Permanent Molars Review

Module Four: Permanent Molars Overview

General Molar Characteristics

• Number: There are 12 permanent molars in total (6 maxillary and 6 mandibular).
• Size and Shape: They are the largest and boxiest teeth in the dentition.
• Eruption Sequence:
  • They erupt after all deciduous teeth have erupted. They are non-succedaneous teeth (meaning they do not replace primary teeth).
  • Usually, the first permanent tooth to erupt is a molar (specifically, the first permanent molar), located posterior to the primary second molar.
  • The permanent mandibular central incisor usually erupts right after the first permanent molar.
• Developmental Features:
  • Each cusp typically represents one developmental lobe.
  • The occlusal surface is dominated by four main cusps: Mesiobuccal (MB), Mesiolingual (ML), Distobuccal (DB), and Distolingual (DL).
  • A fifth cusp, if present, is usually a supplemental cusp and may or may not be located on the occlusal surface.

Eruption and Development of Molars (Non-Succedaneous Teeth)

Maxillary Molars: General Characteristics

• Cusps and Lobes:
  • Typically have 5 cusps and 5 lobes of development.
  • 3 major cusps on the occlusal surface: MB, ML, DB. These form the Primary Cusp Triangle.
  • 1 minor cusp on the occlusal surface: DL.
  • 1 supplemental cusp: The Cusp of Carabelli, located on the lingual side of the ML cusp. It is almost always visible on the first maxillary molar.
• Roots:
  • Possess 3 roots: Mesiobuccal (MB), Distobuccal (DB), and Lingual (LI).
  • There are 3 root furcation openings:
    • Direct facial accessibility.
    • Mesial interproximal accessibility (from the Mesiolingual aspect).
    • Distal interproximal accessibility (from the Distolingual aspect).

Maxillary First Molar

• Developmental Lobes: Possesses 5 lobes of development, including the Cusp of Carabelli.
• Occlusal Outline: Square or rhomboid in shape.
• Cusp Configuration:
  • 4 cusps on the occlusal surface and 1 supplemental cusp (Cusp of Carabelli) on the ML cusp.
  • The DL cusp is the most developed on the maxillary first molar compared to subsequent maxillary molars.
• Roots and Pulp Horns: Has 3 roots and 4 pulp horns. The roots are typically widely separated.
• Nomenclature:
  • Universal Numbering System: 3 (right) and 14 (left).
  • FDI World Dental Federation Notation: 16 (right) and 26 (left).
  • Palmer Notation: _6 (right) and 6_ (left).
• Height of Contour (HOC) / Contact Area:
  • Proximal (Mesial/Distal) HOC/Contact Area: Middle third.
  • Facial (Buccal) HOC: Cervical 1/3.
  • Lingual HOC: Middle 1/3.

Specific Anatomy of Maxillary First Molar

• Cusp Characteristics:
  • The MB cusp is broader than the DB cusp.
  • The ML cusp is the tallest and bears the Cusp of Carabelli on its lingual surface.
  • The DL cusp is the smallest cusp.
• Oblique Ridge: A prominent ridge running from the ML cusp to the DB cusp, which isolates the DL cusp. A transverse groove usually crosses this oblique ridge.
• Mesial Side Dominance: The mesial side of the tooth is usually dominant.
• Fossae: Features a Central Fossa and a Distal Fossa, each typically containing a pit.
• Developmental Grooves: Possesses 3 main developmental grooves:
  • Central Groove: Runs from the Mesial Marginal Ridge (MMR) to the Distal Marginal Ridge (DMR) across the occlusal surface.
  • Buccal Groove: Extends from the central groove, crosses over onto the buccal surface, and is visible from both occlusal and buccal views.
  • Distolingual/Lingual Groove: Originates from the central groove on the distal side of the tooth, defines the DL cusp, and crosses over the occlusal onto the lingual surface toward the distal.

Root Trunk: Definition

• The root trunk is defined as the area extending from the Cementoenamel Junction (CEJ) to the opening of the furcation of the root. It is analogous to the trunk of a tree before its branches (roots) diverge.

Maxillary Second Molar

• Developmental Lobes: Typically has 4 lobes of development. The Cusp of Carabelli is usually absent.
• Nomenclature:
  • Universal Numbering System: 2 (right) and 15 (left).
  • FDI World Dental Federation Notation: 17 (right) and 27 (left).
  • Palmer Notation: _7 (right) and 7_ (left).
• Occlusal Outline: Less square or rhomboid than the first molar.
• Cusp Configuration:
  • Possesses 4 cusps on the occlusal surface.
  • The DL cusp is much smaller on the maxillary second molar compared to the first molar.
• Roots and Pulp Horns: Has 3 roots and 4 pulp horns. The roots are closer together than those of the first molar.
• Height of Contour (HOC) / Contact Area:
  • Proximal (Mesial/Distal) HOC/Contact Area: Middle third.
  • Facial (Buccal) HOC: Cervical 1/3.
  • Lingual HOC: Middle 1/3.
• Occlusal Anatomy: Shares the same general occlusal anatomy as the first molar, but features are less prominent.

Maxillary Third Molar

• Developmental Lobes: Typically has 4 lobes of development. The Cusp of Carabelli is usually absent.
• Nomenclature:
  • Universal Numbering System: 1 (right) and 16 (left).
  • FDI World Dental Federation Notation: 18 (right) and 28 (left).
  • Palmer Notation: _8 (right) and 8_ (left).
• Occlusal Outline: More heart-shaped than the first and second molars.
• Cusp Configuration:
  • Features 3 to 4 cusps on the occlusal surface.
  • The DL cusp is usually missing on the maxillary third molar.
• Roots and Pulp Horns: Has 3 roots and 4 pulp horns. The roots are usually fused together or are very close.
• Height of Contour (HOC) / Contact Area:
  • Proximal (Mesial/Distal) HOC/Contact Area: Middle third.
  • Facial (Buccal) HOC: Cervical 1/3.
  • Lingual HOC: Middle 1/3.
• Occlusal Anatomy: The occlusal anatomy contains numerous supplemental grooves and often appears indistinct.

