A CAD design method for removable partial dentures

Abstract

The present invention relates to a CAD design method for removable partial dentures. The removable partial dentures include a denture body and a retention mesh, and the method comprises the following steps: S1, preparing denture body model data; S2, designing retention mesh model data, S2a, obtaining a curved surface, S2b, mesh parameterization, S2c, arranging mesh holes, S2d, substitution operation. The purpose of the present invention is to solve or at least mitigate the problem that the shape of the retention mesh holes may be greatly deformed when the oral three-dimensional curved surface is rough, and to provide a CAD design method for removable partial dentures.

Description

Technical Field

[0001] The present invention belongs to the technical field of computer-aided design in stomatology, and particularly relates to a CAD design method for removable partial dentures. Background Art

[0002] The metal components (abbreviation: framework) of cast framework removable partial dentures are mainly fabricated by integral casting, and artificial teeth and baseplate plastics are attached to the retention mesh of the cast framework. Commonly used metal materials include cobalt-chromium (Co-Cr) alloy, titanium metal, cobalt-chromium-molybdenum (Co-Cr-Mo) alloy, gold alloy, etc. In the field of dental restoration, framework design is an important branch.

[0003] Retention meshes are usually used in prosthodontics, especially for denture fixation and implant restoration. In denture fixation, the retention mesh can enhance the stability of the denture and improve the comfort of the patient. In implant restoration, the retention mesh is used to connect the implant and the denture to achieve stable occlusion.

[0004] Digital technology also plays an important role in the design and manufacturing process of retention meshes. For example, through computer-aided design (CAD) and computer-aided manufacturing (CAM) technologies, retention meshes can be accurately designed and manufactured to ensure their conformity to the patient's oral structure.

[0005] In general dental CAD design software, such as 3Shape and exocad, the deformation of the retention mesh holes is processed, but when there are certain undulations on the surface, there are significant differences in the hole spacing of the retention mesh.

[0006] The shape and density of the mesh holes of the retention meshes generated by the prior art are greatly affected by the attached oral surface. However, when the selected oral three-dimensional surface is rough and uneven, the shape of the retention mesh holes may be deformed significantly, and the sorting and density of the retention mesh holes change greatly, which is not conducive to the retention mesh playing its role in fixing the position and is not conducive to the control of precision in the manufacturing process. It affects the yield rate and function of the finished product. Summary of the Invention

[0007] The purpose of the present invention is to overcome the deficiencies in the prior art, and to provide a CAD design method for removable partial dentures in order to solve or at least alleviate the problem that when the oral three-dimensional surface is rough and uneven, the shape of the retention mesh holes may be deformed significantly.

[0008] The present invention is achieved by the following technical solutions:

[0009] A CAD design method for removable partial dentures, the removable partial denture includes a denture body and a retention mesh, and includes the following steps:

[0010] S1. Prepare the denture body model data, obtain the scanned data of the dental arch model to get the remaining teeth and tooth positions, and obtain the denture body model data according to the obtained scanned data of the dental arch model and the preset deep learning network model;

[0011] S2. Design the retention net model data;

[0012] S2a. Obtain a surface. Select the retention net area according to the denture body model data to obtain the original surface;

[0013] S2b. Mesh parameterization. Perform arap mesh parameterization on the surface obtained in step S2a to obtain a two-dimensional surface;

[0014] S2c. Layout mesh holes. Uniformly layout mesh holes on the two-dimensional surface obtained in step S2b, and map the center points of the mesh holes back to the original surface;

[0015] S2d. Substitution operation. Generate spheres centered on the center points of the mapped mesh holes on the original surface, and perform a bool difference operation with the original surface. The result of the bool operation is the retention net model data with uniformly distributed mesh holes.

