RESUMO
OBJECTIVES: This study investigated the effect of extreme cooling methods on the flexural strength, reliability and shear bond strength of veneer porcelain for zirconia. METHODS: Vita VM9 porcelain was sintered on zirconia bar specimens and cooled by one of the following methods: inside a switched-off furnace (slow), at room temperature (normal) or immediately by compressed air (fast). Three-point flexural strength tests (FS) were performed on specimens with porcelain under tension (PT, n=30) and zirconia under tension (ZT, n=30). Shear bond strength tests (SBS, n=15) were performed on cylindrical blocks of porcelain, which were applied on zirconia plates. Data were submitted to one-way ANOVA and Tukey's post hoc tests (p<0.05). Weibull analysis was performed on the PT and ZT configurations. RESULTS: One-way ANOVA for the PT configuration was significant, and Tukey's test revealed that fast cooling leads to significantly higher values (p<0.01) than the other cooling methods. One-way ANOVA for the ZT configuration was not significant (p=0.06). Weibull analysis showed that normal cooling had slightly higher reliability for both the PT and ZT configurations. Statistical tests showed that slow cooling decreased the SBS value (p<0.01) and showed less adhesive fracture modes than the other cooling methods. CLINICAL SIGNIFICANCE: Slow cooling seems to affect the veneer resistance and adhesion to the zirconia core; however, the reliability of fast cooling was slightly lower than that of the other methods.
