Analysis of prefabricated myofunctional appliances with different overjet and bumper designs: a three-dimensional finite element analysis

Xiaowei et al. BMC Oral Health (2024) 24:561 https://doi.org/10.1186/s12903-024-04325-3 BMC Oral Health Open Access RESEARCH Analysis of prefabricated myofunctional appliances with different overjet and bumper designs: a three-dimensional finite element analysis Wu Xiaowei1, Lv Haoran1, Chen Xuehui1 and Pan Xiaogang1* Abstract Background Prefabricated myofunctional appliance can guide tooth eruption, improve dentition alignment, correct myofunctional disorders and harmful oral habits. However, its application to skeletal discrepancy may result in unsatisfactory tooth inclination. This study aimed to construct a novel appliance with overjet design to avoid this side effect and investigated its shape and mechanical changes under occlusion using three-dimensional finite element method. Methods We established three samples of prefabricated myofunctional appliances. The first one was edge to edge without overjet, and the outer shield of both jaws were flattened. The second one was 3 mm overjet with stepped the outer shield. The last one was 3 mm overjet, and the outer shield of both jaws were flatted, which meant the front wall of lower jaw was strengthened with bumper, termed as lower bumper. A complete dentition model was applied to the study. 150 N occlusal force was applied to each type of appliance and the deformation displacement and the changes in stress was recorded. Results The deformation was significant in the incisors regions, especially in the vertical and lateral dimensions. The maximum displacements of 3 mm overjet with step shield group were 7.08 mm (vertical), 3.99 mm (lateral), and 2.90 mm (sagittal), while it decreased to 3.92 mm(vertical), 1.94 mm (lateral), and 1.55 mm (sagittal) in overjet with bumper group. Moreover, the upper molar regions exhibited higher vertical and sagittal displacement in 3 mm overjet with step shield group, which were 3.03 mm (vertical) and 1.99 mm (sagittal), and the bumper design could decrease the maximum displacement to 1.72 mm (vertical) and 0.72 mm (sagittal). In addition, the Von Mises stress of appliances was analyzed, and results indicated that 3 mm overjet with step shield generated higher stress than other groups, with the maximum Von Mises stress was 0.9387 MP, which were 0.5858 and 0.5657 MP in edge to edge group and 3 mm overjet with lower bumper group, respectively. Conclusion The prefabricated myofunctional appliances may cause deformation during occlusion. Compared to step shield group, the application of lower bumper exhibited better resistance to occlusal force. *Correspondence: Pan Xiaogang Full list of author information is available at the end of the article © The Author(s) 2024. 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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. Xiaowei et al. BMC Oral Health (2024) 24:561 Page 2 of 9 Keywords Early treatment, Prefabricated myofunctional appliances, Shape deformation, Orthodontics Background The prevalence of malocclusion and occlusal traits is common in early mixed dentition. Previous study showed that 79.4% children lived in Shanghai presented occlusal anomalies in mixed dentition [1]. However, in mixed dentition, the deciduous teeth will loose and fall off, which will influence the integrity of dentition and hinder the application of orthodontic appliance on teeth. Therefore, orthodontic treatment often starts after dental transitional period. Even though 2 × 4 appliance could be applied in mixed dentition patients, it mainly aligns the anterior teeth, and shows little regulatory effects on undesirable oral habits and the balance of intraoral and extraoral muscle groups [2, 3]. Harmful oral habits could induce unbalance of maxillofacial muscles, and result in malocclusions [4, 5]. Therefore, it is important to correct the harmful oral habits and balance the maxillofacial muscles in mixed dentition patients [6]. However, the device for dental transitional period is limited in clinic. Prefabricated myofunctional appliances could guide teeth eruption, improve teeth alignment, correct abnormal functions of muscles, and rectify harmful oral habits, thus enhance the severity of malocclusions, and reduce the difficulties of treatment at the follow up stage [7– 15]. Some commercial prefabricated appliance has been applied in mixed dentition to address such problems for a period of time. Prefabricated myofunctional appliance has also been applied to obstructive sleep apnea (OSA). OSA during childhood could induce neuropsychological and cognitive impairment, hypertension, and endocrine disorder. In the treatment of pediatric OSA, surgery was performed first to remove the enlarged tonsils and adenoids. Although surgery could significantly reduce obstruction and clinical symptoms, it still cannot solve all problems, and there was still a large number of patients who needed follow-up treatment. Previous studies found that prefabricated myofunctional appliance could significantly reduce the apnea and hypopnea index (AHI) in children with mild to moderate OSA [16]. Moreover, the application of prefabricated myofunctional appliance after surgery significantly reduced the AHI compared with surgery only group [17]. In addition, most temporomandibular disorder (TMD) patients suffered from temporomandibular joint clicking, pain, difficulty in mouth opening, and even psychological disorders [18]. A correct position of mandible could relief the symptoms of TMD and even improve an athletes’ performance, and occlusal therapy has been considered as an efficient trail for TMD treatment [19, 20]. As an occlusal appliance, prefabricated myofunctional appliance has been applied for the treatment of TMD. Previous multi-centered randomized controlled trails indicated that of prefabricated myofunctional appliance significantly improved the symptoms of TMD, and both short- term and long- term effectiveness of prefabricated myofunctional appliance was in equilibrium with stabilization appliance [18, 19, 21]. Although prefabricatio (...truncated)