A dental bridge is often used to fill a gap between teeth after the loss of a tooth or several teeth. There are 2 types of bridges as Dr Alford has already alluded to. Removable bridges are often partial dentures and fixed dental bridges are crowns cemented on the adjcent teeth to the gap. If you need to replace a tooth and the adjacent teeth need to be crowned to protect them from breaking then a bridge is the most practical option.
A dental bridge is used instead of dental implants if there is insufficient bone to have a dental implant inserted, there is a medical reason why the individual cannot have surgery or dental implants have failed in the individual in the past.
Furthermore, if the individual cannot tolerate a partial denture for whatever reason, then a fixed dental bridge is the preferred option.
The choice between a fixed or removable dental bridge is dependant on many factors which only your dentist can provide you with and discuss to determine which is the better option. There are pros and cons for each treatment choice, in some cases one will be better than the other.
All the best with your treatment.