A method for determining digital jaw torque attachments

Abstract

This invention discloses a method for determining digital dental malformation torque attachments. First, a digital dental malformation model is established based on the patient's CBCT data. The jawbone and tooth roots are shelled along the normal to obtain a three-dimensional model of the periodontal ligament. Boolean operations between the periodontal ligament and jawbone are used to obtain a digital dental malformation model containing the periodontal ligament. The digital dental malformation model, the constructed attachment model, and the invisible aligner model are assembled to obtain a digital dental malformation finite element simulation model. Then, the digital dental malformation finite element simulation model is meshed, material parameters are defined, and boundary conditions are determined. Finally, the initial tooth displacement and periodontal ligament stress distribution are analyzed based on the constructed digital dental malformation finite element simulation model to determine the safety of the attachment design for the movement of a specific individual incisor and the effectiveness of the torque design. Based on the interpretation results, the attachment design is modified or the attachment design is finalized.

Description

Technical Field

[0001] This invention belongs to the field of orthodontics, and specifically relates to a method for determining digital jaw torque attachments. Background Technology

[0002] With improvements in materials and the development and application of auxiliary structures such as attachments, invisible orthodontics has gradually expanded from its initial application only to mild crowding cases in Angle Class I to more complex cases. However, the actual treatment results differ from expectations, and 100% tooth movement cannot be achieved. According to previous studies and clinical reports, the proportion of cases requiring fine-tuning or fixed orthodontic assistance when using invisible aligners is as high as 70%-80%, with invisible aligners being particularly difficult to control in terms of tooth torque.

[0003] Controlling the incisor torque is a key and challenging aspect throughout orthodontic treatment. Good torque control not only affects the aesthetics of a frontal smile and profile, but also helps to establish appropriate overbite and overjet relationships, achieve stable stomatognathic function, and maintain healthy soft and hard tissue relationships.

[0004] With the development of invisible orthodontic technology, the proportion of complex cases is constantly increasing, placing higher demands on torque control. However, current research shows that the problem of insufficient torque expression in invisible orthodontics still exists, and the design of the pressure ridge increases the risk of "dislodgement." Therefore, whether the shortcomings can be compensated for through optimization of physical attachments and the efficiency of incisor torque control has become a major solution.

[0005] Finite element analysis (FEM), as a non-invasive virtual model, uses computer simulation of the patient's intraoral condition to analyze the forces acting on the model. Currently, the field of orthodontic invisible aligners widely utilizes FEM to analyze tooth movement trends, rotation centers, and periodontal ligament stress under different loading conditions. It can visually present the initial displacement trends of teeth and the distribution of periodontal ligament stress when the aligner is worn, and has significant application prospects in the study of mechanisms of action.

[0006] Current research by scholars both domestically and internationally largely employs the model overlap method, primarily focusing on crown movement while neglecting research on root movement. However, given the current state of affairs, such as weak torque control of incisors in invisible orthodontic treatment and insufficient clinical evidence for judging torque control in invisible orthodontic treatment, there is an urgent need for a method to determine the impact of different accessory designs on incisor torque control. This would enable clinicians to design invisible orthodontic treatment plans more accurately, rationally, and scientifically. Summary of the Invention

[0007] To address the problems in the technical background, this invention provides a method for determining digital dental torque attachments, enabling clinicians to more intuitively and accurately understand the torque force value of the designed incisor attachments, thereby designing orthodontic plans more scientifically and precisely.

[0008] The technical solution adopted in this invention includes the following steps:

[0009] S1: Establish a digital dental model including the jawbone and dentition based on the patient's CBCT data;

[0010] S2: The periodontal ligament is obtained by shelling the jawbone and tooth roots along the normal line. A digital dental model containing the periodontal ligament, jawbone, and dentition is obtained through Boolean operations between the periodontal ligament and the jawbone.

[0011] S3: Constructing the attachment model: The shape and size of the fixed attachment are designed according to the expected torque requirements of the incisors, and the pressure ridge of the structural attachment is simulated by the local concavity of the appliance;

[0012] S4: Assemble the digital dental model, attachment model and digital model of the invisible aligner from step S2 to obtain a digital dental finite element simulation model.

