Apparatus and method for maxillofacial surgery asymmetry assessment and correction

Abstract

The present application relates to a device and method for maxillofacial surgery asymmetry evaluation and correction, which comprises: generating or receiving a 3D digital model of a patient's skull, identifying a median sagittal plane of the skull, determining an optimal symmetry plane of the jaw bone, determining the asymmetry of the patient's jaw bone based on the misalignment between the optimal symmetry plane of the jaw bone and the median sagittal plane of the skull, and performing a correction process to correct the identified asymmetry. In this scheme, the angle between the median sagittal plane of the skull and the optimal symmetry plane of the jaw bone is used to quantify the asymmetry, thereby automatically correcting the jaw bone asymmetry through automatic registration of plane to plane, facilitating the standardization and streamlining of asymmetry evaluation and correction.

Description

Technical Field

[0001] This application relates to the field of computer-assisted surgery, and more particularly to devices and methods for computer-assisted maxillofacial surgery. Background Technology

[0002] Even for experienced surgeons, identifying precise jaw asymmetry can be challenging because routine clinical assessment methods struggle to capture the abnormal orientation, location, and shape of the jaw. This problem is exacerbated when asymmetry is masked by varying soft tissue thickness and compensatory occlusion. Furthermore, abnormal head posture can obscure the true extent of asymmetry, posing further challenges to assessment and correction. In recent years, computer-assisted orthognathic surgery (CAOGS) has enabled three-dimensional visualization of the skull and simulation of bone movement, offering inherent advantages for managing asymmetric deformities.

[0003] However, in current CAOGS practice, asymmetry assessment relies primarily on visual examination, and the correction process involves manually and repeatedly moving bone segments through lateral translation, yaw, and roll rotations until symmetry is achieved in virtual 3D space. This process is complex and highly dependent on the surgeon's experience. Therefore, there is a pressing need for an automated workflow that enables standardized assessments and one-click bone adjustments based on the degree of asymmetry. Summary of the Invention

[0004] This application relates to methods and systems for the assessment and correction of asymmetry in computer-assisted maxillofacial surgery (e.g., orthognathic surgery). The methods and systems described herein provide tools for the automated correction of jaw asymmetry in patients. The method also provides a digital workflow for computer-assisted maxillofacial surgery (e.g., orthognathic surgery). The method offers an advantageous planning approach for identifying and correcting jaw asymmetry in a virtual environment.

[0005] This application relates to methods and / or systems for the assessment and correction of asymmetry in computer-assisted orthognathic surgery, which overcome or substantially improve at least some of the deficiencies of the prior art, or at least provide an alternative.

[0006] According to a first aspect of the embodiments of this application, a computer-implemented method for asymmetry assessment and correction in maxillofacial surgery is provided, comprising: generating or receiving a three-dimensional digital model of a patient’s skull (the model including the patient’s jawbone); identifying the midsagittal plane of the skull; determining the optimal plane of symmetry of the jawbone; determining the asymmetry of the patient’s jawbone; and performing a correction process to correct the identified asymmetry.

[0007] In one example, asymmetry can be determined based on the misalignment between the optimal plane of symmetry of the jawbone and the midsagittal plane of the skull, wherein the asymmetry can be expressed as the angle between the optimal plane of symmetry of the jawbone and the midsagittal plane of the skull.

[0008] In one example, the correction process may include determining the corrected position of the jawbone relative to the skull, where the corrected position may refer to the position where the midsagittal plane of the skull is aligned with the optimal plane of symmetry of the jawbone.

[0009] In one example, the correction process may include automatically aligning (e.g., performing joint connections) the jawbone in the model and repositioning it to the corrected position to eliminate asymmetry.

[0010] In one example, the corrected position of the jawbone can be defined as the position where the optimal plane of symmetry of the jawbone is aligned with the median sagittal plane of the skull, such that the angle between them (also known as the asymmetry angle) is between -5 degrees and +5 degrees. Preferably, the optimal plane of symmetry of the jawbone is aligned with the median sagittal plane of the skull, such that the asymmetry angle is between -2 degrees and +2 degrees.

[0011] In one example, the step of determining the optimal plane of symmetry of the jaw may include determining the optimal plane of symmetry of the maxilla and / or mandible or maxillary and mandibular units or chin.

[0012] In yet another example, the computer-implemented method for asymmetry assessment and correction in maxillofacial surgery may include the following steps: generating or receiving a three-dimensional (3D) digital model of a patient's skull (including the patient's jawbone); identifying the midsagittal plane of the skull; determining the optimal plane of symmetry for the maxilla; determining the optimal plane of symmetry for the mandible; determining the asymmetry of the maxilla by determining the misalignment between the optimal plane of symmetry of the maxilla and the midsagittal plane of the skull; determining the asymmetry of the mandible by determining the misalignment between the optimal plane of symmetry of the mandible and the midsagittal plane of the skull; determining the corrected positions of the maxilla and mandible; aligning the maxilla and mandible to their respective corrected positions in the 3D digital model of the skull; and presenting the maxilla and mandible in their corrected positions on the 3D digital model of the skull.

[0013] Alternatively, in yet another example, the computer-implemented method for asymmetry assessment and correction in maxillofacial surgery may include the following steps: generating or receiving a three-dimensional (3D) digital model of the patient's skull (including the patient's jawbone); identifying the midsagittal plane of the skull; aligning the patient's maxilla and mandible together to a corrective position, for example, aligning them as a single maxillary unit; determining the asymmetry of the maxillary unit (i.e., the maxilla and / or mandible) by determining the misalignment between the optimal plane of symmetry of the maxillary unit and the midsagittal plane of the skull; determining the corrective position of the maxillary unit; and aligning the maxillary unit (i.e., the maxilla and mandible) to its corrective position. In this example, it may also include presenting the maxilla and mandible in the corrective position on the 3D digital model of the skull.

[0014] In one example, the correction procedure may include moving or aligning the maxilla and mandible (e.g., mandibular units) along a sagittal and / or vertical vector. In another example, the correction procedure may also include rotating the mandibular units (e.g., maxilla and mandible) about a lateral vector.

[0015] In one example, the midsagittal plane of the skull can be identified by applying the Iterative Closest Point (ICP) algorithm. In one example, the method uses a midsagittal plane-first approach.

[0016] In one example, identifying the midsagittal plane of the skull may include mirroring and aligning a region of the skull, and the aligned region of the skull will be used to calculate a new mirror plane or optimal symmetry plane. The horizontal plane is defined as a plane perpendicular to the midsagittal plane and passing through the auricular and orbital points (either side is acceptable). Finally, the coronal plane is defined as a plane perpendicular to both the midsagittal and horizontal planes and passing through the sella turcica point.

[0017] In one example, the optimal plane of symmetry for the maxilla and / or mandible can be determined by performing a bilateral sagittal split osteotomy, for example, dividing the jaw (e.g., the mandible) into two proximal segments with condyles and one distal segment with teeth. The optimal plane of symmetry for the distal segment of the mandible is automatically constructed.

[0018] In one example, the maxilla and / or mandible can be aligned by performing a virtual Le Fort I osteotomy.

[0019] In one example, orthodontic positioning can also refer to aligning the maxillary teeth with the mandibular teeth. Alignment can be achieved by adjusting the maxilla and / or mandible until the desired occlusion is reached.

[0020] In one example, the optimal plane of symmetry for the jawbone can be automatically generated.

[0021] In one example, the method according to the first aspect of the embodiments of this application can be executed automatically by a computing device. In another example, the method according to the first aspect of the embodiments of this application can be implemented in the form of a Python script.

[0022] According to a second aspect of the embodiments of this application, an electronic device is provided, including a processor and a memory, on which a computer program is stored, which, when executed by the processor, implements the method of the first aspect of the embodiments of this application for performing asymmetry assessment and correction in maxillofacial surgery (e.g., orthognathic surgery).

[0023] According to a third aspect of the embodiments of this application, a computer program product is provided, including a computer program / instructions that, when executed by a processor, implement the method of performing asymmetry assessment and correction in maxillofacial surgery (e.g., orthognathic surgery) according to a first aspect of the embodiments of this application.

[0024] According to a fourth aspect of an embodiment of this application, a computer-readable storage medium is provided having a computer program / instructions stored thereon that, when executed by a computer or processor, implements the method of the first aspect of an embodiment of this application for performing asymmetry assessment and correction in maxillofacial surgery (e.g., orthognathic surgery).

