Efficacy of different designs of mandibular expanders: A 3-dimensional finite element study

Introduction: Nonsurgical mandibular expansion has been increasingly performed in recent years because it can effectively expand the mandibular dental arch. However, many types of mandibular expanders have been used in previous studies. No relevant studies have compared the biomechanical responses of different designs of mandibular expansion appliances with screws. Therefore, the purpose of this study was to analyze the stress distribution and displacement of the dentoalveolar structures according to different designs of mandibular screw expanders. Methods: Cone-beam computed tomography scans were used for 3-dimensional reconstruction of the mandibular finite element model. Four different designs of mandibular expanders, 1 removable expander (type A) and 3 fixed expanders (types B, C, and D), were added to the finite element models. Expanders were activated transversely for 0.2 mm. The initial tooth displacement and von Mises stress distribution were evaluated. Results: All the expanders enlarged the arch dimensions. In types A and B, the stress was mainly concentrated in the region of the anterior teeth, along with greater tooth displacement, whereas in types C and D, greater stress and displacement occurred in the region of the posterior teeth. Type A showed the greatest amount of transverse displacement. Type D was more efficient in the region of the posterior teeth. Conclusions: Types A and B should be used with great caution in the clinic because of their incompatible expansion pattern. Type D is the recommended mandibular expansion appliance because of its appropriate expansion pattern.