Method for removing tooth model attachment, program, and electronic device

Abstract

The invention relates to a tooth model attachment removal method based on a harmonic function and a finite element algorithm, which comprises the following steps of: firstly, preprocessing boundary conditions, obtaining internal and external rectangles of a definition domain through a bounding box algorithm, and obtaining boundary conditions of the internal and external rectangles through inverse projection mapping; and simply connecting the boundary of the original triangular mesh with the boundary of the circumscribed maximum rectangle. And for a finite element algorithm, a rectangular grid point interpolation method is adopted as a boundary condition, so that the rectangular boundary condition is closer to an original triangular grid boundary condition, and a rectangular curved surface is reconstructed through a method of everywhere reconciliation on a finite curved surface. And finally, converting the reconstructed curved surface into a relatively regular triangular mesh curved surface through Delou inner triangulation. Compared with an original triangular mesh, the function of removing the tooth model accessories is completed. By removing excessive wrinkles of tooth model accessories and gingiva, the real form of teeth is restored, and a solid foundation is built for subsequently realizing the design of an orthodontic scheme.

Description

Technical Field

[0001] The present invention relates to the field of oral digital technology, and in particular to a method, a program and an electronic device for removing attachments of a tooth model. Background Art

[0002] In order to provide oral patients with personalized services that are more in line with clinical conditions, obtaining accurate information about the soft and hard tissues in the mouth is one of the key steps. Before the digital age, obtaining intraoral information often relied on the preparation of impression materials and the infusion of plaster models. With the development of science and technology, digital stomatology has gradually become an emerging diagnosis and treatment model. The acquisition of oral digital information relies on pressure sensing and optical mapping as the basis. The data obtained is processed and digitally modeled by computer, and the actual situation of the soft and hard tissues in the mouth is simulated as much as possible and reflected in the computer software. It is a transformation from physical information to virtual information.

[0003] Therefore, before the digital modeling stage, there are often abnormalities in the digital modeling that do not fit the patient's mouth due to reasons such as the accuracy of the mapping instrument or the patient's improper operation, such as excessive wrinkles caused by the patient's braces carrying accessories and the gums being compressed by the equipment. In the past, these problems needed to be avoided by repeated intraoral scanning and overlapping modeling, but due to the large scanning error of soft tissue and the easy deformation of tissue during the scanning process, it was difficult to meet the expected medical standards in clinical practice.

[0004] Although the digital oral scanning system has limitations such as high price and dependence on instruments, it is an indispensable component for digital diagnosis and treatment due to its high accuracy, strong scanning capability, and easy data storage. With the advancement of Industry 4.0, the integration and sharing of data information is the only way for future oral diagnosis and treatment. Through digital facial scanning, digital oral scanning, and CBCT scanning, the data information of the face, oral soft and hard tissues, jaws and joints are integrated, and combined with AI technology, oral problems can be accurately diagnosed, treatment plans can be reasonably selected, and personalized treatment for patients can be truly achieved. Summary of the invention

[0005] The technical problem to be solved by the present invention is a model restoration method based on digital modeling. In order to restore the actual situation in the patient's mouth, a method, program and electronic equipment for removing tooth model attachments are designed to solve the existing technical problems.

[0006] In order to solve the above technical problems, the present invention provides a method for removing tooth model attachments, based on harmonic function and finite element algorithm, which specifically includes the following steps:

[0007] Step S1: pre-process the boundary conditions, obtain the inscribed rectangles and the boundary conditions of the inscribed rectangles by the bounding box algorithm, and then obtain the boundary conditions of the inscribed rectangles and the boundary of the original triangular mesh and the boundary of the outer maximum rectangle by inverse projection mapping, and then simply connect the boundary of the original triangular mesh and the boundary of the outer maximum rectangle, thus completing the boundary pre-processing.

[0008] Step S2: reconstructing a planar rectangular grid on the average boundary normal orthogonal projection plane of the selected surface area, and reacquiring its corresponding boundary conditions.

[0009] Step S3: Using the finite element algorithm, reconstruct the three-dimensional surface by simulating the changing trend of the boundary conditions of the plane rectangular grid.

[0010] Step S4: The reconstructed surface is re-collapsed and re-divided into triangular facets through Delaunay triangulation to make the triangular facets regularized.

[0011] Step S5: geometrically stitching the reconstructed surface inside the selected area with the remaining surface outside.

[0012] Furthermore, step S1 specifically includes the following steps:

[0013] Step S11: For the target surface, select the surface area to be reconstructed by using a selection tool, extract its internal points, and mark its directed boundaries and boundary points.

