Techniques for defining an orientation of a model of a patient's dental arch anatomy within a global frame of reference

Abstract

A method for defining an orientation of an origin of a model of an anatomical structure of a patient's dental arch (302; 402) within a global reference frame comprises receiving a data set comprising a surface mesh representing a surface of the dental arch (302; 402) defined by a plurality of polygons. For each polygon, an external normal vector is determined. A vector sum of the external normal vectors defines a normal vector of an occlusal plane (412) and thus defines an orientation of the occlusal plane. A first rotation angle is determined for aligning the normal vector of the occlusal plane (412) with a first direction of the reference frame. An anterior side (504) of the dental arch (302; 402) is defined based on geometric properties of the surface mesh. A second rotation angle is determined for aligning an anterior-posterior direction of the dental arch (302; 402) with a second direction of the reference frame.

Description

Background Technology

[0001] Digital software tools used for anatomical treatment planning and / or prosthetic restoration design rely on precise scan data of the anatomical object of interest along with adjacent anatomical structures and artificial structures, such as bones, tissues, nerve bundles, organs and other anatomical structures / objects / features, and artificial structures such as surgical implants, abutments, other anchoring systems, artificial analogs of natural structures, and other naturally and artificially placed anatomical structures.

[0002] In the field of digital dentistry, anatomical scanning data is typically determined optically or radiographically. Optical scanners are common and economical for three-dimensional measurements directly from intraoral or extraoral impressions of oral surface structures. Surface data is usually represented by a surface mesh comprising triangular elements, which are routinely stored and exchanged between different systems in STL or similar surface definition file formats.

[0003] Radiographic scanners such as digital volumetric computed tomography (DVT) or computed tomography (CT) use X-rays to generate volumetric datasets of anatomical structures. Surface representations can also be determined from these datasets by applying thresholding methods, in which the intensity values ​​(measured in Hounsfield units) of individual scan elements (voxels) are analyzed to determine whether they exceed or fall below a specific threshold. Radiation-dense structures (hereinafter referred to as “volume-density” structures or objects), such as teeth, can be identified in this way, and the boundary surfaces of the identified volume-density scan structures can be modeled as triangulated surface data (e.g., a triangular surface mesh) and again saved and exchanged between systems in an STL or similar surface definition format.

[0004] The calculations using magnetic resonance (MR) scan data are more complex, where contour analysis methods can be applied, which operate based on the gradients of adjacent scan elements. However, in these cases, volumetric structures or objects, such as gingiva, gum tissue, and other tissues that are primarily soft tissue, can also be identified, and their boundary surfaces can be modeled as triangulated surface data for further processing.

[0005] Using the described analysis method, triangulated surface data of desired surfaces (such as, for example, visible surfaces) or boundary surfaces (such as, for example, inter-object surfaces between anatomical objects and / or structures in scan data or other invisible surfaces) can be obtained for all modalities (imaging devices).

[0006] Optical surface scanning data is often preferred for the evaluation or calculation of virtual dental restorations because it enables high accuracy without exposing the patient to high doses of radiation.

[0007] In the context of this disclosure, the term "dental restorative component" includes various types of objects that can be manufactured for treating dental aesthetics and / or defects. Examples include inlays, onlays, partial crowns, full crowns, telescopic crowns, fixed bridges, veneers, implant abutments, partial dentures, and complete dentures. Furthermore, in the context of this disclosure, for simplicity, the term "dental replacement component" is also included within the scope of the term "dental restorative component." The term "virtual dental restoration" (hereinafter referred to as "dental restoration") should be understood to include an appropriate electronic representation of the dental restoration, i.e., a digital three-dimensional representation of such a dental restorative component with sufficient accuracy, such as a surface representation. For example, to manufacture a dental restorative component, a CAD / CAM dataset corresponding to the virtual dental restoration can be forwarded to a manufacturing machine.

[0008] In the context of this disclosure, scanned data can be manipulated and transformed using a graphical user interface (in some cases, such manipulation and transformation are primarily interactive), which is often aided by algorithms.

[0009] Any of the steps in the computer-implemented method can be initiated (and / or triggered) directly or indirectly by user input, which can instruct the execution of the corresponding step (e.g., for determining either a rotation angle and / or a translation vector).

[0010] Because of the complex structure of scanned data and the various functional and aesthetic standards that must be met—which may include adjustments to relative dentition considering jaw movements, adjustments to adjacent teeth considering contact points, adjustments to preparation lines to achieve optimal marginal fit, compliance with minimum material strength to achieve satisfactory mechanical stability, consideration of desired tooth shapes in the anterior region, and so on—the process of designing custom dental restorations, even with the assistance of interactive computer-aided design tools, usually requires personnel with knowledge and experience in both dental restoration design and the use of such tools.

[0011] Designing custom prostheses presents another layer of complexity, as they are typically designed to replace anatomical objects removed from an existing oral condition. For example, a designer might be tasked with designing a temporary or permanent prosthesis that will be placed on an abutment attached to an implant, which will then be positioned within the alveolar bone of the extracted object. Designers can achieve greater accuracy by basing the prosthesis design on the actual anatomical contours of the patient within the alveolar bone left at the location where the extracted object previously resided. Therefore, it is often necessary to perform an optical rescan of the area after anatomical extraction before sending a surface model to the designer.

[0012] There is a growing need for immediacy in dental treatment. Specifically, there is a search for new ways to shorten the pre-planning of dental treatments, for procedures that can be completed in a single visit or in fewer visits than in the past.

[0013] When an anatomical object is targeted for extraction, methods are being sought to pre-plan the design of prostheses so that they are ready to be immediately installed in the patient's mouth in place of the extracted anatomical object. For example, it may be desirable to pre-plan implant placement and the design of temporary abutments so that implants can be placed immediately at the time of extraction (i.e., during the same visit), and custom-designed temporary abutments can be installed. It is also desirable to design and manufacture abutments, such as through additive or subtractive manufacturing (e.g., by 3D printing or milling, respectively), and to install them in the patient's mouth during the same visit, to accommodate immediate circumstances as much as possible.

[0014] Ideally, prostheses should be designed to fit and conform to the contours of the alveolar bone created during the extraction of the anatomical object. However, modern prosthesis design tools such as CAD / CAM systems receive only surface data (represented as a 3D triangular mesh, typically in STL format) without being aligned with any three-dimensional (3D) reference frame.

[0015] This could lead to poor fit or misalignment of the prosthesis when placed in the patient's mouth, potentially causing patient discomfort, ineffectiveness, or other treatment-related problems. Summary of the Invention

[0016] The purpose of this disclosure is to help mitigate at least some of the drawbacks of known dental restoration or prosthesis design and placement procedures. Specifically, the purpose of this disclosure is to help provide a method by which a model of the anatomy of at least a portion of a patient's dental arch is oriented (and / or aligned with) a global reference system, which allows for precise planning of dental treatment and prosthesis design. A particular objective is the ability to perform orientation (and / or alignment) for single and double dental arches, as well as full and partial dental arches.

[0017] This objective is achieved by: a computer-implemented method for defining the origin and axis position / orientation of a model of at least a portion of the anatomical structure of a patient's dental arch within a global reference frame; for dental treatment planning (such as object extraction planning, implant planning, crown design, and / or prosthesis design) using a model having a located / oriented origin and associated axis; a computer program product; and a computer-readable storage medium. The dependent claims represent embodiments of the respective independent claims.

[0018] According to a first aspect, a computer-implemented method is provided for defining the origin and the position / orientation of the axis of the origin (i.e., the position of the origin and the orientation of the axis of the origin) of a model of at least a portion of the anatomical structure of a patient's dental arch within a global three-dimensional (3D) reference frame, which may also be referred to in this disclosure as a universal reference frame, a universal coordinate system, a global coordinate system, or a global spatial reference frame.

[0019] The method includes the step of receiving a first dataset comprising a first surface mesh representing a surface topology of at least a portion of a patient's dental arch. Where the patient still has one or more teeth and / or implants, the surface topology may include the crowns of at least one or more teeth. The first surface mesh is defined by multiple polygons (e.g., triangles of different sizes and / or shapes).

