OBJECTIVE The aim of this study was to evaluate changes in the mandibular dental arch and incisor alignment induced by combined bonded Rapid Maxillary Expansion (RME) and Face Mask (FM) therapy in the mixed dentition stage in which leeway space was used throughout the treatment. METHODS This retrospective study evaluates pretreatment (T0) and posttreatment (T1) cephalometric radiographs and orthodontic models of 25 patients (mean age: 10.75±2.64), in mixed dentition, having skeletal Class 3 anomaly (ANB<0) with maxillary retrognatism (SNA=77.2±0.68) and bilateral posterior crossbite treated with bonded Hyrax RME-FM. Mean treatment duration was 10.4 months. Dental model measurements were performed using the 3Shape OrthoAnalyzerTM 2013-1 program. Changes in the mandibular incisor and first molar positions were determined on cephalometric radiographs. Statistical evaluation was done with a paired t-test. RESULTS A significant increase of 1.2 mm was found in intermolar width (p<0.001) in the mandibular dental arch. There was a significant decrease (1.4 mm) (p<0.001) in arch depth and an increase in arch length discrepancy (1.7mm)(p<0.01). There was a significant increase (0.8mm) (p<0.05) in the incisors' irregularity score (LII). IMPA showed a significant decrease (p<0.05). CONCLUSIONS Clinicians should be aware that mandibular crowding tends to increase during this type of combined therapy.