Investigation of mechanical, structural and optical properties of zirconia ceramics with different polycrystalline structures sintered using spark plasma sintering method

Investigation of Mechanical, Structural and Optical Properties of Zirconia Ceramics with Different Polycrystalline Structures Sintered Using Spark Plasma Sintering Method The purpose of this in-vitro study was to evaluate and compare the mechanical, structural and optical properties of zirconium dioxide polycrystalline ceramics sintered by Spark Plasma Sintering and conventional method. A total of 20 specimens were evaluated by two different sintering protocols. The control group (S0) specimens were milled from pre-sintered zirconia discs with 3Y-TZP structure (Upcera Dental Zirconia Blank, Liaoning Upcera Co. Ltd., China) by Cerec Systems(Dentsply Sirona, USA). S0 specimens were sintered by the traditional method (1530 oC, 11 hours; n=10). The experimental group (S3) were evaluated from zirconia powders with %3 yttrium-oxide content (3Y-PSZ, Tosoh, Japan) by Spark Plasma Sintering(FCT GmbH, HPD-50, Germany) method (final temperature 1300 oC, 10 min. ; n=10). All specimens were fabricated with a diameter of 20 mm and thickness of 2.0± 0.2 mm. For each group, the specimens were tested to compare their biaxial flexural strenght (ISO Standart 6872) using universal testing machine(Testometric, Lancashire, UK). The specimens were also submitted to Vickers hardness (on polished and as-received surfaces within the same specimen). And XRD and SEM analyzes were performed to evaluate the microstructure of the specimens. The data were analyzed with oneway ANOVA and/or Mann Whitney-U tests(α=0,05). The biaxial flexural strength values(S) of the control and experimental groups were 761.43± 64.455 MPa and 1101.85± 177.73 MPa, respectively. Differences between groups were statistically significant(p<0.05). The Vickers microhardness value of control group(S0) was 980± 41, whereas hardness values for experimental group(S3) was 1355± 144, respectively, and were statistically different(p< 0.05). Surface roughness values(Ra) were 103± 0.031µm for the S0 group and 0.040± 0.039 µm for the S3 group, and a statistically significant difference was obtained (p<0.05). The result of this study showed that spark plasma sintering method increased the flexural strenght, microhardness. At the same time, it was determined that the surface roughness values decreased. As a result of XRD and SEM analyzes, it was observed that the samples produced with spark plasma condensed without particle growth. The Spark Plasma Sintering method can be performed in much shorter times than the traditional sintering method. In our study, in-vitro and in-vivo studies should be conducted to compare and develop methods, and spark plasma sintering method should be adapted to clinical and dental laboratory conditions in order to be applied in dentistry. Thus, it is thought that it will contribute to the speed of the studies and the conversion of the spark plasma sintering method to dental applications. Keywords: Spark plasma sinter, 3Y-TZP, biaxial flexural strenght