A feature point recognition method based on tooth's own coordinate system

Abstract

The present invention discloses a method for identifying feature points based on the tooth's own coordinate system, and relates to the field of dental orthodontics in a digital oral cavity. The input conditions of the method are the conversion matrix of the tooth model and the coordinate system. All teeth have an axis point and a gingival point. For different teeth, the central incisor and the lateral incisor also have an incisal angle point and an incisal ridge midpoint, the canine also has a cusp point, the premolar also has two cusps in front and behind and a nest point, and the molar also has four cusps and a nest point. The present invention can automatically identify the feature points of different teeth based on the tooth's conversion coordinate system, greatly improving the efficiency of feature point recognition and reducing errors caused by personal subjective factors.

Description

Technical Field

[0001] The present invention relates to the field of digital oral orthodontics, and in particular to a method for identifying feature points based on a tooth's own coordinate system. Technical Background

[0002] In the context of digital dentistry, orthodontics has always been a key area of ​​focus. After obtaining the three-dimensional model data of the teeth, the teeth are then divided and arranged. The characteristic points of the teeth are an important reference for tooth arrangement, so they need to be marked. Due to the influence of damaged or deformed teeth, most automatic feature point recognition methods currently have poor accuracy. If manual marking is used, it is inefficient and time-consuming, and there are large errors and it is easily affected by personal subjective factors. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a feature point recognition method based on the tooth's own coordinate system to improve the efficiency of identifying feature points, reduce the errors caused by manual marking, and reduce the influence of subjective factors.

[0004] In order to achieve the above object, the present invention provides a method for identifying feature points based on the tooth's own coordinate system, comprising the following steps:

[0005] S1 obtains a tooth model and a coordinate system transformation matrix, wherein the tooth model is composed of three-dimensional mesh vertices, and the coordinates of the three-dimensional mesh vertices are in a world coordinate system;

[0006] S2 transforms the coordinate value of each three-dimensional mesh vertex from the world coordinate system to the tooth's own coordinate system by multiplying the coordinate of each mesh vertex with the transformation matrix, and independently establishes the tooth's own coordinates for each tooth. The coordinate system of the tooth's own coordinates is established as follows: the origin of the coordinate system is located at the center point of the tooth model, the positive direction of the X-axis points from the origin to the buccal side, and the positive direction of the Z-axis points from the origin to the root direction; the Y-axis is determined by: for teeth No. 11 to 18 of the maxillary teeth, the positive direction of the Y-axis is determined by the right-hand rule based on the X and Z axes; for teeth No. 21 to 28 of the maxillary teeth, the positive direction of the Y-axis is determined by the left-hand rule based on the X and Z axes; for teeth No. 31 to 38 of the mandibular teeth, the positive direction of the Y-axis is determined by the right-hand rule based on the X and Z axes; for teeth No. 41 to 48 of the mandibular teeth, the positive direction of the Y-axis is determined by the left-hand rule based on the X and Z axes;

[0007] S3 identifies the characteristic points of the tooth in the tooth's own coordinate system to obtain the coordinates of the characteristic points in the tooth's own coordinate system;

[0008] The characteristic points of the teeth include: the distal incisor point, mesial incisor point, incisal ridge midpoint, axis point and gingival point of the central incisor and lateral incisor; the cusp point, axis point and gingival point of the canine; the buccal cusp point, lingual cusp point, pit point, axis point and gingival point of the premolar; the mesiobuccal cusp point, distal buccal cusp point, mesiolingual cusp point, distal lingual cusp point, pit point, axis point and gingival point of the molar;

[0009] S4 converts the coordinates of the feature points in the tooth's own coordinate system into the world coordinate system to obtain the coordinates in the world coordinate system.

[0010] Preferably, in the tooth model, in the tooth's own coordinate system:

[0011] The method for identifying the gingival point in step S3 is:

[0012] Define the area where the positive half axis of the X axis in the tooth model is located as area A1, and then find the area in area A1 whose vertical distance from the Z axis does not exceed 0.005 mm as area B1.

