## 1 Introduction  
The maxillary sinus lift augmentation (MSA) is an effective, frequently employed predictable procedure that results in increased vertical bone or the purpose of implant placement in the previously prequantized sinus or atrophic ridge of the posterior maxilla [1]. Since the first description by [PERSON] in 1977 [2], and eventual publication by Boyne & James in 1980 [3], it has been widely applied in clinical practice and, subsequently, many studies have documented implant survival rate [1, 4, 5]. Documented sequalae of Schneiderian membrane perforation are noted as bone graft displacement, sinus graft infection, ostium obstruction, postoperative maxillary cyst, and acute maxillary sinusitis [6, 7, 8, 9]. Intraoperative perforation of the membrane leads to postoperative complications and these observations have led to multiple proposed techniques for handling perforations. Schneiderian membrane perforation during sinus floor elevation has been documented to cause postoperative membrane thickening [10]. Membrane thickening can transiently block the ostium and impair the mucociliary clearance [11]. Prolonged membrane thickening may cause maxillary sinusitis due to dysregulation. In addition, complications associated with membrane perforation include significant bleeding, hematoma formation, bone graft displacement, oro-antral fistula, and sinus graft infection [12, 13, 14, 15]. When the Schneiderian membrane is perforated, bone graft particles are displaced into the maxillary sinus through the perforation site. Displaced graft particles can cause acute or chronic inflammation [7; 16]. Displaced graft particles can be plugged directly into the ostium [17] and can create an initial phlogosis condition in the mucosa to obstruct the natural ostium [18]. However, with the proposed approach, only transient nasal bleeding and brief facial swelling were observed and no previously reported documented complications occurred. Various sinus elevation instruments have been devised to reduce membrane perforation [19] and various repair methods have been introduced to cover the perforated Schneiderian membrane [8; 20; 21; 22]. The repair method is usually selected according to the size of the perforation, but more importantly, it can vary depending on the skill and preference of the operator. Small perforations are simply repaired with mucosal folding [23]. Membrane perforation of less than 5 mm or 5 to 10 mm in size are usually repaired with a collagen membrane, suture, lamina bone, demineralized freeze-dried lamellar bone sheet, or platelet-rich fibrin membrane [7; 20; 24; 25; 26]. There have been attempts to repair large perforations greater than 10 mm using demineralized freeze-dried lamellar bone sheets, buccal fat pads, and block bones [7; 8; 26]. In addition, a variety of surgical modifications have been introduced [27; 28]. However, it is technically difficult to repair membrane perforations and the implant survival rate is low even if it is repaired [15; 29]. The clinician should decide whether to abort the procedure or plan for re-entry after 6 to 8 weeks [8; 24]. However, [PERSON] et al. reported that there was no difference in implant survival rate and complication in the perforation group of the Schneiderian membrane, which was not repaired during lateral sinus floor elevation, compared to the non-perforation group [4]. Although conflicting opinions exist, this suggests that repair of the perforated Schneiderian membrane is not essential. For cases where large perforations are seen, repair membrane and block grafts are preferred to particulate grafts. For repairs, the source of cells and growth factors come from the sinus wall and not the graft itself. Controversial data suggest that the Schneiderian membrane may have regenerative osteogenic potential [30; 31; 32].