Objective: To evaluate the Impact of multiple firings cycles on color change, translucency, and flexural strength of lithium disilicate ceramic fabricated by press and milled technology.
Material and Methods: Lithium disilicate ceramics fabricated by two methods were used. Sixty disk-shaped samples (10x 1mm) were prepared from ceramics thirty for each group (Amber press (P) and Amber mill (M)) (n=30). Then each group (P and M) was divided into three subgroups according to the number of firing cycles one, three, and five times (n=10). After finishing firing cycles for each group, color change (ΔE) and translucency measurement (TP) were done using Vis-NIR spectrophotometer. The biaxial flexure strength was measured for all samples. Two-way Analysis of Variance (ANOVA) was made to analyze the effect of ceramic type, firing cycles and their interaction on mean TP, ΔE and biaxial flexural strength. When ANOVA test is significant so Bonferroni's post-hoc test was used for pair-wise comparisons. The significance level was set at P ≤ 0.05.
Results: Statistical analysis showed that ceramic type and firing cycles had a statistically significant effect on mean colour change (ΔE), translucency (TP) and biaxial flexural strength. The interaction between the two independent variables had a statistically significant effect on mean ΔE.
Conclusions: Multiple firings affect the color change and translucency of lithium disilicate ceramics. More firing cycles led to more reduction in flexural strength of Amber milled compared to that of Amber press. Amber mill has better translucency and biaxial flexural strength than the Amber Press.