Evaluation of the bond strength of densely sintered ceramics subjected to extended firing

Abstract

Introduction: Critical failures in ceramic materials can be caused by the processing mode, which includes all steps taken in the manufacture of a ceramic part, from molding to firing.  Purpose: To evaluate the effect of extended firing on bond strength in densely sintered ceramics of the zirconium reinforced lithium silicate, lithium disilicate, and feldspathic ceramic.  Materials and Methods: Three types of ceramics were evaluated: Zirconium reinforced lithium silicate, lithium disilicate, feldspathic ceramic. A total of 6 ceramic blocks, two for each material were used in the study. Each block was cut into four square sections. A total of 24 ceramic surfaces were randomly distributed into 6 groups (n = 4 surfaces per group) divided according to the variables: Heat treatment: Conventional firing or extended firing; test time: Immediate (24 hours after cementation) or longevity (after 1000 cycles of thermocycling). The bond strength tests were performed in a semi-universal test machine for microshear bond strength. For data analysis, the Shapiro-Wilk test was performed to evaluate the normality between the groups measured, and regarding homoscedasticity (homogeneity of variances) by the Bartlett test. The comparisons between the groups were made using the nonparametric Kruskal-Wallis test.  Results: There was no statistically significant difference of the resistance values in relation to the thermal treatment methods (conventional firing and extended firing) in any ceramic group (p <0.05). Among the times (immediate and long), there was a statistically significant difference (p <0.05), with higher resistance values for immediate time. Conclusion: Extended firing did not influence the micro-shear bond strength of zirconium reinforced lithium silicate, lithium disilicate, feldspathic ceramic.