ABSTRACT
OBJECTIVES: The purpose of this study was to fabricate functionally graded materials (FGMs) consisting of yttria-stabilised tetragonal zirconia polycrystal (Y-TZP) and porcelain using spark plasma sintering (SPS) and examine the influence of their microstructures and thermal stress on their bending strengths. METHODS: Two types of four-layered Y-TZP/porcelain FGMs having a constant layer thickness and a varying layer thickness, Y-TZP/porcelain composite materials having a microstructure corresponding to each layer in FGMs and monolithic materials of Y-TZP and porcelain were fabricated by SPS. The Y-TZP/porcelain volume fraction of each layer in FGMs was varied over 100/0-70/30. Three-point bending test, X-ray diffraction, density measurement, microstructure observation, and thermal stress estimation were performed to characterise the materials. RESULTS: The bending strength of the Y-TZP/porcelain composite materials decreased with the volume fraction of the porcelain. About FGMs, when the 100%Y-TZP layer was on the tensile stress side during the bending test, the bending strength was almost the same as that of the 100%Y-TZP monolithic material. On the other hand, when the 100%Y-TZP layer was on the compressive stress side, the bending strength of FGM having a constant layer thickness was almost the same as that of the 70%Y-TZP+30%porcelain composite material, while the bending strength of FGM with a varying layer thickness was significantly higher than that of the 70%Y-TZP+30%porcelain composite material. CLINICAL SIGNIFICANCE: The FGMs prepared and analyzed in this research can potentially be used for crowns and bridges as well as for inlays and onlays. CONCLUSION: The SPS method could effectively fabricate the Y-TZP/porcelain FGMs, and the bending strength results revealed that the graded structure was very efficient to raise the bending strength.
