## 4 Discussion  
In the present study, a minimally invasive lateral approach for MSFE with simultaneous implant placement was tried in 49 surgeries. Among all surgeries, 47 were successfully performed by maintaining a minimum-sized (20-30 mm\({}^{2}\)) lateral window. However, two surgeries failed to maintain a minimum-sized window due to perforation of the Schneide-rian membrane (1 case) or limitation of instrument access (1 case). In this study, most surgeries successfully maintained a window size of 20 to 30 mm\({}^{2}\) which was relatively small compared to other studies (Table 2). One study has used a small-sized lateral window using a bone scraper with an average window size of 55 mm\({}^{2}\)[14]. A \"Mini-lateral window\" for minimally invasive surgery with an average window size of 52.3 \(\pm\) 11.4 mm\({}^{2}\) has been introduced [9]. The average window size in another study was 69.71 \(\pm\) 26.24 mm\({}^{2}\), and the smallest was 35.75 mm\({}^{2}\)[15]. [PERSON], [PERSON] et al. (2017) have made a small-sized window with an average size of 30.9 \(\pm\) 4.4 mm\({}^{2}\) and a large-sized window with an average size of 73.7 \(\pm\) 10.1 mm\({}^{2}\)[11]. [PERSON], [PERSON] et al. (2018) have made a small-sized window with an average size of 35.25 \(\pm\) 9.19 mm\({}^{2}\) and a large-sized window with an average size of 47.49 \(\pm\) 8.27 mm\({}^{2}\)[12]. The MSFE using a minimum-sized lateral window has several advantages in the following aspects. If the size of a lateral window is decreased, detachment of the periosteum from maxillary bone can be reduced. Thus, trauma to a patient can also be minimized. Less detachment of the periosteum will result in fewer postoperative periosteal reactions, which will reduce postoperative swelling, pain, and bleeding [16]. A split randomized clinical study has compared the visual analogue scale of post-operative discomfort between small and large windows for 16 patients needing bilateral sinus floor elevation. It was found that \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Implant Position**} & **Number of** & \begin{tabular}{c} **Minimum Sized** \\ **Window** \\ **20-30 mm\({}^{2}\)** \\ \end{tabular} & \begin{tabular}{c} **Non-Minimum** \\ **Sized Window** \\ **>30 mm\({}^{2}\)** \\ \end{tabular} & \
\begin{tabular}{c} **Membrane** \\ **Perforation** \\ **Bleeding** \\ \end{tabular} &
\begin{tabular}{c} **Post-Operative** \\ **Sinus Floor** \\ \end{tabular} \\ \hline \#6 & 13 & 12 & 1 & 1 & 0 & 4 \\ \#7 & 8 & 8 & 0 & 0 & 1 & 5 \\ \hline \#5, 6 & 4 & 4 & 0 & 0 & 0 & 0 \\ \#6, 7 & 18 & 18 & 0 & 0 & 0 & 7 \\ \#4, 5, 6 & 1 & 1 & 0 & 0 & 0 & 0 \\ \#5, 6, 7 & 5 & 4 & 1 & 0 & 0 & 1 \\ \hline Total & 49 & 47 & 2 & 1 & 1 & 17 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The frequency of a non-minimum sized window, a membrane perforation, and a post-operative bleeding according to implant position. the small window approach showed significantly less discomfort than the large window approach [11]. When the window size is reduced, the amount of graft material in contact with the vital bone is increased. This is advantageous in terms of bone regeneration. Regarding the bone healing process after a sinus floor elevation in a mini-pig, the proportion of new bone formation is high in the area close to the sinus wall. As the distance from the vital bone increases, new bone formation decreases gradually [17]. In a clinical study, when the window size is decreased, the amount of new bone formation is increased at six months after a sinus floor elevation [15]. Another study has presented that the small window group has a significantly higher new bone regeneration and a lower ratio of ABB than the large window group at six months after a sinus floor elevation [18]. Another advantage of the minimally invasive lateral approach is that it can prevent graft material displacement, particularly in cases without using a barrier membrane.