RESUMO
Background: To evaluate the stability of the transverse correction with a hybrid maxillary expansion appliance in the bone and tegumental piriformis opening in relation to bone age and maturation of the midpalatal suture (MPS). Material and Methods: 15 patients with a mean initial age of 14.9 years (SD=1.50), 7 (46.7%) were female and 8 (53.3%) were male, treated with a hybrid maxillary expander. Cone beam computed tomographic (CBCT) images were collected in three phases: T1 (orthodontic records), T2 (21.33 days (SD=10.68) after the end of expansion screw activation) and T3 after 9.13 months (DP=2.41) after the expansion screw was activated. In CBCT, measurements were performed in the nasal cavity considering the tegumental piriform opening (sagittal-axial sections) and bone (sagittal-axial-coronal sections) and the stage of MPS maturation (sagittal-axial sections). Repeated measures ANOVA was used for continuous variables and Friedman's ANOVA for the ordinal variable followed by Bonferroni's tests for p<0.001, in relation to time. Results: There were significant differences between T1 and T2 (p=0.041), between T2 and T3 (p<0.001) and between T1 and T3 (p=0.041). Regarding bone age by cervical vertebrae maturation, 20% were in stage CS3, 40% in stage CS4, 26.7% in stage CS5 and 13.3% in stage CS6. There was a significant increase in tegumental piriformis opening between T1 (M=32.19, SD=3.79) and T2 (M=34.82, SD=2.81) (p=0.008), followed by a significant decrease in T3 (M=34.64, SD=2.73) (p=0.021), as well as in the opening of the bone piriform, between T1 (M=21.30, SD=2.47) and T2 (M=25.35, SD=2.21) (p<0.001), followed by a significant decrease in T3 (M=24.89, SD =2.30) (p=0.018). Conclusions: The hybrid maxillary expansion appliance was effective in opening the midpalatal suture of all patients in the present study, without influence of the initial stage of MPS maturation and bone age. There was a relapse of the increase in the bone and tegumental piriform openings. Key words:Maxillary expansion, orthodontic anchorage procedures, nose.