Immediate effects of rapid maxillary expansion on the nasal cavity using Haas-type and Hyrax-type expanders in CBCT

Purpose: To evaluate and compare the immediate effects of rapid maxillary expansion (RME) on the nasal cavity dimensions in subjects treated with Haas-type and Hyrax-type expanders using cone-beam computed tomography (CBCT).Methods: Thirty-one growing patients (mean age=10.8years old) with transverse maxillary deficiency were randomly divided into two groups: Haas group (n=16) and Hyrax group (n=15).All patients had RME with initial screw activation of 4 quarter turns followed by activations of ½ turns per day (0.4mm) until the expansion reached 8mm opening at the screw.CBCT scans were taken before RME (T1) and at the end of the active phase of expansion (T2).Vertical and transverse measurements were performed at different regions of nasal cavity for comparison between groups and treatment times.Intraclass correlation coefficient (ICC), paired Student's t-test and repeated measures ANOVA (α-level p<0.05) were calculated.Results: RME procedure increased every vertical and lateral nasal cavity dimensions (p<0.001).The most significant gains were observed in the lower portions of the nasal cavity located at the anterior and medial regions.Conclusions: Both appliances were able to create significant changes in the dimensions of the nasal cavity immediately after RME.However, the Hyrax-type expander presented greater transverse effects on the airway.