Permanent maxillary first molar and second molar are morphologically very similar to each other. So learning the few differences present between them is important in their differentiation. Starting with some general features. Maxillary first molar is the 6th tooth from the midline and 2nd molar is the 7th tooth from the midline. Which in turn gives the two teeth different tooth numbers in various tooth notation systems. Coming to chronology. Maxillary first molar erupts at the age of 6 years and 2nd molar at the age of 12 to 13 years. This makes the 1st molar the 1st permanent tooth to erupt in the arch. Whereas, 2nd molar the 2nd-last tooth to erupt. Maxillary first molar is also commonly called the 'cornerstone' whereas the second molar the '12-year molar'. Coming to their measurements. The maxillary first molar is larger than maxillary second molar in all dimensions, except the bucco-lingual dimension, where they are same. So generally speaking, first molar is larger than the second molar. Maxillary first molar develops from 5 developmental lobes whereas, second molar from 4 developmental lobes. This feature results in the difference in the number of cusps. First molar has 5 cusps, second molar 4 cusps. Both molars have 3 roots each. Now, let us study the differences in their morphology in detail, starting with the buccal aspect. If we take a look at the crown, both molars are very similar. The outline form is trapezoidal. Both buccal cusps are seen. Both contact areas are at the same position and both have a cervical ridge and a buccal developmental groove. Coming to the roots. Both molars have the same roots. Although the roots of the first molar are more flaring than the second molar. Moreover, roots in the second molar have a distal tilt which is not seen in the first molars. Next, the lingual aspect. Like the buccal aspect, majority of features are same in both molars, but a big difference is the presence of fifth cusp or cusp of Carabelli on the mesio-lingual cusp, in the first molars. No such cusp is present in the second molar. Apart from this, partial disto- buccal cusp is also seen in the second molar. But not in first molar. Coming to the roots. Like the buccal aspect, the distal tilt is seen in the second molar, absent in the first molar. Next, the mesial aspect. Most of the features are same, but similar to the lingual aspect the main difference seen is the appearance of the fifth cusp, on the mesiolingual cusp, which is not present in second molar. No major difference is seen in the roots. Next, the distal aspect. There is absence of any morphological difference between the two molars from this aspect. Finally, the occlusal aspect. The outline form of the crown is rhomboidal in first molar, but can be rhomboidal or heart-shaped in second molar, depending on the size of the disto-lingual cusp. If we compare only the rhomboidal outline form, the acute angles in second molar are more acute or smaller, whereas, the obtuse angles are more obtuse or larger than in the first molar. Both molars have 4 functional cusps mesio-lingual cusp, mesio-buccal cusp, disto-buccal cusp and disto-lingual cusp. Additionally, maxillary first molar has one supplementary cusp, the fifth cusp or cusp of carabelli. Second molars have no supplementary cusp. The order of cusps according to their size is also slightly different in both molars. Mesio-lingual cusp is the largest, than comes the mesio-buccal cusp. The difference comes in the3rd and 4th position. In first molars, the disto-lingual cusp is larger than the disto-buccal cusp. But in second molars it's the reverse. The disto-buccal cusp is larger than the disto-lingual cusp. Aapart from that, both molars are similar with respect to their ridges, their fossa and their developmental grooves. Except, maxillary first molar has a fifth cusp groove associated with the fifth cusp, which is not seen in the second molar. Moreover, the number of supplementary grooves are more in second molar than in the first molar.