Mandibular First Molar

Jul 28, 2024

Mandibular First Molar

General Characteristics

  • Outline Form: Hexagonal from the occlusal aspect
  • Mesio-Distal Dimension: Larger than bucco-lingual dimension (opposite to maxillary first molar)
  • Bucco-Lingual Dimension: More in mesial half than distal half
  • Cusps: All 5 seen from occlusal view

Cusps Overview

  • Largest Cusp: Mesio-buccal
  • Equal Size Cusps: Mesio-lingual and disto-lingual
  • Smaller Cusps: Distobuccal
  • Smallest Cusp: Distal
  • Primary Cusps: 2 buccal cusps, 2 lingual cusps
  • Secondary Cusp: Distal cusp

Ridges

  • Cuspal Ridges: Each cusp has 2 (mesial and distal)
  • Triangular Ridges: 5, running from cusp tip towards the center
  • Marginal Ridges: 2 (mesial and distal)

Fossa and Pits

  • Major Fossa: Central fossa (circular, central on occlusal surface)
  • Minor Fossae: Mesial triangular fossa and distal triangular fossa (adjacent to respective marginal ridges)
  • Pits:
    • Central pit (junction of central, lingual, and mesio-buccal grooves)
    • Mesial pit (in mesial triangular fossa)
    • Distal pit (in distal triangular fossa)

Developmental Grooves

  • Central Developmental Groove: Runs mesio-distally on occlusal surface
    • Starts at mesial pit, crosses central pit, ends at distal pit
  • Lingual Developmental Groove: Originates from central pit, runs lingually between lingual cusps
  • Mesio-Buccal Developmental Groove: Originates from central pit, runs buccally between mesio-buccal and disto-buccal cusps
  • Disto-Buccal Developmental Groove: Originates slightly distal to central pit, runs buccally between disto-buccal cusp and distal cusp
  • Supplemental Grooves: Numerous on occlusal surface

Clinical Considerations

  • Malocclusion: Used with maxillary first molar to classify according to Angle's classification
  • Orthodontic Anchorage: Two strong roots provide anchorage
  • Caries:
    • Most common tooth to have caries
    • First permanent tooth to erupt, exposed to bacteria longest
    • Numerous grooves and pits for food lodgment
  • Endodontic Procedures: Mesial root usually has 2 root canals (mesio-buccal and mesio-lingual)