The Effect of Multiple Firing on the Color, Translucency, and Flexural Strength of Newly Introduced Lithium Disilicate Ceramics

Abstract

Statement of problem:Ceramic is subjected to multiple firing which exposed it to more heat treatments. The effect of these heat treatments on optical and mechanical properties of lithium disilicate glass-ceramics is not fully studied.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 posthoc 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.

Effect of multiple firings on optical and mechanical properties of Virgilite-containing lithium disilicate glass-ceramic of varying thickness

“…The reduction in translucency in this study as a result of repeated firing was in agreement with previously conducted studies [ 19 , 27 ] whose findings were credited to the alteration in crystal size and/or orientation. Also, another study reported an initial increase in translucency with an increased number of firings followed by a decrease in the translucency with increasing the number of sintering cycles.…”

“…A previous study [ 19 ] investigated the effect of multiple firings on zirconia-reinforced glass ceramics, both pressed and machined (Vita Amberia, VITA Zahnfabrik, Germany). They found that multiple firings caused a significant decrease in biaxial flexure strength when it was fired up to 5 times.…”

“…Based on data extracted from Abdel Sadek et al [ 19 ], a minimum sample size of 24 samples ( n = 8 in each group) is enough with effect size d = 0.8868241 and results in 95% power when the significant level is 0.05. The sample size was increased to 10 samples in each group for statistical analysis reliability.…”