A popular name for the last molar tooth on either side of each jaw (see TEETH). These teeth are the last to appear and should develop in early adult life, but often they do not cut the gum until the age of 20 or 25; indeed, they may sometimes remain permanently impacted in the jaw-bone. This occurs in up to 25 per cent of individuals. The lower third molar is often impacted against the second because of the direction in which it erupts.