Tooth Morphology Part 5: Molars – Cusps, Ridges, and Occlusal Maps

Molars are the true workhorses of mastication, bearing the brunt of chewing forces with their broad occlusal surfaces and complex cusp patterns. This chapter explores the differences between maxillary and mandibular molars, with particular attention to cusp number, ridge formation, and root configuration. All references follow the FDI numbering system.

Comparative image of upper and lower molars showing cusps and roots — A comparative illustration of upper and lower molars, highlighting occlusal complexity and root configuration

🔢 FDI Numbers for Molars

Maxillary: 16 (1st), 17 (2nd), 18 (3rd)
Mandibular: 36 (1st), 37 (2nd), 38 (3rd)

📍 Occlusal Anatomy Highlights

Maxillary 1st molar: Usually has 4 major cusps and a possible 5th (cusp of Carabelli), with 3 roots
Mandibular 1st molar: Typically has 5 cusps (3 buccal, 2 lingual) and 2 roots
2nd molars: Show reduced cusp size and more symmetry than 1st molars

The oblique ridge connects the mesiolingual and distobuccal cusps; the transverse ridge links mesial cusps

📊 Maxillary vs Mandibular Molars

Feature	Maxillary Molars	Mandibular Molars
Number of Roots	3 (2 buccal, 1 palatal)	2 (1 mesial, 1 distal)
Cusp Pattern	Rhomboidal, with oblique ridge	Rectangular or pentagonal, with 4 or 5 cusps
Prominent Features	Oblique ridge, cusp of Carabelli	5th distal cusp (on 1st molar), Y-shaped grooves
Root Divergence	More flared	More parallel
Occlusal Surface	More complex and asymmetrical	More symmetrical (especially in 2nd molars)

20250423 1227 Occlusal Molar Comparison simple compose 01jsgayp69fgeatfjbpxvmvqss

Diagram comparing 5-cusp and 4-cusp mandibular molar anatomy — The mandibular first molar typically has five cusps, while the second molar shows a more symmetrical 4-cusp layout

🧠 Clinical Considerations

Restoration: Oblique ridges in maxillary molars require preservation during cavity preparation
Endodontics: Root anatomy complexity affects canal negotiation and shaping
Occlusion: Molars support vertical dimension and handle occlusal load distribution

🌟 Summary: Key Points to Remember

Maxillary molars have 3 roots and feature oblique ridges and occasional accessory cusps
Mandibular 1st molars have 5 cusps and Y-groove patterns, while 2nd molars are more symmetrical
Molars are critical in mastication, load-bearing, and maintaining arch integrity

From archived insight to open reflection – a living note of science and thought.

Next up: Part 6 – Primary vs Permanent Teeth: how to tell them apart at a glance.