There are essentially three types of crowns; non-metallic crowns, all metallic crowns and crowns made from a combination of metal and non-metal. Non-metallic crowns contain no metals at all. They are formed from either ceramics, glass silicates, or some form of composite. Metallic crowns can be made from a wide range of metals. Gold, platinum, and silver are just some examples. Usually these crowns are made from a conglomerate of different metals. The amount of gold content determines the "preciousness" of the restoration. The more gold in the crown, the more noble or precious, the restoration. The final category is the combination crown. This is probable the most common. It has a metal substructure with some type of ceramic bonded onto it. Most often, porcelain is used as the ceramic. This crown give you the best of both worlds; metal in the substructure for strength and a ceramic outer layer for esthetics.
Crowns are an important treatment option for dentists because they allow for superior strength when it comes to chewing. But at the same time, also account for the need for better esthetics and a more tooth- like restoration.