[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) › Lower left first molar [Digestive system](https://durgical.com/en/anatomy/system/digestive-system/) · [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) # Lower left first molar The lower left first molar (tooth 36) is a large back tooth that comes in around age 6; it does much of the chewing. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=head_neck&select=teeth_36&side=r) Opens in the Durgical app, no sign-up needed. ## 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 points - 5 cusps (3 buccal, 2 lingual) and usually 3 canals: 2 in the mesial root and 1, sometimes 2, in the distal root - An [inferior alveolar nerve](https://durgical.com/en/anatomy/inferior-alveolar-nerve/) block numbs the tooth, but the buccal gum needs the buccal nerve, and accessory fibres (for example from the mylohyoid nerve) can explain a failed block - Its deep pits and fissures make it highly prone to decay; it is the main target for fissure sealants soon after it erupts ## Key facts **Joints with** Alveolar socket of the mandible (gomphosis held by the periodontal ligament); bites against the opposing teeth **Landmarks** FDI 36, lower left 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 left second premolar](https://durgical.com/en/anatomy/lower-left-second-premolar/) **Behind** The [lower left second molar](https://durgical.com/en/anatomy/lower-left-second-molar/) **Above** The [upper left second premolar](https://durgical.com/en/anatomy/upper-left-second-premolar/) and the [upper left first molar](https://durgical.com/en/anatomy/upper-left-first-molar/) **Below** Inferior alveolar canal, running below its roots inside the [mandible](https://durgical.com/en/anatomy/mandible/) **Medial** [Tongue](https://durgical.com/en/anatomy/tongue/); its root tips usually lie above the [mylohyoid](https://durgical.com/en/anatomy/mylohyoid-muscle/) line ## How to find it Sixth tooth from the midline on the lower left, the largest lower tooth, with five cusps; the first permanent tooth to appear, at about 6 years. ## On imaging Bitewings show decay at its contacts and in deep fissures under sealants or fillings. Periapicals show the furcation between its two roots, and a panoramic film its distance to the inferior alveolar canal. ## Common problems - Tooth decay (caries) often starts in the grooves of the chewing surface. ## Clinical notes - The area where its two roots divide (furcation) is exposed early in periodontitis and is a classic site of bone loss - Mulberry molars, small first molars with crowded rounded cusps, are a dental sign of congenital syphilis ## Anatomical variants - A third, distolingual root (radix entomolaris) is a known variant, more frequent in people of East Asian ancestry ## Development No predecessor: it erupts behind the primary second molar. It is the first permanent tooth to begin hardening (calcifying), around birth. ## Related conditions - [Dental caries](https://durgical.com/en/conditions/dental-caries/) - [Periodontitis](https://durgical.com/en/conditions/periodontitis/) ## Test yourself Think of the answer, then tap the question to see it. ## How many cusps and canals does the lower left first molar usually have? 5 cusps (3 buccal, 2 lingual) and 3 canals: 2 in the mesial root and 1, sometimes 2, in the distal root. ## Why can an inferior alveolar nerve block fail to fully numb the lower left first molar? Accessory fibres, for example from the mylohyoid nerve, may supply it; the buccal gum also needs the buccal nerve. ## What is radix entomolaris? A third, distolingual root of the lower first molar, more frequent in people of East Asian ancestry. ## Why is the lower left first molar a main target for fissure sealants? Its deep pits and fissures make it one of the teeth most prone to decay soon after it erupts. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/lower-left-first-molar/) Educational information, not medical advice. For any symptom, see a health professional. ## Related - [Mandible](https://durgical.com/en/anatomy/mandible/) Sources: [Anatomy, Head and Neck, Teeth](https://www.ncbi.nlm.nih.gov/books/NBK557543/); [Anatomy, Permanent Dentition](https://www.ncbi.nlm.nih.gov/books/NBK570590/); [Anatomy, Head and Neck, Tooth Eruption](https://www.ncbi.nlm.nih.gov/books/NBK549878/); [Anatomy, Head and Neck: Alveolar Nerve](https://www.ncbi.nlm.nih.gov/books/NBK546712/); [23.3 The Mouth, Pharynx, and Esophagus](https://openstax.org/books/anatomy-and-physiology-2e/pages/23-3-the-mouth-pharynx-and-esophagus) (OpenStax (Rice University), 2022) · adapted, [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/lower-left-first-molar/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/lower-left-first-molar/