Torque loss under mechanical cycling of long‐span zirconia and titanium‐cemented and screw‐retained implant‐supported CAD/CAM frameworks

Abstract

Abstract Objectives This study evaluated the screw joint stability after cyclic loading of implant‐supported titanium and zirconia CAD / CAM frameworks for fixed dental prostheses ( FDP s) with different retention methods. Material and methods Twenty four one‐piece frameworks supported by six threaded implants placed in the maxilla were fabricated using a CAD / CAM technique (NeoShape). Dry‐pressed porcelain crowns were luted to the frameworks to standardize the specimens. The specimens were then divided into four groups ( n = 6) according to framework material (titanium or zirconia) and retention method for the prosthesis (cement‐ or screw‐retained): G1, Ti‐cemented; G2, Ti‐screw‐retained; G3, Zr‐cemented; and G4, Zr‐screw‐retained. A digital torque ratchet was used to assess the initial preload removal torque. Torque was then reapplied and the specimens were submitted to a 200 N cyclic load, at a frequency of 2 Hz, underwater in controlled temperature of 37°, and for 1 × 10 6 cycles. An opposing lower dental arch was fabricated using bis‐acrylic resin to simulate occlusal contacts in centric. After cyclic loading, postload removal torque was measured. Preload and postload torque loss was expressed as a percentage of the initial load. Data were submitted to a linear mixed‐effects model for statistical significance (α = 0.05) to evaluate the effect of cyclic loading in the screw torque loss used with frameworks of different materials and retention methods. Results Significant screw torque loss (%) was found for the tested groups (before/after cyclic loading, respectively): G1 (39.77/61.83), G2 (37.57/50.96), G3 (34.87/54.10), and G4 (47.56/73.50) ( P < 0.05). Conclusions The screw removal torque was significantly reduced for all groups in this study after cyclic loading the specimens. Screw‐retained zirconia specimens presented the highest torque loss before and after the cyclic loadings compared with the other specimens that were tested.