ABDULAZIZ M. ALSHAHRANI
| ABDULAZIZ M. ALSHAHRANI |
Abdulaziz M. Alshahrani, Yu Hang, Chek Hai Lim
Preventive and Restorative Sciences, University of Pennsylvania, School of Dental Medicine
Introduction
Rational: To investigate the impacts of speed and high-speed sintering on the densification, microstructure, phase content, translucency, and flexural strength of yttria-partially stabilized translucent zirconia (YSZ).
Methods
Materials and Methods: A total of 60 disc-shaped specimens (n = 30) were prepared from pre-sintered 4YSZ (Zpex 4) and 5YSZ (Zpex Smile) zirconia rods. Ten specimens from each composition were sintered according to the following protocols: conventional (control group, ~12 h) speed (~60 min), and high-speed (~18 min) sintering. Dimensions of zirconia specimens after sintering and polishing (1 m finish) were 13.75 mm (diameter) and 1 ± 0.02 mm (thickness). The theoretical density of these compositions was calculated, and relative density/apparent porosity estimated. Translucency was assessed using a spectrophotometer against a black and white backgrounds. Biaxial flexural strength was measured using the piston-on-3-ball method. Zirconia specimens were thermally etched for microstructural observations using scanning electron microscopy. X-ray diffraction was used to determine the phase assemblies. Data were analyzed with one-way ANOVA and Tukey's post hoc test (α = 0.05).
Results
Results: 4YSZ exhibited similar strength values in all sintering protocols, whereas speed sintered 5YSZ showed significantly higher flexural strength than conventional sintering. However, all speed and high-speed sintered 4YSZ and 5YSZ exhibited significantly lower translucency parameter (P < .001) compared to their conventionally sintered counterparts. Tellingly, porosities were present in 4YSZ and 5YSZ when sintered with speed and high-speed sintering protocols. For XRD analysis, no significant difference was found in tetragonal and cubic contents among speed, high-speed and conventionally sintered 4YSZ and 5YSZ. However, the conventionally sintered 4YSZ and 5YSZ had a larger average grain size compared to other tested groups, except for high-speed sintered 5YSZ which showed the largest grain size among all groups
Conclusion
Conclusions: Speed and high-speed sintering diminished the translucency of 4YSZ and 5YSZ. Flexural strength seemed not to be affected. However, speed sintered 5YSZ showed the highest flexural strength when compared to other sintering protocols. Lower porosities were found with speed sintering of 4YSZ and 5YSZ, whereas higher porosities were associated with high-speed sintering.