[0025] According to a fifth aspect of an embodiment of this application, a system is provided for asymmetry assessment and correction in computer-assisted maxillofacial surgery (e.g., orthognathic surgery), the system including a computing device. The computing device includes a processor, a user interface, and a memory unit, wherein the processor and the memory unit are operatively coupled to each other. The memory unit is adapted to store instructions that, when executed by a processor, cause the computing device to perform the following steps: generating or receiving a three-dimensional digital model of a patient's skull, wherein the three-dimensional digital model includes the patient's jawbone; identifying the midsagittal plane of the skull (e.g., by applying an Iterative Closest Point (ICP) algorithm to determine the midsagittal plane); determining the optimal plane of symmetry of the jawbone; determining the asymmetry of the patient's jawbone based on the misalignment between the optimal plane of symmetry of the jawbone and the midsagittal plane of the skull, wherein the asymmetry is represented as the angle between the optimal plane of symmetry of the jawbone and the midsagittal plane of the skull; determining the corrected position of the jawbone relative to the skull, wherein the corrected position refers to the position where the midsagittal plane is aligned with the optimal plane of symmetry of the jawbone; automatically comparing and repositioning the jawbone in the three-dimensional digital model to the corrected position to eliminate the asymmetry; and presenting the jawbone in the corrected position on a user interface.

[0026] In one example, the corrected position of the jawbone refers to the position where the optimal plane of symmetry of the jawbone is aligned with the median sagittal plane of the skull, such that the asymmetry angle is between -5 degrees and +5 degrees. Preferably, the corrected position of the jawbone refers to the position where the optimal plane of symmetry of the jawbone is aligned with the median sagittal plane of the skull, such that the asymmetry angle is between -2 degrees and +2 degrees.

[0027] Alternatively, in yet another example, the computing device in the system can also be configured to: align the maxilla and mandible together to a corrective position, for example, align them into a single maxillary unit; determine the asymmetry of the maxillary unit (i.e., the maxilla and / or mandible) by determining the misalignment between the optimal plane of symmetry of the maxillary unit and the midsagittal plane of the skull; and further align the maxillary unit (i.e., the maxilla and mandible) to correct the asymmetry. In one example, the maxilla and mandible (e.g., the maxillary unit) can be further moved or aligned along a sagittal vector and / or a vertical vector. In another example, the maxillary unit (e.g., the maxilla and mandible) can be rotated about a lateral vector.

[0028] In the embodiments described in this application, asymmetry is represented by the misalignment between the optimal plane of symmetry of the maxilla and / or mandible and the midsagittal plane of the skull. Asymmetry can then be corrected by aligning the optimal plane of symmetry of the maxilla or mandible to the midsagittal plane of the skull using a "plane-to-plane" registration method, thus automating asymmetry correction. These methods can be applied to jaw or maxillofacial surgeries involving asymmetry assessment and correction, such as trauma rehabilitation, jaw reconstruction, and craniofacial surgery, and are particularly suitable for computer-assisted orthognathic surgery.

[0029] It should be understood that if any prior art information is cited in this document, such citation does not constitute an admission that such information constitutes part of common general knowledge in the art. Attached Figure Description

[0030] Exemplary embodiments will now be described by way of example with reference to the accompanying drawings, wherein:

[0031] Figure 1 A schematic diagram of the modules of an example system for asymmetry assessment and correction in computer-assisted maxillofacial surgery (e.g., orthognathic surgery) according to an embodiment of this application is shown.

[0032] Figure 2 A flowchart illustrating a method for asymmetry assessment and correction in computer-assisted maxillofacial surgery according to an embodiment of this application is shown.

[0033] Figure 3AA flowchart illustrating a method for asymmetry assessment and correction in computer-assisted maxillofacial surgery according to an embodiment of this application is shown.

[0034] Figure 3B A flowchart illustrating a method for asymmetry assessment and correction in computer-assisted maxillofacial surgery according to an embodiment of this application is shown.

[0035] Figures 4A to 4C A flowchart illustrating an exemplary method for asymmetry assessment and correction in computer-assisted maxillofacial surgery according to an embodiment of this application is shown.

[0036] Figure 5 Three views of a 3D digital skull model are shown, in which the midsagittal plane of the skull is identified and the skull is oriented along the midsagittal plane.

[0037] Figure 6 Three views of a 3D digital skull model are shown, in which asymmetry is calculated and presented on the skull model.

[0038] Figure 7 Three views of a 3D digital skull model are shown, in which asymmetry is corrected by aligning the jawbones (maxilla and / or mandible) to align the optimal plane of symmetry and the midsagittal plane.

[0039] Figure 8 A schematic diagram illustrating an exemplary embodiment of a computing device for implementing a method for asymmetry assessment and correction in computer-assisted maxillofacial surgery is shown. Detailed Implementation

[0040] Orthognathic surgery (OGS), also known as jawbone correction surgery, is performed to correct jawbone skeletal deformities. Patients with skeletal deformities often have varying degrees of jawbone asymmetry. Accurate identification of asymmetry is crucial for effective intervention, but even experienced surgeons face challenges due to the difficulty in capturing the abnormal direction, location, and shape of the jawbone.

[0041] Developing a surgical plan for OGS is a complex process that requires assessing multiple factors, including jaw alignment, occlusion, and facial soft tissues. Traditionally, model surgery and cephalometric tracing have been used to determine ideal jaw-tooth relationships and simulate bone movement. However, this traditional approach has limitations when dealing with asymmetric deformities. Even for experienced surgeons, identifying precise asymmetry is challenging because routine clinical assessment methods struggle to capture abnormal orientation, location, and shape of the jaw. This problem is exacerbated when asymmetry is masked by varying soft tissue thickness and compensatory occlusion. Furthermore, abnormal head posture can obscure the true extent of asymmetry, posing further challenges to assessment and correction. Jaw asymmetry is a characteristic present in everyone, making accurate assessment crucial for effective intervention.

[0042] In recent years, Computer-Assisted Orthognathic Surgery (CAOGS) has enabled 3D visualization of the skull and simulation of bone movement, which has inherent advantages in treating asymmetric deformities. CAOGS is a precise, predictable, and repeatable digital surgery that fully integrates digital technologies such as data acquisition and 3D reconstruction, virtual surgical planning, 3D-printed surgical guides, and intraoperative navigation into the entire process of orthognathic surgery, from preoperative diagnosis and treatment planning to precise intraoperative execution and postoperative evaluation. CAOGS typically includes the following stages: (1) Data acquisition and three-dimensional reconstruction (preoperative diagnosis), which firstly acquires the patient's head and face image data through computed tomography (CT) or cone-beam computed tomography (CBCT), scans the dental arch through intraoral laser, obtains soft tissue related data through facial three-dimensional photography, etc., and then reconstructs a digital three-dimensional model of the skull based on the acquired data; (2) Virtual surgical planning, for example, simulating surgery in specialized software (such as ProPlan CMF, IPS CaseView, etc.); mainly including: virtual osteotomy, drawing osteotomy lines according to standard surgical procedures (Le Fort type I osteotomy, bilateral mandibular ramus sagittal split osteotomy BSSRO, mandibular ramus sagittal split osteotomy SSRO, chinoplasty osteotomy, etc.); bone movement, moving and rotating the jawbone to the preset position; occlusal reconstruction: matching the upper and lower dental arches to establish an ideal occlusal relationship; effect prediction, the software automatically simulates postoperative soft tissue changes (face shape, lip shape, nose shape) and presents the postoperative effect; after confirmation by the doctor and patient, a digital surgical plan is generated. The digital surgical plan records the digital design process for a specific surgery, such as which surgical steps are used, detailed operation specifications, key points, parameter ranges, etc. for each step, and the specific osteotomy techniques (such as Le Fort I, BSSRO / SSRO), osteotomy line position, bone block movement parameters (anterior / posterior / upper / lower / left / right movement, rotation angle), occlusal guide and osteotomy guide design points, with design screenshots and parameter tables, etc. (3) 3D printing physical guides / models (surgical conversion), including 3D printing physical auxiliary tools based on the generated digital surgical plan, such as osteotomy guides, positioning / movement guides (occlusal plates), etc. Therefore, in subsequent surgeries, doctors only need to perform relevant surgical operations based on the generated digital surgical plan.

[0043] However, currently in CAOGS, asymmetry assessment relies primarily on visual examination. For asymmetry correction, surgeons typically define an optimal plane of symmetry based on their experience and then manually reposition the maxilla or mandible to the optimal position. All procedures are performed manually and rely on visual inspection. The correction process involves manually and repeatedly moving bone segments through lateral translation, yaw, rolling, and rotation until symmetry is achieved in virtual 3D space. This process is complex and highly experience-dependent. Surgeons often spend several hours handling a single case. Furthermore, if manual asymmetry correction is unsatisfactory (because it requires addressing three-dimensional asymmetry, especially since patients with jaw asymmetry are often completely asymmetrical), the procedure may take even longer.

