Occlusal Aspect of Maxillary First Molar

Cusps Visibility

• All five cusps visible
  • Mesolingual cusp: Largest
  • Mesobuccal cusp: Second largest
  • Distolingual cusp: Third largest
  • Distobuccal cusp: Fourth largest
  • Fifth cusp (Cusp of Carabelli): Smallest
    • Named after George Carabelli

Crown Outline

• Shape: Rhomboidal
  • Acute angles at mesiobuccal and distolingual cusps
  • Obtuse angles at mesiolingual and distobuccal cusps
• Dimensions:
  • Mesiodistal: Larger in lingual half than buccal half
  • Buccolingual: Larger in mesial half than distal half

Cusps Classification

• Primary cusps: Form the primary cusp triangle
  • Mesiolingual cusp
  • Mesiobuccal cusp
  • Distobuccal cusp
• Secondary cusps
  • Distolingual cusp (becomes smaller from 1st to 3rd molar)
  • Fifth cusp (Cusp of Carabelli)

Ridges and Features

• Cuspal ridges: Each functional cusp has two (mesial and distal)
• Marginal ridges
  • Mesial marginal ridge: Mesial outline
  • Distal marginal ridge: Distal outline
• Triangular ridges: Four total, one for each functional cusp
  • Unions:
    • Transverse ridge: Mesolingual "+" mesobuccal
    • Oblique ridge: Distobuccal "+" distal ridge of mesiolingual
      • Unique to maxillary molars

Fossae

• Major fossae:
  • Central fossa: Triangular, mesial to oblique ridge
  • Distal fossa: Linear, distal to oblique ridge
• Minor fossae:
  • Mesial triangular fossa: Near mesial marginal ridge
  • Distal triangular fossa: Near distal marginal ridge

Pits and Grooves

• Central developmental pit: Bottom of central fossa
• Grooves
  • Buccal developmental groove: From central pit buccally
  • Central developmental groove: From central pit mesially to mesial triangular fossa
  • Distal oblique developmental groove: From distal triangular fossa, turns lingually
  • Lingual developmental groove: Continuation of distal oblique groove onto lingual surface
  • Fifth cusp groove: Formed by cusp of Carabelli
  • Additional transverse groove: Across oblique ridge (in some teeth)
  • Supplemental grooves: Numerous on occlusal surface

Clinical Considerations

• Malocclusion Classification: Maxillary and mandibular first molars (Engel's classification)
• Orthodontic Anchorage: Three strong roots
• Forensic Identification: Cusp of Carabelli's variation
  • Well-developed in Mongoloid and Negroid races
  • Viewed as developmental anomaly by some researchers
• Endodontic Procedures: Mesio-buccal root often has two canals (MB1, MB2)