Mandibular Molar Characteristics

• Size: They are the largest mandibular teeth.
• Number: There are 3 mandibular molars in each quadrant.
• Function: Primarily involved in chewing and grinding food.
• Size Trend: Similar to maxillary molars, the first mandibular molar is the largest, and molars progressively get smaller as they move posteriorly.
• Crown Dimensions:
  • Crowds are shorter cervico-occlusally but larger in all other dimensions compared to anterior mandibular teeth.
  • Crowds are wider mesiodistally (M-D) than buccolingually (B-L).

Key Differences Between Mandibular and Maxillary Molars

• Roots: Mandibular molars have 2 roots (one Mesial and one Distal).
• Furcations: Furcation openings are found on the direct buccal and direct lingual surfaces.
• Cusps: They typically have 4 major cusps, although the first mandibular molar has a fifth, minor cusp.
• Crown Width: Crowns are wider mesiodistally (M-D) than buccolingually (B-L).
• Cusp Similarity: They feature two buccal cusps that are similar in size and two lingual cusps that are similar in size.

Mandibular First Molar

• Eruption and Root Completion: Erupts at 6-7 years of age, with root completion by 9-10 years.
• Nomenclature:
  • Universal Numbering System: 19 (right) and 30 (left).
  • FDI World Dental Federation Notation: 36 (right) and 46 (left).
  • Palmer Notation: 6_ (right) and \underline{6} (left).
• Roots, Pulp Horns, and Canals: Has 2 roots, 5 pulp horns, and usually 3 root canals (the mesial root typically has 2 canals).
• Eruption and Size: Usually the first permanent tooth to erupt, and it is the largest tooth in the mandibular arch.
• Cusps and Lobes: The only mandibular molar with 5 cusps and 5 developmental lobes:
  • 2 buccal cusps.
  • 2 lingual cusps.
  • 1 minor cusp located on the distal aspect.
• Height of Contour (HOC) / Contact Area:
  • Mesial/Distal (contact area) HOC: Middle third.
  • Buccal/Lingual (BU/LI) HOC: Cervical third on buccal, middle third on lingual.

Mandibular First Molar: Specific Visual Aspects

• Buccal (Facial) Aspect: Features facial grooves, distinct roots, a prominent furcation, a root trunk, and a very prominent Facial HOC.
• Lingual Aspect: Features a lingual groove, roots, furcation, and a root trunk.
• Occlusal Aspect: Characterized by grooves, a central pit, and marginal ridges.

Mandibular First Molar: Cusp Sizing (General Questions for Analysis)

• Identifying the largest cusp.
• Identifying the tallest cusp.
• Presence and configuration of grooves on the occlusal surface.
• Presence of pits on the occlusal surface.
• Presence of a pit on the buccal surface.

Mandibular Second Molar

• Eruption and Root Completion: Erupts at 11-13 years of age, with root completion by 14-15 years.
• Nomenclature:
  • Universal Numbering System: 18 (right) and 31 (left).
  • FDI World Dental Federation Notation: 37 (right) and 47 (left).
  • Palmer Notation: 7_ (right) and \underline{7} (left).
• Roots, Pulp Horns, and Canals: Has 2 roots, 4 pulp horns, and 2 or 3 root canals (the mesial root can have 1 or 2 canals).
• Size: Smaller in all dimensions than the mandibular first molar. Its roots are shorter and positioned closer together.
• Cusps and Lobes: Has 4 cusps and 4 developmental lobes:
  • 2 buccal cusps.
  • 2 lingual cusps.
  • Cusps are almost equal in size.
• Occlusal Configuration: The occlusal surface typically exhibits a + configuration (cruciform pattern) formed by the intersecting grooves.
• Height of Contour (HOC) / Contact Area:
  • Mesial/Distal (contact area) HOC: Middle third.
  • Buccal/Lingual (BU/LI) HOC: Cervical third on buccal, middle third on lingual.

Mandibular Second Molar: Specific Visual Aspects

• Occlusal Aspect: Features grooves, a central pit, and marginal ridges.
• Buccal Aspect: Features grooves, a pit, a furcation, and a root trunk.
• Lingual Aspect: Features grooves, a furcation, and a root trunk.

Mandibular Third Molar

• Nomenclature:
  • Universal Numbering System: 17 (right) and 32 (left).
  • FDI World Dental Federation Notation: 38 (right) and 48 (left).
  • Palmer Notation: 8_ (right) and \underline{8} (left).
• Occlusal Outline: Can vary significantly, resembling either a first or second mandibular molar in shape.
• Cusps and Lobes: May have 4 or 5 cusps and 4 or 5 lobes of development.
• Roots and Pulp Horns: Has 2 roots and 4-5 pulp horns. The roots are usually fused together.
• Height of Contour (HOC) / Contact Area:
  • Proximal (contact area) HOC: Middle third.
  • Facial (FA) HOC: Cervical 1/3.
  • Lingual (LI) HOC: Middle 1/3.
  • Mesiodistal (M-D) HOC (contact area): Middle 1/3.
• Variability: This is the most variable mandibular tooth. It most often resembles the second molar, but typically has more supplemental anatomy on the occlusal surface, a smaller central fossa, and smaller roots. Variability includes factors like overall size, shape, number of cusps, and root morphology (ranging from distinct to completely fused).