Three-dimensional finite-element analysis of maxillary protraction with and without rapid palatal expansion

The aims of this study were to determine the reaction of the craniofacial bones on the protraction force transferred to the maxillary body, and whether or not the midpalatal suture had opened during skeletal Class III treatment.A computerized tomograph was obtained from a dry skull with a normal occlusion to construct a three-dimensional finite-element model (3D·FEM) of the craniofacial bones and the maxillary teeth to simulate actual bone reactions. A protraction force of 500 g was applied at the first premolar region, directed 20 degrees inferior to the occlusal plane. The displacement and the stress distribution of the craniofacial bones and sutures were then calculated using the ANSYS 5.3 program dividing the analysis into two simulations, based on whether or not the midpalatal suture was opened.The results showed that there was less compressive stress and greater tensile stress in the circumaxillary suture areas when the midpalatal suture was opened. The amount of displacement and deformation when the midpalatal suture was opened also demonstrated a decrease in upward-forward rotation of the maxilla and zygomatic arch and greater amounts of displacement in the frontal, vertical, and lateral directions compared with no opening of the midpalatal suture. Analysis of these results showed that maxillary protraction produce similar changes to normal downward and forward growth of the maxilla and was achieved with accompanying opening of the midpalatal suture.