For the past 10 years, the use of computer-assisted surgery has expanded and is now widely spread in the orthopaedic domain, but not in maxillary-facial surgery. The main disadvantages of this technique are the necessity to fix a mark on the eyebrow with two transcutaneous pins, which is a long and invasive act, and to connect the infrared transmitter which is in contact with the patient with the computer in a limited surgery area. In this study, we want to show that the new repositioning optic systems are performing similarly to the actual validated one, that they permit to suppress the transcutaneous pins and the computer connection, and that it reduces the financial cost of this surgery. Neither the surgery technique, nor the pre-operative check-up will be modified in the study. The two repositioning systems will be used simultaneously during the mandibular osteotomy.