3D stereophotogrammetry in oral & maxillofacial surgery
A scientific essay in Medical Sciences
DOCTORAL THESIS defended in public on 19th of September 2012
In the beginning years (2005) of the Nijmegen 3D project the sole hardware available for 3D imaging consisted of a 3D camera system from the 3dMD company (3dMDfaceTMSystem, 3dMD, Atlanta, USA). Using this technique it was possible to evaluate changes in three dimensions, but even more important, treatment changes could be evaluated in an objective way and illustrated accurately using color scale images or distance maps. However, at that moment in time, no studies have been performed to investigate the reproducibility of this system in a clinical setting. In order to investigate the error margin of the reproducibility of the system when capturing images of the same individual the study described in chapter 3 was conducted. Fifteen volunteers were invited to participate and 3D photographs were acquired at different moments in time. The results of the study illustrated that the reproducibility of acquiring these 3D photographs at different moments was high. From these results, it could be concluded that surface-based registration is an accurate method to compare 3D photographs of the same individual acquired at different time points. This study was an important first step to assure the reproducibility of acquiring 3D photographs of patients. During the summer of 2006 the 3D imaging facilities of the Nijmegen 3D project were expanded with the installation of a CBCT scanner at the Dentistry department. Apart from the immediate advantages of 3D diagnostics in a lot more clinical cases than before, the CBCT images could be combined with 3D photographs which were already acquired for all surgical patients. Especially in the planning of orthognathic surgery and complex facial reconstructions the combination of the accurate textured information from the 3D photographs with the information about the bony structures from CBCT was very useful. For that reason another validation study to determine the accuracy of three different matching procedures to combine the information from CBCT and 3D stereophotogrammetry was performed (chapter 4). Three-dimensional reconstructions of the facial skeleton and untextured facial soft tissue surface of 15 patients were registered with the textured 3D photograph of the facial soft tissue surface. The results of the study revealed that surface-based registration was an accurate algorithm to fuse CBCT and 3D photograph data. Small dissimilarities between both surfaces were mostly due to the inability of CBCT to capture all facial soft tissue surface of a patient's face correctly (e.g. the tip of the nose is not always present in every CBCT scan). From this study, it could be concluded that a 3D fusion model of the 3D photograph and skull reconstructed from CBCT data provides a precise photorealistic digital 3D representation of a patient's face. After the previously described studies were performed, some new questions were raised. One of these questions was to investigate more in detail which region of the face were the most stable and could best be used during the registration process. In the study conducted in chapter 5, this was investigated by capturing 100 3D photographs of one individual. The variation within the complete face was computed as well as the variation within different anatomical regions. Furthermore, the influence of using a wax bite during acquisition was investigated. The results of the this study illustrated a small overall variation for the face in rest. Within the different anatomical units, the most accurate values were found in the region of the forehead and the nose. The most obvious, but nevertheless expected, variations were found peri-oral and in the region of the eyes. The large variation in the region of the eyes can be explained by the incapability to capture the eyes correctly using 3D stereophotogrammetry. Documentation, diagnosis, analysis and treatment planning of orthognathic patients and patients with complex facial problems improved using fused information from the CBCT scan and 3D photograph. However, for correct planning of orthognathic surgery accurate information of the dentition is required. Therefore, all three structure groups which build up the facial triad were brought together in an integral fusion model in chapter 6. In this fusion model the 3D photograph was combined with the CBCT scan as described in chapter 4. During the CBCT scan of the patient, small titanium markers were glued to the gingiva. After the CBCT scan was acquired, an impression was made from both dental arches. After the impression was hardened the titanium markers were fixed to the alginate and came out together with the impression. Now the impression could be scanned with high precision. From this scan, accurate dental information could be captured using a CBCT scan of only the impressions. The scan from the impression could now be matched with the scan from the bony structures based on the titanium markers. The information from all separate scans now results in an augmented model of the head with accurate textured soft tissue information, accurate