Bridgework has been used for many decades to replace lost teeth or to restore pre-existing gaps. Put simply, Bridgework consists of more than one crown unit joined together. Bridges are fitted over existing teeth and toothless spaces.
Other types of bridge do exist, one example is the Adhesive bridge (usually made of ceramic) which is simply bonded firmly to the adjacent teeth.
Bridges are constructed from similar materials to crowns. They are permanent restorations although in many cases, they have now been superseded by the use of dental implants to replace toothless spaces.