Orthognathic Surgery: Interdisciplinary Orthodontic-Surgical Treatment Planning

Orthognathic surgery, the surgical correction of dentofacial skeletal discrepancies, represents the definitive convergence of orthodontics and oral and maxillofacial surgery. These procedures are indicated not merely for aesthetic enhancement but for the restoration of functional occlusion, airway patency, temporomandibular joint health, and long-term dentofacial stability. The contemporary approach demands a seamless interdisciplinary workflow from initial consultation through postoperative retention, integrating three-dimensional imaging, virtual surgical planning, and evidence-based surgical techniques.

Indications and Diagnostic Framework

Orthognathic surgery is indicated for skeletal discrepancies that exceed the envelope of orthodontic compensation. These include mandibular anteroposterior excess or deficiency (Class II or Class III skeletal patterns), vertical maxillary excess (long face syndrome with gingival display and lip incompetence), vertical maxillary deficiency (short face syndrome with deep bite and reduced lower facial height), transverse maxillary deficiency (posterior crossbite with skeletal origin), and facial asymmetries (hemimandibular hyperplasia, condylar hyperplasia, or traumatic deformities). Increasingly, obstructive sleep apnea (OSA) refractory to continuous positive airway pressure (CPAP) therapy is recognized as a primary indication for maxillomandibular advancement, which enlarges the pharyngeal airway space.

The diagnostic workup begins with a comprehensive clinical examination assessing facial proportions in three dimensions: frontal view (facial symmetry, upper/middle/lower facial thirds, lip competence, incisor display at rest and smile), profile view (nasolabial angle, labiomental fold, chin projection), and intraoral examination (occlusion, arch form, dental compensations, periodontal status). Standardized facial photographs and dental study casts complement the clinical assessment, providing objective documentation and medicolegal records.

Cephalometric Analysis and Treatment Planning

Lateral cephalometric analysis remains the cornerstone of orthognathic treatment planning, despite the growing role of three-dimensional imaging. Key cephalometric measurements include: SNA (sella-nasion-A point) and SNB (sella-nasion-B point) for maxillary and mandibular anteroposterior position; ANB for sagittal discrepancy; mandibular plane angle (SN-GoGn or FMA) for vertical facial pattern; upper incisor to NA and lower incisor to NB for dental inclinations; and soft tissue parameters including nasolabial angle, upper lip to E-line, and lower lip to E-line. The systematic cephalometric analysis allows the clinician to quantify the skeletal, dental, and soft tissue contributions to the overall facial deformity.

The surgical treatment objective (STO) involves a cephalometric prediction tracing that simulates the planned osteotomies and soft tissue response. The STO answers critical questions: which jaws require surgery, in what sequence, with what magnitude and direction of movement, and whether adjunctive procedures such as genioplasty are indicated. Conventional acetate tracing overlays have been largely supplanted by digital cephalometric software (Dolphin Imaging, Quick Ceph) that allows rapid manipulation and quantitative measurement of surgical movements.

Virtual Surgical Planning and 3D Technologies

The advent of cone-beam computed tomography and computer-aided surgical simulation (CASS) has revolutionized orthognathic surgery planning. CBCT provides a volumetric dataset of the craniofacial skeleton, enabling three-dimensional assessment of facial asymmetry, condylar position, and airway dimensions. The digital workflow involves segmentation of the maxillofacial skeleton from the CBCT data, fusion with digital dental models obtained from intraoral scanning, virtual osteotomies and repositioning, fabrication of three-dimensional printed surgical splints, and, increasingly, patient-specific osteosynthesis plates and cutting guides.

Virtual surgical planning (VSP) offers distinct advantages over traditional two-dimensional planning: it enables true three-dimensional assessment and correction of facial asymmetry; it provides quantitative measurement of condylar torque and position changes; it facilitates complex multi-piece maxillary osteotomies by visualizing interferences between osteotomy segments; and it improves surgical efficiency by eliminating the need for intraoperative model surgery. Studies comparing VSP with conventional planning report improved accuracy of maxillary repositioning, particularly in the transverse and vertical dimensions, and reduced operative time.

Osteotomy Techniques

Le Fort I Osteotomy

The Le Fort I osteotomy is the workhorse procedure for maxillary repositioning. The horizontal osteotomy is performed at the Le Fort I level, from the piriform rim anteriorly through the maxillary sinus lateral and posterior walls, extending to the pterygomaxillary junction. Downfracture of the maxilla provides access for septoplasty if needed, turbinate reduction, and mobilization. The mobilized maxilla can be repositioned in all three planes: anteriorly for maxillary advancement, posteriorly for setback, superiorly for impaction (to reduce excessive gingival display), inferiorly for downgraft (to increase incisor display), and rotationally for asymmetry correction. Rigid internal fixation with titanium miniplates at the piriform rim and zygomaticomaxillary buttress provides stable fixation without maxillomandibular fixation (MMF).

