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 Δx = 0.25 and 0.5 mm in the lateral direction with and without RAMPA under a set of external forces {F1 = 2.94, F2 = 1.47, F3 = 4.44} N.


Displacement contours, nodal displacements of 12 landmarks, and von Mises stresses were compared. Combining RAMPA and gHu-1 (with Δx = 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 Δx = 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.


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.

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Author notes


Research Professor, Department of Mechanical Engineering, Sogang University, Seoul, Korea.


Private practice, Tokyo, Japan.


Professor, Department of Mechanical Engineering, Sogang University, Seoul, Korea.


PhD candidate, Mechanical Engineering, Guilan University, Rasht; and CEO, Isra Sanat Shar NoAfarin Engineering Co., Qazvin, Iran.