Mandibular response after rapid maxillary expansion in class II growing patients: a pilot randomized controlled trial

BACKGROUND: The aim of this pilot randomized controlled trial (RCT) was to evaluate the sagittal mandibular response induced by rapid maxillary expansion (RME) therapy in mixed dentition patients with class II malocclusion, comparing the effects of bonded RME and banded RME with a matched untreated class II control group. METHODS: This RCT was designed in parallel with an allocation ratio of 1:1:1. The sample consisted of 30 children with a mean age of 8.1 ± 0.6 years who were randomly assigned to three groups: group 1 treated with bonded RME, group 2 treated with banded RME, and group 3 the untreated control group. All patients met the following inclusion criteria: early mixed dentition, class II molar relationship, transverse discrepancy ≥ 4 mm, overjet ≥ 5 mm, and prepubertal skeletal maturity stage (CS1–CS2). The expansion screw was activated one quarter of a turn per day (0.25 mm) until overcorrection was reached. For each subject, lateral cephalograms and plaster casts were obtained before treatment (T1) and after 1 year (T2). A randomization list was created for the group assignment, with an allocation ratio of 1:1:1. The observer who performed all the measurements was blinded to group assignment. The study was single-blinded in regard to statistical analysis. RESULTS: RME was effective in the correction of maxillary deficiency. Class II patients treated with both types of RME showed no significant improvement of the anteroposterior relationship of the maxilla and the mandible at both skeletal and occlusal levels. The acrylic splint RME had significant effects on reducing the skeletal vertical dimension and the gonial angle. CONCLUSIONS: The orthopedic expansion did not affect the sagittal relationship of class II patients treated in the early mixed dentition when compared with the untreated control group. Additional studies with a larger sample are warranted to elucidate individual variations in dento-skeletal mandibular response to the maxillary expansion protocol in class-II-growing patients. TRIAL REGISTRATION: ClinicalTrials.gov NCT03159962.