Study Of Non-extraction Treatment To Crowding With Damon Self-ligating Bracket

Objective To compare the change of dental arch and cepholomitric before and after non-extraction treatment to dental crowding malocclusion between Damon self-ligating and conventional bracket systems,and to clarify the mechanism of Damon self-ligating technique non-extraction treatment to dental crowding malocclusion.Methods Forty cases with Class I skeletal dental crowding malocclusion were selected.Half of them were treated with Damon self-ligating brackets and the others were treated with conventional ligating brackets.The dental casts and cephalometric radiophotographs were analyzed before and after dental arches crowding correction. Stepwise regression analysis was performed for the two groups.Results There were no statistically significant differences in the changes of upper and lower intercanine widths and upper intermolar widths and lower interpremolar widths and L1-MP angle(p＞0.05).In Damon self-ligating bracket group,U1-SN increased by 4.05°,U1-NA increased by 1.66mm,upper interpremolar widths increased separately by 3.06mm and 2.99mm,lower intermolar width increased by 2.57mm.In conventional ligating brackets group,U1-SN increased by 8.80°,U1-NA increased by 3.75mm,upper interpremolar widths increased separately by 1.84mm and 2.03mm,lower intermolar width increased by 1.05mm.The differences were statistically significant between the two groups(p＜0.05).Stepwise regression analysis indicated that in self-ligating bracket group,the increase of CWU4(X₁) and CU1-SN(X₂) were predictive of the correction of upper dental arch crowding(Y),with the equation of Y=0.343X₁+0.982X₂-0.536;The increase of CWL4(X₁) and CWL6 (X₂) and CL1-MP(X₃) were predictive of the correction of lower dental arch crowding(Y),with the equation of Y=0.773X₁+0.535X₂+0.207X₃-1.641.Conclusions In crowding cases treated with non-extration,there were an overall increase in the proclination of upper and lower incisors and both arch widths in the two bracket groups.Compared with cases treated with conventional appliance,the cases treated with Damon brackets resulted in less upper incisors protrusion increase and greater upper interpremolar and lower intermolar arch widths increases.In Damon3 bracket group,the upper arch crowding was corrected by incisors protrusion and interpremolar widths increases,the lower arch crowding was corrected not only by incisors protrusion and interpremolar widths but also by intermolar widths increases during treatment.