Permanent Mandibular Lateral Incisor

Position and Identification

• Second tool from the midline
• Tooth Numbering Systems:
  • FDI System: 4, 2 and 3, 2
  • Universal System: 26 and 23
  • Zygmunt De Palma System: 2 with appropriate quadrant brackets

Function

• Primary Function: Cutting

Development

• Develops from four developmental lobes:
  • Mesial
  • Labial
  • Distal
  • Lingual (less developed, forms the cingulum)
• Three mamelons seen due to developmental lobes

Age of Eruption

• 7 to 8 years

Dimensions

• Crown length: 9.5 mm
• Root length: 14 mm
• Mesio-distal diameter:
  • Crown: 5.5 mm
  • Cervix: 4 mm
• Labiolingual dimension:
  • Crown: 6.5 mm
  • Cervix: 5.8 mm
• Curvature of cervical line:
  • Mesial side: 3 mm
  • Distal side: 2 mm

Morphology (5 Aspects)

Labial Aspect

• Crown Outline: Trapezoidal (longer side towards incisal ridge)
• Incisal Surface: Straight but distal side is tilted cervically
• Incisal Angles: Mesoincisal angle and distoincisal angle equally sharp
• Contact Areas:
  • Mesial: Incisal third (contacts central incisor)
  • Distal: Incisal third but slightly cervically positioned (contacts canine)
• Outlines:
  • Both mesial and distal converge towards the cervix
  • Cervical line convex (convexity towards the root)
• Surface: Labial surface smooth and convex
• Root: Smooth, conical, tapering, apex with a distal tilt

Lingual Aspect

• Outline Features: Same as labial aspect but narrower
• Surface Differences:
  • Incisal ridge (mesoincisal to distoincisal angle)
  • Mesial and distal marginal ridges
  • Cingulum in cervical third
  • Lingual fossa (concavity in the middle)
• Root: Smooth, conical, tapering, distal tilt

Mesial Aspect

• Crown Outline: Triangular shape
• Incisal Ridge: Slightly lingual to midline axis
• Outlines:
  • Labial outline convex (maximum convexity in cervical third)
  • Lingual outline:
    • Convex in cervical third
    • Concave in middle third
    • Concave in incisal third
• Cervical Line: Convex towards the crown
• Root: Smooth, conical; mesial developmental depression

Distal Aspect

• Similarities: Same features as mesial aspect
• Differences: Deeper distal developmental depression on the root

Incisal Aspect

• Visibility: No part of the root visible
• Dimensions: Labiolingual diameter > Mesodistal diameter
• Outlines:
  • Labial: Smooth and convex
  • Lingual: Shows lingual convergence
• Incisal Ridge: Not straight, distal half tilts lingually, creating a twist over the root
  • Purpose: Maintains mesial contact with central incisor and distal contact with canine in curving mandibular arch