Effect of zinc nanoparticles on the mechanical properties and stability of the resin-dentin bonded interface

To evaluate the effect of zinc oxide and zinc fluoride nanoparticle solution (ZNS) as pretreatment on the mechanical properties and stability of resin-dentin bonded interface. Pretreatment solutions were applied after phosphoric acid: 5 and 10% Zinc Oxide (ZO5; ZO10); 1.5 and 3% Zinc Fluoride (ZF1.5 and ZF3); 0.2% chlorhexidine (CHX-positive control) and no pretreatment (NC-negative control). The treated teeth were restored and stored for 24 h and 12 m prior to microtensile bond strength (mu TBS) testing (n = 8). Failure mode, nanohardness (NH) and young's modulus (YM) (n = 3) were also evaluated. In situ zymography (n = 3) and interface morphology (n = 3) were evaluated after 24 h. The antibacterial activity was determined by minimum inhibitory (MIC) and bacterial (MBC) concentration. The mu TBS was evaluated by two-way mixed ANOVA and NH and YM data were analyzed by two-way mixed repeated-measures ANOVA (alpha = 0.05). In situ zymography, interface morphology, MIC and MBC were descriptively analyzed. The mu TBS of ZF3, ZO10 and CHX was maintained over time, while for ZF1.5 and Z05 it was increased. Mixed failures were the most prevalent for all groups. ZF3 presented higher values of NH and YM with incorporation of nanoparticles being observed within the hybrid layer on the interface morphology image. CHX presented the lowest enzymatic activity followed by ZO5. MIC and MBC for ZO were 62.5 mu g/mL and ZF 3.25 mu g/mL, respectively. Pretreatment with ZNS, specially zinc fluoride, seems to be a promising method to increase the longevity of restorations.