[TA] eighth permanent tooth in the maxilla and mandible on each side, making it the most posterior tooth in human dentition; usually erupts between the 17th and 23rd years; the roots are often fused, the separation being marked only by grooves; because it tends to erupt in an anterosuperior direction, the lower third molar often becomes impacted against the lower second molar; it is common for one third molar (or more) to fail to develop. SYN: dens molaris tertius [TA], dens serotinus*, dens sapientiae, third molar, wisdom tooth.