Abstract
The surgery-first approach has become a new paradigm in orthognathic surgery. With the surgery-first approach, most of the patient’s teeth are in their original positions and have not undergone orthodontic treatment prior to the patient undergoing orthognathic surgery. A ‘treatable’ malocclusion should be attained following orthognathic surgery. Orthodontists must ensure that they can manage the ‘treatable’ malocclusion by actively participating in the patient’s surgical plan. Therefore, orthodontic principles and guidelines must be established. Three-dimensional computed tomography should be used to construct the midfacial plane and then to assess discrepancies in the midfacial structures as well as yaw and roll of the bilateral facial structures. Orthognathic surgery should be performed to improve the alignment of such discrepancies to attain a skeletal class I relationship and to attain an aesthetically pleasing face. The surgery-first approach uses osteotomy to solve most of the skeletal and dental problems and to simplify postoperative orthodontic treatment by providing a treatable malocclusion for which mostly only anteroposterior orthodontic movement is required, with minimal transverse or vertical orthodontic movements. Numerous studies have documented the efficacy and long-term stability. Patients undergoing the surgery-first approach benefit from an immediate improvement in facial aesthetics, oral function, and self-confidence, with a shorter total treatment period.
Since the beginning of orthognathic surgery in the 1960s, surgeons have performed orthognathic surgery either before orthodontic treatment or after the removal of orthodontic appliances. During the earlier years, surgeons typically used a surgery-first approach to orthognathic surgery. However, it was soon realized that in mandibular prognathism, the amount of mandibular setback is limited by the overjet between the maxillary and mandibular anterior incisors. To increase the surgical setback to correct mandibular protrusion, presurgical orthodontic treatment was necessary to arrange the misaligned teeth in the most desirable position in each jaw. Worms et al. extended the orthodontics-first concept to all orthognathic cases and emphasized that the optimal surgical repositioning of the maxillomandibular complex (MMC) is only possible following the presurgical removal of all dental compensation. It was therefore proposed that comprehensive orthodontic treatment to align dental occlusion, incisor decompensation, tooth rotation, and arch coordination should be conducted 8–18 months before orthognathic surgery. The orthodontics-first approach became the standard procedure for orthognathic surgical treatment after the 1970s, and the majority of orthognathic teams have employed this approach.
Some surgeons expressed the view that it would be favourable to reposition the MMC before orthodontic realignment of the teeth; however, this type of surgery-first approach did not gain momentum under the orthodontic doctrine of straightening the teeth before repositioning the MMC. Recently, the surgery-first approach has been repopularized by incorporating a temporary anchorage device into postoperative orthodontic treatment to eliminate lengthy preoperative orthodontic treatment. A series of case reports has been published based on the surgery-first approach to correct skeletal class III and class II malocclusions, as well as dentofacial asymmetry. The results showed that an acceptable facial aesthetic and dental occlusion is attainable within 12 months of treatment. The authors reported that skeletal problems could be corrected immediately by performing orthognathic surgery without preoperative orthodontic treatment. The surgery-first approach has since become a new paradigm for orthognathic surgery. Instead of surgeons requesting orthodontists to first reposition the teeth, orthodontists can ask surgeons to first reposition the MMC. The teeth are easier to reposition if the jaws are correctly aligned, and the patient is not subjected to progressive deterioration of facial aesthetics and dental function for 8–18 months of preoperative orthodontic treatment.
With the surgery-first approach, most teeth remain in their original position without presurgical orthodontic treatment. The maxillary and mandibular teeth might not fit perfectly even if the maxilla and mandible are in a skeletal class I relationship following orthognathic surgery. A treatable malocclusion must be attained following orthognathic surgery. Orthodontists should actively plan their patient’s dental occlusion before orthognathic surgery is performed. Therefore, orthodontic principles and guidelines for the surgery-first approach must be established to ensure that treatable malocclusions are attainable.
Methods
Any orthodontic or orthognathic movement of the MMC has six degrees of freedom for translation (i.e., forward/backward, up/down, right/left) and rotation (i.e., yaw, pitch, and roll) along three perpendicular axes. Three-dimensional computed tomography (3D-CT) is essential for diagnosis and setup when employing the surgery-first approach. Facial aesthetics are the primary reason that patients request orthognathic surgery. A desirable facial aesthetic should be related more to the movement of soft tissue components of the face rather than the hard tissue components. However, orthognathic surgery is performed to correct hard tissue problems before further manipulation of the soft tissue components. Accordingly, the principles proposed by Obwegeser for treating facial skeletal anomalies should be followed.
