DATA AND METHODS I. CLINICAL DATA A total of 86 cases of mandibular angioplasty were admitted between March 2000 and December 2006, from which 18 cases of square jaw deformity accompanied by chin deformity were selected, and the cases of simple mandibular angular hypertrophy or chin deformity did not belong to the scope of this group, and the 18 patients were all female, aged 18-33 years old, with an average age of 23 years old. All patients had no temporomandibular joint pathology, and all of them sought medical treatment to improve their facial appearance. Three of the cases had asymmetric square jaw deformity, with one side of the mandibular angle hypertrophied to a greater extent than the other. Of the 18 patients with square jaw deformity with chin deformity, 8 had short chins (vertical combined with anterior-posterior hypoplasia), 6 had retracted chins, 2 had deviated chins, and 2 had slightly protruding chins. All patients were treated with bilateral mandibular angle osteotomy, partially combined with bone plate grinding and simultaneous chinoplasty. 16 cases of chinoplasty were characterized by horizontal osteotomy and chinoplasty, among which 8 cases underwent bone grafting between the broken ends of the autologous mandibular angle at the same time, and 2 cases of chin protrusion were treated with bone surface grinding. Surgical method: General anesthesia was administered through nasal cannula, the mucoperiosteum was cut backward along the gingivo-buccal groove of the first mandibular molar to the anterior edge of the ascending mandibular branch to the plane of the maxillary dentition, and the masticatory muscles were fully peeled off from under the periosteum, exposing the middle and lower part of the ascending mandibular branch, the angle of the mandible and part of the mandibular body, and the bone surface was ground by the bone grinding head of domestic Crown Eagle to grind the bone outer boards at the elevation of the external oblique line, and the thickness of the bone surface was generally about 3mm, and the thickness did not have to be completely to the cancellous bone. This is especially beneficial to the exposure of the osteotomy line in patients with angle inversion. According to the preoperative design depth, the second osteotomy is performed by oscillating saw, and the intersection angle of two osteotomy lines is simply corrected by inverted taper file to make it rounded, and the masticatory muscle is generally not resected, and the hemostasis is fully stopped afterward. The chin surgery is based on horizontal osteotomy with partial surface grinding. After completing the osteotomy of the mandibular angle on both sides, the mucous membrane of the lip was cut at the bottom of the vestibular groove of the mandibular bicuspid teeth on both sides about 3-5mm above the bottom of the mucous membrane, the chin muscle and the periosteum were cut, and then the lip side of the chin was peeled off and exposed to the surface of the chin bone to protect the chin nerve, and then the bone was horizontally cut at the chin foramen about 5mm below the chin foramen and about 10-15mm away from the lower edge of the mandible with a reciprocating saw. The mandibular angle was cut out to a certain height according to the preoperative design, inserted into the bone gap of the chin, moved the chin osteotomy block to the predetermined position, and fixed with titanium plate and titanium nails. Third, the effect evaluation 1, clinical observation and positioning head shadow measurement analysis Each patient was photographed before the treatment, 3 to 6 months after the treatment of the face front, side and oblique photos and head positioning front and side position film, and then transferred the image data to the workstation, and used the CDViewer software to fix the point of measurement. The previous cranial base planes were overlapped to observe the changes before and after traction. Positioning head shadow measurement and analysis of fixed point and measurement items are shown in Fig. 1. taking the orbital-auricular plane (FH) as the horizontal reference plane, two verticals were made from the soft tissue nasal root point and the subnasal point to the horizontal reference plane, and the position of the localized anterior chin point was observed. 2. Statistical analysis Stata 7.0 statistical software was selected to statistically analyze the relevant variables (P<0.05). Results I. Clinical observation All patients' postoperative wounds healed in stage I. There were no signs and symptoms of injury to the inferior alveolar nerve and facial nerve, no serious complications such as accidental fracture of the mandible, and no symptoms such as restricted opening and discomfort in mastication. 6 patients had numbness of varying degrees in the chin and lip area after the operation, which was self-healed after 3~6 months, and 5 patients had a strain on the corner of the mouth, which was cured in 1 week after the operation. At the follow-up visit after 3~6 months, the angle of the mandibular angle increased, the curve of the mandibular angle was rounded, the shape was natural, the width between the two mandibular angles was obviously reduced, the shape of the face was more in line with the oriental people's aesthetic point of view, and the shape was satisfactory and symmetrical. The shape of the chin meets the aesthetic standard and reaches the expected requirements before surgery, the proportion of the lower 1/3 of the face is harmonious, and the chin-lip groove is natural (Figure 2). Measurements of the angle and line distance of the maxillofacial tissues of different patients before and after treatment (Table 1): the average angle of the mandibular angle of the patients with square jaw deformity in this group was 108.53°, which was significantly smaller than that of the normal population of 120°, and the angle of the mandibular angle was significantly altered after the operation, increasing to 129.11°; the angle of the mandibular plane increased from the average of 20.78° before the operation, to 33.22°. The width of the mandibular angle was reduced from 110.36 mm to 100.47 mm preoperatively.The lower lip chin height and subfacial mastery were improved after surgery, but there was no statistical difference, probably due to the fact that the eight patients with increased chin heights accounted for a small percentage of all cases. DISCUSSION Our scholars have studied the measurement of facial profile of aesthetically pleasing people in accordance with the law of the golden rectangle, the width of the face at the eye level line is wide and the distance from the point of the hair edge to the point of the chin is long, and the ratio of the two is close