1.Injury to the inferior alveolar nerve: The inferior alveolar nerve mainly governs the sensation of the mandibular teeth and the skin near the lower lip. Since the nerve travels in the mandible close to the site of incision during sagittal splitting of the mandible, it may be injured during surgery due to vibration and pulling, or contusion when the bone is fixed. Injury can cause insensitivity of the skin around the lower lip, and the chance of occurrence is about one in ten. About 90 percent of patients will gradually recover after three to four months after surgery, but a few may have incomplete recovery and continue to have dull sensation in the lower lip. However, it does not affect daily life, and the movement of all parts of the face is not affected, and there is no drooling at the corners of the mouth. 2. Postoperative bleeding and hematoma: Since the periosteum within the surgical area needs to be stripped, there is a possibility of blood clotting and swelling, which is medically called hematoma. The chance of occurrence is about 20 to 30 percent. The vast majority of hematomas are very mild and will resolve on their own. Only in rare cases will the hematoma be large, indicating the possibility of continuous bleeding from the surgical site, and it is necessary to go to the operating room urgently to stop the bleeding. 3. Post-operative infection: All surgeries have the chance of infection. Since the incisions of orthognathic surgery are mostly in the mouth, poor oral hygiene and abnormal lifestyle after surgery will increase the chance of infection. Overall, the chance of infection is about three percent. Most post-operative infections are treated with outpatient follow-up and antibiotics. In some cases, the wound may need to be opened slightly during the outpatient visit to drain the infected material and help recovery. Only a very small number of cases require hospitalization, antibiotics or re-treatment with debridement. 4. Exposed titanium plates for fixation: Basically, these titanium nails or plates used to fix the osteotomy are made of titanium alloy, which are very compatible with human tissue and do not need to be removed once they are placed. However, sometimes because of wound infection or poor healing there will be loose exposed situation, at this time can be considered after the bone healing, with local anesthesia to remove the minor surgery, the time is about six months after surgery. 5. Skin abrasions at the corners of the mouth: Since the surgery is performed in the mouth, all instruments must be inserted into the mouth, causing some superficial skin abrasions on the skin near the lips, especially at the corners of the mouth, which will heal on their own in one to two weeks and usually will not leave scars. 6. Bleeding and blood preparation: There will be more bleeding during LEFORT type I maxillary osteotomy or double jaw surgery, so in order to avoid problems caused by excessive bleeding, blood transfusion should be arranged during and after surgery. 7. Patients undergoing mandibular sagittal splitting and posterior jaw thrusting may have snoring and even the possibility of respiratory sleep apnea syndrome (OSAS) after surgery. This is mainly due to the fact that after the mandibular posterior push, the floor of the mouth and the supraglottis muscle group retract at the same time, and the pharyngeal cavity is reduced. If accompanied by obesity appears more likely. 8. Psychological problems after the change of facial shape: After receiving orthognathic surgery, the features of the face will change very obviously. Although the result of the surgery will make the proportion of the face shape become normal, some people will have the problem of self-identification. If they agree with the facial features before the surgery, some negative comments after the surgery may cause psychological stress and adaptation problems.