[0014] Step S12: For the selected area, the triangle facets where the opposite side of the directed boundary is located and their adjacent facets are combined into an area to obtain the selected area plus one boundary area.

[0015] Step S13: The sum of the plus-one boundary area and the selected area is called the plus-one adjacent area. If the plus-one adjacent area is used to replace the original selected area, and then the plus-one boundary adjacent area is calculated for the selected area, the plus-two boundary area can be obtained. This process is repeated and so on, and the plus-N adjacent area can be obtained.

[0016] Step S14: Select a suitable parameter N until the plus N adjacent area can completely wrap the original selected area, that is, all boundary vertices of the original selected area fall inside the plus N adjacent area, cut the plus N adjacent area from the original surface, and the surface remaining after cutting is called the remaining area.

[0017] Step S15: For the plus N boundary regions, obtain the normal average of the facets, and project the plus N adjacent regions onto the normal orthogonal plane as the subsequent definition domain.

[0018] Step S16: For the definition domain on the two-dimensional plane after projection, the inscribed and circumscribed rectangles are obtained by using a two-dimensional bounding box algorithm for the definition domain and its complement, and the grid lines are divided into the rectangles based on this system.

[0019] Step S17: For the rectangular boundary and the projection boundary of the original surface, the two boundary sides are connected by simple line segments by finding the nearest point.

[0020] Furthermore, in step S17, the inner circle boundary and the outer circle boundary are mapped to two concentric circles with different radii (outer circle radius > inner circle radius), so as to achieve an orderly arrangement of the boundary vertices. According to the order of the central angle of the circle from 0 to 2π, a ray is shot from the center of the circle, and the latest vertex swept by the ray is recorded. Then, the latest vertices of the inner and outer circles swept by the ray are connected to realize the construction of a simple triangle connecting the boundaries on both sides.

[0021] Furthermore, in step S2, for the step size selection of the grid lines, N times the average side length of the triangular facets in the selected area is used as the adaptive step size of the rectangular grid lines in each direction, 0.8≤N≤1.2.

[0022] Furthermore, in step S2, for the grid line boundary, the interpolation method is used in the following two cases respectively, so as to obtain the boundary conditions as close to the actual situation as possible:

[0023] For points whose local topology is isomorphic to the half-plane, make the rectangular boundary fall between two grid lines parallel to the half-plane boundary;

[0024] For points that are locally topologically isomorphic to the quarter plane, they are considered to be the intersection of two half planes, so that the rectangle boundary falls between two grid lines parallel to the half plane boundaries, in both directions.

[0025] Furthermore, for the rectangular boundary points, the boundary values ​​are obtained by interpolation of the grid vertices where they are located, and the interpolation weights are taken as the coefficients of the local linear combination.

[0026] Furthermore, in step S3, according to the discrete Laplace operator on the two-dimensional plane and the geometric kernel function on the corresponding mesh patch, the geometric relationship of the two-dimensional rectangular mesh patch is abstracted as the row-column relationship of a sparse matrix, and the target value on each internal point of the matrix mesh is gradually obtained by using Eigen to solve the sparse matrix, so that the harmonic condition is satisfied everywhere.

[0027] Furthermore, in step S4, the rectangular patch area is divided into two right triangles using a diagonal line.

[0028] The present invention also provides a computer program product, comprising computer instructions, which, when executed by a processor, enable a computer device to perform the method for removing tooth model attachments as described above.

[0029] The present invention also provides an electronic device, comprising:

[0030] at least one processor; and

[0031] at least one memory in communication with the processor;

[0032] The memory stores instructions that can be executed by the processor, and the instructions are executed by the processor to enable the electronic device to perform the aforementioned method for removing tooth model attachments.

[0033] Beneficial effects of the present invention:

[0034] The method for removing tooth model attachments of the present invention is based on harmonic functions and finite element algorithms. For the finite element algorithm, the boundary conditions adopt the method of rectangular grid point interpolation, so that the rectangular boundary conditions are closer to the original triangular grid boundary conditions, and the rectangular surface is reconstructed by the method of harmonization everywhere on the finite element surface. Finally, through Delaunay triangulation, the reconstructed surface is converted into a more regular triangular mesh surface. Compared with the original triangular mesh, the function of removing tooth model attachments is completed. By removing tooth model attachments and excessive gingival wrinkles, the real tooth condition can be simulated more effectively according to the patient's intraoral scan, and the children's tooth orthodontic plan can be closer to the patient's actual situation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The specific implementation of the present invention will be further explained below in conjunction with the accompanying drawings.

