art-shaheen-182-186

MAXILLOFACIAL SURGERY
THREE DIMENSIONAL PLANNING OF ORTHOGNATHIC SURGERY: A NARRATIVE
Review Articles
REVIEW OF THE LEUVEN PROTOCOL
Eman Shaheen1,2a , Constantinus Politis1,2b*

1
OMFS IMPATH research group, Department of Imaging & Pathology, Faculty of Medicine, KU Leuven, Leuven, Belgium
2
Oral and Maxillofacial Surgery, University Hospitals Leuven, Leuven, Belgium

a
BSc, MSc, PhD, Clinical Engineer, Responsible
b
MD, DDS, MHA, MM, PhD, Professor and Head of Department of Oral and Maxillofacial Surgery

ABSTRACT DOI: https://doi.org/10.25241/stomaeduj.2019.6(3).art.4
OPEN ACCESS This is an Open Access article under
Background & Objective: The aim of this paper was to present the virtual the CC BY-NC 4.0 license.

surgical planning (VSP) protocol for orthognathic surgery used in daily Peer-Reviewed Article
practice in the department of Oral and Maxillofacial surgery, University Citation: Shaheen E, Politis C. Three dimensional planning of
Hospitals of Leuven, Leuven, Belgium. orthognathic surgery: a narrative review of the Leuven protocol.
Stoma Edu J. 2019;6(3):182-186.
Data Sources: The different steps are presented in details explaining the
protocol and showing an example of a bimaxillary case. Received: August 02, 2019
Revised: August 28, 2019
Data Synthesis: A variety of aspects have been discussed including the Accepted: September 09, 2019
Published: September 10, 2019
different possibilities with respect to the software used and their limitations.
The pros and cons of that software compared to other commercial software *Corresponding author:
Prof. Dr. Constantinus Politis Department of Oral and Maxillofacial
tools have been highlighted. Surgery, University
Hospitals Leuven, Kapucijnenvoer 33, 3000 Leuven, Belgium
Keywords: 3D planning; Orthognathic surgery; Virtual planning; Surgical Tel: / Fax: 0032 (0)16332462,
planning; Virtual surgical planning (VSP). e-mail: constantinus.politis@uzleuven.be

1. Introduction commonly known as Virtual Surgical Planning (VSP),
Surgical virtual planning is currently possible due to but with different algorithms and tools whether semi
the recent developments in maxillofacial radiology or fully automated. In this paper, we present the VSP
with the introduction of low dose cone beam protocol used in University Hospitals of Leuven to
computer tomography (CBCT) especially with CBCT virtually plan orthognathic surgery in daily practice
systems scanning the full skull. The added value of after introducing improvements.
virtual planning of orthognathic surgery has been
proven which include a better and more accurate 2. Methodology
outcome as stated by Stokbro et al in their systematic The VSP protocol can be divided into 10 steps which
review [1]. The virtual planning is significantly faster will be explained in details in this section based on
for single- and double-jaw surgery compared to the the Proplan software (Materialise, Leuven, Belgium)
conventional method [2]. Moreover, Scheinder et as used in the department of Oral and Maxillofacial
al. recommended the use of virtual model surgery surgery, University Hospitals of Leuven, Leuven,
and the prefabricated three dimensionally (3D) Belgium. There is a wizard specifically made for
printed splints to replace traditional orthognathic orthognathic VSP. An example is shown in Fig. 1.
surgery as it becomes cost-effective [3]. Several Ethical approval was obtained from the Ethical
virtual planning protocols have been published in Review Board of the University Hospitals Leuven
the recent years [4-9]. One protocol was called the (S58253).
triple scan CBCT protocol [9] as it relied on 3 CBCT
scans: first the patient is scanned with a thin wax bite 3. Results
in the mouth, which is followed by a limited dose 1. Segmentation
scan with a tray of impression in the mouth. Then The Digital Imaging and Communications in
the last step is a high resolution scan of the patient’s Medicine (DICOM) images of the patient are imported
tray of impression. That protocol had the privilege into the Mimics Inprint software (Materialise)
of automating some preprocessing steps to allow for the segmentation step. Image segmentation
for faster planning. However, this protocol has been is the process of assigning voxels with shared
replaced with the commonly used protocol with only characteristics to an object. For VSP, the segmented
one CBCT of the patient’s full skull with a thin wax objects are typically the full skull, the airway and the
bite. A variety of software programs are available soft tissue and the segmentation is threshold based.
commercially implementing the one-scan protocol, The software tools allow separating the mandible

