Abstract: PURPOSE: To explore the correlation between the soft and hard tissue changes and the vertical direction of early skeletal Class Ⅲ malocclusion treated with Sander Ⅲ appliance. METHODS: Thirty-two patients with skeletal Class Ⅲ malocclusion who underwent Sander Ⅲ appliance correction were enrolled. The changes of soft and hard tissues were observed before and after treatment for 12 months. The correlation between soft tissue and vertical direction was analyzed. SPSS 25.0 software package was used for statistical analysis. RESULTS: After 12 months of treatment, SNB decreased (P <0.05), ANB, A-PTV, Go-Me increased (P<0.05), soft tissue index LL-LI increased (P<0.05), LL-EP decreased (P<0.05). L1/MP was reduced after treatment (P<0.05), and U1E-PTV was increased (P<0.05). Correlation analysis showed that UL-UI was positively correlated with tilt angle, U1E-PP and U6E-PP(P<0.05); LL-LI was negatively correlated with tilt angle, U1E-PP and U6E-PP (P<0.05). Sn-UL/FH and U6E-PP were positively correlated (P<0.05). CONCLUSIONS: Sander Ⅲ appliance can effectively correct the soft and hard tissue deformity of patients with early skeletal Class Ⅲ malocclusion. The shape of the lip tends to be coordinated with the improvement of hard tissue. The soft tissue index is closely related to the vertical direction of the hard tissue.

Key words: Early skeletal Class Ⅲ malocclusion, Sander Ⅲ appliance, Soft and hard tissue, Vertical direction