[Shiau-ROC TAIWAN-P-3] Basic properties of machinable fully-sintered dental zirconia
[Abstract]
[Objective]
Zirconia-based restorations are fabricated by milling semi-sintered zirconia blocks with subsequent sintering in a furnace, as conventional dental zirconia ceramics are challenging to machine after sintering. However, this conventional method is hindered by lengthy fabrication times. Recently, machinable fully-sintered zirconia ceramics have emerged to expedite the fabrication of zirconia-based restorations. This study aims to examine the density, crystallography, mechanical strength, and microstructure of machinable fully-sintered dental zirconia.
[Method]
Two types of machinable fully-sintered zirconia (FS-100Z, Kuraray Noritake Dental) disk-shaped specimens (15.0 mm diameter; 1.2 mm thickness) were prepared: 1) via the uniaxial pressing method and 2) through machining. Specimen density was measured using the Archimedes method following ISO 18754:202. Crystallographic analysis employed X-ray diffraction (XRD) with subsequent Rietveld refinement. Biaxial flexural strength tests were conducted on each specimen (n=30/group) using a universal testing machine (EZ-LX, Shimadzu) at a crosshead speed of 0.5 mm/min, in accordance with ISO 6872(2015). Statistical analysis of biaxial flexural strength utilized Weibull analysis with the maximum likelihood method (R4.2.2, R Foundation for Statistical Computing). Microstructural analysis employed scanning electron microscopy (JSM-IT800, JEOL)
[Results and Discussion]
Uniaxially pressed specimens exhibited a density of 5.963 g/cm3, while machined specimens had a density of 5.978 g/cm3. Weibull analysis demonstrated significantly higher biaxial flexural strength in uniaxially pressed specimens compared to machined ones. Rietveld analysis revealed that uniaxially pressed specimens contained approximately 94 wt% of the tetragonal zirconia phase with minimal monoclinic zirconia phase. Conversely, machined specimens exhibited reduced tetragonal zirconia phase and increased monoclinic and rhombohedral zirconia phases. All specimens displayed high tetragonality (1.204). These findings suggest that machining introduces a monoclinic zirconia phase in machinable FS-100Z. Additionally, microstructural analysis indicated that machining may induce microcracks on the surface, potentially reducing the biaxial flexural strength of machinable FS-100Z.
[Objective]
Zirconia-based restorations are fabricated by milling semi-sintered zirconia blocks with subsequent sintering in a furnace, as conventional dental zirconia ceramics are challenging to machine after sintering. However, this conventional method is hindered by lengthy fabrication times. Recently, machinable fully-sintered zirconia ceramics have emerged to expedite the fabrication of zirconia-based restorations. This study aims to examine the density, crystallography, mechanical strength, and microstructure of machinable fully-sintered dental zirconia.
[Method]
Two types of machinable fully-sintered zirconia (FS-100Z, Kuraray Noritake Dental) disk-shaped specimens (15.0 mm diameter; 1.2 mm thickness) were prepared: 1) via the uniaxial pressing method and 2) through machining. Specimen density was measured using the Archimedes method following ISO 18754:202. Crystallographic analysis employed X-ray diffraction (XRD) with subsequent Rietveld refinement. Biaxial flexural strength tests were conducted on each specimen (n=30/group) using a universal testing machine (EZ-LX, Shimadzu) at a crosshead speed of 0.5 mm/min, in accordance with ISO 6872(2015). Statistical analysis of biaxial flexural strength utilized Weibull analysis with the maximum likelihood method (R4.2.2, R Foundation for Statistical Computing). Microstructural analysis employed scanning electron microscopy (JSM-IT800, JEOL)
[Results and Discussion]
Uniaxially pressed specimens exhibited a density of 5.963 g/cm3, while machined specimens had a density of 5.978 g/cm3. Weibull analysis demonstrated significantly higher biaxial flexural strength in uniaxially pressed specimens compared to machined ones. Rietveld analysis revealed that uniaxially pressed specimens contained approximately 94 wt% of the tetragonal zirconia phase with minimal monoclinic zirconia phase. Conversely, machined specimens exhibited reduced tetragonal zirconia phase and increased monoclinic and rhombohedral zirconia phases. All specimens displayed high tetragonality (1.204). These findings suggest that machining introduces a monoclinic zirconia phase in machinable FS-100Z. Additionally, microstructural analysis indicated that machining may induce microcracks on the surface, potentially reducing the biaxial flexural strength of machinable FS-100Z.