[0044] Therefore, there is an urgent need for an automated workflow that can perform standardized assessments of asymmetry and enable one-click bone adjustment based on the degree of asymmetry.

[0045] Comprehensive assessment of jaw asymmetry falls under the scope of 3D cephalometrics. In this assessment, a cranial reference frame, or 3D coordinate system, is crucial for defining the position and orientation of the skull, ensuring accurate cephalometric measurements. Traditionally, a cranial reference frame is created by manually identifying the ear and orbital points to first establish the Frankfurt plane, then locating the nasal root or sella turcica point to generate the median sagittal and coronal planes. However, this "horizontal plane-first" approach has not been fully validated. Furthermore, constructing a reference frame based on a limited number of coordinate points may not yield accurate results, especially for individuals with asymmetric deformities. Therefore, this application employs a "median sagittal plane-first" approach, first establishing the skull's "optimal plane of symmetry" as its median sagittal plane to construct the cranial reference frame.

[0046] This application provides a computer-based method for assessing and correcting jaw asymmetry in patients. This method offers a digital workflow for asymmetry assessment and correction, enabling dental surgeons to identify jaw asymmetry and determine appropriate correction plans in a virtual environment, thereby simplifying surgery and providing improved surgical outcomes.

[0047] refer to Figure 1An exemplary embodiment of a system 100 for asymmetry assessment and correction in computer-assisted maxillofacial surgery (e.g., orthognathic surgery) is shown. System 100 is described in conjunction with computer-assisted orthognathic surgery. System 100 includes a computing device 200. The computing device 200 includes a processor 202, a user interface 212, and a memory unit 204, wherein the processor 202 and the memory unit 204 are operatively coupled to each other. The memory unit 204 may be a non-transient computer-readable medium. The memory unit 204 is adapted to store instructions that, when executed by the processor, cause the computing device 200 to perform the following operations: receive an image 102 of a patient's skull; generate a 3D digital model of the patient's skull, wherein the model includes the patient's jawbone; identify the midsagittal plane of the skull; determine the optimal plane of symmetry of the jawbone; determine the asymmetry of the patient's jawbone based on the above information; and perform a correction process to correct the identified asymmetry. The computing device 200 is also configured to present the jawbone in the corrected position on the user interface 212.

[0048] The midsagittal plane of the skull is an imaginary plane perpendicular to the horizontal plane of the skull, dividing the skull (and head) into two symmetrical parts. This plane usually passes through the midline of the skull, bisecting the top, bottom, and facial structures, so that symmetrical structures such as the frontal, parietal, temporal, maxillary, and mandibular bones on both sides are mirror images on both sides of the plane; at the same time, this plane passes through key bony landmarks such as the root of the nose, the anterior nasal spine, the premental point, and the external occipital protuberance.

[0049] In one example, the midsagittal plane can be determined by connecting key bony landmarks of the skull. For instance, connecting the root of the nose (midpoint of the anterior part of the craniofacial region), the anterior nasal spine (midpoint of the anterior part of the maxilla), the premental point (midpoint of the anterior part of the chin), and the external occipital protuberance (midpoint of the posterior part of the occipital bone) in the same vertical plane creates the midsagittal plane. In another example, the midsagittal plane can be determined based on the shape and position of symmetrical structures on both sides of the skull (such as the left and right parietal bones, temporal bones, orbits, and maxillary sinuses) to create a mirror image of these structures.

[0050] In another embodiment, the midsagittal plane can be accurately determined based on the acquired three-dimensional data of the skull (e.g., CBCT / CT images). The main process includes: automatically identifying symmetrical bony landmarks of the skull (nasal root, anterior nasal spine, chin point, etc.) from the image data; constructing a fitting plane based on the landmarks, such that the plane bisects the left and right skull structures and passes through the key landmarks; fine-tuning the plane so that the symmetrical structures of the skull and jaw on both sides (such as the mandibular angle and zygomatic bone) are at the same distance from the plane, thereby determining the midsagittal plane as the midsagittal plane. In yet another example, the accuracy of determining the midsagittal plane can be further improved by combining three-dimensional scanning, point cloud registration, and other technologies. For example, a three-dimensional laser scan of the skull is performed to obtain skull point cloud data. The point cloud is mirrored left and right, and the mirrored point cloud is registered with the original point cloud using the ICP (Iterative Closest Point) algorithm. The symmetrical plane formed during the registration process is the midsagittal plane. In yet another example, a trained artificial intelligence model can automatically identify symmetrical structures and key landmarks in a 3D model of the skull, quickly fit and output the midsagittal plane.

[0051] In another embodiment, the optimal plane of symmetry of the skull can be determined using a mirror association method that relies on the symmetry of the skull structure, thus serving as the midsagittal plane. The mirror association method is an automatically executed algorithm that does not rely on manual selection of anatomical landmarks and is entirely based on the geometric symmetry of the 3D model. Its core idea is to mirror the 3D model of the skull along an imaginary plane, and then use rigid body registration technology to achieve "optimal overlap" between the mirror model and the original model. The mirror plane with the highest degree of overlap is the optimal plane of symmetry of the skull (i.e., the midsagittal plane). This process essentially involves solving for an optimal reflection transformation plane. The following details its principle and implementation logic step by step:

[0052] S1: Obtain a 3D digital model of the skull

[0053] Obtain a 3D mesh model of the surface of the target area of ​​the skull as the original model. The model contains a set of vertex coordinates. and topological connections.

[0054] S2: Initial symmetry plane estimation

[0055] For the original model Determine an initial estimated symmetry plane The initial estimate can be made in one of the following ways:

[0056] * Perform principal component analysis on the model vertices, calculate the eigenvectors of the vertex covariance matrix, and use the plane passing through the geometric center of the model as the initial plane with the direction of the first principal component as the normal vector.

[0057] * The bounding box of the calculation model in the left and right directions is taken as the initial plane by the midpoint plane;

[0058] * The operator can roughly specify a plane through the line connecting the root of the nose and the external occipital protuberance via the graphical interface.

[0059] S3: Iterative optimization of loop initialization

[0060] Set the iteration counter Maximum number of iterations and convergence threshold (Including the threshold for the change in the angle of the plane normal vector) and plane translation distance threshold ).

[0061] S4: Mirror Model Generation

[0062] In the In the next iteration, the currently estimated symmetry plane As a reflective surface, for the original model Perform reflection transformation to generate a mirror model The reflection transformation is defined as follows: for any vertex in the original model... Its mirror image corresponding point satisfy:

[0063]

[0064] in, For plane The unit normal vector, For plane Any point on the plane (usually the center of the intersection of the plane and the model's bounding box).

[0065] S5: Solving Transformation Parameters for Rigid Body Registration

[0066] The mirror model As a set of moving points, the original model Using a fixed set of reference points, a rigid body registration calculation is performed. Specifically, a rotation matrix is ​​sought. Translation vector This makes the registered mirror model Compared with the original model The optimization problem is to minimize the sum of squared distances between corresponding points.

[0067]

[0068] in For the original model Center and mirror point The correspondence between the nearest points can be established using the iterative nearest point algorithm or its variants.

[0069] In a preferred embodiment, the rotation matrix can be calculated using a least-squares rigid body transformation solution method based on singular value decomposition. With translation vector .

[0070] S6: Symmetry Plane Update

[0071] Based on the rotation matrix obtained from registration Extract the reflection transformation correction information contained therein and update the symmetry plane parameters.

[0072] First, rotate the matrix Perform feature decomposition. Since the optimal registration between the original model and the mirror model inherently includes a reflection correction component, this can be achieved through analysis. The eigenvalues ​​and eigenvectors are used to extract the rotation axis and rotation angle corresponding to the mirror plane correction.

[0073] In a simplified implementation, the rotation matrix can be used directly. Update the plane normal vectors and adjust them according to the translation vectors. The projection component along the normal vector direction updates the plane position. The specific update rule is as follows:

[0074] * Update normal vector: ,in Representing the rotation matrix A half-angle rotation;

[0075] * Update the plane reference point: .

[0076] The above update yields the [number] [item]. The symmetry plane of the next iteration .

[0077] S7: Convergence Test

[0078] Calculate the difference between the symmetry planes obtained from two adjacent iterations, including the change in the angle between the normal vectors. and the translational changes of the plane reference point along the normal direction .

[0079] If satisfied and If the algorithm converges, the current symmetric plane is output. As the final optimal plane of symmetry; otherwise, let Return to step S4 and continue iterating. If the number of iterations reaches... If convergence is still not achieved, output the current plane and indicate that it may not have fully converged.

