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# Pulp necrosis, apical periodontitis and the dental abscess

- Oral pathology

When the tooth nerve dies, bacteria fill the root canal and inflame the bone at the root tip. Pus there is a dental (periapical) abscess.

Updated Nov 12, 2026

## Key points

- Dead pulp + bacteria = apical periodontitis; pus = periapical abscess.
- Drain and remove the source; antibiotics only for spread or systemic signs.
- A facial sinus tract can be dental.

## What it is

A necrotic pulp no longer responds to cold, but bacteria living in the root canal leak out at the apex and inflame the periodontal ligament and bone: this is apical periodontitis. It may be symptomatic (the tooth is tender to bite) or silent, seen only as a dark area at the root tip on a radiograph (granuloma or cyst). When pus collects, an acute periapical abscess forms with throbbing pain, swelling of the gum or face and sometimes fever. Pus may drain through a sinus tract onto the gum, which relieves pain but does not cure the problem.

## How to recognise it

- No response to cold, tender to percussion, possible dark tooth.
- Radiograph: widened ligament space or radiolucency at the apex (may be absent early).
- Acute abscess: throbbing pain, swelling, tooth feels «high» when biting, possible lymph nodes and fever.
- A sinus tract (gum boil) means chronic drainage.
- The source must be removed: root canal treatment or extraction, with drainage of any abscess.

## Differential and risks

- Antibiotics alone do not cure a dental abscess; it recurs until the canal is cleaned or the tooth is removed.
- Spread beyond the jaw (cellulitis, trismus, dysphagia) turns a dental problem into a medical emergency.
- Chronic sinus tracts can open on the skin of the face or chin and be mistaken for a skin lesion.

## Next step / Initial management

- Localised abscess without systemic signs: refer to the dentist for drainage and root canal treatment or extraction; antibiotics are not routinely needed.
- Spreading cellulitis, fever or systemic illness, or an immunocompromised patient: start an antibiotic (first choice in most guidelines is amoxicillin or penicillin; clindamycin or a macrolide if penicillin-allergic) and arrange dental drainage within a day.
- Any airway red flag (trismus, drooling, floor-of-mouth swelling, dysphagia): refer as an emergency.

## Test yourself

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

## Why do antibiotics alone fail to cure a periapical abscess?

The infected root canal remains as a source; the canal must be cleaned or the tooth extracted, with drainage.

## When are antibiotics indicated for a dental abscess?

With spreading cellulitis, fever or systemic illness, immunocompromise, or when drainage is delayed.

## What is a sinus tract in dental infection?

A drainage channel from the periapical abscess to the gum or skin, often seen as a small pimple.

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## Connections

## Related 4

- [Pulpitis: reversible or irreversible](https://durgical.com/en/dentistry/pulpitis-reversible-or-irreversible/)
- [Facial swelling from a tooth: when it is dangerous](https://durgical.com/en/dentistry/facial-swelling-from-a-tooth-when-it-is-dangerous/)
- [Fascial spaces: where dental infections spread](https://durgical.com/en/dentistry/fascial-spaces-where-dental-infections-spread/)
- [Dental imaging: bitewing, periapical, panoramic and CBCT](https://durgical.com/en/dentistry/dental-imaging-bitewing-periapical-panoramic-and-cbct/)

## Related conditions 1

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

## In Pharmacology 2

- [Amoxicillin](https://durgical.com/en/pharmacology/amoxicillin/)
- [Ibuprofen](https://durgical.com/en/pharmacology/ibuprofen/)

[← All of dentistry](https://durgical.com/en/dentistry/)

Educational content; it does not replace assessment by a dentist or doctor and is not a clinical instruction. For facial or neck swelling with difficulty swallowing or breathing, a knocked-out tooth or bleeding that will not stop, go to an emergency department at once.

Sources: [Apical Periodontitis](https://www.ncbi.nlm.nih.gov/books/NBK589656/) (StatPearls Publishing (NCBI Bookshelf), 2023); [Oral Facial Infection of Dental Origin: A Guide for the Medical Practitioner](https://www.ncbi.nlm.nih.gov/books/NBK542165/) (StatPearls Publishing (NCBI Bookshelf), 2025); [Dental Emergencies](https://www.ncbi.nlm.nih.gov/books/NBK589664/) (StatPearls Publishing (NCBI Bookshelf), 2022).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/dentistry/pulp-necrosis-apical-periodontitis-and-the-dental-abscess/