[0016] To further implement the present invention, the following technical solutions can be preferably selected:

[0017] Preferably, in the preset deep learning network model of step S1, for the input point cloud data, feature extraction and feature transformation are performed, all point features are aggregated through a max pooling layer, and the label of each point is obtained by combining local features and global features to obtain the recognition result of the remaining teeth and tooth positions;

[0018] Among them, feature extraction includes:

[0019] The local features and geometric features of a point are weighted and summed with the features of the points in its neighborhood to obtain the first-layer features. The initial local features and geometric features of the point are cascaded with the first-layer features, and feature extraction is performed on this part of the features again.

[0020] Preferably, in step S2b, the arap parameterization method is used to construct an energy expression model to measure the degree of deformation of the original surface;

[0021] A plurality of continuously spaced points are uniformly arranged on the original surface. Each point and the adjacent edges of this point and all its adjacent points form a deformation unit, and each deformation unit is composed of a plurality of triangular patches;

[0022] The energy formula for the composition of this deformation unit is:

[0023]

[0024] The total energy formula for this deformation unit is:

[0025]

[0026] Among them, C i and C i ' respectively represent the deformed unit corresponding to the model vertices p i and p j before and after deformation. N(i) represents the set of neighboring points of point p i .

[0027] Preferably, the unknown variables in the total energy formula are R i and the deformed coordinate P'. The total energy formula is optimized by the iterative method, and the steps are as follows:

[0028] 1) Fix P', and solve for R using the ICP algorithm i ;

[0029] 2) Fix R i , and solve for P';

[0030] 3) Return to step 1 until the energy is less than the given threshold.

[0031] Preferably, the solution method in step 2 is to directly take the derivative and set the reciprocal equal to 0, and the formula is:

[0032]

[0033] Preferably, in step S2c, the center points evenly distributed on the two-dimensional plane are distributed on the two-dimensional surface, and then the inverse mapping of all the center points is obtained, the triangular patches corresponding to each center point are solved, the triangular coordinates are calculated, and the weighted sum of the original triangular patches is taken to obtain the center point coordinates.

[0034] Preferably, in step S2d, the bool operation is based on the polygon triangulation algorithm with internal edges, and the polygon triangulation algorithm includes the following steps:

[0035] A. Select a suitable triangular patch according to the triangulation requirements, record and remove the triangular patch, update the boundary and the edges inside the boundary. The suitable triangular patch is such that the updated boundary after removing the triangular patch is still a simple non-intersecting polygon, and there are no any boundaries or internal edges inside the triangular patch;

[0036] B. Determine a boundary edge, use this boundary edge as one side of the triangular patch, and find a triangular patch that meets step A. If not found, determine the next boundary edge until a triangular patch that meets step A is found. After finding a triangular patch that meets step A, update the boundary and the internal edges until the boundary degenerates into a triangle and contains no internal edges.

[0037] Through the above technical solutions, the beneficial effects of the present invention are:

[0038] The present invention can solve the problem of the deformation of the shape of the retention mesh holes, that is, the present invention can make the shape of the retention mesh holes not affected by the oral cavity surface and maintain the round hole shape.

[0039] The present invention can solve the problem of uneven arrangement and distribution of the retention mesh holes, that is, the present invention can make the arrangement and distribution of the retention mesh holes not affected by the oral cavity surface and maintain a uniform and orderly distribution.

[0040] Mesh holes with uniform distribution can better disperse the biting force, reduce stress concentration, and thus avoid damage to local tissues. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is the overall flowchart of the present invention;

[0042] Figure 2 is the flowchart of the specific counting of the present invention;

[0043] Figure 3 is the schematic diagram of the surface parameterization of the present invention to a two-dimensional plane;

[0044] Figure 4 is the schematic diagram of the parameterized grid of the present invention flattened on a two-dimensional plane;

[0045] Figure 5 is the schematic diagram of scattering points in the two-dimensional plane where the grid of the present invention is flattened;

[0046] Figure 6 is the schematic diagram of a single triangle of the scattered points of the present invention;

[0047] Figure 7 is the schematic diagram of generating a sphere from the center coordinates of the grid of the present invention and performing a difference set operation with the original grid;

[0048] Figure 8 is the schematic diagram of the present invention based on the polygon triangulation algorithm with internal edges;