[0020] The method further includes the step of determining, for each polygon, a normal vector oriented in an external direction (i.e., the side away from the dental tissue and towards the patient's oral cavity) of the first surface mesh. The method also includes steps such as determining, by calculation, a principal orientation vector defined by the sum of the normal vectors of at least a subset of the polygons, which defines the orientation of the occlusal plane of the patient's dental arch represented by the first surface mesh. The principal orientation vector represents the normal vector of the occlusal plane. The method further includes the step of determining a first rotation angle for aligning the direction of the principal orientation vector with a first principal component of the global spatial reference frame.

[0021] The method also includes a step of defining or identifying the anterior side of the patient's dental arch based on the geometric properties of the first surface mesh.

[0022] In one implementation, defining or identifying the anterior side of a patient's dental arch based on the geometric properties of a first surface mesh may include the following sub-steps: generating a planar projection of at least a selection of the mesh vertices of the first surface mesh onto the occlusal plane, thereby generating a point cloud of the surface mesh vertices in the occlusal plane.

[0023] Additional sub-steps may include fitting a segment of the parabola to the generated planar projection. Yet another sub-step may include defining the anterior aspect of the patient's dental arch by the location of the parabola's vertex. This implementation may be particularly suitable when the first surface mesh represents the complete dental arch or at least a portion of the dental arch including the anterior aspect.

[0024] In another embodiment, defining or identifying the anterior aspect of the patient's dental arch based on the geometric properties of the first surface mesh (which may be combined with another step for defining or identifying the anterior aspect of the patient's dental arch) may include determining at least an approximate orientation of the anterior-posterior vector directions of the patient's dental arch by a weighted sum of at least a subset of the normal vectors. Determining the weighted sum, such as by calculation, may include assigning a higher weight to the component of the normal vector parallel to the occlusal plane than to the component of the normal vector perpendicular to the occlusal plane. Determining the weighted sum may optionally include reversing the orientation of the normal vector pointing inwards towards the patient's dental arch.

[0025] The method also includes the step of determining a second rotation angle for aligning the anterior-posterior vector direction (e.g., an approximately left-right symmetric direction) of the patient's dental arch with a second principal component of the global spatial reference plane.

[0026] The method also includes the step of storing indications of a first rotation angle and a second rotation angle in association with a first surface mesh.

[0027] The method may further include the step of providing a second dataset comprising a model of the anatomy of at least that portion of the patient's dental arch in a global spatial reference frame. The model may include a first surface mesh supplemented with metadata indicating at least a first rotation angle and a second rotation angle. Optionally, the model may also include metadata indicating one or more translations to align the anatomy of at least that portion of the patient's dental arch with the origin of the global spatial reference frame.

[0028] The techniques disclosed herein provide a model of the anatomical structure of at least a portion of a patient's dental arch within a global spatial reference frame, which is adapted to perform one or more downstream tasks with correct and / or precise orientation. Downstream tasks may include virtual dental treatments, such as virtual planning and execution of extraction objects (e.g., teeth or implants), virtual planning of prostheses and / or generation of prosthesis models and / or virtual placement of implants. For these downstream tasks, it is crucial that the digital model of the patient's anatomy is correctly and precisely placed and oriented within the global spatial reference frame to allow for the use of numerous automated processing modules.

[0029] By providing the correct and precise position / orientation of the model's origin and its axes, one or more downstream process steps can thus be used to perform virtual preparation, processing, removal, etc., with improved accuracy.

[0030] The techniques disclosed herein may be particularly advantageous when the first surface grid represents only a portion of the patient's dental arch, such as representing only a few teeth and / or representing missing teeth only along one facial direction.

[0031] The first surface mesh included in the first dataset can be obtained from an intraoral scan of the anatomy of at least a portion of the patient's dental arch, or can be based on such an intraoral scan. Alternatively or additionally, the first surface mesh can be derived from or based on a dental impression or a model obtained from a dental impression (such as, for example, a plaster model).

[0032] Any crowns used in this article may be natural or artificial.

[0033] The first surface mesh or any other surface mesh disclosed herein may include smaller polygons in regions of greater curvature and larger polygons in regions of less curvature or flat regions. The polygons may be triangles, rectangles / quadrilaterals, pentagons, hexagons, and / or higher-order polygons.

[0034] In some embodiments, the first surface grid includes the crowns of one or more teeth and optionally includes at least the adjacent region of the gingiva. In other embodiments, the surface topology of the dentate portion of the dental arch (such as the gingival surface) can be represented by the first surface grid. In this case, the specific topology of the gingiva is represented by the first surface grid.

[0035] The exterior of the first surface mesh may include the side surfaces of the first surface mesh, with the surface envelope being generally convex relative to these side surfaces. Specifically, in the case of the dentate portion of the dental arch, the exterior of the first surface mesh may be oriented away from one or more teeth and / or gingiva. Alternatively or additionally, the exterior of the first surface mesh may be oriented towards the patient's oral cavity.

[0036] Calculating the sum of normal vectors can correspond to performing a summation and / or determining the average orientation of the normal vectors.

[0037] In some implementations, the sum of normal vectors may include only a subset of all polygons of the first surface mesh. For example, the extent of the first surface mesh may be determined by a bounding box that includes at least one or more tooth crowns. To perform the summation of normal vectors, only polygons within a subdomain of the bounding box can be used. The subdomain of the bounding box may include at least the occlusal surface of the tooth crown. Alternatively or additionally, the subset of polygons may be selected statistically and / or by progressively reducing multiple polygons, for example, within a predetermined region or volume of the first surface mesh. Alternatively or additionally, the first surface mesh and / or the bounding box may be cut off near the boundary between the tooth crown and the gingiva of one or more teeth. Thus, normal vectors associated with gingival regions far from the tooth crown can be excluded from the summation.

[0038] The summation can be simplified by using only a subset of the polygons. Alternatively or additionally, if regions far from the tooth crown are excluded, the principal orientation vector can be determined with good accuracy. In some implementations, the sum of the normal vectors may include all polygons associated with the crown of one or more teeth.

[0039] A global reference frame may include a Cartesian coordinate system, a cylindrical coordinate system, or a spherical coordinate system. Alternatively or additionally, a global reference frame may include a predetermined orientation of its principal orientation vector. A Cartesian coordinate system may be spanned by three orthogonal vectors or directions. The X and Y axes may span the horizontal XY plane. The Z axis may span the vertical direction and be perpendicular to the XY plane.

[0040] In one example, the global reference frame can have its vertical, front-back, and lateral directions relative to the upright position of the human body, which are respectively its Z-direction, Y-direction, and X-direction. The X-axis, Y-axis, and Z-axis can also be represented as the frontal axis, sagittal axis, and vertical axis, respectively; the XY plane, YZ plane, and XZ plane can be represented as the transverse plane, sagittal plane, and frontal plane, respectively.

[0041] The location / orientation of the origin and axes of the model defining the anatomical structure may include performing one or more rotations and / or one or more translations. A first rotation may include rotating the occlusal plane to align it with the XY plane of the Cartesian coordinate system, and / or orienting the occlusal plane parallel to the XY plane of the Cartesian coordinate system. A first translation may include translating the occlusal plane after the first rotation to pass through the origin along the vertical direction (Z=0) of the Cartesian coordinate system.

[0042] The second rotation may include rotating the anterior or posterior portion of the patient's dental arch to align it in the XY plane with a predetermined anterior direction (e.g., the Y direction). The posterior portion of the patient's dental arch may include or may be located at the position of the patient's molars (and / or third molars). Alternatively or additionally, the anterior portion of the patient's dental arch may include or may be located at the position of the patient's incisors.

[0043] In any case, the position of a patient's teeth can be related to the conventional anatomical position, even if, for example, one or more teeth are missing from the patient's dental arch due to previous extractions.

[0044] The second translation may include translating the occlusal plane after the second rotation to pass through the origin of the Cartesian coordinate system in the front direction (Y=0). Alternatively or additionally, the second translation may include translating the occlusal plane after the second rotation to pass through the origin of the Cartesian coordinate system in the lateral direction (X=0).

