Biomechanical analysis of the effect of aligner overtreatment on molar distalization with clear aligners: a finite-element study

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Ghaleb, Xian He, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4146638/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Introduction : The objective of this study was to analyze the biomechanical effects of aligner overtreatment on molar distalization with clear aligners. Methods : Various models comprising maxillary dentition, maxilla, periodontal ligaments, attachments, and aligners were meticulously crafted and integrated into finite-element software. Six distinct study models were devised for analysis. The first three models examined second molar distalization with clear aligner, with different configurations of attachments, i.e., no attachment, horizontal attachment or vertical attachment on the second molar. For the fourth and fifth models, class II elastic traction, either implemented via precision cut or button on canines, was applied. Lastly, aligner overtreatment with varying degrees of root distal tipping (0°, 2°, 4°, 6°, 8°, 10°, 12°) for the second molar was designed in the last study model. Results : Distalization of the second molar produced buccal tipping, distal tipping and intrusion of the second molar, and labial proclination and intrusion of the central incisor. These displacement tendencies were enhanced by adding attachments on the second molar, especially the vertical attachment. Class II elastic tractions enhanced molar distalization and diminish anchorage loss of the anterior anchorage teeth, with the precision-cut configuration being biomechanically superior to the button design. Aligner overtreatment produced bodily molar distalization and mitigated adverse biomechanical effects on anterior anchorage teeth. Conclusion : We suggest that class II elastic traction via the precision-cut configuration and the design of vertical attachment on the second molar be applied for molar distalization with clear aligner. Appropriate aligner overtreatment helps achieve bodily molar distalization and minimize adverse biomechanical effects on anterior anchorage teeth. Clinical Relevance: These findings provide valuable insights for orthodontists in optimizing molar distalization outcomes with clear aligners. Integration of overtreatment can enhance treatment efficacy and predictability, ultimately improving patient care and satisfaction. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 INTRODUCTION Clear aligner appeals to orthodontic patients for its advantages of esthetics, comfort and ease of use [ 1 – 5 ]. The predictability of tooth movements with clear aligner varies among different types of orthodontic tooth movements [ 6 – 9 ]. Clear aligner is advantageous in offering “pushing” force rather than “pulling” force [ 10 , 11 ]. Thus, upper molar distalization, achieved by “pushing” force exerted on molars, is one of the most predictable tooth movements with clear aligner [ 12 , 13 ]. However, labial movement of anterior teeth occurs during molar distalization due to its reciprocal force, posing periodontal threats to those with inadequate periodontal support [ 14 , 15 ]. Fortunately, Class II elastic traction is a biomechanical solution counteract incisor proclination during molar distalization by exerting a retraction force on upper anterior teeth [ 16 , 17 ]. However, the biomechanical superiority of the two traction modes (canine precision cut vs. canine button) is yet to be determined [ 14 , 18 ]. Moreover, although the predictability of molar distalization at the distalization stage was as high as 88%, it dropped down to 42% following anterior retraction [ 11 , 19 ]. This relapse of molar distalization may be attributed to distal tipping of the molar during the distalization stage, since only the crowns rather than the roots are distalized during the distalization stage [ 18 , 20 ]. Thus, bodily distalization of molars during the distalization stage is beneficial to increase its predictability at the end of aligner treatment by distalizing both the crowns and roots simultaneously. To achieve bodily distalization of molars, aligner overtreatment might be a viable approach by applying additional distal root tipping on molars [ 21 , 22 ]. However, the biomechanical effect of aligner overtreatment on molar distalization has been poorly understood. Therefore, we conducted this finite-element biomechanical study to examine the effects of aligner overtreatment on molar distalization with clear aligners. MATERIALS AND METHODS The subject of this study was a 22-year-old otherwise healthy orthodontic patient who required molar distalization. Approval for the study was granted by the ethical committee of West China Hospital of Stomatology, Sichuan University (WCHSIRB-D-2023-235). Mimics software (version 22.0; Materialise, Leuven, Belgium) and Geomagic Studio 2014 (3D Systems, Rock Hill, SC) were employed to construct three-dimensional (3D) geometric surface models of the maxilla and maxillary dentition with cone-beam computed tomography data and intraoral scanning data. The periodontal ligament (PDL) was defined by extending 0.25 mm away from the root surfaces[23]. Alveolar fossa models of the maxilla were acquired through Boolean operations by removing maxillary dentitions and periodontal ligaments. Vertical rectangular attachments (3×2×1 mm) or horizontal rectangular attachments (2×3×1mm) were designed on the buccal surfaces of maxillary canines, premolars, and molars. The clear aligner model was created by applying an external offset of 0.5 mm thickness on the dentition and attachments [24, 25]. To simulate second molar distalization, the aligner model was modified by increasing the mesiodistal width of the vacuoles between the first molar and second molar by 0.25 mm [26, 27]. In Hypermesh (version 14.0, Altair Hypermesh; Altair Engineering, Inc, Detroit, Mich), a 3D finite element solid model was constructed by assembling the components (maxilla, dentition, PDL, and aligner) using unstructured 4-node tetrahedral elements. Convergence tests were conducted before running the finite-element analysis. The mesh size of dentition, attachments and aligner was defined as 0.20 mm, while that of PDL and alveolar bone was set at 0.15 mm and 0.5 mm, respectively. The discretization process, detailed in Table 1, resulted in 8,302,768 elements and 1,885,484 nodes. Subsequently, these models were integrated into Abaqus/CAE (version 6.13; Abaqus; Dassault Systemes Simulia Corp, Providence, RI). The finite-element models of all the components are illustrated in Fig. 1. Table 1 Number of nodes and elements of the components of the finite element model Component Number of elements Number of nodes Teeth 1,673,875 355,709 Periodontal ligament 1,651,139 448,808 Bone 4,457,101 938,741 Attachment 37,670 10,189 Clear aligner 482,983 132,037 Despite the inherent biological and mechanical variability of the components, a homogenous representation was adopted. Teeth and bone were treated as isotropic and homogeneous materials, with no differentiation among internal tissues [28]. Linear elasticity properties were assigned to the teeth, attachments, PDL, and aligner. Material properties, as outlined in Table 2, were obtained from established studies [21, 24, 29, 30]. Bonding contacts were established between PDL inner surfaces and teeth, as well as PDL outer surfaces and alveolar bones. Coulomb friction conditions with a coefficient of friction (μ) equal to 0.2 were applied at contact interfaces between aligners and dentition (including attachments) [21, 25]. Table 2 Material properties Component Young’s modulus (MPa) Poisson’s ratio Teeth 1.96×10 4 0.30 Periodontal ligament 0.6 0.45 Bone 2.0×10 4 0.30 Attachment 1.25×10 4 0.36 Clear aligner 528 0.36 For boundary conditions, the upper part of the maxilla was set as a fixed support during force loading. The clear aligner was initially positioned on anterior teeth to replicate the actual sequence of aligner wear. A close fit to the anterior teeth was ensured, followed by the addition of a 0.25 mm displacement condition to simulate the distal stretching of the clear aligner onto posterior teeth [25]. The model's contact calculation convergence was achieved through the aforementioned settings. As illustrated in Fig. 1, six study models were designed in this study. For the first three models, only aligners were fitted onto the dentition to simulate second molar distalization by 0.25 mm, with no attachment, horizontal attachment or vertical attachment on the second molar. For the fourth and fifth models, Class II elastic traction, either through precision cut or button, was applied on canines with vertical attachments designed on the second molars in both groups. For the last model, aligner overtreatment with varying degrees (0, 2, 4, 6, 8, 10 and 12 degrees) was designed for the second molar (with vertical attachments) and Class II elastic traction was applied on the canine through precision-cut design. Aligner overtreatment involved distally rotating the part of aligner corresponding to the