Clear aligners are orthodontic devices that are a transparent, plastic form of dental braces used to adjust teeth.

Clear aligners have undergone changes, making assessment of effectiveness difficult. A 2014 systematic review concluded that published studies were of insufficient quality to determine effectiveness. Experience suggests 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 indicated for patients who have experienced a relapse after fixed orthodontic treatment.

Clear-aligner treatment involves an orthodontist or dentist, or with home-based systems, the person themselves, taking a mold of the patient's teeth, which is used to create a digital tooth scan. The computerized model suggests stages between the current and desired teeth positions, and aligners are created for each stage. Each aligner is worn for 22 hours a day for one or two weeks. These slowly move the teeth into the position agreed between the orthodontist or dentist and the patient. The average treatment time is 13.5 months. Despite patent infringement litigation, no manufacturer has obtained an injunction against another manufacturer.