## 3 Result
### Changes of Arch Width and Molar Rotation  
The changes of arch width and molar rotation as measured from dental casts are shown in Table 5. There was a significant difference in maxillary arch width before and after distalization. There were expansions of 1.52 and 0.93 mm in the maxillary canine and first molar, respectively, and 0.88 and 1.14 mm in the mandibular canine and first molar, respectively. Both intercanine width and intersolar width kept relatively stable during the retention period. Distal-in rotation of the first and second molars was observed after the distalization, but it was not statistically significant and it did not change during the retention period either.  
Figure 8: Horizontal changes of maxillary and mandibular teeth.  
\begin{table}
\begin{tabular}{l c c c c c c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**T0**} & \multicolumn{2}{c}{**T1**} & \multicolumn{2}{c}{**T2**} & \multicolumn{2}{c}{**T1-T0**} & \multicolumn{2}{c}{**T2-T1**} & \multicolumn{2}{c}{**T2-T0**} \\ \cline{2-13}  & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** & **Mean** & **SD** & **Sig** & **Mean** & **SD** & **Sig** \\ \hline \multicolumn{13}{l}{**Inter-canine**} \\
**width(mm)** & 35.26 & 3.53 & 36.78 & 2.56 & 36.13 & 3.06 & 1.52 & 0.33 & *** & \(-\)0.65 & 0.71 & 0.87 & 0.75 & **\(\ast\ast\)** \\
**Mn.** & 27.07 & 3.7 & 27.95 & 2.74 & 27.65 & 2.24 & 0.88 & 1.14 & \(-\)0.35 & 0.55 & 0.58 & 0.98 & \\ \hline \multicolumn{13}{l}{**Inter-molar**} \\
**width(mm)** & 45.36 & 2.34 & 46.29 & 2.51 & 45.99 & 2.68 & 0.93 & 0.31 & **\(\ast\ast\)** & \(-\)0.30 & 1.21 & 0.63 & 1.30 & \(\ast\ast\) \\
**Mn.** & 44.24 & 3.67 & 45.38 & 3.36 & 45.06 & 3.47 & 1.14 & 1.05 & \(-\)0.32 & 2.95 & 0.82 & 1.75 & \\ \hline \multicolumn{13}{l}{**Molar rotation (\(\ast\))**} \\ \hline U**rot** & 138.85 & 11.64 & 143.72 & 9.28 & 140.57 & 11.38 & 4.87 & 2.36 & \(-\)3.15 & 1.36 & 1.72 & 1.62 & \\
**U**rot** & 148.82 & 13.74 & 156.32 & 16.12 & 154.69 & 9.46 & 7.50 & 4.10 & \(-\)1.63 & 2.12 & 5.87 & 2.21 \\
**L**rot** & 156.28 & 9.36 & 159.32 & 15.32 & 157.36 & 17.33 & 3.04 & 2.32 & \(-\)1.96 & 2.36 & 1.08 & 1.71 & \\ L**rot** & 161.34 & 7.35 & 166.35 & 12.25 & 163.15 & 11.95 & 5.01 & 2.95 & \(-\)4.20 & 1.59 & 1.81 & 0.96 & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Model measurements at pretreatment, post-treatment, postretention, pretreatment to post-treatment (T1-T0), post-treatment to postretention (T2-T1) and pretreatment to postretention (T2-T0).  
Figure 7: The schema about comparison of pretreatment to post-treatment (T1-T0) and post-treatment to postretention (T2-T1). \(\ast\)\(p\)\(<\) 0.05; **\(p\)\(<\) 0.01; ***\(p\)\(<\) 0.001.  
[PERSON]'s Correlation Coefficients between Post-Treatment Changes and Other Variables (Initial Skeletal Pattern, Retention Period and Treatment Changes)  
In the maxilla, post-treatment horizontal relapse of the first and second molar was significantly negatively correlated with initial ANB and amounts of distalization--that is, the larger the distal movement during the treatment period, the more the mesial drift during the retention period (Table 6).  
In the mandible, post-treatment horizontal relapse of the first and second molar was not significantly correlated with initial skeletal pattern and retention period. However, they were significantly negatively correlated with amounts of distalization. In particular, angular relapse of the lower second molar was significantly negatively correlated with the amounts of distal tipping (Table 7).