[0013] S5: Finite element analysis was used to analyze the movement trend of incisors and periodontal ligament stress under different attachment loading conditions;

[0014] S6: Compare the analysis results of step S5 with the expected torque setting value for the teeth and the safe force threshold of the periodontal ligament:

[0015] If the analysis results meet the expected torque setting value and the periodontal ligament is under safe force, the attachment design is completed; otherwise, the attachment model is reconstructed by modifying the attachment position or shape, and then the process returns to step S4 to update the attachment model in step S4.

[0016] Specifically, step S1 involves establishing a digital dental model from the patient's CBCT data by adjusting thresholds, region growth, and binarization, followed by precise surface processing including repair and noise reduction to form an optimized digital dental model.

[0017] In step S2, the periodontal ligament is assumed to be a homogeneous, continuous elastic structure with a thickness of 0.25 mm.

[0018] In step S3, the structural attachment pressure ridge has the following parameters: length 4mm, width 1mm, and depth 0.1mm. The fixing attachment is an attachment that is attached to the tooth, and it is designed through sketching, stretching, and cutting.

[0019] In step S4, the method for constructing the digital model of the invisible aligner is as follows: the dentition is shelled along the gingival margin to obtain a three-dimensional model of the clinical crown, and the surface is precisely curved to obtain a digital model of the bracketless invisible aligner; wherein, the thickness of the invisible aligner is set to 0.75mm.

[0020] In the digital finite element simulation model of the jaw in step S4, the rotation center for controlling root movement is set at the crown center of the incisor, and the design amount of the invisible orthodontic torque per step is 1°.

[0021] Step S5 specifically involves:

[0022] 5.1) Mesh generation: The established digital dental finite element simulation model is subjected to tetrahedral mesh generation, and nodes and meshes are automatically generated to obtain the mesh generation results of the digital dental finite element simulation model.

[0023] 5.2) Material parameter definition: Alveolar bone, periodontal ligament, teeth, clear aligners, and attachments are all homogeneous, continuous, and isotropic linear elastomers. Alveolar bone does not distinguish between cortical bone and spongy bone, and teeth do not distinguish between pulp, dentin, and enamel.

[0024] The elastic modulus of teeth is 19600 MPa and Poisson's ratio is 0.30; the elastic modulus of alveolar bone is 13700 MPa and Poisson's ratio is 0.30; the elastic modulus of periodontal ligament is 0.69 MPa and Poisson's ratio is 0.30; the elastic modulus of invisible aligners is 528 MPa and Poisson's ratio is 0.30; the elastic modulus of attachments is 12500 MPa and Poisson's ratio is 0.30.

[0025] 5.3) Boundary constraints and contact conditions:

[0026] The contacts between the alveolar bone and the periodontal ligament, the tooth root and the periodontal ligament, and the surfaces of attachments and the crown are all set as bonded contacts, and no relative sliding occurs between them; the contacts between the clear aligner and each tooth surface and attachment surface are all set as frictional contacts, with a coefficient of friction of 0.2.

[0027] The base of the maxilla, away from the dentition, is set as a fixed support, so that the clear aligner and teeth are not subjected to any load or constraint;

[0028] 5.4) Based on the world coordinate system of the digital dental finite element simulation model, a local coordinate system for a single incisor is established: the sagittal plane of the incisor is defined by the midpoint of the incisal edge, the apex, and the most prominent point of the lingual protuberance; the X-axis is perpendicular to the sagittal plane, with the mesial direction being positive; the Y-axis is perpendicular to the tooth's long axis, with the lingual direction being positive; and the Z-axis is the tooth's long axis, with the apical direction being positive.

[0029] 5.5) The orthodontic appliance is actively positioned on the dentition. Except for the incisors under study, the appliance is in close contact with the other teeth. There is local interference contact or separation between the incisors under study and the appliance. The initial displacement trend of the incisors and the stress distribution of the periodontal ligament are obtained through finite element analysis.

[0030] In step S6, the method for comparing the analysis results of step S5 with the expected torque setting value of the tooth and the safe force threshold of the periodontal ligament is as follows:

[0031] First, determine whether the periodontal ligament stress exceeds the safe threshold (26 kPa, determined based on previous research and clinical experience). If so, the system automatically reduces the size of the attachment to 0.9 times its original size and then returns to step S4.

