Median facial hypoplasia and severe bony Class III malocclusion are among the more common and difficult to treat deformities in craniomaxillofacial surgery. The newly developed traction osteogenesis technique provides a simpler, safer and more effective way to treat severe median facial hypoplasia. In this study, eight patients with severe maxillary hypoplasia were treated with elastic anterior traction of the facial arch brace and anterior traction of the solid external fixed brace to observe the changes in the jaw position and dental relationship before and after treatment, and to further evaluate the therapeutic effects of different external traction osteogenesis techniques. 1. Data and methods 1.1 Clinical data From March 2001 to September 2005, a total of 8 patients with facial mesial hypoplasia were admitted, including 6 males and 2 females, aged 18 to 27 years old; the clinical manifestations were anterior anterior teeth or full arch anterior teeth, concave facial type; the cephalometric analysis was bony class III malocclusion, with facial mesial hypoplasia as the main cause; 5 cases were secondary to postoperative cleft lip and palate malocclusion, 2 cases were Three patients with cleft lip and palate used elastic anterior traction with a facial arch brace, while the remaining five patients used anterior traction with a sturdy external fixation brace using the skull as the support, details of which are shown in Table 1. 1.2 Traction device The traction device consisted of three parts: bone traction hook, external fixation brace and connection part. The bone traction hook is made of pure titanium material, one end is inserted into the bottom edge of the pear-shaped foramen on both sides or screwed to the lateral edge, and the other end is led from the nostril (Figure 1). The external fixation stent is a frontal chin-supporting facial arch stent and a skull-supporting solid external fixation stent (Martin’s RED system), with the facial arch stent connected by a rubber elastic ring for anterior traction and the solid external fixation stent connected by a wire for anterior traction. 1.3 Surgical approach and technical procedure A standard coronal incision was used in three patients, and multiple small incisions were used in five patients, including small incisions under the brow arch on both sides, an inferior lid margin incision, and an intraoral maxillary vestibular groove incision. Subperiosteal separation was performed to reveal all parts of the bone surface, and the nasal root, intraorbital wall, infraorbital wall, anterior and posterior walls of the maxillary sinus were sequentially cut with a reciprocating saw or bone knife. The vertical plate of the sieve bone and the plastron were cut from the nasal frontal suture toward the posterior nasal spine with a narrow osteotome, and the medial wall of the maxillary sinus was incompletely cut posteriorly and inferiorly. The curved osteotome cut the pterygomaxillary union, and the maxillary forceps hold the fracture to loosen the posterior maxillary connection. Patients without cleft are drilled on both sides of the midline of the palate and bolted with traction hooks in the hard palate. In patients with cleft lip and palate, holes were drilled from the lateral edge of the pyriform foramen, and the traction hook was fixed to the lateral edge of the pyriform foramen, and the other end of the traction hook was introduced through the nasal cavity. In 5 patients with RED traction, the RED was fixed to the skull 1 cm above the brow arch, parallel to the orbito-auricular plane, at the end of surgery. In 3 patients with facial arch stent traction, traction was started with the facial arch stent attached on the 3rd postoperative day, with a traction force value of 1500 g/side, and the direction of force applied was 10° to 20° with the palatal plane at a forward inferior angle, with the direction of force applied parallel on both sides, and traction was applied for about 10 to 20 days, and after the desired effect was achieved, the traction force was reduced and continued for 2 to 3 months. In patients with the RED system, a thin wire was attached 3 days after surgery, and the bolt was rotated once a day in the morning and once in the evening, with a traction rate of 1 mm/day, after achieving the desired effect, the traction was maintained for more than 1 month, and then it was changed to elastic traction of the facial arch and continued for 2-3 months. The orthodontic treatment was started after the retractor was removed by local anesthesia. 1.4 Clinical observation and positioning cephalometric analysis Before and after the traction treatment, frontal and lateral photographs of the face and lateral cephalometric films were taken in each patient, and the image data were transferred to the workstation and measured by CDViewer software. The previous cranial base planes were overlapped, and the changes before and after traction were observed. 2 .Results 2.1 Clinical observation The five patients treated with anterior traction using a sturdy external fixation brace successfully completed traction osteogenesis according to the preoperative design, and the patients’ facial shape was significantly improved, with the middle of the face plumped up and the collapsed deformity next to the nose significantly improved. The occlusal relationship was established with normal coverage and no loosening of the traction hook placement. 5 cases were free of complications such as infection and poor osteogenesis (Figure 2). Among the three patients with elastic anterior traction of the facial arch, one case achieved the expected effect, one case had local ischemic bruising in the frontal region due to long-term compression, which was then changed to traction with a firm external fixation brace, and one case stalled after anterior displacement of elastic traction by 3 mm, and the effect was not obvious after changing to anterior traction with a firm external fixation brace. 