A method for accurately positioning and measuring the thickness of an orthodontic appliance at a positioning point on a CT image

Abstract

This invention belongs to the field of medical orthodontic instrument calibration technology, and provides a method for accurately locating and measuring the thickness of orthodontic appliances at positioning points on CT images. The method first establishes a digital coordinate system based on a three-dimensional digital model of the original dentition and sets markers. Then, a physical model of the dentition with markers is created. The orthodontic appliance is worn on this physical model, and CT images are acquired. The required positioning points are accurately located on the CT images using the markers. Finally, the thickness of the orthodontic appliance at the positioning point is obtained on the CT slice image. This method achieves repeatable and accurate positioning and measurement of the orthodontic appliance thickness, solving the technical problems of difficulty in reproducing measurement points, lack of a unified benchmark, and inconsistent measurement directions in traditional methods. Furthermore, it allows for unified measurement of multiple positioning points on clear aligners based on the same benchmark.

Description

Technical Field

[0001] This invention belongs to the field of medical dental orthodontic instrument calibration technology, specifically relating to a method for accurately locating and measuring the thickness of an orthodontic appliance at a positioning point on a CT image. Background Technology

[0002] Orthodontic appliances, such as clear aligners, have become an important technological approach in modern orthodontic treatment due to their advantages such as aesthetics, comfort, ease of cleaning, and digital design and manufacturing. Clear aligners are typically made of thermoplastic polymer materials and manufactured through methods such as thermoforming or direct 3D printing. The thickness of the aligner not only determines its geometry but also directly affects its mechanical properties, orthodontic force output, stress distribution, and tooth movement efficiency. It is a crucial parameter for evaluating the manufacturing quality, material properties, and clinical efficacy of clear aligners. Therefore, accurate measurement of aligner thickness has always been an important aspect of clear aligner design, manufacturing, product quality control, and biomechanical research.

[0003] Currently, several mature technical methods have been developed for measuring the thickness of clear aligners. Manual measurement is one of the commonly used methods, typically employing tools such as electronic thickness gauges, digital micrometers, or vernier calipers. The measuring tool directly contacts the inner and outer surfaces of the aligner to obtain local thickness data. This method has advantages such as simple operation, low cost, and high measurement accuracy, and is therefore widely used in quality inspection and experimental research related to aligner manufacturing. However, due to the complex three-dimensional curved surface of clear aligners, different operators cannot guarantee that the probe will always be applied to the exact same position and direction. The measurement results are easily affected by errors in the positioning of the measuring point and human operational factors, especially in areas with large local curvature, where repeatability and consistency are somewhat limited.

[0004] Besides manual measurement, digital measurement methods are also common thickness measurement techniques. In recent years, three-dimensional optical scanning technology has also been used for digital measurement of clear aligners. However, due to the high transparency of clear aligners, a developing agent is usually sprayed to obtain stable scanning data, and the inhomogeneity of the sprayed layer thickness may introduce additional measurement errors. Furthermore, this type of scanning technology mainly acquires data from the outer surface of the aligner, and still has certain limitations for measuring the true thickness. In addition, Micro-CT (micro-computed tomography) technology is increasingly being applied to the thickness analysis of clear aligners. Micro-CT can acquire complete three-dimensional data of the aligner and simultaneously reconstruct the inner and outer surfaces of the aligner, enabling overall thickness distribution analysis. It has high measurement accuracy and spatial resolution, and therefore has become an important technique for aligner thickness research. This type of method provides high spatial resolution, but it cannot achieve repeated measurements of the same sample and is difficult to use for studying changes in aligner thickness under continuous conditions.

[0005] To address the aforementioned issues, the applicant's prior invention patent, "A Standardized Alignment Device for Measuring the Thickness of Clear Braces and Its Preparation Method" (CN116942337B), provides a standardized alignment device for measuring the thickness of clear braces and its preparation method. This method involves creating a digital model of the dentition corresponding to the clear braces, acquiring a digital model of the measuring needle from a needle thickness gauge, determining and marking measurement points on the dentition or braces digital model, determining and marking the measurement direction based on these points, placing the measuring needle digital model according to the measurement points and direction, and creating a measuring needle navigation channel on the dentition digital model based on the overlapping portion of the dentition and measuring needle digital models. This completes the alignment device. This device assists in measuring the thickness of clear braces at different points using fixed-point, directional, and depth measurements, achieving accurate and repeatable measurements.

[0006] However, due to its structural limitations, the aforementioned alignment device cannot measure multiple measurement points on the same tooth on the clear aligner. Furthermore, since the alignment device needs to be assembled with the clear aligner during measurement, setting measurement needle navigation channels at all corresponding points on all teeth at the same time can easily change its overall structure, leading to instability in the assembly and seriously affecting the accuracy of its measurement.

[0007] Furthermore, during the actual clinical use of clear aligners, as teeth gradually move, the aligners continuously undergo elastic deformation, local stretching, compression, and stress relaxation, resulting in constant changes to their three-dimensional geometry and local structure. Simultaneously, the geometry of the aligners differs depending on the tooth position at adjacent treatment stages. Therefore, clear aligners are a dynamic structure that constantly changes with the treatment process, rather than a fixed static model. Accurately measuring the thickness changes of the aligner at the same location under different deformation states or treatment stages is crucial for revealing the local deformation patterns of the aligner, analyzing changes in orthodontic forces, validating biomechanical models, optimizing aligner design and manufacturing processes, and conducting product quality evaluation.

