Discussion
Most frequent complications of lateral window approach are perforations of the Schneiderian membrane and bleeding. Others include the obstruction of the antral meatal ostium complex, dislocation of the implant into the sinus cavity, perforations in the buccal flap, and less frequently, injury to the infra-orbital nerve(Sindel et al. 2018). The main challenge of the crestal sinus procedure is the uncertainty of a possible perforation of the Schneiderian membrane because the sinus lifting procedure is performed blindly due to the impossibility to visualize the sinus floor(Sindel et al. 2018). The incidence of membrane perforations in crestal sinus lift has been reported to range between 4-25 percent, while such complication has been described in 25-44 percent of external sinus lifting cases making the crestal approach a less risk for perforation (Sindel et al. 2018). The benefit from crestal approach is that it can achieve gain in bone height comparable with the lateral window approach, while maintaining the benefits of the less invasive trans alveolar approach(Mazor et al.2013). Great advantages are reduced chair-side times and minimal graft wastage. In this case review, a minimal invasive crestal approach for sinus augmentation was conceived using a new generation putty-graft. The putty is easy to use and because of its consistency and continuous flow of the biomaterial it results in a gradual and continuous elevation of the minimizing the chance of damaging or perforating the Schneiderian membrane(Kotsakis & Mazor 2015). The presented cases show a significant bone formation around the implants radiographically. Lifting the Schneiderian membrane between 2.4 – 7.3 mm. It has been reported that a gain of up to 10 mm in alveolar height can be achieved using several modifications of transcrestal approach, it has commonly been assumed that the Schneiderian membrane can be safely elevated for 5 mm through the internal sinus lifting(Sindel et al.2018). The lift stays stable for the first three months, but then after time the volume decreases due to pneumatization of the sinus. This is consistent with other studies. The pneumatization of the maxiallary sinus stabilizes after the initial three years shrinkage(Qian & Mo 2020)