[0045] While examples of rotation and / or translation have been described relative to a Cartesian coordinate system with a vertical Z-axis, the techniques disclosed herein are independent of the choice of global spatial reference frame. Translation and / or rotation can be similarly defined for any global spatial reference frame and / or 3D coordinate system.

[0046] Rotation of the engagement plane can alternatively be represented as pitch, yaw, and roll. Correspondingly, rotation about the yaw axis can correspond to a second rotation and / or rotation within the engagement plane (and / or rotation that maintains the orientation of the principal orientation vector and / or the normal vector of the engagement plane). Similarly, rotation about the roll axis and / or about the pitch axis can correspond to a first rotation and / or rotation that changes the orientation of the normal vector (and / or principal orientation vector) of the engagement plane.

[0047] Similar to the use of the terms pitch, yaw, and roll, the biting plane can be associated with the plane in which the aircraft wing is roughly located. Rotating the biting plane (i.e., including its normal vector) to make it a horizontal plane (and correspondingly its normal vector) in the global reference frame can be associated with performing the aircraft's pitch and roll. Rotating the biting plane around its normal vector can be associated with performing the aircraft's yaw.

[0048] The first rotation angle can correspond to a rotation performed about a horizontal axis. Accordingly, the first rotation angle can be expressed as a vertical rotation angle because it is used to rotate the normal vector of the occlusal plane (e.g., the direction of the normal vector) to a vertical direction. The second rotation angle can correspond to a rotation performed about a vertical axis. Accordingly, the second rotation angle can be expressed as a horizontal rotation angle because it is used to rotate the occlusal plane in the horizontal plane.

[0049] Rotation (and / or rotation angle) can be represented by a transformation matrix (also called a rotation matrix). For example, rotation about the Z-axis in a Cartesian coordinate system can be represented by a block diagonal 3×3 matrix, which has (specifically first) a cosine term and a (at least partially negative) sine term for the rotation angle in the upper 2×2 block, and a lower block term of 1. Rotation about the X-axis or Y-axis is represented by simultaneous permutations of the columns and rows of the 3×3 matrix. Translation can be represented by (e.g., 3D) translation vectors (also called offset vectors).

[0050] The representation of the translation used to map the origin of the model and the global reference frame can depend on the order in which the rotation and translation are performed. The transformation matrix can be adapted to transform the first surface mesh to the orientation of the origin of the global spatial reference frame.

[0051] Fitting a line segment of a parabola to the generated plane projection can include applying the parameters of the parabola function (such as the exemplary parabola function x = ay) to the plane projection. 2The parameters a, b, and c of the + by +c function are fitted to the resulting point cloud of the first surface mesh in the biting plane. The parameters for fitting the parabolic function may include minimizing the sum of distances (e.g., squared distances) from points in the point cloud derived from the parabolic function.

[0052] The fitted segment of the parabola can be determined as follows. The parameters of the optimal parabola segment are determined relative to a first fixed (e.g., orthogonal) two-dimensional (2D) coordinate system in the plane by minimizing the sum of the squared (or mean squared) distances of points in the point cloud relative to the parabola segment. The parameters are repeatedly determined for several other fixed 2D coordinate systems, each rotated by a predetermined angle (e.g., 1 degree) relative to the first 2D coordinate system along a principal orientation defined by the principal orientation vector of the interlocking plane and / or within the interlocking plane (such as the Z-axis). The best fit of the parabola segment corresponds to the best values ​​in the different fixed coordinate systems.

[0053] Fitting the parameters of a parabolic function can include providing the parabolic function in multiple 2D coordinate systems at predetermined relative angles within the biting plane. These relative angles can correspond to the relative angles of the axes from one 2D coordinate system to the next. Minimizing the sum of these distances can include selecting 2D coordinate systems where the sum is less than the sum in any of the other coordinate systems.

[0054] Indications of the first rotation angle and the second rotation angle can be stored as metadata associated with the first surface mesh. In addition to the first rotation angle and the second rotation angle, the metadata can indicate one or more translations for aligning the biting plane with the origin, such as, for example, at least along the Z-axis and / or Y-axis of the global reference frame.

[0055] A second dataset can be generated, which includes the first surface mesh and metadata in an associated form, that is, one references the other or the two reference each other.

[0056] The first surface mesh can be obtained by intraoral surface scanning of at least a portion of the patient's oral cavity and / or at least a portion of the patient's dental arch.

[0057] Intraoral surface scanning may include scanning at least a portion of the patient's dental arch (also referred to as the first dental arch), and optionally scanning at least a portion of the patient's opposing dental arch (also referred to as the second dental arch), and / or optionally scanning at least a portion of an occlusal scan associated with the first and second dental arches, wherein at least a portion of the patient's posterior buccal or lingual jawbone is scanned while in occlusion. At least a portion of the second dental arch may include a second occlusal surface opposite to a first occlusal surface of at least a portion of the first dental arch.

[0058] The first occlusal surface may correspond to the exposed surface of the crown, and it has a contact point with the exposed surface of the crown of the second occlusal surface, and vice versa.

[0059] In occlusion, the patient's first and second dental arches, first occlusal surface, second occlusal surface, and occlusal plane may coincide (e.g., coincide point-by-point at the contact point between the first and second dental arches) or the first and second occlusal surfaces may be at least substantially parallel, i.e., their normal vectors point in substantially the same direction.

[0060] By processing intraoral surface scans, a precise geometric representation of at least a portion of the patient's dental arch anatomy can be obtained. This facilitates the precise planning of one or more downstream tasks and / or dental treatments.

[0061] The method may include the step of obtaining a first surface mesh by trimming a second surface mesh in a region representing the gingiva. The first surface mesh may represent the crown and at most the height of the gingiva (which is less than the height of the crown).

[0062] The second surface grid can represent a larger (e.g., more complete) area of ​​an intraoral scan.

[0063] By trimming the gingival region of the second surface grid, the approximately vertically oriented region of the second surface grid belonging to the gingiva on the outer side of the dental arch is trimmed and / or excluded from the first surface grid. Alternatively or additionally, the gingival region on the inner side of the dental arch (which is close to the horizontal direction of the maxilla and / or mandible) may be trimmed and / or excluded from the first surface grid.

[0064] Multiple normal vectors oriented approximately parallel to the occlusal plane on the outer side of the dental arch and / or multiple normal vectors oriented toward the center point of the dental arch and / or away from the occlusal plane (specifically shifted by a predetermined minimum distance, which may correspond to the typical height of the crown) do not need to be considered or can be removed from the processing. This saves computational and / or storage resources and / or increases the computational speed for providing a correctly oriented model, specifically without compromising the quality of the correctly oriented model.

[0065] A portion of the patient's dental arch may include a complete dental arch. Determining the anterior side of the patient's dental arch as the location of the parabola's vertex (the planar projection generated by fitting the parabola's segments to the grid vertices and / or the resulting point cloud) may be particularly suitable when the first surface grid represents the complete dental arch.

[0066] By defining a point cloud projected onto the occlusal plane, the line segment for fitting a parabola can be simplified to fitting a function of a single variable using a predetermined number of points. The fitted line segment of the parabola can extend substantially centrally within the point cloud along the length of the dental arch.

[0067] Determining the point cloud based on the vertices of a first surface mesh that essentially comprises only one or more teeth's crown reduces the number of points in the point cloud located at the inner and / or outer boundaries of the dental arch, compared to determining the point cloud based on the vertices of a second surface mesh that also represents a larger portion of the gingiva. This reduces the computational speed of the parameters for fitting the parabolic function, thus saving processing and / or storage resources.

[0068] The parameters for fitting the parabolic function can include providing the parabolic function at predetermined relative angles within the biting plane in multiple 2D coordinate systems (specifically, 2D coordinate systems rotated relative to the XY subsystem of the global spatial reference). Minimizing the sum of these distances (especially the squared distances) can include selecting 2D coordinate systems where the sum is less than the sum in any of the other coordinate systems.