[0008] Current thickness measurement technologies primarily target static thickness measurements of aligners in a single state. When an aligner deforms, its three-dimensional geometry and local curvature change, making it difficult to guarantee consistency in measurement positions across different states using traditional manual positioning or methods based on local geometric features. Even with high-precision 3D scanning technologies like Micro-CT to obtain 3D models of aligners in multiple states, only the thickness information of each individual aligner can be acquired. It is still impossible to accurately establish the spatial correspondence between the same location in different states, thus hindering precise measurement of thickness changes at the same point. Therefore, current technologies cannot meet the need for quantitative analysis of thickness changes at the same point before and after deformation of clear aligners or at different treatment stages. Summary of the Invention

[0009] This invention addresses the shortcomings of existing technologies by providing a method for accurately locating and measuring the thickness of orthodontic appliances at specific points on CT images. The method first establishes a digital coordinate system based on a three-dimensional digital model of the original dentition and sets markers. Then, a physical model of the dentition with these markers is created. The orthodontic appliance is worn on this physical model, and CT images are acquired. The markers are then used to accurately locate the desired measurement points on the CT images. Finally, the thickness of the orthodontic appliance at these points is obtained from the CT slice images. This method achieves repeatable and precise measurement of the orthodontic appliance thickness, solving the technical problems of traditional methods, such as difficulty in reproducing measurement points, lack of a unified benchmark, and inconsistent measurement directions. Furthermore, it allows for unified measurement of multiple points on clear aligners based on the same benchmark.

[0010] To achieve the above objectives, the present invention employs a technical solution consisting of the following technical measures.

[0011] A method for accurately locating and measuring the thickness of an orthodontic appliance at a positioning point on a CT image, comprising the following steps:

[0012] S-1. Select multiple feature points on the outer surface of the original three-dimensional digital model of the dental arch;

[0013] S-2. Construct a global coordinate system for the dental arch based on feature points;

[0014] S-3. Select the positioning points to be measured on the outer surface of the teeth in the original three-dimensional digital model of the dental arch, and use the grid surface or local fitting plane where the positioning points are located as the local reference plane.

[0015] S-4. Construct a local coordinate system based on the local reference plane and the positioning point. Take the positioning point as the origin of the coordinate system. The X-axis is perpendicular to the sagittal plane of the crown of the tooth where the positioning point is located and its positive direction points to the mesial side. The Y-axis or Z-axis is perpendicular to the local reference plane and its positive direction is determined by the right-hand rule. The positive direction of the remaining axes points to the tooth.

[0016] S-5. At each intersection point between the horizontal plane and the sagittal plane determined by the local coordinate system and the outer surface of the original three-dimensional digital model of the dental arch, at least one auxiliary positioning point shall be selected.

[0017] S-6. Calculate the rotation angle of the local coordinate system relative to the global coordinate system of the dental arch;

[0018] S-7. Model and mark feature points and auxiliary positioning points on the original three-dimensional digital model of the dentition to form a marked three-dimensional digital model of the dentition.

[0019] S-8. Based on the marked three-dimensional digital model of the dentition, a marked dentition model is made. The orthodontic appliance to be measured is worn on the dentition model, and CT three-dimensional volume data is obtained by CT scanning.

[0020] The computer interface displays CT slice images in three orthogonal directions generated based on the CT three-dimensional volume data, and in response to three-dimensional rotation operation and positioning line movement operation, generates coronal slice images, sagittal slice images and axial slice images in real time with corresponding rotation posture and different cutting depths.

[0021] S-9. Based on the feature point labeling, the spatial orientation of the CT three-dimensional volume data is aligned with the global coordinate system of the dental arch. The rotation center of the CT three-dimensional volume data is set at the origin of the global coordinate system of the dental arch. Then, the rotation angle obtained from S-6 is input to make the spatial orientation of the CT three-dimensional volume data aligned with the local coordinate system.

[0022] S-10. By identifying the auxiliary positioning points indicated by the markers, move the positioning lines so that the intersection of the positioning lines in the coronal slice image aligns with the positioning points;

[0023] S-11. Obtain the thickness of the orthodontic appliance at the location point based on the measurement direction on the sagittal slice image.

[0024] In this paper, the original three-dimensional digital model of the dentition mentioned in step S-1 can be a digital model of the dentition obtained during the digital fabrication of orthodontic appliances or other orthodontic treatment processes, or it can be a digital model of the dentition obtained by modeling or 3D scanning based on the human dentition.

[0025] In one of the technical solutions, the step S-1 involves selecting multiple feature points on the outer surface of the original three-dimensional digital model of the dental arch. Specifically, this can involve selecting three non-collinear points on the outer surface of the gingiva of the original three-dimensional digital model of the dental arch as feature points. The plane constructed based on the feature points is the global reference plane, and one point is selected on the outer surface of the teeth or the outer surface of the gingiva as a direction point.

