External Root Resorption

External root resorption is loss of cementum and dentine from the outer surface of the root by clastic cells. It includes several types with different causes and treatment, and it can be physiological in primary teeth.

The types are surface resorption (self-limiting), inflammatory resorption, replacement resorption with ankylosis, external cervical resorption and pressure resorption (from an impacted tooth, cyst, tumour or orthodontic forces).

Pathophysiology. Damage to the protective cementoblast layer and precementum exposes the mineralised root surface to osteoclast like cells.

Inflammatory resorption needs infected pulp or canal contents to sustain the loss, while replacement resorption follows extensive damage to the periodontal ligament (typically after avulsion), with bone fusing to the root. External cervical resorption begins at the cervical region apical to the epithelial attachment, often after orthodontic treatment, trauma or bleaching.

Usually silent, found on radiographs. Replacement resorption gives a metallic percussion note, absent mobility and infraocclusion in a growing patient. Inflammatory resorption may be associated with a non-vital tooth, apical lesion or a sinus.

External cervical resorption may show a pink cervical spot, a gingival defect with bleeding on probing and a rough gingival margin, and pain only when the pulp is involved. Orthodontic cases show root shortening with mobility.

• Periapical and bitewing radiographs, with a second view at a different angle. External lesions move relative to the canal outline with the beam angle, and the canal remains visible through the lesion.
• Cone beam CT for the extent, root canal involvement, perforation and surgical planning.
• Pulp sensibility testing, percussion and mobility testing.
• History of trauma, orthodontics, bleaching, surgery, impacted teeth and systemic disease.
• Classification of cervical lesions into four classes by depth and proximity to the pulp.

Differential diagnosis.

• Internal root resorption
• Caries or cervical abrasion
• Periapical lesion with a root outline overlay
• Dentigerous cyst or tumour displacing and resorbing roots
• Hypercementosis
• Ankylosis from other causes
• Perforation after surgery or instrumentation

• Inflammatory resorption: root canal treatment with calcium hydroxide dressing for 2 to 4 weeks (repeated for up to 6 to 12 months in avulsion cases with tooth replantation), followed by a root filling. Healing means loss of the radiolucency along the root.
• Replacement resorption: no treatment stops it. Monitor, and in growing patients with infraocclusion consider decoronation, to preserve the ridge, or extraction and replacement. Keep a splint time of 1 to 2 weeks for replanted teeth after avulsion, with careful handling of the root surface.
• External cervical resorption: surgical or non-surgical access, curettage of the resorptive tissue, application of 90% trichloroacetic acid for about 1 to 2 minutes to the lesion (protecting the soft tissue), restoration with glass ionomer or calcium silicate cement, with root canal treatment when the pulp is involved. Extraction when the lesion is extensive and unrestorable.
• Pressure resorption: remove the cause (extract or expose the impacted tooth, enucleate the cyst, treat the tumour) and stop or modify orthodontic forces for 2 to 3 months, then review.
• Orthodontic resorption: reduce force and take radiographs after 6 to 9 months of treatment to monitor root shortening.
• Antibiotics only for infection with spread: amoxicillin 500 mg orally three times daily for 5 days with dose reduction when eGFR is under 30.

Monitoring. Radiographs at 3, 6 and 12 months and then annually for 5 years after treatment. Replacement resorption is reviewed every 6 to 12 months, with attention to infraocclusion and ridge height.

Referral and escalation. Refer to an endodontist for cervical or inflammatory lesions, and to a paediatric dentist, orthodontist or oral surgeon for replacement resorption and impacted teeth. Urgent referral for rapidly progressing lesions or unexplained multiple tooth resorption, which needs systemic and pathological review.