Evaluation of dental and skeletal effects of modified rapid maxillary expansion appliance: A three-dimensional finite element study

Transvers maxillary deficiency is one of the most common skeletal anomalies. The incidence of posterior crossbite caused by maxillary stenosis is between 2.7% and 18.2%. Unilateral posterior crossbite is more common than bilateral. Treatment of posterior crossbite differs from patient to patient, depending on many factors such as age, severity of the anomaly. However, the most common treatment for skeletal posterior crossbite is rapid maxillary expansion (RME), in which the base of the maxillary bone is widened by separating the midpalatal suture. The aim of this study is to compare the effects of conventional RME appliance, full cap splint RME appliance and modified asymmetric RME appliance with finite element analysis. The three different models used in the three scenarios are as follows; 1) convantional bonded RME appliance in which molar and premolar teeth are covered with acrylic, 2) F-RME appliance in which all teeth are covered with acrylic so that the palatal mucosa is exposed, 3) Asymmetric modified RME appliance in which all teeth on the right side are covered with acrylic on the left premolars and molars. In all models, stress levels and displacements after applying 5 mm displacement in the horizontal plane to the RME screw were investigated by finite element stress analysis method. Posterior teeth were expanded more with the conventional RME appliance than with the full cap splint RME appliance. With the modified RME appliance, the posterior teeth expanded more on the side where the premolars and molars are covered with acrylic than on the side with full coverage. The anterior teeth were expanded more with the full cap splint RME appliance than with the conventional RME appliance. With the modified RME appliance, the anterior teeth were more expanded on the fully-covered side than the other side, and the midline shifted to the fully-covered side. With the asymmetric modified RME appliance, the deviated midline can be corrected and unilateral expansion in the posterior region can be achieved. Keywords: Modified RME Appliance, Finite Element Analysis, Rapid Maxillary Expansion