Orthodontic treatment at the age of 30 usually does not require lifelong retainers, and wearing retainers usually takes about 2 years, and then stops when the alveolar bone is stabilized, helping to maintain the long-term effects of orthodontic treatment, as described below. Orthodontic treatment utilizes the fact that the alveolar bone can change this property, and the teeth are moved, aligned and leveled in the alveolar bone by means of orthodontic appliances, in order to correct various kinds of malocclusions. A retainer is required after orthodontic treatment because although the shape of the alveolar bone has been remodeled, it is not yet stable, and the teeth may be shifted under the influence of biting force, chewing muscles, and other factors. The alveolar bone can be stabilized in about 2 years after remodeling, so retainers usually need to be worn for about 2 years to maintain the effect of orthodontic treatment. It is recommended to visit a hospital for professional treatment.