Summary
Highlights
The permanent mandibular lateral incisor is the second tooth from the midline. Its FDI system number is 42 and 32, Universal System numbers are 26 and 23, and Zsygmondy Palmar system number is 2 with appropriate quadrant brackets. Its primary function is cutting. The tooth develops from four lobes: mesial, labial, distal, and lingual, with the lingual lobe forming the cingulum and the others forming the incisal ridge with mamelons. It typically erupts between 7 and 8 years of age.
The crown length measures 9.5 mm, and the root length is 14 mm. The mesio-distal diameter of the crown is 5.5 mm, reducing to 4 mm at the cervix. The labio-lingual dimension is 6.5 mm, and 5.8 mm at the cervix. The curvature of the cervical line is 3 mm on the mesial side and 2 mm on the distal side.
From the labial view, the crown is trapezoidal, wider at the incisal ridge than at the cervical line. The incisal surface is straight but not horizontal, with a slight distal tilt cervically, giving the crown a twist on the root. Both mesio-incisal and disto-incisal angles are equally sharp. Mesial and distal contact areas are generally in the incisal third, with the distal being slightly more cervical. Both mesial and distal outlines converge towards the cervix. The cervical line is convex towards the root, and the labial surface is smooth and convex. The root is smooth, conical, tapering, and often tilts distally.
The lingual aspect is narrower than the labial, retaining the same outline form but with distinct surface features. An incisal ridge connects the mesio-incisal and disto-incisal angles. Mesial and distal marginal ridges are present, and a cingulum is found in the cervical third. A concavity called the lingual fossa is located in the middle. The root is smooth, conical, tapering, and has a distal tilt.
From the mesial aspect, the crown is triangular. The incisal ridge is positioned slightly lingual to the tooth's midline. The labial outline is convex with maximum convexity in the cervical third. The lingual outline is convex in the cervical third, concave in the middle third, and convex in the incisal third. The cervical line is convex towards the crown. The root is smooth and conical, featuring a mesial developmental depression along its long axis. The distal aspect shares similar features with the mesial, but the distal developmental depression on the root is deeper than the mesial one.
From the incisal aspect, no part of the root is visible. The labio-lingual diameter is greater than the mesio-distal diameter. The labial outline is smooth and convex, while the lingual outline shows lingual convergence. The incisal ridge is not straight; the distal half tilts lingually, creating a twist in the crown relative to the root. This twist allows the tooth to maintain proper contact with the central incisor and canine within the curving mandibular arch.