Techniques for defining a position of a model of an anatomical structure of a patient's dental arch within a global reference frame

Abstract

The present disclosure relates to a method for defining a position of an origin of a model of an anatomical structure of a patient's dental arch (302; 402) within a reference frame (XYZ), comprising receiving a first data set comprising a surface representation of a surface topology of the patient's dental arch (302; 402) and a split line representing a boundary between a tooth crown and adjacent soft tissue. A projection of the split line into an occlusal plane (412) is generated. A center of a tooth in the occlusal plane (412) is determined as a centroid of a region bounded by the projected split line. A segment of a parabola is fitted to the centroid. An anterior point of the patient's dental arch (302; 402) is identified as a vertex of the parabola. A first translation vector for positioning the anterior point at the origin of a third principal component (X) of the reference frame is determined.

Description

[0001] Digital software tools used for anatomical treatment planning and / or prosthetic restoration design rely on accurate scan data of the anatomical object of interest along with adjacent anatomical structures (e.g., bone, tissue, nerve bundles, organs, and other anatomical structures / objects / features) and artificial structures (e.g., surgical implants, abutments, other anchoring systems, artificial analogs of natural structures, and other natural and artificially placed anatomical structures).

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

[0003] For example, 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, where the intensity values ​​of individual scanning elements (voxels) are analyzed (measured in Hounsfield units) to determine whether they exceed or fall below certain thresholds. Radiometrically dense structures, such as teeth (hereinafter referred to as “volume density” structures or objects), 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., triangular surface meshes), and again saved and exchanged between systems in STL or similar surface definition formats.

[0004] The computations 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 a desired surface can be obtained for all modalities (imaging devices), such as a visible surface or boundary surface (e.g., inter-object surfaces between anatomical objects and / or structures in scan data or other invisible surfaces).

[0006] Because it can achieve high precision without exposing patients to high doses of radiation, optical surface scanning data is often preferred for evaluating or calculating virtual dental restorations.

[0007] In the context of this disclosure, the term "dental restoration portion" encompasses every type of object that can be fabricated for treating dental aesthetics and / or defects. Examples include inlays, onlays, partial crowns, crowns, telescopic crowns, bridges, veneers, implant abutments, partial prostheses, and prostheses. Furthermore, for simplicity, the term "dental restoration portion" also includes "dental replacement portion" in the context of this disclosure. The term "virtual dental restoration" (more simply referred to as "dental restoration" below) should be understood as containing a suitable electronic representation of the dental restoration, i.e., a digital three-dimensional representation of such a dental restoration portion with sufficient accuracy, such as a surface representation. For example, to fabricate a dental restoration portion, a CAD / CAM dataset of the corresponding 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, which in some cases is primarily interactive and often employs algorithmic assistance. Any of the computer-implemented method steps can be initiated and / or triggered directly or indirectly by user input, which may instruct the execution of the corresponding step, for example, determining either a rotation angle and / or a translation vector.

[0009] Due to the complex structure of scan data and the numerous functional aesthetic criteria that must be met—which may involve adjusting relative dentitions while considering jaw movement, adjusting adjacent teeth while considering contact points, adjusting preparation lines to achieve optimal marginal fit, meeting minimum material strength to achieve satisfactory mechanical stability, and considering the desired tooth shape in the anterior region, etc.—the process of designing custom dental restorations often requires individuals with knowledge and experience in dental restoration design and training in using such tools, even with the help of interactive computer-aided design tools.

[0010] To increase the complexity of designing custom prostheses, they are often designed to replace anatomical objects removed from an existing oral condition. For example, a designer may be responsible for designing temporary or permanent prostheses to be placed on an abutment attached to an implant, which is then placed in the alveolar socket of the extracted object. Designers can design prostheses based on the patient's actual anatomical contours within the remaining alveolar socket where the extracted object previously resided, thus achieving greater accuracy. Therefore, typically, an optical rescan of the area must be performed after anatomical object extraction before the surface model is sent to the designer.

[0011] In dental treatment, there is a growing need for greater immediacy. In particular, there is a search for new methods to shorten the pre-planning of dental treatment for procedures that can be completed in a single visit or in fewer visits than were previously possible.

[0012] In cases where the anatomical object is intended for extraction, methods are being sought to pre-plan the design of prostheses so that they are ready for immediate placement in place of the extracted anatomical object in the patient's mouth. For example, it may be necessary to pre-plan the placement of the implant and the design of a temporary abutment so that the implant can be placed immediately after extraction (i.e., during the same visit), and a custom-designed temporary abutment can be installed. It is also desirable to design and manufacture the abutment, for example, through additive or subtractive manufacturing methods such as 3D printing or milling, and to install the abutment in the patient's mouth during the same visit to best suit the immediate situation.

[0013] Ideally, a prosthesis should be designed to fit within and conform to the contour of the alveolar socket created during extraction of the anatomical object. However, modern prosthesis design tools, such as CAD / CAM systems, only receive surface data (represented as a 3D triangular mesh, typically in STL format) without alignment with any three-dimensional (3D) reference frame.

[0014] This could lead to poor fit or misalignment of such a prosthesis when placed in the patient's mouth, potentially causing patient discomfort, inefficiency, or other treatment-related problems.

[0015] The objective of this disclosure is to help alleviate at least some of the drawbacks of known dental restoration or prosthesis design and placement procedures. In particular, the objective 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 positioned within and / or aligned with a global reference system, which allows for precise planning of dental treatment and prosthesis design. Specifically, the objective is to enable positioning and / or alignment for single and double dental arches, as well as for complete and partial dental arches.

[0016] The objective is achieved by a computer-implemented method for defining the origin and axis of the anatomical structure of at least a portion of the patient's dental arch within a global spatial reference frame, for dental treatment planning, object extraction planning, implant planning, artificial crown design, and / or prosthesis design using a model with the located origin and associated axis, through a computer program product, and through a computer-readable storage medium.

[0017] Dependent claims represent embodiments of the corresponding independent claims.

[0018] According to a first aspect, a computer-implemented method is provided for defining the origin and the position of the axis of 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) spatial reference frame, i.e., the position of the origin and the orientation of the axis of origin, the global 3D spatial reference frame may also be referred to in this disclosure as a universal reference frame, a universal coordinate system, or a global coordinate system.

[0019] The method includes the step of receiving a first dataset comprising a surface representation (e.g., a surface mesh) of the surface topology representing 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 dataset also includes multiple dividing lines, each representing a boundary between the crown and adjacent soft tissue, such as the gingiva. The first dataset may also include multiple assigned tooth numbers, each tooth number associated with one of the crowns.

[0020] The first dataset may also include, for example, an indication of at least one rotation defined by a first rotation angle and a second rotation angle, the first rotation angle and the second rotation angle being used to orient the surface representation such that the principal orientation vector representing the normal vector of the occlusal plane is aligned with the first principal component of the global spatial reference frame, and such that the anterior-posterior vector direction of the patient's dental arch is aligned with the second principal component of the global spatial reference frame.

[0021] The method may include the step of generating a planar projection of each dividing line onto a plane parallel to the occlusal plane. While such projection may be beneficial, it is not a necessary element for implementing the methods of this disclosure and achieving its results.

[0022] The method may further include the following steps: for example, determining the projection position of the tooth center onto the occlusal plane for each planar projection dividing line that can be associated with the assigned tooth number, as the centroid (also known as the center of mass) of the region defined by the planar projection of the dividing line.

[0023] The method may further include the step of fitting a segment of the parabola to a determined projection location (also called position) of the centroid of the dividing line and / or the projection center of the tooth. The location and / or position may be provided in terms of coordinates, particularly within the model. The method may also include the step of defining the anterior point of the patient's dental arch as coinciding with the vertex of the parabola.

[0024] The method may further include the step of determining a first (also referred to as: first horizontal) translation vector for positioning the front point at the origin of the third principal component of the global spatial reference frame. The third principal component may be perpendicular to the first principal component and the second principal component of the global spatial reference frame. The method may further include the step of storing an indication of the first translation vector in association with a surface representation.

