Investigation of the elastic properties of ceramic materials after standard and speed firing using acoustic microscopy

Introduction. Modern dental materials, such as multilayer zirconium dioxide (YSZ), lithium disilicate (IPS e.max), and advanced lithium disilicate (CEREC Tessera), must combine high strength and aesthetics. Traditional destructive mechanical tests are not sufficient for their comprehensive evaluation. Non-destructive testing using pulse acoustic microscopy is more promising. This method allows for detailed investigation of the elastic properties and microstructure of ceramics, including after various sintering modes. Materials and methods. Samples in the form of rectangular prisms (14×4×2 mm) were manufactured using CAD/CAM milling. Multilayer zirconium dioxide blanks were oriented in a disc to vary the yttrium oxide content. After milling, they were sintered in standard and high-speed modes. Silicate ceramic samples were treated only by high-speed firing. No additional processing was performed after sintering. The elastic characteristics were evaluated using a SIAM 2017 pulsed acoustic microscope. The velocities of longitudinal and transverse sound waves were measured using A-scans. Based on these velocities and the density of the material, the elastic moduli were calculated: shear (G), bulk compression (K), Young’s (E) and Poisson’s ratio (µ). Results and conclusions. Characteristic values of elastic constants were established for two classes of materials: the Poisson’s ratio of zirconium dioxide (~0.33) is statistically significantly higher than that of lithium disilicate-based glass-ceramics (0.24–0.25). The firing mode has a systematic effect on the structure of the material: speed firing leads to a decrease in density (which is associated with residual porosity) and a slight but measurable decrease in the elastic modulus. The data obtained on the differences in the elastic properties of materials should be taken into account when selecting ceramics for clinical use and designing structures, especially in areas of increased functional load, to ensure the durability of prostheses.