Finite element simulations of the effects of an extraoral device, RAMPA, on anterosuperior protraction of the maxilla and comparison with gHu-1 intraoral device

Objectives: To investigate the effects of an extraoral device, right-angle maxillary protraction appliance (RAMPA), combined with a semi-rapid maxillary expansion intraoral device (gHu-1) on the anterosuperior protraction of maxillary bone. Materials and Methods: The finite element (FE) model included craniofacial bones and all sutures. The linear assumption was assumed for the FE simulations and the material properties of bones and sutures. The gHu-1 was simulated under screw activations equal to Delta x = 0.25 and 0.5 mm in the lateral direction with and without RAMPA under a set of external forces {F-1 = 2.94, F-2 = 1.47, F-3 = 4.44) N. Results: Displacement contours, nodal displacements of 12 landmarks, and von Mises stresses were compared. Combining RAMPA and gHu-1 (with Delta x = 0.25 mm) resulted in changes in the displacement of the front part of the maxilla near the mid-palatal suture from (0.02, -0.1, -0.02) mm to (0.02, 0.3, 0.8) mm. For gHu-1 with Delta x = 0.5 mm, the displacement of the same part changed from (0.04, -0.04, -0.2) mm to (0.04, 0.3, 0) mm. Similar trends were found in other locations. Conclusions: The findings are in agreement with the previous cephalometric clinical data of an 8-year-old patient and prove the positive effects of RAMPA on the anterosuperior protraction of the maxilla when it is combined with the intraoral device gHu-1. In addition, RAMPA does not interfere with the lateral expansion generated by the intraoral device.