[0025] The method may include a first step block for determining a first (also known as: first horizontal) translation vector, a second step block for determining a second (also known as: second horizontal) translation vector, and / or a third step block for determining a third (also known as: vertical) translation vector.

[0026] It should be noted that the ordinal numbers of the translation vectors (e.g., first, second, etc.) do not necessarily correspond to the ordinal numbers of the principal components of the global reference frame, as each translation vector and principal component is numbered according to its order of appearance in the text. To give a clear example, if the global reference frame is a Cartesian coordinate system, where the X and Y axes span the horizontal plane and the Z axis spans the vertical direction, then the interlocking plane lies in the XY plane (especially after rotation), and the first (also called: first horizontal) translation vector extends along the (positive or negative) X-axis, which corresponds to the third principal component of the global reference frame. The second (also called: second horizontal) translation vector extends along the (positive or negative) Y-axis, which corresponds to the second principal component of the global reference frame. The third (also called: vertical) translation vector extends along the (positive or negative) Z-axis, which corresponds to the first principal component of the global reference frame.

[0027] As an alternative to the first step block for determining the first (also known as: the first level) translation vector and the second step block for determining the second (also known as: the second level) translation vector, a single step block can be used to determine a single level translation vector, which can also be represented as a centroid translation vector.

[0028] Independent of the choice of a single (also called: centroid) or first and second level translation vector used to determine the translation in the XY plane of the biting plane and / or Cartesian coordinate system, two or more translation vectors can be determined in any order. In particular, when performing two or more translations corresponds to a commutation operation of adding the corresponding translation vectors.

[0029] The method may further include the step of providing a second dataset comprising a model of the anatomy of at least a portion of a patient's dental arch located in a global spatial reference frame. The model may include a first dataset supplemented with metadata indicating one or more translation vectors and / or first and second rotation angles for aligning the occlusal plane and anterior-posterior vector directions with the principal components of the global spatial reference frame.

[0030] 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. This model is adapted to perform one or more downstream tasks at the origin of the global reference frame with correct and / or precise orientation and positioning. 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 multiple automated processing modules to utilize the digital model.

[0031] By providing the correct and precise position and axis orientation of the model's origin, one or more downstream tasks can be performed and / or prepared, particularly virtually, in the correct position and / or with improved accuracy, and thus enabling one or more downstream processing steps to be used to perform virtual preparation, processing, removal, etc., with improved accuracy.

[0032] The technology disclosed herein enables the automatic localization of at least a portion of the anatomical model of a patient's dental arch within a global reference frame, thereby accelerating localization and / or eliminating the need for highly skilled and experienced users who routinely must perform manual localization.

[0033] A global reference system may include a Cartesian coordinate system, a cylindrical coordinate system, or a spherical coordinate system. Alternatively or additionally, a global reference system may include a predetermined orientation of its principal orientation vector (or its axes). A Cartesian coordinate system may be spanned by three orthogonal vectors or directions. The X-axis and Y-axis may span the horizontal XY plane. The Z-axis may span the vertical direction and be perpendicular to the XY plane.

[0034] In this example, the global reference frame can have its vertical, frontal, and lateral directions relative to the upright position of the human body, i.e., its Z, Y, and X directions. The X-axis, Y-axis, and Z-axis can be alternatively represented as the frontal axis, sagittal axis, and vertical axis, respectively; the XY plane, YZ plane, and XZ plane can be represented as the lateral plane, sagittal plane, and frontal plane, respectively.

[0035] The assigned tooth numbers can be provided based on a reference anatomical model of the dental arch and / or according to a standard tooth position recording method. The tooth position recording method can be the FDI World Dental Federation (ISO) recording method (FDI Recording Method / ISO 3950), the Palmer Recording Method, the Universal Numbering System, the Alphanumeric Recording Method, or the Paleoanthropological Tooth Position Recording Method.

[0036] The assigned tooth numbers can provide information about the location of a segment representing a parabola on the surface. For example, the assigned tooth number corresponding to a molar can indicate the location of an approximately linear segment along the parabola. Alternatively or additionally, the assigned tooth number corresponding to an incisor can indicate the location near the strongest curvature of the parabola. Further alternatively or additionally, the assigned tooth number corresponding to a canine or premolar can indicate the location on the parabola where the curvature transitions from strong to approximately zero.

[0037] For example, in cases where crowns and / or segments of a patient's dental arch are missing, the assigned tooth numbers can be useful. These assigned tooth numbers reveal the clinically target location of the crowns within a (e.g., standard) anatomical model of the dental arch, and / or the expected relative positions and / or expected relative distances of the remaining teeth on the patient's dental arch. These expected relative positions and / or expected relative distances can be used when fitting a segment of a parabola to the remaining centroid of the segmentation line.

[0038] Approximate linear segments of a parabola that are approximately zero curvature and / or parabolic do not need to have strictly zero curvature in a mathematical sense; however, they may have curvature smaller than that of anterior teeth.

[0039] Knowing the assigned tooth numbers can be particularly advantageous when the surface representation represents only a small portion of the dental arch or an incomplete dental arch. Tooth numbers can be assigned to the central teeth represented by the surface mesh. While one tooth number may be sufficient, providing two or more tooth numbers can improve the accuracy of determining segments of a parabola.

[0040] In some embodiments, the projection of the tooth center location can be compared with the target clinical location.

[0041] The target clinical location can be based on a reference anatomical model. This allows for the determination of an approximate location along a segment with a predefined range of curvature. This can serve as a consistency check for the data included in the initial dataset.

[0042] Surface representations can be obtained from, or based on, an intraoral surface scan of a portion of the patient's dental arch anatomical structure. Alternatively or additionally, surface representations can be obtained from, or based on, a dental impression or a model obtained from, a dental impression (e.g., a plaster cast).

[0043] Any dental crown can be a natural crown or an artificial crown, such as an implanted artificial crown.

[0044] Surface representation can be obtained by processing intraoral surface scans of at least a portion of the patient's oral cavity and / or intraoral surface scans of at least a portion of the anatomical structures of the patient's dental arch.

[0045] 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 at least a portion of the patient's opposing dental arch (also referred to as: the second dental arch), and / or optionally 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 occlusal portion is scanned in an occlusal state. 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.

[0046] The first occlusal surface may correspond to the exposed surface of the crown, which has a contact point with the exposed surface of the crown of the second occlusal surface, and vice versa.

[0047] In occlusion, the patient's first and second dental arches, first occlusal surface, second occlusal surface, and occlusal plane may coincide (e.g., at least 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.

[0048] 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.

[0049] Surface representations may include representations of polygons, surface patches, faces, facets, and / or voxels.

[0050] In some embodiments, the surface representation may include a CAD / CAM representation having a regular (or conical) surface, including surfaces of revolution such as cylinders, cones, spheres, tori, etc., and / or ruled surfaces such as extruded surfaces. Alternatively or additionally, the CAD / CAM representation may include free surfaces (e.g., non-uniform rational basis splines, NURBS), thereby allowing more complex shapes to be represented via free surface modeling.

[0051] In other embodiments, the surface representation may include a CAE / FEA representation, which may be a surface mesh defined by multiple polygons.

[0052] A surface representation may include a surface mesh defined by multiple polygons. In particular, the polygons may be selected from a group including triangles, quadrilaterals (e.g., rectangles and / or trapezoids), pentagons, hexagons, and / or higher-order polygons. The surface mesh may optionally include multiple polygons with different sizes and / or different numbers of vertices.

[0053] Surface meshes may include smaller polygons in areas of greater curvature and larger polygons in areas of less curvature or flat areas.

[0054] Surface meshes may include polygons with different numbers of vertices (e.g., triangles and rectangles) and / or polygons with different sizes and / or shapes (e.g., the size of a triangle and / or the angle of a triangle). Different polygons can facilitate the representation of various curvatures (especially strong and weak).

[0055] In some embodiments, the surface representation includes the crown of one or more teeth and optionally includes soft tissue, such as gingiva, in at least adjacent areas. In other embodiments, the surface topology of the toothless portion of the dental arch (e.g., the gingival surface) may be represented by the surface representation. In this case, the specific topology of the gingiva is represented by the surface representation.

