External resorption is the pathological loss of tooth structure that originates from the outer surface of the root, typically beginning at the cementum and progressing inward toward the dentin. Unlike internal resorption, which starts within the pulp canal, external resorption is driven by clastic cells activated along the root surface and the surrounding periodontal ligament.
Common Causes
External resorption is rarely spontaneous. It most often follows a triggering event or ongoing biological disruption that activates osteoclast-like cells against the root surface.
- Dental trauma — luxation injuries and avulsions are among the most common precipitating factors
- Orthodontic treatment — prolonged or heavy forces can stimulate root resorption, particularly at the apex
- Pressure from adjacent structures — impacted teeth, cysts, or tumors pressing against roots
- Periodontal infection — chronic inflammation in the surrounding tissues can initiate resorptive activity
- Intracoronal bleaching — a known risk factor for cervical external resorption when oxidizing agents contact root surfaces
Types and Clinical Presentation
Clinicians generally distinguish several subtypes based on location and mechanism. Apical external resorption shortens the root tip and is frequently seen after orthodontic therapy. Cervical external resorption attacks the root just below the gumline and can be aggressive and invasive, tunneling through cementum and dentin. Replacement resorption, also called ankylosis, occurs when root cementum is replaced by bone, eliminating the normal periodontal ligament space and fusing the tooth directly to alveolar bone.
On radiographs, external resorption typically appears as irregular radiolucency along the root surface. Cone-beam CT (CBCT) imaging is invaluable for assessing the true three-dimensional extent of the defect, especially in cervical cases where depth and proximity to the pulp determine prognosis.
Why It Matters
Left undetected, external resorption can silently destroy significant root structure before any symptoms appear. Early diagnosis is critical because treatment options — which may include monitoring, conservative restorative repair, or extraction — depend heavily on the stage and location of the defect. Teeth with extensive replacement resorption are often non-restorable, and the presence of ankylosis can significantly complicate surgical removal.
Prompt identification through routine radiographic screening and, when indicated, advanced imaging gives clinicians the best opportunity to intervene before irreversible structural loss renders a tooth unsalvageable.