Distraction osteogenesis (DO), also called a "Mandibular Distraction", can be used to correct abnormal smallness of one or both jaws seen in patients with PRS. Enlargement of the lower jaw brings the tongue forward, preventing it from obstructing the upper airway. The process of DO begins with preoperative assessment. Doctors use three-dimensional imaging to identify the parts of the patient's facial skeleton that need repositioning and determine the magnitude and direction of distraction. They may then select the most appropriate distraction device or sometimes have custom devices fabricated. When possible, intraoral devices are used.