[0049] Figure 9 is one of the schematic diagrams of the present invention where the triangle formed by the edges and points does not meet the triangulation requirements;

[0050] Figure 10 is another schematic diagram of the present invention where the triangle formed by the edges and points does not meet the triangulation requirements; Figure 11 is one of the schematic diagrams of the present invention for adding the removed points to the set of triangulated triangles for orderly triangle splitting;

[0051] Figure 12 is another schematic diagram of the present invention for adding the removed points to the set of triangulated triangles for orderly triangle splitting. DETAILED DESCRIPTION OF THE INVENTION

[0052] In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, the terms "set", "install", "connect", and "couple" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0053] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0054] Embodiment 1:

[0055] A CAD design method for a removable partial denture, the removable partial denture including a denture body and a retention mesh, comprising the following steps:

[0056] S1. Prepare the model data of the denture body, obtain the scanned data of the dental arch model, obtain the remaining teeth and tooth positions, and obtain the model data of the denture body according to the obtained scanned data of the dental arch model and a preset deep learning network model;

[0057] S2. Design the model data of the retention mesh, as Figure 1 shown;

[0058] S2a. Obtain a surface, select the retention mesh area according to the model data of the denture body, and obtain the original surface;

[0059] S2b. Mesh parameterization, perform arap mesh parameterization on the surface obtained in step S2a to obtain a two-dimensional surface;

[0060] S2c. Layout mesh holes, evenly layout mesh holes on the two-dimensional surface obtained in step S2b, and map the centers of the mesh holes back to the original surface;

[0061] S2d. Substitution operation, generate a sphere with the center of the mapped mesh hole on the original surface as the center, and perform a bool difference operation with the original surface. The result of the bool operation is the model data of the retention mesh with evenly distributed mesh holes.

[0062] The present invention can solve the problem of the shape deformation of the retention mesh holes, that is, the present invention can make the shape of the retention mesh holes not affected by the oral cavity surface and maintain the round hole shape.

[0063] The present invention can solve the problem of uneven arrangement and distribution of retention mesh holes, that is, the present invention can make the distribution and arrangement of retention mesh holes not affected by the oral cavity curved surface and maintain uniform and orderly distribution.

[0064] Mesh holes with uniform distribution can better disperse the biting force, reduce stress concentration, and thus avoid damage to local tissues.

[0065] The improvement point of the present invention is to use the arap mesh parameterization method to evenly distribute the center points, ensure that the spatial distances between the center points are consistent, the sizes of the circular holes are the same, and there will be no stretching and deformation of the spatial arrangement positions and shapes.

[0066] The mesh generation algorithm in the bool operation of the present invention can handle complex curved surface shapes such as triangular curved surface meshes, and can ensure the stability of the bool operation.

[0067] The present invention greatly alleviates the problem of uneven sizes and distributions of retention mesh holes. Even on an uneven curved surface, a retention mesh patch with consistent and uniform mesh arrangement can be stably generated. The algorithm is stable and the speed is efficient.

[0068] In the preset deep learning network model of step S1, for the input point cloud data, feature extraction and feature transformation are performed. All point features are aggregated through the max pooling layer, and the label of each point is obtained by combining local features and global features, so as to obtain the recognition results of the remaining teeth and tooth positions;

[0069] Among them, feature extraction includes:

[0070] The local features and geometric features of the points are weighted and summed with the features of the points in their neighborhoods to obtain the first-layer features. The initial local features and geometric features of the points are cascaded with the first-layer features, and feature extraction is performed on this part of the features again.

[0071] In step S2b, the arap parameterization method is used to construct an energy expression model to measure the degree of deformation of the original curved surface;

[0072] As Figure 2 shown, a plurality of continuously spaced points are evenly arranged on the original curved surface. Each point and the adjacent edges of this point and all its adjacent points form a deformation unit, and each deformation unit is composed of a plurality of triangular patches;

[0073] The energy formula for the composition of this deformation unit is:

[0074]

[0075] The total energy formula for this deformation unit is:

[0076]

[0077] Among them, Ci and C i ' represent the vertices p of the model before and after deformation i and p j corresponding deformation units. N(i) represents p i point neighborhood point set.