[0056] When a tooth is missing, the dividing line may be missing or replaced with another shape, such as a point representing the imaginary center of the missing tooth or several smaller dividing lines or points representing the location of the alveolar socket where the tooth's root passage is located. If the dividing line is missing and not replaced with any other geometric object, the associated assigned tooth number may not contribute to fitting the segment of the parabola. Alternatively or additionally, if the dividing line is replaced with another geometric object (e.g., one or a few points), the associated assigned tooth number may help fit the segment of the parabola using another geometric object for fitting.

[0057] The surface indicates that it can be bent at the crown of one or more teeth.

[0058] The method may include the step of obtaining a surface representation by clipping a second surface representation in an area representing the gingiva. The surface representation may represent the height of the crown and at most the height of the gingiva, said height being less than the height of the crown.

[0059] The second surface represents a larger (e.g., more complete) area of ​​an intraoral scan.

[0060] By cropping the area represented by the second surface of the gingiva, the approximately vertically oriented area of ​​the gingiva associated with the second surface on the outer side of the dental arch is cropped out and / or excluded from the surface representation. Alternatively or additionally, the gingival area in the horizontal direction on the inner side of the dental arch, approximating the maxilla and / or mandible, may be cropped out and / or excluded from the surface representation.

[0061] When the surface representation is a surface mesh, the normal vector can be associated with each polygon of the surface mesh (or, in particular, equivalently, with each vertex).

[0062] By trimming the second surface mesh to obtain a (particularly smaller) surface mesh, 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, and / or multiple vertices away from the occlusal plane (particularly 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 processing. This saves computational and / or memory resources, and / or increases the computational speed of providing a correctly oriented model, especially without compromising the quality of the correctly oriented model.

[0063] Fitting a segment of a parabola to a determined location of the center may include minimizing the sum of the distances (especially quadratic distances) from the center to the segments of the parabola.

[0064] The method may further include the step of determining the centroid of a parabolic region at least partially defined by the fitted segment of the parabola. The method may further include the step of determining a second (also referred to as a second level) translation vector for locating the centroid of the parabolic region at the origin of a second principal component of a global spatial reference frame. The method may further include the step of storing an indication of the second translation vector in association with a surface representation.

[0065] The first and second translation vectors may each be parallel to the occlusal plane (and / or perpendicular to each other). Alternatively or additionally, the centroid translation vector may correspond to the sum of the first and second translation vectors, and / or may be parallel to the occlusal plane.

[0066] A centroid translation vector can be determined to translate the occlusal plane to a position where the origin of the occlusal plane is located at the origin of the third principal component of the global reference system (e.g., X=0 of the first horizontal X-axis in a Cartesian coordinate system), perpendicular to the second principal component. The centroid translation vector can be determined such that the anterior aspect of the patient's dental arch is located at the origin of the third principal component. The centroid translation vector can also be determined based on positioning the origin of the occlusal plane at the origin of the second principal component of the global reference system (e.g., Y=0 of the second horizontal Y-axis) based on the determination of the patient's dental arch's center of mass.

[0067] The center of mass (also called the centroid) of the parabola segment may be located inside the patient's dental arch. Alternatively or additionally, the center of mass may be imaginary, for example, corresponding to the centroid of an imaginary parabolic region at least partially defined by the parabola segment.

[0068] The parabolic region can be defined at least partially by the fitted segment of the parabola. The parabolic region can be defined in the posterior direction of at least a portion of the dental arch by a line parallel to the third principal component of the global spatial reference frame (and / or a lateral direction perpendicular to the anterior-posterior vector direction).

[0069] As an alternative to locating the centroid of the parabolic region at the origin of the second principal component of the global reference system (e.g., Y=0 in a Cartesian coordinate system), a second translation vector can be determined to position a selected anterior region of the patient's dental arch or cavity at the origin of the second principal component of the global reference system. For example, the third principal component of the global reference system (e.g., the X-axis in a Cartesian coordinate system) can be determined as a line passing through a predetermined pair of left and right teeth (e.g., posterior or third molars, second or first molars), or an axis passing through the temporomandibular joint. Posterior molars may be the most anterior pair of teeth visible in a surface scan.

[0070] Alternatively or additionally, if the third molar is not visible on a surface scan, its position can be determined based on prediction. For example, the third molar may be located below the gum line or may have been previously extracted.

[0071] Further alternatively or additionally, the axis of the temporomandibular joint may be determined based on an anatomical model of the dental arch (e.g., a standard model), or based on scans of a mouth that is at least partially open and / or at a location where the teeth of the maxilla and mandible are not in contact.

[0072] The method may further include the step of determining a bounding box, the bounding box comprising a surface representation and / or a portion of the surface representation representing at least a portion of a 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 facet 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 approximately parallel to the first facet of the bounding box.

[0073] Advantageously, the bounding box can be determined after the positions of the origin and axes of at least a portion of the anatomical model of the patient's dental arch have been aligned with the first and second principal components of the global spatial reference system. In particular, the faces of the bounding box can each be aligned with the principal components of the global spatial reference system, such as a Cartesian coordinate system.

[0074] In one embodiment, the first face of the bounding box may be determined based on the teeth that are furthest apart from each other, such as the posterior molars and anterior incisors represented by the surface representation.

[0075] If the surface representation represents the complete dental arch, the bounding box can typically have a length of 50 mm or more along the direction perpendicular to the height of the crown. Generally, the bounding box of the surface representation is elliptical in shape, where the ratio of the length perpendicular to the longest side to the length of the longest side is less than 0.65.

[0076] If the bounding box extends beyond a threshold length (e.g., 50 mm) in the direction perpendicular to the crown height, and / or if the bounding box has an elliptical shape with a ratio less than a threshold ratio (e.g., less than 0.65), then the surface representation can be determined to represent a complete dental arch. Alternatively, if the bounding box does not extend beyond a threshold length in the direction perpendicular to the crown height, and / or if the bounding box does not have an elliptical shape with a ratio less than a threshold ratio, then the surface representation can be determined to represent a partial dental arch.

[0077] As an alternative to defining the occlusal plane as a first face parallel to the boundary frame, the method may further include the step of determining the position of the first face corresponding to the overlying plane of at least a portion of the dental arch by means of the tip of the crown of each tooth in a predetermined set of teeth. Specifically, the predetermined set of teeth may include the first incisor and the last molar on one or both sides of at least a portion of the dental arch.

[0078] A covering plane may correspond to a plane that substantially covers at least a portion of the dental arch by passing through a few particularly prominent points. The direction of the protrusion may involve the exterior of the patient's oral cavity and / or surface representation. For example, teeth in the lower dental arch may protrude upwards, and / or teeth in the upper dental arch may protrude downwards.

[0079] In some embodiments, the first face corresponding to the covering plane and the first face corresponding to the boundary frame may coincide. In other embodiments, the first face corresponding to the covering plane and the first face corresponding to the boundary frame may be slightly tilted relative to each other, for example, by an angle of less than ten degrees or less than five degrees.

[0080] The first face corresponding to the covering plane can be advantageously determined before or after determining the first rotation angle and / or before or after performing the first rotation. It is advantageous to determine the first face corresponding to the bounding box only after the interlocking plane has been aligned with the global spatial reference frame and / or after performing the first rotation, since the bounding box is typically constructed to have faces with principal components parallel to the global spatial reference frame.

[0081] In an embodiment, at least a portion of the patient's dental arch may include at least a portion of a single dental arch. The single dental arch may include the patient's lower dental arch or the patient's upper dental arch. The method may further include the step of determining an approximate position of the occlusal plane by having a predetermined displacement relative to, for example, a first surface of a boundary frame or a first surface corresponding to an overlay plane, in a direction toward a dividing line and / or in a direction toward the alveolar socket of the tooth and / or toward the root of the tooth.

[0082] The method may further include the step of determining a third (e.g., vertical) translation vector (also simply referred to as: third translation) for translating the occlusal plane to a position at the origin of a first principal component of a 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 an indication of the third (e.g., vertical) translation vector in association with a surface representation.

