Orthognathic surgical simulation of Class III patients using 3-D cone beam CT images

Objective: Our aim is to determine if virtual surgery performed on 3-D cone beam CT models correctly simulated the actual surgical outcome of Class III orthognathic surgical patients. Methods: All data was acquired from the UNC orthognathic surgery stability studies. We created segmentations of the maxillofacial hard tissues of twenty class III patients. We performed virtual surgeries on cone beam CT images using the CranioMaxilloFacial Application software. Results: The virtual surgical models were superimposed on the models of the actual surgical outcomes. The virtual surgery accurately recreated all surgical movements. Surgery residents showed greater variability in lateral ramus positioning than attending faculty. Conclusions: Our methodology demonstrated valid recreation of the subjects' craniofacial skeleton. It allows the surgeon to better predict surgical outcomes. Future validation of occlusal and soft tissue components would be valuable. Virtual surgical training for surgical residents could be beneficial. Supported by NIDCR DE 005215 and the SA

Planeamento cirúrgico 3D em cirurgia oral e maxilofacial

Dissertação para obtenção do grau de Mestre no Instituto Universitário Egas MonizA cirurgia oral e maxilofacial estão em constante crescimento e desenvolvimento, para cada vez mais, apresentarem resultados mais eficazes e menos traumáticos para os doentes. Sendo procedimentos de risco que envolvem um estudo minucioso do crânio e de todas as estruturas faciais, o desenvolvimento tecnológico tem vindo a criar uma alternativa viável que vem simplificar todo este procedimento. Cada doente tem a sua estrutura facial específica, tornando assim cada caso único e inovador. Isto leva à inevitabilidade da realização de uma anamnese e uma recolha de toda a informação pertinente para que se possa realizar um diagnóstico e plano de tratamento mais integralizado possível. Devido à complexidade do tratamento a realizar, é importante que o médico dentista e o cirurgião maxilofacial estejam o melhor preparados possível para trabalharem em conjunto durante o planeamento pré e pós operatório, de maneira a fornecer ao doente o máximo de apoio e informação para que todo o procedimento seja realizado de maneira mais correta e eficaz. Devido à sua complexidade, o sucesso deste tipo de cirurgias está dependente de vários fatores, principalmente o seu estudo prévio, a precisão dos movimentos esqueléticos, o diagnóstico da deformidade óssea e do planeamento dos movimentos pós cirúrgicos. Métodos convencionais de estudo tais como cefalometria bidimensional (2D), modelos de estudo e radiografias panorâmicas, revelaram-se por vezes insuficientes visto não conseguirem reproduzir os complexos movimentos e estruturas tridimensionais envolventes nos mesmos. Nesta revisão será descrito o planeamento cirúrgico, através de métodos tridimensionais para cirurgia oral e maxilofacial, no âmbito da implantologia. A avaliação da sua precisão, da sua fiabilidade e da sua eficácia traduzem-se assim numa maior taxa de sucesso.Oral and maxillofacial surgery are in constant development and growth to deliver each time a more efficient, less traumatizing treatment with better results for the patient. Being high risk procedures, it is very important that a very thorough study of the cranium and all facial structures adjacent to the procedure is conducted. Technological upgrades have created a viable alternative that have come to simplify the entire process. As each patient has his own facial structure, therefore every case is unique and challenging in a different way. It is very important to have a very detailed medical history and to gather as much information as possible of the patient so a complete diagnosis and treatment plan can be achieved. Having this in consideration it is important that the maxillofacial surgeon and the dentist work as a team during the whole pre and post operation planning, assuring that way a better procedure to the patient as well as always being available to provide concise and important information. Due to the high complexity of this kind of surgeries, there are many factors that can disrupt the procedure, enhancing the importance of a proper plan. A well though plan having in mind the skeletal movements, a correct diagnostic of the bone and dental deformity, and the post operation recuperation, requires careful study. Current conventional methods of study such as bidimensional cefalometrics and panoramic radiographics may provide insufficient information to cover all the complex three- dimensional movements and structures affected by this kind of procedures. This literature review aims to describe the surgical planning using 3D dimensional methods (3D) as well as an evaluation on their effectiveness, its precision and its success rate

Image-based 3D planning of maxillofacial distraction procedures including soft tissue implications

Osteodistraction, a technique for new bone formation by the gradual separation of bony fragments, is a possible treatment for dysplasia. of the maxillofacial skeleton. However, preoperative assessment of the optimal distraction direction, of the osteotomy trajectory, and of the influence of this procedure on the outlook of a patient, is difficult to assess preoperatively. We report on an 3D image-based planning system for osteodistraction. Basically we adhere to a scene-based approach in which image derived visualizations and additional 3D structures are co-presented and manipulated. Osteotomy simulation with user-defined cutting trajectories, virtual distraction employing biomechanical models specific to the distraction type and evaluation tools based on a cephalometric reference frame, axe available in our planning environment. According to the surgeon's findings, different choices can be redone in order to optimize the therapy. To account for soft tissue implications, skin tissue deformations are calculated using a finite element elastic model based on tetrahedral elements, We report on results in the field of unilateral mandibular distraction. A detailed overview of the planning procedure is given by a case study

