الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 142 |  |  |
| | | from | 142 | | |
Abstract
Objective : To evaluate the effect of veneer thickness and number of firing cycles on final color and translucency of zirconia cores veneered with IPS e-max Ceram, and the effect of thermal cycling on their translucency and color stability. Materials and methods: Thirty- six disk-shaped cores (0.8 mm thickness ×10mm diameter) were constructed from zirconium oxide (Ceramill zolid ht+ preshade) (HT A2) and divided according to the thickness of the veneering ceramic into two groups (n=18); group A: veneered with 1mm thickness of IPS e-max Ceram and group B: veneered with 1.5mm thickness of IPS e-max Ceram . Each group was further subdivided into three equal subgroups (n=6) according to the number of firing cycles (1, 3 and 5 firing cycles). Color and translucency parameters were measured by using a spectrophotometer after repeating firings and after thermal cycling. Color differences were calculated with a ΔΕ* value (ΔΕ < 3.3 was considered clinically acceptable). Data were analyzed by using Paired t-test, One- way ANOVA and Post Hoc Tukey test at p-value ≤ 0.05. Results : L*, a*, b* values affected by the number of firing cycles (1, 3 or 5 cycles) (P<0.001) and the veneer thickness (1mm or 1.5mm) (P<0.001). Increasing the number of firing cycles resulted in decreasing L* values (darker); however the a* and b* values increased (redder and yellower) for both veneer thicknesses. Increasing the veneer thickness led to increasing L*, a*, b* values. The color difference (ΔΕ*) was the highest between 1F and 5F (acceptable color change as ΔΕ* < 3.3) and the lowest was between 3F and 5F (undetectable by human eyes as ΔΕ* < 1.0) for both veneer thicknesses. Translucency parameter significantly decreased with increasing the veneer thickness, while increased significantly after increasing the number of firing cycles in both veneer thicknesses. After thermal cycling, the L* values decreased, while a* and b* values increased. The greatest color change (ΔΕ*) was in group A5F while; the lowest color change was in group B1F. TP values increased for all subgroups after thermal cycling where statistical significant differences were detected (p<0.05) except for A1F group. Conclusions : 1) The number of firing cycles and veneer thickness affected the final color and translucency of zirconia core veneered ceramics. 2) After thermal cycling, group A (1mm veneer thickness) showed higher color change than group B (1.5mm veneer thickness) and color stability decreased with increasing the number of firings. 3) Thermal cycling had a significant effect on the color change and translucency with both veneer thickness and firing cycles.