Maxillary "All-on-six" treatment using zygomatic implants. Bone loss evaluation by cone beam computed tomography; Three years' follow-up

Purpose: To evaluate radiographic changes around six implants (Two posterior zygomatic and four conventional implants) used with fixed detachable restorations in patients with severe maxillary posterior resorption with either Polyether ether ketone (PEEK) or titanium frameworks. Materials and methods: Twelve maxillary edentulous patients were rehabilitated with six implants, including two posterior zygomatic and 4 conventionally placed implants for each patient following all-on-six distribution, and opposing mandibular all-on-four implant retained fixed detachable prostheses. A two-stage surgical unloaded healing protocol was performed. According to framework and teeth materials, there were two groups; Group I: CAD-CAM milled framework from modified BioHPP PEEK, bonded to polymethylmethacrylate crowns. Group II: screw-retained CAD-CAM milled framework from titanium, bonded to zirconium crowns. Bone loss evaluation for six implants was performed using cone beam computed tomography at the time of insertion (T0), after one year (T1), and after three years (T2). Results: There was a statistically significant difference in bone loss between PEEK and titanium groups. Less bone loss in PEEK groups around anterior conventional implants at buccal surfaces (P =0.01), at mesial surfaces (P <0.001), at distal surfaces (P <0.001), and zygomatic implants at buccal surfaces (P =0.004), and at palatal surfaces (P =0.003). Conclusions: Within the limitations of the study, the full-arch PEEK and titanium frameworks of fixed-detachable prostheses used with an All-on-Six distribution using zygomatic implants for rehabilitation of maxillary edentulous atrophied posterior arches was a promising treatment approach. Less bone loss was observed with the PEEK framework restorations combined with the PMMA crowns group.