Effects of transpalatal arch on molar movement produced by mesial force: A finite element simulation

Introduction: The transpalatal arch (TPA), which splints together 2 maxillary molars, has been believed to preserve anchorage. The purpose of this study was to clarify this effect from a mechanical point of view. Methods: The finite element method was used to simulate the movement of anchor teeth subjected to mesial forces with and without a TPA. Results: In the initial movement produced by elastic deformation of the periodontal ligament, stress magnitude in the periodontal ligament was not changed by the TPA. In the orthodontic movement produced by bone remodeling, the mesial force tipped the anchor teeth irrespective of the TPA. The tipping angles of anchor teeth with and without the TPA were almost the same. The anchor teeth without the TPA were rotated in the occlusal plane and moved transversely. Conclusions: The TPA had no effect on the initial movement. In the orthodontic movement, the TPA had almost no effect, preserving anchorage for mesial movement. However, the TPA prevented rotational and transverse movements of the anchor teeth. These results are valid when the assumptions used in this calculation are satisfied.