When a tooth can no longer be restored due to issues such as it being broken, poorly shaped, discolored, or containing too much decay to be repairable by a dental filling, then a full coverage crown is typically recommended. A dental crown covers the tooth once it is shaped and prepared. Once the decay has been removed and tooth prepared, the crown is then fitted over the original tooth.
Crowns were previously made of full metal which consisted of a semi-precious or precious metal (gold) alloy, or a porcelain fused to metal type. Although these types of crowns are functional, they are not preferable for cosmetic purposes. Porcelain crowns are preferable as they include natural tooth color that matches your own tooth, as opposed to the metal.
A dental bridge is a fixed prostheses that covers a gap of one or more teeth by bridging the neighboring teeth together. In preparation for the bridge, the natural teeth on each side of the missing tooth/teeth are prepared for crowns to serve as abutments (supports) to hold the prosthetic (replacement) crown in place. A bridge can keep your other teeth from moving out of place and restore function and esthetics. Once a bridge is placed, it works and looks like a natural teeth.