阅读说明：本技术 一种基于二维美齿特征线的三维牙齿形状修复方法及系统 (Three-dimensional tooth shape restoration method and system based on two-dimensional tooth beautifying characteristic line ) 是由 杨帅 赵文杰 柯永振 刘佳颖 薛永江 于 2020-02-26 设计创作，主要内容包括：本发明提供了一种基于二维美齿特征线的三维牙齿形状修复方法及系统,属于口腔医疗领域。该方法包括：(1)获得二维美齿特征线和三维牙列模型；(2)将所述二维美齿特征线转换为三维美齿特征线,然后将三维美齿特征线与所述三维牙列模型进行配准得到配准后的三维牙列模型；(3)在所述配准后的三维牙列模型上提取出待修复体牙模轮廓；(4)根据所述待修复体牙模轮廓和三维美齿特征线对所述三维牙列模型进行变形获得三维美齿修复牙模。本发明效率非常高,能够以二维美齿特征线为指导,计算出三维待修复体上的美学修复结果,满足快速实现牙模美学修复的需要。(The invention provides a three-dimensional tooth shape restoration method and a three-dimensional tooth shape restoration system based on two-dimensional tooth beautifying characteristic lines, and belongs to the field of oral medical treatment. The method comprises the following steps: (1) obtaining a two-dimensional tooth beautifying characteristic line and a three-dimensional dentition model; (2) converting the two-dimensional dental characteristic line into a three-dimensional dental characteristic line, and then registering the three-dimensional dental characteristic line and the three-dimensional dentition model to obtain a registered three-dimensional dentition model; (3) extracting a dental model outline to be repaired from the registered three-dimensional dentition model; (4) and deforming the three-dimensional dentition model according to the profile of the dental model to be repaired and the three-dimensional tooth beautifying characteristic line to obtain the three-dimensional tooth beautifying repairing dental model. The method has very high efficiency, can calculate the aesthetic restoration result on the three-dimensional prosthesis to be restored by taking the two-dimensional beautiful tooth characteristic line as guidance, and meets the requirement of quickly realizing the aesthetic restoration of the dental model.)

1. A three-dimensional tooth shape restoration method based on two-dimensional tooth beautifying characteristic lines is characterized by comprising the following steps: the method comprises the following steps:

(1) obtaining a two-dimensional tooth beautifying characteristic line and a three-dimensional dentition model;

(2) converting the two-dimensional dental characteristic line into a three-dimensional dental characteristic line, and then registering the three-dimensional dental characteristic line and the three-dimensional dentition model to obtain a registered three-dimensional dentition model;

(3) extracting a dental model outline to be repaired from the registered three-dimensional dentition model;

(4) and deforming the three-dimensional dentition model according to the profile of the dental model to be repaired and the three-dimensional tooth beautifying characteristic line to obtain the three-dimensional tooth beautifying repairing dental model.

2. The method for restoring a three-dimensional tooth shape based on two-dimensional dental characteristic lines according to claim 1, wherein: the operation of the step (1) comprises the following steps:

inputting the front smile photo and the intraoral orthostatic image of the patient into a two-dimensional tooth beautifying system, and outputting a two-dimensional tooth beautifying characteristic line drawn according to the front smile photo and the intraoral orthostatic image by the two-dimensional tooth beautifying system;

and carrying out three-dimensional optical scanning on the oral cavity of the patient to obtain a three-dimensional dentition model of the patient.

3. The method for restoring a three-dimensional tooth shape based on a two-dimensional dental characteristic line according to claim 2, wherein: the operation of the step (2) comprises the following steps:

registering the intraoral orthostatic image of the patient with the three-dimensional dentition model to obtain the projection direction of the camera;

converting the two-dimensional merry tooth characteristic line into a three-dimensional merry tooth characteristic line in a Cartesian coordinate system;

taking the two-dimensional merry characteristic line as a background image of a window, wherein the background image is vertical to the projection direction of the camera;

and moving the three-dimensional tooth beautifying characteristic line on the three-dimensional dentition model by using a three-dimensional interactive tool to enable the three-dimensional tooth beautifying characteristic line to be superposed with the two-dimensional tooth beautifying characteristic line in the background image, so that the registered three-dimensional dentition model is obtained.

4. The method for restoring a three-dimensional tooth shape based on two-dimensional dental characteristic lines according to claim 3, wherein: the operation of the step (3) comprises:

and selecting contour seed points of the body to be restored on the registered three-dimensional dentition model, and calculating the shortest distance between each vertex on the three-dimensional dentition model and the contour seed points based on anisotropic measurement so as to obtain the contour of the body to be restored.

5. The method for restoring a three-dimensional tooth shape based on two-dimensional dental characteristic lines according to claim 4, wherein: the operation of the step (4) comprises the following steps:

(41) determining an active deformation area, a passive deformation area and a fixed area on the three-dimensional dentition model;

(42) carrying out active deformation on the active deformation area;

(43) and carrying out passive deformation on the passive deformation area to obtain the three-dimensional aesthetic restoration dental model.