skeletal information and accurate dental information. This new method proved to be a non time-consuming, patient and user friendly method and seemed not to be prone to errors. Furthermore, the patient was not exposed to any more radiation than needed. Further studies will be performed to investigate the validity of the proposed method in more detail before it will be implemented into a clinical setting. After performing the validation studies as described in chapters 3 to 6, the second part of this thesis focused on the more clinical applications of the available 3D imaging techniques. One of the goals of the 3D Laboratory was to collect a large number of pre- and postoperative 3D datasets from dysgnathic patients who underwent surgery. In the past few years the planning of orthognathic surgery evolved towards a more digital and three-dimensional approach. Nowadays, all orthognathic patients at our department are planned completely in a 3D environment using the augmented model technique. The study in chapter 7 is the first step towards documenting these surgeries completely three-dimensionally. Eighteen patients with a skeletal Class II who underwent a BSSO advancement were documented completely in 3D. Preoperatively, a CBCT scan and a 3D photograph were acquired. One year postoperative, these images were acquired again. With the information from these images the volumetric hard and soft tissue changes could be documented. The results of the study described in chapter 7 proved that it is possible to objectively document both skeletal and soft tissue changes in 3D and provide new information to improve the planning and predication of orthognathic surgery in the near future. After it was possible to accurately document three-dimensional surgical changes, there was a need for a large amount of reference facial data from healthy controls. The goal of the next study (chapter 8) was to collect a large number of 3D photographs of healthy controls. To collect these photographs, the 3D camera setup was transported to a secondary school in Rotterdam (Rotterdams Montessori Lyceum). This resulted in a lot of 3D photographs of adolescents. Later on, to collect a datagroup with a higher age, 3D photographs were collected of a large number employees in our hospital (Radboud University Nijmegen, Medical Center). These photographs were analyzed and an average face could be computed from the Dutch male and female faces. In chapter 8 this procedure is described and the average faces of the Dutch populations were compared with existing database of the average faces of Egyptian and Houston populations. Differences between male and female faces as well as differences between the different ethnic groups could be investigated. Another advantage of the availability of such an average face is that these faces can be compared with faces of patients, in this way illustrating where disharmonies occur in the patients' face. After different validation studies were performed in the first part of this thesis, chapter 9 illustrated the application of 3D imaging techniques in the field of head and neck surgery. During the past years, 3D stereophotogrammetry, CBCT and digital dental models evolved as valuable and accurate tools in the evaluation and planning in a clinical setting. Within the field of implantology a 3D way of working can be used to find the ideal position of intra- and extra-oral implants and is therefore used in the preoperative phase. Also in the field of facial surgery it is widely adapted as a useful technique in the area of orthognathic surgery, cleft lip and palate surgery and more esthetically interventions such as rhinoplasty and the use of botox in controlling masseter hypertrophia. Using 3D imaging techniques in these specific clinical situations, it is possible to document, plan and objectively evaluate the effect of specific surgical techniques or non surgical treatment options. This is a great benefit compared to conventional imaging techniques for surgeons as well as patients, while both are now able to see the actual differences that are occurring. Also in the field of oncology the use of 3D imaging techniques in a clinical and research setting evolved over the last years. Nowadays 3D imaging is a standard tool in planning free mandibular bone graft procedures. The content of this thesis made clear that there is a nite added value of 3D imaging in oral and maxillofacial surgery. This does not automatically imply that the work of oral and maxillofacial surgeons will become easier by the use of 3D imaging. Throughout the past few years at our department, we learned that a close cooperation between the technicians and surgeons plays a very important role in implementing these techniques in a clinical setting and allows for the further improvement of these techniques. Through the findings of this thesis and research about 3D imaging in general it is believed that 3D imaging does provide the surgeon with more and better information. This information gives the surgeon the opportunity to work and prepare surgery in a more accurate and predictable way. Finally, this will provide the patient with better functional and aesthetic outcomes.