Permanent Mandibular Second Molar

Jul 28, 2024

Permanent Mandibular Second Molar

General Information

  • Position: 7th tooth from the midline
  • Tooth Number:
    • FDI System: 37 and 47
    • Universal System: 18 and 31
    • Zsigmondy-Palmer System: 7 with appropriate quadrant brackets
  • Development: Forms from 4 developmental lobes
    • Mesio-buccal lobe
    • Disto-buccal lobe
    • Mesio-lingual lobe
    • Disto-lingual lobe
  • Cusps: Four
    • Mesio-buccal cusp
    • Disto-buccal cusp
    • Mesio-lingual cusp
    • Disto-lingual cusp
  • Roots: Two
    • Mesial root
    • Distal root
  • Function: Grinding
  • Eruption Age: 11-13 years (also called '12-year molar')

Dimensions

  • Crown Cervico-Occlusal Length: 7 mm
  • Root Length: 13 mm
  • Mesio-Distal Diameter:
    • Crown: 10.5 mm
    • At Cervix: 8 mm
  • Bucco-Lingual Diameter:
    • Crown: 10 mm
    • At Cervix: 9 mm
  • Curvature of Cervical Line:
    • Mesial side: 1 mm
    • Distal side: Flat

Morphology

Buccal Aspect

  • Outline Form: Trapezoidal
  • Cusps: Both buccal cusps (mesio-buccal and disto-buccal) visible and almost equal in size
  • Contact Areas: Middle third (mesial and distal)
  • Outlines: Both mesial and distal outlines are convex
  • Cervical Line: Irregular
  • Buccal Developmental Groove: Present between buccal cusps
  • Cervical Ridge: Faint, running mesio-distally in cervical third
  • Roots: Mesial and distal roots visible with distal tilt

Lingual Aspect

  • Outline Form: Same as buccal aspect
  • Cusps: Mesio-lingual and disto-lingual cusps visible and of equal size
  • Lingual Developmental Groove: Present between lingual cusps

Mesial Aspect

  • Outline Form: Rhomboidal
  • Cusps: Mesio-buccal and mesio-lingual cusps visible
  • Outlines: Both buccal and lingual outlines are convex
    • Lingual outline curvature: Middle third
    • Buccal outline curvature: Cervical third (due to cervical ridge)
  • Cervical Line: Irregular
  • Mesial Marginal Ridge: Horizontal between mesial cusps
  • Roots: Mesial root (conical, with developmental depression) in front; distal root partially visible

Distal Aspect

  • Outline Form: Same as mesial aspect
  • Marginal Ridges:
    • Distal marginal ridge lower than mesial marginal ridge (more occlusal surface visible)
  • Roots: Distal root (conical, with developmental depression) in front; mesial root partially visible

Occlusal Aspect

  • Outline Form: Roughly rectangular
  • Cusps: Four cusps (mesio-buccal, disto-buccal, mesio-lingual, disto-lingual) almost equal in size
  • Ridges:
    • Each cusp has 2 cuspal ridges (mesial and distal)
    • 4 triangular ridges (1 from each cusp tip towards center)
    • 2 marginal ridges (mesial and distal)
  • Fossa:
    • Central fossa: Circular, center of occlusal surface
    • Mesial triangular fossa: Next to mesial marginal ridge
    • Distal triangular fossa: Adjacent to distal marginal ridge
  • Pits:
    • Central pit: In central fossa
    • Mesial pit: In mesial triangular fossa
    • Distal pit: In distal triangular fossa
  • Grooves:
    • Central developmental groove: Extends from mesial pit through central pit to distal pit
    • Buccal developmental groove: From central pit between buccal cusps onto buccal surface
    • Lingual developmental groove: From central pit between lingual cusps onto lingual surface
    • These 3 grooves form a cross pattern, dividing the occlusal surface into 4 parts
    • Numerous supplementary grooves present

Clinical Considerations

  • Fixed orthodontic treatment usually starts after age 13 (post eruption of second molars)