Three dimensional study to quantify the relationship between facial hard and soft tissue movement as a result of orthognathic surgery

Introduction Prediction of soft tissue changes following orthognathic surgery has been frequently attempted in the past decades. It has gradually progressed from the classic “cut and paste” of photographs to the computer assisted 2D surgical prediction planning; and finally, comprehensive 3D surgical planning was introduced to help surgeons and patients to decide on the magnitude and direction of surgical movements as well as the type of surgery to be considered for the correction of facial dysmorphology. A wealth of experience was gained and numerous published literature is available which has augmented the knowledge of facial soft tissue behaviour and helped to improve the ability to closely simulate facial changes following orthognathic surgery. This was particularly noticed following the introduction of the three dimensional imaging into the medical research and clinical applications. Several approaches have been considered to mathematically predict soft tissue changes in three dimensions, following orthognathic surgery. The most common are the Finite element model and Mass tensor Model. These were developed into software packages which are currently used in clinical practice. In general, these methods produce an acceptable level of prediction accuracy of soft tissue changes following orthognathic surgery. Studies, however, have shown a limited prediction accuracy at specific regions of the face, in particular the areas around the lips. Aims The aim of this project is to conduct a comprehensive assessment of hard and soft tissue changes following orthognathic surgery and introduce a new method for prediction of facial soft tissue changes.   Methodology The study was carried out on the pre- and post-operative CBCT images of 100 patients who received their orthognathic surgery treatment at Glasgow dental hospital and school, Glasgow, UK. Three groups of patients were included in the analysis; patients who underwent Le Fort I maxillary advancement surgery; bilateral sagittal split mandibular advancement surgery or bimaxillary advancement surgery. A generic facial mesh was used to standardise the information obtained from individual patient’s facial image and Principal component analysis (PCA) was applied to interpolate the correlations between the skeletal surgical displacement and the resultant soft tissue changes. The identified relationship between hard tissue and soft tissue was then applied on a new set of preoperative 3D facial images and the predicted results were compared to the actual surgical changes measured from their post-operative 3D facial images. A set of validation studies was conducted. To include: • Comparison between voxel based registration and surface registration to analyse changes following orthognathic surgery. The results showed there was no statistically significant difference between the two methods. Voxel based registration, however, showed more reliability as it preserved the link between the soft tissue and skeletal structures of the face during the image registration process. Accordingly, voxel based registration was the method of choice for superimposition of the pre- and post-operative images. The result of this study was published in a refereed journal. • Direct DICOM slice landmarking; a novel technique to quantify the direction and magnitude of skeletal surgical movements. This method represents a new approach to quantify maxillary and mandibular surgical displacement in three dimensions. The technique includes measuring the distance of corresponding landmarks digitized directly on DICOM image slices in relation to three dimensional reference planes. The accuracy of the measurements was assessed against a set of “gold standard” measurements extracted from simulated model surgery. The results confirmed the accuracy of the method within 0.34mm. Therefore, the method was applied in this study. The results of this validation were published in a peer refereed journal. • The use of a generic mesh to assess soft tissue changes using stereophotogrammetry. The generic facial mesh played a major role in the soft tissue dense correspondence analysis. The conformed generic mesh represented the geometrical information of the individual’s facial mesh on which it was conformed (elastically deformed). Therefore, the accuracy of generic mesh conformation is essential to guarantee an accurate replica of the individual facial characteristics. The results showed an acceptable overall mean error of the conformation of generic mesh 1 mm. The results of this study were accepted for publication in peer refereed scientific journal. Skeletal tissue analysis was performed using the validated “Direct DICOM slices landmarking method” while soft tissue analysis was performed using Dense correspondence analysis. The analysis of soft tissue was novel and produced a comprehensive description of facial changes in response to orthognathic surgery. The results were accepted for publication in a refereed scientific Journal. The main soft tissue changes associated with Le Fort I were advancement at the midface region combined with widening of the paranasal, upper lip and nostrils. Minor changes were noticed at the tip of the nose and oral commissures. The main soft tissue changes associated with mandibular advancement surgery were advancement and downward displacement of the chin and lower lip regions, limited widening of the lower lip and slight reversion of the lower lip vermilion combined with minimal backward displacement of the upper lip were recorded. Minimal changes were observed on the oral commissures. The main soft tissue changes associated with bimaxillary advancement surgery were generalized advancement of the middle and lower thirds of the face combined with widening of the paranasal, upper lip and nostrils regions. In Le Fort I cases, the correlation between the changes of the facial soft tissue and the skeletal surgical movements was assessed using PCA. A statistical method known as ’Leave one out cross validation’ was applied on the 30 cases which had Le Fort I osteotomy surgical procedure to effectively utilize the data for the prediction algorithm. The prediction accuracy of soft tissue changes showed a mean error ranging between (0.0006mm±0.582) at the nose region to (-0.0316mm±2.1996) at the various facial regions