Purpose: To evaluate the biological and technical complications associated with sinus elevation versus onlay graft procedures in the posterior resorbed maxilla prior to implant placement. By analyzing existing literature, this review aimed to assess how these two techniques influence implant success and complication rates in the posterior maxilla. Materials and Methods: An electronic search from January 2000 to December 2023 was performed in four databases following PRISMA guidelines with a focused PICO question. The quality of the reports was established using a modified Cochrane Collaboration tool. Results: Out of 1199 studies, 20 articles were selected, including 16 on sinus augmentation (SA) and 4 on both sinus augmentation and onlay grafts (SAOG). The studies involved 1245 patients, with 81.8% receiving SA and 18.1% receiving SAOG. Implant survival rates ranged from 80.25% to 100%, with an overall success rate of 91.5-100%. Complications included biological issues (e.g., membrane perforation) and mechanical issues (e.g., graft loss). The average follow-up period was 60 months. Conclusions: Limited evidence exists on implant outcomes following sinus augmentation versus onlay grafting in the atrophied maxilla. Further randomized controlled trials (RCTs) are needed to compare these techniques, emphasizing prosthetically driven augmentation for optimal implant positioning.