[0069] The predetermined relative angle can be between 1 degree and 5 degrees. The predetermined relative angle can be either 1 degree or 2 degrees.

[0070] By selecting a parabolic function with the minimum sum of distances (especially squared distances) in a 2D coordinate system, the fitting of parabolic segments to the first surface grid included in the first dataset can be optimized.

[0071] A portion of the patient's dental arch may include a complete dental arch. Fitting a parabola segment to at least a portion of the patient's dental arch may include determining the approximate orientation of the anterior-posterior vector direction and / or the anterior direction (e.g., the first horizontal Y-axis in a Cartesian coordinate system) of the patient's dental arch by determining the sum of the normal vectors in at least a subset of the normal vectors (such as, for example, a weighted sum). Determining the weighted sum may include assigning a higher weight to the component of the normal vector parallel to the occlusal plane than to the component of the normal vector perpendicular to the occlusal plane. Determining the weighted sum may optionally include reversing the orientation of the normal vector pointing inwards towards the patient's dental arch.

[0072] By orienting the normal vector towards the outside of the patient's dental arch, cancellation between components located in the occlusal plane can be avoided. By performing a weighted summation, an approximate orientation of the Y-axis and / or a first 2D coordinate system for optimizing the parameters of the parabolic function can be determined. Therefore, the number of iterations required to determine the parameters of the parabolic function for different orientations of the 2D coordinate system can be minimized, improving computational speed and / or saving processing and / or storage resources.

[0073] For polygons whose displacement relative to the occlusal plane gradually increases, the weights can be reduced. By assigning higher weights to the sum of polygons that are relatively closer to the occlusal plane, errors due to divergent shapes (e.g., at the height of the gingiva) and / or due to missing teeth can be minimized.

[0074] Specifically, in addition to the first surface mesh, the first dataset may include at least one identifier for tooth position numbering. Tooth position numbering may be provided based on a reference anatomical model of the dental arch and / or according to a standard dental notation system. The dental notation system may be the FDI World Dental Federation (ISO) Recording System (FDI Recording System / ISO 3950), the Palmer Recording System, a universal numbering system, an alphanumeric recording system, or a paleoanthropological dental notation system.

[0075] The designated tooth position number can provide information about the position of the first surface grid of a segment along a parabola. For example, the tooth position number corresponding to a molar can indicate the position of an approximately straight segment along the parabola. Alternatively or additionally, the tooth position number corresponding to an incisor can indicate the position near the strongest curvature of the parabola. Further alternatively or additionally, the tooth position number corresponding to a canine or premolar can indicate the position on the parabola in a segment where the curvature transitions from strong curvature to an approximately vanishing curvature.

[0076] The approximate vanishing curvature and / or approximate straight line segment of a parabola do not need to have a strictly vanishing curvature in a mathematical sense; however, they can have curvatures smaller than those of anterior teeth.

[0077] Knowledge of tooth position numbers can be particularly advantageous when the first surface grid represents only a small number of teeth in a partial or incomplete dental arch. A tooth position number can be provided for the central tooth represented by the surface grid. While one tooth position number may be sufficient, providing two or more can improve the accuracy of determining the segments of a parabola.

[0078] Fitting a segment of a parabola to at least a portion of the patient's dental arch may include determining the center of the segment based on tooth position numbering and a target clinical location. The target clinical location may be based on a reference anatomical model (specifically, a complete double dental arch). Therefore, an approximate location along a segment having a predefined range of curvature can be determined.

[0079] The segments of a parabola fitted based on the specified tooth position number and target clinical location can be specifically used for a first surface grid that includes a portion of the dental arch. Using the target clinical location facilitates identifying the expected approximate curvature of the parabola segments (e.g., in terms of direction and / or magnitude).

[0080] The method may further include the step of determining a bounding box, which includes a first surface mesh and / or a portion of the first surface mesh representing at least a portion of a partial dental arch. For example, in the case of a double dental arch, two bounding boxes may be determined, one for at least a portion of the upper dental arch and the other for at least a portion of the lower dental arch. A first face of the bounding box may be selected to minimize the distance to the crown of one or more teeth. The occlusal plane may be determined to be parallel to the first face of the bounding box.

[0081] After the origin and axis orientation of a model of at least a portion of the patient's dental arch anatomy have been aligned with the first and second principal components of a global spatial reference system, the bounding box can be advantageously determined. The faces of the bounding box can then be specifically aligned with the principal components of the global spatial reference system (such as a Cartesian coordinate system).

[0082] In one implementation, the first face of the bounding box can be determined based on the teeth that are furthest apart from each other (such as the posterior molars and anterior incisors represented by the first surface grid).

[0083] If the first surface grid represents the complete dental arch, the bounding box typically has a length of 50 mm or longer along the direction perpendicular to the height of the crown. Generally, the bounding box of the first surface grid has an oblong shape with a ratio f (the ratio of the length perpendicular to the longest side to the length of the longest side) less than 0.65.

[0084] If the bounding box exceeds a threshold length (e.g., 50 mm) in a direction perpendicular to the crown height and / or if the bounding box has an elongated oval shape with a ratio less than a threshold ratio (e.g., less than 0.65), then the first surface grid can be determined to represent a complete dental arch. Alternatively, if the bounding box does not exceed a threshold length in a direction perpendicular to the crown height and / or if the bounding box does not have an elongated oval shape with a ratio less than a threshold ratio, then the first surface grid can be determined to represent a partial dental arch.

[0085] As an alternative to defining the occlusal plane as a plane parallel to a first facet of the bounding box, the method may include the step of determining the position of a first facet corresponding to the overlying plane of at least a portion of the dental arch by means of the tip of the crown of each of a predetermined set of teeth. This predetermined set of teeth may specifically include the first incisors and the last molars on one or both sides of at least a portion of the dental arch.

[0086] The overlay plane can correspond to a plane that substantially covers at least a portion of the dental arch by passing through a few particularly prominent points. The orientation of the protrusions can be relative to the outside of the patient's oral cavity and / or the first surface grid. For example, teeth in the lower dental arch may protrude upwards, and / or teeth in the upper dental arch may protrude downwards.

[0087] In some embodiments, the first face corresponding to the cover plane and the first face corresponding to the boundary box may coincide. In other embodiments, the first face corresponding to the cover plane and the first face corresponding to the boundary box may be slightly tilted relative to each other, for example, at an angle of less than 10 degrees.

[0088] The first face corresponding to the covering plane can advantageously be determined before or after the first rotation angle is determined and / or before or after the first rotation is performed. The first face corresponding to the bounding box is advantageously determined only after the interlocking plane has been aligned with the global spatial reference frame and / or after the first rotation has been performed, since the bounding box is typically constructed of faces parallel to the principal components of the global spatial reference frame.

[0089] The method may also include the step of determining the position of the occlusal plane by having a predetermined displacement from, for example, a first face of a bounding box or a first face corresponding to the covering plane in a direction toward the alveolar bone of the tooth and / or toward the root of the tooth.

[0090] Predetermined displacement may be caused by natural overbite, such as natural overbite of the maxilla (also called the maxilla) over the mandible (also called the mandible). The occlusal plane can specifically represent the average value of the occlusal surfaces of the teeth along the dental arch. This average value can be displaced relative to the most prominent end of the tooth (such as, for example, the incisor). Predetermined displacement can range from 2 mm to 5 mm, such as 4 mm.

[0091] Overbite in a normal dentition can range from 2mm to 5mm. Mild overbite can range up to about 9mm. Severe overbite can be greater than 9mm.

[0092] The indication of a predetermined first displacement value can be provided by user input.

[0093] In another embodiment, at least a portion of the patient's dental arch includes at least a portion of a double dental arch. The double dental arch may include the patient's lower dental arch and the patient's upper dental arch. The method also includes the step of determining the position of the occlusal plane as an average, such as an arithmetic mean, of the first surfaces (e.g., a bounding box or overlay plane) of the upper dental arch and the first surfaces (e.g., a bounding box or overlay plane) of the lower dental arch. The average, such as an arithmetic mean, can determine the position of the occlusal plane along the vertical axis in a particularly simple manner and / or without requiring the determination of a specific displacement value.

