Date of Award



Department of Orthodontics

First Advisor

Heesoo Oh

First Committee Member

Heeyeon Suh

Second Committee Member

Sandra Tai

Third Committee Member

Marta Baird


Objectives: This retrospective cohort study compared vertical and transverse changes in mixed dentition patients treated with Invisalign First System (IFS) to those treated with rapid maxillary expansion and fixed appliances (RME), as well as control groups. We also assessed the efficiency of dental arch expansion with IFS. Methods: The study included 80 mixed dentition patients, with 40 in each group (IFS and RME) and 40 controls from the AAOF Legacy Collection. We analyzed skeletal and dental vertical dimension changes from lateral cephalometric radiographs and arch width changes on study casts between pre-treatment (T1) and post-treatment (T2). Results: Age at T1, time interval (T1-T2), sex, and Angle class did not significantly differ among the groups. Mandibular plane angle changes (measured by SNMPA and FMA) showed similar degrees of reduction for the control and IFS groups, with no changes in the RME group. However, these differences among the three groups did not reach statistical significance (p=0.06). The RME group showed a significantly greater expansion in maxillary intermolar width compared to the IFS group (p<0.001). In the IFS group, the efficiency of expansion ranged from 52.3% to 76.87% in the maxilla and 64.25% to 79.95% in the mandible. Higher expansion efficacies were observed in the anterior regions of both the maxillary and mandibular arches compared to the posterior regions in the IFS group. Conclusions: During the mixed dentition stage, no statistically significant changes occurred in the skeletal vertical dimensions among the control, RME, and IFS groups. Although there was a trend suggesting a greater reduction in the mandibular plane angle in the IFS group compared to the RME group, this difference may not be clinically significant given the less than 1-degree discrepancy. IFS can be a viable option for addressing mild to moderate arch width deficiencies, with a predictable increase in intermolar width of approximately 2.5mm.