This book provides insight into external apical root resorption due to orthodontic treatment.External apical root resorption is one of the most common iatrogenic sequelae of orthodontic treatment that results in permanent loss of tooth structure from the root apex. It can occur during treatment or post-treatment, can affect the longevity of therapy and the stability of treatment results.A combination of early diagnosis,preventive measures,and timely treatment would contribute greatly to the management of external apical root resorption.