# Change of Lip Curvature Through Extraction and Non-Extraction Orthodontic Treatment
## 4 Discussion
\begin{table}
\begin{tabular}{l l c c c c} \hline \hline
**Author(s)** & **Ext/Non-Ext (N)** & **Upper Lip** & **Lower Lip** & **Measurement Method** & **Angle Classification** \\ \hline [PERSON] et al., 2020 [17] & Extraction (15) & \(-\)1.61 \(\pm\) 1.62 & \(-\)3.13 \(\pm\) 1.97 & E line & I, II \\  & Non-extraction (17) & \(-\)0.07 \(\pm\) 0.89 & \(-\)0.15 \(\pm\) 0.70 & & \\ [PERSON], 2012 [18] & Extraction (30) & \(-\)2.75 \(\pm\) 1.5 & \(-\)3.34 \(\pm\) 1.75 & E line & I \\  & Non-extraction (32) & \(-\)0.68 \(\pm\) 1.8 & \(\,\)0.67 \(\pm\) 2.24 & & \\ Xu et al., 2006 [19] & Extraction (16) & \(-\)1.00 \(\pm\) 1.9 & \(-\)2.6 \(\pm\) 1.9 & E line & I, II, III \\  & Non-extraction (23) & \(-\)0.9 \(\pm\) 2.4 & \(-\)0.4 \(\pm\) 3.4 & & \\ Freitas et al., 2019 [20] & Extraction (15) & & \(-\)0.2 \(\pm\) 3.7 & E line & I \\  & Non-extraction (17) & & \(-\)0.05 \(\pm\) 1.9 & & Lower limited \\  & Extraction (37) & \(-\)1.51 \(\pm\) 1.43 & \(-\)1.78 \(\pm\) 2.67 & E line & I \\  & Non-extraction (25) & \(-\)0.92 \(\pm\) 1.18 & \(-\)0.82 \(\pm\) 2.64 & & \\ \hline  & & & & & \\ \hline  & & & & & \\ \hline  & & & & & \\ \hline  & & & & & \\ \hline  & & & & & \\ \hline  & & & & & \\ \end{tabular}
\end{table} 
Table 5: Linear changes in the upper and lower lips based on research. with greater magnitudes of change in patients with hyperdivergent class II treated with extraction. The upper lip retracted by an average of \(-\)3.25 \(\pm\) 1.44 mm, while the lower lip showed a more pronounced retraction of \(-\)4.94 \(\pm\) 1.99 mm, proportional to the retraction amount of the incisors [24]. The current study focused on changes in the upper and lower lips after orthodontic treatment and compared these results with those from previous research. In extraction cases, the study found that the upper lip retracted by an average of \(-\)1.51 \(\pm\) 1.43 mm, while the lower lip retracted by \(-\)1.78 \(\pm\) 2.67 mm, measured against the E-line. These results are slightly less pronounced than those reported by [PERSON] [18], who found that the upper lip retracted by \(-\)2.75 \(\pm\) 1.50 mm and the lower lip by \(-\)3.34 \(\pm\) 1.75 mm. However, the findings are similar to those of [PERSON] et al. [17] and [PERSON] et al. [19]. In non-extraction cases, the current study found that the upper lip retracted by an average of \(-\)0.92 \(\pm\) 1.18 mm, while the lower lip retracted by \(-\)0.82 \(\pm\) 2.64 mm. These results differ from findings in other studies, likely due to variations in methodologies. Previous research did not clearly describe the process of space gain. In this study, molar distalization was the primary method used to create space, followed by full arch distalization, depending on the patient's aesthetic preferences. The differing results were likely attributable to the influence of confounding variables, including differences in ethnic background, angle classification, and anchorage value. Regarding the newly introduced variables in this study, the curvature of the upper and lower lips deepened (SAL and PBL depth became deeper, and the angle became smaller, Table 2), but only the change in the upper lip in the extraction group was significant in the extraction group. In other words, in the extraction group, the upper and lower lips were significantly retracted, the curvature deepened instead of flattened, and there was no change in the curvature of the lower lip (Table 2). The SAL depth and SAL angle tended to change before and after treatment compared to the PBL depth and PBL angle (Tables 2 and 3). In particular, in the extraction group, there was a significant difference in SAL depth and SAL angle before and after treatment (Table 2). In this study, the lower lip was retracted, but no significant change in curvature was noted. There may be two reasons for this: first, the extraction itself affects changes in SAL depth and SAL angle; second, the SAL depth and SAL angle also changed significantly because the lip position change was more remarkable in patients with extraction.