Premolars in Maxilla and Mandible

Overview

• Types: 1st premolar and 2nd premolar
• Present in both maxilla and mandible
• Known as bicuspids (though not ideal for mandibular premolars)

General Features

• Maxillary Premolars:
  • Crown shape similar
  • 1st premolar has 2 roots
  • Develop from 4 developmental lobes
• Mandibular Premolars:
  • Crown shapes differ
  • 1st premolar has only one functional cusp, 2nd premolar typically has 3 cusps
  • Both premolars have the same number of roots
  • 1st premolar develops from 4 lobes, 2nd from 5 lobes

Measurements

• Maxillary vs. Mandibular:
  • Overall similar in dimensions
  • Maxillary premolars larger buccolingually
• Within the Same Arch:
  • Maxillary: Both premolars appear equal in size, but 1st premolar larger due to 2 roots
  • Mandibular: 2nd premolar larger, mainly due to 3 cusps

Morphological Differences

Buccal Aspect

• Mandibular:
  • Buccal cusp tip lies mesial
  • Disto-buccal cuspal slope longer
• Maxillary:
  • 1st premolar: Buccal cusp tip distal
  • 2nd premolar: Buccal cusp tip mesial
  • 1st premolar: Mesio-buccal cuspal slope longer
  • 2nd premolar: Disto-buccal cuspal slope longer

Lingual Aspect

• Size of Lingual Cusps:
  • Smaller in mandibular premolars
  • More of the occlusal surface visible in mandibular premolars
• Developmental Grooves:
  • Mandibular: 1st premolar has a mesio-lingual groove, 2nd premolar has a lingual groove
  • Maxillary: No grooves

Mesial Aspect

• Outline Form:
  • Trapezoidal in maxillary premolars
  • Rhomboidal in mandibular premolars
• Lingual Tilt: Present in mandibular, not in maxillary
• Cusp Confines:
  • Maxillary: Cusps within root confines
  • Mandibular: Lingual cusp outside root outline
• Marginal Ridge:
  • Maxillary: Horizontal
  • Mandibular: 2nd premolar horizontal, 1st premolar oblique

Distal Aspect

• Similar to mesial aspect for both maxillary and mandibular premolars

Occlusal Aspect

• Maxillary:
  • 1st premolar: Hexagonal
  • 2nd premolar: Oval
• Mandibular:
  • 1st premolar: Diamond-shaped
  • 2nd premolar: Squarish
• Cusp Distance:
  • Maxillary: Buccal and lingual cusps equidistant from the center
  • Mandibular: Buccal cusp nearer to the center
• Triangular Fossae:
  • Maxillary: Mesial and distal
  • Mandibular: 2nd premolar has triangular fossae, 1st premolar has linear and circular fossae
• Central Developmental Groove: Present in maxillary, absent in mandibular