[0036] Figure 1 A flow chart of a method for removing attachments of a tooth model according to the present invention;

[0037] Figure 2 Expand boundary diagram for boundary preprocessing;

[0038] Figure 3 Preprocess the triangle connection diagram for the boundary;

[0039] Figure 4 This is a schematic diagram of the interpolation of rectangular grid boundary points;

[0040] Figure 5 It is a schematic diagram of the two-dimensional discrete Laplace geometric kernel function;

[0041] Figure 6 This is a before and after comparison of the effect of removing accessories. DETAILED DESCRIPTION

[0042] Example 1

[0043] Combination Figure 1 The method for removing the attachments of the tooth model in this embodiment is based on the harmonic function and the finite element algorithm, and specifically includes the following steps:

[0044] Step S1: pre-process the boundary conditions, obtain the inscribed rectangles and the boundary conditions of the inscribed rectangles by the bounding box algorithm, and then obtain the boundary conditions of the inscribed rectangles and the boundary of the original triangular mesh and the boundary of the outer maximum rectangle by inverse projection mapping, and then simply connect the boundary of the original triangular mesh and the boundary of the outer maximum rectangle, thus completing the boundary pre-processing.

[0045] In this embodiment, preferably, step S1 specifically includes the following steps:

[0046] Step S11: For the target surface, select the surface area to be reconstructed by using a selection tool, extract its internal points, and mark its directed boundaries and boundary points.

[0047] Step S12: For the selected area, the triangle facets where the opposite side of the directed boundary is located and its adjacent facets are combined into an area to obtain the area of ​​the selected area plus one boundary, such as Figure 2 shown.

[0048] Step S13: The sum of the plus-one boundary area and the selected area is called the plus-one adjacent area. If the plus-one adjacent area is used to replace the original selected area, and then the plus-one boundary adjacent area is calculated for the selected area, the plus-two boundary area can be obtained. This process is repeated and so on, and the plus-N adjacent area can be obtained.

[0049] Step S14: Select a suitable parameter N until the plus N adjacent area can completely wrap the original selected area, that is, all boundary vertices of the original selected area fall inside the plus N adjacent area, cut the plus N adjacent area from the original surface, and the surface remaining after cutting is called the remaining area.

[0050] Specifically, in this embodiment, the finer the mesh triangles are divided, the larger N is required.

[0051] Step S15: For the plus N boundary regions, obtain the normal average of the facets, and project the plus N adjacent regions onto the normal orthogonal plane as the subsequent definition domain.

[0052] Step S16: For the definition domain on the two-dimensional plane after projection, the definition domain and its complement are subjected to a two-dimensional bounding box algorithm to obtain the inscribed rectangle, and the rectangle is divided into grid lines based on the grid lines. In this embodiment, the method of grid division is specifically referred to step S2.

[0053] Step S17: For the rectangular boundary and the projection boundary of the original surface, the two boundary sides are connected by simple line segments by finding the nearest point.

[0054] Preferably, in step S17 of this embodiment, the inner circle boundary and the outer circle boundary are mapped to two concentric circles with different radii (the outer circle radius can be greater than the inner circle radius) to achieve orderly arrangement of the boundary vertices, and a ray is shot from the center of the circle in the order of the central angle from 0 to 2π, the latest vertex swept by the ray is recorded, and then the latest vertices of the inner and outer circles swept by the ray are connected to achieve simple triangle construction connecting the boundaries on both sides, such as Figure 3 shown.

[0055] Specifically, in this embodiment, the boundary points on the inscribed and circumscribed rectangles are projected back onto the curved surface through inverse mapping of the average normal projection to obtain their original images, which are used as parameters for calculating boundary conditions.

[0056] Step S2: reconstructing a planar rectangular grid on the average boundary normal orthogonal projection plane of the selected surface area, and reacquiring its corresponding boundary conditions.

[0057] Preferably, in this embodiment, in step S2, for the step size selection of the grid lines, N times the average side length of the triangular facets in the selected area is used as the adaptive step size of the rectangular grid lines in each direction. The shorter the selected step size, the higher the accuracy of the algorithm, but the longer it takes. In this embodiment, the value range of N is selected as 0.8≤N≤1.2.

