CC
A 24-year-old female was referred for combined surgical–orthodontic management of her class III skeletal malocclusion and maxillary hypoplasia. Her chief complaint was her “sunken face.”
HPI
The patient came in after 16 months of orthodontic treatment. The occlusion was aligned and prepared for corrective jaw surgery. No history of temporomandibular joint (TMJ) disorder was reported.
PMHX/PSHX/medications/allergies/SH/FH
The patient had no remarkable medical condition and required no systemic considerations. Elective orthognathic surgeries should be performed with caution in patients with American Society of Anesthesiologists grade III or higher. The risk of reoperation, relapse, and postoperative respiratory complications is increased in medically compromised patients. More specifically, patients with rheumatic diseases must be in remission stage and receive antirheumatic therapy. A history of denosumab uptake necessitates a 6-month drug holiday. Myotonic dystrophy and congenital myopathy hold an increased risk of respiratory distress symptoms, delayed recovery, dysphagia, lower lip ptosis, and drooling. Moreover, patients with numerous syndromic conditions, such as Ehlers-Danlos, osteogenesis imperfecta, neurofibromatosis, and Noonan syndrome, require utmost pre- and postoperative special care.
Examination
The surgeon should observe the lip–teeth relationship before surgery. The maxillary midline, nasal tip, and forehead relationship must be documented. Measuring the alar base and comparing it with the intercanthal distance is recommended.
Presurgical examination of patients occurs in four stages: TMJ, skeletal, dental, and soft tissue. General anesthesia requires special assessments, such as airway, cardiopulmonary, and neurologic assessments. The examination results of the patient are described below.
Temporomandibular joint component
No tenderness was reported for the joint and masticatory muscles. No signs of clicking or crepitus were detected. The patient had a maximum mouth opening of 45 mm with no deviation or deflection.
Skeletal component
No orbital dystopia was reported, and the intercanthal distance was normal. A slight nasal deviation was noted ( Fig. 61.1 ).
Transverse dimensions
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Maxillary dental midline was 2 mm deviated to the right.
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The mandibular dental midline was on.
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The chin point coincided with facial midline.
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The maxillary arch width was adequate.
Anteroposterior dimension
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Overjet: –1.5 mm
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Nasolabial angle: 95 degrees
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Mentolabial fold: shallow
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Leptoprosopic face
Vertical dimension
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Normal facial height
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Maxillary incisor length: 8 mm
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Upper incisor shows at rest (normal, 2–4 mm tooth show): 0 mm
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Upper incisor shows in full smile (normal full crown + 1 mm of gingival margin): 4 mm + interdental gingiva
Dental component
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Open bite
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Overjet (normal, +2.5 to + 3.5): –1.5 mm
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Class III is present at the first molar and canine bilaterally
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Appropriately leveled curve of Spee
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Ideal maxillary and mandibular arch form
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Sufficient dental decompensation was obtained without the need for premolar extraction (a 0.8-mm space is required for 1-degree incisor retraction; 1 mm of arch space will be obtained after 1.25 degrees of incisor proclining)
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Properly repaired dentition with no missing teeth or extractions
Soft tissue
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Adequate upper lip length and thickness
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Paranasal deficiency
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Nasolabial angle: 95 degrees
Imaging
Virtual surgical planning workflow
Data acquisition
The virtual surgical planning (VSP) workflow starts with acquiring data regarding the patient’s dentition; occlusion, orofacial, and pharyngeal hard and soft tissues; and their dynamic relation. This is achieved through standardized cone-beam computed tomography (CBCT) and intraoral and facial three-dimensional (3D) scanning. Images must be taken while the patient is in natural head position and must include the patient’s profile and frontal view and 45-degree pictures on both sides.
Occlusal surface registration can be performed using one of the following three approaches:
- 1.
Scan the patient’s impression using the CBCT. Using laser scanners in this method is not recommended because of the high possibility of undercut missing.
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Scan the fabricated dental cast from the direct impression. It is feasible to use both CBCT and laser scanners. Besides, the patient’s actual occlusion can be registered.
