Immediate Full-Arch Maxillary Rehabilitation Supported by Four Implants: A Retrospective Study with 15 to 20 Years of Follow-Up

<b>Background/Objectives</b>: Edentulism represents a major public health challenge, causing disorders of social, psychological and biological origin. Full-arch implant-supported restorations represent a viable alternative to mitigate this problem. This study aimed to evaluate immediate implant-supported restorations for the rehabilitation of the edentulous maxilla using four implants and distal implant tilting between 15 and 20 years. <b>Methods</b>: A total of 740 patients were included (women: 440; men: 300; average age: 55.3 years) rehabilitated with 740 prostheses, supported by 2960 dental implants. The primary outcome measure was prosthetic/implant cumulative survival and success (CSurR;CSucR). Secondary outcome measures included marginal bone loss (MBL), and the incidence of complications was evaluated as a secondary outcome measure. The outcomes were evaluated at 15 and 20 years. <b>Results</b>: In total, 287 patients (38.8%) with 1148 implants (38.8%) were lost to follow-up. A total of 170 implants (5.7%) in 101 patients (13.6%) failed, resulting in an implant CSurR and CSucR of 90.7% and 84.6%, respectively, after up to 20 years of follow-up. The prosthetic success rate was 98.1%. The average MBL was 1.07 mm ± 1.38 mm and 1.46 mm ± 1.56 mm at 15- and 20-years, respectively. Mechanical complication incidence was 78.5%, occurring in 581 patients (provisional prostheses: n = 448, 60.5%; definitive prostheses: <i>n</i> = 374, 50.5%). Biological complications occurred in 449 implants (15.2%) in 260 patients (35.1%). Biological complications and smoking habits were major risk indicators. <b>Conclusions</b>: Considering the study limitations, it can be concluded that the current rehabilitation concept is a viable treatment option in the long term, with mechanical and biological maintenance being necessary throughout the patients' lives.