[0083] The predetermined displacement can be attributed to natural overbite, such as the maxilla (also called the maxilla) naturally overbiting the mandible (also called the mandible). In particular, the occlusal plane can represent the average value of the occlusal surfaces of the teeth along the dental arch. The average value can be displaced relative to, for example, the most prominent end of the incisor.

[0084] The planned displacement can be in the range of 2 mm to 5 mm, for example, 4 mm. Normal overbite can be in the range of 2 mm to 5 mm. Mild overbite can be in the range of up to approximately 9 mm. Severe overbite can be in the range of more than 9 mm.

[0085] The value of the predetermined first displacement can be provided by user input.

[0086] In another embodiment, at least a portion of the patient's teeth includes at least a portion of a double dental arch. The double dental arch includes the patient's mandibular arch and the patient's maxillary arch. The method may further include the step of determining the position of the occlusal plane as the average, for example, an arithmetic mean, of a first facet (e.g., a bounding box or overlay plane) of the maxillary arch and a first facet (e.g., a bounding box or overlay plane) of the mandibular arch. The method may further include the step of determining a third (e.g., vertical) translation vector for translating the occlusal plane to a position at the origin of a first principal component of a 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 an indication of the third translation vector in association with a surface representation.

[0087] The position of the occlusal plane along the vertical axis can be determined in a particularly simple way and / or without needing to determine a specific displacement value relative to the first face of a single dental arch, using averages, such as arithmetic mean and / or average.

[0088] The third (also known as: vertical) translation may include translating the occlusal plane after the second rotation to pass through the origin in the positive direction (Y=0 in the Cartesian coordinate system). Alternatively or additionally, the third (also known as: vertical) translation may include translating the occlusal plane after the second rotation to pass through the origin in the lateral direction (X=0 in the Cartesian coordinate system).

[0089] Translation can be represented by a three-dimensional (3D) translation vector (also known as a shift vector).

[0090] The representation of translations used to map the origin and global reference frame of the model can depend on the order in which rotations and translations are performed. In particular, the techniques disclosed herein can be based on performing rotations first, followed by translations.

[0091] A transformation matrix (also known as a rotation matrix) can be adapted to transpose a surface representation to the position of the origin of a global spatial reference frame.

[0092] Indicators for at least one rotation used in the orientation surface representation may include an indication of a first rotation angle for aligning the direction of a principal orientation vector perpendicular to the occlusal plane with a first principal component of the global spatial reference frame. The indication may also include an indication of a second rotation angle for aligning the anterior-posterior vector direction of the patient's dental arch with a second principal component of the global spatial reference frame.

[0093] The first rotation angle and / or the second rotation angle can be represented by a transformation matrix adapted to transpose the surface representation to the position of the origin and its axis in the global space reference frame.

[0094] When the surface representation is a surface mesh, the first rotation angle can be determined as follows. For each polygon, a normal vector oriented in an external direction of the surface mesh can be determined, the normal vector being away from the side of the tooth tissue and towards the patient's oral cavity.

[0095] Specifically, the principal orientation vector perpendicular to the occlusal plane, obtained in any coordinate system and / or via intraoral scanning, can be defined by the sum of the normal vectors of at least a subset of the polygon, or equivalently by the sum of the normal vectors of at least a subset of the vertices of the surface mesh. Determining the first rotation angle is equivalent to aligning the direction of the principal orientation vector with the first principal component of the global spatial reference frame.

[0096] To determine the second rotation angle, the anterior aspect of the patient's dental arch can be determined based on the projection center of the tooth and / or the geometric properties of the surface mesh.

[0097] In an embodiment, identifying the anterior aspect of a patient's dental arch based on the geometric properties of the surface mesh may include selecting at least one mesh vertex from the surface mesh and projecting it onto a plane in the occlusal plane, thereby generating a point cloud of surface mesh vertices in the occlusal plane. A segment of a parabola may be fitted to the generated plane projection. The anterior aspect of the patient's dental arch may be defined by the position of the vertex of the parabola. This embodiment may be suitable, particularly when the surface mesh represents a complete dental arch or at least a portion of the dental arch including the anterior aspect.

[0098] In another embodiment, identifying the anterior aspect of a patient's dental arch based on the geometric properties of a surface mesh (which may be combined with any other embodiments for identifying the anterior aspect of a 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 normal vectors. Determining the weighted sum may include assigning a higher weight to the normal vector components parallel to the occlusal plane than to the normal vector components perpendicular to the occlusal plane. Determining the weighted sum may optionally include reversing the orientation of the normal vectors pointing inwards into the patient's dental arch.

[0099] Fitting a segment of a parabola to its vertices using a point cloud based on surface mesh vertices, a weighted sum based on normal vectors, and / or based on the projection center of the teeth can produce the same (or at least sufficiently similar) results.

[0100] Determining the anterior side of the patient's dental arch as the location of the vertex of the parabola may be particularly suitable in the case of representing a surface representation of the complete dental arch, wherein the segment of the parabola is fitted to the generated planar projection of the grid vertex, and / or fitted to the resulting point cloud, and / or fitted to the projection center of the tooth.

[0101] By defining a point cloud projected onto the occlusal plane, fitting a segment of the parabola can be simplified to fitting a univariate function using a predetermined number of points. The fitted segment of the parabola can extend substantially centered within the point cloud along the length of the dental arch.

[0102] Fitting a segment of a parabola to the projection center of a tooth is particularly efficient in terms of computational resources (e.g., processing resources and / or memory resources) because for a single (upper or lower) dental arch, the number of points to be fitted is less than twenty (and / or at most sixteen).

[0103] Determining the point cloud based on the vertices of a surface mesh that essentially comprises only one or more teeth's crown reduces the number of points in the point cloud 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 improves the computational speed for fitting the parameters of a parabolic function, thus saving processing and / or memory resources.

[0104] Fitting a segment of a parabola may include fitting a parabolic function, which in particular may have three parameters. Determining the parameters of the parabolic function may include providing the parabolic function in a plurality of 2D coordinate systems (particularly, rotated relative to the XY subsystem of the global spatial reference frame) at predetermined relative angles within the biting plane. Minimizing the sum over (particularly quadratic) distances may include selecting 2D coordinate systems where the sum is less than the sum in any other coordinate system.

[0105] (Especially for single-variable) parabolic functions can depend on the choice of the 2D coordinate system.

[0106] The predetermined relative angle can be between 1 degree and 5 degrees. The predetermined relative angle can be 1 degree or 2 degrees.

[0107] By selecting a parabolic function with the minimum sum of distances (especially quadratic) in a 2D coordinate system, the fitting of parabolic segments to the surface meshes included in the first dataset can be optimized.

[0108] Fitting a segment of a parabola to at least a portion of the patient's dental arch may include determining an approximate orientation of the anterior-posterior vector direction (and / or anterior direction, such as the second horizontal Y-axis in a Cartesian coordinate system) of the patient's dental arch by determining a (particularly weighted) sum of normal vectors over at least a subset of the normal vectors. Determining the weighted sum may include assigning a higher weight to the normal vector components parallel to the occlusal plane than to the normal vector components perpendicular to the occlusal plane. Determining the weighted sum may optionally include reversing the orientation of the normal vectors pointing inwards into the patient's dental arch.

[0109] By orienting the normal vector towards the outside of the patient's dental arch, cancellation between components within the occlusal plane can be avoided. By performing a weighted sum, 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. This minimizes the number of iterations required to determine the parameters of the parabolic function for different orientations in the 2D coordinate system, improving computational speed and / or saving processing and / or memory resources.

[0110] For polygons that gradually shift away from the occlusal plane, the weights can be reduced. By assigning more weight to the sum towards polygons closer to the occlusal plane, errors caused by divergent shapes (e.g., at the height of the gums) and / or by missing teeth can be minimized.

[0111] A second rotation angle can be determined to align the anterior-posterior vector direction of the patient's dental arch (e.g., an approximately left-right symmetric direction) with the second principal component of the global spatial reference plane.

[0112] Indications of the first and second rotation angles can be stored in association with the surface representation (especially the surface mesh).

[0113] Calculating the sum over the normal vectors can correspond to performing a summation and / or determining the average orientation of the normal vectors.

