The purpose of this study was to compare the skeletal and dentoalveolar effects of expansion in patients who are overexpanded (9-12 mm of RPE screw activation) with patients who are expanded conventionally (minimum of approximately 4 mm of RPE screw activation). This randomized controlled trial included 23 patients (12 males, 11 females) aged 11.3 to 16.2 years (mean 13.5 years), who had RPE planned as part of their orthodontic treatment. Subjects were randomly assigned to the conventional expansion control group (n=12) or the overexpansion experimental group (n=11). CBCT scans were obtained prior to RPE delivery (T1) and after expansion was complete (T2). Linear and angular skeletal and dentoalveolar measurements were made using the CBCT images to evaluate the effects of RPE and to compare the changes between groups. Final results were available for 21 subjects. Mean screw expansion was 5.7 +- 1.2 mm in the conventional group and 9.9 +- 0.5 mm in the overexpansion group (p<0.001). Overexpansion produced significantly greater amounts of skeletal expansion at the nasal cavity (p=0.002-0.004) and maxillary base (p=0.009), as well as greater increases in intermolar width (p<0.001) and molar inclinations (p=0.007-0.013). Skeletal expansion was moderately correlated with appliance activation (r=0.55-0.65). Dental expansion was strongly correlated with appliance activation (r=0.94) and the relationship was approximately 1:1. Expansion of the nasal cavity and maxillary base ranged from 22-32%, with slightly greater percentages observed in the overexpansion group (p=0.222-0.384). The percentages of skeletal expansion obtained were highly variable and were negatively correlated with skeletal maturity (r=-0.47 to -0.64) and skeletal age (r=-0.46 to -0.70). Overexpansion leads to greater amounts of skeletal and dental expansion than conventional expansion. Skeletal expansion is moderately correlated with appliance activation. Dental expansion is very strongly correlated with appliance activation and increases in intermolar width are approximately equal to screw expansion. Expansion of the nasal cavity and maxillary base amount to 20-33% of screw activation. There is a large degree of individual variability in the proportion of skeletal expansion obtained, and this percentage is inversely related to skeletal maturity. The effects of RPE treatment are greater inferiorly than superiorly.
