The bridge is a prosthesis used to replace one or more teeth that are missing or that have had to be extracted.
Every bridge is made up of multiple crowns. The ones in the centre replace the missing teeth, while the outermost ones are fixed on the teeth adjacent to the gap - which for this reason are downsized or removed - serving as a post.
It is precisely to prevent having to operate on these lateral teeth as well that it is preferable to resort to implants instead of the bridge whenever possible.