[0080] S8: Results Output and Application

[0081] The final optimal symmetry plane is output as a parametric equation and can be further used for clinical measurement, surgical planning, or symmetry analysis.

[0082] The method for determining the optimal plane of symmetry for the jawbone is similar to that for determining the midsagittal plane of the skull, and will not be elaborated here.

[0083] In one example, the asymmetry of a patient's jaw is determined based on the misalignment between the optimal plane of symmetry of the jaw and the midsagittal plane of the skull. This asymmetry can be expressed as the angle between the optimal plane of symmetry and the midsagittal plane. For example, an angle greater than +5 degrees or less than -5 degrees indicates the presence of asymmetry. Similarly, an angle greater than +2 degrees or less than -2 degrees indicates the presence of asymmetry. Alternatively, an angle greater than 0 degrees indicates the presence of asymmetry.

[0084] In one example, the correction process may include determining the corrected position of the jawbone relative to the skull, and automatically aligning and repositioning the jawbone to the determined corrected position in a three-dimensional digital model of the skull by performing plane-to-plane registration of the jawbone's optimal plane of symmetry with the midsagittal plane of the skull. This corrected position may refer to a position where the angle between the jawbone's optimal plane of symmetry and the midsagittal plane of the skull is within a preset range (e.g., [+5, -5] or [+2, -2]). In another example, the corrected position refers to a position where the jawbone's optimal plane of symmetry is aligned with the midsagittal plane of the skull (i.e., the angle between them is 0). In yet another example, in addition to satisfying the above conditions, the corrected position of the jawbone also refers to a position where the maxillary teeth are aligned with the mandibular teeth. In yet another example, the correction process may also include recording each surgical operation performed during the automatic alignment of the jawbone and its associated parameters (e.g., which segments of the frontal bone were moved and the extent of movement) for subsequent generation of a digital surgical plan.

[0085] Figure 2 An exemplary embodiment of a method 300 for asymmetry assessment and correction in computer-assisted maxillofacial surgery (e.g., orthognathic surgery) is shown. Method 300 can be performed by system 100. In particular, method 300 can be performed by computing device 200.

[0086] The method 300 may include multiple steps that can be performed by the computing device 200. For example... Figure 2As shown, step 302 includes generating or receiving a 3D digital model of the patient's skull, wherein the 3D digital model includes the patient's jawbone. This 3D digital model may be generated based on received images of the patient's skull and jawbone. These images may be CT scan images, color photographs, X-ray images, or other suitable images. Alternatively, the 3D digital model may be received from a source. Step 304 includes identifying the midsagittal plane of the skull. Step 306 includes determining the optimal plane of symmetry for the jawbone. Step 308 includes determining the asymmetry of the patient's jawbone. For example, if there is any deviation greater than +5 degrees or less than -5 degrees between the midsagittal plane of the skull and the optimal plane of symmetry for the jawbone, it is determined to be misalignment, i.e., asymmetry exists. Optionally, any deviation greater than +2 degrees or less than -2 degrees may also be determined to be asymmetry. In another optional example, any deviation greater than 0 degrees may also be determined to be asymmetry.

[0087] If an asymmetry is found at step 308, step 310 is executed, including performing an orthodontic procedure to correct the identified asymmetry. Step 312 includes presenting the corrected position of the jawbone on a user interface to provide guidance to the dental surgeon. If no asymmetry is found, no orthodontic treatment is required. In one example, step 312 may also optionally include presenting one or more surgical procedures and their associated parameters required to correct the asymmetry. These surgical procedures can be presented as instructions to the dental surgeon for correcting the patient's jawbone asymmetry.

[0088] In one example, the orthodontic process may include determining the corrected position of the jawbone relative to the skull, and automatically aligning and repositioning the jawbone to the determined corrected position within a three-dimensional digital model of the skull. At this corrected position, the optimal plane of symmetry of the jawbone is aligned with the median sagittal plane, such that the angle between them (also known as the asymmetry angle) is between -5 degrees and +5 degrees, or between -2 degrees and +2 degrees, or even 0 degrees. Furthermore, at this corrected position, the maxillary teeth can also be aligned with the mandibular teeth.

[0089] In one example, the steps to determine the optimal plane of symmetry for the jawbone include determining the optimal plane of symmetry for the maxilla and / or mandible.

[0090] Figure 3AAnother exemplary embodiment of a method 400 for asymmetry assessment and correction in computer-assisted maxillofacial surgery (e.g., orthognathic surgery) is shown. Method 400 can be performed by a computing device 200. Method 400 begins at step 402. Step 402 includes generating or receiving a 3D digital model of the patient's skull (the model includes the patient's jawbone). Step 404 includes identifying the midsagittal plane of the skull. In one example, the midsagittal plane of the skull is determined by applying an iterative closest point (ICP) algorithm.

[0091] Step 406 includes determining the optimal plane of symmetry for the maxilla. Step 408 includes determining the asymmetry of the maxilla by determining the misalignment between the optimal plane of symmetry for the maxilla and the midsagittal plane of the skull. Step 410 includes determining the optimal plane of symmetry for the mandible. Step 412 includes determining the asymmetry of the mandible by determining the misalignment between the optimal plane of symmetry for the mandible and the midsagittal plane of the skull. Any deviation greater than +5 degrees and less than -5 degrees between the midsagittal plane of the skull and the optimal plane of symmetry for the maxilla or mandible is considered a misalignment, i.e., asymmetry. Optionally, any deviation greater than +2 degrees or less than -2 degrees may be considered asymmetry. In another optional example, any deviation greater than 0 degrees may be considered asymmetry.

[0092] Step 414 includes determining the corrected position of the maxilla and the mandible. Step 416 includes aligning the maxilla and mandible to their respective corrected positions in a 3D digital model of the skull. Step 418 includes presenting the maxilla and mandible in their corrected positions on a 3D digital model of the skull. In one example, at the corrected position, the optimal plane of symmetry of the maxilla, the optimal plane of symmetry of the mandible, and the midsagittal plane of the skull are aligned such that the asymmetry angle is less than -5 degrees to +5 degrees. Preferably, the corrected position refers to a position where the angle between the optimal plane of symmetry of the maxilla and / or mandible and the midsagittal plane of the skull is between -2 degrees and +2 degrees.

[0093] The advantage of methods 300 and 400 lies in representing the asymmetry as a misalignment between the midsagittal plane of the skull and the optimal plane of symmetry of the maxilla and / or mandible. The optimal plane of asymmetry of the maxilla and / or mandible can be registered to the midsagittal plane of the skull via a "plane-to-plane" registration method to correct the asymmetry, thus facilitating the automation of methods 300 or 400. Because plane-to-plane registration can be achieved using existing automated algorithms, the following steps can typically be completed with the click of a button: (a) parameterizing the two planes (i.e., representing them in the form of plane parametric equations) and determining the unit normal vectors of the two planes; (b) rotation transformation, rotating the normal vector of one plane using a rotation matrix constructed based on the unit normal vectors of the two planes so that it completely coincides with (or is parallel to) the normal vector of the other plane; (c) translation transformation: based on parallelism, calculating the shortest distance between the two planes (e.g., the projection distance from a point to a plane), and then translating the target object along the direction of the normal vector to make this distance zero, thereby achieving automatic alignment of the two planes. Thus, methods 300 and 400 can be executed automatically. In one example, methods 300 and / or 400 can be implemented using a Python script. Alternatively, the method can be executed by clicking a few buttons, which also provides a simple, streamlined, and standardized process.

[0094] Figure 3B Another exemplary embodiment of method 420 for asymmetry assessment and correction in computer-assisted maxillofacial surgery is shown. Method 420 may be an alternative to method 400 or a workflow. Method 420 includes steps 402 and 404 similar to method 400.

[0095] Step 422 involves aligning the maxilla and mandible (e.g., articulating them) into a single maxillary unit. Step 424 involves determining the optimal plane of symmetry for this maxillary unit (i.e., the maxilla and mandible). Step 426 involves determining the asymmetry of this maxillary unit. This asymmetry can be determined as a misalignment between the optimal plane of symmetry of the maxillary unit and the midsagittal plane of the skull, i.e., an alignment difference. Any deviation greater than +5 degrees or less than -5 degrees between the midsagittal plane of the skull and the optimal plane of symmetry of the maxillary unit is considered a misalignment, i.e., an asymmetry exists. Optionally, any deviation greater than +2 degrees or less than -2 degrees can be considered an asymmetry. In another optional example, any deviation greater than 0 degrees can be considered an asymmetry. Step 428 involves determining the corrected position of the maxillary unit. Step 430 involves presenting the maxilla and mandible in the corrected position on a 3D model of the skull.

