[Clear aligner in orthodontic retreatment].

Improper diagnosis and design, misusing orthodontic technique, relapse after orthodontic treatment, and poor patient compliance may lead to treatment failure, requiring orthodontic retreatment. While in such cases, patients usually have already had their teeth extracted, or are with periodontal, joint, and other dental problems, which often require multidisciplinary treatment. The retreatment of orthodontic patients is difficult, and the treatment options are limited. The characteristics of clear aligner treatment, such as comfortable and beautiful appearance, high degree of digital precision, and personalized tooth arrangement to simulate the final outcome, make it popular in the orthodontic retreatment. This article discusses and summarizes the details of orthodontic design, case monitoring, and the application of clear aligner in orthodontic retreatment of failed cases. Before starting treatment, the difficulty assessment tool (clear aligner treatment complexity assessment tool) can be used to evaluate the difficulty of clear aligner treatment. Orthodontists are recommended to treat orthodontic patients with clear aligners within their ability to avoid treatment failure. The key to the success of the extraction case treatment with clear aligner is to make the correct diagnosis and select the right cases. In the treatment planning, attention should be paid to the restoration of anterior tooth torque, making good use of molar distalization to obtain the space, vertical control, and improving posterior tooth relationship. Proper selection of cases and reasonable design in clear aligner treatment are expected to obtain tooth alignment, good intercuspation, normal overbite and overjet, periodontal health, parallel roots, and to achieve the goal of aesthetic, functional, stable, and healthy orthodontic treatment.