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

Aim: To compare the dental and skeletal effect of a modified Hyrax rapid maxillary expander (RME) appliance with a vestibular arm with a conventional Hyrax expander in growing patients presenting with asymmetric transverse maxillary deficiency and upper midline deviation. Material and methods: The study included 50 growing patients (27 females, 23 males; age range 6-9 years) in early mixed dentition, characterized by maxillary narrowness, premature loss of deciduous teeth, unilateral or bilateral crossbite, and upper midline deviation. Patients were divided into two groups: 25 treated with the notified Hyrax (with vestibular arm) and 25 with a conventional Hyrax. Dental cats and posteroanterior cephalograms were analysed at baseline (T0) and after a 6-month retention period (T1). Parameters evaluated included: intermolar width (IM-W), intercanina width (IC-W), arch length (AL), arch perimeter (AP), lateral incisor drift (ILD), space between lateral incisor and first deciduous molar (I-1MS), and midline deviation. Statistical analysis was performed using paired t-test (p<0,05). Results and conclusion: Both appliances significantly increased IM-W, IC-W, AL and AP (p<0,0001), with no statistically significant differences between groups in transverse skeletal expansion. however, the modified Hyrax showed a highly significant reduction in lateral incisor drift (mean reduction 5,15 mm; p<0,0001) and a significant space gain in the canine area (mean increase 6,4 mm; p<0.0001). midline coincidence was restored by up to 5-6 mm, creating 7-9 mm of space for permanent canine eruption. In conclusion, while both devices effectively correct maxillary narrowness, the modified Hyrax expander is the treatment choice for correcting upper midline deviations and restoring dental symmetry, potentially reducing the need for subsequent fixed appliance therapy.