6. The method for restoring a three-dimensional tooth shape based on two-dimensional dental characteristic lines according to claim 5, wherein: the active deformation zone in the step (41) refers to: a triangular mesh adjacent to the outline of the dental model of the body to be repaired on the three-dimensional dentition model;

the passive deformation region is as follows: a region on the three-dimensional dentition model adjacent to the active deformation zone; the vertex of the passive deformation area is passively deformed along with the movement of the vertex of the active deformation area;

the fixed area refers to: other areas outside the active deformation area and the passive deformation area on the three-dimensional dentition model; the coordinates of all vertices in the fixed area do not change.

7. The method for restoring a three-dimensional tooth shape based on two-dimensional dental characteristic lines according to claim 6, wherein: the operation of step (42) comprises:

(421) pairing the vertex of the three-dimensional beautiful tooth characteristic line with the vertex of the active deformation area to obtain n pairs of vertexes in the active deformation area:

firstly, acquiring a vertex p in the active deformation region₁Y of coordinates of₁Value, then finding the corresponding vertex p on the three-dimensional tooth-shaping characteristic line₁Paired vertices p₂Of y is₂The value of y and the vertex of the active deformation zone₁Equal in value, or | y₁-y₂< Δ d, thus defining a pair of vertices; repeating the step for n vertexes of the active deformation area in sequence to obtain n pairs of vertexes;

(422) and calculating the target position coordinate of each vertex on the active deformation area according to the n pairs of vertices to finish active deformation:

firstly, respectively averaging x, y and z values of all vertexes in the active deformation area to obtain a central point p of the active deformation area₀The coordinate is (x)₀，y₀，z₀)；

Will actively deform the vertex p in the region₁And the center point p₀The connecting line obtains a straight line L₁Said straight line L₁As shown in equation (3):

according to the projection direction of the camera and the point p on the three-dimensional beautiful tooth characteristic line₂Determine another straight line L₂Said straight line L₂As shown in equation (4):

the straight line L is obtained by simultaneous equations (3) and (4)₁And L₂Coordinates of the intersection point, straight line L₁And L₂The intersection point coordinate is the target position coordinate p₃(x₃，y₃，z₃)。

8. The method for restoring a three-dimensional tooth shape based on two-dimensional dental characteristic lines according to claim 7, wherein: the operation of said step (43) comprises:

and (3) calculating coordinates of each vertex of the passive deformation region after deformation by using a grid deformation algorithm based on an L aplace operator, and finishing passive deformation to obtain the three-dimensional aesthetic restoration dental model.

9. The method for restoring a three-dimensional tooth shape based on two-dimensional dental characteristic lines according to claim 8, wherein: the step (4) further comprises:

(44) and smoothing the deformed active deformation area and the deformed passive deformation area to obtain the optimized three-dimensional aesthetic restoration dental model.

10. A three-dimensional tooth shape restoration system based on two-dimensional tooth beautifying characteristic lines is characterized in that: the system comprises:

a collecting unit: obtaining a two-dimensional tooth beautifying characteristic line and a three-dimensional dentition model;

a registration unit: the three-dimensional dentition model is connected with the acquisition unit, the two-dimensional dentition characteristic line is converted into a three-dimensional dentition characteristic line, and then the three-dimensional dentition characteristic line and the three-dimensional dentition model are registered to obtain a registered three-dimensional dentition model;

an extraction unit: the three-dimensional dentition model is connected with the registration unit, and the outline of the dental model to be repaired is extracted from the registered three-dimensional dentition model;

a repair unit: and the three-dimensional dentition model is deformed according to the profile of the dental model to be restored and the three-dimensional dentition characteristic line to obtain the three-dimensional dentition restoration dental model.

Technical Field

The invention belongs to the field of oral medical treatment, and particularly relates to a three-dimensional tooth shape restoration method and system based on a two-dimensional tooth beautifying characteristic line.

Background

With the development of economy, people's interest in oral medical treatment has shifted from addressing ailments to improving people's quality of life. For example, it has been shown that patients not only have to recover the basic chewing function, but also have more attention to the aesthetic and cosmetic changes of their own restored teeth. There are many defects affecting the aesthetic appearance of anterior teeth, including tooth defects, poor tooth color, misaligned teeth, excessive interproximal spaces, missing teeth, poor gingival aesthetics, etc. The aesthetics is extremely subjective, and the traditional method for manufacturing the restoration body with low efficiency cannot meet the requirement. The application of digitization techniques offers great possibilities and convenience for the realization of such personalized aesthetic needs.

In the field of tooth aesthetic restoration, two-dimensional dental photographs made by DSD (Digital Smile design) can preview tooth beautifying effects for patients, and are important media for communication between doctors and patients. However, in the practical use of the two-dimensional dental system, the guidance of the two-dimensional dental information on the oral repair operation itself is still limited, and a three-dimensional dentition model repair method using the two-dimensional dental information as guidance is urgently needed in the market. The method uses the tooth-beautifying characteristic line as constraint to enable the three-dimensional tooth model to be repaired to be deformed smoothly, and the aesthetic repair tooth model is obtained. The method can simplify manual operation steps under the condition of satisfying doctor-patient communication, and the beautified and repaired three-dimensional dentition model is printed out by a 3D printing technology and is directly applied to clinical operation. The efficiency of implementing the medical scheme can be greatly improved, and convenient and personalized aesthetic repair treatment is provided for patients.