[0032] If not, the system then determines whether the tooth torque expressed by the designed attachment is greater than the expected required torque. If so, the attachment cutting bevel is reduced by 1°, and then the process returns to step S4.

[0033] If not, the system continues to determine whether the tooth torque expressed by the designed attachment is less than the expected required torque. If so, the attachment cutting bevel is increased by 1°, and then the process returns to step S4.

[0034] If not, then complete the revision of the attachment and the design of the attachment.

[0035] The beneficial effects of this invention are:

[0036] 1. The method of the present invention has automatic analysis and result interpretation functions, which can more intuitively display the results of the mechanical expression of the attachments, improve the convenience for clinicians to modify the invisible orthodontic treatment plan, and improve the efficiency of clinical treatment.

[0037] 2. The method of the present invention can perform mechanical analysis of invisible orthodontic attachments and check the periodontal ligament stress of orthodontic teeth. If the periodontal ligament stress exceeds the safety threshold, the system will automatically reduce the size of the attachment until the periodontal ligament stress expressed by the attachment is within the safe range, which greatly improves the safety of invisible orthodontic treatment.

[0038] 3. Based on the periodontal ligament stress safety assessment of the designed torque attachment, the method of the present invention assesses whether the tooth torque force value of the designed attachment meets expectations. If it does not meet expectations, suggestions are given, such as increasing or decreasing the cutting surface of the attachment, to help clinicians more accurately adjust the incisor torque attachment in the invisible orthodontic treatment plan. Attached Figure Description

[0039] Figure 1 This is a schematic flowchart of the method for determining digital jaw torque attachments according to the present invention.

[0040] Figure 2 This is a schematic flowchart illustrating the modification of the digital jaw torque attachment in the method of this invention.

[0041] Figure 3This is a schematic diagram of a digital dental finite element simulation model and its components, where d represents alveolar bone, b represents the dentition, a represents the periodontal ligament, c represents the clear aligner, and e represents the digital dental finite element simulation model.

[0042] Figure 4 This is a schematic diagram of the attached model.

[0043] Figure 5 This is a schematic diagram of the finite element model of the structural attachment pressure ridge-orthodontic appliance. 1 represents the interference formed by the 0.1mm local concavity of the appliance and the tooth surface, 2 represents the appliance, 3 represents the tooth, and 4 represents the deformation space of the appliance.

[0044] Figure 6 This is a diagram illustrating how the incisors move.

[0045] Figure 7 This is a schematic diagram of boundary constraints and contact conditions. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] like Figure 1 The diagram shows a schematic flowchart of the method for determining digital dental torque attachments according to the present invention. First, a digital dental model including the jawbone and dentition is established based on the patient's CBCT data. The jawbone and tooth roots are then shelled along the normal to obtain a three-dimensional model of the periodontal ligament. Boolean operations between the periodontal ligament and jawbone are used to obtain a digital dental model including the periodontal ligament, jawbone, and dentition. Simultaneously, a finite element model of the attachment is constructed. The digital dental model, attachment model, and digital model of the clear aligner are assembled to obtain a digital dental finite element simulation model. Then, the digital dental finite element simulation model is meshed, material parameters are defined, and boundary conditions are determined. Finally, the initial tooth displacement and periodontal ligament stress distribution are analyzed based on the constructed digital dental finite element simulation model to determine the safety of the attachment design for the movement of a specific individual incisor and the effectiveness of the torque design. Based on the interpretation results, the attachment design is modified or the attachment design is finalized.

[0048] like Figure 3 This is a schematic diagram of a digital finite element simulation model of the dental jaw and its components. The patient's dental jaw includes the patient's alveolar bone d (maxillary bone d and / or mandibular bone d), dentition b, and its periodontal ligament a. The patient's dental jaw includes one or more teeth from the maxillary or mandibular dentition b and their periodontal ligament a. The overall assembled model obtained together with the clear aligner c is denoted as e.

[0049] This invention obtains a three-dimensional model of the periodontal ligament (a) by shelling the entire maxillary tooth root along the normal. A digital dental model containing the periodontal ligament is then obtained through Boolean operations between the periodontal ligament (a) and either the maxilla (d) or mandible (d).

