Factors Of Lip Changes After Leveling With Damon Self-ligating Brackets In Skeletal Class ? Non-extraction Case

Objective : To evaluate the influence of bracket thickness,arch expansion effects of Damon 3MX and structure of lips on incisor positioned during leveling phase in non-extraction case.Methods:In the first part,cephalometric and plaster model of 29 Chinese female patients(20treated with Damon 3MX,8 treated with conventional ligating brackets,and 1 treated with Damon Q)were taken before and after leveling.Cephalometric and plaster model study were also analyzed.Percentile groups were created according to the magnitude of maxillary lip thickness and lip strain.Statistical analysis was performed using Pearson tests(P =0.05).In the second part,cephalometric and plaster models of 20 Chinese female patients treated with Damon 3MX self-ligating appliance,were taken before and after leveling.Cephalometric and plaster study model were also analyzed.Arch expansion was compared between different groups based on lip strain and lip thickness.Statistical analysis was performed using both paired t tests and independent t tests(P =0.05).In the third part,cephalometric of 33 patients aged 14 to 24 years(20 Damon self-ligating brackets and 13 conventional brackets)were taken before and after debonding the labial brackets.Two images acquired from each subject were superimposed,and 15 soft tissue landmarks around the lips were plotted and analyzed.Statistical analysis was performed using both paired and independent t test(P=0.05).Results:1.In the first part,regardless of the type of brackets,the upper lips tend to protrude up-front forward,the lower lips tend to protrude down-front forward;A linear correlation between upper incisor and upper lip was calculated,almost 1mm advancement of upper incisor tip accompanied with 0.67 mm protrusion of upper lip.A significant correlation between changes of lip and incisor were detected in thelarger lip strain and thick lip groups;A strong correlation(P<0.05)between lower lip and lower incisor,while the larger protrusion of lower lip was observed,compared to the upper lip.2.In the second part,there was no significant difference in the arch expansion and lip protrusion between the larger lip strain group and lower lip strain group after the application of Damon 3MX;Arch width were significantly increased in the first premolar and the first molar area as well as the protrusion of upper lips after the application of Damon 3MX,the difference was statistically significant.3.In the third part,no difference was found in lips after brackets debonding through the cephalometric analysis.Conclusion:The thickness of Damon brackets may influence the well-balanced profile.For the thinner lip the female possessed,they may undergo prominent protrusion of lips.Once the force of lip muscle is inferior to the force required in leveling,the “arch expansion ”and the “lip bumper effect” may not work well for the Damon system.