maxillary second molar around its crown center. The CBCT coordinate system was employed to define the x-, y-, and z-axes directions. The x-axis, signifying the line of intersection between the coronal and occlusal planes, was oriented with the patient's left side as the positive direction. The sagittal plane was represented by the y-axis, where the positive direction denoted posterior movement. The y-axis and x-axis were mutually perpendicular. The z-axis, perpendicular to both the x-axis and y-axis, had the positive direction aligned with the crown. RESULTS For the first model (no attachment on the second molar), molar distalization by the clear aligner generated distal tipping, buccal tipping and intrusion of the second molar, mesial and lingual tipping of the first molar and the canine, and mesial tipping, labial proclination and intrusion of the central incisor (Fig. 2). Similar displacement tendencies were found for the second group (horizontal attachment) and the third group (vertical attachment), except for that the aforementioned tendencies were greater in the horizontal attachment group while the greatest in the vertical attachment group (Fig. 3). As displayed in Fig. 4, stress was greater on the roots of the central incisor, canine, first molar and second molar. Moreover, more stress was presented on the vertical attachment as compared to that on the horizontal attachment, indicating that vertical attachment is more advantageous over horizontal attachment or no attachment. Thus, for the following models, the vertical attachment design was adopted. Compared with no Class II traction (third group), the addition of Class II elastic tractions (either via button or precision cut) resulted in greater displacement tendencies of the second molar while less movement tendencies of the anchorage teeth (the first molar, canine and central incisor) (Fig. 5). The effects were more enhanced for the precision cut group as compared to the button group, except for that the canine exhibited more distal rotation and distal tipping in the button group (Fig. 6). The stress distribution of the central incisor was more uniform and the stress distribution on the remaining teeth was relatively stable in the precision cut group (Fig. 7). Therefore, the precision-cut design was designed for the following models. With the aligner overtreatment (Fig. 8), the second molar tended to exhibit more buccal tipping, less distal tipping (bodily distal movement) and greater intrusion. The first molar exhibited more lingual tipping, less mesial tipping, and greater extrusion. Moreover, in the condition of aligner overtreatment, the central incisor exhibited less distal tipping, more lingual tipping and greater extrusion, while the canine displayed less lingual tipping, more mesial tipping and greater intrusion. As displayed in Fig. 9, stress was more evenly distributed on the central incisor and the second molar, but greater stress was concentrated on the attachment of the second molar. DISSCUSSION Distalization of upper molars exhibits the highest predictability, reaching 88%, particularly when a prescribed bodily movement of at least 1.5 mm is implemented [ 8 , 31 ]. Nonetheless, the inherent challenge arises from the reciprocal force exerted on the anterior teeth during molar distalization, leading to unavoidable anchorage loss of the anterior teeth [ 20 , 32 ]. This phenomenon can significantly contribute to the occurrence of alveolar defects, including dehiscence and fenestration, especially in patients characterized by thin cortical plates in the anterior region [ 33 ]. For the first three models with aligners only, distalization of the second molar resulted in buccal tipping, distal tipping and intrusion of the second molar. This could be explained by the fact that the distalization force has buccal and distal components that pass occlusally to the center of resistance, resulting in buccal and distal tipping. From the perspectives of biomechanics, the second molar tended to rotate around its center of resistance during distal tipping, resulting in intrusion of the distal cusp and extrusion of the mesial cusp. However, the presence of the aligner on the occlusal surface of the second molar prevented the mesial cusp from being extruded and resulted in a net effect of molar intrusion. The reciprocal force applied on the adjacent anchorage tooth (the first molar) produced an opposite movement tendency, i.e., lingual tipping, mesial tipping and extrusion. Similarly, the reciprocal force acted on the central incisor passed occlusally to the center of resistance, resulting in labial tipping and intrusion of the central incisor. Previous biomechanical analysis and clinical research have confirmed the results of this study [ 11 , 13 , 34 ]. Attachments are essential for clear aligner therapy, since they can help the fitting of the aligner and ensure the expression of the aligner biomechanics [ 17 , 20 , 35 ]. Ayidağa et al. found that the displacement of molar distalization with vertical attachment and guideline attachment was greater than that of no attachment, but only one tooth was involved in the study [ 36 ]. Rossini et al. compared vertical attachment and no attachment on the second molar, but did not study horizontal attachment or emphasize the importance of the push surface [ 26 ]. Our study proved that the addition of the attachments (either the horizontal or vertical attachment) on the second molar resulted in greater tooth movement tendency. To achieve molar distalization, the aligner should offer distal “pushing” force on the second molar. Since the attachment surface that received the distal “pushing” force was greater for the vertical attachment, the tooth movement tendency was greater in the vertical attachment group than in the horizontal attachment group. This is supported by the finding that more stress was presented on the mesial surface of second-molar attachment in the vertical attachment group (Fig. 4). Therefore, we recommend the design of vertical attachment on the second molar for molar distalization with clear aligner. To counteract the side effects of molar distalization on anchorage teeth, we designed Class II elastic tractions (either via the button or the precision cut) to strengthen anchorage of anterior teeth. Compared to no Class II traction, the application of Class II elastics, either through the button or the precision cut, produced greater displacement tendencies on the second molar and less displacement tendency of the anchorage teeth (Figs. 5 and 6 ). The precision cut was situated as a notch on the aligner, while the button was bonded onto the canine. Thus, the Class II elastic traction force can be better expressed onto the anterior teeth for the precision cut group. This could explain the finding that less adverse displacement tendency was presented on the anterior teeth in the precision cut group as compared to the button group, i.e., less labial tipping and less intrusion of the central incisor. Moreover, since the Class II elastic traction was directly applied onto the canine, the canine exhibited more lingual tipping, distal tipping and extrusion in the button group. Other biomechanical studies had confirmed this result [ 13 , 37 ]. Thus, we suggest that Class II elastic traction is able to enhance molar distalization and to prevent anchorage loss (proclination) of the anterior teeth. Moreover, the precision-cut mode is biomechanically superior to the button mode. Aligner overtreatment is an effective measure to enhance designated tooth movement by designing additional tooth movements [ 21 ]. As dictated by the biomechanical nature of the molar distalization, the second molar tended to exhibit distal tipping during its distalization. Thus, to counteract distal tipping and to achieve bodily movement, we designed aligner overtreatment for molar distalization by designing greater distal root tipping. We found that aligner overtreatment produced less distal tipping of the second molar during distalization and resulted in bodily distalization. As displayed in Fig. 10 , from the perspectives of biomechanics, the aligner overtreatment generated a counterclockwise moment that counteracted the clockwise moment produced by the aligner distalization force. Thus, the two moments that have opposite directions resulted in a net effect of bodily distalization of the second molar. Moreover, the aforementioned counterclockwise moment by the aligner generated a reciprocal moment on the anchorage teeth, i.e., clockwise moment on the first molar and central incisor. Thus, this biomechanical effect can explain the displacement tendency of the first molar and central incisor, i.e., less mesial tipping and greater extrusion of the first molar, and more lingual tipping and greater extrusion. All these displacement tendencies of the anchorage teeth indicated that the adverse biomechanical effects produced by molar distalization with clear aligner can be mitigated by the aligner overtreatment. Therefore, we suggest that appropriate aligner overtreatment is able to achieve bodily distalization of the second molar and diminish