External root resorption commonly occurs in teeth that are impacted due to pressure exerted by adjacent teeth or surrounding bone. This pressure disrupts the protective cementoblast layer on the root surface, exposing dentin to clastic cells that cause resorption. Impacted teeth often fail to erupt normally and remain embedded, making them susceptible to this process. Unlike trauma or orthodontic treatment, which typically cause internal or localized resorption, impaction leads to generalized external root resorption due to sustained pressure. This makes it a frequent clinical finding in impacted third molars or canines.

Reference: Shafer’s Textbook of Oral Pathology, 7th Edition.