[0078] There are unknown variables R in the total energy formula i and the deformed coordinates P'. The total energy formula is optimized by the iterative method, and the steps are as follows:

[0079] 1) Fix P' and use the ICP algorithm to solve for R i ;

[0080] 2) Fix R i , solve for P';

[0081] 3) Return to step 1 until the energy is less than the given threshold.

[0082] The solution method in step 2 is to directly take the derivative and set the reciprocal equal to 0, and its formula is:

[0083]

[0084] If you want to parameterize the surface to a two-dimensional plane, you only need to give an initial parameterization, such as a harmonic mapping, and then limit the third component of the new points to zero. After parameterization, the surface is mapped to the plane, as Figure 3 shown.

[0085] In step S2c, the center points evenly distributed on the two-dimensional plane are distributed on the two-dimensional surface, and then the inverse mapping of all the center points is obtained, the triangular patches corresponding to each center point are solved, and the triangular coordinates are calculated. Then, the weighted sum of the original triangular patches is used to obtain the center point coordinates.

[0086] The specific example is as follows: Spread the parameterized mesh on the two-dimensional plane, as Figure 4 shown; then sprinkle some points on the plane, as Figure 5 shown; Figure 6 The red points in are the points pre-sprinkled on the plane. Calculate which triangle the red points fall into and calculate the triangular coordinates. The definition and calculation of the triangular coordinates are as follows:

[0087]

[0088] λ in the above formula is the triangular coordinate, and solving this equation can obtain it. Then, the weighted sum of the original three-dimensional coordinates of each triangle will map Q back to the original triangular mesh.

[0089] Generate a sphere with the obtained center coordinates and perform a bool difference operation with the original mesh, asFigure 7 as shown

[0090] As Figure 8 shown, in step S2d, the bool operation is based on a polygon triangulation algorithm with internal edges, and the polygon triangulation algorithm includes the following steps:

[0091] A. Select a suitable triangular patch according to the triangulation requirements, record and remove the triangular patch, update the boundary and the edges inside the boundary. The suitable triangular patch is such that the updated boundary after removing the triangular patch is still a simple non - intersecting polygon, and there are no any boundaries or internal edges inside the triangular patch;

[0092] B. Determine a boundary edge, use this boundary edge as one side of the triangular patch, and look for a triangular patch that meets the requirements of step A. If not found, determine the next boundary edge until a triangular patch that meets the requirements of step A is found. After finding a triangular patch that meets the requirements of step A, update the boundary and the internal edges until the boundary degenerates into a triangle and contains no internal edges.

[0093] The specific steps are as follows:

[0094] 1. Obtain all the information of the polygon, including the boundary points arranged counter - clockwise, the internal edges of the polygon, and the internal points of the polygon.

[0095] 2. Due to calculation precision issues, it is necessary to simplify the polygon information. Only keep one of the point sets that are too close (remove the rest). For some points, the two sides to which they belong are almost on the same straight line. Removing these points should not cause the boundaries of the polygon region to intersect, nor will it cause the connection relationship between the internal boundary and the polygon.

[0096] 3. Traverse each edge of the polygon and try a suitable edge. The definition of a suitable edge is: there exists a point, and the triangle formed by this point and this edge is a triangle that meets the triangulation requirements.

[0097] As Figure 9 shown, the figure shows two examples where the triangles formed by the edges and points do not meet the triangulation requirements. The triangle formed by the CD edge and point B does not meet the triangulation requirements because the triangle intersects with the internal edge. The triangle formed by the CD edge and point A does not meet the triangulation requirements because the normal of the triangle is not in the same direction as the normal of the polygon.

[0098] As Figure 10 shown, in the figure, the triangle formed by the AD edge and point B also does not meet the requirements because there is a boundary point C inside the triangle.