the adverse biomechanical effect of the anterior teeth. The results of this simulation are confined to the analysis of stress and displacement patterns during the initial phase of tooth movement. However, recognizing tooth movement as a dynamic, long-term process, accompanied by alterations in the force system and the mechanical response of tissues, is crucial. Tooth movement and the force generated by aligners peak at the beginning of the process and subsequently diminish [ 38 ]. This would facilitate clinicians in comprehending the intricate interactions among dental units when subjected to concurrent force applications. CONCLUSIONS Molar distalization with clear aligner generates distal tipping, buccal tipping and intrusion of the molar, and mesial tipping, labial proclination and intrusion of the incisors. Vertical attachment on the second molar produces more enhanced molar distalization than horizontal attachment. Class II elastic traction is recommended to enhance molar distalization and to eliminate adverse biomechanical effect of the anterior anchorage teeth. Precision cut is biomechanically superior to button on the canine. Appropriate aligner overtreatment is able to achieve bodily distalization of the second molar and diminish the adverse biomechanical effect of the anterior teeth. Declarations Author Contribution Jialun Li: Writing - Original Draft, Conceptualization, Software, Formal analysis. Yi Yang: Methodology, Software. Ziwei Tang: Validation, Invetigation. Qi Fan: Methodology. Omar M. Ghaleb: Data Curation, Visualization. Xian He: Formal analysis. Wenli Lai: Supervision. Hu Long: Data Curation, Project administration, Funding acquisition, Writing - Review & Editing, Supervision. References Frongia G, Castroflorio T (2012) Correction of severe tooth rotations using clear aligners: a case report. Aust Orthod J 28:245–249 Haouili N, Kravitz ND, Vaid NR et al (2020) Has Invisalign improved? A prospective follow-up study on the efficacy of tooth movement with Invisalign. Am J Orthod Dentofac Orthop 158:420–425 Zhu Ya-fen, Li Xlong, Wen li Lai (2019) Treatment of Severe Anterior Crowding with the Invisalign G6 First-Premolar Extraction Solution. J Clin Orthod 53:459–469 Gao M, Yan X, Zhao R et al (2021) Comparison of pain perception, anxiety, and impacts on oral health-related quality of life between patients receiving clear aligners and fixed appliances during the initial stage of orthodontic treatment. Eur J Orthod 43:353–359 Rouzi M, Zhang X, Jiang Q et al (2023) Impact of Clear Aligners on Oral Health and Oral Microbiome During Orthodontic Treatment. Int Dent J 73:603–611 Long H, Wu Z, Yan X et al (2020) An objective system for appraising clear aligner treatment difficulty: clear aligner treatment complexity assessment tool (CAT-CAT). BMC Oral Health 20:312 Jiahong Lyu M, Gao S, Zhang et al (2021) Clear aligner treatment for a re-treated adult patient with a unilateral full-cusp Class II malocclusion and severe dental midline discrepancy. J Aligner Orthod 5:1–12 Ren L, Liu L, Wu Z et al (2022) The predictability of orthodontic tooth movements through clear aligner among first-premolar extraction patients: a multivariate analysis. Prog Orthod 23:52 Zhao R, Mei L, Long H et al (2023) Changing clear aligner every 10 days or 14 days ? A randomised controlled trial. Australas Orthod J 39:1–12 Karras T, Singh M, Karkazis E et al (2021) Efficacy of Invisalign attachments: A retrospective study. Am J Orthod Dentofac Orthop 160:250–258 Simon M, Keilig L, Schwarze J et al (2014) Treatment outcome and efficacy of an aligner technique–regarding incisor torque, premolar derotation and molar distalization. BMC Oral Health 14:68 Rossini G, Parrini S, Castroflorio T et al (2015) Efficacy of clear aligners in controlling orthodontic tooth movement: a systematic review. Angle Orthod 85:881–889 Liu X, Wu J, Cheng Y et al (2023) Effective contribution ratio of the molar during sequential distalization using clear aligners and micro-implant anchorage: a finite element study. Prog Orthod 24:35 Alhammadi MS, Qasem AAA, Yamani AMS et al (2022) Skeletal and dentoalveolar effects of class II malocclusion treatment using bi-maxillary skeletal anchorage: a systematic review. BMC Oral Health 22:339 Sheng Y, Guo H-M, Bai Y-X, Li S (2020) Dehiscence and fenestration in anterior teeth: Comparison before and after orthodontic treatment. J Orofac Orthop 81:1–9 Janson G, Sathler R, Fernandes TMF et al (2013) Correction of Class II malocclusion with Class II elastics: a systematic review. Am J Orthod Dentofac Orthop 143:383–392 Comba B, Parrini S, Rossini G et al (2017) A Three-Dimensional Finite Element Analysis of Upper-Canine Distalization with Clear Aligners, Composite Attachments, and Class II Elastics. J Clin Orthod 51:24–28 Mao B, Tian Y, Xiao Y et al (2023) The effect of maxillary molar distalization with clear aligner: a 4D finite-element study with staging simulation. Prog Orthod 24:16 Li L, Guo R, Zhang L et al (2023) Maxillary molar distalization with a 2-week clear aligner protocol in patients with Class II malocclusion: A retrospective study. Am J Orthod Dentofac Orthop 164:123–130 Ravera S, Castroflorio T, Garino F et al (2016) Maxillary molar distalization with aligners in adult patients: a multicenter retrospective study. Prog Orthod 17:12 Liu L, Song Q, Zhou J et al (2022) The effects of aligner overtreatment on torque control and intrusion of incisors for anterior retraction with clear aligners: A finite-element study. Am J Orthod Dentofac Orthop 162:33–41 Palone M, Pignotti A, Morin E et al (2023) Analysis of overcorrection to be included for planning clear aligner therapy: a retrospective study. Angle Orthod 93:11–18 Wang C-Y, Su M-Z, Chang H-H et al (2012) Tension-compression viscoelastic behaviors of the periodontal ligament. J Formos Med Assoc 111:471–481 Cortona A, Rossini G, Parrini S et al (2020) Clear aligner orthodontic therapy of rotated mandibular round-shaped teeth: A finite element study. Angle Orthod 90:247–254 Yang Y, Yang R, Liu L et al (2023) The effects of aligner anchorage preparation on mandibular first molars during premolar-extraction space closure with clear aligners: A finite element study. Am J Orthod Dentofac Orthop 164:226–238 Rossini G, Schiaffino M, Parrini S et al (2020) Upper Second Molar Distalization with Clear Aligners: A Finite Element Study. Appl Sci 10:7739 Liu L, Zhan Q, Zhou J et al (2021) Effectiveness of an anterior mini-screw in achieving incisor intrusion and palatal root torque for anterior retraction with clear aligners. Angle Orthod 91:794–803 Barone S, Paoli A, Razionale AV, Savignano R (2017) Computational design and engineering of polymeric orthodontic aligners. Int J Numer Methods Biomed Eng 33:e2839 Gomez JP, Peña FM, Martínez V et al (2015) Initial force systems during bodily tooth movement with plastic aligners and composite attachments: A three-dimensional finite element analysis. Angle Orthod 85:454–460 Liang W, Rong Q, Lin J, Xu B (2009) Torque control of the maxillary incisors in lingual and labial orthodontics: a 3-dimensional finite element analysis. Am J Orthod Dentofac Orthop 135:316–322 Brezniak N (2008) The clear plastic appliance: a biomechanical point of view. Angle Orthod 78:381–382 Yan X, Zhang X, Ren L et al (2023) Effectiveness of clear aligners in achieving proclination and intrusion of incisors among Class II division 2 patients: a multivariate analysis. Prog Orthod 24:12 Tao T, Liang H, Yan X et al (2022) Comparison of Root Parallelism in Extraction Cases Treated with Clear Aligners vs. Fixed Appliances Appl Sci 12:11756 Saif BS, Pan F, Mou Q et al (2022) Efficiency evaluation of maxillary molar distalization using Invisalign based on palatal rugae registration. Am J Orthod Dentofac Orthop 161:e372–e379 Yokoi Y, Arai A, Kawamura J et al (2019) Effects of Attachment of Plastic Aligner in Closing of Diastema of Maxillary Dentition by Finite Element Method. J Healthc Eng 2019:1075097 Ayidağa C, Kamiloğlu B (2021) Effects of Variable Composite Attachment Shapes in Controlling Upper Molar Distalization with Aligners: A Nonlinear Finite Element Study. J Healthc Eng 2021:5557483 Kwak K-H, Oh S, Choi Y-K et al (2023) Effects of different distalization directions and methods on maxillary total distalization with clear aligners: a finite element study. Angle Orthod 93:348–356 Cai Y, Yang X, He B, Yao J (2015) Finite element method analysis of the periodontal ligament in mandibular canine movement with transparent tooth correction treatment. BMC Oral Health 15:106 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4146638","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":283399437,"identity":"c26acc3f-26a8-4e82-a169-3ff71010a082","order_by":0,"name":"Jialun Li","email":"","orcid":"","institution":"Department of Orthodontics, West China Hospital of Stomatology, Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Jialun","middleName":"","lastName":"Li","suffix":""},{"id":283399438,"identity":"6af3f064-853a-464c-8142-78ac3d5c31bf","order_by":1,"name":"yi yang","email":"","orcid":"","institution":"Department of Orthodontics, West China Hospital of