The loss of hard dental tissue (cement or dentine) by cementoclastic or osteoclastic activity. It may be external or internal. External root resorption ( surface resorption) can lead to a shortening of the root, when occurring in the apical area, or perforation of the pulp canal, when occurring on the lateral surface. External resorption may be caused by inflammation following trauma or infection, excessive forces applied to the tooth root during orthodontic therapy, or due to the eruptive pressure from an adjacent impacted tooth. It occurs in the primary dentition as a normal physiological process during exfoliation. Internal root resorption can occur due to osteoclastic activity, which removes the dentine creating an internal concavity which may be characterized externally by a pink discoloration (pink spot); it can occur anywhere in the root and may produce tenderness over the root apex or pulp sensitivity. Internal resorption may be caused by incomplete caries removal. See also odontoclastoma.
Patel S., Pitt Ford T. Is the resorption external or internal? Dent Update 2007;34:218–29.