Permanent mandibular central incisor is the first tooth from the midline. Its tooth number in FDI system is 4-1 and 3-1. In universal system, it's 25 and 24 and in Zygmunti-Palmar system, it is 1 with appropriate quadrant brackets. Like all incisors, its function is cutting. Also, like all anterior teeth, it develops from four developmental lobes and shows memelons in a newly erupted tooth. Chronologically, the tooth erupts at the age of 6 to 7 years. Coming to measurements, mandibular central incisor is the smallest permanent tooth in the oral cavity. Its crown length is 9.5 mm and root length is 12.5 mm. The mesodistal diameter of the crown is 5 mm and at cervix it is 3.5 mm. The labiolingual diameter of the crown is 6 mm and at cervix it is 5.3 mm. The curvature of cervical line on mesal side is 3 mm and on distal side it is 2 mm. Now let us study the morphological details from each aspect starting with the labial aspect. The outline form of the crown is trapezoidal in shape with the longer side towards the incisal surface and shorter side towards the cervical line. The incisal surface is horizontal at right angle to the long axis of the tooth. Both mesoincisal angle and distoincisal angle are sharp. Both contact areas, the mesial contact area and distal contact area are in the incisal third. Both outlines, mesial outline and distal outline are almost straight and the cervical line is convex towards the root. The labial surface is smooth and convex with slight flattening in the incisal third. So we see that the crown's mesial half and distal half are almost symmetrical. The single root is conical and tapering with root tip frequently curving towards the distal side. Next, the lingual aspect. The features of the outline form from the labial aspect are same from the lingual aspect as well. However, the lingual surface is very different with convexities and concavities. Three ridges, incisal ridge running from the mesioincisal angle and distoincisal angle, mesial marginal ridge on mesial border and distal marginal ridge on distal border. A cingulum is present at the cervical third. A concavity is seen in the center of all these convexities called the lingual fossa. In comparison to maxillary central incisor, all the ridges, cingulum and fossa are less prominent. Coming to the mesial aspect, the outline form of the crown from the mesial aspect is triangular in shape. The incisal ridge is lingual to the midline axis of the tooth. This feature is seen in all mandibular incisors which helps in placing them lingual to the maxillary incisors. The labial outline is convex with its maximum convexity in the cervical third. In comparison to maxillary central incisors, this convexity is less and is almost flat in the incisal third. The lingual outline is convex in the incisal third, concave in the middle third and convex again in the cervical third. Coming to the root, its labial outline and lingual outline are stretched till the middle third and then starts tapering till the apex. A mesial developmental depression runs along the long axis in the middle third. Next the distal aspect. All the features from the mesial aspect are same from the distal aspect as well. though the distal developmental depression on the root is deeper than the mesial developmental depression. Finally, the incisal aspect. As with all permanent teeth, no part of the root is visible from the incisal aspect. The labiolingual diameter is more than the mesodistal diameter. The labial outline is smooth and convex and the lingual outline is narrower, showing the lingual convergence which is a feature of all anterior teeth.