Aim: To evaluate the relationship of lip changes in anteroposterior direction and incisor retraction in Thai female patients with class II division 1 malocclusion.
Materials and methods: The sample consisted of 100 pairs of pre- and posttreatment lateral cephalograms. All cephalograms were derived from class II division 1 Thai female adults who were treated with four premolar extraction and edgewise technique. Sixteen linear and eight angular measurements were made and evaluated for dental and lip changes. Paired t-test was used for testing the difference between before and after orthodontic treatment. Pearson correlation analysis was used for evaluating factors that correlate with lip changes and stepwise multiple linear regression was performed to make the prediction of lip changes and incisor retraction.
Results: There was a significant correlation between lip changes and incisor retraction. The prediction of upper and lower lip changes in antero-posterior direction was mainly described by the cervical point of upper incisors (HcUI) (R2= 0.29), the tip of lower incisors (HtLI) and lower lip thickness (LL thickness) (R2 = 0.48).
Conclusion: Ratios of upper and lower incisors at tip point to upper and lower lips retraction were 1:0.46 and 1:1, respectively. The coefficient of determination for predicting upper and lower lips was 0.29 and 0.48 showing low to moderate predictability for lip changes.
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