[0013] Compare the Z values ​​of all 3D mesh vertices in area B1, and identify the 3D mesh vertex with the largest Z value as the gingival point.

[0014] The method for identifying the midpoint of the cutting ridge in step S3 is:

[0015] Obtain all 3D mesh vertices with Z values ​​less than 0 in the tooth model and project them onto the XOY plane to obtain a 2D point set Q. Calculate the distance between each point in the point set Q and the origin of the coordinate system. The 3D mesh vertex corresponding to the point with the smallest distance is identified as the midpoint of the incisal ridge.

[0016] The method for identifying the axis points of the central incisor and the lateral incisor in step S3 is:

[0017] Get the midpoint P between the midpoint of the current tooth incisal ridge and the gingival point, calculate the distance between each 3D mesh vertex in the tooth model and point P, and identify the point with the smallest distance as the axis point;

[0018] The method for identifying the mesial corner point in step S3 is:

[0019] First, find the point with the largest Y value among all the 3D mesh vertices in the tooth model within the positive half-Y axis region, denoted as point P1. In the coordinate axis space, the region with a Z value less than 0 and a Y value between P1.Y and P1.Y-0.8 is denoted as B1. The point set in region B1 is projected onto the YOZ two-dimensional plane, and the distance from the projected point set to the coordinate origin is calculated. The 3D mesh vertex corresponding to the point with the farthest distance is identified as the mesial incisal corner point.

[0020] The method for identifying the distal incisal point in step S3 is:

[0021] In the space where the coordinate axis is located, first find the point with the smallest Y value among all the 3D mesh vertices in the tooth model in the negative half-axis area B2 of the Y axis, record it as point P2, and record the area with Z value less than 0 and Y value between P2.Y and P1.Y+0.8 as C. Project the point set in area C onto the YOZ two-dimensional plane, calculate the distance from each point after projection to the origin of the coordinate system, and identify the 3D mesh vertex corresponding to the point with the farthest distance as the distal incisal point.

[0022] Preferably, in the tooth model, in the tooth's own coordinate system:

[0023] The method for identifying the cusp in step S3 is as follows: finding the point with the smallest Z value among all vertices of the three-dimensional mesh in the tooth model and identifying it as the cusp;

[0024] Method for identifying the axis point of the canine in step S3:

[0025] Obtain the cusp and gingival point of the canine, calculate the midpoint P2 between the two points, and in the coordinate axis space, denote the area with X values ​​greater than 0 as A3. Calculate the distance from each 3D mesh vertex in area A3 to point P2. The point with the smallest distance is identified as the canine axis point.

[0026] Preferably, in the tooth model, in the tooth's own coordinate system:

[0027] Method for identifying the premolar dens in step S3:

[0028] In the space where the coordinate axes are located, the area with a Z value less than 0 is denoted as A4. All 3D mesh vertices in area A4 are projected onto the XOY 2D plane. The distance from the projected points to the origin is calculated. Points with a distance less than 0.5 mm are retained. The points that meet the requirements are denoted as point set P3. The point with the largest Z value among all the points in point set P3 is found. This 3D mesh vertex is identified as the premolar dens.

[0029] Method for identifying the buccal cusp of the premolar in step S3:

[0030] In the space where the coordinate axis is located, the area with a Z value less than 0 and an X value greater than 0 is recorded as A5. Find the point with the smallest Z value among all the 3D mesh vertices in area A5 and identify it as the buccal cusp of the premolar.

[0031] Method for identifying the lingual cusp point of the premolar in step S3:

[0032] In the space where the coordinate axes are located, the area with Z value less than 0 and X value less than 0 is recorded as A6. Find the point with the smallest Z value among all the 3D mesh vertices in area A6 and identify it as the lingual tip of the premolar.

[0033] Method for identifying the axis point of the premolar in step S3:

[0034] Obtain the midpoint P4 between the buccal cusp and the gingival point of the premolar. In the coordinate axis space, denote the region with an X value greater than 0 as A7. Calculate the distance from each 3D mesh vertex in region A7 to point P4, and identify the closest 3D mesh vertex as the premolar axis point.

