Lip Curvature Change With Miniscrew Anchorage In Class II Patients

The aim of this study was to assess whether lip curvature flattening occurred in Class II hyper-divergent patients undergoing extraction orthodontic treatment with maximum anchorage and analyze its associated factors. Twenty skeletal Class II patients who underwent fixed orthodontic treatment with premolar extraction and maximum anchorage were enrolled. Cephalometric measurements of hard tissue and lip soft tissue were compared statistically (P < 0.05) before and after treatment using paired sample T-test. Multiple regression analysis was performed to assess associations between lip curvature changes and corresponding measurements. The post-treatment lip curvature slightly deepened but was not statistically significant. Stepwise multiple regression analysis produced the following equation:Stepwise multiple regression analysis produced the following equation:①ΔPBL angle=214.26+13.95*ΔANB-2.26*pre.Us-x-1.57*pre.BLLT, ②ΔPBL depth=2.25-0.70*pre.PBL depth-0.23*ΔL1c-x, ③ΔSAU angle=-56.11-1.17*ΔL1/MP+1.41*pre.MP/FH, ④ΔSAU depth=0.04*ΔL1/MP-0.18*ΔL1c-y-0.23*Δ MP/SN-0.43*pre.SAU depth. No significant difference on lip curvature was observed. This would suggest that even maximum anchorage for premolar extraction patients does not exert negative effect on lip curvature with proper patient selection. Even with the same treatment strategy, there is still significant individual variation in the response of lip curvature to treatment. After treatment, lip curvature changes show high variability and are related to the pre-treatment lip morphology.