Crowns slide over teeth, strengthening them and concealing cosmetic issues. They're made of a variety of durable materials, including porcelain, porcelain-fused-to-metal, nickel, gold, ceramic and resin. Crowns must be tough because they're subjected to very strong forces when you bite.
Bridges consist of two crowns that anchor one or more false teeth, called pontics. They're used to replace missing teeth. Bridges are usually made of porcelain or porcelain-fused-to-metal.