Dental Anatomy: Mandibular First Molar

Introduction

• Focus on the mandibular first molar
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Key Features

• Eruption and Caries Risk: Erupts at age 6; prone to caries due to pits and fissures.
• Numbering: Teeth #19 and #30 in the universal numbering system.
• Dimensions: Widest tooth mesio-distally in the mouth.

Facial Aspect

• Roots: Two widespread roots - mesial curves more than distal.
• Cusps: Lingual cusps slightly longer than facial; mesiofacial cusp is largest.
• Grooves and Pits:
  • Only tooth with two grooves on facial surface (facial and distofacial grooves).
  • Facial pit present at end of facial groove.
  • Consider sealant in facial pit to prevent caries.
• Cervical Ridge: Known as the facial height of contour.

Lingual Aspect

• Lingual Groove: Small, almost never fissured, aligned with bifurcation.
• Height of Contour: More prominent to hold tongue back.

Mesial and Distal Aspects

• Mesial Root: Deep root flute, usually has two canals.
• Distal Side: Shorter marginal ridge, flatter cervical line.
• Cusps: Taller lingual cusps, facial aimed for holding.

Occlusal Table

• Pentagon Shape: Resembles a house, disto cusp as the roof.
• Cusp Arrangement: Three facial cusps, two lingual cusps.
• Convergence: Converges lingually and distally.
• Y5 Pattern: Five main cusps and groove forming a 'Y'.

Canals and Pulp

• Pulp Horns: Five pulp horns (one per cusp).
• Root Canals:
  • 65% have three canals (2 mesial, 1 distal).
  • 32% have four canals.
  • 3% have two canals.

Cross Section

• Mid-Root Cross Section:
  • Distal root oval-shaped.
  • Mesial root biconcave/ribbon-shaped.
• Longest molar roots.

Summary Characteristics

• Dimensions: Mesio-distal > facio-lingual > occluso-cervical.
• Patterns: Trapezoidal facial view, rhombus side view, pentagon occlusal view.
• Developmental Lobes & Canals: Five lobes, pulp horns, and typically three canals.

Conclusion

• Part of a Dental Anatomy series with more videos available.
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