182 Stoma Edu J. 2019;6(3): 182-186 http://www.stomaeduj.com
THREE DIMENSIONAL PLANNING OF ORTHOGNATHIC SURGERY:
A NARRATIVE REVIEW OF THE LEUVEN PROTOCOL

Review Articles
Figure 1. An example of a patient undergoing bimaxillary orthognathic surgery: a) the preoperative situation (steps 1 to 3); b) the
intermediate situation (clinical plan was: Le Fort I advancement 1mm and translation 2 mm to the left); c) the final situation with
registered BSSO and genioplasty advancement 6mm; d) the preoperative 3D photo; e) the soft tissue simulation (step 9).

from the rest of the skull semi-automatically and also 3. Cephalometric analysis
refining the segmentation of each object as needed. The Leuven cephalometric analysis is used which
For example when the condyles are not fully is based on selected measurements of different
segmented, 3D interpolation tools can be applied analyses to analyze the hard tissue, soft tissue,
to add the missing parts or when some artifacts proportions, angular and linear measurements. This
are presented in the segmented objects, these analysis was previously developed in 2D and called
can be manually removed. 3D models are then Genk Surgical then adopted and extended into 3D.
reconstructed and exported to the Proplan software. The landmarks, planes and measurements are once
1. Augmented models created. The software guides the user to place the
Since the slice thickness of CBCT scans of a full skull landmarks then the measurements are automatically
is typically within the range of 0.3 – 1 mm, along calculated and shown on the 3D models.
with the artefacts introduced into the images due to 4. Nerve tracing
the orthodontic brackets, the teeth cannot be used For patients undergoing a bilateral sagittal split
later for the fabrication of the splints. Therefore, osteotomy (BSSO), the mandibular inferior alveolar
high resolution scans of the upper and lower teeth nerves are traced to assist the surgeon with the decision
are superimposed on the maxilla and the mandible of handling the nerve during the surgery [10].
respectively to create augmented models (maxillary 5. Osteotomy simulation
and mandibular). The high resolution scans of the In the orthognathic wizard, the commonly used
teeth can either be the plaster models scanned or osteotomies such as Le Fort 1, BSSO, genioplasty
direct scan using an intra oral scanner. Either way the are implemented with a user friendly guide to
output has to be 2 stereolithography (STL) files that place specific points then press apply and your
are imported into the software and superimposed objects are cut according to the chosen osteotomy.
on the CBCT teeth using surface based registration Furthermore, other osteotomies are allowed using
(Fig. 1a). the curve tool in which the user can draw curved
2. Natural Head Position (NHP) planes. This is commonly used for multiple pieces Le
NHP is allowed in the software using three Fort 1 or any type of segmental osteotomies.
possibilities: manually, Frankfurt horizontal plane 6. Occlusion registration
(FHP) or occlusal plane. In our protocol, we start with The STL of the occlusion cast is then imported into
FHP then manually adjusted according to the clinical the software and registered using surface based
images of the patient. registration on the maxilla then the BSSO mandibular

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THREE DIMENSIONAL PLANNING OF ORTHOGNATHIC SURGERY:
A NARRATIVE REVIEW OF THE LEUVEN PROTOCOL

