Effect of Firing Cycle and Thickness on the Opacity of a Glass Ceramic

Objectives: To evaluate the effect of multiple firing cycles and different thicknesses on the opacity or contrast ratio (CR) values of a zirconia reinforced lithium di-silicate material (VITA SUPRINITY).
Methods: VITA SUPRINITY blocks shade A2 translucent (A2-T) (VITA Zahnfabrik, Bad Säckingen, Germany) were sectioned into tiles with 14mm in length, 12mm in width and thicknesses of 0.5, 1 and 1.5mm. Tiles or samples were then subjected to firing (crystallization) using the VITA VACUMAT 6000 M (VITA Zahnfabrik, Bad Säckingen, Germany) according to the manufacturer’s instructions. Following the first cycle, opacity (CR) scores were obtained by using a spectrophotometer (Gretag Macbeth, X-rite, Grand Rapids, MI, USA). Opacity (CR) levels range from 0, which represents the highest opacity (lowest translucency) to 100, which represents the lowest opacity (highest translucency). Afterwards, opacity (CR) was measured after each firing cycle up to the 5^th cycle. One-way ANOVA analysis was conducted in addition to comparing each pair of means using Tukey-Kramer HSD test (p=0.05).
Results: Opacity (CR) values in different firing cycles among different thicknesses of VITA SUPRINITY are described in table 1.
Conclusions: Firing cycles have shown a significant effect in increasing opacity levels among different thicknesses of VITA SUPRINITY up to the 4^th cycle (p≤0.05). Deceasing thickness levels shows a significant decrease in opacity (p≤0.05).