[0114] In some embodiments, the summation of normal vectors may include only a subset of all polygons of the surface mesh. For example, the extent of the surface mesh can be determined by a bounding box that includes at least one or more teeth's 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 crown. Alternatively or additionally, a subset of polygons may be selected statistically and / or by, for example, gradually decreasing the number of polygons within a predetermined region or volume of the surface mesh. Alternatively or additionally, the surface mesh and / or bounding box may be cut off at the boundary between the crown and gingiva near one or more teeth. Thus, normal vectors associated with gingival regions spaced away from the crown can be excluded from the summation.

[0115] The summation can be simplified by using only a subset of the polygons. Alternatively or additionally, if regions of the crown far from the tooth are excluded, the alignment of the principal orientation vector and / or the second principal component with respect to the global reference frame can be determined with good accuracy. In some embodiments, the summation over the normal vectors may include all polygons associated with the crowns of one or more teeth.

[0116] Given that the assigned tooth numbers of all or most of the patient’s dental arch are known, the approximate position of the anterior side of the patient’s dental arch can be derived from the assigned tooth numbers (especially the assigned tooth numbers of the incisors) and the corresponding projection centers of the teeth.

[0117] When fitting a segment of a parabola to a point cloud of a surface mesh, the approximate location of the anterior aspect of the patient's dental arch may not be known if no or only a few assigned tooth numbers are provided. In this case, fitting the segment of the parabola to the generated planar projection may include fitting the parameters of the parabolic function to the resulting point cloud of the surface mesh in the occlusal plane. Fitting the parameters of the parabolic function may include minimizing the sum of (e.g., quadratic) distances from points in the point cloud of the parabolic function.

[0118] Any technique used to determine the anterior aspect of the dental arch can utilize statistical methods (e.g., in fitting a segment of a parabola to multiple points, or in performing a weighted summation on the normal vector).

[0119] Defining the orientation of the origin and axes of a model of an anatomical structure (also known as: orienting the origin and axes of a model of an anatomical structure) may include performing one or more rotations. Alternatively or additionally, defining the location of the origin of a model of an anatomical structure (also known as: positioning the origin of a model of an anatomical structure) may include one or more translations.

[0120] The 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 to be parallel to the XY plane of the Cartesian coordinate system.

[0121] The second rotation may include rotating the anterior (and / or posterior) portion of the patient's dental arch to align with a predetermined forward direction (e.g., the Y direction) in the XY plane. 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.

[0122] The first (also referred to as: first horizontal) translation and / or the second (also referred to as: second horizontal) translation may include translating the origin of the occlusal plane after the first and second rotations to pass through the origin along the first and / or second horizontal directions (X=0 and / or Y=0, respectively).

[0123] The third (also known as: vertical) translation may include translating the biting plane after the first rotation (and optionally including the second rotation) to pass through the origin along the vertical direction (Z=0) of the Cartesian coordinate system.

[0124] In any case, even if one or more teeth are missing, for example, due to previous extraction from the patient's dental arch, the position of the patient's teeth may be related to the conventional anatomical position.

[0125] While examples of rotation and / or translation have been described with respect to Cartesian coordinate systems 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 either a global spatial reference frame or a 3D coordinate system.

[0126] Rotation of the bite 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 bite plane (and / or rotation that maintains the orientation of the principal orientation vector and / or the normal vector of the bite plane). Similarly, rotation about the roll axis and / or about the pitch axis can correspond to a first rotation and / or rotation of the bite plane that alters the orientation of the normal vector (and / or the principal orientation vector) of the bite plane.

[0127] Similar to the use of the terms pitch, yaw, and roll, the biting plane can correspond to the plane on which the aircraft wing approximately rests. Rotating the biting plane (i.e., its normal vector) to a horizontal plane and its normal vector that reach the global reference frame can correspond to performing a combination of pitch and roll on the aircraft. Rotating the biting plane about its normal vector can correspond to performing a yaw on the aircraft.

[0128] The first rotation angle can correspond to performing a rotation about a horizontal axis. Correspondingly, 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 the vertical direction. The second rotation angle can correspond to performing a rotation about a vertical axis. Correspondingly, the second rotation angle can be expressed as a horizontal rotation angle because it is used to rotate the occlusal plane into the horizontal plane.

[0129] Rotation (and / or rotation angle) can be represented by a transformation matrix (also known as a rotation matrix). For example, rotation about the Z-axis of a Cartesian coordinate system can be represented by a block-diagonal 3×3 matrix having cosine and (at least partially negative) sine entries for the rotation angle in the upper 2×2 block and 1 as an entry in the lower block, wherein rotation about the X or Y axis is represented by simultaneous permutations of the columns and rows of the 3×3 matrix and corresponding (e.g., second and / or third) rotation angles as independent variables of trigonometric functions.

[0130] Indications for first, second, and / or third translation vectors used to align the occlusal plane with the origin of the global reference system (e.g., at least along the Z-axis and / or Y-axis), and / or indications for first and second rotation angles, may be stored as metadata associated with the surface representation.

[0131] A second dataset can be generated, which includes surface representation and metadata in an associative manner.

[0132] Storing any indications of translation vectors and / or rotation angles in association with the surface representation can be performed jointly. Specifically, the indications of rotation angles and translation vectors can be stored in a second dataset, which includes the surface representation and metadata indicating the rotation angles and translation vectors. Thus, a model of the anatomy of at least a portion of the patient's dental arch can be set with an origin positioned within a global spatial reference frame.

[0133] The model, based on the methodological positioning within a global spatial reference frame, can be used for dental treatment planning, object extraction planning, implant planning, artificial crown design, and / or prosthesis design.

[0134] Using the origin and axis positions of the model does not necessarily require perfect orientation and / or position of the occlusal plane.

[0135] 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 method aspect.

[0136] According to another aspect, a computer-readable storage medium including a carrier wave is provided, 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.

[0137] In all aspects of this disclosure, the location and axial orientation of the origin of the digital patient model do not require a perfect position of the occlusal plane or the origin; however, a generally close approximation of the correct location of the origin of the digital patient model is usually sufficient. Sufficiently close accuracy can be, for example, a rotation of three degrees or less from the perfect orientation of the model and / or a translation of 3 mm or less from the perfect position.

[0138] Unless otherwise stated, the features of the embodiments of this disclosure presented above and below can be combined with each other, wherein such combinations are considered technically feasible and possible by those skilled in the art. Attached Figure Description

[0139] Figure 1 A schematic exemplary flowchart illustrates the method for determining the location 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.

[0140] Figure 2 The architecture of a computational device for defining the origin and axis positions of a model of at least a portion of the anatomical structure of a patient's dental arch within a global spatial reference frame is illustrated schematically. The computational device can be configured to perform the method described herein.

[0141] Figure 3 A schematic exemplary top view of the lower dental arch is shown, with a segment of a parabola fitted to the lower dental arch, wherein the vertex of the parabola determines the position of the lower dental arch in the forward direction, and provides the assigned tooth number and the projection center of the tooth for the complete dental arch.

[0142] Figure 4 A schematic exemplary side view of a double dental arch, including an upper and lower dental arch, is shown. The bounding box of each dental arch and the location of the occlusal plane are indicated.

[0143] Figure 5A and 5B The surface representations of a portion of the double dental arch are schematically shown, wherein the occlusal plane is aligned with the XY plane and has an arbitrary position relative to the Y-axis, and after being aligned with the Y-axis in the forward direction.

[0144] Figure 6A and 6B The double dental arches are schematically shown before and after translating the occlusal plane to align with the XY plane at position Z=0. Detailed Implementation

[0145] Figure 1 An exemplary flowchart of a method 100 for defining the location 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 shown.

[0146] Method 100 includes a step S102 of receiving a first dataset, the first dataset comprising a surface representation of the surface topology representing at least a portion of a patient's dental arch. The first dataset also includes multiple dividing lines. Each dividing line represents a boundary (also referred to as a contour line) between a crown and adjacent soft tissue, such as the gingiva. The first dataset may also include multiple assigned tooth numbers. Each assigned tooth number may be associated with one of the crowns.

