Dentofacial malformation refers to abnormalities in the volume, shape, and relationship between the upper and lower jaws and other bones in the craniofacial area caused by abnormal jaw development, and the consequent abnormalities in the jaws, dental relationships, and the function of the oromandibular system and facial morphology. The purpose of orthognathic surgery is to correct the misaligned teeth, adjust the uncoordinated dental arch and jaw relationship, eliminate dental and jaw interference, align the teeth, and eliminate the compensatory tilt of the teeth so that the incised bone segment can be moved smoothly to the designed corrective position and establish a good dental and jaw relationship during surgery.
I. Treatment steps
Formulation of combined orthognathic orthodontic treatment plan: perfect examination, including maxillofacial X-ray examination, oral panoramic film, cranial front and lateral film, maxillofacial dimensional CT examination, ECT examination is required for patients with deviated jaw deformity, and temporomandibular key MRI examination is required for class II malocclusion, orthognathic and orthodontic surgeons need to discuss and formulate treatment plan with patients according to the examination results.
Second, preoperative orthodontic treatment
After the surgical plan is determined and the patient and family members agree, orthodontic treatment must be performed first according to the planned orthodontic position, in order to align the teeth, eliminate interference, facilitate the movement of the bone segment during surgery and achieve the ideal treatment effect.
III. Surgical plan
After the completion of orthodontic treatment before surgery, a final evaluation and prediction of the original surgical plan is needed, and necessary adjustments to the surgical plan or necessary additions to the orthodontic treatment are made so that the upcoming surgery can meet the reality and achieve the best results.
IV. Model surgery
Model surgery is the process of truncating and assembling the dental plaster model transferred to the dental frame according to the conclusions drawn from clinical examination and cephalometric analysis and prediction, and finally obtaining good maxillary and mandibular bone position relationship and maxillary and mandibular teeth occlusion relationship and preparing the occlusal guide plate.
V. Preoperative preparation
In addition to the routine preparation for general anesthesia and blood transfusion, the occlusal guide plate and the required fixation device after bone block movement should be prepared according to the designed surgical style and fully explained to the patient according to the surgical plan, predicted results and possible problems, and full understanding and consent should be obtained.
VI. Orthognathic surgery
The surgery must be performed strictly according to the predicted and preoperative reconfirmed surgical design, and must not be altered at will during the operation. The purpose of orthognathic surgery is to cut and shift the craniomandibular bone through different surgical designs, to reshape the balance and proportion of the bone surface, to restore the normal shape of the patient, and to maintain the long-term stability of its morphology and functional activities.
Common orthognathic surgical procedures include maxillary anterior osteotomy, LeFort type I osteotomy, mandibular anterior subapical osteotomy, mandibular branch sagittal osteotomy, vertical osteotomy of mandibular branch through intraoral approach, chinplasty, bimaxillary surgery and mandibular angioplasty. Clinically, a certain procedure or a combination of several procedures can be selected for the correction of different types of malocclusion. The following are the most commonly used LeFort type I osteotomy, mandibular branch sagittal osteotomy and chinplasty.
LeFort type I osteotomy
In this procedure, the walls of the maxillary sinus are cut according to the maxillary LeFort type I fracture line, the pterygomandibular junction is severed, and only the soft tissue tip, mainly the palatal mucoperiosteum, is retained, so that the severed maxilla moves in the three-dimensional direction according to the preoperative design, thus correcting various maxillary deformities.
Sagittal splitting of the mandibular branch
The mandibular branch is split along the sagittal osteotomy line to form a proximal bone segment connecting the ankylosis and the lateral bone plate of the mandibular branch and a distal bone segment containing the inferior alveolar neurovascular bundle and the dentition, and then the distal bone segment is moved or rotated forward or backward to the designed ideal position after wearing the prefabricated jaw plate. It is suitable for the treatment of over (or under) development of the lower jaw and bony anterior open jaws.
Chinplasty
Through the intraoral approach, a horizontal osteotomy with the lingual muscle of the chin as the blood supply tip is performed, and the severed jaw bone is pulled forward to the desired position, and the chin can also be squared, receded, lowered or raised, narrowed or widened. It is suitable for the reconstruction of chin morphology in patients with underdeveloped, overdeveloped or asymmetrical chins.
Seven, post-operative orthodontic treatment
Even for successful surgical procedures, there are usually problems such as uncoordinated cusp-fossa relationship between upper and lower teeth and unbalanced occlusion after surgery, so postoperative orthodontic treatment is usually required, aiming to improve the occlusal relationship from functional and cosmetic effects, and to stabilize and consolidate the effect after surgical correction. If the situation is normal, postoperative orthodontic treatment can be carried out 3 months after orthognathic surgery, while rehabilitation treatment is carried out for the purpose of restoring the function of peri-maxillary muscles and temporomandibular joints.
VIII. Follow-up observation
Understand the possible changes of jaw and tooth relationship after surgery and perform postoperative effect evaluation. Mobile, corrected bone blocks usually show slight displacement during the healing process. As long as it does not affect the clinical effect, postoperative orthodontic treatment will be performed to consolidate the efficacy. However, if there is an obvious tendency of recurrence, it is necessary to treat accordingly. According to the healing process of osteotomy and its biomechanical characteristics, the postoperative follow-up observation should continue for at least 6 months.