative to traditional PFM restorations. Unfortunately, these newer techniques have not been evaluated long-term.