Purpose: This study aimed to evaluate clinical and prosthetic outcomes of metal-ceramic and polyether ether ketone (PEEK) fixed prostheses supported by four maxillary implants and opposed by distal extension removable partial dentures.

Materials and methods: Thirty participants with edentulous maxillary and distal extension mandibular ridges received four implants according to the All-on-4 treatment concept. The implants were immediately loaded by fixed acrylic prostheses. After 6 months, patients received either metal frameworks covered with porcelain teeth (metal group) or PEEK framework veneered with composite teeth (PEEK group). Plaque Index (PI), Gingival Index (GI), pocket depth (PD), implant stability quotient (ISQ), peri-implant marginal bone loss (MBL, using digital periapical radiographs), and implant survival were measured at baseline, 1 year, and 3 years. Prosthetic complications were measured on the patient and implant levels after 3 years.

Results: No implant failures occurred after insertion of the definitive prosthesis, and the implant survival rate was 100% in both groups. PI, GI, PD, ISQ, and MBL increased significantly with time. The most frequent complications were veneer fracture for the PEEK group and prosthetic screw loosening for the metal group. The metal group showed significantly higher PI, PD, and MBL than the PEEK group after 3 years. PEEK was associated with significantly higher veneer fracture than metal, while metal was associated with significantly higher prosthetic screw loosening than PEEK.

Conclusion: Within the limitations of this study, the PEEK framework veneered with composite may be a suitable alternative to a metal porcelain prosthesis for All-on-4 implant rehabilitation in patients with maxillary edentulous arches opposed by distal extension mandibular ridges, as it was associated with favorable clinical and prosthetic outcomes after 3 years. However, it was associated with an increased rate of veneer or artificial gingiva fracture.