Effect of Surface Treatment with Alkaline Agents at Two Different Temperatures on Microshear Bond Strength of Zirconia to Composite Resin

Background

Zirconia, with its excellent mechanical properties, has become a popular choice for esthetic and durable restorations due to the increasing demand of patients. It has overcome most of the limitations of all ceramic restorations. However, bonding to zirconia remains a challenge.

Objectives

This study is aimed at assessing the effect of surface treatment with alkaline agents at two different temperatures on microshear bond strength (μSBS) of zirconia to composite resin.

Materials and Methods

This in vitro, experimental study was conducted on zirconia blocks measuring 2 × 4 × 8 mm. The blocks were sandblasted with alumina powder and randomly assigned to 5 groups (n = 16 each). The blocks in groups 1 and 2 underwent surface treatment with sodium hydroxide (NaOH) and groups 3 and 4 with zirconium hydroxide (Zr(OH)4) at room temperature and 70°C. Group 5 served as the control group and did not receive any surface treatment. After the application of bonding agent and its light-curing, composite cylinders in plastic tubes were bonded to the surface of each block and cured. After incubation, they underwent μSBS test. Data were analyzed by one-way ANOVA and Tukey's test (alpha = 0.05).

Results

The μSBS was significantly higher in all intervention groups than that in the control group (P < 0.05). The μSBS in Zr(OH)4 groups was significantly higher than that in NaOH groups (P < 0.05). The mean μSBS of heated groups was slightly, but not significantly, higher than the corresponding room temperature groups (P > 0.05).

Conclusion

Surface treatment of zirconia with NaOH and Zr(OH)4 alkaline agents can increase its μSBS to composite resin; Zr(OH)4 was significantly more effective than NAOH for this purpose, but heating did not have a significant effect on μSBS.

Color agreement between try-in paste and resin cement: Effect of thickness and regions of ultra-translucent multilayered zirconia veneers

Background. The current study aimed at identifying the color agreement between try-in pastes and the respective resin cements and investigated the effect of thickness and regions of Ultra-Translucent Multilayered Zirconia Veneers.

Methods. A total of 90 cubic zirconia discs were prepared at two different thicknesses (0.5 mm and 0.7 mm) (n=45) in five groups in terms of the shade of the try-in paste and resin cement as follows: Universal, Clear, Brown, White and Opaque. Try-in paste and the respective resin cement were applied between the specimens and composite substrate, respectively, and colorimetric evaluation was carried out using CIE-Lab system. For each specimen, ΔE between the try-in paste and cement was calculated. Data were analyzed with SPSS 17 using Multifactor ANOVA (P<0.05).

Results. Multifactor ANOVA results showed that ΔE values were significantly affected by the resin cement shade and the thickness of ceramic veneer (P<0.05). The results showed better shade agreement between the try-in paste and the respective resin cement with thicker ceramic veneers. The results of Tukey HSD revealed that ΔE values for the Clear, Universal and Brown shades were less than those of the White and Opaque shades. Lighter shades exhibited better agreement between the try-in paste and the respective resin cement.

Conclusion. Perceptible color difference was found between the try-in pastes and the respective resin cement in most colors investigated. Although, the agreement of the try-in pastes and the respective resin cement was affected by the thickness of zirconia veneers, the different regions of multilayered ultra-translucent zirconia ceramic showed no significant effect.