Comparison of the dental and skeletal effects of two different rapid palatal expansion appliances for the correction of the maxillary asymmetric transverse discrepancies.

AIM: The aim was to compare the skeletal and dental effects of a new type of a modified Hyrax rapid palatal expander with vestibular arm with the Hyrax expander in patients with maxillary asymmetric deficiencies.
METHODS: This study includes 50 growing patients in early mixed dentition, suffering from a maxillary narrowness combined with the exfoliation of one or more deciduous teeth, a monolateral or bilateral crossbite and a deviation of the upper midline. Twenty-five patients were treated with a modified Hyrax expander and 25 patients with a Hyrax expander (RME). Dental casts and posteroanterior radiographs were obtained before treatment [T0] and six months after maxillary expansion [T1]. Measurements of intermolar width, intercanine width, arch length, arch perimeter, space between lateral incisor and I deciduous molar, and midline discrepancy were made with a digital calliper on photocopies taken from the dental casts. Cephalometric tracing on frontal teleradiographies were evaluated.
RESULTS: Results showed no statistically significant differences between T0 and T1 in the modified RME appliance and the RME except lateral drift of incisor and space between lateral incisor and first deciduous molar. The modified RME permitted to obtain the restoration of the coincidence of the midlines of almost 5/6 mm and to create 7 to 9 mm of space in the canine area.
CONCLUSION: both the appliances are effective in correcting maxillary narrowness but the modified hyrax expander represents the best choice for the correction of upper midline deviations, and to restore the correct symmetry of dental midlines.