Abstract: Objective To investigate whether the torque capacity of Damon Q selfligating brackets and conventional MBT brackets have difference. Method A total of 44 patients followed up prospectively, were divided into two groups , one receiving Damon Q selfligating bracket and the other treated with a conventional MBT appliance, both groups using the twostep method to close extraction space. Computerized cephalometric analysis and statistics analysis (Ttest)were carried out before treatment and after treatment. The control effect of the torque of upper anterior teeth between the two groups was compared using SPSS23 software. Results Both groups had a significant average reduction in incisor and lib protrusion without changes of occlusion plane. U1SN, U1NA,U1NA°,ULP and LLP of both groups decreased significantly and there was significant difference(P<0.05).Changes of two groups were similar in the skeletal，dental and soft tissue (P>0.05).The torques of upper anterior teeth, U1SN, U1NA,U1NA°, were all within normal limits. The treatment duration of Damon Q selfligating group was longer with (24.1±0.5) months than that of conventional MBT bracket group with (22.4±0.7) months, having statistically significance(P<0.05). Conclusion For extraction treatment, using Damon Q selfligating brackets can achieve similar results while with likely longer treatment durations compared to conventional MBT brackets.

Key words: extraction treatment, Damon Q selfligating brackets, MBT, torque