Evaluation of the Structural Stability and Mechanical Performance of a Multilayer Dental Zirconia

Background: Zirconia has become a widely used material in dentistry, and it is easy to see why. It offers excellent mechanical strength, great biocompatibility, and from an aesthetic point of view, it closely resembles natural teeth. Add to that the growing adoption of digital workflows and the fact that dentists are becoming more and more comfortable with CAD/CAM technology, and it is no surprise that multilayer zirconia is gaining so much traction. Objective: To evaluate the structural stability, interlayer cohesion, and flexural behavior of a multilayer zirconia developed for dental applications. Materials and Methods: A total of 10 samples of multilayer fully sintered zirconia specimens supplied by Biodynamic were subjected to accelerated aging according to conditions simulating ISO 13356 requirements. Crystalline phases were investigated by X-ray diffraction (XRD) before and after aging. Interlayer cohesion was assessed by environmental scanning electron microscopy (ESEM) and elemental analysis (EDAX). Flexural properties were evaluated through bending tests on ten specimens. Results: XRD analysis demonstrated no significant increase in monoclinic phase after aging (1%), indicating a tetragonal phase content exceeding 99%. ESEM observations showed a continuous microstructure without evidence of interfacial separation between layers. EDAX analysis confirmed the expected zirconia-based composition stabilized with yttria. Flexural testing revealed a mean maximum load of 980.54 ± 28.5 MPa and a mean fracture load of 1177.6 ± 34.2 MPa. Although some variability was observed among specimens, all samples exhibited high mechanical resistance. Conclusions: The choice of prosthetic material significantly affects the long-term clinical success of tooth- or implant-supported dental restorations. Since prolonged exposure to the oral environment and hydrothermal aging processes can alter the structural and mechanical properties of zirconia, this study was designed to evaluate the aging resistance, phase stability, interlayer cohesion, and flexural behavior of a multilayer dental zirconia produced using a graded-strength technology. The investigated multilayer zirconia demonstrated excellent phase stability, strong interlayer cohesion, and high flexural performance. These findings support its potential use in demanding dental prosthetic applications.