Effect of Multiple Firing Cycles on the Physical Properties of Three Pressable Lithium Silicate Glass Ceramics

Abstract

Statement of the problem To achieve esthetic perfection with dental ceramics, ceramic dental restorations may need to undergo multiple firing cycles for characterization. The behavior of lithium silicate ceramics when exposed to those firing cycles is not well understood, the way it might affect the optical and mechanical properties of restorations. Purpose The aim of this in-vitro study was to investigate the effect of multiple firing cycles on translucency and biaxial flexure strength Of 3 different types of pressable lithium silicate ceramics. Materials and methods A total of 72 disc shape specimens (10mm diameter and 1mm thickness) were fabricated by heat pressing of LT A1 shaded ingots. 24 specimens of Celtra press and the same number of IPS e.max press and Livento press lithium silicates materials. Each material group were subdivided in to three subgroups (8 samples per group) according to the number of firing cycles. One, three, and five firing cycles’ protocols were constructed, to simulate the firing protocols of the three common laboratory fabrication techniques (staining, cutback, and layering) of glass ceramic restorations. Translucency parameters and biaxial flexural strength were evaluated for specimens to detect the effect of multiple firing cycles. Results All tested materials showed statistically significant decrease in translucency parameters values with multiple firing cycles. No significant effect was detected on the biaxial flexural strength values after repeated firing. Conclusion Translucency of tested materials is negatively affected by multiple firing cycles. Multiple firings have no effect on the biaxial flexural strength of lithium silicate ceramics.