[0147] The first dataset may also include at least one rotation indication, said at least one rotation for orienting the surface representation such that the principal orientation vector representing the normal vector of the occlusal plane is aligned with the first principal component of the global spatial reference frame, and such that the anterior-posterior vector direction of the patient's dental arch is aligned with the second principal component of the global spatial reference frame.

[0148] Figure 1The exemplary method 100 depicted further includes step S104 of generating a planar projection of each segmentation line into a plane parallel to the occlusal plane. Method 100 also includes step S106: determining the projection position of the tooth center into the occlusal plane for each planar projection segmentation line, as the centroid (also referred to as: center of mass) of the region defined by the planar projection of the segmentation line. Method 100 further includes step S108 of fitting a segment of a parabola to the determined projection position of the centroid of the segmentation line from step S106. Method 100 further includes step S110 of identifying (also referred to as: defining) the anterior point of the patient's dental arch as coinciding with the vertex of the parabola. Method 100 further includes step S112 of determining a first translation vector for positioning the anterior point at the origin of a third principal component, the third principal component being perpendicular to the first and second principal components of the global spatial reference system. Method 100 further includes step S114 of storing the indication of the first translation vector in association with a surface representation.

[0149] Method 100 may include step S116 of determining the centroid of a parabolic region at least partially defined by the fitted segment of the parabola. Method 100 may also include step S118 of determining a second translation vector for locating the centroid of the parabolic region at the origin of a second principal component of a global spatial reference frame. Method 100 may further include step S120 of storing an indication of the second translation vector in association with a surface representation.

[0150] In an alternative embodiment, step S116 may include determining a specific point on the posterior-anterior vector direction and / or approximate axis of symmetry of the patient's dental arch, such as the center point of the line connecting the left and right temporomandibular joints, the third molars, or another pair of left and right teeth in the same dental arch. Step S118 may include determining a second translation vector for locating the specific point at the origin of a second principal component of the global spatial reference frame.

[0151] Method 100 may include step S122-1 of determining a bounding box including a surface representation. 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.

[0152] Alternatively or additionally, method 100 may include step S122-2: determining the position of a first surface corresponding to the overlying plane of at least a portion of the dental arch by means of the tip of the crown of each tooth in a predetermined set of teeth. In particular, the predetermined set of teeth may include the first incisor and the last molar on one or each side of at least a portion of the dental arch.

[0153] Step S122-1 or step S122-2 can be used to obtain a first surface, and based on the first surface, to determine a third translation vector for positioning the occlusal plane at the origin of the global reference system.

[0154] In some embodiments, the first face obtained by step S122-1 or step S122-2 may be the same. In other embodiments, the first face of the bounding box may be slightly different from the first face corresponding to the covering plane.

[0155] In one embodiment, at least a portion of the patient's dental arch may include at least a portion of a single dental arch. The single dental arch may include the patient's mandibular or maxillary dental arch. Method 100 may further include steps S124-S: determining the position of the occlusal plane by having a predetermined displacement relative to the first surface in a direction toward the dividing line (and / or in a direction toward the alveolar socket and / or the root of the tooth). Method 100 may further include steps S126-S: determining a third translation vector for translating the occlusal plane to the origin of a first principal component of the global spatial reference system. Method 100 may further include steps S128-S: storing an indication of the third translation vector in association with a surface representation.

[0156] In another embodiment, at least a portion of the patient's dental arch may include at least a portion of a double dental arch. The double dental arch may include the patient's mandibular arch and the patient's maxillary arch. Method 100 may further include step S124-D: determining the position of the occlusal plane as the average (particularly the arithmetic mean) of the first surfaces of the maxillary and mandibular arches. Method 100 may further include step S126-D: determining a third translation vector for translating the occlusal plane to the origin of a first principal component of a global spatial reference system. Method 100 may further include step S128-D: storing the indication of the third translation vector in association with a surface representation.

[0157] The step blocks S116, S118, and S120 associated with the second translation vector can be executed independently of the step blocks S124-S, S126-S, and S128-S associated with the third translation vector for a single dental arch or the step blocks S124-D, S126-D, and S128-D associated with a double dental arch (especially before or after the step blocks).

[0158] Alternatively or additionally, the step blocks S104; S106; S108; S110; S112; S114 associated with the first translation vector may be performed independently of the step blocks S116; S118; S120 associated with the second translation vector and / or the step blocks S124-S; S126-S; S128-S associated with the third translation vector for a single dental arch or the step blocks S124-D; S126-D; S128-D associated with a double dental arch (particularly before or after said step blocks).

[0159] Since the order in which the first, second, and / or third translation vectors are determined is arbitrary, therefore Figure 1The exemplary method 100 depicted in the text only shows one possible ordering of the independent step blocks, where other orders are allowed and possible.

[0160] Figure 2 The architecture of a computing device 200 for defining the position 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 shown.

[0161] Figure 2 The computing device 200 in the example includes a receiving interface 202 configured to receive a first dataset comprising a surface representation of the surface topology of at least a portion of a patient's dental arch. The first dataset also includes multiple dividing lines, each representing a boundary between a crown and adjacent soft tissue, such as the gingiva. The first dataset may also include multiple assigned tooth numbers, each associated with one of the crowns.

[0162] The first dataset may also include indications of at least a first rotation angle and a second rotation angle, the first rotation angle being used to orient the surface representation such that the principal orientation vector representing the normal vector of the occlusal plane is aligned with the first principal component of the global spatial reference frame, and the second rotation angle being used to orient the surface representation such that the anterior-posterior vector direction of the patient's dental arch is aligned with the second principal component of the global spatial reference frame.

[0163] The computing device 200 includes a generation unit 204 configured to generate a planar projection of each dividing line into a plane parallel to the occlusal plane. The computing device 200 also includes a first determining unit 206 configured to determine, for each planar projection dividing line and in some cases for each assigned tooth number, the projected position of the tooth's center in the plane parallel to the occlusal plane, as the centroid of the region defined by the planar projection of the dividing line. The computing device 200 further includes a fitting unit 208 configured to fit a segment of a parabola to the determined projected position of the centroid of the dividing line.

[0164] The computing device 200 further includes an identification unit (also referred to as a definition unit) 210, configured to identify (also referred to as define) the anterior point of the patient's dental arch as coinciding with the vertex of a parabola. The computing device 200 also includes a second determination unit 212, configured to determine a first translation vector for locating the anterior point at the origin of a third principal component of a global spatial reference frame. The third principal component may be perpendicular to the first and second principal components. The computing device 200 also includes a first storage unit 214, configured to store the first translation vector in association with a surface representation.

[0165] The computing device 200 may include a third determining unit 216 configured to determine a specific point on the posterior-anterior vector direction and / or approximate axis of symmetry of the patient's dental arch, such as the centroid of a parabolic region at least partially defined by a fitted segment of a parabola. The computing device 200 may also include a fourth determining unit 218 configured to determine a second translation vector for locating, for example, the specific point of the centroid of the parabolic region at the origin of a second principal component of a global spatial reference frame. The computing device 200 may also include a second storage unit 220 configured to store the second translation vector in association with a surface representation.

[0166] The computing device 200 may include a first variant 222-1 of the fifth determining unit, the first variant being configured to determine a bounding box including a surface representation. 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.

[0167] Alternatively or additionally, the computing device 200 may include a second variant 222-2 of the fifth determining unit, the second variant being configured to: determine the position of a first surface corresponding to a covering plane of at least a portion of the dental arch, determined by the tip of the crown of each tooth in a predetermined set of teeth. Specifically, the predetermined set of teeth may include a first incisor and a last molar on one or each side of at least a portion of the dental arch.

[0168] In some embodiments, at least a portion of the patient's dental arch includes at least a portion of a single dental arch. To cover the single dental arch case, the computing device 200 may include a first variant 224-S of a sixth determining unit, the first variant being configured to: determine the position of the occlusal plane by having a predetermined displacement relative to a first surface in a direction toward the dividing line. The computing device 200 may also include a first variant 226-S of a seventh determining unit, the first variant being configured to: determine a third translation vector for translating the occlusal plane to the origin of a first principal component of a global spatial reference frame. The computing device 200 may also include a first variant 228-S of a third storage unit, the first variant being configured to store the third translation vector in association with a surface representation.

