Lip changes after premolar extraction in Class I bimaxillary protrusion: A retrospective study in Thai female adults

The ratios of upper and lower anterior teeth retraction and upper and lower lip changes were 1:0.56 and 1:0.87, respectively. The predictive equations of upper and lower lip reductions were ΔH-U-lip = 0.34(ΔH-tUI) + 1.19 and ΔH-L-lip = 0.57(ΔH-cLI) + 2.11, respectively.