Maxillary First and Second Molars

General Features

• Maxillary First Molar
  • 6th tooth from the midline
  • Erupts at age 6
  • Called the 'cornerstone' tooth
• Maxillary Second Molar
  • 7th tooth from the midline
  • Erupts at age 12-13
  • Called the '12-year molar'
• The first molar is generally larger than the second in all dimensions except bucco-lingual

Developmental Lobes

• First Molar: 5 developmental lobes
• Second Molar: 4 developmental lobes
• Cusps:
  • First Molar: 5 cusps
  • Second Molar: 4 cusps

Root Structure

• Both molars have 3 roots each
• First Molar: Roots are more flaring
• Second Molar: Roots have a distal tilt

Buccal Aspect

• Crown outline: Trapezoidal for both
• Similar contact areas, cervical ridges, and buccal developmental grooves
• Roots:
  • First Molar: More flaring
  • Second Molar: Distal tilt

Lingual Aspect

• Both molars share most features
• First Molar: Presence of fifth cusp (Cusp of Carabelli) on mesio-lingual cusp
• Second Molar: No Cusp of Carabelli; Partial disto-buccal cusp
• Roots: Distal tilt in second molar

Mesial Aspect

• First Molar: Fifth cusp on mesio-lingual cusp
• Second Molar: No fifth cusp

Distal Aspect

• No major differences between the two molars

Occlusal Aspect

• Crown outline:
  • First Molar: Rhomboidal
  • Second Molar: Rhomboidal or heart-shaped (depends on disto-lingual cusp size)
• Angle Differences:
  • Second Molar: More acute angles are more acute, obtuse angles are more obtuse
• Functional Cusps: Both have 4
• First Molar: Additional fifth cusp (Cusp of Carabelli)

Order of Cusp Size

• First Molar: Mesio-lingual > Mesio-buccal > Disto-lingual > Disto-buccal
• Second Molar: Mesio-lingual > Mesio-buccal > Disto-buccal > Disto-lingual

Additional Features

• First Molar: Fifth cusp groove; fewer supplementary grooves
• Second Molar: More supplementary grooves