to 0.618 [1]. The aesthetic characteristics of the facial side, the angle of the mandibular angle in the normal population [2]: male (122.84 ± 5.86)°, female (123.97 ± 4.55)°; the angle of the mandibular plane: male (24.64 ± 5.09), female (27.14 ± 4.44)°. According to the classification of orthodontics, the development of the human face in the vertical direction is divided into three categories: ① normal vertical osteofacial type, the angle of the mandibular angle of 110 ° ~ 120 °; ② high angle type, the angle of the mandibular angle is greater than 120 °; ③ low angle type, the angle of the mandibular angle is less than the normal value. According to the classification of orthodontics square jaw deformity is a low angle type of face, which is characterized by facial height and width disproportion, wider spacing of mandibular angle, lateral mandibular angle protruding or sinking, and the angle of mandibular angle is less than 120°. Some square jaw deformities are accompanied by shortness of the lower 1/3 of the face and underdevelopment of the chin. Therefore, preoperative comprehensive measurements of the ratio of facial height to facial width and the ratio of the lower 1/3 of the face are necessary for the overall design of the facial and lower contour surgery. In this group of data all patients before and after treatment to take a frontal and lateral photographs with the positioning of the head frontal and lateral X-rays, to carry out frontal and lateral facial proportion measurements. Combined with the aesthetic criteria the anterior chin point should be located between the two vertical lines of the FH (orbital-auricular plane) made from the soft tissue nasal root point and the inferior nasal point [3]. The ratio of upper lip height (inferior nasal point to the lower edge of the upper lip) to chin-lip height (upper edge of the lower lip to the chin point) is 1:1.7 to 2 [2], and the position of the anterior point of the chin and the position of the inferior point of the chin are decided by comprehensive consideration. At the same time of bilateral mandibular angle osteotomy, chin reshaping was performed to improve the overall contouring effect of the lower part of the face. The transoral approach to mandibular angioplasty, despite the operational difficulties, avoids skin scarring, reduces the chance of facial nerve injury, and has been accepted by more and more doctors and patients in today's general trend of attaching importance to facial aesthetics. Currently, the main types of mandibular angioplasty are bone plate removal and mandibular angle osteotomy, and Han et al. showed that bilateral bone plate amputation can reduce the spacing of bilateral mandibular angle by 10-12mm. However, square jaw deformity is not only the problem of the lower third of the face is wider, but also the posterior protrusion of the lateral angle of the mandible is also another factor for most patients to ask for surgery, and the ideal surgery is still mandibular angle osteotomy, such as the same period of time bone plate removal, the effect is better. The ideal operation is still mandibular angle osteotomy. There are oblique osteotomies, curved osteotomies, and secondary or multiple osteotomies in mandibular angle osteotomies. Oblique osteotomy is prone to "secondary angulation", while curved osteotomy, secondary or multiple osteotomies are good choices, which are conducive to the smooth and natural curve of the mandibular angular contour. In the case of square jaw deformity combined with a short chin, the change of the vertical height or protuberance of the chin during the same period of time can drastically change the angle of the mandibular plane, so that the low angle of the mandibular angle can be changed to a normal vertical bone face or a high angle of the face. When there is a chin deformity in patients with square jaw deformity, most of them have insufficient chin height or anterior-posterior retrusion, and there are rare cases of asymmetrical chin deformity or excessively wide chin. In the jaw angle plastic surgery at the same time chin shaping, can make the chin shape to achieve three-dimensional direction of symmetry and coordination, but also make the overall contour of the plastic surgery to achieve a more perfect corrective effect. As one of the earliest facial contouring surgeries, chinoplasty has many surgical methods, the most basic of which are chin augmentation with prosthesis placement and horizontal osteotomy and displacement. Existing chin augmentation prosthesis is mainly to solve the insufficiency of anterior and posterior chin, with a narrow range of application. Horizontal chin osteotomies, on the other hand, have a wide range of applications and can correct almost all three-dimensional chin deformities. Horizontal chin osteotomy is essentially a translocation transplantation with a tipped bone flap, which has the advantages of easy operation, safety, reliability, and preservation of the naturalness and coordination of the soft tissues of the chin. On the basis of horizontal chin osteotomy, it is designed and modified according to the deformity, such as horizontal displacement to solve the skewed chin, or the middle of the osteotomy block vertically amputate the corresponding bone segment to narrow the chin, so as to make the masculine chin become more feminine. In the past, iliac bone transplantation was often utilized to increase the vertical height of the chin, but the simultaneous mandibular angle osteotomy can provide sufficient bone source in the vicinity, avoiding the transplantation of iliac bone, and at the same time, after the correction of the osteotomy block, the cortical bone and cancellous bone are fixed accordingly to ensure the survival of the bone, and avoiding the recurrence of the postoperative period. Due to the square jaw deformity there is a facial height and width of the imbalance, the vertical extension of the chin helps to improve the overall facial contour, and facilitates the transformation from a square or round face to an oval one, but it is not absolute, in the case of the harmonization of the upper and lower lip height ratios in line with the ratio of 1:1.7 to 2, inappropriately prolonging the vertical height of the chin is to add to the problem, so it is necessary to take into account the proportion of the overall facial height and width, and not all of them can be changed from a square face to a goose egg or a goose face, so it is important to consider the overall facial height and width of the ratio. Not all people can go from a square face to a goose egg face or an oval face, which suggests the importance of preoperative computerized predictive analysis and comprehensive facial measurements.