[0094] The method may further include the step of determining a first translation vector (also simply referred to as a first translation or vertical translation), such as, for example, a vertical translation vector, which is used to translate the engagement plane to a position at the origin of a first principal component of the global spatial reference system (e.g., Z=0 of the vertical Z-axis in a Cartesian coordinate system). The method may further include the step of storing the defined first translation vector in association with a first surface mesh.

[0095] The method may further include the step of determining a second translation vector (also called a second translation or horizontal translation) in the occlusal plane to the origin of the occlusal plane, the origin of which is located at the origin of a third principal component perpendicular to the second principal component of the global reference system (e.g., X=0 of the second horizontal axis X of the Cartesian coordinate system).

[0096] A second translation vector can be determined such that the anterior side of the patient's dental arch is located at the origin of the third principal component. The method may also include the step of storing an indication of the second translation vector in association with a first surface mesh.

[0097] Determining the second (e.g., horizontal) translation vector can be further based on determining the centroid of the patient's dental arch to locate the origin of the occlusal plane at the origin of the second principal component of the global reference frame (e.g., Y=0 of the first horizontal Y-axis).

[0098] The centroid of the parabola's line segment can be located inside the patient's dental arch. Alternatively or additionally, the centroid can be fictitious, that is, it can correspond to the centroid of a fictitious parabolic region at least partially defined by the parabola's line segment. The fictitious parabolic region can be defined posteriorly by a straight line parallel to the line connecting the first, second, or third molars on either side of the dental arch. Determining the second translation vector can include the step of determining the centroid of the parabolic region at least partially defined by the fitted line segment of the parabola. The parabolic region can be defined posteriorly in at least a portion of the dental arch by a line parallel to the third principal component of the global spatial reference system (and / or a transverse direction perpendicular to the anterior-posterior vector direction).

[0099] The method may also include the step of locating the centroid of the parabolic region at the origin of the second principal component of the global spatial reference frame.

[0100] The storage of indications for the first and second translation vectors associated with the first surface mesh can be performed jointly, and in some cases, also jointly with the storage of indications for the first and second rotation angles. The indications for the rotation angles and translation vectors can be specifically stored in a second dataset, which includes the first surface mesh and metadata indicating the rotation angles and translation vectors. Therefore, an origin oriented in a global spatial reference frame can be provided for a model of the anatomical structure of at least a portion of the patient's dental arch.

[0101] According to the second aspect, the orientation of the origin and axis of the model provided by the method of the first aspect can be used in conjunction with processes for digital dental treatment planning, digital object extraction planning, digital implant planning, digital artificial crown design and / or digital prosthesis design, as well as other uses.

[0102] According to another aspect, a computer program product is provided that, when executed by a computing device, causes the computing device to perform the steps of the method according to the first aspect.

[0103] According to another aspect, a computer-readable storage medium (including a carrier wave) is provided, the computer-readable storage medium including instructions that, when executed by a computing device, cause the computing device to perform the steps of the method according to the first aspect.

[0104] In all aspects of this disclosure, the position / orientation of the origin and axis of the digital patient model does not require a perfect position / orientation of the occlusal plane; however, a fairly close approximation of the origin and axis for the correct positioning / orientation of the digital patient model is generally sufficient. A fairly close accuracy could be, for example, an accuracy of 3 degrees or less of rotation from the ideal orientation of the model and / or an accuracy of 3 mm or less of translation from the ideal position.

[0105] Unless otherwise stated, the features of the embodiments of this disclosure presented above and below can be combined with each other, provided that such combination is considered technically feasible and possible by a person skilled in the art. Attached Figure Description

[0106] Figure 1 An exemplary flowchart illustrates a method for determining the position / orientation of the origin and axis of a digital model of the anatomy of at least a portion of a patient's dental arch within a global spatial reference frame.

[0107] Figure 2 The architecture of a computational device for determining the position / orientation of the origin and axes of a model defining at least a portion of the patient's dental arch within a global spatial reference frame is schematically illustrated. The computational device can be configured to perform this method.

[0108] Figure 3 An exemplary schematic perspective view of the upper dental arch is shown, indicating a global spatial reference frame and exemplary normal vectors associated with polygons representing the surface mesh of the upper dental arch.

[0109] Figure 4 An exemplary schematic side view of a double dental arch system, including both the upper and lower dental arches, is shown. The bounding box of each dental arch and the location of the occlusal plane are indicated.

[0110] Figure 5An exemplary schematic top view of the mandibular arch is shown, with a parabolic segment fitted to the arch, wherein the vertex of the parabola defines the anterior direction of the mandibular arch. As an example, tooth position numbers are provided for the complete dental arch.

[0111] Figure 6A and Figure 6B The surface representations of the complete double dental arches with arbitrary orientation and after alignment of the occlusal plane with the global spatial reference frame are schematically illustrated respectively.

[0112] Figure 7A and Figure 7B The surface representations of partial double dental arches with arbitrary orientations and after alignment of the occlusal plane with the global spatial reference frame are schematically illustrated respectively.

[0113] Figure 8A and Figure 8B The surface representations of the complete double dental arch are schematically illustrated with the occlusal plane aligned with the XY plane and the Y-axis in any orientation, and with the Y-axis aligned with the anterior direction.

[0114] Figure 9A and Figure 9B The surface representations of a portion of the double dental arch are schematically illustrated, showing the occlusal plane aligned with the XY plane and having an arbitrary orientation relative to the Y-axis, as well as the portion aligned with the Y-axis in the anterior direction.

[0115] Figure 10A and Figure 10B The double dental arches are schematically illustrated before and after translating the occlusal plane to align with the XY plane at Z=0.

[0116] Figure 11A and Figure 11B Two examples are shown, one with a normal vector and the other with a size that varies according to the local curvature of the surface. Detailed Implementation

[0117] Figure 1 An exemplary flowchart illustrates a computer-implemented method 100 for the location / orientation of the origin and axis of a model for defining at least a portion of the anatomical structure of a patient's dental arch within a global spatial reference frame.

[0118] Method 100 includes a step S102 of receiving a first dataset, the first dataset comprising a first surface mesh representing the surface topology of at least a portion of a patient's dental arch (and in some cases including the crowns of at least one or more teeth in the patient's teeth). The first surface mesh is defined by a plurality of polygons.

[0119] Method 100 further includes step S104 of determining a normal vector for each polygon of the first surface mesh, oriented outward toward the first surface mesh. Method 100 further includes step S106 of determining a principal orientation vector defined by the vector sum of at least a subset of the normal vectors, the principal orientation vector defining the orientation of the occlusal plane of the patient's dental arch represented by the first surface mesh. The principal orientation vector represents the normal vector of the occlusal plane.

[0120] Method 100 further includes step S108 of determining a first rotation angle for aligning the direction of the principal orientation vector with the first principal component of the global spatial reference frame.

[0121] Method 100 may further include step S109 of determining the anteroposterior vector direction of the patient's dental arch by determining a weighted sum of at least a subset of the normal vectors. Determining the weighted sum may include assigning a higher weight to the component of the normal vector parallel to the occlusal plane than to the component of the normal vector perpendicular to the occlusal plane. Determining the weighted sum may optionally include reversing the orientation of the normal vector toward the interior of the patient's dental arch.

[0122] Method 100 may also include step S110 of defining the anterior side of the patient's dental arch based on the geometric properties of the first surface mesh.

[0123] Step S110 may include a first sub-step S110-1, which generates a planar projection of at least a selection of the vertices of the first surface mesh onto the interlocking plane, thereby generating a point cloud of the surface mesh vertices in the interlocking plane.

[0124] Step S110 may also include a second sub-step S110-2, which fits the line segment of the parabola to the generated planar projection.

[0125] Step S110 may also include a third sub-step S110-3, which defines the anterior side of the patient's dental arch by the position of the vertex of the parabola.

[0126] Method 100 further includes step S112 of determining a second rotation angle for aligning the anterior-posterior vector direction of the patient's dental arch through the anterior side with a second principal component of the global spatial reference frame. Method 100 further includes step S114 of storing indications of the first and second rotation angles in association with a first surface mesh. This indication may be provided as metadata associated with the first surface mesh.