[0035] Preferably, in the tooth model, in the tooth's own coordinate system:

[0036] The method for identifying the molar dens in step S3 is:

[0037] In the coordinate axis space, the area with a Z value less than 0 is designated as A8. All 3D mesh vertices within area A8 are projected onto the XOY 2D plane. The distance from the projected point to the origin is calculated. All points with a distance less than 0.5 mm are obtained. From all points with a distance less than 0.5 mm, the point with the largest Z value is found. The 3D mesh vertex corresponding to this point is identified as the molar dens.

[0038] The method for identifying the mesiobuccal cusp of the molar in step S3 is:

[0039] In the space where the coordinate axes are located, the area with a Z value less than 0, an X value greater than 1, and a Y value greater than 1 is designated as A9. The distances from all 3D mesh vertices in area A9 to the origin of the coordinate system are calculated, and the point with the largest distance is identified as the mesio-buccal cusp of the molar.

[0040] The method for identifying the distal buccal cusp of the molar in step S3 is:

[0041] In the space where the coordinate axes are located, the area with a Z value less than 0, an X value greater than 1, and a Y value less than -1 is designated as A10. The distances from all 3D mesh vertices in area A10 to the origin of the coordinate system are calculated, and the 3D mesh vertex with the largest distance is identified as the distal buccal cusp of the molar.

[0042] The method for identifying the mesial lingual cusp point of the molar in step S3 is:

[0043] In the space where the coordinate axes are located, the area with a Z value less than 0, an X value less than -1, and a Y value greater than 1 is designated as A11. The distances from all 3D mesh vertices in area A11 to the origin of the coordinate system are calculated, and the 3D mesh vertex with the largest distance is identified as the mesiolingual cusp of the molar.

[0044] The method for identifying the distal lingual cusp point of the molar in step S3 is:

[0045] In the space where the coordinate axes are located, the area with a Z value less than 0, an X value less than -1, and a Y value less than -1 is designated as A12. The distances from all 3D mesh vertices in area A12 to the origin of the coordinate system are calculated, and the 3D mesh vertex with the largest distance is identified as the distal lingual cusp of the molar.

[0046] The method for identifying the axis point of the molar in step S3 is:

[0047] After finding the mesio-buccal cusp, distal-buccal cusp, and gingival point of the molar, first record the midpoint of the line connecting the distal-buccal and mesio-buccal cusps as point P5. Then find the midpoint P6 between point P5 and the gingival point of the molar. In the coordinate axis space, record the area with X values ​​greater than 0 as A13. Calculate the distance from each 3D mesh vertex in area A13 to point P6, and identify the 3D mesh vertex with the smallest distance as the molar axis point.

[0048] The present invention realizes the recognition of tooth feature points through the tooth's own coordinate system, can obtain feature points that are more in line with the actual situation, saves working time, and reduces human errors to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the specific embodiments or the description of the prior art. Hereinafter, some specific embodiments of the present invention will be described in detail in an illustrative and non-limiting manner with reference to the drawings. The same reference numerals in the drawings indicate the same or similar components or parts. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0050] Figure 1 Type and number of teeth

[0051] Figure 2 Schematic diagram of the mesiodistal, buccal and lingual sides of the teeth

[0052] Figure 3 Schematic diagram of the tooth model mesh

[0053] Figure 4 Schematic diagram of the lingual surface of the central incisor DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0055] The embodiments and specific processes of the present invention are as follows:

[0056] 1) Import the tooth model and coordinate system transformation matrix. The tooth model is composed of a series of three-dimensional mesh vertices. The mesh vertex coordinates of the imported tooth model are all located in the world coordinate system.

