Effect of full-step versus simplified resin cement luting strategies on the push-out bond strength of indirect resin composite restorations bonded to dentin

Indirect restorations made of resin composite materials are increasingly used yet there is no consensus in the literature on how different luting strategies influence the bond strength. The aim of this was to study the influence of luting strategy and aging on the adhesion of indirect restorations on dentin. Bovine incisors (N = 120) received conical cavities and filled them with resin composite. The cone sets were divided into 8 groups (n = 15 each) and the cylinders were cemented according to: 'Luting strategy' (U200: Self-adhesive cement resin; ULT: Scotchbond Universal + RelyX Ultimate; SB2: Phosphoric Acid + Adper Single Bond 2 + RelyX ARC; SBMP: Phosphoric Acid + Scotchbond Multi-purpose + ARC) and 'Aging' (Tc: With thermocycling/10.000 cycles: 5-55 degrees C; Without thermocycling). The specimens were subjected to a Push-out Bond Strength (sigma) (100 kgf; 0.5 mm/min). Stereomicroscope and scanning electron microscopy (SEM) images were made to classify the failures. Data (MPa) were submitted to two-way-ANOVA, Tukey (alpha = 5%), and Weibull tests. ANOVA revealed that 'luting strategy' and 'aging' were statistically significant. When the factor 'TC' was evaluated separately, the TC groups presented higher bond strength than the unaged groups. As for the non-thermocycling groups, the different luting strategies had no statistical difference, except for the SB2 group, which was lower than ULT. Among all groups, TC, U200_Tc, SBMP_Tc, and ULT_Tc were statistically similar and significantly higher than that of the SB2-Tc group. The Weibull modulus was statistically different among the groups but characteristic strength was significant. Mixed failures were predominantly observed. Self-conditioning strategy promoted higher bond strength than the two-step conventional strategy but after thermocycling, the two-step conventional strategy presented the worst performance among the experimental groups.