By Dr. Ir. Eman SHAHEEN, BSc, MSc, PhD, Responsible of the 3D orthognathic surgical lab, Department of Oral and Maxillo-facial Surgery - UZ Leuven - Belgium
The department of Oral and Maxillofacial Surgery (OMFS) of Leuven University Hospitals (Belgium) is a tertiary referral centre with a strong focus on omfs-resident training, education of dental students and scientific research. Clinical pillars are head and neck oncology, cleft lip and palate, facial deformities, orthognathic surgery, chronic facial pain, severe trauma, maxillofacial imaging and dental oral cripples.
The Amira software is used in our department for both research and clinical evaluation. In this article, we will focus on postoperative evaluation of orthognathic patients to quantify the accuracy of the surgical outcome of bimaxillary surgeries by comparing it to the 3D virtual preoperative planning.
For the treatment of significant skeletal malocclusion 1 orthognathic surgery is indicated. Examples for skeletal malocclusion are diminished bite forces, restricted mandibular excursions, abnormal chewing patterns and temporomandibular disorders. Orthognathic surgeries are normally prepared by performing model surgery on plaster cast models in articulators using conventional face bows combined with 2D cephalometrics. With the recent developments in oral imaging, more orthognathic surgeries are planned using 3D software for more accurate planning, time saving and better results.
For the preoperative preparation, Computed Tomography (CT) images are used for implementing the clinical plan virtually where surgical splints are designed and 3D printed in biocompatible material. For postoperative evaluations, Cone Beam Computed Tomography (CBCT) are taken for each patient 6 weeks, 6 months and 1 year after the surgery.
The main steps of the protocol contains voxel based registration, transformations, cephalometric analysis to get the output measurements between the post operative maxilla and the planned maxilla. The first three steps are performed in the Amira software as described by Baan et al. 2 and the cephalometric and results part are obtained from another software.
The postoperative CBCT is registered to the preoperative CT using voxel based registration with mutual information. Only the the cranial and orbital parts were used for the registration because these are not displaced during surgery.
The maxillary part of the preoperative CT is registered on the maxillary part of the registered postoperative CBCT. This second registration mimics the movements of the preoperative maxilla position to the postoperative position which is captured in a transformation matrix. The preoperative composite maxilla is imported into the Amira software and the transformation matrix is used to perform the actual transformation of the planned position of the maxilla to the postoperative achieved location of the maxilla in the Amira software.
The maxilla in postoperative position is then compared to the maxilla of the virtual planning via 3 landmarks using angular and linear measurements.
We currently changed our protocol to the use of the same CBCT for preoperative as well as postoperative imaging which will be beneficiary to the patients. Further improvements would be to include the evaluation of the distal and proximal parts of the mandible and to make it work also for orthognathic surgeries creating multiple segments. This protocol can also be used to evaluate the occurrence of relapse after 6 months and 1 year after surgery.
The department of Oral and Maxillofacial Surgery (OMFS) of Leuven University Hospitals in Belgium is a tertiary referral centre with a strong focus on omfs-resident training, education of dental students and scientific research. Clinical pillars are head and neck oncology, cleft lip and palate, facial deformities, orthognathic surgery, chronic facial pain, severe trauma, maxillofacial imaging and dental oral cripples. Its research-branch OMFS-IMPATH had 35 collaborators with a yearly output of PhD's in several domains of OMF Surgery. With about 10.000 unique patients per year visiting the department, translational research finds an easy way to clinical reality.
Amira and Avizo are high-performance 3D software for visualizing, analyzing, and understanding scientific and industrial data coming from all types of sources and modalities.
Images and text are courtesy of UZ Leuven
1 AAOMS Parameters of Care: Clinical Practice Guidelines for Oral and Maxillofacial Surgery (AAOMS ParCare '12)
2 Baan F, Liebregts J, Xi T, Schreurs R, de Koning M, Bergé S, et al. (2016) A New 3D Tool for Assessing the Accuracy of Bimaxillary Surgery: The OrthoGnathicAnalyser. PLoS ONE 11(2): e0149625