Bridges can be used for the replacement of multiple teeth. A single tooth would obviously require one implant fixture and replacement of two teeth would in the majority of cases require 2 implant fixtures to counter the rotational forces that are applied during eating. It is though possible to replace 3 or even 4 teeth using two implants and restoring the gap between the implant teeth by what is known as a bridge pontic.
The bridges can either be screwed onto the implant abutments or cemented.
The advantage of having a bridge that is screw retained is that it can be removed by the dentist quite easily for maintenance or repair. The advantage of a cement retained bridge is that it is slightly less bulky and there are no screw holes visible but obviously it would be very difficult to remove.
It is possible to replace all of the teeth in a jaw with a bridge supported by a number of dental implants. The number of implants required is dictated by the number of teeth to be replaced and the quality of the bone and the potential load. In the upper jaw a minimum of 6 to 8 implants are required to support a bridge of 10 or more teeth. In the lower jaw where the bone is more solid it is often possible to provide a full bridge with an adequate number of teeth for efficient masticatory function on 4 implants.
It is generally not considered wise to use a combination of a natural tooth and an implant to support a fixed bridge.