Effect of different surface treatments on the shear bond strength of lithium disilicate ceramic
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Statement of problem: During clinical try-in, it is almost inevitable that the fitting surfaces of a lithium disilicate ceramic fixed prosthesis be contaminated with saliva and silicone disclosing medium. Purpose: This in vitro study used a shear bond strength (SBS) test to evaluate the effect of saliva and silicone disclosing medium contamination on the adhesive luting material bond to porcelain, and the effectiveness of various materials used to remove such contamination. Hypothesis: The resin-ceramic bond strength and its durability are related to ceramic surface contamination and subsequent surface treatment. Material and methods: Ninety ceramic specimens were milled from lithium disilicate blocks using an electrical high precision saw, crystallized, and then randomly assigned into six groups (n=15). Excluding the control group, each group underwent contamination with saliva and silicon disclosing medium, then received a different surface cleaning treatment. After bonding and thermocycling, shear bond strength values were measured on an Instron machine. Fracture modes were determined by examination with a scanning electron microscope. Results: Salivary contamination of porcelain surfaces significantly reduced the resin cement-to-porcelain bond compared to the control (P<. 05). The most effective methods of cleaning salivary & silicone disclosing medium contamination at the try-in stage were by re-etching the fitting surface with 5% hydrofluoric acid or by applying Ivoclean® paste. A weaker but still effective method is cleaning with 37% phosphoric acid. Conclusion: Contamination of lithium disilicate surfaces with saliva is detrimental to the resin cement-to-porcelain bond. Of the procedures investigated to overcome this contamination, re-etching with 5% hydrofluoric acid, applying Ivoclean® paste or cleaning with 37% phosphoric acid to decontaminate the surface were the most beneficial in terms of shear bond strength preserve. Within the limits of the procedures investigated in this study, the results are applicable to the ceramic and luting system evaluated.