Effect of Test Design on Ceramic/Resin Cement Interfacial Bond Strength

Objectives: Selection of a test design for analysis of bond strength is generally based on personal preferences or familiarity with the technique. The aim of the present study was to evaluate the effect of different test designs on the interfacial bond strength between lithium-disilicate ceramic and resin cement.
Methods: Lithium disilicate (LD - IPS E.max CAD, Ivoclar) samples with different shapes and dimensions were prepared according to the parameters of each proposed test (n=10): microtensile, tensile, microshear, shear, micropush-out, push-out, interfacial fracture toughness. The LD surface to be bonded to was treated according to manufacturer’s recommendations. A dual cure resin cement (Multilink Automix, Ivoclar) was used either to build micro-shear cylinders or to bond LD to composite resin (Tetric N-Ceram, Ivoclar), and both were light-activated (950mW/cm²). Samples were stored (distilled water, 37°C, 24 hours) and all bond strength tests were performed in a universal testing machine (Instron - 0.5mm/min). Data analysis was performed at p=0.05.
Results: A significant value was observed for the Shapiro-Wilk normality test. Data was analyzed by Kruskal-Wallis and Post-Hoc test (Table). Overall, micro-tests resulted in significantly higher bond strength than conventional designs (p<0.001), except for the push-out configuration, when the conventional design resulted in significantly higher bond strength (p<0.001). The lowest bond strength values were obtained with the interfacial fracture toughness design.
Conclusions: The design of the test used for analysis of interfacial bond strength between LD/resin cement significantly affected the results. The lowest bond strength was presented by the interfacial fracture toughness test, where a defect was purposely created on the interface.