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# Lower right second molar

The lower right second molar (tooth 47) 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 points

- Four almost equal cusps and a cross-shaped (+) groove; 2 roots set close together and often bent backward
- The inferior alveolar canal runs closer to its roots than to those of the first molar

## Key facts

**Joints with**
Alveolar socket of the [mandible](https://durgical.com/en/anatomy/mandible/) (gomphosis held by the periodontal ligament); bites against the opposing teeth

**Landmarks**
FDI 47, lower right second molar: 2 roots; erupts behind the first molar around age 12; erupts at about 11–13 years; nerve: [inferior alveolar nerve](https://durgical.com/en/anatomy/inferior-alveolar-nerve/) (V3)

## Relations

**In front**
The [lower right first molar](https://durgical.com/en/anatomy/lower-right-first-molar/)

**Behind**
The [lower right third molar](https://durgical.com/en/anatomy/lower-right-third-molar/); when that tooth is impacted it often leans against this tooth's back surface

**Above**
Meets the [upper right first molar](https://durgical.com/en/anatomy/upper-right-first-molar/) and the [upper right second molar](https://durgical.com/en/anatomy/upper-right-second-molar/)

**Medial**
[Tongue](https://durgical.com/en/anatomy/tongue/) and floor of the mouth, with the [lingual nerve](https://durgical.com/en/anatomy/lingual-nerve/) running a little higher and further back

## How to find it

The seventh tooth from the midline on the lower right, with four almost equal cusps; it comes in at about 12 years behind the first molar.

## On imaging

On a panoramic film its roots sit nearer the inferior alveolar canal than the first molar's; a C-shaped canal shows as fused roots and is confirmed by CBCT.

## Common problems

- Tooth decay (caries) in the grooves of the chewing surface.

## Clinical notes

- Supplied by the inferior alveolar nerve (V3), so it needs an inferior alveolar nerve block; the thick outer bone of the mandible here stops infiltration from working well
- Its root tips lie below the [mylohyoid](https://durgical.com/en/anatomy/mylohyoid-muscle/) line, so infection spreads to the submandibular space

## Anatomical variants

- C-shaped root canal, where the roots fuse into a horseshoe-shaped root, is a known variant of this tooth, more frequent in East Asian populations

## Development

No primary predecessor: it develops from the dental lamina behind the first molar and erupts at about 12 years.

## 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.

## Why does the lower right second molar need an inferior alveolar nerve block rather than infiltration?

The thick outer bone of the mandible here stops infiltration from working well.

## Which root canal variant is typical of the lower right second molar?

The C-shaped canal, where the roots fuse into a horseshoe-shaped root; more frequent in East Asian populations.

## Where does infection from the roots of the lower right second molar spread?

To the submandibular space, because its root tips lie below the mylohyoid line.

## On a panoramic film, how do the roots of the lower right second molar relate to the inferior alveolar canal?

They lie closer to the canal than the first molar's roots.

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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/).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/lower-right-second-molar/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/lower-right-second-molar/