The research is mainly used for a three-dimensional Mesh deformation method (Mesh deformation), which is an important method for modeling and computer animation and provides a flexible method for editing an original Mesh to meet various design requirements. Because of its importance, there has been a great deal of research on mesh deformation since the 80's of the 20 th century. The existing grid deformation methods comprise a free deformation method, a multi-resolution method, a grid deformation method based on RBF, a deformation method based on curves, a skeleton method and a physical simulation method.

In the aspect of an oral cavity restoration system, most of automatic tooth restoration researches are based on a standard tooth library, only single tooth is functionally restored, and the integral attractiveness of dentition is rarely considered. Secondly, many tooth restoration systems adjust the shape and size of the three-dimensional tooth model through manual point selection and manual dragging, so that the operation is complex and troublesome, the requirement on the three-dimensional operation skill of a doctor is high, and the application and popularization of the three-dimensional restoration system are not facilitated.

Disclosure of Invention

The invention aims to solve the problems in the prior art and provides a three-dimensional tooth shape restoration method and a three-dimensional tooth shape restoration system based on a two-dimensional tooth beautifying feature line.

The invention is realized by the following technical scheme:

a three-dimensional tooth shape restoration method based on two-dimensional tooth beautifying characteristic lines comprises the following steps:

(1) obtaining a two-dimensional tooth beautifying characteristic line and a three-dimensional dentition model;

(2) converting the two-dimensional dental characteristic line into a three-dimensional dental characteristic line, and then registering the three-dimensional dental characteristic line and the three-dimensional dentition model to obtain a registered three-dimensional dentition model;

(3) extracting a dental model outline to be repaired from the registered three-dimensional dentition model;

(4) and deforming the three-dimensional dentition model according to the profile of the dental model to be repaired and the three-dimensional tooth beautifying characteristic line to obtain the three-dimensional tooth beautifying repairing dental model.

The operation of the step (1) comprises the following steps:

inputting the front smile photo and the intraoral orthostatic image of the patient into a two-dimensional tooth beautifying system, and outputting a two-dimensional tooth beautifying characteristic line drawn according to the front smile photo and the intraoral orthostatic image by the two-dimensional tooth beautifying system;

and carrying out three-dimensional optical scanning on the oral cavity of the patient to obtain a three-dimensional dentition model of the patient.

The operation of the step (2) comprises the following steps:

registering the intraoral orthostatic image of the patient with the three-dimensional dentition model to obtain the projection direction of the camera;

converting the two-dimensional merry tooth characteristic line into a three-dimensional merry tooth characteristic line in a Cartesian coordinate system;

taking the two-dimensional merry characteristic line as a background image of a window, wherein the background image is vertical to the projection direction of the camera;

and moving the three-dimensional tooth beautifying characteristic line on the three-dimensional dentition model by using a three-dimensional interactive tool to enable the three-dimensional tooth beautifying characteristic line to be superposed with the two-dimensional tooth beautifying characteristic line in the background image, so that the registered three-dimensional dentition model is obtained.

The operation of the step (3) comprises:

and selecting contour seed points of the body to be restored on the registered three-dimensional dentition model, and calculating the shortest distance between each vertex on the three-dimensional dentition model and the contour seed points based on anisotropic measurement so as to obtain the contour of the body to be restored.

The operation of the step (4) comprises the following steps:

(41) determining an active deformation area, a passive deformation area and a fixed area on the three-dimensional dentition model;

(42) carrying out active deformation on the active deformation area;

(43) and carrying out passive deformation on the passive deformation area to obtain the three-dimensional aesthetic restoration dental model.

The active deformation zone in the step (41) refers to: a triangular mesh adjacent to the outline of the dental model of the body to be repaired on the three-dimensional dentition model;

the passive deformation region is as follows: a region on the three-dimensional dentition model adjacent to the active deformation zone; the vertex of the passive deformation area is passively deformed along with the movement of the vertex of the active deformation area;

the fixed area refers to: other areas outside the active deformation area and the passive deformation area on the three-dimensional dentition model; the coordinates of all vertices in the fixed area do not change.

The operation of step (42) comprises:

(421) pairing the vertex of the three-dimensional beautiful tooth characteristic line with the vertex of the active deformation area to obtain n pairs of vertexes in the active deformation area:

firstly, acquiring a vertex p in the active deformation region₁Y of coordinates of₁Value, then finding the corresponding vertex p on the three-dimensional tooth-shaping characteristic line₁Paired vertices p₂Of y is₂The value of y and the vertex of the active deformation zone₁Equal in value, or | y₁-y₂< Δ d, thus defining a pair of vertices; repeating the step for n vertexes of the active deformation area in sequence to obtain n pairs of vertexes;

(422) and calculating the target position coordinate of each vertex on the active deformation area according to the n pairs of vertices to finish active deformation:

firstly, respectively averaging x, y and z values of all vertexes in the active deformation area to obtain a central point p of the active deformation area₀The coordinate is (x)₀，y₀，z₀)；

