Effect of Firing Cycles on the Optical Performance of Zirconia Reinforced Lithium Disilicate Ceramics: A Comparison of Translucency and Color Stability Parameters.

Abstract

Purpose: Lithium disilicate ceramics are aesthetic alternatives to metal-ceramic restorations, offering sufficient mechanical properties to withstand anterior occlusal loads. The introduction of zirconia-reinforced lithium disilicate (ZLS) may enhance both mechanical and aesthetic performance compared with non-reinforced lithium disilicate. This in vitro study evaluated the parameters translucency (TP) and color stability (DE) of Vita Ambria's A1 shade in high translucent (HT) and translucent (H) zirconia reinforced lithium disilicate after three firing cycles, comparing them to lithium disilicate glass-ceramic.

Material and methods: Forty five disk-shaped specimens (1.2mm thickness) were allocated to three groups: G1: Vita Ambria translucent (VAT), G2: Vita Ambria high translucent (VAHT), and G3: IPS e.max press. Each group underwent one, three or five firing cycles. TP and DE were measured using a spectrophotometer. Two-way ANOVA and post hoc Tukey's tests analyzed the effects of firing cycles and ceramic type (P<.05).

Results: Both ceramic type and firing cycles significantly affected TP and ΔE. Multiple firing cycles led to a greater reduction in TP for IPS Emax Press compared to Vita Ambria. VAHT demonstrated superior translucency compared to the VAT and IPS Emax Press.

Conclusions: Multiple firing cycles caused alterations in the translucency and color stability of the lithium disilicate and zirconia-reinforced lithium disilicate glass ceramic materials tested. Heat-pressed zirconia-reinforced lithium disilicate exhibited the best optical performance, suggesting a potential advantage in clinical situations requiring repeated firings. However, further clinical studies are necessary to evaluate its long-term optical performance.