Comparison of a modified RME appliance with other appliances for transverse maxillary expansion

Plate appliances or fixed appliances for transverse expansion are used to treat lateral crossbites in early mixed dentition. The aim of this study was to compare these appliances' dentoalveolar effects with those of a modified appliance with altered anchorage.

Forty patients with early mixed dentition were examined. Twenty patients in the study group were treated with a modified RME appliance firmly anchored to the first permanent molars and with palatal rests in the first and second deciduous molar region. The appliance had wire extensions to the palatal aspects of the canines. One of the two comparison groups comprised 10 patients whose maxillary dental arch was transversally expanded with a split-plate appliance, and the other group contained 10 patients treated with a Hyrax-type rapid palatal expander fixed to the first permanent molars. After the plaster casts' transverse parameters before and after expansion and after retention were measured to ascertain the treatment result, statistical analysis was performed applying the Wilcoxon test and Mann-Whitney U test.

The modified RME appliance expanded the anterior and posterior arch width highly significantly in transversal direction (p < 0.001). At the end of the retention phase, there were no significant differences between the modified RME appliance and the RME appliance with shortened arms. Compared to the split-plate appliance, the modified RME (p < 0.05) expanded the anterior arch width significantly.

The modified RME appliance can be used effectively for rapid maxillary expansion in the early mixed dentition. At the end of the retention phase, the overall effect of the modified appliance is similar to that of the other methods.