Bridges are used to fill gaps long term, where teeth have been lost. 

There are usually two crowns on either side of a pontic (false tooth).  

Depending on the size of the gap, bridges can be a great fixed (meaning not removable like dentures) and aesthetic option. In certain circumstances, implants may be a preferred alternative to bridges.  This may be because the gap is too wide. It is always best to discuss with your treating cosmetic dentist first to ensure bridges are suitable for you.