Reliability and aging behavior of three different zirconia grades used for monolithic four-unit fixed dental prostheses

Objective. To investigate the fracture resistance and phase composition of tooth supported four-unit fixed dental prostheses (FDPs) made from three different zirconia grades after loading and aging. Methods. Seventy-two FDPs were fabricated from 3Y-TZP, 4Y-PSZ and 5Y-PSZ. This resulted in 24 FDPs per grade, subdivided into three groups (n = 8): a control group (C), a hydrothermally aged (H2O, 85 degrees C, 90 days) group (A) and a group subjected to loading (2.5M cycles, 98N) with simultaneous thermal cycling (H2O, 5-55 degrees C) subsequent to treatment A (AL). Subsequently, FDPs were statically loaded to fracture. Phase composition was quantified by X-ray diffraction (XRD) and -Raman spectroscopy. Focused ion beam (FIB) - Scanning electron microscopy (SEM) was used for visualization in-depth. Results. Compared to 3Y-C FDPs (1233 +/- 165N), reduced fracture load was found for 5Y-C FDPs (889 +/- 80 N; p <.001). This did not apply for 4Y-C samples (1065 +/- 111N). Treatments (A, AL) did not negatively affect the fracture load for the three grades of zirconia (p >.645). Both A and AL increased monoclinic phase content for 3Y and 4Y FDPs, whereas FIB-SEM suggests no transformability of 5Y-PSZ. 5Y-AL FDPs showed cracks and fractures at the abutment walls and restoration margins after dynamic loading. Reduced fracture load of 5Y samples as compared to 3Y and 4Y was associated with deficient transformability in the fracture zone. Significance. Aging and loading did not negatively affect the fracture resistance of monolithic four-unit FDPs made from three grades of zirconia. Due to cracks after dynamic loading, 5Y-PSZ cannot be recommended for the clinical application of four-unit FDPs. (C) 2020 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.