Objective: To assess the influence of changing the thickness ratio between the framework material which was either 3-YTZP or PEEK, and the veneering milled lithium disilicate on color difference and translucency parameter of bilayered restorations.
Materials and Methods: Sixty disc-shaped specimens composed of partially stabilized tetragonal nano-crystalline zirconia or PEEK veneered with milled lithium disilicate (IPS e.max CAD) were randomly divided into two groups (n=30) according to the framework material implemented. Each group was split into 3 subgroups based on the thickness ratio between the framework and the overlying lithium disilicate. The thickness ratios of the framework to the lithium disilicate (TFM: TVLD) were 0.5mm:1mm, 0.7mm:0.8mm, and 1mm:0.5mm. Color difference (∆E) and translucency parameter (TP) of all specimens were measured using a laboratory spectrophotometer.
Results: Two-way ANOVA results showed that the type of framework, the thickness ratio, and the interaction between both variables, had a significant effect (p<0.001) on (∆E). TFM: TVLD =0.5mm:1mm subgroup showed the lowest (∆E) values in both groups. For (TP), two-way ANOVA results showed that only the framework material and thickness ratio had a significant effect (p<0.001) on (TP). (ZIR) group specimens showed statistically significantly (p<0.001) higher (TP) values than (PK) group specimens when all thickness ratios were considered. TFM: TVLD =0.5mm:1mm subgroup in both groups displayed the highest (TP) values.
Conclusions: Changing the ratio between the framework thickness and that of IPS e.max CAD had a significant impact on color difference and translucency parameter with both materials in all thickness ratios.