[0026] Furthermore, the construction of the global coordinate system of the dental arch based on feature points in step S-2 can be specifically based on the global reference plane and direction points. Any feature point is used as the origin of the coordinate system, the vector direction from the origin to another feature point is used as the positive direction of the X-axis, the Y-axis is located in the global reference plane and its positive direction is determined by the right-hand rule, and the Z-axis is perpendicular to the global reference plane and its positive direction points to the side where the direction point is located.

[0027] In one preferred embodiment, three non-collinear points are selected as feature points on the outer surface of the gingiva of the original three-dimensional digital model of the dentition. The plane constructed based on the feature points is the global reference plane, which is preferably parallel to the α plane.

[0028] In one preferred embodiment, three non-collinear points are selected as feature points on the outer surface of the gingiva of the original three-dimensional digital model of the dentition, and all feature points are located on the labial surface of the original three-dimensional digital model of the dentition, with a distance of at least 1 cm between them.

[0029] In one preferred embodiment, a point is selected on the outer surface of the tooth or the outer surface of the gum as a direction point, and the direction point is close to the 𬌗 direction.

[0030] In this paper, the positioning point to be measured in step S-3 is any point on the outer surface of the tooth, based on oral anatomy.

[0031] In one of the technical solutions, the positioning point to be measured in step S-3 is preferably located at any point on the labial / buccal tooth surface.

[0032] Furthermore, the positioning points to be measured in step S-3 can be based on the conventional measurement points in the prior art for measuring the thickness of orthodontic appliances, such as the midpoint of the labial / buccal surface of the tooth, the midpoint of the labial / buccal gingival margin, the midpoint of the incisal edge of the incisor, the cusp of other teeth, the midpoint of the palatal / lingual surface of the tooth, the midpoint of the palatal / lingual gingival margin, etc.

[0033] In one of the technical solutions, the local fitting plane mentioned in step S-3 is obtained by extracting multiple sampling points located on the outer surface within a preset neighborhood centered on the positioning point, and using a fitting algorithm to perform plane fitting on the multiple sampling points to obtain the local fitting plane.

[0034] Specifically, 10 to 50 three-dimensional surface sampling points located on the outer surface of the tooth can be extracted within a preset neighborhood range with a radius of 0.5 to 2.0 mm, centered on the positioning point. Based on the spatial coordinates of the sampling points, a local fitting plane corresponding to the positioning point can be calculated using the least squares local plane fitting method.

[0035] In this article, the sagittal plane of the tooth crown described in step S-4 is a longitudinal section made along the labial (buccal) lingual direction of the tooth crown, passing through specific anatomical landmarks (such as the midpoint of the incisal edge), which divides the tooth crown into mesial and distal parts, referring to the definition of the sagittal plane in oral anatomy.

[0036] It should be noted that in step S-4, the X-axis is perpendicular to the sagittal plane of the tooth crown where the positioning point is located, and its positive direction points to the mesial side. The Y-axis or Z-axis is perpendicular to the local reference plane, and its positive direction is determined by the right-hand rule. The positive direction of the remaining axes points to the tooth. This is based on oral anatomy. Because different points on the tooth surface have different definitions for the Y-axis and Z-axis of the local coordinate system to obtain the horizontal and sagittal planes required in step S-5.

[0037] For example, when the positioning point is the midpoint of the labial / buccal surface of the tooth or the midpoint of the labial / buccal gingival margin, in step S-4, the Y-axis of the local coordinate system is perpendicular to the local reference plane and its positive direction is determined by the right-hand rule, and the positive direction of the Z-axis points towards the tooth. In step S-5, the plane formed by the X-axis and Y-axis of the local coordinate system is the horizontal plane, and the plane formed by the Y-axis and Z-axis is the sagittal plane.

[0038] When the positioning point is the midpoint of the incisal edge of the incisor and the cusp of other teeth, in step S-4, the Z-axis of the local coordinate system is perpendicular to the local reference plane and its positive direction is determined by the right-hand rule, and the positive direction of the Y-axis points to the tooth. In step S-5, the plane formed by the X-axis and Z-axis of the local coordinate system is the horizontal plane, and the plane formed by the Y-axis and Z-axis is the sagittal plane.

[0039] When the positioning point is the midpoint of the palatal / lingual surface of the tooth or the midpoint of the palatal / lingual gingival margin, in step S-4, the Y-axis of the local coordinate system is perpendicular to the local reference plane and its positive direction is determined by the right-hand rule, and the positive direction of the Z-axis points towards the tooth. In step S-5, the plane formed by the X-axis and Y-axis of the local coordinate system is the horizontal plane, and the plane formed by the Y-axis and Z-axis is the sagittal plane.

[0040] In this document, in step S-5, at each intersection position of the horizontal plane and the sagittal plane determined by the local coordinate system with the outer surface of the original dentition three-dimensional digital model, at least one auxiliary positioning point is selected. That is, at each intersection position of the horizontal plane with the outer surface of the original dentition three-dimensional digital model, at least one auxiliary positioning point corresponding to the horizontal plane is selected, and at each intersection position of the sagittal plane with the outer surface of the original dentition three-dimensional digital model, at least one auxiliary positioning point corresponding to the sagittal plane is selected.

