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# Upper left second premolar

The upper left second premolar (tooth 25) 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

- Its buccal and palatal cusps are almost the same height, unlike the upper first premolar, and it usually has a single canal (some have two)
- Of the premolars, this is the one whose root most often lies against the maxillary sinus floor

## 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 25, upper left second premolar: 1 root; two cusps of about equal height; erupts at about 10–12 years; nerve: middle superior alveolar nerve (V2)

## Relations

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

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

**Above**
The [maxillary sinus](https://durgical.com/en/anatomy/maxillary-sinus/) floor, often only thin bone away

**Below**
Meets the [lower left second premolar](https://durgical.com/en/anatomy/lower-left-second-premolar/) and the [lower left first molar](https://durgical.com/en/anatomy/lower-left-first-molar/)

## How to find it

The fifth tooth from the midline on the upper left, just ahead of the first molar, with a cheek-side and a palate-side cusp of similar height.

## On imaging

On a panoramic or periapical film its root tip often overlaps the sinus floor; in children the panoramic shows the germ cradled between the primary molar's roots.

## Clinical notes

- Supplied by the middle superior alveolar nerve, which many people lack; buccal infiltration still numbs it through the upper dental plexus
- Infection at its apex can spread into the maxillary sinus and cause odontogenic sinusitis, typically one-sided and foul-smelling
- Notches at the gum line from wear and flexing (non-carious cervical lesions) often affect upper premolars like this one

## Development

Replaces the primary [upper left second molar](https://durgical.com/en/anatomy/upper-left-second-molar/) (FDI 65); if the premolar is missing from birth, that primary molar can stay in the mouth into adult life.

## Related conditions

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

## Test yourself

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

## Of the premolars, which one's root most often lies against the maxillary sinus floor?

The upper second premolar, such as the upper left second premolar.

## What sinus complication can infection at the apex of the upper left second premolar cause?

Odontogenic sinusitis, typically one-sided and foul-smelling.

## What happens if the upper left second premolar is missing from birth?

The primary upper left second molar (FDI 65) can stay in the mouth into adult life.

## In a child, where does a panoramic film show the germ of the upper left second premolar?

Between the roots of the primary second molar it will replace.

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