- 3.
Use intraoral scanners to record the dental arches and occlusal relationship with the accuracy of one micron. However, the intraoral scanning speed is significantly lower than for extraoral scanning procedures.
Data alignment, fusion, and synchronization
The next step is to record synchronization. The CBCT data are imported as Digital Imaging and Communications in Medicine (DICOM), and the orientation is set to natural head position in axial, frontal, and sagittal planes. The algorithms and the 3D outcome must be clinically validated. If necessary, the 3D outcome can be fine-tuned manually based on overlap of contours in CBCT images when moving or rotating the models.
Virtual patient model: Image rendering and segmentation
DICOM and stereolithography/standard triangle language (STL) files are visualized through volume and surface rendering. Volume rendering is obtained by assigning a color and opacity to voxels based on their Hounsfield unit (i.e., radiodensity). Using surface rendering includes identifying structure boundaries according to Hounsfield unit thresholds, allowing osteotomy simulation and movement of bony segments. Sequential two-dimensional visualization of voxel layers or contours is obtained with slicing in sagittal, coronal, or axial planes.
The compromised CBCT resolution prevents defining condylar heads from glenoid fossae surfaces and upper and lower dentition. These structures can be separated in segmentation process. Extraneous information can be eliminated from the volume, and a panoramic radiograph can be constructed from CBCT.
Virtual diagnosis
Using simulation imaging systems, 3D spatial positional changes can be visualized in real time ( Fig. 61.2 ). Virtual diagnosis necessitates providing the operation team with clinical photographs of the patient to confirm natural head position, incisor show both in repose and during animation, and the relation of soft tissue facial midline and bony midline. The following sequence is recommended in the diagnosis phase: (1) dento-maxillo-facial deformity and bite, (2) individual anatomy and pathology (e.g., fenestration or dehiscence), (3) airway, (4) TMJ, and (5) 3D cephalometric analyses on both hard and soft tissue.
Certain established methods are used to detect bony discrepancies, including (1) simulated cephalometric analysis, (2) virtual mirroring and performing color distance mapping on the contralateral side, and (3) volumetric analysis of the upper respiratory tract and facial bones.
Surgical planning and simulation
Virtual maxillary osteotomies can be made, and bony segments can be repositioned and adjusted with translational movements in all three spatial planes and rotational movements as roll, pitch, and yaw with up to six degrees of freedom ( Figs. 61.3 and 61.4 ).
Three-dimensional VSP allows these adjustments while referencing planes that are derived from the patient’s facial bones. For instance, when no orbital dystopia is present, the orbits can be considered as reference to adjust the roll of the osteotomized maxillary segment in patients with maxillary cant. Upper incisor inclination can be corrected through adjusting the pitch of osteotomized maxillary segment based on the true vertical plane. Yaw correction is performed to align maxillary and facial midlines.
Designing of cutting and positioning guides and hard tissue prediction
Le Fort cutting guides and plates can be designed and modified. The locations of plate screw holes can be determined according to the teeth roots, adjacent nerve branches, the antrum, and bone quality. Thus, pilot hole locators and drilling vectors can be aligned in ideal regions.
Achieving maximum intercuspation and detection of potential occlusal or bony collisions manually includes identification on dental casts and virtual replication. Detection of collisions is achieved through increasing the translucency of bony segments and finding anatomic overlaps via volume rendering. Another method is to scroll through axial, sagittal, and transverse slices in search of possible contacts. A combination of embedded algorithms for automation and manual handling is often used. During this step, the 3D skeletal prediction can be generated.
