In vitro and practical guide for the analysis of bond strength to ceramics

The purpose of this study was to characterize different test designs applied for analysis of the bond strength between ceramic and resin cement. One lithium disilicate (LD, IPS Emax CAD®, Ivoclar) and one zirconia (YZ, Ceramill, Amann-Girrbach) ceramic were used for specimens’ preparation (n = 10) according to the proposed test: Microtensile, Tensile, Microshear, Shear, Micropush-out, Push-out, and Interfacial Fracture Toughness. A resin cement (Multilink Automix dualcure, Ivoclar) was used to bond the ceramic to the substrate (composite resin, Tetric N-Ceram, Ivoclar) selected according to the test design. During preparation and testing of the specimens, the time required, amount of material and level of difficulty were assessed. Bond strength data were analyzed using one-way ANOVA and Tukey test (P < 0.05). The homogeneity and magnitude of the bond strength values were verified by calculating the Weibull modulus. Failure mode was analyzed by stereomicroscope for all tests. Microshear resulted in the highest (LD: 41.00 ± 14.96 MPa; YZ: 48.95 ± 6.64 MPa) and Interfacial Fracture Toughness in the lowest (LD: 3.54 ± 0.94 MPa; YZ: 4.10 ± 1.65 MPa) bond strength values, regardless of the ceramic. The analysis of the mode of failure showed 100% adhesive failure for Microtensile and Micropush-out samples for both, LD and YZ. Interfacial Fracture Toughness samples of LD also presented 100% adhesive failure. Most of the samples presented mixed failure modes, and only Tensile and Push-out tests presented cohesive failure in the resin cement layer. Overall, the test design affected bond strength results. Weibull modulus indicated that a smaller sample size may be adequate for the analysis of bond strength to ceramic materials. Microtensile test was classified as the most difficult test in terms of preparing the specimen and performing the test.