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.
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.
Connections
In Pharmacology2
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 (StatPearls Publishing (NCBI Bookshelf), 2023); Oral Facial Infection of Dental Origin: A Guide for the Medical Practitioner (StatPearls Publishing (NCBI Bookshelf), 2025); Dental Emergencies (StatPearls Publishing (NCBI Bookshelf), 2022).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.