[0127] Figure 2 The architecture of a computing device 200 for the position / orientation of the origin and axis of a model for defining at least a portion of the anatomical structure of a patient’s dental arch within a global spatial reference frame is schematically illustrated.

[0128] The computing device 200 includes a receiving interface 202 configured to receive a first dataset comprising a first surface mesh representing the surface topology of at least a portion of a patient's dental arch (and in some examples, the crowns of at least one or more teeth in the patient's teeth). The first surface mesh is defined by a plurality of polygons.

[0129] The computing device 200 further includes a first determining unit 204 configured to determine a normal vector toward the outside of the first surface mesh for each polygon of the first surface mesh. The computing device 200 also includes a second determining unit 206 configured to determine a principal orientation vector defined by the vector sum of at least a subset of the normal vectors, the principal orientation vector defining the orientation of the occlusal plane of the patient's dental arch represented by the first surface mesh. The principal orientation vector represents the normal vector of the occlusal plane. The computing device 200 also includes a third determining unit 208 configured to determine a first rotation angle for aligning the direction of the principal orientation vector with a first principal component of the global spatial reference frame.

[0130] The computing device 200 may further include a weighted summation execution unit 209 configured to determine the anterior-posterior vector direction of the patient's dental arch by determining a weighted sum of at least a subset of the normal vectors. Determining the weighted sum may include assigning a higher weight to the component of the normal vector parallel to the occlusal plane than to the component of the normal vector perpendicular to the occlusal plane. Determining the weighted sum may optionally include reversing the orientation of the normal vector toward the interior of the patient's dental arch.

[0131] The computing device 200 may also include anterior defining unit 210, which is configured to define or identify the anterior side of the patient's dental arch based on the geometric properties of the first surface mesh.

[0132] The front defining unit 210 may include a first subunit 210-1, which is configured to generate a planar projection of at least a selection of the mesh vertices of the first surface mesh onto the occlusal plane, thereby generating a point cloud of the surface mesh vertices in the occlusal plane.

[0133] The front defining unit 210 may also include a second subunit 210-2, which is configured to fit the parabola's line segment to the generated planar projection.

[0134] The anterior defining unit 210 may also include a third subunit 210-3, which is configured to define the anterior aspect of the patient's dental arch by the position of the vertex of the parabola.

[0135] The computing device 200 also includes a fourth determining unit 212 configured to align the anterior-posterior vector direction of the patient's dental arch through the anterior side with the second principal component of the global spatial reference frame.

[0136] The computing device 200 also includes a storage unit (also referred to as memory) 214 configured to store indications of a first rotation angle and a second rotation angle in association with the first surface mesh. This indication can be provided as metadata associated with the first surface mesh.

[0137] The computing device 200 may also include a transmission interface 216. The receiving interface 202 and the transmission interface 216 may be implemented by an input / output (I / O) interface 218.

[0138] The computing device 200 may include at least one processor 220. The at least one processor 220 may implement the first determining unit 204, the second determining unit 206, the third determining unit 208, the front defining unit 210 and / or the fourth determining unit 212.

[0139] The computing device 200 can be configured to execute method 100.

[0140] The techniques disclosed herein (e.g., including method 100 and / or computing device 200) can be used for automated dental arch orientation. These techniques can be based on surface meshes representing the dental arch, such as a first surface mesh and / or a second surface mesh.

[0141] When proceeding to the acquisition step for obtaining intraoral surface scans, coarse automatic arch orientation can be performed based on heuristics. Automatic orientation should be performed if the case is not already sufficiently precise. Therefore, orientation can be skipped in certain cases, including those where an acquisition step has already been performed, those from a DW laboratory scanner, or those where automatic orientation would only produce minor changes (e.g., rotation less than 1.5 degrees and / or translation less than 1 mm), as these cases can be considered sufficiently precise in terms of positioning / orientation.

[0142] The automatic positioning and / or automatic orientation techniques disclosed herein (e.g., including method 100 and / or computing device 200) can be used for all combinations of complete and / or partial dental arches, as well as single and / or double dental arches. Specifically, the techniques disclosed herein are particularly suitable for semi-edentulous dental arches, or even edentulous dental arches.

[0143] In some implementations, the distinction between a complete dental arch and a partial dental arch can occur internally.

[0144] When the complete dental arch (such as the dental arch covering the two molars (also known as molars) as well as the incisors (also known as incisors) and canines) is represented by a first surface mesh, it may not be necessary to have further input for automatically locating / orienting the digital model of the dental arch in a global spatial reference frame.

[0145] When the first surface mesh represents only a portion of the dental arch, a tooth designation number may be required as an additional parameter to identify the teeth present in that portion of the arch, even if no specific location is specified. If no tooth designation number is available, for example in a model-only workflow, the orientation of the surface mesh representing a scan of a portion of the dental arch (also known as a partial scan) may be only partially completed in some cases.

[0146] Figure 3 A schematic example of an upper dental arch (also known as the maxilla) 302 is shown, which has a global 3D reference frame having an XY plane parallel to the occlusal plane of the upper dental arch, wherein the X-axis (e.g., from the left molar to the right molar) extends laterally and the Y-axis is oriented toward the front of the dental arch (and / or toward the incisors).

[0147] exist Figure 3 In the example shown, several normal vectors 304 of the surface region represented by different polygons of the first surface mesh representing the upper dental arch 302 are illustrated. Figure 3 The upper dental arch 302 in the image is an example of a complete single dental arch.

[0148] It should be noted that Figure 3 An exemplary location of the global spatial reference frame is shown as follows: Z=0 is located at the occlusal plane, and Y=0 is located at any position along the frontal direction and / or along the Y-axis.

[0149] Although Figures 3 to 10B An example of a Cartesian coordinate system is shown, in which the Z-axis is oriented vertically, the X-axis is oriented laterally, and the Y-axis is oriented in the direction of the front of the standing patient; however, the techniques disclosed herein are generally applicable to different choices of global reference systems.

[0150] Figure 4 A schematic side view of a complete double dental arch is shown, comprising an upper dental arch (also known as the maxilla) 302 and a lower dental arch (also known as the mandible) 402. Figure 4 The image schematically illustrates a double dental arch in a closed position (i.e., in occlusion).

[0151] exist Figure 4In this configuration, a first bounding box 404 surrounds the crown of the upper dental arch 302, and a second bounding box 406 surrounds the crown of the lower dental arch 402. The lower surface 408 of the first (maxillary) bounding box 404 is selected to ensure that the occlusal surface of the upper dental arch 302 is just contained within the first bounding box 404 without extending the first bounding box 404 further downward. Similarly, the upper surface 410 of the second (mandibular) bounding box 406 is selected to ensure that the occlusal surface of the lower dental arch 402 is just contained within the second bounding box 406 without extending the second bounding box 406 further upward.

[0152] Figure 4 The occlusal plane 412 is an example of its position relative to the double dental arches 302, 402, wherein the occlusal plane 412 is determined by the average of the lower surface 408 of the first bounding box 404 and the upper surface 410 of the second bounding box 406. Alternatively, the occlusal surfaces of each of the mandible and maxilla can be determined and averaged as a common occlusal surface 412.

[0153] Figure 5 The diagram schematically shows the planar projection of the mandibular arch 402 on the occlusal plane or a top view of the mandibular arch 402, wherein the teeth on the right side are numbered 48, 47, 46, 45, 44, 43, 42, and 41, and the teeth on the left side are numbered 31, 32, 33, 34, 35, 36, 37, and 38. These numbers are marked on the outside of the arch and adjacent to the positions of the corresponding teeth.

[0154] Figure 5 The diagram further illustrates, for example, fitting a segment of parabola 502 to the planar projection of the lower dental arch 402 according to substep S110-2. At reference numeral 504, the vertex of parabola 502 is indicated, for example, as determined according to substep S110-3. The Y-axis is essentially the axis of symmetry between the left and right sides of the dental arch 402, with the Y-axis passing through vertex 502.

