Changes in Occlusal Relationships in Mixed Dentition Patients Treated with Rapid Maxillary Expansion A Prospective Clinical Study

Objective: To prospectively measure occlusal changes in mixed dentition patients who underwent a standardized early expansion protocol. Materials and Methods: The treatment sample consisted of 500 patients who were assigned to three groups according to molar relationship: Class I (n = 204), end-to-end (n = 166), and Class 11 (n = 130). All patients were treated with a bonded rapid maxillary expander (RME) followed by a removable maintenance plate and a transpalatal arch. Mean age at the start of treatment was 8.8 years (T-1), with a pre-phase 2 treatment cephalogram (T-2) taken 3.7 years later. The control sample consisted of the cephalometric records of 188 untreated subjects (Class 1, n = 79; end-to-end, n = 51; Class 11, n = 58). Results: The largest change in molar relationship was noted when the Class 11 treatment group (1.8 mm) was compared with the matched control group (0.3 mm). A positive change was seen in 81% of the Class 11 treatment group, with almost half of the group improving by >= 2.0 mm. The end-to-end treatment group had a positive change of 1.4 mm, compared with a control value of 0.6 mm, and the Class I group of about 1 mm compared with controls, who remained unchanged (0.1 mm). Skeletal changes were not significant when any of the groups were compared with controls. Conclusion: The expansion protocol had a significantly favorable effect on the sagittal occlusal relationships of Class 11, end-to-end, and Class patients treated in the early mixed dentition. (Angle Orthod. 2010;80:230-238.)