[0058] In this embodiment, preferably, in step S2, for the grid line boundary, the interpolation method is used in the following two cases respectively, so as to obtain the boundary conditions as close to the actual situation as possible:

[0059] For points whose local topology is isomorphic to the half-plane, make the rectangular boundary fall between two grid lines parallel to the half-plane boundary;

[0060] For points whose local topology is isomorphic to the quarter plane, we treat them as the intersection of two half planes, so that the rectangular boundary falls between two grid lines parallel to the half plane boundary, in both directions, to achieve the effect as follows Figure 4 shown.

[0061] In this embodiment, preferably, for the rectangular boundary points, the boundary values ​​are obtained by interpolation calculation of the grid vertices where the points are located, and the interpolation weights are taken as coefficients of local linear combinations.

[0062] Step S3: Using the finite element algorithm, reconstruct the three-dimensional surface by simulating the changing trend of the boundary conditions of the plane rectangular grid.

[0063] In this embodiment, preferably, in step S3, according to the definition of the Laplace operator, it can be known that the discrete Laplace operator on the two-dimensional plane can be expressed as:

[0064]

[0065] in,

[0066] is the discrete second-order derivative in the x direction of the two-dimensional plane, which is specifically expressed as:

[0067]

[0068] is the discrete second-order derivative in the y direction of the two-dimensional plane, which is specifically expressed as:

[0069]

[0070] According to the discrete Laplace operator on the two-dimensional plane, equation (1) corresponds to a geometric kernel function on a mesh patch, such as Figure 5 As shown in the figure, the geometric relationship of the two-dimensional rectangular grid patches is abstracted as the row-column relationship of a sparse matrix, and the target value at each internal point of the matrix grid is gradually obtained by using Eigen to solve the sparse matrix, so that the harmonic conditions are met everywhere.

[0071] Step S4: The reconstructed surface is re-collapsed and re-divided into triangular facets through Delaunay triangulation to make the triangular facets regularized.

[0072] In this embodiment, preferably, in step S4, the rectangular patch area is divided into two right triangles by using diagonal lines. For the area outside the rectangular patch, the triangle connection with the projection boundary of the original curved surface has been realized in step S17.

[0073] Step S5: geometrically stitching the reconstructed surface inside the selected area with the remaining surface outside.

[0074] Specifically, in this embodiment, after the selected surface and the adjacent surface are cut off from the original surface according to step S14, a remaining surface is obtained, and its boundary is continuous with the boundary of the internal surface. By selecting a sufficiently large N, the boundary of the remaining surface and the boundary of the reconstructed surface can still maintain the original smoothness in the normal direction of the cutting line.

[0075] Therefore, the two current surfaces, namely the reconstructed surface inside the selected area and the remaining surface outside, can be geometrically stitched. The target triangular surface reconstruction is achieved, and the attachments and abnormal protrusions and wrinkles are removed, restoring the true shape of the teeth, and building a solid foundation for the subsequent design of tooth correction schemes. The effect before and after the attachment removal is shown in the figure below. Figure 6 As shown in the figure, the real dental condition can be simulated more effectively based on the patient's intraoral scan, and the children's orthodontic plan can be closer to the patient's actual situation.

[0076] Example 2

[0077] This embodiment provides a computer program product, including computer instructions, which, when executed by a processor, enable a computer device to execute the method for removing tooth model attachments as in Embodiment 1.

[0078] Example 3

[0079] This embodiment provides an electronic device, including:

[0080] at least one processor; and

[0081] at least one memory in communication with the processor;

[0082] The memory stores instructions that can be executed by the processor, and the instructions are executed by the processor to enable the electronic device to perform the method for removing tooth model attachments in Example 1.

[0083] Many specific details are described in the above description to facilitate a full understanding of the present invention. However, the above description is only a preferred embodiment of the present invention. The present invention can be implemented in many other ways different from those described herein, so the present invention is not limited to the specific implementation disclosed above. At the same time, any person familiar with the art can make many possible changes and modifications to the technical solution of the present invention using the methods and technical contents disclosed above without departing from the scope of the technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A method for removing attachments of a tooth model, characterized in that: Based on the harmonic function and finite element algorithm, the specific steps include: Step S1: pre-process the boundary conditions, obtain the inscribed rectangles and the boundary conditions of the inscribed rectangles by using the bounding box algorithm, and then obtain the boundary conditions of the inscribed rectangles and the boundary of the original triangle mesh and the boundary of the outer maximum rectangle by using the inverse projection mapping; Step S2: reconstructing a planar rectangular grid on the average boundary normal orthogonal projection plane of the selected surface area, and reacquiring its corresponding boundary conditions; Step S3: using a finite element algorithm to reconstruct a three-dimensional surface by simulating the changing trend of the boundary conditions of a plane rectangular grid; Step S4: collapsing and re-dividing the triangular facets of the reconstructed surface through Delaunay triangulation to make the triangular facets regularized; Step S5: geometrically stitching the reconstructed surface inside the selected area with the remaining surface outside.

