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# Upper right first molar

The upper right first molar (tooth 16) 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 four cusps and three roots.

## What it does

Grinds food before swallowing.

## Key points

- Its mesiobuccal root often holds a second canal (MB2), so the tooth commonly has 4 canals; a missed MB2 is a frequent cause of failed root canal treatment
- The posterior superior alveolar nerve supplies most of it, but the mesiobuccal root may get fibres from the middle superior alveolar nerve when present, so one posterior injection may not numb it fully
- Angle's classification of the bite is based on this tooth: in Class I its mesiobuccal cusp sits in the buccal groove of the lower first molar

## Key facts

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

**Landmarks**
FDI 16, upper right first molar: 3 roots (2 buccal, 1 palatal); first permanent tooth to erupt; key to the bite (occlusion); erupts at about 6–7 years; nerve: posterior superior alveolar nerve (V2); roots near the floor of the maxillary sinus

## Relations

**In front**
The [upper right second premolar](https://durgical.com/en/anatomy/upper-right-second-premolar/)

**Behind**
The [upper right second molar](https://durgical.com/en/anatomy/upper-right-second-molar/)

**Medial**
Palate, with the palatal root, the largest of the three

**Above**
Floor of the [maxillary sinus](https://durgical.com/en/anatomy/maxillary-sinus/); the root tips can raise small bumps in it

**Below**
Opposes the [lower right first molar](https://durgical.com/en/anatomy/lower-right-first-molar/) and the front of the [lower right second molar](https://durgical.com/en/anatomy/lower-right-second-molar/)

## How to find it

Sixth tooth from the midline on the upper right, the largest upper tooth, with four main cusps; in children it appears at about 6 years behind the last primary molar.

## On imaging

Bitewings show decay between it and its neighbours and under old fillings. On a panoramic film its three roots project over the sinus floor; periapicals show the furcation.

## Common problems

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

## Clinical notes

- After extraction the thin bone between the roots and the maxillary sinus can break through, leaving an oroantral communication; a root tip can also be pushed into the sinus
- Molar-incisor hypomineralisation: chalky, soft enamel patches on the first permanent molars that break down and decay early

## Anatomical variants

- Cusp of Carabelli: a small extra cusp on the palatal side of the mesiopalatal cusp, common in many populations

## Development

No predecessor: permanent molars do not replace any primary tooth; this one erupts behind the primary second molar.

## Memory aid

Upper eruption order: 6-1-2-4-5-3-7-8. The first molar opens the sequence, hence its nickname, the 6-year molar.

## 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.

## Which canal is often missed in root canal treatment of the upper right first molar?

The second mesiobuccal canal (MB2), in the mesiobuccal root, so the tooth commonly has 4 canals.

## What is the relation of the upper first molar in Angle Class I occlusion?

The mesiobuccal cusp of the upper right first molar sits in the buccal groove of the lower first molar.

## Why may a posterior superior alveolar injection not fully numb the upper right first molar?

Its mesiobuccal root may get fibres from the middle superior alveolar nerve when present.

## What is the cusp of Carabelli?

A small extra cusp on the palatal side of the mesiopalatal cusp of the upper first molar.

## What is molar-incisor hypomineralisation, and which molar does it affect?

Chalky, soft enamel patches that break down and decay early, on first permanent molars such as the upper right first molar.

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Educational information, not medical advice. For any symptom, see a health professional.

## Related

- [Maxillae](https://durgical.com/en/anatomy/maxilla/)

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