[0169] In another embodiment, at least a portion of the patient's dental arch includes at least a portion of a double dental arch. To cover the double dental arch case, the computing device 200 may include a second variant 224-D of a sixth determining unit, the second variant being configured to determine the position of the occlusal plane as the average (specifically, the arithmetic mean) of the first surfaces of the upper and lower dental arches. The computing device 200 may also include a second variant 226-D of a seventh determining unit, the second variant being configured to: determine a third translation vector for translating the occlusal plane to the origin of a first principal component of a global spatial reference frame. The computing device 200 may also include a second variant 228-D of a third storage unit, the second variant being configured to store the third translation vector in association with a surface representation.

[0170] The computing device 200 may include an input-output (I / O) interface 230, which may embody a receive interface 202. The I / O interface 230 (or...) Figure 2 The transmission interface (not shown) can be configured to send a localization model of at least a portion of the patient's dental arch within a global spatial reference frame to another computing device and / or storage unit, particularly for dental treatment planning, object extraction planning, implant planning, artificial crown design and / or prosthesis design.

[0171] The computing device 200 may include at least one processor 232. The processor 232 may embody a generation unit 204, a first determining unit 206, a fitting unit 208, an identification unit 210, a second determining unit 212, an optional third determining unit 216, an optional fourth determining unit 218, any variant 222-1; 222-2 of a fifth determining unit, any variant 224-S; 224-D of a sixth determining unit, and / or any variant 226-S; 226-D of a seventh determining unit.

[0172] The computing device 200 may include at least one memory 234. The memory 234 may embody a first storage unit 214, an optional second storage unit 220, and / or an optional third storage unit 228-S; 228-D.

[0173] The computing device 200 can be configured to execute method 100. Similar to... Figure 1 Exemplary method 100, Figure 2 The computing device 200 is provided only as an exemplary implementation. According to other instances (not shown), the units for determining (and / or storing) the first, second, and / or third translation vectors may be assigned as optional or non-optional.

[0174] When proceeding to the acquisition step for obtaining intraoral surface scans, coarse automatic arch orientation can be performed based on a probing method. This automatic orientation should be performed if the orientation is not already sufficiently precise. Therefore, orientation can be skipped for cases that include those already in previous acquisition steps (undesired paths), originating from a DW laboratory scanner, or those that will only be slightly altered by automatic orientation (e.g., rotation less than 3 degrees and / or translation less than 3 mm), as these cases are assumed to be accurately oriented.

[0175] The automatic positioning technology disclosed herein is applicable to all combinations of complete and / or partial dental arches, as well as single and / or double dental arches.

[0176] In some embodiments, the distinction between a complete dental arch and a partial dental arch may occur internally (particularly in a computing device such as computing device 200).

[0177] When the complete dental arch (specifically, the molars covering both sides, also known as molars; and the incisors, also known as incisors and canines) is represented by a surface representation (e.g., a surface grid), additional input for automatic orientation of the dental arch may not be required.

[0178] When only a portion of the dental arch is represented by a surface representation (e.g., a mesh), the assigned tooth number (which may not have a location) is typically required as an additional parameter. If no assigned tooth number is available (e.g., in a model-only workflow), the orientation of the surface mesh representing the scan of the partial dental arch (also known as: partial scan) can be done only partially in some cases.

[0179] The calculation of the rotation matrix can be performed in an automated program (e.g., represented as cAutomatedArchPreOrientation and the classes called therein).

[0180] Any rotation can be represented by a rotation matrix (in particular, trigonometric functions such as cosine and sine with rotation angles as matrix terms), and the total rotation matrix can be given by a product.

[0181] Any translation can be represented by a translation vector.

[0182] According to an exemplary embodiment, the first step is to perform an occlusal plane transformation (also known as: bringing the dental arch into the occlusal plane). This may mean that the dental arch (or multiple dental arches, especially in the case of double dental arches) is centered and oriented 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 with the Z-axis. The normals of the upper dental arch can be counted in reverse. This step can be performed using an automation program and the class cAutomatedArchPreOrientation.mGetOclusalPlaneTransformation().

[0183] According to an exemplary embodiment, the next step is to find the appropriate orientation within the occlusal plane. Here, the calculation differs between a complete dental arch and a partial dental arch. To check whether the intraoral scan (and / or surface mesh) represents a complete or partial dental arch, the position and / or orientation of the scan (and / or surface mesh) can be transformed to the sagittal plane. For example, if both sides of the bounding box are greater than 50 mm, and if the shape is elliptical, defined as (length perpendicular to the longest side) / (length of the longest side) < 0.65, then the scan (and / or surface mesh) is considered to represent a complete dental arch.

[0184] 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.

[0185] For a full dental arch, the target could be to identify the anterior side of the arch (e.g., using the automation program cAutomatedPreOrientationForFullArch.mComputeAnteriorVector()). This can be done by fitting a segment of a parabola and determining its vertices, and / or by summing the surface normals (e.g., each polygon of the surface mesh representing the full dental arch), where the inward (also known as: in the lingual direction) normals are reversed, the normals are weighted with a dot product normal*point_coordinates which gives more weight to the radial (and / or horizontal) normals, and / or the normals are weighted inversely to their distance from the occlusal plane.

[0186] When a vector 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, provided that the global reference frame is a Cartesian coordinate system.

[0187] Assuming the scan is performed symmetrically around the assigned tooth number, the average tooth position can be calculated from the scan (or the surface grid representing the scan) centered on the tooth.

[0188] As a next step, the longest side of the dental arch can be aligned with the tangent of the dental arch, for example, according to the automated subroutine mComputeOcclusionRotation.

[0189] Finally, the curvature of the dental arch needs to be identified to determine, for example, whether the desired orientation has been achieved, or whether a 180° rotation (e.g., flipping between upper and lower arch orientations) is necessary, based on the automated subprogrammIsPiFlipNeeded. To identify the arch orientation, the two furthest points of the scan (or multiple scans) can be calculated, for example, based on the automated subprogrammmFindFarestPoint. These two points are considered the chord of the dental arch, with the arch's center of mass (also known as the centroid and / or bary center) located inside the chord.

[0190] The techniques disclosed herein (e.g., including method 100 and / or computing device 200) can be used for automated dental arch positioning (and optionally for orientation).

[0191] In some instances, the technique may be based on a surface mesh representing a dental arch.

[0192] Figure 3 An exemplary diagram shows the planar projection of the lower dental arch 302 (which may correspond to a top view of the lower dental arch 302) onto the occlusal plane, wherein the teeth assigned on the right side are numbered 48, 47, 46, 45, 44, 43, 42, and 41, and the teeth assigned on the left side are numbered 31, 32, 33, 34, 35, 36, 37, and 38, which are marked exactly outside the dental arch.

[0193] Figure 3 The projection of the dividing line 310 of each tooth into the occlusal plane is also shown (e.g., as generated according to step S104). The dividing line 310 indicates the line where the crown of the tooth is adjacent to soft tissue such as the gingiva. Figure 3 The diagram also shows the projection of the center (also referred to as: centroid) 308 of each tooth onto the occlusal plane (e.g., as determined according to step S106). The projection of the center 308 is obtained from the projection of the dividing line 310 of the corresponding tooth. In particular, the projection of the center 308 is determined as the location of the center of mass (also referred to as: centroid) of the region enclosed by the projection of the dividing line 310 of the tooth.

[0194] Figure 3A segment of parabola 306, fitted to a planar projection of the lower dental arch 302, is further illustrated by example. Parabola 306 is fitted to the projection of center 308, for example, by minimizing the sum of squared distances between center 308 and parabola 306.

[0195] At reference numeral 304 in the attached figure, the vertex of parabola 306 is indicated. The Y-axis is essentially a symmetrical Y-axis between the left and right sides of dental arch 302, with the Y-axis passing through vertex 304. Figure 3 The lower dental arch 302 has not yet been translated along the Y-axis to provide its final position relative to the origin of the XY plane.

