Effect of additional pressing on the color and translucency of pressable ceramic materials: An in vitro study

Statement of problem. Whether reusing the buttons of pressable ceramic materials affects their color or translucency is unclear. Purpose. The purpose of this in vitro study was to investigate the effect of additional pressing on the color and translucency of 3 different lithium disilicate ceramic brands. Materials and methods. Seventy-two disk-shaped ceramic specimens (empty set14x1.5 mm) were divided into 2 groups: pressed group and additionally pressed group, each containing 36 specimens. These groups were further divided into 3 subgroups: lithium disilicate (LDS), lithium disilicate with high-density micronization technology (LDS-HDM), and zirconia-reinforced lithium silicate (ZLS). Pressing was performed in the press group yielding 36 pressed specimens. Additional pressing was performed by using the buttons resulting from the press group, yielding 36 additionally pressed specimens. Color differences and translucency between pressed and additionally pressed groups were measured with a portable spectrophotometer (VITA Easyshade Compact). The translucency parameter (TP) was measured on black and white backgrounds. Color differences between the 2 groups were analyzed statistically by using the Kruskal-Wallis nonparametric test followed by the Dunn-Sidek method for individual comparison among means of all groups (alpha=.05). Results. A statistically significant difference was found in color after additional pressing among the 3 tested materials (P=.005). After additional pressing, color difference (SE) values were found between the LDS group (3.78 +/- 1.11) and the ZLS group (3.03 +/- 1.44). These Delta E values were beyond the selected clinical perceptible threshold (Delta E=2.6). However, the LDS-HDM group had a Delta E value of 1.80 +/- 1.22, which is considered clinically not perceivable. Furthermore, LDS showed a statistically significant decrease in translucency after additional pressing (P=.002). However, after additional pressing, ZLS and LDS-HDM showed no statistically significant differences in translucency (P>.05). Conclusions. The colors of the 3 tested materials were affected by additional pressing. Only LDS-HDM showed color changes below the selected clinically perceptible threshold (Delta E=2.6). Furthermore, only LDS showed a significant decrease in translucency.