Evaluation of Surface Roughness of Monolithic Zirconia after Using Different Polishing Kits

Objective: To evaluate the effect of different kits to polish monolithic zirconia on its surface roughness. Material and Methods: Five samples were fabricated using zirconia blocks. Each sintered block was divided into four areas of equal size and each area was subjected to a specific surface treatment according to the four groups of the study: GC: no surface treatment, GG: unidirectional grinding with high speed tapered bur under refrigeration, GP1: wear similar to GG followed by polishing with zirconia polishing kit Kenda at the same wear direction, and GP2: wear similar to GG followed by polishing with zirconia polishing kit Diacera at the same wear direction. Qualitative and quantitative analyses of ceramic topography and roughness were performed using a digital optical profilometer, and Roughness measurements were performed using two parameters (Ra and Rz: arithmetical mean of the absolute values of the surface departures and of the five highest peaks and valleys, respectively). Scanning electron micrographs of each ceramic surface were obtained to illustrate sample roughness. The means of each group were analyzed by 1-way ANOVA followed by Tukey's test. Results: Morphological analysis showed that polishing kits provided the same pattern of a smooth surface. To statistical analysis, this study showed that different polishing kits influenced zirconia roughness for both Ra and Rz after surface wear (p < 0.05) with both situations improved the surface roughness observed immediately after zirconia sintering. Conclusion: According to the results, both polish kits resulted in a surface texture within acceptable clinical parameters.

Strength of 3Y-TZP and feldspathic porcelain subjected to different cooling methods

AIM: To investigate the effect of the cooling rate on flexural strength of monolayer and bilayer porcelain/zirconia (Y-TZP) bars. METHODS: Forty-five specimens were made for each design group: (PM) monolithic specimens of veneer porcelain Vita VM9 (Vita, Germany); (ZM) monolithic specimens of zirconia (ZiHP; ProtMat, Brazil); (PB) bilayer specimens zirconia/porcelain with porcelain on lower surface; and (ZB) bilayer specimens porcelain/zirconia with zirconia on lower surface. Each group was cooled by three different methods after porcelain sintering: slow specimens were cooled inside the turned-off furnace; normal specimens were removed from the furnace and cooled in air at room temperature; and fast specimens were removed from the furnace at 910°C and cooled by compressed air for 10 s. Specimens were polished and flexural strength was measured in water at 37 °C (n=15). Maximum load at fracture was recorded, and equations for simple (monolayer) and composite (bilayer) structures were used to calculate the flexural strength. RESULTS were analyzed using one-way ANOVA (p<0.05) and Tukey test separately for each design. RESULTS: The results of one-way ANOVA were statistically significant only for the PB group. The post-hoc Tukey test showed the highest flexural strength for fast cooling and the lowest for slow cooling; the normal cooling was statistically similar to both. CONCLUSIONS: Cooling methods affected only the flexural strength of bilayer specimens with porcelain on low surface (under tension) when the slow cooling method was used...