Summary of Permanent mandibular First premolar

Summary of the Video: Permanent mandibular first premolar

Main Ideas and Concepts

• Identification and Numbering:
  • Permanent mandibular first premolar is the 4th tooth from the midline.
  • Tooth numbering systems:
    • FDI system: 3 4 (left) and 4 4 (right)
    • Universal system: 21 (left) and 28 (right)
    • Zsigmondy-Palmer system: 4 with quadrant brackets
• Development and Lobes:
  • Develops from 4 developmental lobes:
    • Buccal lobe → Buccal cusp (functional cusp)
    • Mesial lobe → mesial marginal ridge
    • Distal lobe → distal marginal ridge
    • Lingual lobe → Lingual cusp (very small, poorly developed)
  • Lingual cusp is non-functional as it does not contact the opposite arch.
  • The term “bicuspid” is a misnomer here, as only one cusp is functional.
• Eruption and Dimensions:
  • Eruption age: 10 to 12 years
  • Crown length: 8.5 mm
  • Root length: 14 mm
  • Mesiodistal crown diameter: 7 mm (crown), 5 mm (cervix)
  • Buccolingual crown diameter: 7.5 mm (crown), 6.5 mm (cervix)
  • Cervical line curvature: 1 mm convex on mesial side, flat on distal side

Morphological Features by Aspect

• Buccal Aspect:
  • Crown shape: trapezoidal (longer side toward cusp, shorter side toward root)
  • Only Buccal cusp visible; Lingual cusp hidden behind
  • Buccal cusp tip is slightly mesial to midline axis
  • Distal cuspal slope longer than mesial cuspal slope
  • Contact areas (mesial and distal) located in the middle third of the crown
  • Mesial and distal outlines slightly concave
  • Cervical line convex toward root
  • Prominent buccal ridge from cusp tip to cervical line
  • Single, smooth, conical root
• Lingual Aspect:
  • Both buccal and lingual cusps visible
  • Lingual cusp tip aligned with Buccal cusp tip
  • Lingual cusp narrower and much smaller → marked lingual convergence
  • Mesial and distal surfaces visible due to convergence
  • Occlusal landmarks visible: mesial and distal marginal ridges, buccal triangular ridge
  • Mesial and distal fossae partially visible
  • Mesio-lingual developmental groove present between mesial marginal ridge and Lingual cusp
• Mesial Aspect:
  • Crown outline: rhomboidal (common to all mandibular posterior teeth)
  • Both cusps visible; Lingual cusp ~2/3 height of Buccal cusp
  • Buccal cusp tip reaches midline; Lingual cusp tip aligns with lingual root border
  • Buccal and lingual outlines convex (buccal more so)
  • Buccal and lingual triangular ridges meet above mesio-lingual groove
  • Mesial marginal ridge slants, nearly parallel to buccal triangular ridge, ends at mesio-lingual groove
• Distal Aspect:
  • Similar rhomboidal outline
  • Distal marginal ridge higher and more horizontal than mesial marginal ridge
  • Less occlusal surface visible from distal view
  • No developmental groove on distal side
• Occlusal Aspect:
  • Crown outline: diamond-shaped due to sharp lingual convergence
  • Large Buccal cusp centrally located; small Lingual cusp near lingual outline
  • Cuspal ridges: each cusp has mesial and distal cuspal ridges
  • Two triangular ridges: buccal (longer) and lingual (smaller)
  • Two marginal ridges: mesial and distal
  • Two fossae: mesial (linear) and distal (circular), not triangular fossae
  • Grooves:
    • Mesial developmental groove in mesial fossa, joins mesio-lingual groove
    • Distal developmental groove in distal fossa
    • Supplementary grooves may be present

Clinical Considerations

• Crown’s rhomboidal shape and lingual tilt require careful consideration during restorative procedures.
• Though normally having a single root and root canal, the mandibular first premolar exhibits many root canal variations.
• Root canal treatment can be challenging, earning the nickname “Endodontist’s enigma.”

Methodology / Key Points for Identification and Study

Recognize tooth position and numbering in different systems.

Category

Educational

Video