Enhancing Accuracy in Digital Orthognathic Surgery for Facial Asymmetry: A Data-Driven Approach
- Dr. Park
- Jul 1
- 5 min read
A Message from Dr. Park Jong-chul, Oral and Maxillofacial Surgeon
Facial asymmetry, a condition where the left and right sides of the face are not balanced, is a source of significant cosmetic stress for many individuals. It can also be accompanied by functional problems such as malocclusion. The most effective method for fundamentally correcting severe facial asymmetry is orthognathic surgery (double jaw surgery), which repositions the jawbones to an ideal location.
With the remarkable advancements in modern medical technology, the field of orthognathic surgery has entered an innovative new paradigm: digital orthognathic surgery. This approach, which utilizes computer technology for precise 3D planning and safe execution, is no longer an option but a necessity.
However, does the term 'digital orthognathic surgery,' as used by all clinics, guarantee the same level of precision? Simply taking a CT scan and creating a computer-based plan does not ensure identical outcomes.
In this posting, I will provide an in-depth explanation, based on my extensive clinical experience and data analysis, of a differentiated approach to increasing the accuracy of digital orthognathic surgery for asymmetry, supported by actual patient cases.
The Current State of "Digital Orthognathic Surgery"
Generally, the process for what is known as 3D or digital orthognathic surgery involves the following steps:
3D CT Scan: The patient's facial bone structure is captured in a detailed, three-dimensional image.
CAD (Computer-Aided Design): Based on the CT data, a computer simulation is used to plan the amount of jaw movement, the location of bone incisions (osteotomies), and other critical details.
CAM (Computer-Aided Manufacturing): According to the established plan, a 3D printer fabricates a 'wafer' (or surgical splint), a device used to guide the dental occlusion during surgery.
This process is a significant advancement over past methods that relied on 2D X-rays, dramatically improving the predictability and stability of the surgery. I fully endorse the adoption and application of this digital technology and utilize it in all my orthognathic procedures.
However, I believe we must take it a step further. Can we truly, without error, transfer the dozens or hundreds of precise measurements from our computer plan to the patient's actual bone using only a 3D-printed wafer?
How Can We Verify the "Error" Between Plan and Reality?
Confirming that a surgery was performed exactly as planned is the most critical step in evaluating its success and striving for better future outcomes. Many clinics superimpose pre- and post-operative CT scans and conclude that "the surgery went according to plan."
While CT comparison is a useful method for intuitively checking if the chin is centered or if the overall contour has improved symmetrically, it is not sufficient on its own.
STL image comparison analysis
Orthognathic surgical plans contain highly specific numerical values, such as 'move the maxilla 6.5mm superiorly and 0.7mm to the right.' CT images alone have clear limitations in objectively measuring how much these specific figures deviate from the plan—that is, the 'surgical error.'
To overcome this limitation, I perform STL image comparison analysis.
STL (Standard Tessellation Language) is a file format that converts CT data into 3D surface model information. By precisely superimposing the virtual surgical plan (Plan STL) and the actual post-operative result (Post STL) on a computer, we can compare the three-dimensional positional changes at various points. This allows for the objective measurement of the surgeon's performance with a precision of 0.01mm.
Through this process of direct data verification, I have confirmed that relying solely on a 3D-printed wafer, which is based on dental occlusion, is somewhat inadequate for controlling the position of the skeletal bone segments themselves.
The Solution for Enhanced Surgical Accuracy: The 'Patient-Specific Instrument'
My solution for minimizing surgical error and implementing the plan as accurately as possible is the Patient-Specific Instrument (PSI), specifically a custom-fabricated fixation plate.
This method goes beyond merely fabricating a wafer. Using 3D printing technology, we create both a custom-made metal plate tailored to the patient's unique bone shape and surgical plan, and a guide to position it perfectly.
The application method is as follows:
During the virtual planning phase, we pre-design the screw hole locations and the precise position of the fixation plate on the bone segments that will be cut.
Before the osteotomy (bone cut), we drill the screw holes into the actual bone according to surgical guide.
After moving the bone segments as planned, the 'custom fixation plate,' which fits the patient perfectly, is secured into the pre-drilled holes.
This approach eliminates the guesswork of finding where to fixate the bone after it has been moved. It allows us to secure the bone in its planned position with unparalleled accuracy, much like fitting a puzzle piece into its designated spot. This is the key differentiator that dramatically enhances surgical precision.
A Real Case of 'Differentiated Digital Orthognathic Surgery' for Asymmetry
This is the case of a male patient with a chin deviated 12.79mm to the left. Despite a long period of pre-surgical orthodontics, the dental compensation was not fully resolved, demanding even greater precision in the surgical planning.
Precise Surgical Planning with Digital Orthognathic Surgery:
To correct the asymmetry, the maxilla was moved to the right, and the positions of both the upper and lower jaws were reset.
Image caption: A precise surgical plan created using digital orthognathic surgery to correct asymmetry
Surgery and Verification:
To execute this intricate plan with minimal error, the surgery was performed using both a 3D wafer and the patient-specific fixation plates.
Post-operative CT and STL image comparisons confirmed the successful outcome of the surgery.
Image caption: Post-operative result comparison using CT image superimposition. 
Image caption: Post-operative result comparison using STL image superimposition, demonstrating high accuracy
Conclusion: Is Your 'Digital Orthognathic Surgery' Verifying Its Accuracy?
If you are considering orthognathic surgery to correct asymmetry through digital methods, it is time to look beyond the simple fact that a 'computer is used' and examine the depth of the process.
How is the surgical plan created? (CAD)
What tools are used to execute the plan? (CAM - Wafer only? Or Wafer + Custom Plate?)
And most importantly, how are the surgical results objectively verified and evaluated? (CT overlay? Or CT + STL analysis?)
I use STL image analysis to compare my surgical results, and based on this data, I apply technologies like patient-specific fixation plates to reduce my surgical error.
This is what I believe constitutes true 'digital orthognathic surgery.' Of course, even with these maximal efforts, it's impossible for surgical results to be absolutely identical to the plan.
However, through tireless effort, that margin of error is continuously being reduced.
If you are struggling with severe facial asymmetry, I urge you to have a thorough consultation with an oral and maxillofacial surgeon. Please take the time to diligently check how your surgery will be planned, executed, and verified to ensure you receive the safest and most accurate procedure possible.
Thank you.
For additional case studies on asymmetry correction through digital orthognathic surgery, please refer to the following post: https://blog.naver.com/vvsaz144/223915324503
Enhancing Accuracy in Digital Orthognathic Surgery for Facial Asymmetry
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