A comparative study of mandibular changes induced by rapid maxillary expansion vs sagittal-guided Twin-block therapy during the mixed dentition period.

INTRODUCTION: It is generally accepted that the optimal timing for functional orthodontic treatment in patients with Class II malocclusion and mandibular retrusion is during the circumpubertal growth period (cervical vertebral maturation stage [CS] 3-CS4). However, these patients often present with excessive overjet and a retrusive facial profile, which compromises esthetics and increases the risk of dental trauma. Early intervention during the mixed dentition period may reduce the risk of dental trauma and help safeguard children's psychological well-being. This study aimed to evaluate the therapeutic effects of rapid maxillary expansion (RME) and a modified Twin-block appliance-sagittal-guidance Twin-block (SGTB)-in mixed dentition patients and to compare the outcomes with an untreated Class II malocclusion control group. METHODS: After matching cervical vertebral maturation stages and observation/treatment durations, 3 groups-RME, SGTB, and untreated controls-were compared. Linear and angular cephalometric variables related to mandibular morphology were analyzed. All variables followed a normal distribution. In addition, one-way analysis of variance was performed, followed by Tukey's post-hoc tests. RESULTS: One-way analysis of variance of treatment-induced changes (T2 to T1) revealed statistically significant intergroup differences in vertical parameters, including FMA, posterior facial height (PFH), lower anterior facial height (LAFH), PFH/LAFH ratio, and mandibular ramus length, and sagittal parameters, including NSGn, total mandibular length (Co-Gn), and gonial angle. Tukey's post-hoc analysis revealed no statistically significant differences between the RME and control groups across all evaluated variables. In contrast, the SGTB group exhibited significant changes in vertical measurements (FMA, PFH, LAFH, and mandibular ramus length) and sagittal measurements (NSGn, Steiner analysis, Co-Gn, and Go-Gn) compared with controls. Annualized growth analysis demonstrated an additional Co-Gn increase of 4.53 mm/y in the SGTB group compared with the untreated controls. CONCLUSIONS: In mixed-dentition patients with Class II malocclusion and mandibular retrusion, RME alone does not significantly stimulate mandibular growth in the short term; its long-term effects require further investigation. SGTB significantly increased Co-Gn compared with the control group, primarily through enhanced vertical growth. However, given its limited vertical control, careful case selection is essential.