The tooth that replaces the primary first molar located in the permanent dentition of the maxilla between the canine and the second premolar tooth. Viewed from the occlusal aspect, the crown is oval in shape, being broader buccally than palatally and narrower mesio-distally than bucco-palatally. The buccal, palatal, and distal surfaces of the crown are convex; the mesial surface is convex towards the occlusal surface but has a concavity towards the cervical margin (canine fossa). The crown has a palatal cusp and a larger buccal cusp, the mesial slope of which is longer than the distal slope. The two cusps are separated by a well-defined central groove (fissure) running mesio-distally and terminating in two small pits bounded by mesial and distal marginal ridges. A shallow extension of the central groove usually crosses the mesial marginal ridge to end on the mesial surface. There are normally two roots, located buccally and palatally, although occasionally there may only be one, within well-demarcated vertical grooves on the mesial and distal surfaces. The pulp chamber is oval in cross-section, being longer bucco-palatally than mesio-distally. Two pulp horns extend into the buccal and palatal cusps. If there are two roots, there are normally two root canals, although this may be subject to considerable variation. Calcification of the tooth begins at about 1½–2 years after birth and the crown is normally complete by 5–6 years of age. The tooth erupts at about 10–11 years and the calcification of the root is complete at about 12–13 years.