Dental Hygiene – Molar Anatomy

Functions of Molars

• Mastication: primary grinding teeth of the dentition.
• Maintain vertical dimension of the face—prevent over-closure of jaws.
• Preserve arch continuity → ensures proper alignment/occlusion of posterior teeth.
• Provide facial esthetics by supporting the cheeks.

General Molar Class Traits (All Permanent Molars)

• Develop from 3\text{–}5 lobes → produce 3\text{–}5 major cusps.
• Crown proportions
  • Mesiodistal width > occlusocervical height (molars appear “wider than tall”).
  • Shorter occlusocervically than any other permanent crowns.
• Marginal ridge hierarchy: distal marginal ridge set more cervically than mesial → better visualization from distal viewpoint.
• Heights of contour
  • Buccal: cervical third.
  • Lingual: middle third.
• Proximal contacts
  • Mesial: at the junction of occlusal & middle thirds.
  • Distal: within middle third.

Contact Areas & Embrasure Patterns (Posterior Progression)

• Proximal contacts move cervically: incisal → middle thirds as you proceed posteriorly.*
• Occlusal view
  • Contacts positioned slightly facial → lingual embrasure space becomes larger than buccal.
    *Exception(s) noted in specialized literature but not elaborated in transcript.

Mandibular Molars — Arch-Specific Traits

• Roots: "double-rooted"—one mesial, one distal.
• Crown exhibits lingual tilt (shared with mandibular premolars).
• Lingual cusps taller & suffer less wear than buccal cusps.
• Crown dimensions: mesiodistal width > buccolingual width (opposite of maxillary molars).
• CEJ pattern
  • Mesial: curves occlusally.
  • Distal, buccal, lingual: comparatively flat.
• Buccal pit commonly terminates main buccal groove.
• Marginal ridge grooves
  • Mesial: present ~50\% of time.
  • Distal: present ~33\% of time.
• Fossae present: central fossa plus mesial & distal triangular fossae.
• Supplemental grooves/ridges may exist but are unnamed.

Mandibular First Molar — Type Traits

• Root morphology
  • Short root trunk → early furcation.
  • Roots widely separated; mesial root broad with two canals; mesial root curves mesially then distally.
• Occlusal outline: pentagon.
• Cuspal anatomy
  • Total 5 cusps: 3 buccal (MB, DB, D) & 2 lingual (ML — largest, DL).
  • Fifth (distal) cusp congenitally absent ~20\% of cases.
• Groove pattern
  • Two buccal grooves (MB, DB) meet central groove.
  • Additional grooves: central, lingual, mesial marginal ridge.
• Fossae: central plus mesial & distal triangular fossae.

Mandibular Second Molar — Type Traits

• Longer root trunk; roots straighter & may tilt distally; overall root spread diminished ("pliers" closer together).
• Mesial root still broad; lingual cusps tall.
• Occlusal outline: rectangle.
• Cuspal anatomy: 4 cusps (MB, DB, ML, DL); ML remains tallest.
• Groove pattern: central, buccal, lingual intersect to form classic + configuration.
• Identifying cervical ridge on MB cusp (buccal prominence).

Mandibular Molar Roots & Concavities

• Mesial root: pronounced mesial & deeper distal longitudinal depressions.
• Distal root: mesial depression present; distal surface variable.
• Concavities on inner (inter-radicular) surfaces often deeper than outer surfaces—critical for dental hygiene instrumentation.
• First molar vs. second
  • First: shorter root trunk & greater root divergence; mesial root more curved.

Maxillary Molars — Arch-Specific Traits

• Trifurcated root system: one palatal (broadest) and two buccal roots (MB & DB).
• Lingual cusps taller than buccal; crowns centered over roots (no lingual tilt).
• Crown dimensions: buccolingual width > mesiodistal width (rhomboidal outline).
• Oblique ridge travels ML → DB cusp.
• CEJ typically curves more on mesial surface.

Maxillary First Molar — Type Traits

• Roots widely spread with short root trunk; trifurcation located within cervical to middle thirds.
• Cuspal anatomy
  • 5 cusps: MB, DB, ML, DL, and supplemental Cusp of Carabelli on ML (present \approx70\%; size highly variable).
• Crown tapers buccally (appears fuller lingually due to large lingual cusps).
• Grooves
  • Central, buccal (less extensive than mandibular), lingual, distal oblique; occasional marginal ridge grooves.
• Fossae
  • Central fossa; mesial & distal triangular fossae; distal cigar-shaped fossa along distal oblique groove (absent on 3-cusp variant).

Maxillary Second Molar — Type Traits

• Root trunk longer; roots less divergent.
• Possible cusp arrangements
  1. Rhomboid (4-cusp) form—no Carabelli.
  2. Heart-shaped (3-cusp) form—DL cusp absent.
• Crown tapers lingually (opposite of first molar’s taper).
• Dimensions: buccolingual > mesiodistal.
• Grooves: central & buccal present; distal oblique persists only in 4-cusp variety.
• Fossae: central, mesial triangular, distal triangular; distal cigar-shaped fossa appears only when DL cusp present.

Maxillary Molar Roots — Comparative Notes

• First molar: shorter trunk, greater spread, & largest palatal ("banana-shaped") root; MB root larger than DB root (visible from distal view).
• Second molar: longer trunk; roots converge distally.

Ridges, Grooves & Fossae of Maxillary Molars (Consolidated)

• Standard features: oblique ridge (ML → DB), distal oblique groove & distal fossa.
• 3-cusp (“heart-shaped”) maxillary molars lack DL cusp, oblique ridge, and distal fossa.

Root Depressions (Maxillary Specific)

• Palatal root: longitudinal depression on lingual surface.
• Mesiobuccal root: distinct mesial depression; distal surface variable.
• Distobuccal root: depression variable/absent mesially; none distally.
• Distal root-trunk concavity present between CEJ & DB furcation.

Cusp of Carabelli — Clinical Variations

• Present on ~70\% of first molars.
• May manifest as full cusp, tubercle, groove, pit, or shallow depression.
• Occasionally enlarged; can shift lingual height of contour into occlusal third (clinical plaque trap).

Enamel Extensions

• Cervical enamel projections occasionally extend from CEJ toward root furcation; predispose sites to periodontal issues.