Crowns are cast or milled restorations made to reinforce a tooth when a significant amount of structure has been lost or the tooth itself has been weakened due to a crack or root canal treatment. They can be made out of a variety of materials.
All ceramic crowns are popular because they contain no metals and look closest to natural teeth. They can be made entirely of porcelain when esthetics are the primary concern and situation doesn’t expose the crown to very high biting pressure. Crowns under higher load can be made with a zirconia core for added strength at the expense of some translucency. Solid zirconia crowns are the most durable of all ceramic materials. While zirconia is white it is also very opaque and has a “chalky” appearance when compared to porcelain. Solid zirconia is used on molars where extreme biting pressure is encountered or when the back teeth are very short and the crown must be made thin.
Porcelain fused to a metal core is time honored standard for crowns. The metal core adds strength and can be cast to almost any irregular shape. The porcelain exterior gives the crown its tooth colored appearance. The combination of materials is a compromise of strength and esthetics.
Gold alloy crowns are made primarily on back teeth where esthetics are not the primary concern. The softer material is less abrasive to the opposing teeth than ceramics. Gold will not chip or shatter when encountering an unexpected hard object and can be placed on very short teeth where there isn’t enough room for porcelain.