TWI556798B - The method of establishing three - dimensional image of tooth - Google Patents

Description

Method for establishing stereoscopic image of tooth

This creation is about a method for establishing a stereoscopic image of a tooth. The accurate tooth model is obtained by correcting the initial coordinate displacement and the arch curve.

Please refer to the Republic of China Patent Publication No. 201302166, which discloses a method of position of a tooth mold. The method requires a plurality of hardware devices, including an articulator, a marking module and a sensing device provided with a marking element and a reference object. The pre-case is applied to the reconstruction and localization of computed tomography (CT) images. The patient must operate in the articulator and bite the marking module to perform positional marking, resulting in patient discomfort in clinical treatment. Moreover, the fixture of the previous case has a complicated structure and is liable to cause errors in position sensing.

In order to solve the shortcomings of the prior art that the error is easy to generate due to the complicated structure, the main purpose of the present invention is to provide a method for establishing a dental caries model.

The method for establishing a stereoscopic image of the tooth includes: capturing a plurality of teeth with a probe to generate the first point cloud data and the second point cloud data of the plurality of teeth, wherein the first point cloud data and the second point cloud data respectively have corresponding The X-axis, the Y-axis and the Z-axis rotation index value; the first point cloud data, the second point cloud data and the rotation index value are received by an image processing device, and the rotation index value is superimposed on the rotation index value according to an image displacement comparison table The first point cloud data of the tooth and the second point cloud data form a stereoscopic image of the clinical tooth; the vertices on the stereoscopic image of the clinical tooth are screened, so that the selected vertices are only correspondingly distributed on the occlusal surface of the tooth; Performing a polynomial fitting calculation on the selected vertices to obtain a preliminary dental arch curve; after averaging the preliminary dental arch curve, generating a complex true subset, each true subset containing at least one vertex; defining in each set of true subsets a fitting reference point; fitting the fitting reference points by a polynomial to obtain a clinical dental arch curve; performing Kth according to any gravity point of the clinical dental arch curve and all data points on a standard dental arch curve The k-th nearest neighbor method (KNN method) is used to obtain a data point closest to each center of gravity point; the clinical semi-ankle image is corrected according to the offset of each centroid point and its corresponding data point .

Therefore, this creation uses only the probe to take the patient's dental image, and uses the image processing method to establish the dental model. Naturally, there is no disadvantage of using the complicated hardware device to cause the patient to feel uncomfortable as described in the prior art; The creation does not use complex hardware structures. This creation mainly establishes the tooth model through the algorithm, which naturally avoids the lack of sensing error caused by the structural factors described in the prior art.

10‧‧‧ probe

11‧‧‧ attitude sensor

12‧‧‧ Point cloud data sampling unit

100‧‧‧ teeth

101‧‧‧ teeth side

102‧‧‧ teeth cheek side

20‧‧‧Image processing device

21‧‧‧Coordinate numerical feedback unit

22‧‧‧Standard tooth model alignment coordinate database

23‧‧‧ tooth point cloud data processing unit

24‧‧‧First stage fitting calculation unit

25‧‧‧Comparative calculation unit

26‧‧‧Second stage fitting calculation unit

31‧‧‧Standard arch curve

310‧‧‧Information points

32‧‧‧ Clinical dental arch curve

320‧‧‧ Center of gravity

40‧‧‧Standard tooth stereo image

401‧‧‧ occlusal surface

402‧‧‧ teeth

41‧‧‧ vertex

42‧‧‧Fitting reference point

50‧‧‧ preliminary arch curve

51‧‧‧Standard arch curve

500‧‧‧ bisector

Figure 1: Schematic diagram of the circuit of the three-dimensional tooth modeling system.

Figure 2: Schematic diagram of the process of establishing a standard dental stereoscopic image and a standard dental arch curve in this creation.

Figure 3: This is a schematic view of the side of the tongue.

Figure 4: This is a schematic view of the cheek side of the tooth.

Figure 5: Overlay of the first standard image and the second standard image of the creation

Figure 6: Schematic representation of the creation of the occlusal plane Y _OCC .

Figure 7: Schematic representation of the apex of the creation distributed over the occlusal surface of the teeth and the gums.

Figure 8: Schematic diagram of the vertices of this creation distributed only on the occlusal surface of the teeth.

Figure 9: Schematic representation of the preliminary arch curve fitted to the apex of Figure 7 by this creation.

Figure 10: Schematic diagram of the creation of a fitting reference point in the true subset.

Figure 11: This fit fits the fitted reference points of Figure 10 to obtain a schematic representation of the clinical arch curve.

Figure 12: Schematic diagram of the process of establishing a clinical dental stereoscopic image and a clinical dental arch curve in this creation.

Figure 13: Schematic diagram of the standard arch curve and clinical arch curve.