Stomatology, Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"yi","middleName":"","lastName":"yang","suffix":""},{"id":283399439,"identity":"5bd799e6-6946-401f-8fa5-26986c61ac5d","order_by":2,"name":"Ziwei Tang","email":"","orcid":"","institution":"Department of Orthodontics, West China Hospital of Stomatology, Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Ziwei","middleName":"","lastName":"Tang","suffix":""},{"id":283399440,"identity":"60ad61b5-24e0-4931-ac39-a7278d061e24","order_by":3,"name":"qi Fan","email":"","orcid":"","institution":"Department of Orthodontics, West China Hospital of Stomatology, Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"qi","middleName":"","lastName":"Fan","suffix":""},{"id":283399441,"identity":"4a381ea4-a107-498f-9549-15ba0fb726ac","order_by":4,"name":"Omar M. Ghaleb","email":"","orcid":"","institution":"Department of Orthodontics, West China Hospital of Stomatology, Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Omar","middleName":"M.","lastName":"Ghaleb","suffix":""},{"id":283399442,"identity":"da7e268c-1d12-4105-8e5d-df4c5185bdc9","order_by":5,"name":"Xian He","email":"","orcid":"","institution":"Department of Orthodontics, West China Hospital of Stomatology, Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Xian","middleName":"","lastName":"He","suffix":""},{"id":283399444,"identity":"821cd77b-1c17-4b43-9a35-43166266081b","order_by":6,"name":"Wenli Lai","email":"","orcid":"","institution":"Department of Orthodontics, West China Hospital of Stomatology, Sichuan University","correspondingAuthor":false,"prefix":"","firstName":"Wenli","middleName":"","lastName":"Lai","suffix":""},{"id":283399446,"identity":"84eea55f-d0cf-4fca-8868-e4aa30ad1120","order_by":7,"name":"hu Long","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAsUlEQVRIiWNgGAWjYBACA3YQWQHhSBCnhRlEniFZC2MbKVrMmZmPPfw6r07e4ADzwds8DHZ5BLVYNrOlG8tuO2y44QBbsjUPQ3IxYYcd5jGTltx2IMHgAJDBw3AgsYE4LXPqgFr4vxGvRfJjAzPIFjZitbClSTMcO2w48zCbseUcg2QitBxvPib5o6ZOnu9488MbbyrsCGsBAWYeMAk2gRj1QMD4g0iFo2AUjIJRMEIBAA42NTVUwEwtAAAAAElFTkSuQmCC","orcid":"","institution":"Department of Orthodontics, West China Hospital of Stomatology, Sichuan University","correspondingAuthor":true,"prefix":"","firstName":"hu","middleName":"","lastName":"Long","suffix":""}],"badges":[],"createdAt":"2024-03-22 02:59:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4146638/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4146638/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":53674812,"identity":"c8dc123c-fa9e-45f8-a5e1-0e62c8b46c13","added_by":"auto","created_at":"2024-03-28 18:30:27","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":168849,"visible":true,"origin":"","legend":"\u003cp\u003eFinite element models. \u003cstrong\u003ea\u003c/strong\u003e: upper molar distalization with different types of attachment on the second molar. \u003cstrong\u003eb\u003c/strong\u003e: Class II elastic traction via button or precision cut (100 g). \u003cstrong\u003ec\u003c/strong\u003e: Aligner overtreatment on the second molar.\u003c/p\u003e","description":"","filename":"floatimage1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4146638/v1/184c6600600b4b00526cc892.jpg"},{"id":53674813,"identity":"62311220-f687-46a1-9a8b-aa281a66f72c","added_by":"auto","created_at":"2024-03-28 18:30:27","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":197470,"visible":true,"origin":"","legend":"\u003cp\u003eThe initial displacement tendencies of maxillary dentition with clear aligners with different attachments on the second molars in sagittal and axial views.\u003c/p\u003e","description":"","filename":"floatimage2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4146638/v1/752f9f5d5ce2bf5254e5ac30.jpg"},{"id":53674815,"identity":"a39dc8a6-fbc4-4670-9752-9c9722fbc49d","added_by":"auto","created_at":"2024-03-28 18:30:27","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":379818,"visible":true,"origin":"","legend":"\u003cp\u003eDisplacement tendencies of central incisors, canines, and molars with different types of attachments on second molars.\u003c/p\u003e","description":"","filename":"floatimage3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4146638/v1/8e6c28e55dbf87b18d4bf894.jpg"},{"id":53675327,"identity":"a6762819-2308-4223-b2f7-b233078cb2d2","added_by":"auto","created_at":"2024-03-28 18:38:28","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":293579,"visible":true,"origin":"","legend":"\u003cp\u003eStress distribution on central incisors, canines and molars with different types of attachments on second molars. Note that stress was concentrated on the attachments of the second molars and that more stress was present on the vertical attachment than on the horizontal attachment of the second molar, from both the buccal and mesial views.\u003c/p\u003e","description":"","filename":"floatimage4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4146638/v1/58aa12a6228a134c6d553aec.jpg"},{"id":53674814,"identity":"acbcb5ad-73a7-4988-91ee-3215c9b195af","added_by":"auto","created_at":"2024-03-28 18:30:27","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":166989,"visible":true,"origin":"","legend":"\u003cp\u003eThe initial displacement tendencies of maxillary dentition with and without Class II elastic tractions.\u003c/p\u003e","description":"","filename":"floatimage5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4146638/v1/6ed7c2402bc62375fb0e4892.jpg"},{"id":53674817,"identity":"3dd5c984-cd40-46b0-98f6-acca2590a56b","added_by":"auto","created_at":"2024-03-28 18:30:28","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":550173,"visible":true,"origin":"","legend":"\u003cp\u003eDisplacement tendencies of central incisors, canines, and molars with and without Class II elastic tractions.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4146638/v1/bec7902ce4c57956d9a37252.jpg"},{"id":53674821,"identity":"29c7bf0d-abe9-4a14-838e-f9030f57da47","added_by":"auto","created_at":"2024-03-28 18:30:28","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":611733,"visible":true,"origin":"","legend":"\u003cp\u003eStress distribution of central incisors, canines, and molars and their attachments with and without Class II elastic traction. Note the concentrated stress on the button of the canine for the button group.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4146638/v1/55b2d983bd728d0e76aca085.jpg"},{"id":53674822,"identity":"2f46c32d-c35c-43af-8909-fbd065578557","added_by":"auto","created_at":"2024-03-28 18:30:28","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":486738,"visible":true,"origin":"","legend":"\u003cp\u003eDisplacement tendencies of central incisors, canines and molars with varying degrees of aligner \u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u003cbr\u003e\n overtreatment. Note the differences of displacement tendencies of the second molars subject to aligner overtreatment.\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4146638/v1/8422d781c25b7c1f2ee1074d.jpg"},{"id":53674819,"identity":"594eda34-7861-4caf-9fe5-1c60277767e0","added_by":"auto","created_at":"2024-03-28 18:30:28","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":460476,"visible":true,"origin":"","legend":"\u003cp\u003eStress distribution of central incisors, canines, and molars and their attachments with and without overtreatment. Note that stress was less in the overtreatment groups for the central incisors. With an increase in the degree of aligner overtreatment, more stress was present on the vertical attachment of the second molar.\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4146638/v1/76e503605a6478aeeb1476a7.jpg"},{"id":53674816,"identity":"d5a5ab61-ac5a-491c-8070-1e763395b602","added_by":"auto","created_at":"2024-03-28 18:30:27","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":117727,"visible":true,"origin":"","legend":"\u003cp\u003eBiomechanical analysis of molar distalization with or without aligner overtreatment. \u003cstrong\u003ea\u003c/strong\u003e: Molar distalization without aligner overtreatment. The distalization force exerted on the second molar by the aligner produced a clockwise moment (blue curved arrow) that leads to distal tipping of the second molar. The reaction force applied on the first molar and central incior generates counterclockwise moments (blue curved arrows) that lead to mesial tipping of the first molar and labial proclination of the central incisor. \u003cstrong\u003eb\u003c/strong\u003e: Molar distalization with aligner overtreatment. Aligner overtreatment produces a counterclockwise moment (red curved arrow) on the second molar and counteracts the clockwise moment (blue curved arrow) produced by the distalization force, resulting in bodily distalization of the second molar. The reciprocal moments (red curved arrows) on anterior anchorage teeth that produced by the aligner overtreatment counteracts the counterclockwise moments (blue curved arrows), reducing the mesial tipping of the first molar and the labial proclination of the central incisor. \u003cem\u003e(CR: center of