[0057] 2) Convert the coordinates of each mesh vertex of the tooth from the world coordinate system to its own coordinate system. Multiply the coordinates of each mesh vertex by the transformation matrix to convert the coordinate values ​​of the mesh vertex from the world coordinate system to its own coordinate system. The method for establishing the tooth's own coordinate system is as follows: the origin of the coordinate system is located at the center of the tooth model, the positive direction of the X axis points from the origin to the buccal side, the positive direction of the Z axis points from the origin to the root direction, and the Y axis is determined as follows: Figure 1 As shown, for teeth 11 to 18 in the maxilla, the positive direction of the Y axis is determined by the right-hand rule based on the X and Z axes. For teeth 21 to 28 in the maxilla, the positive direction of the Y axis is determined by the left-hand rule based on the X and Z axes. For teeth 31 to 38 in the mandible, the positive direction of the Y axis is determined by the right-hand rule based on the X and Z axes. For teeth 41 to 48 in the mandible, the positive direction of the Y axis is determined by the left-hand rule based on the X and Z axes. The positive direction of the Y axis should be "pointing" to the midline of the tooth. The midline is as shown in the figure. Figure 2 shown.

[0058] 3) The specific method for identifying the characteristic points of each tooth is:

[0059] 1.1) Identifying the Gingival Point on a Tooth: The method for identifying the gingival point on each tooth is the same. First, find area A, which is the positive half of the X-axis in the model. Then, find area B within area A, where the vertical distance from the Z-axis does not exceed 0.005mm. Compare the Z values ​​of all points in area B. The point with the largest Z value is the gingival point. The method for finding the gingival point is the same for all teeth.

[0060] 1.2) Method for identifying the characteristic points of central incisors and lateral incisors:

[0061] a. Identifying the midpoint of the incisal ridge of the central and lateral incisors: Extend the negative half of the Z axis in the coordinate system. The intersection of this extension and the model is the midpoint of the incisal ridge. To do this, first find an area A within the point set where the Z value is less than 0. Then project the points in area A onto the XOY plane to obtain a two-dimensional point set Q. Calculate the distances from the origin of the coordinate system to the points in Q. The point with the closest distance is the midpoint of the incisal ridge.

[0062] b. Method for identifying the axis points of the central incisor and lateral incisor: After finding the midpoint of the incisal ridge and the gingival point, calculate the middle point P between the two points, traverse the vertex set of the tooth model, and calculate the distance between each point and point P. The point with the closest distance is the calculated axis point.

[0063] c. Method for identifying the mesial incisal point of the central incisor and lateral incisor: First find the point with the largest Y value in the positive half-axis area of ​​the Y axis, record it as point P1, record the area B where the Z value is less than 0 and the Y value is between P1.Y and P1.Y-0.8, project the point set in area B onto the YOZ two-dimensional plane, calculate the distance from the projected point set to the origin of the coordinate system, and the point with the farthest distance is the mesial incisal point.

[0064] d. Method for identifying the distal incisor point of the central incisor and lateral incisor: first find the point with the smallest Y value in the negative half-axis area B of the Y axis, record it as point P2, record the area with Z value less than 0 and Y value between P2.Y and P1.Y+0.8 as C, project the point set in area C onto the YOZ two-dimensional plane, calculate the distance from the projected point set to the origin of the coordinate system, and the point with the farthest distance is the distal incisor point.

[0065] 1.3) Method for identifying feature points of canines:

[0066] a. Method for identifying the cusp of the canine: find the point with the smallest Z value in the tooth model point set. This point is the cusp of the canine.

[0067] b. Method for identifying the canine axis point: After finding the canine tip and canine gingival point, calculate the midpoint P between the two points. Let the area with X value greater than 0 be A3. Calculate the distance from each point in area A3 to point P, and find the point with the closest distance. This point is the axis point of the canine feature point.

[0068] 1.4) Method for identifying feature points of premolars:

[0069] a. Identification method of premolar dens: let the area with Z value less than 0 be A, project all points in area A onto the XOY two-dimensional plane, calculate the distance from the projected point to the origin, retain the points with distance less than 0.5mm, record the points that meet the requirements as point set P1, find the point with the largest Z value in point set P1, this point is the premolar dens.

