Understanding Skeletal Discrepancies Requiring Surgery
Orthodontic treatment alone cannot correct skeletal discrepancies—tooth movement occurs within the existing bony framework, and teeth cannot move beyond alveolar bone boundaries. Severe Class II skeletal patterns with anteroposterior maxillomandibular discrepancies exceeding 8-10mm, Class III patterns where the mandible significantly exceeds maxillary width, severe vertical abnormalities (anterior open bite or excessive overbite), or transverse deficiencies (crossbite with skeletal origin) require surgical correction combined with orthodontics.
Surgical-orthodontic treatment planning begins with comprehensive analysis including cephalometric radiographs, CBCT imaging, and facial photographs in multiple planes. The cephalometric analysis quantifies skeletal discrepancies: SNB angle minus SNA angle reveals anteroposterior jaw relationship (normal approximately 1-2 degrees, Class II skeletal patients present 5-10+ degree discrepancy, Class III patients present negative values). Vertical dimensions including facial height, palatal plane inclination, and mandibular plane angle reveal whether vertical abnormalities exist. Diagnostic wax-ups simulate final occlusion; surgical prediction tracing determines necessary jaw movement to achieve normalized occlusal relationships.
Patient expectations require careful assessment. Orthognathic surgery produces substantial facial changes visible to family and friends. While correction often improves esthetics, breathing, and function dramatically, patients must understand the commitment. Proffit et al. (2012) demonstrated that surgical-orthodontic treatment requires 6-12 months of pre-surgical orthodontics (decompensation), a surgical event requiring 1-2 weeks of restricted activity, post-operative swelling lasting 3-6 weeks, and 3-6 months of post-surgical orthodontics. Total treatment duration spans 12-24 months from pre-surgical consultation to treatment completion.
Le Fort I Osteotomy for Maxillary Correction
The Le Fort I osteotomy, named after French surgeon René Le Fort who identified the fracture pattern in 1901, allows superior-inferior repositioning, anteroposterior advancement or setback, and transverse widening of the maxilla. The surgical technique involves creating a horizontal cut through the maxilla above the apices of the teeth, extending posteriorly along the lateral maxillary walls, separating the maxilla from the midfacial skeleton while maintaining palatal blood supply through the greater and lesser palatine vessels.
The surgical cut begins with access through a vestibular incision in the maxillary buccal sulcus, separating mucosa and periosteum to expose the lateral maxillary walls. Using oscillating saws and chisels, the surgeon creates horizontal cuts extending from the pyriform aperture posteriorly toward the pterygoid plates. A transpalatal cut separates the hard palate from the nasopharyngeal soft tissues. Once the maxilla is fully mobilized, it can be repositioned superiorly for anterior open bite correction, inferiorly for excessive vertical dimension reduction, advanced anteriorly for Class II correction, or set back for anterior protrusion correction.
Multiple maxillary segments may be created. The standard Le Fort I uses a single segment; segmental Le Fort I involves additional vertical cuts through the maxilla, creating separate alveolar segments that can be moved independently. This approach accommodates complex occlusal requirements or corrects cant (asymmetric vertical maxillary position). Maxillary expansion can be accomplished with Le Fort I by cutting and rotating the palatal segments outward. Surgeons select specific Le Fort I variants based on the three-dimensional correction required.
Fixation techniques have evolved from external skeletal fixation and internal wiring to modern rigid fixation using titanium plates and screws. Plates positioned along the lateral maxillary walls at the zygomaticomaxillary suture areas provide stable fixation that permits earlier oral function and allows application of orthodontic forces within 1-2 weeks post-operatively. Segmental osteosynthesis with separate fixation of palatal and alveolar segments increases stability but adds surgical complexity.
Bilateral Sagittal Split Osteotomy for Mandibular Correction
The Bilateral Sagittal Split Ramus Osteotomy (BSSO), developed as an improvement over older condylectomy procedures, allows advancement or setback of the mandible while preserving the temporomandibular joint and maintaining blood supply. The procedure involves sagittal cuts through the mandibular rami (vertical plates posterior to the dentition), extending from above the lingula (where the inferior alveolar neurovascular bundle enters) to below the inferior border of the mandible, creating a split in the bone with the proximal segment attached to the condyle and the distal segment containing the tooth-bearing portion.