resistance)\u003c/em\u003e\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4146638/v1/aff7dfeeea0d314e38b3b03f.jpg"},{"id":57598959,"identity":"41890ff9-9ad3-446c-a2ea-23b163394405","added_by":"auto","created_at":"2024-06-03 07:37:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3764465,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4146638/v1/493d999b-34a9-4fd7-b665-0dc6e0d5ea2c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Biomechanical analysis of the effect of aligner overtreatment on molar distalization with clear aligners: a finite-element study","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eClear aligner appeals to orthodontic patients for its advantages of esthetics, comfort and ease of use [\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The predictability of tooth movements with clear aligner varies among different types of orthodontic tooth movements [\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Clear aligner is advantageous in offering \u0026ldquo;pushing\u0026rdquo; force rather than \u0026ldquo;pulling\u0026rdquo; force [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Thus, upper molar distalization, achieved by \u0026ldquo;pushing\u0026rdquo; force exerted on molars, is one of the most predictable tooth movements with clear aligner [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. However, labial movement of anterior teeth occurs during molar distalization due to its reciprocal force, posing periodontal threats to those with inadequate periodontal support [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Fortunately, Class II elastic traction is a biomechanical solution counteract incisor proclination during molar distalization by exerting a retraction force on upper anterior teeth [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. However, the biomechanical superiority of the two traction modes (canine precision cut vs. canine button) is yet to be determined [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMoreover, although the predictability of molar distalization at the distalization stage was as high as 88%, it dropped down to 42% following anterior retraction [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. This relapse of molar distalization may be attributed to distal tipping of the molar during the distalization stage, since only the crowns rather than the roots are distalized during the distalization stage [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Thus, bodily distalization of molars during the distalization stage is beneficial to increase its predictability at the end of aligner treatment by distalizing both the crowns and roots simultaneously. To achieve bodily distalization of molars, aligner overtreatment might be a viable approach by applying additional distal root tipping on molars [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. However, the biomechanical effect of aligner overtreatment on molar distalization has been poorly understood.\u003c/p\u003e \u003cp\u003eTherefore, we conducted this finite-element biomechanical study to examine the effects of aligner overtreatment on molar distalization with clear aligners.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cp\u003eThe subject of this study was a 22-year-old otherwise healthy orthodontic patient who required molar distalization. Approval for the study was granted by the ethical committee of \u0026nbsp;West China Hospital of Stomatology, Sichuan University (WCHSIRB-D-2023-235).\u003c/p\u003e\n\u003cp\u003eMimics software (version 22.0; Materialise, Leuven, Belgium) and Geomagic Studio 2014 (3D Systems, Rock Hill, SC) were employed to construct three-dimensional (3D) geometric surface models of the maxilla and maxillary dentition with cone-beam computed tomography data and intraoral scanning data. The periodontal ligament (PDL) was defined by extending 0.25 mm away from the root surfaces[23]. Alveolar fossa models of the maxilla were acquired through Boolean operations by removing maxillary dentitions and periodontal ligaments. Vertical rectangular attachments (3\u0026times;2\u0026times;1 mm) or horizontal rectangular attachments (2\u0026times;3\u0026times;1mm) were designed on the buccal surfaces of maxillary canines, premolars, and molars. The clear aligner model was created by applying an external offset of 0.5 mm thickness on the dentition and attachments\u0026nbsp;[24, 25]. To simulate second molar distalization, the aligner model was modified by increasing the mesiodistal width of the vacuoles between the first molar and second molar by 0.25 mm\u0026nbsp;[26, 27].\u003c/p\u003e\n\u003cp\u003eIn Hypermesh (version 14.0, Altair Hypermesh; Altair Engineering, Inc, Detroit, Mich), a 3D finite element solid model was constructed by assembling the components (maxilla, dentition, PDL, and aligner) using unstructured 4-node tetrahedral elements. Convergence tests were conducted before running the finite-element analysis. The mesh size of dentition, attachments and aligner was defined as 0.20 mm, while that of PDL and alveolar bone was set at 0.15 mm and 0.5 mm, respectively. The discretization process, detailed in Table 1, resulted in 8,302,768 elements and 1,885,484 nodes. Subsequently, these models were integrated into Abaqus/CAE (version 6.13; Abaqus; Dassault Systemes Simulia Corp, Providence, RI). The finite-element models of all the components are illustrated in Fig. 1.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e Number of nodes and elements of the components of the finite element model\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.39350180505415%\" valign=\"top\"\u003e\n \u003cp\u003eComponent\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.39350180505415%\" valign=\"top\"\u003e\n \u003cp\u003eNumber of elements\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.2129963898917%\" valign=\"top\"\u003e\n \u003cp\u003eNumber of nodes\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.39350180505415%\" valign=\"top\"\u003e\n \u003cp\u003eTeeth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.39350180505415%\" valign=\"top\"\u003e\n \u003cp\u003e1,673,875\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.2129963898917%\" valign=\"top\"\u003e\n \u003cp\u003e355,709\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.39350180505415%\" valign=\"top\"\u003e\n \u003cp\u003ePeriodontal ligament\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.39350180505415%\" valign=\"top\"\u003e\n \u003cp\u003e1,651,139\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.2129963898917%\" valign=\"top\"\u003e\n \u003cp\u003e448,808\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.39350180505415%\" valign=\"top\"\u003e\n \u003cp\u003eBone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.39350180505415%\" valign=\"top\"\u003e\n \u003cp\u003e4,457,101\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.2129963898917%\" valign=\"top\"\u003e\n \u003cp\u003e938,741\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.39350180505415%\" valign=\"top\"\u003e\n \u003cp\u003eAttachment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.39350180505415%\" valign=\"top\"\u003e\n \u003cp\u003e37,670\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.2129963898917%\" valign=\"top\"\u003e\n \u003cp\u003e10,189\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.39350180505415%\" valign=\"top\"\u003e\n \u003cp\u003eClear aligner\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.39350180505415%\" valign=\"top\"\u003e\n \u003cp\u003e482,983\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.2129963898917%\" valign=\"top\"\u003e\n \u003cp\u003e132,037\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eDespite the inherent biological and mechanical variability of the components, a homogenous representation was adopted. Teeth and bone were treated as isotropic and homogeneous materials, with no differentiation among internal tissues [28]. Linear elasticity properties were assigned to the teeth, attachments, PDL, and aligner. Material properties, as outlined in Table 2, were obtained from established studies [21, 24, 29, 30]. Bonding contacts were established between PDL inner surfaces and teeth, as well as PDL outer surfaces and alveolar bones. Coulomb friction conditions with a coefficient of friction (\u0026mu;) equal to 0.2 were applied at contact interfaces between aligners and dentition (including attachments) [21, 25].