segment is registered onto the registered cast as objects or to experiment with other technologies
Review Articles explained by Shaheen et al. [11,12]. This order is such as pre-bended metal plates. Soft tissue
followed for BSSO and bimaxillary cases. As for a simulation is an important tool even though still
single Le Fort 1 operation, the registration of the not completely accurate especially around the nose
cast starts with the mandible then the maxilla is and lips regions. However, it provides an estimate
registered to the registered cast. The occlusion cast of what the patient will look like postoperatively,
is the final required occlusion defined and set by the especially patients with obvious facial asymmetry.
surgeon which can be the plaster cast models in final Some software does not allow superimposing 3D
occlusion scanned by a high resolution CBCT or the photos which makes it difficult to show the patients
printed models from the intra oral scanner scanned the simulation of their postoperative approximate
once more in final occlusion. situation due to lack of reality. A software without a
1. Virtual planning clear wizard of the steps is not a strong user friendly
For bimaxillary surgery, 3 objects are moved together tool. A wizard decreases human error as the user
(Le Fort 1, BSSO and registered occlusion cast). follows instructions. The less interference from the
Manual or defined translations and rotations are user, the more accurate the results will be therefore,
allowed. Choices of rotations around cephalometric more automated tools are needed but refinement
points are also possible. There is freedom of choice tools are strongly recommended to overcome
while visualizing the amount of movements on the complex situations. Automatic final occlusion should
selected cephalometric points (Fig. 1b,c). also be implemented in the software but again
2. Soft tissue simulation with the possibility to perform manual corrections.
Once the bony parts are displaced, the soft tissue Unfortunately not all software tools allow more than
simulation can be activated and immediately the predefined osteotomies which limits the use of
shown. The software allows visualizing the changes the software for complex cases. Moreover, the lack
occurring on the soft tissue live while changing of segmentation and only allowing visualization
the bony structures which facilitates updating or threshold restricts the capabilities of the software.
improving the final plan. The soft tissue simulation After two validation studies [11,12] introducing
algorithm is based on an improved finite element improvements into the protocol, this specific
model [13]. Another advantage is the possibility to protocol was implemented on 500 orthognathic
visualize the soft tissue simulation on a 3D photo patients from 2016. Prior to 2016, another software
which is superimposed on the soft tissue segmented was used for only simulation purposes without using
object using a combination of landmarks followed 3D printed splints and preoperative scans were CT
by surface based registration (Fig. 1d,e). based. An in-house tool was implemented to evaluate
3. Splints design the accuracy of the achieved outcome versus the
The final step of the orthognathic wizard is to virtually planned maxilla for bimaxillary cases [14].
design the splints. For single jaw operation, one After testing on 55 skeletal class III patients, we
final splint is needed. For double jaw surgery, a final concluded that our 3D VSP of maxilla was generally
and an intermediate splints are needed. The splint accurate when compared to the outcome achieved
is designed by means of placing minimum three [15]. Both advantages and disadvantages need to
points on the upper jaw and three on the lower jaw. be recognized. According to our experience in over
Then a first design is presented that can be further 500 patients, the following advantages are clinically
refined according to the need of the surgeon. Holes relevant:
and different inclinations can also be implemented. - the 3D-reconstructed virtual head set is a great
The splints are then labeled and exported as STL files communication tool to be used when explaining
to be 3D printed. the planned movements to the patient
- the introduction of the virtual planning process
4. Discussion has profoundly influenced the life-cycle of the
In this paper, we presented the protocol used in learning process in orthognathic surgery. The ease
Leuven for VSP of orthognathic surgery which is also of superimposition allows the surgeon quickly to
in line with the general VSP protocol recently used understand which distances and which directions
worldwide. Proplan is our choice for VSP but there of change are difficult to deliver peroperatively.
are other software available on the market that - postoperative problems with wafers can easily be
follow the same protocol. However, in some detailed solved by reprinting the stored STL-file of the wafer
steps some software could be faster/slower, more - as the original position of the ascendic ramus
or less accurate, etc. Some software tools limit the can be visualized during the entire planning
user to specific scanning protocols to automate the process, lingual bony interferences distal to the
preprocessing steps for faster use, but, with more tooth bearing area can be readily identified and
complex situations it could ask the user to manually anticipated, mainly during rotations of the lower
interfere to solve some problems. Other software jaw, as well as any bone grafting needs in the
allow exporting the STL files to only the splints osteotomy gaps.
which limits the ability of the user to 3D print other - the influence of the surgical plan on the airway can

184 Stoma Edu J. 2019;6(3): 182-186 http://www.stomaeduj.com
THREE DIMENSIONAL PLANNING OF ORTHOGNATHIC SURGERY:
A NARRATIVE REVIEW OF THE LEUVEN PROTOCOL

- readily be predicted during the planning process - presurgical planning with plaster casts allows the