[0096] Figures 4A to 4CAn exemplary embodiment of a method 500 for asymmetry assessment and correction in computer-assisted maxillofacial surgery (e.g., orthognathic surgery) is shown. Method 500 illustrates a continuous implementation process. The implementation process of the method is shown in three figures, but should be considered as a continuous overall scheme. The method is broadly divided into four parts: 1) preoperative preparation; 2) surgical planning and review; 3) surgical procedure; and 4) postoperative management.

[0097] First, during the preoperative process, a clinical assessment can be conducted and clinical records collected. During the clinical assessment, the patient's perception of facial deformity and surgical expectations, as well as their previous treatment history and any potential medical conditions, can be documented. A comprehensive examination, including extraoral and intraoral assessments, can be performed according to the established orthognathic surgical plan. A case report can be prepared. Notably, the symmetry of the eyes, cheeks, nose, ears, lips, and mandible can be assessed, as well as the deviation of the nasal, chin, and upper and lower dental midlines relative to the facial midline, and the tilting of the maxilla and mandible. A comprehensive clinical assessment can aid in clinical decisions regarding the initial surgical plan and help determine whether asymmetry correction is necessary.

[0098] Simultaneously, comprehensive clinical records can be collected for treatment planning. These records include photographs, cephalometric X-rays, dental molds, dental X-rays, and facial arch records. For example, when acquiring relevant data on the patient's head and face, cone-beam computed tomography (CBCT) can be performed, covering the skull from the supraorbital margin to the chin, using the Planmeca ProMax® 3D Mid imaging unit with standard preset parameters for full maxillofacial imaging. Patients can also be guided to maintain occlusal position for better assessment of jaw asymmetry under static conditions rather than dynamic mouth-opening states. Facial scans in .obj format can be performed using the 3dMDface™ system for soft tissue analysis and simulation. If needed, the patient's occlusion will be scanned using the 3Shape TRIOS 4 Wireless Pod (3Shape, Poland). Scan models can be exported in .stl format.

[0099] After initial preoperative preparation, the acquired images can be received by the computing device 200, after which the surgical planning and review process can begin. (Reference) Figures 4A to 4CIn step 502, CBCT data of the skull is received. Step 504 includes automatic CBCT segmentation, separating different structures such as the skull, maxilla, mandible, and teeth to generate independent digital models that can be used for 3D modeling. Skull segmentation can be performed using AI models or AI programs. In one example, fully automated bone and tooth segmentation driven by AI in Mimics Viewer and Blue Sky Plan v4.12 can be used to perform skull segmentation. The segmented files can be transferred to Mimics 21.0 and 3-matic 13.0 for quality control and refinement, especially for repairing the thin bone structure of the anterior wall of the maxillary sinus.

[0100] Step 506 includes creating a 3D model of the patient's skull based on CBCT data. The 3D model can be a 3D digital model of the skull. Step 508 may include using a surface- or voxel-based ICP algorithm to determine a preliminary midsagittal plane. Step 510 includes determining the horizontal plane of the skull model. Step 512 includes determining the coronal plane of the skull model. Step 514 includes establishing (i.e., identifying) a skull reference frame, i.e., identifying the midsagittal plane of the skull model using a midsagittal-first approach.

[0101] In maxillofacial surgery, the midsagittal plane is typically determined first, followed by the horizontal plane (Frankfurt plane), and finally the coronal plane. The midsagittal plane is a key parameter for automated asymmetry assessment and correction. After determining the midsagittal plane, the horizontal and coronal planes can be selectively determined. Alternatively, the horizontal and coronal planes can be left undefined, and only the midsagittal plane can be determined or calculated.

[0102] A skull reference system can be established in 3-matic 13.0 (Materialise) using a Python script. The skull reference system is a three-dimensional coordinate system used to define the position and orientation of the skull, consisting of three mutually orthogonal planes—the median sagittal plane, the horizontal plane, and the coronal plane. The process for generating the skull reference system follows a "median sagittal plane first" approach. The initial median sagittal plane is defined as the optimal symmetry plane of the skull, created using a surface-based ICP algorithm. This involves mirroring and aligning a region of the skull; the aligned region can then be used to calculate a new mirrored plane or the optimal symmetry plane. The horizontal plane is defined as a plane perpendicular to the initial median sagittal plane and passing through the auricular and orbital points (either side is acceptable). Finally, the coronal plane is defined as a plane perpendicular to both the initial median sagittal plane and the horizontal plane, passing through the sella turcica point. The median sagittal plane can be calculated using the methods described above and based on the determined horizontal plane (in step 510) and coronal plane (in step 512).

[0103] In step 516, based on the skull reference frame, the skull is automatically repositioned and registered to the world coordinate system for visualization and manipulation. In step 518, it is checked whether the skull has been correctly repositioned to the world coordinate system. If not, steps 514 and 516 can be repeated (i.e., reprocessed).

[0104] Figure 5 A 3D digital model 600 of the skull, the midsagittal plane, and an example of the skull reoriented based on the determined reference frame are shown. Figure 5 View 602 in the image shows an example of a patient skull model created from CBCT scan data. Figure 5 View 604 in the figure shows the reference frame R of the skull. The reference frame R includes the midsagittal plane (MSP) and the horizontal plane (HP). Figure 5 View 606 in the diagram shows the skull model reoriented (i.e., repositioned and registered) to the world coordinate system. The world coordinate system is based on the reference system R and the x, y, and z axes defined on it.

[0105] Step 520 involves performing 3D cephalometrics to provide an analysis of mandibular asymmetry. A comprehensive analysis of mandibular asymmetry is provided in ProPlan CMF 3.0 using 3D cephalometrics. In step 522, multiple cephalometric landmarks can be manually defined. After manually indicating the cephalometric landmarks, as defined in step 524, all lines, planes, and measurements can be automatically generated to produce a comprehensive cephalometric analysis report. Step 526 includes automatic tracking of bone movement. Furthermore, as bone segments are repositioned, the cephalometric landmarks are automatically adjusted, allowing for the tracking of quantitative changes in the surgical plan. In step 528, a virtual surgical plan can be developed.

[0106] Steps 530 to 534 define the steps for generating or identifying the optimal symmetry plane of the jawbone. The output of step 538 is also used as the input to step 534 to determine the optimal symmetry plane of the jawbone.

[0107] Step 530 includes performing a virtual Le Fort type I osteotomy. This procedure can be performed in a standard manner. Step 532 includes identifying or locating the dental segments (also referred to as tooth-bearing segments) of the maxilla and / or mandible. Step 534 includes generating an optimal plane of symmetry for the jaws (i.e., the maxilla and / or mandible). The optimal plane of symmetry for the jaws is determined for the dental segments. The output of Step 536 is used to generate the optimal plane of symmetry. Step 536 includes aligning the maxilla and / or mandible to achieve occlusion of the maxilla and / or mandible. Step 538 includes identifying the occlusion between the maxilla and / or mandible.

[0108] The optimal plane of symmetry for the maxillary dentate segment can be constructed using the same method as the midsagittal plane of the skull. Similarly, a virtual bilateral sagittal splitosteotomy (BSSO) can be performed to divide the mandible into two proximal condylar segments (also known as condylar-bearing segments) and a distal dentate segment. Therefore, the optimal plane of symmetry for the distal mandibular segment will be automatically constructed.

[0109] Figure 6 A skull model 600 is shown, and the best symmetry plane (BSP) is being identified. Figure 6 In view 610, the optimal plane of symmetry is drawn on the skull model. The optimal plane of symmetry divides the maxilla and / or mandible into two symmetrical parts. Figure 6 View 612 shows the toothed bone segment 620 as a single piece.

[0110] Step 542 includes performing an automated asymmetry assessment. In step 542, the deviation between the midsagittal plane of the skull and the optimal plane of symmetry for the maxilla and / or mandible is calculated. A comprehensive asymmetry assessment is presented in 3D cephalometric measurements. The asymmetry assessment is represented by the deviation between the midsagittal plane of the skull and the optimal plane of symmetry for the maxilla or mandible. The deviation is quantified as a 3D angle, as well as angles in the sagittal, horizontal, and coronal planes. Furthermore, the maxilla and mandible are separated along the midsagittal plane of the skull, both before and after asymmetry correction. Subsequently, the 3D deviations of the left and right sides of the maxilla and mandible are compared to illustrate the degree of asymmetry and the effectiveness of the asymmetry correction.