[0070] b. Method for identifying the buccal cusp of the premolar: let the area with Z value less than 0 and X value greater than 0 be A1, and find the point with the smallest Z value among all points in area A1. This point is the buccal cusp of the premolar.

[0071] c. The method for identifying the lingual tip of the premolar is as follows: let the area with Z value less than 0 and X value less than 0 be A2, and find the point with the smallest Z value among all points in area A2. This point is the lingual tip of the premolar.

[0072] d. Identification of the premolar axis: After finding the buccal cusp and gingival cusp of the premolar, calculate the midpoint P between the two points. The region with X values ​​greater than 0 is designated as A3. Calculate the distance from each point in region A3 to point P, and find the point with the closest distance. This point is the premolar axis.

[0073] 1.5) Method for identifying molar feature points:

[0074] a. Method for identifying molar pits: Let the area with Z value less than 0 be A, project all points in area A onto the XOY two-dimensional plane, calculate the distance from the projected points to the origin, retain the points with distance less than 0.5mm, and record the points that meet the requirements as point set P1. Find the point with the largest Z value in point set P1, which is the molar pit.

[0075] b. The method for identifying the mesiobuccal cusp of the molar is as follows: let the area with Z value less than 0, X value greater than 1, and Y value greater than 1 be A1, calculate the distance from all points in area A1 to the origin of the coordinate system, and find the point with the largest distance. This point is the mesiobuccal cusp of the molar.

[0076] c. The method for identifying the distal buccal cusp of the molar is as follows: let the area with Z value less than 0, X value greater than 1, and Y value less than -1 be A2. Calculate the distance from all points in area A2 to the origin of the coordinate system and find the point with the largest distance. This point is the distal buccal cusp of the molar.

[0077] d. The method for identifying the mesial lingual cusp of the molar is as follows: let the area with a Z value less than 0, an X value less than -1, and a Y value greater than 1 be A3. Calculate the distance from all points in area A3 to the origin of the coordinate system and find the point with the largest distance. This point is the mesial lingual cusp of the molar.

[0078] e. The method for identifying the distal lingual cusp of the molar is as follows: let the area with a Z value less than 0, an X value less than -1, and a Y value less than -1 be A4. Calculate the distance from all points in area A4 to the origin of the coordinate system and find the point with the largest distance. This point is the distal lingual cusp of the molar.

[0079] f. Method for identifying the molar axis: After finding the mesio-buccal cusp, distal buccal cusp, and molar gingival point of the molar, first calculate the midpoint between the distal buccal cusp and the mesio-buccal cusp, and record this point as point P. Then calculate the midpoint between point P and the molar gingival point, and record this midpoint as P1. Finally, record the area with X values ​​greater than 0 as A3. Calculate the distance from each point in area A3 to point P1, and find the point with the closest distance. This point is the molar axis.

[0080] 4) The feature points corresponding to each tooth are found by the above method, and then the three-dimensional coordinates of these feature points are converted into the world coordinate system. At this point, the present invention has completed the entire feature point recognition process.

