Abstract: Objective To evaluate the arch width changes induced by Quick active and Damon passive self-ligating appliances on non-extraction correction of dental crowding. Methods 19 adolescent cases of mild-to-moderate skeletal class I dental crowding were reviewed in this randomized controlled trial. The patients were randomized into 2 groups: 10 subjects were treated with Quick active self-ligating system and the other 9 subjects were treated with Damon passive self-ligating system. The dental casts were analyzed before and after arch alignment and leveling. The changes of arch widths were analyzed with spss15.0 software. Results In Quick group, statistically significant increase in upper, lower premolar widths and widths between upper first molar was noted after treatment. Meanwhile in Damon group, statistically significant increase in upper premolar widths was noted after treatment. There was no significant difference in arch width changes before and after treatment between two groups. Conclusion The self-ligating system can effectively increase the arch widths. in order to achieve the purpose of non-extraction. There was no significant difference in efficiency of arch width increase between active and passive self-ligating systems.

Key words: active self-ligating, passive self-ligating, non-extraction treatment, arch width