The Le Fort I segmented osteotomy divides the maxilla into two, three, or four segments to address transverse discrepancies, arch form mismatches, and occlusal plane canting simultaneously with anteroposterior and vertical repositioning. Segmentation increases surgical complexity and requires precise preoperative planning; VSP with intermediate and final splints is essential for accurate segment positioning.

Bilateral Sagittal Split Osteotomy (BSSO)

The bilateral sagittal split osteotomy (BSSO), originally described by Trauner and Obwegeser and modified by Dal Pont and Epker, enables mandibular advancement, setback, or rotation. The osteotomy consists of a medial horizontal cut above the lingula, a vertical buccal cut through the external oblique ridge, and a sagittal split connecting the two cuts through the mandibular body. The split separates the tooth-bearing distal segment from the proximal condyle-bearing segment. Following mobilization, the mandible is positioned into the planned occlusion using an intermediate or final surgical splint, and rigid fixation is achieved with bicortical positional screws or a titanium miniplate with monocortical screws.

The key advantage of BSSO with rigid internal fixation is the avoidance of prolonged MMF, allowing early jaw mobilization, improved postoperative nutrition, and enhanced airway safety. The primary risk is injury to the inferior alveolar nerve, which traverses the mandibular canal within the distal segment of the split. Temporary neurosensory disturbance in the distribution of the inferior alveolar and mental nerves occurs in 30% to 80% of patients, while permanent sensory deficit occurs in approximately 5% to 10%. Careful osteotomy technique, preservation of the nerve within the distal segment, and avoidance of compression during fixation minimize nerve injury risk.

Genioplasty

Genioplasty (osseous chin surgery) is a frequent adjunctive procedure that refines chin projection, height, and symmetry. The horizontal sliding genioplasty involves an osteotomy below the mental foramen with anterior, posterior, superior, or inferior repositioning of the inferior segment. Genioplasty is preferred over alloplastic chin implants for its versatility (allowing three-dimensional repositioning), long-term stability (bone union without resorption of the underlying bone), and avoidance of a foreign body. The mental nerves must be visualized and protected during the osteotomy to prevent paresthesia of the lower lip.

Interdisciplinary Workflow

The orthognathic surgical-orthodontic workflow spans approximately 18 to 24 months and proceeds through distinct phases. Pre-surgical orthodontics, typically lasting 12 to 18 months, aims to decompensate the dentition: removing the natural dental compensations that mask the underlying skeletal discrepancy. In a Class III patient, the mandibular incisors are tipped lingually, and in a Class II patient, they are tipped labially as the body attempts to achieve functional occlusion despite the skeletal mismatch. Pre-surgical orthodontics aligns and levels the arches, coordinates arch forms, and positions the teeth ideally on their respective skeletal bases so that the surgical correction addresses the full skeletal discrepancy, creating maximum occlusal interdigitation at surgery.

The surgical phase involves the planned osteotomies, with rigid internal fixation. Interim elastic guidance rather than rigid MMF facilitates postoperative recovery and airway management. Post-surgical orthodontics, lasting 4 to 6 months, provides fine occlusal detailing, settling the occlusion through light vertical elastics to achieve maximum intercuspation.

Stability and Relapse

Postoperative stability varies by the direction and magnitude of movement and the specific osteotomy performed. Maxillary impaction and mandibular setback are the most stable movements, with less than 1 mm of long-term relapse. Maxillary advancement is moderately stable, with approximately 10% to 20% horizontal relapse, primarily due to soft tissue tension from the palatal and buccal mucoperiosteum. Maxillary downgraft is the least stable movement, with vertical relapse of 20% to 40%, attributed to the stretch of the masticatory musculature and the compressive forces of occlusion. Mandibular advancement stability depends on the magnitude of movement and the method of fixation; advancements exceeding 10 mm benefit from bicortical screw fixation and consideration of suprahyoid myotomy or skeletal suspension techniques to reduce relapse from suprahyoid muscle tension.

Complications and Risk Management

Beyond neurosensory disturbance, potential complications of orthognathic surgery include hemorrhage (primarily from the descending palatine artery during Le Fort I or the facial artery and retromandibular vein during BSSO), unfavorable fractures (bad splits during BSSO, which occur in 2% to 5% of cases), infection (1% to 5%, higher in segmented cases), malunion or nonunion, temporomandibular joint dysfunction, and airway compromise immediately postoperatively. The risk of bad split is increased in the presence of impacted third molars, thin mandibular ramus, and advanced patient age. Prophylactic removal of mandibular third molars 6 to 9 months before BSSO allows bone fill of the extraction socket, reducing the risk of unfavorable fracture along the weakened mandibular angle.

Orthognathic surgery, executed within a well-coordinated interdisciplinary framework with contemporary three-dimensional planning and rigid internal fixation, achieves predictable and stable correction of dentofacial deformities. The dual benefit of enhanced facial aesthetics and restored occlusal function yields high patient satisfaction rates exceeding 90%, with profound improvements in oral health-related quality of life, psychosocial well-being, and in appropriately selected OSA patients, objective improvement in polysomnographic parameters and cardiovascular health.