[0155] The calculation of the rotation matrix can be performed in an automated program (e.g., represented as cAutomatedArchPreOrientation and the classes defined therein).

[0156] Any rotation can be represented by a rotation matrix, specifically including trigonometric functions of the rotation angle such as cosine and sine as matrix terms, and the total rotation matrix can be given by a product. Any translation can be represented by a translation vector.

[0157] According to an exemplary implementation, the first step is to perform an occlusal plane transformation (also known as bringing the dental arches into the occlusal plane). This may mean centering and orienting one or more dental arches such that the occlusal surface of the lower dental arch is oriented upwards and the occlusal surface of the upper dental arch is oriented downwards. Orientation can be performed by aligning the average vertex normal vector with the Z-axis. The upper dental arch normal vector can be calculated in reverse. This step can be performed by calling the automation function cAutomatedArchPreOrientation.mGetOclusalPlaneTransformation().

[0158] Figure 6A and Figure 6B Schematic examples of the complete double dental arches 302 and 402 before and after occlusal plane transformation are shown respectively. Occlusal plane transformation may include method steps S104, S106 and S108.

[0159] exist Figure 6A On the left side, the global reference frame is indicated by its XY plane and its YZ plane, and the anterior region of the scanned dental arch is indicated by the tooth positions 11 and 21 of the upper incisors. Figure 6B The image shows the expected position of the complete dental arch in the XY plane after rotating and translating the model of the patient's dental arch anatomy.

[0160] exist Figure 6B In the diagram, the occlusal plane 412 is aligned with the XY plane of the global 3D reference system. However, it shows cases where the horizontal direction and / or the direction within the occlusal plane and / or the anterior aspect of the dental arch are not aligned with the global reference system. The vertical plane 602 is at a random angle and random displacement to the maxillary incisor 11.

[0161] Figure 7A and Figure 7B Schematic examples of a two-part dental arch are shown before and after the change of occlusal plane. Figure 7A In this context, the occlusal plane is at any position and angle relative to the XY plane of the global 3D reference frame.

[0162] exist Figure 7A and Figure 7B In the figure, at reference number 602, the expected position of the complete dental arch in the XY plane is shown.

[0163] exist Figure 7B In this configuration, the occlusal plane 412 is aligned with the XY plane of the global reference system but shifted upwards parallel to it. The anteroposterior orientation of the dental arch is not yet correctly positioned; that is, it needs to be shifted parallel to the vertical plane YZ of the global reference system to serve as the plane of symmetry for the two dental arches, as indicated by the intended position of the complete dental arch 602. The portions of the two dental arches 302 and 402 are oriented relative to this intended position. Figure 7BShift to the left.

[0164] According to an exemplary implementation, the next step is to find a suitable orientation within the occlusal plane. Here, the calculations for a complete dental arch and a partial dental arch are different. To check whether the intraoral scan and / or the first surface mesh represents a complete or partial dental arch, the position and / or orientation of the scan and / or the first surface mesh can be transformed to the occlusal plane. For example, if both sides of the bounding box are greater than 50 mm, and if the shape is an oblong (defined as (length perpendicular to the longest side) / (length of the longest side) < 0.65), then the scan and / or the first surface mesh is considered to represent a complete dental arch.

[0165] Different automation programs or subroutines (e.g., cAutomatedPreOrientationForFullArch for a full dental arch and / or cAutomatedPreOrientationForPartialArch for a partial dental arch) can be used to perform the individual calculation steps.

[0166] For a full dental arch, the target can be (e.g., using the automation program cAutomatedPreOrientationForFullArch.mComputeAnteriorVector()) defined or identified as the anterior side of the arch. This can be achieved by accumulating surface normal vectors (e.g., for each polygon of the surface mesh representing the full dental arch), where inward-pointing normal vectors are inverted, normal vectors are weighted based on the dot product of the normal vector and point coordinates (normal vector * point coordinates) (which gives higher weight to radial (and / or horizontal) normal vectors), and / or normal vectors are weighted inversely proportional to their distance from the occlusal plane.

[0167] When a vector (or sum of vectors) pointing to the front of the dental arch is found, the orientation of the dental arch in the occlusal plane can be given by a matrix and / or angle that aligns the front vector with the Y-axis.

[0168] Figure 8A and Figure 8B The complete double dental arches are schematically shown before and after the transformation within the occlusal plane. Figure 8A In this context, the anterior aspect of the dental arch is not aligned with the vertical plane YZ of the global reference system, as can be seen from the incisor numbered 11. Figure 8B In the middle, the front side of the dental arch is basically aligned with the Y-axis, as shown by the position of the YZ plane and the incisor 12.

[0169] For the placement of a portion of the dental arch within the occlusal plane, in one implementation, it may be necessary, or at least advantageously, to know the tooth position number. Based on the tooth position number and the target clinical location, the following can be calculated: the central and / or average tooth position number, the position of the average tooth position number relative to the target clinical location, the bow direction, and / or the tangent at that location. For example, the automated program cAutomatedPreOrientationForPartialArch.mGetAverageAssignationInformation() can be used in this case. Assuming a symmetrical scan is performed around the tooth with the specified tooth position number, the scan (or the first surface grid representing the scan) can be centered on the calculated average tooth position.

[0170] As a next step, for example, the longest side of the dental arch can be aligned with the tangent of the dental arch using the automation subroutine mComputeOcclusionRotation.

[0171] Finally, the curvature of the dental arch can be determined or identified to determine whether the desired orientation has been achieved, or, for example, whether a 180-degree rotation (such as flipping between upper and lower arch orientations) is required, according to the automation subroutine mIsPiFlipNeeded. To determine or identify the arch orientation, the two furthest points of one or more scans can be calculated, for example, according to the automation subroutine mFindFarestPoint. These two points are considered as the chord of the dental arch, with the arch's centroid and / or center of gravity located inside the chord.

[0172] Figure 9A and Figure 9B The positions of the partial double dental arches 302, 402 are schematically shown before and after translation and / or before and after the application of the second translation vector in the occlusal plane.

[0173] exist Figure 9A In this context, the intended position of the complete dental arch at reference number 602 is shifted from partial dental arches 302 and 402 before translation, and the occlusal plane is shifted from the XY plane. Figure 9B In the process, partial dental arches 302 and 402 are placed at the expected position 602 of the complete dental arch after translation, and the occlusal plane 412 is located in the XY plane.

[0174] Positioning in the Z direction can initially be performed simply by centering. This may lead to undesirable results in the Z-position of the bite. Ultimately, Z-alignment can improve bite positioning. In the case of double arches, in the example of Cartesian coordinates, the average of the lowest point of the upper arch and the highest point of the lower arch can be aligned with the Z=0 level.

[0175] Figure 10A and Figure 10B The double dental arches before and after occlusal alignment are illustrated schematically. Figure 10A In this context, before translation and / or before applying the first translation vector, the engagement plane (not shown) lies below the XY plane of the Cartesian coordinate system. Figure 10B In the middle, the occlusal plane 412 coincides with the XY plane after translation.

[0176] For the case of a single dental arch, the dental arch can be moved according to the automation subroutine cAutomatedArchPreOrientation.OCCLUSION_OVERLAP so that the occlusal plane overlaps with the Z=0 level by, for example, 4 mm.

[0177] Figure 11A A first example of a triangular surface mesh with normal vectors is shown. Figure 11A In this context, vertex normals are depicted, not surface normals.

[0178] Vertex normals can be determined by averaging the surface normals of the polygons directly surrounding the vertex. Optionally, averaging the surface normals can include weighting the surface normals of each polygon by a function of the area enclosed by the polygons (e.g., by normalizing the area). For a smoother approximation, the surface normals of polygons farther from the vertex could also be considered in principle. However, such a smoother approximation may be less accurate.

[0179] exist Figure 11A In the example, the triangular surface mesh is shown only along the crown. No surface mesh is shown along the adjacent gingiva.

[0180] Figure 11B Another example of a triangular surface mesh is shown, in which smaller triangles are present in regions of greater curvature on the surface, and larger triangles are present in regions of less curvature on the surface.

