If you have one missing tooth, your bridgework will require three crowns. Two of those crowns will cover abutment teeth on either side of the gap left by the missing tooth. These two crowned abutment teeth will then become supports for a third crown placed in between them, filling in the empty space. This arrangement is known as a three-unit bridge.
If you have more than one tooth missing, several variable will be taken into account to determine the best course of treatment: the number of missing teeth, the size and length of the abutment tooth roots, the amount of bone support each abutment tooth has, as well as where in the mouth the teeth were lost.