Long-term Evaluation of Bonding Performance of Universal Adhesives based on Different Dentinal Moisture Levels

To evaluate the microtensile bond strength (μTBS) and silver nitrate uptake (SNU) of three universal adhesives used in etch-and-rinse (ER) and self-etch (SE) modes on dry, wet, and oversaturated dentin surfaces after 24 h and 1 year of water storage. The morphology of the hybrid layer (MHL) and the degree of conversion (DC) were also evaluated.

Human molars were divided into 36 groups according to combinations of the following variables: (i) universal adhesives (Ambar Universal APS [AMB], Prime&Bond Active [PBA], Scotchbond Universal Adhesive [SBU]), (ii) adhesive strategies (ER or SE), (iii) moisture level (dry, wet, or oversaturated dentin surface), and (iv) storage time (24 h or 1 year). After restoration, the specimens were sectioned into resin-dentin sticks and tested for μTBS and SNU according to storage time. For MHL, the specimens were sectioned and evaluated after 24 h using SEM. DC was evaluated using FTIR. ANOVA and Tukey's test were used for statistical analyses (5%).

When 24-h vs 1-year data were compared, there was a significant decrease in μTBS and an increase in SNU values for the majority of experimental groups (p < 0.0001). On dry (ER) and oversaturated (ER and SE) dentin, AMB showed higher μTBS than did PBA (p < 0.00001). No significant decrease in μTBS was observed when universal adhesives were applied in the SE mode to dry dentin (p > 0.05). Regarding SNU, at all moisture levels, AMB showed lower SNU values than SBU (p < 0.001). Regarding MHL, SBU showed several imperfections when applied to oversaturated dentin in comparison with AMB and PBA. Regarding DC, when dentin was kept dry or was oversaturated, AMB showed a higher DC than PBA (p < 0.0001).

The behavior of the different universal adhesives evaluated did not vary when applied to wet or dry dentin. However, the results with oversaturated dentin were dependent on the universal adhesive. Independent of the moisture level and the universal adhesive evaluated, significant degradation of the bonding properties occurred after 1 year of water storage, with the exception of universal adhesives applied to dry dentin in the SE strategy.