[0111] Any deviation greater than +5 degrees and less than -5 degrees between the midsagittal plane of the skull and the optimal plane of symmetry of the maxilla and / or mandible is considered misalignment, i.e., asymmetry. Alternatively, any deviation greater than +2 degrees or less than -2 degrees may be considered asymmetry. In another optional example, any deviation greater than 0 degrees may be considered asymmetry. Reference Figure 6 View 614 shows the deviation between the optimal plane of symmetry and the midsagittal plane. (As shown...) Figure 6 As shown in view 614, the deviation of the chin is 6.08 degrees. Variations may also exist along the maxilla. In the example shown, a deviation of 3.53 degrees is displayed.

[0112] Step 544 includes automatically performing asymmetry correction. Asymmetry correction includes performing plane-to-plane alignment. In step 542, the optimal plane of symmetry of the jawbone (i.e., the maxilla and / or mandible) is aligned with the midsagittal plane of the skull. The jawbone (maxilla and / or mandible) can be moved to the corrected position. The corrected position refers to the position where the midsagittal plane is aligned with the optimal plane of symmetry of the jawbone. Alternatively, the corrected position can also refer to the position where the upper and lower teeth are aligned with each other to achieve precise occlusion.

[0113] Since asymmetry is represented as a misalignment between the midsagittal plane of the skull and the optimal plane of symmetry for the maxilla or mandible, automatic asymmetry correction will be performed using a "plane-to-plane" alignment. For the maxilla, a new sagittal plane parallel to the midsagittal plane of the skull with its origin at the same point as the optimal plane of symmetry for the maxilla can be created and set as a fixed entity. The optimal plane of symmetry for the maxilla can then be aligned with this new sagittal plane while moving the maxilla with teeth, thereby correcting the asymmetry of the maxilla with movement in both the sagittal and vertical vectors. The mandible and chin will be corrected in a similar manner.

[0114] Figure 7 Automatic asymmetry correction, i.e., automatic realignment of the jaws, is illustrated. View 620 shows the maxilla 630 and mandible 632 being reoriented such that two planes, namely the midsagittal plane and the optimal symmetry plane, are aligned such that the difference between the two planes is 0 degrees or substantially 0 degrees.

[0115] This method checks whether occlusal registration has been performed. If not, the method proceeds to step 560 below; if yes, the method proceeds to step 546. In step 546, maxillofacial surgery is modeled in a dental plaster model. A complete OGS plan requires optimal final occlusion. The occlusion is achieved in the dental plaster model and scanned using a 3Shape intraoral scanner. In step 548, it is checked whether the occlusion is optimal. If not, the method proceeds to step 538, adjusting the maxilla and / or mandible to achieve proper occlusion. This feedback leads to recalculation of the optimal plane of symmetry and recalculation and correction of asymmetry.

[0116] If the occlusion does not meet the desired outcome of asymmetry correction, minor adjustments to the maxilla or mandible will be made, if clinically permissible. Otherwise, skeletal symmetry will be prioritized, and the occlusion will be refined during postoperative orthodontic treatment. Collision detection will be activated to monitor occlusal contact maps. If the occlusion is still unsatisfactory, a multi-piece LeFort I osteotomy (2 or 4 pieces) or a mandibular osteotomy (BSSO combined with Hofer osteotomy) will be performed as indicated below, which will be further detailed below.

[0117] If the result of step 548 is yes, meaning optimal occlusion has been achieved, the method proceeds to step 550. In step 550, the final occlusion is confirmed. The final occlusion can be scanned. The scanned occlusion will be imported into ProPlan CMF 3.0 to guide occlusal registration in the virtual surgical plan. The scanned upper teeth can be registered to the maxilla first, and then the mandible can be registered to the scanned lower teeth, thereby aligning the mandible to the maxilla based on the scanned occlusion.

[0118] Figure 7 Examples of occlusion checks and final occlusion checks are shown. View 622 shows that optimal occlusion has been achieved, and the midsagittal plane and the optimal plane of symmetry are aligned with each other. This indicates that optimal alignment and asymmetry correction have been achieved.

[0119] In step 552, the occlusal mandibular complex is generated, for example, according to view 622. The occlusal mandibular complex can be manually moved to translate along the sagittal (anteroposterior) and vertical (hyper-hyper) vectors, and rotated about the lateral (medial-lateral) vector (pitch). In step 554, the optimal occlusion and skeletal relationship are checked. If minor discrepancies exist, some fine-tuning is performed in step 558.

[0120] If significant discrepancies exist, the method proceeds to step 556. Step 556 involves performing multi-piece bone segmentation. Multi-piece bone segmentation complements mono-piece LeFort I osteotomy or BSSO. Two-piece LeFort I osteotomy (according to step 540) is used to expand or narrow the palatal arch, while four-piece LeFort I osteotomy aims to level the occlusal plane, correct anterior open bite, improve midfacial defects, and prevent steep occlusal planes. Hofer osteotomy is primarily used to correct alveolar bone hyperplasia. In multi-piece bone segmentation, the final occlusion can be confirmed to guide the alignment of each individual bone segment. Once properly aligned, these segments are treated and manipulated in the same manner as a mono-piece dental maxilla or mandible. This multi-piece bone segmentation can be used to recalculate the optimal symmetry plane as well as asymmetry calculations and corrections.

[0121] If an optimal occlusion and skeletal relationship exists, then step 560 is performed. Step 560 includes translation of the jawbone along the sagittal vector. The jawbone is translated along the sagittal vector, i.e., forward or backward. Step 562 includes vertical translation of the jawbone along the vertical vector, i.e., upward or downward. Step 564 includes rotation of the jawbone about the transverse vector, i.e., clockwise or counterclockwise rotation.

[0122] Step 566 includes checking whether a satisfactory midface profile and occlusal plane have been achieved. If not, the method proceeds to step 556. If yes, the method proceeds to step 568. Step 568 includes checking whether genioplasty is required. Genioplasty (i.e., genioplasty) is evaluated and performed in step 568. If asymmetry correction in the chin region is necessary, a virtual genioplasty osteotomy is performed in step 572 to separate the chin, thereby enabling the creation of an optimal symmetry plane for the chin and facilitating automatic asymmetry correction. Correction will also be performed in the sagittal and vertical directions as described above. Step 574 includes chin dissection as part of chin correction. Figure 7 View 624 illustrates chin correction. The chin 634 of the model can be segmented from the rest of the mandible and positioned correctly. As part of a virtual chin augmentation, portions of the mandible can be adjusted to correctly position the chin. Portions of the mandible can be cut and / or adjusted in three-dimensional space to ensure chin symmetry and correct positioning. Once step 574 is completed, the method returns to step 542.

[0123] When genioplasty is no longer required, or when genioplasty has been completed, the method proceeds to step 570. Step 570 includes generating an automated surgical plan, which includes the relevant surgical procedures and corresponding parameter information involved in the steps described above. As part of the automated surgical plan, step 576 includes performing a soft tissue simulation. After the bone segments have been surgically repositioned, 3D facial soft tissue can be simulated using ProPlanCMF 3.0. Initially, a 3D facial image of the patient in .obj format is mapped onto a 3D soft tissue model segmented from CBCT and registered using corresponding points. Then, a new simulation can be calculated by selecting the original (preoperative) soft tissue as well as all repositioned and fixed bone segments. Once the simulation is generated, animation can be played to visualize the changes in soft tissue. Finally, the preoperative and planned soft tissues are compared by selecting and aligning 3D objects, and the differences are visualized using color mapping.

[0124] The method proceeds to step 578. Step 578 includes performing a review and modification. The initial virtual surgical plan, which may be referred to as the “automated surgical plan,” can be reviewed by an experienced surgeon and modified as necessary. Step 578 instructs this review. The revised plan is then referred to as the “reviewed surgical plan.” Any modifications made can be automatically tracked by 3D cephalometrics and used in studies evaluating clinical feasibility and effectiveness. The review may consider the key factors indicated at step 580. The key factors for review include one or more of the following: 1) midlines of the teeth and jawbone, 2) maxillary incisor points: vertical and anteroposterior dimensions, 3) occlusion and jawbone tilt, and 4) jawbone symmetry.

[0125] The review in step 578 may also consider the additional factors mentioned in step 582. Additional factors may include any one or more of the following: a) orthodontic preference versus surgical preference, b) other better surgical methods, c) additional surgical procedures, such as bone contouring, mandibular angle reduction, zygomatic augmentation or enlargement, and d) soft tissue asymmetry.