[0196] Although Figures 3 to 6B An example of a Cartesian coordinate system is shown, in which the Z-axis is oriented vertically, the X-axis is oriented horizontally, and the Y-axis is oriented in the direction in front of the standing patient, but the techniques disclosed herein are generally applicable to different choices of global reference systems.

[0197] Figure 4 A schematic side view of a complete double dental arch is shown, comprising an upper dental arch (also known as the maxilla) 402 and a lower dental arch (also known as the mandible) 302. Figure 4 In the diagram, the double dental arches are schematically shown in the closed position, i.e., in occlusion.

[0198] exist Figure 4 In this configuration, a first bounding box 404 surrounds the crown of the upper dental arch 402, and a second bounding box 406 surrounds the crown of the lower dental arch 302. The lower surface 408 of the first (maxillary) bounding box 404 is selected to ensure that the occlusal surface of the upper dental arch 402 is 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 302 is contained within the second bounding box 406 without extending the second bounding box 406 further upward.

[0199] Figure 4 The occlusal plane 412 is an example of the occlusal plane location of the double dental arches 302, 402, wherein the occlusal plane 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 surface of each of the mandible and maxilla may be determined and averaged to form a common occlusal surface 412.

[0200] Any translation (e.g., translation of the occlusal plane 412 and / or translation along the occlusal plane 412) can be represented by a translation vector.

[0201] Figure 5A and 5BThe positions of portions of the double dental arches 302 and 402 before and after translation and / or before and after the application of the first horizontal translation within the occlusal plane are schematically shown respectively.

[0202] exist Figure 5A In the diagram, prior to translation, the intended position of the complete dental arch at reference numeral 502 is shifted from the partial dental arches 302 and 402, and the occlusal plane is shifted from the XY plane. Figure 5B In the process, after translation, partial dental arches 302 and 402 are placed at the expected position 502 of the complete dental arch, and the occlusal plane 412 is in the XY plane.

[0203] Positioning in the Z direction can initially be performed simply by centering. This may have undesirable results for the Z-position of the bite. Final Z-alignment improves bite positioning. In the case of double arches, in the Cartesian coordinate system, 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.

[0204] Figure 6A and 6B The double dental arches 302 and 402 are schematically shown before and after occlusal alignment. Figure 6A In this context, before the translation and / or before the application of the third translation vector, the engagement plane (not shown) is below the XY plane of the Cartesian coordinate system. Figure 6B In the middle, the occlusal plane 412 coincides with the XY plane after translation.

[0205] For the case of a single dental arch, the dental arch can be moved, for example, according to the automation subroutine cAutomatedArchPreOrientation.OCCLUSION_OVERLAP, so that the occlusion overlaps with the Z=0 level, for example, by 4 mm.

Claims

1. A computer-implemented method (100) for defining the origin and axis positions 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, comprising the steps of: - Receive (S102) a first dataset, the first dataset including a representation of the patient's dental arch (302); The first dataset includes: a surface representation of at least a portion of the surface topology of the crown of at least one or more teeth (402), and a surface representation of the surface topology of the crown of at least one or more teeth. - Multiple dividing lines, each representing the boundary between the crown and adjacent soft tissue, and - An indication of a first rotation angle and optionally an indication of a second rotation angle, the first rotation angle being used to orient the surface representation such that the principal orientation vector representing the normal vector of the occlusal plane (412) is aligned with the first principal component of the global spatial reference system, and the second rotation angle being used to orient the surface representation such that the anterior-posterior vector direction of the patient dental arch (302; 402) is aligned with the second principal component of the global spatial reference system; -Optionally, generate (S104) a planar projection of each dividing line into a plane parallel to the occlusal plane (412); - For each plane projection dividing line, determine (S106) the projection position of the center of the tooth in the plane parallel to the occlusal plane (412), for example, as the centroid of the region defined by the plane projection of the dividing line; - Fit (S108) a segment of the parabola (306) to the determined (S106) projection position of the centroid of the dividing line; - Define (S110) the anterior point (304) of the patient's dental arch (302; 402) as coinciding with the vertex (304) of the parabola (306); - Determine (S112) the first translation vector used to position the front point (304) at the origin of the third principal component of the global spatial reference system; and - Store the indication of the first translation vector in association with the surface representation (S114).

2. The method (100) according to claim 1, wherein the surface representation is obtained from an intraoral surface scan of the anatomical structure of the portion of the patient's dental arch (302; 402).

3. The method (100) according to claim 1 or 2, wherein the surface representation comprises a surface mesh defined by a plurality of polygons, wherein the polygons are selected from the group comprising triangles, rectangles, pentagons, hexagons and / or higher-order polygons, and optionally, wherein the surface mesh comprises a plurality of polygons having different sizes and / or different numbers of vertices.

4. The method (100) according to any one of claims 1 to 3, wherein fitting (S108) the segment of the parabola (306) to the determined (S106) position of the centroid optionally includes: Minimize the sum of the quadratic distances between the centroid of the dividing line and the segment of the parabola.

5. The method (100) according to any one of claims 1 to 4, wherein the first dataset further includes a plurality of tooth numbers assigned to the plurality of segmentation lines, and wherein the segment of the parabola (306) fitted (S108) is also based on the tooth number associated with each determined (S106) projection position of the centroid of the segmentation line.

6. The method (100) according to any one of claims 1 to 5, further comprising the following step: - Determine (S116) the centroid of the parabolic region at least partially defined by the fitted (S108) segment of the parabola (306); - Determine (S118) a second translation vector for locating the centroid of the parabolic region at the origin of the second principal component of the global spatial reference system; and - Store the indication of the second translation vector in association with the surface representation (S120).

7. The method (100) according to any one of claims 1 to 6, further comprising the following step: - Determine (S122-1) the bounding box (404; 406) representing the surface, wherein the 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).

8. The method (100) according to any one of claims 1 to 6, further comprising the following step: - The position of the first surface corresponding to the covering plane of the at least part of the dental arch is determined by the tip of the crown of each tooth in a predetermined set of teeth (S122-2), wherein, in particular, the predetermined set of teeth includes the first incisor and the last molar on one or each side of the at least part of the dental arch.

9. The method (100) according to claim 7 or 8, wherein the at least portion of the patient dental arch (302; 402) comprises at least a portion of a single dental arch, wherein the single dental arch comprises a patient mandibular arch (302) or a patient maxillary arch (402), wherein the method (100) further comprises the following steps: - The position of the occlusal plane (412) is defined by having a predetermined displacement relative to the first surface (408; 410) in the direction toward the dividing line; - Determine (S126-S) a third translation vector for translating the defined (S124-S) position of the occlusal plane (412) to the position at the origin of the first principal component of the global spatial reference system; and - Store the indication of the third translation vector in association with the surface representation (S128-S).

10. The method (100) according to claim 9, wherein the predetermined displacement is in the range of 2 mm to 5 mm, preferably 4 mm.

11. The method (100) according to claim 7 or 8, wherein the at least portion of the patient dental arch (302; 402) comprises at least a portion of a double dental arch, wherein the double dental arch comprises a patient mandibular arch (302) and a patient maxillary arch (402), wherein the method (100) further comprises the following steps: -The position of the occlusal plane (412) is defined (S124-D) as the average value, in particular the arithmetic mean, of the first surface (408) of the upper dental arch (402) and the first surface (410) of the lower dental arch (302); - Determine (S126-D) a third translation vector for translating the defined (S124-D) position of the occlusal plane (412) to the position at the origin of the first principal component of the global spatial reference system; and - The indication of the third translation vector is stored in association with the surface representation (S128-D).

12. The method (100) according to any one of claims 1 to 11, wherein the first rotation angle and / or the second rotation angle is represented by a transformation matrix adapted to position and axial orientation of the model representing the surface as an anatomical structure of at least a portion of the patient's dental arch (302; 402) within the origin of the global spatial reference system.

13. Use of the model located in the global spatial reference system according to any one of claims 1 to 12 in dental treatment planning, object extraction planning, implant planning, artificial crown design and / or prosthesis design.

14. A computer program product that, when executed by a computing device (200), causes the computing device (200) to perform the steps of the method (100) according to any one of claims 1 to 12.

15. A computer-readable storage medium comprising 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 12.

Images