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Objective: A retrospective study to compare skeletal and dentoalveolar changes between hyperdivergent and normovergent Class II division 1 Thai patients treated with twin block appliance.
Materials and Methods: Pretreatment and posttreatment lateral cephalometric radiographs of 17 hyperdivergent [9 boys, 8 girls] and 26 normovergent [16 boys, 10 girls] Class II division 1 Thai subjects treated with twin block appliance were analysed. The subjects were divided into 2 different vertical growth patterns, hyperdivergent and normovergent groups by SN-MP angle. Cephalometric analysis and Pancherz analysis were performed and the treatment effects between 2 groups were compared by using an independent t-test.
Results: Pretreatment SN-MP of hyperdivergent group was 38.98 ± 1.84°, while it was 30.06 ± 2.71° in normovergent group. According to MU analysis, normovergent group showed a statistically significant greater improvement in sagittal skeletal changes (increased SNB, decreased ANB, improved AF-BF and increased Pg to N perpend) when compared to the hyperdivergent group. There was no significant difference of vertical skeletal changes between the two groups except the mandibular angle which showed a slight increase after twin block treatment in the normovergent group. According to Pancherz analysis, the skeletal/ dental contribution for overjet correction was 36.6 /63.4 percent and molar correction was 47.5 /52.5 percent in hyperdivergent group. While the skeletal/ dental contribution for overjet correction in normovergent group was 52.1 /47.9 percent and molar correction was 58.7 /41.3 percent. However, skeletal change is not significant between hyperdivergent and normovergent group.
Conclusions: Normovergent patients responded to the twin block appliance more favorably than hyperdivergent patients according to MU analysis but skeletal change in term of mandibular advancement was similar.
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