The rubber dam serves to keep the tooth dry for a more optimal treatment.
The rubber dam consists of a rubber piece in which one or more holes are made, in which the tooth (s) fit and which is stretched on a frame. The mouth is a humid environment. In addition, the saliva contains many bacteria. In order to be able to work clean and dry,use is made of the rubber dam (also called cofferdam). For example, the tooth to be cared for is protected from the rest of the mouth.
The advantage for you is that keeping the mouth open can happen in a much more relaxed way. You can swallow regularly and no bits of material can fall into the mouth.