[0041] In this paper, the calculation of the rotation angle of the local coordinate system relative to the global dental coordinate system in step S-6 is usually based on the rotation angle of the local coordinate system relative to the X-axis, Y-axis and Z-axis of the global dental coordinate system, and the X-axis rotation angle, Y-axis rotation angle and Z-axis rotation angle are calculated respectively.

[0042] Specifically, the aforementioned X-axis rotation angle, Y-axis rotation angle, and Z-axis rotation angle can be calculated using the built-in functions of 3D digital model processing software, such as the matrix loading function of Geomagic Studio software.

[0043] In one technical solution, step S-7 involves modeling and marking feature points and auxiliary positioning points on the original three-dimensional digital model of the dentition. To ensure correct assembly and installation with the orthodontic appliance, the modeling and marking involves establishing a 3D sphere model with a diameter of 0.5~2.0 mm, centered on each feature point and auxiliary positioning point. This sphere model is retained, or it is removed from the original three-dimensional digital model of the dentition to form a recess, serving as a visually identifiable marker. It should be noted that since auxiliary positioning points are mostly located on the outer surface of the teeth, to ensure correct placement of the orthodontic appliance on the subsequent physical model, it is preferable to remove the sphere model corresponding to the auxiliary positioning point from the original three-dimensional digital model of the dentition to form a recess.

[0044] Furthermore, different shapes of modeling marks can be used for the auxiliary positioning points corresponding to the horizontal plane and the auxiliary positioning points corresponding to the sagittal plane to facilitate identification.

[0045] In one technical solution, step S-7 involves modeling and marking feature points and auxiliary positioning points on the original three-dimensional digital model of the dental arch. When the global coordinate system of the dental arch is constructed based on a global reference plane and direction points according to the above technical solution, the modeling and marking of direction points is also included. For ease of description, the modeling and marking of feature points is referred to as feature point marking, and the modeling and marking of auxiliary positioning points is referred to as auxiliary positioning point marking.

[0046] Similarly, in step S-9, the feature point-based marking aligns the spatial orientation of the CT three-dimensional volume data with the global coordinate system of the dental arch. When the global coordinate system of the dental arch is constructed based on the global reference plane and direction points according to the above technical solution, the spatial orientation of the CT three-dimensional volume data is aligned with the global coordinate system of the dental arch based on the feature point and direction point marking.

[0047] In this paper, the positioning line mentioned in step S-8 is the intersection line between another slice image perpendicular to the cross-section of the current slice image and the cross-section of the current slice image. The movement operation of the positioning line is used to adjust the cutting depth of the cross-section of the other slice image. In the computer interface of CT 3D volumetric data processing software, it is usually represented by red, blue, and green lines. For ease of description, the positioning line corresponding to the coronal slice image is denoted as the coronal slice positioning line, the positioning line corresponding to the sagittal slice image is denoted as the sagittal slice positioning line, and the positioning line corresponding to the axial slice image is denoted as the axial slice positioning line.

[0048] In this document, step S-10, which involves identifying the auxiliary positioning point indicated by the marker and moving the positioning line so that the intersection of the positioning lines in the coronal slice image aligns with the positioning point, may specifically include the following operations:

[0049] By moving the positioning lines on the sagittal and axial slice images, the intersection of the positioning lines is located on the tooth where the positioning point is located. The auxiliary positioning point mark corresponding to the positioning point can be identified on the coronal slice image. The sagittal slice positioning line is moved on the coronal slice image to intersect with the auxiliary positioning point mark corresponding to the sagittal plane, and the axial slice positioning line is moved to intersect with the auxiliary positioning point mark corresponding to the horizontal plane. At this time, the intersection of the positioning lines in the coronal slice image is aligned with the positioning point.

[0050] In this paper, the orthodontic appliance thickness at the positioning point is obtained based on the measurement direction on the sagittal slice image in step S-11. The measurement direction can usually be selected as the positioning line direction on the sagittal slice image, or a custom measurement direction according to actual needs. Since the sagittal slice image has the uniformity of rotation posture and cross-sectional thickness based on steps S-9 and S-10 of this invention, the measurement direction is unique and definite.

[0051] In one preferred technical solution, when the orthodontic appliance is a transparent brace, in order to avoid spraying the developing agent and to facilitate the determination of boundary points when measuring the thickness, after performing step S-5 and before step S-8, the tooth model corresponding to the marked points is removed from the original three-dimensional digital model of the dentition to form a three-dimensional digital model of the dentition similar to "missing teeth".

[0052] Furthermore, the auxiliary positioning point mentioned in step S-5 is not on the same tooth as the positioning point.

[0053] It should be noted that in current software or applications that display CT 3D volumetric data and perform local structural measurements using a computer-interactive interface, the establishment of measurement benchmarks for specific positioning points typically relies on the operator manually adjusting the 3D spatial attitude, cross-sectional position, and positioning of the local measurement plane. Specifically, determining the spatial attitude at a positioning point usually requires the use of three or more auxiliary marker points for spatial constraints. When multiple positioning points need to be measured or designed continuously, repeatedly setting auxiliary marker points not only increases the complexity of the operation steps and process but is also susceptible to the influence of marker recognition accuracy and human positioning errors. Furthermore, the process of manually adjusting the 3D spatial attitude depends on the operator's experience, making it difficult to ensure the consistency of measurement benchmarks between different positioning points, thus affecting measurement efficiency, operational stability, and result repeatability.

