Objectives: To evaluate the shear bond strength (SBS) of a nano-composite, a flowable nano-composite and a nano glass ionomer to dentin in vitro.
Materials and methods: Sixty human molars were ground flat, exposing the dentin surfaces, and they were randomly divided into five groups according to the restorative materials and adhesive systems used (n = 12/group). The restoratives were applied to all dentin surfaces according to the manufacturer's instructions, using a special jig (Ultradent) in the following manner: Group 1: a nano-composite (NC) (Filtek Supreme XT-3M ESPE) was applied with a two-step self-etch adhesive (SE) (Adper SE Plus-3M ESPE); Group 2: NC was applied with an etch&rinse adhesive (SB) (Adper Single Bond 2-3M ESPE); Group 3: a flowable nano-composite (FNC, Filtek Supreme XT Flow-3M ESPE) was applied with SE; Group 4: FNC was applied with SB and Group 5: a nanofilled resin-modified glass ionomer (Ketac N100-3M ESPE) was applied with Ketac Nano Primer (3M ESPE). The bonded specimens were stored in distilled water (37 degrees C, 24 hours) and tested for SBS in a universal testing machine (1 mm/minute). Two specimens from each group were subjected to SEM evaluations of the adhesive interfaces. Failure modes were determined using a stereomicroscope. The mean SBS values were calculated and the data were analyzed with the Kruskal Wallis and Mann-Whitney-U tests (p < 0.05).
Results: Mean SBS values (MPa) for the groups were 13.64; 7.83; 11.20; 4.12 and 0.64 for Groups 1, 2, 3, 4 and 5, respectively. Group 1 exhibited a significantly higher value than all the other groups; whereas, Group 5 had the lowest value (p < 0.05). The SE adhesive yielded higher bond values than the SB adhesive with NC and FNC restorative materials. Failure modes in all the groups were primarily adhesive.
Conclusion: The results demonstrate the capacity of the current two-step self-etch adhesive to outperform the etch&rinse adhesive in conjunction with the two nano-restoratives tested.