A finite element analysis of two Class II correction modalities: Intermaxillary elastics and the forsus fatigue resistant device

Background: Class II Division 1 malocclusion is commonly associated with mandibular retrusion and is treated using Class II intermaxillary elastics or fixed functional appliances such as the Forsus Fatigue Resistant Device (FFRD).Aims and Objectives: To compare the displacement and stress distribution patterns produced by Class II elastics and FFRD using finite element analysis (FEA).Materials and Methods: A three-dimensional finite element model was developed from computed tomography data of a 15-year-old female patient with skeletal Class II Division 1 malocclusion and mandibular retrusion. Two models incorporating MBT fixed appliances were constructed: one with bilateral Class II elastics and the other with FFRD. Material properties, masticatory muscle forces, and cranial base constraints were standardized. Stress distribution and displacement in dentoalveolar and skeletal structures were analyzed using Hypermesh 2019 and ANSYS 2017.2.Results: Both appliances produced posterior maxillary displacement, anterior mandibular displacement, and posterosuperior condylar loading. Elastics demonstrated diffuse dentoalveolar stress with focal condylar loading, whereas FFRD produced focal dentoalveolar stress and diffuse condylar loading extending into the neck and ramus. Elastics concentrated maxillary stress anteriorly and mandibular stress posteriorly, while FFRD demonstrated posterior maxillary and anterior mandibular stress concentration. FFRD produced greater stress and displacement magnitudes.Conclusion: Both modalities demonstrated comparable Class II correction patterns, predominantly through dentoalveolar effects, but differed in stress distribution and biomechanical side effects. Appliance selection should consider patient compliance, skeletal divergence, and anticipated biomechanical effects.