[0181] For example, significant curvature, such as near-right angles, can occur between adjacent areas of teeth and missing teeth. Another example of areas with significant curvature is the posterior end of the dental arch, such as from the last molar toward the gum and pointing toward the temporomandibular joint.

Claims

1. A computer-implemented method (100) for defining the origin and orientation of an axis of a model of at least a portion of the anatomical structure of a patient's dental arch (302; 402) within a global spatial reference frame, the computer-implemented method comprising the steps of: - Receive (S102) a first dataset, the first dataset including a first surface mesh representing the surface topology of at least a portion of the patient's dental arch (302; 402), wherein the first surface mesh is defined by a plurality of polygons; - For each polygon of the first surface mesh, determine (S104) a normal vector (304) oriented towards the outside of the first surface mesh; - Determine (S106) the principal orientation vector defined by the sum of vectors of at least a subset of the normal vectors (304), the principal orientation vector defining the orientation of the occlusal plane (412) of the patient dental arch (302; 402) represented by the first surface mesh, wherein the principal orientation vector represents the normal vector of the occlusal plane (412); - Determine (S108) a first rotation angle for aligning the direction of the principal orientation vector with the first principal component of the global spatial reference frame; - Define (S110) the anterior side (504) of the patient's dental arch (302; 402) based on the geometric properties of the first surface mesh; - Determine (S112) a second rotation angle for aligning the anterior-posterior vector direction of the patient dental arch (302; 402) through the anterior side (504) with the second principal component of the global spatial reference frame; and - Store (S114) indications of the first rotation angle and the second rotation angle in association with the first surface mesh.

2. The method (100) of claim 1, wherein the first surface mesh is obtained from an intraoral surface scan of at least a portion of the anatomical structure of the patient's dental arch (302; 402).

3. The method (100) of claim 1 or 2, wherein defining (S110) the anterior side (504) of the patient dental arch (302; 402) based on the geometric properties of the first surface mesh comprises: - Generate (S110-1) at least a selection of the mesh vertices of the first surface mesh onto the planar projection in the occlusal plane (412), thereby generating a point cloud of the surface mesh vertices in the occlusal plane (412); - Fit the line segment of the parabola (502) to (S110-2) and project it onto the generated (S110-1) plane; as well as - The anterior side (504) of the patient's dental arch (302; 402) is defined (S110-3) by the position of the vertex (504) of the parabola (502).

4. The method (100) of any one of claims 1 to 3, wherein the polygon is selected from the group consisting of triangles, rectangles, pentagons, hexagons and / or higher-order polygons.

5. The method (100) of claim 4, wherein the first surface mesh comprises a plurality of polygons having different sizes and / or different numbers of vertices.

6. The method (100) of any one of claims 1 to 5, wherein the first rotation angle and / or the second rotation angle are represented by a transformation matrix adapted to transform the first dataset into the orientation of the origin within the global spatial reference frame.

7. The method (100) of any one of claims 1 to 6 in conjunction with claim 3, wherein fitting (S110-2) a segment of the parabola (502) to the generated (S110-1) plane projection comprises fitting the parameters of the parabolic function to the point cloud, wherein fitting the parameters of the parabolic function comprises minimizing the sum of the distances between points in the point cloud and the parabolic function, in particular the sum of the squared distances.

8. The method (100) of claim 7, wherein the parameters for fitting the parabolic function include providing the parabolic function in a plurality of two-dimensional 2D coordinate systems at predetermined relative angles to each other within the biting plane (412), and wherein minimizing the sum of the distances, particularly the squares of the distances, includes selecting a two-dimensional coordinate system in which the sum is less than the sum in any of the other coordinate systems.

9. The method (100) of any one of claims 1 to 8, wherein defining (S110) the anterior side (504) of the patient's dental arch (302; 402) based on the geometric properties of the first surface mesh comprises determining (S109) an approximate orientation of the anterior-posterior vector direction of the patient's dental arch (302; 402) by determining a weighted sum of at least a subset of the normal vector (304), wherein determining the weighted sum comprises applying a higher weight to the component of the normal vector (304) parallel to the occlusal plane (412) than to the component of the normal vector (304) perpendicular to the occlusal plane (412), wherein determining the weighted sum optionally comprises reversing the orientation of the normal vector (304) pointing inwards into the patient's dental arch (302; 402).

10. The method (100) of claim 9, wherein the weight is further reduced for polygons with increasing displacement relative to the biting plane (412).

11. The method (100) of any one of claims 1 to 10, wherein the first dataset further includes an identifier of a tooth position number at the corresponding position of the tooth.

12. The method (100) of claim 11 in conjunction with claim 3, wherein fitting (S110-2) a segment of the parabola (502) onto the generated (S110-1) plane projection comprises determining the center of the segment of the parabola (502) to be fitted (S110-2) based on the tooth position number and the target clinical position.

13. The method (100) of any one of claims 1 to 12, the method further comprising the step of determining a bounding box (404; 406) including the first surface mesh, wherein a first face (408; 410) of the bounding box (404; 406) is selected to minimize the distance to the crown of one or more teeth, and wherein the occlusal plane (412) is determined to be parallel to the first face (408; 410) of the bounding box (404; 406).

14. The method (100) of any one of claims 1 to 12, further comprising the step of determining the position of a first surface corresponding to a covering plane of at least a portion of the dental arch by means of the tip of the crown of each of a predetermined set of teeth, wherein the predetermined set of teeth specifically includes a first incisor and a last molar on one or each side of the at least portion of the dental arch.

15. The method (100) of claim 13 or 14, wherein the at least portion of the patient's dental arch (302; 402) comprises at least a portion of a single dental arch, wherein the single dental arch comprises the patient's lower dental arch (402) or the patient's upper dental arch (302), wherein the method (100) further comprises the step of: - The position of the occlusal plane (412) is determined by having a predetermined displacement from the first surface (408; 410) in the direction toward the alveolar bone of the tooth and / or toward the root of the tooth; - Determine a first translation vector for translating the occlusal plane (412) to a position at the origin of the first principal component of the global spatial reference system; as well as - The first translation vector is stored in association with the first surface mesh.

16. The method (100) of claim 8, wherein the predetermined displacement is in the range of 2 mm to 5 mm, preferably 4 mm.

17. The method (100) of claim 6 or 7, wherein the at least portion of the patient's dental arch (302; 402) comprises at least a portion of a double dental arch, wherein the double dental arch comprises the patient's lower dental arch (402) and the patient's upper dental arch (302), wherein the method (100) further comprises the step of: -The position of the occlusal plane (412) is determined as the average of the first surface (408) of the upper dental arch (302) and the first surface (410) of the lower dental arch (402), specifically the arithmetic mean; - Determine a first translation vector for translating the occlusal plane (412) to a position at the origin of the first principal component of the global spatial reference system; as well as - The first translation vector is stored in association with the first surface mesh.

18. The method (100) of any one of claims 1 to 17, further comprising the step of: - Determine a second translation vector in the occlusal plane (412) to the position of the origin of the occlusal plane (412), the position of the origin of the occlusal plane being located at the origin of a third principal component perpendicular to the second principal component of the global spatial reference system, such that the anterior side (504) of the patient's dental arch is located at the origin of the third principal component; and - The second translation vector is stored in association with the first surface mesh.

19. The method (100) of claim 18 in conjunction with claim 3, wherein determining the second translation vector further comprises: - Determine the centroid of the parabolic region that is at least partially defined by the line segment fitted (S110-2) of the parabola (502); as well as - Position the centroid of the parabolic region at the origin of the second principal component of the global spatial reference frame.

20. Use of the model oriented within the global reference frame according to any one of claims 1 to 19 in dental treatment planning, object extraction planning, implant planning, artificial crown design and / or prosthesis design.

21. A computer program product, when executed by a computing device (200), causes the computing device (200) to perform the steps of the method (100) as claimed in any one of claims 1 to 19.

22. A computer-readable storage medium including instructions that, when executed by a computing device (200), cause the computing device (200) to perform the steps of the method (100) according to any one of claims 1 to 19.

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