A wisdom tooth or third molar refers to one of the four molars per quadrant of the human dentition. Wisdom teeth generally appear between the ages of 17 and 25. Most adults have four wisdom teeth, but it is possible to have fewer or more, in which case the extras are called supernumerary teeth. Wisdom teeth commonly affect other teeth as they develop, becoming impacted or “coming in sideways.” They are often extracted when this occurs.