Objective: To clarify the mechanism of Damon 3 in non-extraction treatment for crowding malocclusion.
Methods: Forty non-extraction cases with crowding were selected. Twenty were treated with Damon 3 and the others with conventional brackets. Dental casts and cephalometric radiophotographs were analyzed before and after treatment. Stepwise regression analysis was performed.
Results: There were no statistically significant differences in the changes of upper and lower intercanine widths, upper intermolar, lower interpremolar and L1-MP (p>0.05). In Damon group, U1-SN increased by 4.05°,U1-NA 1.66mm, upper interpremolar widths 3.06mm and 2.99mm separately, lower intermolar 2.57mm. In conventional group, U1-SN increased by 8.80°,U1-NA 3.75mm, upper interpremolar 1.84mm and 2.03mm separately, lower intermolar 1.05mm. The differences were statistically significant between the two groups (p<0.05). Stepwise regression analysis indicated that in Damon group,the increase of CWU4(X1)and CU1-SN(X2) were predictive of the correction of upper crowding(Y), with equation Y=0.343X1+0.982X2-0.536. The increase of CWL4(X1), CWL6(X2) and CL1-MP(X3) were predictive of the correction of lower crowding(Y), with equation Y=0.773X1+0.535X2+0.207X3-1.641.
Conclusions: In crowding cases treated with non-extraction, Damon 3 system results in less protrusion of upper incisors and more increases in arch widths of upper interpremolar and lower intermolar. The upper crowding is corrected by incisors protrusion and interpremolar widths increases; the lower not only by incisors protrusion and interpremolar widths but also by intermolar width increases.