Retainers are devices that are used to consolidate the healing effect of orthodontic treatment after completion. There are many different types of retainers, which can be divided into the following three categories: movable retainers, fixed retainers and retainers with a therapeutic role. After the removal of fixed orthodontic appliances, almost all patients must be maintained accordingly to avoid relapse. Active retainers are the most used in clinical practice. The duration of retainer wear is influenced by a variety of factors, which are related to the patient’s age, health status, the etiology of the malocclusion, the type of malocclusion, the duration of orthodontic treatment, and the method of correction. As a result, the retention time varies considerably. In general, patients are required to wear retainers all day for the first 6 months after orthodontic treatment is completed, and only temporarily when eating, brushing, and cleaning retainers. During the 6-12 month period after orthodontic treatment, the retainer is worn every night and may be worn every other day during the day or longer depending on the patient’s condition. During the 12-18 month period, wear every other day at night until the position of the teeth is basically stable. Retainers should generally be worn for at least 2 years. The movable retainer should be soaked in cold water when not worn to avoid deformation. In recent years, the proportion of adults receiving orthodontic treatment has been increasing. Adults are more socially active and have higher aesthetic requirements, so more and more adults are choosing fixed retainers. The most common type of retainer is the lingual adhesive retainer, the advantage of which is that there is no metal lip arch exposed on the lip side, which is good for aesthetics and easy to maintain oral hygiene and improve the health of periodontal tissues. Retainers that also have a therapeutic effect are less commonly used in clinical practice, mainly for simple, individual misalignments (malocclusions), or in cases where the patient is in a hurry to remove the fixed aligner at the end of treatment and there are a few problems.