The length of time a dental retainer is worn is determined by the degree and type of malocclusion of the teeth prior to orthodontic treatment, and there are three types of retainers: no retention, limited retention, and long-term retention. 1. No retention: For some individual teeth inversion and misalignment, the good contact and occlusal relationship between teeth after orthodontic treatment will have the function of retention, so it can not be retained. 2. Limited retention: generally 1~2 years, belongs to the most common type, most of the orthodontic treatment is required to carry out a short period of retention, the first year generally try to wear 24 hours, the second year wear at night, specific need to be adjusted according to the individual situation. 3. Long-term retention: For some teeth that are sparse and severely twisted and prone to recurrence, it may be necessary to delay the retention time and wear them for life if necessary. Each person wears retainers for different periods of time due to different oral conditions, and it is recommended to follow the advice of your orthodontist.