A wisdom tooth or third molar is one of the three molars per quadrant of the human dentition. It is the most posterior (most distal) of the three. Wisdom teeth generally erupt between the ages of 17 and 25. Most adults have four wisdom teeth (a third molar in each of the four quadrants), 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.