Maxillary First Molar

General Information

• 6th tooth from the midline
• FDI Numbering System: 1 6 (right), 2 6 (left)
• Universal Numbering System: 3 (right), 14 (left)
• Zsigmondy-Palmer System: 6 with quadrant brackets
• Eruption: First permanent tooth to erupt in the arch, posterior to the 2nd deciduous molar at around 6 years of age.
• Not a succedaneous tooth (no primary predecessor)
• Location: Approximately middle of fully grown jaw antero-posteriorly, known as the 'Cornerstone'.
• Strength: Strongest tooth in the arch.

Anatomy and Characteristics

• Cusps: 4 well-formed cusps and a 5th supplemental cusp (Cusp of Carabelli)
• Roots: 3 roots (lingual, mesiobuccal, distobuccal)
• Development: Formed from 5 developmental lobes (one lobe per cusp)
• Function: Grinding

Measurements

• Crown cervico-occlusal length: 7.5 mm
• Buccal roots length: 12 mm
• Lingual root length: 13 mm
• Crown mesio-distal diameter: 10 mm
• Cervix mesio-distal diameter: 8 mm
• Crown bucco-lingual diameter: 11 mm
• Cervix bucco-lingual diameter: 10 mm
• Cervical line curvature: 1 mm on mesial side, flat on distal side

Morphology (5 Aspects)

Buccal Aspect

• Crown shape: Trapezoidal (shorter side cervically, longer side cusps)
• Visible cusps: Mesio-buccal (larger), Disto-buccal (sharper, right angle), parts of Mesio-lingual and Disto-lingual
• Contact areas:
  • Mesial: Junction of occlusal third and middle third
  • Distal: Middle of middle third
• Crown outline:
  • Distal is more convex
  • More distal surface visible due to rhomboidal occlusal shape (obtuse disto-buccal line angle)
• Cervical line: Irregular/slightly convex toward the root
• Buccal developmental groove: Middle of buccal surface, terminates halfway from cervical line, with faint concavities
• Roots visibility: All three roots visible, with bifurcation at 4 mm from cervical line

Lingual Aspect

• Crown shape: Similar to buccal
• Visible cusps: Mesio-lingual (larger, obtuse angle), Disto-lingual (spherical), 5th cusp not visible
• Lingual developmental groove: Between lingual cusps, runs cervically
• Roots visibility: All three roots visible, larger lingual root in front

Mesial Aspect

• Crown shape: Trapezoidal (shorter side towards cusps)
• Visible cusps: Mesio-lingual, Mesio-buccal, 5th cusp
• Buccal outline: Generally convex, height of contour in cervical third
• Lingual outline: Smoothly convex, height of contour in middle third
• Cervical line: Convex towards the crown
• Mesial marginal ridge: Occlusal third, confluent with mesio-buccal and mesio-lingual cusp ridges
• Roots visibility: Lingual and Mesio-buccal roots
• Bifurcation: More cervical, mesio-buccal root 2/3rd width of root trunk, lingual root 'banana-like'

Distal Aspect

• Crown shape: Similar to mesial
• Visible cusps: Disto-buccal, Disto-lingual
• Distal marginal ridge: More cervical, triangular ridges on occlusal surface visible
• Roots visibility: All three roots, disto-buccal root narrowest at base
• Bifurcation: More apical, at 5 mm from cervical line