The BSSO permits anteroposterior repositioning of 10mm or greater and can accomplish limited rotational correction. For Class II correction, the mandible is advanced (moved forward), increasing the SNB angle and reducing the ANB discrepancy. For Class III correction, the mandible is set back (moved posteriorly), decreasing SNB angle. The procedure preserves the temporomandibular joint condyle position, allowing normal post-operative joint function if proper surgical technique maintains correct condylar position during fixation.
Split location and sagittal split position critically influence inferior alveolar nerve (IAN) location and injury risk. The nerve runs within the mandibular canal from the lingula posteriorly to the mental foramen anteriorly. During BSSO, the surgeon must visualize the IAN location, preserve its integrity, and ensure the split creates adequate bony separation between the nerve and the osteotomy sites. Kamer et al. (2013) analyzed nerve injury risks during BSSO, finding that IAN injury occurred in 15-20% of cases, with most injuries representing temporary sensory disturbance lasting weeks to months. Permanent nerve injury affecting function or sensation occurred in less than 2% of properly performed cases.
Sagittal split position affects final outcomes. A split positioned too far lingually compromises the medial pterygoid muscle attachment, altering post-operative muscle function and potentially increasing open bite relapse. A split positioned too far buccally increases risk of IAN transection. Optimal positioning places the split approximately 5-8mm medial to the buccal cortex, balancing visualization and safety.
Virtual Surgical Planning and 3D Simulation
Modern orthognathic surgery increasingly uses 3D virtual surgical planning (VSP) software that creates digital surgical simulations before actual surgery. High-resolution CBCT imaging is converted to 3D digital models; the surgeon creates virtual osteotomy cuts, repositions maxillary and mandibular segments to achieve planned positions, and evaluates the simulated occlusion and facial changes. This planning allows precise definition of surgical movements and communication of surgical objectives to the entire team.
3D virtual planning improves surgical accuracy significantly. Kobayashi et al. (2012) compared patients treated with traditional cephalometric planning versus 3D virtual planning, demonstrating that VSP patients achieved final occlusal and skeletal relationships more closely matching surgical predictions. VSP reduces the risk of under-correction or over-correction and permits identification of potential complications before actual surgery. If the simulated surgical movements create inferior alveolar nerve impingement or incomplete disassociation of bone segments, the surgeon recognizes these issues during planning and modifies the approach accordingly.
Patient-specific surgical guides created through 3D printing and modeling technologies further improve accuracy. A surgical splint is fabricated from the virtual plan, guiding the surgeon's maxillary repositioning intraoperatively. Mandibular cutting guides ensure accurate sagittal split position and angulation, reducing deviation from planned osteotomy sites. While these technologies add cost and require surgical infrastructure investment, they improve outcomes and reduce operative time, particularly for complex asymmetric cases.
Orthodontic Decompensation: Uncovering the Skeletal Discrepancy
Pre-surgical orthodontics differs fundamentally from conventional treatment—the objective is not to create a perfect bite but to decompress the dentition by moving teeth opposite to planned surgical correction. In a Class II skeletal patient planned for mandibular advancement, pre-surgical orthodontics flattens the curve of Spee, increases the overbite, and creates anterior open bite tendency by moving maxillary incisors lingually and mandibular incisors buccally. This decompensation fully reveals the underlying skeletal discrepancy that surgery will correct.
The decompensation timeline typically requires 6-12 months depending on the magnitude of skeletal discrepancy and complexity of the pre-surgical dentition. During this phase, the patient experiences progressively worsening occlusion—what would normally represent treatment failure in conventional orthodontics represents successful progress in surgical cases. Decompensation confirms that the surgical plan will achieve adequate correction; if the predicted decompensated bite appears unstable or if decompensation creates excessive TMJ loading, the surgical plan may require adjustment.
Proffit and Jackson (1976) established that timing of decompensation influences final outcomes. Excessive pre-surgical decompensation creates stress on the temporomandibular joint and increases surgical correction requirements; insufficient decompensation leaves residual skeletal or dental discrepancy. The orthodontist and surgeon coordinate decompensation magnitude through review of cephalometric radiographs and surgical prediction tracings, ensuring that the surgical movement precisely corrects the skeletal discrepancy created by decompensation.