Figure 14: Schematic diagram of the partial line segment of the standard dental arch curve and the clinical dental arch curve.

Referring to FIG. 1 , the present invention provides a probe 10 and an image processing device 20 . The probe 10 has a photographing function and is provided with an attitude sensor 11 and a point cloud data sampling unit 12, wherein the attitude sensor 11 can be a gyroscope. The image processing device 20 can be a computer disposed outside the probe 10, and the image processing device 20 is connected to the probe 10 for data transmission, and is responsible for establishing and correcting a stereoscopic image model of the tooth. The image processing device 20 includes a standard value feedback matching unit 21, a standard dental model coordinate coordinate database 22, a dental point cloud data processing unit 23, a first stage bonding calculation unit 24, and a comparison. The calculation unit 25 is attached to the calculation unit 26 with a second stage.

The author establishes a standard dental stereoscopic image and a clinical dental stereoscopic image for the standard dental solid model and the teeth in the patient's mouth, and calculates a standard dental arch curve and a clinical dental arch curve respectively. After the error of the clinical dental arch curve and the standard dental arch curve, the clinical dental stereoscopic image is corrected. Please refer to Figure 2 below for the establishment of the standard arch curve as an example.

The user can take the standard dental solid model with the probe 10. This embodiment is only illustrated by taking a lower jaw tooth, but the present invention is equally applicable to the upper jaw tooth. For a single tooth 100, a first standard image and a second standard image are mainly taken for the tooth 100. The first and second standard images are point cloud data, wherein the point cloud data refers to As shown in FIG. 3, the first standard image may be an image taken toward the tongue side 101 of the tooth, and the shooting angle is The angle is 45 degrees with respect to a horizontal plane. Referring to FIG. 4, the second standard image may be an image taken toward the buccal side 102 of the tooth, and the shooting angle is 45 degrees with respect to a horizontal plane. At the time of shooting, the attitude sensor 11 generates a spatial coordinate parameter according to the spatial position of the probe 10 at the time of shooting. Under the rectangular coordinate system, the spatial coordinate parameter includes an x-axis rotation index value (yaw) and a y-axis rotation index value. (pitch), z-axis rotation index value (roll), x coordinate (dx), y coordinate (dy), z coordinate (dz) (step 101). Therefore, each standard image captured has a corresponding space coordinate parameter.

After obtaining the first and second standard images, the user can operate the image processing device 20 to align and overlap the teeth of the first standard image and the second standard image, as shown in FIG. 5 . A schematic diagram of superimposing a standard image A and a second standard image B, and recording the amount of translation of the first standard image and the second standard image in the x-axis direction, the y-axis direction, and the z-axis direction. Therefore, after all the teeth of the standard tooth solid model are photographed and the superimposition motion is completed, a standard dental stereoscopic image is formed, and a series of rotation index values of the teeth and corresponding translation amounts are obtained, and the rotation index values are obtained. An image displacement comparison table can be created in the standard dental model alignment coordinate database 22 with the amount of translation (step 102).

After the stereoscopic image of the standard tooth is established, the comparison tooth calculation unit 25 receives the standard dental stereoscopic image to calculate the standard dental arch curve. The following is a study of the dental arch crowding analysis technique according to Hu Yuyu et al. <http://www.zclw.net/article/sort040/sort046/info-7554.html> Describe the calculation of the arch curve, as attached.

Referring to FIG. 6 , the comparison calculation unit 25 first defines four feature points B1 , B2 , B3 , and B4 in the standard tooth stereo image 40 , and the four feature points B1 , B2 , B3 , and B4 are respectively The buccal cusps of the left and right permanent teeth and the buccal cusps of the left and right canines were calculated by the mean standard deviation method. The occlusal plane Y _{OCC was} calculated, and the aforementioned characteristic points B1 to B4 were the closest to the occlusal plane Y. Four points of the _OCC .

After calculating the occlusal plane Y _OCC , the feature points are selected in the point cloud data of the standard tooth stereo image 40 to calculate the subsequent standard arch curve according to the selected feature points. In the point cloud data of the standard tooth stereo image 40, any three points can construct a triangular mesh, so the complex point can construct a complex triangular mesh, and the triangular mesh approximates the curved surface of the tooth and the surrounding tissue. Since the approximate curved surface formed by the complex triangular mesh is piecewise linear approximation, this creation uses the area weighting method to calculate the feature vector of the triangular mesh vertex point cloud data. The feature vector of the vertex can be expressed as follows:

A _{i , j} and Represents the area and unit vector of the jth triangle mesh, respectively. If x _i , y _i and z _i represent the vertex coordinates of the triangular mesh, then the set of all triangular mesh vertices is defined as follows:

The vertex near the occlusal plane Y _OCC can be used as a reference point for establishing a preliminary arch curve, and the occlusal plane Y _OCC can be approximated as a tangent plane of each vertex, thus merging the plane of the plane Y _OCC and the triangle mesh vertex at the vertex The direction of the vector is approximately the same, so the vertex vector is represented by a set S _φ Occlusal surface vector (ie, the normal vector of the occlusal plane Y _OCC ) is less than a fixed point set of a predetermined angle φ , and S _{φ is} defined as follows, wherein the preset angle φ = 10° is a better result from the experimental simulation.

