A comparative study on the physical and mechanical properties of two different multilayer zirconia based dental restorative materials

Comparison of Physical and Mechanical Properties of Two Different Multilayer Zirconium Oxide Restoration Materials The integration of advanced CAD/CAM (Computer-Aided Design/Manufacturing) technologies into modern dentistry has enabled single-visit restorative treatments. These approaches aim to achieve the clinical success and patient satisfaction typically associated with multi-session procedures in a single appointment. The aim of this experimental thesis study is to evaluate the effects of different sintering protocols applied to multilayered monolithic zirconia materials on translucency, color stability, surface roughness, microhardness, and flexural strength. Additionally, the effectiveness of surface finishing procedures (glazing and polishing) on translucency, color stability, surface roughness, and microhardness was also investigated. Sixty samples (n=10 per group) with a thickness of 1,4 mm were prepared from two different zirconia blocks: Katana YML (Kuraray Noritake Dental Inc., Japan) and Ivoclar ZirCAD Prime (Ivoclar Vivadent, Liechtenstein). The specimens were sequentially ground using silicon carbide abrasive papers (800–2000 grit) and then divided into three groups based on the sintering protocol: conventional, fast, and high-speed. Following sintering, the specimens were re-polished using the same grinding sequence. Color measurements were carried out using a spectrophotometer (Vita EasyShade V) under a D65 light source in a standardized color box, and color differences were calculated using the CIEDE2000 formula. Translucency parameters (TP00) were assessed using both white and black backgrounds. Surface roughness and microhardness values were measured before and after glaze application, which was performed on all polished surfaces. Finally, the flexural strength of the specimens was evaluated using a piston-on-three-ball test setup in a universal testing machine. Statistical analysis was conducted using SPSS software. The Kolmogorov-Smirnov test assessed data normality, while Levene's test evaluated variance homogeneity. One-way ANOVA and Tukey's HSD post hoc tests were used to determine intergroup differences, and paired t-tests were performed to analyze pre- and post-glaze measurements. The significance level was set at α = 0.05. The results showed that sintering time and temperature did not significantly influence the color parameters or microhardness of the zirconia materials. However, the translucency parameter was significantly affected in the Katana conventional sintering group. Glaze application increased translucency across all groups. Surface roughness was significantly reduced after glazing in all Ivoclar subgroups. The flexural strength of the Ivoclar fast-sintering group was significantly different from the other Ivoclar groups. In conclusion, sintering parameters and surface finishing protocols play a critical role in determining the optical and mechanical properties of zirconium dioxide restorations. Keywords: CAD/CAM, Zirconium Dioxide, Flexural Strength, Color Stability, Surface Roughness, Microhardness, Translucency