Abstract: Objective: To evaluate the changes of vertical dimension in class Ⅱ¹ malocclusions during two-phase treatment and explore the method of vertical control with Twin-block functional orthopedic treatments preliminarily. Methods: The treatment changes were evaluated by retrospectively analyzing the Pre- and posttreatment's lateral cephalograms of 20 adolescents with class Ⅱ¹ malocclusions who were treated with Twin-block functional orthopedic treatments and fixed orthodontic treatment for two-phase treatment. Results: SN-OP, SN-FOP, IMPA, UADH, UPDH, LADH, and LPDH increased, while U1-SN decreased during phase-I treatment (P<0.05). FHI, U6-SN, and UPDH increased while SN-MP and SN-FOP decreased during phase-Ⅱ treatment (P<0.05). FHI, SN-OP, MPA, UADH, UPDH, LADH, and LPDH increased while SN-FOP, U1-SN, and U6-SN decreased after two-phase treatment (P<0.05). The changes of skeletal indexes had a certain degree of correlation with the changes of dental and occlusal indexes in vertical dimension. Conclusion: There was no evidence of adverse vertical change caused by functional orthopedic treatments with Twin-block appliance. The key to vertical control in functional orthopedic treatments may be the occlusal plane, especially UADH.

Key words: Class Ⅱ division 1 malocclusions, Twin-block appliance, vertical dimension