Soft tissue prediction and outcome monitoring
Virtual patient models can aid patient communication and provide predicted response to surgery. However, the nonlinear relationship between the soft tissue and bony movements complicates the soft tissue prediction after orthognathic surgery ( Fig. 61.5 ). Although the accuracy of predictions remains questionable, implementation of finite element methods and artificial intelligence may solve problems ( Table 61.1 ).
| Measurements in Patient | Normal Parameters for White Patients | Patient Notes |
|---|---|---|
| Cranial base angle: normal | SN to Frankfurt horizontal angle: 6.6 degrees | |
| SNA: 77.4 degrees | 78–84 degrees |
|
| SNB: 78.3 degrees | 75–80 degrees | |
| ANB: 0.9 degrees |
|
|
| SN-Pog: 78.4 degrees | 78–83 degrees | |
| Wits: 6.4 mm | +1 mm | |
| Maxilla incisor to mandible incisor: 1.9 mm | ||
| Maxilla right canine to mandible right canine: 2.9 mm | ||
| Maxilla left canine to mandible left canine: 3.4 mm | ||
| Open bite: 3.4 mm | Maxillary counterclockwise rotation | |
| Occlusal plane angle: 13.7 degrees | 8 ± 4 degrees | |
| Occlusal cant: 2.2 degrees | Distances between in the orbital point to occlusal plane: 46.4 mm on the left and 43.2 mm on the right |
Labs
Appropriate preoperative laboratory tests are selected based on each patient’s unique systemic health condition and associated risks depending on the procedure and anesthetic method of choice. Complete blood count, platelet count, and coagulation studies (i.e., prothrombin time, partial thromboplastin time, international normalized ratio) are routinely warranted.
Assessment
Maxillary deficiency in the sagittal plane direction resulting in class III skeletal deformity, anterior skeletal open bite, midline shift to the right side, and occlusal cant.
Treatment
Treatment involves both orthodontic and surgical phases. Presurgical orthodontic treatment is performed to align and level the occlusion, coordinate arches and decompensation, and provide sufficient space for osteotomies. The postoperative orthodontic treatment is done to achieve a stable occlusion and close the posterior open bite after surgery.
Le Fort I osteotomy is an optimal treatment for maxillary repositioning in all three directions. In this case, 4-mm maxillary advancement was done to solve the maxillary deficient. Considering the anterior open bite and absence of tooth show in rest position, 3-mm posterior maxillary impaction and 2-mm anterior inferior disimpaction were performed. Moreover, 2-mm inferior repositioning of the left side and 1-mm superior repositioning of the right side of the maxilla were considered to correct occlusal cant. Last, to correct the midline, maxilla had to be rotated 2.2 mm to the left side.
To treat vertical maxillary excess, Le Fort I is used in the case of less than 6 mm of impaction. For higher levels, horseshoe osteotomy, a modification of Le Fort I, is recommended. This procedure can accompany segmental osteotomies in the case of transverse deficiencies or dual occlusal plan. Surgically assisted rapid palatal expansion is the treatment choice in the case of having pure transverse issues.
The necessity of using hypotensive anesthesia should be discussed with the anesthesiologist. Using hypotension induced by beta-blockers is recommended because they are more effective and more easily titrated than gases. In healthy patients, arterial blood pressure can be reduced at most 30% below the baseline level with a minimum amount of 50 mm Hg. In patients who underwent bimaxillary surgery without hypotension, blood transfusion was necessary in 13% to 48% of the cases. In case of hypotension, an indwelling bladder catheter monitors the intraoperative output and renal perfusion. Next, nasotracheal intubation is performed. The tube should be placed below the vocal cords for proper stability during premaxillary manipulations. A shoulder roll is placed to extend the neck.
Incision
Anterior, lateral, and pterygomaxillary regions are exposed most commonly via horizontal circumvestibular incision, extending contralaterally from one upper first molar to another. A full mucoperiosteal incision is placed above keratinized gingiva and over the level of teeth apices using electrocautery or a scalpel. The parotid papilla of Stensen’s duct must be identified and protected. Keeping the incision perpendicular to its underlying bone curvature averts buccal fat pad extrusion. An inverted V design is used to release the frenulum. At the anterior region, the incision must be kept below the anterior nasal spine (ANS) to prevent nasal mucosa perforation into the nasal cavity.