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u0026nbsp;\u003c/strong\u003eMaterial properties\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.45388788426763%\" valign=\"top\"\u003e\n \u003cp\u003eComponent\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.273056057866185%\" valign=\"top\"\u003e\n \u003cp\u003eYoung\u0026rsquo;s modulus (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.273056057866185%\" valign=\"top\"\u003e\n \u003cp\u003ePoisson\u0026rsquo;s ratio\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.45388788426763%\" valign=\"top\"\u003e\n \u003cp\u003eTeeth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.273056057866185%\" valign=\"top\"\u003e\n \u003cp\u003e1.96\u0026times;10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.273056057866185%\" valign=\"top\"\u003e\n \u003cp\u003e0.30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.45388788426763%\" valign=\"top\"\u003e\n \u003cp\u003ePeriodontal ligament\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.273056057866185%\" valign=\"top\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.273056057866185%\" valign=\"top\"\u003e\n \u003cp\u003e0.45\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.45388788426763%\" valign=\"top\"\u003e\n \u003cp\u003eBone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.273056057866185%\" valign=\"top\"\u003e\n \u003cp\u003e2.0\u0026times;10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.273056057866185%\" valign=\"top\"\u003e\n \u003cp\u003e0.30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.45388788426763%\" valign=\"top\"\u003e\n \u003cp\u003eAttachment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.273056057866185%\" valign=\"top\"\u003e\n \u003cp\u003e1.25\u0026times;10\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.273056057866185%\" valign=\"top\"\u003e\n \u003cp\u003e0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"33.45388788426763%\" valign=\"top\"\u003e\n \u003cp\u003eClear aligner\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.273056057866185%\" valign=\"top\"\u003e\n \u003cp\u003e528\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"33.273056057866185%\" valign=\"top\"\u003e\n \u003cp\u003e0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eFor boundary conditions, the upper part of the maxilla was set as a fixed support during force loading. The clear aligner was initially positioned on anterior teeth to replicate the actual sequence of aligner wear. A close fit to the anterior teeth was ensured, followed by the addition of a 0.25 mm displacement condition to simulate the distal stretching of the clear aligner onto posterior teeth\u0026nbsp;[25]. The model\u0026apos;s contact calculation convergence was achieved through the aforementioned settings.\u003c/p\u003e\n\u003cp\u003eAs illustrated in Fig. 1, six study models were designed in this study. For the first three models, only aligners were fitted onto the dentition to simulate second molar distalization by 0.25 mm, with no attachment, horizontal attachment or vertical attachment on the second molar. For the fourth and fifth models, Class II elastic traction, either through precision cut or button, was applied on canines with vertical attachments designed on the second molars in both groups. For the last model, aligner overtreatment with varying degrees (0, 2, 4, 6, 8, 10 and 12 degrees) was designed for the second molar (with vertical attachments) and Class II elastic traction was applied on the canine through precision-cut design. Aligner overtreatment involved distally rotating the part of aligner corresponding to the maxillary second molar around its crown center.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe CBCT coordinate system was employed to define the x-, y-, and z-axes directions. The x-axis, signifying the line of intersection between the coronal and occlusal planes, was oriented with the patient\u0026apos;s left side as the positive direction. The sagittal plane was represented by the y-axis, where the positive direction denoted posterior movement. The y-axis and x-axis were mutually perpendicular. The z-axis, perpendicular to both the x-axis and y-axis, had the positive direction aligned with the crown.\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cp\u003eFor the first model (no attachment on the second molar), molar distalization by the clear aligner generated distal tipping, buccal tipping and intrusion of the second molar, mesial and lingual tipping of the first molar and the canine, and mesial tipping, labial proclination and intrusion of the central incisor (Fig. 2). Similar displacement tendencies were found for the second group (horizontal attachment) and the third group (vertical attachment), except for that the aforementioned tendencies were greater in the horizontal attachment group while the greatest in the vertical attachment group (Fig. 3). As displayed in Fig. 4, stress was greater on the roots of the central incisor, canine, first molar and second molar. Moreover, more stress was presented on the vertical attachment as compared to that on the horizontal attachment, indicating that vertical attachment is more advantageous over horizontal attachment or no attachment. Thus, for the following models, the vertical attachment design was adopted.\u003c/p\u003e\n\u003cp\u003eCompared with no Class II traction (third group), the addition of Class II elastic tractions (either via button or precision cut) resulted in greater displacement tendencies of the second molar while less movement tendencies of the anchorage teeth (the first molar, canine and central incisor) (Fig. 5). The effects were more enhanced for the precision cut group as compared to the button group, except for that the canine exhibited more distal rotation and distal tipping in the button group (Fig. 6). The stress distribution of the central incisor was more uniform and the stress distribution on the remaining teeth was relatively stable in the precision cut group (Fig. 7). Therefore, the precision-cut design was designed for the following models.\u003c/p\u003e\n\u003cp\u003eWith the aligner overtreatment (Fig. 8), the second molar tended to exhibit more buccal tipping, less distal tipping (bodily distal movement) and greater intrusion. The first molar exhibited more lingual tipping, less mesial tipping, and greater extrusion. Moreover, in the condition of aligner overtreatment, the central incisor exhibited less distal tipping, more lingual tipping and greater extrusion, while the canine displayed less lingual tipping, more mesial tipping and greater intrusion. As displayed in Fig. 9, stress was more evenly distributed on the central incisor and the second molar, but greater stress was concentrated on the attachment of the second molar.\u003c/p\u003e"},{"header":"DISSCUSSION","content":"\u003cp\u003eDistalization of upper molars exhibits the highest predictability, reaching 88%, particularly when a prescribed bodily movement of at least 1.5 mm is implemented [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Nonetheless, the inherent challenge arises from the reciprocal force exerted on the anterior teeth during molar distalization, leading to unavoidable anchorage loss of the anterior teeth [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. This phenomenon can significantly contribute to the occurrence of alveolar defects, including dehiscence and fenestration, especially in patients characterized by thin cortical plates in the anterior region [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFor the first three models with aligners only, distalization of the second molar resulted in buccal tipping, distal tipping and intrusion of the second molar. This could be explained by the fact that the distalization force has buccal and distal components that pass occlusally to the center of resistance, resulting in buccal and distal tipping. From the perspectives of biomechanics, the second molar tended to rotate around its center of resistance during distal tipping, resulting in intrusion of the distal cusp and extrusion of the mesial cusp. However, the presence of the aligner on the occlusal surface of the second molar prevented the mesial cusp from being extruded and resulted in a net effect of molar intrusion. The reciprocal force applied on the adjacent anchorage tooth (the first molar) produced an opposite movement tendency, i.e., lingual tipping, mesial tipping and extrusion. Similarly, the reciprocal force acted on the central incisor passed occlusally to the center of resistance, resulting in labial tipping and intrusion of the central incisor. Previous biomechanical analysis and clinical research have confirmed the results of this study [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAttachments are essential for clear aligner therapy, since they can help the fitting of the aligner and ensure the expression of the aligner biomechanics [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Ayidağa et al. found that the displacement of molar distalization with vertical attachment and guideline attachment was greater than that of no attachment, but only one tooth was involved in the study [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Rossini et al. compared vertical attachment and no attachment on the second molar, but did not study horizontal attachment or emphasize the importance of the push surface [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Our study proved that the addition of the attachments (either the horizontal or vertical attachment) on the second molar resulted in greater tooth movement tendency. To achieve molar distalization, the aligner should offer distal \u0026ldquo;pushing\u0026rdquo; force on the second molar. Since the attachment surface that received the distal \u0026ldquo;pushing\u0026rdquo; force was greater for the vertical attachment, the tooth movement tendency was greater in the vertical attachment group than in the horizontal attachment group. This is supported by the finding that more stress was presented on the mesial surface of second-molar attachment in the vertical attachment group (Fig.