## 3 Discussion  
This study reported the healing outcomes of lateral MSA and simultaneous removal of inflammatory tissue/product by puncturing the SM in asymptomatic patients with severe SM thickening. There was no implant failure reported over 23.7 \(\pm\) 12.0 months after the final prosthesis insertion. The SM thickness was reduced with no recurrence; however, increased discomfort (pain, swelling, and nasal bleeding) was reported in the immediate postoperative period. Figure 4: Cone-beam computed tomographic (CBCT) radiographs of the patients. (**a–d**) CBCT views of the patient 1; (**e–h**) CBCT views of the patient 2; (**i–l**) CBCT views of the patient 3; (**a,e,i**) Pre-operative CBCT view; (**b,f,j**) Immediate postoperative CBCT view; (**c,g,k**) CBCT view immediately after final prosthesis insertion; (**d,h,l**) CBCT at 23, 12 and 36 months after final prosthesis insertion in the patient 1, 2 and 3, respectively. Figure 3: Histological observation of the retrieved tissues during intentional sinus membrane perforation procedure. The development of sinonasal symptoms may not correspond to the degree of SM thickening. One study exhibited that most of the opacified maxillary sinuses were related to sinonasal inflammatory diseases [14]. However, another study demonstrated that various sinus pathologies in cone-beam computed tomographic (CBCT) scans were found even in asymptomatic patients, wherein SM thickening greater >3 mm was observed in 66% (838 out of 1406 sinuses) and complete or partial opacification in 7.8% (100 out of 1406) [15]. In line with those findings, all patients in the present case report did not present any sinonasal symptoms. Despite the absence of the symptoms, SM thickening may carry a potential risk of complication in MSA. Especially, membrane thickening above a certain threshold could increase the risk due to the impaired clearance function of the maxillary sinus via the ostiomeatal complex [4]. Thus, until ostitium patency and a decrease in mucosal thickening are achieved, MSA is generally contraindicated for the maxillary sinus with an osti obstruction or severe opacification [16]. Some studies demonstrated simultaneous MSA and endoscopic sinus surgery under general anesthesia [16; 17; 18]. Therefore, the present approach could be debatable. There was no sure way to ensure that the inflammatory membrane thickening would resolve, and the grafted bone substitute material would consolidate. However, on an empirical basis of one of the authors (W-B, P), puncturing the SM was performed simultaneously with lateral MSA in the present study. A recent retrospective study partially supported the feasibility of the protocol in this study [13]. When the SM was accidentally perforated during lateral MSA, the amount of reduction in the SM thickening was more significant (from 6.14 mm to 2.39 mm) than that of cases with no membrane perforation (from 2.29 mm to 0.96 mm). The authors explained that cystic or inflammatory exudate could be discharged and washed out via the perforated site, reducing the inflammatory burden and preventing contamination of the grafted bone material [19]. In all the patients in this study, CBCT scans revealed a marked reduction of SM thickness, which indicates a decline in the pathologic status of the sinus [20]. Previously, puncturing the SM was predominantly used to manage antral pseudocyst simultaneously with MSA [21; 22]. However, the aim of the procedure differed between that for antral pseudocyst and in the present cases. Antral pseudocyst generally does not require surgical removal upon detection [21; 23]. However, for MSA, it was sometimes recommended to remove the antral pseudocyst to ease the SM elevation and prevent potential ostitium blockage [8; 22; 24]. The current approach leaves room for safety issue. Even though all patients in the present study were asymptomatic preoperatively, this did not indicate a clinically acceptable state for MSA. Moreover, the cause of SM thickening was not revealed before MSA.