Tissue reflection at a subperiosteal plane is initiated at piriform rims using a periosteal elevator. The subperiosteal dissection is limited to the tissue above the incision line, and the mucogingival tissue cuff remains untouched. Any vertical or horizontal vestibular incision that leads to periosteal tearing can divulge the anterior lobe of buccal fat pad, and its subsequent herniation in severe cases of tearing complicates the surgical approach and manipulation of posterior maxillary soft and hard tissue.
Subperiosteal dissection on the labial portion of the maxilla causes detachment of muscle insertions, which are responsible for facial expressions. This can result in altered anatomic landmarks (e.g., lip line). The facial expression muscles are entrapped within a superficial musculoaponeurotic system (SMAS) and function as a connected gear because of their attachments either to one another or to facial bones.
Gentle dissection restricts manipulation to the subperiosteal plane, averting displacement of muscle insertions and tearing periosteum and supraperiosteal tissue, leading to injured terminal branches of neurologic and vascular components. Exposed and manipulated muscular structures depend on selected incision design and position and the dissection technique’s extension and nature (i.e., submucosal, trans- or paramuscular).
Muscular transections
Facial expression muscles of the nasolabial region are responsible for upper lip and nasal base movements. Their attachment to the labial portion of the maxilla also determines the vestibular depth. Vestibular incisions, such as the horizontal circumvestibular incision, can approach deep layers of SMAS, consisting of the incisivus labi superiorirs (ILS), depressor septi nasalis, myrtiformis, transverse nasalis, and dilator naris muscles. The transverse nasalis, myrtiformis muscle, and levator anguli oris muscles are transected when performing horizontal circumvestibular incision for Le Fort I surgery. The incision can lead to loss of tension in the intact superior layer of midface musculature because of its intertwining with the deep layer. However, the majority of depressor septi nasi remains intact.
The horizontal cirumvestibular incision can often transect with the ILS when placed 5 to 10 mm superior to the mucogingival junction. If cut, muscular fiber ends can be visualized and approximated via double-layer suturing.
Deep-layer SMAS muscles in the posterior maxilla that may be transected by horizontal incision during Le Fort I are the levator anguli oris (LAO) and buccinator. The LAO originates 1 cm below the infraorbital foramen at the maxillary canine fossa. Transecting the LAO can impede the elevation of angles of the mouth and the patient’s smiling profile.
In-depth cognition of the precise location of these muscular attachments can improve incision design and minimize adverse postoperative changes in facial expression.
Retraction
A reverse-angled Obwegeser retractor is placed at the pterygomaxillary junction for feasible exposure, careful enough to avert iatrogenic periosteal laceration.
Tissue inferior to the incision is slightly or not at all elevated. If interdental osteotomies are to be performed, the keratinized gingiva is subperiosteally elevated conservatively using a Woodson elevator.
Osteotomy
Lateral wall osteotomy
Osteotomy cuts can be created with steps or in a sloping shape. The osteotomy must be below the infraorbital foramen and pterygomaxillary fissure and above root apices. Osteotomy starts from a point 3 to 4 mm above the nasal floor and goes toward the first molar region. In the anterior part, the osteotomy should be performed below the level of the inferior turbinate to prevent harming the nasolacrimal complex. At this stage, a point 30 to 35 mm above the first molar bracket is reached.
A 5-mm space from the root apices and the osteotomy cut must be preserved. To avoid infraorbital pedicle injury, the osteotomy cut should not exceed 30 mm from the alveolar border. Besides, the osteotomy cut should be performed less than 20 mm from the inferior border of the pterygomaxillary suture to avoid injury to the maxillary artery. The distance between the inferior extent of the pterygomaxillary fissure to the posterior superior alveolar artery, infraorbital artery, and descending palatine artery are 15 mm, 32 mm, and 25 mm, respectively.
For maxillary impaction, two osteotomy lines are required. Both of them should follow the rules mentioned earlier. Osteotomies are parallel and are created downward from the piriform rim to the zygomaticomaxillary (ZM) buttress. The distance between two cuts is defined in the treatment planning phase. Thereafter, the bony segment between the osteotomies is removed.
