## 4 Discussion  
In the literature, several patterns relating to the cortical bone thickness at the buccal site of the posterior maxilla have been described. Some researchers have concluded that moving apically, the cortical bone thickness decreases at a distance of 4 mm from the alveolar bone crest, and then increases again up to the 6 mm level [25], and the same pattern is indicated by [PERSON] et al. [43], who found that the cortical bone is thickest closest to and farthest from the CEJ, and thinnest in the middle. On the other hand, according to [PERSON] et al. [28], the buccal cortical thickness of the maxilla increases from the CEJ to the 4 mm level, and then decreases again from the 4 mm level to the 6 mm level. However, the measurements in these studies are on a different plane basis, as the level of the bony crest in the interradicular space is located at a distance of about 1.5 mm apically from the CEJ of the adjacent teeth. In the current study, the borders of the attached gingiva were utilized as the reference for the measurement of the cortical bone thickness, as these are easy to identify in clinical practice. The use of either the CEJ, or the contour of the alveolar crest, in deciding at which height a mini-implant should be placed, might be difficult or even impossible without acquiring radiographic imaging. On the other hand, the limit between the free and attached gingiva is easy to clinically determine, and so is the mucogingival junction. The results of this study suggest that at the upper level of the attached gingiva \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & & \multicolumn{6}{c}{**Right Side**} & \multicolumn{6}{c}{**Left Side**} \\ \hline  & \begin{tabular}{c} **Gingival** \\ **Height** \\ \end{tabular} & **Min** & **Max** & **Mean** & **SD** & **Min** & **Max** & **Mean** & **SD** \\ \hline \multirow{4}{*}{\begin{tabular}{c} Cortical \\ thickness (mm) \\ \end{tabular} } & Lower & 0.44 & 1.07 & 0.71 & 0.19 & 0.38 & 0.95 & 0.67 & 0.15 \\ \cline{2-10}  & Middle & 0.53 & 1.34 & 0.98 & 0.26 & 0.51 & 1.26 & 0.88 & 0.23 \\ \cline{2-10}  & Upper & 0.61 & 1.63 & 1.1 & 0.32 & 0.54 & 1.43 & 0.99 & 0.23 \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} Cortical \\ density (HU) \\ \end{tabular} } & Lower & 586 & 1877 & 1155.75 & 386.72 & 618 & 1550 & 995.85 & 238.05 \\ \cline{2-10}  & Middle & 567 & 1896 & 1250.40 & 372.52 & 737 & 1853 & 1171.20 & 260.55 \\ \cline{2-10}  & Upper & 692 & 2044 & 1395.10 & 414.80 & 821 & 2234 & 1224.30 & 342.37 \\ \hline \multirow{4}{*}{
\begin{tabular}{c} Trapecular \\ density (HU) \\ \end{tabular} } & Lower & 152 & 1364 & 615.25 & 357.17 & 160 & 1576 & 604.10 & 299.69 \\ \cline{2-10}  & Middle & 285 & 1636 & 732.95 & 174.29 & 61 & 1195 & 510.95 & 300.92 \\ \cline{1-1} \cline{2-10}  & Upper & 41 & 1779 & 689.35 & 420.12 & 44 & 1299 & 590.25 & 372.49 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Descriptive statistics. \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{3}{c}{**Cortical Bone Density**} \\ \hline  & \multicolumn{2}{c}{**Right Side/\(p\)-Value**} & \multicolumn{2}{c}{**Left Side/\(p\)-Value**} \\ \hline Cortical bone thickness & 0.018 & 0.001 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Pearson correlation between the cortical bone thickness and cortical bone density. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Gingival Height**} \\ \cline{2-5}  & \multicolumn{2}{c}{**Right Side**} & \multicolumn{2}{c}{**Left Side**} \\ \cline{2-5}  & **Eta Value** & **Association** & **Eta Value** & **Association** \\ \hline Cortical bone thickness & 0.490 & medium & 0.526 & medium \\ \hline Cortical bone density & 0.251 & weak & 0.353 & weak \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Eta correlations among the gingival height and cortical bone thickness and density, and the trabecular bone density. region, the cortical bone is probably thicker than at the lower and middle levels.