Will actively deform the vertex p in the region₁And the center point p₀The connecting line obtains a straight line L₁Said straight line L₁As shown in equation (3):

according to the projection direction of the camera and the point p on the three-dimensional beautiful tooth characteristic line₂Determine another straight line L₂Said straight line L₂As shown in equation (4):

the straight line L is obtained by simultaneous equations (3) and (4)₁And L₂Coordinates of the intersection point, straight line L₁And L₂The intersection point coordinate is the target position coordinate p₃(x₃，y₃，z₃)。

The operation of said step (43) comprises:

and (3) calculating coordinates of each vertex of the passive deformation region after deformation by using a grid deformation algorithm based on an L aplace operator, and finishing passive deformation to obtain the three-dimensional aesthetic restoration dental model.

The step (4) further comprises:

(44) and smoothing the deformed active deformation area and the deformed passive deformation area to obtain the optimized three-dimensional aesthetic restoration dental model.

The invention also provides a three-dimensional tooth shape restoration system based on the two-dimensional tooth beautifying characteristic line, which comprises:

a collecting unit: obtaining a two-dimensional tooth beautifying characteristic line and a three-dimensional dentition model;

a registration unit: the three-dimensional dentition model is connected with the acquisition unit, the two-dimensional dentition characteristic line is converted into a three-dimensional dentition characteristic line, and then the three-dimensional dentition characteristic line and the three-dimensional dentition model are registered to obtain a registered three-dimensional dentition model;

an extraction unit: the three-dimensional dentition model is connected with the registration unit, and the outline of the dental model to be repaired is extracted from the registered three-dimensional dentition model;

a repair unit: and the three-dimensional dentition model is deformed according to the profile of the dental model to be restored and the three-dimensional dentition characteristic line to obtain the three-dimensional dentition restoration dental model.

Compared with the prior art, the invention has the beneficial effects that:

the method of the invention realizes the deformation repair of the three-dimensional prosthesis to be repaired and obtains the aesthetic repair dental model. The restoration is printed by the 3D printing technology, so that the implementation efficiency of the medical scheme is greatly improved, and the possibility is provided for the individualized aesthetic restoration requirement of the patient.

In addition, the method has very high efficiency, can calculate the aesthetic repair result on the three-dimensional prosthesis to be repaired by taking the two-dimensional tooth beautifying characteristic line as the guide, and meets the requirement of quickly realizing the aesthetic repair of the dental model.

By using the method, the three-dimensional tooth model after the restoration of the patient can be quickly obtained on the basis of the doctor-patient communication result, and the restoration can be printed by using a 3D printing technology, so that the possibility is provided for quickly implementing an individual tooth aesthetic restoration scheme.

Drawings

FIG. 1 is a block diagram of the steps of the method of the present invention;

FIG. 2-1 shows two-dimensional merry features in input data;

FIG. 2-2 shows three-dimensional optical scan data in input data;

2-3 illustrate registration of the dentition feature lines with a three-dimensional dentition model;

FIGS. 2-4 illustrate the constrained deformation results;

FIG. 3 is a two-dimensional dental profile plotted in step 1 of the method of the present invention;

FIG. 4 is a graph of the result of region partitioning;

FIG. 5 is a schematic diagram of calculating a target point;

FIG. 6-1 corresponds to the body model to be repaired 1 in Table 1;

FIG. 6-2 corresponds to the body model to be repaired 2 in Table 1;

FIG. 7-1 shows the original model before restoration of the model 1 to be restored in the experiment;

FIG. 7-2 shows a left side view of the repaired model 1 of the test object;

FIG. 7-3 is a model front view of the body model 1 to be repaired after repair;

FIG. 7-4 shows a right side view of the repaired model 1 of the test object;

FIG. 8-1 shows the original model before restoration of the model 2 to be restored in the experiment;

FIG. 8-2 shows a left side view of a repaired model 2 of the test object;

FIG. 8-3 is a model front view of the body model 2 to be repaired in the experiment after repair;

FIG. 8-4 shows a right side view of the repaired model 2 of the test object;

FIG. 9 shows a two-dimensional dental system used to generate a dental profile for a patient;

FIG. 10-1 shows the two-dimensional dental profile as a window background and the black outline as a two-dimensional dental profile;

FIG. 10-2 shows the result of the registration of the three-dimensional contour with the body to be repaired in the experiment;

figure 11 contour of the prosthesis to be repaired calculated in the experiment.

Detailed Description

The invention is described in further detail below with reference to the accompanying drawings:

fig. 2-1 to 2-4 show schematic diagrams of the method of the present invention, which include two-dimensional dental characteristic lines created by using a two-dimensional dental system and a three-dimensional dentition model obtained by using three-dimensional optical scanning data, wherein fig. 2-1 shows the two-dimensional dental characteristic lines in input data, fig. 2-2 shows the three-dimensional dentition model in input data, fig. 2-3 shows the registration of the two-dimensional dental characteristic lines with the three-dimensional dentition model, which mainly shows the conversion of the two-dimensional dental characteristic lines into three-dimensional characteristic lines, and the registration of the three-dimensional dentition model, and the profile of the dental model to be repaired is calculated on the three-dimensional dentition model, and fig. 2-4 shows a constrained deformation result, i.e., the final deformation result of the method of the present invention.