\u0026nbsp;4). Therefore, we recommend the design of vertical attachment on the second molar for molar distalization with clear aligner.\u003c/p\u003e \u003cp\u003eTo counteract the side effects of molar distalization on anchorage teeth, we designed Class II elastic tractions (either via the button or the precision cut) to strengthen anchorage of anterior teeth. Compared to no Class II traction, the application of Class II elastics, either through the button or the precision cut, produced greater displacement tendencies on the second molar and less displacement tendency of the anchorage teeth (Figs.\u0026nbsp;5 and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e6\u003c/span\u003e). The precision cut was situated as a notch on the aligner, while the button was bonded onto the canine. Thus, the Class II elastic traction force can be better expressed onto the anterior teeth for the precision cut group. This could explain the finding that less adverse displacement tendency was presented on the anterior teeth in the precision cut group as compared to the button group, i.e., less labial tipping and less intrusion of the central incisor. Moreover, since the Class II elastic traction was directly applied onto the canine, the canine exhibited more lingual tipping, distal tipping and extrusion in the button group. Other biomechanical studies had confirmed this result [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Thus, we suggest that Class II elastic traction is able to enhance molar distalization and to prevent anchorage loss (proclination) of the anterior teeth. Moreover, the precision-cut mode is biomechanically superior to the button mode.\u003c/p\u003e \u003cp\u003eAligner overtreatment is an effective measure to enhance designated tooth movement by designing additional tooth movements [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. As dictated by the biomechanical nature of the molar distalization, the second molar tended to exhibit distal tipping during its distalization. Thus, to counteract distal tipping and to achieve bodily movement, we designed aligner overtreatment for molar distalization by designing greater distal root tipping. We found that aligner overtreatment produced less distal tipping of the second molar during distalization and resulted in bodily distalization. As displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e10\u003c/span\u003e, from the perspectives of biomechanics, the aligner overtreatment generated a counterclockwise moment that counteracted the clockwise moment produced by the aligner distalization force. Thus, the two moments that have opposite directions resulted in a net effect of bodily distalization of the second molar. Moreover, the aforementioned counterclockwise moment by the aligner generated a reciprocal moment on the anchorage teeth, i.e., clockwise moment on the first molar and central incisor. Thus, this biomechanical effect can explain the displacement tendency of the first molar and central incisor, i.e., less mesial tipping and greater extrusion of the first molar, and more lingual tipping and greater extrusion. All these displacement tendencies of the anchorage teeth indicated that the adverse biomechanical effects produced by molar distalization with clear aligner can be mitigated by the aligner overtreatment. Therefore, we suggest that appropriate aligner overtreatment is able to achieve bodily distalization of the second molar and diminish the adverse biomechanical effect of the anterior teeth.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe results of this simulation are confined to the analysis of stress and displacement patterns during the initial phase of tooth movement. However, recognizing tooth movement as a dynamic, long-term process, accompanied by alterations in the force system and the mechanical response of tissues, is crucial. Tooth movement and the force generated by aligners peak at the beginning of the process and subsequently diminish [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. This would facilitate clinicians in comprehending the intricate interactions among dental units when subjected to concurrent force applications.\u003c/p\u003e"},{"header":"CONCLUSIONS","content":"\u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eMolar distalization with clear aligner generates distal tipping, buccal tipping and intrusion of the molar, and mesial tipping, labial proclination and intrusion of the incisors.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eVertical attachment on the second molar produces more enhanced molar distalization than horizontal attachment.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eClass II elastic traction is recommended to enhance molar distalization and to eliminate adverse biomechanical effect of the anterior anchorage teeth.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003ePrecision cut is biomechanically superior to button on the canine.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAppropriate aligner overtreatment is able to achieve bodily distalization of the second molar and diminish the adverse biomechanical effect of the anterior teeth.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eJialun Li: Writing - Original Draft, Conceptualization, Software, Formal analysis. Yi Yang: Methodology, Software. Ziwei Tang: Validation, Invetigation. Qi Fan: Methodology. Omar M. Ghaleb: Data Curation, Visualization. Xian He: Formal analysis. Wenli Lai: Supervision. Hu Long: Data Curation, Project administration, Funding acquisition, Writing - Review \u0026amp; Editing, Supervision.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eFrongia G, Castroflorio T (2012) Correction of severe tooth rotations using clear aligners: a case report. Aust Orthod J 28:245\u0026ndash;249\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHaouili N, Kravitz ND, Vaid NR et al (2020) Has Invisalign improved? A prospective follow-up study on the efficacy of tooth movement with Invisalign. Am J Orthod Dentofac Orthop 158:420\u0026ndash;425\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhu Ya-fen, Li Xlong, Wen li Lai (2019) Treatment of Severe Anterior Crowding with the Invisalign G6 First-Premolar Extraction Solution. J Clin Orthod 53:459\u0026ndash;469\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGao M, Yan X, Zhao R et al (2021) Comparison of pain perception, anxiety, and impacts on oral health-related quality of life between patients receiving clear aligners and fixed appliances during the initial stage of orthodontic treatment. Eur J Orthod 43:353\u0026ndash;359\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRouzi M, Zhang X, Jiang Q et al (2023) Impact of Clear Aligners on Oral Health and Oral Microbiome During Orthodontic Treatment. Int Dent J 73:603\u0026ndash;611\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLong H, Wu Z, Yan X et al (2020) An objective system for appraising clear aligner treatment difficulty: clear aligner treatment complexity assessment tool (CAT-CAT). BMC Oral Health 20:312\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJiahong Lyu M, Gao S, Zhang et al (2021) Clear aligner treatment for a re-treated adult patient with a unilateral full-cusp Class II malocclusion and severe dental midline discrepancy. J Aligner Orthod 5:1\u0026ndash;12\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRen L, Liu L, Wu Z et al (2022) The predictability of orthodontic tooth movements through clear aligner among first-premolar extraction patients: a multivariate analysis. Prog Orthod 23:52\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhao R, Mei L, Long H et al (2023) Changing clear aligner every 10 days or 14 days ? A randomised controlled trial. Australas Orthod J 39:1\u0026ndash;12\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKarras T, Singh M, Karkazis E et al (2021) Efficacy of Invisalign attachments: A retrospective study. Am J Orthod Dentofac Orthop 160:250\u0026ndash;258\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSimon M, Keilig L, Schwarze J et al (2014) Treatment outcome and efficacy of an aligner technique\u0026ndash;regarding incisor torque, premolar derotation and molar distalization. BMC Oral Health 14:68\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRossini G, Parrini S, Castroflorio T et al (2015) Efficacy of clear aligners in controlling orthodontic tooth movement: a systematic review. Angle Orthod 85:881\u0026ndash;889\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu X, Wu J, Cheng Y et al (2023) Effective contribution ratio of the molar during sequential distalization using clear aligners and micro-implant anchorage: a finite element study. Prog Orthod 24:35\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlhammadi MS, Qasem AAA, Yamani AMS et al (2022) Skeletal and dentoalveolar effects of class II malocclusion treatment