2.2 Positioning cephalometric measurements The positioning cephalometric measurements of the 5 patients treated with anterior traction with a solid external fixation brace were compared before and after treatment. The maxilla moved significantly forward, with a maximum increase in SNA angle of about 11.5° and an average increase of 8.5°; the coverage relationship changed from anti-coverage to normal coverage relationship; the horizontal advancement of the A-point ranged from 9 to 14.5 mm, with a maximum of 14.5 mm; the average advancement of the maxilla was 11.6 mm. In the three patients with elastic traction of the facial arch, the maxilla moved forward by 8 mm in one case, and in the other two cases, the maxilla moved forward by 8 mm and 10 mm, respectively, after traction with the replacement of a strong external fixation bracket. 3. Discussion Severe bony Class III malocclusion or cleft lip and palate secondary to facial mesial hypoplasia is difficult to be resolved by conventional orthognathic surgery. The literature reports that the average distance of maxillary advancement in conventional orthognathic surgery is 5-7 mm, and there is 20-25% retraction in the sagittal direction in the follow-up study. It has been reported that the maxillary sagittal retraction is close to 40%. In contrast, the maxillary advancement distance of distraction osteogenesis is large, generally 8-13 mm, with the longest being 20 mm. Compared with conventional orthognathic surgery, distraction osteogenesis does not require microplate fixation; does not require bone grafting; does not require intermaxillary ligation; can gradually adjust the incongruity of the jaws in the sagittal and vertical directions; is more effective in correcting the midface depression deformity with proper osteotomy; and soft tissues are also expanded during the bone expansion process. In the process of bone expansion, the soft tissue also expands. The distraction technique is becoming the best choice for severe bony Class III malocclusion or cleft lip and palate secondary to facial mesial hypoplasia. Currently, the main maxillary distraction osteogenesis techniques are built-in traction and external traction, both of which have their advantages and disadvantages. The built-in retraction has the advantages of being small, easy to wear, does not require arch support, and does not leave external traces, but the surgical operation is more complicated. The retractor is often fixed on both sides of the zygomatic alveolar ridge, and the direction of retraction is difficult to control precisely, and it cannot ensure that the extension axis on both sides is in a parallel line, and there may be interference or antagonism of force. The disadvantage of external retractor is its large size, poor appearance and inconvenient life. At the same time, the intra-oral support of external retractor is mostly maxillary dentition or dentition, and the point of force is inferior and far from the center of maxillary resistance, and its lower structure moves a large distance during maxillary traction, while the upper moves a small distance, showing counterclockwise rotation. However, it is easy to control the extension axis and traction direction, and does not require secondary surgery to remove. Therefore the choice of traction device depends on the specific clinical conditions of the patient. In 1998, Molina et al. reported that in 34 patients aged 6-12 years with cleft lip and palate with maxillary hypoplasia, after Le Fort I osteotomy, the average maxillary advancement was 4-12 mm within 3-4 weeks with mask elastic retraction. Diner et al. also reported the same method of maxillary traction with a mean anterior displacement of 7.2 mm versus 3 mm, respectively. In terms of traction results, the available studies show that the small amount of anterior jaw displacement by facemask elastic traction does not correct severe maxillary hypoplasia deformities [2]. In our group of 3 patients with maxillary traction data using a facebow brace, only 1 case achieved the expected effect with maxillary anterior displacement of 8 mm, and 2 cases achieved the effect after the elastic traction was not obvious changed to a solid external fixation brace anterior traction. We believe that the main factor affecting the effect of facial arch traction is that the size of the traction force is limited, and the prolonged excessive traction force causes pain in the frontal area and chin, and even local ischemic necrosis. Another disadvantage of the facial arch stent is the poor stability, unlike the cranial solid external fixation stent, the frontal chin bearing point of the facial arch stent is easily displaced, resulting in the change of traction direction. Small intersegmental activity can interfere with local vascular regeneration, reduce oxygen tension, cause cartilage or fibrous connective tissue to form in the distraction gap, and eventually form new bone by chondrogenesis, so it is necessary to improve the stability of elastic traction of the face arch. In 1997, Polley first treated a 10-year-old child with severe cleft lip and palate maxillary hypoplasia with an adjustable sturdy external retractor, with 15 mm of maxillary advancement and no complications, and this device was simple to use with stable results at 1-year follow-up. Later, many scholars at home and abroad applied it to the treatment of various severe maxillary hypoplasia and achieved good results. The sturdy external retractor (RED system) can be adjusted in height and width with the skull as the support resistance, and compared with the facial arch brace, it can precisely control the direction of traction force and traction speed, with good stability and high efficiency, and the forward distance is large, which can fully correct the mid-facial hypoplasia, especially in the treatment of severe maxillary hypoplasia with good effect. The disadvantage is the need to place fixation nails on the skull, which has a certain impact on daily life and social activities. In our data, all 5 cases achieved the expected results with RED system after 10-15 days of traction, and the average anterior displacement of the maxilla was 11.6 mm. 2 patients with poor traction of the facial arch changed to traction of the RED system, and the final anterior displacement of the maxilla was 8 mm and 10 mm. due to the expensive price of strong external fixation brackets, elastic anterior traction of the facial arch is a convenient and inexpensive way of traction, and if it can increase the force-bearing surface to disperse the soft tissue The RED is the best choice given the strong pulling force of the palatal scar in cleft lip and palate maxillary hypoplasia.