Objective: To evaluate the effects of rapid maxillary expansion (RME) on nasal patency and naso-maxillary dimensions in mouth-breathing children and adolescents through an eight-year clinical follow-up. Methods: RME was performed with a Hyrax orthodontic appliance in 28 mouth-breathers (6-13 y.o.). During follow-up, objective tests of nasal respiratory function were conducted: acoustic rhinometry provided minimum cross-sectional areas of the nasal cavity and active anterior computed rhinomanometry measured inspiratory nasal resistance. Also, tomographic widths of coronal sections of the nose and the maxilla were measured. Fisher's exact and Mann-Whitney tests were used to compare categorical and numerical variables, respectively, in mouth-breathers with and without allergic rhinitis. Temporal evolution was assessed using the Generalized Estimating Equation models. Statistical significance was set at P < 0.05. Results: There was a reduction in inspiratory resistance after ERM, with a stable improvement in nasal patency during the eight-year follow-up period (P = 0.0179). All nasal and maxillary tomographic widths had statistically significant increases in the short term (P < 0.0001), and most of them showed significant increases in the long term, when compared with the pre-expansion period. The tomographic measurements were not influenced by allergic rhinitis. Conclusion: Although limited by a small sample size and the lack of a control group, our study showed that RME promoted and maintained the widening of the posterior maxillary structure in mouth-breathing children and adolescents, with a decrease in inspiratory nasal resistance during the eight-year follow-up period. These findings highlight the importance of performing RME in mouth-breathers with maxillary atresia.

Keywords: child, mouth-breathing, palatal expansion technique