# Virtual Surgical Planning in Orthognathic Surgery
## Overview
Virtual surgical planning (VSP) uses three-dimensional digital imaging and computer-aided design to plan orthognathic surgical procedures. It replaces or supplements traditional 2D cephalometric analysis and model surgery on articulator-mounted casts. VSP enables simulation of osteotomies and skeletal movements with real-time visualization of soft tissue changes, and CAD/CAM splints, cutting guides, and patient-specific fixation plates are generated from the virtual plan.
## VSP Workflow
### Step 1: Data Acquisition
A full-skull CBCT scan is obtained with an appropriate field of view covering the entire craniofacial skeleton. The patient is scanned in natural head position or with digital correction applied afterward, with a centric relation bite or wax bite registration in place and slice thickness of 0.5 mm or less for optimal resolution. Digital dental models are obtained via intraoral scanning (preferred) or optical scanning of alginate or polyvinyl siloxane impressions, capturing accurate occlusal detail that CBCT alone cannot provide due to metal artifact and limited resolution at dental surfaces. Standardized facial photographs in eight views (frontal, profile, oblique, smile, and submental) are obtained, and an optional 3D facial surface scan using stereophotogrammetry or structured light scanning can be acquired for soft tissue overlay.
### Step 2: Data Processing and Segmentation
CBCT DICOM data are imported into VSP software such as ProPlan CMF, Dolphin 3D, IPS CaseDesigner, or Materialise. A 3D skeletal model is generated through segmentation using thresholding of bone density. Digital dental models are then merged with the CBCT skeletal model using surface-matching algorithms, replacing the teeth in the CBCT model with higher-resolution intraoral scan data and eliminating CBCT dental artifacts from brackets, restorations, or fillings.
### Step 3: 3D Cephalometric Analysis
Skeletal, dental, and soft tissue landmarks are placed on the 3D model, and automated or semi-automated cephalometric analysis is performed. The advantages over 2D analysis are substantial: superimposition errors are eliminated, asymmetry can be assessed in roll, yaw, and pitch, true 3D distances and angles are measured, and the transverse dimension is evaluated accurately.
### Step 4: Virtual Osteotomies
The surgeon performs virtual osteotomy cuts on the 3D model, including the Le Fort I horizontal maxillary cut with adjustable level, BSSO sagittal cuts on the mandibular ramus and body, horizontal chin osteotomy for genioplasty, and interdental cuts for segmental osteotomies in multi-piece maxillary procedures. Osteotomy lines can be adjusted for optimal anatomy, avoiding roots, nerves, and sinuses.
### Step 5: Skeletal Movement Simulation
Each segment is independently moved in six degrees of freedom (three translational and three rotational), and movements are quantified in millimeters and degrees. The planned occlusion from the dental setup or orthodontic plan guides the final position. For two-jaw cases, the intermediate position places the first jaw operated in relation to the unoperated jaw. Color-coded collision detection identifies bony interferences.
### Step 6: Soft Tissue Prediction
Finite element modeling or mass-spring models simulate the soft tissue response to skeletal movements, predicting changes to the nose, lips, chin, and facial contour. Accuracy varies but is generally within 1-2 mm for most points. This feature is useful for patient communication and setting realistic expectations, though it is not yet reliable enough to replace clinical judgment.
### Step 7: Splint and Guide Design
The intermediate splint positions the first jaw in its planned relationship to the unoperated jaw when the second jaw is being operated. The final splint positions both jaws in the planned final occlusion. Both splints are designed digitally with the planned occlusal relationship. Optional cutting guides are patient-specific guides that fit onto the maxilla or mandible to mark exact osteotomy positions. Optional patient-specific fixation plates are pre-bent plates designed from the planned skeletal position, eliminating intraoperative plate bending.
### Step 8: Manufacturing
Splints are 3D printed using stereolithography (SLA) or fused deposition modeling (FDM), or milled from acrylic or nylon. Cutting guides are 3D printed in biocompatible resin or nylon. Patient-specific plates are CNC-milled from titanium. Turnaround time is typically 2-4 weeks from the planning session to delivery.
Flowchart diagram illustrating the complete VSP workflow from CBCT and intraoral scan acquisition through data merging, 3D cephalometric analysis, virtual osteotomies, skeletal movement simulation, splint design, and 3D printing of the final CAD/CAM surgical splints
## VSP Planning Session
### Interactive Planning
Most VSP services offer a live web-based planning session with a biomedical engineer. The surgeon directs the movements while the engineer executes them in the software. Real-time adjustments are made based on surgeon preferences and clinical goals. The session typically lasts 30-60 minutes, and the final plan is approved by the surgeon before manufacturing.
### Key Decisions During Planning
Critical decisions include the maxilla-first versus mandible-first sequence, the amount of maxillary impaction, advancement, or rotation, mandibular advancement or setback distance, occlusal plane angle (with counterclockwise rotation for aesthetic and airway benefit), cant correction (roll of the maxilla), yaw correction (rotational asymmetry), genioplasty movements, and the need for segmental osteotomy.
