A bridge is a means of replacing a missing tooth with a fixed alternative, unlike a denture which is taken in and out on a daily basis.
The simplest type of bridge is a so-called Resin retained bridge. These consist of a porcelain tooth bonded on to a metal wing. This wing is glued onto the neighbouring tooth, so the artificial tooth fills the gap.
By comparison, a conventional bridge consists of a crown fitted over one or both neighbouring teeth from which an artificial tooth is suspended. This provides a good aesthetic and functional result but is best limited to cases when the neighbouring tooth is in need of treatment.
A bridge is usually more expensive than a denture but cheaper than an implant.
Before:
After (3 unit porcelain bonded to metal bridge):