[0081] The above description is only part of the specific implementation methods of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person familiar with the art within the technical scope disclosed in the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for identifying feature points based on the tooth's own coordinate system, characterized in that The following steps are included: S1 obtains a tooth model and a coordinate system transformation matrix, wherein the tooth model is composed of three-dimensional mesh vertices, and the coordinates of the three-dimensional mesh vertices are in a world coordinate system; S2 transforms the coordinate value of each three-dimensional mesh vertex from the world coordinate system to the tooth's own coordinate system by multiplying the coordinate of each mesh vertex with the transformation matrix, and independently establishes the tooth's own coordinates for each tooth. The coordinate system of the tooth's own coordinates is established as follows: the origin of the coordinate system is located at the center point of the tooth model, the positive direction of the X-axis points from the origin to the buccal side, and the positive direction of the Z-axis points from the origin to the root direction; the Y-axis is determined by: for teeth No. 11 to 18 of the maxillary teeth, the positive direction of the Y-axis is determined by the right-hand rule based on the X and Z axes; for teeth No. 21 to 28 of the maxillary teeth, the positive direction of the Y-axis is determined by the left-hand rule based on the X and Z axes; for teeth No. 31 to 38 of the mandibular teeth, the positive direction of the Y-axis is determined by the right-hand rule based on the X and Z axes; for teeth No. 41 to 48 of the mandibular teeth, the positive direction of the Y-axis is determined by the left-hand rule based on the X and Z axes; S3 identifies the characteristic points of the tooth in the tooth's own coordinate system to obtain the coordinates of the characteristic points in the tooth's own coordinate system; The characteristic points of the teeth include: the distal incisor point, mesial incisor point, incisal ridge midpoint, axis point and gingival point of the central incisor and lateral incisor; the cusp point, axis point and gingival point of the canine; the buccal cusp point, lingual cusp point, pit point, axis point and gingival point of the premolar; the mesiobuccal cusp point, distal buccal cusp point, mesiolingual cusp point, distal lingual cusp point, pit point, axis point and gingival point of the molar; S4 converts the coordinates of the feature points in the tooth's own coordinate system into the world coordinate system to obtain the coordinates in the world coordinate system.

2. The method for identifying feature points based on the tooth's own coordinate system according to claim 1, wherein: In the tooth model, in the tooth's own coordinate system: The method for identifying the gingival point in step S3 is: Define the area where the positive half axis of the X axis in the tooth model is located as area A1, and then find the area in area A1 whose vertical distance from the Z axis does not exceed 0.005 mm as area B1. Compare the Z values ​​of all 3D mesh vertices in area B1, and identify the 3D mesh vertex with the largest Z value as the gingival point. The method for identifying the midpoint of the cutting ridge in step S3 is: Obtain all 3D mesh vertices with Z values ​​less than 0 in the tooth model and project them onto the XOY plane to obtain a 2D point set Q. Calculate the distance between each point in the point set Q and the origin of the coordinate system. The 3D mesh vertex corresponding to the point with the smallest distance is identified as the midpoint of the incisal ridge. The method for identifying the axis points of the central incisor and the lateral incisor in step S3 is: Get the midpoint P between the midpoint of the current tooth incisal ridge and the gingival point, calculate the distance between each 3D mesh vertex in the tooth model and point P, and identify the point with the smallest distance as the axis point; The method for identifying the mesial corner point in step S3 is: First, find the point with the largest Y value among all the 3D mesh vertices in the tooth model within the positive half-Y axis region, denoted as point P1. In the coordinate axis space, the region with a Z value less than 0 and a Y value between P1.Y and P1.Y-0.8 is denoted as B1. The point set in region B1 is projected onto the YOZ two-dimensional plane, and the distance from the projected point set to the coordinate origin is calculated. The 3D mesh vertex corresponding to the point with the farthest distance is identified as the mesial incisal corner point. The method for identifying the distal incisal point in step S3 is: In the space where the coordinate axis is located, first find the point with the smallest Y value among all the 3D mesh vertices in the tooth model in the negative half-axis area B2 of the Y axis, record it as point P2, and record the area with Z value less than 0 and Y value between P2.Y and P1.Y+0.8 as C. Project the point set in area C onto the YOZ two-dimensional plane, calculate the distance from each point after projection to the origin of the coordinate system, and identify the 3D mesh vertex corresponding to the point with the farthest distance as the distal incisal point.

3. The method for identifying feature points based on the tooth's own coordinate system according to claim 2, wherein: In the tooth model, in the tooth's own coordinate system: The method for identifying the cusp in step S3 is as follows: finding the point with the smallest Z value among all vertices of the three-dimensional mesh in the tooth model and identifying it as the cusp; Method for identifying the axis point of the canine in step S3: Obtain the cusp and gingival point of the canine, calculate the midpoint P2 between the two points, and in the coordinate axis space, denote the area with X values ​​greater than 0 as A3. Calculate the distance from each 3D mesh vertex in area A3 to point P2. The point with the smallest distance is identified as the canine axis point.