[0054] This invention proposes a method for accurately locating and measuring the thickness of orthodontic appliances at positioning points by combining three-dimensional attitude parameters based on a global and local coordinate system of the dentition. The method first establishes a unified global coordinate system of the dentition based on the overall structure of the dentition, achieving overall accuracy of CT three-dimensional volume data through a single spatial orientation calibration. Subsequently, based on the three-dimensional rotational attitude parameters of the local coordinate system of each positioning point relative to the global coordinate system of the dentition, the spatial orientation of the measurement section is digitally adjusted to achieve accurate reproduction of the measurement reference for different positioning points.

[0055] This method transforms the traditional 3D spatial positioning process, which relies on repeated manual adjustments, into a standardized operational procedure based on spatial parameters. It eliminates the need for re-calibrating rotations at each positioning point; simply inputting the corresponding rotation angle parameters and performing position translation allows for the rapid establishment of measurement benchmarks at multiple positioning points. This approach reduces reliance on operator experience, improves the efficiency, feasibility, and repeatability of measurement and positioning during orthodontic appliance design and manufacturing, and provides a stable and reliable technical solution for precise thickness measurement based on CT 3D volumetric data.

[0056] In addition, we have noted that existing technologies cannot yet meet the need for quantitative analysis of thickness changes at the same point before and after or at different treatment stages of orthodontic appliances.

[0057] Based on this, in one technical solution, the method for accurately locating and measuring the thickness of the orthodontic appliance at the positioning point on a CT image further includes the following steps:

[0058] S-12. Based on the original three-dimensional digital model of the dentition described in S-1, obtain a three-dimensional digital model of the orthodontic dentition by rotating and / or translating the teeth; or, obtain a three-dimensional digital model of the orthodontic dentition by modeling or 3D scanning after the orthodontic cycle.

[0059] S-13. Using the three-dimensional digital model of the orthodontic dentition obtained in S-12 as the original three-dimensional digital model of the dentition, the thickness of the orthodontic appliance at the positioning point is obtained according to S-1~S-11.

[0060] Among them, the positioning points of the three-dimensional digital model of the orthodontic dentition are consistent with the positioning points of the original three-dimensional digital model of the dentition based on the positional relationship of oral anatomy on the teeth;

[0061] The orthodontic appliances to be measured in S-8 are either made based on a three-dimensional digital model of the orthodontic arch or are orthodontic appliances after the treatment cycle.

[0062] The above technical solution can meet the quantitative analysis needs of thickness changes at the same point before and after deformation of orthodontic appliances or at different treatment stages.

[0063] The present invention has the following beneficial effects:

[0064] (1) This invention provides a method for accurately locating and measuring the thickness of orthodontic appliances at positioning points on CT images. This method combines three-dimensional posture parameters based on the global and local coordinate systems of the dentition to achieve rapid reproduction and positioning of multiple positioning points, reduce manual adjustments, and improve the convenience, efficiency and repeatability of orthodontic appliance thickness measurement, especially transparent appliances.

[0065] (2) The method of the present invention is relatively simple and convenient in subsequent operations. It has low requirements for equipment and process conditions and has good feasibility and application value.

[0066] (3) The method of the present invention can be directly applied to the thickness measurement of orthodontic appliances such as clear aligners, providing data support for their design, manufacturing and clinical application. In one of the technical solutions, the quantitative analysis needs of thickness changes at the same point before and after deformation of the orthodontic appliance or at different treatment stages can be met. Attached Figure Description

[0067] Figure 1 This is a partial operational diagram of steps S-1 to S-2 in Embodiment 1 of the present invention.

[0068] Figure 2 This is a partial operational diagram of step S-3 in Embodiment 1 of the present invention.

[0069] Figure 3 This is a partial operational diagram of step S-3 in Embodiment 1 of the present invention.

[0070] Figure 4 The diagram above shows a partial operation diagram of step S-9 in Embodiment 1 of the present invention, and the diagram below shows a comparison model.

[0071] Figure 5 This is a partial operational schematic diagram (left) and a comparative model schematic diagram (right) of step S-10 in Embodiment 1 of the present invention.

[0072] Figure 6 This is a partial operational diagram of step S-11 in Embodiment 1 of the present invention. Detailed Implementation

[0073] To further understand the present invention, preferred embodiments are described below with reference to examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. Those skilled in the art can refer to the content of this document to appropriately improve the process parameters. It is particularly important to note that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the scope of this invention. The methods and applications of the present invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate changes and combinations to the methods and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0074] Example 1

[0075] A method for accurately locating and measuring the thickness of an orthodontic appliance at a positioning point on a CT image, comprising the following steps:

[0076] S-1, such as Figure 1 As shown, non-collinear points P1, P2, and P3 are selected as feature points on the outer surface of the gingiva of the original three-dimensional digital model of the dentition. The plane constructed based on the feature points is the global reference plane, and point P4 is selected as the direction point on the outer surface of the gingiva.

