نبذة مختصرة : Introduction: Etching the internal surface of ceramic restorations with hydrofluoric (HF) acid and silane is a well-accepted technique to enhance the bond strength. The aim of this study was to assess the effect of concentration of hydrofluoric acid and etching time on microtensile bond strength (µTBS) of zirconia-reinforced lithium silicate (ZLS) ceramics in 2021. Materials & Methods: This in vitro study was conducted on 8 Celtra-Duo ceramic blocks size 14 measuring 12×14×18 mm. Each ceramic block was divided into three equal pieces by a cutting machine to obtain a total of 24 specimens. The specimens were randomly divided into 6 groups for etching with 5% and 10% HF acid for 30, 60, and120 seconds. Silane (Clearfil porcelain activator) and bonding agent (Clearfil SE Bond) were applied to the etched specimens. Panavia F2 resin cement was applied on the surfaces and light-cured. The mTBS of resin cement to porcelain was measured by a universal testing machine. The mode of failure was determined under a stereomicroscope at x40 magnification. Data were analyzed by one- and two-way ANOVA (P0.05). Two-way ANOVA showed that the effects of HF acid concentration and etching time, and their interaction effect were not significant on µTBS of CAD/CAM Celtra-Duo ceramics (P>0.05). The mode of failure was dominantly adhesive in both concentrations of 5% and 10% HF acid. No mixed failure occurred in both concentrations. Conclusion: Considering the non-significant difference in µTBS of ceramics subjected to different concentrations of HF acid for different times, the application of HF acid with lower concentration for a shorter period is recommended to prevent possible adverse effects on ceramic strength.
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