Clear aligners are orthodontic devices that are a transparent, plastic form of dental braces used to adjust teeth. They are effective for moderate crowding of the front teeth, but less effective than conventional braces for several other issues and are not recommended for children. In particular they are indicated for "mild to moderate crowding (1-6 mm) and mild to moderate spacing (1-6 mm)", in cases where there are no discrepancies of the jawbone. They are also ndicated for patients who have experienced a relapse after fixed orthodontic treatment.