[0126] Step 584 involves modifying the automated surgical plan based on the considerations defined in steps 580 and 582. If no further modifications are needed, the method proceeds to step 586; if modifications are still required, it returns to step 576. A reviewed surgical plan is generated in step 586 and can be provided to the dental surgeon. In step 588, the reviewed surgical plan can be used for 3D design of occlusal plates and / or other implants or orthodontic devices. In step 590, the reviewed surgical plan can be used for 3D printing of occlusal plates and / or other implants or orthodontic devices. The reviewed surgical plan can be used to design a digital occlusal plate in ProPlan CMF 3.0, or to design patient-specific surgical guides and bone plates in 3-matic 13.0, following a surgeon-led approach. Optionally, the occlusal plate can be printed using a NextDent 5100 DLP 3D printer (3D Systems, USA) and NextDent SG resin (3D Systems). Patient-specific surgical guides and bone plates can be printed using commercially pure secondary titanium powder with a Mlab cusing R SLM printer (GE Additive, USA). The printed occlusal plates and titanium components can be post-processed using standard procedures and autoclaved before use.

[0127] Examples of some surgical procedures are described below. Standard perioperative management of OGS, including surgical procedures, can be performed. For example, in the maxilla, a standard LeFort type I osteotomy combined with bilateral tubercle osteotomy can be performed to allow for descent and mobility of the toothed CAOGS AutoSymmetry. The maxilla can be reconstructed using an occlusal plate and fixed with four standard L-shaped miniature bone plates. In the mandible, a standard BSSO osteotomy with a Hansuck modification can be performed for bilateral mandibular ramus splitting. The mandible can be reconstructed using an occlusal plate and fixed with a standard straight miniature bone plate on each side. Multi-piece bone division can be performed in a standard manner according to instructions. In cases where 3D-printed patient-specific surgical guides and bone plates are used for the maxilla or chin, the surgical procedures can remain unchanged, except that the osteotomy can be guided by the surgical guide and fixation will be achieved using patient-specific surgical bone plates.

[0128] Standard postoperative management can be performed. Patients can have routine follow-up at one, three, six, three, six, one, and two years postoperatively. X-rays and clinical photographs can be taken as instructed. CBCT can be performed one year postoperatively for asymmetry assessment. Asymmetry assessment and 3D cephalometric analysis can be performed as described in this article (300, 400, or 500), just as preoperatively. Patient-reported results can also be collected. Any side effects should be documented and managed in a routine manner. Any residual asymmetry or recurrence should be documented for detailed analysis, and any additional treatment should be recorded.

[0129] In this exemplary embodiment, any one or more of methods 300, 400, and 500 can be implemented by computing device 200. Computing device 200 can be implemented by any computing architecture, including portable computers, tablet computers, standalone personal computers, smart devices, Internet of Things devices, edge computing devices, client / server architectures, "dumb" terminal / mainframe architectures, cloud computing-based architectures, or any other suitable architecture. Computing device 200 can be appropriately programmed to implement the methods described herein for the assessment and correction of asymmetry in computer-assisted orthognathic surgery.

[0130] Figure 8 A schematic diagram of a computing device or computer or computing apparatus 200 is shown, arranged as an exemplary embodiment of a system for the assessment and correction of asymmetry in computer-assisted orthognathic surgery. Figure 8 In the example shown, the computing device includes suitable components required to receive, store, and execute appropriate computer instructions. These components may include a processing unit 202, a read-only memory (ROM) 204, a random access memory (RAM) 206, a communication link 214, and input / output devices such as a disk drive 208, an input device 210 (e.g., an Ethernet port, a USB port, etc.), a display 212, etc. The processing unit 202 may include a central processing unit (CPU), a math coprocessor (math processor), a graphics processing unit (GPU), or a tensor processing unit (TPU) for tensor or multidimensional array calculations or operations. The display 212 may be, for example, a liquid crystal display, a light-emitting display, or any other suitable display. The display 212 may be a user interface that presents information, data, or images to a user (e.g., a dental surgeon). The display 212 (i.e., the user interface 212) may display the calculated asymmetry of the patient's digital skull and the proposed asymmetry correction scheme.

[0131] A computing device (e.g., server 200) may include instructions, which may be contained in ROM 204, RAM 206, or disk drive 208 and executed by processing unit 202. When executed, these instructions may cause computing device 200 to perform steps (i.e., methods 300, 400, or 500) of a method for asymmetry assessment and correction in computer-assisted orthognathic surgery, as described herein. Each ROM and RAM may be a non-transient computer-readable medium storing computer-readable and executable instructions. Processor 202 may be adapted to read and execute the stored instructions. Any one or more of the methods 300, 400, or 500 described herein for asymmetry assessment and correction in computer-assisted orthognathic surgery may be embodied as computer-readable and executable instructions stored in a storage unit (e.g., RAM or ROM).

[0132] Multiple communication links 214 can be provided, which can be connected to one or more computing devices, such as servers, personal computers, terminals, wireless or handheld computing devices, Internet of Things devices, smart devices, and edge computing devices. At least one of the multiple communication links can be connected to an external computing network via a telephone line or other types of communication link.

[0133] Server 100 may include a storage device, such as disk drive 208, which may include a solid-state drive, hard disk drive, optical disk drive, tape drive, or remote or cloud-based storage device. Computing device 200 may use a single disk drive or multiple disk drives, or remote storage services. Computing device 200 may also have a suitable operating system residing on the disk drive or in the ROM of server 100.

[0134] The computing device may further include one or more databases 220 adapted to store one or more data entries. For example, the database may store patient-related calculations or detected asymmetries. The database may also store correction plans applied to each patient. This data can be used for postoperative follow-up or as a record.

[0135] The computing device may also provide the necessary computing power to operate or interact with machine learning networks (such as neural networks) to provide various functions and outputs. Neural networks may be implemented locally or accessed, or partially accessed, via a server or cloud-based service. Machine learning networks may also be untrained, partially trained, or fully trained, and / or may be retrained, tuned, or updated over time. The computing device may include one or more GPUs operatively coupled to a CPU (i.e., a processor). The computing device may include additional hardware components operatively coupled to the CPU and / or GPU to provide the computing device components required to implement the machine learning network or machine learning model. The learning network or model may be stored in a storage unit (e.g., ROM).

[0136] The methods (300, 400, 500) and system 100 described herein for asymmetry assessment and correction in computer-assisted orthognathic surgery are beneficial because asymmetry is represented by the misalignment between the midsagittal plane of the skull and the optimal plane of symmetry of the maxilla or mandible. Asymmetry can thus be corrected by aligning the optimal plane of symmetry of the maxilla or mandible to the midsagittal plane of the skull using a "plane-to-plane" registration method, automating asymmetry correction. This process can be automated using Python scripts or by clicking buttons within the software, which is more standardized and simplified. This method can be integrated with and enhanced within existing CAOGS workflows, simplifying asymmetry correction operations such as lateral translation, yaw rotation, and rolling rotation.

[0137] To better understand the scheme of this application, a brief introduction to the plane-to-plane registration method is provided, which mainly includes the following steps:

[0138] A1: Parameterization of Plane Equations

[0139] Plane fitting is performed on the extracted source plane features and target plane features to obtain the parametric equations of the source plane and target plane, respectively. The parametric equation of each plane takes the following form:

[0140]

[0141] in, For unit normal vector, The sign distance is the distance from the plane to the origin of the coordinate system.

[0142] A2: Normal Vector Extraction and Reference Point Determination

[0143] Extract the source plane unit normal vector from the source plane parametric equations. and the coordinates of the geometric center of the source plane Extract the unit normal vector of the target plane from the target plane parametric equations. and the coordinates of the geometric center of the target plane .

[0144] A3: Construction of Rotation Matrix

[0145] Based on the source plane normal vector Normal vector of the target plane Construct rotation matrix , so that the following conditions are met:

[0146]

[0147] The steps for constructing the rotation matrix specifically include:

[0148] (1) Calculate the rotation axis vector It is defined as the cross product of two normal vectors and normalized:

[0149]

[0150] (2) Calculate the rotation angle It is defined as the angle between two normal vectors:

[0151]

[0152] (3) Construct the rotation matrix using Rodriguez's rotation formula :

[0153]

[0154] in, for The identity matrix, Rotation axis vector The antisymmetric cross product matrix has the following form:

[0155]

[0156] A4: Translation Vector Calculation

[0157] According to the geometric center of the source plane and the geometric center of the target plane and rotation matrix Calculate the translation vector This ensures that the center of the rotated source plane falls on the target plane. The formula for calculating the translation vector is:

[0158]

[0159] Alternatively, optimization calculations can be performed based on the principle of minimizing the point-to-plane distance to further improve alignment accuracy.

