Objectives: To evaluate the effect of a methacryloyloxydecyl dihydrogen phosphate (MDP)- containing silane coupling agent and universal adhesive, used alone or in combination, on the microshear bond strength (lSBS) to zirconia after 24 hours of water storage (24h) and after Mario Felipe Gutierrez, DDS, MSc, PhD, professor, Institute for 10,000 thermocycles (TC), complemented with chemical analysis of the surface to establish the presence of MDP on the surface of the zirconia after bonding procedures. Methods and Materials: Thirty computer-aided design/computed-aided manufacturing blocks of zirconia were cut into four sections (63636 mm) and sintered. Zirconia sections (n=96) were assigned to 24 groups according to three factors: 1) silane (no silane, Monobond S [MBS], Monobond P [MB+]), 2) adhesive + resin cement (no adhesive + Enforce [ENF], no adhesive + RelyX Ultimate [REX], Prime&Bond Elect + Enforce [PBE/ENF], Scotchbond Universal + RelyX Ultimate [SBU/REX]), and 3) thermocycling (no thermocycling [24h], 10,000 thermocycles [TC]). Upon silane/adhesive application, cylinder-shaped matrices were filled with resin cement and light cured. Specimens were tested in lSBS (1.0 mm/min) after 24h or TC. The lSBS data were analyzed using twoway ANOVA and Tukey's post hoc test (a=0.05). In addition, micro-Raman spectroscopy was used to analyze the zirconia surface for immediate chemical interaction analysis (n=24). Results: For the 24h condition, PBE/ENF resulted in lower mean lSBS than both groups with silane without PBE (MBS and MB+ groups; p<0.001). SBU alone or MB+ alone and MB+ associated with SBU showed the highest mean lSBS (p,0.001). For the TC condition, all groups showed a significant decrease in mean lSBS compared with those of 24h (p<0.001), with the exception of MB+ associated to SBU (p.0.05). However, the application of MB+ alone or MB+ associated to SBU resulted in higher mean lSBS (p<0.001) after TC than the remaining TC groups. In terms of chemical interaction, only the SBU groups, alone or combined with both of the silane agents, were associated with the methacrylate groups after rinsing. Conclusions: The results of the current study support the use of an MDP-containing silane solution or an MDP-containing silane solution associated with an MDP-containing universal adhesive for bonding to air-abraded zirconia, as a more stable bonding after thermocycling.
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