Statement of the problem: Multiple firing cycles and different temperatures may adversely affect the mechanical properties of ceramic restoration.
Objective: This study was designed to evaluate the effect of multiple firing cycles with different firing temperatures on the Flexural strength and Micro shear bond strength of the lithium silicate.
Materials and methods: Specimens of Lithium Silicate (obsidian) were divided into 2 groups according to the tests done. The first group, Obsidian blocks were sectioned into 36 bar-shaped samples for the three point bending test, according to ISO 6872 standard. While the second group, the blocks were used to prepare 32 slices for measuring microshear bond strength. Each group was then divided into four subgroups according to the number of the firing cycles which were 1, 2, 3 and 5 firing cycles respectively. The flexural strength and microshear bond strength were measured separately.
Results: For the first group, the highest flexural strength value was found in control samples, while the lowest value was found in 3 cycles' samples. As for the second group, the highest micro shear bond strength value was found in samples subjected to 3 cycles, while the lowest value was found in 2 cycles' samples. This shows that there was no significant difference between values of each group.
Conclusion: Obsidian can be fired up to 5 firing cycles with no adverse effect on bond strength or flexural strength.