A dental bridge is usually used where there are fewer teeth to replace, or when the missing teeth are only on one side of the mouth. Bridges are usually made of a precious metal base.
If the bridge will show, porcelain is then bonded to the base. Sometimes, there are other non-precious metals used in the base to reduce the cost.
You should replace missing teeth for a number of reasons. Your appearance is one reason. Another is that the gap left by a missing tooth can mean greater strain is put on the teeth at either side.