## 2 Case Presentation
### Patients  
#### 2.2.1 Case 1  
A 43-year-old male smoker visited the private clinic due to severe tooth mobility and chewing discomfort. On the pre-operative panoramic radiography, alveolar bone resorption was very severe due to advanced periodontitis and the height of residual bone was about 1-2 mm. Maximillary upper left, first molar tooth was missing (Figure 1a). A panoramic image of the preoperative CBCT showed no thickening of the left and right maxillary sinuses and severely pneumatized sinus (Figure 1b). During the lateral window approach for sinus floor elevation, the Schneiderian membrane was widely perforated during sinus floor elevation and the lateral bone lid was pushed up while attached to the sinus membrane. Implant site preparation was performed before filling the bone graft substitute. The osteotomy site was undersized drilled. Bone grafting using Osteon III (Genoss, Suwon, Korea) was performed on the sinus floor and the upper part of the lateral window was opened. Two 4.8 \(\times\) 10 mm implants (Implantium, Dentium, Suwon, Korea) were installed (Figure 1c). On panoramic radiography taken immediately after surgery, bone graft substitute supporting the implants on the sinus floor was observed (Figure 1d). Patient reported minimal nasal bleeding and moderate facial swelling until 3 days after surgery. No other clinical events were reported during the healing process. Second stage surgery for uncovering of implants was performed 6 months after surgery. Implant placed at left upper second molar osseeintegrated, but the implant at the left upper first molar was removed due to loss of osseeintegration and immediately replaced with a wider 6.0 \(\times\) 10 mm implant. On the coronal image of the left maxillary sinus CBCT before surgery at the first molar site, no sinus membrane thickening was noted, and the thickness of the buccal bone was thin (Figure 1e). Coronal image of CBCT immediately after MSA shows it in a state in which the Schneiderian membrane is irreparably perforated. A space between the elevated lateral bone lid and the sinus graft was observed, and displacement of the bone graft particles was not observed (Figure 1f). In the coronal image of CBCT 7 days after surgery, there was no leakage of bone graft substitute, and the sinus membrane thickening was insignificant (Figure 1g). The upper left maxillary first molar implant was uncovered after 4 months. At this time, the flap was reflected up to the opened lateral window site. The open lateral window site was closed with regenerated bone (Figure 1h). After 2 months of uncovering, the splinted prosthesis was delivered. In the CBCT taken immediately after the prosthesis delivery, the bone graft substitute was well consolidated without displacement and no volume change was observed (Figure 1i). In addition, the continuity of the buccal bone contour was well maintained at the lateral window site (Figure 1i). After 1 year follow-up, the patient's chewing function was well maintained and no sinonasal complications were noted. No loss of marginal bone was observed on the panoramic radiograph (Figure 1j). Figure 1: Case 1. Preoperative and postoperative radiographic findings of case 1, and clinical pictures of the open lateral window technique. (**a**) On the preoperative panoramic radiograph, advanced periodontitis  
was accompanied by severe alveolar bone loss; (**b**) A panoramic image of the preoperative CBCT showed no thickening of the left and right maxillary sinuses; (**c**) The sinus membrane was widely perforated during sinus floor elevation. Bone grafting was performed on the sinus floor and the upper part of the lateral window was opened; (**d**) Panoramic radiograph after MSA and implant placement at the same time. (**e**) On the coronal image of the left maxillary sinus CBCT before surgery, there was no sinus membrane thickening and the thickness of the buccal bone was thin; (**f**) Coronal image of CBCT immediately after MSA in a state in which the maxillary sinus membrane is widely perforated.