Digestive system · Head and neck
Lower left second molar !
The lower left second molar (tooth 37) is the back tooth behind the first molar that comes in around age 12; it grinds food.
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What it is
A large back tooth behind the first molar, with two roots.
What it does
Grinds food before swallowing.
Key facts
- Joints with
- Alveolar socket of the mandible (gomphosis held by the periodontal ligament); bites against the opposing teeth
- Landmarks
- FDI 37, lower left second molar: 2 roots; erupts behind the first molar around age 12; erupts at about 11–13 years; nerve: inferior alveolar nerve (V3)
Relations
- In front
- The lower left first molar
- Behind
- The lower left third molar
- Above
- The upper left first molar and the upper left second molar
- Below
- Inferior alveolar canal, closer to these roots than to the first molar's
- Medial
- Tongue; its root tips usually lie below the mylohyoid line
How to find it
Seventh tooth from the midline on the lower left, between the first and third molars; four cusps meet at a cross-shaped groove.
On imaging
A panoramic film shows its roots close to the inferior alveolar canal and any third molar leaning on it; bitewings show decay on its back surface caused by that contact.
Common problems
- Tooth decay (caries) in the grooves of the chewing surface.
Clinical notes
- Inferior alveolar nerve block; the lingual nerve, numbed by the same injection, supplies its lingual gum
- An abscess from roots below the mylohyoid line spreads into the submandibular space and, when both sides are involved, can be part of Ludwig's angina
Anatomical variants
- C-shaped canal: the roots join into one horseshoe-shaped root, a known variant of the lower second molar that is more frequent in East Asian populations
Development
No primary predecessor: it erupts behind the first molar near the end of the mixed dentition.
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
What is the cusp pattern of the lower left second molar?
4 cusps of nearly equal size divided by a cross-shaped groove.
Where does an abscess from the roots of the lower left second molar spread, and which serious infection can it be part of?
Below the mylohyoid line into the submandibular space; when both sides are involved it can be part of Ludwig's angina.
How can an impacted lower third molar harm the lower left second molar?
Leaning against its back surface, it can cause hidden decay or root resorption there.
Which radiograph shows decay on the back surface of the lower left second molar from an impacted third molar?
A bitewing, with a panoramic film to show the impacted tooth.
Educational information, not medical advice. For any symptom, see a health professional.
Related
Sources: Anatomy, Head and Neck, Teeth; Anatomy, Permanent Dentition; Anatomy, Head and Neck, Tooth Eruption; Anatomy, Head and Neck: Alveolar Nerve; 23.3 The Mouth, Pharynx, and Esophagus (OpenStax (Rice University), 2022) · adapted, CC BY 4.0.
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Representative model, for educational purposes only.
