[4] Root resorption is a normal physiological process that occurs in the exfoliation of the primary dentition.

Chronic stimuli that damage these protective layers expose underlying dentin to the action of osteoclasts.

[3] Less common causes include pressure from malpositioned ectopic teeth, cysts, and tumors.

[9][10] In physiological bone turn over, osteoblasts and stromal cells release RANKL, this acts on macrophages and monocytes which fuse and become osteoclasts.

Radiographically, a radiolucent area of uniform density within the root canal may be visible with well-defined borders.

If the pulp becomes totally necrosed the resorption will cease unless lateral canals are present to supply osteoclasts with nutrients.

Specifically, application of heavy, continuous, and intrusive (i.e. directed toward the bone) forces during  orthodontic tooth movement are associated with external root resorption.

It is a transient, self-limiting process of resorption that ceases after removal of the traumatic stimulus and is followed by healing of root surface, cementum, and periodontal ligament.

The causes of external cervical root resorption are poorly understood but trauma, periodontal treatment, and/or tooth whitening may be predisposing factors.

ERRR can be further categorized as transient or progressive depending on the extent of periodontal ligament damage with the latter resulting in complete root resorption.

[17] Furthermore, endodontically treated teeth do not increase OIERR due to the absence of a vital pulp that can induce inflammation.

[18] Thus, it is recommended to take screening radiographs to detect for OIERR as indicated, use light forces especially for intrusive movements, and perform endodontic treatment if needed.