A Clinical Study of Edentulous Patients Rehabilitated According to the "All on Four" Immediate Function Protocol

Purpose: The aim of this study was to compare definitive acrylic resin prostheses with or without a cast metal framework that were immediately loaded and supported by axial and tilted implants in completely edentulous patients after 3 years of function. Materials and Methods: Patients who were completely or partially edentulous in one or both arches with severe atrophy of the posterior regions were selected for this study. All patients immediately received prosthetic rehabilitations, each supported by four implants (two axial and two tilted). The patients were randomized to receive a definitive prosthesis with a cast metal framework or one made of acrylic resin only. Follow-up visits were performed up to 36 months after implant insertion and included radiographic assessments of bone levels around the implants. Results: Thirty-six patients participated, and 44 complete-arch immediately loaded prostheses (24 maxillary and 20 mandibular ), each supported by four implants (in total 176 implants), were placed. In all, 21 screw-retained full-arch acrylic resin prostheses and 23 cast-metal-framework prostheses were delivered to the patients. The 3-year overall implant survival rate was 100% for axially positioned implants and 96.59% for tilted implants. Implant survival rates were 98.96% in the maxilla and 97.5% in the mandible. None of the 44 fixed prostheses were lost during the observation period, representing a prosthetic survival rate of 100%. No statistically significant differences were seen in crestal bone loss between tilted and axial implants at 12, 24, and 36 months in either arch. Conclusions: The same clinical outcome was seen for patients treated with the so-called All on Four protocol, regardless of whether the acrylic resin restorations were reinforced with metal. Keywords: acrylic resin prostheses, All on Four, metal-reinforced prostheses, tilted implants