Effect of surface acid etching on the biaxial flexural strength of two hot-pressed glass ceramics

Abstract

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. © 2008 by The American College of Prosthodontists.