4. The method for identifying feature points based on a tooth's own coordinate system according to claim 1, wherein: In the tooth model, in the tooth's own coordinate system: Method for identifying the premolar dens in step S3: In the space where the coordinate axes are located, the area with a Z value less than 0 is denoted as A4. All 3D mesh vertices in area A4 are projected onto the XOY 2D plane. The distance from the projected points to the origin is calculated. Points with a distance less than 0.5 mm are retained. The points that meet the requirements are denoted as point set P3. The point with the largest Z value among all the points in point set P3 is found. This 3D mesh vertex is identified as the premolar dens. Method for identifying the buccal cusp of the premolar in step S3: In the space where the coordinate axis is located, the area with a Z value less than 0 and an X value greater than 0 is recorded as A5. Find the point with the smallest Z value among all the 3D mesh vertices in area A5 and identify it as the buccal cusp of the premolar. Method for identifying the lingual cusp point of the premolar in step S3: In the space where the coordinate axes are located, the area with Z value less than 0 and X value less than 0 is recorded as A6. Find the point with the smallest Z value among all the 3D mesh vertices in area A6 and identify it as the lingual tip of the premolar. Method for identifying the axis point of the premolar in step S3: Obtain the midpoint P4 between the buccal cusp and the gingival point of the premolar. In the coordinate axis space, denote the region with an X value greater than 0 as A7. Calculate the distance from each 3D mesh vertex in region A7 to point P4, and identify the closest 3D mesh vertex as the premolar axis point.

5. The method for identifying feature points based on the tooth's own coordinate system according to claim 1, wherein: In the tooth model, in the tooth's own coordinate system: The method for identifying the molar dens in step S3 is: In the coordinate axis space, the area with a Z value less than 0 is designated as A8. All 3D mesh vertices within area A8 are projected onto the XOY 2D plane. The distance from the projected point to the origin is calculated. All points with a distance less than 0.5 mm are obtained. From all points with a distance less than 0.5 mm, the point with the largest Z value is found. The 3D mesh vertex corresponding to this point is identified as the molar dens. The method for identifying the mesiobuccal cusp of the molar in step S3 is: In the space where the coordinate axes are located, the area with a Z value less than 0, an X value greater than 1, and a Y value greater than 1 is designated as A9. The distances from all 3D mesh vertices in area A9 to the origin of the coordinate system are calculated, and the point with the largest distance is identified as the mesio-buccal cusp of the molar. The method for identifying the distal buccal cusp of the molar in step S3 is: In the space where the coordinate axes are located, the area with a Z value less than 0, an X value greater than 1, and a Y value less than -1 is designated as A10. The distances from all 3D mesh vertices in area A10 to the origin of the coordinate system are calculated, and the 3D mesh vertex with the largest distance is identified as the distal buccal cusp of the molar. The method for identifying the mesial lingual cusp point of the molar in step S3 is: In the space where the coordinate axes are located, the area with a Z value less than 0, an X value less than -1, and a Y value greater than 1 is designated as A11. The distances from all 3D mesh vertices in area A11 to the origin of the coordinate system are calculated, and the 3D mesh vertex with the largest distance is identified as the mesiolingual cusp of the molar. The method for identifying the distal lingual cusp point of the molar in step S3 is: In the space where the coordinate axes are located, the area with a Z value less than 0, an X value less than -1, and a Y value less than -1 is designated as A12. The distances from all 3D mesh vertices in area A12 to the origin of the coordinate system are calculated, and the 3D mesh vertex with the largest distance is identified as the distal lingual cusp of the molar. The method for identifying the axis point of the molar in step S3 is: After finding the mesio-buccal cusp, distal-buccal cusp, and gingival point of the molar, first record the midpoint of the line connecting the distal-buccal and mesio-buccal cusps as point P5. Then find the midpoint P6 between point P5 and the gingival point of the molar. In the coordinate axis space, record the area with X values ​​greater than 0 as A13. Calculate the distance from each 3D mesh vertex in area A13 to point P6, and identify the 3D mesh vertex with the smallest distance as the molar axis point.

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