Digestive system · Head and neck
Lower right first molar !
The lower right first molar (tooth 46) is a large back tooth that comes in around age 6; it does much of the chewing.
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What it is
A large back tooth with a broad chewing surface of five cusps (three on the cheek side, two on the tongue side) and 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 46, lower right first molar: 2 roots (mesial and distal); first permanent tooth to erupt; key to the bite (occlusion); erupts at about 6–7 years; nerve: inferior alveolar nerve (V3)
Relations
- In front
- The lower right second premolar
- Behind
- The lower right second molar
- Above
- Meets the upper right second premolar and the upper right first molar
- Below
- Inferior alveolar canal with the inferior alveolar nerve, artery and vein
How to find it
The five-cusped tooth sixth from the midline on the lower right; it comes in at about 6 years behind the primary second molar, often unnoticed because no tooth falls out.
On imaging
Bitewing radiographs reveal decay hidden in its contacts and fissures; periapicals show its two roots, the furcation and the apices against the canal below.
Common problems
- Tooth decay (caries) often starts in the grooves of the chewing surface.
Clinical notes
- It replaces no tooth and is often mistaken for a baby tooth, so decay in its deep grooves can go unnoticed in children
- When it is lost early, the second molar tips forward into the gap and the opposing upper teeth drift down
- Molar-incisor hypomineralisation often affects this tooth: soft, discoloured enamel that crumbles and decays early
Anatomical variants
- A third root on the distolingual side (radix entomolaris) is a recognised variant, seen more often in people of East Asian ancestry
Development
No primary predecessor: it grows from a backward extension of the dental lamina and begins to calcify around birth, so disturbances in the first months of life can show in its enamel.
Memory aid
Lower eruption order: 6-1-2-3-4-5-7-8 (the first molar and the central incisor often come in together). Compare the upper arch, where the canine comes after the premolars.
Related conditions
Test yourself
Think of the answer, then tap the question to see it.
Where does the mesiobuccal cusp of the upper right first molar sit on the lower right first molar in Angle Class I occlusion?
In the buccal groove of the lower right first molar.
What happens when the lower right first molar is lost early?
The second molar tips forward into the gap and the opposing upper teeth drift down.
Why can decay of the lower right first molar go unnoticed in children?
It replaces no tooth and is often mistaken for a baby tooth, so decay in its deep grooves is missed.
Which permanent molar is the usual target of fissure sealants in children?
The first permanent molar, such as the lower right first molar, soon after it erupts at about 6 years.
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.
