Effect of the framework material on the final color of all-ceramic restorations

OBJECTIVES: to evaluate the effect of the type of ceramic framework material on the final color of all-ceramic restorations. The hypotheses tested were: (1) the final color of the restoration is different than the porcelain shade selected initially to veneer the framework and (2) different framework materials result in different colors of all-ceramic restorations. METHODS: Steel models simulating abutment teeth were used to design all-ceramic fixed partial dentures (FPDs). The FPDs were produced using three different framework materials (n=8): (YZ) yttria partially stabilized tetragonal zirconia polycrystal (LAVA, 3M); (IZ) glass-infiltrated alumina/zirconia (Vita In-Ceram Zirconia); (AL) polycrystalline alumina (Vita In-Ceram AL). Each framework was veneered with the recommended porcelain, VM9 for YZ and VM7 for IZ and AL groups (Vita). The porcelain shade used was 2M2. A uniform thickness of 1.2 mm of porcelain was applied around the retainers. The color difference (ΔE) and lightness difference (ΔL) between the selected porcelain shade (2M2) and the color of the final restoration were obtained using a clinical spectrophotometer (VITA Easyshade). Statistical analysis was performed using One-Way ANOVA and Tukey’s test (α=0.05). RESULTS: The ΔE mean values, standard deviation and statistical ranking for the experimental groups were: (YZ) 2.38 ± 0.44b; (IZ) 2.92 ± 0.67ab; (AL) 3.43 ± 0.84a. AL group showed the highest ΔE and ΔL mean values. IZ showed an intermediate ΔE value and statistically similar to AL and YZ groups. There was no significant difference between ΔL values for YZ and IZ groups. CONCLUSION:  Although the color difference between all experimental groups and the porcelain shade selected to veneer the restorations could be visually detected (ΔE>1.0), only AL showed a difference above the clinical threshold (ΔE>3.0). Thus, the first study hypothesis was partially accepted. In addition, the type of framework ceramic influenced the final restoration color, accepting the second study hypothesis.