The tooth located in the permanent dentition of the maxilla between the first and third molar teeth. The form of the crown is similar to that of the first maxillary molar although it shows more variation and is smaller. The mesio-distal diameter is reduced and the diamond shape is usually more pronounced. Both the disto-palatal and disto-buccal cusps are reduced and sometimes the disto-palatal cusp is replaced by two smaller cusps or absent completely to give a tricuspid, triangular-shaped tooth where the distal margin of the crown is replaced by the oblique ridge joining the mesio-palatal and disto-buccal cusps. In a third variation the crown is compressed across the mesio-palatal disto-buccal diameter to give the crown the shape of a long oval, the long diameter of which runs from mesio-buccal to disto-palatal. It is very rare for a fifth cusp (the tubercle of Carabelli) to be present on the palatal surface as in the upper first molar. The root pattern is usually similar to the first molar although the divergence is less pronounced. Sometimes the palatal root may be united with one of the buccal roots, usually the mesio-buccal. The pulp chamber and root canals are similar to the first molar but can show considerable variation. Calcification of the tooth begins at 2½–3 years after birth and the crown is normally complete by 7–8 years of age. The tooth erupts at about 12–13 years and the calcification of the root is complete at about 14–16 years.