A crown is a cap placed over a tooth to protect it and make it seem and function like a natural tooth. Crowns are typically composed of porcelain, metal, or ceramic. It is glued on top of an already strong and protected tooth root. A bridge is a prosthetic device consisting of two crowns used to replace a lost tooth in a grin. The abutments, or teeth next to it, are protected by the crowns. An artificial tooth (called a pontic) serves as the bridge's "vertical" component and should match the aesthetics of your natural teeth.