[0099] But after we find a triangle that meets the requirements, we proceed to the next step.

[0100] 4. Remove this triangle from the polygon region and update the information of the polygon region. Go back to step 2 until the polygon region has no internal edges and is a triangle.

[0101] 5. Add the points removed in the first step to the set of triangulated triangles and perform an ordered triangle split, as Figure 11 and Figure 12 shown.

[0102] p1 and p2 are the points removed in the first step. Now add these points. Then triangulate the relevant triangles as follows (process p1 first and then p2):

[0103] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A CAD design method for a removable partial denture, the removable partial denture comprising a denture body and a retention mesh, characterized in that: The following steps are involved: S1. Prepare denture body model data, obtain dentition model scan data, obtain reserved teeth and tooth positions, and obtain denture body model data based on the obtained dentition model scan data and a preset deep learning network model; S2, design the retention network model data; S2a, obtaining the curved surface, selecting the retention mesh area according to the denture body model data, and obtaining the original curved surface; S2b, mesh parameterization, performing arap mesh parameterization on the surface obtained in step S2a to obtain a two-dimensional surface; S2c, arranging meshes, evenly arranging meshes on the two-dimensional surface obtained in step S2b, and mapping the centers of the meshes back to the original surface; S2d, substitution operation, generating a sphere with the center of the mesh circle mapped on the original surface as the center, and performing a bool difference operation with the original surface. The result of the bool operation is the retention network model data of the mesh uniformly distributed; In the step S2b, the arap parameterized component energy expression model is used to measure the degree of deformation of the original curved surface; A plurality of continuously spaced points are evenly arranged on the original surface, each point and the edges adjacent to the point and all its adjacent points form a deformation unit, and each deformation unit is composed of a plurality of triangular facets; The energy formula of the deformation unit is: The total energy formula of the deformation unit is: Among them C i and C i 'represents the model vertex p before and after deformation i and p j The corresponding deformation unit, N(i) represents p i The neighborhood point set of a point; The total energy formula has an unknown variable R i and the deformed coordinates P', the iterative method is used to optimize the total energy formula, the steps are as follows: 1) Fix P' and use ICP algorithm to solve R i ; 2) Fixed R i , solve for P'; 3) Return to step 1 until the energy is less than the given threshold.

2. A CAD design method for a removable partial denture according to claim 1, characterized in that: In the preset deep learning network model in step S1, feature extraction and feature transformation are performed on the input point cloud data, all point features are aggregated through the maximum pooling layer, and the label of each point is obtained by combining local features and global features to obtain the remaining teeth and tooth position recognition results; Among them, feature extraction includes: The local features and geometric features of the point are weightedly summed with the features of the points in its neighborhood to obtain the first layer of features. The initial local features and geometric features of the point are cascaded with the first layer of features, and feature extraction is performed on the cascaded features.

3. The CAD design method for a removable partial denture according to claim 1, characterized in that: In the step S2c, the center points uniformly distributed on the two-dimensional plane are distributed on the two-dimensional surface, and then the inverse mapping of all the center points is calculated, the triangular facets corresponding to each center point are solved, and the triangular coordinates are calculated, and then the weighted sum of the original triangular facets is performed to obtain the coordinates of the center point.

4. The CAD design method for a removable partial denture according to claim 1, characterized in that: The bool operation in step S2d is based on a polygon partitioning algorithm with internal edges, and the polygon partitioning algorithm includes the following steps: A. Select a suitable triangular face according to the segmentation requirements, record and remove the triangular face, and update the boundary and the edges inside the boundary. The suitable triangular face is a simple non-intersecting polygon whose updated boundary after removing the triangular face is still a simple non-intersecting polygon, and the triangular face does not contain any boundary or internal edge; B. Determine a boundary edge and use it as one side of the triangle. Look for a triangle that meets step A. If not found, determine the next boundary edge until a triangle that meets step A is found. After finding a triangle that meets step A, update the boundary and internal edges until the boundary degenerates into a triangle and does not contain internal edges.

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