2. The method for removing tooth model attachments according to claim 1, characterized in that: Step S1 specifically includes the following steps: Step S11: For the target surface, select the surface area to be reconstructed by using a selection tool, extract its internal points, and mark its directed boundaries and boundary points; Step S12: for the selected area, the triangle facets where the opposite side of the directed boundary is located and their adjacent facets are combined into an area to obtain the area of ​​the selected area plus one boundary; Step S13: The sum of the plus-one boundary region and the selected region is called the plus-one adjacent region. If the plus-one adjacent region is used to replace the original selected region, and the plus-one boundary adjacent region is calculated for the selected region, the plus-two boundary region can be obtained. This process is repeated and so on, and the plus-N adjacent region can be obtained. Step S14: Select a suitable parameter N until the plus N adjacent region can completely wrap the original selected region, that is, all the boundary vertices of the original selected region fall inside the plus N adjacent region, cut the plus N adjacent region from the original surface, and the surface remaining after cutting is called the remaining region; Step S15: for the plus N boundary region, obtain the normal average of its facets, and project the plus N adjacent regions onto the normal orthogonal plane as the subsequent definition domain; Step S16: for the definition domain on the two-dimensional plane after projection, the inscribed rectangles are obtained by using a two-dimensional bounding box algorithm for the definition domain and its complement, and a grid line division is performed on the rectangle based on the constructed system; Step S17: For the rectangular boundary and the projection boundary of the original surface, the two boundary sides are connected by simple line segments by finding the nearest point.

3. The method for removing tooth model attachments according to claim 2, characterized in that: In step S17, the inner circle boundary and the outer circle boundary are mapped to two concentric circles with different radii to achieve an orderly arrangement of the boundary vertices, and a ray is shot from the center of the circle in the order of the central angle from 0 to 2π, and the latest vertex swept by the ray is recorded, and then the latest vertices of the inner and outer circles swept by the ray are connected to achieve the construction of a simple triangle connecting the boundaries on both sides.

4. The method for removing tooth model attachments according to claim 1, characterized in that: In step S2, for the step size selection of the grid lines, N times the average side length of the triangular facets in the selected area is used as the adaptive step size of the rectangular grid lines in each direction, 0.8≤N≤1.

2.

5. The method for removing tooth model attachments according to claim 1, characterized in that: In step S2, for the grid line boundary, the interpolation method is used in the following two cases respectively, so as to get the boundary conditions as close to the actual situation as possible: For points whose local topology is isomorphic to the half-plane, make the rectangular boundary fall between two grid lines parallel to the half-plane boundary; For points that are locally topologically isomorphic to the quarter plane, they are considered to be the intersection of two half planes, so that the rectangle boundary falls between two grid lines parallel to the half plane boundaries, in both directions.

6. The method for removing attachments of a tooth model according to claim 5, characterized in that: For rectangular boundary points, the boundary values ​​are obtained by interpolating the vertices of the grid squares where they are located, and the interpolation weights are taken as the coefficients of the local linear combination.

7. The method for removing attachments of a tooth model according to claim 1, characterized in that: In step S3, according to the discrete Laplace operator on the two-dimensional plane and the geometric kernel function on the corresponding mesh patch, the geometric relationship of the two-dimensional rectangular mesh patch is abstracted as the row-column relationship of a sparse matrix, and the target value on each internal point of the matrix mesh is gradually obtained by using Eigen to solve the sparse matrix, so that the harmonic condition is satisfied everywhere.

8. The method for removing attachments of a tooth model according to claim 1, characterized in that: In step S4, the rectangular patch area is divided into two right triangles using a diagonal line.

9. A computer program product, characterized in that: The method comprises computer instructions, which, when executed by a processor, cause a computer device to perform the method for removing tooth model attachments according to any one of claims 1 to 8.

10. An electronic device, characterized in that: include: at least one processor; as well as at least one memory in communication with the processor; The memory stores instructions executable by the processor, and the instructions are executed by the processor to enable the electronic device to perform the method for removing tooth model attachments according to any one of claims 1 to 8.

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