Retainers are mostly used as the last phase of orthodontics treatment. After the braces have been removed, teeth can shift back to their original position. So, retainers worn regularly overnight can help maintain the position of straightened teeth. 

Retainers are useful for reasons other than shifting teeth. Some kids have a tongue thrust (a condition where the tongue slides through the teeth when you talk). Some retainers can be specially designed to train your tongue not to move forward when you speak. 

Retainers keep your teeth in place after straightening with braces, aligners, or other devices. Oral healthcare providers, such as orthodontists, can also use retainers to improve your bite, move one or two teeth, or help you speak more clearly.