using bi-maxillary skeletal anchorage: a systematic review. BMC Oral Health 22:339\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSheng Y, Guo H-M, Bai Y-X, Li S (2020) Dehiscence and fenestration in anterior teeth: Comparison before and after orthodontic treatment. J Orofac Orthop 81:1\u0026ndash;9\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJanson G, Sathler R, Fernandes TMF et al (2013) Correction of Class II malocclusion with Class II elastics: a systematic review. Am J Orthod Dentofac Orthop 143:383\u0026ndash;392\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eComba B, Parrini S, Rossini G et al (2017) A Three-Dimensional Finite Element Analysis of Upper-Canine Distalization with Clear Aligners, Composite Attachments, and Class II Elastics. J Clin Orthod 51:24\u0026ndash;28\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMao B, Tian Y, Xiao Y et al (2023) The effect of maxillary molar distalization with clear aligner: a 4D finite-element study with staging simulation. Prog Orthod 24:16\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi L, Guo R, Zhang L et al (2023) Maxillary molar distalization with a 2-week clear aligner protocol in patients with Class II malocclusion: A retrospective study. Am J Orthod Dentofac Orthop 164:123\u0026ndash;130\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRavera S, Castroflorio T, Garino F et al (2016) Maxillary molar distalization with aligners in adult patients: a multicenter retrospective study. Prog Orthod 17:12\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu L, Song Q, Zhou J et al (2022) The effects of aligner overtreatment on torque control and intrusion of incisors for anterior retraction with clear aligners: A finite-element study. Am J Orthod Dentofac Orthop 162:33\u0026ndash;41\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePalone M, Pignotti A, Morin E et al (2023) Analysis of overcorrection to be included for planning clear aligner therapy: a retrospective study. Angle Orthod 93:11\u0026ndash;18\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang C-Y, Su M-Z, Chang H-H et al (2012) Tension-compression viscoelastic behaviors of the periodontal ligament. J Formos Med Assoc 111:471\u0026ndash;481\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCortona A, Rossini G, Parrini S et al (2020) Clear aligner orthodontic therapy of rotated mandibular round-shaped teeth: A finite element study. Angle Orthod 90:247\u0026ndash;254\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang Y, Yang R, Liu L et al (2023) The effects of aligner anchorage preparation on mandibular first molars during premolar-extraction space closure with clear aligners: A finite element study. Am J Orthod Dentofac Orthop 164:226\u0026ndash;238\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRossini G, Schiaffino M, Parrini S et al (2020) Upper Second Molar Distalization with Clear Aligners: A Finite Element Study. Appl Sci 10:7739\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu L, Zhan Q, Zhou J et al (2021) Effectiveness of an anterior mini-screw in achieving incisor intrusion and palatal root torque for anterior retraction with clear aligners. Angle Orthod 91:794\u0026ndash;803\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBarone S, Paoli A, Razionale AV, Savignano R (2017) Computational design and engineering of polymeric orthodontic aligners. Int J Numer Methods Biomed Eng 33:e2839\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGomez JP, Pe\u0026ntilde;a FM, Mart\u0026iacute;nez V et al (2015) Initial force systems during bodily tooth movement with plastic aligners and composite attachments: A three-dimensional finite element analysis. Angle Orthod 85:454\u0026ndash;460\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiang W, Rong Q, Lin J, Xu B (2009) Torque control of the maxillary incisors in lingual and labial orthodontics: a 3-dimensional finite element analysis. Am J Orthod Dentofac Orthop 135:316\u0026ndash;322\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrezniak N (2008) The clear plastic appliance: a biomechanical point of view. Angle Orthod 78:381\u0026ndash;382\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYan X, Zhang X, Ren L et al (2023) Effectiveness of clear aligners in achieving proclination and intrusion of incisors among Class II division 2 patients: a multivariate analysis. Prog Orthod 24:12\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTao T, Liang H, Yan X et al (2022) Comparison of Root Parallelism in Extraction Cases Treated with Clear Aligners vs. Fixed Appliances Appl Sci 12:11756\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSaif BS, Pan F, Mou Q et al (2022) Efficiency evaluation of maxillary molar distalization using Invisalign based on palatal rugae registration. Am J Orthod Dentofac Orthop 161:e372\u0026ndash;e379\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYokoi Y, Arai A, Kawamura J et al (2019) Effects of Attachment of Plastic Aligner in Closing of Diastema of Maxillary Dentition by Finite Element Method. J Healthc Eng 2019:1075097\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAyidağa C, Kamiloğlu B (2021) Effects of Variable Composite Attachment Shapes in Controlling Upper Molar Distalization with Aligners: A Nonlinear Finite Element Study. J Healthc Eng 2021:5557483\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKwak K-H, Oh S, Choi Y-K et al (2023) Effects of different distalization directions and methods on maxillary total distalization with clear aligners: a finite element study. Angle Orthod 93:348\u0026ndash;356\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCai Y, Yang X, He B, Yao J (2015) Finite element method analysis of the periodontal ligament in mandibular canine movement with transparent tooth correction treatment. BMC Oral Health 15:106\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4146638/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4146638/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eIntroduction\u003c/strong\u003e: The objective of this study was to analyze the biomechanical effects of aligner overtreatment on molar distalization with clear aligners.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods\u003c/strong\u003e: Various models comprising maxillary dentition, maxilla, periodontal ligaments, attachments, and aligners were meticulously crafted and integrated into finite-element software. Six distinct study models were devised for analysis. The first three models examined second molar distalization with clear aligner, with different configurations of attachments, i.e., no attachment, horizontal attachment or vertical attachment on the second molar. For the fourth and fifth models, class II elastic traction, either implemented via precision cut or button on canines, was applied. Lastly, aligner overtreatment with varying degrees of root distal tipping (0°, 2°, 4°, 6°, 8°, 10°, 12°) for the second molar was designed in the last study model.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e: Distalization of the second molar produced buccal tipping, distal tipping and intrusion of the second molar, and labial proclination and intrusion of the central incisor. These displacement tendencies were enhanced by adding attachments on the second molar, especially the vertical attachment. Class II elastic tractions enhanced molar distalization and diminish anchorage loss of the anterior anchorage teeth, with the precision-cut configuration being biomechanically superior to the button design. Aligner overtreatment produced bodily molar distalization and mitigated adverse biomechanical effects on anterior anchorage teeth.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion\u003c/strong\u003e: We suggest that class II elastic traction via the precision-cut configuration and the design of vertical attachment on the second molar be applied for molar distalization with clear aligner. Appropriate aligner overtreatment helps achieve bodily molar distalization and minimize adverse biomechanical effects on anterior anchorage teeth.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical Relevance: \u003c/strong\u003eThese findings provide valuable insights for orthodontists in optimizing molar distalization outcomes with clear aligners. Integration of overtreatment can enhance treatment efficacy and predictability, ultimately improving patient care and satisfaction.\u003c/p\u003e","manuscriptTitle":"Biomechanical analysis of the effect of aligner overtreatment on molar distalization with clear aligners: a finite-element study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-28 18:30:22","doi":"10.21203/rs.3.rs-4146638/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"5f6769f3-5f7c-42f2-9d5c-e4e6ed4fc9af","owner":[],"postedDate":"March 28th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-06-03T07:29:41+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-28 18:30:22","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4146638","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4146638","identity":"rs-4146638","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}