Effect of Thermocycling, Degree of Conversion, and Cavity Configuration on the Bonding Effectiveness of All-in-One Adhesives

The aim of this study was to compare five all-in-one bonding agents with respect to microleakage, microtensile bond strength (mu TBS), degree of conversion (DC) and the impact of cavity configuration. The materials tested were Adper Easy Bond, Clearfil S3 Bond, iBond, Optibond All-in-One, Xeno IV, and Adper Single Bond Plus as a control. The DC of each adhesive was measured on the surfaces of dentin discs (n=5) by attenuated total reflectance Fourier transform infrared spectroscopy. One hundred and forty-four extracted human molars were randomly divided and assigned to one of the five tested adhesives and the control group. The mu TBS to dentin was measured on flat occlusal dentin with and without thermocycling and to the gingival floor dentin of class II cavities (n=8). All specimens were restored with Filtek Z250 resin composite. Class II samples were immersed in a 5% methylene blue dye solution for 24 hours, and microleakage was examined under a stereomicroscope. Micromorphological analysis of demineralized/deproteinized specimens was done using scanning electron microscopy. The DC and microleakage data were statistically analyzed by one-way analysis of variance (ANOVA) and mu TBS data by two-way ANOVA followed by a Bonferroni multiple comparison post hoc test (alpha=0.05) and Weibull-distribution survival analysis. The relation between different variables and mu TBS and microleakage was tested by the Pearson correlation coefficient and regression statistics. A moderate direct relation between DC and mu TBS durability was found for all the adhesives tested. Significant wide variations exist among the results obtained for single-bottle adhesives tested regarding their mu TBS and microleakage. Some of the all-in-one materials tested have shown significantly inferior results under a high C-factor or after aging. The use of these materials should be carefully considered.