[0077] The feature points are spaced at least 1 cm apart from each other;

[0078] S-2. Construct a global coordinate system for the tooth row based on the global reference plane and direction points. Take point P1 as the origin of the coordinate system, the vector direction from the origin to point P2 as the positive direction of the X-axis, the Y-axis is located in the global reference plane and its positive direction is determined by the right-hand rule, and the Z-axis is perpendicular to the global reference plane and its positive direction points to the side where the direction point is located.

[0079] S-3. Select the positioning points to be measured on the outer surface of the teeth in the original three-dimensional digital model of the dental arch, and use the grid surface where the positioning points are located as the local reference plane.

[0080] like Figure 2 As shown, the positioning points include the midpoint of the buccal gingival margin of the central incisor (11-bg), the midpoint of the buccal surface of the central incisor (11-bu), the midpoint of the incisal margin of the central incisor (11-o), the midpoint of the buccal gingival margin of the canine (13-bg), the midpoint of the buccal surface of the canine (13-bu), the cusp of the canine (13-o), the midpoint of the buccal gingival margin of the first premolar (14-bg), the midpoint of the buccal surface of the first premolar (14-bu), the cusp of the first premolar (14-o), the midpoint of the buccal gingival margin of the first molar (16-bg), the midpoint of the buccal surface of the first molar (16-bu), and the cusp of the first molar (16-o).

[0081] like Figure 3As shown, the positioning points include the midpoint of the palatal gingival margin of the central incisor (11-pg), the midpoint of the palatal surface of the central incisor (11-pu), the midpoint of the palatal gingival margin of the canine (13-pg), the midpoint of the palatal surface of the canine (13-pu), the midpoint of the palatal gingival margin of the first premolar (14-pg), the midpoint of the palatal surface of the first premolar (14-pu), the midpoint of the palatal gingival margin of the first molar (16-pg), and the midpoint of the palatal surface of the first molar (16-pu).

[0082] S-4. Construct a local coordinate system based on the local reference plane and the positioning point, with the positioning point as the origin of the coordinate system;

[0083] When the positioning point is the midpoint of the buccal surface of the tooth or the midpoint of the buccal gingival margin, in step S-4, the Y-axis of the local coordinate system is perpendicular to the local reference plane and its positive direction is determined by the right-hand rule, and the positive direction of the Z-axis points to the tooth. In step S-5, the plane formed by the X-axis and Y-axis of the local coordinate system is the horizontal plane, and the plane formed by the Y-axis and Z-axis is the sagittal plane.

[0084] When the positioning point is the midpoint of the incisal edge of the central incisor and the cusp of other teeth, in step S-4, the Z-axis of the local coordinate system is perpendicular to the local reference plane and its positive direction is determined by the right-hand rule, and the positive direction of the Y-axis points to the tooth. In step S-5, the plane formed by the X-axis and Z-axis of the local coordinate system is the horizontal plane, and the plane formed by the Y-axis and Z-axis is the sagittal plane.

[0085] When the positioning point is the midpoint of the palatal surface of the tooth or the midpoint of the palatal gingival margin, in step S-4, the Y-axis of the local coordinate system is perpendicular to the local reference plane and its positive direction is determined by the right-hand rule, and the positive direction of the Z-axis points to the tooth. In step S-5, the plane formed by the X-axis and Y-axis of the local coordinate system is the horizontal plane, and the plane formed by the Y-axis and Z-axis is the sagittal plane.

[0086] S-5. At each intersection of the horizontal plane and the outer surface of the original three-dimensional digital model of the dental arch, select one auxiliary positioning point corresponding to the horizontal plane; at each intersection of the sagittal plane and the outer surface of the original three-dimensional digital model of the dental arch, select one auxiliary positioning point corresponding to the sagittal plane.

[0087] S-6. Calculate the rotation angle of the local coordinate system relative to the global coordinate system of the dental arch using the matrix loading function of Geomagic Studio software;

[0088] S-7. Model and mark feature points and auxiliary positioning points on the original three-dimensional digital model of the dentition to form a marked three-dimensional digital model of the dentition.

[0089] The modeling markers are created by establishing a 3D sphere model with a diameter of 1 mm, with each feature point, direction point, and auxiliary positioning point as the center. The 3D sphere model corresponding to the auxiliary positioning point is removed from the original 3D digital model of the dental arch to form a pit, while the 3D sphere model corresponding to the feature point and direction point is retained as a visually identifiable and distinguishable marker.

[0090] S-8. Based on the marked three-dimensional digital model of the dentition, a marked dentition model is made. The orthodontic appliance to be measured is worn on the dentition model, and CT three-dimensional volume data is obtained by CT scanning.

[0091] The computer interface displays CT slice images in three orthogonal directions generated based on the CT three-dimensional volume data, and in response to three-dimensional rotation operation and positioning line movement operation, generates coronal slice images, sagittal slice images and axial slice images in real time with corresponding rotation posture and different cutting depths.

