Effect of shading and hydrothermal aging on optical properties of partially and fully stabilized zirconia

Statement of problem: Zirconia undergoes phase transformation due to low temperature degradation LTD which could deteriorate its optical properties. Objectives: Current study was conducted to evaluate the effect of shading and hydrothermal aging on optical properties of partially and fully stabilized zirconia. Materials and methods: Two commercially available zirconia products, high-translucent PSZ (Prettau®, Zirkonzahn) and ultra-translucent FSZ (Prettau®, Anterior, Zirkonzahn) were assessed. 80 disc shaped specimens (12×1 mm) were prepared; half of the specimens were shaded using acid-free coloring solution. Half of the specimens were subjected to accelerated aging using autoclave (134°c at 2 MPa) for 5 hours. The specimens were divided into 4 subgroups. Non-shaded, non-aged (control), (non-shaded, aged group), (shaded, non-aged group) and (shaded, aged group). Contrast ratio CR and translucency parameter TP were evaluated in each subgroup using reflective spectrophotometer. X-ray diffraction analysis was used to measure the amount of tetragonal to monoclinic phase transformation. Microstructural analysis was evaluated using atomic force microscope. SPSS program was used to evaluate the data (P≤0.05). Results: FSZ recorded higher translucency parameter and lower contrast ratio than PSZ; which were significantly affected by shading and aging in all subgroups except for non-shaded aged subgroups of PSZ. Conclusions: Shading and aging induced tetragonal to monoclinic transformation in PSZ and FSZ which lead to changes in their optical properties.