The last and furthest back tooth at each end of each row of teeth is called a wisdom tooth. They are the third of the molars, and they usually start breaking through between the ages of 17 and 24. It is common, however, for a wisdom tooth not to come through at all, or to break through only partially. This can happen if there is not enough room in the jaw or other teeth are standing in the way. A wisdom tooth that has not broken through properly is called an impacted wisdom tooth.