Specifically, the input data shown in fig. 2-1 includes two-dimensional dental characteristic lines generated by using a two-dimensional dental system and a three-dimensional dentition model obtained by using three-dimensional optical scanning data, and the obtained three-dimensional dentition model is a triangular mesh model. And converting the pixel point information of the two-dimensional dental characteristic line into a point coordinate in a three-dimensional space, and then registering the dentition model of the body to be repaired with the three-dimensional dental characteristic line.

Next, selecting contour seed points of a to-be-restored body (namely the tooth to be restored) on the three-dimensional dentition model, calculating the shortest distance between each vertex on the three-dimensional dentition model and the seed points based on anisotropic measurement, further calculating a contour line on the to-be-restored body, and determining an active deformation area, a passive deformation area and a fixed area of the three-dimensional mesh according to the contour line of the to-be-restored body dentition model;

and finally, carrying out smooth processing on the triangular mesh to obtain the ideal three-dimensional beautiful tooth restoration model.

The three-dimensional tooth shape restoration method based on the two-dimensional merry characteristic line comprises three key steps of characteristic line registration, extraction of a tooth model outline of a body to be restored, calculation of the target point position of an active deformation area and triangular grid deformation of a passive deformation area by using an L-based apple operator, and as shown in figure 1, the method comprises the following steps:

(1) preparation work: first, a two-dimensional dental system (using existing software, for example, "dental assistant" software manufactured by hendall technologies ltd., tianjin) is used to obtain two-dimensional dental characteristic lines, specifically, a front smile photo and an intraoral facial image of a patient are input into the software, the software draws and outputs two-dimensional dental characteristic lines according to the front smile photo and the intraoral facial image, and the drawing result of the characteristic lines is shown in fig. 3.

(2) Feature line registration

After the two-dimensional merry tooth characteristic line is drawn, the two-dimensional pixel point coordinates on the two-dimensional merry tooth characteristic line need to be converted into a three-dimensional merry tooth characteristic line in a cartesian coordinate system. Because the two-dimensional merry characteristic line drawn by the existing merry system is a red contour with the RGB value of (255,0,0,), an OpenCV (open content computer vision library) can be used for searching a pixel with the R value of 255 by traversing a Mat matrix of an image, and storing two-dimensional coordinate information of the pixel into a container Vector. Because the distance between the pixel points is too small, after the pixel points are directly converted into the three-dimensional vertexes, the vertex density is far higher than the actual requirement, so that the two-dimensional pixel points stored in the Vector are selectively removed, the two-dimensional pixel points can be removed by adopting various existing methods, for example, the two-dimensional pixel points can be removed according to the Euclidean distance d between the adjacent vertexes, and the specific methods are known methods and are not repeated herein.

And then, a L ibigl three-dimensional processing library is used for creating a three-dimensional vertex matrix MatrixXd, namely, the coordinates of two-dimensional pixel points in the Vector are copied into the MatrixXd, the z value of the three-dimensional vertex coordinates is set to be 0 by default, in order to better display the merry tooth characteristic line in a three-dimensional space, a three-dimensional vertex needs to be connected, L ibigl three-dimensional processing library provides a related method, and the description is omitted, so that the three-dimensional merry tooth characteristic line in a Cartesian coordinate system can be obtained finally.

Next, the three-dimensional merlons are registered with the three-dimensional dentition model by first registering the patient's intraoral ortho image with the input three-dimensional dentition model using an existing registration method of two-dimensional images with the three-dimensional dentition model (see, for example, Walter Y.H. L am, Richard T.C.Hsung, &lTtTtranslation = L "&gTtT L &lTt/T &gTtTeoY.Y.Cheng., Edmond H.N.Pow, Mapping intraoral photographs on virtual dental model, Journal of Dentistry, Volume 79,2018, Pages 107-110, ISSN 0300-5712, or the method disclosed in the patent application No. 201910698286.2).

The background image is always parallel to the visual plane of the camera (the projection direction of the camera obtained by the registration method of the two-dimensional image and the three-dimensional dentition model (namely, the normal vector n (a, b, c)) of the visual plane is perpendicular to the visual plane of the camera), and the step can be realized by a processing library of three-dimensional graphics (namely, the L ibigl three-dimensional processing library) so that the three-dimensional dentition feature line can be manually moved to a proper position of the three-dimensional dentition model by using a three-dimensional interactive tool through translation, rotation and scaling by referring to the background image of the visual plane so as to be superposed with the displayed outline of the two-dimensional dentition feature line in the background image, and the registration of the three-dimensional dentition feature line and the dentition model of the restoration body is realized.

(3) Extracting the profile of the dental model to be repaired

After the three-dimensional beautiful tooth characteristic line is registered with the three-dimensional dentition model, the characteristic contour line on the body to be restored needs to be extracted, and the outline of the dental model of the body to be restored is obtained.

