Unilateral Scissor Bite Managed with Prefabricated Functional Appliances in Primary Dentition—A New Interceptive Orthodontic Protocol

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

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.

Clinical Effectiveness of Vestibular Shields in Orthodontic Treatment: A Scoping Review

This systematic literature search was performed to determine the clinical effectiveness of vestibular shields (VSs) in children undergoing orthodontic treatment. A comprehensive electronic search was performed in May 2022 using three databases (Medline via PubMed, the Cochrane Central Register of Controlled Trials, and Ovid). The initial screening of articles was based on titles and abstracts. Studies meeting the inclusion criteria were retrieved for the final quality assessment and the methodological qualities were assessed according to the Newcastle-Ottawa Scale and Cochrane risk of bias. The initial search identified 262 publications, of which 15 studies were potentially eligible, with excellent intra-examiner reliability (K = 0.88). A total of five studies were selected for the final analysis, including one randomized controlled trial, three clinical trials, and one cohort study. VS may have potential impacts on orthodontic treatment, lips and dental arches, but further high-quality studies are warranted.