The tooth that replaces the primary second molar located in the permanent dentition of the maxilla between the first premolar and the first molar tooth. The crown has a similar shape to the upper first molar but is slightly smaller and more oval and the two cusps are more equal in size. It has a mesio-distal central groove (fissure) confined to the occlusal surface and less well defined than that of the upper first premolar. The buccal, palatal, mesial, and distal surfaces are all convex and, unlike the upper first premolar, there is no concavity on the mesial surface. There is normally only one root with vertical grooves on the flattened mesial and distal surfaces. The pulp chamber is similar in shape to the upper first premolar, with two pulp horns extending into the cusps. There are usually two root canals, although this may be subject to considerable variation. Calcification of the tooth begins at about 2 years after birth and the crown is normally complete by 6–7 years of age. The tooth erupts at about 10–12 years and the calcification of the root is complete at about 12–14 years.