The face is a relatively symmetrical structure divided by the midfacial plane. Perfect facial symmetry is a theoretical concept that is rarely observed in the real world. Slight facial asymmetry is a common biological variation in healthy humans. However, symmetrical faces are perceived to be more attractive in both men and women. To assess facial symmetry in three dimensions, a midfacial plane must first be determined. The midfacial plane is typically constructed based on three skeletal structures along the facial midline (e.g., the sella, basion, and anterior nasal spine), or the vertical plane perpendicular to the Frankfort plane and passing through a midfacial structure (e.g., the nasion). This skeletal midfacial plane might differ from the midfacial plane constructed based on the reference points relative to the soft tissue structures along the facial midline (i.e., the soft tissue nasion, nasal tip, subnasale). For clinical evaluation purposes, the midfacial plane must be closely related to the external facial structures (i.e., the face perceived by the patient) and internal skeletal structures (i.e., the major site of orthognathic surgery moved by surgeons). Surgical reconstruction of the midfacial plane should align those reference points located on external facial structures. Therefore, a midfacial plane should be selected based on the position of external facial structures and internal skeletal structures.
Determining the midfacial plane in the upper and middle regions of the face
The midline of the skeletal structures might not correlate with that of the soft tissue structures. These midlines should be combined to form a single midfacial plane to assess facial and skeletal symmetry. The skeletal midline should be determined based on the axial and coronal views in multiplanar reformation (MPR) images obtained using 3D-CT. First, regarding the upper facial region, the skeletal midline should be selected to pass through most of the skeletal landmarks along the midline (e.g., the internal frontal crest, sagittal suture of the cranium, sella, nasion, and vomer). The skeletal midline should then be adjusted to pass through most of the soft tissue landmarks along the midline (e.g., the soft tissue nasion and nasal dorsum). It might be necessary to adjust the yaw and roll to symmetrically align most of the bilateral skeletal and soft tissue structures in the upper facial region. Because only facial soft tissue is viewable to the patient, the selected midfacial plane should pass through most of the soft tissue midlines. After determining the midfacial plane of the upper facial region, it should be moved to the middle facial region to confirm whether it is aligned with most of the skeletal and soft tissue midlines. If the midfacial plane is aligned with most of the skeletal midlines in the middle facial region (e.g., anterior nasal spine, posterior nasal spine, nasal septum, the midpoint of the foramen magnum, basion, opisthion, prosthion, and the mesial contact point of the maxillary central incisors) and also with the soft tissue midlines (e.g., nasal dorsum, nasal tip, subnasale, and stomion superior), the upper and middle facial regions should be positioned on a single midfacial plane. Otherwise, further analysis should be conducted to select a new midfacial plane that fits most of the skeletal and soft tissue midline points in the upper and middle facial regions. As soon as a suitable midfacial plane is determined, it can be used as the midfacial plane for further analysis and planning for surgical treatment. The midfacial plane (the green line in Fig. 1 a and b ) should be maintained throughout all facial symmetry assessments. In most 3D-CT software applications, the midfacial plane and the axial and coronal planes are perpendicular to each other ( Fig. 1 ). These three reference planes are used to assess the facial symmetry of the upper, middle, and lower facial regions.
Determining the skeletal, dental, and facial symmetry of the upper, middle, and lower facial regions
First, the axial plane (the red line in Fig. 1 c) should be levelled to the soft tissue nasion. By moving the axial plane inferiorly, the transverse discrepancy of each midline structure relative to the midfacial plane and yaw of each paired bilateral landmark can then be observed ( Fig. 1 a). Second, the coronal plane (the blue line in Fig. 1 c) should be levelled with the tip of the nose. Subsequently, by moving the axial plane posteriorly, the transverse discrepancy of each midline structure relative to the midfacial plane and roll of each paired bilateral landmark can be observed ( Fig. 1 b). Particular attention should be paid to the soft tissue midline points (e.g., soft tissue nasion, nasal dorsum, nasal tip, subnasale, stomion superior, stomion inferior, and chin) and their discrepancies relative to the midfacial plane, as well as all paired bilateral landmarks and their discrepancies in yaw or roll. Orthognathic surgery should be performed to align the soft tissue midlines with the midfacial plane and to correct the yaw and roll of each paired bilateral landmark in the MMC.
Optimizing the position of facial components to attain the most desirable results in aesthetics, function, and stability
- 1.
As soon as all discrepancies of the midline structures relative to the midfacial plane are determined and all discrepancies of bilateral structures in yaw and roll at various facial levels are measured, orthodontists and surgeons should design a treatment plan to adjust the MMC according to the patient’s needs, and to correct all 3D discrepancies (if possible). Any surgical movement combines 3D translation and rotation within six degrees of freedom.
