Effect of multiple firings on optical and mechanical properties of Virgilite-containing lithium disilicate glass-ceramic of varying thickness
Amr Rizk, Ahmed Abdou, Reem Ashraf, Sarah Omar
Abstract
Abstract Objectives To investigate the effect of multiple firings on color, translucency, and biaxial flexure strength of Virgilite-containing (Li 0.5 Al 0.5 Si 2.5 O 6 ) lithium disilicate glass ceramics of varying thickness. Materials and methods Sixty discs were prepared from Virgilite-containing lithium disilicate blocks. Discs were divided according to thickness ( n = 30) into T 0.5 (0.5 mm) and T 1.0 (1.0 mm). Each thickness was divided according to the number of firing cycles ( n = 10); F 1 (Control group): 1 firing cycle; F 3 : 3 firing cycles, and F 5 : 5 firing cycles. The discs were tested for color change (ΔE 00 ) and translucency (TP 00 ) using a spectrophotometer. Then, all samples were subjected to biaxial flexure strength testing using a universal testing machine. Data were collected and statistically analyzed (α = 0.5). For chemical analysis, six additional T 0.5 discs (2 for each firing cycle) were prepared; for each firing cycle one disc was subjected to X-ray diffraction analysis (XRD) and another disc was subjected to Energy dispersive X-ray spectroscopy (EDX) and Scanning electron microscope (SEM). Results Repeated firing significantly reduced the translucency of F 3 and F 5 compared to F 1 in T 0.5 ( p < 0.001), while for T 1.0 only F 5 showed a significant decrease in TP 00 ( p < 0.001). For ΔE 00 , a significant increase was recorded with repeated firings ( p < 0.05) while a significant decrease resulted in the biaxial flexure strength regardless of thickness. Conclusions Repeated firings had a negative effect on both the optical and mechanical properties of the Virgilite-containing lithium disilicate glass ceramics. Clinical relevance Repeated firings should be avoided with Virgilite-containing lithium disilicate ceramics to decrease fracture liability and preserve restoration esthetics.