[0092] S-9, such as Figure 4 As shown, on the coronal slice image, the axial slice positioning line intersects with points P1 and P2, and the intersection of the two positioning lines overlaps with point P1. On the sagittal slice image, the axial slice positioning line intersects with points P1 and P3, and point P4 is located above the axial slice positioning line. On the axial slice image, the coronal slice positioning line intersects with points P1 and P2, so that the spatial direction of the CT three-dimensional volume data is aligned with the global coordinate system of the dentition. Then, the rotation center of the CT three-dimensional volume data is set at the origin of the global coordinate system of the dentition. Then, the rotation angle obtained by S-6 is input to align the spatial direction of the CT three-dimensional volume data with the local coordinate system.

[0093] S-10, such as Figure 5 As shown, by moving the positioning lines on the sagittal slice image and the axial slice image, the intersection of the positioning lines is located on the tooth where the positioning point is located, and the auxiliary positioning point mark corresponding to the positioning point can be identified on the coronal slice image. The sagittal slice positioning line is moved on the coronal slice image to intersect with the auxiliary positioning point mark corresponding to the sagittal plane, and the axial slice positioning line is moved to intersect with the auxiliary positioning point mark corresponding to the horizontal plane. At this time, the intersection of the positioning lines in the coronal slice image is aligned with the positioning point.

[0094] S-11, such as Figure 6 As shown, based on the axial slice positioning line on the sagittal slice image as the measurement direction, the boundary between the outer and inner surfaces of the orthodontic appliance can be clearly observed, thereby obtaining the thickness of the orthodontic appliance at the positioning point.

[0095] Example 2

[0096] Example 2, to meet the quantitative analysis needs of thickness changes at the same point before and after or at different treatment stages of orthodontic appliance deformation, further includes the following steps based on the method of Example 1:

[0097] S-12. Based on the original three-dimensional digital model of the dentition described in S-1, obtain a three-dimensional digital model of the orthodontic dentition by rotating and / or translating the teeth; or, obtain a three-dimensional digital model of the orthodontic dentition by modeling or 3D scanning after the orthodontic cycle.

[0098] S-13. Using the three-dimensional digital model of the orthodontic dentition obtained in S-12 as the original three-dimensional digital model of the dentition, the thickness of the orthodontic appliance at the positioning point is obtained according to S-1~S-11.

[0099] Among them, the positioning points of the three-dimensional digital model of the orthodontic dentition are consistent with the positioning points of the original three-dimensional digital model of the dentition based on the positional relationship of oral anatomy on the teeth;

[0100] The orthodontic appliances to be measured in S-8 are either made based on a three-dimensional digital model of the orthodontic arch or are orthodontic appliances after the treatment cycle.

[0101] The implementation method of Example 2 can meet the quantitative analysis requirements of thickness changes at the same point before and after deformation of orthodontic appliances or at different treatment stages.

[0102] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for accurately locating and measuring the thickness of an orthodontic appliance at a positioning point on a CT image, characterized in that... Includes the following steps: S-1. Select multiple feature points on the outer surface of the original three-dimensional digital model of the dental arch; S-2. Construct a global coordinate system for the dental arch based on feature points; S-3. Select the positioning points to be measured on the outer surface of the teeth in the original three-dimensional digital model of the dental arch, and use the grid surface or local fitting plane where the positioning points are located as the local reference plane. S-4. Construct a local coordinate system based on the local reference plane and the positioning point. Take the positioning point as the origin of the coordinate system. The X-axis is perpendicular to the sagittal plane of the crown of the tooth where the positioning point is located and its positive direction points to the mesial side. The Y-axis or Z-axis is perpendicular to the local reference plane and its positive direction is determined by the right-hand rule. The positive direction of the remaining axes points to the tooth. S-5. At each intersection point between the horizontal plane and the sagittal plane determined by the local coordinate system and the outer surface of the original three-dimensional digital model of the dental arch, at least one auxiliary positioning point shall be selected. S-6. Calculate the rotation angle of the local coordinate system relative to the global coordinate system of the dental arch; S-7. Model and mark feature points and auxiliary positioning points on the original three-dimensional digital model of the dentition to form a marked three-dimensional digital model of the dentition. S-8. Based on the marked three-dimensional digital model of the dentition, a marked dentition model is made. The orthodontic appliance to be measured is worn on the dentition model, and CT three-dimensional volume data is obtained by CT scanning. The computer interface displays CT slice images in three orthogonal directions generated based on the CT three-dimensional volume data, and in response to three-dimensional rotation operation and positioning line movement operation, generates coronal slice images, sagittal slice images and axial slice images in real time with corresponding rotation posture and different cutting depths. S-9. Based on the feature point labeling, the spatial orientation of the CT three-dimensional volume data is aligned with the global coordinate system of the dental arch. The rotation center of the CT three-dimensional volume data is set at the origin of the global coordinate system of the dental arch. Then, the rotation angle obtained from S-6 is input to make the spatial orientation of the CT three-dimensional volume data aligned with the local coordinate system. S-10. By identifying the auxiliary positioning points indicated by the markers, move the positioning lines so that the intersection of the positioning lines in the coronal slice image aligns with the positioning points; S-11. Obtain the thickness of the orthodontic appliance at the location point based on the measurement direction on the sagittal slice image.

2. The method according to claim 1, characterized in that: The step S-1, which involves selecting multiple feature points on the outer surface of the original three-dimensional digital model of the dentition, involves selecting three non-collinear points on the outer surface of the gingiva of the original three-dimensional digital model of the dentition as feature points. The plane constructed based on the feature points is the global reference plane, and one point is selected on the outer surface of the teeth or the outer surface of the gingiva as a direction point.