- 2.
Midline discrepancy, yaw, and roll should be corrected first to attain a correlation between the midfacial plane and the symmetry of all bilateral structures. Adjustment of the yaw and roll of the MMC might be necessary to ensure that all soft tissue midlines correlate with the midfacial plane. All paired bilateral skeletal and soft tissue structures should then be symmetrical in the axial and coronal views, and all midfacial landmarks should be aligned with the midfacial plane. Biologically, it is difficult to align all midfacial landmarks along one midfacial plane and attain perfect symmetry of all bilateral structures. Orthodontists and surgeons should reach a consensus and detail why certain discrepancies will not be corrected (e.g., danger to vital organs, not visible on the external face, within normal range). Patients should be consulted on any discrepancies that will remain following surgery.
- 3.
Finally, surgical correction of the MMC along the sagittal plane should be considered last. The maxillary movement should be considered before the mandibular movement. The maxillary incisor show and lip incompetency, nasolabial angle, and smiling arc determine the vertical, anteroposterior, and transverse position of the anterior maxilla, respectively.
- 4.
After identifying the maxillary movements, the anteroposterior, vertical, and transverse mandibular movements should be determined based on the lower lip and chin contour, height of the lower facial region, and the consonance of the smile arc, respectively. Cephalometric norm or aesthetic guidelines can assist in determining the mandibular position (pending the patient’s preference).
- 5.
If the required anteroposterior mandibular movement exceeds the initial overjet, clockwise (CW) or counter-clockwise rotation (CCW) of the MMC should be considered to facilitate further chin advancement (in skeletal class II cases) or setback (in skeletal class III cases). Wolford et al. proposed the vertical displacement of the occlusal plane to enhance the horizontal movement of the jaw, which has become an integral part of orthognathic surgery. Skeletal class III cases are typically associated with maxillary deficiency, upper dental crowding, and labially proclined upper incisors. CW rotation of the MMC can accentuate the appearance of midfacial fullness and correct the axis of proclined incisors. Maxillary dental crowding can be relieved by premolar extraction during surgery. Skeletal class II cases are typically characterized by a severely retruded chin and considerably protruded mandibular incisors. Although CCW rotation of the MMC can attain greater anterior repositioning of the chin than would be attained using traditional surgical procedures, the resulting alignment of the mandibular and maxillary incisors causes a negative overjet. Premolar extractions and postoperative orthodontic treatment should be planned in advance to move the proclined mandibular incisors back to the normal inclination and to attain a positive overbite and overjet postoperatively. Therefore, the postoperative orthodontic treatment should be planned ahead to attain a positive overbite and overjet of the anterior teeth, as well as final dental interdigitation during postoperative orthodontic treatment.
- 6.
Posterior open bite in the molar area and premature contact in the canine or premolar areas can occur after the setup of MMC movements. Posterior open bite resulting from an excessive curve of Spee can be levelled through maxillary segmental osteotomy, or improved postoperatively through regional acceleratory phenomena (RAP) and orthodontic movement. Premature contact caused by transverse discrepancy in the canine or premolar areas can be corrected through surgical midline splitting of the maxilla, or improved postoperatively through selective grinding, RAP, and orthodontic movement.
- 7.
Genioplasty can create a labiomental fold, maintain sufficient chin–throat length, correlate the midfacial plane, and attain appropriate vertical facial proportions.
- 8.
Contouring of the gonial angle, mandibular body, and zygomatic arch can improve the facial soft tissue components.
Postoperative orthodontic treatment and attaining treatable malocclusions
- 1.
Following orthognathic surgery, the MMC should be symmetrical along the midfacial plane. Any yaw or roll of the MMC should be corrected through orthognathic surgery. The maxillary dental arch should correspond with the mandibular dental arch along a single midfacial plane, and there should be no tilting of the occlusal plane. All three dimensional dentofacial problems (i.e., translations and rotations along three axes) should be solved through osteotomy. Since the jaws are in a class I skeletal relationship, postoperative orthodontic treatment can be simplified to primarily anteroposterior dental movement to improve dental interdigitation. Therefore, treatable malocclusion typically implies that the malocclusion attained through orthognathic surgery primarily requires only anteroposterior orthodontic movement with minimal transverse or vertical orthodontic movement.
- 2.
For cases that combine CW or CCW rotation of the MMC, there might exist a certain degree of posterior open contact for dental occlusion in the molar area. If no intermaxillary fixation is used, patients should be encouraged to exercise their jaws and to commence a soft food diet as soon as possible after surgery.
- 3.
Postoperative orthodontic treatment can typically be finalized within 12–18 months of orthognathic surgery.
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