[0050] like Figure 4 As shown, based on the shape, size, and location of commonly used clinical attachments, a semi-elliptical attachment model is obtained through sketching, stretching, and excision.

[0051] like Figure 5 The image shows the pressure ridge of the invisible aligner's structural accessory, simulated by a local indentation in the aligner. Its parameters are selected as 4mm in length, 1mm in width, and 0.1mm in depth.

[0052] like Figure 6 The diagram shows that this invention sets the rotation center for root movement control at the crown center, aiming to achieve lingual root movement while simultaneously expressing torque. The torque design for each step in invisible orthodontic treatment is generally around 1°.

[0053] like Figure 7 The diagram illustrates the boundary constraints and contact conditions in the method of this invention. The contacts between the alveolar bone and the periodontal ligament, the tooth root and the periodontal ligament, and the surfaces of attachments and the crown are all set as bonded contacts, meaning no relative sliding occurs between them. The contacts between the clear aligner and each tooth surface and attachment surface are set as frictional contacts, with a coefficient of friction of 0.2. The base of the jawbone, away from the dentition, is set as a fixed support, and no load or constraint is applied to the aligner or teeth. Specific implementation examples:

[0055] This invention sets the rotation center for root movement at the crown center, aiming to achieve lingual root movement while expressing torque. The torque design for each step in invisible aligner treatment is generally around 1°. Therefore, the right maxillary central incisor in the established maxillary alveolar bone-periodontal ligament-dental arch model is rotated counterclockwise by 1° with the crown center as the rotation center to obtain the final position. Then, the maxillary dentition is trimmed along the gingival margin to obtain clinical crown data. After removing 0.75mm along the normal direction, a precise curved surface is created to obtain a clear aligner model. The resulting alveolar bone (d), periodontal ligament (a), dentition (b), and attachments (...) are then... Figure 4 The invisible aligner (c) is assembled to obtain the final digital finite element simulation model (e) of the dental jaw. Using this digital finite element simulation model (e), a detailed analysis of the initial displacement trend of the incisors and the stress distribution of the periodontal ligament under different attachment designs is achieved, thereby determining the torque control effect of different attachment designs on the corresponding incisors.

[0056] The analysis results were compared with the expected torque setting for the teeth and the safe stress threshold for the periodontal ligament: First, through... Figure 1Finite element analysis is used to obtain the initial displacement and periodontal ligament stress distribution of the tooth caused by the constructed initial attachment. If the interpretation results show that the safety of the designed attachment for the corresponding tooth movement and the effectiveness of the torque design do not meet the requirements, then proceed to... Figure 2 Modify the attachments according to the process shown. For example... Figure 2 As shown, the safety of tooth movement (i.e., the periodontal ligament force exceeds the safety threshold) based on the above analysis results is first assessed. If yes, the size of the attachment is reduced to 0.9 times the original size, and this process is repeated until the safety requirements for tooth movement are met. If no, it is determined whether the tooth torque expressed by the designed attachment is greater than the expected torque. If yes, the cutting bevel of the attachment is reduced by 1°. If no, it is determined whether the tooth torque expressed by the designed attachment is less than the expected torque. If yes, the cutting bevel of the attachment is increased by 1°. If no, the attachment modification is completed.

Claims

1. A method for determining a digital dentomaxillofacial torque attachment, characterized in that, The method comprises the following steps: S1: establishing a digital dental model containing the jaw bone and the dentition according to the CBCT data of the patient's dental arch; S2: obtaining a periodontal ligament three-dimensional model by shell extraction along the normal of the jaw bone and the tooth root as a whole, and obtaining a digital dental model containing the periodontal ligament, the jaw bone and the dentition through the Boolean operation of the periodontal ligament and the jaw bone; S3: constructing an attachment model: the shape and size of the fixed attachment are designed according to the expected torque demand of the incisor, and the pressure ridge of the structural attachment is simulated by the local depression of the appliance; S4: assembling the digital dental model of step S2, the attachment model and the digital model of the invisible appliance to obtain a digital dental finite element simulation model; S5: performing finite element analysis on the moving trend of the incisor and the stress of the periodontal ligament under the attachment loading condition by using the digital dental finite element simulation model; S6: comparing the analysis result of step S5 with the expected torque setting value of the tooth and the safety stress threshold of the periodontal ligament: If the analysis result reaches the expected torque setting value and the stress of the periodontal ligament is safe, the attachment design is completed; otherwise, the attachment model is reconstructed by modifying the position or shape of the attachment, and then returning to step S4 to update the attachment model of step S4; In step S6, the method for comparing the analysis result of step S5 with the expected torque setting value of the tooth and the safety stress threshold of the periodontal ligament is specifically: Firstly, it is judged whether the stress of the periodontal ligament exceeds the safety threshold, if yes, the size of the attachment is automatically reduced to 0.9 times of the original size, and then returning to step S4; If not, the system then judges whether the torque of the tooth expressed by the designed attachment is greater than the expected torque, if yes, the cutting bevel of the attachment is reduced by 1°, and then returning to step S4; If not, the system continues to judge whether the torque of the tooth expressed by the designed attachment is less than the expected torque, if yes, the cutting bevel of the attachment is increased by 1°, and then returning to step S4; If not, the attachment modification is completed, and the attachment design is completed.

