It is supported by either another crown or an adhesive wing bonded to teeth on one or both sides of the space depending on how big the gap is. They can also be used to connect multiple dental implants.
A bridge unlike a removable denture is a fixed replacement.
They can provide a nice looking replacement for a tooth but the compromise is that the supporting tooth/teeth can undergo fatigue with time and develop problems. Also, the natural teeth supporting the bridge may need to be drilled down to receive the bridge which again can shorten its lifespan.
Adhesive (Maryland) or fibre reinforced composite bridges reduce the risks associated with the drilling of the teeth but there is a higher risk of the bridge coming off.
Unlike dental implants, the gum under a bridge can shrink away with time leaving a gap.