A Hemispherical Contact Model for Simplifying 3D Occlusal Surfaces

Statement of problem Currently, dental articulators can recreate mandibular movements and occlusal contacts. However, whether virtual articulators can also provide information about occluding dental surfaces, functional movements, and the mandibular condyles is unclear. Purpose The purpose of this in vitro study was to evaluate the occluding surfaces on dental casts obtained from a patient and approximate them to a hemispherical contact model. Both models were tested by digitizing the Dentatus ARL dental articulator. Material and methods A combination of photogrammetry and structure from motion methods were used to scan a Dentatus ARL articulator and representative dental casts. Using computer-aided engineering and finite element analysis, contact points and action vectors to the forces on occluding surfaces and condyles were obtained for cast and hemispherical models. This experiment was performed using centric occlusion and 3 different condylar inclinations. The Kruskal-Wallis 1-way analysis of variance on ranks test was used to allow all pairwise comparisons between condylar inclination and mechanical action vector values in each location (α=.05). Results Action vectors from the cast model and each location of the hemispherical model were calculated to show the mechanical consequences and the similarity among models. Overall, no significant differences were observed for action vectors (A20 versus A40 versus A60) at each location (dental cast/hemisphere, right condylar, and left condylar) in the analysis of dental casts and the hemisphere model (.382≤P≤.999). Conclusions This study provided graphical information that may assist the dental professional in determining which occlusal contacts should be modified to attain condylar and balanced centric occlusion

Geometrical modeling of complete dental shapes by using panoramic X-ray, digital mouth data and anatomical templates

In the field of orthodontic planning, the creation of a complete digital dental model to simulate and predict treatments is of utmost importance. Nowadays, orthodontists use panoramic radiographs (PAN) and dental crown representations obtained by optical scanning. However, these data do not contain any 3D information regarding tooth root geometries. A reliable orthodontic treatment should instead take into account entire geometrical models of dental shapes in order to better predict tooth movements. This paper presents a methodology to create complete 3D patient dental anatomies by combining digital mouth models and panoramic radiographs. The modeling process is based on using crown surfaces, reconstructed by optical scanning, and root geometries, obtained by adapting anatomical CAD templates over patient specific information extracted from radiographic data. The radiographic process is virtually replicated on crown digital geometries through the Discrete Radon Transform (DRT). The resulting virtual PAN image is used to integrate the actual radiographic data and the digital mouth model. This procedure provides the root references on the 3D digital crown models, which guide a shape adjustment of the dental CAD templates. The entire geometrical models are finally created by merging dental crowns, captured by optical scanning, and root geometries, obtained from the CAD templates

Automatic 3D tooth segmentation using convolutional neural networks in harmonic parameter space

Automatic segmentation of 3D tooth models into individual teeth is an important step in orthodontic CAD systems. 3D tooth segmentation is a mesh instance segmentation task. Complex geometric features on the surface of 3D tooth models often lead to failure of tooth boundary detection, so it is difficult to achieve automatic and accurate segmentation by traditional mesh segmentation methods. We propose a novel solution to address this problem. We map a 3D tooth model isomorphically to a 2D harmonic parameter space and convert it into an image. This allows us to use a CNN to learn a highly robust image segmentation model to achieve automated and accurate segmentation of 3D tooth models. Finally, we map the image segmentation mask back to the 3D tooth model and refine the segmentation result using an improved Fuzzy Clustering-and-Cuts algorithm. Our method has been incorporated into an orthodontic CAD system, and performs well in practice

