There are three types of full-coverage crowns: full-gold crowns, porcelain-fused-to-metal crowns and all-ceramic crowns. The full-gold crowns offer more durability and predictability than the ceramic options, but do not have the appearance of natural tooth structure that porcelain has.
Porcelain-fused-to-metal crowns are made with a layer of noble metals covered by a layer of porcelain. They are quite strong. The porcelain is highly resistant to wear, but may actually wear opposing tooth structure if the porcelain becomes rough or if the patient clenches or grinds his or her teeth. For most patients, porcelain-fused to metal crowns are highly biocompatible, but some patients may have sensitity to some of the metals used under the porcelain.
All-ceramic crowns, as the name implies, have no metal substructure. Historically, these crowns have been considered to be excellent restorations for front teeth, but not durable enough for the back teeth. Today, however, there are several newer types of ceramics that are now available for making all-ceramic crowns and studies are now showing some of these materials to produce crowns that are stronger and more durable than the porcelain-fused-to-metal crowns.