Surgical Sequence and Bimaxillary Procedures
Many patients require both maxillary and mandibular osteotomies to achieve skeletal and occlusal correction. Bimaxillary procedures (Le Fort I plus BSSO) address Class II or Class III patterns that require correction of both jaws. The surgical sequence—whether to mobilize maxilla first or mandible first—influences the final position achieved and the stress distribution during fixation.
Most surgeons prefer maxilla-first sequencing, mobilizing and repositioning the maxilla first, then adjusting mandibular position relative to the repositioned maxilla. This approach allows the maxilla to establish the aesthetic maxillary incisor position and establish maxillary arch form, with the mandible then positioned to achieve proper occlusal contacts and intermaxillary relationships. Mandible-first sequencing (mobilizing mandible first, then maxilla) can address situations where specific mandibular positioning is critical but adds complexity.
The surgical day involves general anesthesia with intubation allowing full surgical access. For Le Fort I, incisions are made within the mouth (intraoral) to avoid facial scarring. BSSO incisions remain intraoral (internal to the mandibular ramus). Once mobilized, the maxilla and mandible are positioned using surgical splints, wires, or fixation devices guiding them to previously planned positions. Intermaxillary fixation (IMF) traditionally wired the teeth together for 6-8 weeks post-operatively; modern rigid plate fixation permits earlier removal of IMF (sometimes none at all), allowing oral function within 1-2 weeks.
Post-operative Management and Healing Timeline
Immediate post-operative period involves pain management (typically opioid-based analgesics for 3-7 days, then NSAIDs), swelling control through ice application and elevation, and diet restricted to soft foods. Patients should expect significant facial swelling peaking at 48-72 hours post-operatively and persisting noticeably for 2-3 weeks. Normal social appearance returns gradually over 6-8 weeks; minor residual swelling may persist for 3-6 months.
Bony healing at osteotomy sites follows predictable remodeling. Cancellous bone at the Le Fort I osteotomy site achieves union within 6-8 weeks; cortical bone contact may require 8-12 weeks for complete fusion. BSSO sites, involving cancellous bone with good vascularization, similarly heal within 8-12 weeks with adequate rigid fixation. During this healing period, orthodontic forces should remain minimal or discontinued; aggressive orthodontics during bone healing risks non-union or malunion.
Post-operative orthodontics begins approximately 2-4 weeks post-operatively once initial healing is confirmed radiographically. This finishing phase refines the occlusion, achieves proper intercuspation, and often reveals that the surgical movement created slightly different occlusal relationships than anticipated. The post-surgical phase typically requires 3-6 months of additional orthodontic treatment. Bell, Proffit, and White (1980) demonstrated that combined surgical-orthodontic treatment achieves superior esthetic and functional outcomes compared to either modality alone, with 92% of surgically treated patients maintaining skeletal corrections beyond 2 years follow-up.
Relapse Prevention and Long-Term Stability
Relapse—partial reversal of surgical correction—represents the primary long-term concern. Vertical changes show greater relapse tendency than anteroposterior changes; mandibular correction shows slightly greater relapse than maxillary. Relapse typically occurs within the first 6 months post-operatively as muscles and soft tissues adapt to new jaw positions. Proper decompensation, adequate surgical correction, and careful post-surgical orthodontics minimize relapse but cannot completely prevent it.
Orthodontic retention becomes particularly important after surgical correction. Fixed lingual bonded retainers maintain anterior alignment; removable retainers prevent relapse. Many post-surgical patients benefit from extended retention—fixed retainers remaining indefinitely on anterior teeth, removable retainers worn nightly for 6-12 months then several times weekly thereafter. This extended retention compensates for the greater relapse tendency compared to non-surgical orthodontic cases.
Skeletal stability of surgically repositioned jaws relates directly to final occlusal stability. If post-surgical orthodontics achieves stable intercuspation with good posterior contacts and appropriate anterior-posterior and vertical relationships, relapse remains minimal. Conversely, if post-surgical orthodontics fails to achieve stable occlusion, the jaws tend to relapse significantly toward pre-surgical positions. This emphasizes why careful post-surgical orthodontic finishing represents a critical phase determining long-term surgical success.