The mandibular first molars are the largest teeth in the lower jaw (Universal 30 on the right and 19 on the left, FDI 46 and 36). Each has five cusps, three on the cheek side and two on the tongue side, and two well-separated roots, mesial and distal, with the mesial root usually holding two canals. They erupt at about 6-7 years and are among the first permanent teeth to appear.
| Location | Lower dental arch, behind the second premolar on each side |
|---|---|
| Parts |
|
| Nerve Supply | Inferior alveolar nerve (mandibular division of the trigeminal nerve); Buccal nerve (buccal gingiva); Lingual nerve (lingual gingiva) |
| Blood Supply | Inferior alveolar artery (from the maxillary artery) |
| Venous drainage |
|
| Lymphatic drainage |
|
Grind food and bear much of the chewing force; their position sets the molar relationship of the bite.
Because they erupt so early and have deep fissures, lower first molars are the permanent teeth most often decayed, filled and lost, and they are a priority for fissure sealants. Their roots lie above the inferior alveolar canal, and a numbing injection near the mandibular foramen (inferior alveolar nerve block) is used to anaesthetise them. Infection here can spread to the floor of the mouth or the buccal space.
Decay in the deep fissures soon after eruption, the commonest site of decay in the permanent teeth.
Infection of the pulp spreading to the root tips, causing pain, swelling and sometimes facial abscess.
Soft, discoloured enamel on the first permanent molars that breaks down and decays quickly.
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