The main advantages of using bridgework for replacing teeth is that it is fixed into the mouth, is quicker and less invasive than implants, can be carried out where there is inadequate bone for implants and is often cheaper than implants. The main disadvantage compared with implants is that it links the prognosis of several teeth together and has a shorter average survival time.
Conventional cemented bridges are like a series of crowns joined together to span from existing teeth over gaps. The advantage of this cemented approach is that you can improve the appearance of the teeth that support the bridge, whilst at the same time, filling the gaps. However, this involves heavier preparation of the supporting teeth than is required for a resin retained bridge. We tend to use a conventional cemented bridge when the supporting teeth could benefit from being crowned.
Gaps are filled with teeth much like crowns but the supporting teeth have little or no preparation and metal wings are bonded with resins onto the backs of supporting teeth. We use resin retained bridgework where the support teeth are largely still intact. This allows most of the tooth structure of the supporting teeth to be retained and therefore maintains the integral strength of the teeth. In the 1970s and 80s, the early designs were unpredictable which lead to many dentists abandoning this type of bridgework. However, researchers at the UCL Eastman Dental Institute carried out extensive testing until predictable designs parameters were discovered. The modern resin-retained bridge is both conservative of tooth structure and highly predictable.
You do not always need an implant for each tooth which is missing. For example, we will often replace two teeth with a single implant supporting the two replacement teeth.