Mandibular First and Second Premolars

Jun 22, 2024

Mandibular First and Second Premolars

Tooth Position and Eruption

  • First Premolar
    • 4th tooth from the midline
    • Erupts at age 10-12 years
  • Second Premolar
    • 5th tooth from the midline
    • Erupts at age 11-12 years

Measurements

  • First Premolar
    • Longer crown
    • Shorter root
    • Same total length as second premolar
  • Second Premolar
    • Crown and root make it same total length as first premolar
    • Larger bucco-lingual diameter

Developmental Lobes

  • First Premolar
    • Develops from 4 lobes
    • 2 cusps (buccal functional, lingual non-functional)
  • Second Premolar
    • Develops from 4 or 5 lobes
    • 2 or 3 cusps (all functional)

Morphological Differences (3 cusp type for second premolar)

Buccal Aspect

  • Both: Trapezoidal outline
  • First Premolar
    • Sharper, longer buccal cusp
    • Lower contact area in middle third
    • Root: thinner, apex sharper
  • Second Premolar
    • Shorter, less sharp buccal cusp
    • Higher contact area in middle third
    • Root: thicker, apex blunt

Lingual Aspect

  • First Premolar
    • 1 lingual cusp, smaller and narrower
    • More occlusal surface visible
    • Significant lingual convergence
    • Mesio-lingual developmental groove
  • Second Premolar
    • 2 lingual cusps (mesio-lingual & disto-lingual)
    • Less occlusal surface visible
    • Minimal lingual convergence
    • Lingual developmental groove between lingual cusps

Mesial Aspect

  • Both: Rhomboid outline
  • First Premolar
    • Both cusps visible
    • Lingual cusp 2/3 height of buccal cusp
    • Slanting mesial marginal ridge
    • Mesio-lingual groove visible
  • Second Premolar
    • Buccal and mesio-lingual cusps visible
    • Mesio-lingual cusp smaller but closer in size to buccal cusp
    • Horizontal mesial marginal ridge
    • No mesio-lingual groove

Distal Aspect

  • First Premolar
    • Both buccal and lingual cusps visible
    • Less occlusal surface visible compared to mesial aspect
  • Second Premolar
    • All three cusps visible
    • More occlusal surface visible compared to mesial aspect

Occlusal Aspect

  • First Premolar
    • Diamond-shaped outline
    • Both cusps visible
    • Mesial and distal fossae linear and circular
    • No central pit
    • 3 developmental grooves (mesial, distal, mesio-lingual)
  • Second Premolar
    • Square-shaped outline
    • All three cusps visible
    • Mesial and distal triangular fossae
    • Central pit present
    • 3 developmental grooves (mesial, distal, lingual) forming Y-shaped pattern