A bridge is a single appliance that is generally attached to two teeth on each side of the space where a tooth is missing. An artificial tooth attached in the middle of the bridge fills in the gap where the missing tooth was. The teeth on either side of the gap are prepared for crowns (see crowns) and a highly accurate impression or mold is made of the prepared area. This mold is used to create a gold or porcelain (tooth colored) bridge in a special laboratory. The bridge is then cemented onto the prepared surface of the teeth, effectively creating the appearance of a new tooth.