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

Abstract

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 $2\times 4\times 8$ 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 ($\text{alpha}=0.05$). 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.