Review Articles
- refinements to the planning concerning pitch, roll surgeon to easily identify which teeth need to be
and yaw are taken more often into consideration ground during or before surgery. This is a far more
in the digitized planning process. difficult exercise with VSP.
- it is the only way towards waferless planning with - if scanning of dental casts is used, the errors of
preprinted osteosynthesis plates and it allows plaster dental casts will be transferred into the VSP
the surgeons the freedom to choose between Virtual surgical planning is also prone to intrinsic
wafer and waferless transfer of the virtual surgical weaknesses which urge for validation of methods
planning to the operating room used:
- the planning process allows mirroring techniques - 3D-CBCT superimposition algorithms are based on
in hemimandibular or hemifacial hypoplasia to a variety of methods, each with their advantages
predict the amount of bone/soft tissue needed to and disadvantages, but hardly any of them can
reach symmetry. be considered accurate in growing individuals;
- severe asymmetry cases are poorly planned in different segmentation techniques can result in
conventional planning tools where the lateral significant variances [16].
cephalogram remains the main starting file; VSP - the resulting differences in volume usually are
eliminates this shortcoming as the frontal plane is depicted in color-maps, representing color-
equally visualized as the sagittal plane coded surface distances, allowing a qualitative
- cutting guides can be designed in delicate surgical interpretation of the changes but hardly any
osteotomy lines where the inferior alveolar nerve robust volumetric changes.
could be compromised. - many methods of superimposition using other
- during the VSP the position of the condyles anatomical structures than the mandible to study
is checked and compared, readily identifying condylar resorption after orthognathic surgery fail
incongruences to be accurate due to possible changes of condylar
According to our experience the following position between the two measurements.
disadvantages need to be recognized: A number of advantages of the availability of
- since the soft tissue changes at the area of the nose CBCT-data should not be attributed to VSP, such as
are poorly predicted, the amount of advancement the traceability of the inferior alveolar nerve, the
of the maxilla remains a decision of mere clinical positioning of the condyle in the fossa, the follow-up
judgement of qualitative changes of the condyle.
- the sagittal position of the maxilla remains as
accurate as the initial waxbite. If the waxbite which 5. Conclusion
had been used during planning was erroneous, the Virtual Surgical Planning can safely replace Custom
sagittal position of the maxilla will be erroneous Manual Surgical Planning but does not constitute
too if wafers are used a major advantage if its use is limited to digital
- mild canting of the occlusal plane or upper midline splint design and production. It is a necessary step
deviations tend to be corrected in respect of the towards a renewed orthognathic planning process
bony 3D reference lines instead of being judged where the bony changes are reliably deducted from
against the soft tissues of the upper lip and nose. the desired functional and esthetic orthognathic
- in multisegmental osteotomies of the upper jaw outcome using validated processes and methods.
this digital planning process in no way facilitates
designing transpalatal arches in order to stabilize Author contributions
the transverse dimension. All authors contributed to reporting the case,
- the cost of software purchase, maintenance and performing literature review and drafting the
upgrade is considerable and limits its in-house use manuscript.
only to high volume orthognathic practices.
- the workflow does not allow anticipatind nor Conflict of interest
predicting postoperative condylar resorption, nor No conflict of interest to declare.
temporomandibular joint dysfunction

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Eman SHAHEEN
BSc, MSc, PhD, Clinical Engineer
Responsible 3D Surgical Orthognathic Lab
Department of Oral and Maxillofacial Surgery
University Hospitals Leuven
BE-3000 Leuven, Belgium

CV
Eman Shaheen graduated with honor from the faculty of Computer Sciences (2003), Cairo University, Egypt where she worked
as a teaching assistant till 2007 when she obtained her Master’s Degree in Video Processing. In 2008, she joined the team of
Medical Physics where she completed with distinction her pre-doctoral studies (2009) followed by her doctoral degree (2014)
after developing a simulation framework to optimize the performance of breast tomosynthesis, KU Leuven, Belgium. In the
same year, she started working for the CMF department (University hospitals Leuven, Belgium) as a clinical engineer focusing
on 3D planning of orthognathic surgery. She is also the lead engineer of the research group “OMFSIMPATH” (KU Leuven,
Belgium) where she supervises masters and PhD students to support different research projects related to 3D printing and
simulations.

Questions
1. The software used by UZ Leuven for VSP is:
qa. Proplan;
qb. Simplant O&O;
qc. IPS;
qd. Mimics.

2. The UZ Leuven protocol was implemented on over:
qa. 50 patients;
qb. 150 patients;
qc. 300 patients;
qd. 500 patients.

3. One of the following is considered an advantage of VSP:
qa. Dependency on initial waxbite;
qb. Registering occlusion casts;
qc. Reprint of STL of wafers;
qd. Nerve tracing.

4. One of the following is considered a disadvantage of VSP:
qa. Dependency on initial waxbite;
qb. Registering occlusion casts;
qc. Reprint of STL of wafers;
qd. Nerve tracing.

186 Stoma Edu J. 2019;6(3): 182-186. http://www.stomaeduj.com