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EndodonticsAdvanced

How an abscess forms

A periapical abscess develops when the pulp dies and the infection exits through the tip of the root into the bone.
Periapical radiograph. The arrows point to dark areas at the tips of the roots, where the infection destroyed bone.
Periapical radiograph. The arrows point to dark areas at the tips of the roots, where the infection destroyed bone.Photo: Coronation Dental Specialty Group · CC BY-SA 3.0, Wikimedia Commons

What you need to know

  • Sequence: caries → pulpitis → pulp necrosis → apical periodontitis or abscess.
  • Signs: constant pain that gets worse on biting, the tooth hurts when tapped gently (percussion), and there may be swelling of the gingiva, cheek or lip.
  • The pus can drain through the gingiva or spread into the tissues of the face (cellulitis).
  • Warning signs: fever, swelling of the floor of the mouth or difficulty swallowing (Ludwig's angina). It is an emergency.
  • Treatment: remove the source of the infection (root canal or extraction) and drain the pus if needed. Antibiotics are used if the infection spreads or same-day care is not available.

Terms in plain words

PeriapicalAround the tip (apex) of the root.
Percussion testGentle taps on the tooth: if it hurts, there is inflammation around the root.
Ludwig's anginaA severe infection of the floor of the mouth that can close off the airway.

For the exam

Which test is usually positive in a periapical abscess?

Show answerHide answer

Percussion: gently tapping the tooth causes pain.

Sources

  1. Hennessy BJ. Toothache and Infection. MSD Manual, Professional Version (2026 revision). View source
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