## Accuracy of VSP
### Translational and Rotational Accuracy
| Movement Type | Parameter | Typical Accuracy | Notes |
|--------------|-----------|-----------------|-------|
| Translational | Maxillary impaction | Within 1 mm | Most accurate movement |
| Translational | Sagittal (advancement/setback) | Within 1-2 mm | Better in maxilla than mandible |
| Translational | Transverse | Within 1-1.5 mm | Dependent on splint fit |
| Rotational | Roll (cant correction) | Within 1-2 degrees | Good accuracy |
| Rotational | Pitch (occlusal plane angle) | Within 1-2 degrees | Good accuracy |
| Rotational | Yaw (rotational asymmetry) | Within 2-3 degrees | Most variable; hardest to control |
The mean positional deviation is 1.0-1.5 mm at most measured points. Accuracy is better in the maxilla than the mandible, since mandibular accuracy is influenced by condylar seating. Maxillary impaction accuracy is within 1 mm in most studies, and sagittal movements (advancement and setback) are within 1-2 mm.
Roll (cant correction) is accurate within 1-2 degrees. Pitch (occlusal plane angle) is also within 1-2 degrees. Yaw is the most variable, with accuracy within 2-3 degrees.
### Compared to Conventional Planning
VSP shows statistically significant improvement over conventional model surgery for maxillary yaw and roll correction, complex asymmetry cases, segmental Le Fort I osteotomies, and bimaxillary surgery. For straightforward single-jaw cases, the difference may be clinically insignificant.
## Advantages of VSP
### Clinical
VSP provides 3D visualization of the deformity and planned correction, accurate assessment and correction of facial asymmetry, simulation of soft tissue outcomes, reduced intraoperative decision-making since the plan is executed from a guide, reduced operative time through pre-bent plates and pre-planned osteotomies, and digital archiving of plans for future reference.
### Communication
VSP enhances surgeon-orthodontist communication through a shared digital plan, improves patient education and consent through 3D before-and-after visualization, and creates a reproducible and standardized planning process.
### Manufacturing
CAD/CAM splints achieve precise occlusal fit. Cutting guides improve osteotomy accuracy. Patient-specific plates eliminate intraoperative bending and improve fixation accuracy.
## Limitations of VSP
VSP services and manufacturing add $1,500-$5,000 per case. The turnaround time of 2-4 weeks from planning to delivery introduces delay. CBCT artifacts from metal restorations and brackets require manual correction. Soft tissue prediction accuracy is limited and should not be solely relied upon for planning. VSP plans assume ideal condylar seating, but intraoperative condylar position remains surgeon-dependent. There is a learning curve requiring familiarity with software and 3D planning concepts. Intraoperative deviation from the plan is difficult if cutting guides and pre-bent plates have already been manufactured. System failures, manufacturing errors, or incorrect data input can compromise the plan.
Screen capture from a VSP planning session showing the pre-surgical 3D skeletal model overlaid with the planned post-surgical position (color-coded for maxillary and mandibular movements), with the designed intermediate and final occlusal splints and patient-specific cutting guides displayed
## Intraoperative Navigation
### Computer-Assisted Navigation
Computer-assisted navigation provides real-time intraoperative tracking of surgical instruments and skeletal positions. The system links the virtual plan to the surgical field using infrared tracking systems, verifying maxillary position after fixation to confirm accuracy of planned movements. It is particularly useful for complex midface cases and secondary deformity correction. Available systems include Brainlab, Stryker Navigation, and Medtronic StealthStation.
### Advantages
Navigation provides real-time feedback on skeletal position, can be used instead of or in addition to splints, and is useful when condylar position or temporomandibular joint issues complicate splint-based planning.
### Limitations
Equipment cost and operating room setup time are significant. Registration accuracy depends on fiducial markers or surface matching, and navigation does not replace the need for surgical skill and judgment.
## Clinical Pearls
VSP is most beneficial for complex cases including bimaxillary surgery, facial asymmetry, segmental osteotomies, and revision cases. For straightforward single-jaw cases, conventional planning may be sufficient and more cost-effective. The VSP plan should always be verified against clinical findings, as the computer does not replace clinical judgment. Condylar seating remains the Achilles heel of orthognathic surgery -- no amount of VSP accuracy can compensate for improperly seated condyles at the time of fixation. Patient-specific cutting guides should be requested when the osteotomy level is critical, such as in differential impaction for cant correction. When reviewing the soft tissue prediction with the patient, it should be discussed as an approximation rather than a guarantee. The VSP plan should be archived digitally, as it serves as valuable documentation and can facilitate revision planning if needed.
## References
- Stokbro K, et al. Virtual planning in orthognathic surgery. Int J Oral Maxillofac Surg. 2014.
- Swennen GR, et al. A cone-beam CT triple scan procedure. Clin Oral Investig. 2009.
- Hsu SS, et al. Accuracy of a computer-aided surgical simulation protocol for orthognathic surgery. J Oral Maxillofac Surg. 2013.
- Ritto FG, et al. Accuracy of maxillary positioning in bimaxillary surgery with conventional and computer-aided planning. Int J Oral Maxillofac Surg. 2018.
- Hammoudeh JA, et al. Virtual surgical planning in craniomaxillofacial surgery. Plast Reconstr Surg. 2015.
- Schneider D, et al. Computer-assisted planning in orthognathic surgery. J Craniomaxillofac Surg. 2019.