Upper arch expansion and spontaneous upper firstmolar distorotation with Ni–Ti leaf springs and rapid maxillary expander compared to clear aligners. A randomized controlled trial

Abstract Purpose This study aimed to compare the distorotation of the upper first molars (U6) and the expansion of the upper dental arch achieved using clear aligners (CA), Leaf Expander® (LE; Leone, Sesto Fiorentino, Italy), and rapid maxillary expander (RME), all anchored to the second primary molars. Materials and methods The research was structured as a superiority randomized controlled trial conducted in two academic medical centers in Italy. Participants included children in growth phase presenting transverse maxillary deficiency with intermolar width less than 30mm, early mixed dentition with fully erupted upper first molars, and a cervical vertebral maturation stage (CVMS) 1 or 2, without systemic diseases or syndromes. Subjects were randomly assigned to one of the three treatment groups: CA, LE, or RME. The main variable measured was the distorotation of U6, with secondary variables including the width between canines, first molars, and second primary molars. Results In all, 60 subjects were randomized equally into the three groups. Average treatment time was 8± 3 months for the LE group and 9± 1 months for the RME group (p= 0.089). Mean treatment time for the CA group was 15 months with a standard deviation of 2 months. A significant difference was observed in the number of clinical visits: 6± 2 for LE and 8± 1 for RME (p< 0.001). The RME group completed the active treatment phase in 10± 2 days, which was notably shorter than the 3.5± 0.71 months required for the LE group (p< 0.001). Analysis of variance (ANOVA) revealed statistically significant differences among the groups in terms of U6 distorotation (p< 0.05), whereas no significant differences were found for the expansion of the upper arch. Overall molar distorotation was highest in the LE group (11.73°), surpassing the RME group (6.22°), and was similar to the result observed in the CA group (11.89°). Conclusion Both CA and maxillary expanders fixed to upper primary molars produced comparable levels of dentoalveolar expansion. The spontaneous distorotation of the U6 obtained with LE was similar to the planned distorotation achieved with CA and significantly higher than that observed with RME.