Lateral wall osteotomy can be done using customized osteotomy guides fabricated based on the patient’s CT. Two screw holes are considered in each part of the guide for fixation. After the osteotomy, the bridging structure is segmented and replaced with a repositioning guide. The superior portion of the osteotomy guide acts as the retainer for the repositioning guides and remains at the site. Commonly used guides consist of the following components: occlusal splint, bone attachments, connecting arms, and osteotomy line indicator. Splints can be eliminated from the design when creating definitive repositioning holes.
Pterygoid plate separation
The pterygoid plate is separated using a curved osteotomy placed behind the tuberosity at the pterygomaxillary junction downward and inferiorly. The upper edge of the instrument must be above the previously created horizontal osteotomy. A finger is placed at the palatal side at the hamulus and tuberosity junction to feel the extent of the osteotomy and avoid soft tissue perforation. The anterior edge of the osteotome must be angled inferiorly and medially. The created osteotomy should have a width of 6 to 8 mm.
Lateral nasal wall and septal osteotomy
At the anterior extension of the lateral maxillary osteotomy, the lateral nasal wall is osteotomized using a safe-ended straight osteotome. The cut is made parallel to the nasal floor below the inferior turbinate. Lateral walls are positioned divergently, and the osteotomy should follow the direction. Caution must be taken not to go deeper than 25 to 30 mm. A U -shaped cut is created to separate the nasal septum. The osteotomy line starts above the ANS and extends posterior and inferiorly parallel to the nasal floor.
The Le Fort I osteotomy usually affects the nasal and labial esthetic, especially when advancement or impaction procedures are performed. Several methods have been proposed to confine the adverse effects, such as the alar cinch technique with or without a V-Y mucosal suturing, ANS reduction, nasal floor reduction, excision of the alar base, adjusting the caudal septum, or different nasal tip corrections. In addition to the mentioned approaches, subnasal maxillary osteotomy design can maintain the perinasal musculature insertions and the ANS or septum position with excellent clinical outcomes. In this approach, instead of the conventional circumferential incision, a V -shaped one is made in the anterior portion that saves the soft tissue adjacent to the piriform apparatus. Thus, the attachment of the muscles is preserved. Without undermining the flap, an anterior subspinal osteotomy is performed. The rest of the procedure is performed the same as the traditional approach.
Downfracture and mobilization
A bilateral inferior digital pressure at the canine fossa can readily separate the osteotomized segment. Cautions must be taken to avoid nasal mucosa tearing. A Seldin elevator or tongue retractor is placed at the posterior tuberosity to complete mobilization and push the posterior maxilla downward. If unexpected resistance is felt, osteotomies should be revised.
Posterior interference removal
During maxillary impaction, nasal septum deviation can be prevented by making a deep groove in the midline with a round bur or trimming the inferior part of the septum. Bony interferences may also be seen at the tuberosity and lateral nasal walls and can be trimmed with a rongeur. Besides, partial inferior turbinectomy is necessary when more than 5 mm of impaction is indicated. Complete removal of the inferior turbinate may cause some complications.
The pyramidal processes of the palatine bone must also be reduced. The greater palatine nerve and artery should be retracted to prevent any injuries. In addition, the posterior tuberosity, anterior pterygoid plate, and posterior lateral maxillary can also be reduced to allow facile displacement.
Surgical splint placement
The surgical splint is ligated to the upper teeth using arch wire. Next, the upper and lower jaws are fixated together. The triangle finger maneuver is performed to place the mandibular condyle at the optimal position. In detail, two fingers are placed at the gonial notch and thumbs at the chin. Two fingers apply upward pressure, and the thumbs exert a downward force in the posterior direction. In the VSP method, splints are fabricated based on the occlusal scan rather than plaster model surgery ( Fig. 61.6 ). Surgical splints can be either separated from the osteotomy or repositioning guides or be a part of them to increase their stability.