The step is realized by adopting the existing method (reference can be made to the documents of Yang S, Wang R, ZHao W, et al.3Dinterlingt sciences for Dental Mesh Segmentation [ J ]. Computational and chemical Methods in Medicine, 2020.) and is mainly realized by calculating the anisotropy metric tensor of each vertex in the triangular grid, then selecting seed points on the body to be repaired (the seed points are manually selected and only need to be selected on the tooth profile under the current view), and calculating the shortest distance between the seed points based on the anisotropy metric. The calculated shortest path (the shortest distance between two seed points) can be smoothed to obtain an ideal path.

(4) And determining an active deformation area, a passive deformation area and a fixed area, and performing active deformation on the active deformation area and performing passive deformation on the passive deformation area.

After calculating the profile of the dental model to be repaired, the method of the invention determines three areas of a three-dimensional grid by using a method provided by a document 'Robust tooth surface construction by iterative deformation [ J ]. Computers in Biology and Medicine,2016,68: 90-100': as shown in fig. 4, the darkest region in the drawing is the active deformation region in the repair deformation process, the lightest region is the passive deformation region in the repair deformation process, and the lighter region is the fixed region in the repair deformation process.

1, active deformation region: this area is on the adjacent triangular mesh of the contour of the dental model of the body to be restored.

2, passive deformation zone: the vertex of the area is positioned in the adjacent area of the active deformation area of the body to be repaired and is close to the active deformation area. The vertex of the area will be passively deformed along with the movement of the vertex of the active deformation area

3, a fixed area: except for the other areas of the active deformation area and the passive deformation area, the coordinates of all vertexes in the area are not changed, and the natural connection between the deformation area and the body to be repaired is ensured.

And performing active deformation on the active deformation area, specifically as follows:

in the deformation process, the vertex coordinates in the active deformation area are paired with the vertices of the merry-tooth characteristic lines to calculate the coordinates of the target points, and the target points are actively deformed to the target positions (after the coordinates of the target points are obtained, each point is changed into the corresponding target point, namely the active deformation to the target position is realized, namely the active deformation is realized by each target point), specifically as follows:

the vertex of the active deformation area is matched with the vertex of the three-dimensional beautiful tooth characteristic line and is mainly determined by the y-axis coordinates of two points. Firstly, acquiring a vertex p in an active deformation region₁Y of coordinates₁Then, the vertex p on the three-dimensional beautiful tooth characteristic line is found by traversing the vertex on the three-dimensional beautiful tooth characteristic line in the three-dimensional space₂Of y is₂Value and vertex y of active deformation region₁Equal in value, or | y₁-y₂And | is less than Δ d (Δ d is a set threshold and is set according to actual needs). Such that a pair of vertex pairs p can be determined₁(x₁，y₁，z₃) And p₂(x₂，y₂，z₂). The steps are repeated for n vertexes of the active deformation area in sequence to obtain n pairs of vertexes. In fig. 1, when m is 0, each pair of vertices is obtained, m is m +1, and then the next pair of vertices is searched until m is n-1, that is, all n pairs of vertices are searched, and n pairs of vertices are obtained. The coordinates of the target points are then calculated from these two points, and a schematic solution of the target points is shown in fig. 5.

The three-dimensional beautiful tooth characteristic line can only limit the transformation of a three-dimensional point on a two-dimensional plane (although the two-dimensional beautiful tooth characteristic line is transformed into the three-dimensional beautiful tooth characteristic line in a three-dimensional space, all three-dimensional vertexes are still on the same plane and do not have depth information, and the contour vertexes on the body to be repaired are not on the same plane. After vertex pairing, z-axis coordinate information of the target position also needs to be calculated. Firstly, the x, y and z values of all vertexes of the active deformation area are averaged, and the central point p of the active deformation area is calculated₀The coordinate is (x)₀，y₀，z₀) Wherein x is₀Is the average of the x values, y, of all vertices in the active deformation zone₀Is the average of the y values of all vertices in the active deformation zone, z₀Is the average of the z-values of all vertices in the active deformation zone. Thus, the vertex p on the active deformation zone₁And a central point p₀The connecting line obtains a straight line L₁The target point to be calculated by the present invention is at line L₁Upper line L₁Can be obtained by two-point calculation of a straight line as shown in equation (3).

At this time, find out the point p on the curve of the beautiful tooth characteristic₂At line L₁The position of the target point can be calculated by the projection. To calculate the point p on the three-dimensional tooth-shaping characteristic line₂At line L₁The projection of (a) needs to use the projection direction of the camera calculated in the existing 2D-3D registration method, i.e. the normal vector n of the viewing plane is (a, b, c), and the projection is based on the vector and the point p on the three-dimensional merry tooth characteristic line₂Another straight line L may be determined₂Line L₂It can be calculated by a point-wise equation, as shown in equation (4). in this case, equation (3) and equation (4) are combined to obtain straight line L₁And L₂Line L₁And L₂The coordinates of the intersection point are the target point p required by the invention₃(x₃，y₃，z₃) And (4) coordinates.

