A retainer is a dental device used to maintain the position of teeth after orthodontic treatment, such as braces. It is typically made of plastic and metal and is custom-fitted to the patient's mouth. Retainers help prevent teeth from shifting back to their original positions, ensuring the results of orthodontic work are preserved. There are two main types of retainers: fixed and removable. Fixed retainers are bonded to the back of the teeth, while removable retainers can be taken out for eating and cleaning. Regular use of a retainer is essential for long-term dental health and alignment.