2. A method for determining a digital dental arch torque attachment according to claim 1, wherein, In step S1, the CBCT data of the patient's dental arch is processed through threshold adjustment, region growing and binaryzation to establish a digital dental model, and then the optimized digital dental model is formed through accurate curve processing of repair and noise reduction.

3. A method for determining a digital dental arch torque attachment according to claim 1, wherein, In step S2, the periodontal ligament is assumed to be a homogeneous and continuous elastic structure, and the thickness is set to 0.25mm.

4. A method for determining a digital dental arch torque attachment according to claim 1, wherein, In step S3, the parameters of the structural attachment pressure ridge are 4mm in length, 1mm in width and 0.1mm in depth.

5. A method for determining a digital dental arch torque attachment according to claim 1, wherein, In step S4, the digital model of the invisible appliance is constructed by: obtaining a clinical tooth crown three-dimensional model by shell extraction along the gum margin, and then obtaining a digital model of the bracketless invisible appliance through accurate curve processing; wherein the thickness of the invisible appliance is set to 0.75mm.

6. A method for determining a digital dental arch torque attachment according to claim 1, wherein, In the digital dental finite element simulation model of step S4, the rotation center of the root control movement is set at the center of the incisor crown, and the invisible appliance torque is designed by 1° per step.

7. A method for determining a digital dental arch torque attachment according to claim 1, wherein, Step S5 is specifically: 5.1) meshing: the established digital dental finite element simulation model is tetrahedral meshed, the nodes and meshes are automatically divided, and the meshing result of the digital dental finite element simulation model is obtained; 5.2) Material parameters definition: alveolar bone, periodontal ligament, tooth, invisible aligner, attachment are homogeneous, continuous, isotropic, linear elastic body, alveolar bone does not distinguish cortical bone and cancellous bone, tooth does not distinguish dental pulp, dentin and enamel; Tooth elastic modulus is 19600 MPa, Poisson's ratio is 0.30; alveolar bone elastic modulus is 13700 MPa, Poisson's ratio is 0.30; periodontal ligament elastic modulus is 0.69 MPa, Poisson's ratio is 0.30; invisible aligner elastic modulus is 528 MPa, Poisson's ratio is 0.30; attachment elastic modulus is 12500 MPa, Poisson's ratio is 0.30; 5.3) Boundary constraints and contact conditions: The contact between alveolar bone and periodontal ligament, tooth root and periodontal ligament, attachment and tooth crown surface is set as binding contact, and no relative sliding occurs between them; the invisible aligner and each tooth surface and attachment surface are set as frictional contact; The base of the maxilla away from the dentition is set as fixed constraint, and the invisible aligner and tooth do not exert any load or constraint; 5.4) On the basis of the world coordinate system of the digitalized dental finite element simulation model, the incisor local coordinate system is established: define the midpoint of the incisal edge, the apical point and the most prominent point of the lingual protuberance as the sagittal plane of the incisor; the vertical sagittal plane is X axis, mesial direction is positive; the sagittal plane perpendicular to the tooth long axis is Y axis, lingual direction is positive; the tooth long axis is Z axis, root direction is positive; 5.5) The aligner is actively positioned on the dentition, and the initial displacement trend of the incisor and the stress distribution of the periodontal ligament are obtained through finite element analysis.

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