And passively deforming the passive deformation region, specifically as follows:

the laplacian-Based triangular Mesh deformation algorithm is a common three-dimensional Mesh processing algorithm, and can be referred to in the literature [ y.yu, k.zhou, d.xu, x.shi, h.bao, b.guo, and h.shell. "Mesh electronic with pos-Based Gradient Field manipulation." ACM computational dynamics (protein: sigraph) 23:3(2004),644-51.], [ r.zayer, c.rossl, z.karni, and h.seido. "monolithic grid behavior for Surface deformation" Computer Graphics (r.s.c. for Computer) 1. for the purpose of "reconstruction" r.s.p.seid Mesh 3 (r.s.r.r.r.r.r.r.r.r.r.r.r.r.r.r.m. for Surface deformation "r.e. for Surface deformation, Computer Graphics (r.s.p.s.s.s.g.: Mesh 3, and Mesh 3. c. 3. Mesh 3. r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.r.c. z.k.k.k.k.k.k.c. k.c. k.g. m. c.

After the triangular mesh based on the laplace is deformed, smoothing treatment can be further performed on the three-dimensional meshes of the deformed active deformation area and the deformed passive deformation area (smoothing treatment is a common method for three-dimensional mesh treatment and is not repeated here), transition of the deformed area is more natural and smooth, and the aesthetic restoration dental model is obtained after smoothing treatment. And finally outputting the aesthetic restoration dental model.

In summary, the invention uses a two-dimensional dental system to manufacture a dental characteristic line of a patient, converts pixel point information of the two-dimensional dental characteristic line into point coordinates in a three-dimensional space, uses a 2D-3D registration method to register a three-dimensional dentition model with an intraoral orthotopic image, selects contour seed points of teeth to be restored (one tooth is processed at a time, if a plurality of teeth to be restored exist, the same processing needs to be carried out on each tooth to be restored) on the three-dimensional dentition model, calculates the shortest distance between each vertex and the seed points on a dental model based on anisotropic measurement, further calculates a contour line on the three-dimensional dentition model, pairs the vertices of a dental contour line and the contour line of the dental model to be restored, calculates target position coordinates of each point, deforms the body to be restored to a target shape by using a triangular mesh deformation algorithm based on L aplae operator, and carries out smoothing treatment to obtain the three-dimensional dental restoration dental model.

The invention also provides a three-dimensional tooth shape restoration system based on the two-dimensional tooth beautifying characteristic line, which comprises:

a collecting unit: obtaining a two-dimensional tooth beautifying characteristic line and a three-dimensional dentition model;

a registration unit: the three-dimensional dentition model is connected with the acquisition unit, the two-dimensional dentition characteristic line is converted into a three-dimensional dentition characteristic line, and then the three-dimensional dentition characteristic line and the three-dimensional dentition model are registered to obtain a registered three-dimensional dentition model;

an extraction unit: the three-dimensional dentition model is connected with the registration unit, and the outline of the dental model to be repaired is extracted from the registered three-dimensional dentition model;

a repair unit: and the three-dimensional dentition model is deformed according to the profile of the dental model to be restored and the three-dimensional dentition characteristic line to obtain the three-dimensional dentition restoration dental model.

To evaluate the effectiveness and algorithmic time consumption of the method of the invention, the following experiments were performed:

the equipment used in the experiment comprises an optical scanner (AutoScan-DS100+), a single lens reflex camera (Canon EOS 60D, matched with EF 100mm f/2.8L IS USM macro lens and MR-14EX II micro ring flash lamp), a computer (Intel (R) core (TM) i7-6700HQ CPU @2.60GHz, a memory 16G and a display card Nvidia GeForce GTX 960M), and the software systems used in the experiment comprise a Windows 10 operating system, a VS 2017 compiler, OpenCV and VTK.

Experiment 1 oral cavity front color photograph was taken of 1 male volunteer and 1 female volunteer respectively, and their dental impressions were scanned with an optical scanner to obtain maxillary three-dimensional dentition data. Firstly, 1 volunteer is used for carrying out experimental analysis, and the effectiveness of the method for extracting the dental model contour of the to-be-repaired body is tested. The final three-dimensional aesthetic repair experiment results for both volunteers were then presented. Since the dental preparation is mainly performed for the anterior teeth, the front photograph is used in the present experiment, and if the dental preparation is performed for the other part of the teeth, the photograph in the other direction may be used, and the other processing steps are the same as the following steps.

The method comprises the following specific steps:

1, extracting the profile of the dental model to be repaired

In order to analyze the effectiveness and the high efficiency of the extraction method of the dental model outline of the body to be repaired, the invention counts the grids and the vertexes of the three-dimensional dentition models of two volunteers, and also counts the total time consumed for calculating the shortest distance of the anisotropic measurement according to a plurality of selected seed points, and the experimental result is shown in the table 1.

TABLE 1

As can be seen from table 1, for the models to be repaired with different precisions, the total time consumption is different under the condition of the same number of seed points. Wherein the higher the grid accuracy, the longer the total time consumption. However, even with a high-precision mesh model, the algorithm can still calculate accurate results within 1 s. The experiments show that the method has high efficiency.

