1.Data and methods
(1)Clinical data
From March 2001 to September 2005, a total of 8 patients were admitted with facial middle part hypoplasia, including 6 males and 2 females, aged 18-27 years old; the clinical manifestations were anterior retrusion or full arch retrusion with concave facial shape; the cephalometric analysis was bony type III malocclusion, with facial middle part hypoplasia as the main cause; 5 patients with cleft lip and palate and 3 patients without cleft, including 1 case with Siemens syndrome.
(2) Traction device
The traction device consisted of three parts: bone traction hook, external fixation bracket and connection part. The bone traction hook was made of pure titanium material with a component structure, and one end was inserted into the bottom edge of the pear-shaped foramen on both sides and fixed by the oral side screw, and the other end was led from the nostril. The external fixation bracket was a facial arch bracket consisting of a frontal plate, a chin rest and a wire arch connected between them in the early stage, and was changed to a sturdy external fixation bracket (RED system) with the skull as the support. The connecting part includes rubber elastic ring or wire, which connects the traction hook with the facial arch brace.
(3) Surgical methods and technical procedures
Le Fort type III osteotomy: General anesthesia via oral intubation, with standard coronal incision (later changed to small incisions under the brow arch on both sides), lower lid margin incision and intraoral maxillary vestibular groove incision. The subperiosteal separation reveals the bony surface of each part of the bone, and the bony connection is cut in turn with a compound saw or bone knife. The zygomatic frontal and zygomatic temporal processes are cut at the zygomatic frontal and zygomatic temporal sutures, and the lateral orbital wall is cut vertically downward to the front of the infraorbital fissure, and the posterior wall of the maxillary sinus is cut downward to the plane of the zygomatic alveolar ridge. The anterior portion of the orbital floor was exposed through the lower lid margin incision, and the inferior orbital wall was cut with a small bone cutter. The nasofrontal and frontomandibular sutures are incised with a fissure drill, and the infraorbital wall is incised with a small osteotome along the medial canthal ligament and posterior to the nasolacrimal sulcus. The vertical plate of the septum and the plastron were cut from the 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. A small section of the posterior lateral wall of the maxillary sinus was incised horizontally to reach the pterygomaxillary union, and the pterygomaxillary union was incised with a curved osteotome. At this point, the entire Le
Fort III osteotomy was completed. The maxillary forceps hold the truncated maxilla anteriorly and inferiorly wrench and pull to loosen the posterior maxillary connection.
② Retractor placement: Patients without cleft use a slow-speed electric drill to drill a hole on each side of the palatal midline inside the mouth, equivalent to 3⊥3 continuous line, to connect with the nasal floor, and introduce the bone retractor hook from the nasal cavity with silicone tubing and bolt fixation. In patients with cleft lip and palate, the flap was turned from the maxillary vestibular groove, the lateral edge of the pear-shaped foramen was drilled, and the traction hook was introduced from the nasal cavity with a silicone tube and bolted in place.
(③Traction period: traction was started 3 days after surgery by connecting the facial arch brace, with a traction force value of 1500 g/side, the direction of force applied was 10°～20° with the palatal plane at a forward downward angle, and the direction of force applied on both sides was parallel, and traction was applied for about 10～20 days, and after the expected effect was achieved, the traction force was reduced and continued for 2～3 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, and after the desired effect was achieved, the traction was maintained for more than 1 month, and then replaced by a facial arch for 2 to 3 months. The traction device was removed under local anesthesia.
(4) Evaluation of traction effect
①
Clinical observation and analysis of positioning cephalometric measurements: each patient took frontal and lateral facial photographs and lateral cephalometric films before and after traction treatment, and then transferred the image data to the workstation and used CDViewer software to fix the measurements. The previous skull base planes were overlapped to observe the changes before and after traction. Positioning cephalometric analysis fixation, measurement standard and horizontal distance measurement.
②Eye prominence: The eye prominence of the left and right eyes was measured before and after treatment with a Hertel eye prominence meter, and the difference between the outer orbital rim of the eye and the highest point of the eye (mm) was expressed.
2 .Results
(1) Clinical observation
Eight patients with facial middle part hypoplasia showed significant improvement in their posterior shape after treatment, and the middle part of the face was plumped up, and the collapsed deformity of the cheek and paranasal area was significantly improved. The occlusal relationship was established with normal coverage, and there was no infection and loosening of the traction hook placement.
(2) Positioning cephalometric measurements
The cephalometric measurements were changed before and after treatment in different patients. The maxilla moved forward significantly, and the maximum increase of SNA angle was about 11.5°; the coverage relationship changed from anti-coverage to normal coverage relationship;
The horizontal anterior shift of point A ranged from 9 to 14.5 mm, with a maximum of 14.5 mm; the maxillary height increased significantly, and the mandibular and incisor angles did not change significantly before and after treatment.
(3) Comparison of eye prominence before and after surgery
Patients with facial middle portion hypoplasia had different degrees of eye protrusion, and the protrusion ranged from 13.5 to 16.5 mm. After osteotomy and traction, the prominence of the eye changed significantly in each patient.
