Effect of Surface Acid Etching on the Biaxial Flexural Strength of Two Hot‐Pressed Glass Ceramics

Purpose: The purpose of this study was to assess the effect of surface acid etching on the biaxial flexural strength of two hot‐pressed glass ceramics reinforced by leucite or lithium disilicate crystals. Materials and Methods: Forty glass ceramic disks (14‐mm diameter, 2‐mm thick) consisting of 20 leucite‐based ceramic disks (IPS Empress®) and 20 lithia disilicate‐based ceramic (IPS Empress 2®) were produced by hot‐pressing technique. All specimens were polished and then cleaned ultrasonically in distilled water. Ten specimens of each ceramic group were then etched with 9% hydrofluoric (HF) acid gel for 2 minutes and cleaned ultrasonically again. The biaxial flexural strength was measured by the piston‐on‐three‐ball test in a universal testing machine. Data based on ten specimens in each group were analyzed by two‐way ANOVA (α= 0.05) . Microstructure of ceramic surfaces before and after acid etching was also examined by a scanning electron microscope. Results: The mean biaxial flexural strength values for each group tested were (in MPa): nonetched IPS Empress = 118.6 ± 25.5; etched IPS Empress = 102.9 ± 15.4; nonetched IPS Empress 2 = 283.0 ± 48.5; and etched IPS Empress 2 = 250.6 ± 34.6. The results showed that the etching process reduced the biaxial flexural strengths significantly for both ceramic types ( p = 0.025). No significant interaction between the ceramic type and etching process was found ( p = 0.407). Conclusion: From the results, it was concluded that surface HF acid etching could have a weakening effect on hot‐pressed leucite or lithia disilicate‐based glass ceramic systems.