Even with high efficiency, how does the result of the contour calculation of the body to be repaired? The analysis is further followed by showing two sets of examples of profiles calculated on the three-dimensional prosthesis to be repaired according to the method of the invention, as shown in fig. 6-1 and fig. 6-2.

Fig. 6-1 corresponds to the body model to be repaired 1 in table 1, and fig. 6-2 corresponds to the body model to be repaired 2 in table 1. From the two pictures, it can be seen that the three-dimensional contour on the three-dimensional prosthesis to be repaired can be effectively calculated according to the method of the invention, which is important for the further research on the back side.

The experimental result analysis proves that the method has high execution efficiency, can effectively calculate the three-dimensional outline required by the later research, and meets the requirement of quickly realizing the aesthetic restoration of the dental cast.

In order to analyze the effectiveness and the algorithm efficiency of the three-dimensional grid deformation algorithm based on the L aplace operator, the number of vertexes of an active deformation region and the number of vertexes of a passive deformation region of the three-dimensional dentition model of two volunteers are counted in the experiment, the total time consumed by deformation of each volunteer is calculated, and the experiment result is shown in table 2.

As can be seen from table 2, the number of vertices in the active deformation region and the number of vertices in the passive deformation region are different for mesh models with different accuracies. With the increase of the number of the vertexes of the active deformation area and the passive deformation area, the total time consumption is increased. However, even with a high-precision mesh model, the algorithm can still calculate accurate results within 0.5 s. This set of experiments demonstrates the high efficiency of the algorithm.

TABLE 2

Even with high efficiency, how does the deformation result of the prosthesis to be repaired? Further analysis is next performed by showing example pictures of the deformation process of two sets of prostheses, as shown in fig. 7-1 to 7-4 and fig. 8-1 to 8-4.

Fig. 7-1 is an original model of the body model 1 to be repaired before repair, fig. 7-2 is a left side view of the model after repair, fig. 7-3 is a front view of the model after repair, fig. 7-4 is a right side view of the model after repair, wherein a green contour in fig. 7-3 is a three-dimensional beauty tooth characteristic line of the body model 1 to be repaired. Fig. 8-1 is an original model of the body model 2 to be repaired before repair, fig. 8-2 is a left side view of the model after repair, fig. 8-3 is a front view of the model after repair, fig. 8-4 is a right side view of the model after repair, wherein a black outline in fig. 8-3 is a three-dimensional beauty tooth characteristic line of the body model 2 to be repaired. From the figure 8-3, the result of the deformed prosthesis is perfectly attached to the three-dimensional beautiful tooth characteristic line, and the three-dimensional shape repairing purpose based on the two-dimensional beautiful tooth characteristic line is achieved.

The complete repair process in this experiment is as follows:

a patient's dental profile is first created using a two-dimensional dental system, as shown in fig. 9. And converting the pixel point information of the two-dimensional dental characteristic line into point coordinates in a three-dimensional space, and registering the three-dimensional dentition model and the three-dimensional dental characteristic line by using the multi-characteristic-based 2D-3D registration method provided by the invention, as shown in fig. 10-1 and 10-2. Wherein FIG. 10-1 shows the two-dimensional merry feature lines as the black outline when the two-dimensional merry feature lines are set as the window background. Fig. 10-2 shows the result of the registration of the three-dimensional contour with the body to be repaired.

After the registration is completed, the seed points are manually clicked on the body to be repaired, and the contour of the body to be repaired is calculated, as shown in fig. 11. The black dots in the figure are seed points and the black outline is the calculation result. Then, according to the contour of the body to be repaired, area division is performed on the triangular mesh to obtain an active deformation area, a passive deformation area and a fixed area, as shown in fig. 4, the darkest color is the active deformation area, the lightest color is the passive deformation area, and the lighter color is the fixed area.

Then, the coordinates of the passive deformation region after the vertex deformation are calculated by using a triangular mesh deformation algorithm based on an L aplace operator, and the smooth processing is performed, and the result is shown in fig. 7-2 to fig. 7-3.

Therefore, the method provided by the invention achieves the purpose of repairing the three-dimensional shape based on the two-dimensional tooth-beautifying characteristic line. In addition, the method has very high execution efficiency, can calculate the aesthetic repair result on the three-dimensional prosthesis to be repaired by taking the two-dimensional tooth beautifying characteristic line as guidance, and meets the requirement of quickly realizing the aesthetic repair of the dental model.

In conclusion, the invention provides an efficient and reliable method for realizing the three-dimensional dentition model restoration guided by the two-dimensional dental photos. The method can help doctors to carry out tooth beautifying design and medical skill interaction, and improves the efficiency. The doctor can show the effect after restoreing for the patient the very first time, and the patient also can be timely knows the effect after the cosmetic restoration of tooth. In addition, the cooperation degree between doctors and technicians is improved, the effect of tooth cosmetic restoration is improved, and better medical service experience is finally brought to users.

The above-described embodiment is only one embodiment of the present invention, and it will be apparent to those skilled in the art that various modifications and variations can be easily made based on the application and principle of the present invention disclosed in the present application, and the present invention is not limited to the method described in the above-described embodiment of the present invention, so that the above-described embodiment is only preferred, and not restrictive.