3. The method according to claim 2, characterized in that: The construction of the global coordinate system for the dental arch based on feature points in step S-2 is based on the global reference plane and direction points. Any feature point is used as the origin of the coordinate system, and the vector direction from the origin to another feature point is used as the positive direction of the X-axis. The Y-axis is located in the global reference plane and its positive direction is determined by the right-hand rule. The Z-axis is perpendicular to the global reference plane and its positive direction points to the side where the direction point is located.

4. The method according to claim 1, characterized in that: The required positioning points for measurement in step S-3 include at least one of the following: the midpoint of the labial / buccal surface of the tooth, the midpoint of the labial / buccal gingival margin, the midpoint of the incisal edge of the incisor, the cusp of the other teeth, the midpoint of the palatal / lingual surface of the tooth, and the midpoint of the palatal / lingual gingival margin.

5. The method according to claim 4, characterized in that: When the positioning point is the midpoint of the labial / buccal surface of the tooth or the midpoint of the labial / buccal gingival margin, in step S-4, the Y-axis of the local coordinate system is perpendicular to the local reference plane and its positive direction is determined by the right-hand rule, and the positive direction of the Z-axis points towards the tooth. In step S-5, the plane formed by the X-axis and Y-axis of the local coordinate system is the horizontal plane, and the plane formed by the Y-axis and Z-axis is the sagittal plane. When the positioning point is the midpoint of the incisal edge of the incisor and the cusp of other teeth, in step S-4, the Z-axis of the local coordinate system is perpendicular to the local reference plane and its positive direction is determined by the right-hand rule, and the positive direction of the Y-axis points to the tooth. In step S-5, the plane formed by the X-axis and Z-axis of the local coordinate system is the horizontal plane, and the plane formed by the Y-axis and Z-axis is the sagittal plane. When the positioning point is the midpoint of the palatal / lingual surface of the tooth or the midpoint of the palatal / lingual gingival margin, in step S-4, the Y-axis of the local coordinate system is perpendicular to the local reference plane and its positive direction is determined by the right-hand rule, and the positive direction of the Z-axis points towards the tooth. In step S-5, the plane formed by the X-axis and Y-axis of the local coordinate system is the horizontal plane, and the plane formed by the Y-axis and Z-axis is the sagittal plane.

6. The method according to claim 1, characterized in that: In step S-7, feature points and auxiliary positioning points are modeled and marked on the original three-dimensional digital model of the dental arch. The modeling and marking are based on each feature point and auxiliary positioning point as the center of the sphere, and a three-dimensional sphere model with a diameter of 0.5~2.0 mm is established. The three-dimensional sphere model is retained or the three-dimensional sphere model is removed from the original three-dimensional digital model of the dental arch to form a pit, which serves as a visually recognizable mark.

7. The method according to claim 3, characterized in that: Step S-7 also includes modeling and marking the direction points; Step S-9 aligns the spatial orientation of the CT 3D volumetric data with the global coordinate system of the dental arch based on the marking of feature points and orientation points.

8. The method according to claim 1, characterized in that: Step S-10, which involves identifying the auxiliary positioning point indicated by the marker and moving the positioning line so that the intersection of the positioning lines in the coronal slice image aligns with the positioning point, specifically includes the following operations: By moving the positioning lines on the sagittal and axial slice images, the intersection of the positioning lines is located on the tooth where the positioning point is located. The auxiliary positioning point mark corresponding to the positioning point can be identified on the coronal slice image. The sagittal slice positioning line is moved on the coronal slice image to intersect with the auxiliary positioning point mark corresponding to the sagittal plane, and the axial slice positioning line is moved to intersect with the auxiliary positioning point mark corresponding to the horizontal plane. At this time, the intersection of the positioning lines in the coronal slice image is aligned with the positioning point.

9. The method according to claim 1, characterized in that: After performing step S-5 and before performing step S-8, the process also includes removing the tooth model corresponding to the marked points from the original three-dimensional digital model of the dentition to form a three-dimensional digital model of the dentition that resembles a "missing tooth". Furthermore, the auxiliary positioning point mentioned in step S-5 is not on the same tooth as the positioning point.

10. The method according to claim 1, characterized in that... It also includes the following steps: S-12. Based on the original three-dimensional digital model of the dentition described in S-1, obtain a three-dimensional digital model of the orthodontic dentition by rotating and / or translating the teeth; or, obtain a three-dimensional digital model of the orthodontic dentition by modeling or 3D scanning after the orthodontic cycle. S-13. Using the three-dimensional digital model of the orthodontic dentition obtained in S-12 as the original three-dimensional digital model of the dentition, the thickness of the orthodontic appliance at the positioning point is obtained according to S-1~S-11. Among them, the positioning points of the three-dimensional digital model of the orthodontic dentition are consistent with the positioning points of the original three-dimensional digital model of the dentition based on the positional relationship of oral anatomy on the teeth; The orthodontic appliances to be measured in S-8 are either made based on a three-dimensional digital model of the orthodontic arch or are orthodontic appliances after the treatment cycle.

Images