3. Discussion
Severe bony Class III malocclusion or cleft lip and palate facial hypoplasia is difficult to resolve by means of 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 anterior displacement of the maxilla in traction orthognathic surgery is large, with a general anterior displacement distance of 8-13 mm and a maximum of 20 mm.
Compared with traditional orthognathic surgery, the distraction osteogenesis technique does not require microplate fixation; does not require bone grafting; does not require intermaxillary ligation; can gradually adjust the jaws in the sagittal and vertical directions of incongruity; is more effective in correcting depressed deformities of the middle part of the face (including depressions of the infraorbital, nasal roots, and zygomatic areas); and expands the soft tissues during the process of bone expansion. The longer treatment period required for the distraction technique is its disadvantage; therefore, for mild deformities, traditional orthognathic surgery should be preferred.
At present, the main maxillary distraction osteogenesis techniques are built-in traction and external traction. With built-in traction, the placement of the tractor requires sufficient bone retention and cannot damage the tooth germ or root, so it is mostly used clinically for Le Fort Ⅱ and Ⅲ
type osteotomy or high Le Fort
type I osteotomy. The built-in retraction has the advantages of being small, easy to wear, does not require arch bearing, and does not leave external traces. However, the surgical operation is complicated, and the direction of retraction is difficult to control precisely, and the extension axis on both sides cannot be guaranteed to be in a parallel line.
Postacchini et al. showed that the stability of the bone segment in traction is very important for the osteogenic effect, and that small activities between bone segments 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 way of chondrogenesis. External brace traction was used in all of our data, and the first three patients used facial arch traction with the frontal and chin as the support resistance for the upper jaw. The facial arch traction was easy to remove and put on, but the amount of force was limited.
Excessive and prolonged traction showed pain in the frontal and chin areas, local ischemia and even necrosis. Another drawback is the poor stability. Compared with the facial arch, it can precisely control the direction of traction force and traction speed, with good stability and high efficiency, and the forward distance is large, but the disadvantage is that the fixation nail needs to be placed on the skull, which has some influence on daily life and social activities. Several cases after the data of this group have used RED system to achieve the expected effect after 7-10 days of traction, and after keeping it for about 1 month, it was changed to face arch traction to keep it with good effect.
At present, fixed or movable orthodontic appliances are mostly used clinically as intraoral fixtures for anterior traction, but the principles used are all based on the use of teeth or teeth as force points. The force area is located below the maxillary complex, the front traction will inevitably appear to move the lower part of the distance, the upper part of the distance is small, showing a “fan” shaped movement, especially the zygomatic orbital area is not conducive to the correction of the depression. Experiments have confirmed that the maxilla can move forward in parallel when the force line passes through the center of resistance.
In 1999, Ahn et al. conducted the first study on the biomechanics of extra-oral retractor for correction of maxillary hypoplasia and revealed that the position of the maxillary force center after Le Fort I osteotomy was different from that without Le Fort I osteotomy.
Le Fort I osteotomy. It was inferred that the position of the maxillary resistance center after Le Fort III osteotomy was also different from the previous findings. Although there are no studies on the location of the resistance center after Le Fort type III osteotomy, the location of the resistance center after Le Fort type III osteotomy is different from previous studies.
The position of the resistance center after Le Fort III osteotomy has not been studied yet, but most scholars still agree that its position is still in the mid-facial position. Based on this understanding, we placed the bearing point near the pear-shaped foramen to bring it closer to the resisting center of the maxilla,
The results show that median anterior traction can effectively move the maxilla forward and avoid counterclockwise rotation of the maxillary complex.
Maxillary hypoplasia is characterized by maxillary recession, abnormal jaw relationship, paranasal collapse deformity, and incongruity of upper and lower lip relationship. Facial mid-portion hypoplasia includes not only all signs of maxillary hypoplasia in addition to all deformities of nasal, infraorbital, and zygomatic recession. Strictly speaking, maxillary hypoplasia is inevitably accompanied by varying degrees of developmental restriction of the surrounding bone. Thus, we examined the patient’s ocular prominence preoperatively and found different degrees of ocular prominence in patients with facial middle portion hypoplasia.
The prominence of the eye is the vertical distance from the outer edge of the orbit to the apex of the cornea, and the normal prominence of the eye may vary according to race and age. Each patient was treated with Le
The prominence of the eye was significantly changed after Le Fort III osteotomy.
Patients with facial middle part hypoplasia, in addition to severe An III malocclusion, often have crowded and uneven teeth, and irregular arch width. Therefore, it is necessary to discuss the orthodontic treatment plan with the orthodontist before the traction osteogenic treatment, and preoperative or postoperative orthodontic treatment according to the situation. Two patients in this group underwent preoperative orthodontic treatment and achieved satisfactory occlusal relations. The rest of the patients started postoperative orthodontic treatment after the completion of traction, and the occlusal relationship was significantly improved.