Fracture resistance of monolithic zirconia cantilevered frameworks in complete arch-prostheses supported by tilted or parallel implants

Aim. The aim of this in vitro study was to compare the loading force at the fracture of monolitithic zirconia cantilever substructure in complete arch-prostheses supported by tilted or parallel implants. Material and methods. Ten anatomical models of edentulous mandible were fabricated. Five of these models had five screw-type implants embedded vertically in the intraforamica area (Brånemark protocols). The other five models had four screw-type implants in the intraforaminal area, two in front were placed vertically and two rear were tilted 30 degrees distally (All-on-4). Twelve superstructure in monolithic zirconia were fabricated, ten for the Brånemark protocols and ten All-on-4, with two cantilever for each superstructure. A static load was applied on the cantilever with a universal machine. The fracture load was monitored and the sites of fracture were identified. Results. No statistical significant difference was found between the two techniques. Mean fracture load values was 998 N (SD 83N) for Brånemark protocols while 905 N (SD 37N) for All-on-4. Most fractures occurred at the mesial connector attack to the last abutment. Conclusion. Zirconia cantilevered frameworks on vertical implants may tolerate higher occlusal forces before fracturing.