[0160] A5: Transformation Matrix Composition and Application

[0161] Rotation matrix With translation vector Combined into rigid body transformation matrix Its form is:

[0162]

[0163] By applying this transformation matrix to all spatial points in the first dataset, the source plane and its associated 3D data can be transformed as a whole to a position aligned with the target plane.

[0164] The system and method described in this paper for asymmetry assessment and correction in computer-assisted orthognathic surgery enable 3D visualization of the skull and simulation of bone movement, which has inherent advantages in addressing asymmetric deformities. The method described provides an automated workflow that standardizes asymmetry assessment and simplifies asymmetry correction.

[0165] The method described in this paper for asymmetry assessment and correction in computer-assisted orthognathic surgery is advantageous because it provides an automated digital workflow via Python scripts. Furthermore, the method employs a "median sagittal plane priority" approach and an "iterative nearest point (ICP)" algorithm to establish a robust cranial reference frame. This method is also advantageous because jaw asymmetry is represented by the misalignment between the midsagittal plane of the skull and the optimal plane of symmetry of the maxilla or mandible. This method provides an automated approach to asymmetry correction. Moreover, it is advantageous because asymmetry correction is automated by aligning the optimal plane of symmetry of the maxilla and / or mandible with the midsagittal plane of the skull using a "plane-to-plane" registration method.

[0166] As mentioned above, the methods used for asymmetry assessment and correction can be applied to orthognathic surgery, but also to other types of maxillofacial surgery, such as jaw reconstruction, craniofacial surgery, or other jaw surgeries requiring asymmetry correction. Furthermore, these methods can also be applied to other types of maxillofacial surgery that may require correction of jaw alignment or asymmetry.

[0167] Although not strictly necessary, the embodiments described with reference to the accompanying drawings can be implemented as an application programming interface (API) or as a series of libraries for developers to use, or can be included in another software application, such as a terminal or personal computer operating system or a portable computing device operating system. Typically, since program modules include routines, programs, objects, components, and data files that assist in performing specific functions, those skilled in the art will understand that the functionality of a software application can be distributed across multiple routines, objects, or components to achieve the same functionality required herein.

[0168] It will also be understood that, where the methods and systems of this application are implemented entirely or partially by a computing system, any suitable computing system architecture may be used. This will include stand-alone computers, network computers, and dedicated hardware devices. When the terms "computing system" and "computing device" are used, these terms are intended to cover any suitable computer hardware arrangement capable of implementing the functions described above.

[0169] Those skilled in the art will understand that various changes and / or modifications can be made to the embodiments of this application without departing from the spirit or scope of this application as broadly described. Therefore, the various embodiments of this application should be considered illustrative rather than restrictive in all respects.

[0170] Unless otherwise stated, any references to prior art contained herein should not be construed as an admission that the information is common general knowledge.

[0171] As used in this application, the terms "computer-readable medium" or "machine-readable medium" should include single or multiple media, unless the context otherwise requires. Examples of multiple media include centralized or distributed databases and / or associated caches. These multiple media store one or more sets of computer-executable instructions. The phrase "computer-readable medium" or "machine-readable medium" should also be considered to include any medium capable of storing, encoding, or carrying a set of instructions executable by a processor of a computing device, and causing the processor to perform any one or more of the methods described herein. Computer-readable media can also store, encode, or carry data structures used by or associated with these sets of instructions. The phrases "computer-readable medium" and "machine-readable medium" include, but are not limited to, portable fixed storage devices, solid-state storage, optical media or optical storage devices, magnetic media, and / or various other media capable of storing, containing, or carrying instructions and / or data. "Computer-readable medium" or "machine-readable medium" can be non-transient. The term "comprising" (and its grammatical variations) as used herein is used in the sense of inclusion, i.e., "having" or "containing," rather than in the sense of exclusivity (i.e., "consisting of only").

[0172] Furthermore, it is worth noting that an embodiment can be described as a process, which can be depicted as a flowchart, flow diagram, structure diagram, or block diagram. Although a flowchart can describe operations as a sequential process, many operations can be executed in parallel or simultaneously. Moreover, the order of operations can be rearranged. The process terminates when its operations are completed. A process can correspond to a method, function, procedure, subroutine, subroutine, etc., in a computer program. When a process corresponds to a function, its termination corresponds to the function returning to the calling function or the main function.

[0173] The aspects of the above-described systems and methods are operable or achievable on any type of dedicated or special computer, or any machine or computer or server or electronic device with a microprocessor, processor, microcontroller, programmable controller, etc., or cloud-based platform or other processor and / or server network (whether local or remote), or any combination of such devices.

[0174] The methods or algorithms described in conjunction with the examples disclosed herein can be implemented directly in hardware, in a processor-executable software module, or a combination of both, as a processing unit, programming instructions, or other indications, and can be contained in a single device or distributed across multiple devices. The software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art. The storage medium can be coupled to the processor, enabling the processor to read information from and write information to the storage medium. Alternatively, the storage medium can be integrated with the processor.

[0175] Without departing from the scope of this application, one or more components and functions shown in the accompanying drawings may be rearranged and / or combined into a single component, or implemented in multiple components. Additional elements or components may also be added without departing from the scope of this application. Furthermore, the features described herein may be implemented in software, hardware, as a business method, and / or combinations thereof.

Claims

1. A computer device for the assessment and correction of asymmetry in maxillofacial surgery, comprising a processor and a memory, wherein instructions are stored in the memory, and the processor executes the instructions to: Generate or receive a three-dimensional digital model of the patient's skull, the three-dimensional digital model also including the patient's jawbone; Identify the midsagittal plane of the skull; Determine the optimal plane of symmetry for the jawbone; Asymmetry is determined based on the misalignment between the optimal plane of symmetry of the jawbone and the midsagittal plane of the skull, wherein the asymmetry is expressed as the angle between the optimal plane of symmetry and the midsagittal plane; For the optimal symmetry plane of the jawbone and the midsagittal plane of the skull, the determined asymmetry is corrected by plane-to-plane registration so that the angle between the optimal symmetry plane and the midsagittal plane is within a preset range.

2. The computing device of claim 1, wherein the asymmetry is represented as any angle greater than +5 degrees or less than -5 degrees between the optimal symmetry plane and the median sagittal plane, and the preset range is +5 degrees to -5 degrees.

3. The computing device according to claim 1, wherein the asymmetry is represented as any angle greater than +2 degrees or less than -2 degrees between the optimal symmetry plane and the median sagittal plane, and the preset range is +2 degrees to -2 degrees.

4. The computing device according to any one of claims 1-3, wherein, The asymmetries identified by correction include: Determine the corrected position of the jawbone relative to the skull, wherein the corrected position refers to the position where the angle between the optimal plane of symmetry of the jawbone and the midsagittal plane of the skull is within the preset range; In the three-dimensional digital model, the jawbone is automatically aligned and repositioned to the corrected position by performing plane-to-plane registration between the optimal symmetry plane of the jawbone and the midsagittal plane of the skull.

5. The computing device according to claim 4, wherein, The asymmetry identified by correction also includes: Record and save the surgical procedures and related parameters performed during the automatic alignment of the jawbone.

6. The computer device according to claim 4, wherein the corrected position of the jawbone is a position where the optimal plane of symmetry of the jawbone is aligned with the midsagittal plane of the skull.

7. The computer device of claim 6, wherein the corrective positioning of the jawbone further includes aligning the maxillary teeth with the mandibular teeth.

8. The computer device according to any one of claims 1-3, wherein, Determining the optimal plane of symmetry for the jaw includes determining the optimal plane of symmetry for the maxilla and / or mandible.

9. The computer device according to any one of claims 1-3, wherein, Determining the optimal plane of symmetry for the jawbone involves aligning the patient's maxilla and mandible into a single maxillary unit, determining the optimal plane of symmetry for that unit, and expressing the asymmetry as the angle between the optimal plane of symmetry for that maxillary unit and the midsagittal plane of the skull.

10. A computer-implemented method for asymmetry assessment and correction in maxillofacial surgery, comprising: Generate or receive a three-dimensional digital model of the patient's skull, the three-dimensional digital model also including the patient's jawbone; Identify the midsagittal plane of the skull; Determine the optimal plane of symmetry for the jawbone; Asymmetry is determined based on the misalignment between the optimal plane of symmetry of the jawbone and the midsagittal plane of the skull, wherein the asymmetry is expressed as the angle between the optimal plane of symmetry and the midsagittal plane; For the optimal symmetry plane of the jawbone and the midsagittal plane of the skull, the determined asymmetry is corrected by plane-to-plane registration so that the angle between the optimal symmetry plane and the midsagittal plane is within a preset range.

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