3D orthodontics visualization

Master'sMASTER OF ENGINEERIN

Study and Development of Techniques for 3D Dental Identification

Ph.DDOCTOR OF PHILOSOPH

Enhanced Computerized Surgical Planning System in Craniomaxillofacial Surgery

In the field of craniomaxillofacial (CMF) surgery, surgical planning is an important and necessary procedure due to the complex nature of the craniofacial skeleton. Computed tomography (CT) has brought about a revolution in virtual diagnosis, surgical planning and simulation, and evaluation of treatment outcomes. It provides high-quality 3D image and model of skull for Computer-aided surgical planning system (CSPS). During the planning process, one of the essential steps is to reestablish the dental occlusion. In the first project, a new approach is presented to automatically and efficiently reestablish dental occlusion. It includes two steps. The first step is to initially position the models based on dental curves and a point matching technique. The second step is to reposition the models to the final desired occlusion based on iterative surface-based minimum distance mapping with collision constraints. With linearization of rotation matrix, the alignment is modeled by solving quadratic programming. The simulation was completed on 12 sets of digital dental models. Two sets of dental models were partially edentulous, and another two sets have first premolar extractions for orthodontic treatment. Two validation methods were applied to the articulated models. The results show that using the proposed method, the dental models can be successfully articulated with a small degree of deviations from the occlusion achieved with the gold-standard method. Low contrast resolution in CBCT image has become its major limitation in building skull model. Intensive hand-segmentation is required to reconstruct the skull model. Thin bone images are particularly affected by this limitation. In the second project, a novel segmentation approach is presented based on wavelet active shape model (WASM) for a particular interest in the outer surface of the anterior wall of maxilla. 19 CBCT datasets are used to conduct two experiments. This model-based segmentation approach is validated and compared with three different segmentation approaches. The results show that the performance of this model-based segmentation approach is better than those of the other approaches. It can achieve 0.25 +/- 0.2mm of surface error distance from the ground truth of the bone surface. Field of view (FOV) can be reduced in order to reduce unnecessary radiation dose in CBCT. This ROI imaging is common in most of the dentomaxillofacial imaging and orthodontic practices. However, a truncation effect is created due to the truncation of projection images and becomes one of the limitation in CBCT. In the third project, a method for small region of interest (ROI) imaging and reconstruction of the image of ROI in CBCT and two experiments for measurement of dosage are presented. The first experiment shows at least 60% and 70% of radiation dose can be reduced. It also demonstrates that the image quality was still acceptable with little variation of gray by using the traditional truncation correction approach for ROI imaging. The second experiment demonstrates that the images reconstructed by CBCT reconstruction algorithms without truncation correction can be degraded to unacceptable image quality

Estudio de la dinámica mandibular humana en un articulador dental virtual individualizable

Problemática. Actualmente, los articuladores dentales pueden recrear los movimientos mandibulares y contactos oclusales en ausencia de pacientes. Pero ¿pueden también los articuladores virtuales facilitar información respecto a lo que ocurre sobre las superficies dentales oclusales y en los cóndilos durante sus movimientos funcionales? Objetivo. Este estudio pretende desarrollar un análisis mecánico de las superficies de oclusión en modelos de yeso de pacientes y aproximarlos a un modelo de contacto hemisférico. Ambos modelos son testeados a través de la digitalización del articulador dental Dentatus ARL. Materiales y metodología. Se emplea el análisis de elementos finitos, donde se obtienen los vectores de acción de las fuerzas en las superficies de oclusión y en cóndilos. Este experimento es realizado usando la oclusión céntrica y 3 diferentes inclinaciones condilares. Resultado. Los resultados demuestran la caracterización única de los vectores de acción para el estudio de paciente, el comportamiento de sistema bucal con el modelo hemisférico y la independencia de la oclusión céntrica del paciente. Conclusiones. El presente trabajo ofrece una información gráfica amigable para el usuario que puede ayudar al profesional dental en la determinación en qué contactos oclusales debería ser preferiblemente modificados en aras de obtener el balance entre las acciones en cóndilos y la oclusión céntrica.Statement of problem. Currently, dental articulators can recreate mandibular movements and occlusal contacts in a patient’s absence. Can virtual articulators also provide information about occluding dental surfaces, functional movements and the mandibular condyles? Purpose. This study aims to perform a mechanical study of occluding surfaces on patient dental casts and approximating them to a hemispherical contact models. Both models are tested through the digitization of the Dentatus ARL dental articulator. Material and methods. Using finite element analysis, action vectors to the forces on occluding surfaces and condyles are obtained. This experiment was performed using centric occlusion and 3 different condylar inclinations (CI). Results. The results demonstrate the unique characterization of action vectors for the studied patient, the behavior of the oral system with the hemispherical model and CI independence of the patient on centric occlusion. Conclusions. This work provides user-friendly graphical information that may assist the dental professional in determining which occlusal contacts should be preferentially modified in order to attain condylar and centric occlusion balance