Wisdom teeth are the last teeth to erupt at the back of the mouth and due to lack of space often become jammed in position, this is called impaction. When a wisdom tooth is impacted it is often only partially visible in the mouth; as a result the gum over the tooth can become a source of infection. This can lead to significant pain and often difficulty in opening the mouth. When this occurs, removal of the tooth is often recommended. If, however, the tooth has caused no problems, it is often recommended that it is left in place.