Effect of short dentin etching and water storage on bonding of resin composite to dentin with universal and two-step self-etch adhesive systems

To evaluate the effect of short dentin etching and 6-month water storage on the microtensile bond strength (µTBS) of universal and two-step self-etch adhesives to dentin. Mid-coronal dentin specimens obtained from 56 third molars were assigned into two groups according to the adhesive type (n = 28); universal adhesive (Scotchbond Universal Plus Adhesive, 3 M Oral Care) and two-step self-etch adhesive (Clearfil SE Bond, Kuraray Noritake). Each group was further divided into two subgroups (n = 14) based on the application protocol: self-etch (SE) and etch-and-rinse with short dentin etching (E&R/SDE) for 3 s. After bonding and composite application, half of the specimens were stored in 37 ± 1 °C distilled water for 24 h (immediate), while the other half were stored for 6 months (aged). Thereafter, specimens were cut into 1 mm² beams using a slow-speed diamond saw under copious water cooling. The beams were then subjected to a tensile force at a cross-head speed of 0.5 mm/min in a universal testing machine until failure occurred. The µTBS was then calculated in megapascals (MPa) by dividing the load at failure by the cross-sectional area of each beam. The values of five beams were averaged to obtain one µTBS value per tooth, and accordingly, data were analyzed using three-way ANOVA and Tukey HSD post-hoc tests (p < 0.05). Failure modes were recorded. The application protocol and the storage time significantly influenced the µTBS results (p < 0.001). Regarding the application protocol, E&R/SDE for 3 s yielded significantly higher bond strength values than the SE for both adhesives (p < 0.05). In terms of storage-time, all groups exhibited a statistically significant reduction in bond strength after 6-month water storage (p < 0.05). On the contrary, no statistically significant difference was detected between the two adhesives irrespective of the application protocol or the storage time (p > 0.05). The predominant failure mode observed for immediate groups was mixed failure, while adhesive failure was the most frequently noted after 6 months. Despite the beneficial effect of E&R/SDE for 3 s in improving the bond strength of universal and 2-step self-etch adhesives to dentin, the 6-month water storage negatively affected the bonding performance of both adhesives.Clinical relevance: E&R/SDE enhanced μTBS at both storage times and may contribute to better bond stability, although all groups exhibited degradation after 6-month water storage, which necessitates further clinical validation.