Effects of overtreatment with different attachment positions on maxillary anchorage enhancement with clear aligners: a finite element analysis study

Wang et al. BMC Oral Health (2023) 23:693 https://doi.org/10.1186/s12903-023-03340-0 BMC Oral Health Open Access RESEARCH Effects of overtreatment with different attachment positions on maxillary anchorage enhancement with clear aligners: a finite element analysis study Shiyu Wang1, Yangyang Huang1, Dian Fan1, Hao Liu2, Changyong Yuan1,3, Li Yang2 and Penglai Wang1,3* Abstract Background The effect of attachment positions on anchorage has not been fully explored. The aim of the present study is to analyze the effect of overtreatment with different anchorage positions on maxillary anchorage enhancement with clear aligners in extraction cases. Methods Models of the maxilla and maxillary dentition were constructed and imported into SOLIDWORKS software to create periodontal ligament (PDL), clear aligners, and attachments. Attachment positions on second premolars included: without attachment (WOA), buccal attachment (BA), and bucco-palatal attachment (BPA). Overtreatment degrees were divided into five groups (0°, 1°, 2°, 3°, 4°) and added on the second premolars. The calculation and analysis of the displacement trends and stress were performed using ANSYS software. Results Distal tipping and extrusion of the canines, and mesial tipping and intrusion of the posterior teeth occurred during retraction. A strong anchorage was achieved in cases of overtreatment of 2.8° with BA and 2.4° with BPA. Moreover, the BPA showed the best in achieving bodily control of the second premolars. When the overtreatment was performed, the canines and first molars also showed reduced tipping trends with second premolars attachments. And the stress on the PDL and the alveolar bone was significantly relieved and more evenly distributed in the BPA group. Conclusions Overtreatment is an effective means for anchorage enhancement. However, the biomechanical effect of overtreatment differs across attachment positions. The BPA design performs at its best for stronger overtreatment effects with fewer adverse effects. Keywords Clear aligners, Extraction cases, Overtreatment, Attachment, Finite element analysis *Correspondence: Penglai Wang 1 School of stomatology, Xuzhou Medical University, 221000 Xuzhou, China 2 Department of Orthodontics, Affiliated Stomatological Hospital of Xuzhou Medical University, 221000 Xuzhou, China 3 Department of Implantology, Affiliated Stomatological Hospital of Xuzhou Medical University, 221000 Xuzhou, China © The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Wang et al. BMC Oral Health (2023) 23:693 Background The increasing demand of esthetic and comfortable appliances has prompted the development of clear aligners [1]. Compared to fixed appliances, clear aligners have advantages of better periodontal maintenance and lesser root resorption [2, 3]. Nowadays, clear aligners can effectively achieve various tooth movements, such as molar distalization and arch expansion [4, 5]. However, due to limitations in material properties, the control deficiency of clear aligners in complex tooth movements limits its application in extraction cases. A successful treatment depends on the well-controlled anchorage. However, anchorage loss is frequently seen and manifests as mesial tilt and intrusion of the posterior teeth [6, 7]. Overtreatment has been widely employed in clear aligners to improve its efficiency [8]. In extraction cases of the posterior region, overtreatment manifests as preset distal tipping [9]. During overtreatment, the attachment design is critical and is typically located on the buccal surfaces of the teeth. We previously found that the combined use of buccal and palatal attachments produced better results in molar intrusion than using single buccal attachment (BA) [10]. However, Ahmed et al. reported the opposite results in torque control [11]. Whether or not the bucco-palatal attachment (BPA) design is effective in anchorage control or further amplifies the effect of overtreatment remains unexplored. Attachments are not curative in clinical practice. Anchorage loss occurs because of shortage of overtreatment. Dai et al. reported mesial tipping of the molars with overtreatment [12]. Due to the lack of relevant studies, the adequate amount of overtreatment has not been determined. As an effective and reliable method, the finite element analysis (FEA) is widely used in biomechanical studies [13–15]. To simplify the analysis, a complicated assembly is divided into a finite number of units. The overall mechanical properties are obtained by analyzing and integrating the properties of each unit. Under a virtual clinical condition, the displacement tendencies of teeth and stress distributions of periodontal ligaments (PDLs) can be calculated and visualized [16], which helps to better understand the mechanisms of clear aligners. The aim of the present study was to compare the biomechanical effect of overtreatment between three groups: without attachment (WOA), BA and BPA groups. We established a model of the maxillary dentition with first premolars extracted. Through the parameter settings and calculations, the relevant results were presented in the software. And the conclusions could be obtained in the subsequent data collection and analysis. Page 2 of 10 Methods Sample selection and data acquisition A 26-year-old man was recruited for the present study. Imaging data were obtained from the cone-beam computed tomography (CBCT) database. The study protocol was approved by the Ethical Committee of the Affiliated Stomatological Hospital of Xuzhou Medical University (2022-KY-004-01). Model establishment A total of 340 images were obtained from the archive and imported into MIMICS Research 21.0 (Materialize, Leuven, Belgium). Three-dimensional reconstruction of the maxilla and maxillary teeth was carried out through threshold separation and editing. Subsequently, the three-dimensional model was imported into GEOMAGIC Wrap 2017 (Geomagic, North Carolina, U (...truncated)