Referring to the comparison diagram shown in FIG. 7, the triangular mesh vertices 41 selected by S _φ are distributed on the tooth occlusal surface 401 and the gum 402. This creation uses a true subset S ^* _φτ to exclude vertices 41 located at the gum 402, and the true subset S ^* _{φτ is} defined as follows:

Where dis ( V _i , Y _OCC ) represents the distance between the vertex 41 and the occlusal plane Y _OCC , and τ is a constant. In the preferred embodiment, τ = 3 (mm), and the value of τ is preset in the image processing apparatus. 20, the true subset S ^* _φτ screened out the apex, please refer to Figure 8, it can be seen that the apex 41 is only distributed on the occlusal surface 401, not distributed in the gums, leaving the apex 41 as a reference for establishing the initial arch curve Point (step 103).

Please refer to FIG. 8 , and then perform the polynomial fitting calculation according to the vertices 41 selected by the true subset S ^* _φτ to obtain the preliminary dental arch curve. The present method is to fit the preliminary dental arch curve equation f ( x) by a fourth-order polynomial. , y )= ax ⁴ + bx ³ + cx ² + dx + e - y , wherein the polynomial coefficients a to e are obtained by the weighted least squares method (step 104).

Referring to FIG. 9, the projected points of the filtered vertices 41 on the XOY coordinate plane are revealed, and the preliminary arch curve 50 is fitted according to the projection points.

Subsequently, the initial curve 50 of a plurality of arch bisector 500 is equally divided into n segments, and for division of the set _S ^* φτ aliquot of each point in a plane normal insertion, i.e., to obtain _S ^* φτ The complex array true subset S ^*1 _φτ , S ^*2 _φτ ... S ^{* n} _φτ (step 105). Assume that the tangent vector of the initial arch curve 50 at the i-th aliquot (ie, the normal vector of the bisector) is , The component on the X axis is the direction increasing along the X axis, and S ^{* i} _{φτ is} defined as follows:

Referring to FIG. 10, the distance from the vertex 41 in each set of true subsets S ^*1 _φτ , S ^*2 _φτ ... S ^{* n} _φτ to the occlusal plane Y _OCC is _calculated to distance the occlusal plane Y _The longest vertex of the _OCC is taken as the fit reference point 42, and the other vertices are filtered and only the fit reference point 42 is retained (step 106). Referring to Figure 11, the fitted reference points 42 are fitted in a fourth degree polynomial to obtain a standard arch curve 51 (step 107).

The foregoing is a calculation for describing the standard arch curve. Referring to the flowchart shown in FIG. 12, the following describes the calculation of the clinical dental stereo image and its clinical arch curve. The user can take the actual tooth image of the patient with the probe 10. This embodiment is only taken as an example of taking a lower jaw tooth. For a single tooth of the patient, as in the foregoing step 101, a first image and a second image are taken on the patient's teeth, and the first image may be an image taken toward the side of the tongue of the tooth, and the shooting angle is relative. A horizontal plane is at an angle, and the second image can be an image taken toward the cheek side of the tooth, and the angle of view is at an angle of 45 degrees with respect to a horizontal plane. The probe 10 also produces a corresponding rotation index value. When the probe 10 is photographed first After the image and the second image, the point cloud data sampling unit 12 respectively generates a first point cloud data and a second point cloud data corresponding to the first image and the second image (step 101').

After the probe 10 generates the first point cloud data, the second point cloud data and the corresponding rotation index value of the single tooth, the image processing device 20 receives the first point cloud data and the second point cloud data from the probe 10 . With rotating index values. The coordinate value feedback matching unit 21 receives the rotation index values of the first point cloud data and the second point cloud data, so as to compare the image displacements of the standard tooth model alignment coordinate database 22 according to the rotation index values. The table reads the corresponding displacement amount, and transmits the rotation index value and the corresponding displacement amount to the first stage bonding calculation unit 24. The tooth point cloud data processing unit 23 transmits the first point cloud data and the second point cloud data to the first stage bonding calculation unit 24.

