Thermocycling effects on bond strength of two dual-curing composites

Purpose:To investigate the effect of thermocycling on bond strength of two dual-curing composites, used in the adhesive cementation of posts, as a function of the distance from the CEJ. Methods and materials: 24 single-rooted teeth recently extracted for periodontal reasons were cut at the CEJ, endodontically treated and a 8-mmdeep post spacewasmade in each specimen. For the test a single kind of composite fiberreinforced post was chosen: Relyx Fiber Post size 2. Teethwere randomly split into two groups (n=12), and posts were luted using two resin composites: Multilink Automix (group A – control) and RelyX Unicem 2 Automix (group B – self-adhesive). The composite was cured for 120 s with a 400mW/cm2 light curing unit. The samples were subjected to thermocycling (5000 cycles in distilled water, 5–55 ◦C, with a dwell time of 30 s in each). Than samples were cut, perpendicularly to the long axis, in 2mm-thick slices starting from the CEJ to the apex. Subsequently the sections corresponding to 1mm, 3mm, 5mm underwent a push-out test to evaluate the resistance to the displacement of the post. Results: The statistical analysis (ANOVA, Tukey’s, p<0.05) of the data obtained from the push-out test shows that the bonding strength of group B is significantly greater than group A in all sections analyzed. No statistically significant difference was found between the bond strength of the tested materials and the distance from the CE. Conclusion: The bonding strength, after thermocycling, of RelyX Unicem 2 has proven to be statistically higher if compared to Multilink; Materials analyzed, after being subjected to thermocycling, have not shown values of adhesion strength significantly different in relation to the distance of the section from the CEJ.