Objective:To investigate the differences in facial soft tissue profile alterations after orthodontic extraction treatment between protrusive patients of skeletal classⅠand class Ⅱ

and to explore the mechanics of soft tissue profile changes by extraction treatment.Methods:The photogrammetric films of 76 young protrusive patients(38 of skeletal classⅠand 38 of skeletal class Ⅱ) with satisfactorily improved profile after orthodontic extraction treatment were chosen by visualized analogue scale.Twelve Angular measurements of the lateral photograph were measured and the soft tissue profile alterations of both groups were analyzed.Results:In the skeletal classⅠgroup Sn-Cm/N-Prn

Li-Sm-Pg

and Trg-Ort/Sn-Sm were significantly increased;while Cm-Sn-Ls and N-Trg-Sn were significantly decreased.In the skeletal class Ⅱ group G-N-Prn

Sn-Cm/N-Prn

N-Trg-Sn

Sn-Trg-Me

and G-Prn-Pg were significantly decreased

while Cm-Sn-Ls、G-Pg/C-Me and G-Sn-Pg were significantly increased.Conclusion:The facial profiles improved greatly by orthodontic extraction treatment and the differences in the soft tissue profile alteration were closely related to the treatment mechanics and skeletal pattern of malocclusion.