Ceramic core materials: relative translucency of zirconia and alumina

Objective: This study investigated translucency differences in three all-ceramic systems fabricated to clinically appropriate core thicknesses. Methods: Presintered disk specimens were cut to obtain 3 groups from the following high-strength materials: In-Ceram YZ -Vita Zahnfabrik (YZ), In-Ceram AL -Vita Zahnfabrik (AL) and Cercon – Dentsply Int.(CE). Slices of three different thicknesses, obtained taking into account the shrinkage of the sinterization process, were assigned to each ceramic group: 0.3 (T1), 0.5 (T2) and 0.8 (T3) mm. Disks were addressed to a relative translucency (RT) test employing a dental color meter (ShadeEye NCC – Shofu®): the light source was CIE illuminant D65 brightness, and the degree of luminous reflectance (Y) of the specimens between black (0) and white (100) backings measured the RT. RT was calculated as ((Yb- Yw)+100)/100. The calculated value ranged from 0.0 (totally transparent) to 1.0 (totally opaque). Data for RT were analyzed by one-way ANOVA, followed by Tukey's multiple comparison tests for significant findings (∝= 0.05). Results: Means of RT were: AL Group 0.84 ± 0.001, 0.87 ± 0.011, 0.89 ± 0.003 at T1, T2 and T3 respectively; YZ Group 0.81 ± 0.013, 0.84 ± 0.012, 0.86 ± 0.001 at T1, T2 and T3 respectively; CE Group 0.86 ± 0.001, 0.88 ± 0.008, 0.91 ± 0.001 at T1, T2 and T3 respectively. Within AL group, mean RT value for each thickness is statistically different from the others (p=0.0001); comparing zirconia groups, a statistically significant difference was found between YZ and  CE at thicknesses of T1 (p=0.0139) and T2 (p=0.0014). No differences were found between YZ and AL translucencies, considering all samples. Conclusion: Relative translucency increased with the samples thickness; no differences for zirconia and alumina were found at a clinical thickness of 0.8 mm.