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# Lower right second premolar

The lower right second premolar (tooth 45) is the tooth between the first premolar and the first molar; it helps crush and grind food.

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## What it is

A transition tooth with two cusps and one root, just in front of the molars.

## What it does

Crushes and tears food.

## Key points

- After the third molars it is one of the teeth most often missing from birth; the primary second molar then may stay into adult life
- The mental foramen is most often found below or just in front of its root tip; on a radiograph the foramen can mimic a lesion at the apex

## 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 45, lower right second premolar: 1 root; two or three cusps; lies near the mental foramen; erupts at about 11–12 years; nerve: [inferior alveolar nerve](https://durgical.com/en/anatomy/inferior-alveolar-nerve/) (V3)

## Relations

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

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

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

**Below**
[Mental foramen](https://durgical.com/en/anatomy/mental-foramen/) and mental nerve, near its apex

## How to find it

The fifth tooth from the midline on the lower right, just ahead of the first molar; the mental foramen usually lies below its root tip.

## On imaging

On a periapical radiograph the dark mental foramen over the apex is told apart from an abscess because it shifts relative to the root when the beam angle changes, and the periodontal ligament space stays intact.

## Clinical notes

- Supplied by the inferior alveolar nerve (V3); a numb lower lip after surgery here points to injury of the mental nerve
- Its root tip lies above the [mylohyoid](https://durgical.com/en/anatomy/mylohyoid-muscle/) line, so an abscess from it spreads toward the sublingual space or the buccal vestibule

## Anatomical variants

- Dens evaginatus, a small extra tubercle on the biting surface, is found mainly on lower premolars; it can break and leave the pulp exposed

## Development

Replaces the primary [lower right second molar](https://durgical.com/en/anatomy/lower-right-second-molar/) (FDI 85).

## Related conditions

- [Dental caries](https://durgical.com/en/conditions/dental-caries/)

## Test yourself

Think of the answer, then tap the question to see it.

## How is the mental foramen told apart from an abscess at the apex of the lower right second premolar on a radiograph?

The foramen shifts relative to the root when the beam angle changes, and the periodontal ligament space stays intact.

## What does a numb lower lip after surgery near the lower right second premolar point to?

Injury of the mental nerve, which leaves the mental foramen near its root.

## Where does an abscess from the lower right second premolar spread?

Toward the sublingual space or the buccal vestibule, because its root tip lies above the mylohyoid line.

## On which teeth is dens evaginatus mainly found?

On the lower premolars, such as the lower right second premolar.

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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-premolar/
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-premolar/