Abstract: Objective　 To compare the difference of root resorption after treatment of self-ligating and conventional preadjusted brackets evaluated by computed tomography. Methods: 60 young adult orthodontic patients, regardless of gender, were chosen in Wujiang Chinese Medicine Hospital. 30 of them were Angle Class I malocclusion and treated with self-ligating (15) and conventional preadjusted brackets (15). The other 30 cases were Class Ⅱ malocclusion treated by extraction therapy with self-ligating (15) and conventional preadjusted brackets (15). Spiral CT was scanned before and after the treatment. The root length (distance between cemento-enamel junction and root apical ) of maxillary central incisors was measured. Results: Both kinds of brackets could cause shortening of root length. More root resorption was found in Class II patients treated with extraction therapy compared with non extraction group and the difference had statistical significance. Less root resorption was found in patients treated by self-ligating brackets than in conventional preadjusted brackets in both Class I and Class Ⅱ groups and the difference had also statistical significance. Conclusion: Both conventional and self ligating brackets can cause shortening of root length. Self-ligating brackets can reduce the degree of orthodontically induced inflammatory root resorption and the possible reasons are lower values of tooth movement force and shortening of orthodontic treatment time.

Key words: self-ligating brackets, root resorption, spiral CT