After the first stage bonding calculation unit 24 receives the first point cloud data, the second point cloud data, and the corresponding displacement amount, the first stage bonding calculation unit 24 automatically selects the first point cloud according to the displacement amount. The data and the second point cloud data overlap each other to form a preliminary superimposed image of the single tooth. Repeating the foregoing steps to create a preliminary superimposed image for each of the plurality of teeth. Since the two adjacent preliminary superimposed images contain a common image feature, such as capturing the same tooth, the first stage of the fitting calculation unit 24 will The plurality of preliminary superimposed images are joined to each other according to a common image feature to form a clinical dental stereoscopic image (step 102'). After the first stage fitting calculation unit 24 completes the stereoscopic image of the clinical tooth, the comparison tooth calculation unit 25 receives the stereoscopic image of the clinical tooth to calculate the clinical dental arch curve of the clinical dental stereoscopic image. The calculation method of the dental arch curve is the same as the calculation method of the standard dental arch curve. In short, the vertices of each tooth occlusal surface in the clinical dental stereoscopic image are screened (step 103'), and formed according to the selected apex. a preliminary arch curve (step 104'), generating a complex true subset (step 105'), defining a fitted reference point (step 106'), and fitting the clinical arch curve according to the fitted reference point (step 107') , will not be described in detail here.

After the clinical dental arch curve is obtained according to the foregoing steps, the offset data of the clinical dental arch curve relative to the standard dental arch curve is calculated, and the stereoscopic image of the clinical dental body is entered according to the offset data. Line correction (step 108'), as shown in Figure 13, reveals the standard arch curve 31 and the clinical arch curve 32, which will calculate the offset of the clinical arch curve 32 To approximate the standard arch curve 31. As shown in the partial arch line 31 of the clinical arch curve 31 and the clinical dental arch curve 32, a plurality of center of gravity points 320 are first defined for the clinical dental arch curve 32, and the center of gravity points 320 are equally divided into the clinical dental arch curve 32. Point (as shown in Figure 10, the intersection of the bisector and the arch curve), the coordinates are (xa, ya), (xb, yb), ..., (xf, yf), ..., the standard The arch curve 31 also defines a plurality of data points 310, which are bisectors of the standard arch curve 31, and the coordinates of the data points 310 are (x1, y1), (x2, y2), respectively. ,...,(x6,y6),... The present invention performs a K-th nearest neighbor method (KNN method) according to any gravity point 320 of the clinical dental arch curve 32 and all data points 310 on the standard dental arch curve 31 to find out A data point 310 closest to the center of gravity point 320, for example, the data point closest to the center of gravity point 320 (xa, ya) is (x1, y1). When the two closest data points 310 and the center of gravity point 320 are obtained, the offset value (Xi, Yi) of the center of gravity point 320 is calculated, Xi = xa - x1, Yi = ya - y1.

Therefore, the (Xi, Yi) data in the second stage bonding calculation unit 26 is used as the basis for the stereoscopic image offset correction of the clinical tooth, that is, the point cloud data of the clinical dental stereoscopic image includes FIG. The center of gravity point 320 is shown. The stereoscopic image of the clinical tooth includes a corresponding point data group around the center of gravity point 320. The point data group is performed on the x-axis and the y-axis according to the offset data of the center of gravity point 320. The offset, as a whole, causes the clinical dental stereoscopic image to be shifted according to the standard dental arch curve (refer to European Patent No. EP2026279 "Method and system for aligning three-dimensional surfaces"), thereby producing more accurate Stereoscopic image of the teeth.

Claims (2)

A method for establishing a stereoscopic image of a tooth comprises: capturing a plurality of teeth with a probe to generate first point cloud data and second point cloud data of the plurality of teeth, wherein the first point cloud data and the second point cloud data respectively have corresponding X The axis, the Y-axis and the Z-axis rotation index value; the first point cloud data, the second point cloud data and the rotation index value are received by an image processing device, and the plurality of teeth are superimposed on the rotation index value according to an image displacement reference table The first point cloud data and the second point cloud data form a stereoscopic image of the clinical tooth; the vertices on the stereoscopic image of the clinical tooth are screened, so that the selected vertices are only correspondingly distributed on the occlusal surface of the teeth; The apex of the vertices is calculated by polynomial fitting to obtain a preliminary arch curve. The equation f ( x , y ) = ax ⁴ + bx ³ + cx ² + dx + e - is fitted to the preliminary arch curve by a fourth-order polynomial. y , the polynomial coefficients a~e are obtained by the least square method with weights; after the initial arch curve is equally divided, a complex true subset is generated, each true subset contains at least one vertex; and is defined in each true subset. Fitting reference Point; fitting the fitted reference points with a polynomial to obtain a clinical dental arch curve; performing Kth adjacent sampling method according to any gravity point of the clinical dental arch curve and all data points on a standard dental arch curve ( The k-th nearest neighbor method (KNN method) is used to obtain a data point closest to each gravity point; the clinical semi-caries image is corrected according to the offset of each gravity point and its corresponding data point. The method for establishing a stereoscopic image according to claim 1, wherein the first point cloud data is an image taken toward a side of the tooth tongue, and the second point cloud data is an image taken toward a cheek side of the tooth.