Research And Application On The Technologies For Computer-Aided Fixed Bridge Framework Design

With the CAD/CAM technologies widely used in dental medical treatment, the dental repair process can be finished with computer system, which is much more automatic and smarter than the traditional method. The PFM fixed bridge framework is one of the most important parts of the dental restoration. Combined with the demands of dental clinic, system structure, relevant theories and key technologies are studied deeply in this dissertation and the PFM fixed bridge framework CAD prototype software is developed. The main contents and achievements are as follows:1. The half-edge topological reconstruction algorithm based on Red-Black tree is presented to efficiently reconstruct the topological structure of the bridge which consists of several mesh models. The algorithm takes the triangular facet as unit. Filtering the redundant vertexes and searching neighbor information are merged into one process. The vertices, edges and facets and many other information can be rapidly checked with this topological structure.2. The standard bridge and connector database is built. 28 standard bridge models are designed based on modifying the standard crowns. They are beautiful and smooth, and moreover, fit the Chinese very well. Two kinds of standard connectors are designed based on the difference of the molar and the incisor, which have different cutting plane shapes for different uses.3. The precise location algorithm is presented to locate the bridge and connector to the perfect positions. Firstly, the curvature of every vertex is computed, and the occlusal plane is located based on the trend plane analysis. Secondly, the model is located to the rough position automatically based on the volume weight method of the coping crowns. Finally, the model is located to the perfect position with manual fine tuning.4. The scale transformation is used to realize the bridge global deformation and the algorithm based on area restriction is put forward to realize the connector cutting plane shape deformation. The deformation algorithm based on gradient is presented to realize the bridge's maxillofacial local deformation. The algorithm iterates the linear Laplacian deformation, rotation extraction and differential coordinate update to deform the original mesh to the target mesh step by step. The deformed mesh keeps smooth and retains the detail feature very well.5. The mesh mergence algorithm is presented to merge several separate parts into a whole one, which consists of four steps: intersection line extraction, mesh cutting, mesh fixing and mesh smoothing. The intersection line extraction algorithm based on the topological structure get the line rapidly. The meshes are cut based on the line, and then connected together with the triangles constructed with the boundry points. Finally, the transitional regions are smoothed with Taubin smooth algorithm. After all parts are merged, the design process of the PFM fixed bridge framework is accomplished.6. The total development framework of the PFM fixed bridge framework CAD system is presented. The system includes three main parts: design of the coping crowns, design of the bridge and design of the connectors. The function and design process of every part are also expatiated. Based on the practical demands in clinical prosthodontics, the dental PFM fixed bridge framework CAD prototype system is developed. And several special patients'bridges are designed accurately and efficiently with this system.